Method for supplying hydrogen-containing reducing gas to shaft part of blast furnace
10961596 ยท 2021-03-30
Assignee
- Nippon Steel Corporation (Tokyo, JP)
- Jfe Steel Corporation (Tokyo, JP)
- Kobe Steel, Ltd. (Kobe, JP)
- Nisshin Steel Co., Ltd. (Tokyo, JP)
- Nippon Steel Engineering Co., Ltd. (Tokyo, JP)
Inventors
- Nobuaki Ito (Tokyo, JP)
- Hitoshi Donomae (Tokyo, JP)
- Kimihito SUZUKI (Tokyo, JP)
- Kenji Nakao (Tokyo, JP)
- Toshio Isohara (Tokyo, JP)
Cpc classification
C21B5/001
CHEMISTRY; METALLURGY
C21B2100/26
CHEMISTRY; METALLURGY
Y02P10/122
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
C21B2005/005
CHEMISTRY; METALLURGY
Y02P10/25
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
International classification
Abstract
The present invention provides a novel method for supplying a reducing gas to the shaft part of a blast furnace with which a large amount of reducing gas containing hydrogen at a high concentration can be supplied to a deeper position in the blast furnace (location of the blast furnace closer to the center axis in the radial direction) and with which it is possible to reduce the total generated amount of CO.sub.2 of the CO.sub.2 amount that is reduced by conducting hydrogen smelting in the blast furnace and the CO.sub.2 amount that is generated during production of the reducing gas supplied to the blast furnace. The method for supplying a reducing gas to the shaft part of a blast furnace according to the present invention is characterized by reforming coke oven gas by increasing the temperature thereof to 1200 to 1800 C. in a reactor in which an oxygen-containing gas is supplied to preheated coke oven gas to generate reformed gas in which hydrogen gas is enriched; mixing the reformed gas with CO-containing gas in the reactor so that the hydrogen concentration of the reducing gas is adjusted to 15-35 vol % (wet); and supplying the resultant reducing gas to the shaft part of the blast furnace under a condition of a ratio of a flow rate of reducing gas blown into shaft part/flow rate of reducing gas blown into tuyere >0.42.
Claims
1. A method for supplying a hydrogen-containing reducing gas to a shaft part of a blast furnace, the method comprising manufacturing the hydrogen-containing reducing gas by raising a temperature inside a reactor in which an oxygen-containing gas is supplied to a preheated coke oven gas to 1200 to 1800 C. to reform the coke oven gas and thereby produce reformed gas enriched in hydrogen gas, then mixing a CO-containing gas with that reformed gas in the reactor to adjust a concentration of hydrogen to 15 to 35 vol % (wet) and supplying the hydrogen-containing reducing gas to the shaft part of the blast furnace under a condition of a ratio of a flow rate of blowing the hydrogen-containing reducing gas to the shaft part/a flow rate of blowing an air and/or oxygen to a tuyere>0.42.
2. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 1 wherein the oxygen-containing gas is oxygen gas and the method of reforming the gas by raising the temperature in the reactor to 1200 to 1800 C. is partial oxidation of the preheated coke oven gas.
3. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 1 wherein the oxygen-containing gas is steam produced by combustion of hydrocarbons and the method of reforming the gas by raising the temperature in the reactor to 1200 to 1800 C. is mixing combustion gas of the hydrocarbons with the preheated coke oven gas.
4. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 1, further comprising: a) a step of raising a pressure of the coke oven gas, b) a step of adjusting a flow rate of the coke oven gas, c) a step of preheating the coke oven gas, and d) a step of raising the temperature of the preheated coke oven gas inside the reactor in which oxygen gas is supplied to 1200 to 1800 C. and reforming the coke oven gas by partial oxidation to produce reformed gas enriched in hydrogen gas, then mixing into that reformed gas the CO-containing gas in the reactor to adjust the concentration of hydrogen of the reformed gas to 15 to 35 vol % (wet) and the temperature to 800 to 1000 C. to produce reforming-use hydrogen gas for supplying to the shaft part of the blast furnace.
5. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 4, wherein a concentration of CO in the CO-containing gas is 50 vol % to less than 99 vol % (dry), a concentration of CO.sub.2 is 0 vol % (dry) to less than 1 vol % (dry), a concentration of H.sub.2 is 0 vol % (dry) to less than 35 vol % (dry), and a concentration of N.sub.2 is 1 vol % (dry) to less than 20 vol % (dry).
6. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 4, wherein the CO-containing gas is blast furnace gas, converter gas, or synthesis gas treated to remove CO.sub.2.
7. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 4, wherein the hydrogen-enriched reformed gas contains a hydrocarbon gas in an amount of 1% to 5%.
8. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 4, wherein a flow rate of supply (mol/s) of the oxygen gas is 0.4 to less than 0.5 time a flow rate of supply (mol/s) of carbon atoms contained in the hydrocarbons in the coke oven gas.
9. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 4, wherein as the coke oven gas, reformed coke oven gas obtained by treating crude coke oven gas, obtained from a coke oven that reduces a moisture in crude coke oven gas emitted, in a carbonization furnace held at 700 C. or more to break down the hydrocarbons in the crude coke oven gas is used.
10. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 4, wherein the step of raising the pressure of the coke oven gas and the step of adjusting the flow rate of the coke oven gas are performed in that order or in reverse order before the step of preheating the coke oven gas.
11. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 1, further comprising a) a step of running coke oven gas from the coke oven through a carbonization furnace and breaking down hydrocarbons in the coke oven gas into coke and hydrogen to thereby make a concentration of hydrogen increase, b) a step of removing a tar and at least part of a moisture in the gas run through the carbonization furnace to manufacture a first reformed gas, c) a step of raising a pressure of the first reformed gas, d) a step of preheating the raised pressure first reformed gas, e) a step of supplying the preheated first reformed gas to a partial oxidation reforming apparatus and supplying combustion gas to that partial oxidation reforming apparatus to further reform the hydrocarbons in the first reformed gas to make the concentration of hydrogen increase to manufacture a second reformed gas, and f) a step of supplying the second reformed gas from a gas supply port leading to the shaft part of the blast furnace to an inside of the blast furnace.
12. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 11, further comprising raising the pressure of the first reformed gas to at least 0.2 MPa in pressure.
13. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 11, further comprising preheating the first reformed gas to 800 C. to 1000 C.
14. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 11, further comprising supplying combustion gas to the partial oxidation reforming apparatus by (i) supplying combustion gas obtained by supplying oxygen gas and flammable gas to a burner, (ii) supplying oxygen gas and flammable gas to the partial oxidation reforming apparatus to generate combustion gas inside that partial oxidation reforming apparatus and supplying the same, or (iii) supplying oxygen gas to the inside of the partial oxidation reforming apparatus to make part of the first reformed gas burn and supplying the same.
15. The method for supplying hydrogen-containing reducing gas to a shaft part of a blast furnace according to claim 11, further comprising, before preheating the first reformed gas, temporarily holding the raised pressure gas in a gas holder and further raising the pressure of the gas from this gas holder.
Description
BRIEF DESCRIPTION OF DRAWINGS
(1)
(2)
(3)
(4)
(5)
(6)
DESCRIPTION OF EMBODIMENTS
(7) In the present invention, reducing gas adjusted to a concentration of hydrogen of 15 to 35 vol % (wet) is supplied to the shaft part of a blast furnace under the condition of a ratio of a flow rate in blowing reducing gas to the shaft part/flow rate in blowing a gas to the tuyere>0.42. As the reducing gas supplied to the shaft part, it is preferable to use gas obtained by heat treating coke oven gas to reform it and manufacture low CO concentration and high H.sub.2 concentration gas and diluting it to adjust the concentration of hydrogen.
(8) Here, the process performed by the inventors in perfecting the present invention will be explained in brief.
(9) The hydrogen-containing reducing gas adjusted to a temperature suitable as a reducing gas to be supplied to the shaft part of a blast furnace (in the following explanation, sometimes simply referred to as the reducing gas) is supplied to the shaft part of a blast furnace (part configured by providing plurality of through holes around shaft of blast furnace and supplying reducing gas there). For the structure and materials of the shaft part of a blast furnace, ones of the prior art can be applied.
(10) 1) Constituents of Reducing Gas and Method of Calculating Temperature
(11) Reforming Reaction
(12) The reforming reaction predicated upon for obtaining the reducing gas used in the present invention is as follows if taking the example of methane as the hydrocarbons of the raw material:
Steam reforming reaction: CH.sub.4(hydrocarbon)+H.sub.2O.fwdarw.3H.sub.2+CO(formula 1)
Heat decomposition reforming reaction: CH.sub.4(hydrocarbon).fwdarw.C(solid carbon)+2H.sub.2(formula 2)
Partial oxidation reforming reaction: CH.sub.4(hydrocarbon)+0.5O.sub.2 .fwdarw.2H.sub.2+CO(formula 3)
Further, if using coke oven gas as the raw material, the partial oxidation reaction of formula 3 is generally made a general reaction in which the reaction of the formula 1 continues after the following reaction:
Combustion of hydrogen gas: H.sub.2+0.5O.sub.2.fwdarw.H.sub.2O(formula 4)
In addition to this, as the main reaction in which hydrogen gas is increased and decreased, there is the following:
Aqueous shift reaction: CO+H.sub.2O.fwdarw.H.sub.2+CO.sub.2(formula 5)
(13) The solid carbon generated in the heat decomposition reforming reaction is mainly coke. This contains some hydrogen in addition to carbon, so the right side of the heat decomposition reforming reaction strictly speaking is C.sub.nH.sub.m (solid carbon), but in general, n>m, so for simplification of the explanation, the expression of formula 2 is used.
(14) Composition of Reformed Gas at Time of Partial Oxidation Reforming Reaction
(15) The gas can be sampled at an exit side of the partial oxidation apparatus and its composition found using gas chromatography etc. Here, the hydrocarbon (for example, methane) decomposition rate is defined as the ratio of the volume flow rate of the hydrocarbons contained in the gas after partial oxidation (converted to standard state) to the volume flow rate of hydrocarbons contained in the raw material gas (converted to standard state). For example, methane decomposition rate 70% means 30% of the methane present in the raw material gas remains in the reformed gas.
(16) It is known that the constituents of the gas obtained by a partial oxidation reforming reaction or steam reforming reaction (no catalyst) of hydrocarbons under conditions greatly exceeding 1000 C. are close to the equilibrium composition of the reaction end temperature (substantially reactor exit side temperature) if providing a sufficient residence time of the gas in the reactor. Therefore, by calculating the equilibrium constituents, it is possible to evaluate the reforming performance of the partial oxidation reaction and steam reforming reaction (no catalyst) under conditions greatly exceeding 1000 C. Further, a thermocouple or other thermometer is provided inside the partial oxidation apparatus to measure the peak temperature.
(17) 2) Method of Evaluation of Effect of Blowing Reducing Gas into Shaft of Blast Furnace
(18) A test was run blowing hydrogen gas into the blast furnace shaft of a test blast furnace. To reproduce the results, a numerical simulation of the flow of gas inside the blast furnace was performed. This simulation was used to calculate and evaluate the flow of gas inside the blast furnace under various blowing conditions.
(19) Method of Simulation
(20) Numerical simulation was performed simulating the dimensions and shape of a test blast furnace. This is a technique of direct solution by setting discrete equations of motion and equation of energy of a fluid. With this technique, it is possible to individually set the conditions for supply of gas to the blast furnace tuyere and the conditions for supply of gas to the shaft part of a blast furnace. At the test blast furnace, as described in PTL 2, the phenomenon of the gas blown into the shaft part rising only near the furnace walls was confirmed. To reproduce this flow, various parameters were adjusted to secure the precision of the numerical simulation.
(21) The flow rate of hydrogen gas for supply to the shaft part/flow rate of gas for supply to the tuyere was simulated under various conditions and the depth in the blast furnace reached by the hydrogen gas supplied to the shaft part and the distribution of concentration of the hydrogen gas supplied to the shaft part in a blast furnace were found.
(22) 3) Behavior of Reducing Gas Inside Blast Furnace
(23) The upper limit of the flow rate of H.sub.2-containing gas (reformed COG etc.) blown into the shaft part in the test blast furnace is defined by the amount of drop of local temperature accompanying reduction (endothermic reaction) at a certain location inside the blast furnace (near furnace walls) due to H.sub.2 reduction. If blowing gas by more than the upper limit of the inflowing flow rate (flow rate of gas blown into shaft), the concentration of H.sub.2 at a certain location will become excessive and a temperature enabling reduction will no longer be able to maintained there, so H.sub.2 reduction will stop and the effect of reduction of the carbon input (effect of reduction of amount of carbon input when producing 1 ton of pig ironthis being an important factor in measures against global warming) will no longer be improved. Further, at this time, the majority of the H.sub.2 supplied to the shaft part is wastefully discharged from the top of the blast furnace without participating in any reaction. In the tests at the test blast furnace, in tests where the effect of reduction of the carbon input could be sufficiently observed due to the effect of hydrogen reduction inside the blast furnace, it is conceivable that the concentration of H.sub.2 at a certain location was not excessive, so the concentration of H.sub.2 at a certain location in conditions resulting in the maximum flow rate of gas blown into the shaft of a blast furnace among such test conditions can be defined as the upper limit value of the concentration of H.sub.2 at the shaft part at a certain location. Measurement inside the blast furnace is difficult, so the upper limit of concentration of H.sub.2 cannot be directly measured, so the average concentration of H.sub.2 in a predetermined region near the furnace walls of a region where the H.sub.2 gas in the reducing gas supplied from the shaft part passes when supplying reducing gas for supply to the shaft part to the shaft part of a blast furnace is calculated from the results of a numerical simulation of the flow inside the blast furnace reproducing the test under the maximum condition of the inflowing flow rate. The value of this average concentration of H.sub.2 can be made the upper limit value of the concentration of H.sub.2 at the shaft part. As the predetermined region for obtaining an average of the concentration of H.sub.2 near the furnace walls, for example, outside by 95% of the inside diameter of the blast furnace is possible. As a result of running the above simulation based on the test results in the test blast furnace, it was discovered that the upper limit value of the concentration of H.sub.2 at the shaft part is 35%. The concentration of H.sub.2 in the inflowing gas (concentration of inflowing H.sub.2) can change in various ways due to differences in the raw material gas etc., but as an indicator for maintaining a good H.sub.2 reduction reaction in a blast furnace, as explained above, it was learned that it is sufficient to set the operating conditions so that the upper limit concentration of H.sub.2 at the shaft part becomes 35% or less. That is, if the upper limit value of the concentration of H.sub.2 at the shaft part or less inside the blast furnace, it can be judged that the endothermic reaction at the time of hydrogen reduction is not excessive and that hydrogen reduction is proceeding well at that location.
(24) The concentration of reducing gas inside the blast furnace when making the flow rate of hydrogen gas (reducing gas) for supply to the shaft part of the blast furnace increase more can be found by a similar numerical simulation. If using the calculated value of the concentration of reducing gas in this region near the furnace walls so as to set the concentration of H.sub.2 in the reducing gas so that the average concentration of H.sub.2 at the above region near the furnace walls (at time corresponding to flow rate of reducing gas supplied at the test blast furnace) becomes not more than the upper limit value of the concentration of H.sub.2 at the shaft part, hydrogen reduction in the blast furnace becomes possible (this is because at the deeper part of the blast furnace, the concentration of H.sub.2 falls from that at the region near the furnace walls, so the effect of the endothermic reaction at the time of hydrogen reduction becomes smaller). At this time, the upper limit value of the flow rate of supply of H.sub.2 in the reducing gas to the shaft part of the blast furnace can be found by
[Upper limit value of concentration of H.sub.2 in reducing gas(upper limit value of concentration of inflowing H.sub.2)][Flow rate of supply of reducing gas(inflowing gas)].
(25) Even if the allowed concentration of H.sub.2 at the shaft part is constant, the upper limit value of the concentration of inflowing H.sub.2 will change depending on the flow rate of the reducing gas. The relationship of the upper limit value of the concentration of inflowing H.sub.2 (upper limit value of concentration of H.sub.2 in reducing gas) to the ratio of flow rates of blowing operations (=[flow rate of gas flowing in (blown into shaft)]/[flow rate of gas blown into tuyere]) will be explained using
(26) As shown in
(27) Furthermore, in terms of the object of the present invention, it is advantageous to increase the flow rate of H.sub.2 supplied to the shaft part of a blast furnace. From this viewpoint, there is a further restrictive condition on the concentration of inflowing H.sub.2. This restrictive condition will be explained using
(28) A concentration of inflowing H.sub.2 of less than 35% can also be employed, but to make the flow rate of inflowing H.sub.2 increase, the concentration of inflowing H.sub.2 has to be one where the flow rate of inflowing H.sub.2 can become larger than the past. From
(29) If considering the object of the present invention of obtaining a flow rate of inflowing H.sub.2 above the upper limit value of the flow rate of inflowing H.sub.2 in the prior art in addition to the above restrictive condition on the concentration of inflowing H.sub.2, as a more preferable operating condition, the SUITABLE OPERATING RANGE shown by the hatching in
(30) This SUITABLE OPERATING RANGE corresponds to the range where the concentration of H.sub.2 which can be blown into the shaft part can be made to increase. It is learned that to realize this range, the ratio of the flow rate of shaft blowing/flow rate of tuyere blowing has to be made at least the value at the cross point of the line of the flow rate of inflowing H.sub.2/upper limit value of flow rate of inflowing H.sub.2=1.0 and the curve of a concentration of inflowing H.sub.2 of 35% in
(31) Further, the lower limit value of the concentration of inflowing H.sub.2 satisfying the SUITABLE OPERATING RANGE can be expressed by the following formula:
[Lower limit value of concentration of inflowing H.sub.2]=[Upper limit value of flow rate of inflowing H.sub.2 in prior art(blowing only COG into shaft)]/[Flow rate of inflowing gas]
(32) Further, increasing the ratio of flow rates of blowing operations also has the effect of improving the spatial uniformity of the H.sub.2 reduction reaction in the blast furnace such as shown in
(33) Further, in the present invention, gas obtained by diluting by the blast furnace gas the low CO concentration and high H.sub.2 concentration gas manufactured from the coke oven gas is used as the reducing gas, so the inflowing gas unavoidably contains steam. The steam in the reducing gas acts to reduce the concentration of H.sub.2 and acts to enable the reducing gas to reach a deeper part of the blast furnace. Regarding this, it has a similar effect as the blast furnace gas for dilution use in the present invention, so the concentration of inflowing H.sub.2 should be defined by the wet % including steam.
(34) Next, the reducing gas for supply to the shaft part will be explained. As explained previously, the reducing gas for supply to the shaft part has to have a hydrogen concentration of 15 to 35 vol % (wet). The reducing gas should be supplied to the shaft part at 800 to 1000 C. in temperature so that the operation of the blast furnace is not impeded further.
(35) As the reducing gas satisfying such a condition, it is not possible to directly utilize the coke oven gas or blast furnace gas usually emitted in an ironmaking plant. Therefore, in the present invention, low CO concentration and H.sub.2 concentration gas manufactured from coke oven gas is diluted by blast furnace gas to adjust the hydrogen concentration for use of the gas.
(36) For example, the reducing gas used in the present invention can be prepared by reforming coke oven gas by heat treatment and mixing with the reformed gas enriched in hydrogen gas one of the gases selected from (i) a gas containing CO, (ii) combustion gas obtained by combustion of flammable gas and oxygen, and (iii) oxygen.
(37) First, an embodiment reforming coke oven gas by heat treatment and mixing with the reformed gas enriched in hydrogen gas a flammable gas containing CO and oxygen will be explained with reference to
(38) Raw Material Coke Oven Gas (COG)
(39) In the present invention, reformed COG obtained by heat decomposition of coke oven gas (COG) emitted in a coke oven, that is, crude COG, in a carbonization furnace to increase the hydrogen and otherwise adjust the constituents is most preferably used as the raw material COG from the viewpoint of reducing CO.sub.2 emission. Alternatively, refined COG obtained by refining the crude COG emitted in a coke oven and generally used as fuel in an ironmaking plant may be used as the raw material COG. The raw material COG gas may be supplied from the COG supply source 1 shown in
(40) The crude COG emitted at the time of coal dry distillation at the coke oven (not shown) contains methane, ethane, and other aliphatic organic gases, benzene, toluene, and other aromatic hydrocarbon light oil gases, tar gas mainly comprised of aromatic heavy hydrocarbons, etc. Further, the moisture deposited on or contained in the coal used evaporates inside the coke oven so the COG generally contains steam.
(41) In an embodiment using refined COG obtained by treating the crude COG in a carbonization furnace, as the main substance decomposed by heat in the hydrogen generation reaction in the carbonization furnace, tar is suitable. This is because when decomposing by heat the aromatic hydrocarbons of the main ingredient of tar, the remaining hydrocarbons after the release of hydrogen easily grow into macromolecules comprised of two-dimensional aromatic polycyclic structures whereby solid carbon granules of diameters of several m to several mm are easily obtained and whereby solid carbon is easily held in the carbonization furnace. By holding the produced solid carbon in the carbonization furnace for a certain time period, the hydrogen which remained in the solid carbon also gradually disassociates as hydrogen gas, so the heat decomposition is promoted much more. On the other hand, aliphatic organic substances can also be decomposed by heat, but the solid carbon generated at that time generally often becomes an amorphous state structure with diamond-like crystal structures scattered at random. The solid carbon is generated as ultrafine particles with diameters of the nanometer to submicron size. Therefore, it tends to be difficult to hold the generated solid carbon in the carbonization furnace or separate and discharge it all together from the carbonization furnace. Further, in the case of COG unavoidably containing a high concentration of hydrogen sulfide gas, in the hydrogen generation reaction using a catalyst, the reaction of the tar generally proceeds at a faster reaction speed than the reaction of the aliphatic hydrocarbons. On this point as well, heat decomposition of tar is advantageous.
(42) Raising COG in Pressure
(43) According to the present invention, the blast furnace 10 with the shaft part to which the reducing gas is supplied is usually operated at a pressure of several thousand kPa to 1 MPa, so to supply gas from the shaft part 11 of the blast furnace to the inside of the blast furnace 10, the ordinary pressure COG at the gas holder 1 has to be raised in pressure to at least the inside pressure at the shaft part of the blast furnace. This rise in pressure may be performed using a compressor 2. For the compressor 2, a commercially available one can be applied. For example, a multistage axial flow compressor or centrifugal type compressor can be used. A compressor operating at the temperature of the supply of gas at the shaft part of the blast furnace (about 900 C.) is not generally available, so the COG can also be compressed at an ordinary temperature part.
(44) Adjustment of Flow Rate of COG
(45) The flow rate of the hydrogen gas supplied to the shaft part 11 of a blast furnace is adjusted to match with the operating state of the blast furnace 10 by adjusting the flow rate of the raw material COG. The flow rate of the COG can be adjusted by a flow rate adjustment apparatus 3 suitably configured by combining a commercially available flowmeter, flow rate regulator, computer, and other control devices. A high temperature specification flow rate regulator is not generally available, so COG can also be adjusted in the flow rate at an ordinary temperature part. In the embodiment of
(46) Partial Oxidation Reforming Reaction of COG
(47) The raw material COG is mixed with oxygen gas in the partial oxidation reforming reactor 5 and part of the COG is made to burn (partial oxidation) to raise the COG to a temperature of over 1200 C. and thereby raise the reaction speed. The methane and other hydrocarbons in the COG are decomposed and reformed without using a catalyst so as to manufacture hydrogen gas. As explained later, in the present invention, it is not necessary to break down all of the hydrocarbons in the raw material COG, so the gas temperature may be allowed to fall due to the absorption of heat due to the steam reforming reaction occurring after the partial oxidation and become less than the steam reforming reaction temperature before all of the hydrocarbons decompose. If raising the temperature to a sufficiently high temperature over 1200 C. at the time of partial oxidation, the subsequent steam reforming reaction will enable the majority of the hydrocarbons, though not all, to be decomposed, so there is no problem.
(48) The oxygen gas is preferably supplied in the form of pure oxygen from the viewpoint of the quality of the hydrogen gas manufactured. Oxygen-enriched air or other oxygen-containing gas can also be supplied as the oxygen gas. The flow rate of supply of the oxygen gas (molar flow rate) is preferably 0.4 to less than 0.5 of the total value of the molar flow rate of carbon atoms contained in the hydrocarbons (methane etc.) in the COG (that is, O.sub.2/C=0.4 to less than 0.5) from the viewpoint of the quality of the gas. If the O.sub.2/C ratio is less than 0.4, hydrogen is not sufficiently enriched at the time of the partial oxidation, so it is not possible to sufficiently manufacture the hydrogen gas required for hydrogen smelting in the blast furnace and the hydrocarbon decomposition rate becomes excessively low and the restrictions on the constituents of the reducing gas supplied to the shaft part of the blast furnace are not satisfied. Further, if the O.sub.2/C ratio is 0.5 or more, with a partial oxidation operation predicated on a nonequilibrium reaction like in the present invention, a large amount of steam generated due to combustion of the hydrogen remains in the gas after the partial oxidation, so this is not preferable.
(49) Preheating of COG
(50) In the present invention, the flow rate of O.sub.2 supplied at the time of partial oxidation is made the minimum extent by preheating the raw material COG. For the preheating apparatus 4 for this, various types of commercially available heat exchangers can be used. As the preheating method, the outside heat system not causing contamination of the raw material COG is preferable. The temperature of the raw material COG after preheating is preferably made 800 C. to 1000 C. If the preheating temperature is less than 500 C., the peak temperature of the gas temperature at the time of partial oxidation becomes lower than the reforming reaction temperature during reforming of the hydrocarbons and there is the problem that the hydrocarbons cannot be sufficiently decomposed. Preheating up to a temperature of over 1000 C. is not a problem from the viewpoint of the reactivity, but a high temperature unnecessary for decomposition of hydrocarbons is reached at the time of partial oxidation, so the energy required for the excessive preheating becomes wasted, so this is not preferable from the viewpoint of reducing CO.sub.2 emission. Further, preheating up to a high temperature such as one over 1000 C. requires a special heating apparatus, so this is not preferable from the viewpoint of capital costs.
(51) Operating Conditions of Partial Oxidation Step
(52) Stoichiometrically, the O.sub.2/C ratio in the partial oxidation of the raw material COG can become optimal when 0.5. This is because all of the H.sub.2O emitted by formula 4 due to the supply of oxygen gas is consumed by the steam reforming reaction of formula 1 and because all of the hydrocarbons are broken down into CO and H.sub.2 due to the steam reforming reaction. However, to cause such a reaction under the pressure conditions of the reducing gas supplied to the shaft part of a blast furnace, in terms of equilibrium theory, a 1300 C. or more temperature has to be maintained during the steam reforming occurring after the partial oxidation. In the case of a temperature lower than this, for example an order of several % of hydrocarbons and a large amount of H.sub.2O derived from the excess O.sub.2 remain in the gas after partial oxidation. For achieving such a high temperature by just partial oxidation, a large amount of O.sub.2 has to be supplied. It is also possible to cut the amount of supply of O.sub.2 by preheating the raw material gas, but in the past, the exhaust heat generated in the plant was used for this preheating, so at the highest, only preheating up to about 500 C. was performed. This is because preheating up to a temperature higher than this becomes disadvantageous in terms of heat efficiency. For this reason, in conventional partial oxidation of hydrocarbons, the complete decomposition of the hydrocarbons was aimed at and the O.sub.2/C ratio, in the case of using natural gas or naphtha or other pure hydrocarbon as a raw material, was 0.6 to 0.7 or so (if the hydrocarbon is methane, the supplied O.sub.2 volume flow rate is 0.6 to 0.7 time the raw material volume flow rate) and, in the case of using purified COG with a concentration of hydrocarbons of 30% or so as a raw material, was 0.8 or more (if the hydrocarbon is methane, the supplied O.sub.2 volume flow rate is 0.24 time or more the raw material volume flow rate). If using such a high O.sub.2/C ratio, if possible to maintain a high temperature at the time of steam reforming, the residual amount of CO.sub.2 becomes a level of several % to 10 odd %, while if not possible to maintain a sufficiently high temperature at the time of steam reforming, 10% or more steam remains, so in each case, the already explained restrictive conditions relating to the constituents of the reducing gas supplied to the shaft part of a blast furnace cannot be satisfied. In the present invention, reformed COG having a concentration of hydrocarbons further smaller than refined COG (20% or so or less) is used as the raw material, so the amount of oxygen supplied per flow rate of the raw material gas is smaller than the case of using such gases as the raw material (if the hydrocarbon is methane and the O.sub.2/C ratio is made 0.8, the supplied O.sub.2 volume flow rate is 0.16 time or less of the raw material volume flow rate) and the amount of temperature rise due to partial oxidation is also very small, so this is more disadvantageous in the point of maintaining the temperature required for the steam reforming reaction.
(53) In the present invention, the concentration of hydrocarbons in the reducing gas is made to become the already explained restricted range by mixing it with CO-containing gas to dilute the residual hydrocarbons. In the present invention, complete decomposition of hydrocarbons is not aimed at, so the O.sub.2/C may also be less than 0.5. The supplied O.sub.2 may be further reduced (if the O.sub.2/C ratio is 0.4 and the hydrocarbons are methane, the supplied O.sub.2 volume flow rate is 0.08 time or less the raw material volume flow rate), and the CO.sub.2 and H.sub.2O in the reducing gas can be made the already explained restricted ranges. Furthermore, in the present invention, to secure the temperature required for steam reforming after partial oxidation for a certain time, as the method of making up for the deficient amount of temperature rise, preheating at 800 C. to 1000 C. is jointly used. Such high temperature preheating in the partial oxidation process is a cause of deterioration of the heat efficiency compared with the prior art if viewing the partial oxidation step alone, so in the past, such high temperature preheating had been considered difficult economically. However, after partial oxidation, it is possible to directly supply the reducing gas diluted by the CO-containing gas to the shaft part of a blast furnace, so if considering the fact that the supply of heat energy for reheating the reducing gas after cooling it once so as to adjust the constituents after partial oxidation in the prior art is unnecessary in the present invention etc., in the present invention, it is possible to slash the overall energy consumption, so in the present invention, preheating at such a high temperature is possible. In this way, by preheating the raw material to 800 C. to 1000 C., using reformed COG as the raw material, performing partial oxidation combined with supply of oxygen making O.sub.2/C 0.4 to less than 0.5, and diluting the gas after partial oxidation by CO-containing gas in a joint manner, in the present invention, it is possible to manufacture reducing gas suitable as the reducing gas for supply to the shaft part of the blast furnace under conditions of reduced CO.sub.2 emission.
(54) A burner or other igniting means (not shown) may also be provided inside of the partial oxidation reforming reactor 5 or upstream of the partial oxidation reforming reactor 5. If the inside walls of the partial oxidation reforming reactor are held at a temperature sufficiently higher than the ignition point of the raw material COG, the partial oxidation reaction can be stably continued inside the partial oxidation reforming reactor without relying on the temperature of supply of the raw material COG or the supplied oxygen gas.
(55) The gas temperature after raising the temperature by combustion in the reactor 5 is preferably made 1200 C. to 1800 C. in range. If less than 1200 C. gas temperature, the chemical reaction speed is excessively slow, so if trying to proceed with the reforming operation at this range of temperature, the problem arises of the dimensions of the reactor becoming gigantic. If the highest temperature of the gas exceeds 1800 C., there is the problem that the temperature of the inside walls of the reactor which contact the gas becomes too high and the lifetime of the furnace members is remarkably shortened. Due to the absorption of heat at the time of the steam reforming reaction occurring after the partial oxidation, the gas temperature will fall at the downstream side of the partial oxidation furnace and may become one of the above temperature or less, but if the peak temperature of the gas after partial oxidation is in the above range, there is no problem since the majority of the hydrocarbons in the raw material COG can be decomposed.
(56) The volume of the reactor 5 is preferably one by which the apparent average residence time of the gas ([Reactor volume]/([Flow rate of treated COG (standard state)]+[Flow rate of oxygen supplied from outside (standard state)])) becomes 5 seconds to 120 seconds. If less than this range, the reactor residence time of the treated gas is excessively small and the problem arises of the reforming reaction of the methane not sufficiently proceeding. Further, if over this range, the reactor residence time is excessively large and the problem arises of excessive capital costs being required.
(57) At the downstream side in the partial oxidation reforming reactor after the elapse of a predetermined apparent average residence time, the gas can be considered to have been sufficiently reformed, so gas at the downstream side of this will be called reformed gas.
(58) Supply of CO-Containing Gas
(59) Next, CO-containing gas is supplied to the reformed gas in the partial oxidation reforming reactor to dilute the reformed gas and reduce in particular the concentration of hydrogen gas in the reformed gas to a suitable range. By supplying such a gas in a greater amount to the shaft part of a blast furnace, it is possible to supply the larger amount of hydrogen gas contained in the reformed gas to a deeper position inside the blast furnace (location of blast furnace closer to center axis in radial direction).
(60) The supply of CO-containing gas to the reformed gas in the partial oxidation reforming reactor also acts to cause heat exchange (mixture) between the high temperature reformed gas and low temperature CO-containing gas to thereby obtain a temperature range suitable for the reducing gas to be supplied to the shaft part of a blast furnace. Further, due to this, preheating of the CO-containing gas to be supplied to the partial oxidation reforming reactor becomes unnecessary or can be greatly reduced in extent. Further, the reformed gas finishes being cooled inside the partial oxidation reforming reactor which inherently has heat resistance, so due to this, in the downstream equipment, there is no longer a need for extreme heat resistance specifications (for example: 1200 C. or more), the lifetime of the equipment can be extended, and the apparatus also becomes inexpensive.
(61) The CO-containing gas is supplied from a supply port provided at a location where gas passes after the elapse of the above predetermined residence time inside the partial oxidation reforming reactor 5 to the inside of the partial oxidation reforming reactor 5. This supply port must be provided downstream from the location of supply of oxygen gas to the partial oxidation reforming reactor 5.
(62) The CO-containing gas is supplied by a CO-containing gas supplying means 9 comprised of a CO-containing gas supply source 7, a CO-containing gas flow rate adjusting means 8, and a CO-containing gas supply port to the partial oxidation reforming reactor 5 connected to the gas pipe in that order.
(63) CO-Containing Gas
(64) The necessary conditions of the CO-containing gas supplied to the reducing gas obtained at the partial oxidation reforming reactor 5 are as follows:
(65) It be mainly comprised of CO so as to secure the reducibility of the gas after dilution of COG.
(66) It be dry gas not containing tar or other hydrocarbons or steam impeding the operation of the blast furnace.
(67) It as much as possible not contain H.sub.2 or CO.sub.2 which might cause an endothermic reaction from the viewpoint of securing the temperature at the shaft part of the blast furnace.
(68) It have a sufficiently small N.sub.2 content so as to avoid energy loss due to running useless gas through the inside of the blast furnace.
(69) There is no existing inexpensive gas which satisfies all of these conditions, so the desired gas is manufactured based on a specific raw material. As the raw material, for example, blast furnace gas, converter gas, synthesis gas, etc. can be used. These gases all contain CO.sub.2. From the above-mentioned restriction 2 of the constituents of the reducing gas, the smaller the concentration of this CO.sub.2, the greater the reduced CO.sub.2 emission, so when manufacturing the CO-containing gas, means for removing CO.sub.2 are applied. As the means for removing CO.sub.2, for example, a commercially available physical adsorption method CO separation apparatus or CO.sub.2 separation apparatus can be used. The CO-containing gas to which the means for removing CO.sub.2 has been applied should not contain 1 vol % (dry) or more of CO.sub.2 so as to keep the detrimental effect of heat absorption due to the CO.sub.2 decomposition reaction which can occur in a blast furnace from being manifested. That is, the concentration of CO.sub.2 of the CO-containing gas supplied to the partial oxidation reactor is preferably 0 vol % (dry) to less than 1 vol % (dry). In the case of using synthesis gas or other gas containing H.sub.2 as the raw material, the concentration of H.sub.2 in the CO-containing gas for mixture with the gas after partial oxidation, which generally has a concentration of H.sub.2 higher than the upper limit value 35% of the preferable concentration of H.sub.2 in the reducing gas explained above, so as to obtain 35% or less of a reducing gas has to be at least less than 35%. To use gas containing excessive H.sub.2 as CO-containing gas, it is possible to use means for removing H.sub.2 to reduce the concentration of H.sub.2. As the means for removing H.sub.2, it is possible to use a commercially available membrane separation apparatus etc. The N.sub.2 concentration is also preferably at least less than 20 vol % from the viewpoint of the above-mentioned restrictions on the constituents of the reducing gas. For this reason, this can be realized by reducing the amount of use and amount of mixture of air (that is, the N.sub.2 source) at the time of manufacture of the CO-containing gas. However, to lower the amount of use and amount of mixture of air at the time of manufacturing the CO-containing gas to the extremely low concentration of less than 1%, a large amount of additional energy has to be supplied, so this is not preferable from the viewpoint of reduced CO.sub.2 emissions. For this reason, the N.sub.2 concentration is preferably 1 vol % or more.
(70) Supply of Manufactured Hydrogen-Containing Reducing Gas to Shaft Part of Blast Furnace
(71) The hydrogen gas-containing reducing gas adjusted by supply of CO-containing gas to a temperature suitable for hydrogen gas for supply to the shaft part of a blast furnace is supplied to the shaft part 11 of the blast furnace (part around blast furnace shaft where plurality of through holes are provided from which hydrogen gas is supplied). For the structure and materials of the shaft part of a blast furnace, ones of the prior art can be applied.
(72) Water Content Reducing Means of COG
(73) The coal supplied to the coke oven may be made to dry in advance using a known DAPS or SCOPE21 furnace. If dry distilling the thus dried coal, it is possible to make the moisture in the COG emitted decrease. Alternatively, in the case of a smaller system, it is also possible to store the coal in a stock house for a long period of time of several months or more and allow the moisture to naturally evaporate during that time.
(74) In some cases, it is also possible to supply the moisture of the coal to the coke oven without decreasing it, extract the COG containing a high concentration of steam generated in the coke oven, and run it through high temperature use zeolite or other adsorbent to thereby decrease the moisture in the COG.
(75) Carbonization Furnace
(76) In the present invention, if using the reformed coke oven gas (refined COG) obtained by treating the crude coke oven gas from the coke oven 11 (
(77) Catalyst
(78) Inside of the carbonization furnace 12, a pyrolysis catalyst (not shown) can be placed. For the pyrolysis catalyst, for example, a catalyst comprised of a composite oxide containing nickel, magnesium, cerium, and aluminum but not containing alumina, in which catalyst the composite oxide uses a catalyst comprised of NiMgO, MgAl.sub.2O.sub.4, and CeO.sub.2 crystal phases can be used.
(79) Gas Refining Apparatus
(80) In the primary reformed gas extracted from the carbonization furnace 12, at least the tar, light oil, benzene and other high boiling point hydrocarbons or moisture and other condensable gases can be removed by a gas refining apparatus 13. The condensable gas can be removed by using a water cooling apparatus of gas using a scrubber etc. or by using a distillation tower. If necessary, treatment for removing sulfur or treatment for removing ammonia may also be added. The high temperature primary reformed gas from the carbonization furnace 12 is cooled by treatment at the gas refining apparatus 13 at least down to a temperature lower than the heat resistance temperature of the gas conveyor apparatus 14, usually down to close to ordinary temperature.
(81) Gas Conveyor Apparatus
(82) The gas conveyor apparatus 14 is an apparatus for taking in primary reformed gas from the carbonization furnace 12 and for raising it in pressure and sending it to the partial oxidation reforming apparatus 16 (explained later). For this reason, the gas conveyor apparatus 14 requires a head enabling the entrance side pressure to be maintained at 10 kPa or so and the exit side pressure to be maintained at least at 0.2 MPa, generally 0.2 to 1 MPa or so. For the gas conveyor apparatus 14, it is possible to use a commercially available multistage axial flow compressor etc.
(83) Preheating Apparatus
(84) The primary reformed gas raised in pressure at the gas conveyor apparatus 14 is subsequently sent to the reforming apparatus 16 for further reforming by partial oxidation. In this reforming apparatus 16, gas combustion using oxygen gas is utilized to raise the temperature of the running gas, but from the viewpoint of reducing the amount of CO.sub.2 generated and from the prime units of hydrogen, the amount of oxygen supplied should be set to the minimum necessary limit. However, if raising the temperature of the ordinary temperature primary reformed gas by gas combustion, the temperature of the running gas after being raised in temperature will often not rise to an extent enabling promotion of decomposition of methane by steam reforming. For this reason, it is possible to preheat the primary reformed gas from the carbonization furnace 12 by the preheating apparatus 15, then raise the temperature of the running gas by gas combustion to make the temperature of the running gas after being raised in temperature a suitable range. The preheating temperature of the primary reformed gas is preferably 300 to 800 C. or so.
(85) The primary reformed gas can be preheated in the preheating apparatus 15 by, for example, using a commercially available heat exchanger or by causing heat exchange with combustion gas generated in a separately provided combustion furnace.
(86) Next, an embodiment in which coke oven gas is reformed by heat treatment and in which the reformed gas enriched in hydrogen gas is mixed with a combustion gas obtained by burning a flammable gas and oxygen will be explained with reference to
(87) Partial Oxidation Reforming Apparatus
(88) The partial oxidation reforming apparatus 16 is an apparatus which mixes combustion gas with the primary reformed gas to raise the temperature of the primary reformed gas to a temperature greatly exceeding 1000 C. (for example, 1500 C.) and thereby increase the reaction speed and break down the methane and other hydrocarbons in the primary reformed gas without the use of a catalyst and thus emit hydrogen gas or CO gas. As the partial oxidation reforming apparatus 16, any one can be used so long as satisfying these requirements.
(89) The reforming apparatus 16 has a burner 18 connected to it. The burner 18 is supplied with oxygen gas and flammable gas. These are mixed and made to ignite inside the burner and the combustion gas is exhausted to the inside of the reforming apparatus 16. As the burner 18, a commercially available axial flow burner etc. can be used.
(90) The oxygen gas is preferably supplied in the form of pure oxygen from the viewpoint of the quality of the secondary reformed gas, but air or oxygen-enriched air or other oxygen-containing gas can also be supplied as the oxygen gas.
(91) The flow rate of supply of oxygen gas (molar flow rate) is preferably 0.4 time to less than 0.5 time the total value of the molar flow rates of carbon atoms contained in the hydrocarbons in the primary reformed gas and the hydrocarbons in the flammable gas (that is, corresponding to O.sub.2/C=0.4 to less than 0.5) from the viewpoint of the quality of the secondary reformed gas.
(92) On the other hand, the flow rate of flammable gas supplied to the burner 18 (molar flow rate) is preferably 0.2 to 1 time the flow rate of oxygen gas (molar flow rate).
(93) For the flammable gas, natural gas, liquefied petroleum gas, etc. can be used. Further, naphtha, light oil, heavy oil, and other liquid fuels can also be used if atomized for supply to the inside of the burner since they are fundamentally no different from flammable gas.
(94) Among these flammable gases, use of natural gas mainly comprised of methane is particularly advantageous. Natural gas is advantageous in that the price per amount of heat generated is inexpensive, the amount of CO.sub.2 generated per amount of heat generated is relatively small, the gas does not (like COG) contain hydrogen gas, so hydrogen is not consumed at the time of combustion, etc.
(95) Oxygen gas and flammable gas may be supplied to the burner 18 at ordinary temperature or may be supplied after preheating. If supplying them at less than the ignition temperature of the flammable gas, it is necessary to provide an igniting means (not shown) at the burner 18. For example, it is possible to provide a pilot burner (not shown) at the burner 16 to make the mixed gas of the flammable gas and oxygen gas ignite.
(96) The gas temperature inside the reforming apparatus 16 has to be maintained at least at 1000 C. or more. The maximum temperature is preferably 1200 to 1800 C. in range. This is because if less than this temperature range, the chemical reaction speed becomes excessively slow, so the problem arises of the dimensions of the reforming apparatus 6 used as a reactor becoming gigantic and because if over this temperature range, there is the problem that the temperature of the inside walls of the reforming apparatus contacting the gas becomes too high and the lifetime of the material forming the inside walls is remarkably shortened.
(97) A thermometer (not shown) may be provided inside the partial oxidation reforming apparatus 16 to measure the temperature of the gas inside the apparatus and this measured value may be used as the basis to control the temperature of the gas inside the apparatus. For the thermometer, an R-type or B-type thermocouple covered by ceramic or another heat resistant material for protection may be used.
(98) The volume of the reforming apparatus 16 used as the reactor is preferably one whereby the apparent average residence time of the gas ([Volume of reaction vessel]/([Flow rate of treated primary reformed gas (standard state)]+[Flow rate of combustion gas supplied from outside (converted to ordinary pressure and 100 C.)])) becomes 30 seconds to 100 seconds. If less than this range, the residence time of the treatment gas in the reforming apparatus becomes excessively small and the problem arises of the reaction not sufficiently proceeding. Further, if over this range, the residence time in the reforming apparatus becomes excessively large and the problem arises of excessive capital costs being required.
(99) Supply of Manufactured Reducing Gas (Secondary Reformed Gas) to Shaft Part of Blast Furnace
(100) The reducing gas (secondary reformed gas) containing hydrogen obtained from the partial oxidation reforming apparatus 16 is supplied to the shaft part 7 of a blast furnace. In some cases, before introduction into the blast furnace, the reducing gas may also be adjusted in temperature. The art of supplying reducing gas to a blast furnace is broadly known. There is no need to explain it in detail here.
(101) Next, an embodiment mixing unburned flammable gas and oxygen with the reformed gas enriched in hydrogen gas by reforming the coke oven gas by heat treatment will be explained with reference to
(102) In the reforming apparatus 16 of this embodiment, the independent burner is eliminated and the oxygen gas and the flammable gas are closely and directly supplied to the reforming apparatus. In this case, the supplied oxygen gas and flammable gas are in close proximity, so a combustion region is formed near the gas supply port. Here, mainly oxygen gas and flammable gas burn, so this combustion region plays substantially the same role as a burner. In some cases, the oxygen gas and the flammable gas may be supplied to the inside of the reforming apparatus together in advance.
(103) Further, in the embodiment shown in
(104) The other apparatuses and equipment in the embodiment of
(105) In the embodiment utilizing reforming by heat decomposition in the carbonization furnace explained with reference to
(106) Note that, the primary reformed gas contains a large amount of hydrogen gas along with methane. The speed of combustion of hydrogen gas is generally faster compared with methane gas, so if oxygen is supplied inside the reforming apparatus 16, the hydrogen in the primary reformed gas is consumed and steam is produced. If this gas is maintained at a high temperature inside the reforming apparatus 16, the generated steam reforms the methane to produce hydrogen, so if a sufficient time period for holding the gas at a high temperature can be set inside the reforming apparatus 16, there is no problem in breaking down the methane in the primary reformed gas. However, if the time period for holding the gas is not sufficient, the secondary reformed gas is exhausted before the steam reforming of the methane sufficiently proceeds, so it becomes impossible to restore the hydrogen gas consumed by combustion. Therefore, if directly supplying oxygen to the inside of the reforming apparatus 16, it is necessary to set the dimensions of the reforming apparatus 6 used as the reaction vessel sufficiently large.
(107) If directly supplying oxygen gas into the primary reformed gas, it would be difficult to separate the amount of the primary reformed gas of the combustion gas from the primary reformed gas as a whole, so the flow rate of supply of flammable gas in this case may be less than 0.2 time the lower limit flow rate of supply of oxygen gas (molar flow rate) in the case of supply as combustion gas to the reforming apparatus through the burner 18.
EXAMPLES
(108) Using the following examples, the present invention will be further explained. This being said, the present invention is not limited to these examples.
Example 1
(109) The apparatus of the embodiment shown in
(110) For the partial oxidation furnace, one with an inside diameter of 0.6 m and a length of 2 m was used. The residence time of the raw material gas inside the partial oxidation furnace was 80 seconds predicated on converting the raw material gas to a flow rate in the standard state.
(111) The main constituents of the refined COG for raw material use were H.sub.2: 55%, CH.sub.4: 30%, CO: 7%, and CO.sub.2: 2% (actually measured values of refined COG obtained by treating crude COG from coke oven using coal not treated to reduce moisture). The CO-containing gas for use for manufacturing the reducing gas is blast furnace gas (BFG) treated by a physical adsorption apparatus to remove CO.sub.2. The main constituents of the CO-containing gas were CO: 80% and N.sub.2: 18% (actually measured values).
(112) To the partial oxidation reforming reactor, CO-containing gas was supplied under the following three conditions:
(113) a. 0.8 time flow rate of reformed gas
(114) b. 1 time flow rate of reformed gas
(115) c. 2 times flow rate of reformed gas
(116) The above refined COG was supplied to the partial oxidation furnace and partially oxidized to obtain the compositions of reformed gases shown in Table 1. Table 1 shows the results obtained under the following three partial oxidation conditions:
O.sub.2/C=0.48,raw material COG preheating temperature=1000 C.Partial oxidation 1:
O.sub.2/C=0.48,raw material COG preheating temperature=800 C.Partial oxidation 2:
O.sub.2/C=0.7,raw material COG preheating temperature=500 C.Partial oxidation 3 (comparative example):
In terms of the compositions of the reformed gases, in each case, the concentration of H.sub.2 greatly exceeded 35%, so with this, the gases are not suitable as reducing gases for supply to the shaft part of a blast furnace.
(117) TABLE-US-00001 TABLE 1 Reformed gas Reformed gas (partial (partial Reformed gas oxidation 1) oxidation 2) (partial oxidation 3) Mole CH.sub.4 0.03 0.06 0.06 fraction C.sub.2H.sub.4 0.00 0.01 0.01 CO 0.26 0.20 0.19 CO.sub.2 0.01 0.01 0.02 H.sub.2 0.65 0.61 0.50 H.sub.2O 0.03 0.08 0.19 N.sub.2 0.02 0.02 0.02
(118) Next, the reformed gases of Table 1 were used mixed with CO-containing gas under the following conditions to manufacture reducing gases.
(119) Reducing gas (1):
(120) Reformed gas (partial oxidation 1) diluted by 1.0 time the flow rate of the above CO-containing gas
(121) Reducing gas (2):
(122) Reformed gas (partial oxidation 2) diluted by 1.0 time the flow rate of the above CO-containing gas
(123) Reducing gas (3):
(124) Reformed gas (partial oxidation 2) diluted by 2.0 times the flow rate of the above CO-containing gas
(125) Reducing gas (4):
(126) Reformed gas (partial oxidation 3) diluted by 2.0 times the flow rate of the above CO-containing gas
(127) The compositions of the reducing gases supplied to the shaft part of a blast furnace obtained as a result are shown in Table 2. The concentrations of CO.sub.2 and H.sub.2O in all examples were of levels not problems as reducing gases to be supplied to the shaft part of a blast furnace. Regarding the concentrations of the hydrocarbons CH.sub.4 and C.sub.2H.sub.4, in the reducing gas (2), the upper limit values of the restriction on the constituents of the reducing gas supplied to the shaft part of a blast furnace are exceeded and therefore not suitable. As opposed to this, the same reformed gas mixed with more CO-containing gas (3) satisfied the condition of concentration of hydrocarbons. The other reducing gases also satisfied the above-mentioned restrictive condition of the concentration of hydrocarbons. The CO.sub.2 in the reducing gas (4) is equal to the absolute value of the CO.sub.2 cut, so the effect of cutting CO.sub.2 added up through the manufacture of the reducing gas and the hydrogen smelting at the blast furnace is not obtained. With the reducing gases (1) to (3), the CO.sub.2 was smaller than the absolute value of the CO.sub.2 cut by hydrogen smelting in the blast furnace so it is possible to cut the total amount of generation of CO.sub.2 of the time of manufacturing the reducing gas and hydrogen smelting at the blast furnace. However, with the reducing gases (1) and (3), the CO.sub.2 was close to the absolute value of the CO.sub.2 at the blast furnace. This is because of the supply of the heat required for preheating the raw material COG (case of 1) and the supply of heat required for preheating the CO-containing gas for mixing a large amount of CO-containing gas for diluting the concentration of hydrocarbons in the reducing gas to an allowable value (case of 3 and 4).
(128) TABLE-US-00002 TABLE 2 Reducing Reducing gas gas Reducing gas Reducing gas (1) (2) (3) (4) Mole CH.sub.4 0.01 0.03 0.02 0.02 fraction C.sub.2H.sub.4 0.00 0.01 0.00 0.00 CO 0.53 0.50 0.60 0.60 CO.sub.2 0.00 0.005 0.00 0.007 H.sub.2 0.33 0.30 0.20 0.16 H.sub.2O 0.02 0.04 0.03 0.06 N.sub.2 0.10 0.11 0.14 0.14 CO.sub.2 0.12 0.08 0.14 0.16 (mol/mol.sub.H2)
(129) Furthermore, from the measurements, the following results were obtained:
(130) Peak temperature of reformed gas: 1200 C. to 1800 C. in range
(131) Temperature of hydrogen gas supplied to shaft part of blast furnace: 800 C. to 900 C. in range
(132) Range of concentration of H.sub.2 of hydrogen gas supplied to shaft part of blast furnace: 16% to 33%
(133) At the reducing gases (1) and (3), the manufactured gas satisfied the required temperature and composition conditions of the hydrogen gas supplied to the shaft part of a blast furnace.
(134) From the results of the simulation explained above, if making the flow rate of supply of the reducing gas to the shaft part of a blast furnace a rate exceeding 0.42 time the flow rate of the gas supplied to the blast furnace tuyere, it is possible to supply hydrogen to a deeper part of the blast furnace and possible to enhance the hydrogen smelting effect at the blast furnace.
Example 2
(135) COG extracted from a coke oven using coal reduced in moisture by a DAPS as a raw material was reformed by a carbonization furnace and refined. The reformed COG recovered at a gas holder used as the source of supply of COG was used as the raw material COG for a partial oxidation reforming reaction.
(136) The reformed COG was manufactured as follows by an actual machine. Coal reduced in moisture by a DAPS from 10% to 4% was conveyed by a belt conveyor to a stock vat above the coke oven. For conveying the coal from the stock vat to the inside of the coke oven, a commercially available skip car was used. From a branch pipe provided at the coke raising pipe of the coke oven, approximately 800 C. reduced moisture crude COG was extracted by suction. The extracted reduced moisture crude COG was supplied to the carbonization furnace by a gas pipe maintained in temperature at its surroundings so as to keep the temperature from falling.
(137) The carbonization furnace had gas passage cross-section (horizontal plane) dimensions of 120 mm900 mm and a gas passage direction height of 1200 mm. The layer of the granular bodies in the carbonization furnace was formed while holding the catalyst filled in the carbonization furnace (diameter 15 mm NiMgO-based catalyst) by a holder with a bottom of a drainboard shape. The height was 600 mm. During operation, the carbonization furnace was maintained at 800 C. in temperature by outside heating.
(138) The crude reformed COG from the carbonization furnace was refined using a scrubber to remove the tar and majority of moisture in the gas and obtain reformed COG. The gas temperature of the reformed COG after passing through the scrubber was about 50 C.
(139) The refined reformed COG was transferred by a Roots blower to a gas holder. A branch was provided at the gas pipe to the gas holder, the reformed COG was extracted, then this was supplied to a commercially available gas chromatography apparatus for on-line analysis of the constituents.
(140) Based on the composition of the reformed COG obtained by analysis (see Table 3), partial oxidation reforming similar to Example 1 was performed (under conditions of O.sub.2/C=0.48 and a preheating temperature of reformed COG of 800 C.). The rate of decomposition of the hydrocarbons in the partial oxidation was 70%. The reaction was a nonequilibrium reaction. Next, this reformed gas was mixed with 1.0 time the flow rate of CO-containing gas (constituents similar to Example 1). As a result, reducing gas of the composition shown in Table 3 for supply to the shaft part of a blast furnace was obtained.
(141) TABLE-US-00003 TABLE 3 Reformed COG (manufacture in Reformed gas Reducing carbonization furnace) (partial oxidation 4) gas 4 Mole CH.sub.4 0.22 0.05 0.02 fraction C.sub.2H.sub.4 0.03 0.01 0.00 CO 0.09 0.17 0.48 CO.sub.2 0.02 0.00 0.00 H.sub.2 0.61 0.68 0.35 H.sub.2O 0.00 0.07 0.04 N.sub.2 0.03 0.02 0.10 CO.sub.2 0.09 (mol/mol.sub.H2)
(142) From the results of Table 3, the reducing gases obtained in this example satisfy all of the above-mentioned restrictive conditions on the constituents of a reducing gas to be supplied to the shaft part of a blast furnace. The CO.sub.2 also is a sufficiently smaller one of about half of the absolute value of the CO.sub.2 at the blast furnace so it is possible to cut the CO.sub.2 when added with the amount of CO.sub.2 cut by the hydrogen smelting at the blast furnace. Furthermore, comparing the present example with the actual values of the refined COG composition obtained by treating crude COG from a coke oven using coal not treated to reduce moisture as the raw material gas in partial oxidation (see Example 1), it is learned that the reformed COG obtained from a coal raw material treated to reduce moisture in the present example is increased in concentration of H.sub.2. From this, it is shown that by using reformed COG obtained from a coal raw material treated to reduce moisture so as to work the present invention, it becomes possible to supply a greater amount of H.sub.2 to the blast furnace. Further, the present example is more advantageous than any of the reducing gases of Example 1 in that the CO.sub.2 is smaller (except for reducing gas 2 not suitable in composition) and in the point of reduced CO.sub.2 emission.
(143) From the results of the simulation explained above, if making the flow rate of supply of the reducing gas to the shaft part of a blast furnace a rate exceeding 0.42 time the flow rate of the gas supplied to the blast furnace tuyere, it is possible to supply hydrogen to a deeper part of the blast furnace and possible to enhance the hydrogen smelting effect at the blast furnace.
Comparative Example 1
(144) A conventional type of partial oxidation reforming reactor not supplying CO-containing gas to the inside of the partial oxidation reforming reactor was used to manufacture reformed gas. CO-containing gas was separately independently heated to 800 C. by outside heating using a heat exchanger, then was mixed with the above reformed gas to find the CO.sub.2 when supplied to the shaft part of a blast furnace. As the method for this, the amount of CO.sub.2 emitted was calculated from the measured value of the amount of heat consumption when independently making the CO-containing gas rise in temperature to 800 C. Next, this was added to the CO.sub.2 of the reducing gas 3 of Example 1 to calculate the overall CO.sub.2. As a result, the CO.sub.2 was 0.19 molCO.sub.2/mol.sub.H2. This is a value greatly exceeding the results of Example 1 shown as a preferable example (reducing gases (1) and (3) of Table 2) and exceeding the absolute value of the CO.sub.2 emission at the blast furnace (0.16 molCO.sub.2/mol.sub.H2), so the CO.sub.2 cannot be cut. This is due to the heating efficiency of the CO-containing gas in the present comparative example being lower compared with the present invention.
(145) Below, a comparison will be made with a method of manufacture of hydrogen gas for supply to the shaft part of a blast furnace using another method of reforming using COG as a raw material.
Comparative Example 2
(146) Catalytic Steam Reforming of Crude COG
(147) Here, an actual oven was operated for 2 hours and the following procedure was followed to manufacture hydrogen gas for supply to the shaft part of a blast furnace from crude COG. The crude COG extracted from the coke oven was treated by a catalytic reforming reactor (with steam added (S/C (number of molecules of H.sub.2O/number of atoms of C in hydrocarbons)=2) at 700 C. or more (NiMgO-based catalyst used) to steam reform it, then was refined by a scrubber to manufacture reformed COG. After gas sampling, the reformed COG was raised in pressure (0.3 MPa) and raised in temperature (800 C.) then supplied to the shaft part of a blast furnace. Just the moisture in the crude COG is not sufficient for steam reforming, so 800 C. steam was added from the outside so that S/C=2 at the catalytic reforming reactor.
(148) The chemical composition of the hydrogen gas supplied to the shaft part of a blast furnace obtained as a result and the actual value of the amount of CO.sub.2 emitted CO.sub.2 during manufacture of hydrogen are shown in Table 4. CO.sub.2 was calculated from the CO.sub.2 in the hydrogen gas supplied to the shaft part of a blast furnace and the theoretical amount of CO.sub.2 in the combustion exhaust gas in the case of obtaining the theoretical heat of reaction in the catalytic steam reforming reaction+the energy required for raising the temperature and raising the pressure of the reformed COG by complete combustion of natural gas.
(149) TABLE-US-00004 TABLE 4 Hydrogen gas supplied to shaft part of blast furnace manufactured by catalytic steam reforming of crude COG Mole CH.sub.4 0.22 fraction C.sub.2H.sub.4 0.01 CO 0.06 CO.sub.2 0.11 H.sub.2 0.58 H.sub.2O N.sub.2 0.02 CO.sub.2 0.43 (mol/mol.sub.H2)
(150) In the results of Table 4, the concentration of methane and concentration of CO.sub.2 were excessive, so the gas was not suitable as hydrogen gas for supply to the shaft of a blast furnace. Further, it was learned that with just a reforming step, the CO.sub.2 exceeded the allowable value (0.16 molCO.sub.2/mol.sub.H2) so was excessive.
Comparative Example 3
(151) Partial Oxidation Reforming of Crude COG
(152) The manufacture of hydrogen gas for supply to the shaft part of a blast furnace by partial oxidation reforming of crude COG described in Japanese Patent Publication No. 2001-220584 will be studied next.
(153) In Japanese Patent Publication No. 2001-220584, crude COG extracted from a coke oven is reformed by partial oxidation by addition of pure oxygen (using the crude COG itself as the flammable gas), then refined by a scrubber to obtain reformed COG. Consider supplying this reformed COG as the reducing gas (hydrogen gas supplied to shaft part of a blast furnace) to the shaft part of a blast furnace. The chemical composition of the reformed COG obtained by partial oxidation shown in the examples of Japanese Patent Publication No. 2001-220584A and the amount of CO.sub.2 emitted CO.sub.2 during production of hydrogen calculated from the amounts of CO.sub.2 emitted and the amounts of hydrogen emitted of the same are shown in Table 5.
(154) TABLE-US-00005 TABLE 5 Hydrogen gas supplied to shaft part of blast furnace manufactured by partial oxidation reforming of crude COG Mole CH.sub.4 0.02 fraction C.sub.2H.sub.4 0.00 CO 0.23 CO.sub.2 0.08 H.sub.2 0.65 H.sub.2O N.sub.2 0.01 CO.sub.2 0.24 or more (mol/mol.sub.H2)
(155) Here as well, it was learned that with just the reforming stage, the CO.sub.2 exceeded the above allowable value (0.16 molCO.sub.2/mol.sub.H2) and was excessive. Further, the concentration of CO.sub.2 also greatly exceeded the upper limit concentration as a reducing gas supplied to the shaft of a blast furnace. This was also not suitable in terms of constituents.
Comparative Example 4
(156) Catalytic Steam Reforming of Refined COG
(157) Catalytic steam reforming of refined COG (crude COG refined to remove the majority of the tar, BTX (benzene and other aromatic compounds), moisture, sulfides, and nitrides to obtain fuel gas. Widely used as fuel in ironmaking plants) will be studied next.
(158) Refined COG from the gas holder was raised in temperature (800 C.) and treated by a catalytic reactor (steam added (S/C=2), reaction temperature 700 C. or more, NiMgO-based catalyst used) to manufacture reformed COG. This was cooled, raised in pressure (0.3 MPa), then raised in temperature by indirect heating (800 C.) to obtain a gas for supply to the shaft part of a blast furnace. The composition of the reformed COG was found by a small scale test. Assuming this process, the reason why not directly supplying high temperature reformed COG to the shaft part of a blast furnace is as follows: With this process, due to the residual H.sub.2S contained in a large amount in the refined COG, the catalyst is poisoned and loses activity in a short period of time (several hours to several tens of hours). Each time the catalyst loses activity, the reforming operation has to be suspended and a catalyst regeneration operation has to be performed. Therefore, the operation cannot be said to be a continuous reforming operation. For this reason, it is difficult to directly connect such a batch type reaction apparatus to the shaft part of a blast furnace where continuous supply of hydrogen gas is sought for securing stability of operations (gas holder or other production buffer is necessary).
(159) The amount of CO.sub.2 emitted CO.sub.2 during production of hydrogen was calculated from the CO.sub.2 in the above constituents and the theoretical amount of CO.sub.2 in the combustion exhaust gas in the case of obtaining the theoretical heat of reaction in the steam reforming reaction+energy required for raising temperature and raising pressure of reformed COG by complete combustion of natural gas. The results are shown in Table 6.
(160) TABLE-US-00006 TABLE 6 Composition of reducing gas Mole CH.sub.4 0.01 fraction C.sub.2H.sub.4 0.00 CO 0.10 CO.sub.2 0.21 H.sub.2 0.66 H.sub.2O N.sub.2 0.02 CO.sub.2 0.70 (mol/mol.sub.H2)
(161) In Table 6, the concentration of CO.sub.2 exceeds the upper limit concentration of the reducing gas supplied to the shaft part of a blast furnace, so is not suitable. Further, the CO.sub.2 exceeds the above allowable value (0.16 molCO.sub.2/mol.sub.H2), so the gas manufactured in this example is not suitable as the reducing gas to be supplied to the shaft part of a blast furnace.
(162) From the above results, in the typical prior art, it is difficult to efficiently manufacture hydrogen gas for supply to the shaft part of a blast furnace under the condition of reduced CO.sub.2 emission. The superiority of the present invention is clear.
(163) In the following example, crude COG obtained from a coke oven without using a moisture reducing means and reduced moisture crude COG obtained from a coke oven operating using a DAPS as a moisture reducing means and reducing the coal moisture were used as the raw material gases. The chemical compositions of the crude COG and reduced moisture crude COG are shown in Table 7.
(164) TABLE-US-00007 TABLE 7 Reduced moisture Crude COG crude COG Mole CH.sub.4 0.22 0.25 fraction C.sub.2H.sub.4 0.04 0.04 CO 0.05 0.06 CO.sub.2 0.02 0.02 H.sub.2 0.39 0.44 H.sub.2O 0.25 0.17 N.sub.2 0.03 0.03
Comparative Example 5
(165) COG extracted from a coke oven using coal treated to reduce moisture by DAPS was treated in a carbonization furnace (temperature 700 C. or more, NiMgO-based catalyst used) to manufacture primary reformed gas. This was passed through a scrubber to refine it, then was raised in pressure (0.3 MPa) and raised in temperature, without partial oxidation, by indirect heating (800 C.) and was supplied to the shaft part of a blast furnace.
(166) In the treatment to reduce moisture by DAPS, the coal moisture was reduced from 7% to 4%. The coal reduced in moisture was conveyed by a belt conveyor to a stock vat above the coke oven, then was conveyed by a commercially available skip car from the stock vat to the inside of the coke oven. From a branch pipe provided at the coke raising pipe of the coke oven, approximately 800 C. reduced moisture crude COG was extracted by suction. The extracted reduced moisture crude COG was supplied to the carbonization furnace by a gas pipe maintained in temperature at its surroundings so as to keep the temperature from falling.
(167) The carbonization furnace had gas passage cross-section (horizontal plane) dimensions of 120 mm900 mm and a gas passage direction height of 1200 mm. The layer of the granular bodies (catalyst layer) in the carbonization furnace was formed while holding the catalyst (diameter 15 mm) filled in the carbonization furnace by a holder with a bottom of a drainboard shape. The height was 600 mm. During operation, the carbonization furnace was maintained at 800 C. in temperature by external heating and was operated for 2 hours to generate 4 kg of coke. Unless otherwise indicated, the coke (solid carbon) deposited at the catalyst layer of the carbonization furnace was not separated and recovered from the catalyst layer during operation. If periodically separating and recovering the coke (solid carbon) deposited on the catalyst layer, the operating time was made 24 hours.
(168) As the refining apparatus, a scrubber was used. The tar and majority of moisture in the reduced moisture crude COG were removed to manufacture the primary reformed gas. The temperature of the gas after passing through the scrubber was about 50 C. A branch for sampling use was provided at the gas passage pipe at the exit side of the scrubber, the primary reformed gas was extracted, then this was supplied to a commercially available gas chromatography apparatus for on-line analysis of the constituents. The results of analysis are shown in Table 8 (Heat decomposition of reduced moisture crude COG).
(169) TABLE-US-00008 TABLE 8 Heat decomposition of reduced moisture crude COG Mole CH.sub.4 0.18 fraction C.sub.2H.sub.4 0.03 CO 0.10 CO.sub.2 0.02 H.sub.2 0.66 H.sub.2O 0.00 N.sub.2 0.02 CO.sub.2 0.13 (mol/mol.sub.H2)
(170) The amount of CO.sub.2 emitted during manufacture of hydrogen was calculated from the amount of CO.sub.2 in the primary reformed gas and the theoretical amount of CO.sub.2 in the combustion exhaust gas in the case of obtaining the theoretical heat of reaction in the above heat decomposition reaction+energy required for raising the temperature and raising the pressure of the primary reformed gas by complete combustion of natural gas. The results of calculation are shown in Table 2 as the CO.sub.2 values. The obtained value (0.13%) is within the range of the allowable value of the amount of CO.sub.2 generated when producing hydrogen allowed when producing the above-mentioned 1 mol of hydrogen gas (0.16 molCO.sub.2/mol.sub.H2) (in NPTL 2, amount of CO.sub.2 emitted during manufacture of hydrogen allowed when producing hydrogen gas 1 mol), while the concentrations of methane and hydrogen are excessive. With this, application to reducing gas for supply to the shaft part of a blast furnace is not possible.
Comparative Example 6
(171) The secondary reformed gas chemical composition and the amount of CO.sub.2 emitted during manufacture of hydrogen combining primary and secondary reforming in the case of using primary reformed gas obtained by heat decomposition of the reduced moisture crude COG of Comparative Example 5 with an amount of CO.sub.2 emitted during manufacture of hydrogen within the above range of allowable values to manufacture the secondary reformed gas by catalytic steam reforming were calculated by thermodynamic calculations assuming equilibrium conditions at the reaction temperature of the secondary reforming. Regarding the secondary reforming, the values of the amounts of generation of the constituents at the time of 100% methane decomposition obtained by equilibrium calculations and the values obtained when making the amounts of generation of the constituents respectively 70% of the values at the time of about 100% methane decomposition and assuming 30% of methane in the primary reformed gas remaining as reformed gas were used (in reforming, about 100% methane decomposition (equilibrium) is not always obtained, so an example where methane is incompletely decomposed will also be studied.) Table 9 shows the amounts of generation of the constituents at the time of 100% decomposition of the methane used and the amounts of generation of the constituents at the time of 70% decomposition.
(172) TABLE-US-00009 TABLE 9 Equilibrium catalytic Nonequilibrium catalytic steam reforming steam 70% of reduced moisture reforming of reduced crude COG primary moisture crude reformed gas COG primary reformed gas Mole CH.sub.4 0.00 0.04 fraction C.sub.2H.sub.4 0.00 0.01 CO 0.16 0.09 CO.sub.2 0.03 0.02 H.sub.2 0.68 0.65 H.sub.2O 0.12 0.19 N.sub.2 0.01 0.02 CO.sub.2 0.19 0.19 (mol/ mol.sub.H2)
(173) The constituents of the gas obtained by a steam reforming reaction or partial oxidation reaction (no catalyst) under conditions greatly exceeding 1000 C. are known to be close to the equilibrium composition at the reaction end temperature (substantially the reactor exit side temperature) if sufficiently setting the residence time of the gas in the reactor, so by calculating the equilibrium constituents, it is possible to evaluate the reforming performance of a steam reforming reaction or partial oxidation reaction (no catalyst) under conditions greatly exceeding 1000 C.
(174) The secondary reformed gas obtained by catalytic steam reforming was manufactured by raising the primary reformed gas in temperature (to 800 C.) and treating it in the catalytic reactor (steam added (S/C (number of molecules of H.sub.2O/number of atoms of C in hydrocarbons)=2, reaction temperature 700 C. or more, and NiMgO-based catalyst used). The thus manufactured secondary reformed gas was cooled once, raised in pressure (0.3 MPa), then raised in temperature by indirect heating (800 C.) to obtain a gas to be supplied to the shaft part of a blast furnace.
(175) The amount of CO.sub.2 emitted during manufacture of hydrogen was calculated from the CO.sub.2 derived from the energy supplied at the time of primary reforming, the CO.sub.2 in the above constituents, and the theoretical amount of CO.sub.2 in the combustion exhaust gas in the case of obtaining the theoretical heat of reaction in the above steam reforming reaction+energy required for raising temperature and raising pressure of secondary reformed gas by complete combustion of natural gas. The results are shown in Table 9.
(176) In both the equilibrium composition at the time of 100% methane decomposition and the nonequilibrium 70% reformed composition, the amount of CO.sub.2 emitted during manufacture of hydrogen exceeded the above allowable value (0.16 molCO.sub.2/mol.sub.H2) so was excessive. Accordingly, the secondary reformed gas of this example is not suitable as the reducing gas for supply to the shaft part of a blast furnace. Furthermore, the moisture and hydrogen in the secondary reformed gas were excessive (allowable value: 10%). With that, supply to the shaft part of a blast furnace is not possible.
Comparative Example 7
(177) The catalytic steam reforming of crude COG (COG obtained from coke oven without using moisture reducing means, for composition, see Table 7) will be explained next.
(178) Crude COG extracted from a coke oven (operated for 24 hours) was treated by a catalytic reactor (800 C. steam added (S/C=2), reaction temperature 700 C. or more, NiMgO-based catalyst used) to manufacture secondary reformed gas. This was passed through a scrubber to refine it, then was raised in pressure (0.3 MPa) and raised in temperature by indirect heating (800 C.) to obtain gas for supply to the shaft part of a blast furnace. As explained in Comparative Example 6, the amounts of generation of the constituents of the secondary reformed gas at the time of 100% methane decomposition and the amounts of generation of the constituents at the time of 70% decomposition were found by calculation. Further, the amount of CO.sub.2 emitted during manufacture of hydrogen was calculated from the CO.sub.2 in the above constituents and the theoretical amount of CO.sub.2 in the combustion exhaust gas in the case of obtaining the theoretical heat of reaction in the above catalytic steam reaction+energy required for raising the temperature and raising the pressure of the reformed gas by complete combustion of natural gas. The obtained results are shown in Table 10.
(179) TABLE-US-00010 TABLE 10 Nonequilibrium partial oxidation Catalytic Equilibrium partial 70% reforming steam oxidation of of crude COG reforming of crude COG primary crude COG primary reformed gas reformed gas Mole CH.sub.4 0.22 0.01 0.05 fraction C.sub.2H.sub.4 0.01 0.00 0.00 CO 0.06 0.26 0.19 CO.sub.2 0.11 0.02 0.02 H.sub.2 0.58 0.63 0.61 H.sub.2O 0.07 0.11 N.sub.2 0.02 0.01 0.02 CO.sub.2 0.43 0.32 0.38 (mol/mol.sub.H2)
(180) In both the equilibrium composition at the time of 100% methane decomposition and the nonequilibrium 70% reformed composition, the amount of CO.sub.2 emitted during manufacture of hydrogen exceeded the above allowable value (0.16 molCO.sub.2/mol.sub.H2) so was excessive. Accordingly, the secondary reformed gas of this example is not suitable as the reducing gas for supply to the shaft part of a blast furnace.
Comparative Example 8
(181) The example of manufacture of primary reformed gas by heat decomposition of the reduced moisture crude COG in a carbonization furnace and manufacture of secondary reformed gas by catalytic steam reforming will be explained.
(182) For manufacture of the primary reformed gas, primary reformed gas obtained by heat decomposition of the reduced moisture crude COG of Comparative Example 5 was used. Next, the primary reformed gas was raised in temperature (800 C.) and was treated by the catalytic reactor (steam added (S/C=2, reaction temperature 700 C. or more, NiMgO-based catalyst used) to manufacture the secondary reformed gas. This was cooled once down to ordinary temperature, then raised in pressure (0.3 MPa) and raised in temperature (800 C.) to obtain gas for supply to the shaft part of a blast furnace. As explained in Comparative Example 6, the amounts of generation of the constituents at the time of 100% methane decomposition of the secondary reformed gas and the amounts of generation of the constituents at the time of 70% decomposition were found by calculations.
(183) The amount of CO.sub.2 emitted during manufacture of hydrogen was calculated from the CO.sub.2 derived from the energy supplied at the time of primary reforming, the CO.sub.2 in the above constituents, and the theoretical amount of CO.sub.2 in the combustion exhaust gas in the case of obtaining the theoretical heat of reaction in the above catalytic steam reforming reaction+energy required for raising temperature and raising pressure of secondary reformed gas by complete combustion of natural gas. The results are shown in Table 11.
(184) TABLE-US-00011 TABLE 11 Nonequilibrium steam Equilibrium steam reforming 70% reforming of of reduced reduced moisture moisture crude COG crude COG primary primary reformed gas reformed gas Mole CH.sub.4 0.00 0.04 fraction C.sub.2H.sub.4 0.00 0.01 CO 0.16 0.10 CO.sub.2 0.03 0.02 H.sub.2 0.66 0.60 H.sub.2O 0.13 0.21 N.sub.2 0.01 0.02 CO.sub.2 0.21 0.21 (mol/mol.sub.H2)
(185) In both the equilibrium composition at the time of 100% methane decomposition and the nonequilibrium 70% reforming composition, the amount of CO.sub.2 emitted during manufacture of hydrogen exceeded the allowable value (0.16 molCO.sub.2/mol.sub.H2) and was excessive. Accordingly, in this example, the secondary reformed gas is not suitable as reducing gas for supply to the shaft part of a blast furnace. Furthermore, the moisture and hydrogen in the secondary reformed gas are excessive. With this as is, supply to the shaft part of a blast furnace is not possible.