GAS DISTRIBUTION ARRANGEMENT FOR ROTARY REACTOR

Abstract

A port assembly for controlling the delivery of gases into the horizontal rotating reactor such as kiln gasifier is disclosed for introducing reactant gases. The port assembly comprises a cylindrical conduit is divided into noncommunicating four or more sections extending through the entire length of the kiln and supported by the stationary end plates of the rotating kiln gasifier. Each section of the conduit communicates with external supply of the reactant gases and each supply of reactant gases is independently controlled in terms of the composition and quantity. Each section of the port assembly communicates with the interior of the kiln gasifier through the plurality of nozzles are confined in the lower part of the conduit. The number and the size of the nozzles in individual section of the conduit is based on the desired flow of gases and available pressure for the supply of the reactant gases.

Claims

1. An apparatus for reacting solid reactants with gaseous reactants, comprising: (a) a gas port assembly having (i) a main horizontal rotating cylindrical hollow conduit with sealed stationary caps at a front end and the back end, wherein the vessel is divided into at least four sections, (ii) a gas port for introducing gas at the front end and at the back end, (b) an introduction conduit for introducing solid reactants at the front end and connected to the main conduit, (c) a withdrawal conduit to withdraw processed solids and solid residues at the back end of the cylindrical conduit and connected to the main conduit, (d) an independent conduit, connected to the main conduit, for combustion of the gas and the reactants, and (e) a stationary conduit inside the cylindrical conduit commutating with inside of the cylindrical conduit and traversing the length of the cylindrical conduit.

2. The apparatus as claimed in claim 1, wherein the stationary caps allow free rotation of the cylindrical hollow conduit.

3. The apparatus as claimed in claim 1, wherein the introduction conduit commutates with the conduit through the stationary front end cap of the cylindrical conduit.

4. The apparatus as claimed in claim 1, wherein the withdrawal conduit is located at the bottom of the rear end stationary cap of the cylindrical conduit.

5. The apparatus as claimed in claim 1, wherein the withdrawal conduit is located on the rear end stationary cap of the cylindrical conduit.

6. The apparatus as claimed in claim 1, wherein the stationary conduit commutates with inside of the cylindrical conduit with a plurality of nozzles along the length of the length of the conduit.

7. The apparatus as claimed in claim 7, wherein the plurality of nozzles are provided along the one third and one half of the circumference of the conduit.

8. The apparatus as claimed in claim 1, wherein the sections commutate with a separate gas supply.

9. The apparatus as claimed in claim 1, the rotating conduit is positioned in the lower half quadrant of the apparatus and is embedded within a boundary layer of the solid reactants or is outside of the boundary layer of the solid reactants and wherein the ports are positioned directly towards a solid reactant boundary layer on a circumferential wall of the rotating conduit.

10. The apparatus as claimed in claim 1, wherein the stationary conduit is above solid reactant boundary layer on a circumferential wall of the rotating conduit.

11. The apparatus as claimed in claim 1, wherein the apparatus is within a rotary kiln and rotating conduit communicates with kiln through at least one nozzle.

12. A method for gasifying carbonaceous material, comprising: (a) providing a port assembly having (i) a main horizontal rotating cylindrical hollow conduit with sealed stationary caps at a front end and the back end, wherein the vessel is divided into at least four sections, (ii) a gas port at the front end and at the back end; (b) introducing solid reactants through a conduit connected to the rotating conduit and drying the solid reactants in a section of the rotating conduit, (c) introducing gas at the front end and the back end of the main conduit, (d) igniting the gas and solid reactants, and (e) withdrawing processed solids and solid residues at the back end of the main conduit.

13. The method as claimed in claim 12, further comprising manipulating gas plugs at the gas ports to improve mixing of the gas and carbonaceous materials.

14. The method as claimed in claim 12, wherein the main conduit has four section and the four sections include a drying section, a devolatization section, a combustion section, and a gasification section.

15. The method as claimed in claim 12, wherein the ignition occurs in gasification section.

16. The method as claimed in claim 12, wherein the drying section is at a temperature of about 500 F, the devolation section is at a temperature between about 1000 and 2000 F, the combustion section is a temperature between about 1900 F and 2200 F.

17. An apparatus for reacting solid reactants with gaseous reactants, comprising: (a) a gas port assembly having (i) a main horizontal rotating cylindrical hollow conduit with sealed stationary caps at a front end and the back end, wherein the vessel is divided four section along the conduit and the four sections are a drying section, a devolatization section, a combustion section, and a gasification section, wherein the drying section is at a temperature of about 500 F, the devolation section is at a temperature between about 1000 and 2000 F, the combustion section is a temperature between about 1900 F and 2200 F, (ii) a gas port at the front end and at the back end; (b) an introduction conduit for introducing solid reactants at the front end and connected to drying section, (c) a withdrawal conduit to withdraw processed solids and solid residues devolatization section, (d) a combustion conduit at the back end of the rotating conduit.

18. The apparatus as claimed in claim 17, the drying section is next to the devolatization section that is next to the combustion section that is next to the gasification section.

19. The apparatus as claimed in claim 17, wherein the four sections communicates with the interior of a kiln gasifier through a plurality of nozzles confined in the lower part of the main conduit.

20. The apparatus as claimed in claim 17, wherein the apparatus is a kiln and the rotating conduit is positioned in the lower half quadrant of the kiln and is embedded within a boundary layer of the solid reactants or is outside of the boundary layer of the solid reactants.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a schematic of general arrangement of the gas distribution port for a rotating kiln gasifier.

[0031] FIG. 2 is a depiction of reactions taking place within the rotary kiln gasifier.

[0032] FIG. 3 is a bottom view of the interior portion of the gas distribution port.

[0033] FIG. 4 is a cross section of the kiln gasifier with gas distribution port.

[0034] FIG. 5 is an expanded cross section view of the port assembly section in the interior of the rotary kiln.

[0035] FIG. 6 is a depiction of temperature profile inside the rotary kiln gasifier.

DETAILED DESCRIPTION OF THE INVENTION

[0036] FIG. 1 depicts one of many types of rotary kiln apparatus with which the present invention can be practiced. Referring to FIG. 1, the rotary kiln gasifier 1 is a hollow refractory lined vessel with suitable inlets for feeding carbonaceous material 2, suitable inlet for feeding reactant gases such as air and steam 3, suitable outlet for fuel gas 4, and suitable outlet for ash 5. The rotary kiln depicted in FIG. 1 can also operate as combustor with equal effectiveness. The gasifier 1 should be large enough to gasify desired capacity of carbonaceous material and to provide adequate residence time for the gasification reactions between carbonaceous materials and the gaseous reactants. The interior of the gasifier 1 is preferably refractory lined 6 or alternatively surrounded by heat transfer devices such as tubes containing flowing liquids to absorb heat. The refractory lined kiln is preferred because the hot refractory retains heat and transfers that heat to the carbonaceous material coming in its contact thereby raising the temperature of the said carbonaceous material and thereby making it easier for gaseous reactant to initiate gasification reactions with the said solids.

[0037] Because of the nature of the rotating kiln, when the carbonaceous solid material is introduced into the said kiln, the solid carbonaceous material generally gravitates towards the walls and ultimately to the bottom of the said kiln. In contrast the flow of gas introduced at the head of the kiln flows through the middle of the kiln and as a result minimal interaction between the solids and gas is expected in this type of devices. In order to get maximum benefit out of this type of devices it is essential to maximize gas-solid interaction. This is exactly what the rotating gas distributor 7 of the present invention achieves.

[0038] The gas distributor 3 is essentially a gas port as a means of introducing and distributing reactant gases such as gaseous fuel, air, oxygen, and steam into the rotary kiln for processing of any solids to attain maximum interaction between the solid materials present in the kiln with the reactant gases that are being introduced through the said gas distributor. The example here depicts one application of the invention for the gasification of biomass which requires four stages of reaction for converting it into gaseous fuel gas. The invention is described for this specific application without departing from the main spirit of the invention so that the embodiments of the invention are properly understood.

[0039] The gas port 3 is supported at both ends of the kiln by the front and rear hoods of the kiln with sealed insertions 7 and 8 respectively and comprises of a conduit which is divided into four noncommunicating sections 9, 10, 11, and 12. Each of the section 9, 10, 11, and 12 communicates with the gas supply via other conduits 13, 14, 15, and 16. The supplies of gas to each of these conduits are independently controlled by control valves 17, 18, 19, and 20. The quantity and the composition of the reactant gases vary according to the dictates of the solids processing. For gasification of biomass exemplified here, the reactant gases comprises primarily of air, oxygen, and steam. The length of each of the four noncommunicating sections 9, 10, 11, and 12 are dependent upon type of material being processed. Similarly, the diameters of the conduits 13, 14, 15, and 16 also depend upon the material being processed and the processing capacity of the rotary kiln gasifier.

[0040] The four stages of reactions required for complete gasification of the biomass include drying to remove moisture from the biomass; devolatalization of organic compounds from the biomass; partial combustion of biomass to provide heat required for sustaining reactions necessary for drying, devolatalization, and gasification; and finally the gasification of residual biomass after the moisture and volatile organic compounds are removed from the biomass. FIG. 2 depicts the sections of rotary kiln where these reactions occur. Following is brief description of reactions occurring in these four sections of the rotary kiln and which are supported by reactant gases supplied independently to each of the sections 9, 10, 11, and 12 of the gas distribution port.

[0041] In the first stage of reaction, as soon as the biomass is introduced into the rotary kiln gasifier, the biomass gravitates towards the bottom of the kiln and comes into contact with hot refractory lining 6 which is holding the heat. The heat is transferred from the refractory to the biomass and as a result the temperature of the biomass rises which in turn causes the moisture in the biomass to evaporate. The reactant gases introduced in this zone merely helps to carry the devolatilized moisture into the main gas stream of the kiln. In the first zone depending upon the size of the zone 9, capacity of the kiln in terms of the feed rate of the carbonaceous material into the kiln through inlet 2, the temperature of the refractory 6, and the heat capacity of the refractory 6, the temperature of the biomass may attain temperature as high as 500 deg F. This zone of the rotary kiln gasifier 1 is termed as drying section 9 as shown in FIG. 2.

[0042] The primary reaction in this drying section of the rotary kiln 1 is evolution of the moisture from the biomass represented as:

Wet Biomass+Heat.fwdarw.Dry Biomass+Steam

[0043] In the second stage of the gasification reactions, termed as devolatalization section 10, the temperature of the biomass continues to rise as the heat continues to transfer from the refractory 6 to the biomass. As the temperature of the biomass continues to rise, the volatile organics begin to be released from the biomass. The temperature in this zone typically rises to more than 1000 deg F. which corresponds to flash point of many of the organic compounds which are being released from the biomass. The reactant gases introduced in this zone, especially the oxygen-bearing gases such as air will begin reacting with these organic compounds to break them into simpler compounds. The steam present in the reactant gases would do the likewise destruction of the heavier organic compounds to yield simpler compounds.

[0044] The gasification reactions occurring in devolatalization section of the rotary kiln 1 are represented as:

[0045] Pyrolysis

Biomass+Heat.fwdarw.CH.sub.4+CO+CO.sub.2+H.sub.2O+H.sub.2+Alcohols+Oils+Tars+C

[0046] Gasification

CnHmOp+xO.sub.2+(2n−2x−p)H2O+Heat.frwdarw.(n−y)CO2+(2n−2x−p+m/2−y)H2+yCO—+yH2O

[0047] Where x the oxygen-to-fuel molar ratio and y is the number of moles of CO2 that reacts with H2 to produce CO and H2O due to the water gas shift reaction. This reaction is exothermic at low values of x, and exothermic at high values of .xi. At an intermediate value (x0), the heat of reaction is zero, and is called auto-thermal reforming.

[0048] In the third stage of gasification depicted in FIG. 2 as Combustion/Gasification section corresponding to the third section 11 of the gas distribution port 3 some of the crucial reactions occur. Because of continued exposure to heat from the refractory lining 6 and because of partial combustion of evolved organic compounds in devolatalization, the biomass is sufficiently heated up to reach ignition temperature with incoming reactant gases especially with oxygen bearing gases. Once the biomass and the attendant organic compounds have attained this ignition temperature in the third zone of the reactions, the air and/or oxygen present in the reactant gases begin to partially combust the volatile organic compounds emanating from the biomass in contact with the hot refractory 6 and also begins to combust portion of carbon present in the devolatalized biomass. This combustion is necessary to carry out the reactions between gases and solids and also to maintain temperature in the rotary kiln reactor 1 that would sustain endothermic reactions between steam and the carbonaceous materials to yield synthesis fuel gas. The temperature in this zone could rise way beyond 2000 deg F. but it is generally controlled to less than 2200 deg F. by limiting the amount of oxidant introduced in this zone. The temperature control is also necessary to maintain the integrity of the refractory 6. The combustion reaction also replenishes the heat to the refractory lining so that process can be carried out in a continuous manner. The combination of high temperature and availability of heat released from partial combustion also allow the endothermic reaction between the carbon present in the devolatalized biomass and steam present in the reactant gases to take place in this zone. The partial combustion reactions produces mixture of carbon monoxide and carbon dioxide and the reactions between steam and carbon produces the mixture of hydrogen, carbon monoxide, and carbon dioxide. In this zone, since the temperature is high, some of the steam will also react with organic compounds formed in the second zone and break those organic compounds to methane, hydrogen, carbon monoxide, and carbon dioxide. This zone of partial combustion and gasification is termed as combustion/gasification section. Ideally, major fraction of the reactant gases is introduced in this section 11 of the gas distribution apparatus.

[0049] The following reactions take place in this combustion/gasification section of the rotary kiln:

[0050] Pyrolysis

Biomass+Heat.fwdarw.CH4+CO+CO2+H2O+H2+Alcohols+Oils+Tars+C

[0051] Gasification

[0052] CnHmOp+xO2+(2n−2x−p)H2O+Heat.fwdarw.(n−y)CO2+(2n−2x−p+m/2−y)H2+yCO—+yH2O

[0053] Where x the oxygen-to-fuel molar ratio and y is the number of moles of CO2 that reacts with H2 to produce CO and H2O due to the water gas shift reaction. This reaction is exothermic at low values of x, and exothermic at high values of .xi. At an intermediate value (x0), the heat of reaction is zero, and is called auto-thermal reforming.

[0054] Char Combustion

C+O2.fwdarw.CO2+Heat

[0055] Carbon Steam Reaction

C+H2O+Heat.fwdarw.CO+H2

[0056] Hydrogen Combustion

H2+½O2.fwdarw.H2O+Heat

[0057] Reverse Boudard Reaction

C+CO2+Heat.fwdarw.2CO

[0058] Water-Gas Shift

CO+H2O.fwdarw.CO2+H2+Heat

[0059] In the fourth zone of the reaction reactions, termed as gasification section corresponding to fourth section 12 of the gas distribution assembly 3, the reactant gases comprise primarily of steam. The use of oxidant is generally avoided since oxygen in this zone may preferentially tend to react with fuel gases produced in the earlier sections and thereby depleting its calorific value. In contrast, because of the reaction conditions at high temperature are more conducive for carbon steam reactions, it is preferred that steam is allowed to react with last bit of carbon present in the devolatalized and partially combusted biomass to produce more hydrogen and carbon monoxide. This zone also provides additional residence time for remaining heavy volatile compounds to break down into smaller and simpler compounds by reactions with steam. Because of promoting endothermic reaction in gasification zone, and because the heat of reaction is derived from the bulk of the gases leaving the combustion/gasification section of the rotary kiln gasifier 1, the bulk temperature of gases in this zone drops by 200 to 300 deg F. The drop in gas temperature is largely dependent upon amount of residual carbon as well as on the amount of steam introduced in the fourth section 12 of the gas distribution assembly 3.

[0060] The primary reaction promoted in gasification zone of the rotary kiln 1 is the gasification of residual carbon present in the devolatalized and partially combusted biomass and which is represented by:

[0061] Carbon Steam Reaction

C+H2O+Heatlwdarw.CO+H2

[0062] When the fuel gas exits the fuel gas outlet 4, the temperature of the gas would be 1700 to 1900 deg F. and the fuel gas would be made up mostly of C, CO2, H2, N2, H2O, and CH4. Some traces of impurities such as ammonia, hydrogen chloride, and hydrogen sulfide may also be present. These impurities will be washed down by a suitable chemical scrubber prior to using the fuel gas.

[0063] FIG. 3 is a depiction of one of many possible nozzle arrangements that is provided at the bottom of each of the interior section 9, 10, 11, and 12 of the gas distribution port 3. The total area of the plurality of the nozzles 21, 22, 23, and 24 corresponding to each of the interior section 9, 10, 11, and 12 corresponds with the area of the conduits 13, 14, 15, and 16 that communicates each of the interior sections 9, 10, 11, and 12 with the corresponding reactant gas supply. This way the reactant gases are introduced to the interior of the rotary kiln without significant loss of pressure.

[0064] FIG. 4 is a cross section of one of the four sections 10 of the gas distribution port 3 to illustrate the circumferential confinement of the plurality of the nozzles 22. For best results, the nozzles are confined within the bottom third circumference of the conduit of the gas distribution port 25 and disbursed all along the length of the interior section of the gas distribution port 3. The circumferential confinement of the nozzles 25 is largely dependent upon the thickness layer of solids 27 present at the bottom of the refractory lined rotary kiln 6 and the relative positioning of the gas distribution port 3 because as preferred embodiment of this invention, all of the nozzles 21, 22, 23, and 24 are embedded within the layer of solids 26 that are processed in the rotary kiln 1. The circumferential confinement for the nozzle can be extended or reduced from one third of the circumference for specific applications to meet the condition of embedding all of the nozzles within the solid layer at the bottom of the rotary kiln. The positioning of the conduits 13, 14, 15, and 16 within the corresponding sections 9, 10, 11, and 12 of the gas distribution port are not critical as long as they communicate unhampered with the corresponding reactant gas supplies.

[0065] FIG. 5 is merely an expanded view of the cross section of one of the section 10 of the gas distribution port 3.

[0066] FIG. 6 is a depiction of typical temperature profile inside of the rotary kiln 1 when it is used as biomass gasifier. The maximum temperature is reached in the combustion/gasification section of the kiln.

[0067] The present invention is also useful when practiced as combustor instead of gasification. In this case, only air and/or oxygen is used for reactant gas in all sections 9, 10, 11, and 12 of the gas distribution port 3. The amount of air or oxygen introduced will commensurate with the combustor capacity with respect to the carbonaceous material being combusted. The principles stated with respect to nozzle locations, spacing, and orientation as well as the gas flow in each of the sections 9, 10, 11, and 12 will be somewhat different than in the case of the gasification in order to attain complete combustion of the carbonaceous material as well as to maintain suitable temperatures within the rotary kiln.

[0068] For person familiar with the art of gasification and combustion will recognize that for gasification, the amount of air or oxygen introduced into the gasifier 1 is less than fifty percent of the stoichiometric requirement for the complete combustion of the carbonaceous material being gasified whereas in the case of complete combustion, the amount of air introduced into the kiln reactor 1 sometimes exceeds 200 percent of the stoichiometric requirement of the complete combustion of the carbonaceous material to modulate the temperature inside the rotary kiln and also depending upon the specified exit temperature for the outlet gas in the gas outlet 4.

[0069] The present invention has several advantages.

[0070] One advantage is that by allowing intimate contact between gas and carbonaceous solids within the kiln gasifier, it is possible to obtain complete utilization of the carbonaceous material.

[0071] Another advantage is that by allowing intimate contact between the gas and the solids in the vicinity of heated refractory lining of the kiln, the drying, devolatalization, partial combustion, and gasification reactions of the carbonaceous material with reactant gases occur much more rapidly since the requisite heat for gasification is provided by the heat retained by the refractory lining as well as by the partial combustion of the carbonaceous material.

[0072] Yet another advantage is rotation of the gas distributor which enables added turbulence at the wall of the rotary kiln gasifier thereby increasing the interaction between gas and the solids for attaining optimal reaction and better utilization of carbonaceous material.

[0073] Whilst the invention has been described in detail in terms of specific embodiment thereof, it will be apparent that various changes and modifications can be made by one skilled in the art without deviating from the spirit and scope thereof. One skilled in art will also realize that this invention is applicable for broad range of solids processing in the rotary kiln, all of which are included by inference.

REFERENCES

[0074] 1. J. H. Howson and K. Casnello “Risk Reduction Measures for the Development of Biomass Rotary Kiln Gasification,” Report No. ETSU B/U1/00646/REP and DTI/Pub URN 02/754, issued by DTI Sustainable Energy Programmes for CPL Industries, 2002. [0075] 2. G. P. Androutsopoulos, K. S. Hatzilyberis, “Electricity Generation And Atmospheric Pollution The Role Of Solid Fuels Gasification” presented at 7th International Conference on Environmental Science and Technology Ermoupolis, Syros island, Greece, September 2001 [0076] 3. Francesco Fantozzi, Bruno D'Alessandro, and Umberto Desideri, “An IPRP (Integrated Pyrolysis Regenerated Plant) Microscale Demonstrative Unit in Central Italy” Proceedings of ASME Turbo Expo 2007: Power for Land, Sea and Air, May 14-17, 2007, Montreal, Canada