FLUE GAS TREATMENT METHOD AND INSTALLATION

Abstract

Method and installation for treating a CO.sub.2- and H.sub.2O-containing flue gas generated by an industrial process unit before CCUS, whereby the flue gas evacuated from the unit is subjected to cooling to a temperature T2 between 100 and 600° C., whereby the cooled flue gas is pretreated in one or more particle removal and/or gas cleaning and/or drying stages and the temperature of the cooled flue gas is further reduced to a temperature T3<T2, before a first part of pretreated flue gas is subjected to CCUS, a second part of the pretreated flue gas being recycled at temperature T3 as a cooling agent and mixed with the flue gas during the controlled cooling thereof, partially or fully purified CO.sub.2 from the CCUS may be recycled at temperature T4<T2 may be recycled as a cooling agent and mixed with the flue gas during the controlled cooling.

Claims

1. A method of treating a carbon dioxide and water containing flue gas generated by a flue-gas-generating unit, comprising: a. evacuating a flue gas from a flue-gas-generating unit at a first temperature T1, b. controlled cooling of the evacuated flue gas to a second temperature T2, wherein T2<T1 and wherein T2 is between 100 and 600° C., and c. pretreating the cooled flue gas in one or more particle removal and/or gas cleaning and/or drying stages, whereby the temperature of the cooled flue gas is further reduced to a third temperature T3, wherein T3<T2, d. subjecting a first part of the pretreated flue gas to Carbon Capture Utilization and/or Storage, wherein: a second part of the pretreated flue gas is recycled at the third temperature T3 as a cooling agent and mixed with the flue gas in step b and/or wherein the Carbon Capture Utilization and/or Storage includes a substep of purifying the first part by removing gaseous components other than carbon dioxide which are present at a level of at least 1% vol therefrom so as to obtain purified carbon dioxide whereby said substep optionally comprises a succession of multiple purification stages terminating in a final purification stage, whereby the stage or stages preceding the final purification generate partially purified carbon dioxide, whereby a fraction of the partially or fully purified carbon dioxide obtained at a fourth temperature T4, wherein T4<T2 is recycled as a cooling agent and mixed with the flue gas.

2. The method according to claim 1, whereby the first part of the pretreated flue gas, which is subjected to Carbon Capture Utilization and/or Storage, contains at least 50% of the CO.sub.2 present in the evacuated flue gas.

3. The method according to claim 1, whereby pretreating step c comprises one or more gas-cleaning stages to remove particles and/or gaseous impurities which are present at a level below 1% vol in the flue gas (evacuated from the unit (B-100).

4. The method according to claim 1, whereby pretreating step c comprises a drying stage during which water is removed from the flue gas through condensation at a temperature below 100° C.

5. The method according to claim 4, whereby during the drying stage, water is removed from the flue gas through condensation at the third temperature and whereby a portion of the dried flue gas thereby obtained at the third temperature is recycled to step b as the second part of pretreated flue gas.

6. The method according to claim 1, further comprising a step of detecting a temperature of the evacuated flue gas before, during and/or after step b and whereby the amount of pretreated flue gas which is recycled as the second part of pretreated flue gas and mixed with the evacuated flue gas in step b and/or the fraction of the partially or fully purified carbon dioxide obtained which is recycled as a cooling agent and mixed with the flue gas in step b is/are regulated in function of the detected temperature or temperatures so as to obtain, at the end of step b, cooled flue gas at the second temperature.

7. The method according to claim 1, whereby the flue gas evacuated in step a comprises combustion gas generated by combustion of a carbon-containing fuel with a combustion oxidant containing 21% to 100% by volume oxygen.

8. The method according to claim 1, whereby flue gas evacuated in step a contains, for a total of 100% vol of gaseous components, concentration based on wet basis: 5 to 20% vol carbon dioxide; 5 to 30% vol water; 0 to 10% vol oxygen 50 to 80% vol nitrogen, 0 to 3% vol of one or more other gases.

9. The method according to claim 1, whereby flue gas evacuated in step a contains, for a total of 100% vol of gaseous components, concentration based on wet basis: 15 to 55% vol carbon dioxide; 40 to 80% vol water; 0 to 10% vol oxygen 0 to 3% vol argon; 0 to 20% vol nitrogen 0 to 3% vol of one or more other gases.

10. The method according to claim 1, whereby the flue-gas-generating unit comprises a unit selected from glass melting furnaces, glass refining furnaces, glass melting-and-refining furnaces, steel reheating furnaces, Electric Arc furnace, non-ferrous smelting and melting furnaces, cement furnaces, lime furnaces, enamel furnaces, hot stoves, electrolysers for primary metal production, cokery furnaces, electric furnaces for glass melting, electric furnaces for special metal melting and electrical furnaces for metal heat treatment.

11. An installation for treating a carbon dioxide- and water containing stream of flue gas generated by a flue-gas-generating unit, the installation defining a flue-gas flow path, the flue-gas flow path comprising: e. an inlet for receiving the gas stream from the unit, f. a cooling unit for controlled cooling to a second temperature of the gas stream received through the inlet, g. a pretreating unit for pretreating the cooled gas stream from the cooling unit, the pretreating unit comprising one or more of the following gas-pretreatment devices: gas dryer/dehumidifier, particle remover and gas cleaner, at least one device of the pretreating unit including a cooler adapted to cool the gas stream further to a third temperature T3, wherein T3<T2, and h. an outlet downstream of the pretreating unit, said outlet connecting the flue-gas flow path to a Carbon Capture Utilization and/or Storage plant, wherein: the cooling unit comprises a gas mixer at or downstream of the inlet of the flue-gas flow path and the installation further comprises a gas recycle loop between, on the one hand, a tapping point at or downstream of the pretreating unit, and, on the other hand, the gas mixer of the cooling unit, the recycle loop being adapted to recycle a portion of the gas stream at a third temperature to the gas mixer where the recycled portion of the flue gas) is mixed with the gas stream, thereby causing the gas stream to be cooled.

12. The installation according to claim 11, further comprising: a control unit and a recycle flow controller, the control unit being adapted to regulate, by means of the recycle flow controller, the portion of the gas stream which is recycled through the gas recycle loop so that in the cooling unit the gas stream is cooled to the second temperature.

13. The installation according to claim 12, further comprising: at least one temperature sensor for detecting a temperature of the gas stream upstream of, in, and/or downstream of the gas mixer, whereby the control unit is connected to the at least one temperature sensor and whereby the control unit is adapted to regulate, by means of the recycle flow controller, the portion of the gas stream and/or the fraction of partially or purified carbon dioxide which is recycled in function of the at least one temperature detected by the at least one temperature sensor.

14. The installation according to claim 11, whereby the pretreating unit comprises at least one gas dryer in the form of a water condenser equipped with a cooler adapted to cool the gas stream to a temperature below 100° C. and whereby the tapping point is located downstream of the water condenser.

15. The installation according to claim 11, whereby the flue-gas-generating unit comprises a combustion unit and/or another industrial process like electrolyser for primary metal production, whereby the combustion unit is preferably selected from glass melting furnaces, glass refining furnaces, glass melting-and-refining furnaces, steel reheating furnaces, Electric Arc furnace, non-ferrous smelting and melting furnaces, cement furnaces, lime furnaces, enamel furnaces, hot stoves, electrolysers for primary metal production, cokery furnaces, electric furnaces for glass melting, electric furnaces for special metal melting and electrical furnaces for metal or heat treatment.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0132] The present invention and its advantages will be better understood in the light of the following example of an embodiment, whereby the cooling agent consists of part of the pretreated flue gas, reference being made to the FIGURE.

[0133] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawing, in which like elements are given the same or analogous reference numbers and wherein:

[0134] FIG. 1 illustrates a schematic representation of an installation in which the method according to the present invention is used to treat a furnace flue gas which contains CO.sub.2 and H.sub.2O.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0135] The present invention and its advantages will be better understood in the light of the following example of an embodiment, whereby the cooling agent consists of part of the pretreated flue gas, reference being made to the FIGURE, which is a schematic representation of an installation in which the method according to the present invention is used to treat a furnace flue gas which contains CO.sub.2 and H.sub.2O.

[0136] Furnace (oven) B-100 burns fuel with an oxidizer agent to produce thermal energy to heat a charge, such as a non-ferrous metal charge to be melted. As a byproduct, flue gas 100 containing carbon dioxide and water vapour is produced. At least a major part of the carbon dioxide and of the water vapour in the flue gas results directly from the oxidation (combustion) of the fuel.

[0137] The flue gas 100 leaves furnace B-100 at high temperature T1 and contains a non-negligible portion of the thermal energy generated in furnace B-100 (also referred to as “residual heat”).

[0138] Flue gas 100 also contains entrained particulate matter (in particular, dust) and sulphur oxides (SOx) which must be removed from flue gas by filtration.

[0139] However, the initial temperature T1 of the evacuated flue gas 100 is so high that introducing flue gas 100 directly into the filtration equipment would rapidly damage the latter.

[0140] It would be useful if one could simply recover the residual thermal energy from flue gas and use said residual thermal energy in the production process, for example by using said thermal energy to preheat the fuel and/or the oxidizer agent through heat exchange between the flue gas and the respective combustion agents. However, initial temperature T1 of the evacuated flue gas 100 is also too high for the heat exchangers normally used for that purpose.

[0141] It is thus necessary to reduce the temperature of flue gas 100 before filtration or even energy recovery may be performed.

[0142] In the illustrated method according to the invention, this is achieved by controlled cooling of flue gas 100 to a temperature T2 below T1 which is compatible with heat exchangers and filtration equipment.

[0143] In accordance with the invention, said controlled cooling of flue gas 100 is more specifically achieved by mixing flue gas 100 in mixer V200 with a controlled amount of recycle gas 301, which has a temperature T3 below T2. The result is a stream of cooled flue gas 200, consisting of a mixture of flue gas 100 and recycle gas 301. The amount of recycle gas 301 mixed with flue gas 100 is chosen so that temperature T2 of the cooled flue gas 200 is temperature compatible with the downstream equipment to which cooled flue gas 200 is sent.

[0144] Although not illustrated in the FIGURE, the step of controlled cooling by mixing with recycle gas 301 can be combined with additional cooling, in particular through heat recovery.

[0145] The cooled mixed flue gas 200 is processed in one or more cleaning steps, such as dedusting, SOx removal and NOx removal. In the illustrated embodiment, Ca(OH).sub.2 201 is injected into cooled flue gas 200 as a first cleaning agent causing the SOx present therein to react with the Ca(OH).sub.2 to form CaSO.sub.3 and/or CaSO.sub.4. Cooled flue gas 200 is then sent to filter F-210, where particles, such as dust, and the sulfur salts are removed from the cooled flue gas 200. Thereafter, the partially cleaned flue gas 210, is subjected to a further cleaning step to eliminate NOx present in the flue gas. Thereto, urea 211 is introduced into the partially cleaned flue gas 210. In reactor R220, the NOx is reduced to N.sub.2 by reaction with the urea 211, used as a reducing agent.

[0146] The resulting dedusted, deSOxed and deNOxed flue gas 220 is thereafter dehumidified in condenser D230. In condenser D230 the cleaned flue gas 220 is cooled to temperature T3.sub.bis so as to cause water vapour present in the flue gas to condense to liquid water which is drained from D230.

[0147] The cleaned and dried flue gas 230 at temperature T3.sub.bis i is then slightly reheated to temperature T3 in heat exchanger E240 to avoid liquid water condensation in the downstream equipment. The cleaned and dried flue gas 240 is then split into a stream 400 towards CCUS and a recycle stream 300. The fan C300 is increasing the pressure of stream 300. The so obtained stream 301 then has sufficient pressure to be mixed with evacuated flue gas 100 to cool it. The advantages of the method according to the present invention are multiple and immediately apparent.

[0148] Recycle gas 301 consists of cleaned dried flue gas and has a CO.sub.2 content which is higher than that of evacuated flue gas 100.

[0149] As indicated earlier, the installation advantageously includes at least one temperature sensor (not shown) for detecting a temperature of the gas stream upstream of, in, and/or downstream of the gas mixer, a control unit (not shown) connected to the at least one temperature sensor and adapted to regulate, by means of fan C300 the flow (in Nm.sup.3) of pretreated flue gas 301 which is recycled in function of the at least one temperature or temperatures detected by said temperature sensor or sensors.

[0150] Compared to the known method of cooling by ambient air injection, whereby the evacuated flue gas is diluted with ambient air, with the method according to the invention, the controlled cooling step does not cause a reduction of the CO.sub.2 content of the flue gas, but instead actually causes an increase of the CO.sub.2 content of the flue gas, thereby improving the efficiency of the CCUS process in step d.

[0151] In addition, compared to said known method, the changes to the equipment are minimal and the known particle removal, cleaning, drying and CCUS equipment can also be used in the method and installation of the invention.

[0152] The effectiveness and interest of the present invention is illustrated in the table below, which lists the properties, more specifically temperature, flow rate and composition (gaseous components with concentration higher than 1% volume), of the different flue gas streams when a combustion flue gas containing 37% by weight CO.sub.2 and 56% by weight H.sub.2O was evacuated from a furnace at a rate of 1000 Nm.sup.3/h and at a temperature of 750° C., is treated in by means of an installation as illustrated in the FIGURE.

[0153] For the sake of clarity, the enthalpy of the vapour phase is also shown,

[0154] Regarding the enthalpy flows also shown in the table, the values include both chemical and sensible enthalpy, and lead to thermal losses of 140 kW between the cooled flue gas 200 and pretreated flue gas 220, and 550 kW between 220 and 230.

TABLE-US-00001 flue gas stream (reference number as used in the figure) 100 200 210 220 230 240 300/301 400 Temperature (° C.) 750 (T1) 455 (T2) 350 300 25 (T3.sub.bis) 30 (T3) 30 30 Flow rate (Nm.sup.3/h) 1000 1726 1726 1726 1181 1181 726 455 Water (H.sub.2O) 56 33.8 33.8 33.8 3.3 3.3 3.3 3.3 content (% volume) Oxygen (O.sub.2) 1 1.5 1.5 1.5 2.2 2.2 2.2 2.2 content (% volume) Nitrogen (N.sub.2) 6.0 9.1 9.1 9.1 13.2 13.2 13.2 13.2 content (% volume) Carbon dioxide 37 55.6 55.6 55.6 81.3 81.3 81.3 81.3 CO.sub.2 content (% volume) Enthalpy flow −3105 −6049 −6189 −4811 −4810 −2944 −1865 (kW)

[0155] As shown, the method according to the present invention makes it possible to more than double the CO.sub.2 content (from 37 to 80.4% volume) through the controlled cooling and controlled cooling and pretreatment of the evacuated flue gas upstream of CCUS.

[0156] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.