METHOD OF PROCESSING EXHAUST GAS

Abstract

A method of processing exhaust gas containing CO.sub.2, such as exhaust gas from a cement production plant, includes burning fuel in the combustion reactor with the O.sub.2 content of the exhaust gas being used as an oxidizing agent, controlling the combustion in the combustion reactor so that the exhaust gas from the combustion reactor contains less than 10 vol.-% of oxygen and at least 80 vol.-% of a mixture of CO and CO.sub.2, and feeding the exhaust gas from the combustion reactor into a conversion reactor, in which the CO.sub.2 and optionally the CO contained in the exhaust gas is converted into a hydrocarbon fuel.

Claims

1. A method of processing exhaust gas containing CO.sub.2 and O.sub.2, comprising the steps of: introducing the exhaust gas into a combustion reactor, burning fuel in the combustion reactor with the O.sub.2 content of the exhaust gas being used as an oxidizing agent, controlling the combustion in the combustion reactor so that the exhaust gas from the combustion reactor contains less than 10 vol.-% of oxygen and at least 80 vol.-% of a mixture of CO and CO.sub.2 , and feeding the exhaust gas from the combustion reactor into a CO.sub.2/CO conversion reactor, in which the CO.sub.2 and optionally the CO contained in the exhaust gas is converted into a hydrocarbon fuel.

2. A method according to claim 1, wherein at least a part of the exhaust gas, before being introduced into the combustion reactor, is used to dry a solid fuel, in a first drying unit, thereby obtaining a dried fuel, whereupon the dried fuel is optionally ground to obtain a ground fuel.

3. A method according to claim 2, wherein the dried and optionally ground fuel is used as the fuel in the combustion reactor.

4. A method according to claim 1, wherein at least part of the exhaust gas is used to dry cement raw meal in a second drying unit, thereby obtaining a dried raw meal, wherein the dried raw meal is ground to obtain a ground raw meal, which is fed into a preheater of a cement production plant.

5. A method according to claim 1, wherein the CO.sub.2/CO conversion reactor is a bioreactor, a catalytic reactor or a power-to-fuel reactor.

6. A method according to claim 1, wherein by-products produced in the CO.sub.2/CO conversion reactor are fed to a combustion process as a fuel.

7. A method according to claim 1, wherein the hydrocarbon fuel obtained from the CO.sub.2/CO conversion reactor is fed to a combustion process as a fuel.

8. A method according to claim 1, wherein the exhaust gas from the combustion reactor, before being fed into the CO.sub.2/CO conversion reactor, is conducted through a heat exchanger to cool the exhaust gas to a temperature of 20-300° C.

9. A method according to claim 1, wherein the exhaust gas is taken from a cement raw meal preheater of a cement production plant.

10. A method according to claim 1, wherein the exhaust gas containing CO.sub.2 and O.sub.2 is exhaust gas from a cement production plant.

11. A method according to claim 2, wherein the solid fuel is a solid renewable fuel.

12. A method according to claim 6, wherein the by-products produced in the CO.sub.2/CO conversion reactor are proteins.

13. A method according to claim 6, wherein the combustion process is a burner of a cement kiln, a pre-calciner burner and/or a combustion reactor burner of a cement production plant.

14. A method according to claim 7, wherein the combustion process is a burner of a cement kiln, a pre-calciner burner and/or a combustion reactor burner of a cement production plant.

Description

[0037] The invention will now be described in more detail with reference to the attached drawing.

[0038] FIG. 1 schematically illustrates a cement production process, into which the inventive method has been incorporated. In the cement clinker production plant raw meal is charged into a raw meal mill 1 and the ground raw meal is stored in a raw meal silo 2. The ground raw meal stored in the raw meal silo 2 is charged into a preheater 3, where it is preheated in counter-current to the hot exhaust gases coming from a rotary clinker kiln 4. The preheated and optionally pre-calcined raw meal is then introduced into the rotary kiln 4, where it is calcined to obtain cement clinker. The clinker leaves the rotary kiln 4 at a point denoted by 5 and is cooled in a clinker cooler 6. The cooled clinker leaves the clinker cooler 6 at the point denoted by 7.

[0039] The firing system of the rotary kiln 4 is fed with fuel, as is schematically illustrated by 8. Additional fuel may be introduced into the pre-calciner of the preheater 3, as is schematically illustrated by 9. Preferably, an alternative fuel, such as a renewable fuel is used in the firing system of the rotary kiln 4 and/or in the pre-calciner.

[0040] The exhaust gas exiting the preheater 3 at 10 contains CO.sub.2 and O.sub.2. According to the invention, the exhaust gas is introduced into a mill 11, in which solid fuel, such as charcoal, bio coal, biomass or petcoke is dried by means of the heat of the exhaust gas and is ground. The mill 11 thus serves as a drying unit for the solid fuel.

[0041] Preferably, a portion of the exhaust gas exiting the preheater 3 may be used to dry the raw meal in the raw meal mill 1, as denoted by 17.

[0042] Preferably, a portion of the exhaust gas exiting the preheater 3 may be fed into a high temperature dust separator 26 to remove dust contained in the exhaust gases.

[0043] The ground solid fuel is discharged from the mill 11 and introduced into a combustion reactor 12 via the line 13. In the combustion reactor 12 the ground fuel is burnt with the exhaust gas coming from the mill 11 via the line 14, and optionally with the exhaust gas coming from the mill 1 via the line 18, wherein the carbon contained in the ground fuel is converted into carbon monoxide and carbon dioxide, while consuming the O.sub.2 contained in the exhaust gas. The combustion in the combustion reactor 12 is controlled so as to maximize the content of CO and CO.sub.2, and to minimize the O.sub.2 content, in the exhaust gas leaving the combustion reactor via the line 15. In particular, the exhaust gas from the combustion reactor 12 contains less than 10 vol.-% of O.sub.2 and at least 80 vol.-% of a mixture of: CO and CO.sub.2.

[0044] The exhaust gas from the combustion reactor 12 is conducted through a heat exchanger 16 to cool the exhaust gas. Then, the exhaust gas is introduced into a CO.sub.2/CO conversion reactor 19, in order to convert the CO.sub.2 and optionally the CO content of the exhaust gas into a combustible fuel. Hydrogen may be introduced into the CO.sub.2/CO conversion reactor 19 at 20, in order to assist the reaction taking place in the CO.sub.2/CO conversion reactor 19. Preferably, the hydrogen has been produced from a renewable energy source or by using renewable energy, such as electricity from a renewal energy source. The product produced by the CO.sub.2/CO conversion reactor 19 is collected in a separator 21, in which by-products e.g. protein 22 is separated from a gaseous or liquid combustible fuel 23, such as biomethane, methanol or any other hydrocarbon fuel, in particular low molecular weight hydrocarbon fuel.

[0045] The combustible fuel may be used for firing the firing system of the rotary kiln 4, as illustrated by the line 24 or may be dispatched at 25 and used for any other purpose.