Process for producing synthesis gas and electrical energy

Abstract

The invention relates to a process for producing synthesis gas, in which carbon and hydrogen are obtained from hydrocarbon by thermal decomposition. At least a portion of the carbon obtained by the thermal decomposition is reacted, and at least a portion of the hydrogen obtained is reacted with carbon dioxide by a reverse water-gas shift reaction to give carbon monoxide and water. Carbon obtained by the thermal hydrocarbon decomposition is used as fuel in a power plant operation wherein the carbon is combusted to produce electrical power, and carbon dioxide formed in the combustion of the carbon is used in the reverse water-gas shift reaction.

Claims

1. A process for producing synthesis gas, said process comprising: subjecting a hydrocarbon feedstock containing methane to thermal decomposition to obtain carbon and hydrogen, using at least a portion of the carbon obtained by said thermal decomposition as fuel in a power plant operation to produce electrical power wherein said at least a portion of the carbon is combusted to produce a carbon dioxide-containing flue gas, subjecting the carbon dioxide-containing flue gas to a chemical and/or physical gas scrubbing operation to yield carbon dioxide and a residual gas, reacting at least a portion of the hydrogen obtained by said thermal decomposition with at least a portion of the obtained carbon dioxide obtained from said scrubbing operation in a reverse water-gas shift reaction to produce a synthesis gas containing carbon monoxide and water, and converting said synthesis gas to methanol and/or dimethyl ether and/or hydrocarbons wherein waste heat is generated, and using at least a portion of the waste heat generated in the conversion of said synthesis gas in said scrubbing operation, wherein the thermal decomposition is conducted in the presence of a solid granular material, wherein the thermal energy required for synthesis gas production is generated by oxidation or partial oxidation of a fuel comprising hydrocarbons and/or hydrogen and/or by electrical power.

2. The process according to claim 1, wherein a portion of the waste heat (12) generated in the conversion of said synthesis gas is used in a power plant operation for production of electrical power.

3. The process according to claim 1, wherein said thermal decomposition is conducted in a first reaction zone (Z1) and hydrogen formed during said thermal decomposition is passed out of the first reaction zone (Z1) into a second reaction zone (Z2) where said hydrogen is reacted with carbon dioxide in said reverse water-gas shift reaction to produce water and carbon monoxide.

4. The process according to claim 3, wherein energy required for said thermal decomposition in said first reaction zone (Z1) is supplied from said second reaction zone (Z2).

5. The process according to claim 3, wherein hydrocarbon material that is undecomposed or incompletely decomposed in said first reaction zone (Z1) is passed into said second reaction zone (Z2) and reacted therein with water to produce hydrogen and carbon dioxide.

6. The process according to claim 3, wherein said first reaction zone (Z1) and said second reaction zone (Z2) are connected by means of a moving bed (W) containing said solid granular material and said moving bed moves from said second reaction zone (Z2) to said first reaction zone (Z1).

7. The process according to claim 6, wherein gas discharged from said second reaction zone (Z2) is conducted in countercurrent flow to said moving bed (W) and is cooled down by direct heat exchange with said moving bed.

8. The process according to claim 6, wherein said hydrocarbon material (2) is conducted through said first reaction zone (Z1) in countercurrent to said moving bed (W) and said hydrocarbon material (2) is heated up by direct heat exchange with said moving bed.

9. The process according to claim 6, wherein carbon deposited on said solid granular material is separated (A) downstream of said first reaction zone (Z1) and removed from said moving bed (W).

10. The process according to claim 6, wherein said solid granular materials comprises corundum (Al.sub.2O.sub.3), quartz glass (SiO.sub.2), mullite (Al.sub.2O.sub.3.SiO.sub.2), cordierite ((Mg,Fe).sub.2(Al.sub.2Si)[Al.sub.2Si.sub.4O.sub.18]), steatite (SiO.sub.2.MgO.Al.sub.2O.sub.3), coal, coke or carbon produced in by thermal hydrocarbon decomposition, or combinations thereof.

11. The process according to claim 6, wherein said solid granular material is a carbon-rich granular material formed from solid grains having at least 95% by weight.

12. The process according to claim 11, wherein said solid grains have an equivalent diameter of 0.05 to 50 mm.

13. The process according to claim 6, wherein said solid granular material has a porosity of 0.1 to 0.85 ml/ml.

14. The process according to claim 6, wherein said solid granular material is macroporous and has a mean pore radius of 0.01 to 50 m.

15. The process according to claim 6, wherein said solid granular material has a specific surface area of 0.02 to 100 m.sup.2/g.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details and advantages of the invention will be illustrated by the description hereinafter of an exemplary embodiment shown in the FIGURE, wherein:

(2) FIG. 1 illustrates a working example of the invention.

(3) FIG. 1 shows a preferred configuration of the process according to the invention, in which synthesis gas is produced using a reactor wherein a moving bed composed of a solid granular material is conducted through the reaction space thereof which comprises a first and a second reaction zone.

(4) Via the feed 1, a solid granular material, which is, for example, carbon produced by thermal hydrocarbon decomposition in the process, is introduced at ambient temperature from the top into the reaction space R of the reactor K, through which it is subsequently conducted downward in a moving bed W under the action of gravity. A hydrocarbon-containing input gas 2 which is preferably natural gas is simultaneously passed into the reaction space R from the bottom and conducted upward through the moving bed W in countercurrent. The input gas 2 which is at ambient temperature on entry into the reaction space R is heated up on its way upward by direct heat exchange with the moving bed W until it reaches the decomposition temperature of the hydrocarbon in the first reaction zone Z1. Under these conditions, the hydrocarbons decompose in an endothermic reaction to produce hydrogen and carbon. The carbon formed here is predominantly deposited on the solid granular material of the moving bed W. Together with unconverted or only incompletely converted hydrocarbon, the hot hydrogen formed flows into the second reaction zone Z2 which is disposed above the first reaction zone Z1. As the hydrogen and hydrocarbons flow through the second reaction zone Z2, they are heated up further by direct heat exchange with the moving bed W. In the second reaction zone Z2, a portion of the hydrogen is combusted with oxygen which is fed in via line 3, and thus provides the heat of reaction required for the synthesis gas production. Alternatively or additionally, the heat of reaction can also be introduced into the reaction zone Z2 by means of electrical power 17. At least a further portion of the hydrogen is reacted with carbon dioxide supplied via line 4 to give water and carbon monoxide. Hydrocarbon feedstock, undecomposed or incompletely decomposed in the first reaction zone Z1, is reformed in the second reaction zone Z2 with water to produce hydrogen and carbon monoxide. As a result, a synthesis gas flows out of the second reaction zone Z2 and is cooled in countercurrent with the moving bed W and is drawn off at the upper end of the reactor K via line 5 with a temperature of about 50 to 500 C. Subsequently, the synthesis gas 5 is fed to the synthesis unit S, where it is converted to products 13 such as methanol, dimethyl ether or hydrocarbons. Any residual gas 20 which comprises hydrocarbons and is obtained in the synthesis unit S is recycled into the reactor K in order to likewise thermally decompose the hydrocarbons.

(5) At the lower end of the reactor K, solid granular material 6 is drawn off at a temperature close to ambient temperature and is fed to a processing unit A, in order to process it by removal of the carbon deposited in the first reaction zone Z1 and then to recycle it back into the reaction space R via line 7. The carbon 8 removed is fed to the power plant D, where it is combusted with an oxidizing agent 9 which is air or oxygen-enriched air or oxygen of technical grade purity for production of power 10, of which between 0% and 100% is fed into the public grid according to demand. Power 17 not fed into the public grid is used for providing the heat of reaction for the reactions that proceed in the second reaction zone Z2. For removal of carbon dioxide, the carbon dioxide-containing flue gas 11 that forms in the combustion is fed to a removal unit B which is, for example, an amine scrubbing operation, the operation of which is facilitated by a portion 18 of the waste heat 12 from the synthesis unit S. Another portion 19 of the waste heat 12 is fed to the power plant D where it is utilized to raise steam for power production. A portion 4 of the carbon dioxide 14 removed is subsequently conducted into the second reaction zone Z2, while the remainder 15 is added to the oxidizing agent 9, such that any residual gas 16 obtained can be released to the atmosphere in substantially carbon dioxide-free form.

(6) Depending on the way in which the thermal energy required for the synthesis gas production is provided, different mass balances arise. In order, however, to be able to always operate both the thermal carbon 8 decomposition and the oxidation of the carbon 8 and the scrubbing of the carbon dioxide-containing gas mixture 11 produced under constant conditions, it is proposed that carbon 21 not utilizable at that time and non-utilizable carbon dioxide 22 be stored intermediately and be fed back to the operation as required. Preferably, carbon dioxide 22 is stored intermediately here in liquid form.

(7) Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

(8) The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

(9) From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

(10) The entire disclosures of all applications, patents and publications, cited herein and of corresponding European patent application EP 14002871.3, filed Aug. 19, 2014, are incorporated by reference herein.