MXPA01000346A - Process for generating electric energy, steam and carbon dioxide from hydrocarbon feedstock - Google Patents

Abstract

The present invention relates to a process for production of electric energy, steam and carbon dioxide in concentrated form from a hydrocarbon feedstock comprising formation of synthesis gas inan air driven autothermal thermal reactor unit (ATR), heat exchanging the formed synthesis gas and thereby producing steam, treating at least part of the synthesis gas in a CO-shift reactor unit and carbon dioxide separation unit for formation of concentrated carbon dioxide and a lean hydrogen containing gas which combusted in a combined cycle gas turbine for production of electric energy, and where air from said turbine unit is supplied to the ATR unit. The exhaust from the gas turbine is heat exchanged for production of steam which together with steam generated upstream is utilized in a steam turbine for production of substantially CO2-free electric energy. Steam may be fed to the gas turbine for diluting the hydrogen containing gas mixture. The process may also be combined with production of synthesis gas products such as methanol and/or ammonia. Part of the gas from the carbon dioxide removal unit may be utilized in a fuel cell.

Description

PROCESS TO GENERATE ELECTRIC POWER, STEAM AND CARBON DIOXIDE FROM FEEDING HYDROCARBONS The invention relates to a process comprising the production of electrical energy, steam and carbon dioxide in the concentrated form from a hydrocarbon feed. The invention also comprises the optional production of products based on synthesis gas combined with the process.

The electric power is produced in a combined cycle power plant integrated with the reforming plant where the gas turbine is fueled by the hydrogen-containing gas, (Combined Integrated Reform Cycle (IRCC)). A major problem in such a process is to operate the gas turbine at the conditions that give the minimum emission of nitrogen oxide and simultaneously achieve optimal production of electric power and steam.

A process to produce electric power, steam and concentrated carbon dioxide is published on the internet, http: /www.hydro. com / konsern / eng / 1998 / 980423e.html. This publication describes a process that REF. DO NOT. 126455 comprises reacting natural gas with steam resulting subsequently in a gas containing hydrogen that is subjected to combustion in a combined cycle gas turbine that produces electrical energy.

From the Japanese patent application JP 608041 it is also known to apply a hydrogen combustion turbine for the production of electrical energy. According to this request, natural gas and oxygen in a mol ratio of 1: 0.5 to 1: 0.7 is reacted by partially oxidizing the fuel to generate hydrogen and carbon monoxide. Air is supplied to a pressure swing absorption oxygen separator (PSA) and the oxygen is then released to an autothermal reactor (ATR), where the natural gas is converted to hydrogen and carbon monoxide. The reformed gas enters a conversion reactor in which the carbon monoxide is converted to carbon dioxide. The gas mixture is then introduced into a membrane separator in which the hydrogen is separated from the carbon dioxide. The separated C02 is then washed and desorbed. The hydrogen substantially free of the carbon compounds is used in a gas turbine to generate electric power. This process requires oxygen, demanding a PSA unit of energy consumption. According to the flow chart of the application, natural gas must be decompressed almost at ambient pressure to allow the addition of oxygen. After PSA separation oxygen must be compressed a second time. All these additional compressions reduce the efficiency of the process.

The main objective of the invention is to provide an improved process for generating energy using steam reforming of a hydrocarbon feed, in which a substantial part of the generated CO 2 is separated as a highly concentrated C 0 2 gas stream and where the emission of oxides of nitrogen is within acceptable levels for conventional gas turbines.

Another object of the invention is to use at least part of the gas synthesis formed from the energy generation process for the production of synthesis gas products, especially ammonia, methanol and / or dimethyl ether.

With respect to the generation of electric power, the present process will compete with conventional power plants based on the combustion of hydrocarbon feeds, such as natural gas. However, a major disadvantage of simple combustion hydrocarbons is the emission of carbon dioxide as the combustion discharge that only contains minor amounts of carbon dioxide that can not be economically recovered at present. The emission of nitrogen oxides (NOX), which varies depending on the operating conditions, could also be a problem of emissions.

A major problem when reducing the emission of carbon dioxide and NOX is to obtain the reduction of the desired emission without the unacceptable reduction of the efficiency of the process with respect to the generation of energy. The first stage in the evaluation of the basic process from the point of view of the previous requirements was the synthesis gas production stage. Having considered several methods, the inventors found that an ATR would give several advantages and it was decided to investigate the best way to run the ATR. Contrary to the teachings of the above Japanese patent application, it was found that the ATR should be an air powered reactor, i.e. not an oxygen-powered reactor. The application of the ATR seemed to offer several advantages in terms of degrees of freedom. In this way, the operating pressure could be chosen from the point of view of the global economy of the concept. The methane diversion could be varied from the point of view of the operation of the downstream units and finally the synthesis gas produced in the ATR would be a relatively poor gas suitable for the gas-driven turbine and comparable with the fuel mixtures that are used in large-scale combined cycle (CCRF) plants, tested.

The hydrocarbon stream used for such process will be natural gas, naphtha, various petroleum distillates, etc. By applying a pre-reformer ahead of the ATR the flexibility with regard to feeding will be quite large. The preferred food will be natural gas.

The NOX problem was found to be strongly related to the operating conditions of the gas turbine. The formation of NOX correlates with the flame temperature in this turbine. Therefore, measures should be taken to regulate the flame temperature. The range of the gas mixture to be combusted in the turbine could be selected by the design of the process to maintain the flame temperature at a desired level and still maintain an acceptable power generation. The flame temperature in the turbine is determined largely by the composition of the fuel gas. It was found that an air-powered ATR would provide a lean hydrogen based on the gas mixture of fuel compatible with the gases used in the IGCC plants. It was found advantageous to extract the process air for the ATR to the discharge of the air compressor from the gas turbine and increase the required ATR injection pressure. In addition, the air flow could be adjusted to meet the acceptable level of methane deviation, and the composition of the fuel gas mixture compatible with the acceptable level of NOX formation in the gas turbine combustion system. The nitrogen extracted with the air from the gas turbine is returned to the turbine part as a component of the fuel gas mixture, in this way the mass flow to the turbine is widely maintained.

If needed, moderate steam injection can be applied to reduce NOX formation in the turbine. The optimal design of the burner design can also reduce NOX emission.

An alternative within the concept of the invention is to combine the ATR with a reforming exchanger. It was found that this option could increase the recovery of C02 in the concentrated form.

To obtain maximum flexibility, the concept of basic power generation could be combined with the production of several products based on the existing process streams. In this way, a methanol unit could use some of the synthesis gas of the ATR and an ammonia plant could use some of the hydrogen / nitrogen gas separated from the subsequent carbon dioxide with respect to the conversion reaction of the synthesis gas. The only additional units required for the ammonia plant would be a conventional membrane separation unit and a metanator upstream of the ammonia synthesis reactor.

The scope of the invention comprises the formation of synthesis gas in an ATR unit operated with air, heat exchange of the synthesis gas formed and whereby steam is produced. At least part of the cooled synthesis gas is then treated in a CO conversion reactor, which could be a simple unit or two CO conversion reactors, a low temperature reactor and a high temperature reactor. The gas stream is then treated in a carbon dioxide unit for the formation of a concentrated stream of carbon dioxide and a stream which is a stream containing poor hydrogen, which at least is partially combusted in a turbine of combined cycle gas for the production of electrical energy. The air from the turbine is supplied to the ATR unit. The discharge of the gas turbine is exchanged by heat for the production of steam that together with the upstream generated steam is used in a steam turbine for the production of electrical energy.

The ATR unit can be combined with a reformer exchanger and the supply can be divided between these two units, preferably 50-80% of the feed is fed to the ATR.

A pre-reformer upstream of the ATR unit can be arranged.

A smaller part of the steam generated in the process can be fed into the gas turbine to dilute the hydrogen-containing gas and thereby lower the flame temperature in the gas turbine.

At least part of the discharge from the gas turbine can be recirculated to the ATR as the oxygen source or combined with the air supply to the gas turbine Part of the synthesis gas can be used for the production of methanol and this production can be carried out in various ways as described above in connection with Figure 1.

Part of the gas from the carbon dioxide separation unit can be used for the production of ammonia. In such a case a current is fed to a membrane separation unit to separate the hydrogen that is mixed with another stream of hydrogen-containing gas, whereby the mixed stream will have a ratio of nitrogen: hydrogen of 1: 3. The nitrogen in the membrane unit is returned to the main stream of gas containing hydrogen subsequently fed to the gas turbine.

The invention will be further explained and elucidated in conjunction with the examples and the description of the appended figures.

Figure 1 shows a simplified flow chart of the concept of basic power generation.

Figure 2 shows a simplified flow diagram of the basic concept combined with a methanol plant and / or an ammonia plant.

Figure 1 shows an example for carrying out the invention. The feed of gaseous hydrocarbons, for example natural gas, is supplied as stream 1, heated and compressed before through conduit 2, is carried out to a saturator 3 where it is mixed with process water 4 and the water of demineralized recirculation supplied via line 4b. The hydrocarbon feed that is at least partially saturated with water is then fed to the ATR unit 6 as the stream 5. Compressed air is supplied via line 7 to the ATR unit 6. Optionally, a current pre-reformer could be arranged. above ATR. This will give increased flexibility with respect to the hydrocarbon feed. The increased content of the heavier hydrocarbons can then be accepted. At least part of the air supply 29 may be supplied from the air compressor of the gas turbine and be increased to the required injection pressure. The unit 6 may also be a combined unit comprising an ATR and a reforming exchanger. How much of the food will be fed to the respective units can be varied within wide limits. A practical division will be 50-80% of the feed to the ATR and the remaining part to the reformer exchanger. The synthesis gas 8 of the ATR 6 unit is cooled in a boiler (steam generator) 9 before being supplied to a converter unit of deflection 12 as current 11. This unit could comprise two conventional CO conversion reactor, a low temperature reactor (LT) and a high temperature reactor (HT), or just a simple CO conversion reactor. The resulting gas mixture 13 is cooled, water condensed in unit 14 is removed and the resulting gas mixture is then supplied as stream 15 to a CO 2 absorber 16 of which C02 and the adsorbent are supplied via line 18 to a desorber 19. Recirculation of the absorber can be supplied to unit 19 as stream 20b. The regenerated absorbent, for example an amine solution, is recirculated to the absorber 16 by means of the conduit 20. Water is removed in the unit 22 of the C02 stream 21. The process water of the units 22 and 14 are recirculated to the saturator 3. The highly concentrated C02 stream can then be compressed and released via line 23 for further use, for example as an injection gas in an oil or gas section. The gas stream 17 of the C02 16 absorber consists mainly of hydrogen and nitrogen, with smaller amounts of CO, C02, CH4. This stream 17 will then be used as fuel for a combined cycle gas turbine 24 to which air 25 is supplied. Optionally, the vapor 10 can be supplied to the turbine 24 for the NOX decrease. At least part of the stream 17 can be used in a fuel cell to generate direct current electric power. If electric power will be used for electrolysis there will be no need for a rectifier with this optional electric power generation. The discharge 26 of the turbine. 24 is exchanged by heat with water in a steam generator 27 and the steam from here could overheat in the heat exchanger 30 before the current 31 is supplied to an energy generator 32 to which also the steam 10 could be supplied. The discharge 28 could be recirculated to the reformer unit 6 or combined with the air supply 25 to the gas turbine 24.

In figure 2 an ammonia plant and a methanol plant are integrated into the basic process according to figure 1. The combined process could comprise both plants or one of these. The synthesis gas 34 can then be taken from stream 11 and fed to a synthesis of methanol 35. The unconverted synthesis gas * can be recirculated to the stream of synthesis gas 11 and the product methanol is extracted via the conduit 36. The synthesis gas 34 could alternatively be treated in a gas separation membrane unit to remove the hydrogen and carbon dioxide to feed the methanol synthesis. This feed could be supplied with the additional carbon dioxide of stream 23. The other fraction of the membrane unit will then be recirculated to stream 11.

The feed for an ammonia synthesis could be extracted from line 17. A side stream 38 is first fed to a membrane gas separation unit 40 to supply hydrogen 42 to line 39 to adjust the ratio of H2: N2 to 3: 1, before this gaseous mixture is treated in a methanation unit 43 prior to the synthesis of ammonia 44 which produces ammonia 45. The nitrogen of the membrane unit 40 is recirculated through line 41 to feed 17 for the hydrogen turbine 24.

Example 1 This example shows the effect of the present invention with respect to the production of electrical energy, efficiency and recovery of carbon dioxide as a concentrated stream in a process within Figure 1. The example also shows the efficiency, recovery of carbon dioxide Concentrated and the total energy production of the process compared with it for a process that applies a primary-secondary reformer for synthesis gas production. This illustrative example shows the effects of the discharge recirculation to the ATR and also shows the effects of combining the ATR with a reforming exchanger. In the following table the combination is ATR-RE. The process according to the invention is compared with the use of a combination of a secondary-primary reformer to produce the synthesis gas, SR / PR in the table. The steam: carbon molar ratio in the feed to the reformer unit is set to Steam: C in the table.

Table 1 From the above results it can be seen that the process according to the invention can recover as much as 95.8% of the CO 2 produced. The results also show that within the inventive concept the efficiency, energy production and C02 vary depending on the operating conditions and such process has greater flexibility. The formation of NOX in general, will be a function of% hydrogen in the gas fed to the gas turbine.

The present invention provides a process that produces clean carbon dioxide suitable as a drive gas for injection into oil reservoirs. The IRCC plant in this way will operate with minimal emission of carbon dioxide. In addition, the process provides a fuel mixture of poor combustion based on hydrogen, suitable for combustion in the current gas turbine technology. The moderate dilution with steam of the gas mixture fed to the gas turbine can be applied as only the required NOX decrease.

It is noted that with gelation to this date, the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property.

Claims (11)

1. A process for the production of electrical energy, steam and carbon dioxide in the concentrated form from a stream of hydrocarbons comprising the formation of the synthesis gas in an air-powered autothermal thermal reactor unit (ATR), heat exchange of the synthesis gas formed and whereby steam is produced, characterized in that at least part of the synthesis gas is treated in a CO conversion reactor unit and carbon dioxide separation units for the formation of concentrated carbon dioxide, and a gas containing poor hydrogen, which is at least partially combusted in a combined-cycle gas turbine for the production of electrical energy, and wherein the air from the turbine unit is supplied to the ATR unit, such a discharge of the gas turbine is exchanged for heat for the production of steam which, together with the steam generated from the upper stream, is used in a steam turbine to the production of electrical energy substantially free of C02.

2. A process according to claim 1, characterized in that a reformer unit comprises an ATR combined with a reformer exchanger.

3. A process according to claim 1, characterized in that 50-80% of the hydrocarbon feed is supplied to the ATR and the remaining feed to the reformer exchanger.

4. A process according to claim 1, characterized in that a pre-reformer is used in front of the ATR unit.

5. A process according to claim 1, characterized in that a simple CO conversion reactor unit is used.

6. A process according to claim 1, characterized in that the steam is fed to the gas turbine to dilute the gas mixture containing hydrogen.

7. A process according to claim 1, characterized in that the discharge gas is recirculated from the gas turbine to the ATR unit.

8. A process according to claim 1, characterized in that at least part of the discharge of the gas turbine is combined with the supply of air to the turbine.

9. A process according to the rei indication 1, characterized in that part of the synthesis gas is used for the production of methanol and such remaining synthesis gas is further treated in the downstream units before use for the production of electrical energy.

10. A process according to claim 1, characterized in that part of the hydrogen-containing gas from the carbon dioxide removal unit is used for the production of ammonia, which comprises separating the gas in a membrane unit to adjust the ratio of trógeno: hydrogen at the ammonia conditions and return the separated nitrogen to the main stream of hydrogen-containing gas, and where the stream that contains neither trógeno: hydrogen in a ratio of 1: 3 is treated in a methanation unit before the Ammonia synthesis

11. A process according to claim 1, characterized in that part of the hydrogen-containing gas is fed from the carbon dioxide removal unit for use as fuel to a fuel cell that produces electrical energy. SUMMARY OF THE INVENTION The present invention relates to a process for the production of electrical energy, steam and carbon dioxide in the concentrated form from a stream of hydrocarbons comprising the formation of the synthesis gas in a powered thermal reactor unit (ATR). by air, heat exchange of the synthesis gas formed and by which steam is produced, treating at least part of the synthesis gas in a CO conversion reactor unit and carbon dioxide separation unit for the formation of dioxide concentrated carbon and a gas containing poor hydrogen that is subjected to combustion in a combined-cycle gas turbine for the production of electrical energy, and where the air from the turbine unit is supplied to the ATR unit. The discharge of the gas turbine is exchanged for heat for steam production which together with the steam generated upstream is used in a steam turbine for the production of electrical energy substantially free of C02. The steam could be fed to the gas turbine to dilute the gas mixture containing hydrogen. The process could also be combined with the production of synthesis gas products such as methanol and / or ammonia. Part of the gas from the carbon dioxide removal unit could be used in a fuel cell.