Patent Application
20090165377
The present invention relates to a process for producing syngas and electricity, in which the oxidizer necessary for combustion to enable the syngas formation reaction consists of an oxygen-containing gas produced by at least one gas turbine.
The invention applies to various branches of activity, such as heavy chemicals, the petrochemical industries, the refining industry, the energy industry, all concerned by environmental conservation. All these industries are capable of converting heavy hydrocarbons to chemicals that can be utilized for producing a syngas. A syngas is a gas mixture containing at least CO, H2, CH4, CO2, N2, Ar and H2O obtained by steam methane reforming (SMR), by partial oxidation (POX) of hydrocarbons, by autothermal reforming (ATR), by convective reforming, by secondary reforming, or by heat exchange reforming. All these methods implement a combustion reaction in order to supply the heat necessary for the syngas formation reaction.
The present invention relates to syngas production sites in which at least one gas turbine is also present. According to the invention, “gas turbine” (CT) means a device comprising at least one air compressor, one combustion chamber and a flash turbine. The site may have a plurality of gas turbines. In the gas turbine, the compressed air produced is introduced with at least one fuel into the combustion chamber of the turbine and the flue gases produced pass through the flash turbine to generate electricity using a generator. In general, these gases then pass through a waste heat boiler to produce steam. The fuel of the gas turbine is usually natural gas, but may comprise hydrogen or syngas produced by the syngas production unit or a liquid hydrocarbon fuel.
It is the object of the present invention to propose a syngas production process having improved energy efficiency by combining the syngas production process with a cogeneration unit.
For this purpose, the invention relates to a method for supplying oxidizer to the combustion device of a unit for producing syngas from the exhaust gas produced by a gas turbine, in which the exhaust gas flow introduced into the combustion device is controlled according to the value of the oxygen concentration and/or of the pressure in the furnace of the syngas production unit.
The invention also relates to a device for implementing said method.
Other features and advantages of the invention will appear from a reading of the description that follows. The exemplary embodiments of the invention are provided as nonlimiting examples, illustrated by the appended drawings in which:
The invention therefore relates to a process for producing syngas on an industrial site comprising at least one gas turbine, in which the oxygen-containing gas produced by the gas turbine is utilized in the combustion reaction implemented for producing syngas: according to the invention, the oxidizer necessary for the combustion to enable the syngas formation reaction consists of an oxygen-containing gas produced by at least one gas turbine. The facilities enabling the production of the raw syngas may be a steam reforming reactor (SMR), followed by a secondary reforming reactor, or a partial oxidation (POX) reactor using hydrocarbons to produce the raw syngas. The raw syngas comprises hydrogen, carbon monoxide, carbon dioxide and other compounds. It may also involve a reactor for implementing an ATR process or a convective reforming process. These syngas production reactions take place at high temperature, requiring combustion in a reactor for implementing and maintaining the synthesis reaction. This combustion demands the presence of an oxidizer which, according to the invention, issues at least partly from the gas turbine. This combustion is implemented using burners fed with the exhaust gas from the turbine and with an oxidizer. The latter is usually natural gas, but it may also be a liquid or solid containing hydrocarbons.
Thus, said oxidizer is an oxygen-containing gas which consists fully or partially of the exhaust gas from the gas turbine. In fact, the gas turbine produces an exhaust gas generally comprising 13% to 16% by volume of oxygen on wet gas. According to the invention, the exhaust gases are recovered and introduced into the burners of the SMR, ATR, POX or the convective reformer for implementing the combustion necessary for the syngas production reaction. These exhaust gases generally have a temperature of between 450° and 650° C.
One direct consequence of the implementation of the method according to the invention is that the heat produced during the combustion to enable the syngas formation reaction can then be used to produce steam or preheated air. In fact, in certain cases, due to the use of the oxygen-containing gas from the gas turbine, the syngas production process produces surplus heat compared to a method only using air for the combustion implemented in the syngas production. This surplus heat can be utilized by heating any type of fluid, and in particular, water or water vapor or air, by contacting the latter fluids in a heat exchanger with the syngas produced and/or the flue gases produced by the combustion in the syngas reactor and/or the flue gases produced by the combustion in the gas turbine.
According to an alternative of the invention, part of the oxygen-containing gas produced by the gas turbine can be used in a heat recovery unit. This alternative applies when the gas turbine produces a quantity of oxygen-containing gas that is larger than that necessary for the combustion required to enable the syngas formation reaction. The surplus oxygen-containing gas can then be used as oxidizer in the combustion implemented by a heat recovery unit. According to the invention, the heat recovery unit may be the combustion gas heat recovery zone from the syngas production device. This zone is present on all syngas production sites and serves to recover the heat from the exhaust gases produced by the combustion that enables the syngas formation reaction. The combustion implemented in this zone is that of the hydrocarbons used in the production of syngas and of the oxygen-containing gas produced by the gas turbine. This zone is called the combustion gas heat recovery zone in the present invention. The heat recovery unit may also be a steam production unit or heat recovery steam generator (HRSG). In this case, the steam produced can be used to generate electricity using a steam turbine, or it may also be used for an industrial process using steam (in which case, it is a product exported from the site). The heat recovery unit may also be an air preheater.
According to a particular embodiment of the invention, the air compressed by the compressor of the gas turbine can be heated in a heat exchanger built into the convective zone of the syngas production facility.
According to the invention, the flow of exhaust gas from the turbine introduced into the burners of the syngas production unit is controlled. This control can be carried out by at least one control means placed on the device for distributing exhaust gas from the turbine to the combustion device: it may be a valve or a louver placed on the distribution line of this gas, or it may be an extractor fan placed at the outlet of the exhaust gases from the syngas production unit. This extractor fan creates a vacuum in the combustion furnace of the syngas production unit, indirectly causing suction of the exhaust gases from the turbine into the burners of the syngas production unit.
Preferably, the flow of exhaust gas introduced into the combustion device is controlled so that the oxygen concentration downstream of the combustion chamber of the syngas production unit is between 2 and 3% by volume of dry gas and/or the pressure in the furnace of the syngas production unit is between 5 mm and −15 mm H2O. In practice, an oxygen pressure and/or concentration sensor is generally placed downstream of the combustion chamber of the syngas production unit, in order to measure this concentration and this pressure. Said sensor is connected to the means for controlling the flow of exhaust gas to be introduced into the combustion device by feedback loop in order to servocontrol the introduction of the exhaust gas from the turbine to said concentration and/or said pressure.
Since the combustion chamber of a syngas production unit often is under vacuum with regard to the atmospheric pressure, the invention advantageously uses this property to ensure the introduction of the exhaust gases from the gas turbine into the burners of the combustion chamber of the syngas production unit: these are readily taken in; no compression means is necessary to introduce them into the burners.
According to the invention, it is also possible to control the introduction, into the combustion chamber of the syngas production unit, of the oxygen-containing gas necessary for the combustion enabling the syngas formation reaction to take place. Thus:
According to a particular embodiment, the method also provides that:
In general, the atmospheric air is heated before being introduced into the combustion chamber of the syngas production unit, in the combustion gas heat recovery zone and/or in a steam production unit. The atmospheric air is generally heated by a burner. The atmospheric air introduced into the combustion gas heat recovery zone and/or into a steam production unit may be heated using a burner fed with at least part of the exhaust gas produced by the syngas production device. The recirculation of said exhaust gas serves to increase the production of steam while reducing the NOx partial pressure.
The invention further relates to a device for supplying oxidizer to the combustion device of a unit for producing syngas from the exhaust gas produced by a gas turbine for implementing the controlled feed method described above. Said device consists of at least two lines:
the first line comprising:
the second line comprising:
One of the means for controlling the opening for introducing secondary oxygen-containing gas is a hatch. The hatch serves to open or close said opening: it is opened to introduce the secondary oxygen-containing gas into the line and it is closed to prevent the introduction of the secondary oxygen-containing gas into the line. Another means for controlling the opening serving to introduce secondary oxygen-containing gas is an air blower.
The means for regulating the exhaust gas flow into the second line generally consists of inlet guide vanes or louvers. Regulation may extend to the total closure of the exhaust gas flow from the turbine. According to a preferable embodiment of the invention, the means for regulating the flow of exhaust gas from the gas turbine (3) into the second line is servocontrolled by an oxygen pressure and/or concentration sensor located downstream of the combustion chamber of the syngas production unit.
The invention also relates to an alternative of the previous device enabling the distribution of exhaust gas from the turbine and of a secondary oxygen-containing gas into the combustion device of the syngas production unit, and also into the combustion gas heat recovery zone and/or to a steam production unit. According to this alternative, the device comprises three lines and:
the first line comprises another opening cooperating with the third line and enabling the removal of the gas present in the first line to the third line,
the third line comprises:
This device is suitable for implementing the method for controlling the introduction, into the combustion chambers of a syngas production device, of the oxygen-containing gas necessary for combustion to enable the syngas formation reaction previously defined. It serves to select the type of oxygen-containing gas to be introduced into the combustion chamber of the syngas unit and into the boiler of the steam production unit. The means for controlling the opening enabling the introduction of the oxygen-containing gas into the third line is the same type as that described for the second line. The third line may also comprise means for regulating the flow of exhaust gas; this regulating means generally consists of inlet guide vanes or louvers.
The first line of the alternative device may comprise means for dividing the exhaust gas from the gas turbine between the second line and the third line, and, preferably, said dividing means are servocontrolled by an oxygen concentration sensor located downstream of the combustion chamber of the syngas production unit. Thus, if the oxygen concentration downstream of the combustion chamber of the syngas production unit is too low, more oxygen-containing exhaust gas from the gas turbine can be introduced into the second line leading to the combustion device of the syngas production unit, and less into the third line.
The first line comprises an opening enabling the removal of the oxygen-containing gas present in said line to the atmosphere. According to the invention, the removal of the gas present in the first line to the atmosphere is provided when the gas turbine is under partial or no load and does not produce exhaust gas. The partial or total removal of the gas may also be provided when the gas turbine operates but when the syngas production device is under partial load or shut down.
The previous device normally comprises duct burners placed in the second and third lines. These burners serve to heat the oxygen-containing gases, and this is useful in particular when the oxygen-containing gas is atmospheric air or oxygen, or when steam production is to be increased by heating the main oxygen-containing gas present in the third line. Thus, the burners are generally placed in the second and third lines downstream of the opening enabling the introduction of the secondary oxygen-containing gas into the lines, in comparison with the flow direction of the secondary oxygen-containing gas in the lines.
Preferably, the first line comprises an opening enabling the removal of the oxygen-containing gas present in the line to the atmosphere. This opening, which enables the removal of the oxygen-containing gas present in the line to the atmosphere, generally cooperates with a line comprising means for regulating the exhaust gas flow.
The heat liberated by the combustion enabling the syngas formation reaction to take place in the combustion chamber of the unit 7 is recovered in the combustion gas heat recovery zone 5 which produces steam 6 and heats the compressed air 35 producing preheated air 27, the latter issuing from the compressed air 35 produced by the compressor of the gas turbine 3. The steam 6 is added to that 61 already produced by the unit 17 for recovering steam from the syngas production device, said unit 17 being intended to recover the waste heat from the cooled syngas 19. Part 22 of the exhaust gas from the gas turbine 2 issuing from the gas turbine 3 feeds the heat recovery unit 5, particularly during the startup of the syngas production unit 7. If the gas turbine 3 is inoperative and does not produce oxygen-containing exhaust gas 2, atmospheric air 8 is used as oxidizer in the combustion chambers of the unit 7 and/or in the combustion gas heat recovery zone 5. This air 8 is generally preheated using burners 120 and 20, supplied with fuels 18 and/or 71. In this case, the exhaust gas 2 from the turbine 3 is removed via the stack 40. In this arrangement, part 121 of the steam 12 produced by the steam recovery unit 17 and the combustion gas heat recovery zone 5 may be directly exported, while another part 41 is exported after having been expanded in the steam turbine 50 to produce more electricity 39 and steam condensates 51. Another part 14 of the steam 12 produced forms a mixture 48 with the hydrocarbons 18 before their introduction into the unit 7.
As in any syngas production unit, an exhaust gas 37 is produced and extracted by the fan 29 to the discharge stack 401. The cooled syngas 19 is purified in the carbon dioxide stripper 191 to produce a syngas 192 containing about 50 ppm of carbon dioxide. Part 280 or all 280 of the CO2 removed can be recycled to the syngas production device by mixing with the hydrocarbons and steam 14. The other part 284 or all 280 of the CO2 removed may be compressed and liquefied for export. Part 34 of the low CO2 syngas is used as fuel in the gas turbine 3. The remainder of the low CO2 syngas 192 is purified in the purification unit 26 which adjusts the H2/CO ratio to produce a purified syngas 28 whereof part 286 is exported. The products 33 removed from the low CO2 syngas 192 may be recycled to the syngas production unit 7. The purified syngas 28 may also be introduced into the H2 and CO separation units 261 to produce purified hydrogen 281 for export or compression on the one hand, and purified CO 282 for export or compression on the other. The mixture of purged gas issuing from the separation units 261 is used as fuel in the combustion chamber of the syngas production device.
For implementing the invention, an analyzer 100 measures the pressurized oxygen concentration in the zone downstream of the combustion chamber and a pressure sensor 104 measures the oxygen concentration at the outlet of the furnace 7. The means for controlling the exhaust gas flow from the gas turbine 103 is servocontrolled by a feedback loop 101, to the values given by the analyzer 100 and the sensor 100 and increases or decreases the flow of exhaust gas 2 from the gas turbine 3 in order to maintain the oxygen pressure and concentration of the syngas production unit within normal operating limits. Similarly, the fan 29 for extracting the combustion products 37 from the syngas production unit is servocontrolled by a feedback loop 102, to the values given by the sensor 104 and the analyzer 100 and increases or decreases its rate in order to influence the flow of exhaust gas 2 from the gas turbine 3.
For the two configurations in
the opening 10 enables the introduction of the oxygen-containing gas 2 from the gas turbine 3 into the line 9,
the opening 161 and the opening 211 respectively enable the introduction of part 21 of the oxygen-containing gas 2 into the line 91 and part 22 of the oxygen-containing exhaust gas 2 into the line 92,
the louvers 16 and 4 enable the regulation of the flow of the gas 21 and of the gas 22,
the opening 11 and the opening 112 respectively enable the introduction of the atmospheric air 8 into the line 91 and into the line 92,
the hatches 111 and 113 serve to select the introduction of either the oxygen-containing gas 21 or 22, or of the atmospheric air 8 into their respective line 91 or 92,
the burners 120 and 20 serve to heat the gas flowing in the lines 91 and 92,
the opening 162 serves to remove the gas present in the line 91 to the combustion chamber of the syngas production device 7,
the opening 212 serves to remove the gas present in the line 92 to the combustion gas heat recovery zone 5,
the opening 151 serves to remove the oxygen-containing gas present in the line 9 to the atmosphere via the stack 40, the louvers 15 serving to regulate this flow.
If the gas turbine 3 is in operation and produces an oxygen-containing gas, the hatches 111 and 113 are installed so as to close the openings 11 and 112: this serves to supply the combustion chamber of the unit 7 and the combustion gas heat recovery zone 5 with exhaust gas from the turbine 3. Using the louvers 4 and 16, it is possible to send as required more or less exhaust gas from the turbine 3 either to the line 91 and the combustion chamber of the unit 7, or to the line 92 and the combustion gas heat recovery zone 5. Furthermore, the louver 16 is servocontrolled by the sensor 100 for measuring the oxygen pressure and/or concentration of the syngas production unit by feedback loop: its opening can be adjusted as a function of this control in order to regulate the flow of exhaust gas 2 from the turbine 3 flowing in the line 91.
If the gas turbine 3 is not in operation, the hatches 111 and 113 are installed so as to open the openings 11 and 112 and thereby supply the combustion chamber 7 and the combustion gas heat recovery zone 5 with atmospheric air (secondary oxygen-containing gas). In this case, the burners 20 and 120 serve to preheat the atmospheric air. If the gas turbine 3 is inoperative and does not produce oxygen-containing gas, the louvers 4 and 16 are closed, the louvers 15 are adjusted in order to remove the gas from the turbine to the atmosphere via the stack 40. Simultaneously, the hatches 111 and 113 are installed so as to open the openings 11 and 112 and thereby supply the combustion chamber 7 and the combustion gas heat recovery zone 5 with atmospheric air (secondary oxygen-containing gas).
By the implementation of the invention, it has been found that the temporary or continuous use of the oxygen-containing gas from the gas turbine in the syngas production device allows the use of a single heat recovery section in said syngas production device, as shown in
Furthermore, the fuel and the hydrocarbon raw material and fuel used for the coproduction of electricity, steam and syngas are converted with 80% to 90% efficiency; this conversion rate cannot be reached by an independent power generation unit. The hot oxygen-containing gas issuing from the gas turbine helps to reduce the consumption of fuel required by the combustion chamber of the syngas production unit. The combustion gases are therefore more available for producing additional steam which can pass through a steam turbine to generate more electricity. This invention also serves to produce preheated air which can be used for regenerating catalysts in certain industrial processes. In short, a sharp increase in thermal and electrical efficiency is achieved by an increase in the production of steam and electricity, accompanied by a drop in consumption of gas as fuel.
According to the invention, the fact that the oxygen-containing gas issuing from the gas turbine is hot serves to decrease the fuel consumption in the combustion chamber of the syngas production device. The combustion gas heat recovery zone can also replace a steam production unit of a cogeneration unit. Once the heat of the oxygen-containing gas and the combustion gas is recovered, the cooled exhaust gas is tapped off by a blower and removed via a stack. The steam obtained in the steam recovery unit of the syngas production device 17, the combustion gas heat recovery zone 5 and the steam production unit 13, can be introduced either into a backpressure steam turbine which produces steam and electricity, or into a steam condensing turbine producing hot water and electricity.
Furthermore, the generator of the gas turbine produces electricity which can be used by the auxiliary facilities, for example fans, compressors and pumps, which are found in the integrated plant.
In the arrangement shown in
The invention provides flexibility to the industrial site and a wider product range for the production of syngas, CO, hydrogen, oxogas (mixture of H2 and CO in a precise ratio), steam, hot air and electricity.
The syngas production device can be equipped with exhaust gas treatment systems such as a “Selective Catalytic Removal of NOx” (SCR) unit to control the NOx content issuing from the combustion gas, or a device for cleaning exhaust gas to remove the carbon dioxide, particulates and sulfur oxides.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0552804 | Sep 2005 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2006/050894 | 9/15/2006 | WO | 00 | 11/3/2008 |
