FR2872566A1 - Oxy-combustion process for the production of energy from a fossil fuel with subsequent sequestration of carbon dioxide produced - Google Patents

Abstract

The process involves the mixing of oxygen-rich and carbon dioxide-rich currents, introduction of the mixture with a fuel in a pressurised combustion chamber, treatment of the combustion fumes by cooling(to condense water and sulfur compounds) and liquefaction of the residual fumes by compression and cooling.

Description

The present invention relates to a method for producing energy from

  fossil fuel with capture of carbon dioxide for sequestration.

  The burning of fossil fuels of oil, natural gas, or coal, produces in return carbon dioxide, which then accumulates in the atmosphere. But carbon dioxide is the main greenhouse gas. It prevents solar infrared radiation from returning to space, thus helping to warm the Earth's surface in proportions that could be much greater than anything that has been observed so far during geological time.

  Since it does not seem possible in the foreseeable future to dispense with fossil fuels for the supply of economies, a large number of actions are envisaged or initiated to try to reduce the amount of CO2 released into the atmosphere or to reduce the effects.

  The present invention aims to propose a combustion process for capturing CO, for the purpose of sequestering in suitable geological layers (old oil or gas fields, sealed saline aquifers, coal mines ...).

  Document US Pat. No. 6,202,574 proposes carrying out an oxy-combustion of the fuel in a CO 2 and O 2 atmosphere, then recovering the CO, released by combustion to liquefy it.

  The present invention provides a combustion process that allows in particular to achieve liquefaction of carbon dioxide at room temperature.

  In general, the present invention relates to a combustion process with capture of carbon dioxide, in which at least the following steps are carried out: a) a flow rich in oxygen is mixed with a stream rich in carbon dioxide, b) introduces the mixture and a fuel into a combustion chamber, c) maintains the internal pressure of the combustion chamber to a value higher than atmospheric pressure, d) the combustion fumes are treated by cooling to condense the water and sulfur compounds, and e) liquefies at least a portion of the treated fumes obtained in step d), by compression and cooling.

  According to the invention, a portion of the treated fumes obtained in step d) can be used to be mixed with the oxygen-rich stream in step a).

  According to the invention, the internal pressure of the combustion chamber can be between 0.1 and 100 millibar.

  To keep the chamber under pressure, the mixture and the fuel can be introduced into the combustion chamber at a pressure between 0.1 and 100 millibar. It is also possible to introduce, at a relative pressure of between 0.1 and 100 millibars, a stream rich in gaseous carbon dioxide into the combustion chamber.

  According to the invention, in step e), the liquefaction of the treated fumes can be carried out by at least one compression of the fumes at a pressure of between 50 and 70 bars and by cooling the fumes compressed to a temperature between 0 C and 30 C.

  In step b), the flow rates of the fuel and of the mixture introduced into the chamber can be adjusted so as to produce combustion fumes containing an excess of oxygen of less than 3% by volume. In step a), the oxygen content of the mixture can be adjusted to a value of between 30% and 40% by volume.

  According to the invention, at the start of the process, the combustion chamber can be purged by combustion with a fuel and a mixture comprising oxygen and carbon dioxide from a liquid carbon dioxide storage tank, the combustion fumes being released into the atmosphere.

  The liquid obtained in step e) can be injected and sequestered in an underground reservoir.

  The process according to the invention makes it possible to produce pure CO2 greater than 98.5% which can therefore be liquefied at ambient temperature by compression and simple cooling.

  Other features and advantages of the invention will be better understood and will become clear from reading the description given below with reference to the drawings in which: FIG. 1 shows a combustion plant, FIG. the equilibrium diagram of a pure CO2 at 98.5%.

  The combustion plant shown in Figure 1 can be implemented in different industries. For example, the combustion plant is a steam and electricity production facility, a refinery or petrochemical furnace. The installation may, for example, be a steam reforming furnace which makes it possible to have a process for producing hydrogen with capture and storage of CO 2.

  According to the invention, the operating conditions of the combustion plant, shown in FIG. 1, are chosen so that the fumes produced during combustion in the chamber CC contain at least 98.5% by volume of CO, .

  In Figure 1, air is introduced through the conduit 1 in the unit O of oxygen production. Nitrogen is discharged from unit O via line 2 and can be released to the atmosphere at a temperature close to room temperature. It is possible to carry out a thermal integration of the unit O with the CO liquefaction unit LI: the frigories recovered on the nitrogen rejection circuit can be used during the liquefaction of the CO 2. Unit O produces pure oxygen at least 95% by volume, preferably at greater than 99% by volume, in order to avoid or limit the presence of inert compounds (in particular nitrogen) in the fumes. of combustion.

  The oxygen produced by unit O is sent through line 3 into the gas / gas mixer M to be mixed with CO, arriving via line 4. Thus, mixer M makes it possible to reconstitute an oxidizer equivalent to air by dilution of the oxygen from the unit O. The mixture of oxygen and CO, is removed from the mixer M by the conduit 5. The oxygen analyzer A can measure the oxygen content of the mixture flowing in. the duct 5. This measurement is transmitted to the FC device which acts on the opening of the valve V1 in order to modify the oxygen flow rate entering the mixer M and thus makes it possible to adjust the oxygen content of the mixture circulating in the duct 5. The oxygen content may be adjusted relative to a setpoint which depends in particular on the flow rate and the nature of the fuel that arrives through the conduit 8. Preferably, the oxygen content of the oxidant flowing in the conduit 5 is between % and 40% by volume.

  Alternatively, the unit O for producing oxygen and the mixer M can be grouped into a single organ. This organ may be a membrane separator in which oxygen is separated from air through a membrane. The air flows on one side of the membrane, the other side to which the oxygen migrates being in contact with circulating CO2 gas. Oxygen is then directly incorporated into the CO2 that serves as the flushing gas.

  The combustion chamber CC is supplied with oxidant via the conduit 6 and with fuel via the conduit 8.

  Fuel is a fuel of fossil origin. For example, natural gas, liquid fuel oil, coal, petroleum coke, or a mixture of these fossil fuels may be used.

  The flows of fuel and oxidant circulating in the ducts 6 and 8 are controlled and adjusted to achieve combustion with very little excess oxygen. For example, the excess oxygen is less than 3% by volume in the flue gases flowing in the duct 9.

  In normal operation of the combustion plant, the valve V2 is closed and the oxidant arriving via the pipe 6 is the mixture of oxygen and CO2 produced by the mixer M. When the valve V2 is opened, the chamber is supplied with DC combustion air arriving through the conduit 7 which allows to return to a combustion in air in case of problems on the unit O of oxygen production or the unit of liquefaction of CO2.

  The interior of the combustion chamber CC is maintained under a pressure slightly above atmospheric pressure. This pressurization of the combustion chamber CC makes it possible to avoid or limit the entry of air. Thus, it limits the presence of inert compounds (eg nitrogen) in the combustion fumes. For example, the combustion chamber CC is maintained under a relative pressure of between 0.1 and 100 millibars.

  This excess pressure can be achieved by introducing the oxidant and the pressurized fuel into the chamber CC, under a relative pressure of between 0.1 and 100 millibars.

  In addition, it is possible to pressurize the combustion chamber CC using CO, under pressure introduced through the conduit 18. For example, the CO2 is introduced at a relative pressure of between 0.1 and 100 millibars. Pressurization has the advantage of avoiding or limiting the entry of stray air and, therefore, of inert compounds (in particular nitrogen) into the combustion chamber CC. Pressurization results in a slight leakage through the walls of the combustion chamber, a gas containing mainly CO, which is released to the atmosphere. The leak is represented by the conduit 19. The CO used for the pressurization can come from the storage tanks SG or SL, or from another source of CO 2.

  The combustion chamber CC consists of a metal casing, commonly called casing, this envelope being lined with heat-resistant material. In addition, the combustion chamber comprises one or more burners, as well as tubes in which circulates the fluid to be heated. This fluid can be boiler water that turns into steam (case of a steam generator and / or electricity), a mixture of hydrocarbons in the case of a refinery furnace, a mixture of hydrocarbons and water vapor in the case of a steam reforming furnace.

  The fumes produced by the combustion carried out in the chamber CC may undergo, in the unit T, dust removal and removal of the oxides of nitrogen and / or sulfur. For dedusting, electrostatic filters are preferably used. Some treatments can be performed in the DC combustion chamber. For example, in the case of using high sulfur content fuel, the injection of limestone into the chamber CC allows a first reduction of the sulfur oxide content which is generally followed by a second stage of desulfurization on the fumes coming out of the combustion chamber.

  Then, the fumes are evacuated through the conduit 9 and the extractor El. Then, the path followed by the fumes is determined by the valves or registers V5 and V6, that is to say by means for controlling the flow of fumes. in the ducts.

  When the V6 register is closed and the V5 register is open, the fumes are released into the atmosphere by the chimney C. When the V6 register is open and the V5 register is closed, the fumes are introduced into the condensation unit CT . The CT unit cools the fumes. The condensed water also entrains the sulfur compounds and the dusts which would not have been eliminated in the treatment unit T. The condensate of water and sulfur compounds is evacuated via the conduit 10 to a treatment unit of the water and sulfur compounds.

  The fumes desulfurized and freed from condensed water, comprise at least 98.5% of CO 2. These fumes are stored in the SG balloon.

  Part of the CO contained in the tank SG is withdrawn through the conduit 11 and the extractor E2, and is then recycled via the conduit 4 into the mixer M, which allows the reconstitution of an oxidant. Part of the CO, flowing in the duct 4 can be taken to be injected into the combustion chamber CC via the duct 18.

  Another part of the CO contained in the balloon SG is introduced via line 12 into the liquefaction unit LI. In stabilized operation, the flow rate of CO, thus liquefied, corresponds to the flow rate of CO, produced by combustion. The liquefaction is carried out by a succession of compression and cooling steps.

  The thermodynamic conditions imposed on the CO2 during the liquefaction are represented in FIG. 2 which represents the thermodynamic diagram T temperature and pressure P of CO, pure at 98.5% by volume. On the thermodynamic diagram, the liquid domain is indicated by L, the liquid equilibrium and gas range is indicated by L + G, the gas domain is indicated by G, and the curve H delimits the formation domain of the CO hydrates, . Curves 50 to 56 indicate the thermodynamic conditions imposed on CO during liquefaction. The gas phase compression stages of the CO correspond to the curves 50, 52 and 54. Between two compression stages, the CO has been cooled between the temperature reached at the end of compression to a temperature close to room temperature. . These cooling steps correspond to the curves 51 and 53. The cooling can be performed by heat exchange with air, water, or other refrigerant. In particular, the cooling can be carried out using the frigories obtained during the expansion of the nitrogen of the duct 2 produced by the unit O. The curve 55 also represents a step of cooling the CO under high pressure (between 50 bar and 100 bars). During this cooling represented by the curve 55, the CO passes from the gaseous phase to the liquid phase. During the different cooling stages corresponding to the curves 51, 53 and 55, the CO 2 is cooled to a temperature greater than 0 ° C., preferably 10 ° C. In the liquid phase, the CO 2 is compressed by one or more pumps. for example arranged in series, following the pressure and temperature conditions of the curve 56. The CO can be compressed to its injection pressure in the underground reservoir where it will be trapped. In general, the sequestering pressure is between 80 and 200 bar, and preferably between 100 and 120 bar.

  According to the invention, CO is liquefied under thermodynamic conditions where there is no risk of hydrate formation and at a pressure below the critical pressure. This domain, represented with hatching in FIG. 2, is situated to the right of the curve H, to the left of the L + G domain and below the critical pressure Pc. Preferably, the CO2 is liquefied at about 69 bars and 25 C. Under these conditions, the maximum content of inert compounds must be limited to 1.5% by volume in order to achieve liquefaction of CO2 by simple compression and cooling. If the purity of the CO2 is less than 98.5% by volume, then it is necessary to have a distillation operation to remove the inert compounds. This distillation is expensive in energy and leads to a release of CO2 to the atmosphere mixed with the inert compounds.

  During the liquefaction of CO2, the water collected during successive cooling after each compression step is discharged through line 13.

  The liquid CO2 produced by the unit LI is introduced via line 14 into the storage tank SL. The CO 2 in the flask SL is at a pressure of between 50 bars and 70 bars and at a temperature of between 10 ° C. and 40 ° C.

  The liquid CO2 contained in the storage tank SL can be intended for sequestration in an underground tank, for example in old oil or gas fields, in sealed salt aquifers, or in coal mines. The CO2 is evacuated from the flask SL via the duct 15, and is then pumped into the tank, for example by circulation in pipes or by transport in containers.

  The liquid CO2 contained in the SL tank can also be used for the proper functioning of the combustion plant. For example, CO2 can be taken by the pipe 16, expanded and vaporized by the valve V7 and directed by the conduit 4 to the mixer M, especially in the purge phase at startup. Furthermore, CO2 can be taken by the pipe 17, expanded and vaporized by the valve V8, then directed towards the conduit 18 to pressurize the combustion chamber and possibly serve as pneumatic transport gas and pressurization of hoppers in the case of combustion of solids, which avoids the entry of parasitic air into the combustion chamber.

  The combustion plant according to the invention can be implemented using a combustion chamber and an already existing chimney. This operation, commonly known as remodeling or revamping, makes it possible to reuse existing installations that are costly in terms of investment, in a context of CO2 capture.

  In normal or stabilized operation, the mixer M supplies the chamber CC with a mixture of oxygen from the unit O and CO2 from the storage tank SG. The chamber CC is fed with oxidant from the mixer M and fuel arriving via the conduit 8. The combustion fumes are completely directed into the treatment units T and condensation CT, then introduced into the storage tank SG. Part of the CO2 contained in the flask SG is introduced into the mixer M. Another part of the CO2 contained in the flask SG is liquefied in the liquefaction unit LI, then stored in the flask SL, and finally discharged via the flue 15 to be stored in an underground tank.

  At the start of the combustion in the installation shown in FIG. 1, the following three phases are carried out intended to eliminate the inert compounds, in particular nitrogen, present inside the various components of the combustion plant.

  In the first phase or purge phase, unit O is started to produce oxygen. The mixer M produces a mixture of oxygen and CO2 from the expansion through the CO2 valve V7 stored in the balloon SL. All of the combustion fumes are discharged through the chimney C. This first phase is carried out until the dry fumes from the combustion chamber contain at least 98.5% by volume of CO2.

  At the first start of the combustion plant or when purging for equipment inspection, the CO2 tank SL is empty. It is necessary to have a first quantity of CO2 to purge the quantity of nitrogen present inside the installation. CO2 can be produced using a distillation column, or the amount of CO2 needed for the first start can be imported. Alternatively, at the first start, instead of CO2, water vapor produced in an auxiliary boiler can be used to dilute the oxygen.

  During the second phase, a portion of the combustion fumes from the chamber CC is recycled. These recycled fumes are processed in the CT unit, stored in the SG flask and returned by the extractor E2 and the duct 4 in the mixer M. Thus, the mixture of oxygen and CO2 introduced into the chamber CC is produced. from the CO2 from the CC chamber. The part of the non-recycled fumes is evacuated by the chimney C. The third phase corresponds to the return to the normal or stabilized operating mode previously described. In the third phase, the entire flue gas stream from the CC chamber to the CT unit and the storage tank is directed. The portion of CO2 that is not recycled to the mixer M is introduced into the liquefaction unit LI and then into the storage tank SL.

Claims (10)

  1) Combustion process with capture of carbon dioxide, in which at least the following steps are carried out: a) a flow rich in oxygen is mixed with a flow rich in carbon dioxide, b) the mixture is introduced and a fuel in a combustion chamber (CC), c) the internal pressure of the combustion chamber (CC) is maintained above atmospheric pressure, d) the combustion fumes are treated by cooling to condense the water and compounds sulfur, and e) liquefies at least a portion of the treated fumes obtained in step d), by compression and cooling.   2) A process according to claim 1, wherein a portion of the treated fumes obtained in step d) is used to be mixed with the oxygen-rich stream in step a).   3) Method according to one of claims 1 and 2, wherein the internal pressure of the combustion chamber (CC) is between 0.1 and 100 millibar relative.   4) Process according to claim 3, wherein the mixture and the fuel are introduced into the combustion chamber (CC) at a pressure between 0.1 and 100 millibar relative.   5) Method according to one of claims 3 and 4, wherein is introduced, at a relative pressure of between 0.1 and 100 millibars, a rich carbon dioxide gas stream in the combustion chamber (CC).   6) Method according to one of the preceding claims, wherein, in step e), the liquefaction of the treated fumes is carried out by at least one compression of fumes at a pressure between 50 and 70 bar and by cooling the compressed fumes at a temperature between 0 C and 30 C.   7) Method according to one of the preceding claims, wherein in step b), the flow rates of the fuel and the mixture introduced into the chamber (CC) are adjusted so as to produce combustion fumes containing an excess of oxygen. less than 3% by volume.   8) The method of claim 7, wherein in step a), the oxygen content of the mixture is adjusted to a value between 30% and 40% by volume.   9) Method according to one of the preceding claims, wherein at the start of the process, purge the combustion chamber (CC) by performing a combustion with a fuel and a mixture comprising oxygen and carbon dioxide from a reservoir (SL) for storing liquid carbon dioxide, the combustion fumes being released into the atmosphere.   10) Method according to one of the preceding claims, wherein the liquid obtained in step e) is injected and sequestered in an underground reservoir.