Method for operating a plant for producing carbon dioxide

Abstract

The invention relates to a plant (1) for producing carbon dioxide (CO2), comprising: a separation system (2), wherein the separation system (2) is fluidically connected to a gas mixture (4) consisting of flue gas and carbon dioxide (CO2), wherein the separation system (2) is designed such that the carbon dioxide (CO2) contained in the flue gas and the steam (H2O) are separated, referred to in the following merely as carbon dioxide, wherein the water is not condensed by a stripper or a desorber top condenser before entry into the preheater (6), wherein, during operation, the separation system (2) is operable with steam from a steam line (7); a first carbon dioxide line (5) which is fluidically connected to the separation system (2) and out of which the carbon dioxide (CO2) that has been separated in the separation system (2) flows during operation; a preheater (6) through which the carbon dioxide line (5) leads and which is designed such that the temperature of the carbon dioxide (CO2) is increased; and a multi-stage compressor (13) which is fluidically connected at an inlet side to the carbon dioxide line (12) leading out of the preheater (6), wherein: after a stage (30), the temperature and the pressure of the carbon dioxide (CO2) are increased; after said stage (30), the carbon dioxide (CO2) passes via a line (14) through a steam generator (15); the steam generator (15) is designed such that water (31) fed into the steam generator (15) is used to generate steam by way of an exchange of energy with the thermal energy of the carbon dioxide (CO2) coming from the compressor (13) after a stage (30); the carbon dioxide that has cooled down in the steam generator (15) is recirculated to a subsequent stage in the compressor (13); the steam generated in the steam generator (15) is fluidically connected via the steam line (7) to the separation system (2); the carbon dioxide (CO2) flowing out of the compressor (13) after the stage flows through a first separator (32); and the separator is designed to separate the water (45) condensed in the last steam generator (15).

Description

[0001] Description

[0002] METHOD FOR OPERATING A PLANT FOR PROVIDING CARBON DIOXIDE

[0003] The invention relates to a system and a method for operating a system.

[0004] The invention particularly relates to a plant and a method for the separation and processing of carbon dioxide (CO2) for transport in a pipeline.

[0005] It is well known that carbon dioxide (CO2) emissions from power plants and other processes must be reduced. CO2 capture is considered an important factor in achieving the global goal of reducing CO2 emissions to as low a level as possible.

[0006] The International Energy Agency (IEA) predicts that the amount of captured CO2 could increase from today's 50 million tons per year to 7,600 million tons per year by 2050 in order to meet climate targets.

[0007] To capture carbon dioxide (CO2) from exhaust gases, such as flue gas, the only currently commercially available, large-scale technology is the amine system. Amine systems require significant amounts of low-pressure steam and thus heat for the process and are quite costly, which often makes CO2 capture economically unattractive for operators.

[0008] Another consideration is that after sequestration, the carbon dioxide (CO2) usually has to be transported over long distances if storage or utilization is not nearby. Pipeline transport in the supercritical phase is often considered a good approach for this. To bring the carbon dioxide (CO2) into the supercritical phase, it must be compressed from near-atmospheric pressure to supercritical pressure (over 73 bar and 31°C), typically between 100 and 200 bar.

[0009] During compression, a considerable amount of heat is released, which currently remains unused due to the low temperature level.

[0010] Depending on the process used to operate the amine system, different potential heat sources exist. Some processes are exothermic, so waste heat streams can be utilized for low-pressure (LP) steam treatment. However, if this is not the case and there is no alternative heat source, a fuel- or electrically fired boiler must be installed. Natural gas boilers are often used, which consume large quantities of gas and also produce additional carbon dioxide (CO2), which also must be captured, thus leading to even higher energy and capital requirements for the amine system.

[0011] With regard to the compression heat, it is important to use it sensibly and possibly combine it with the low-pressure steam processing required for the amine plant. However, the low-pressure heat must first be converted into high-pressure heat. One possible approach is to use fewer intercoolers between the compression stages, so that the carbon dioxide (CO2) is only cooled when it is above the temperature at which the heat can be used for low-pressure steam processing. However, the carbon dioxide (CO2) is then cooled back to atmospheric temperature, so that the amount of steam that can be generated is comparatively small and the heat is only partially utilized. If 100% of the heat is to be utilized and steam production maximized, a high-temperature heat pump can be used. However, this is associated with significantly higher investment costs and space requirements.The carbon dioxide (CO2) coming from the amine system typically contains a small amount of water vapor. This is achieved by forming the amine system with a desorber-top condenser. The water vapor contained in the carbon dioxide (CO2) is condensed in the desorber-top condenser. However, the latent heat of the water vapor remains unused.

[0012] The invention is based on the idea that the desorber top condenser can be dispensed with. This means that the carbon dioxide (CO2) coming from the amine system has a comparatively high proportion of water vapor. Typically, this mixture contains approximately 50 mol% water and 50 mol% carbon dioxide (CO2) and has a pressure between 1 and 4 bar and a temperature between 90 and 130 °C.

[0013] Against this background, the invention has set itself the task of providing a plant and a method for the provision of carbon dioxide (CO2) in a cost-optimized manner.

[0014] Another object of the invention is to maximize heat recovery for low-pressure (LP) steam processing at the lowest possible cost and space requirements.

[0015] This object is achieved by a plant for providing carbon dioxide (CO2) comprising a separation plant, wherein the separation plant is fluidically connected to a gas mixture of flue gas and carbon dioxide (CO2), wherein the separation plant is designed such that the carbon dioxide (CO2) contained in the flue gas is separated, wherein the separation plant can be operated with steam from a steam line during operation, wherein the stripper or desorber top condenser in the separation plant (2) is dispensed with, further comprising a first carbon dioxide line which is fluidically connected to the separation plant and from which the carbon dioxide (CO2) separated in the separation plant flows during operation, further comprising a preheater through which the carbon dioxide line leads and which is designed such that the temperature of the carbon dioxide (CO2) is increased,further comprising a multi-stage compressor, which is fluidically connected on the inlet side to the carbon dioxide line coming from the preheater, wherein after one stage the temperature and pressure of the carbon dioxide (CO2) are increased, wherein after the stage the carbon dioxide (CO2) is led via a line through a steam generator, wherein the steam generator is designed such that water fed into the steam generator is generated by means of energy exchange with the thermal energy of the carbon dioxide (CO2) coming from the compressor after one stage, wherein the carbon dioxide cooled in the steam generator is returned to a next stage in the compressor, wherein the steam generated in the steam generator is fluidically connected to the separation system via the steam line, wherein the carbon dioxide (CO2) flowing out of the compressor after the stage flows through a first separator,wherein the separator is designed to dewater the carbon dioxide (CO2) coming from the compressor stage.,

[0016] The task directed towards the procedure is solved with the following steps:

[0017] - Flow-controlled feeding of a gas mixture of flue gas and carbon dioxide (CO2) into a separation plant, - Separation of carbon dioxide (CO2) and water vapor (H20) in the separation plant, - Feeding the mixture of carbon dioxide (CO2) and water vapor (H20) to a preheater, wherein the mixture is heated in the preheater, - Forwarding the mixture heated in the preheater to a first stage of a multi-stage compressor, wherein the pressure and temperature of the mixture are increased in the first stage, - Forwarding the heated mixture after the first stage to a steam generator, wherein the thermal energy of the mixture is used to generate steam in the steam generator, - Carrying out a recirculation step, wherein in the recirculation step the carbon dioxide (CO2) cooled in the steam generator is fed to a further stage of the compressor,In the next stage, the temperature and pressure of the carbon dioxide (CO2) are increased,

[0018] - passing the heated carbon dioxide (CO2) after the further stage into a further steam generator, whereby the thermal energy of the carbon dioxide (CO2) is used to generate steam in the further steam generator, - repeating the recirculation step up to a final stage, - passing the carbon dioxide (CO2) flowing out after the last stage through the preheater, - passing the carbon dioxide (CO2) flowing out of the preheater into an outlet line,

[0019] -whereby the steam generated in the steam generator is fluidly connected to the separation plant via the steam line

[0020] -wherein separators and a dewatering unit are arranged between the stages of the compressor, wherein the separators are designed to separate condensed water and the dewatering unit is designed to remove the remaining water content in the carbon dioxide.

[0021] A key feature of the invention is the compressor, which typically comprises six to eight stages for compression from atmospheric to supercritical pressure. This means that the compression and steam conditioning process in the heat recovery steam generator (HRSG) actually occurs multiple times, depending on the final number of stages required to achieve the discharge pressure.

[0022] The preheater and all other downstream components are used only once, regardless of the number of stages. According to the invention, the carbon dioxide (CO2) is cooled only to the point where the heat can still be used for steam treatment in the waste heat boiler. This temperature is typically 5-10 °C above the final steam temperature required for the amine system, but this depends on the final design of the heat exchanger. However, this means that the carbon dioxide (CO2) is not cooled back to atmospheric temperature before it reaches the next compression stage. This allows steam treatment after each compression stage with the same number of heat exchangers / HRSGs as in conventional operation.

[0023] In reality, however, this process might not begin until after the second or even third compressor stage, since the carbon dioxide (CO2) must first be heated from the atmospheric outlet temperature after the amine system to the usable temperature level. To further maximize steam processing, the high temperature of the carbon dioxide (CO2) after the last HRSG can be used to preheat the carbon dioxide (CO2) at the compressor inlet to the usable temperature level. This allows the entire compressor, from intake to outlet, to operate at the temperature level at which steam can be processed, allowing steam processing to begin after the first compressor stage.

[0024] According to the invention, the high water content of the carbon dioxide (CO2) coming from the amine system is not reduced before entering the compressor. In the typical, current configuration, a so-called stripper or desorber top condenser is used to condense significant amounts of water upstream of the compressor. The invention assumes that this condenser is omitted. The condenser is typically part of the separation system. This allows the latent heat of the condensing steam to be captured at the usable temperature level within the steam generator for steam treatment between the compressor stages. Condensation begins in the steam generator after the compression stage, which compresses the stream to over approximately 15 bar. The condensed water is separated in a separator downstream of the corresponding heat exchanger / HRSG.

[0025] The stream then proceeds to the next process stage, where further water is condensed and separated during cooling in the steam generator before it is finally dehydrated in a dehydration system to the final permissible water content (e.g. for a pipeline) (typically triethylene glycol, but other technologies may also be applicable).

[0026] Typically, the stream must be cooled back to near atmospheric temperature to enter the dehydration system. Since the stream can only be cooled to approximately 5-10°C above steam temperature in the steam generator, the stream after the steam generator or separator still contains considerable heat, which is used to preheat the stream at the compressor inlet to maximize steam production.

[0027] The dry carbon dioxide leaving the drying system is still at atmospheric temperature. To improve heat recovery even within the final process stage, the carbon dioxide is reheated to a usable temperature level by the stream leaving the compressor, which must be cooled back to atmospheric temperature.

[0028] The solution significantly reduces the energy requirements of the amine system, which, depending on the alternative heat source, leads to fuel savings, including carbon dioxide (CO2) savings when a fossil fuel is used. Therefore, in this context, it also leads to CAPEX savings for the amine system, since less carbon dioxide (CO2) needs to be captured, while no additional machinery and only slightly additional drive power are required. Advantageous further developments are specified in the subclaims.

[0029] The advantage of the invention lies in the maximization of heat utilization and recovery of carbon dioxide (CO2) compression heat with almost no additional machinery or space requirements.

[0030] A further advantage is the reduction of external heat requirements for LP steam preparation for the amine system.

[0031] A further advantage arises from the significant saving of cooling water for the carbon dioxide (CO2) compressor, since the feed water for the steam treatment of the amine system is used for the intermediate cooling.

[0032] A further advantage is achieved through the potential carbon dioxide (CO2) savings when fossil fuel is used as a heat source for the boiler.

[0033] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0034] Identical components or components with the same function are marked with the same reference symbols.

[0035] Embodiments of the invention are described below with reference to the drawings. These are not intended to represent the embodiments to scale; rather, where useful for explanation, the drawings are presented in a schematic and / or slightly distorted form. For supplements to the teachings immediately apparent in the drawings, reference is made to the relevant prior art. They show:

[0036] Figure 1 is a schematic representation of an embodiment of a system according to the invention

[0037] Figure 1 shows a schematic representation of an embodiment of a system 1 according to the invention.

[0038] Plant 1 is designed to provide carbon dioxide (CO2) and includes a separation plant 2. The separation plant 2 is fluidly connected to a gas mixture 44 of flue gas and carbon dioxide (CO2) via a line 4. The separation plant 2 is designed such that the carbon dioxide (CO2) contained in the flue gas 44 is separated. The separated carbon dioxide (CO2) flows via a first carbon dioxide line 5 from the separation plant 2 through a preheater 6. In the preheater 6, the temperature of the carbon dioxide (CO2) is increased.

[0039] The first carbon dioxide line 5 is fluidically connected to the separation system 2. The separation system 2 is designed as an amine system. However, the carbon dioxide (CO2) coming from the separation system is still mixed with a comparatively large amount of water vapor. The ratio of carbon dioxide (CO2) to water vapor can be approximately 50 mol% water and 50 mol% CO2. The water vapor contained in the carbon dioxide (CO2) therefore still contains thermal energy, which is utilized according to the invention.

[0040] During operation, the separation plant 2 is operated with steam from a steam line 7. The carbon dioxide (CO2) 46 generated in the boiler 8 is also optionally fed into the separation plant 2 via a line 10 if a fossil fuel is used. The steam generated in the boiler 8 is fed into the separation plant 2 via a line 11. The carbon dioxide (CO2) heated downstream of the preheater 6 is fed to a multi-stage compressor 13 via a line 12. The multi-stage compressor 13 is fluidly connected on the inlet side to the carbon dioxide line 5 coming from the preheater 6.

[0041] In the compressor 13, the heated carbon dioxide (CO2) is fed to a first stage 30, wherein in the first stage 30 the temperature and pressure of the carbon dioxide (CO2) are increased.

[0042] After the first stage 30, the carbon dioxide (CO2) is fed via a line 14 to a steam generator 15, which can be designed as an HRSG (Heat Recovery Steam Generator).

[0043] The steam generator 15 is designed such that water 47 supplied to the steam generator 15 is converted into steam by means of energy exchange with the thermal energy of the carbon dioxide (CO2) coming from the compressor 13 after a stage 30.

[0044] The compressor 13 has five to ten stages, in particular six to nine and most particularly seven or eight stages.

[0045] The carbon dioxide (CO2) cooled in the steam generator 15 is returned to the stage 30 via a line 16 in the compressor 13. This occurs several times, i.e. several stages in the process stage 30 are flowed through, with the thermal energy of the carbon dioxide (CO2) being used after each stage to generate steam in the steam generator 15. For reasons of clarity, Figure 1 only shows one compressor stage 30, one steam generator 15, one line 14 to the steam generator 15 and one line 16 from the steam generator 15 to the compressor 13 and to the process stage 30. For reasons of clarity, the individual lines to the steam generator 15 and back to the compressor 13 have been omitted.

[0046] In the final steam generator 15, significant amounts of the water vapor contained in the carbon dioxide begin to condense. Before the carbon dioxide (CO2) flows through the stages 34 of the compressor 13, it flows through a separator 32. In the separator 32, water 45 is separated from the carbon dioxide (CO2) and discharged via a pipe.

[0047] The steam generated in the steam generator 15 and in the further steam generator 36 is fluidly connected to the separation plant 2 via the steam line 7.

[0048] The carbon dioxide (CO2) flowing out of the compressor 13 after the stage 34 flows through the preheater 6 via a line 17. Before the carbon dioxide (CO2) flows through the preheater 6, it flows through a second separator 37. In the second separator 37, water 45 is separated from the carbon dioxide (CO2) and discharged via a line.

[0049] After the preheater 6, the carbon dioxide (CO2) flows through a dewatering unit 38, which is designed to dewater the carbon dioxide (CO2) coming from the preheater 6. The water 45 separated in the dewatering unit 38 is discharged via a drainage line.

[0050] The additional dewatering unit 38 is designed, for example, as a tri-ethylene glycol (TEG) system.

[0051] The carbon dioxide (CO2) flowing out of the additional dewatering unit 38 flows through another preheater 39, where the temperature of the carbon dioxide (CO2) is increased. After the preheater 39, the carbon dioxide (CO2) flows through a next stage 40 of the compressor 13, where the temperature and pressure of the carbon dioxide (CO2) are increased. The thermal energy of the carbon dioxide (CO2) is used in another steam generator 42 to generate steam for the separation plant 2.

[0052] For example, the carbon dioxide (CO2) produced and supplied in Plant 1 is subsequently processed for transport in a pipeline 33.

Claims

Patent claims 1. Plant (1) for providing carbon dioxide (CO2), comprising a separation plant (2), wherein the separation plant (2) is fluidically connected to a gas mixture (4) of flue gas and carbon dioxide (CO2), wherein the separation plant (2) is designed such that the carbon dioxide (CO2) and water vapor (H2O) contained in the flue gas are separated, wherein the separation plant (2) is operable with steam from a steam line (7) during operation, further comprising a first carbon dioxide line (5) which is fluidically connected to the separation plant (2) and from which the carbon dioxide (CO2) separated in the separation plant (2) flows during operation, further comprising a preheater (6) through which the carbon dioxide line (5) leads and is designed such that the temperature of the carbon dioxide (CO2) is increased, further comprising a multi-stage compressor (13) ,which is fluidically connected on the inlet side to the carbon dioxide line (12) coming from the preheater (6), wherein after a stage (30) the temperature and the pressure of the carbon dioxide (CO2) are increased, wherein after the stage (30) the carbon dioxide (CO2) is led via a line (14) through a steam generator (15), wherein the steam generator (15) is designed in such a way that a water (31) fed into the steam generator (15) by means of energy exchange with the thermal energy, steam is generated from the energy of the carbon dioxide (CCt) coming from the compressor (13) after a stage (30), wherein the carbon dioxide cooled in the steam generator (15) is returned to a next stage in the compressor (13), wherein the steam generated in the steam generator (15) is fluidly connected to the separation plant (2) via the steam line (7), wherein the carbon dioxide (CCt) flowing out of the compressor (13) after the first process stage flows through a first separator (32), wherein the separator (32) is designed to separate the water condensed in the last steam generator (15). Plant (1) according to claim 1, wherein the carbon dioxide (CO2) generated in the plant (1) is processed for transport in a pipeline (33). Plant (1) according to claim 1 or 2, wherein the separation plant (2) is designed as an amine plant.Plant (1) according to claim 1, 2 or 3, wherein the compressor (13) has five to ten stages, in particular six to nine and most particularly seven or eight stages. Plant (1) according to one of the preceding claims, wherein a next stage (34) of the compressor (13) is arranged after the first separator (32), wherein in the next stage (34) the temperature and the pressure of the carbon dioxide (CO2) are increased, wherein after the next stage (34) the carbon dioxide (CO2) is led via a line (35) through a further steam generator (36), wherein the further steam generator (36) is designed such that a... Steam is generated from the water supplied by means of energy exchange with the thermal energy of the carbon dioxide (CCt) coming from the compressor (13) after the next stage (34), wherein the carbon dioxide cooled in the steam generator (36) is returned to the compressor (13). Plant (1) according to claim 5, wherein the carbon dioxide (CO2) flowing out of the compressor (13) after the next stage (34) flows through a second separator (37), wherein the second separator (37) is designed to separate the water condensed in the steam generator (36). Plant (1) according to one of the preceding claims, with an additional dewatering unit (38) which is fluidically coupled to the preheater (6). Plant (1) according to claim 7, wherein the additional dewatering unit (38) is designed as a triethylene glycol (TEG) system.Plant (1) according to claim 7 or 8, with a further preheater (39) which is fluidically coupled to the additional dewatering unit (38). Plant (1) according to claim 9, wherein the compressor (13) has an additional stage (40) which is fluidically coupled to the further preheater (39), wherein the temperature and pressure of the carbon dioxide (CO2) are increased in the additional stage (40). Plant according to claim 10, wherein after the additional stage (40), the carbon dioxide (CO2) is passed through a steam generator (42) via a line (41). wherein the steam generator (42) is designed such that water (43) supplied to the steam generator (42) is generated by means of energy exchange with the thermal energy of the carbon dioxide (CO2) coming from the compressor (13) after the additional stage (40), wherein the carbon dioxide cooled in the steam generator (42) is recycled to a next stage in the compressor (13). A method for providing carbon dioxide (CO2), comprising the steps: - Flow-technical feeding of a gas mixture (44) of flue gas and carbon dioxide (CO2) into a separation plant (2), - Separation of the carbon dioxide (CO2) and water vapor (H2O) in the separation plant (2), - Feeding the carbon dioxide (CO2) to a preheater (6), wherein the carbon dioxide (CO2) is heated in the preheater (6), - Forwarding of the carbon dioxide (CO2) heated in the preheater (6) into a first stage (30) of a multi-stage compressor (13), wherein the pressure and the temperature of the carbon dioxide (CO2) are increased in the first stage (30), - Forwarding of the heated carbon dioxide (CO2) after the first stage (30) into a steam generator (15), wherein the thermal energy of the carbon dioxide (CO2) is used to generate steam in the steam generator (15), - Carrying out a return step,wherein in the recirculation step the carbon dioxide (CO2) cooled in the steam generator (15) is fed into a further stage (34) of the compressor (13), wherein in the further stage (34) the temperature and pressure of the carbon dioxide (CO2) are increased, - passing the heated carbon dioxide (CO2) after the further stage (34) into a further steam generator (36), wherein the thermal energy of the carbon dioxide (CO2) is used to generate steam in the further steam generator (36), - repeating the recirculation step up to a last stage, - passing the carbon dioxide (CO2) flowing out after the last stage through the preheater (6), - passing the carbon dioxide (CO2) flowing out of the preheater (6) into an outlet line, - wherein the steam generated in the steam generator (15, 36, 42) is fluidically connected to the separation system (2) via the steam line (7), - wherein separators (32, 37) and a dewatering unit (38) are arranged between the stages (30, 34, 40) of the compressor (13), wherein the separators (32,37) for separating condensed water (45), and the dewatering unit (38) for removing the remaining water content (45) in the carbon dioxide. The method according to claim 12, wherein an additional dewatering unit (38) is arranged downstream of the preheater (6). The method according to claim 13, wherein the additional dewatering unit (38) is designed as a triethylene glycol (TEG) system.

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