CH717568A2 - Process for separating CO2 from fumes by isobaric cryogenics using heat exchangers. - Google Patents

Abstract

The invention relates to a method for extracting carbon dioxide CO 2 from a gas smoke stream. Said method is based on isobaric cryogenics and preferably uses a series of heat exchangers (10, 11, 12, 18, 19, 23, 24) designed and mounted in such a way as to cool the smoke according to several stages. The passage of the smoke, through exchangers mounted in series, aims to cool the CO 2 until its solidification phase to recover it in the form of ice particles using a cyclone and a rotary valve . This process is done without the addition of chemical additives. It enables cost-effective CO 2 separation; it makes it possible to recover part of the cooling energy by reusing the cooled gas as cooling fluid in the exchangers (10, 11, 18, 23) located upstream, makes it possible to be adjusted to extract other greenhouse gases greenhouse offers the possibility of modifying the size and number of heat exchangers in order to adapt it to a variation in volume and concentration of gases.

Description

[0001] Emissions of greenhouse gases (GHGs) are currently subject to several regulations, and polluting factories are forced to comply with increasingly stringent GHG emission standards.

[0002] Various processes have been developed to remove carbon dioxide from tributaries such as pre-combustion, post-combustion and oxy-combustion. These various technologies require chemicals: amines, enzymes, oxygen or hydrogen as well as subsequent separation devices. These technologies have the disadvantage of being complicated to install, require significant investments, in addition to consuming a lot of energy, which reduces their performance by several points.

The method disclosed here is completely different; it is based on the successive cooling of a flow of gas through several heat exchangers, until the carbon dioxide CO2, contained in the smoke, is converted into solid form with a view to collecting it at the end of the process in the form of dry ice.

[0004] There are two methods of obtaining CO2 in the form of ice, the first is compression and expansion, the second is isobaric cooling. It is the isobaric cooling process which is developed below.

[0005] Compared to the other methods, this is the method which allows the best yield. If the compression system is commonly used, it is viable for the production of CO2 ice when dealing only with the latter. When it comes to separating CO2 from flue gases, it is expensive to treat the entire mass of gas by compression when the CO2 only represents a fraction of this mass.

[0006] On an industrial scale, it is complicated to extract components harmful to the environment having different natures from the same mixture of gases. Unlike other processes, this one makes it possible, with the same installation, to recover different chemical elements at different cooling stages.

[0007] This method has the potential to work without the addition of chemicals, reduces 99% of the CO2 contained in the smoke and avoids the cost of complicated installations.

[0008] In addition, isobaric cryogenics makes it possible, through the interplay of heat exchangers, with optimum pinching, which corresponds to the minimum temperature difference between the hot fluid and the cold fluid, to recover part of the energy supplied for gas cooling, whereas in the case of compression and expansion, the compression energy is not recoverable.

Description of the process

[0009] The object of this patent is to propose a new process for the separation of carbon dioxide CO2 from a flow of gas smoke (9) released, without limitation, by polluting industries such as power stations thermal, cement works, refineries or metallurgies. It is a process based on an isobaric cryogenization technique. This process is mainly based on the use of heat exchangers mounted in series and connected to cooling circuits.

An isobaric cryogenic process for capturing carbon dioxide from a gas smoke stream (9) through a series of exchangers (10) (11) (12) (18) (19) (23 ) and (24) is described. Details of one or more non-limiting embodiments of the invention, which may be encompassed by the claims, are set forth in the description and drawings below.

[0011] The method, explained in this disclosure, deals with a specific example (diagram in Fig. 4), however, other embodiments of the method should be apparent to those skilled in the art after reviewing this description. . For example, although this description relates in particular to the removal of carbon dioxide from a smoke stream, the method and the elements of the installation described here can be easily adapted to remove other polluting components such as, for example, nitrogen dioxide NO2. Someone familiar with reading the specs for this area would understand what, if any, modification would need to be made in order to capture the other components.

[0012] The example of this process relates to the treatment of gas smoke, on a reduced scale. Said smoke contains 13% CO2, 5% water vapor H2O, sulfuric acid H2SO4, hydrochloric acid HCL and other elements. The inlet temperature of this smoke is 50°C, the flow rate is 1Nm3/h, the density is 1.3495 kg/m3, the specific heat is 0.23355 kcal/kg and the effective hourly volume is 50 °C is 1.14 m3/h.

The cooling takes place without contact between the smoke and the cooling fluids. According to some embodiment, such heat exchange is achieved in single pass countercurrent tubular heat exchangers, in which heat is transferred by convection continuously through an impermeable metallic partition wall.

The tube bundle of said exchangers is characterized by a low wall thickness. Inside the grille, baffles are arranged in a helical manner and kept at a short distance in order to increase the heat exchange coefficient and reduce pinch to a minimum, which corresponds to the difference between the temperatures of the two fluid at the outlet of the exchangers.

[0015] To obtain dry ice in this case (example of calculation in Figure 4), an installation is required consisting of 7 heat exchangers (10) (11) (12) (18) (19) (23) and (24), fitted in series to enable the smoke temperature to be lowered to -80°C. The smoke passes successively through these exchangers undergoing a gradual cooling. Throughout the process, the cooling takes place at a pressure close to atmospheric pressure. Based on its phase diagram, CO2 passes from the gaseous state to the solid state, in the form of dry ice, at a temperature of - 78.5°C. Cooling to this temperature takes place in a double jacket exchanger (24) equipped with rotating vanes and cooled with liquid nitrogen (25).

[0016] According to the aspects illustrated here, successive refrigeration systems are added for the solidification of carbon dioxide CO2 in a flue gas stream. Said system comprising at least three refrigeration circuits containing a refrigerant in liquid form such as ammonia, nitrogen or liquid CO2. Said refrigeration circuits comprising two tubular refrigerant exchangers (12) and (19) and a double jacket exchanger with rotary vanes (24) cooled with liquid nitrogen. At least one cryogenic compressor and a pump are connected to each refrigerant tank to compress and discharge the flue gas cooler refrigerant.

According to certain embodiments, the cryogenic process comprises at least one exchanger (12) configured to cool at least part of the smoke using ammonia or liquid CO2 stored in a tank (13) specific for these coolants. A cryogenic compressor compresses and cools the return fluid which heats up as it passes through the exchanger (12). At the outlet of the pressure tank, the cooling fluid is discharged by the pump (15) and undergoes expansion and a drop in temperature during its passage through the exchanger (12). Depending on the case, this drop in temperature can cause evaporation of the refrigerator liquid, the cryogenic compressor (14) allows it to be compressed and cooled. The cooling fluid condenses, and it is returned to the reservoir (13) at its initial temperature and pressure.

According to some embodiments, the flue gas treatment system further comprises a condenser exchanger (12) for removing water vapor from the flue gas flow, disposed upstream of the exchanger (18) with reference to the direction of flow of the flue gas flow.

[0019] The residual water in the CO2-rich flue gas can cause the formation of ice in the heat exchangers cooled below the temperature of 0° C., which possibly leads to a problem of clogging of these heat exchangers. According to this embodiment, the water is recovered, in the form of liquid condensates, at the outlet of the exchanger (12) via a purge valve (16) at a temperature of 2°C and upstream of the exchanger ( 18).

[0020] The carbon dioxide-rich flue gas may typically include, in addition to water vapour, contaminants in the form of, for example, dust particles which are removed by filters (3).

The combustion gas rich in carbon dioxide may include, in addition to water vapor and dust, other contaminants such as hydrochloric acid or sulfuric acid. According to this embodiment, the water content of the flue gas can be eliminated at the outlet of the exchanger (12). Depending on the pH and the temperature in this fume exchanger-condenser, the condensation of the fumes can also lead to a reduction of other elements such as hydrochloric acid HCL and sulfuric acid H2SO4. These elements are captured in the form of condensates evacuated by the conduit (17) via a purge valve (16).

[0022] According to certain embodiments, the cryogenic process comprises at least one exchanger (19) configured to cool at least part of the smoke using liquid CO2 stored in a specific tank (20) for this cooling liquid. A cryogenic compressor compresses and cools the return fluid which heats up as it passes through the exchanger (19). At the outlet of the pressure tank, the cooling fluid is discharged by the pump (22) and undergoes expansion and a drop in temperature during its passage through the exchanger (19). Depending on the case, this drop in temperature can cause evaporation of the refrigerator liquid, the cryogenic compressor (21) allows it to be compressed and cooled. The cooling fluid condenses and is returned to the tank (20) at its initial temperature and pressure.

The cyclone (29) uses centrifugal action as the principle of operation. The gas loaded with dry ice particles, coming from the outlet of the double jacket exchanger (24), enters the cyclone (29) through a tangential inlet (37). The centrifugal action forces the particles to spin and be precipitated against the cylinder wall causing a downward whirlwind of particles to the discharge outlet (38). As for the smoke devoid of CO2, it is evacuated to the central chimney (39), located inside the cyclone (29), created by the pressure difference internal to the cyclone (29).

A rotary valve (30) installed at the outlet of the cyclone (29) maintains the seal between two media of different pressures. This method of collecting the CO2 at the exit of the installation allows an easy and fast maintenance.

The rotary valve (30) provided with a rotor (35) with sealed vanes (36) receives the dry ice and drives it into a reservoir of CO2 ice (32). The rotor (35) is driven by an electric motor (31) via a speed reducer. Said rotation speed is determined according to the volume and the flow rate of the CO2 to be recovered.

The smoke evacuated by the chimney (39) of the cyclone (29) is returned, through the conduit (33), to the inlet of the exchanger (23). At a temperature of -80°C, this smoke, devoid of CO2, is used to cool the exchangers (23) (18) (11) and (10).

[0027] According to a preferred embodiment, the heat exchangers (10), (11), (18) and (23) are dimensioned to reuse the flow of gas smoke depleted in CO2, already cooled at the outlet of the cyclone at -80°C as refrigerant. Said gas is redirected through the pipe (33) to the inlet of the exchanger (23) at a temperature of -80°C. Said gas leaves at a temperature of -28°C and can be redirected to the inlet of the exchanger (18) to then be returned to the inlet of the exchanger (11) at -7°C, and leaves said exchanger at a temperature of 11° C. to then cool the exchanger (10). At the outlet of said exchanger, this CO2-free gas flow can be released into the atmosphere through the conduit (1).

According to a preferred embodiment, increasing the power of the exchangers by adding tubular heat exchanger modules in series, in parallel or in series/parallel. By way of example, each module can have dimensions of approximately 2 to 3 meters. The modules can be made of stainless steel.

[0029] It should be understood that the embodiments disclosed herein are for illustrative purposes and should not be construed as limiting in any way. At this level, the method for extracting carbon dioxide disclosed here can be based on other types of exchanger such as plate exchangers or other types of tubular exchangers.

[0030] According to a preferred embodiment, temperature (Tl) and flow (FI) sensors are connected to different points of the installation and make it possible to supervise the operation of the process. Valves are also installed to allow easy isolation of components for maintenance and cleaning (Figure 2).

Fans ensure the circulation of fumes; the fan (6) ensures the circulation of the smoke between the dedusting unit (3), containing filters, and the desulfurization unit (4). The fan (7) ensures the circulation of the smoke between the outlet of the desulphurization unit (4) and the inlet of the cryogenic process (5). The fan (8) evacuates the smoke devoid of CO2 at the outlet of the cryogenic process (5) to the outside atmosphere via the duct (1) (chimney).

According to another embodiment, this process can be modified to extract other types of greenhouse gas elements, such as nitrogen dioxide NO2 which solidifies at a temperature of - 11.25 °C under normal pressure of 1.013 bar. This separation of the NO2 can be done at the level of the exchanger (18), which can be a tubular exchanger with a scraped surface making it possible to evacuate the pieces of ice from the NO2 through a pipe.

The entry of the smoke is through the conduit (9) separated from the outlet (1) by a check valve (2). Said valve could open during the transitional phase of starting to allow the gas to pass from conduit (1) to conduit (9) in a unidirectional direction. This passage makes it possible to compensate for the reduction in the volume of the gas contained in the process circuit caused by the cooling.

When starting the process, a transitional state takes place for a few minutes, during which the flue gas gradually cools in the heat exchangers until it reaches stationary temperatures.

[0035] The CO2 recovered in the form of ice can advantageously be recovered and used in a wide range of applications: fuel in a fuel cell to generate electricity, fertilizer in agriculture, additive in the food industry, cooler or freezer, fire extinguisher, pH regulator, etc.

Brief description of the drawings

[0036] The characteristics described above and other characteristics are illustrated by the following figures and the detailed description. Other objects and characteristics of the present invention will appear on reading the description and the claims.

[0037] Embodiments are described with reference to the figures, in which similar reference characters denote similar elements, by way of example, and in which:

[0038] FIGURE 1 is a block diagram that illustrates an overview of a process for extracting carbon dioxide from a smoke stream. In this diagram, one can distinguish the parts of the chimney (9) and (1) with the non-return valve (2). In this same diagram, (3) represents a dedusting unit composed of filters, (4) represents a desulfurization unit and (5) represents the cryogenic process that is the subject of this patent. (6), (7) and (8) represent fans which ensure the circulation of gas flows.

FIG. 2 schematically represents an embodiment of the CO2 separation system. This is a P&ID piping and instrumentation diagram of the CO2 extraction process. This diagram illustrates the connection between the various heat exchangers for the successive cooling with other circuits allowing the cooling of these exchangers. The system illustrated here includes, as main components, six tubular exchangers and a cylindrical exchanger with rotary vane. In this system, four exchangers are advantageously cooled by the cooled return gas and three exchangers (12) (19) (24) cooled by a supply of external refrigerants stored in tanks (13) (20) and (25). The exchanger (24) is a cylindrical exchanger with rotating blades cooled by liquid nitrogen in a double jacket.

In this same figure, we can distinguish cryogenic compressors (14) (21) (26) which are operational to compress and cool the cooling fluids. There are also pumps (15) (22) (27) to ensure the circulation of fluids and conduits to convey the fluids between the various elements of the installation. Also shown is a device (16) for removing other chemical elements.

[0041] FIGURE 3 shows the cyclone, which is a centrifugal separator, connected with a rotary valve (30). This is the part of the process that separates dry ice from the cooled gas stream. One can distinguish in this figure the tangential inlet (37), and in the middle is the chimney (39) making it possible to evacuate the cold gas devoid of CO2.

Claims (11)

1. In the claims, the word "comprising" is used in its inclusive sense and does not exclude other elements present. The indefinite article "a" before a claim feature does not exclude more than one of the features present. Each of the individual features described herein may be used in one or more embodiments and is not, by any description given herein, to be considered essential to all embodiments as defined by the revendications. The embodiments of the invention, in respect of which an exclusive right of ownership or privilege is claimed, are defined as follows: 1. Process for the extraction of greenhouse gases by isobaric cryogenics from a gas stream comprising carbon dioxide CO2 in an initial proportion, water vapor, one or more acid compounds, and one or more others harmful gases such as sulfur dioxide or nitrogen dioxide. 2. Process for the extraction of carbon dioxide CO2 based on isobaric cryogenics using a system of stage heat exchangers for the successive cooling of a flow of gas fumes containing carbon dioxide CO2, said system comprising refrigeration. 3. Method according to claim 2 characterized in that it allows the recovery of a cold gas stream free of CO2 or containing a much lower final proportion of CO2 than the initial proportion of CO2 in the hot gas stream to be treated. 4. Method according to claim 3 characterized in that the cooling of the gas stream can be done down to a temperature of approximately - 80°C for the elimination of CO2 and characterized in that the number and size of the heat exchangers can be modified to reach other temperatures allowing the solidification of other polluting chemical elements. 5. Process for cooling gas according to claims 1, 2, 3 and 4 making it possible to recover part of the cooling energy by using the cooled gas recovered at the end of the process as cooling fluid in the series of exchangers located in upstream by referring to the direction of flow of the hot gas. 6. Method for extracting CO2 from a gas smoke stream according to claims 1, 2, 3 and 5, based on a set of heat exchangers connected in series, a cyclone and a rotary valve for the collection of CO2 in the form dry ice. Said process comprising several steps: a) passage of the smoke through a set of heat exchangers, connected in series, in which one or more exchangers are fed back by the cold gas from the outlet of the process. b) intermediate cooling with a supply of external refrigerants such as ammonia, nitrogen or liquid CO2, external refrigerants cooled and condensed in closed circuits by cryogenic compressors connected to heat exchangers, c) separation of other elements such as water and acids returned in condensates.d) separation using a cyclone and a rotary valve of dry ice from the gas stream.e) separation of other greenhouse gas elements which solidifies from a way identical to that of carbon dioxide, such as nitrogen dioxide NO2 for example, extracted using a scraped surface exchanger or using a cyclone, f) Reinjection of the cold gas into the exchangers used at the step a). 7. Method according to claim 6 characterized in that it allows the recovery of a gas stream free of CO2 or containing a much lower final proportion of CO2 than the initial proportion of CO2 in the stream to be treated, characterized in that it comprises, in step c), a step of condensing the stream in order to eliminate therefrom at least a part of the water vapor which it contains, and at least a part of the other components condensable at this temperature in a heat exchanger cooled by a fluid . 8. Method according to one of the preceding claims, characterized in that the cooling of at least one exchanger is ensured with the cold return gas in which the CO2 is already extracted and which is routed through ducts to release it into the 'atmosphere. 9. Isobaric cryogenic process for the solidification of carbon dioxide (CO2) in a flue gas stream according to claims 2, 5 and 6. Said process comprising refrigeration circuits. Said refrigeration circuits include refrigerant compressors (14) (21) (26). A first stage of heat exchangers (10), configured to cool the CO2-containing gas, is cooled with the cold return gas. A second stage of heat exchangers (11), configured to cool the CO2-containing gas, is cooled with the cold return gas. A third stage of heat exchangers (12), configured to cool the gas containing CO2, is cooled in a closed circuit preferably with ammonia or liquid CO2. Said exchangers are connected to purge valves in order to evacuate the condensates. A fourth stage of heat exchangers (18), configured to cool the CO2-containing gas, is cooled with the cold return gas. A fifth stage of heat exchangers (19), configured to cool the gas containing CO2, is cooled in a closed circuit preferably with liquid CO2. A sixth stage of heat exchangers (23), configured to cool the CO2-containing gas, is cooled with the cold return gas. A seventh and final heat exchanger with a double jacket and rotating blades to solidify the CO2 contained in the gas. Said exchanger is cooled to the solid condensation temperature of CO2. Said exchanger is preferably cooled with liquid nitrogen. 10. A method of extracting CO2 from a gas stream according to any one of claims 1 to 9, further comprising a cyclone (29) used as a centrifugal separator. The dry ice-laden gas enters the cyclone through a tangential inlet (37). The centrifugal action forces the dry ice to spin and be precipitated against the cylinder wall causing a downward whirlwind of particles to the exhaust outlet (38). The cold smoke devoid of CO2 is evacuated to the central chimney (39), located inside the cyclone (29), created by the pressure difference inside the cyclone (29). 11. A method of extracting CO2 from a gas stream according to any one of claims 1 to 10, further comprising a rotary valve (30) with variable speed, installed at the outlet of the cyclone (29). Said rotary valve maintains the seal between two different media and makes it possible to modify the rate of precipitation of dry ice in a reservoir by adjusting its speed of rotation.