EA012122B1 - Process and apparatus for the liquefaction of carbon dioxide - Google Patents

Abstract

Apparatus for carbon dioxide liquefaction comprising a flow channel for carbon dioxide passage from an inlet port to an outlet port. The channel comprises a plurality of compressors (2, 5, 8) and coolers (4, 7, 9, 10, 13) arranged in series with an expansion chamber (14, 15) in said flow channel downstream of the final compressor (8) and cooler (9, 10, 13). The apparatus also comprises a recirculation channel (16) arranged to return gaseous carbon dioxide from said expansion chamber (15) into said flow channel (3) upstream of said final compressor (8) and cooler (9, 10, 13).

Description

The present invention relates to a method for producing liquid carbon dioxide and a plant for use in said method.

Carbon dioxide (CO ₂ ) is a gas produced as a by-product in large quantities in some industrial processes, for example, in the production of ammonia or the production of energy by coal or gas power plants. Emission of this by-product into the atmosphere is undesirable from the point of view of ecology, as it is a greenhouse gas. Thus, much effort has been made to develop technologies for the removal of CO ₂ in ways other than simple emissions into the atmosphere. One of the technologies of particular interest is the injection of CO ₂ into porous subterranean formations (i.e. rock), for example, through an injection well into an oil field.

Underground disposal can be carried out simply in porous reservoirs, or the favorable advantage of underground disposal can be realized if the reservoir in which it is located contains hydrocarbon, as the injected CO2 serves to conduct the hydrocarbon (for example, oil or gas) in the reservoir towards the production wells ( Ie to wells from which hydrocarbon is extracted). Thus, CO ₂ injection is one of the standard technologies at a late stage of field development to achieve improved hydrocarbon recovery.

The amounts of such carbon dioxide when buried by injection into the underground layers are huge, usually of the order of millions of tons. This creates problems in terms of transportation of CO2 from the place of its formation to the place of its injection, especially if the injection site is located in the open sea. Carbon dioxide at ambient temperatures and pressures is gaseous, and, if transported in batches, such bulky containers are required that the method would be impractical. While pipeline transport might be feasible in some circumstances, the required infrastructure is expensive. Therefore, it is desirable to transport carbon dioxide, especially to the injection sites located in the open sea, in batches in liquid form.

However, transporting liquid carbon dioxide is not a problem-free or cheap task. If liquid CO _{2 is} not cooled, the pressures required to maintain it in a liquid state are high (6-8 MPa abs. (60-80 bar abs.)), Which makes the required wall thicknesses of the containers under pressure large and Such containers for transporting non-refrigerated liquid CO2 are very expensive. Transporting liquid CO2 at temperatures below ambient lowers the required pressures and the required wall thicknesses of the container, but is expensive because cooling is required, and since CO2 has a solid phase, there is a danger that solid carbon dioxide can form. The formation of solid carbon dioxide makes the transfer of CO2 by pumping problematic and, due to the risks of blockage of pipes or valves, potentially dangerous.

Thus, summing up the economic balance arising from the cooling and cost of the container, and avoiding the danger of the formation of solid CO ₂ , in any given circumstances, there will usually be temperature and pressure that are optimal for liquid CO ₂ in containers, for example, a temperature that is below ambient temperature. medium, and pressure, which is higher than the ambient pressure, but still is subcritical (the critical point for CO ₂ is 7.38 MPa abs. (73.8 bar abs.)). Usually for large-scale transportation of liquid CO _{2 the} optimum temperature can be in the range from -55 to -45 ° C and the pressure can be from 0.55 to 0.75 MPa abs. (5.5 to 7.5 bar abs.), i.e. parameters corresponding to the position on the phase diagram for CO2, which is slightly above the triple point in terms of temperature and pressure. The triple point for CO ₂ has a pressure of 0.52 MPa abs. (5.2 bar abs.) And a temperature of -56.6 ° C. Lower temperatures and pressures increase the risk of dry ice formation; higher pressures require more expensive containers; lower pressures increase the formation of gas or solids.

While small-scale production (for example, currently typically 0.1 tons / year) of liquid carbon dioxide is relatively trivial and usually involves two, three or four cycles of compression and cooling / expansion, mass production at the level of millions of tons is by no means case is not usual, since, starting from a gas, which is or mainly carbon dioxide at a temperature and pressure of approximately the environment, the conversion of this raw material into liquid carbon dioxide at a temperature The x and pressures that are desirable for mass transportation include a significant increase in pressure and energy consumption.

Applicants have found that the production of liquid carbon dioxide in bulk and at temperatures and pressures desirable for mass transportation can be carried out in an environmentally safe and efficient way by producing liquid carbon dioxide or carbon dioxide in the form of a dense fluid (i.e. supercritical) at temperatures and pressures above the desired values, its expansion to form liquid carbon dioxide at the desired values, and cold carbon dioxide gas, which is fed iklom in compression and cooling cycles / expansion, by reducing the value of such cycles CO2 flow enthalpy. With this way

- 1 012122 ba does not require an expensive cooling agent and it is possible to avoid the release of CO ₂ into the atmosphere.

Thus, from the point of view of one of the aspects, the invention provides a method for producing from feed gas, which includes carbon dioxide, liquid carbon dioxide at the desired temperature and pressure, this temperature being lower than the ambient temperature, higher than the triple point temperature for carbon dioxide and lower than the critical point for carbon dioxide and this pressure is higher than the ambient pressure, higher than the triple point pressure for carbon dioxide and lower than the critical point pressure for carbon dioxide; said method comprises supplying said feed gas to an inlet opening of a liquefaction plant having a flow path from said inlet opening to an outlet opening connected to an expansion chamber; passing said gas in the form of a fluid through a flow path through said installation and processing said fluid through multiple compression and cooling cycles to thereby form liquid or supercritical carbon dioxide having a temperature and pressure higher than said desired temperature and pressure; passing said liquid or supercritical carbon dioxide through said outlet to said expansion chamber to form carbon dioxide gas and liquid carbon dioxide in said chamber at the desired temperature and pressure, and recycling said carbon dioxide gas into the fluid flowing through said compression cycle and cooling, and possibly removing the specified liquid carbon dioxide at the specified desired temperature and pressure from the specified extender hydrochloric chamber.

One or more cycles of compression and cooling, and preferably all such cycles, may additionally include an expansion stage, which, of course, will further cool the fluid. It is particularly preferable that the fluid flowing at each stage of compression is single phase, i.e. gaseous or dense fluid (supercritical); however, perhaps either of the two products of the final stage of compression and cooling includes liquid carbon dioxide or carbon dioxide in the form of a dense fluid.

If desired, the expansion chamber can be disconnected from the liquefaction plant, and it can thus serve as a vessel for transporting liquid carbon dioxide. However, it is preferable that the expansion chamber has an opening for the removal of liquid through which liquid carbon dioxide can be discharged into a vessel for transport. The expansion chamber can be any element suitable for expansion, such as an expansion valve and similar devices.

The carbon dioxide gas that is recycled is preferably passed through one or more heat exchangers to extract energy from the fluid stream before it is recycled to the fluid stream at a point upstream.

Since the feed gas may contain impurities, such as water, nitrogen, etc., it is desirable to subject the fluid stream to one or more treatments to remove them. Depending on the plant design, these removal steps may cause some side removal of carbon dioxide from the plant in a form other than liquid CO ₂ . However, careful design can only lead to minimal removal of such non-liquid carbon dioxide.

In general, at least 2 (eg, from 2 to 8, preferably 4) compression steps are required to convert the fluid into liquid or supercritical carbon dioxide. It is preferable to remove water after at least one compression stage and before the final compression stage, for example, between the second and third compression stages, usually after the cooling stage following the preceding compression stage. It is especially preferable to carry out the removal of water before each stage of compression. It is desirable to dry the CO ₂ gas to the level of parts per million (ppm) by adsorption after the last separator.

Water should be removed to avoid hydrates, freezing of water, corrosion and water droplets in the compressor feed. The solubility of water in a CO ₂ gas decreases at higher pressures and lower temperatures. Water can be removed in several ways, for example using separators or by passing water through an adsorbent, or an adsorbent layer, or a filter. Preferably, most of the water is removed in the separators after each stage of compression and cooling.

To remove water by condensation and using separators, CO ₂ gas with liquid pollutants (for example, water, as well as other liquids, such as liquefied heavy hydrocarbons) enters the separator, where condensed liquids are removed from the base of the separator and CO2 remains in the upper part of the separator in gaseous form.

It is desirable to dry the gas leaving the separator or separators through an adsorption unit before passing to the next compression stage. In order to carry out continuous work, it is desirable to have two or more such adsorption units arranged in parallel, so that one can be regenerated (for example, by passing hot gas through it) and at that time use another. The gas used for regeneration is typically carbon dioxide gas, which is recycled. Hot, humid carbon dioxide leaving the regenerated plant can, if desired, be recycled to the fluid at a point above

- 2,012,122 downstream, for example, between the first and second compression stages, preferably between the compression stage and the subsequent cooling stages.

Particularly preferably, the last free water is removed in the separator before the last compression stage at a pressure of 2 to 4 MPa (20 to 40 bar) and a temperature close to the hydrate formation curve, which is in the range of 10 to 15 ° C. It is desirable to dry the CO ₂ gas to the level of ppm by adsorption after the last separator.

When the feed gas contains additional gases that undergo a phase transition to the liquid phase at ambient temperature at a temperature lower than this value for carbon dioxide, such as gases such as nitrogen, oxygen, methane or ethane, it is desirable to remove these gases before the last expansion.

Therefore, for such feed gases, it is desirable that the liquefaction method includes a stage in which such "volatile components" are removed. This preferably occurs after a compression or cooling stage, which forms liquid CO ₂ or, more preferably, a fluid that consists of that amount of gas that must be removed during the extraction stage, and the remainder in the liquid phase. If heat is removed at pressures above critical (KD) in the supercritical phase, the removal of volatile components is carried out after the first expansion stage, where the fluid is in the two-phase region below the KD with a small fraction of gas.

Removal of volatile components can be carried out in a separation column after the heat is removed near the dew point line. At transportation pressures of 0.6-0.7 MPa abs. (6-7 bar abs.) Only small portions of volatile components, usually 0.2-0.5 mol.%, Can be included in the product to ensure no formation of dry ice. If there are more volatile components in the load, they should be removed. A separating tank can be used; however, a separation column is preferably used to avoid the release of large quantities of CO2 into the atmosphere. Refrigeration in the refrigerator is provided by evaporation of liquid CO2 at stages with intermediate pressure or from a tank with a product. As a rule of thumb, the loss of CO ₂ is equal to the amount of volatile components in the load.

To further improve the removal of volatile components, some or all of the liquid CO ₂ discharged from the separation column can be heated (for example, in a reboiler) and returned to this separation column. Alternatively, the reboiler can be combined with a separation column.

Cooling devices for cooling fluid flow can use carbon dioxide as a cooling agent. However, cooling devices, at least in the early stages of compression and cooling, simply use fluid from an external source, usually water, such as sea, river or lake water, or ambient air.

The installation used in the method of the present invention preferably includes gas-tight pipelines connecting various operating devices, i.e. compressors, cooling devices, heaters, heat exchangers, etc., fitted with suitable valves. Ideally, the flow path has only one inlet (for feed gas) and only one outlet (for liquid CO ₂ ); however, in some versions there are outlet openings for removing water or volatile components.

The charge gas according to the invention is preferably mainly carbon dioxide (based on the molar ratio), for example from 55 to 100 mol.% CO ₂ or from 70 to 95 mol.% CO ₂ , in particular at least 70 mol.% CO ₂ , mainly at least 90 mol.% CO ₂ , especially up to 95 mol.% CO ₂ . More preferably, the feed gas contains less than 0.5 mol.% Volatile components and less than 0.1 mol.% Water. Preferably the water content does not exceed 500 ppm by weight. As noted above, carbon dioxide produced as a by-product of ammonia production, or carbon dioxide captured in coal or gas power plants, is particularly suitable.

In terms of another aspect, the invention also provides a liquefaction facility for carbon dioxide, including a flow channel for passing carbon dioxide from the inlet to the outlet, and said channel includes a plurality of compressors and cooling devices arranged in series, an expansion chamber in said flow channel located downstream of the final compressor and cooling unit, and a recirculation channel placed to return gaseous carbon dioxide Erode from said expansion chamber into said flow channel upstream of said final compressor and cooling device.

For convenience, the plant according to the invention is provided with additional structural units discussed above in connection with the method of the invention.

Embodiments of the invention will now be discussed by way of illustration and with reference to the following non-limiting examples and accompanying drawings.

FIG. 1 shows a diagram of an embodiment of an installation according to the invention;

and in FIG. 2 shows a preferred embodiment of the installation according to the invention.

FIG. 1 is a diagram of the main elements of the installation. Downloadable gas containing 100 mol.% Carbon dioxide, is fed from a source (not shown) into the inlet of the pipeline 1.

- 3 012122

The gas is fed to the first compressor 2 and then to the first intermediate cooling device 4 through pipe 3. The second stage of compression and cooling is performed using a compressor 5 and a cooling device 7 of the second stage (connected by pipe 6), and the final stage of compression is achieved using compressor 8 and the cooling device 9. Heat is extracted in each of the cooling devices 4, 7 and 9 using ambient air or water (pipelines not shown) as the cooling medium.

The outlet for the fluid from the last compression stage is connected to the first inlet 10a of the heat exchanger 10. The first outlet 10b of the heat exchanger 10 is connected to the first inlet 13a of the second heat exchanger 13. In addition, the first outlet 10b is connected via pipe 12 and the expansion valve 11 to the second outlet 10c of the heat exchanger 10 The expansion valve 11 is positioned to expand and cool the flow from the first outlet 10b of the heat exchanger 10. It works to cool the fluid flowing between 10 and 10b. The recycled carbon dioxide gas flowing between the third inlet 10e and 101 also cools the fluid flowing from 10a to 10b. The second outlet 10 is connected to the pipeline 6 located between the compressor 5 and the cooling device 7, to recycle the gas discharged down the pipeline 12.

The fluid from the first outlet 10b of the heat exchanger 10 passes through an additional heat exchanger 13 to the expansion valve 14. The fluid is then expanded to transport pressure using the expansion valve 14 and fed to the separator 15. The gas phase (or instantaneous gas) is returned through pipe 16 and heat exchangers 13 and 10, respectively, in the pipeline 3, located between the first compressor 2 and the first cooling device 4. The placement of two heat exchangers 10 and 13 is carried out to cool the flow of fluid cf rows passing between 10a, 10b, 13a and 13b because the flash gas in line 16 and expanded loadable gas in line 12 are at a lower temperature. This improves the performance of the method.

The liquid phase separated in the separator 15 is discharged through the outlet 17 into the storage or into the vessel for transportation (not shown).

The expansion of compressed fluids, as described above, may simply involve the use of a Joule-Thompson valve. Alternatively, a turboexpander can be used to expand compressed fluids, as noted above. This increases the energy efficiency in the method.

As shown in FIG. 2, the feed gas is supplied to the inlet of the pipeline 18 at the installation and from there to the separator 20, which serves to condense water, which is removed through the pipeline 21. The gas then passes through the pipeline 22 to the first stage compressor 23 and to the intermediate cooling device 24 of the first stage. This first stage of water removal, compression and intermediate cooling is repeated, as shown in FIG. 2, using a separator 25, a second compressor 26 and a second cooling device 27. The effluent from the second intermediate cooling device 27 is passed through line 29 through a heat exchanger 28, where the temperature of the feed gas is further reduced by heat exchange with carbon dioxide gas recycled from a point, downstream installation.

Intermediate cooling devices 24 and 27 remove heat into the sea water.

The feed gas flows from the heat exchanger 28 to the separator 30 through the pipe 31. Water removed in the separators 25 and 30 is returned to the first separator 20 through the pipes 32 and 33.

Water is removed from the feed gas through three separators 20, 25 and 30 by condensation. It is highly desirable to remove water from the feed gas in order to avoid the formation of hydrates and corrosion, which can occur if water is present in an amount significantly greater than 50 ppm (wt.). Removing water also increases the productivity of the process.

The feed gas is then supplied from the third separator 30 through line 34 to one or two units 35a and 35b for adsorption of water, where the water content is further reduced to about 50 ppm.

At any stage, one water adsorption unit is in operation, while the other is regenerated (dried) with hot carbon dioxide gas from conduit 36. Moist carbon dioxide from the regenerated plant is recycled to the pipeline after the first compressor 23 via conduit 37.

Charging gas with a water content of approximately 50 ppm or less is fed through line 38 to a compressor 39 and a cooling device 40 of the final stage. The charge gas leaves the compressor 39 at the maximum pressure of the method (position 39 is the final stage of compression), and it is cooled in a cooling device 40, which transfers heat to seawater.

Liquid CO _{2 then} passes through conduit 41 to the column to remove volatile components, where the volatile components are removed by distillation. The volatile components are removed at the top of the column, leaving the bulk of the CO ₂ in the liquid phase. Liquid carbon dioxide is removed through conduit 43. To improve the removal of volatile components, a reboiler 44 is attached to the bottom of the column. The reboiler provides heat at the bottom of the column for separation by volatile components and thus improves the separation of volatile components from CO ₂ . To improve from

- 4 012122 attraction of CO ₂ in the gas flow enriched with volatile components at the top of the column, a refrigerator is placed in the upper part of the column. The required cooling function of the refrigerator is provided by evaporation of liquid CO ₂ at intermediate or final pressure.

The remaining liquid carbon dioxide passes through heat exchanger 45 to an expansion device 46, which produces cold carbon dioxide gas and liquid carbon dioxide. The fluid is directed through line 47 and heat exchanger 48 to the final expansion tank 49, in which the desired temperature and pressure exist. Gas is separated, part flows through pipe 50 back through heat exchanger 45 and from there through pipe 51 to heat exchanger 28, and part through pipeline 52 through heat exchanger 53 and from there through pipes 54 and 51 to heat exchanger 28. Heat exchanger 53 serves as a cooler for the column 42

The gas formed in the final expansion tank 49 is fed through heat exchangers 48, 28 and 55 to the heater 56, in which it is heated to a temperature sufficient to regenerate the units 35a and 35b to adsorb water.

Liquid carbon dioxide in the expansion tank 49 can be removed through the pipe 57 into the vessel for transportation.

In the embodiment of the invention shown in FIG. 1, the pressure and temperature before compressor 2 and after it are preferably 0.5 MPa abs. (5 bar abs.) / 25 ° C and 1.1 MPa abs. (11 bar abs.) / 25 ° C.

In the embodiment of the invention shown in FIG. 2, pressures and temperatures in places designated A, B, C, Ό, etc., are preferably as shown in the table below.

Flow Location __________ Pressure _____________ Temperature

MPa abs. bar abs ° С BUT 0.11 1.1 25 AT 0.11 1.1 25 WITH 0.5 five 140 ϋ 0.45 4.5 20 E 0.45 4.5 20 E 2 20 140 WITH 1.95 19.5 20 H 1.95 19.5 ten one 1.95 19.5 ten ϋ 1.95 19.5 ten TO 6 60 180 one_ 6 60 20 m 6 60 18 N 6 60 -15 ABOUT 2.1 21 -20 R 2.1 21 -20 ABOUT 2.1 21 -22 TO 0.65 6.5 -50 eight 0.63 6.3 -27 T 0.61 6.1 -five and 0.59 5.9 200 V 0.57 5.7 400 νν 0.55 5.5 200 X 2.05 20.5 -22

The following three examples relate to alternative ways in which the method can be carried out with regard to the removal of heat above or below the critical point of the gas being loaded.

Example 1. Heat removal to sea water / atmosphere below the critical point.

Carbon dioxide is compressed from a feed pressure of 0.1 MPa (1 bar) to a maximum pressure of approximately 6 MPa (60 bar) in three stages of compression. Between each compression stage, the feed gas is cooled

- 5 012122 wait using sea water or atmospheric air. Fully compressed feed gas, i.e. leaving the final compressor, condense with a heat exchanger, again using seawater. The condensed feed gas is expanded to transport pressure using an expansion valve and communicated with a flash tank or a separator. In the separator, the liquid phase is removed and sent to a vessel for transportation or storage and the gas phase is returned to the compression stage.

Example 2. Heat removal to the external cooling circuit below the critical point.

The charge gas is compressed from a supply pressure of 0.1 MPa (1 bar) to a maximum pressure of approximately 2.5 MPa (25 bar) in two stages of compression. Intermediate cooling (between compression stages) is achieved using seawater or atmospheric air. The compressed feed gas is then condensed using a heat exchanger connected to an external cooling circuit. The condensed charge gas is then expanded using an expansion valve to transport pressure and communicated with the flash tank or the separator. In the separator, the liquid phase is removed and sent to a vessel for transportation or storage and the gas phase is returned to the compression stage.

Example 3. Heat removal to sea water / atmosphere above the critical point.

The charge gas is compressed from a supply pressure of 0.1 MPa (1 bar) to a maximum pressure of approximately 8.5 MPa (85 bar) (i.e., above the critical pressure of 7.38 MPa (73.8 bar)) in four compression stages. Intermediate cooling (between compression stages) is performed using seawater or atmospheric air. The compressed charge gas is then cooled to form the supercritical phase using seawater or atmospheric air. The compressed fluid is then expanded from the supercritical phase to the transport pressure in the two-phase region, using expansion means, and communicated with the flash tank or the separator. In the separator, the liquid phase is removed and sent to a vessel for transportation or storage and the gas phase is returned to the compression stage.

Claims (9)

1. A method of producing liquid carbon dioxide from a feed gas containing carbon dioxide, carried out at a predetermined temperature and pressure, the temperature being lower than ambient temperature, higher than the triple point temperature for carbon dioxide and lower than the critical point temperature for carbon dioxide, and this pressure is higher ambient pressure above the triple point pressure for carbon dioxide and below the critical point pressure for carbon dioxide; wherein said method comprises supplying said feed gas to an inlet of a liquefaction apparatus having a flow path from said inlet to an outlet connected to an expansion chamber; passing the specified gas in the form of a fluid through the flow path through the specified installation and processing the fluid in it through many compression and cooling cycles to form liquid or supercritical carbon dioxide having a temperature and pressure above the specified temperature and pressure; water removal after at least one compression cycle, but before the final compression cycle; passing liquid or supercritical carbon dioxide through said outlet opening into the expansion chamber to form gaseous carbon dioxide and liquid carbon dioxide therein at a predetermined temperature and pressure; feeding recycle said gaseous carbon dioxide into a fluid flowing through said compression and cooling cycle; and recovering, if necessary, liquid carbon dioxide at said predetermined temperature and pressure from the expansion chamber. 2. The method according to claim 1, in which one or more compression cycles further include the stage of expansion. 3. The method according to claim 1 or 2, in which the fluid flowing for each compression cycle is single-phase. 4. The method according to any one of the preceding paragraphs, in which the expansion chamber is provided with an opening for removing liquid through which liquid carbon dioxide is recovered. 5. The method according to any one of the preceding paragraphs, in which the supplied recycle carbon dioxide passes through one or more heat exchangers. 6. The method according to any one of the preceding paragraphs, in which the supplied recycle carbon dioxide is returned to the fluid stream at a point located upstream. 7. The method according to any one of the preceding paragraphs, comprising four compression cycles. 8. A carbon dioxide liquefaction plant designed to produce liquid carbon dioxide at a predetermined temperature and pressure, the temperature being lower than the ambient temperature, higher than the triple point temperature for carbon dioxide and lower than the critical point temperature for carbon dioxide, and this pressure above ambient pressure, above triple point pressure for carbon dioxide and below critical point pressure for carbon dioxide; wherein the installation contains a flow channel for the passage of carbon dioxide from the inlet to the outlet, and the specified channel contains many compressors and cooling devices arranged in series, a separator for removing water, located after at least one compressor and in front of the final compressor, an expansion chamber in the specified flow channel located downstream of the final compressor and cooling device; and a recirculation channel for returning gaseous carbon dioxide from said expansion chamber to said flow channel upstream of said final compressor and cooling device. 9. The installation of claim 8, in which the expansion chamber has an opening for removing liquid, allowing you to remove from it, if necessary, liquid carbon dioxide.