Carbon dioxide abatement system and method based on cold ammonia

Abstract

To condense the water vapor at the top of the ammonia stripper column, an overhead condenser is fluidly coupled to the water connection pipe between the direct contact heater and the direct contact cooler at the bottom of the direct contact cooler.

Description

[0001] manual Technical Field

[0002] Embodiments of the present invention generally relate to techniques for reducing carbon dioxide emissions from flue gas or other carbon dioxide sources, and more specifically to systems and methods for ammonia-based carbon dioxide emission reduction (i.e., for removing carbon dioxide from flue gas). Background Technology

[0003] Most of the world's energy comes from the combustion of carbon and hydrogen fuels such as coal, oil, and natural gas (fossil fuels). In addition to carbon and hydrogen, these fuels also contain oxygen, moisture, and pollutants such as ash and sulfur (usually in the form of sulfur oxides, known as SO₂). x ), nitrogen compounds (usually in the form of nitrogen oxides, called NO) x ), chlorine, mercury and other trace elements.

[0004] Recognition of the destructive effects of pollutants released into the atmosphere during combustion has triggered increasingly stringent restrictions on emissions from power plants, refineries, and other industrial processes. This has increased pressure on operators of such facilities to achieve near-zero emissions.

[0005] Hot flue gas is generated during the combustion of fuels (e.g., coal, oil, peat, waste, biofuels, natural gas, etc.) used for power generation or for the production of materials such as cement, steel, glass, steam, heating media, and hydrogen. Among other pollutants, hot flue gas contains significant amounts of carbon dioxide (CO2), which contributes to the so-called greenhouse effect and associated global warming.

[0006] Numerous systems and processes have been developed to reduce pollutant emissions. These systems and processes include, but are not limited to, desulfurization systems, particulate filters, and the use of one or more adsorbents to absorb pollutants from flue gas. Examples of adsorbents include, but are not limited to, activated carbon, ammonia, limestone, etc.

[0007] Ammonia has been shown to effectively remove carbon dioxide and other pollutants, such as sulfur dioxide and hydrogen chloride, from flue gas streams. In a particular application, the absorption and removal of carbon dioxide from flue gas streams using ammonia is carried out at low temperatures, such as between 0°C and 20°C. These systems are based on the so-called Cold Ammonia Process (CAP). To protect system efficiency and comply with emission standards, it is desirable to retain the ammonia within the flue gas treatment system, i.e., to prevent its release into the atmosphere.

[0008] In existing CAP systems, after CO2 has been removed from the flue gas stream in the CO2 absorber, the flue gas contains a significant amount of ammonia released from the solvent used in the CO2 absorber. To limit ammonia loss, CAP technology is characterized by a so-called ammonia scrubbing section (NH3 scrubbing), also known as an ammonia water scrubbing section. The ammonia water scrubbing section, or NH3 scrubbing section, comprises a packed bed column in which the flue gas comes into direct contact with a water stream. The ammonia-rich water leaving the NH3 water scrubbing section is then regenerated in a dedicated column system (i.e., a stripper column), where water and ammonia are separated. The water is routed back to the NH3 water scrubbing section, and the ammonia is recycled back to the CO2 absorber.

[0009] The direct contact heater is another tower that heats the flue gas exiting the NH3 water scrubbing section. This has two effects: generating a stream of cold water used in the direct contact cooler; and heating the flue gas to the minimum temperature required for its dispersion at the chimney. The water fed to the direct contact heater comes from the direct contact cooler.

[0010] Current CAP technology still needs further development to achieve greater efficiency, for example, in reducing the space required and the number of components in the system or plant, or in reducing investment costs. Summary of the Invention

[0011] According to the embodiments disclosed herein, a cold ammonia-based carbon dioxide removal system includes a direct contact cooler adapted to receive and cool flue gas containing gaseous carbon dioxide. The system also includes a carbon dioxide absorber disposed downstream of and fluidly coupled to the direct contact cooler. The carbon dioxide absorber is adapted to receive cooled flue gas from the direct contact cooler and absorb gaseous carbon dioxide from the flue gas via an ammonia-based lean CO2 solution to form an ammonia-based rich CO2 solution stream and a lean CO2 flue gas stream. An ammonia water scrubbing section is fluidly coupled to the absorber and adapted to: receive the lean CO2 flue gas stream from the absorber, absorb ammonia escape from the flue gas via a scrubbing solution, and form an ammonia-rich water stream. A regenerator is fluidly coupled to the absorber and adapted to: receive the ammonia-based rich CO2 solution stream from the absorber, release gaseous CO2 from the ammonia-based rich CO2 solution stream, and return the ammonia-based lean CO2 solution to the absorber. The CO2 water scrubbing section is adapted to: receive gaseous carbon dioxide from the regenerator, absorb ammonia from the carbon dioxide stream via a scrubbing solution, and form an ammonia-rich water stream. The ammonia stripping tower includes an overhead condenser and is adapted to: receive the ammonia-rich water stream from both the CO2 water scrubbing section and the ammonia water scrubbing section, remove ammonia from the ammonia-rich water stream, and return the ammonia towards the CO2 water scrubbing section and towards the ammonia water scrubbing section to the absorber and the lean ammonia scrubbing solution. A direct contact heater is fluidly coupled to the ammonia water scrubbing section and is adapted to: receive ammonia- and CO2-lean flue gas from the ammonia water scrubbing section and heat the flue gas before venting it to the atmosphere. A water loop circulates water from the direct contact heater to the direct contact cooler and vice versa. The water loop is fluidly coupled to the overhead condenser of the ammonia stripping tower to provide refrigeration capacity to the overhead condenser.

[0012] Therefore, the vapor contained in the ammonia-rich solution flowing through the ammonia stripping tower is condensed through heat exchange with water from the bottom of the direct contact cooler. As will become apparent from the detailed description of the implementation scheme, this produces several beneficial effects in terms of system simplification and efficiency improvement.

[0013] According to another aspect, this document discloses a method for recovering ammonia in an ammonia stripping tower in a cold ammonia-based carbon dioxide removal system. The method includes the step of collecting an ammonia-rich stream from an ammonia water washing section and / or a CO2 water washing section in the ammonia stripping tower. Furthermore, the method includes the step of condensing water in a top condenser of the ammonia stripping tower by heat exchange with a water stream circulating in a water loop adapted to circulate water between a direct-contact cooler and a direct-contact heater. Attached Figure Description

[0014] A more comprehensive understanding of the embodiments disclosed in the invention and their many accompanying advantages will become readily apparent when considered in conjunction with the accompanying drawings, and will also become better understood by referring to the following detailed description, in which:

[0015] Figure 1 This is a schematic diagram of an ammonia-based carbon dioxide removal system using the cold ammonia process (CAP) according to this disclosure. Detailed Implementation

[0016] To improve the efficiency and reduce the cost of the CO2 emission reduction system, the overhead condenser of the ammonia stripping tower is fluidly coupled to a water conduit that fluidly connects the direct contact heater and the direct contact cooler. Specifically, water from the bottom of the direct contact cooler is pumped back to the direct contact heater via a high-head pump. The high-head pump provides sufficient hydraulic head to pump water into the overhead condenser of the ammonia stripping tower. This reduces the number of mechanical parts and eliminates the need for an additional pump to pump the cooling medium into the overhead condenser of the stripping tower. The water at the outlet of the direct contact cooler has a temperature suitable for condensation at the top of the ammonia stripping tower. No additional cooling water is required for the condenser. This reduces the overall system cost and improves its efficiency.

[0017] Furthermore, using partially heated water from a direct-contact cooler as the cooling medium to condense the top water in the ammonia stripping tower avoids excessively high cooling water return temperatures when the capacity is reduced. Further advantages of this arrangement will become clear from the detailed description below.

[0018] Now turn to the attached diagram, Figure 1 A schematic diagram of a cold ammonia-based CO2 capture or emission reduction system 1 according to an embodiment of the present disclosure is shown.

[0019] System 1 includes a direct-contact cooler 3, wherein the incoming CO2-rich flue gas flow FG is cooled before being supplied via pipeline 4 to a carbon dioxide absorber 5 fluidly coupled to the direct-contact cooler 3. In the carbon dioxide absorber 5, CO2 contained in the flue gas is removed from the flue gas by absorption using an ammonia-water solution flowing counter-currently to the flue gas. The ammonia-rich and CO2-lean flue gas exits the carbon dioxide absorber 5 at the top, and an ammonia-based CO2-rich solution flow, i.e., a CO2-rich ammonia-water solution, is collected at the bottom of the absorber 5.

[0020] The CO2-rich ammonia solution collected at the bottom of absorber 5 is conveyed to regenerator 7 via pipeline 6, where carbon dioxide is removed from the CO2-rich ammonia solution collected at the bottom of absorber 5 by heating provided by heat exchanger 8.

[0021] The carbon dioxide stream leaving regenerator 7 still contains ammonia and is conveyed through CO2 water scrubbing section 9, which is fluidly coupled to regenerator 7 and adapted to receive carbon dioxide from regenerator 7 to remove residual ammonia, and then the carbon dioxide is discharged from the system through carbon dioxide outlet 9.2.

[0022] The ammonia-rich and CO2-lean solutions generated by the release of carbon dioxide in regenerator 7 are returned to absorber 5 from the bottom of regenerator 7 via line 12 through heat exchanger 14, which is designed to recover heat from regenerator 7. In heat exchanger 14, heat is removed from the ammonia-rich solution from the bottom of regenerator 7 and used to preheat the CO2-rich solution flowing from the bottom of absorber 5 to regenerator 7 via line 6.

[0023] The lean CO2 and rich ammonia flue gas discharged from the top of the carbon dioxide absorber 5 is conveyed through pipeline 10 to the ammonia scrubbing section 11 (or NH3 scrubbing section), where most of the ammonia escaping with the flue gas from the absorber 5 is removed by countercurrent flow of the flue gas stream and lean ammonia scrubbing water from the ammonia stripping tower 20 through the ammonia scrubbing section 11. The lean CO2 and lean ammonia flue gas stream is then conveyed to the direct contact heater 13 and heated before being conveyed to the chimney (not shown) for emission into the atmosphere.

[0024] Ammonia-rich water is collected at the bottom of ammonia washing section 11. A portion of the ammonia-rich water is recirculated in ammonia washing section 11 (line 16), and a portion is delivered to ammonia stripping tower 20 via line 18. A heat exchanger 21 is arranged along line 18, in which the ammonia-rich water from ammonia washing section 11 exchanges heat with the ammonia-lean water from the bottom of ammonia stripping tower 20.

[0025] Return line 23 returns water from the bottom of ammonia stripping tower 20 to the top of ammonia washing section 11.

[0026] In addition to the ammonia-rich water from the ammonia washing section, the ammonia stripping tower 20 receives the ammonia-rich water flow from the bottom of the CO2 water washing section 9 via line 19. A portion of the water collected at the bottom of the CO2 water washing section 9 is recirculated through the CO2 water washing section (line 27), while a portion of the clean water from line 23 flows to the top of the CO2 water washing section 9 (line 29).

[0027] After water condensation, the ammonia collected at the top of the ammonia stripping tower 20 is returned to the bottom of the absorber 5 through pipeline 31.

[0028] Hot water circulates counter-currently from top to bottom in the direct contact heater 13 relative to the lean ammonia and lean CO2 flue gas, transferring heat to the flue gas and bringing it to a temperature suitable for discharge into the environment. The hot water flowing in the direct contact heater 13 for heating the flue gas is supplied by a water pump 33, which is arranged to pump water collected at the bottom of the direct contact cooler 3 after the water has cooled the incoming flue gas FG.

[0029] Water is pumped by pump 33 through riser line 35 toward the top of direct contact heater 13. Connecting line 37 couples the fluid from riser line 35 to the top of direct contact heater 13, from which hot water flows countercurrently downward relative to the CO2- and ammonia-deficient flue gas.

[0030] Water, which has already been partially cooled in the direct contact heater through heat exchange with the flue gas, is collected at the bottom of the direct contact heater 13 and returned to the direct contact cooler 3 via line 39. Figure 1 In one embodiment, the descending water flow is cooled in a first water cooler 41 (e.g., a cooling tower) before being supplied to the middle section of the direct contact cooler 3. A portion of the water flowing through line 39 and water cooler 41 is further cooled in a second water cooler 43 before being supplied to the top of the direct contact cooler 3 via line 45.

[0031] To condense the water released from the ammonia-rich aqueous solution treated in the ammonia stripping tower 20, a condenser 51 is provided at the top of the ammonia stripping tower 20. In a particularly advantageous and novel method, the cold side of the condenser 51 is adapted to circulate water from the bottom of the direct contact cooler 3. Specifically, as Figure 1 As shown, the cold-side inlet of condenser 51 is fluidly coupled via cooling water inlet line 53, which is directly fluidly connected to line 35 through which water pumped from the bottom of direct contact cooler 3 by water pump 33 returns to the top of direct contact heater 13. The cold-side outlet of condenser 51 is fluidly coupled via line 55 to line 39, which connects direct contact heater 13 and direct contact cooler 3.

[0032] Alternatively, as shown by the dashed line, the water outlet from the condenser 51 can be fluidly coupled to the line 37 leading to the top of the direct contact heater 13.

[0033] The water collected at the bottom of the direct contact cooler 3 is at a higher temperature than the usual source of cooling water available in system 1 and is typically used to condense steam at the top of the ammonia stripper 20. However, the water at the bottom of the direct contact cooler 3 is cold enough to condense and return the water to the ammonia stripper 20, while the ammonia returns to the absorber (line 31).

[0034] Using water from the bottom of the direct contact cooler 3 to condense the water at the top of the ammonia stripping tower 20 has several advantages compared to other methods of water condensation used in existing ammonia-based CO2 recovery plants.

[0035] First, the water pump 33 located at the bottom of the direct contact cooler 3 is a high-head pump, adapted to reach the top of the direct contact heater 13. The pump's hydraulic head is sufficient to reach the top of the ammonia stripping tower 20. Therefore, the same pump 33 can serve two different functions, thus avoiding the need for an additional high-head pump to pump cooling water to the condenser located at the top of the ammonia stripping tower 20. Reducing the number of pumps in system 1 is advantageous from both a plant cost perspective and from the perspective of reducing maintenance costs and the risk of plant downtime due to machine failure.

[0036] Furthermore, using partially heated water from the direct contact cooler 3 as the cooling medium for condensation at the top of the ammonia stripping tower 20 avoids (excessively) high cooling water return temperatures under reduced capacity or clean heat exchanger conditions when only a portion of the cooling water flow is routed to the condenser. High cooling water return temperatures are undesirable due to increased scaling tendency and potential building material and mechanical design temperature limitations.

[0037] like Figure 1 As shown in the schematic diagram, in a particularly advantageous embodiment, the regenerator 7, the CO2 water scrubbing section 9, and the ammonia stripping tower 20 are stacked on top of each other to form a single tower. This results in a particularly compact arrangement, thereby reducing the footprint of system 1. Furthermore, it reduces civil engineering, equipment quantity, space requirements, and water circulation systems (piping and pumps), thus offering advantages in installation, operation, and maintenance costs.

[0038] By stacking the ammonia stripping tower 20 on top of the regenerator 7 and the CO2 water washing section 9, the condenser 51 of the ammonia stripping tower 20 is located at a particularly high position. Therefore, it becomes particularly advantageous to use a high-hydraulic head pump 33 located at the bottom of the direct contact cooler 3 to provide cooling for the condenser 51.

[0039] exist Figure 1In the current preferred embodiment, the aforementioned advantages are maximized by also stacking the direct contact heater, the ammonia washing section 11, and the direct contact cooler 3. However, it should be understood that the stacking of the ammonia stripping tower 20, the CO2 washing section 9, and the regenerator 7, and the associated beneficial effects, are foreseeable regardless of the relative arrangement of the direct contact heater 13, the direct contact cooler 3, and the ammonia washing section 11. For example, in some embodiments, the direct contact cooler 3, the ammonia washing section 11, and the direct contact heater 13 can be configured as three separate towers. Alternatively, two of these devices (e.g., the direct contact cooler 3 and the ammonia washing section 11, or the direct contact heater 13 and the ammonia washing section 11) can be stacked in a single tower, while the third device remains separate.

[0040] Furthermore, the advantages of stacking multiple devices and sections as described above can be achieved by combining different configurations of the condenser 51 at the top of the ammonia stripping tower 20.

[0041] The beneficial effects of using water circulating between the direct contact cooler 3 and the direct contact heater 13 to condense the top of the ammonia stripping tower 20 can also be achieved in a system in which the various parts and equipment are not stacked on top of each other, or arranged in accordance with the presently described and Figure 1 The images show different ways of stacking.

[0042] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. Those skilled in the art will understand that various changes, omissions, and additions may be made to the specific disclosure herein without departing from the scope of the invention as defined in the following claims.

Claims

1. A carbon dioxide removal system based on cold ammonia, comprising: A direct contact cooler, the direct contact cooler being adapted to receive and cool flue gas containing gaseous carbon dioxide; A carbon dioxide absorber is disposed downstream of and fluidly coupled to the direct contact cooler; wherein the carbon dioxide absorber is adapted to receive cooled flue gas from the direct contact cooler and absorb gaseous carbon dioxide from the flue gas via an ammonia-based lean CO2 solution to form an ammonia-based rich CO2 solution stream and a lean CO2 flue gas stream. The ammonia washing section is fluidly coupled to the absorber and adapted to: receive the lean CO2 flue gas flow from the absorber, absorb ammonia escape from the flue gas via a washing solution, and form an ammonia-rich water flow; A regenerator, fluidly coupled to the absorber and adapted to: receive the ammonia-based CO2-rich solution stream from the absorber, release gaseous CO2 from the ammonia-based CO2-rich solution stream, and return the ammonia-based CO2-lean solution to the absorber; The CO2 water washing section is adapted to: receive gaseous carbon dioxide from the regenerator, absorb ammonia from the carbon dioxide stream via a washing solution, and form an ammonia-rich water stream; An ammonia stripping column, comprising a top condenser, and adapted to: receive an ammonia-rich water stream from the CO2 water washing section and from the ammonia water washing section, remove ammonia from the ammonia-rich water stream, and return the ammonia towards the CO2 water washing section and towards the ammonia water washing section to the absorber and the lean ammonia washing solution; and A direct contact heater, fluidly coupled to the ammonia scrubbing section and adapted to: receive the ammonia-lean, CO2-lean flue gas from the ammonia scrubbing section and heat the flue gas before discharging it into the atmosphere; The water loop circulates water from the direct contact heater to the direct contact cooler and vice versa; the water loop is fluidly coupled to the overhead condenser of the ammonia stripping tower to provide refrigeration capacity to the overhead condenser. The water circuit includes: A first water pipeline, which delivers water from the direct contact heater to the direct contact cooler via at least one water cooling device; and A second water line, which returns water from the direct contact cooler to the direct contact heater via a water supply pump; The first water pipeline and the second water pipeline are fluidly coupled to the top condenser of the ammonia stripping tower to provide refrigeration capacity to the top condenser. The inlet fluid of the condenser at the top of the tower is coupled to the second water pipeline downstream of the feed water pump. The outlet fluid of the condenser at the top of the tower is coupled to the first water pipeline.

2. The system according to claim 1, wherein, The outlet fluid of the tower top condenser is coupled to the first water pipeline upstream of the water cooling device.

3. The system according to claim 1, wherein, The outlet fluid of the tower top condenser is coupled to the second water pipeline.

4. A method for recovering ammonia in an ammonia stripping tower in a cold ammonia-based carbon dioxide removal system, the method comprising: Collect the ammonia-rich stream from the ammonia water washing section and / or CO2 water washing section of the ammonia stripping tower; as well as Water is condensed in the overhead condenser of the ammonia stripping tower by heat exchange with water circulating in a water loop, the water loop being adapted to circulate water between a direct contact cooler and a direct contact heater. Water is transported from the direct contact heater to the direct contact cooler through the first water pipeline of the water circuit, and a water cooling device is arranged along the first water pipeline. as well as Water is pumped from the direct contact cooler to the direct contact heater via a second water pipeline and a water supply pump. The side water flow from the second water pipeline downstream of the feedwater pump is transferred to the top condenser of the ammonia stripping tower. Water from the top condenser of the tower is returned to the first water pipeline.

5. The method according to claim 4, wherein, The water from the condenser at the top of the tower returns to the first water line upstream of the water cooling device.

6. The method according to claim 4, wherein, The water from the top condenser returns to the second water line and then from the second water line to the direct contact heater.

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