Ammonia-based carbon dioxide abatement system and method and direct contact cooler therefor

Abstract

A direct contact cooler (3) is disclosed, comprising a flue gas flow path (19) extending from a flue gas inlet (3.4) to a flue gas outlet (3.5). The direct contact cooler further comprises a first treatment section (3.2) and a second treatment section (3.3) arranged along the flue gas flow path (19). The first treatment section (3.2) is arranged upstream of the second treatment section (3.3) relative to the flue gas flow along the flue gas flow path (19). The direct contact cooler comprises an ammonia-rich scrubbing water inlet (3.6) and an ammonia-lean scrubbing water outlet (3.8). The ammonia-rich scrubbing water inlet (3.6) is arranged between the first treatment section (3.2) and the second treatment section (3.3), and the ammonia-lean scrubbing water outlet (3.8) is arranged upstream of the first treatment section (3.2). An ammonia-based carbon dioxide removal system comprising a direct contact cooler (3) as defined above and a related method for carbon dioxide emission reduction are also disclosed.

Description

[0001] describe 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 such as coal, oil, peat, waste, biofuels, and natural gas used for power generation or in the production of materials such as cement, steel, and glass. 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 keep the ammonia within the flue gas treatment system, i.e., to prevent ammonia from being released 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 a water scrubbing station. The water scrubbing station or NH3 scrubbing section comprises a packed bed tower in which the flue gas comes into direct contact with a water stream. To improve the removal of NH3 from the flue gas, the pH of the water stream can be pre-adjusted using a suitable acid such as sulfuric acid. The ammonia-rich water leaving the NH3 scrubbing station is then regenerated in a dedicated tower system—a stripper tower—where water and ammonia are separated. The water is routed to a direct-contact heater, and the ammonia is recycled back to the CO2 absorber.

[0009] The direct contact heater is another tower for heating the flue gas exiting the NH3 scrubber. 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] When the ionic solution circulates between the CO2 capture system and the regeneration system, moisture in the flue gas can accumulate in the ionic solution. To remove this moisture, an auxiliary stripper, configured as a gas-liquid contact unit, receives a portion of the circulating ionic solution. In this unit, the warm ionic solution is depressurized to form a gas phase containing vapors of the low-boiling components of the solution (mainly ammonia and carbon dioxide) and a liquid phase containing the high-boiling components of the solution. A portion of the gaseous compounds is absorbed in the residual flue gas stripping medium and returned to the cold ammonia process absorber vessel. The liquid phase containing ammonium sulfate is sent to a direct contact cooler system for purging with the ammonium sulfate effluent stream.

[0011] Existing CAP technology requires a considerable amount of steam for the operation of the stripper system.

[0012] Similar problems have emerged in other ammonia-based CO2 reduction or capture systems and methods, such as those using ammonia and potassium carbonate or potassium hydroxide.

[0013] Several efforts and studies have been undertaken to reduce this steam demand. One of the most promising ideas is the use of introduced flue gas as a stripping agent. In other application areas, ammonia emission reduction strategies have been developed (see, for example, EP 0 885 843A1). These are considered to establish the background of basic ideas, as also outlined in the paper "Process Modeling of an Advanced NH3 Abatement and Recy-cling Technology in the Ammonia-Based CO2 Capture Process" by Kangkang Li, Hai Yu, Moses Tade, Paul Feron, Jingwen Yu, and Shujuan Wang. The authors simply transfer the background of phosphate-based principles to carbonate-based reaction systems. However, the authors do not address the problems associated with treating actual flue gas streams. Since flue gas from combustion processes, while containing nitrogen, carbon dioxide, and oxygen, typically also contains water plus trace components such as sulfur oxides, nitrous oxide, and solid matter, functional methods and systems must cover the management of all these classes.

[0014] For example, US2018 / 0169569 discloses an enhanced apparatus and method for CAP-based carbon dioxide removal, the contents of which are incorporated herein by reference.

[0015] Current CAP technology still needs further development to achieve improved efficiency, such as in terms of energy consumption and efficient material handling involved in the process. Summary of the Invention

[0016] According to one aspect, this document discloses a direct contact cooler for an ammonia-based carbon dioxide emission reduction system. The direct contact cooler includes a flue gas flow path extending from a flue gas inlet to a flue gas outlet. The direct contact cooler also includes a first treatment section and a second treatment section disposed along the flue gas flow path. The first treatment section is adapted to strip ammonia from an ammonia-rich scrubbing water stream via the flue gas flow, such that the ammonia is removed from the ammonia-rich scrubbing water stream and drawn into the flue gas in the subsequent second treatment section.

[0017] The second treatment section is adapted to cool the ammonia-rich flue gas exiting the first treatment section, so that the ammonia-rich flue gas is obtained at the outlet of the direct contact cooler at the correct temperature for carbon dioxide removal.

[0018] The first treatment section is arranged upstream of the second treatment section relative to the flue gas flow path. Furthermore, the direct contact cooler includes an ammonia-rich scrub water inlet and a lean ammonia scrub water outlet. The ammonia-rich scrub water inlet is located between the first and second treatment sections. The lean ammonia scrub water outlet is located upstream of the first treatment section.

[0019] Therefore, in contrast to existing direct contact coolers, the new direct contact cooler disclosed herein has a processing section arranged such that ammonia is stripped from the wash water at a higher temperature, and the flue gas is cooled to a suitable temperature for subsequent carbon dioxide removal once it has been stripped and loaded with ammonia.

[0020] When a direct-contact cooler is arranged in an ammonia-based carbon dioxide reduction system, a particularly efficient process for carbon dioxide removal is achieved. In the embodiments disclosed herein, for example, a reduction in the required thermal energy is realized.

[0021] According to another aspect, this document discloses an ammonia-based carbon dioxide emission reduction system. The system includes a direct-contact cooler as outlined above, and other units, such as, in particular, a carbon dioxide absorber disposed downstream of and fluidly connected to the direct-contact cooler, and having a flue gas inlet and a flue gas outlet. In the embodiments disclosed herein, the carbon dioxide absorber is adapted to absorb gaseous carbon dioxide from the flue gas entering the carbon dioxide absorber from the direct-contact cooler via an ammonia-based solution, to form a CO2-rich ammonia-based solution exiting the absorber through the carbon dioxide outlet. The system may also include a water scrubbing station fluidly connected to the carbon dioxide absorber via the flue gas inlet and adapted to absorb ammonia leaking from the flue gas.

[0022] In another aspect, this paper discloses a method for carbon dioxide emission reduction (i.e., carbon dioxide removal) using an ammonia-based system.

[0023] According to the implementation plan disclosed in this article, the carbon dioxide emission reduction process includes the following steps:

[0024] The CO2-rich flue gas flow is made to flow counter-currently with the ammonia-rich scrubbing water flow, and ammonia is stripped from the ammonia-rich scrubbing water flow to obtain a CO2-rich ammonia-rich flue gas flow.

[0025] The CO2-rich ammonia-rich flue gas is cooled by direct contact cooling with cold water to achieve a flue gas temperature suitable for carbon dioxide removal.

[0026] The cooled CO2-rich ammonia-rich flue gas flow is passed through a carbon dioxide absorber and the cooled CO2-rich ammonia-rich flue gas flow is contacted with an ammonia-based solution to absorb carbon dioxide from it and produce a CO2-rich ammonia-based solution, and a CO2-lean ammonia-lean flue gas flow is obtained.

[0027] Remove carbon dioxide from ammonia-based solutions rich in CO2.

[0028] Further embodiments and features of the direct contact cooler, carbon dioxide emission reduction system, and method for carbon dioxide removal according to this disclosure are outlined in the following detailed description. Attached Figure Description

[0029] 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:

[0030] 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;

[0031] Figure 2 yes Figure 1 An enlarged view of the system's direct contact cooler; and

[0032] Figure 3 This is a schematic diagram of an ammonia-based carbon dioxide removal system using a mixed salt process (MSP) according to the present disclosure. Detailed Implementation

[0033] This paper discloses improvements to a system for removing or reducing carbon dioxide emissions from flue gas streams using ammonia-based technologies. To improve the overall system efficiency, a novel direct-contact cooler is disclosed through which the flue gas flows before being treated in an absorber. The direct-contact cooler includes a first section in which a stream of carbon dioxide-rich flue gas and a stream of ammonia-rich scrubbing water flow in direct contact with each other, such that the introduced hot gas stream strips ammonia from the scrubbing water stream. The direct-contact cooler also includes a cooling section in which the ammonia-rich flue gas is cooled in direct contact with a stream of cold water.

[0034] This paper also discloses an ammonia-based carbon dioxide removal or reduction system, including the aforementioned direct contact cooler, and a method for carbon dioxide removal or reduction. This results in a more efficient carbon dioxide removal process with a simpler loop layout, more accurate water balance, and reduced heat energy consumption.

[0035] exist Figure 1 A schematic diagram of an ammonia-based CO2 capture or emission reduction system 1 according to an embodiment of the present disclosure is shown. Figure 1The implementation scheme is based on the cold ammonia process (CAP). However, those skilled in the art will understand that several novel features of this disclosure can be incorporated into other ammonia-based CO2 capture or emission reduction systems to achieve similar advantages.

[0036] System 1 includes a direct contact cooler 3, in which the introduced CO2-rich flue gas flow is loaded with ammonia and cooled before being fed into a carbon dioxide absorber 5, which is fluidly connected 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 with an ammonia solution. The ammonia-rich and CO2-lean flue gas exits the carbon dioxide absorber 5 at the top, and the CO2-rich ammonia solution is collected at the bottom of the absorber 5.

[0037] In the regenerator 7, which is fluidly connected to the carbon dioxide absorber 5, carbon dioxide is removed from the CO2-rich ammonia solution collected at the bottom of the absorber 5. The CO2 scrubbing station 9 is fluidly connected to the regenerator 7 through the carbon dioxide inlet 9.1 and receives carbon dioxide from the regenerator 7 to remove residual ammonia therefrom, and then discharges the carbon dioxide from the system through the carbon dioxide outlet 9.2.

[0038] The CO2-lean, ammonia-rich flue gas exiting at the top of the carbon dioxide absorber 5 is delivered to a water scrubbing station 11 (or an NH3 scrubbing station), where most of the ammonia in the flue gas is removed by counter-current flow of the flue gas stream against the ammonia-lean scrubbing water from the direct contact heater 13. The CO2-lean, ammonia-lean flue gas stream is then delivered to the direct contact heater 13 and finally discharged into the atmosphere.

[0039] At the outlet of the water washing station 11, the ammonia-rich water stream is collected and delivered to the direct contact cooler 3, as described in more detail below.

[0040] exist Figure 1 In one embodiment, the direct contact heater 13 and the water washing station 11 are combined in a single tower 12, wherein the direct contact heater 13 is arranged in the upper section of the tower 12 and the water washing station 11 is arranged in the lower section of the tower 12. This arrangement is particularly advantageous, for example, from the viewpoint of compactness and simplicity.

[0041] However, in other embodiments not shown, the water washing station 11 and the direct contact heater 13 may be configured as separate loop components fluidly connected to each other.

[0042] As will be understood from the following description, System 1 may include additional equipment as needed, depending on the requirements of a particular CAP or other processes performed therein. Equipment known in the art and not essential for a full understanding of this disclosure is not shown or specifically described.

[0043] Generally, the hot flue gas flow flows counter-currently with the flow of liquid coolant (cold water) and ammonia-rich washing solution (ammonia-rich aqueous solution) through the direct contact cooler 3. The ammonia-rich washing solution is received from the direct contact heater 13, from the water washing station 11, and from the CO2 washing station 9, as will be described in more detail below.

[0044] Ammonia is stripped from the scrubbing solution by the flue gas, and the ammonia-loaded flue gas stream flows countercurrently through the carbon dioxide absorber 5 against the stream of ammonia-based solution from regenerator 7, which is lean with CO2. In the carbon dioxide absorber 5, CO2 is removed from the ammonia-rich flue gas by the ammonia-based solution, and the ammonia-based solution rich in CO2 collected at the bottom of the carbon dioxide absorber 5 is delivered to regenerator 7. Ammonia and CO2 are separated during endothermic regeneration, whereby the ammonia is returned to the carbon dioxide absorber 5 and the CO2 is delivered to the CO2 scrubbing station 9 for further removal of residual ammonia, as described above.

[0045] In the water scrubbing station 11, ammonia still contained in the CO2-deficient ammonia-deficient flue gas is further recovered before the CO2-deficient flue gas flows through the direct contact heater 13, in which the flue gas is heated by direct contact with the heating fluid before being discharged into the atmosphere. Residual ammonia is removed from the CO2-deficient ammonia-deficient flue gas by counter-current flow of the flue gas with the CO2-deficient scrubbing water from the direct contact heater 13.

[0046] As described above, carbon dioxide is removed from the flue gas at the top of the CO2 scrubbing station 9 and is collected and stored or used for appropriate chemical processes, thus reducing CO2 emissions from the flue gas, which is released into the environment from the direct contact heater 13.

[0047] Now described in more detail, the direct contact cooler 3 includes a housing 3.1 that forms a tower having multiple inlets and outlets, which will be described further. Figure 2 A more detailed illustration of the direct contact cooler 3 is shown below. The direct contact cooler 3 includes a first processing section 3.2 and a second processing section 3.3 (see in particular). Figure 2 For reasons that will become apparent below, the first processing section 3.2 will also be referred to as the stripping section, and the second processing section 3.3 will also be referred to as the cooling section. It is particularly advantageous to arrange these two sections one on top of the other, especially since this allows for easy circulation of flue gas through both sections. However, in principle, arranging these sections side by side is not excluded.

[0048] The direct contact cooler 3 also includes a first inlet 3.4 adapted to receive the flue gas inlet flow. The first inlet 3.4 will also be referred to herein as flue gas inlet 3.4. Flue gas inlet 3.4 is fluidly connected to flue gas delivery pipe 15 through which the flue gas to be treated enters system 1.

[0049] The direct contact cooler 3 also includes a first outlet 3.5, which is also referred to herein as flue gas outlet 3.5. Flue gas outlet 3.5 is fluidly connected to the bottom of carbon dioxide absorber 5 via duct 17. As disclosed in more detail below, ammonia-rich, cold flue gas flows toward carbon dioxide absorber 5 through the first outlet 3.5. A fan (not shown) along duct 17 facilitates the circulation of the flue gas therein.

[0050] More specifically, the first inlet 3.4 and the first outlet 3.5 are respectively arranged at the bottom and top of the direct contact cooler 3. The first inlet 3.4 is arranged below the first processing section 3.2 (stripping section), and the first outlet 3.5 is arranged above the second processing section 3.3 (cooling section).

[0051] The flue gas flow path 19 is thus confined within the direct contact cooler 3, extending in a downward-upward direction from the first inlet 3.4 to the first outlet 3.5. The flue gas flow path 19 extends sequentially through a first processing section 3.2 and through a second processing section 3.3, with the first processing section 3.2 positioned upstream of the second processing section 3.3 relative to the flow direction of the flue gas from the first inlet 3.4 to the first outlet 3.5.

[0052] As described above, the direct contact cooler 3 performs two functions. First, the flue gas entering the direct contact cooler 3 through the flue gas inlet 3.4 flows counter-currently (i.e., convection) with the ammonia-rich scrubbing water flow to strip ammonia from it. The ammonia-rich flue gas then flows through the flue gas outlet 3.5 into the duct 17 and toward the carbon dioxide absorber 5. Second, the flue gas entering the direct contact cooler 3 at a high temperature (e.g., approximately or above 70°C) is cooled through direct contact heat exchange with the coolant fluid (particularly circulating chilled water). The cooled ammonia-rich flue gas leaving the direct contact cooler 3 has a temperature, for example, approximately 5°C to 10°C, which is suitable for performing carbon dioxide removal in the carbon dioxide absorber 5.

[0053] Advantageously, ammonia stripping from the ammonia-rich scrubbing water is performed in the first treatment section 3.2 upstream of the second treatment section 3.3, wherein the flue gas is cooled before leaving the direct contact cooler 3.

[0054] The direct contact cooler 3 includes a second inlet 3.6 adapted to deliver an ammonia-rich wash water flow therein. The second inlet 3.6 will also be referred to hereinafter as the ammonia-rich wash water inlet 3.6. A nozzle 3.7 may be fluidly connected to the second inlet 3.6 to receive the ammonia-rich wash water and may be adapted to spray the ammonia-rich wash water in a convective manner into the flue gas flow flowing upward through the first treatment section 3.2. Figure 2 As shown, the second inlet 3.6 and the nozzle 3.7 are arranged between the first processing section 3.2 and the second processing section 3.3.

[0055] As will be explained below and as Figure 1 As can be seen, the ammonia-rich washing water flow is delivered by the water washing station 11 and the carbon dioxide washing station 9.

[0056] The direct contact cooler 3 also includes a second outlet 3.8 at its bottom, from which the stripped (lean ammonia) heated wash water is removed from the direct contact cooler 3 and returned to the direct contact heater 13. The second outlet 3.8 will also be referred to as the lean ammonia wash water outlet 3.8. The water leaving the direct contact cooler 3 at 3.8 is lean ammonia wash water, i.e., a stream of wash water containing a small amount of ammonia, as most of the ammonia content has been stripped by the flue gas flow and flows with it to the second treatment section 3.3 of the direct contact cooler 3.

[0057] The direct contact cooler 3 also includes a third inlet 3.9 and a third outlet 3.10, also referred to as a cold water inlet 3.9 and a cold water outlet 3.10. More specifically, the cold water inlet 3.9 is located in the upper part of the second processing section 3.3, and the cold water outlet 3.10 is located in the lower part of the second processing section 3.3. Cold water circulates in a cooling circuit 21, which includes the cold water inlet 3.9, a nozzle 22 fluidly connected to the cold water inlet 3.9, the second processing section 3.3 of the direct contact cooler 3, the cold water outlet 3.10, and a circulation conduit 23.

[0058] Heat exchanger 25 and refrigerant-driven cooler 27 are positioned along circulation duct 23. In heat exchanger 25, cold water is partially cooled by heat exchange with ammonia-rich wash water from water scrubbing station 11 and carbon dioxide scrubbing station 9. In cooler 27, water circulating in cooling circuit 21 is further cooled by heat exchange with refrigerant.

[0059] Therefore, cold water enters the direct contact cooler 3 through the third inlet 3.9 and is sprayed counter-currently into the ammonia-rich flue gas flowing through the second processing section 3.3. Water heated by the heat removed from the ammonia-rich flue gas is collected at a cold water collection device 26 arranged between the first processing section 3.2 and the second processing section 3.3. The cold water collection device 26 may include a chimney-type tray or other similar device that allows the ammonia-rich flue gas to flow upwards through it and through which the heated cold water is collected and delivered to the third outlet 3.10.

[0060] Due to heat exchange in the second processing section 3.3 of the direct contact cooler 3, the temperature of the ammonia-rich flue gas is reduced to the value required for carbon dioxide recovery through absorption in the carbon dioxide absorber 5.

[0061] The heat removed from the ammonia-rich flue gas flow by the second treatment section 3.3 of the direct contact cooler 3 is used to preheat the ammonia-rich wash water that passes through the ammonia-rich wash water inlet 3.6 and is delivered to the first treatment section 3.2 through the nozzle 3.7. If the ammonia-rich wash water leaving the heat exchanger 25 has not yet reached the desired temperature, another heater 31 may be installed along the pipe 33 leading to the ammonia-rich wash water inlet 3.6.

[0062] As described above, the humid flue gas entering the direct contact heater 3 through the first inlet 3.4 comes into contact with preheated, ammonia-rich, and decarbonized water in the first treatment section 3.2 of the direct contact cooler 3. The temperature of the ammonia-rich, preheated wash water in pipe 33 is selected to maximize the ammonia stripping effect performed by the flue gas in the first treatment section 3.2 of the direct contact cooler 3 and to limit the condensation of water contained in the introduced flue gas. For this purpose, the water is preferably heated to near the flue gas dew point temperature via heat exchanger 25 and heater 31.

[0063] In the first treatment section 3.2 of the direct contact cooler 3, the removal of sulfur oxides (SOx) and halides that form salts can also be carried out. This can further reduce the amount of free ammonia present in the water collected at the bottom of the direct contact cooler 3 and removed through the second outlet (water outlet) 3.8. The lean ammonia wash water exiting the direct contact cooler 3 at the second outlet 3.8 is delivered to the direct contact heater 13 through pipe 35.

[0064] Before reaching the direct contact heater 13, the pH of the ammonia-deficient water is adjusted to 36 by adding a suitable acid. Figure 1 This allows for the disposal of excess water previously added to the circulation, as well as the disposal of accumulated ammonium sulfate resulting from the removal of SOx from the flue gas in the direct contact cooler 3.

[0065] SOx can be removed from the flue gas as follows: SOx combines with ammonia in the second treatment section 3.3, and the resulting ammonium sulfate dissolves in the condensate from the second treatment section 3.3. In the separator 44, which will be described, the ammonium sulfate is retained in water recirculated through pipe 75, which is combined with the main circulation in the first treatment section 3.2 and removed from therefrom from the lean ammonia scrub water outlet 3.8.

[0066] Ammonium sulfate is passed through Figure 1 The wastewater discharge pipes shown at point 37 are removed. After wastewater is extracted at point 37, it can be removed through point 39 ( Figure 1 A suitable acid is added to further adjust the pH of the lean ammonia water to allow the use of the lean ammonia hot water flow in the direct contact heater 13, as described in more detail below.

[0067] As described above, after ammonia is stripped from the ammonia-rich, preheated wash water in the first treatment section (stripping section) 3.2, the flue gas flows through the second treatment section 3.3, where it is cooled by direct contact with cold water until it reaches the temperature level required to operate the carbon dioxide absorber 5.

[0068] In the second treatment section (cooling section) 3.3, primary condensation of water contained in the wet flue gas also occurs. During water condensation, ammonia (stripped from the flue gas in the stripping section 3.2) and CO2 are absorbed in the condensate. Ammonia and CO2 react to form ammonium carbonate and ammonium bicarbonate, which, along with the hot cold water flow, are removed from the direct contact cooler 3 through the cold water outlet 3.10.

[0069] In this implementation, control of the formation of ammonium carbonate in the condensate stream in the second treatment section 3.3 of the direct contact cooler 3 is achieved as follows: Water containing ammonium carbonate (including ammonium carbonate and / or ammonium bicarbonate) collected at the bottom of the second treatment section (cooling section) 3.3 is cooled back and recirculated. Excess water rich in carbonates and NH3, which has already formed during condensation, is separated from the recirculated stream at 41. The excess water containing high concentrations of carbonates and NH3 is fed through pipe 43 to an ammonium carbonate separator 44 comprising a heater / evaporator 45, where heat Q from a suitable heat source (not shown) is delivered to cause the ammonium carbonate and ammonium bicarbonate contained in the excess water fed through pipe 43 to decompose into ammonia and carbon dioxide. The latter is readily separated from the water stream in a condenser or tower having a condenser system as part of unit 45 and delivered to a carbon dioxide absorber 5. More specifically, the ammonia-rich gas stream in the carbon dioxide absorber 5 is used to form a solvent for CO2 capture. In some implementations, the ammonia and carbon dioxide leaving separator 44 are delivered via pipe 46 to the second inlet 5.2 of carbon dioxide absorber 5.

[0070] In other embodiments, the gas phase (ammonia and carbon dioxide) exiting the heater / separator 45 may be delivered to the direct contact cooler 3.

[0071] Excess water from the ammonium-lean water separator 44 is returned to the third inlet 3.6 (pipe 75) and mixed with the ammonia-rich water flow fed to the first treatment section (stripping section) 3.2. This minimizes the heat Q required in heater 31 to preheat the ammonia-rich wash water flow fed to the third inlet 3.6. Furthermore, adding excess water to the preheated ammonia-rich water flow keeps the overall salt content in the water circulation system low.

[0072] As described above, in the second treatment section 3.3 of the direct contact cooler 3, the ammonia-loaded cooling flue gas undergoes CO2 removal in the carbon dioxide absorber 5. The ammonia-rich flue gas exiting the direct contact cooler 3 at 3.5 is delivered through duct 17 to the flue gas inlet 5.1 of the carbon dioxide absorber 5 and comes into contact with regenerated ammonia-rich water, wherein contaminants such as SOx and most of the water have been removed from the ammonia-rich flue gas in the second treatment section 3.3.

[0073] More specifically, an ammonia-based solution of lean CO2 from regenerator 7 is countercurrently contacted with the flue gas to absorb gaseous CO2 from the flue gas flow, forming a CO2-lean flue gas collected at the top of carbon dioxide absorber 5 and a CO2-rich ammonified solution or slurry collected at the bottom of carbon dioxide absorber 5. Therefore, the ammonia-based solution acts as an adsorbent relative to the carbon dioxide contained in the flue gas flow entering carbon dioxide absorber 5 from direct contact cooler 3.

[0074] The carbon dioxide absorber 5 is fluidly connected to the regenerator 7 via pipes 47 and 49. More specifically, pipe 47 is fluidly connected to the carbon dioxide outlet 5.4 at the bottom of the carbon dioxide absorber 5, and pipe 49 is fluidly connected to the ammonia inlet 5.5 at the top of the carbon dioxide absorber 5. The CO2-rich ammonia-based solution exiting the carbon dioxide absorber 5 at the bottom through the carbon dioxide outlet 5.4 is fed to the regenerator 7 via pipe 47 and regenerated therein. The CO2-lean ammonia-based solution fed from the regenerator 7 through pipe 49 is fed to the top of the carbon dioxide absorber 5 via the ammonia inlet 5.5.

[0075] In regenerator 7, the CO2-rich ammonia-based solution is regenerated using heat Q from a heat source (not shown), which is delivered, for example, using steam or another heat transfer fluid. Carbon dioxide is thus separated from and evaporates from the ammonia solution, and is collected at the top of regenerator 7.

[0076] The lean CO2 regenerated ammonification solution is fed back to the carbon dioxide absorber 5 via pipe 49. Heat exchanger 51 is configured to recover heat from the regenerated lean CO2-based ammonium solution flowing in pipe 49 and to preheat the CO2-rich ammonification solution flowing through pipe 47, thus reducing the amount of heat Q that should be supplied to regenerator 7 for regenerating the ammonification solution.

[0077] The CO2-rich gas stream exiting the regenerator 7 at the top is delivered to the CO2 scrubbing station 9 via pipe 53 to remove residual ammonia. The CO2-rich gas stream flowing through the CO2 scrubbing station 9 comes into contact with and is scrubbed by a portion of the scrubbing solution delivered from the water scrubbing station 11 via pipe 57. In the CO2 scrubbing station 9, ammonia that may have leaked from the regenerator 7 by the CO2-rich gas stream is removed from the CO2 stream, captured by the scrubbing solution, and eventually returned to the direct contact cooler 3 via pipe 59. The cleaned CO2 is collected at the top of the CO2 scrubbing station 9 in pipe 61 and delivered to a storage system (not shown) or other facility.

[0078] After CO2 removal, the CO2-lean, ammonia-rich flue gas stream exiting the CO2 absorber 5 through flue gas outlet 5.3 is delivered through pipe 63 to the water scrubbing station 11 to remove ammonia from the flue gas before it is released into the atmosphere. The CO2-lean, ammonia-rich flue gas stream from the CO2 absorber 5 enters the water scrubbing station 11 through flue gas inlet 11.1. In the water scrubbing (NH3 scrubbing) station 11, the flue gas stream is brought into contact with a low-temperature circulating water stream exiting from the top of the water scrubbing station 11 to enter the direct contact heater 13.

[0079] Most of the water used in the water scrubbing station 11 is fed from the direct contact heater 13 via pipe 65. In an embodiment, pipe 65 may include a refrigerant-driven cooler 67 to bring the scrubbing water to a desired temperature, such as about 5°C to 10°C, to remove residual ammonia from the CO2-deficient ammonia flue gas stream flowing from the carbon dioxide absorber 5 through the water scrubbing station 11.

[0080] The water circulating in the water scrubbing station 11 absorbs most of the ammonia present in the flue gas delivered from the carbon dioxide absorber 5 to the water scrubbing station 11. The cold, ammonia-rich water is collected at the bottom of the water scrubbing station 11 and leaves the water scrubbing station 11 through outlet 11.2, and is fed through pipes 69 and 70 through inlet 3.6 to the first treatment section 3.2 of the direct contact cooler 3. In addition to the ammonia-rich water from the water scrubbing station 11, additional ammonia-rich water from the CO2 scrubbing station 9 is fed through pipe 59 to the first treatment section 3.2 of the direct contact cooler 3.

[0081] Before entering the first processing section 3.2, the ammonia-rich water from pipes 59, 69, and 70 is preheated in heat exchanger 25. Here, the ammonia-rich water is heated by exchanging heat with cold water circulating in the second processing section 3.3 of the direct contact cooler 3. Thus, the refrigeration load used to cool the wash water in cooler 67 is recovered. The heated ammonia-rich water is then mixed in 74 with excess water containing lean ammonium carbonate recovered from separator 44 via pipe 75, and finally routed via pipe 33 and heater 31 to the first processing section (stripping section) 3.2 of the direct contact cooler 3 to provide the required ammonia to be stripped by flue gas stream 19.

[0082] If necessary, a portion of the ammonia-rich water from pipe 70 can be returned via pipe 72 to the refrigerant-driven cooler 67, and from there back to the water scrubbing station 11, thereby reducing the ammonia-rich water flow rate to the first treatment section 3.2 of the direct contact cooler 3.

[0083] In order to limit the ammonia concentration in the flue gas leaving system 1 and thus meet the stringent requirements for reducing ammonia release into the environment, according to this disclosure, ammonia is removed from the flue gas not only in the water scrubbing station 11 but also in the direct contact heater 13.

[0084] In the direct contact heater 13, the flue gas returning from CO2 emission reduction (carbon dioxide absorber 5) and the first ammonia removal at low temperature (water scrubbing station 11) is heated by direct contact heat exchange with lean ammonia hot water returning from the direct contact cooler 3 via pipe 35. The water returning from the bottom of the direct contact cooler 3 to the top of the direct contact heater 13 can have a temperature of about 55°C to 60°C. In this way, a considerable amount of water condensed in the upper section 3.3 of the direct contact cooler 3 evaporates again.

[0085] Furthermore, due to the low pH of the water returning from the direct contact cooler 3 to the direct contact heater 13 (which has been achieved through the acid dosage at 36 and 39 as described above), the water entering the direct contact heater 13 at the top also removes residual ammonia from the flue gas that has not yet been removed in the water scrubbing station 11. Appropriate pH adjustment of the water entering the direct contact heater 13 is a useful factor in controlling the free ammonia present in the water, and thus ultimately controlling the ammonia content in the flue gas before it is released into the atmosphere through the chimney 81.

[0086] Removing any volatile salts (such as ammonium carbonate and ammonium bicarbonate) present in the water added to the circulation system via pipe 43 is another useful factor that not only contributes to the ammonia stripping and flue gas purification performance in stripping section 3.2, but also minimizes sulfuric acid consumption.

[0087] By adding excess water, problems caused by high salt concentrations in the circulating water flow, such as sedimentation on packing materials in towers, are avoided or significantly reduced.

[0088] In cases where ammonium sulfate exiting at point 37 should be separated as a byproduct, existing solutions have been established and combinations of systems based on the prior art of this disclosure are possible. This may require the addition of a circulation loop for the direct contact heater 13 and a tower system for the wastewater flow, either in place of or parallel to the aforementioned evaporator / condenser unit.

[0089] The aforementioned water management covers water entering with the flue gas, water entrained in the carbon dioxide absorber 5, excess water / wastewater control in the direct contact cooler 3, and the balancing of water picked up by the flue gas in the direct contact heater 13. This provides the opportunity to set process conditions that allow the omission of the auxiliary stripper anticipated in the CAP according to existing technology.

[0090] Management of non-volatile and low-volatile trace contaminants and associated salts covers the control of salt, solids, and trace concentrations in the circulating water, as well as adsorption control between the stripping section 3.2 and the cooling section 3.3 of the direct contact cooler 3. Operating below salt solubility equilibrium improves system reliability and availability. Furthermore, the process meets stringent regulations regarding ammonia emissions.

[0091] Ammonium carbonate management covers the control of salt formation between the stripping section 3.2 and the cooling section 3.3 of the direct contact cooler 3, as well as the control of salt carryover via the excess water flow. This minimizes the amount of acid required and thus reduces the salt content of the wastewater.

[0092] The comprehensive application of all the above-described operation and management steps allows for the omission of the installation of conventional stripper tower systems, where reboilers typically require up to 40% of the total process heat demand. The heat demand of the system according to this disclosure can be reduced to 10% or less of the total heat demand required by the entire CO2 emission reduction system. This is a major improvement in CAP performance.

[0093] The new arrangement of the first processing section 3.2 and the second processing section 3.3 of the direct contact cooler 3 results in a more efficient design of the remaining loops of the system 1, because, for example, only one water loop is required instead of two water loops as required in other prior art systems.

[0094] As mentioned, although Figure 1 System 1 is based on a cold ammonia process, but the novel aspects of this disclosure can be embodied, for example, in different ammonia-based carbon dioxide emission reduction processes, such as the mixed salt process (MSP). Figure 3 A schematic diagram of an ammonia-based carbon dioxide removal or emission reduction system using a mixed salt process, modified according to this disclosure, is shown. The same reference numerals indicate... Figure 1 The parts and components shown are the same as or corresponding to those described above. Specifically, Figure 3 The system and Figure 1 The main difference between the systems lies in the different properties of the ammonia-based solution used in absorber 5 and regenerated in regenerator 7. Figure 3 The diagram shows a slightly modified layout of the carbon dioxide absorber 5 and regenerator 7, which is suitable for use with a mixed salt process.

[0095] Compared to existing systems and methods, the direct contact cooler and associated carbon dioxide removal system and method according to the embodiments disclosed herein achieve a reduction in heat consumption. Specifically, ammonia stripping is performed using the heat contained in the flue gas, thus reducing the need to supply heat to the system, since the ammonia stripping step is performed upstream of the flue gas cooling step in the direct contact cooler.

[0096] Furthermore, compared to existing systems and methods, this system is simpler and requires fewer components, in addition to improved energy balance. Not only is the ammonia stripping tower eliminated, as stripping is performed in a direct contact cooler, as disclosed in the prior art references cited in the introduction of this specification, but substantial savings in structural components are also achieved compared to the most efficient prior art systems, as, for example, a single water circuit is required instead of two.

[0097] 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. An ammonia-based carbon dioxide emission reduction system (1), comprising: Direct contact cooler (3), the direct contact cooler comprising: The flue gas flow path (19) extends from the flue gas inlet (3.4) to the flue gas outlet (3.5). A first ammonia stripping section (3.2) and a second flue gas direct contact cooling section (3.3) are arranged along the flue gas flow path (19), wherein the first ammonia stripping section (3.2) is arranged upstream of the second flue gas direct contact cooling section (3.3) relative to the flue gas flow path (19); and Ammonia-rich wash water inlet (3.6) and ammonia-lean wash water outlet (3.8), wherein the ammonia-rich wash water inlet (3.6) is located between the first ammonia stripping section (3.2) and the second flue gas direct contact cooling section (3.3); and wherein the ammonia-lean wash water outlet (3.8) is located upstream of the first ammonia stripping section (3.2); A carbon dioxide absorber (5) is disposed downstream of and fluidly connected to the direct contact cooler (3), and the carbon dioxide absorber has a flue gas inlet (5.1) and a flue gas outlet (5.3); wherein the carbon dioxide absorber (5) is adapted to absorb gaseous carbon dioxide from the flue gas entering the carbon dioxide absorber (5) from the direct contact cooler (3) via an ammonia-based solution to form a CO2-rich ammonia-based solution exiting the carbon dioxide absorber (5) through a carbon dioxide outlet (5.4); A water scrubbing station (11), fluidly connected to the carbon dioxide absorber (5) via a flue gas inlet (11.1), and adapted to absorb the ammonia leaking from the flue gas, wherein the direct contact cooler (3) is also fluidly connected to the water scrubbing station (11) to receive ammonia-rich scrubbing water from the water scrubbing station via the ammonia-rich scrubbing water inlet (3.6); and A heat exchanger (25) is adapted to transfer heat from cold water circulating in the second flue gas direct contact cooling section (3.3) of the direct contact cooler (3) to ammonia-rich wash water flowing from the water washing station (11) to the direct contact cooler (3).

2. The system (1) according to claim 1, wherein the first ammonia stripping section (3.2) and the second flue gas direct contact cooling section (3.3) are arranged in the tower (3.1), and the second flue gas direct contact cooling section (3.3) is located at the top of the first ammonia stripping section (3.2).

3. The system (1) according to claim 1 or 2, wherein the direct contact cooler further comprises a cold water inlet (3.9) and a cold water outlet (3.10), the cold water inlet and the cold water outlet being disposed in the second flue gas direct contact cooling section (3.3) and adapted to allow the cold water in the second flue gas direct contact cooling section (3.3) to circulate relative to the flue gas in the flue gas flow path (19).

4. The system (1) according to claim 3, wherein the cold water inlet (3.9) and the cold water outlet (3.10) are fluidly connected to the circulation conduit (23), and wherein the refrigeration arrangement (27, 25) is arranged along the circulation conduit (23) and adapted to remove heat from the circulating cold water.

5. The system (1) according to claim 3, wherein a cold water collection device (26) is arranged between the first ammonia stripping section (3.2) and the second flue gas direct contact cooling section (3.3), and is adapted to collect cold water and ammonium carbonate from the second flue gas direct contact cooling section (3.3) and deliver the collected cold water and ammonium carbonate toward the cold water outlet (3.10), and is also adapted to allow ammonia-rich flue gas to flow from the first ammonia stripping section (3.2) to the second flue gas direct contact cooling section (3.3) through it.

6. The system (1) according to claim 3, wherein the water washing station (11) is fluidly connected to a direct contact heater (13) adapted to receive flue gas from the water washing station (11).

7. The system (1) according to claim 6, wherein the water washing station (11) and the direct contact heater (13) are integrated in a single tower, wherein the water washing station (11) is arranged in the bottom section of the tower and the direct contact heater (13) is arranged in the top section of the tower.

8. The system (1) according to claim 6, wherein the direct contact cooler (3) is also fluidly connected to the direct contact heater (13) via the lean ammonia wash water outlet (3.8), such that lean ammonia wash water from the direct contact cooler (3) is delivered to the direct contact heater (13); and wherein the direct contact heater (13) is adapted to heat the flue gas by direct contact heat exchange with the lean ammonia wash water from the direct contact cooler (3).

9. The system (1) according to claim 8, the system further comprising a connecting conduit (35) fluidly connecting the lean ammonia wash water outlet (3.8) of the direct contact cooler (3) to the direct contact heater (13); wherein at least one acid inlet (36) is arranged along the connecting conduit (35); and wherein an ammonium sulfate discharge conduit (37) is disposed downstream of the acid inlet (36).

10. The system (1) according to claim 1 or 2, the system further comprising a heater (31) connected to the ammonia-rich wash water inlet (3.6) of the direct contact cooler (3), adapted to heat the ammonia-rich wash water delivered from the water washing station (11) to the direct contact cooler (3).

11. The system (1) according to claim 6, the system further comprising an ammonium carbonate separator (44) fluidly connected to the cold water outlet (3.10) and adapted to receive a side flow of water loaded with ammonium carbonate from the cold water outlet (3.10) of the direct contact cooler (3), and adapted to decompose the ammonium carbonate into ammonia and carbon dioxide.

12. The system (1) according to claim 11, wherein the ammonium carbonate separator (44) has a water outlet fluidly connected to the ammonia-rich wash water inlet (3.6) of the direct contact cooler (3) to return ammonium-poor water from the ammonium carbonate separator (44) to the direct contact cooler (3).

13. The system (1) according to claim 12, wherein the ammonium carbonate separator (44) has a vapor outlet to return the ammonia-rich gas stream to one of: the carbon dioxide absorber (5); the direct contact cooler (3).

14. The system (1) according to claim 13, the system further comprising a regenerator (7) fluidly connected to the carbon dioxide absorber (5) and adapted to receive a CO2-rich ammonia-based solution exiting the carbon dioxide absorber (5), separate carbon dioxide therefrom, and return a CO2-poor ammonia-based solution to the carbon dioxide absorber (5).

15. The system (1) according to claim 14, wherein the ammonium carbonate separator (44) has a vapor outlet fluidly connected to the regenerator (7), the vapor outlet being adapted to return the ammonia-rich gas stream to the regenerator (7).

16. The system (1) according to claim 14, further comprising a CO2 scrubbing station (9) having a carbon dioxide inlet (9.1) fluidly connected to the regenerator (7) to receive carbon dioxide therefrom and a carbon dioxide outlet (9.2) adapted to discharge carbon dioxide therefrom; wherein the CO2 scrubbing station (9) is adapted to receive water from the direct contact heater (13) to remove residual ammonia from the carbon dioxide flowing through the CO2 scrubbing station (9); and wherein the CO2 scrubbing station (9) includes an ammoniated water outlet (9.3) fluidly connected to the ammonia-rich scrubbing water inlet (3.6) of the direct contact cooler (3).

17. A method for removing carbon dioxide from flue gas using an ammonia-based carbon dioxide emission reduction process in a system (1) according to any one of claims 1-16, the method comprising the steps of: The CO2-rich flue gas flow is made to flow counter-currently with the ammonia-rich scrubbing water flow, and ammonia is stripped from the ammonia-rich scrubbing water flow to obtain a CO2-rich ammonia-rich flue gas flow. The CO2-rich ammonia-rich flue gas is cooled by direct contact cooling with a cold water flow to achieve a flue gas temperature suitable for carbon dioxide removal. The cooled CO2-rich ammonia-rich flue gas flow is passed through the carbon dioxide absorber (5) and the cooled CO2-rich ammonia-rich flue gas flow is contacted with an ammonia-based solution to absorb carbon dioxide from it and produce a CO2-rich ammonia-based solution, and a CO2-poor ammonia-poor flue gas flow is obtained. as well as Carbon dioxide is removed from the CO2-rich ammonia-based solution. Before stripping ammonia from the CO2-rich flue gas stream by counter-current flow, the ammonia-rich wash water stream from the water washing station (11) is heated, including after the cold water stream has removed heat from the CO2-rich ammonia-rich flue gas stream, and the ammonia-rich wash water stream flows with the cold water stream in a heat exchange relationship.

18. The method of claim 17, wherein the step of removing carbon dioxide from the CO2-rich ammonia-based solution comprises regenerating the CO2-rich ammonia-based solution in a regenerator (7) to remove carbon dioxide therefrom and recycling the CO2-poor ammonia-based solution back to the carbon dioxide absorber (5).

19. The method according to claim 17 or 18, further comprising the step of removing ammonia from the CO2-poor ammonia-poor flue gas stream exiting the carbon dioxide absorber (5) by contacting the CO2-poor ammonia-poor flue gas stream with a lean ammonia aqueous solution in a water scrubbing station (11), thereby obtaining the ammonia-rich scrubbing water stream.

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