Process and device for capturing and removing CO2 from exhaust gas of power plant

Abstract

The invention discloses a process and a device for capturing and removing CO2 from gas such as exhaust gas of a power plant by using water. Water is cooled and circulated in fuel preheating and drying and gas-water heat exchange processes for CO2 absorption and CO2 desorption, and the water is kept clean enough to the maximum extent. According to the invention, two or more than two quasi-cylinders provided with one or two rotatable shaftless / shaftless strip-shaped spiral bodies with ripples on the surfaces are used as a CO2 absorber and a CO2 desorber; water is used as a CO2 absorbent and a CO2 desorption agent to realize physical absorption and desorption of CO2, and a common chemical method for absorbing CO2 absorbent regeneration is not needed, so that new environmental problems are avoided. Environment energy is utilized to the maximum extent, and the cost is controlled through the process and the device.

Description

Technical Field

[0001] The present invention relates to a process and device for capturing and removing CO2, and in particular to a process and device for capturing and removing CO2 from flue gas discharged from a power plant. Background Art

[0002] The current global temperature is rising, posing a threat to future life, and it has become a consensus that CO2 emissions must be reduced. At present, chemical methods are widely used to capture CO2 from boiler flue gas, but these methods have complex processes, high energy consumption due to the rise and fall of flue gas temperature during the capture process, and uneven CO2 capture rates. In addition, the capture process may produce harmful substances and have new adverse effects on the environment. For example, although the process energy consumption in the patent CN202310480584.6 document is stated to be low, it is still equivalent to about 1.5 gigajoules of energy per ton of CO2 captured. In many cases, the CO2 capture process actually increases CO2.

[0003] When CO2 is captured and extracted by the currently known chemical method, or even when CO2 is captured by the physical method, the incidental substances in the boiler exhaust gas will accumulate in the CO2 absorbent, so it must be purified and may consume a large amount of fresh water resources. However, there is currently no low-cost process or device that uses water instead of chemicals as an absorbent to absorb, capture and remove CO2 from gases, especially waste heat flue gas from large power plants. Summary of the invention

[0004] The task of the present invention is to absorb and remove CO2 from the flue gas of a power plant based on the principle of physical absorption, capture and removal of CO2. Water is used as an absorbent to absorb and remove CO2 from the flue gas of a boiler, and a safe and simple process and device are proposed to reduce the temperature of the flue gas of a power plant to below 20°C. In addition, the process and device do not require consumption of other chemical reagents except water for the regeneration of the aqueous solution that absorbs CO2 and the removal of CO2. Therefore, in addition to being used to capture CO2 from the flue gas of a power plant, the present invention can also be used to capture and remove CO2 from gases from steelmaking, cement or other sources.

[0005] The present invention includes a cylindrical device, on which pairs of openings can be arranged as needed, and one or two rotatable ribbon-shaped spirals with corrugated surfaces and with or without axes can be arranged in the longitudinal direction of the cylindrical device. The outer edges of the ribbon-shaped spiral surfaces are parallel and equidistant to each other in the longitudinal direction of the cylindrical device. There is a certain gap between the outer edges of the ribbon-shaped spiral surfaces and the outer shell of the cylindrical device. The ribbon-shaped spiral can be partially immersed in the solution in the cylindrical device, so that the gas and liquid on the surface of the ribbon-shaped spiral flow together. The present invention includes two or more cylindrical devices connected in sequence and arranged with "ribbon-shaped spirals", one or more of which are used as CO2 absorbers for dissolving and absorbing CO2 in gas at a pressure of 24000Pa, and another one or more cylindrical devices are used as CO2 desorbers for desorbing CO2 from CO2-rich liquid at a pressure of -450Pa.

[0006] The present invention also includes a fuel preheating dryer, a modular smoke tube type air-water heat exchanger composed of two or more front smoke tube type air-steam heat exchange modules and a rear smoke tube type air-steam heat exchange module, one or more CO2 absorbers, one or more CO2 desorbers, a condensing chimney and an evaporative cooler operating in combination with a cold water storage tank.

[0007] The task of the present invention is mainly achieved through the following process. First, the waste heat flue gas rich in CO2 (generally 120-140°C) from the combustion system such as the power plant boiler is blown through the fuel preheating and drying device to reduce the temperature of the waste heat flue gas to about 52-56°C, and then sent to the modular smoke tube type gas-water heat exchanger for further cooling. The above modular smoke tube type gas-water heat exchanger is composed of two or more front smoke tube type gas-water heat exchange modules and a terminal smoke tube type gas-water heat exchange module, and these smoke tube type gas-water heat exchange modules are fastened together with bolts through flanges. The waste heat flue gas reduced to about 52-56°C flows through heat exchange tubes made of materials such as silicon carbide that are corrosion-resistant, have high heat transfer efficiency and are suitable for high-speed flue gas to complete gas-water heat exchange. The above-mentioned smoke tube type air-water heat exchange modules are separated by a middle partition wall with a certain number of micropores. Under normal conditions, cooling water of different temperatures is mainly distributed in different heat exchange modules. However, when the cooling water is under certain pressure conditions, it can pass through the micropores in the middle partition of the smoke tube type air-water heat exchange module and flow in the opposite direction of the waste heat flue gas flow at a speed of up to 3 meters per second. At this time, the cooling water will form turbulence around the silicon carbide heat exchange tube to improve the air-water heat exchange efficiency. The temperature of the cooling water in the modular smoke tube type air-water heat exchange module decreases from the front end to the back. The cooling water temperature of the heat exchange module at the end is the lowest and can cool the waste heat flue gas to below 20°C. The waste heat flue gas cooled to below 20°C by the modular smoke tube gas-water heat exchanger enters the CO2 absorber through the gas inlet. The CO2 in the waste heat flue gas contacts the water as the CO2 absorption liquid through the rotatable, corrugated, axial / non-axial ribbon spiral under pressure and dissolves in the water to generate a CO2-rich liquid, and the gas after the absorbed and dissolved CO2 is discharged from the gas outlet. The CO2-rich liquid that absorbs CO2 in the CO2 absorber enters the CO2 desorber and completes the desorption and removal of CO2 under variable pressure conditions. The desorbed CO2 is discharged through the gas outlet. The CO2-poor liquid after the CO2 is desorbed and removed in the CO2 desorber leaves the CO2 desorber again and is pumped into the CO2 absorber and used in the closed cycle of CO2 absorption / desorption, or used to cool the fresh air entering the evaporative cooler. The above process flow completes the absorption, capture and desorption of CO2 in the waste heat flue gas.

[0008] In the present invention, water is used as the absorbent to complete the CO2 absorption and desorption process, so that the absorbent does not need to be regenerated during the CO2 absorption and desorption process in the exhaust gas of the power plant, and CO2 absorption, desorption and removal are completed from the exhaust gas without generating chemical absorption or CO2 by-products.

[0009] The waste heat flue gas from the power plant boiler is cooled and reaches a near-saturated state during the fuel preheating and drying process, so a considerable amount of condensed water will be produced during the further cooling process, which can be recycled in the CO2 absorption process without purification. The long and thick corrugated polypropylene cooling pipe is coiled into a vertical cylindrical shape together with the partition plate and loaded into the evaporative cooler. The low-temperature cooling water cooled by the evaporative cooler is sent to the smoke tube type air-water heat exchange module arranged at the end. When the cooling water in the evaporative cooler flows through the thick polypropylene cooling pipe, impurities, especially scale produced by surface evaporation, will not adhere to the polypropylene cooling pipe.

[0010] The cold water storage tank can store low-temperature cold water. In winter, only an ordinary air-water heat exchanger and an evaporative cooler that no longer needs water spraying can be used to generate low-temperature cold water that meets the temperature requirements of the present invention, or even close to the freezing point.

[0011] The consumption of water used as absorbent in the present invention is determined by the CO2 capture rate in the gas and the number of cycles of absorption / desorption in a set period. The goal of the present invention is to absorb, capture and remove more than 60% of CO2 from flue gas such as power plant exhaust gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Shown is a schematic cross-section of a cylindrical-like device containing a rotatable, corrugated, axisymmetric or axisless ribbon-like helix.

[0013] Figure 2 Shown is a longitudinal partial cross-sectional view of a cylindrical-like device comprising a rotatable, corrugated, shafted / shaftless ribbon-like helix.

[0014] Figure 3 The display is from 80000Nm 3 Schematic diagram of the process and device for extracting CO2 from waste heat flue gas from a 15MW biomass power plant with a temperature of about 120-140°C and containing 10% CO2.

[0015] In the figure: 1-8 exhaust flue gas, 2-fuel preheating dryer, 3-waste heat flue gas, 4-front smoke pipe type air-water heat exchange module, 5-evaporative cooler, 6-cold water storage tank, 7-ordinary air-water heat exchanger, 8-fan, 9-CO2 absorber, 10-air pressure control valve, 11-condensing chimney, 12-CO2 desorber, 13-water pressure control valve, 14-pump with check valve, 15-evaporation channel, 16-fresh air, 17-spray water, 18-end smoke pipe Gas-water heat exchange module, 19-heat exchange tube, 20-middle partition wall, 21-removed CO2, 22-induced draft fan, 23-waste water, 24, -waste gas, 25-cooling tube, 26-partition plate, 27-solution box, 28-solution, 29-ribbon spiral, 30-gas inlet, 31-gas outlet, 32-solution inlet, 33-solution outlet, 34-outer shell, 35-motor, 36-modular smoke tube type gas-water heat exchanger, 37-waste heat flue gas inlet. DETAILED DESCRIPTION

[0016] The present invention will be described in detail by an embodiment. Figure 1 Shown is a schematic cross-section of a cylindrical-like device containing a rotatable, corrugated, axisymmetric or axisless ribbon-like helix.

[0017] Two pairs of openings (30, 31, 32, 33) can be arranged on the cylindrical device and the positions of the openings can be selected as required. A rotatable ribbon spiral (29) with a corrugated surface and with or without an axis is arranged in the longitudinal direction of the cylindrical device. The outer edges of the ribbon spiral (29) are parallel and equidistant to each other in the longitudinal direction of the cylindrical device. There is a certain gap between the outer edges of the ribbon spiral and the outer shell (34) of the cylindrical device. The ribbon spiral (29) can be partially immersed in the solution (28) in the cylindrical device, so that the gas and the solution (28) on the surface of the ribbon spiral (29) flow together.

[0018] Figure 2 Shown is a longitudinal partial cross-sectional view of a cylindrical device comprising a rotatable, corrugated, shafted / shaftless ribbon spiral. The ribbon spiral (29) is driven by a motor (35).

[0019] Figure 3 The display is from 80000Nm 3 Schematic diagram of the process and device for extracting CO2 from waste heat flue gas from a 15MW biomass power plant with a flow rate of about 120-140°C and 10% CO2 per hour.

[0020] In this embodiment, the exhaust flue gas (1) with a temperature of about 120-140°C and containing 10% CO2 from a 15MW biomass power plant is first blown into a fuel preheating dryer (2) and the exhaust flue gas (1) is cooled to a waste heat flue gas (3) with a temperature of about 52-56°C.

[0021] The waste heat flue gas (3) flowing out of the fuel preheating dryer (2) is then sent into a modular smoke tube type air-water heat exchanger (36). The modular smoke tube type air-water heat exchanger (36) of this embodiment is composed of three front smoke tube type air-water heat exchange modules (4) and one end smoke tube type air-water heat exchange module (18). An intermediate partition wall (20) is arranged between the smoke tube type air-water heat exchange modules (4, 18), and the smoke tube type air-water heat exchange modules (4, 18) are fastened together by bolts through flanges.

[0022] Since the waste heat flue gas (3) is continuously cooled with a small temperature difference, an effective heat exchange process is required. The smoke tube type air-water heat exchange module (4, 18) of this embodiment has an outer diameter of 3.4 meters and a total length of about 14 meters. Arranged in the smoke tube type air-water heat exchange module (4, 18) are 250 silicon carbide heat exchange tubes (19) with an inner diameter of 88 mm and passing through the middle partition wall (20) which are corrosion-resistant, have high heat transfer efficiency, are wear-resistant and suitable for high-speed flue gas. The thermal conductivity of silicon carbide is about 120W / mxK, which is several times that of steel. An intermediate partition wall (20) is arranged between the smoke tube type air-water heat exchange modules. Cooling water of different temperatures is input into different smoke tube type air-water heat exchange modules, and the cooling water of the lowest temperature is input into the end smoke tube type air-water heat exchange module (18) so as to cool the waste heat flue gas (3) as low as possible.

[0023] In order to ensure rapid transmission of the waste heat flue gas (3), the flow rate of the waste heat flue gas (3) at the waste heat flue gas inlet (37) is controlled to be approximately 39 m / s, and the flow rate of the waste heat flue gas (3) at the outlet of the end of the heat exchange tube (19) is approximately 34.6 m / s.

[0024] The heat exchange tubes (19) of the smoke tube type air-water heat exchange modules (4, 18) pass through the middle partition wall (20), and cooling water of different temperatures is distributed in different smoke tube type air-water heat exchange modules (4, 18). The micropores arranged on the middle partition wall (20) enable the cooling water in the modular smoke tube type air-water heat exchanger (36) to flow in the opposite direction of the flow of the waste heat flue gas (3). The flow rate of the cooling water flowing in the opposite direction of the flow of the waste heat flue gas (3) can be adjusted to be greater than 3 meters per second by adjusting the width, number and arrangement of the micropores arranged on the middle partition wall (20). The cooling water will generate turbulence around the heat exchange tube (19), thereby improving the air-water heat exchange efficiency.

[0025] The cooling water is operated in a closed system. In addition to the aforementioned modular smoke tube type air-water heat exchanger (36), the present invention also includes an evaporative cooler (5), a cold water storage tank (6), a common air-water heat exchanger (7), and pumps and pipelines required by regulations.

[0026] Fresh air (16) is sucked into the evaporative cooler (5) by the fan through the evaporative channel (15). The fresh air (16) is cooled by an average of about 10-15°C by the condensed water from the condensation chimney (11) in the evaporative channel (15) and the CO2-poor aqueous solution discharged through the opening of the CO2 desorber (12), and is used as cooling air for the evaporative cooler (5). The cooling water cooled by the evaporative cooler (5) is sent to the smoke tube type air-water heat exchange module (18) at the end.

[0027] In summer, the temperature of cooling water and waste heat flue gas (3) will rise. The evaporative cooling process through the evaporative cooler (5) is particularly necessary in summer. We must cool the waste heat flue gas (3) to about 17°C so that the CO2 absorption and capture rate in the waste heat flue gas (3) can reach more than 60%. In winter, relying only on ordinary air-water heat exchangers (7) or evaporative coolers (5) that no longer require spray cooling can make the cooling water temperature close to 10°C or lower, and the CO2 absorption and capture rate in the waste heat flue gas can reach more than 60%. In winter, antifreeze can be added to the closed cooling water circuit as needed.

[0028] The cooling water of the present invention circulates in a closed cooling water loop, and the cooling water flow rate can be controlled as needed by adjusting the variable frequency water pumps of two closed water loop systems.

[0029] The waste heat flue gas (3) cooled to about 17°C by the aforementioned modular smoke tube air-water heat exchanger (36) is pressurized to about 24000Pa by the fan (8) and enters the CO2 absorber (9) through the gas inlet (30). In the CO2 absorber (9), the waste heat flue gas (3) flows together with the solution (28) and is repeatedly immersed in the solution (28) serving as the absorbent through the rotatable, corrugated, axial / axial-free belt spiral (29) through the belt surface. The waste heat flue gas after CO2 is dissolved and absorbed by the CO2 absorber (9) enters the condensation chimney (11) through the gas outlet (31) and the gas pressure control valve (10).

[0030] In the present invention, the capture rate of CO2 in the waste heat flue gas (3) can be further improved by increasing the number of CO2 absorbers (9). In this embodiment, three CO2 absorbers (9) with a length of 10 meters, a width of 3 meters, and a height of 3.4 meters are arranged.

[0031] The CO2-rich liquid in the CO2 absorber (9) after absorbing the dissolved CO2 enters into a cylindrical CO2 desorber (12) arranged with a "ribbon spiral" through another opening of the CO2 absorber (9) and a water pressure control valve (13). The CO2-rich liquid is decomposed and released under the pressure condition of -450Pa generated by the induced draft fan (22) to release the released CO2 (21). The negative pressure condition generated by the induced draft fan (22) here helps to accelerate the desorption and release of the released CO2 (21) and increase the CO2 release rate.

[0032] After the CO2 desorber (12) desorbs and releases the CO2 (21), the lean CO2 liquid is pumped into the CO2 absorber (9) again through another opening of the CO2 desorber (12) for recycling or passes through the evaporation channel (15) to be used as the air coolant required by the evaporative cooler (5).

[0033] The CO2 absorber (9) and CO2 desorber (12) of the present invention have a circulating solution (28) loop, and the solution (28) is circulated by a pump (14) with a check valve.

[0034] In this embodiment, when the waste heat flue gas (3) is cooled to about 17°C by the modular smoke tube type air-water heat exchanger (36), the water discharged per hour from the modular smoke tube type air-water heat exchanger (36) and the CO2 absorber (9) can reach 20 tons, which can basically meet the operation requirements of the evaporative cooler (5). Therefore, the present invention can be installed anywhere, which meets the requirements of the future "green" resource principle that conforms to nature. On the other hand, if fresh water resources are abundant and low in price, it is easy to integrate cooling fresh water into the present invention. The size of the cooling water storage tank (6) can be changed and can conveniently supply low-temperature cooling water, thereby better utilizing the potential of nature.

[0035] The function of the air pressure control valve (10) in the present invention is to stabilize the gas pressure of about 24000Pa in the CO2 absorber (9) and not be affected by changes in the gas flow rate. It can also adjust the gas flow to the condensation chimney (11), where the gas flowing into the condensation chimney (11) will produce spray water (17) that can be used to cool the fresh air of the evaporative cooler (5).

[0036] Since the water sprayed into the evaporation channel (15) or the evaporative cooler (5) is greater than the water absorbed when cooling the fresh air, a certain cleaning effect can be produced and the heat exchange surface of the evaporative cooler (5) can be kept clean.

[0037] Research has found that scale and other pollutants will not adhere to polypropylene materials during the continuous surface evaporation process, so this material is particularly suitable for manufacturing cooling tubes (25) in evaporative coolers (5). The cooling tubes (25) together with the spacer (26) will be rolled together and inserted into the vertical cylindrical space in the evaporative cooler (5). The cooling tube (25) is preferably made of a bendable corrugated polypropylene tube. Since the evaporative cooler (5) always operates in a low temperature environment below 20°C, the cooling tube (25) made of polypropylene material will have a longer service life.

[0038] Since the material is cheap, the size of the evaporative cooler (5) can be made large to compensate for the thermal conductivity defect so as to better adapt to the heat exchange of low temperature difference. Other parts of the evaporative cooler (5) can also be made of plastic. Only a small part of the condensed water is discharged as waste water (23) which may contain impurities from the waste heat flue gas (3). The above cycle process enables the present invention to have a certain self-cleaning function.

[0039] The present invention can also be regarded as a highly efficient flue gas purification system, because the exhaust smoke passing through the condensation chimney (11) is clean and odorless, and the dust and sulfide content in the exhaust smoke can meet the emission standards.

[0040] The present invention can recover most of the waste heat in the flue gas (1) of the power plant through fuel preheating and drying, thereby reducing the fuel procurement cost. The fuel cost in this embodiment is expected to be reduced by 10%. The saved funds are sufficient to invest in and operate the device of the present invention including fuel preheating and drying, and may even be profitable, which makes it easier to raise funds for CO2 capture, which is the key to being able to use the present invention to immediately start CO2 capture.

[0041] The purpose of the present invention is to capture CO2 at low cost and low power consumption throughout the year including summer and to achieve a CO2 capture rate target of absorbing, capturing and removing more than 60% of CO2 from flue gas and other gases from power plant exhaust.

[0042] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A process and device for capturing and removing CO2 from flue gas from a power plant, comprising a cylindrical device; characterized in that: Two pairs of openings (30, 31, 32, 33) can be arranged on the cylindrical device as needed and the positions of the openings can be selected as needed. A rotatable, corrugated, shaftless / shafted ribbon spiral (29) is arranged longitudinally in the cylindrical device. The outer edges of the ribbon spiral (29) are parallel and equidistant to each other in the longitudinal direction of the cylindrical device. There is a certain gap between the outer edges of the ribbon spiral (29) and the outer shell (34) of the cylindrical device. The ribbon spiral (29) can be partially immersed in the solution (28) in the cylindrical device, so that the gas and liquid (28) on the surface of the ribbon spiral (29) flow together.

2. The process and device for capturing and removing CO2 from flue gas from a power plant according to claim 1, characterized in that: It comprises two or more cylindrical devices (9, 12) connected in series and provided with "ribbon spirals (29)", wherein one or more of the cylindrical devices are used as a CO2 absorber (9) for dissolving and absorbing CO2 in gas at a pressure of 24000Pa, and another one or more of the cylindrical devices are used as a desorber (12) for desorbing CO2 from a CO2-rich liquid at a pressure of -450Pa.

3. The process and device for capturing and removing CO2 from flue gas from a power plant according to claim 2, characterized in that: The solution used for CO2 absorption and desorption in the CO2 absorber (9) and CO2 desorber (12) is water.

4. The process and device for capturing and removing CO2 from flue gas from a power plant according to claim 1, characterized in that: The waste heat flue gas (3) from the fuel preheating dryer (2) flows into the silicon carbide heat exchange tube (19) arranged in the heat exchange module (4, 18) of the modular smoke tube type air-water heat exchanger (36), and the cooling water in the heat exchange module (4, 18) can flow through the heat exchange module (4, 18) in the opposite direction of the flow direction of the waste heat flue gas (3) through the micropores on the middle partition wall (20).

5. The process and device for capturing and removing CO2 from flue gas from a power plant according to claim 4, characterized in that: The cooling water flows through a modular smoke tube type air-water heat exchanger (36) composed of heat exchange modules (4, 18), the water solution of which comes from an evaporative cooler (5) operating on condensed water in the waste heat flue gas (3) and a conventional water-air heat exchanger (7).

6. The process and device for capturing and removing CO2 from flue gas from a power plant according to claim 5, characterized in that: The evaporative cooler (5) comprises cooling tubes (25) made of corrugated polypropylene, which are arranged in a coil together with spacer plates (26) in a vertical cylindrical space of the evaporative cooler (5).

7. The process and device for capturing and removing CO2 from flue gas from a power plant according to claim 6, characterized in that: The evaporative cooler (5) operates in combination with the cold water storage tank (6).

8. The process and device for capturing and removing CO2 from flue gas from a power plant according to claim 1, characterized in that: The process is implemented in a system, which includes a fuel preheating dryer (2), a modular smoke tube type air-water heat exchanger (36) composed of two or more front smoke tube type air-steam heat exchange modules (4) and a rear smoke tube type air-steam heat exchange module (18), one or more CO2 absorbers (9), one or more CO2 desorbers (12), a condensing chimney (11) and an evaporative cooler (5) operating in combination with a cold water storage tank (6).

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