CN102580466B - A flue gas decarbonization system and method for carbon dioxide two-step regeneration - Google Patents

Abstract

The invention discloses a flue gas decarbonization system and a flue gas decarbonization method for two-step regeneration of carbon dioxide. The flue gas decarbonization system is formed by coupling an alkylol amine and methanol mixed solution adsorption system with a two-step carbon dioxide regeneration system, wherein when the two-step carbon dioxide regeneration system works, two steps of removing methanol before regeneration and regenerating alkylol amine carbonate are carried out. In the step of removing methanol before regeneration, flue gas waste heat is utilized to provide a heat source to remove the methanol in rich liquor after adsorption; the regeneration process only aims at the alkylol amine carbonate; the energy consumption of sensible heat and evaporation heat are avoided; and the steam consumption of the thermal regeneration process is reduced. Two regeneration towers alternately implement removal of the methanol and regeneration of the alkylol amine carbonate by two sets of valve equipment, so that the continuous operation of a trapping system is ensured. According to the invention, both the flue gas waste heat and the condensation heat of methanol steam are utilized, the temperature of the regenerated carbon dioxide is reduced, the flue gas decarbonization of a power plant is efficiently implemented, and the flue gas decarbonization system and the flue gas decarbonization method for two-step regeneration of carbon dioxide have the characteristics of cleanness, high efficiency, energy saving, high decarbonization rate and the like.

Description

A flue gas decarbonization system and method for carbon dioxide two-step regeneration

technical field

The invention belongs to the technical field of carbon dioxide emission reduction in flue gas, and relates to a flue gas decarbonization system with two-step regeneration of carbon dioxide and a method thereof.

Background technique

With the rapid development of the global economy, the demand for energy consumption has become prominent, and the resulting environmental problems such as the greenhouse effect are posing great challenges to the sustainable development of human beings. Carrying out basic and applied research on efficient flue gas purification technology from concentrated emission sources is of great practical significance for effectively reducing carbon dioxide emissions into the atmosphere, protecting the living environment of human beings, and promoting sustainable development. Reducing CO2 emissions from concentrated emission point sources such as power plants is the most effective way to reduce emissions.

At present, the main methods for purifying carbon dioxide in flue gas from centralized emission point sources include absorption method, adsorption method, cryogenic capture, membrane separation and chemical looping combustion method. According to different absorption principles, absorption methods can be divided into chemical absorption and physical absorption, among which chemical absorption is one of the most industrially applicable methods for capturing carbon dioxide. The chemical absorption method is often used in the purification and decarbonization of flue gas from centralized point sources such as coal-fired power plants. However, due to high regeneration energy consumption, it leads to high capture costs. Therefore, it is of great practical significance to study the technology and method of efficient capture around the process of purifying flue gas of power plants by chemical absorption method, for realizing the efficient reduction of carbon dioxide emission.

Currently developed power plant flue gas purification systems mainly include the following categories:

(1) Amine-based decarbonization system for flue gas in coal-fired power plants: At present, there are many discussions on the decarbonization of flue gas in coal-fired power plants, and the industrialized examples are mainly chemical absorption methods. This type of flue gas purification system has the characteristics of large processing capacity, good stability, fast reaction rate, and low solvent cost (Abu-Zahra MRM, Schneiders LHJ, Niederer JPM. CO ₂ capture from power plants Part I. Aparametric study of the technical performance. Int. J. Greenhouse Gas Control, 2007; 1(1): 37-46.). However, the huge energy consumption in the process of regenerating CO2 becomes the main disadvantage of applying such purification system.

(2) Step-by-step and simultaneous desulfurization and decarbonization system of flue gas in power plants: Some researchers have proposed a flue gas purification system using ammonia water as an absorbent. This type of purification system has the advantages of high efficiency and environmental protection. It can first remove sulfur dioxide in the first scrubber, and then remove carbon dioxide in the second scrubber to achieve the purpose of simultaneous desulfurization and decarbonization in steps (Resnik K.P., Yeh J.T. , Pennline H.W.. Carbon Dioxide Capture by a Continuous, Regenerative Ammonia-Based Scrubbing Process [C]. 2006 American Filtration & Separations Society Topical Conference and Exposition, October 17, 2006. Pittsburgh, PA.). However, such purification systems need to solve the problem of solidification and blockage of pipelines during the absorption process of ammonia absorption solvent. At the same time, the system does not achieve one-step desulfurization and decarbonization, and the cost is still high.

(3) Non-aqueous solvent capture carbon dioxide system: This type of carbon dioxide capture system uses a non-aqueous solvent and alcohol amine mixed absorbent to replace the conventional alcohol amine aqueous solution. The researchers explored the kinetics of the reaction between it and carbon dioxide, and revealed its advantages in mass transfer rate, which can remove carbon dioxide faster. (Park SW, Lee JW, Choi BS, and Lee JW. Kinetics of Absorption of CarbonDioxide in Monoethanolamine Solutions of Polar Organic Solvents. J. Ind. Eng. Chem., 2005, 11(2), 202-209.). The disadvantage is that it is based on the experimental system, and does not consider the tower equipment design and cost issues involved in industrial applications. At the same time, if conventional thermal regeneration is considered, the cost of regeneration energy consumption is still relatively high.

(4) Amine-based adsorbent capture carbon dioxide system: This type of purification system prepares an amine-based adsorbent mixed with alcohol amine and metal oxide to capture carbon dioxide. Since the desorption process is the decomposition of solid alcohol amine carbonate, the regeneration energy consumption (Sun ZY, Fan MH, Argyle M. Desorption Kinetics of the Monoethanolamine/Macroporous TiO ₂ -Based CO ₂ Separation Process. Energ. Fuel. 2011, 25(7), 2988-2996.). The disadvantage is that according to the experimental results at this stage, the preparation process of the adsorbent is complicated, the cost of the metal oxide used is high, and the adsorption efficiency of the adsorbent is about 20% to 30% lower than that of the chemical absorption method.

Due to the above defects, the existing power plant flue gas purification systems still have a lot of room for development in terms of system design, energy saving, and environmental protection, and have not been able to effectively achieve the goals of energy saving and low cost.

Contents of the invention

The problem to be solved by the present invention is to provide a flue gas decarburization system and method for two-step regeneration of carbon dioxide, which fully utilizes the waste heat of flue gas and the condensation heat of methanol, and removes methanol and regenerates alcohol amine carbonate in two steps. A system for regenerating carbon dioxide below 373K temperature has been established.

The present invention is realized through the following technical solutions:

A flue gas decarbonization system for carbon dioxide two-step regeneration, including an absorption tower with a flue gas inlet at the bottom and a regeneration tower with an N-level packed tower structure, and an alcohol amine-methanol mixed solvent for absorbing carbon dioxide is installed in the absorption tower , the flue gas enters the absorption tower after passing through the first stage heat transfer of the regeneration tower, absorbs carbon dioxide through the alcohol amine-methanol mixed solvent, and then discharges from the top outlet;

The alcohol amine-methanol mixed solvent absorbs carbon dioxide and then splits into the first to N stages of the regeneration tower. The first stage of the regeneration tower at the bottom is equipped with a heat exchange pipeline for flue gas heat transfer, and the first stage is also equipped with an external heat source; The top of the regeneration tower is equipped with a condenser and a carbon dioxide collection device.

The absorption tower is connected with multiple regeneration towers, and the multiple regeneration towers are used alternately to realize the continuous regeneration of the alcohol amine-methanol mixed solvent for absorbing carbon dioxide.

The alcoholamine-methanol mixed solvent is a mixture of ethanolamine and methanol in a mass ratio of 1:1-2.

A method for decarbonizing flue gas with carbon dioxide two-step regeneration, comprising the following steps:

1) Lead the flue gas into the flue gas inlet at the bottom of the regeneration tower, and enter the absorption tower after passing through the first-stage heat exchange pipeline at the bottom of the regeneration tower. The absorption tower is equipped with an alcohol amine-methanol mixed solvent for absorbing carbon dioxide; The amine-methanol mixed solvent absorbs carbon dioxide in the flue gas, and the remaining gas is evacuated;

2) The alcohol amine-methanol mixed solvent absorbs carbon dioxide to generate rich liquid containing ethanolamine carbonate; the rich liquid splits into the first to N stages of the regeneration tower, and the regeneration of ethanolamine and carbon dioxide is realized after the regeneration tower is heated;

After the rich liquid is heated in the regeneration tower, methanol vapor is evaporated to generate ethanolamine carbonate; the heat of the first stage at the bottom of the regeneration tower is provided by the passing flue gas, and the first stage rich liquid is heated to generate methanol vapor Entering the upper stage of the regeneration tower to condense, the heat released during the condensation provides heat for the regeneration of the rich liquid at this stage;

The heat for regeneration of rich liquid from the second to N stages is provided by the methanol vapor of the next stage when condensing, and the methanol vapor generated by the N stage is condensed by the condenser;

Collect the ethanolamine carbonate and condensed methanol regenerated from the first to N stages in the regeneration tower, heat the ethanolamine carbonate with an external heat source to generate ethanolamine and carbon dioxide, return ethanolamine and methanol to the absorption tower, and compress the carbon dioxide centralized storage.

The absorption tower is respectively connected with the first regeneration tower and the second regeneration tower, and the two regeneration towers are used alternately to realize the continuous regeneration of the alkanolamine-methanol mixed solvent for absorbing carbon dioxide:

First close the pipeline connecting the absorption tower and the second regeneration tower. The flue gas enters the first stage of the first regeneration tower to heat the rich liquid from the absorption tower. After the temperature of the flue gas is lowered, it enters the absorption tower. Absorb carbon dioxide in the flue gas, and empty the remaining gas;

The rich liquid produced by the ethanolamine-methanol mixed solvent absorbs carbon dioxide and enters the first regeneration tower. In the first regeneration tower, it is heated to remove methanol. The methanol vapor generated in the first stage is condensed and provided, and the methanol vapor generated in the N stage is cooled by the condenser;

The external heat source provides heat to the ethanolamine carbonate, and the ethanolamine regenerated by heating the ethanolamine carbonate and the condensed methanol pass into the absorption tower; then, close the pipeline connecting the absorption tower to the first regeneration tower, and open the pipeline connected to the second regeneration tower Connected pipelines, the rich liquid splits into the second regeneration tower, regenerates ethanolamine and methanol in the second regeneration tower, and then returns to the absorption tower;

Alternately control the connecting pipelines between the absorption tower and the first regeneration tower and the second regeneration tower to realize continuous capture of carbon dioxide.

In the flue gas decarburization method of the two-step regeneration of carbon dioxide, the purge gas is also fed into the bottom of the regeneration tower to assist the methanol vapor.

The ethanolamine carbonate is heated by an external heat source to generate ethanolamine and carbon dioxide: the ethanolamine carbonate adopts the steam heating method in the chemical absorption method, utilizes the condensation heat of the steam generated by the energy provided by the external heat source, and then generates ethanolamine and carbon dioxide.

Compared with the prior art, the present invention has the following beneficial technical effects:

The flue gas decarbonization system with two-step regeneration of carbon dioxide provided by the present invention uses a mixed solvent of ethanolamine and methanol to capture carbon dioxide, and combines the characteristics of methanol with a low boiling point to realize methanol removal and alcoholamine carbonate regeneration in the regeneration tower The two-step carbon dioxide regeneration process makes full use of the waste heat of flue gas and the condensation heat of methanol to remove methanol before regeneration and realize the regeneration of carbon dioxide system. It is a new type of high-efficiency power plant flue gas carbon dioxide removal purification system. Compared with the currently developed flue gas purification system of power plants, this system has the advantages of simple structure and energy saving. Process integration research has a promotional effect.

The flue gas decarburization method of carbon dioxide two-step regeneration provided by the present invention adopts the feature that the waste heat of flue gas can be utilized, alternately introduces high-temperature flue gas into the first stage of the two regeneration towers to remove part of the methanol in the rich liquid, and regenerates The methanol vapor is used as an energy source to evaporate the methanol in the rich liquid in the next stage until all the methanol is removed. After the methanol is removed, all ethanolamine carbonate is in the regeneration tower, so the sensible heat and evaporation heat in the regeneration process of the conventional ethanolamine aqueous solution are saved, and the regeneration energy consumption is reduced. At the same time, the condensed methanol is mixed with the regenerated ethanolamine to absorb carbon dioxide in the absorption tower to realize the continuous operation of the capture system. The above-mentioned methanol removal before regeneration and ethanolamine carbonate regeneration constitute a two-step carbon dioxide regeneration process, which simultaneously realizes energy cascade utilization, effectively reduces the regeneration temperature, and realizes efficient capture of power plant carbon dioxide.

The flue gas decarburization system and method using the two-step regeneration of carbon dioxide provided by the invention have the characteristics of cleanliness, high efficiency, energy saving and high decarbonization rate.

Description of drawings

Fig. 1 is a schematic flow diagram of the system of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations of the present invention rather than limitations.

Referring to Figure 1, a flue gas decarbonization system with two-step regeneration of carbon dioxide, including an absorption tower with a flue gas inlet at the bottom and a regeneration tower with an N-level packed tower structure, the absorption tower is equipped with alcohol amines for absorbing carbon dioxide -Methanol mixed solvent, the flue gas enters the absorption tower after passing through the first heat transfer of the regeneration tower, absorbs carbon dioxide through the alcohol amine-methanol mixed solvent, and then discharges from the top outlet;

The alcohol amine-methanol mixed solvent absorbs carbon dioxide and then splits into the first to N stages of the regeneration tower. The first stage of the regeneration tower at the bottom is equipped with a heat exchange pipeline for flue gas heat transfer, and the first stage is also equipped with an external heat source; The top of the regeneration tower is equipped with a condenser and a carbon dioxide collection device.

The above-mentioned system consists of two parts, namely: (1) a mixed solvent of alcohol, amine and methanol (wherein the mass ratio of ethanolamine and methanol is mixed in a ratio of 1:1-2) to absorb carbon dioxide; (2) a two-step carbon dioxide regeneration system. Alcohol amine methanol mixed solvent absorption carbon dioxide system efficiently absorbs carbon dioxide in flue gas to generate ethanolamine carbonate dissolved in methanol solvent. The two-step regenerative carbon dioxide system removes methanol in the rich solution and regenerates ethanolamine carbonate in sequence, reducing the wasteful sensible heat consumption during solution regeneration and evaporation heat consumption during high-temperature regeneration. These two parts of the system enable the entire flue gas purification system to meet energy-saving requirements.

In order to realize the continuous capture of carbon dioxide, the absorption tower is connected with a plurality of regeneration towers, and the regeneration towers are used alternately to realize the continuous regeneration of the alcohol amine-methanol mixed solvent for absorbing carbon dioxide. The specific working method is as follows:

1) Lead the flue gas into the flue gas inlet at the bottom of the regeneration tower, and enter the absorption tower after passing through the first-stage heat exchange pipeline at the bottom of the regeneration tower. The absorption tower is equipped with an alcohol amine-methanol mixed solvent for absorbing carbon dioxide; The amine-methanol mixed solvent absorbs carbon dioxide in the flue gas, and the remaining gas is evacuated;

2) Alcoholamine-methanol mixed solvent absorbs carbon dioxide to generate a rich liquid containing ethanolamine carbonate; the rich liquid splits into the first to N stages of the regeneration tower, and the regeneration of ethanolamine and carbon dioxide is realized after the regeneration tower is heated; The distribution of each stage in the stage regeneration tower is based on the temperature and flow of the flue gas, and the N times heat of the energy recoverable by the flue gas is equal to the vaporization heat of methanol in the rich liquid;

After the rich liquid is heated in the regeneration tower, methanol vapor is evaporated to generate ethanolamine carbonate; the heat of the first stage at the bottom of the regeneration tower is provided by the passing flue gas, and the first stage rich liquid is heated to generate methanol vapor Entering the upper stage of the regeneration tower to condense, the heat released during the condensation provides heat for the regeneration of the rich liquid at this stage; specifically, a small amount of purge gas can also be introduced at the bottom of the regeneration tower to assist the methanol vapor to enter the upper stage more smoothly. class

The heat for regeneration of rich liquid from the second to N stages is provided by the methanol vapor of the next stage when condensing, and the methanol vapor generated by the N stage is condensed by the condenser;

Ethanolamine carbonate is enriched in the regeneration tower by using the auxiliary partitions closed at the bottom of each stage of the regeneration tower. During regeneration, the auxiliary partitions are opened to realize the collection channels of ethanolamine and carbon dioxide. The ethanolamine carbonate adopts the steam heating method in the chemical absorption method, and uses the condensation heat of steam (energy provided by external heat sources H1 and H2) to realize thermal regeneration of ethanolamine carbonate;

Collect the ethanolamine carbonate and condensed methanol regenerated from the first to N stages in the regeneration tower, heat the ethanolamine carbonate with an external heat source to generate ethanolamine and carbon dioxide, return ethanolamine and methanol to the absorption tower, and compress the carbon dioxide centralized storage.

Referring to Figure 1, the continuous regulation of the first regeneration tower S1 and the second regeneration tower S2 is as follows:

First close the valves V1 and V6, and open the valves V2-V5. The flue gas enters the regeneration tower S1 through the valve V5 and heats the rich liquid from the absorption tower A in the first stage. After the temperature of the flue gas decreases, it enters the absorption tower A to react with the mixed solvent of ethanolamine and methanol to remove carbon dioxide, and the remaining nitrogen is exhausted. null. The rich liquid after absorbing carbon dioxide is pumped into the multi-stage (N) regeneration tower S1 through V2-V4 to remove methanol. The heat of methanol removal in the first stage is provided by the high-temperature flue gas from V5, and the heat of other stages is provided by the condensation of methanol vapor generated in the previous stage. The methanol vapor generated in the N stage is cooled by the condenser E1. Finally, the external heat source H1 heats the ethanolamine carbonate in the regeneration tower S1, and the generated ethanolamine and condensed methanol are passed into the absorption tower A, and the regenerated carbon dioxide enters the pipeline network and is sent to the compression stage to boost the pressure and then sent to the geological storage process. At the same time, the valves V2-V5 are closed, and the valves V1 and V6 are opened. At this time, the regeneration tower S2 removes the methanol in the rich liquid and regenerates the ethanolamine carbonate according to the same process in the regeneration tower S1.

When the regeneration process in the regeneration tower S1 and the methanol removal in the regeneration tower S2 are completed at the same time, the valves (V1 and V6) and the valves (V2-V5) are controlled alternately to realize continuous and efficient capture of carbon dioxide.

Specifically, the above-mentioned system and method are used to purify flue gas containing 13.3% carbon dioxide at a flow rate of 616 kg/s (flue gas temperature: 150° C.) discharged from a 600 MW power plant. The flow rate of the ethanolamine-methanol solvent used is 350kg/s, wherein the mass fraction of ethanolamine is 40%. A three-stage regenerative packed tower structure was designed to satisfy methanol removal and ethanolamine carbonate regeneration in rich liquid.

During regeneration, the methanol solution is removed by heat at a temperature of 338K, the temperature of the regenerated ethanolamine carbonate is set at 363K, and the pressure is 0.1MPa. It is calculated that 90% of carbon dioxide in the flue gas can be removed, and the regeneration energy consumption is 1.85GJ/t, which is about 45% lower than that of the conventional ethanolamine aqueous solution for capturing carbon dioxide. At the same time, the economic analysis calculates that the efficiency of the power plant is only reduced by 7%, and the cost of carbon dioxide capture is about 193 yuan/t, which is 46% lower than that of conventional ethanolamine aqueous solution.

Claims (7)

1. A carbon dioxide two-step regeneration flue gas decarbonization system is characterized in that, comprising an absorption tower with a flue gas inlet at the bottom and a regeneration tower with N-level packing tower structure, the absorption tower is provided with a carbon dioxide absorption tower Alcohol amine-methanol mixed solvent, the flue gas enters the absorption tower after passing through the first stage heat transfer of the regeneration tower, absorbs carbon dioxide through the alcohol amine-methanol mixed solvent, and then discharges from the top outlet; The alcohol amine-methanol mixed solvent absorbs carbon dioxide and then splits into the first to N stages of the regeneration tower. The first stage of the regeneration tower at the bottom is equipped with a heat exchange pipeline for flue gas heat transfer, and the first stage is also equipped with an external heat source; The top of the regeneration tower is equipped with a condenser and a carbon dioxide collection device. 2. The flue gas decarburization system of a kind of carbon dioxide two-step regeneration as claimed in claim 1, is characterized in that, described absorption tower is connected with a plurality of regeneration towers, and a plurality of regeneration towers are used alternately, realize absorption Continuous regeneration of carbon dioxide from alkanolamine-methanol mixed solvents. 3. The flue gas decarburization system with two-step regeneration of carbon dioxide as claimed in claim 1, wherein the alcohol amine-methanol mixed solvent is ethanolamine and methanol with a mass ratio of 1:1 to 2 Proportional mix. 4. A flue gas decarburization method for carbon dioxide two-step regeneration, characterized in that, comprising the following steps: 1) The flue gas is passed into the flue gas inlet at the bottom of the regeneration tower, and then enters the absorption tower after passing through the first-stage heat exchange pipeline at the bottom of the regeneration tower. The absorption tower is equipped with an alcohol amine-methanol mixed solvent for absorbing carbon dioxide; The amine-methanol mixed solvent absorbs carbon dioxide in the flue gas, and the remaining gas is evacuated; 2) Alcoholamine-methanol mixed solvent absorbs carbon dioxide to generate rich liquid containing ethanolamine carbonate; the rich liquid splits into the first to N stages of the regeneration tower, and the regeneration of ethanolamine and carbon dioxide is realized after the regeneration tower is heated; After the rich liquid is heated in the regeneration tower, methanol vapor is evaporated to generate ethanolamine carbonate; the heat of the first stage at the bottom of the regeneration tower is provided by the passing flue gas, and the first stage rich liquid is heated to generate methanol vapor Entering the upper stage of the regeneration tower to condense, the heat released during the condensation provides heat for the regeneration of the rich liquid at this stage; The heat for regeneration of rich liquid from the second to N stages is provided by the methanol vapor of the next stage when condensing, and the methanol vapor generated by the N stage is condensed by the condenser; Collect the ethanolamine carbonate and condensed methanol regenerated from the first to N stages in the regeneration tower, heat the ethanolamine carbonate with an external heat source to generate ethanolamine and carbon dioxide, return ethanolamine and methanol to the absorption tower, and compress the carbon dioxide centralized storage. 5. The flue gas decarburization method of carbon dioxide two-step regeneration as claimed in claim 4, is characterized in that, described absorption tower is connected with the first regeneration tower and the second regeneration tower respectively, alternately in the two regeneration towers Use to realize the continuous regeneration of alcohol amine-methanol mixed solvent for absorbing carbon dioxide: First close the pipeline connecting the absorption tower and the second regeneration tower. The flue gas enters the first stage of the first regeneration tower to heat the rich liquid from the absorption tower. After the temperature of the flue gas is lowered, it enters the absorption tower. Absorb carbon dioxide in the flue gas, and empty the remaining gas; The rich liquid produced by the ethanolamine-methanol mixed solvent absorbs carbon dioxide and enters the first regeneration tower. In the first regeneration tower, it is heated to remove methanol. The methanol vapor generated in the first stage is condensed and provided, and the methanol vapor generated in the N stage is cooled by the condenser; The external heat source provides heat to the ethanolamine carbonate, and the ethanolamine regenerated by heating the ethanolamine carbonate and the condensed methanol pass into the absorption tower; then, close the pipeline connecting the absorption tower to the first regeneration tower, and open the pipeline connected to the second regeneration tower Connected pipelines, the rich liquid splits into the second regeneration tower, regenerates ethanolamine and methanol in the second regeneration tower, and then returns to the absorption tower; Alternately control the connecting pipelines between the absorption tower and the first regeneration tower and the second regeneration tower to realize continuous capture of carbon dioxide. 6. The flue gas decarburization method for two-step regeneration of carbon dioxide as claimed in claim 4, characterized in that purge gas is also introduced into the bottom of the regeneration tower to assist the methanol vapor to enter the upper stage more smoothly. 7. The flue gas decarburization method of carbon dioxide two-step regeneration as claimed in claim 4, is characterized in that, after described ethanolamine carbonate is heated with an external heat source, ethanolamine and carbon dioxide are generated: ethanolamine carbonate adopts chemical The steam heating method in the absorption method uses the condensation heat of the steam generated by the energy provided by the external heat source, and then generates ethanolamine and carbon dioxide.

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