JP2007069075A - Method and system for separation of carbon dioxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a system for separation of carbon dioxide which have a system arrangement with excellent energy efficiency and employ a lithium compound oxide. <P>SOLUTION: A method of separating carbon dioxide has an absorption process of incorporating, as an absorption material, a lithium composite oxide into an apparatus behaving as a carbon dioxide release source to make the oxide absorb carbon dioxide in the gas and a release process of causing the absorption material to release carbon dioxide in a regeneration unit. The operating conditions of the system are set so that the removal rate of carbon dioxide in the gas is 20-40%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a carbon dioxide separation method and a carbon dioxide separation system for reducing carbon dioxide from a fixed emission source of carbon dioxide.

  Carbon dioxide is recognized as one of the greenhouse gases that cause global warming. On the other hand, interest in greenhouse gas reduction technology has increased following the entry into force of the Kyoto Protocol, which specifically quantifies these greenhouse gas emission reduction targets. A thermal power plant is a fixed emission source that emits a large amount of carbon dioxide, and it is easy to take measures for separation and recovery. For example, a gas absorption liquid technology such as an amine absorption method has been established.

On the other hand, more efficient carbon dioxide reduction technologies have been sought, and for example, solid absorbent materials that can be used at high temperatures have been researched and developed. Among them, the lithium composite oxide absorbs carbon dioxide while causing an exothermic reaction at 500 ° C. to 600 ° C., and releases the carbon dioxide with an endothermic reaction at 750 ° C. to 850 ° C. to regenerate and recover the carbon dioxide. It has material characteristics to do. A system for separating carbon dioxide from exhaust gas of a thermal power plant using coal or petroleum as a fuel has been devised using the properties of this lithium composite oxide (see, for example, Patent Document 1 and Patent Document 2).
Japanese Patent Laying-Open No. 2005-075683 JP 2003-054927 A

  In a carbon dioxide separation system using a lithium composite oxide, a packed bed packed with pellets of lithium composite oxide having a particle diameter of several millimeters is generally used as a reactor for absorbing carbon dioxide. In order to effectively predict the performance of a carbon dioxide separation system with such a configuration, it is necessary to understand in detail the absorption / release characteristics of the absorbent in the carbon dioxide absorption reactor and the carbon dioxide release section. The behavior of absorption and release reactions in the reactor is predicted using the changes in weight obtained with a differential thermobalance and the results of laboratory-scale tests in which a tube with an inner diameter of several tens of millimeters filled with pellets is heated from the outside in an electric furnace. It was.

  However, in the actual carbon dioxide absorption / release reaction of lithium composite oxide, reaction heat of about 75 kJ is generated per mole of carbon dioxide, and the heat is transported as a medium by the process gas. Specifically, the boiler exhaust gas exchanges heat during the absorption reaction and the circulating carbon dioxide exchanges heat as the heat supply medium during the release regeneration reaction. In addition, the absorption / release reaction occurs only in the above temperature range, but the temperature of the packed bed solid during each reaction is heated and cooled by reaction heat and heat transport by the process gas, and thus increases with time. fluctuate. Furthermore, although this heat transport amount is determined by the flow rate of the process gas, since the pressure loss in the packed bed is large, it is necessary to consider the blower power with this amount as the energy loss. It is difficult to control the behavior of reactions involving such physical phenomena from experimental values on a laboratory scale.

  Therefore, in order to estimate the performance of a realistic carbon dioxide separation system and perform precise control, the size of the reactor, the superficial velocity of the process gas, and the system operation method are logically determined in consideration of the above conditions. There was a need to do.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a carbon dioxide separation method and a carbon dioxide separation system using a lithium composite oxide having a system configuration excellent in energy efficiency.

  In order to solve the above-described problems, the carbon dioxide separation method of the present invention uses a lithium composite oxide as an absorbent, and incorporates the absorbent into an apparatus that is a carbon dioxide generation source to absorb carbon dioxide in the gas. In a carbon dioxide separation method comprising an absorption process and a release process in which carbon dioxide is released to the absorbent by a regenerator, the removal rate of carbon dioxide contained in the gas is in the range of 20% to 40%. This is a method characterized by setting operating conditions to

  The carbon dioxide separation system of the present invention includes a carbon dioxide absorption reactor that contains an absorbent material made of a lithium composite oxide that absorbs carbon dioxide contained in a gas generated by a carbon dioxide generation source, and carbon dioxide. A carbon dioxide releasing part for heating the absorbed material to release carbon dioxide, a carbon dioxide heater for supplying a heating medium to the carbon dioxide releasing part, and the carbon dioxide releasing part for releasing carbon dioxide. Means for returning the absorbent to the carbon dioxide absorption reactor, and the system is operated under the condition that the removal rate of carbon dioxide contained in the gas is in the range of 20% to 40%. .

  According to the carbon dioxide separation method and the carbon dioxide separation system of the present invention, it is possible to provide a carbon dioxide separation method and a carbon dioxide separation system that efficiently and effectively separate carbon dioxide by setting optimum operating conditions. It becomes possible.

  Preferred embodiments of a carbon dioxide separation method and a carbon dioxide separation system according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 shows a system diagram in which the carbon dioxide separation system according to the present invention is applied to a boiler plant incorporated in a thermal power plant.

  First, the configuration and operation of a boiler plant and the carbon dioxide separation system of the present invention incorporated in the boiler plant will be described with reference to FIG.

  The boiler plant 10 incorporated in the thermal power plant includes a combustion chamber 18, a radial first superheater 19, a second superheater 20, a first reheater 21, and a third superheater in order along the flow of the combustion gas 17. A boiler main body 27 that houses a condenser 22, an electrostatic precipitator 23, a desulfurizer 24, a second reheater 25, and a economizer 26; 30.

  Combustion gas 17 is generated by fuel 31 such as coal supplied to combustion chamber 18 and air 32 supplied via air preheater 28, and the generated combustion gas 17 having a temperature of about 1200 ° C. is radiated by heat. Saturated water or saturated steam that passes through each of the first superheater 19, the second superheater 20, the first reheater 21, the third superheater 22, the second reheater 25, and the economizer 26 is heated. And overheated into steam (superheated steam). On the other hand, impurities such as fly ash contained in the combustion gas 17 are removed by the electric dust collector 23, and sulfur oxide (SOx) is further removed by the desulfurizer 24.

  On the other hand, the combustion gas 17 having a temperature of 350 ° C. to 400 ° C. exiting the economizer 26 is supplied to the air preheater 28, and the air 32 that generates the combustion gas 17 is preheated by the air preheater 28 to preheat the air. The combustion gas 17 is supplied to the denitrifier 29, where nitrogen oxides (NOx) are removed, and then discharged from the chimney 30 to the atmosphere as exhaust gas having a temperature of 120 ° C to 150 ° C.

  In the boiler plant applied to the thermal power plant having such a configuration, the carbon dioxide separation system of the present embodiment is an area where the temperature of the combustion gas 17 in the boiler body 27 is 800 ° C. or higher, for example, the second superheater 20 and the second superheater 20. A carbon dioxide heater 33 is provided between the first reheater 21 and the temperature of the combustion gas 17 is about 350 ° C. to 650 ° C., for example, the electrostatic precipitator 23 or the desulfurizer 24 and the second reheater 25. A carbon dioxide absorption reactor 34 is provided between them.

The absorbent material is a material containing lithium silicate (Li ₄ SO ₄ ), which is a lithium composite oxide, and is formed by forming it into a pellet shape. This absorbent material is filled to form a packed bed, which is operated on a moving bed to cause the carbon dioxide absorption reactor 34 and the carbon dioxide release section 36 to perform absorption and release reactions, respectively.

  Both the carbon dioxide heater 33 and the carbon dioxide absorption reactor 34 are connected to a regenerator 35 installed separately from the boiler body 27. The regenerator 35 is formed of, for example, a cylindrical body, and a carbon dioxide release unit 36 is provided in the body. An absorbent that has absorbed carbon dioxide is absorbed in the carbon dioxide absorption reactor 34 in the carbon dioxide release unit 36. To release carbon dioxide under high temperature conditions. In addition, the regenerator 35 accommodates a cooler 37 that cools the carbon dioxide emitted from the carbon dioxide emission part 36.

  Between the carbon dioxide absorption reactor 34 and the cooler 37 of the regenerator 35, a nitrogen circulation system 41 is provided, a nitrogen tank 39 provided with a cooler 38, and a transport nitrogen blower 40. This nitrogen circulation system 41 seals the surface of the absorbent with the circulating nitrogen when returning the absorbent released with the carbon dioxide release part 36 of the regenerator 35 to the carbon dioxide absorption reactor 34. The carbon dioxide is not absorbed, and a pressing force (moving force) is applied so that the absorbent can smoothly return to the carbon dioxide absorption reactor 34.

  On the other hand, the carbon dioxide release part 36 disposed in the regenerator 35 is provided with a first carbon dioxide circulation system 45 and a carbon dioxide tank 44 provided with a transfer carbon dioxide blower 42 and a cooler 43. The first carbon dioxide circulation system 45 is moved from the carbon dioxide tank 44 when the absorbent that has absorbed carbon dioxide in the carbon dioxide absorption reactor 34 provided in the boiler body 27 is moved to the carbon dioxide discharge section 36 of the regenerator 35. The carbon dioxide is given to the absorbent so that the absorbent can move smoothly.

  Further, the regenerator 35 includes a second carbon dioxide circulation system 47. The second carbon dioxide circulation system 47 cools the carbon dioxide released from the absorbent in the carbon dioxide release part 36 by the cooler 37, and a part of the carbon dioxide is supplied to the carbon dioxide in the boiler body 27 through the blower 46. The carbon dioxide that is supplied to the heater 33 and heated to increase the temperature is given to the carbon dioxide releasing section 36 as a heating source.

  Next, the operation of the carbon dioxide separation system according to the present embodiment will be described.

  The combustion gas 17 generated in the combustion chamber 18 of the boiler body 27 heats the carbon dioxide heater 33 at a temperature of 800 ° C. or higher, and the heating carbon dioxide supplied from the regenerator 35 via the blower 46 has a temperature of 750 ° C. The carbon dioxide for heating heated to 850 ° C. is heated as a heating source to the carbon dioxide discharge part 36 of the regenerator 35 through the second carbon dioxide circulation system 47. In the carbon dioxide absorption reactor 34, the carbon dioxide absorbed by the absorbent is released.

  On the other hand, the combustion gas 17 exiting the carbon dioxide heater 33 is subjected to carbon dioxide absorption reaction after impurities such as fly ash are removed by the electric dust collector 23 and sulfur oxide (SOx) is removed by the desulfurizer 24. The vessel 34 is supplied at a temperature ranging from 350 ° C to 500 ° C. Here, carbon dioxide is absorbed by the absorbent material.

  The absorbent that has absorbed the carbon dioxide is moved and supplied to the carbon dioxide discharge section 36 of the regenerator 35 by the propulsive force by the carbon dioxide from the transfer carbon dioxide blower 42 in the first carbon dioxide circulation system 45. Here, heated carbon dioxide having a temperature of 800 ° C. or more is supplied from the second carbon dioxide circulation system 47 as a heating source, and the carbon dioxide absorbed by the absorbent material is released.

  The regeneration carbon dioxide released from the absorbent in the carbon dioxide release part 36 is cooled by the cooler 38 in the nitrogen circulation system 41, and the nitrogen supplied from the nitrogen tank 39 through the transport nitrogen blower 40 is used as a refrigerant source. It cools with the cooler 37.

  When the carbon dioxide for regeneration cooled by the cooler 37 is excessive, it is adjusted by the blower 52 and supplied to other devices. The remaining carbon dioxide for regeneration is always maintained at a constant amount and supplied to the carbon dioxide heater 33 accommodated in the boiler body 27.

  Further, nitrogen used as a refrigerant in the cooler 37 is circulated to the carbon dioxide absorption reactor 34 via the nitrogen circulation system 41, and carbon dioxide is released at the carbon dioxide release section 36 to the carbon dioxide absorption reactor 34. The surface of the returning absorbent material is sealed, and it is also used as a force for promoting the movement of the absorbent material.

In this carbon dioxide separation system, a carbon dioxide heater 33 is accommodated in a high temperature portion of the boiler body 27, and a carbon dioxide absorption reactor 34 is accommodated in a relatively low temperature portion of the boiler body 27. Each of the absorption reactors 34 is connected to a regenerator 35 installed separately from the boiler body 27 via a second carbon dioxide circulation system 47, a first carbon dioxide circulation system 45, and a nitrogen circulation system 41, respectively. Also in the carbon absorption reactor 34, carbon dioxide contained in the combustion gas is absorbed by an absorbent material configured in pellets in which lithium silicate (Li ₄ SiO ₄ ) is contained in the particles, and the carbon dioxide-absorbed absorbent material is regenerated. The carbon dioxide discharge part 36 of 35 is heated using carbon dioxide from the carbon dioxide heater 33 as a heating source, and the carbon dioxide absorbed at that time is released. Since the absorption material released and released carbon dioxide is returned to the carbon dioxide absorption reactor 34 to absorb carbon dioxide, carbon dioxide can be processed and recovered in a larger amount without waste.

Example 1
As an example of a carbon dioxide separation system having the above configuration, a pulverized coal-fired thermal power plant with 500 MW and power generation efficiency of 40% is assumed, and lithium silicate which is a kind of lithium composite oxide is used as an absorbent in exhaust gas. As a result of calculating the mass balance of the system for separating and recovering carbon dioxide, the exhaust gas flow rate was 460 kg / s, and the carbon dioxide concentration in the exhaust gas was 11%. From this, the carbon dioxide flow rate to be treated was calculated as 77 kg / s.

  The maximum carbon dioxide absorption capacity of lithium silicate is 35% with respect to the initial weight not absorbed. The reaction rate in the carbon dioxide absorption reaction is affected by three parameters: temperature, carbon dioxide partial pressure, and the amount of carbon dioxide absorbed, that is, the change in the weight of the absorbent, but the absorption reaction rate increases as the amount of carbon dioxide absorption increases. Decreases. In addition, the reaction rate decreases almost linearly with a decrease in carbon dioxide concentration.

  FIG. 2 shows a schematic diagram of the behavior of the absorbent in the carbon dioxide absorption reactor. FIG. 2 schematically shows how exhaust gas flows through the absorbent in the carbon dioxide absorption reactor 34 of FIG.

  It is assumed that the absorbent material that has finished the regeneration process has a uniform temperature at 850 ° C. The absorbent material is carried into the exhaust gas duct by the moving bed and the absorption process is started. In this absorption process, the absorbent is cooled by the exhaust gas, and is maintained in a temperature range (500 ° C. to 600 ° C.) optimum for the absorption process, thereby causing an exothermic carbon dioxide absorption reaction. The absorbent material is finally lowered in solid temperature to near 400 ° C. of the exhaust gas temperature and sent to the regeneration process.

  The carbon dioxide concentration at the exhaust gas inlet is about 11% as calculated above, but since carbon dioxide is sequentially absorbed into the absorbent, the carbon dioxide concentration in the exhaust gas gradually decreases. On the other hand, carbon dioxide is also accumulated in the absorbent material, thereby reducing the absorption reaction rate. Here, the absorption rate of the absorbent was set to 30% with respect to the maximum 35%, which is the upper limit of the material characteristics, and the required amount of the absorbent was calculated with the system's carbon dioxide removal rate being 30%. As a result, the amount of the necessary absorbent was calculated as 77 kg / s.

  FIG. 3 is a graph showing changes in the carbon dioxide removal rate with respect to the elapsed time in the absorption process, focusing on the local area of the absorbent material.

  According to the implementation of the present inventors, the carbon dioxide removal rate shows a tendency as shown in FIG. 3 and changes with time. That is, as shown in FIG. 3, if the absorbent material is used under an operating condition where the carbon dioxide removal rate is 20% to 40%, a 30% average carbon dioxide removal rate can be achieved, and sufficient carbon dioxide removal performance is maintained. It is clear that we can do it.

  Moreover, when 30 minutes or more pass in an absorption process, the temperature of an absorber falls from the temperature range suitable for absorption reaction. Therefore, the removal rate is reduced to 20% or less, and the carbon dioxide recovery efficiency is reduced. From this, it was found that the operating conditions in the carbon dioxide separation system should be set so that the carbon dioxide removal rate is 20% to 40%. Moreover, the time required for the absorption process in the carbon dioxide separation system was set within 30 minutes.

  Next, an allowable value of pressure loss in the carbon dioxide absorption reactor 34 is estimated. Since the carbon dioxide absorption reactor 34 has a shape incorporated in the boiler body 27, it is necessary to evaluate the pressure loss of the exhaust gas. The pressure loss in the carbon dioxide absorption reactor 34 increases the power of the blower that pushes the combustion gas of the boiler. To calculate the power required to boost atmospheric pressure by cascading blowers with a pressure of 10 kPa and the amount of incremental carbon dioxide discharged as a result, for each stage, to suppress the power increase to within 2% It was obtained as an indicator that the pressure loss does not exceed 30 kPa.

Next, the size of the carbon dioxide absorption reactor 34 is designed. The absorption capacity per unit volume of the lithium silicate as the absorbent is calculated as 0.05 kg-carbon dioxide / m ³ / s based on the test results when the particle shape is a spherical pellet having a diameter of 5 mm. The volume of the reactor 34 is calculated to be 440 m ³ . Here, when the shape of the carbon dioxide absorption reactor 34 is considered to be a rectangular parallelepiped, the reactor volume is represented by the product of the cross-sectional area of the exhaust gas flow path and the packed bed thickness. The pressure loss in the packed bed is determined by the approaching flow velocity and the packed bed thickness.

FIG. 4 shows the relationship between the pressure loss and the cross-sectional area with respect to the thickness of the packed bed (absorbent) in the absorption process. When the carbon dioxide separation system of the present embodiment is applied to an existing boiler, a flow path with significant expansion / contraction is not realistic, and about 900 m ² is considered as the upper limit of the cross-sectional area, and in this case, the absorbent material is filled. The thickness of the packed layer is 0.5 m. If the pressure loss is set so as not to exceed 30 kPa in consideration of the above consideration, the thickness of the packed layer is 1.5 m. From these considerations, the range of the thickness of the packed bed filled with the absorbent of the carbon dioxide separation system was set to 0.5 m to 1.5 m.

Next, let us consider the superficial velocity. Since the power generation efficiency of the plant is around 40% and the air ratio is substantially constant, when the power generation capacity increases or decreases, it may increase or decrease substantially linearly with respect to the exhaust gas flow rate. Therefore, since the required carbon dioxide absorption reactor volume also increases and decreases linearly, the cross-sectional mass flux, that is, the superficial velocity and thickness, hardly changes. Further, the cross section need not be square, and may have any shape as long as it has the same superficial velocity. The superficial velocity corresponding to a thickness of 0.5 m to 1.5 m is obtained from FIG. 4 and is 0.52 kg / m ² / s to 1.56 kg / m ² / s. Therefore, the superficial velocity in the absorption process of the carbon dioxide separation system was set in the range of 0.5 kg / m ² / s to 1.6 kg / m ² / s.

  Next, the actual behavior of the carbon dioxide absorption reactor 34 is predicted. The absorption process is started by taking over the physical state immediately after the end of the release process, that is, the history of the absorber solid temperature, the density distribution of the absorber, and the like.

Here, it is assumed that the absorber solid temperature distribution and density distribution are uniform at 850 ° C. and initial state 600 kg / m ³ , respectively, and the exhaust gas temperature is assumed to be about 400 ° C. select.

  The present inventors perform one-dimensional numerical analysis using a model in which a part of the carbon dioxide absorption reactor 34 is cut out under these initial conditions and inlet boundary conditions. The change of physical quantity with time was predicted. In the analysis, non-homogeneous systems with different process gas and solid packed bed temperatures are treated, and heat transfer including solid and gas radiation, solid-solid and gas-gas, with respect to the heat transfer mechanism governed by forced convection. Considering heat diffusion and heat of reaction between each other.

  On the other hand, the distribution of the absorber density with respect to the dimensionless packed bed thickness was investigated. FIG. 5 shows the absorbent density distribution. As a result, even if the absorbent material is kept in contact with the exhaust gas for a long time, the absorbent material is cooled sequentially from the exhaust gas inlet, and the amount of carbon dioxide absorbed does not change, and the weight change of the absorbent material exceeds 15%. It became clear that there was nothing.

As described above, according to the present example, the thickness of the packed layer filled with the absorbent is in the range of 0.5 m to 1.5 m, and the mass change of the absorbent in the absorption process is based on the initial weight of the absorbent. The knowledge that it was appropriate to use within 15% was obtained. On the other hand, as conditions for the absorption process, it is appropriate that the superficial velocity is in the range of 0.5 kg / m ² / s to 1.6 kg / m ² / s and that the substantial absorption time is within 30 minutes. Obtained knowledge. Moreover, the carbon dioxide removal rate was estimated to be 30%, and the knowledge that the operating conditions should be determined by designing the carbon dioxide absorption reactor was also obtained.

  As described above, according to the carbon dioxide separation system of the present embodiment, it is possible to provide design conditions and operation conditions capable of realizing an efficient absorption process of the carbon dioxide separation system using the lithium composite oxide. .

(Example 2)
Next, the carbon dioxide separation system of Example 2 will be described. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 6 shows the reaction rate of the carbon dioxide release (regeneration) reaction with respect to the carbon dioxide circulation pressure. Similarly to the absorption process handled in Example 1, the regeneration process is also affected by three parameters: temperature, carbon dioxide partial pressure, and the amount of absorbed carbon dioxide, that is, the change in weight of the absorbent. As shown in FIG. 6, when the pressure is low, the release reaction rate is ensured even if the temperature is low. However, the higher the pressure is, the lower the reaction rate is regardless of the temperature, and the tendency changes greatly especially around 0.08 MPa. The trend was obvious. Therefore, the carbon dioxide circulation pressure in the regeneration process of the carbon dioxide separation system was set to 0.08 MPa or less.

  FIG. 7 shows a schematic diagram of the absorbent material in the carbon dioxide releasing part 36 in the regeneration process. FIG. 7 schematically shows how the circulating carbon dioxide circulates through the absorbent in the carbon dioxide release part 36 of FIG.

  The absorbent material that has finished the absorption process has a temperature distribution and a density distribution around 400 ° C., and is carried by the moving bed into the flow path of the carbon dioxide circulation system, which is the regeneration process gas, and the regeneration process is resumed. Here, a carbon dioxide releasing reaction which is an endothermic reaction, that is, a regeneration reaction of the absorbent material occurs by passing through a temperature range optimum for the regeneration process while being heated by the regenerated circulating carbon dioxide at about 850 ° C. The absorbent material is finally sent to the absorption process again, raising the solid temperature to about 850 ° C. of the circulating carbon dioxide temperature.

Next, the superficial velocity of circulating carbon dioxide is calculated. The circulating carbon dioxide is heated to 750 ° C. and an absorbent material of 77 kg / s up to 750 ° C., and the flow rate required to give reaction heat that completely releases carbon dioxide that has absorbed 30% of the initial dead weight; Considering the pressure loss at 08 MPa, the upper limit superficial velocity of 1.3 kg / m ² / s is first determined.

Next, the present inventors set the absorbent solid temperature distribution and the density (weight change) distribution after the absorption process as an initial state in the same manner as in Example 1 in one dimension in the time course of the behavior of the absorbent in the carbon dioxide absorber. Changes were analyzed. FIG. 8 shows the relationship between the superficial velocity and the time required for regeneration. As shown in Example 1, if the upper limit of the absorption time is 30 minutes and the regenerating apparatus is switched by three towers, the regenerating time of the absorbent material is limited to 60 minutes, which is twice as long. The superficial velocity at this time is obtained as 0.5 kg / m ² / s from FIG. Therefore, the superficial velocity of the circulating carbon dioxide was set to 0.5 kg / m ² / s to 1.3 kg / m ² / s.

  In addition, the shortest regeneration time of the absorbent material in the regeneration process is 30 minutes, and if the regeneration time is shorter than this, many absorbent materials that are not regenerated remain. Therefore, the regeneration time of the carbon dioxide separation system was set to 30 minutes or more.

  The temperature of the absorbent material at the end of the absorption process has a temperature distribution lower than the optimum temperature range for absorption, but when the absorbent material is heated, it passes through this optimum temperature range again. At this time, the circulating carbon dioxide is almost 100% carbon dioxide, and the absorbing capacity of the absorbent material is still sufficient, so the circulating carbon dioxide is absorbed. For this reason, the density increased in a part of the absorbent material. In order to shorten the regeneration time of the absorbent material, it is effective to suppress this increase in density.

  Therefore, the present inventors tried to circulate the regenerated circulating carbon dioxide flowing into the absorbent material in the regeneration process in the direction opposite to the exhaust gas inflow direction in the absorption process. The time change of the carbon dioxide accumulation amount of the whole absorbent material when circulating carbon dioxide was circulated in the forward and reverse directions was examined. FIG. 9 shows the examination results. As shown in this figure, the amount of unreleased carbon dioxide was circulated in the reverse direction, compared with the case where circulated carbon dioxide was circulated in the forward direction, that is, in the same direction as the exhaust gas flow direction in the absorption process. The trend of steadily decreasing in cases was revealed.

As described above, from the consideration of this example, it was determined that the superficial velocity from 0.5 kg / m ² / s to 1.3 kg / m ² / s was appropriate as a condition for the regeneration process. Further, it has become clear that the substantial regeneration time needs to be 30 minutes or longer in the regeneration process of the absorbent material. Further, it was found that the pressure of the circulating carbon dioxide is preferably 0.08 MPa or less to shorten the regeneration time. Furthermore, the knowledge that the regeneration time of the absorbent can be effectively shortened by circulating the carbon dioxide in the reverse direction with the carbon dioxide inlet in the regeneration process opposite to the exhaust gas inlet in the absorption process. Obtained.

  As described above, according to the carbon dioxide separation system of the present embodiment, it is possible to provide design conditions and operation conditions that can realize an efficient regeneration process of the carbon dioxide separation system using the lithium composite oxide. .

The block diagram which incorporated the carbon dioxide separation system of the present invention in the boiler plant. The schematic diagram of the absorber in an absorption process. The figure which shows the time change of a carbon dioxide removal rate. The figure which shows the relationship between the pressure loss with respect to the filling layer thickness of an absorber in an absorption process, and a cross-sectional area. The figure which shows the absorber density distribution with respect to the packed bed thickness. The figure which shows the relationship between the carbon dioxide circulation pressure and the reaction rate of reproduction | regeneration. The schematic diagram of the absorber in a reproduction | regeneration process. The figure which shows the relationship between the superficial velocity in a regeneration process, regeneration time, and pressure loss. The figure which compares the time change of the carbon dioxide accumulation amount in an absorber with the case where carbon dioxide is distribute | circulated in the same direction as an exhaust gas distribution direction, and the case where carbon dioxide is distribute | circulated to a reverse direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Boiler plant 17 Combustion gas 18 Combustion chamber 19 1st superheater 20 2nd superheater 21 1st reheater 22 3rd superheater 23 Electric dust collector 24 Desulfurizer 25 2nd reheater 26 Carbon-saving device 27 Boiler Main body 28 Air preheater 29 Denitrator 30 Chimney 31 Fuel 32 Air 33 Carbon dioxide heater 34 Carbon dioxide absorption reactor 35 Regeneration device 36 Carbon dioxide discharge part 37, 38 Cooler 39 Nitrogen tank 40 Nitrogen blower 41 for transportation Nitrogen circulation system 42 Carbon dioxide blower for conveyance 43 Cooler 44 Carbon dioxide tank 45 First carbon dioxide circulation system 46 Blower 47 Second carbon dioxide circulation system 48 Flow path 49 Rotor 50 Belt conveyor 51 Cylindrical body 52 Blower

Claims (10)

An absorption process in which lithium composite oxide is used as an absorbing material, and the absorbing material absorbs carbon dioxide in a gas generated at a carbon dioxide generation source, and the carbon dioxide absorbed in the absorbing material is released by a regenerator. A carbon dioxide separation method comprising: a carbon dioxide separation method, wherein operating conditions are set so that a removal rate of carbon dioxide contained in the gas is in a range of 20% to 40%. ^2. The carbon dioxide separation method according to claim 1, wherein an exhaust gas superficial velocity in the absorption process is in a range of 0.5 kg / m ² / s to 1.6 kg / m ² / s. 2. The carbon dioxide separation method according to claim 1, wherein a thickness of the packed bed filled with the absorbent is set in a range of 0.5 m to 1.5 m. 2. The carbon dioxide separation method according to claim 1, wherein the time required for the absorption process is 30 minutes or less. 2. The carbon dioxide separation method according to claim 1, wherein a mass change of the absorbent material in the absorption process is set to 15% or less in a mass ratio with respect to a mass of the absorbent material in a state where carbon dioxide is not absorbed. . The carbon dioxide separation method according to claim 1, wherein a superficial velocity of circulating carbon dioxide in the regeneration process is set in a range of 0.5 kg / m ² / s to 1.3 kg / m ² / s. The carbon dioxide separation method according to claim 1, wherein the pressure of the circulating carbon dioxide in the regeneration process is set to 0.08 MPa or less. The carbon dioxide separation method according to claim 1, wherein a time required for the regeneration process is 30 minutes or more. The inlet of the circulating carbon dioxide in the regeneration process is opposite to the inlet of the exhaust gas in the absorption process, and the circulating carbon dioxide is circulated in the absorbent material in the direction opposite to the exhaust gas flow direction in the absorption process. The carbon dioxide separation method according to claim 1. A carbon dioxide absorption reactor that contains an absorbent material made of a lithium composite oxide that absorbs carbon dioxide contained in a gas generated at a carbon dioxide generation source, and carbon dioxide by heating the absorbent material that has absorbed carbon dioxide A carbon dioxide releasing part for releasing carbon dioxide, a carbon dioxide heater for supplying a heating medium to the carbon dioxide releasing part, and the absorbent material from which carbon dioxide has been released by the carbon dioxide releasing part is returned to the carbon dioxide absorption reactor. And a carbon dioxide separation system, characterized in that the carbon dioxide separation system is operated under conditions where the removal rate of carbon dioxide contained in the gas is in the range of 20% to 40%.

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