Patent Publication Number: US-2016220943-A1

Title: Carbon-dioxide recovery apparatus, and carbon-dioxide recovery method

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus and a method for recovering carbon dioxide using a carbon dioxide capturing material. 
     BACKGROUND ART 
     For reducing a global warming, it is demanded to reduce a carbon dioxide emission, where carbon dioxide serves as a greenhouse gas and has a great impact on the global warming. Specifically, examples of the carbon dioxide emission control include techniques of separation and recovery typically using an absorbent (absorbing liquid) or an adsorbent. 
     In a known technique for adsorbing and separating a gas, generally, in order to adsorb and separate a specific component in the gas, the specific component is first adsorbed by an adsorbent contained in an adsorption column. The adsorption column housing the adsorbent adsorbing a predetermined amount of the specific component is then heated, and a gas is supplied thereto to desorb the specific component from the adsorbent and to regenerate the adsorbent. 
     As the gas, it is desirable to use steam (water vapor) or another regeneration gas that can be easily separated from a liquid at room temperature and normal atmospheric pressure, the gas being supplied to eliminate or minimize reduction in gas purity of the recovered specific component. Typically disadvantageously, however, steam condensation occurs at a carbon dioxide capturing material (adsorbent) surface due to steam flow when the carbon dioxide capturing material has a temperature lower than the steam temperature. 
     In a technique as a possible solution to eliminate or minimize the steam condensation, the carbon dioxide absorbent is heated, and superheated steam is still supplied in the step of regenerating the carbon dioxide absorbent. Disadvantageously, however, the steam is continuously supplied during the regeneration of the carbon dioxide absorbent, and this leads to great loss of condensation heat and increased operation cost upon gas-liquid separation of the recovered carbon dioxide from the steam. 
     Patent Literature 1 discloses a technique relating to a carbon dioxide recovery system for recovering high-concentration carbon dioxide from a carbon-dioxide-containing gas. With this technique, the recovery of carbon dioxide from the carbon dioxide capturing material is performed using a carrier gas having a boiling point of about 100° C.±50° C. at 1 atm, where the carrier gas of this type can be easily separable from carbon dioxide by cooling. The carrier gas is exemplified by, but not limited to, steam, methanol, and ethanol. In addition, carbon dioxide, once sorbed, is desorbed not only by heating with a temperature rise of 200° C. or lower, but also by disposing a vacuum pump in a channel that recovers high-concentration carbon dioxide so as to reduce the pressure in the container by a pressure difference of 15 atm or less. 
     Patent Literature 2 discloses a technique as follows. With this technique, a purge gas having a low CO 2  partial pressure is blown in a desorbing step in CO 2  separation and recovery. This eliminates the need for pressure reduction in the desorption. This literature also describes that the steam pressure is set higher than the atmospheric pressure. For example, the steam pressure is set at 105 kPa. 
     CITATION LIST 
     Patent Literatures 
     Patent Literature 1: Japanese Patent Application Laid-Open No. 2013-59704 
     Patent Literature 2: Japanese Patent Application Laid-Open No. 2010-69398 
     SUMMARY OF INVENTION 
     Technical Problem 
     The present invention has an object to reduce the amount of a regeneration gas to be supplied into a carbon dioxide recovery column in a carbon dioxide capturing material regeneration process, to increase the energy efficiency, and to perform the regeneration process in a shorter time. 
     Solution to Problem 
     The present invention provides a carbon dioxide recovery apparatus. The apparatus includes a carbon dioxide sorbing column, a heating unit, and first, second, and third channels. The carbon dioxide sorbing column contains a carbon dioxide capturing material. The heating unit heats the carbon dioxide capturing material. A carbon-dioxide-containing gas is introduced via the first channel into the carbon dioxide sorbing column. A regeneration gas is introduced via the second channel into the carbon dioxide sorbing column. A gaseous mixture containing a gas desorbed from the carbon dioxide capturing material is recovered via the third channel. The apparatus is configured so that the heating unit preheats the carbon dioxide capturing material, and then the regeneration gas is introduced into the carbon dioxide sorbing column to recover carbon dioxide from the carbon dioxide capturing material. 
     Advantageous Effects of Invention 
     The present invention reduces the amount of a regeneration gas to be supplied to a carbon dioxide recovery column in the step of regenerating a carbon dioxide capturing material, increases the energy efficiency, and performs the regenerating step in a shorter time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a general schematic diagram illustrating how valves are in a carbon dioxide recovery apparatus in the step of preheating a carbon dioxide capturing material for the carbon dioxide capturing material regeneration; 
         FIG. 1B  is a general schematic diagram illustrating how the valves are in the step of introducing a regeneration gas to regenerate the carbon dioxide capturing material, where this step is performed after the heating step illustrated in  FIG. 1A ; 
         FIG. 2  is a schematic diagram illustrating an instrument for carbon dioxide capturing material regeneration tests, where the instrument was used in Comparative Example 1 and Examples 1 to 3; 
         FIG. 3  is a graph illustrating the carbon dioxide desorption in the tests in Comparative Example 1 and Examples 1 to 3; and 
         FIG. 4  is a graph illustrating the time taken to complete the carbon dioxide desorption in the tests in Comparative Example 1 and Examples 1 to 3. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A carbon dioxide sorbing column constituting part of a carbon dioxide recovery apparatus according to an embodiment of the present invention will be illustrated below with reference to the attached drawings. 
       FIGS. 1A and 1B  illustrate the carbon dioxide sorbing column in the carbon dioxide recovery apparatus. 
       FIG. 1A  is a general schematic diagram illustrating how valves are in the carbon dioxide recovery apparatus in the step of preliminary heating a carbon dioxide capturing material for the sorbent regeneration. 
       FIG. 1B  is a general schematic diagram illustrating how the valves are in the step of introducing a regeneration gas to regenerate the carbon dioxide capturing material, where this step is performed after the heating step illustrated in  FIG. 1A . 
     In these figures, a carbon dioxide sorbing column  100  contains a carbon dioxide capturing material  101 . 
     The carbon dioxide sorbing column  100  is coupled to a carbon-dioxide-containing gas channel  102 , to a carbon dioxide removed gas recovery channel  103 , and to a gaseous mixture recovery channel  105 . These channels each have a valve so as to control gas flows. The carbon dioxide sorbing column  100  is also coupled to a regeneration gas channel  104  equipped with a regeneration gas flow rate control unit  109 . The carbon dioxide sorbing column  100  is equipped with heat-transfer medium channels  107  and  108  so as to heat the carbon dioxide capturing material  101 . 
     There is a need for performing following three steps (1), (2), and (3) in this order to recover carbon dioxide from a carbon-dioxide-containing gas. 
     The step (1) is the “step of sorbing” carbon dioxide by the carbon dioxide capturing material. 
     The step (2) is the “step of regenerating” the carbon dioxide capturing material, in which carbon dioxide, once sorbed, is desorbed from the carbon dioxide capturing material by heating, and a regeneration gas is supplied after the desorption to expel carbon dioxide from the carbon dioxide sorbing column, and the carbon dioxide capturing material is made reusable in another sorbing step. 
     The step (3) is the “step of cooling” the carbon dioxide capturing material after heating, down to a temperature equal to or slightly higher than the temperature of the carbon-dioxide-containing gas. 
     Continuous recovery of carbon dioxide from the carbon-dioxide-containing gas can be performed by disposing at least three carbon dioxide sorbing columns  100  and dividing the three steps among the three carbon dioxide sorbing columns  100 . 
     Upon sorption of carbon dioxide, the on-off valve  106  is opened to introduce the carbon-dioxide-containing gas via the carbon-dioxide-containing gas channel  102  into the carbon dioxide sorbing column  100 . Thus, the carbon dioxide capturing material  101  selectively sorbs carbon dioxide from the carbon-dioxide-containing gas. The residual gas from which carbon dioxide has been removed is discharged from the carbon dioxide removed gas recovery channel  103 . When the carbon dioxide concentration in the gas in the carbon dioxide removed gas recovery channel  103  reaches a predetermined level, or after a lapse of a predetermined time from the start of the carbon-dioxide-containing gas supply, the valves in carbon-dioxide-containing gas channel  102  and the carbon dioxide removed gas recovery channel  103  are closed. 
     Next, the carbon dioxide capturing material regeneration step will be described. 
       FIG. 1A  illustrates how valves are opened or closed in the step of heating the carbon dioxide capturing material to regenerate the sorbent. 
     In the heating step illustrated in this figure, the gaseous mixture recovery channel  105  is opened so as to desorb and recover carbon dioxide from the carbon dioxide capturing material  101 . The carbon dioxide capturing material  101  is heated by heat transfer media passing through the heat-transfer medium channel  107  and the heat-transfer medium channel  108 . The heat-transfer medium channel  107  and the heat-transfer medium channel  108  are disposed respectively inside and outside of the carbon dioxide sorbing column  100 . Carbon dioxide desorbed from the carbon dioxide capturing material  101  by heating is recovered via the gaseous mixture recovery channel  105 . The heat-transfer medium channel  108  which is disposed outside of the carbon dioxide sorbing column  100  in this embodiment may also be disposed outside of the carbon dioxide sorbing column  100  or typically in the wall of the carbon dioxide sorbing column  100 . The heat-transfer medium channels  107  and  108  are hereinafter together referred to as a “heating unit”. 
     After a lapse of a predetermined time from the start of the heating, or after the temperature of the carbon dioxide capturing material at a measurement point reaches a level higher than the temperature of the regeneration gas, the regeneration gas, whose flow rate is controlled by the regeneration gas flow rate control unit  109 , is supplied from the regeneration gas channel  104  to the carbon dioxide sorbing column  100 . 
     Specifically, the heating unit preheats the carbon dioxide capturing material  101  (preheating step), and thereafter the regeneration gas (steam) is introduced into the carbon dioxide sorbing column  100  (regeneration gas supplying step) to recover carbon dioxide from the carbon dioxide capturing material  101 . The control in switching (on-off) in these operations may be performed manually by an operator, or by allowing an attached control unit to issue electrical or mechanical instructions based on detected data. 
     To shorten the flow time (supply time) of the regeneration gas, the regeneration gas is preferably allowed to flow at a flow rate of 0.5 m/sec or more in terms of a linear velocity in the carbon dioxide sorbing column  100 . The flow rate (linear velocity) is more preferably from 0.5 m/sec to 2.5 m/sec from the viewpoint of pressure drop. Assume that the carbon dioxide capturing material has a particle size of 2.5 cm, a voidage of 0.4, and a viscosity of 2.8×10 −4 , and is packed to a height of 10 m to form a carbon dioxide capturing material-packed bed. In this case, the pressure drop is calculated according to the Ergun equation for pressure drop calculation and is found to be 52 kPa at the linear velocity of the regeneration gas of 2.5 m/sec. This pressure drop is higher than an assumed allowable pressure drop of 50 kPa. Accordingly, it has been decided that the regeneration gas preferably has the linear velocity of 2.5 m/sec or less. 
     The valves in the heat-transfer medium channels  107  and  108  may be closed or not upon supply of the regeneration gas into the carbon dioxide sorbing column. 
       FIG. 1B  illustrates how the valves are opened or closed when the regeneration gas flow is started while the heat-transfer medium is still supplied (the valve is opened). 
     The carbon dioxide partial pressure around the carbon dioxide capturing material  101  can be reduced when the apparatus is in the state illustrated in  FIG. 1B . This promotes the desorption of carbon dioxide from the carbon dioxide capturing material  101  and allows the carbon dioxide capturing material  101  to be regenerated with a higher regeneration rate. The switching from the heating to the regeneration gas supply may be performed by determining based on data from a temperature metering means (thermometer) disposed in the carbon dioxide sorbing column  100 ; or by empirically or computationally estimating the time until the temperature reaches a preset temperature, and determining the switching timing based on the time; or by measuring the flow rate (concentration) of the outlet gas (carbon dioxide) desorbed from the carbon dioxide capturing material, and switching the valves when the flow rate reaches a predetermined level (concentration) or lower. Specifically, the apparatus (the operation) may be controlled so that the regeneration gas supply is stopped when the concentration of carbon dioxide in the gaseous mixture reaches a predetermined level or lower. 
     In another embodiment, the apparatus (the operation) may be controlled so that the regeneration gas supply is stopped when the concentration of the regeneration gas in the gaseous mixture reaches a predetermined level or higher. The concentration of the regeneration gas may be detected by measuring the dew point of the gaseous mixture. 
     In yet another embodiment, the apparatus (the operation) may be controlled so that the regeneration gas supply is stopped when the regeneration gas is supplied for a predetermined time. Namely, the regeneration gas may be supplied for a preset time. 
     The regeneration gas for use herein may be any gas other than carbon dioxide, but is preferably a gas that readily condenses. Examples of such regeneration gas include, but are not limited to, gases having a boiling point of about 100° C.±50° C. at 1 atm, including steam; alcohols such as methanol and ethanol; and ketones such as acetone. Among them, steam is particularly preferred from the viewpoints typically of safety. This is because the regeneration gas of this type can be separated and recovered by cooling the recovered gaseous mixture containing the regeneration gas and carbon dioxide. 
     The carbon dioxide capturing material  101  may be any of materials having a high specific surface area, such as silica, alumina, titania, zirconia, ceria, zeolite, polymeric materials, activated carbon, molecular organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs); and materials containing compounds, such as oxides and carbonates, of alkali metals and alkaline earth metals. The carbon dioxide capturing material  101  may have such a shape that the smallest unit of the component(s) is any of a granule, an aggregate of granules, or a composite of them. Assume that the carbon dioxide capturing material  101  is formed as a member (structural component). In this case, the carbon dioxide capturing material  101  preferably has such a shape as to offer gas-permeability. Typically, carbon dioxide capturing material  101  in this case may be formed as a porous article or as a honeycomb article. The carbon dioxide capturing material  101  may also have an outer shape selected typically from bulk and plate-like shapes. The carbon dioxide capturing material  101  is particularly preferably an oxide containing cerium (Ce) (ceria combined with one or more other elements to offer higher performance). 
     A preferred, but non-limiting example of the Ce-containing oxide is an oxide containing Al in addition to Ce. This oxide preferably contains Ce as an element that is contained in a highest content among metal elements in the oxide, and contains Al in a content of from 0.01% by mole to 40% by mole. 
     The Ce-containing oxide preferably contains Ce in a content of 40% by mole or more. 
     The Ce-containing oxide preferably further contains 0.01% by mole or more of at least one element selected from the group consisting of Fe, Cu, V, and Mo. 
     The Ce-containing oxide preferably contains Fe, Cu, V, and Mo in contents meeting a condition specified by Expression (1): 
       (Fe content)×1.0+(Cu content)×1.3+(V content)×3.3+(Mo content)×3.3≦10  (1)
 
     where contents in the expression are indicated in percent by mole. 
     The Ce-containing oxide preferably further contains at least one element selected from the group consisting of La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu in a total content of 0.01% to 50% by mole. 
     The present invention will be illustrated in further detail with reference to a comparative example and examples. 
       FIG. 2  illustrates the schematic configuration of a test instrument used in Comparative Example 1 and Examples 1 to 3 below. 
     The test instrument illustrated in  FIG. 2  includes a tubular reactor  110 , a steam generator  114 , a bubbling pot  115 , and a steam-recovering water tank  118 . The tubular reactor  110  is equipped with a heater  122 . The bubbling pot  115  is disposed in a thermostat  116 . The steam-recovering water tank  118  is disposed in a cooling water tank  117 . The tubular reactor  110  is packed with (filled with) a carbon dioxide capturing material  111 . The steam generator  114  and the bubbling pot  115  are coupled respectively via lines  112  and  113  to the tubular reactor  110 . The flow amount of steam generated by the steam generator  114  can be measured with sampling the steam via a steam flow measurement channel  123 . 
     The apparatus is configured so that the carbon dioxide concentration and flow rate of a gas passed through the steam-recovering water tank  118  can be measured respectively by a carbon dioxide concentration meter  119  and a flowmeter  120 . 
     Comparative Example 1 
     A test as follows was performed as Comparative Example 1. In the test, saturated steam at 100° C. was supplied to a carbon dioxide capturing material to regenerate the sorbent, where the carbon dioxide capturing material had reached sorption equilibrium (adsorption equilibrium) at 50° C. and a carbon dioxide partial pressure of 13 kPa. 
     The carbon dioxide capturing material used herein was high specific surface area ceria (HS) supplied by DAIICHI KIGENSO KAGAKU CO., LTD. The carbon dioxide capturing material molded into granules of a size of 0.5 to 1.0 mm was prepared in an amount of 16 cm 3 , charged into a tubular reactor having a cross-sectional area of 0.9 cm 2 , and the test was performed in the following manner. 
     As illustrated in  FIG. 2 , nitrogen was supplied to the carbon dioxide capturing material  111  at a flow rate of 400 cc/min and a heater temperature of 300° C. for 2 hours to cleanse the carbon dioxide capturing material. 
     Next, a sorbing step so as to allow the carbon dioxide capturing material  111  to reach sorption equilibrium was performed. In this step, a carbon-dioxide-containing gas was supplied via the bubbling pot  115  in the thermostat  116  set at 50° C. to be combined with steam, and the resulting gas further containing the steam was supplied into the tubular reactor  110  to come in contact with the carbon dioxide capturing material  111 . The temperature of the heater  122  was set at 50° C. 
     A tubular reactor outlet gas was supplied via the steam-recovering water tank  118  to remove steam (moisture vapor) therefrom, where the steam-recovering water tank  118  was cooled by the cooling water tank  117  set at 10° C. The residual gas was fed to the carbon dioxide concentration meter  119  to measure the carbon dioxide concentration. In this step, a valve  121  in a line leading to the flowmeter  120  was closed. The flow rate of steam generated by the steam generator  114  was measured via the steam flow measurement channel  123  and was found to be 898 cc/min, corresponding to 0.2 m/sec in terms of the linear velocity in the tubular reactor  110 . Upon lapse of a sufficient time after the concentration measured with the carbon dioxide concentration meter  119  became equal to the concentration of the tubular reactor inlet gas, the sorbing step was completed, and the supply of the carbon-dioxide-containing gas was stopped. 
     The regeneration step was started simultaneously with the completion of the sorbing step. The regeneration step included a preheating step and a subsequent regeneration gas supplying step. 
     In the preheating step, the heater  122  was set at 200° C., a valve in the channel leading to the carbon dioxide concentration meter  119  was closed, but the valve  121  in the line leading to the flowmeter  120  was opened. An integrated flow rate was calculated from data from the flowmeter  120 , and based on this, the carbon dioxide desorption at an output of the heater  122  of 200° C. was calculated. Thus, the carbon dioxide desorption in the preheating step was found to be about 500 mmol/L. 
     Next, the regeneration gas supplying step was performed. Specifically, saturated steam (regeneration gas) at 100° C. and 0.1 MPa was generated by the steam generator  114  and supplied via a line  113  (steam channel) to the tubular reactor  110 . In this step, the output of the heater  122  was still set at 200° C. to eliminate or minimize steam condensation. An integrated flow rate was calculated based on data from the flowmeter  120 , and a change with time of the accumulated carbon dioxide desorption during the steam supply was determined. 
     Example 1 
     A test including a sorbing step and a desorbing step was performed as Example 1 by a procedure similar to Comparative Example 1. However, the output of the steam generator was changed, and the flow rate of the generated steam was measured via the steam flow measurement channel and was found to be 2781 cc/min, corresponding to 0.5 m/sec in terms of the linear velocity in the tubular reactor. An integrated flow rate was calculated based on data from the flow rate measuring and recording means (flowmeter)  120 , based on which a change with time of the integrated carbon dioxide desorption during the steam supply was determined. 
     Example 2 
     A test including a sorbing step and a desorbing step was performed as Example 2 by a procedure similar to Comparative Example 1. However, the output of the steam generator was changed, and the flow rate of the generated steam was measured via the steam flow measurement channel and was found to be 7021 cc/min, corresponding to 1.3 m/sec in terms of the linear velocity in the tubular reactor. An integrated flow rate was calculated based on data from the flow rate measuring and recording means (flowmeter)  120 , based on which a change with time of the integrated carbon dioxide desorption during the steam supply was determined. 
     Example 3 
     A test including a sorbing step and a desorbing step was performed as Example 3 by a procedure similar to Comparative Example 1. However, the output of the steam generator was changed, and the flow rate of the generated steam was measured via the steam flow measurement channel and was found to be 10691 cc/min, which corresponds to 2.0 m/sec in terms of the linear velocity in the tubular reactor. An integrated flow rate was calculated based on data from the flow rate measuring and recording means (flowmeter)  120 , based on which a change with time of the integrated carbon dioxide desorption during the steam supply was determined. 
       FIG. 3  presents the integrated desorbed amounts of CO 2  upon lapse of 0.5 min, 1 min, 1.5 min, 2 min, and 2.5 min. The abscissa indicates the linear velocity of the steam in Comparative Example 1 and Examples 1 to 3. 
       FIG. 4  presents the time taken to desorb the whole quantity of CO 2  after the steam supply start. 
     In  FIGS. 3 and 4 , Comparative Example 1 and Examples 1 to 3 are contrasted with each other. 
       FIG. 3  demonstrates that the desorption amount and desorption rate of CO 2  increase with an increasing steam linear velocity. 
       FIG. 4  demonstrates as follows. 
     According to Example 1, the time taken to desorb the whole quantity of CO 2  is shortened to about 6 min which is about one half of the time in Comparative Example 1. 
     According to Example 2, the time taken to desorb the whole quantity of CO 2  is shortened to about 3 min which is about one fourth of the time in Comparative Example 1. 
     According to Example 3, the time taken to desorb the whole quantity of CO 2  is shortened to about 3 min which is about one fourth of the time in Comparative Example 1. 
     REFERENCE SIGNS LIST 
     
         
         
           
               100 : carbon dioxide sorbing column, 
               101 : carbon dioxide capturing material, 
               102 : carbon-dioxide-containing gas channel, 
               103 : carbon dioxide-removed gas recovery channel, 
               104 : regeneration gas channel, 
               105 : gaseous mixture recovery channel, 
               106 : on-off valve, 
               107 ,  108 : heat-transfer medium channel, 
               109 : regeneration gas flow rate control unit, 
               110 : tubular reactor, 
               111 : carbon dioxide capturing material, 
               112 ,  113 : line, 
               114 : steam generator, 
               115 : bubbling pot, 
               116 : thermostat, 
               117 : cooling water tank, 
               118 : steam-recovering water tank, 
               119 : carbon dioxide concentration meter, 
               120 : flowmeter, 
               121 : valve, 
               122 : heater, and 
               123 : steam flow measurement channel.