Patent Description:
CO<NUM> devices configured to control CO<NUM> emission by removing CO<NUM> (carbon dioxide) from emission gas have been used in plants. In a CO<NUM> recovery device, emission gas is brought into contact with an amine-based absorbent solution (hereinafter, referred to as an absorbent solution) in an absorption tower to produce a rich solution of an absorbent solution having absorbed CO<NUM>. Subsequently, the CO<NUM> recovery device sends out a rich solution to a regeneration tower to isolate CO<NUM> included in a rich salutation, to regenerate an absorbent solution, and to thereby circulate the absorbent solution to the absorption tower again. The CO<NUM> recovery device may press the isolated CO<NUM> gas into an oil field or may reserve the CO<NUM> gas in an aquifer, thus preventing CO<NUM> from being emitted into the atmosphere. In this connection, Patent Document <NUM> discloses a related art. Other related concepts are disclosed in Patent Documents <NUM> and <NUM>.

In the above CO<NUM> recovery device, it is required to efficiently circulate an absorbent solution or a rich solution by reducing a failure rate of the device.

The present invention aims to provide a CO<NUM> recovery device and a CO<NUM> recovery method, which can solve the above problem.

In a first aspect of the present invention, a CO<NUM> recovery device includes an absorption tower configured to bring an emission gas including CO<NUM> in contact with an absorbent solution, to remove the CO<NUM> from the emission gas, and to thereby generate a rich solution corresponding to the absorbent solution having absorbed the CO<NUM>; a regeneration tower configured to regenerate the absorbent solution by removing the CO<NUM> from the rich solution; a heat exchanger configured to carry out heat exchange between the rich solution and the absorbent solution which is higher in temperature than the rich solution and from which the CO<NUM> is removed; an absorbent-solution delivery pipe configured to deliver the absorbent solution subjected to the heat exchange in the heat exchanger to the absorption tower; and a bypass pipe configured to deliver the rich solution before the heat exchange, which will be introduced into the heat exchanger, to the absorbent-solution delivery pipe by controlling a bypass control valve.

The CO<NUM> recovery device may further include a first pressure measurement part configured to measure first pressure applied to the rich-solution delivery pipe configured to deliver the rich solution to the heat exchanger; and a bypass control part configured to increase the opening of the bypass control valve attached to the bypass pipe when the first pressure exceeds a predetermined threshold, thus delivering the rich solution before the heat exchange, which will be introduced into the heat exchanger, to the absorbent-solution delivery pipe.

The CO<NUM> recover device further includes a rich-solution delivery pipe configured to deliver the rich solution to the regeneration tower; a rich-solution control valve configured to adjust a flow rate of the rich solution, which is disposed adjacent to the regeneration tower rather than the heat exchanger configured to carry out the heat exchange between the rich solution flowing through the rich-solution delivery pipe and the absorbent solution; a liquid level measurement part configured to measure a liquid level of the absorbent solution accumulated in the base of the regeneration tower; and a liquid level control part configured to control the rich-solution control valve to increase its opening according to a reduction of the liquid level when a change rate of the liquid level shows an increasing trend but to control the bypass control valve to increase its opening according to a reduction of the liquid level when the change rate of the liquid level shows a deceasing trend.

In a second aspect of the present invention, a CO<NUM> recovery method for a CO<NUM> recovery device includes the steps of: bringing an emission gas including CO<NUM> in contact with an absorbent solution, removing the CO<NUM> from the emission gas, and thereby generating a rich solution in an absorption tower; regenerating the absorbent solution by removing the CO<NUM> from the rich solution in a regeneration tower; carrying out by a heat exchanger a heat exchange between the rich solution and the absorbent solution which is higher in temperature than the rich solution and from which the CO<NUM> is removed; delivering by an absorbent-solution delivery pipe the absorbent solution subjected to the heat exchange in the heat exchanger to the absorption tower; and delivering by a bypass pipe the rich solution before the heat exchange in the heat exchanger to the absorbent-solution delivery pipe by controlling a bypass control valve.

The CO<NUM> recovery method may further includes the steps of: measuring by a first pressure measurement part a first pressure applied to the absorbent-solution delivery pipe configured to deliver the rich solution before the heat exchange, which will be introduced into the heat exchanger; and increasing by a bypass control part the opening of the bypass control valve attached to the bypass pipe when the first pressure exceeds a predetermined threshold, thus delivering the rich solution before the heat exchange, which will be introduced into the heat exchanger, to the absorbent-solution delivery pipe.

The CO<NUM> recovery method further includes the steps of: delivering by a rich-solution delivery pipe the rich solution to the regeneration tower; adjusting a flow rate of the rich solution using a rich-solution control valve, which is disposed adjacent to the regeneration tower rather than the heat exchanger configured to carry out the heat exchange between the absorbent solution and the rich solution flowing through the rich-solution delivery pipe; measuring by a liquid level measurement part the liquid level of the absorbent solution accumulated in the base of the regeneration tower; and controlling by a liquid level control part the rich-solution control valve to increase its opening according to a reduction of the liquid level when a change rate of the liquid level shows an increasing trend while controlling the bypass control valve to increase its opening according to a reduction of the liquid level when the change rate of the liquid level shows a decreasing trend.

According to the present invention, it is possible to reduce a failure rate so that a CO<NUM> recover device can efficiently circulate an absorbent solution or a rich solution.

Hereinafter, a CO<NUM> recovery device according to one embodiment of the present invention will be described with reference to the drawings.

<FIG> is a schematic diagram of a CO<NUM> recovery device of the present embodiment.

As shown in <FIG>, a CO<NUM> recovery device <NUM> mainly includes a control device <NUM>, an absorption tower <NUM>, a regeneration tower <NUM>, and a heat exchanger <NUM>.

Emission gas <NUM> emitted from industrial combustion facilities such as a boiler and a gas turbine will be sent to an emission-gas cooling device in which the emission gas <NUM> is cooled in cooling water and then sent to the absorption tower <NUM> of the CO<NUM> recovery device <NUM>. In the absorption tower <NUM>, the emission gas <NUM> communicates and contacts with an absorbent solution based on an amine-based solution such that CO<NUM> included in the emission gas <NUM> may be absorbed into the absorbent solution (a lean solution <NUM>) in chemical reaction. An absorbent solution absorbing CO<NUM> will be referred to as a rich solution <NUM>. The emission gas <NUM> after removal of CO<NUM> in the absorption tower <NUM> will be discharged to the outside. The rich solution <NUM> is pressurized by a rich-solution delivery pump <NUM> and then sent out to the heat exchanger <NUM> through a first rich-solution delivery pipe <NUM>. In the heat exchanger <NUM>, the rich solution <NUM> is heated by the lean solution <NUM> which is an absorbent solution regenerated by the regeneration tower <NUM> and which is higher in temperature than the rich solution <NUM>, and then the heated rich solution <NUM> will be supplied to the regeneration tower <NUM> through a second rich-solution delivery pipe <NUM>.

The rich solution <NUM> supplied to the regeneration tower <NUM> will be emitted from the upper section of the regeneration tower <NUM> into its inside. Inside the regeneration tower <NUM>, the rich solution <NUM> may emit a majority of CO<NUM> due to an endothermic reaction. An absorbent solution having emitted part or majority of CO<NUM> in the regeneration tower <NUM> will be referred to as a semi-lean solution. When the semi-lean solution reaches the lower section of the regeneration tower <NUM>, the semi-lean solution will be turned into the absorbent solution (i.e. the lean solution <NUM>) from which roughly all of CO<NUM> has been removed. In the lower section of the regeneration tower <NUM>, the absorbent solution is heated by a reboiler such that CO<NUM> included in the semi-lean solution may be emitted from the absorbent solution. Moisture is used as a heating source of a reboiler. The lean solution <NUM> will be sent to the heat exchanger <NUM> through a first absorbent-solution delivery pipe <NUM>. A CO<NUM> gas <NUM> accompanied with moisture, which is emitted from the rich solution <NUM> and the semi-lean solution in the regeneration tower <NUM>, is derived from the upper section of the regeneration tower <NUM>. The moisture included in the emitted CO<NUM> gas <NUM> is condensed and sent back to the regeneration tower <NUM>. In addition, the CO<NUM> gas <NUM> is emitted to the outside and then recovered separately. The recovered CO<NUM> gas <NUM> is pressed into an oil field using an enhanced oil recovery (EOR) or reserved in an aquifer, thus working out warming countermeasures. The lean solution <NUM>, which is sent out to the heat exchanger <NUM> through the first absorbent-solution delivery pipe <NUM>, is cooled by the rich solution <NUM> in the heat exchanger <NUM>, and then the cooled lean solution <NUM> is supplied to the absorption tower <NUM> through a second absorbent-solution delivery pipe <NUM>.

A rich-solution control valve <NUM> is attached to the second rich-solution delivery pipe <NUM>. The control device <NUM> controls the rich-solution control valve <NUM> to control an amount of rich solution <NUM> delivered to the regeneration tower <NUM> in each unit time. The liquid level (or the level) of the lean solution <NUM> reserved in the lower section of the regeneration tower <NUM> may be fluctuated due to a varying amount of rich solution <NUM> delivered to the regeneration tower <NUM> in each unit time. A lean-solution control valve <NUM> is attached to the second absorbent-solution delivery pipe <NUM>. The control device <NUM> controls the lean-solution control valve <NUM> to control an amount of lean solution <NUM> delivered to the absorption tower <NUM> in each unit time.

A rich-solution delivery pump <NUM> is attached to the first rich-solution delivery pipe <NUM>. The control device <NUM> controls the rich-solution delivery pump <NUM> such that the rich solution <NUM> reserved in the lower section of the absorption tower <NUM> can be forcedly delivered to the heat exchanger <NUM> and the regeneration tower <NUM>. A lean-solution delivery pump <NUM> is attached to the first absorbent-solution delivery pipe <NUM>. The control device <NUM> controls the lean-solution delivery pump <NUM> such that the lean solution <NUM> reserved in the lower section of the regeneration tower <NUM> can be forcedly delivered to the heat exchanger <NUM> and the absorption tower <NUM>.

According to the present embodiment, the CO<NUM> recovery device <NUM> provides a bypass pipe <NUM> connected between the first rich-solution delivery pipe <NUM> and the second absorbent-solution delivery pipe <NUM>. A bypass control valve <NUM> is attached to the bypass pipe <NUM>. The control device <NUM> controls the bypass control valve <NUM> to be opened such that the rich solution <NUM> prior to heat exchange, which will be applied to the heat exchanger <NUM>, can be delivered to the second absorbent-solution delivery pipe <NUM>.

The control device <NUM> may cause the rich solution <NUM> and the lean solution <NUM> to circulate in the CO<NUM> recovery device <NUM> by controlling the pressed delivery of the rich solution <NUM> via the rich-solution deliver pump <NUM>, the pressed delivery of the lean solution <NUM> via the lean-solution delivery pump <NUM>, the opening of the rich-solution control valve <NUM>, and the opening of the lean-solution control valve <NUM>. Specifically, the control device <NUM> acquires a flow rate per unit time which is obtained from a rich-solution flowmeter <NUM> and a lean-solution flowmeter <NUM>, the liquid level of the lean solution <NUM> in the lower section of the regeneration tower <NUM>, the liquid level of the rich solution <NUM> in the lower section of the absorption tower <NUM>, and a load value (or an output value) of an industrial combustion facility such as a boiler and a gas turbine, and therefore the control device <NUM> may control the pressed delivery of the rich solution <NUM> via the rich-solution deliver pump <NUM>, the pressed delivery of the lean solution <NUM> via the lean-solution delivery pump <NUM>, the opening of the rich-solution control valve <NUM>, and the opening of the lean-solution control valve <NUM> based on those pieces of information.

A level gauge L1 configured to detect the liquid level of the lean solution <NUM> is attached to the lower section of the regeneration tower <NUM>. An excessive descending of the liquid level of the lean solution <NUM> in the lower section of the regeneration tower <NUM> may likely cause a failure such as cavitation due to an incapacity of the lean-solution delivery pump <NUM> to sufficiently deliver the lean solution <NUM>. Therefore, it is required that the liquid level be set to a reference position. The control device <NUM> measures the liquid level of the lean solution <NUM> in the lower section of the regeneration tower <NUM> based on a measurement of the level gauge L1, and therefore the control device <NUM> carries out a feedback control for the opening of the rich-solution control valve <NUM> to thereby fix the liquid level. Specifically, the control device <NUM> decreases the opening of the rich-solution control valve <NUM> in preparation for a reduction of a flow rate of the rich solution <NUM> per unit time to be forcedly delivered from the absorption tower <NUM> via the rich-solution delivery pump <NUM> due to a reduction of load. This may increase the pressure of the first rich-solution delivery pipe <NUM>. A pressure gauge P1 measures the pressure of the first rich-solution pipe <NUM> to output its measurement to the control device <NUM>. A malfunction such as a failure of the heat exchanger <NUM> may occur when the heat exchanger <NUM> bears a load of pressure due to an increased pressure applied to the first rich-solution delivery pipe <NUM>. For this reason, as described above, the CO<NUM> recovery device <NUM> of the present embodiment provides the bypass pipe <NUM>, by which the rich-solution <NUM> is brought into the second absorbent-solution delivery pipe <NUM> when the control device <NUM> controls the bypass control valve <NUM> from CLOSE to OPEN. This may reduce the pressure of the first rich-solution delivery pipe <NUM>, and therefore it is possible to allay a fear of causing a failure of the heat exchanger <NUM>.

<FIG> is a block diagram showing the hardware configuration of the control device <NUM> of the present embodiment.

The control device <NUM> is a computer, as shown in <FIG>, which includes various hardware elements such as a CPU <NUM>, a ROM (Read-Only Memory) <NUM>, a RAM (Random-Access Memory) <NUM>, a storage unit such as a HDD (Hard-Disk Drive) <NUM>, a user interface <NUM> such as a touch panel, and a communication module <NUM> to communicate with sensors.

<FIG> is a functional block diagram of the control device <NUM> of the present embodiment.

The CPU <NUM> of the control device <NUM> may execute preinstalled control programs after starting the operation of the control device <NUM>. Thus, the control device <NUM> may realize a controller <NUM>, a pressure measurement part <NUM>, a liquid level measurement part <NUM>, a bypass control part <NUM>, a liquid level control part <NUM>, a valve-opening adjustment part <NUM>, an absorbent-solution-flow measurement part <NUM>, and an absorbent-solution-flow adjustment part <NUM>.

The controller <NUM> is configured to control various functional parts of the control device <NUM>.

The pressure measurement part <NUM> is configured to measure the pressure of a predetermined pipe such as the pressure of the first rich solution delivery pipe <NUM> configured to deliver the rich solution <NUM> to the heat exchanger <NUM>.

The liquid-surface measurement part <NUM> is configured to measure the liquid level of the lean solution <NUM> accumulated in the base of the regeneration tower <NUM>.

The absorbent-solution-flow measurement part <NUM> is configured to measure a flow rate per unit time given by the rich-solution flowmeter <NUM> and the lean-solution flowmeter <NUM>.

The bypass control part <NUM> may instruct the valve-opening adjustment part <NUM> to increase the opening of the bypass control valve <NUM> when the pressure measured by the pressure measurement part <NUM> exceeds a predetermined threshold. As a result, the bypass control part <NUM> controls the rich solution <NUM> before heat exchange, which will be sent to the heat exchanger <NUM>, to be delivered to the second absorbent-solution delivery pipe <NUM>.

The liquid level control part <NUM> may instruct the absorbent-solution-flow adjustment part <NUM> to increase the opening of the rich-solution control valve <NUM> according to a reduction of the liquid level when the liquid level of the lean solution <NUM> accumulated in the bottom of the regeneration tower <NUM> is equal to or above a predetermine position. The liquid level control part <NUM> may instruct the absorbent-solution-flow adjustment part <NUM> to increase the opening of the bypass control valve <NUM> according to a reduction of the liquid level when the liquid level of the lean solution <NUM> accumulated in the base of the regeneration tower <NUM> is below a predetermined position.

The absorbent-solution-flow adjustment part <NUM> is configured to calculate the opening of the rich-solution control valve <NUM> and the opening of the lean-solution control valve <NUM> such that a flow rate measured by the absorbent-solution-flow measurement part <NUM> may reach a predetermined target value. The liquid level control part <NUM> may determine a target value for a rich-solution flow rate.

The valve-opening adjustment part <NUM> is configured to control the opening of the rich-solution control valve <NUM> and the opening of the bypass control valve <NUM> according to instructions from the bypass control part <NUM> and the absorbent-solution-flow adjustment part <NUM>.

<FIG> is a first flowchart showing a processing flow of the control device <NUM>.

It is necessary to realize a fear that an excessive load may be imparted to the heat exchanger <NUM> due to an increasing pressure of the first rich-solution delivery pipe <NUM>. The control device <NUM> is designed to reduce a load of pressure imparted to the heat exchanger <NUM> according to the following process.

First, the pressure measurement part <NUM> of the control device <NUM> acquires a measurement a from the pressure gauge P1 (step S1). The bypass controller <NUM> compares the measurement a with a threshold b of pressure (step S2). For example, the threshold b is produced by adding a predetermined value to pressure c of the first rich-solution delivery pipe <NUM> in its setting (b>c). The absorbent-solution-flow measurement part <NUM> measures a flow rate per unit time using the rich-solution flowmeter <NUM> and the lean-solution flowmeter <NUM>, and therefore the absorbent-solution-flow adjustment part <NUM> acquires the measurement result. The absorbent-solution-flow adjustment part <NUM> controls the opening of the rich-solution control valve <NUM> and the opening of the lean-solution control valve <NUM> such that the flow rate per unit time, which is obtained from the rich-solution flowmeter <NUM> or the lean-solution flowmeter <NUM>, may match a predetermined value. Herein, the opening control would be a circulation control for the rich solution <NUM> and the lean solution <NUM>. It is assumed that the absorbent-solution-flow adjustment part <NUM> would instruct the valve-opening adjustment part <NUM> to decrease the opening of the rich-solution control valve <NUM>. Accordingly, the valve-opening adjustment part <NUM> may decrease the opening of the rich-solution control valve <NUM> to the instructed opening. This may establish a relationship of "measurement a > threshold b" with respect to the pressure of the first rich-solution delivery pipe <NUM>.

Upon determining through the above comparison that the measurement a exceeds the threshold b, the bypass control part <NUM> determines to carry out a bypass control. The bypass control part <NUM> instructs the valve-opening adjustment part <NUM> to change the bypass control valve <NUM> from CLOSE to OPEN (step S3). The bypass control part <NUM> may give an opening instruction to the valve-opening adjustment part <NUM> such that the opening of the bypass control valve <NUM> will be increased as the measurement a becomes a larger value; hence, the valve-opening adjustment part <NUM> may control the opening of the bypass control valve <NUM> according to the opening instruction. The bypass control part <NUM> determines to terminate the process (step S4), wherein the process will be resumed from step S1 unless the process is terminated.

According to the above process, it is possible for the control device <NUM> to reduce a load of pressure imparted to the heat exchanger <NUM> due to an increasing pressure applied to the first rich-solution delivery pipe <NUM>. In addition, the control device <NUM> may constitute a minimum flowline using the bypass pipe <NUM>, and therefore even when the rich-solution control valve <NUM> would be fully closed due to some reasons, it is possible to automatically circulate the rich solution <NUM> through the minimum flowline configured of the bypass pipe <NUM> adjacent to the absorption tower <NUM> by opening the bypass control valve <NUM>.

In this connection, it is possible to attach a pressure gauge P2 to the first absorbent-solution delivery pipe <NUM> in the CO<NUM> recovery device <NUM>, and therefore the control device <NUM> may control the rich solution <NUM> before heat exchange, which will be put into the heat exchanger <NUM>, to be delivered to the second absorbent-solution delivery pipe <NUM> using the measurement a of the pressure gauge P1 as well as a measurement d of the pressure gauge P2.

Specifically, the bypass control part <NUM> obtains the measurement a from the pressure gauge P1 while obtaining the measurement d from the pressure gauge P2. Subsequently, when "measurement a > measurement d + α", the bypass control part <NUM> may instruct the valve-opening adjustment part <NUM> to change the bypass control valve <NUM> from CLOSE to OPEN.

Similar to the aforementioned effect, it is possible to reduce a load of pressure imparted to the heat exchanger <NUM> due to an increasing pressure applied to the first rich-solution delivery pipe <NUM>.

<FIG> is a second flowchart showing a processing flow of the control device <NUM>.

In the CO<NUM> recovery device <NUM>, it takes several minutes for the lean solution <NUM>, corresponding to the rich solution <NUM> having removed CO<NUM> therefrom, to reach the lower section of the regeneration tower <NUM>. For this reason, it is difficult to stabilize the liquid level of the lean solution <NUM> in the lower section of the regeneration tower <NUM>. To solve this problem, the control device <NUM> of the CO<NUM> recover device <NUM> according to the second embodiment may control the rich solution <NUM> before heat exchange, which will be put into the heat exchanger <NUM>, to be delivered to the second absorption-solution delivery pipe <NUM> using the bypass pipe <NUM>.

Specifically, the liquid level control part <NUM> may acquire the liquid level of the lean solution <NUM> from the level gauge L1 configured to detect the liquid level of the lean solution <NUM> (step S11). The liquid level control part <NUM> is configured to control the liquid level of the lean solution <NUM> to be set to a predetermined reference value. The liquid level control part <NUM> compares the liquid level of the lean solution <NUM> with a lower-limit threshold which is below the predetermined reference value by a predetermined value or more (step S12). Upon determining that the liquid level of the lean solution <NUM> to be equal to or less than the lower-limit threshold, the liquid level control part <NUM> instructs an opening for the valve-opening adjustment part <NUM> to increase the opening of the bypass control valve <NUM>. The valve-opening adjustment part <NUM> controls the bypass control valve <NUM> to be changed from CLOSE to OPEN (step S13). Accordingly, it is possible to deliver the rich solution <NUM> to the second absorbent-solution deliver pipe <NUM> through the bypass pipe <NUM> when the liquid level is significantly lowered. This makes the rich solution <NUM> flow into the second absorbent-solution delivery pipe <NUM> so as to decrease a flow rate per unit time for the lean solution <NUM> to flow from the first absorbent-solution deliver pipe <NUM> to the second absorbent-solution deliver pipe <NUM>, thus decreasing an amount of emission per unit time for emitting the lean solution <NUM> from the lower section of the regeneration tower <NUM>. Due to a good response in decreasing the amount of emission, it is possible to rapidly increase the liquid level of the lean solution <NUM>. The liquid level control part <NUM> determined whether to terminate the process (step S14), wherein the process will be resumed from step S11 unless the process is terminated.

<FIG> is a third flowchart showing a processing flow of the control device <NUM>.

<FIG> includes graphs showing the relationship between the openings and the liquid levels according to a function f×<NUM> and a function f×<NUM>.

As described below, the control device <NUM> may carry out a control according to a change rate of the liquid level of the lean solution <NUM>. Specifically, the liquid level control part <NUM> may acquire the liquid level of the lean solution <NUM> from the level gauge L1 configured to detect the liquid level of the lean solution <NUM> (step S21). The liquid level control part <NUM> is configured to control the liquid level of the lean solution <NUM> to be set to a predetermined reference value. The liquid level control part <NUM> determines a change rate of the liquid level of the lean solution <NUM> (step S22). When the change rate of the liquid level shows an increasing trend, the liquid level control part <NUM> may calculate an opening by inputting the current liquid level into the function f×<NUM> (see a graph of <FIG>) for calculating the opening of the rich-solution control valve <NUM> to be decreased linearly as the increasing rate of the liquid level becomes large (step S23). The liquid level control part <NUM> instructs the valve-opening adjustment part <NUM> to make a control to achieve the calculated opening. The valve-opening adjustment part <NUM> controls the rich-solution control valve <NUM> to have the instructed opening (step S24). Accordingly, it is possible to reduce the liquid level of the lean solution <NUM> over time since a flow rate per unit time of the rich solution <NUM> to flow into the regeneration tower <NUM> may decrease as the increasing rate of the liquid level becomes large.

On the other hand, when the change rate of the liquid level shows a decreasing trend, the liquid level control part <NUM> may calculate an opening by inputting the current liquid level into the function f×<NUM> (see a graph of <FIG>) for calculating the opening of the bypass control valve <NUM> to be linearly increased as the decreasing rate of the liquid level becomes large (step S25). The liquid level control part <NUM> instructs the valve-opening adjustment part <NUM> to make a control to achieve the calculated opening. The valve-opening adjustment part <NUM> controls the bypass control valve <NUM> to have the instructed opening (step S26). Accordingly, it is possible to deliver the rich solution <NUM> to the second absorbent-solution deliver pipe <NUM> through the bypass pipe <NUM> as the decreasing rate of the liquid level becomes large. This may decrease a flow rate per unit time of the lean solution <NUM> to flow from the first absorbent-solution deliver pipe <NUM> to the second absorbent-solution deliver pipe <NUM>, thus decreasing an amount of emission per unit time for emitting the lean solution <NUM> from the lower section of the regeneration tower <NUM>. Due to a good response in decreasing the amount of emission, it is possible to rapidly increase the liquid level of the lean solution <NUM>. The liquid level control part <NUM> determines whether to terminate the process (step S27), wherein the process will be resumed from step S21 unless the process is terminated.

According to the aforementioned process of the control device <NUM>, it is possible to make a control to stabilize the liquid level of the lean solution <NUM> in the lower section of the regeneration tower <NUM> in comparison with the conventional technology.

The aforementioned control device includes a computer system. The foregoing processes are stored in computer-readable storage media in the form of programs, wherein a computer may read and execute programs to achieve the foregoing processes. Herein, computer-readable storage media refer to magnetic disks, magneto-optical disks, CD-ROM, DVD-ROM, and semiconductor memory. In addition, computer programs may be delivered to computers through communication lines, and therefore a computer may receive and execute programs.

Claim 1:
A CO<NUM> recovery device (<NUM>) comprising:
an absorption tower (<NUM>) configured to bring an emission gas including CO<NUM> in contact with an absorbent solution so as to remove the CO<NUM> from the emission gas, thus generating a rich solution (<NUM>) corresponding to the absorbent solution having absorbed the CO<NUM>;
a regeneration tower (<NUM>) configured to regenerate the absorbent solution (<NUM>) by removing the CO<NUM> from the rich solution (<NUM>);
a heat exchanger (<NUM>) configured to carry out heat exchange between the rich solution (<NUM>) and the regenerated absorbent solution (<NUM>) which is higher in temperature than the rich solution (<NUM>);
a rich-solution delivery pipe (<NUM>, <NUM>) configured to deliver the rich solution (<NUM>) from the absorption tower (<NUM>) to the regeneration tower (<NUM>) through the heat exchanger (<NUM>);
an absorbent-solution delivery pipe (<NUM>, <NUM>) configured to deliver the absorbent solution (<NUM>) from the regeneration tower (<NUM>) to the absorption tower (<NUM>) through the heat exchanger (<NUM>);
a bypass pipe (<NUM>) configured to deliver the rich solution (<NUM>) before the heat exchanger (<NUM>) to the absorbent-solution delivery pipe (<NUM>) via a bypass control valve (<NUM>);
a rich-solution control valve (<NUM>) configured to adjust a flow rate of the rich solution (<NUM>) flowing through the rich-solution delivery pipe (<NUM>) after the heat exchanger (<NUM>) toward the regeneration tower (<NUM>); and
a level gauge (L1) configured to measure a liquid level of the absorbent solution (<NUM>) accumulated in the base of the regeneration tower (<NUM>), wherein an opening of the rich-solution control valve (<NUM>) is increased according to a reduction of the liquid level when a change rate of the liquid level shows an increasing trend,
wherein the opening of the bypass control valve (<NUM>) is increased according to a reduction of the liquid level when the change rate of the liquid level shows a deceasing trend.