Provided are a CO 2 absorber that reduces CO 2 contained in flue gas; a regenerator that reduces CO 2 contained in rich solvent absorbing CO 2 to regenerate the rich solvent, so that lean solvent having the CO 2 reduced in the regenerator is reused in the CO 2 absorber; a heat exchanger that allows the rich solvent to exchange heat with the lean solvent; and a controller that controls to extract rich solvent portion that is part of the rich solvent, to allow the rich solvent portion to bypass the heat exchanger, and to be supplied into the top of the regenerator without exchanging heat so as to minimize a sum of an enthalpy that is taken out of the regenerator as CO 2 gas accompanying steam and an enthalpy of the lean solvent after heat exchange with the rich solvent in the heat exchanger.
1. A CO 2 recovery method, for a CO 2 absorber that brings flue gas containing CO 2 into contact with a CO 2 absorbent to reduce the CO 2 contained in the flue gas, and a regenerator that reduces CO 2 contained in rich solvent absorbing CO 2 in the CO 2 absorber to regenerate the rich solvent, so that lean solvent from which the CO 2 is reduced in the regenerator is reused in the CO 2 absorber, the method comprising the steps of:
allowing the rich solvent to exchange heat with the lean solvent; and
controlling to extract part of the rich solvent to allow the part to bypass the heat exchanger, and to be supplied into a top of the regenerator without exchanging heat so as to minimize a sum of an enthalpy (E1) that is taken out of the regenerator as CO 2 gas accompanying steam and an enthalpy (E2) that is a result of subtracting an enthalpy of the rich solvent before heat exchange in the heat exchanger from an enthalpy of the lean solvent after the heat exchange;
characterized in that the controlling step includes adjusting the amount of the rich solvent to be split under an instruction of a controller by adjusting an adjusting valve provided on a split rich solvent supplying line based on information obtained by a plurality of sensors for detecting at least temperatures provided on a rich solvent supplying line and a lean solvent supplying line, respectively, and a flow meter provided on the split rich solvent supplying line upstream of the adjusting valve so as to approximate a temperature difference ΔTa between the rich solvent and the lean solvent at an entering side of the heat exchanger and a temperature difference ΔTG between the rich solvent and the lean solvent at an exiting side of the heat exchanger.
2. The CO 2 recovery method according to claim 1 further comprising allowing the part of the rich solvent that has bypassed the heat exchanger and been guided into the top of the regenerator to exchange heat in an upper section of the regenerator.
3. The CO 2 recovery method according to claim 1 further comprising allowing the part of the rich solvent that has bypassed the heat exchanger to exchange heat with the CO 2 gas accompanying steam extracted from the regenerator.