System for chemically absorbing carbon dioxide in combustion exhaust gas

Abstract

A carbon dioxide (CO.sub.2) chemical absorption system comprising: a CO.sub.2 absorption column for separating CO.sub.2 from combustion exhaust gas by absorbing the CO.sub.2 in the combustion exhaust gas with a CO.sub.2 absorbing liquid mainly composed of an aqueous alkanolamine solution; a regeneration column for regenerating the CO.sub.2 absorbing liquid by desorbing CO.sub.2 gas from the CO.sub.2 absorbing liquid that has absorbed CO.sub.2; a condenser for condensing water vapor entrained in the desorbed CO.sub.2 gas discharged from the top of the regeneration column, thereby obtaining reflux water; a pipe for returning all or part of the reflux water obtained by the condenser to the top of the regeneration column, and dispersing the reflux water in the regeneration column; a collection plate for collecting the reflux water dispersed in an upper portion of a packed bed in the regeneration column; a pipe for sending the regenerated CO.sub.2 absorbing liquid from the bottom of the regeneration column to the top of the absorption column; and a pipe for joining the reflux water collected by the collection plate into the pipe for sending the regenerated CO.sub.2 absorbing liquid.

Claims

1. A carbon dioxide (CO.sub.2) chemical absorption system comprising: a CO.sub.2 absorption column for separating CO.sub.2 from combustion exhaust gas by absorbing the CO.sub.2 in the combustion exhaust gas with a CO.sub.2 absorbing liquid mainly composed of an aqueous alkanolamine solution; a regeneration column for regenerating the CO.sub.2 absorbing liquid by desorbing CO.sub.2 gas from the CO.sub.2 absorbing liquid that has absorbed CO.sub.2, wherein the regeneration column comprises a packed bed, a water washing part over the packed bed and a reboiler, and the CO.sub.2 absorbing liquid that has absorbed CO.sub.2 is fed to a top portion of the packed bed; a condenser for condensing water vapor entrained in the desorbed CO.sub.2 gas discharged from the top of the regeneration column, thereby obtaining reflux water; a pipe for returning all or part of the reflux water obtained by the condenser to the top of the regeneration column, and for dispersing the reflux water to the water washing part in the regeneration column; a collection plate for collecting the reflux water dispersed to the water washing part in the regeneration column, and for preventing the dispersed reflux water from flowing into the packed bed; a pipe for sending the regenerated CO.sub.2 absorbing liquid from the bottom of the regeneration column to the top of a packed bed in the absorption column; and a pipe for joining the reflux water collected by the collection plate into the pipe for sending the regenerated CO.sub.2 absorbing liquid.

2. A carbon dioxide (CO.sub.2) chemical absorption system comprising: a CO.sub.2 absorption column for separating CO.sub.2 from combustion exhaust gas by absorbing the CO.sub.2 in the combustion exhaust gas with a CO.sub.2 absorbing liquid mainly composed of an aqueous alkanolamine solution; a regeneration column for regenerating the CO.sub.2 absorbing liquid by desorbing CO.sub.2 gas from the CO.sub.2 absorbing liquid that has absorbed CO.sub.2, wherein the regeneration column comprises a packed bed, a water washing part over the packed bed and a reboiler, and the CO.sub.2 absorbing liquid that has absorbed CO.sub.2 is fed to a top portion of the packed bed; a condenser for condensing water vapor entrained in the desorbed CO.sub.2 gas discharged from the top of the regeneration column, thereby obtaining reflux water; a pipe for returning a part of the reflux water obtained by the condenser to the top of the regeneration column, and for dispersing the reflux water to the water washing part in the regeneration column; an instrument for measuring the temperature in the top portion of the packed bed in the regeneration column, and for controlling the flow rate of the reflux water dispersed to the water washing part in the regeneration column so that the temperature is a predetermined value; a pipe for sending the regenerated CO.sub.2 absorbing liquid from the bottom of the regeneration column to the top of a packed bed in the absorption column; and a pipe for joining the remaining reflux water obtained by the condenser into the pipe for sending the regenerated CO.sub.2 absorbing liquid.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 an apparatus flow diagram showing one embodiment of a CO.sub.2 chemical absorption system in the present invention.

(2) FIG. 2 an apparatus flow diagram showing another embodiment of a CO.sub.2 chemical absorption system in the present invention.

(3) FIG. 3 an apparatus flow diagram showing the structure of a conventional CO.sub.2 chemical absorption system.

DESCRIPTION OF EMBODIMENTS

(4) FIG. 1 shows one embodiment of the CO.sub.2 chemical absorption system according to the present invention. The difference from the conventional system shown in FIG. 3 is that a reflux water collection plate 70 is provided directly below the water washing part packed bed 43 in the regeneration column 40 so that the liquid collected by the reflux water collection plate 70 is returned to the pipe 66 from the regeneration column 40 toward the absorption column 20.

(5) The absorbing liquid vapor fed from the reboiler 60 passes through an absorbing liquid collection plate 51, and is sent to the packed bed 41. In the packed bed 41, the absorbing liquid vapor and a CO.sub.2-rich liquid are brought into direct contact to desorb CO.sub.2 gas from the CO.sub.2-rich liquid. Water vapor entrained in the desorbed CO.sub.2 gas passes through the reflux water collection plate 70 and is fed to the water washing part 43, wherein the water vapor is cooled and amine mist is removed. The mist is further removed by the mist eliminator 45, and the gas is discharged from the regeneration column 40. The discharged gas is cooled by the condenser 47, and separated into gas and condensed water. In the reflux water drum 48, the CO.sub.2 gas is sent out of the system, and the condensed water (reflux water) is returned to the system. The reflux water separated in the reflux water drum 48 passes through the pump 50, and is dispersed from the water washing feed part 44 in the regeneration column. The reflux water is used to cool the gas and to remove the amine mist in the water washing part 43. Thereafter, the reflux water is collected by the collection plate 70 provided above the packed bed 41 (preferably in a position higher than the feed part 42). The collected reflux water is joined to the absorbing liquid in the pipe 66 located before the cooler 30. The water balance of the entire system is maintained in this manner. Here, a pipe 71 extending from the reflux water collection plate 70 to the joining part of the reflux water and the lean liquid is optionally provided with a pump 73, a resister (e.g., a valve 74), and a liquid storage drum. In this embodiment, the reflux water and the absorbing liquid are joined before they reach the cooler 30; however, the reflux water may be joined to the absorbing liquid at any place in a lean liquid line extending from the outlet of the reboiler 60 to the inlet of the absorption column 20.

(6) FIG. 2 shows another embodiment of the CO.sub.2 chemical absorption system according to the present invention. The differences from the conventional system shown in FIG. 3 are that as a feed pipe for the reflux water from the CO.sub.2 collection drum 48, a line 76 is provided, in addition to the feed line to the water washing part packed bed 43, so as to feed the reflux water to the pipe 66 before the cooler 30 without passing through the packed bed 41; and that a thermometer 72 is provided in the upper portion of the packed bed 41, and valves 74 and 75 are adjusted to control the amount of reflux water fed to the line 76 and the water washing feed part 44 so that the temperature measured by the thermometer is a predetermined value.

(7) The absorbing liquid vapor fed from the reboiler 60 passes through the absorbing liquid collection plate 51, and is sent to the packed bed 41. In the packed bed 41, the absorbing liquid vapor and a CO.sub.2-rich liquid are brought into direct contact to desorb CO.sub.2 gas from the CO.sub.2-rich liquid. Water vapor entrained in the desorbed CO.sub.2 gas is fed to the water washing part 43, wherein the water vapor is cooled and amine mist is removed. The mist is further removed by the mist eliminator 45, and the gas is discharged from the regeneration column 40. The discharged gas is cooled by the condenser 47, and separated into gas and condensed water. In the reflux water drum 48, the CO.sub.2 gas is sent out of the system, and the condensed water (reflux water) is returned to the system. In this case, the liquid temperature is measured by the thermometer 72 provided in the upper portion of the packed bed 41, and the amount of reflux water dispersed from the water washing feed part 44 is controlled so that the liquid temperature is 100 C., for example. The excess reflux water is returned to the absorbing liquid line 66 via the line 76, without passing through the packed bed 41. The water balance of the entire system is maintained in this manner. Here, the pipe extending from the reflux water drum 48 to the water washing feed part 44, and the pipe 76 extending from the reflux water drum 48 to the joining part of the reflux water and the lean liquid are optionally provided with a resister (e.g., a valve) and a liquid storage drum. In this embodiment, the reflux water and the absorbing liquid are joined before they reach the cooler 30; however, the reflux water may be joined to the absorbing liquid at any place in the lean liquid line extending from the outlet of the reboiler 60 to the inlet of the absorption column 20.

(8) Although a collection plate 42 is not provided in the embodiment shown in FIG. 2, the collection plate 42 may be further provided, if necessary, as in the embodiment shown in FIG. 1, so that the reflux water collected by the collection plate 42 and the reflux water the flow rate of which has been controlled by the valve 75 may be joined to the lean liquid.

REFERENCE SIGNS LIST

(9) 20: Absorbing liquid 30: Cooler 40: Regeneration column 41: Packed bed 43: Water washing part packed bed 51: Absorbing liquid collection plate 60: Reboiler 70: Reflux water collection plate 72: Thermometer 74, 75: Valves