System and method for improving water quality of dehydration tower in purified terephthalic acid device

1 . A treatment system for improving the water quality of a dehydration tower in a purified terephthalic acid device, the system comprising a dehydration washing device, a tail gas condensation device communicating with a top of the dehydration washing device, and a water separation device communicating with the tail gas condensation device, wherein:

the dehydration washing device comprises a first-stage purified water washing unit located at the top of the dehydration washing device, a second-stage concentrated water washing unit located in the middle of the dehydration washing device, and/or a third-stage refined mother liquor washing unit located at a lower portion of the dehydration washing device;

the tail gas condensation device comprises oxidized tail gas condensers;

the tail gas condensation device is connected with a first high-temperature condensed liquid tank for containing a first condensed liquid obtained after a first heat exchange by the oxidized tail gas condensers in the system, a second condensed liquid tank for containing a second condensed liquid obtained after a second heat exchange, and a second vapor channel for exporting vapor; and

the water separation device comprises multi-effect evaporation units for purifying and separating the second condensed liquid, as well as a purified water outlet and a concentrated water outlet, wherein the multi-effect evaporation units comprise a first-effect evaporation unit and a second-effect evaporation unit, the purified water outlet communicates to the first-stage purified water washing unit through a purified water pipeline, the second condensed liquid tank communicates to the bottom of the first-effect evaporation unit through a second condensed liquid pipeline to separate the second condensed liquid, and the second vapor channel extends into the first-effect evaporation unit through a second vapor pipeline to provide a heat source for heat exchange during the separation of the second condensed liquid;

the concentrated water outlet communicates to the second-stage concentrated water washing unit through a concentrated water pipeline; and

a purified water heat exchanger is disposed on the purified water pipeline, the first high-temperature condensed liquid tank conducts heat exchange by the purified water heat exchanger through a high-temperature condensed liquid pipeline, a concentrated water heat exchanger is disposed on the concentrated water pipeline, and the first high-temperature condensed liquid tank conducts heat exchange by the concentrated water heat exchanger through a second high-temperature condensed liquid pipeline.

2 . The treatment system for improving the water quality of a dehydration tower in a purified terephthalic acid device according to claim 1 , wherein the tail gas condensation device comprises a first oxidized tail gas condensation system comprising one or more stages of the oxidized tail gas condensers that communicate in sequence and a second oxidized tail gas condensation system located downstream of the first oxidized tail gas condensation system and comprising one or more further stages of the oxidized tail gas condensers that communicate in sequence, each stage of the one or more stages of the oxidized tail gas condensers in the first oxidized tail gas condensation system communicates to the first high-temperature condensed liquid tank for containing the first condensed liquid obtained after heat exchange by the one or more stages of oxidized tail gas condensers in the system, and each stage of the one or more further stages of the oxidized tail gas condenser in the second oxidized tail gas condensation system communicates to the second condensed liquid tank for containing the second condensed liquid obtained after the heat exchange by the oxidized tail gas condensers in the system.

3 . The treatment system for improving the water quality of a dehydration tower in a purified terephthalic acid device according to claim 1 , wherein the dehydration washing device is a dehydration washing tower, the bottom of the dehydration washing tower communicates with a purified terephthalic acid (PTA) oxidation reactor, and a concentrated reaction liquid after washing is returned to the oxidation reactor to continue to react.

4 . The treatment system for improving the water quality of a dehydration tower in a purified terephthalic acid device according to claim 1 , wherein the first-stage purified water washing unit, the second-stage concentrated water washing unit and the third-stage refined mother liquor washing unit are respectively provided with spray heads to wash tail gas by spraying.

5 . The treatment system for improving the water quality of a dehydration tower in a purified terephthalic acid device according to claim 2 , wherein the first oxidized tail gas condensation system comprises 1-4 stages of oxidized tail gas condensers, and/or the second oxidized tail gas condensation system comprises 1-4 stages of oxidized tail gas condensers.

6 . The treatment system for improving the water quality of a dehydration tower in a purified terephthalic acid device according to claim 1 , wherein the water separation device is a water separation tower, the multi-effect evaporation units for purifying the second condensed liquid are disposed in a tower body, a final-effect condensation unit is disposed below the multi-effect evaporation units, and a vacuum pump is connected to the bottom of the final-effect condensation unit.

7 . The treatment system for improving the water quality of a dehydration tower in a purified terephthalic acid device according to claim 6 , wherein:

the first-effect evaporation unit comprises a second condensed liquid inlet and a first heat exchange chamber, an upper portion of the first heat exchange chamber is connected with a first vapor passage for a vapor phase to enter the second-effect evaporation unit and a first downcomer for a liquid phase to flow to the second-effect evaporation unit, and the bottom of the first downcomer is provided with a first device;

the second-effect evaporation unit comprises a second heat exchange chamber, an upper portion of the second heat exchange chamber is provided with a second vapor passage for a vapor phase to pass through after a heat exchange with condensed water and a second downcomer for a liquid phase to pass through, and the bottom of the second downcomer is provided with a second device;

a lower portion of the second heat exchange chamber is provided with a first condensed liquid channel for the condensed water to flow out of the second heat exchange chamber after the heat exchange, and the bottom of the first condensed liquid channel is provided with a first U-shaped tube;

and the first device is located between the second heat exchange chamber and a second demister.

8 . A method for improving the water quality of a dehydration tower in a purified terephthalic acid device according to claim 1 , the method comprising the following steps:

1) introducing, after reaction tail gas comes out from the bottom of an oxidation reactor, the reaction tail gas into a lower portion of the third-stage refined mother liquor washing unit, enabling the reaction tail gas to firstly pass sequentially through the third-stage refined mother liquor washing unit to be subjected to spray washing with a refined mother liquor, the second-stage concentrated water washing unit to be subjected to spray washing with concentrated watery and the first-stage purified water washing unit to be subjected to spray washing with purified water;

2) enabling, after the reaction tail gas washed with the dehydration washing device comes out from a top of the tail gas condensation device, the reaction tail gas to firstly enter a first oxidized tail gas condensation system to form the first condensed liquid, which flows into the first high-temperature condensed liquid tank through a pipeline; and after a portion of the reaction tail gas is condensed through the first oxidized tail gas condensation system, enabling a remaining uncondensed portion of the reaction tail gas to enter a second oxidized tail gas condensation system to form the second condensed liquid, then enabling the second condensed liquid to enter the second condensed liquid tank through a pipeline, and discharging vapor that is not condensed;

3) enabling the second condensed liquid to enter a water separation tower to be continuously separated and purified via the following sub-steps:

turning on a vacuum pump located at the bottom of the water separation tower,

enabling the second condensed liquid to enter a first heat exchange chamber of the first-effect evaporation unit from a second condensed liquid inlet to be partially evaporated,

enabling the second vapor to enter a pipeline in the first heat exchange chamber from the second vapor pipeline,

enabling the second vapor and the second condensed liquid to exchange heat in the first heat exchange chamber,

enabling a further part of the second condensed liquid to be volatilized and enter a first vapor passage upwards as a first-effect vapor,

enabling the first-effect vapor to enter a pipeline in the second-effect evaporation unit through the first vapor passage to continue to be used as a heat source to exchange heat with a remaining liquid phase of the second condensed liquid flowing out of a first downcomer,

enabling heat of the first-effect vapor to flow to the remaining liquid phase of the second condensed liquid,

enabling the first-effect vapor to be cooled and condensed to form condensed water that flows out of a first condensed liquid channel,

enabling a part of the condensed liquid water to be gathered in a first U-shaped tube and finally flow to a purified water storage area at the bottom of the water separation tower; and

enabling a part of the second condensed liquid that is not evaporated to enter the first downcomer and then enter the second-effect evaporation unit to continue to be evaporated or stay at a first device, wherein the water separation device is the water separation tower; and

4) after separation and purification of the second condensed liquid in step 3, discharging purified water from a purified water outlet of the purified water storage area through the purified water pipeline, exchanging heat through the purified water heat exchanger disposed on the purified water pipeline to increase the temperature of the purified water, and then spraying the reaction tail gas with the purified water as a washing liquid of the first-stage purified water washing unit; and discharging the concentrated water from the concentrated water outlet through the concentrated water pipeline, and performing spray washing on the reaction tail gas with the concentrated water as a washing liquid of the second-stage concentrated water washing unit.