Method and system for processing hot humid air resulting from an industrial process, prior to expelling it into the outside air, to recover water and remove the plume

Abstract

Systems and methods are disclosed for processing hot, humid air resulting from an industrial process, such as paper production. These systems and methods allow a large amount of water to be recovered from the air and the plume emitted into the environment to be reduced, all with reasonable energy consumption. The exhaust stream of air is passed through two heat exchangers, which cool the exhaust air by heating respective streams of water. The heated streams of water are routed to and cooled by an absorption cooler before being returned as input to the heat exchangers. Some embodiments may also include a scrubber, which allows direct air-water contact, positioned between the two heat exchangers. The scrubber also aids removal of pollutants. Some embodiments may mix heated outside air with the exhaust stream of air prior to discharge in order to reduce the emitted plume.

What is claimed is: 
     
         1 . A system for treating an exhaust stream of hot, humid air from an industrial process, comprising:
 a first heat exchanger receiving the exhaust stream of air from the industrial process, the first heat exchanger cooling the exhaust stream of air to a first reduced temperature by use of a first stream of cooler water, the first stream of cooler water being heated by heat exchange with the exhaust stream of air in the first heat exchanger;   a second heat exchanger in fluid communication with the first heat exchanger to receive the exhaust stream of air at the first reduced temperature and cool the exhaust stream of air to a second reduced temperature by use of a second stream of cooler water, the second stream of cooler water being heated by heat exchange with the exhaust stream of air in the second heat exchanger;   an outlet in fluid communication with the second heat exchanger to receive and discharge the exhaust stream of air at a temperature equal to or lower than the second reduced temperature; and   an absorption cooler in association with the first heat exchanger and the second heat exchanger but isolated from the exhaust stream of air that (1) receives the heated second stream of cooler water from the second heat exchanger, and (2) receives the heated first stream of cooler water from the first heat exchanger and cools them by an absorptive process with a coolant, the absorption cooler being arranged with respect to the first and second heat exchangers such that the cooled first stream of water is returned as input to the first heat exchanger and the cooled second stream of water is returned as input to the second heat exchanger;   wherein the heated first and second streams of water provide input energy in the form of heat to the absorption cooler.   
     
     
         2 . The system of  claim 1 , further comprising an outside air heating and mixing system including:
 a third heat exchanger positioned between and in fluid communication with the first heat exchanger and the second heat exchanger that accepts the exhaust stream of air from the first heat exchanger and cools it by heat exchange with a third stream of water before passing the exhaust stream of air to the second heat exchanger;   an inlet arranged to accept a stream of outside air;   a fourth heat exchanger that accepts the stream of outside air and the heated third stream of water from the third heat exchanger and heats the stream of outside air; and   a mixer positioned upstream of the outlet that receives the heated stream of outside air and mixes it with the exhaust stream of air after the exhaust stream of air is discharged from the second heat exchanger and before the exhaust stream of air reaches the outlet;   wherein the third stream of water flows in a circuit between the third and fourth heat exchangers.   
     
     
         3 . The system of  claim 2 , further comprising a fifth heat exchanger positioned between the inlet and the fourth heat exchanger, the fifth heat exchanger being in fluid communication with a condenser of the absorption cooler so as to receive a stream of water heated by the condenser and heat the outside air by direct contact heat exchange with the stream of water heated by the condenser. 
     
     
         4 . The system of  claim 2 , further comprising a scrubber disposed between and in fluid communication with the first heat exchanger and the second heat exchanger to receive the exhaust stream of air, the scrubber providing direct contact between the exhaust stream of air and scrubber fluid. 
     
     
         5 . The system of  claim 4 , wherein the scrubber removes one or more pollutants from the exhaust stream of air. 
     
     
         6 . The system of  claim 2 , further comprising a water extractor disposed between and in fluid communication with the second heat exchanger and the mixer. 
     
     
         7 . The system of  claim 1 , further comprising a scrubber disposed between and in fluid communication with the first heat exchanger and the second heat exchanger to receive the exhaust stream of air, the scrubber providing direct contact between the exhaust stream of air and scrubber fluid. 
     
     
         8 . The system of  claim 7 , wherein the scrubber removes one or more pollutants from the exhaust stream of air. 
     
     
         9 . The system of  claim 7 , further comprising a water extractor disposed between and in fluid communication with the second heat exchanger and the outlet. 
     
     
         10 . The system of  claim 9 , wherein the system reduces the temperature of the exhaust stream of air from about 250-300° C. to about 40-70° C. 
     
     
         11 . The system of  claim 10 , wherein the system reduces the water content of the exhaust stream of air from about 0.4-0.6 kilograms of water per kilogram of dry air to about 0.01-0.05 kilograms of water per kilogram of dry air. 
     
     
         12 . The system of  claim 1 , wherein heat energy from the exhaust stream of air provides substantially all of the energy to operate the system. 
     
     
         13 . The system of  claim 12 , wherein the heated first stream of water from the first heat exchanger provides an input heat for a generator of the absorption cooler and the heated second stream of water from the second heat exchanger provides an input heat for an evaporator of the absorption cooler. 
     
     
         14 . The system of  claim 1 , wherein the industrial process comprises paper manufacture. 
     
     
         15 . A method for processing an exhaust stream of hot, humid air from an industrial process prior to expelling it into outside air, comprising:
 passing the exhaust stream of air through a first heat exchanger, thereby cooling the exhaust stream of air and heating a first stream of water;   receiving the exhaust stream of air at a second heat exchanger after said passing and cooling the exhaust stream using the second heat exchanger and a second stream of water, thereby heating the second stream of water;   extracting at least a portion of the water suspended in the exhaust stream using a water extractor;   exhausting the exhaust stream to outside air; and   cooling the first and second streams of water using an absorption cooler that is isolated from the exhaust stream of air such that the cooled first stream of water is returned as input to the first heat exchanger and the cooled second stream of water is returned as input to the second heat exchanger;   wherein the heated first stream of water and the heated second stream of water provide input heat to the absorption cooler.   
     
     
         16 . The method of  claim 15 , further comprising, after passing the exhaust stream of air through the first heat exchanger, directing the exhaust stream of air through a scrubber in communication with the first heat exchanger and the second heat exchanger, the scrubber providing direct contact between the exhaust stream of air and scrubber fluid. 
     
     
         17 . The method of  claim 15 , further comprising heating outside air and mixing the heated outside air with the exhaust stream of air prior to exhausting the exhaust stream to outside air. 
     
     
         18 . The method of  claim 17 , wherein heating the outside air comprises passing the outside air through a third heat exchanger, the third heat exchanger being in fluid communication with a fourth heat exchanger in fluid communication with the first and second heat exchangers and in the path of the exhaust air, the fourth heat exchanger providing a third stream of heated water as input to the third heat exchanger. 
     
     
         19 . The method of  claim 17 , wherein heating the outside air comprises providing a third heat exchanger that draws heat from a condenser of the absorption cooler. 
     
     
         20 . The method of  claim 17 , further comprising, after passing the exhaust stream of air through the first heat exchanger, directing the exhaust stream of air through a scrubber in communication with the first heat exchanger and the second heat exchanger, the scrubber providing direct contact between the exhaust stream of air and scrubber fluid.