Evaporative concentration apparatus for waste water

Abstract: The present invention provides an evaporative concentration apparatus for waste water having an evaporating vessel 2 for evaporatively concentrating waste water and a heater 3 for circularly heating an in-vessel liquid in the evaporating vessel 2, in which the whole or part of thermal energy of generated steam 6 discharged from the evaporating vessel 2 is recovered by an absorption heat pump 29, and the thermal energy is supplied to the heater 3. According to the present invention, evaporative concentration can be effected efficiently in the evaporating vessel by effectively utilizing the thermal energy of generated steam, and also the operation of evaporative concentration apparatus can be performed stably by stably securing heating steam quantity.

Description: 1. FIELD OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to an evaporative concentration apparatus for waste water and, more particularly, to an evaporative concentration apparatus for waste water in which evaporative concentration of flue gas desulfurization waste water discharged from a flue gas desulfurization plant can be carried out very efficiently and stably, and a small-scale facility and the like are possible. A conventional evaporative concentration apparatus and a treatment system using the apparatus will be described below with reference to FIG. 2. Waste water 1 is introduced into an evaporating vessel 2 or into an inlet line of a heater 3 for a concentrated liquid 9, and mixed with an in-vessel liquid. The mixed in-vessel liquid is drawn from the lower part of the evaporating vessel 2 by means of a circulating pump 10 and sent to the heater 3 as the concentrated liquid 9, and a surplus concentrated liquid 12 is sent to a concentrated liquid tank 11. The concentrated liquid 12 sent to the concentrated liquid tank 11 is further treated by a solidifier 14 as a concentrated liquid 12b, and discharged to the outside of the system as a harmless solid matter 15. Also, generated steam 6 discharged by the evaporation of the in-vessel liquid is sent to a cooler 7. The concentrated liquid 9 sent to the heater 3 is heated while passing through a heating tube in the heater 3. The heater 3 is a multitubular cylindrical heat exchanger, in which heating steam 4 introduced to a shell of the heater 3 is condensed by the absorption of latent heat caused by heat exchange, and discharged to the outside of the system as condensate 5 through a steam trap. The concentrated liquid 9 having passed through the heater 3 is allowed to flow back to the evaporating vessel 2, and the evaporative concentration is repeated. The generated steam 6 generated in the evaporating vessel 2 is sent to the cooler 7, and cooled into condensed water 8 in a shell of the cooler 7. Cooling water (cold) passes through a cooling tube of the cooler 7. After the cooling water (cold) cools the generated steam 6 by heat exchange, the cooling water is discharged to the outside of the cooler as cooling water (warm). Thereafter, the cooling water (warm) is cooled into cold water (cold) again by a cooling tower or the like, and used in a circulating manner. Noncondensable gas generated in the cooler 7 is sucked by a vacuum pump 13 and discharged to the atmosphere. Here, the noncondensible gas means a gas that is not liquefied by cooling. Desulfurization waste water 1 is saturated with gypsum, so that the temperature of the heating steam 4 must be not higher than 75°C to prevent scale generation. Therefore, the heating steam 4 must be low-temperature steam. Also, the generated steam 6 generated from the evaporating vessel 2 condenses in the cooler, and is recovered to a desulfurizer as condensed water 8. According to the above-described prior art, the waste water in the evaporating vessel 2 is heated by the heat of the heating steam sent from the heater 3. The generated steam 6 heated in the evaporating vessel 2 is condensed by cooling water in the cooler 7 by heat exchange, and the exchanged heat is dissipated to the atmosphere as heat of evaporation in a cooling tower. In other words, most the heat of the heating steam is thrown away to the atmosphere as heat of evaporation in a cooling tower. Also, the prior art has a drawback in that the quantity of the heating steam sent from the heater 3 is very large. As a result, the conventional evaporative concentration apparatus has a problem in that the thermal energy supplied to the heater 3 as steam is discharged to the atmosphere, so that new thermal energy is required to send the steam 4 to the heater 3 again. Also, there arises a problem in that when the heating steam cannot be supplied sufficiently to the heater 3, the evaporative condensing capacity in the evaporating vessel 2 decreases, and the operation of the evaporative concentration apparatus becomes unstable, so that the evaporative concentration ratio of waste water cannot be kept constant. WO9720606 discloses amethod for purifying water, wherein water to be purified is sent into an evaporator, causing heating thereof and at least partial transformation into steam with consequent concentration of the liquid phase. The steam is then compressed and sent to a heatexchanger so as to give up its latent heat to the incoming water, with consequent condensation of the steam. The concentrated liquid phase and the condensed steam are drawn off for subsequent re-use. In particular, WO9720606 discloses an evaporative concentration apparatus for waste water and comprising an evaporating vessel for evaporatively concentrating waste water, a heater for circularly heating an in-vessel liquid in said evaporating vessel, extracting means for extracting generated steam from the evaporating vessel, and heat-exchanging means coupled to the extracting means for recovering the whole or part of thermal energy of generated steam discharged from said evaporating vessel and supplying said thermal energy supplied to said heater. 2. OBJECT AND SUMMARY OF THE INVENTION In view of the above problems, the inventors made studies earnestly to develop an evaporative concentration apparatus for desulfurization waste water, in which evaporative concentration can be effected efficiently in an evaporating vessel by effectively utilizing the thermal energy of generated steam, and also the operation of evaporative concentration apparatus can be performed stably by stably securing heating steam quantity. As a result, the inventors found that such problems could be solved by an evaporative concentration apparatus as recited by claim 1. Here, it is preferable that the absorption heat pump use water (H 2 O) as a refrigerant and lithium bromide (LiBr) solution as an absorbent (absorbing liquid), and include an evaporator for evaporating a refrigerant by the thermal energy from the generated steam, an absorber for absorbing the refrigerant steam in the absorbent, and a regenerator for making the absorbent concentrated by evaporating the refrigerant from the absorbent by using a driving heat source so as to be made reusable in the absorber. Also, the absorption heat pump may be provided with a condenser for heating circulating warm water again by using the refrigerant steam generated in the regenerator. Preferably, the driving heat source should be steam, or fuel combustion direct fire or combustion gas, and the pressure in the evaporating vessel should be lower than the atmospheric pressure. The evaporative concentration apparatus in accordance with the present invention is most effective in the case where the waste water evaporatively concentrated by the evaporating vessel is wet type desulfurization waste water when sulfur oxides in combustion exhaust gas of coal or oil are removed. According to the evaporative concentration apparatus in accordance with the present invention, the heating steam quantity necessary for evaporative concentration of waste water can be decreased significantly as compared with the conventional apparatus. Also, the capacity of cooler and cooling tower facility necessary for condensation of generated steam from the evaporating vessel can be reduced significantly as compared with the conventional apparatus. Further, according to the apparatus of the present invention, the condensate of steam of driving heat source is clean without being polluted, so that it can be sent back to a steam generating plant for reuse. 4. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an arrangement view showing one embodiment of an evaporative concentration apparatus for waste water in accordance with the present invention; and FIG. 2 is an arrangement view of a conventional evaporative concentration apparatus for waste water. In the drawings, reference numeral 1 denotes desulfurization waste water, 2 denotes an evaporating vessel, 3 denotes a heater, 4 denotes steam, 5 denotes condensate, 6 denotes generated steam, 7 denotes a cooler, 8a and 8b denote condensed water, 9 denotes concentrated liquid, 10 denotes a circulating pump, 11 denotes a concentrated liquid tank, 12 and 12b denote concentrated liquid, 13a denotes a vacuum pump, 13b denotes a pump, 14 denotes a solidifier, 15 denotes a solid matter, 16 denotes a condensed water tank, 17a denotes cooling water (cold), 17b denotes cooling water (warm), 18 denotes an evaporator, 19 denotes an absorber, 20 denotes a regenerator, 21 denotes plant steam, 22 denotes condensate, 23 denotes heated water, 24 denotes a circulating water tank, 25a and 25b denote circulating warm water, 26a and 26b denote pumps, 27 denotes circulating warm water, 28 denotes a condenser, and 29 denotes an absorption heat pump. 5. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS An evaporative concentration apparatus in accordance with the present invention and a treatment system using the concentration apparatus will be described below with reference to FIG. 1. In the evaporative concentration apparatus shown in FIG. 1, unlike the conventional apparatus shown in FIG. 2, the whole or part of thermal energy of generated steam discharged from an evaporating vessel is recovered by an absorption heat pump, and the thermal energy is supplied to a heater. In this embodiment, as explained in FIG. 2 regarding the prior art, waste water 1 is introduced into an evaporating vessel 2 and mixed with an in-vessel liquid. The mixed in-vessel liquid is heated by a circulating liquid sent from a heater 3, and part of water is evaporated and concentrated. The concentrated in-vessel liquid is drawn from the lower part of the evaporating vessel 2 by means of a circulating pump 10, and sent to the heater 3 as a concentrated liquid 9. A surplus concentrated liquid 12 is discharged to the outside of the system, and treated into a harmless solid matter by a solidifier 14 or the like. The whole or part of generated steam 6 discharged by the evaporation of in-vessel liquid is sent to an absorption heat pump 29, and other part thereof is sent to a cooler 7. The concentrated liquid 9 sent to the heater 3 is heated by heat exchange while passing through a heating tube of the heater 3. In the heater 3, for which a multitubular cylindrical heat exchanger is usually used, circulating warm water (warm) 25a introduced to a shell of the heater 3 is cooled by the absorption of latent heat caused by heat exchange, turning to circulating warm water (cold) 25b. Most of the circulating warm water (cold) 25b is sent to the absorption heat pump 29, and other part thereof is sent to a steam generating plant. After the concentrated liquid 9 having passed through the heater 3 is allowed to flow back to the evaporating vessel, the evaporative concentration is repeated. Here, the circulating warm water 25a supplied to the heater 3 should preferably be warm water having a saturation temperature of 70 to 80°C. In the above treatment process, the operating conditions in the evaporating vessel 2 are set as follows: Evaporation temperature Normally 45 to 90°C Preferably 50 to 70°C Evaporated steam pressure Normally 70 to 530 Torr (9.33 to 70.66 kPa) Preferably 90 to 190 Torr (12.00 to 25.33 kPa) For example, if the evaporation temperature is lower than 45°C, the interior of the evaporating vessel 2 must be made high vacuum, so that there arises a problem in that a high-performance vacuum pump is needed, which is uneconomical. If it exceeds 90°C, there is a drawback in that gypsum scale increases, and the calorie for heating during the evaporative concentration increases. In the present invention, the whole or part of the generated steam 6 generated in the evaporating vessel 2 is sent to the absorption heat pump 29. The absorption heat pump 29, which usually uses water as a refrigerant and lithium bromide solution as an absorbent, includes a refrigerant evaporator 18 for evaporating a refrigerant by the thermal energy from the generated steam 6, an absorber 19 for absorbing refrigerant steam in the absorbent, and regenerator 20 for making the absorbent concentrated by evaporating the refrigerant from the absorbent so as to be made reusable in the absorber. Also, it is preferable that the absorption heat pump 29 be provided with a condenser 28 for heating circulating warm water 27 again by the refrigerant steam generated in the regenerator. In FIG. 1, The whole or part of the generated steam 6 is introduced to the evaporator 18 in the absorption heat pump 29. In the evaporator 18, water is heated by the generated steam 6, refrigerant steam at a low temperature is generated, and the refrigerant steam is supplied to the absorber 19. By this heat exchange caused by the movement of the refrigerant steam in the absorption heat pump 29, the introduced generated steam 6 dissipates thermal energy for the refrigerant evaporation and is condensed in the evaporator 18, and then is discharged from the evaporator 18 as a condensed liquid 8b. The aforesaid absorber 19 is supplied with low-pressure refrigerant steam generated in the evaporator 18 and a concentrated absorbent from the regenerator 20. In this absorber 19, the concentrated absorbent of lithium bromide absorbs the low-pressure refrigerant steam and turns to a dilute solution, and the absorption heat is discharged. That is, the refrigerant steam is absorbed in a concentrated absorbent with high lithium bromide concentrations while holding steam enthalpy. The aforesaid dilute solution with low lithium bromide concentrations is sent to the regenerator 20, and heated by plant steam 21 in the regenerator 20. By this heating, the refrigerant steam (water vapor) in the dilute solution is evaporated, and supplied to the condenser 28. Also, the dilute solution is concentrated into a concentrated absorbent with high lithium bromide concentrations. This concentrated absorbent is supplied again to the absorber 19. The circulating warm water 27 is introduced into the absorber 19 and heated by the absorption heat, and further is introduced into the condenser 28, where it is heated again by the refrigerant steam. Then, the circulating warm water 27 is discharged from the condenser 28 as high-temperature heated water 23. The thermal energy given to the heated water 23 usually reaches about 1.7 times the calorie of the plant steam 21, and the temperature thereof usually reaches 70 to 90°C depending on the quantity and temperature of the heated water 23. Here, the refrigerant steam (water vapor) having heated the circulating warm water 27 in the condenser 28 is condensed into water, and supplied to the evaporator 18 as necessary. Also, the dilute solution having absorbed the low-pressure refrigerant steam in the absorber 19 is supplied to the regenerator 20. Thus, the heated water 23 heated two times in the absorption heat pump is sent to a circulating water tank 24, and combined with condensate 22 of the plant steam 21 in the tank 24. The warm water in the circulating water tank 24 is sent to the heater 3 as the circulating warm water (warm) 25a by a pump 26a. The circulating warm water 25a introduced into the heater 3 is cooled by the absorption of latent heat caused by heat exchange, and flows out as the circulating warm water (cold) 25b. Part thereof is sent to the absorption heat pump 29 as the circulating warm water 27, and other part is sent to the steam generating plant. On the other hand, other part of the generated steam 6 generated in the evaporating vessel 2 is sent to the cooler 7, and cooled into condensed water 8a in the shell of the cooler 7. In a cooling tube of the cooler 7, usually cooling water (cold) flows through, cools the generated steam 6 by heat exchange, and then is discharged to the outside of the apparatus as cooling water (warm) 17b. Thereafter, the cooling water (warm) 17b is cooled into the cooling water (cold) again by a cooling tower or the like, by which it is used for circulation. The noncondensible gas generated in the cooler 7 is sucked by a vacuum pump 13a, and discharged to the atmosphere. Here, the noncondensible gas means a gas that is not liquefied by cooling. The condensed water 8a sent from the cooler 7 is introduced into a condensed water tank 16 together with the condensed water 8b sent from the absorption heat pump 29. In this condensed water tank 16 as well, the generated noncondensible gas is sucked by the vacuum pump 13a and discharged to the atmosphere. The condensed water in the condensed water tank 16 is sent to a desulfurizer by means of a pump 13b. The evaporative concentration apparatus for waste water in accordance with the present invention is not limited to the above embodiment, and can be modified variously in the scope of the technical concept of the present invention. In the evaporative concentration apparatus for waste water in accordance with the present invention, evaporative concentration can be effected efficiently in an evaporating vessel by effectively utilizing the thermal energy of generated steam, and also the operation of evaporative concentration apparatus can be performed stably by stably securing heating steam quantity. That is, according to the present invention, the thermal energy obtained from generated steam is taken out to heat circulating warm water, by which heating steam used for a heater can be supplied efficiently in large quantities. Thereupon, new heating steam quantity necessary for evaporative concentration of waste water can be decreased significantly (dl 40 to 50%) as compared with the conventional apparatus. Also, the evaporative concentration apparatus can be operated stably, and the evaporative concentration ratio of waste water can be kept constant. Further, the capacity of cooler and cooling tower facility necessary for condensation of generated steam from an evaporating vessel can be reduced significantly (dl 40 to 50%) as compared with the conventional apparatus. Further, according to the apparatus of the present invention, the condensate of steam of driving heat source is clean without being polluted, so that it can be sent back to a steam generating plant for reuse.

Claims: An evaporative concentration apparatus for waste water; the apparatus comprising an evaporating vessel (2) for evaporatively concentrating waste water, a heater (3) for circularly heating an in-vessel liquid in said evaporating vessel (2), and a conduit for extracting generated steam (6) from the evaporating vessel (2), the apparatus being characterized by an absorption heat pump (29) coupled to the conduit for recovering at least part of thermal energy of generated steam discharged from said evaporating vessel (2) and for supplying said thermal energy supplied to said heater (3); dl said conduit being able to feed at least part of the extracted generated steam (6) to the absorption heat pump (29) and other part thereof to a cooler (7); said heater (3) comprising a heat exchanger, through which is fed the in-vessel liquid of said evaporating vessel (2) and warm water (25); and feeding means are coupled for sending to the heat exchanger most of the water (25b) coming from the heat exchanger to the absorption heat pump (29) for being heated by the extracting generated steam (6), and other part thereof to a steam generating plant. Apparatus according to claim 1, and comprising a common condensed water tank (16) for collecting the condensed water (8a) from the cooler (7) and the condensed water (8b) from the absorption heat pump (29). Apparatus according to claim 2, wherein sucking means (13) are provided for sucking and discharging to the atmosphere the noncondensible gas generated in the cooler (7) and the generated noncondensible gas present in the condensed water tank (16). Apparatus according to claim 2 or 3, wherein sending means (13b) are provided for sending the condensed water in the condensed water tank (16) to a desulfurizer. Apparatus according to any preceding claims, wherein said absorption heat pump (29) includes an evaporator (18) for evaporating a refrigerant by the thermal energy from said generated steam (6), an absorber (19) for absorbing said refrigerant steam in the absorbent, and a regenerator (20) for making the absorbent concentrated by evaporating the refrigerant from said absorbent by using a steam so as to be made reusable in said absorber (19). Apparatus according to claim 5, wherein said absorption heat pump (29) uses water as a refrigerant and lithium bromide solution as an absorbent. Apparatus according to claim 5 or 6, wherein an outlet of said regenerator (20) is connected to the heater (3) via a circulating water tank (24) in order to supply the thermal energy of condensed water obtained by condensing said steam by using said absorption heat pump (29) to said heater (3). Apparatus according to claim 7, wherein the outlet of said regenerator (20) is connected to a circulating water tank (24); connecting means being provided for sending to the circulating water tank (24) the water (25b) coming from the heat exchanger after being passed through the absorption heat pump (29); pump means (26a) being provided for sending the water in the circulating water tank (24) to the heater (3) Apparatus according to anyone of the previous claims, wherein the pressure in said evaporating vessel (2) is lower than the atmospheric pressure. Apparatus according to any one of the previous claims, wherein the waste water evaporatively concentrated by said evaporating vessel (2) is wet type desulfurization waste water when sulfur oxides in combustion exhaust gas of coal or oil are removed.

Inventors: ENDO ATSUMASA, KAMIYOSHI HIDEKI, OCHI EIJI, SHINODA TAKEO, YOSHIOKA ATSUSHI, ENDO, ATSUMASA, KAMIYOSHI, HIDEKI, OCHI, EIJI, SHINODA, TAKEO, YOSHIOKA, ATSUSHI, Endo, Atsumasa, Shinryo High Technologies Ltd., Kamiyoshi, Hideki, Shinryo High Technologies Ltd., Ochi, Eiji, Mitsubishi Heavy Industries, Ltd., Shinoda, Takeo, Mitsubishi Heavy Industries, Ltd., Yoshioka, Atsushi, Mitsubishi Heavy Industr., Ltd.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: C02F1
IPC codes: B01D3, F25B29, B01D53, C02F1, F25B27, B01D1, F25B15