SYSTEM AND PROCESS FOR PREHEATING EVAPORATOR FEEDWATER

Abstract

An evaporation system employs a thermocompressor to recover heat associated with a distillate produced by an evaporator and to use the recovered heat to preheat evaporator feedwater. In one example, the thermocompressor produces a thermocompressor discharge that is directed into the deaerator, contacting and preheating the evaporator feedwater passing therethrough. In another example, the thermocompressor discharge is directed through a barometric condenser which contacts evaporator feedwater therein and condenses and in the process preheats the evaporator feedwater.

Claims

1-18. (canceled)

19. A method of pre-heating and treating evaporator feedwater comprising: directing evaporator feedwater to and through a deaerator; directing the evaporator feedwater from the deaerator to an evaporator and evaporating the feedwater to produce a distillate; flash cooling the distillate and producing flash vapor; directing motive steam into a thermocompressor and inducing the flash vapor resulting from the flash cooling of the distillate into the thermocompressor where the flash vapor mixes with the motive steam to form a thermocompressor discharge; directing the thermocompressor discharge to the deaerator; and directing the thermocompressor discharge through the deaerator and contacting the evaporator feedwater therein to preheat and deaerate the evaporator feedwater.

20. The method of claim 19 including directing the distillate to a distillate tank and flash cooling the distillate in the distillate tank.

21. The method of claim 19 including: directing the distillate to a distillate tank; employing the thermocompressor to draw a vacuum on the distillate tank; and recovering heat from the distillate by flash cooling the distillate in the distillate tank and employing at least a portion of the recovered heat to preheat the evaporator feedwater.

22. The method of claim 19 including: directing the distillate from the evaporator to a distillate tank where the distillate undergoes a pressure drop which results in the distillate flashing the vapor; and inducing the vapor from the distillate tank into a suction inlet of the thermocompressor where the vapor mixes with the steam to form the thermocompressor discharge.

23. The method of claim 22 wherein the distillate tank includes a vent and wherein the vent is operative to direct the vapor from the distillate tank into a vapor line that is operatively connected between the suction inlet of the thermocompressor and the vent.

24. The method of claim 19 further including directing steam into an inlet of the thermocompressor which induces the vapor produced by flash cooling the distillate into a suction inlet of the thermocompressor.

25. The method of claim 19 wherein the evaporator produces steam and the method includes mixing the steam produced by the evaporator with the compressor discharge prior to the compressor discharge preheating the evaporator feedwater.

26. A method of preheating and treating evaporator feedwater comprising: directing the evaporator feedwater to an evaporator and evaporating the feedwater to produce a distillate; flash cooling the distillate and producing flash vapor; directing motive steam to a thermocompressor and inducing the flash vapor resulting from the flash cooling of the distillate into the thermocompressor where the flash vapor mixes with the motive steam to form a thermocompressor discharge; prior to directing the evaporator feedwater to the evaporator, directing the evaporator feedwater to a barometric condenser; preheating the evaporator feedwater in the barometric condenser by directing the thermocompressor discharge into the barometric compressor and contacting the evaporator feedwater with the thermocompressor discharge; and directing the preheated evaporator feedwater to a deaerator and deaerating the evaporator feedwater and directing the deaerated feedwater to the evaporator.

27. The method of claim 26 further including: directing the distillate from the evaporator to a distillate tank where the distillate undergoes a pressure drop which results in the distillate flashing the vapor; and inducing the vapor from the distillate tank into a suction inlet of the thermocompressor where the vapor mixes with the steam to form the thermocompressor discharge.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a schematic illustration of an evaporation system for treating a feedwater where a thermocompressor is employed to preheat the evaporator feedwater.

[0014] FIG. 2 is a schematic illustration of a similar evaporation system where the thermocompressor is employed along with a barometric condenser to preheat evaporator feedwater.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0015] The present invention relates to a system and process for preheating evaporator feedwater, especially feedwater that is prone to scale surfaces of a heat exchanger. As described below, in one embodiment evaporator feedwater is directed into and through a deaerator 14 from which the feedwater is directed into an evaporator 12 which produces a distillate. The distillate is flash cooled and produces flash vapors that are induced into a thermocompressor or eductor 20 where the vapors mix with a motive fluid such as steam to form a thermocompressor discharge. As used herein, the term thermocompressor encompasses an eductor. The thermocompressor discharge, in one embodiment, is directed from the thermocompressor or eductor 20 to the deaerator 14 and moves through the deaerator contacting the evaporator feedwater passing therethrough. A portion of the thermocompressor discharge condenses in the deaerator and transfers its latent heat to the evaporator feedwater passing therethrough, thereby increasing the temperature of the evaporator feedwater. The remaining thermocompressor discharge strips any non-condensable gases present form the evaporator feedwater and exits the deaerator through a vent. Also discussed herein is a second embodiment where the evaporator feedwater and thermocompressor discharge are both directed to and through a barometric condenser. Here the evaporator feedwater is preheated by heat transferred from the thermocompressor discharge to the evaporator feedwater.

[0016] With particular reference to the drawings and FIG. 1, there is shown therein an evaporation system indicated generally by the numeral 10. Evaporation system 10 is operative to treat various feedwater or wastewater streams. Evaporation system 10 includes the evaporator 12. Various types of evaporators can be employed. In one embodiment, the evaporator 12 may comprise a vertical falling film evaporator that produces steam and a concentrate. The steam produced condenses to form a distillate that can be used in various ways.

[0017] Upstream of the evaporator 12 is a deaerator 14. Deaerator 14 is employed to strip non-condensable gases from the evaporator feedwater. As is discussed below, in the present process the deaerator 14 performs an additional function. The deaerator 14 is used to preheat the evaporator feedwater passing through the deaerator.

[0018] Distillate produced by the evaporator 12 is directed to a distillate tank 16. A distillate pump 18 is operatively connected or associated with the distillate tank 16 to pump distillate therefrom. Distillate tank 16 includes a vent for venting flash vapors from the distillate tank via a vapor line to the thermocompressor or eductor 20. Thermocompressor 20 includes a motive fluid or steam inlet 20A, a suction inlet 20B and a discharge outlet 20C. The vapor line extending from the distillate tank 16 is operatively connected to the suction inlet 20B of the thermocompressor 20. To drive the thermocompressor, motive steam is directed into the motive fluid inlet 20A of the thermocompressor 20. This results in the thermocompressor 20 drawing a vacuum on the distillate tank 16. Distillate directed from the evaporator 12 into the distillate tank 16 undergoes a pressure drop resulting in the distillate flashing vapors (and being cooled in the process) which are induced into the thermocompressor 20. The vapors from the distillate are mixed with the motive steam to form a steam-vapor mixture which is referred to as thermocompressor discharge. In some cases, as illustrated in the drawings, steam produced by the evaporator 12 can be mixed with the thermocompressor discharge prior to the thermocompressor discharge preheating the evaporator feedwater.

[0019] Thermocompressor discharge from the thermocompressor 20 is directed into the deaerator 14 and moves through the deaerator generally counter to the flow of evaporator feedwater therein. A portion of the thermocompressor discharge condenses in the deaerator 14 and in the process transfers latent heat to the evaporator feedwater and preheats the same. Remaining thermocompressor discharge passing through the deaerator 14 strips non-condensable gases from the evaporator feedwater and is vented from the deaerator.

[0020] It is appreciated that the system and process described above avoids heat exchanger scaling when preheating evaporator feedwater that includes relatively high concentrations of scaling components. Preheating the evaporator feedwater in the deaerator 14 allows any scaling components to precipitate in the bulk liquid instead of directly on heat transfer surfaces.

[0021] In addition, the system and process is energy efficient. The process maximizes heat recovery from the outgoing distillate through flash cooling. As noted above, the thermocompressor 20 imparts a vacuum on the distillate tank 16 to achieve a desirable distillate temperature. At the same time, the thermocompressor 20 boosts the flash vapors up to a pressure that can be used for preheating the evaporator feedwater in the deaerator 14. This provides at least two benefits. First, this reduces or even eliminates cooling duty to meet distillate discharge requirements. Secondly, this system and process reduces the makeup steam required to sufficiently preheat the evaporator feedwater.

[0022] FIG. 2 depicts an alternate embodiment of a system and process for preheating evaporator feedwater. The system and process shown in FIG. 2 is particularly applicable in cases where the temperature of the evaporator feedwater is relatively low. Shown in FIG. 2 is a barometric condenser 22 that is disposed upstream of the evaporator 12 and downstream of the thermocompressor 20. The thermocompressor discharge and the evaporator feedwater are directed into and through the barometric condenser 22. Thermocompressor discharge contacts the evaporator feedwater in the barometric condenser 22 and condenses, thereby preheating the evaporator feedwater passing through the barometric condenser. The preheated evaporator feedwater exiting the barometric condenser 22 is then directed into and through the deaerator 14 where non-condensable gases are stripped from the evaporator feedwater. As in the FIG. 1 embodiment, evaporator feedwater discharged from the deaerator 14 is directed to the evaporator 12.

[0023] The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.