Patent Publication Number: US-2004045682-A1

Title: Cogeneration wasteheat evaporation system and method for wastewater treatment utilizing wasteheat recovery

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] The present application claims priority to U.S. Provisional Patent Application Serial No. 60/375,845, filed Apr. 24, 2002, the entire contents of which are expressly incorporated herein by reference in its entirety. 
    
    
     
       BACKGROUND  
       [0002] Currently, there are a variety of methods utilized to treat wastewater, or leachate. Such methods may include, for example, bio-treatment facilities, options for offsite deepwell injection, onsite wastewater evaporation, and the like.  
       [0003] One exemplary method of leachate wastewater evaporation utilizes evaporation ponds. However, these leachate wastewater systems may be used only in dry climates. Another exemplary method of leachate wastewater evaporation utilizes landfill gas extraction facilities, which use methane gas extracted from refuse type landfills. In such a system, leachate wastewater is fired in a fuel demand type evaporation system.  
       [0004] A more versatile and more efficient leachate wastewater evaporation system would be greatly desired by the art.  
       SUMMARY  
       [0005] The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the described cogeneration waste heat evaporation system and method for wastewater treatment utilizing waste heat recovery from, e.g., a gas turbine. Such method comprises recovering engine waste heat by capturing and routing such waste heat through a unique evaporator system.  
       [0006] In one exemplary embodiment, the evaporator system collects exhaust through a bypass throttle system, which controls the flow such exhaust through one or both of a bypass duct and an evaporator duct. In another exemplary embodiment, such bypass throttle system controls the rate of evaporation by selectively varying the amount of waste heat provided to the evaporator and by routing excess undesired amounts of exhaust through a bypass duct. In another exemplary embodiment, the bypass throttle directs substantially all of the waste heat through the bypass duct to allow the evaporator system to be taken offline, while maintaining the performance of the engine generating such waste heat.  
       [0007] In another exemplary embodiment, an electrical generator tied to the engine, e.g., a gas turbine, is tied to one of at least one electrical thermal resistance heater and at least one electric dryer. In such system, the at least one heater and/or at least one dryer may be operated to modulate demand on the engine, and thus, modulate output of waste heat into the evaporation system. Such configuration may be particularly advantageous where demand on the electric generator is otherwise low enough to reduce the output of waste heat into the evaporator system to less than desirable levels.  
       [0008] In another exemplary embodiment, such at least one electrical thermal resistance heater is submerged in the leachate wastewater to be evaporated. In such a scenario, the at least one heater may be used not only to modulate demand on the engine, but also to increase evaporation capacity by providing an additional heat energy input for the leachate wastewater.  
       [0009] In another embodiment, the electrical generator tied to the engine, e.g., a gas turbine, is intertied to a municipality for resale of excess electricity to the municipality. In such system, the output of the exhaust may be maintained in a desired range by demanding varying amounts of electricity from the electrical generator for resale to the municipality.  
       [0010] In another embodiment, a downstream afterburner is utilized in conjunction with a gas turbine engine. The afterburner is positioned between the evaporator and/or the bypass duct and the atmosphere outlet. Such afterburner burns the excess oxygen carried in the exhaust stream. Combustion provided by the afterburner is effective to both increase stack gas compression and to achieve higher atmospheric release height of constituents (with a given stack height) to provide better atmospheric dispersion.  
       [0011] The above discussed and other features and advantages of the present cogeneration waste heat evaporation system and method for wastewater treatment utilizing waste heat recovery will be appreciated and understood by those skilled in the art from the following detailed description and drawing. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] Referring now to the drawing, wherein like elements are numbered alike in the FIGURES:  
     [0013]FIG. 1 depicts in plan view an exemplary wastewater evaporation system with cogeneration.  
    
    
     DETAILED DESCRIPTION  
     [0014] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawing.  
     [0015] Referring now to FIG. 1, an exemplary cogeneration waste heat evaporation system and method for wastewater treatment utilizing waste heat recovery is illustrated. A fuel fired turbine engine  10  is provided with a turbine air inlet  12 , a fuel inlet  14 , a turbine exhaust outlet  16  and a connection  18  to an electric generator  20 . While a fuel fired turbine engine  10  is described with reference to an exemplary embodiment, it should be recognized that any heat engine that does useful work may be utilized. The presently described system finds particular application with turbine engines since a large proportion of fuel input energy is typically lost as waste. For turbine engines, thermal efficiency ranges near 25%. Thus, approximately 75% of the input fuel energy to escapes in the form of waste heat through the engine exhaust system. The presently described system and method routes this otherwise unused waste heat through the turbine exhaust outlet  16  and to a waste heat recovery evaporator  22 .  
     [0016] The turbine  10  generally works on the theoretical principal of the Brayton Cycle (thermodynamically speaking). This type of engine provides generous amounts of waste heat in the form of hot gas/air. Without limitation, the waste heat exhaust temperatures will generally range between 850-1100 F°. The turbine may provide primary work energy by spinning a shaft (not shown). This shaft contains useful mechanical energy that can be coupled to the illustrated electric generator  20  and/or to any other useful function requiring shaft energy. In one exemplary embodiment, a turbine is utilized producing above about 0.75 Megawatt of power.  
     [0017] The waste heat exhaust stream is ducted into and through the evaporator and or bypass system as will be described below in more detail. In one exemplary embodiment, such ducting is via heat resistant piping, for example, constructed of high temperature alloy steels such as stainless steel, hastalloy, etc.  
     [0018] In one exemplary embodiment, a bypass throttle system is provided between the exhaust outlet  16  and the waste heat recovery evaporator  22 . Referring again to the exemplary embodiment illustrated by FIG. 1, the turbine exhaust is routed, via introductory duct  24 , to a flow control damper valve  26 . In one exemplary embodiment, the flow control damper valve  26  selectively controls the flow of exhaust through one or both of a bypass duct  28  and an evaporator duct  30 . The term “flow control damper valve” is not intended to be limited, but is intended to encompass any kind of valve that performs diversion or equivalents.  
     [0019] In another exemplary embodiment, such flow control damper valve  26  controls the rate of evaporation in the waste heat recovery evaporator  22  by selectively varying the amount of waste heat provided to the evaporator  22  through the evaporator duct  30  and by routing excess, undesired amounts of exhaust through the bypass duct  28 . Such embodiment permits throttling of the exhaust through the evaporator  22  at a controlled rate and allows the evaporator boiling rate to be scaled up or down depending on operational preferences.  
     [0020] In another exemplary embodiment, the flow control damper valve  26  directs substantially all of the waste heat through the bypass duct  28  to allow the evaporator  22  to be taken offline, while maintaining the performance of the engine  10  generating such waste heat. Such embodiment permits the engine  10  to continue to operate, thereby not creating, for example, an electrical outage while the evaporator  22  is offline.  
     [0021] In another exemplary embodiment, exhaust provided by the flow control damper valve  26  to the evaporator duct  30  is passed through a high temperature blower fan  32  prior to entering the evaporator  22 . In one exemplary embodiment, the blower fan  32  may be selectively configured to transfer up to and including 100 percent of the turbine waste heat. In another embodiment, the blower fan  32  may be selectively configured to maintain a turbine exhaust backpressure to optimize the performance of the turbine engine. For example, the blower fan  32  may be controlled to maintain about six inches of water pressure for the turbine exhaust back pressure and to increase air stream static pressure to a higher pressure state, for example, between about 15 and 48 inches of water pressure.  
     [0022] Referring again to FIG. 1, the exhaust directed through the evaporator duct  30  is further directed into the evaporator  22 . The evaporator  22  may be configured as a heat exchanger either to transfer of heat directly or indirectly (e.g., via metal tubes, plates, etc.) to the leachate wastewater. In one exemplary embodiment, the evaporator  22  comprises a direct contact submerged tube type heat exchanger. In such embodiment, the exhaust is ducted into the evaporator  22  such that hot exhaust percolates directly through the leachate wastewater, thus providing for heating and/or boiling of the leachate wastewater. In another embodiment, the heating/boiling process in the evaporator  22  takes place at approximately atmospheric pressure and at temperatures between about 195 and 220 degrees Fahrenheit.  
     [0023] During evaporation of the leachate wastewater, the wastewater in the evaporator  22  begins to concentrate with dissolved and suspended particles of solid materials. In one embodiment, when concentration levels of the wastewater increase to approximately 40 percent to 60 percent, the solid particles and/or concentrated wastewater are removed from the bottom of the evaporator (removal may be effected, for example, by a liquid slurry pump or a material auger, depending on the type of concentrates in the wastewater stream). Removal of such solid particles and/or concentrated wastewater is shown generally at  34 .  
     [0024] Such particles and/or wastewater may then be subjected to a dewatering device  36  for final moisture removal. In one embodiment, the dewatering device  36  generally comprises a device effective to further remove water from solids/concentrated wastewater. For example, the solids/concentrated wastewater can be directed into a dewatering device, comprising a filter press, drying vat or batch tank.  
     [0025] In another exemplary embodiment, this tank utilizes surplus waste heat from the turbine process to dry the solids for future treatment and/or proper disposal. Such surplus exhaust heat may be selectively ducted into a dewatering exhaust duct  40  from the bypass duct  28  via a second flow control valve  42  to provide such heating.  
     [0026] In another exemplary embodiment, this tank utilizes at least one electrical resistance heater  44 , or electric dryer, to dry the solids  37  for future treatment and/or proper disposal. Such heater  44  may be powered by electrical connection  46  to electric generator  20 . The electrical resistance heater  44  may incorporate variable heat controls which may be tailored To the needs of the dewatering device and, as will be discussed in more detail below (with regard to optional placement of resistance heaters  44  in the evaporator  22 ), to modulate the demand on the engine  10  and the related production of exhaust.  
     [0027] Subsequent to dewatering, the solids  37  may be removed and collected into suitable portable container  38 . Wastewater removed from the dewatering process may be ducted through a return duct  48  and reintroduced either into the initial wastewater stream  50  or directly into the evaporator  22 .  
     [0028] Referring again to FIG. 1, in another exemplary embodiment, at least one electrical resistance heater  44  may be provided in the evaporator  22 . Such heater  44  may be powered by electrical connection  52  to electric generator  20 . The electrical resistance heater  44  may incorporate variable heat controls that regulate the additional heat added to the wastewater in the evaporator and modulate the demand on the engine  10  and the related production of exhaust. Specifically, the heater  44  may transfer electric energy into thermal energy and may be submerged in the wastewater or liquid in the evaporator  22 . The electric thermal resistance heater  44  also provides a means of compensating for electrical load variations and demand changes on the electric generator  20 . As general electrical usage (demand) decreases over the course of a given operational period, the engine  10  would do less work turning the electric generator  20 .  
     [0029] This condition would result in less available waste heat as less work is being done. The exemplary electric thermal resistance heater  44  may be staged in via controls, to maintain an optimal demand on the generator  20  to increase engine temperature, decrease engine temperature, or minimize variations in engine temperature.  
     [0030] The exemplary inclusion of at least one heater  44 , as described above, finds particular application in remote locations, where electrical interconnection to a municipal power system is not feasible and/or available. This exemplary inclusion also finds application in situations wherein local demand on the engine (draw on electrical generator output  54 ) is not sufficient to run the engine at optimal levels for production of evaporation waste heat.  
     [0031] Referring again to the exemplary system illustrated by FIG. 1, the water vapor evaporated from the evaporator  22  is ducted via a post-evaporation duct  56  for release into the atmosphere at a release port or stack  58 . In one exemplary embodiment, the water vapor/gas being removed from the evaporator  22  or within the post-evaporation duct  56  is treated, e.g., with one or more demister pads, thermal oxidizers and chemical scrubbers  60 . In another exemplary embodiment, at a point between the evaporator  22  and the release port or stack  58 , the exhaust in the bypass duct  28  is combined with the water vapor/gas in the post-evaporation duct  56 .  
     [0032] In another exemplary embodiment, one or both of the water vapor/gas in the post-evaporation duct  56  and the bypass duct  28  may also be processed in an afterburner  62 , provided upstream of the release port or stack  58 . Such embodiment finds particular use with gas turbine exhaust, which typically contains 18 percent to 20 percent excess air in the exhaust stream. This excess air contains enough oxygen to promote further combustion when combined with supplemental fuel in the afterburner. Combustion in the afterburner  62  may serve to superheat the water vapor and provide means of controlling emissions of chemical constituents and foul odors, respectively, in the exhaust stack  58 . Combustion provided by the afterburner  62  is also effective to both increase stack gas compression and to achieve higher atmospheric release height of constituents (with a given stack height) to provide better atmospheric dispersion.  
     [0033] It will be apparent to those skilled in the art that, while exemplary embodiments have been shown and described, various modifications and variations can be made in the present board game without departing from the spirit or scope of the invention. For example, without limitation, dewatering control, use of air scrubbers, use of the afterburner for odor control, among others, include optional components/compositions in recognition of the fact that various waste streams comprise varying chemical constituents, total solids (dissolved and suspended), and air emission characteristics that certain of the above described and other optional devices may be advantageously suited for. Indeed, the above described, and below claimed, system and method finds application in a broad range of fields, including without limitation, processing of wastewater generated from rainfall infiltrating hazardous, non-hazardous, etc. landfills, and other sources such as bio-medical wastewater streams, oilfield effluent wastewater streams, onshore and offshore industrial oil/gas industrial platforms, municipal wastewater effluent, etc. Accordingly, it is to be understood that the various embodiments have been described by way of illustration and not limitation.