Real Power Solutions’ Leachate Evaporation System employs a patented design (U.S. Patent #108,859,256) that utilizes waste heat harnessed from both the engine cooling circuits and the exhaust systems associated with the landfill-gas-to-energy (LFGTE) power plant generators.  We can use nearly any type of waste heat; this is merely one application.  Our patented method is a combination of enthlapy generated flash steam and psychrometric liquid removal.

In traditional LFGTE power generation systems, coolant circulating through the prime mover (in this case, a landfill gas fired, internal combustion engine) and/or its associated peripheral devices such as aftercoolers, gear boxes and alternators, is typically sent straight to a water to air heat exchanger (radiator) to provide heat rejection for the devices.  The coolant circuit or circuits in a prime mover and its associated peripheral devices may be configured in one or more coolant loops servicing all heat rejecting components in one loop, or more often, two or more loops servicing various combinations of the heat rejecting components associated with the prime mover and alternator.

In the RPS evaporation process, the engine coolant is diverted before entering the traditional radiator to first flow through one or more liquid to liquid heat exchangers (HX’s) to transfer the energy in the coolant into the leachate that will be converted to steam.  The leachate in the loop is filtered before it enters the evaporator, filling the piping, pumps, flash tank and other related components.  Once the evaporator is filled, a leachate circulation pump powers on and begins circulating the leachate through the HX’s.  This begins the heat exchange process that extracts heat from the coolant, transfers it to the leachate, and ultimately causes steam production in the flash tank.  The pump circulating hot leachate through the system ensures the leachate pressure remains comfortably above the flash point until it is de-pressurized in the flash steam nozzles, where the energy is released in the form of steam production. 

An additional filtration process takes place in the leachate flash steam loop.  This filtration process removes solids and precipitates contained in the leachate. The filtration of the leachate provides mechanical protection of the devices in the system and allows for collection of particulate matter present in the process.  In addition, filtration of the leachate helps minimize the residuals that may contribute to foam production in the flash tank.  As the process begins to convert the water component of the leachate to steam, make up leachate is introduced to hold the system level constant.  The makeup leachate is pre-heated in a heat exchange process with one or more of the cooling loops in the engine and generator.

The steam produced in this process is saturated.  To improve steam quality, very large volumes of extremely hot ambient air are introduced into the flash tank and forced to comingle with the steam.  This ambient air is heated in a gas to gas HX, extracting heat from the exhaust system. This added energy helps deliver the higher quality steam we desire so we ensure no liquid form of the leachate is released from the exhaust stack. These large volumes of air also remove water vapor from the system through an absorption process.  This absorption process cools the flash tank environment as it also increases water removal capacity.  The air handler (or blower) used to move air through the HX, thence to the flash tank and out the exhaust stack, does so by drawing the heated ambient air through the system versus pushing it through from the inlet side.  This has the effect of lowering the pressure in the flash tank to some level below atmospheric pressure, which in turn increases efficiency of the process by lowering the flash temperature of the water component of the leachate in accordance with the saturated temperature and pressure relationship.

The design of the evaporator utilizing waste heat from both the coolant fluid and exhaust stack improves the performance of the generator prime mover because it allows for higher power density and better performance in high ambient conditions where traditional radiators fail.  This is due to the efficiencies delivered in cooling the generator with liquid (the water that leachate consists of, chiefly) instead of air, which is how traditional radiators provide cooling.  Since the LFGTE plant may not have to operate radiator fans while the evaporator is in operation, the parasitic load on the power plant can drop by a significant margin, providing the power generation plant with more net power to sell.