Cold Water for Plants in the Desert: Heat Rejection for Water-starved Locations
Zero effluent and zero water makeup is possible, and even economically attractive, when it is made a priority during process design. The 3.3 million MMBtu per year San Joaquin Renewables biomass-to-natural gas plant designed by Frontline BioEnergy has achieved this goal. Traditional evaporative cooling towers may require 0.06 gpm per ton of cooling load (300 gallons per MMBtu) for evaporation and blowdown makeup. For the San Joaquin Renewables biomass to natural gas plant requiring 50MMBtu per hour, that would have amounted to an unattractive consumption of 360,000 gallons of water per day, or 30% more than the entire residential consumption of the city of McFarland, California (3,300 homes) where the plant will be located. Instead of this, all of the cooling load is provided through a combination of efficient electric chillers and absorption chillers utilizing waste heat from internal combustion engine exhaust. The result is a plant that neither requires makeup water nor produces wastewater. The plant design makes extensive use of chilled water for process cooling needs, condensers, and product cooling. Additionally, a detailed study revealed significant efficiency gains possible through cooling of compressor inlets and interstage cooling.