Water-Conserving Steam Ammonia Power Cycle

Fresh water is growing scarcer and costlier. Power production is the second largest user of fresh water, consuming about 25 gallons per kilowatt-hour in coal-fired plants. In particular, steam power plants, which use air-cooling to reduce water usage, suffer large economic and efficiency penalties, due to the deep vacuum at which steam condensers operate. This project will develop a new power cycle (Steam-Ammonia Power Cycle) that markedly reduces water usage without increasing fuel consumption or cost. The approach involves a hybrid cycle, in which the vacuum portion of a conventional steam cycle is replaced with a tandem ammonia Rankine cycle. The condensing pressure is thereby raised to 150 psig, which makes possible very compact and economical air-cooled condensers. High cycle efficiency is achieved by superheating the ammonia vapor. In Phase I, the new cycle was thermodynamically analyzed in three different important applications: state-of-art combined cycle plant (600 MW), mid-size gas turbine bottoming cycle (12 MW), and reciprocating engine bottoming cycle (2 MW). The results validated the high cycle efficiency at all size ranges for both the air-cooled and water-cooled variants of the cycle. In Phase II, the new cycle will be developed and field-demonstrated at the smallest scale. Waste heat from an 840 kW reciprocating engine will be used to generate 130 kW of additional power, with minimal water consumption. The cycle is expected to be at least 50% more efficient than any existing reciprocating engine bottoming cycle, due to the ability of the cycle to use the cylinder jacket heat as well as the exhaust heat. Commercial Applications and other Benefits as described by the awardee: The improved power cycle should be applicable to virtually all types of existing thermoelectric power plants. Due to the temperature glide of the heat rejection, this new cycle requires 5% less cooling water than current cycles when it is water cooled, equating to a fresh water savings of 6.2 billion gallons per day nationwide. Power plants with this modification also would achieve a reduction in fuel consumption. The multi-turbine variant of this cycle would apply to steam-based power plants, including coal gasification combined cycle plants, while the single-turbine variant would apply to small-scale plants powered by waste heat