Economic implications of open versus closed cycle cooling for new steam electric power plants : a national and regional survey

Originally published as the author's thesis (M.S.), M.I.T., Dept. of Civil Engineering, 1979.Current and anticipated thermal pollution regulations will prevent many new steam electric power plants from operating with once-through cooling. Alternative cooling systems acceptable from an environmental view fail to operate with the same efficiencies, in terms of resources consumed per Kwh of electricity produced, offered by once-through cooling systems. As a consequence there are clear conflicts between meeting environmental objectives and meeting minimum cost and minimum resource consumption objectives. This report examines, at both the regional and national level, the costs of satisfying environmental objec- tives through the existing thermal pollution regulations. This study forecasts the costs of operating those megawatts of new generating capacity to be installed between the years 1975 and 2000 which will be required to install closed cycle cooling solely to comply with thermal regulations. A regionally disaggregated approach is used in the forecasts in order to preserve as much of the anticipated inter-regional variation in future capacity growth rates and economic trends as possible. The net costs of closed cycle cooling over once- through cooling are based on comparisons of the costs of owning and operating optimal closed and open-cycle cooling configurations in separate regions, using computer codes to simulate joint power plant/ cooling system operation. The expected future costs of current thermal pollution regulations are determined for the mutually exclusive - collectively exhaustive eighteen Water Resources Council Regions within the contiguous U.S., and are expressed in terms of additional dollar expenditures, water losses and energy consumption. These costs are then compared with the expected resource commitments associated with the normal operation of the steam electric power industry. It is found that while energy losses appear to be small, the dollar costs could threaten the profitability of those utility systems which have historically used once-through cooling extensively throughout their system. In addition the additional water demands of closed cycle cooling are likely to disrupt the water supplies in those coastal areas having few untapped freshwater supplies available

Ocean thermal energy conversion plants : experimental and analytical study of mixing and recirculation

Also issued as Massachusetts Institute of Technology. Ralph M. Parsons Laboratory for Water Resources and Hydrodynamics. Report no.231. Prepared by the Energy Laboratory in association with Ralph M. Parsons Laboratory for Water Resources and Hydrodynamics.Ocean thermal energy conversion (OTEC) is a method of generating power using the vertical temperature gradient of the tropical ocean as an energy source. Experimental and analytical studies have been carried out to determine the characteristics of the temperature and velocity fields induced in the surrounding ocean by the operation of an OTEC plant. The condition of recirculation, i.e. the reentering of mixed discharge water back into the plant intake, was of particular interest because of its adverse effect on plant efficiency. The studies were directed at the mixed discharge concept, in which the evaporator and condenser water flows are exhausted jointly at the approximate level of the ambient ocean thermocline. The OTEC plant was of the symmetric spar-buoy type with radial or separate discharge configurations. A distinctly stratified ocean with uniform, ambient current velocity was assumed. The following conclusions are obtained: The recirculation potential of an OTEC plant in a stagnant ocean is determined by the interaction of the jet discharge zone and a double sink return flow (one sink being the evaporator intake, the other the jet entrainment). This process occurs in the near-field of an OTEC plant up to a distance of about three times the ocean mixed layer depth. The stratified internal flow beyond this zone has little effect on recirculation, as have small ocean current velocities (up to 0.10 m/s prototype). Conditions which are conducive to recirculation are characterized by high discharge velocities and large plant flow rates. A design formula is proposed which determines whether recirculation would occur or not as a function of plant design and ocean conditions. On the basis of these results, it can be concluded that a 100 MW OTEC plant with the mixed discharge mode can operate at a typical candidate ocean site without incurring any discharge recirculation.Prepared under the support of Division of Solar Energy, U.S. Energy Research and Development Administration, Contract no. EY-76-S-02-2909.M001