COMBINED CYCLE COGENERATION POWER PLANTS BENEFIT FROM COLD DEAERATED HRSG FEEDWATER
ABSTRACT
Combined cycle/cogeneration power plants burning clean fuels, such as natural gas, gain efficiency and increase power when gas turbine exhaust temperatures are reduced. To achieve lower exhaust temperatures, HRSG feedwater must be cold. This cold feedwater should also be deaerated in order to permit the use of less expensive materials in the HRSG.
Steam condenser condensate, the usual source for cold deaerated water, is often highly oxygenated, particularly at off-design conditions. Excessive makeup required by cogeneration systems adds substantial quantities of dissolved oxygen to the HRSG feedwater.
A new system is described which assures condensate dissolved oxygen levels will not exceed 7 ppb. The deaeration of large quantities of makeup water wIth turbine exhaust steam results in additional economic advantages. The resultant combined cycle is simpler, less costly, and more efficient. Field results have verified the oxygen removal capabilities of this system.
INTRODUCTION
Power plants designed for base loading are often required to operate at off design conditions, producing dissolved oxygen levels in surface condenser condensate well above the desired 7 parts per billion (ppb)/0.005 cc per liter level. A number of studies sponsored by EPRI investigated the problems associated with increased oxygen in condensate and reported on them in References 1-3....