Combined Cycle Conversion and Case Study for an Existing 1,200 MW Utility Plant

摘要

Combined Cycle Conversion ("CCC") is a proven, economical way of significantly reducing emissions while improving the efficiency of older, fossil fuel fired utility power plants. The basic concept is to replace the existing boiler forced draft fan with a high efficiency gas turbine ("GT"}, fueled with natural gas. The hot exhaust from the GT is ducted to the boiler windboxes where it is used as primary and secondary combustion air to fire the boiler fuel, which is usually residual oil or coal. The heat in the gas turbine exhaust is also recovered in the existing heat transfer surfaces of the boiler. The improvement in efficiency is primarily attributed to recovering the waste heat from the GT thus allowing the existing power plant to now operate in a combined cycle mode. The use of natural gas in the GT and recovery of this unfired, waste heat in the boiler results in the overall air emissions being reduced significantly (generally by 50%), and also, provides for an increase in net electrical capacity. This conversion has been demonstrated on over 8,000 MW of capacity on utility sized units in commercial operation. A conventional boiler steam turbine facility converted to combined cycle enjoys the following benefits: 1. Fuel consumption savings in the range of 20%. 2. Reductions of priority pollutant emissions of up to 50%) without any added back-end controls. This conversion will meet the SIP call limit of 0.15 lb NOx/MMBtu in most applications. 3. Ability to continue to fire a lower cost fuel in the boiler because the emissions reduction will meet the targeted levels in most new State regulations. 4. Reduction in CO2 emissions in the range of 25%) to 35%) with proportional reductions of mercury and other metal oxide emissions. 5. Additional integrated net capacity (MW) of up to 20%). 6. Additional electric production (MW-hrs) when operating under economic dispatch because of the improved heat rate. 7. Reduced start-up times. The GT is at full load in about 30 minutes. 8. Reduced O&M costs because the air heater and most of the feed water heaters are no longer required. For coal fired plants the required operating load on the pulverizers is significantly reduced. 9. Increased load following capability because of improved part load efficiency. A case study will be presented for an existing 1,200 MW (2 x 600 MW) facility evaluating the heat rate improvement, emissions reductions (i.e., past actual to future potential), and the significant utilization increase with the emissions reductions.