Moundsville Power LLC is working at the West Virginia Department of Environmental Protection on some needed changes to an air permit issued last November for its gas-fired, combined-cycle project in Marshall County, W.Va.
Consultant Environmental Resources Management Inc. (ERM) prepared the amendment application, which was filed with the department on April 22.
The air permit revision is to reflect changes in project equipment and design that have evolved since the original air permit approval, which came in November 2014. There have been various changes in the emissions and performance profile of the General Electric (GE) Frame 7FA.04 combustion turbines (CTs), and their associated Heat Recovery Steam Generators (HRSGs). These changes include:
- Increase in the maximum heat input of each CT from 2,087 million Btu per hour (MMBtu/hr) to 2,232 MMBtu/hr;
- Increase in the maximum duct firing rate for each HRSG from 72.1 MMBtu/hr to 187.61 MMBtu/hr;
- A slight reduction in the exhaust stack height of each CT/HRSG from 180.5 feet to 175 feet; and
- Minor variations in exhaust gas flow rates and temperatures for each CT/HRSG.
There are several changes in the design configuration, circulating water rate, make-up water rates, and Total Dissolved Solids (TDS) concentrations for the Cooling Tower. These changes include:
- Use of a 6 cell Cooling Tower in a 1 x 6 configuration, instead of the original 10 cell Cooling Tower in a 2 x 5 configuration;
- Increase in the diameter of each cell from 30 feet to 40 feet;
- Slight increase in the Cooling Tower design circulating water rate from 159,000 gallons per minute (gpm) to 164,110 gpm;
- Decrease in the Cooling Tower design make-up water rate from 185,500 gallons per hour (gph) to 155,600 gph;
- Decrease in the Cooling Tower design exhaust flow rate per cell from 1,800,000 actual cubic feet per minute (acfm) to 1,450,000 acfm; and
- Increase in the maximum design TDS concentration of the Cooling Tower circulating water from 1,800 milligrams per liter (mg/L) to 2,400 mg/L.
The Moundsville Power Plant will generate approximately 631 MW that will be sold on the PJM Interconnection regional electric grid. Pipeline-quality natural gas used by the plant’s combustion turbines will be purchased from local suppliers, and will take advantage of the gas produced in nearby natural gas shale plays. In addition, the combustion turbines may fire a blend of pipeline-quality natural gas with up to 25% ethane.
Electricity will be generated using two combined-cycle combustion turbines (CCCT-1 and CCCT-2) each rated at 197 MW (at various ambient temperature design conditions) and 2,232 million Btu per hour (MMBtu/hr). Electricity generated by the combustion turbines will be routed through a local electrical substation and sold on the grid. To enhance the plant’s overall efficiency and increase the amount of electric generated by the plant, the hot exhaust gases from the combustion turbines is routed to downstream Heat Recovery Steam Generators (HRSGs). The HRSGs contain a series of heat exchangers designed to recover the heat from the turbines’ exhaust gas and produce steam, as in a boiler. Each combustion turbine will have its own HRSG. Cooled exhaust gas passing through the HRSGs is vented to the atmosphere through emission points CCCT-1 and CCCT-2.
The Selective Catalytic Reduction (SCR) and Oxidation Catalyst control devices used to reduce NOx and carbon monoxide (CO) emissions from the combustion turbines will be incorporated into the HRSGs, at locations where the emission control reactions optimally occur.
Notable is that plant output varies by several factors, including ambient temperature, relative humidity, fuel, load level, whether duct firing or evaporative cooling are in use. For Moundsville, 630.874 MW is the expected plant output at a 40˚F ambient temperature design condition, 60% relative humidity, at base load, firing a natural gas/ethane fuel mix, with 65% duct firing, and with the combustion turbine evaporative cooling systems off.