Thermal energy storage for power plant applications

This study was conducted by Pacific Northwest Laboratory (PNL) to evaluate alternative methods of using coal to generate peak and intermediate load power. The approach was to review the technical and economic feasibility of using thermal energy storage (TES) with a conventional coal-fired power plant and an integrated gasification combined cycle (IGCC) power plant. In the first case, conventional pulverized coal combustion equipment was continuously operated to heat molten nitrate salt which was then stored in a tank. During peak demand periods, hot salt was withdrawn from storage and used to generate steam for a Rankine steam power cycle. This coal-fired salt heater can be approximately one-third the size of a coal-fired boiler in a conventional cycling plant. The use of nitrate salt TES also reduces the levelized cost of power from 5-24 percent depending on the operating schedule. The second case evaluates the use of thermal energy storage with an integrated gasification combined cycle (IGCC) power plant. In this case, the nitrate salt was heated by a combination of the gas turbine exhaust and the hot fuel gas. The IGCC plant also contained a low-temperature storage unit that uses a mixture of oil and rock as the thermal storagemore » medium. Thermal energy stored in the low-temperature TES was used to preheat the feedwater after it leaves the condenser and to produce process steam for other applications in the IGCC plant. This concept study also predicted lower cost power compared to the natural gas-fired alternative if significant escalation rates in the price of fuel were assumed. A sensitivity analysis showed a significant reduction in the installed capital cost of a direct-contact heat exchanger instead of the conventional finnned-tube design.« less