Increasing fossil power plant flexibility by integrating molten-salt thermal storage

Abstract

Increasing market penetration of renewable energy sources requires measures to stabilize the electric grid. This includes reducing generator output fluctuations as well as providing control reserve. The present study investigates the use of molten-salt storage systems in fossil-fired power plants by conducting a series of numerical process simulations. Two case studies are performed: First, an incinerator representing a heat-controlled facility with fluctuating output due to varying customer steam demand. Second, a small-size lignite-fired power plant for providing control reserve, representing a power-controlled facility.The results show that the concept allows significant attenuation of fluctuations in the heat-controlled facility. For a broad range of customer steam extraction, a steady production of electrical energy could be obtained without substantial modifications to the plant. Positive and negative control reserve in the power-controlled facility can be provided through the use of a storage system with relatively low exergetic losses. However, a number of additional heat exchangers and significant modifications to the steam cycle are required.