Improving high temperature heat capture for power generation in gasification plants

As part of the gasification process, hot syngas is cooled to low temperatures for gas cleaning by generating high pressure steam in a radiant heat exchanger. The steam, in turn, is used to generate electric power. However, the very large temperature difference that exists between the syngas and generated high pressure steam results in significant losses during the heat transfer process. These losses can be reduced, and hence the overall plant efficiency improved, by choosing materials and working fluids that reduce the temperature difference in the syngas heat exchanger. A set of alternatives to high pressure steam is liquid metals or molten salts. These liquids can be kept at a pressure equal to the syngas pressure, reducing the tensile hoop stress in the heat exchanger tubes. Since the strength of steel decreases with temperature, reducing the hoop stress allows tubes (and the liquids inside them) to reach higher temperatures. The liquid metals or molten salt can then be used in a secondary heat transfer loop to transfer heat to a steam generator. This paper describes a cost-effective radiant heat exchanger that can be used to transfer heat from high temperature syngas to these alternative heat transfer fluids, and also quantifies the increase in overall IGCC plant efficiency by doing so. A capital cost assessment shows a small payback time and improved revenue is achieved by using this technology, making this a realistic option for gasification processes.