Optimization of a shell-and-tube district heat condenser for a small back pressure combined heat and power plant

Abstract

Wood-fired combined heat and power (CHP) plants are a proven technology for producing domestic, carbon-neutral heat and power in Nordic countries. Such plants are often of backpressure configuration, the district heat condenser replacing the vacuum condenser of a condensing power plant. The condenser is usually a shell-and-tube heat exchanger with district heating water on the tube side. In this paper, a new approach is presented to optimize the condenser design considering not only the design-point performance, but also variations in the operating conditions. A power plant model is used to determine the plant performance (net power output and boiler fuel consumption) as a function of the main performance parameters of the condenser at each point. Cuckoo search algorithm is used for the optimization. The results show that although electricity price variation has a significant impact on plant net cash flow rate, the effects of electricity price and heat exchanger specific cost on condenser design are low.