Optimal Heat Integration in a Coal-Natural Gas Energy Park with CO2 Capture

Abstract

Computational techniques are used to optimize the design of an integrated energy park consisting of a coal-fired power plant, a CO₂ capture system, and an auxiliary natural gas combined cycle plant. Emphasis is placed on the design of heat integration in the combined cycle system, as this heat constitutes most of the energy required for temperature-swing CO₂ capture. The facility is constrained to meet a maximum CO₂ emission intensity limit while flexibly capturing CO₂ to maximize profit. The process and capital cost models of the facility include a detailed treatment of the heat recovery steam generator (HRSG). Computational optimization techniques are used to select gas turbine size, CO₂ capture capacity, and the sizes and pressures of HRSG components for HRSG configurations with one, two, and three pressure levels. Facility design is jointly optimized with dispatch using an electricity price- duration curve and natural gas price scenarios of $3/MMBtu, $4.50/MMBtu and $6/MMBtu. System configuration is shown to have a significant impact on economics, with spread in net present value (NPV) among configurations of $39-54 million (2.6-26% of NPV). Joint optimization of design with optimized flexible dispatch is observed to improve NPV by $18-56 million (1.2-27%) as compared to optimization with constant dispatch. Gains from optimization increase with higher natural gas price. Optimal capital cost, approximately $2.1-2.2 billion in all configurations, is higher for configurations with higher number of pressure levels, but does not exhibit strong trends with gas price.