Joint optimization design of insulation and electric heat tracing of molten salt pipelines in concentrating solar power plants

Given that the molten salt pipelines and equipment of Concentrating Solar Power (CSP) plants are equipped with Electric Heat Tracing (EHT) system in addition to the thermal insulation layer, a joint optimization design method for the insulation layer and EHT system is proposed. The design point that minimizes the total investment in insulation and the EHT system is defined as optimum design point A, while the point minimizing the sum of equipment investment and whole life cycle Operation and Maintenance (O&M) cost of the EHT system is defined as optimum design point B. Taking the typical low and high-temperature molten salt pipelines with large/medium/small diameters as examples, the distribution characteristics of optimal design points are analyzed and discussed. Results indicate that the insulation thickness, heat loss, corresponding EHT heating capacity, and amounts of heat tracing cables are very sensitive to the required insulation outer surface temperature. While the optimum design point A and point B are not the same under normal conditions, the selection of the optimum design point should be made based on comprehensive consideration including the specific design requirements and the space constraints for insulation installation. For low-temperature pipelines, the optimum design point A is selected with an insulation outer surface temperature of 8~9°C, and for high-temperature pipelines, the optimum design point A is still recommended with the insulation outer surface temperature of 16~18°C. The corresponding insulation thickness and EHT heating capacity are the optimal design values.