Air tube preheating model of linear Fresnel systems and application of variable duty ratio following control

Abstract

Through the analysis of the key factors that affect linear Fresnel collection efficiency, a thermal efficiency model for linear Fresnel systems is established. On the basis of the model, a suitable method of variable duty cycle following control is used for the hollow tube preheating of linear Fresnel systems. Through calculating the system concentrated duty ratio in each preheating cycle based on the real-time data, the linear Fresnel system constant speed control is achieved. MATLAB is used to simulate the focus duty ratio of the preheating system under different time and different irradiation, and the method is applied to the air tube preheating of Dunhuang molten salts in a Fresnel demonstration station. Experimental results show that compared with commonly prescribed duty ratio preheating methods, the proposed control method can achieve a constant rate of preheating control of the hollow tube in the linear Fresnel system under the premise that the requirements of hollow-tube temperature rise rate are met. Furthermore, the method can effectively shorten the overall preheating process to achieve maximum efficiency of solar resource utilization.