Analysis of the thermal inertia of pipelines in SHIP

Solar heat for industrial process (SHIP) is the term used to refer to the application of solar radiation to supply the heat consumed in an industrial process. Some solar concentrators, such as Parabolic Trough Collectors and Linear Fresnel Reflectors, are specially designed for industrial heat production and can reach temperatures up to 400 ºC. The 67% of the total energy in the industry is consumed as heat and half of it requires temperatures below 400ºC. However, there are some limitations in the integration of industrial heat with solar energy, for example, space, the diurnal and dynamic behavior of solar radiation, and the need for storage. The study described in this paper is part of the ASTEP project (Application of Solar Thermal Energy to Processes), whose goal is to challenge these limitations by achieving a low-cost, modular, and flexible integration between the solar field, the storage system, and the process.

Solar radiation is an intermittent source, so a storage system with an adequate control strategy is needed to achieve a constant supply to the industrial process, especially when the demand is not diurnal. Most research studies that analyze SHIP systems with dynamic simulation focus on the effect of different transients, such as clouds, start-up, and shutdown. The main objective of this study is to analyze the dynamic effect of the thermal inertia of the pipelines in the solar system designed for ASTEP. A few authors study this aspect, but none of them are addressed   to SHIP nor of a size like the ASTEP system (supply power, solar field dimensions, and temperatures).

To achieve the objective of this study, we design two dynamic simulations of the entire system. One of the simulations consider the thermal inertia of all the system pipelines, which summed a total of 70 meters. The other simulation is identical except for the omission of thermal inertia of the pipelines. The process demand is composed of two heat exchangers with a capacity of 7 kW each. To evaluate the control strategy throughout the day, a simulation was carried out with weather data from Iasi, Romania, where the factory (a steel tube producer) is located. Finally, the results were compared with those of previous studies and some differences were found.