Study of the soil temperature effect on the operation of a low-capacity power plant’s condenser

Abstract

Every year, the share of decentralized energy generation in Russia is increasing. The following factors contribute to the development of this scenario: increased wear of the country’s energy system equipment, energy shortages, and lack of centralized energy supply in a number of regions and constantly rising tariffs. One of the methods of decentralized energy generation is the use of low-capacity power plants based on the Rankine cycle with an organic working fluid. The operation of such plants requires cooling and condensation of the working fluid by transferring its heat to the environment. This study discusses the design of such a power plant and the heat removal system to a cold source. is the authors consider the design of a condenser which is a horizontal pipeline placed in the ground. Seasonal fluctuations of the soil temperatures affect the operation of the condenser. Thereby, to ensure the stable operation of the power plant, it is necessary to quantitatively assess the effect of the annual dynamics of the soil temperature state on cooling and condensation of the coolant. The study of the temperature fields of the soil, pipeline and working fluid, as well as the lengths required for cooling and condensation of the working fluid, was carried out in the ANSYS CFX software package for numerical hydrodynamic modeling. A homogeneous flow model was chosen to simulate the momentum and condensation of a vapor-liquid medium. Also, the calculations were conducted in a one-dimensional formulation using an engineering method. A methodology for modeling complex processes of heat transfer to the soil using numerical modeling has been developed and verified. 12 calculations were made; the distributions of the steam dryness and temperature in the simulated region depending on the time of the year were obtained. The functions of the total length of the pipeline, cooling and condensation lengths on the soil temperature are analyzed. It has been established that the harmonic change in the temperature of the soil set as the initial condition determines a similar change in the lengths required for cooling and condensation of the working fluid. Using this technique, it is possible to calculate pipelines of more complex shapes. The obtained temperature distributions in cross sections allow to establish the optimal distance between the axes of the pipes when designing a condenser in the form of a bundle of horizontal pipes or a bent pipeline.