Rafał Laskowski

Determining the Optimum Inner Diameter of Condenser Tubes Based on Thermodynamic Objective Functions and an Economic Analysis

The diameter and configuration of tubes are important design parameters of power condensers. If a proper tube diameter is applied during the design of a power unit, a high energy efficiency of the condenser itself can be achieved and the performance of the whole power generation unit can be improved. If a tube assembly is to be replaced, one should verify whether the chosen condenser tube diameter is correct. Using a diameter that is too large increases the heat transfer area, leading to over-dimensioning and higher costs of building the condenser. On the other hand, if the diameter is too small, water flows faster through the tubes, which results in larger flow resistance and larger pumping power of the cooling-water pump. Both simple and complex methods can be applied to determine the condenser tube diameter. The paper proposes a method of technical and economic optimisation taking into account the performance of a condenser, the low-pressure (LP) part of a turbine, and a cooling-water pump as well as the profit from electric power generation and costs of building the condenser and pumping cooling water. The results obtained by this method were compared with those provided by the following simpler methods: minimization of the entropy generation rate per unit length of a condenser tube (considering entropy generation due to heat transfer and resistance of cooling-water flow), minimization of the total entropy generation rate (considering entropy generation for the system comprising the LP part of the turbine, the condenser, and the cooling-water pump), and maximization of the power unit’s output. The proposed methods were used to verify diameters of tubes in power condensers in a200-MW and a 500-MW power units.

An Approximate Relation of a Regenerative Heat Exchanger Effectiveness in Off-Design Conditions

Abstract A regenerative heat exchanger is an important component of a thermal system in power units. It is crucial to know the performance of the regenerative heat exchanger in off-design conditions during its design and operation. Advanced regenerative heat exchanger simulators have been developed for many years to describe the performance in off-design conditions. The simulators involve the use of equations for mass, momentum, and energy balances and criteria relations for heat transfer coefficients; the geometrical data of the heat exchanger are also required. Due to high complexity, the calculations are performed iteratively. For this paper, a different approach was taken: The heat exchanger was considered as a “black box.” Based on the data obtained from the simulator, the effect of input variables on the output ones was investigated, so as to propose a relation describing the regenerative heat exchanger performance. To assess this performance, heat transfer effectiveness was proposed, and its two variants were considered. Since two heat transfer effectiveness definitions were assumed, two approximate relations concerning the regenerative heat exchanger were determined. The relations were verified against data obtained from a simulator of a high-pressure regenerative heat exchanger in a medium-power steam condensing unit. A satisfactory accuracy of the proposed relations was obtained.