CFD validation of optimized compact heat exchanger designs

Abstract

In offshore oil and gas production gas turbines are used for both power production and to provide process heat. CO2 emissions from the gas turbines accounts for about 25 % of the total Norwegian emissions and installing a bottoming cycle to produce power by recovering heat from the gas turbine exhaust is one way to reduce these missions. When installing a steam bottoming cycle offshore, the total weight and size will be important, and there is a need for a compact heat recovery steam generator (HRSG). A compact HRSG will often need to be designed with smaller tube diameters than conventional on-shore steam generators. To increase confidence in the compact design, the heat transfer and pressure loss models need to be accurate for the relevant geometry ranges. In this work, a compact Once Through Steam Generator (OTSG) is designed using optimisation procedures where the total weight of the steam generator has been minimised for a desired duty with restrictions for pressure losses. A range of correlations from the literature were used for the calculation of the performance. The results from the optimisation show that the ’heaviest’ results were about three times the minimum weight than the ’lightest’. To increase confidence in the results, and to provide arecommendation for design models, a validated CFD model was used to perform a numerical analysis of the optimised geometry and compare this with the correlations.