Steady State and Transient Modelling of A Three-Core Once-Through Steam Generator

Abstract

To reduce emissions and save fuel in offshore power production using gas turbines, one can use the gas turbine exhaust as a heat source for a bottoming cycle for heat and power production. This can replace about one in four gas turbines. In offshore applications weight and size become more important and thus a once-through steam generator (OTSG) is a way to achieve low weight for the bottoming cycle. To reduce the size and weight of the OTSG further, one can reduce the tube diameter in the tube bundles. In this work a three-core OTSG, representing the economizer, evaporator, and superheater, was modelled and the design optimized to achieve minimum weight, while producing a certain amount of power and keeping within constraints of flue gas and steam pressure losses. This was done for varying tube diameters in each of the cores, in steady state. Afterwards transient simulations were performed for each optimized design to find their response times to a step change in the gas turbine load. The evaporator has the biggest impact on both the weight and the response time, while the superheater and economizer had similar and smaller impacts on both the weight and response time.