Steam Injected Gas Turbine (STIG) for Load Flexible CHP: Aspects of Dynamic Behaviour, Control and Water Recovery

Abstract

Abstract Industrial combined heat and power (CHP) plants are often faced with highly variable demand of heat and power. Demand fluctuations up to 50% of nominal load are not uncommonly. The cost and revenue situation in the energy market represents a challenge, also for cogeneration of heat and power (CHP). More frequent and rapid load changes and a wide operating range are required for economic operation of industrial power plants. Maintaining pressure in steam network is commonly done directly by a condensation steam turbine in a combined cycle or indirectly by load changes of the gas turbine in a gas turbine and heat recovery steam generator arrangement. Both result in a change of the electric output of the plant. However, operating cost of a steam turbine are higher than a single gas turbine. The steam injected gas turbine (STIG) cycle with water recovery is a beneficial alternative. It provides an equivalent degree of freedom of power and heat generation. High process efficiency is achieved over a wide operating range. Although STIG is a proven technology, it is not yet widespread. The emphasis of this paper is placed on modeling the system behavior, process control and experiences in water recovery. A dynamic simulation model, based on OpenModelica, has been developed. It provides relevant information on system response for fluctuating steam injection and helps to optimize instrumentation and control. Considerable experience has been gained on water recovery with respect to condensate quality, optimum water treatment architecture and water recovery rate, which is also presented.