engleski

Optimisation model for cogeneration plant

An optimisation model is presented in this paper with the way how to optimise a complex refinery energy plant. The total energy system is divided in appertained subsystems: steam production, turbogenerators, and power distribution. They are considered separately to find the total optimum for whole system. The analysed plant consists of more different steam generators, turbogenerators and of the power distribution subsystem which can purchase or sell electricity to the local utility grid. The problem of the energy management is derived with the aim to find the optimum steam load allocation among several boilers, and the optimum electric load allocation among several turbogenerators. Steam boilers in a parallel operation usually have different efficiency characteristics depending of their type, operating load and fired fuel. These variables make the optimisation problem of steam generation subsystem pretty complex. The optimisation procedure presented in this paper is based on the least-cost operation, that will be achieved when all boilers produce steam at the same incremental cost. It means that the next increment of steam can be produced at the same cost from any of included boilers. The turbogenerators subsystem consists of different steam turbines. Some can be condensing, some noncondensing and also extraction pressures may differ. The optimum allocation of electric power generation is preeminently governed by steam demands at various pressures, by prices of purchased or sold electric power and by individual efficiency of operating steam turbines. The final part of the paper presents an analysis of gas turbine cycle introduction for combined heat and power production into the existing energy system with the aim to improve operating flexibility, efficiency and reliability. The steam injection gas turbine cycle is analysed and proposed for this case. The whole work presented in this paper can be useful for an implementation into computer systems for the cogeneration plants advance control and for similar problems of renewing or retrofitting activities on energy plants in process industry.

cogeneration; process industry; optimisation; boilers; steam turbine; gas turbine

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