engleski

Optimization of waste heat utilization in pipeline compressor station process

Gas turbine driven pipeline compressor stations employed in existing pipelines and also in those that shall be built due to increasing demand for natural gas present significant potential for production of additional electricity and useful heat by utilizing the waste heat from the gas turbine process. For utilizing the waste heat existing systems are usually upgraded with a heat recovery steam generator, steam turbine and balance of plant equipment, which are used to produce electricity via combined gas and steam cycle process. The thesis analyzes and compares several HRSG configurations both in the terms of thermodynamic and thermoeconomic criteria. In order to find an optimal configuration of a new system an exergo-economic HRSG optimization is conducted for finding the compromise between the exergy losses and investment costs of HRSG surfaces. Initial optimization results show insensibility of the objective function on the cost of surfaces by resulting in zero pinch point. Such result demonstrates low surface costs compared to the cost of exergy losses for given parameters of available flue gases and assumed factors of the objective function. Incorporation of exergy of inlet feed water and outlet gas (which are neglected by author of the selected optimization method) result in max. pinch point and high values of pressure close to critical one. Such result of pressure value is however not feasible for design of the industrial steam turbine. Furthermore tendency of reaching upper limit of pinch point shows inadequacy of this approach. So as to obtain positive but realistic pinch point values a surface exponent is introduced into equation for calculating the HRSG surface cost. Idea is to find the value of the surface exponent obtaining minimal feasible pinch point provided by the heat recovery steam generator manufacturer. Referent minimal feasible pinch point is selected for unfired case. Proper value of the surface exponent is determined on the basic single pressure configuration. Upon defining optimization criteria this value is further used for optimization of other configurations. Predefined single pressure, dual pressure and triple pressure system configurations are further examined in operating regimes of the pipeline compressor station. Thereby are cost of electricity, cash flow and internal rate of return calculated. Comparison of configurations is based on diagram presenting dependency of electricity cost on net system efficiency. Pareto front with respect to both criteria ; maximal system efficiency and minimal cost of electricity is constructed. Thereof 2P3 and 3P3 configurations are the closest to the Pareto front whereby the first is characterized by the lowest cost of electricity and the latter by the highest system efficiency. Finally sensitivity analysis has been performed in order to estimate system viability in case of varying fuel prices and CO2 emission certificates. The results of the performed investigation are based on realistic compressor station data and could be used as a guideline for further research and development in this field.

pipeline compressor station; booster station; waste heat utilization; combined

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