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Energy-economic analysis of CHP turbine with three-stage heating of district heating system water

Today the district heating is predominantly based on cogeneration power plants with steam turbines for combined heat and power production (CHPT) with controlled steam extractions (CE). In case of stagewise heating of district heating system water, the whole heating is realised in a number of successively connected water heaters by steam extracted from the turbine. This results in additional production of electric power because heating steam extracted for the first stage in the direction of system water flow, has lower pressure than for the second stage. In CHPTCE when operating in heating load regimes, the steam flow to the condenser still is not permitted to be zero. There is minimal steam flow rate which is required for the cooling of the low-pressure stages. For recovering this heat, the condenser has additional built-in bundle tubes, which can be fed with returned system water from district heating. On this way the built-in bundles in condensers of CHPTCE make the third stage of stagewise heating of system water. The paper objective is to determine feasibility of the three-stage heating of system water by Cleaner Production Methodology on example of CHPTCE of 120 MW power installed in the Cogeneration Power Plant Zagreb (TE-TO Zagreb). The results of the energy and economic analysis show high feasibility of the three-stage system water heating application.

cogeneration power plant ; CHP steam turbine ; district heating ; energy-economic analysis

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