Methodology for Modernizing Local Gas-Fired District Heating Systems into a Central District Heating System Using Gas-Fired Cogeneration Engines-A Case Study

Sustainability can be achieved by improving process efficiency, among other methods. In the case of heat supply systems for cities, one of the ways to increase the efficiency of fuel use, and thus reduce resource consumption and greenhouse gas emissions, is the generation of heat and electricity in one process-the use of cogeneration (CHP). The main goal of this paper is to deliver the methodology for a step-by-step modernization process for local gas-fired heating plants through the use of gas cogeneration engines in common central district heating systems. The presented methodology was applied on the basis of a real system located in north-western Poland (case study from Bialogard). The profitability of cogeneration was simulated against the background of changing gas prices. The financial and environmental profit from modernization was calculated. The technical requirements that had to be met in order to adapt the existing heating system to cooperation with the new energy source were also presented. The importance of selecting the supply and return temperature of water in the heating system after modernization was emphasized. Based on investment experience, we show that installing a cogeneration engine improves a company's financial result by 33% (calculated as the difference between the revenue from the sale of energy and the cost of gas only) and is less harmful to the environment, among other benefits, significantly reducing CO2 emissions by 78%.