Convesion of industrial compression cooling to absorption cooling in an integrated district heating and cooling system

Sammanfattning: Astra Zeneca plant in Gärtuna has many compression cooling machines for comfort that consume about 11.7 GWh of electricity per year. Many of the cooling machines are old; due to the increase of production of the plant, cooling capacity was limited and new machines have been built. Now, the cooling capacity is over-sized. Söderenergi is the district heating plant that supplies heating to Astra Zeneca plant. Due to the strict environmental policy in the energy plant, last year, a bio-fuelled CHP plant was built. It is awarded with the electricity certificate system. The study investigates the possibility for converting some of the compression cooling to absorption cooling and then analyzes the effects of the district heating system through MODEST optimizations. The effects of the analysis are studied in a system composed by the district heating system in Södertälje and cooling system in Astra Zeneca. In the current system the district heating production is from boiler and compression system supplies cooling to Astra Zeneca. The future system includes a CHP plant for the heating production, and compression system is converted to absorption system in Astra Zeneca. Four effects are analyzed in the system: optimal distribution of the district heating production with the plants available, saving fuel, environmental impact and total cost. The environmental impact has been analyzed considering the marginal electricity from coal condensing plants. The total cost is divided in two parts: production cost, in which district heating cost, purchase of electricity and Emissions Trading cost are included, and investment costs. The progressive changes are introduced in the system as four different scenarios. The introduction of the absorption machines in the system with the current district heating production increases the total cost due to the low electricity price in Sweden. The introduction of the CHP plant in the district heating production supposes a profit of the production cost with compression system due to the high income of the electricity produced that is sold to the grid; it profit increases when compression is replaced by absorption system. The fuel used in the production of the future system decreases and also the emissions. Then, the future system becomes an opportunity from an environmental and economical point of view. At higher purchase electricity prices predicted in the open electricity market for an immediately future, the future system will become more economically advantageous.