Applikation av småskalig värme- och elproduktion : Simulering av anläggningsdrift samt nyttjande av hästgödsel för lokal biogasproduktion vid Sundbyholms travbana

Sammanfattning: The global community is facing great challenges as the energy system is transforming towards more reliable, effective, clean and renewable production. Small-scale and micro networks will play an important role in this changeover. Its advantages over today’s large conventional energy systems are their reliability and stability. In small-scale and micro networks, there is usually a variety of production units such as photovoltaic, wind power and micro-combined heat and power (micro-CHP). In this study, a small-scale network with an application of two different types of biogas fueled micro-CHPs is analyzed. The units are a micro gas engine (MGM) and a micro gas turbine (MGT). The application of micro-CHP is validated using a reference facility connected to a small-scale district heating network. The reference facility is a heat production plant at a horse race track outside Eskilstuna, Sweden consisting of an oil boiler, a pellet boiler and a heat storage tank. The potential in replacing the oil boiler with renewable micro-CHP is investigated. A simulation model is built in the software GAMS, using Mixed Integer Linear Programming (MILP) and the solver CPLEX, and the model is simulated using the heat demand from the horse race track. Results from the model validation shows that it is possible for both the MGM or the MGT together with the pellet boiler and the heat storage tank to fulfill the heat demand of the facility. The horse race track handles 4 000 m3 of horse manure annually, which is transported 124 km to a compost treatment facility. Therefore, a general analysis of biogas production from horse manure is conducted in order to investigate the possibilities for better horse manure treatment on site. A calculation for a biogas reactor with a capacity for the maximum biogas requirement of the micro-CHP is implemented. Horse manure is suggested to be co-digested with food waste, in order to provide a higher biogas exchange. The result of a Life Cycle Cost (LCC) analysis indicates difficulties in justifying an investment of a micro-CHP together with a biogas plant at current prices for heat and electricity. The results show that the payback period for the MGM is 7 years which is 2 years shorter than its lifetime and the MGT payback period is 12 year which also is it lifetime. The MGM shows the largest investment potential since it has an investment cost approximately 860 kSEK lower than for the MGT. The MGM also has a slightly higher electrical efficiency which results in higher revenues from produced electricity. The chosen MGM in this study is slightly smaller than the MGT, resulting in a lower biogas demand and a lower investment cost for a biogas plant. A sensitivity analysis shows great impact of the electricity price on the payback period for both types of micro-CHP. The results show that with an electricity price of 280 SEK/MWh, both the MGM and the MGT repays within their lifetime. But since MGM has a higher net present value at all electric prices, is the MGM considered to be a more economical feasible investment. What the authors think should be highlighted is also the environmental benefits of more efficient treatment of horse manure at the horse race track together with the possibility of local production of fuel resulting in reduced CO2 emissions by 47 tons/year.