Economic and Environmental Benefits of the ORC and the Willingness to Invest : A case study from a wastewater treatment plant and a small-scale combined heat and power plant

Abstract: In Sweden, as many other European countries, centralized large-scale electricity production has traditionally been used to meet the electricity and heat demand. During recent years however, small-scale producers have gained more ground and contributes more to the total electricity generation. Industrial systems such as sewage plants and small-scale district heating plants both have potential thermal power sources available and utilizing this to generate electricity could be an important contribution towards increasing the ratio and effectiveness of renewable energy sources and reduce the primary energy supply. The potential of the Organic Rankine Cycle has been acknowledged by many, with commercial development increasing exponentially during the recent decades. Unlike the traditional Rankine cycle which uses water as a working fluid, the ORC uses a refrigerant with a lower evaporation temperature, which makes it possible to produce electricity from heat of lower temperatures. This thesis has through reading literature and plant visits analyzed the effect of implementing an operation strategy at two different plants where ORCs has been installed. One wastewater treatment plant in Norrköping and one combined heat and power plant in Ronneby, Sweden. The operation strategy includes moving production of electricity to high demand hours as well as analyzing options for increasing the efficiency at the plants. In addition, this thesis also includes a questionnaire made in order to analyze what obstacles and motivations that affect the willingness to invest in ORC technology in Sweden. The result from this provides useful information for future work in order to see an increased establishment of the ORC on the Swedish market.The results show that by implementing an operation strategy at plant Norrköping the avoided electricity and heat cost from installing the ORC could be increased by 47% and the avoided emissions increased by 436%. For plant Ronneby the avoided electricity cost could be increased by 8% and the avoided emissions increased by 31%. The questionnaire shows that different plants have different prerequisites and viewpoints when it comes to investing in ORC technology. This can for example be differences in budget for investments, the workload of the employees or if there is available fuel to run the ORC. From this finding it becomes clear that if one wish to see an increase in ORC technology in today’s industry, it becomes vital to look at each individual plant and assess the situation from there. However, a trend shows that the reduced electricity cost and the reduction in global emissions are two strong motivations for heat plants and wastewater treatment plants to invest in ORC systems.