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Open access

Magdalena Wolf and Tobias Pröll

Summary

Three different process types of heat supply for industrial production processes requiring low temperature heat at 140°C are analyzed and compared with each other. The thermodynamic and economic efficiency of a gas turbine process with a heat recovery boiler (GT), a gas and steam turbine combined cycle process with a back-pressure turbine (GT-CC) and a high temperature heat pump (HTHP) system recovering waste heat from humid exhaust air between 90°C and 50°C are assessed based on energy flows, exergy flows and costs of heat provided as 4 bar (abs) saturated steam. The economic analysis bases on the comparison of the consumption-related costs of heat, the capital-related costs of heat and the operation-related costs of heat. The payback-times are calculated for different HTHP investment cost levels (1000 EUR/kWQ, 750 EUR/kWQ, 500 EUR/kWQ and 250 EUR/kWQ). To evaluate the effects of fluctuating energy costs, a sensitivity analysis with varying gas and electricity prices has been carried out.

The results show that the HTHP system, even with modest performance assumptions, has a higher exergetic efficiency than the GT or the GT-CC process. For the consumption-related costs, the economic calculation shows that the operation of a HTHP, working with a coefficient of performance (COP) of four and for a natural gas price of 25 EUR/MWh, is the cheapest way of heat production as long as the electricity price is lower than 45 EUR/MWh. An electricity price above 45 EUR/MWh makes a GT-CC process more favorable. For the period from January 2013 until June 2016, the total costs of heat and the payback times, based on real gas and electricity prices from the EEX, are calculated and analyzed. For overall cost-optimized heat supply, the results show that the share of heat provided by the HTHP system varies between 45% and 76% between January 2013 and June 2016. Especially in 2013 and 2014, the economic conditions for operating heat pumps were very good. Since October 2015, the natural gas prices have seen a decrease and the economic conditions shifted again favoring the industrial heat supply with combined heat and power systems.

Open access

Wolf Schluchter and Magdalena Rybaczewska- Błażejowska

Abstract

Life cycle sustainability assessment of municipal waste management systems The core element of all waste management systems that determines further treatment is the collection, transportation and sorting of waste. There is a spectrum of options that ranges from the complete source separation of waste with little or no consecutive sorting to the minimum separation at source and the consecutive central sorting of fully commingle waste. As each of the collection - transportation - sorting methods has particular characteristics, in assessing the most sustainable solution, a number of factors have to be taken into consideration. To assist decision makers (ad exemplum local authorities), the authors of this article has specified environmental, economic and social criteria that need to be considered while designing the integrated waste management systems. They can be grouped into environmental effectiveness (conservation of resources and reduction of environmental pollution), economic affordability and social acceptability. The article refers to the authors’ research on “The application of life cycle assessment in the integrated municipal waste management” founded by DAAD (Deutscher Akademischer Austauschdienst).