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2024
Conference Paper
Title
Industrial Process Steam Generation from Deep Geothermal Reservoirs
Abstract
Deep geothermal reservoirs (depth > 400 m) have been used to provide heat and electricity for decades. Heating of industrial processes, however, is one of the less common applications and accounts for under 1 % of the total installed capacity. One of the main reasons for this low share is the temperature level of geothermal sources, which is often unsuitable for direct heating of industrial processes. In addition, process steam is commonly used as heat transfer medium in industry, making the integration of geothermal energy even more challenging. This paper presents technical solutions to overcome these restrictions. In a first step, state-of-the-art systems are presented. These systems are limited to generating process steam at a temperature level below that of the geothermal source. Subsequently, R&D approaches from the literature are presented which aim to provide higher temperatures through additional energetic upgrading. Based on these findings, three promising concepts with steam
generating heat pumps (SGHP) are presented and examined in a simulative case study. The first concept is using a closed-loop compression heat pump (CLCHP) with direct steam generation in the heat pump condenser. The second concept consists of a combination of CLCHP with direct steam generation and a downstream mechanical vapor recompression (MVR) unit. In the third concept, an evaporator and an MVR are used. In the case study, two geothermal sources with a temperature of 100 °C (50 l/s) and 80 °C (50 l/s) are considered and cooled down to up to 60 °C. On the sink side, superheated steam with 150 °C and 4 bar is generated from a water source with 20 °C and 1 bar. A sensitivity analysis is conducted to investigate the effects of the isentropic compressor efficiency (MVR) and the efficiency of the CLCHP. An extended coefficient of performance COPPR is used for the evaluation, which, in addition to the electrical demand of the heat pump, also includes the required pumping effort for the geothermal fluid. For the investigated cases, the third process route achieves the highest COPPR of 4.25, when cooling the geothermal source from 100 °C to about 84 °C and 3.4 when cooling the geothermal source from 80 °C to about 64 °C. A comparison with alternative steam generation technologies (gas boilers, electric boilers and green hydrogen boilers) also highlights the ecological advantages (CO2-Emissions and primary energy demand) of geothermal steam generation.
generating heat pumps (SGHP) are presented and examined in a simulative case study. The first concept is using a closed-loop compression heat pump (CLCHP) with direct steam generation in the heat pump condenser. The second concept consists of a combination of CLCHP with direct steam generation and a downstream mechanical vapor recompression (MVR) unit. In the third concept, an evaporator and an MVR are used. In the case study, two geothermal sources with a temperature of 100 °C (50 l/s) and 80 °C (50 l/s) are considered and cooled down to up to 60 °C. On the sink side, superheated steam with 150 °C and 4 bar is generated from a water source with 20 °C and 1 bar. A sensitivity analysis is conducted to investigate the effects of the isentropic compressor efficiency (MVR) and the efficiency of the CLCHP. An extended coefficient of performance COPPR is used for the evaluation, which, in addition to the electrical demand of the heat pump, also includes the required pumping effort for the geothermal fluid. For the investigated cases, the third process route achieves the highest COPPR of 4.25, when cooling the geothermal source from 100 °C to about 84 °C and 3.4 when cooling the geothermal source from 80 °C to about 64 °C. A comparison with alternative steam generation technologies (gas boilers, electric boilers and green hydrogen boilers) also highlights the ecological advantages (CO2-Emissions and primary energy demand) of geothermal steam generation.
