Abstract
• It is crucial to account for the price of CO 2 emissions when considering heat pumps. • The thermodynamic optimum is, in general, far off the economic one for CRHP. • The payback period for CRHP can be within 3 years for large range of conditions. Heat pumps can efficiently upgrade waste heat from the industry and in that way reduce emissions. One of the main reasons why heat pumps are not applied to a greater extent in industry are large payback periods. Compression–resorption heat pumps (CRHP) enhanced by wet compression are considered a very promising option that can have higher coefficient of performance compared to traditional technologies when the heat source and/or sink have a large temperature glide. In this study the thermodynamic and economic performance of two potential industrial cases are examined for CRHP operating with NH 3 –H 2 O and NH 3 –CO 2 –H 2 O. A detailed thermodynamic model of the compressor is used to evaluate the isentropic efficiency for each case. The results are used to calculate the simple payback period, when a boiler is replaced by a CRHP, as a function of the predicted gas and electricity prices in the Netherlands from 2020 to 2035. The results indicate that adding CO 2 to the NH 3 –H 2 O mixture increases the cycle COP when the temperature glide of the heat sink is 40 K while the opposite occurs when the glide is 80 K. The highest COPs and lowest payback times are obtained when the outlet vapor quality is around 0.50 for both the binary and ternary mixtures. Larger glides require higher outlet qualities. However, it is clear that even for high temperature glides the payback period can be within acceptable limits, especially if the cost of CO 2 emissions is taken into account.
Highlights
Heat pumps have the potential to reduce dramatically the use of expensive utilities in the process industry, with significant energy savings and associated major reduction in GHG emissions (Kiss and Infante Ferreira, 2016)
The results indicate that adding CO2 to the NH3–H2O mixture increases the cycle coefficient of performance (COP) when the temperature glide of the heat sink is 40 K while the opposite occurs when the glide is
It is clear that Compression–resorption heat pumps (CRHP) are a very promising option to upgrade waste heat streams
Summary
Heat pumps have the potential to reduce dramatically the use of expensive utilities in the process industry, with significant energy savings and associated major reduction in GHG emissions (Kiss and Infante Ferreira, 2016). Limited number of studies have looked at mixtures for high temperature applications and in two recent cases the thermodynamic properties are not reported (Xiaohui et al, 2014; Zhang et al, 2017). Both water and ammonia have 0 GWP. They predicted that the price would be around 7 € ton−1 CO2 in 2020 and not go up to 25 € ton−1 CO2 until 2035, which it has already reached in 2019 This increase is positive news for heat pumps that can, as mentioned at the beginning of the introduction, significantly reduce CO2 emissions in industry. The cost of CO2 emission is, as well, taken into account
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