Abstract
We assess the technoeconomic feasibility of onsite electricity and steam generation from recovered low-grade thermal energy in oil refineries using organic Rankine cycle (ORC) engines and mechanical vapour compression (MVC) heat pumps in various countries. The efficiencies of 34 ORC and 20 MVC current commercial systems are regressed against modified theoretical models. The resulting theoretical relations predict the thermal efficiency of commercial ORC engines within 4–5% and the coefficient of performance (COP) of commercial MVC heat pumps within 10–15%, on average. Using these models, the economic viability of ORC engines and MVC heat pumps is then assessed for 19 refinery streams as a function of heat source and sink temperatures, and the available stream thermal energy, for gas and electricity prices in selected countries. Results show that: (i) conversion to electrical power with ORC engines is, in general, economically feasible for heat-source temperatures >70 °C, however with high sensitivity to energy prices; and (ii) steam generation in MVC heat pumps, even more sensitive to energy prices, is in some cases not economical under any conditions—it is only viable with high gas/low electricity prices, for large heat sources (>2 MW) and higher temperatures (>140 °C). In countries and conditions with positive economics, payback periods down to two years are found for both technologies.
Highlights
The recovery and reuse of surplus/waste energy in industry is of increasing environmental and economic importance
This paper considers the recovery of the abundant low-grade thermal energy within the oil refining industry and its use by currently-available technologies, in particular: (i) organic Rankine cycle (ORC) engines to convert thermal to electrical energy; and (ii) mechanical vapour compression (MVC) heat pumps to generate steam by upgrading thermal energy to a higher temperature
The recovery of low-grade heat from waste-heat sources typically found in the refining sector, followed by either thermal-energy conversion or upgrading, comparing onsite electricity or steam generation in a range of countries with different gas and electricity prices that has been performed this study, leads to several key conclusions concerning the deployment of these technologies, as follows:
Summary
The recovery and reuse of surplus/waste energy in industry is of increasing environmental and economic importance. Opportunities for converting or upgrading recovered low-grade heat to power or higher-temperature heat have been less well-explored, even though the majority of surplus (waste) heat in most industries is low-grade, i.e., available at low temperatures This has been confirmed in recent studies [2,6,15,16], with Ferland et al [15], for example, estimating a potential of generating about 1200 MW of electricity (10.5 TWh.yr−1 ) by using the low-grade energy available in the oil refining sector of the US. As an example of the potential benefits from such practices, the 590 MW of low-grade heat estimated to be available for recovery within the UK oil refining sector [2] translates into potential savings of between £90–250 million.yr−1 depending on the technology employed. Reliable guidelines for the establishment of the economic feasibility of different low-grade heat recovery options, in particular in refining, are clearly still needed
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