A Review of the Performance of Minewater Heating and Cooling Systems

Abstract

As the decarbonisation of heating and cooling becomes a matter of critical importance, it has been shown that flooded mines can provide a reliable source of low-carbon thermal energy production and storage when coupled with appropriate demand via an appropriate heat transfer technology. This paper summarises the potential resource represented by a long legacy of mining operations, the means heat can be extracted from (or rejected to) flooded mine workings, and then considers the risks and challenges faced by minewater geothermal energy (MWG) schemes in the planning, construction, and operational phases. A combination of site visits, interviews and literature reviews has informed concise, updated accounts for many of the minewater geothermal energy systems installed across the world, including accounts of hitherto unpublished systems. The paper has found that a number of previously reported MWG schemes are now non-operational. Key risks encountered by MWG schemes (which in some cases have led to decommissioning) include clogging of system components with mineral precipitates (e.g., ochre), uncertainty in targeting open mine voids and their hydraulic behaviour, uncertainty regarding longevity of access to minewater resource, and accumulated ongoing monitoring and maintenance burdens.

Conceptual Modelling of Two Large-Scale Mine Water Geothermal Energy Schemes: Felling, Gateshead, UK

“…The abstraction-reinjection borehole systems at Nest Road (54.959 • N 1.564 • W) and Abbotsford Road (54.955 • N 1.556 • W), Gateshead, are the first large-scale examples of Mine water Geothermal Energy Schemes (MGES) operating in the UK (Figures 1 and 2). Such MGES are a widely discussed, but relatively seldom implemented, means of delivering low-carbon space-heating and cooling [1,2]. They typically use mine water pumped from flooded mine voids, which is then passed through a heat exchanger, coupled to a heat pump.…”

“…The heat pump/exchanger system extracts heat from the mine water (typically ∆T = 3-5 • C of temperature drop) and the chilled, thermally spent water is discharged, either to the environment or back to the mine workings. The rate of heat extracted (H ex ) from the mine water is given by: H ex = Q × ρ.c × ∆T (in kW th ) (1) where Q = mine water flow rate (L/s) The rate of heat supplied (H sup ) to the customer by the heat pump is given, in slightly simplified form, by: H sup = H ex /(1 − 1/COP) (in kW th ) (2) where COP is the coefficient of performance of the heat pump. The quantity of electrical energy (E) used by the heat pump is given by E = H sup /COP (in kW e )…”

“…The following observations from the Nest Road and Abbotsford Road sites should assist future developers in designing and constructing MGES schemes [2]:…”

“…One might expect to drill 2-3 boreholes into pillar and room mine workings in order to obtain a "good" borehole (which corresponds with commonly cited ratios of room/pillar). The likely verticality of boreholes should also be considered in this context and appropriate drilling techniques selected [2]. 4.…”

“…Progressive scaling or clogging with iron oxyhydroxides is a very common (though not inevitable [2]) occurrence in mine water geothermal systems. This can occur in abstraction or reinjection wells, heat exchangers or pipelines.…”