Water from abandoned mines as a heat source: practical experiences of open- and closed-loop strategies, United Kingdom

TLDR

Pilot heat pump systems were installed at two former collieries in Yorkshire/Derbyshire to extract heat from mine water, representing three fundamental heat‑exchanger configurations. The study tested three configurations: an open‑loop system at Caphouse where mine water is pumped through a heat exchanger and discharged; a standing‑column system at Markham where water is pumped from depth, circulated, and returned at a different depth; and a closed‑loop system at Caphouse where a heat exchanger is submerged in a treatment pond. The open‑loop system achieved high thermal efficiency but could only operate during active mine pumping and required regular filter cleaning due to iron precipitation; the standing‑column system suffered reduced efficiency from pump power but had minimal clogging; the closed‑loop system could run at any time and was not prone to clogging.

Abstract

Pilot heat pump systems have been installed at two former collieries in Yorkshire/Derbyshire, England, to extract heat from mine water. The installations represent three fundamental configurations of heat exchanger. At Caphouse Colliery, mine water is pumped through a heat exchanger coupled to a heat pump and then discharged to waste (an open-loop heat exchange system). The system performs with high thermal efficiency, but the drawbacks are: (1) it can only be operated when mine water is being actively pumped from the colliery shaft for the purposes of regional water-level management, and (2) the fact that the water is partially oxygenated means that iron oxyhydroxide precipitation occurs, necessitating regular removal of filters for cleaning. At Markham Colliery, near Bolsover, a small amount of mine water is pumped from depth in a flooded shaft, circulated through a heat exchanger coupled to a heat pump and then returned to the same mine shaft at a slightly different depth (a standing column arrangement). This system's fundamental thermal efficiency is negatively impacted by the electrical power required to run the shaft submersible pump, but clogging issues are not significant. In the third system, at Caphouse, a heat exchanger is submerged in a mine water treatment pond (a closed-loop system). This can be run at any time, irrespective of mine pumping regime, and being a closed-loop system, is not susceptible to clogging issues.