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.
Highlights
At Caphouse, a heat exchanger is submerged in a mine water treatment pond
The Coal Authority’s Dawdon mine water heat pump scheme (Watson 2012; Bailey et al 2013) found that passing iron-rich aerated mine water through a heat exchanger led to very rapid ochre clogging
In the case of Dawdon, this was solved using raw, unaerated mine water. This supports the observations and modelling work of Banks et al (2009), which indicated that chemically reducing, ironrich mine water can be used in heat exchange systems provided that it is not allowed to come into contact with atmospheric oxygen, such that the iron remains in its soluble ferrous (Fe2+) form
Summary
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. In active mines, inflowing mine water needs to be removed from the mine system to allow working. This is often achieved in shallow mines by gravity drainage via soughs or adits to nearby valleys or watercourses. 2. the mine continues to be pumped to prevent it filling with water and threatening other working mines downdip (Janson et al 2009). 3. the mine, or interconnected mine system, continues to be pumped at one locality (or a limited number of localities) in order to prevent uncontrolled outbreaks of water at the surface (Banks et al 1997a)
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