Minewater as an environmental heat source or sink: “Geothermal” heating and cooling

ThermalEnergyfromMineWorkingsDaveBanks

UniversityofGlasgowHolymoorConsultancy,Chesterfield

“No;thismyhandwillratherThemultitudinousseasincarnadine,Makingthegreenonered.”

Macbeth,Crucible,Sheffield.

“....makingtheredonegreen”

Minewater

Water

Minewater

Water

Pyrite+water+O2 =acid+sulphate+iron

Water

Pumpandtreat

Caphouseminewatertreatmentscheme,nearWakefield

Katowicemine,Poland

Closedloop– thelowriskway

HeatpumpHeattoabuilding

Heatabsorbedfromrockinshaft/boreholewall

Ifadvectionofwaterinshaft:greaterheatyieldsachievable

Advantages:

No abstraction of mine water

No risk of geochemical fouling of heat exchanger

Disdvantages:

May interfere with desludging of basins

Modest heat yield

Heatpump/exchanger

Totreatmentsystem/surfacewaterrecipient

Ortore‐injection

Typicalopenloopsystem

TheBigRisksGeochemistry

Thermalfeedback

Inwinter

Warmwaterabstractedfromdeepinshaft(ultimatelythroughdeeproadways)

Thermally“spent”coolerwaterflowsawayviahigherroadways

Ifminewaterthroughflowisbigenough…..Heatpump/exchanger

Whyminewater?

MostGSHPschemesdeliversavingsonCO2 emissionsandonOPEX.BUTtheyrequireconsiderableCAPEXonboreholedrillingandsubsurfaceheatexchangers.

Theuseofminesandminewatercanreducecapitalexpenditurebecause:

1. Flooded,interconnectedmineworkingsallowaccesstoahugereservoirofwarmmine‐waterviaonlyoneortwoboreholes,orviaexistingshafts.

2. Theinterconnectednetworkoftunnelswithinthemineitselfrepresentsanenormousheatexchangesurface.

3. Someabandonedminesarealreadycommittedtoexpenditureonpumpingand/ortreatmentmerelyforthepurposesofenvironmentalprotection,whileregardingthepumpedwatermerelyasatroublesome“waste”product.

4. TheUKCoalAuthoritypumpsand/ortreatsaround3000L/swaterfromabandonedmines,withtemperaturesof9‐18°C,3000L/sx4200J/K/Lx5°C=63MW

GlenalmondStreet,Shettleston,GlasgowWorkingsinEllCoalSeam

GlenalmondStreet,Shettleston,Glasgow

Photos by D Banks

Completed1999Serves16newly‐builtdwellings(1600m2)Source=100mboreholeinfloodedcoalmine

workingsoftheEllSeamWaterpumpedat12°Ccirculatedviawater‐to‐water

heatpump(65kWpeakoutput),andreturnedviashallowerreinjectionborehole

Heatpumpoutput=55°Ctothermalstore.Designedwithsupplementarysolarthermalheating.

FeedsDHW(withsupplementaryimmersionheater)andcentralheating

20kWheatpump

2‐3L/sat15.4°Cfrom235m

Returnto255mat12°C

Heatat60°CtoAlkane’soffices

Alkane,MarkhamColliery,nearBolsover

Alkane,MarkhamColliery,nearBolsover

Feat4mg/L

Nocloggingorfeedbackproblemsobserved

Ochil View, Lumphinnans, nr. Cowdenbeath, Fife

Photos by D Banks

pH 6.16Eh +29 mV (reducing, H2S smell)Temperature 12.1oCAlkalinity 6.5 meq/LSulphate 1339 mg/LChloride 20.3 mg/LCalcium 315 mg/LMagnesium 224 mg/LSodium 15.6 mg/LPotassium 21.6 mg/LIron 57.9 mg/LManganese 3 mg/L

Hitherto...

TheShettlestonschemehashadnoproblemsofcloggingatall...

ButtherechargewelloftheLumphinnansschemewasvandalised(2005)...

DegassingofCO2

ExposuretoO2

Precipitationofochre,other

metalhydroxides,calcite

CoalAuthorityTrialatDawdon,Co.Durham

75to150L/sminewatertreatmentcapacityDanfoss12kWheatpumpheatsofficeandDHW1.5L/softreatedminewateratc.20°CsupportsheatpumpMinewatersaline,withc.0.8mg/Liron(peaksof2‐4mg/L)

fromCoalAuthoritywebsite

CoalAuthoritytrialatDawdon

Whentreated(aerated)waterused,heatexchangerandfilterrapidlybecameclogged

but,afterraw(unoxygenated)waterused,fewproblems

Thesecretsofsuccess

A good understanding of subsurface geometry and hydraulics of mine workings

A good understanding of hydrochemistry

Gas management!