GEOTHERMAL DEICING IN A MINE TUNNEL

Transcription

1 POCEEDINGS, Thirty-Sith rkhp n Getheral eervir Engineering Stanfrd Univerity, Stanfrd, Califrnia, January - February, 0 SGP-T-9 GEOTHEMAL DEICING IN A MINE TUNNEL Anik Tth Univerity f Miklc Miklc-Egyetevar, 55 Hungary e-ail: tth.anik@uni-iklc.hu ABSTACT The flr f the entrance tunnel t an undergrund wate depit yte in Hungary i eped t frt and icing in winter. Thi i rather dangeru fr the heavy vehicle traffic. T avid thi danger, a flr deicing yte wa intalled. Thi cnit f a heating grid yte placed in the flr f the tunnel entrance ectin. Initially, a fuel il yte wa utilized t heat the incing air. Mre recently getheral heat pup were recended fr the epanin f the facility. In thi cae getheral energy i utilized indirectly by tw different yte. The firt i air-water heat pup utilizing the heat cntent f the wared up air a it flw f the ine tunnel. The ther urce i the heat cntent f the drained water fr the deep part f the ine. The benefit f thi yte i ultiplied: decreaing f the theral pwer a cpared t the riginal fuel il heating yte, eliinating f the ue f fuel il, and decreaing the CO eiin. BACKOUND In the hwetern part f Hungary in the Bátaapáti regin a all-t-ediu-level undergrund radiactive wate depit yte wa built. The trage pace i cnnected by tw 800 -lng ine tunnel. The trage area wa cntructed thrugh thee tunnel, and afterward they were ued fr the peratinal traffic and ventilatin. If the ide teperature i le than -5C, then t iprve the wrkplace cliate and prevent the icing f the entrance ectin t the ine tunnel, it i neceary t war the intake air t the tunnel. The riginal deign included the ue f traditinal il burner t war the air. During the cntructin perid 80 / f air-flw wa ued. Thi wa the aiu air deand. During nral peratin 5 / air-flw i utilized. egardle f the ean thee airflw had t be heated t between + C and +5 C. In cae f an etree weather cnditin, (fr eaple -8 C), the air teperature ut be increaed t between +0 C and + C. In thi latter cae,,6k f heating capacity i required. Thi require 47 l/h f fuel fr the il burner. The net phae f the develpent f the wate depit yte wuld have required the intallatin f tw re il burner. Intead f thi epenive lutin, and t decreae f the huge CO eiin fr the il burner, I recended a getheral lutin fr the flr and the rf heating. Deicing the flr f the tunnel and avid the fratin f icicle n the rf. USING GEOTHEMAL ENEGY Tepering the air f the ine tunnel i neceary n the ne hand t enure that the facility' cliate i cfrtable fr the wrker, and n the ther hand deicing the flr f the entrance ectin. Getheral energy ha alway had a dinant rle in the cliate f undergrund facilitie and ine tunnel. The wall teperature f the ine tunnel i ab +7 t +8 C, which i uch higher than the inflwing air teperature in winter. The urface f the tunnel wall i a very large heat tranfer area. The air intake tunnel wall with the flr and the rf cntitute 6,000 f urface area ver the length f,800. The heat flw i cntant ver thi ajr urface and thu, heat the air flw in the ine tunnel. Thi can be deterined by a iple calculatin. Heating requireent fr the icing intake tunnel It i enugh t heat the firt 00 ectin f the intake-air tunnel jut the icing appear. The heating yte ue ht water and glycl lutin being circulated in pipe lp belw the flr and n the rf f the ine tunnel. Siilar intallatin like idewalk, radway, and bridge deicing yte have been dentrated in everal cuntrie, including Argentina, Japan and the United State. In ur cae the heating requireent can be et by tw urce. The firt i air-water heat pup utilizing the heat cntent f the wared up air a it flw f the ine tunnel. The ther urce i the heat cntent f the drained water fr the deep part f the ine. Chapan (95) derive and eplain equatin fr the heating requireent f a nw-elting yte. Chapan and Katunich (956) derive the general equatin fr the required heat put (q) in /. e can ue it fr the tunnel flr. q q + q + A( qe + qh ) ()

2 q enible heat tranferred t the ice (/ ), q heat f fuin (/ ), A rati f nw-free area t ttal area (dieninle), q e heat f evapratin (/ ), q h heat tranfer by cnvectin (/ ). The enible heat q t bring the ice t 0 C ( F) i: q h ρi () rate f taken in nw layer n the flr (0.005 /day) ρ denity f ice (97 kg/ ), c p pecific heat f nw (J/kg C) h enthalpy f fuin fr water (J/kg), c cnverin factr (86,400 ). It can be aued that the ice and nw carried by vehicle iediately tart t elt, reulting that it de nt cl belw 0 C. Thu, in the q eber can be ignred. Suppe that the thickne f nw cver entered int the tunnel i.5 by day. The heat f fuin q t elt the nw i: q cp ρ () c The heat f evapratin f the lten nw q e : q e c ρw 7.8 c (4) ρ w denity f water (000 kg/ ), c heat f evapratin (,5 kj/kg) The heat tranfer q h between the water fil n the flr and the intake air. e can calculate the heat tranfer cefficient by turbulent flw. In thi cae the heat tranfer cefficient depend n the eynld nuber. q h T T 9.4 (5) h ( w ) T w water fil teperature ( C), uually taken a C ( F) T intake air teperature at the entrance cr ectin in winter ( -5 C) Suing the flue, give: q 47.5 /. (6) The heated area in the length f 00 i,800, thu the needed theral pwer n the flr f the tunnel i: Qf A q 85. k (7) Q f theral pwer fr the flr heating (k), In winter tie, e water i appear fr the rf f the ine tunnel the icing i fr ccur a icicle. It i appear nly the firt 00 part f the tunnel. If we can war the rf urface ver the freezing pint (0 C) culdn t develp icicle, and the water drp culd diperged in the intake air flw. If we heat the 6 arch f the tunnel rf, in the length f 00 get,800 area. Thu the needed theral pwer n the rf i: Q r h A T 70.6 k (8) T 6 C teperature difference between the freezing pint and the intake air (-(-5)) C, Q r theral pwer fr the rf heating (k). The flr and the rf heating deand tgether i QT Qf + Qr k (9) Q T ttal theral pwer deand (k). Getheral urce fr Heating the ine tunnel Enthalpy f the wared up air The aiu inflwing air i 80 / which ccurred during cntructin. In thi cae the crectinal average velcity i: c 80 Q A 0.67 c cr-ectinal average velcity (/) Q aiu inflwing air ( /) A cr-ectin f the tunnel ( ) (0) The hydraulic radiu f the tunnel: A 0. H.5 K 0. () K hydraulically active perieter (Bbk, 99) The eynld nuber c 4 H e 6680 ν 5 0 () The Prandtl nuber: ρνc Pr p 0.54 () k here ρ air denity (.9kg/ ) ν kineatic vicity cefficient (0.04 /) c p pecific heat (005J/kg C)

3 k theral cnductivity (0.04/ C) The Nuelt nuber can be calculated fr the eynld nuber and the Prandtl nuber Nu 0.05 e Pr (4) The heat tranfer cefficient n the wall: Nu k h 6.54 (5) 4 H C Bbk(99) derive and eplain equatin fr the teperature ditributin alng the length. T T 4 HπLh c & p ( T T ) e wall wall (6) L length f the air in the tunnel (), T wared up air teperature after the length L ( C), T wall tunnel wall teperature ( C), T ide air teperature ( C), & a flw rate f air (kg/). If the length f the tunnel i,800 and the ide teperature i -5 C, the air teperature at the end f the intake tunnel can be calculated. 4.5 π, ( 8 ( 5) ) e C TL 8 (7) Thi calculated teperature wa checked by the eaured teperature at the end f the intake tunnel, when the ide teperature wa -5 C. The reult wa very cle. The eaured teperature wa 6 C. In an average winter day the air teperature after paing thrugh the intake tunnel i wared fr -5 C t +5. C. It ean: T 0. C. During the cntructin perid 80 / (0 kg/) f air-flw i ued. Thi i the aiu air deand. In thi cae the aiu theral pwer Q & a i: a pwer c & p ( TL T ),0k (8) It can be een the theral pwer fr the tunnel wall i alt a uch a the theral pwer f traditinal il burner at,0 k at the aiu air deand. In rder t heat the ine tunnel, it i nt pible t ue all f the aiu heat pwer. It can be eplited the enthalpy difference between the inlet and let air f the heat pup, belnging t the teperature drp: T5.-5. C. In thi cae the ueful theral pwer fr the air i: aira c & p ( TL T ) 8.7 k (9) T let air teperature (5 C), During nral peratin 5 / (.kg/ f) airflw i utilized. In thi cae the theral pwer Q & n i: c & p L ( T T ) 65.8 k n The ueful pwer in the nral peratin i: & c & T T 57 ( ) k Qairin p L (0) () Enthalpy f the cllected ine water Every day in the ine tunnel ab 500 /day f kg water i prduced, which ean ṁ 5.79 a flw rate. After a lng ter tet the teperature f thi ine water i ab 5 C. Thi teperature den t depend n the ean, a it i the ae in winter r uer. At nral peratin thi water i cllected in a up under the urface in the ine. Fr tie t tie thi water i puped t a creek n the urface. Since the flw rate f thi inflwing water i teady, and it teperature i cntant, we can ue it theral pwer a a natural getheral urce. The heat pwer fr the ine water i then: Q w c & w ( Tw T ) 4.4 k () & a flw rate f the cllected ine water (57.9 kg/), c w pecific heat f water ( 4.87kJ/kg C), T w ine water teperature (5. C), T let water teperature (5 C). It can be een that the heating deand i 56k. The heat upply fr the air i 57k and fr the ine water i 4k. Thu either heat urce i enugh t atify the heating deand f the ine tunnel deicing. Lp yte fr the ine tunnel T cllect the ine water a 00 diaeter pipe i ued. Every day ab 500 /day ( /) i prduced in the ine tunnel. The cr ectinal average velcity in the pipe i: Q v 0.77 D π 0. π () v D e 7700 ν -6 0 (4) The eynld nuber i high and in thi cae the flw i turbulent. A heating lp yte i deigned n the flr and n the rf fr the firt 00 ectin in the ine tunnel. Preent practice i t ue platic pipe, with the typical

4 being plyethylene accrding t Lund (000). The relative rughne (the rati between pipe diaeter and ablute rughne) f the PE pipe i D/k 0,000. Thee eynld nuber and relative rughne value deterine a hydraulically th behavir f the flw. In thi cae the frictin factr (Karan 90) i λ e λ lg,5 (5) Fr thi iplicit fr by iteratin we get λ The ttal preure l i the u f the preure l fr the tube and the preure le fr the reitance f the 500 elbw by Varga (970). The tube pacing i 0.4 in the 750 lp and alng the 00 length. The prcedure i iilar t running radiant heat in a building flr lab. L v v p' λ ρ + Σξkρ D (6) λ frictin factr (0.099 dienin le), L ttal length f the tube (5000), ρ water denity (000 kg/ ), v cr ectinal average velcity (0.7 /), D pipe diaeter (0. ), ξ k 0. elbw l cefficient. N p' 908 (7) hich i ab 9 bar. The teperature ditributin alng the length i T T 4UL e ρcvd ( T T ) (8) T 0 wall teperature f the ine tunnel ( C), T intake water teperature in the tube ( C), U verall heat tranfer cefficient (/ C), c w pecific heat f water (kj/kg C). e can calculate the verall heat tranfer cefficient. in in + ln + lnφ U h k tube in kceent (9) h heat tranfer cefficient between the flwing water and the tube wall (/ C), in internal diaeter f the tube (), eternal diaeter f the tube (M), k theral cnductivity f the PE tube (/ C), φ hape cefficient. The hape cefficient can be ued fr cnideratin the ayetric heat flw pattern arund the heating pipe (Bbk, 99) Nu 0,05 e Pr 7.4 (0) Nu k h D () h 4 / Φ C, C 0,00045 h () () ditance between the flr urface and the centerline f the tube (). Φ 0,679 (4) Finally the verall heat tranfer cefficient i U C (5) If the teperature f the wall tunnel i T wall C and the let teperature f the heat pup i T hp 4 C, then the let water teperature fr the tube i T 4 U L ρ v D ( T T ) c Twall + hp wall e , ( 4 ) e 4.75 C T + (6) (7) The theral pwer fr the heating lp i Q & & c( T T ) (8) kg KJ Q & ( 4 4.8) 488 k (9) CONCLUSION kg C The tunnel flr f the entrance ectin f an undergrund wate depit yte in Hungary i eped t frt and icing in winter. Thi i rather dangeru fr the heavy vehicle traffic. T avid thi danger, an in-itu flr deicing heating lp yte i deigned. Thi flr heating yte i uch re effective than the riginally deigned intake air heating by traditinal il burner. There are tw heat urce f the getheral energy. One f the i the heat cntent f the urrunding rck, which war up the ventilated air. The ther i the heat cntent f the cllected ine water. The teperature f the ine water and the circulated air i the ae. It i ab 5 C. The flr heating yte fr the wared intake air i a tw-tage getheral direct ue. The firt tage i the getheral heating f the intake air by the rck thrugh the huge heat tranfer

5 urface f the tunnel wall. The ecnd tage i an air-water heat pup epliting the enthalpy f the circulated air and tranfer it t the heating lp yte. Uing the theral pwer f the ine water ake neceary t apply a water-water heat pup. Bth theral urce are enugh t atify the deicing heat deand. In thi cae the getheral ptential f the ine tunnel i prven greater than the deicing heat deand. The benefit f the getheral lutin in pite f the il burner are lwer heating pwer, eliinatin f the ue f fuel il, and decreaing the CO eiin radically. EFEENCES Bbk, E. (99), "Fluid Mechanic fr Petrleu Engineer, Elevier, Aterda Tth A.. (007), "A prpect Getheral Ptential f an Abandned Cpper Mine, POCEEDINGS, Thirty-Tw rkhp n Getheral eervir Engineering Stanfrd Univerity, Stanfrd, Califrnia. Bbk E, Tth A.. (974), "Getheral energy fr dry hle, Getheral eurce Cuncil Tranactin en, USA 00. Vl. 6. pp Chapan. P. (95), Deign f Snw Melting Syte, Heating and Ventilating (April): 95 and (Nveber): 88 Karan T. Mechaniche Ahnlichkeit und turbulenz, Gttingen Mat. Phy. 90. Lund, J.. (999), ecntructin f a Paveent Getheral Deicing Syte, Ge-Heat Center Quarterly Bulletin, Vl. 0. N., Klaath Fall, Or, pp Lund J. (000), Paveent Snw Melting, Ge- Heat Center, Oregn Intitute f Technlgy Varga J. (970), Hidrauliku é pneuatiku gépek Műzaki Könyvkiadó, Budapet