Control of Heat and Humidity in German Mines

Transcription

1 357 Control of Heat and Humdty n German Mnes Dr. Wolfgang Schlotte DMT-Gesellschaft fr Forschung und PrUfung mbh ProTec Dvson: Fre and Exploson Protecton, Clmate Franz-Fscher-Weg 61,4537 Essen, Germany ABS'IRACT In order to ncrease the economc effcency of West European hard coal, great efforts are beng made at present n the coalproducng countres to lower producton costs. Ths am s to be acheved n Germany, among other thngs, by a drastc ncrease n the saleable output per workng face up to an average of 1, td n these cases where very long longwall faces (4 m ±5 m) are possble. Wth the substantally greater heat nput nto the ar stream whch ths nvolves, there s the danger that clmatc lmts wll be exceeded even at longwall faces wth lower than average rock temperatures. Workng n hgh temperatures and/or humdtes can lead to rsky lack of concentraton of the mners or to heat collapse and extremely dangerous heat stroke. In order to mnmze the costs for mne clmate control well-proven plannng software and clmtzaton technology s necessary for underground workngs. Wth the DMT clmate smulaton programs, both the dry and the extremely sgnfcant humd heat transfer can be calculated and the optmum ar coolng system for a mne can be desgned wth due regard to techncal and economc aspects. KEYWORDS Task of Ar-Condtonng n Mnes, Reasons for Clmate Plannng, Dfferent Ar-Condtonng Systems, Locaton of Central Refrgeraton Plants, Dependency of Ar-Coolers of Workng Condtons, and Pressure Reducng Facltes. INTRODUCTION The average depth of Gennan coal mnes today s n the 1, m range, wth the greatest depth beng around 1,6 m. Here the rock temperature exceeds 6 C whch s just the same as n 3,5 m deep South Afrcan gold mnes. The average run-of-mne coal per workng face at present s approxmately 5, td, peak values of more than 2, t/d are obtaned. On average, the longwall faces are 31 m long, the maxmum length beng around 45 m. The average effectve work seam thckness s 1.9 m. In long and hgh performance faces the nomnal electrcal power of the nstalled machnery can be up to 4.5 MW ncludng the conveyor belts n the panels. The wdely branched mnes wth roadway systems of sometmes more than 1 km total length and the control of dust, methane nflows as well as rock and machne heat place the hghest demands on the qualty of the ventlaton. Moreover, also on the ar condtonng, whch s necessary today n practcally all wnnng operatons and mechancal roadway headngs n German hard coal mnng. At present German hard coal mnng has nstalled refrgeraton facltes wth a coolng capacty totallng more than 24 MW. DMTs experence n the felds of ventlaton and ar condtonng s based on: - plannng work for the ventlaton and ar condtonng of complex mnes ncludng auxlarly ventlated roadway headngs and tunnel structures, - acceptance nspectons underground and consultancy for mne and tunnel operators, - development projects on varous problematc felds n ventlaton and ar condtonng. TASK OF THE AIR CONDITIONING The major task of an ar condtonng system at workng faces, n road headngs or n entre mnes s to guarantee tolerable clmatc condtons. For the evaluaton of the clmatc burden for mners n Germany, frst the dry-bulb temperature s used and then the so-called effectve temperature. The latter s a quantty determned by calculaton or taken from a chart, and t s made up of the physologcally effectve nfluences of temperature, relatve humdty and ar s lower than the "normal" dry temperature. It conforms to ths wth statc ar and I % relatve humdty.

2 358 PROCEEDINGS OF THE 8TH US MINE VENTLATION SYMPOSIUM Based on the Ar condtonng n Mnes Regulaton (Kmabergverordnung, 19 _ ) of the German coal mnng ndustry there s no restrcton for on-ste workng hours at dry-bulb temperatures of up to 28 C or effectve temperatures of up to 25 C when workng underground. At hgher dry-bulb or effectve temperatures workng hours are shortened from the normal level of 8 hours per shft to 6 or 5 hours per shft. Above an effectve temperature of 3 C work underground s allowed under exceptonal crcumstances only and t s completely forbdden at temperatures above 32 C. A survey of the "Klmabergverordnung" s gven n Table 1. Furthermore, a number of European countres have taken over at least parts of ths regulaton for tunnellng operatons. Table 1. Summary of the German Mne Regulatons for Clmatc Condtons n non-salt mnes T nmm :I:mmmrl Adl&ml fct tt«rlsdft tne Wlk h h nn 28C 25C 8 N>rerdm - >28C >25C >29C or >OC >32C N> If ventlaton of mnes s not by tself suffcent to comply wth the clmatc lmts regardng costly workng tme cuts and complete work prohbton, addtonal facltes for mechancal ar coolng wll be used. OBJECTIVES OF CLIMATE PLANNING Before new mnes are developed, panels or workng faces are developed n places where clmatc dffcultes are to expected, one should nvestgate among other thngs whether and at what expense tolerable clmate condtons can be created. A precondton for ths s a relable clmate plan. Wth such a plan t s possble to determne whch measures and, f necessary, whch refrgeraton capactes are requred, as well as whch workng condtons can be created for the work force. Wth great success clmate plans have been drawn up for German salt, ore and especally for hard coal mnng wth ther exceptonally hgh rock temperatures, and also for mnng as well as tunnellng n other countres for over 3 years wth the exclusve use of clmate predcton programs developed by DMT, thanks to the hgh plannng relablty they offer. It s possble to calculate the dry heat exchange as well as the hghly sgnfcant humd heat exchange wth them. The software s adapted to keep pace wth mnng and mechancal developments n underground operatons by our experenced mnng engneers as the need arses. In the clmate plalmng of entre mnes, ndvdual workng faces or roadway headng, the prme queston s whether t s possble to prevent the clmatc lmts lad down relably from beng exceeded. And ths wthout havng to enforce a reducton n the planned headng speed or producton rate. Bascally the am n roadway headng n German mnng and n European tunnellng s to keep the clmatc values at the workng face below a dry-bulb temperature of 28 C and the effectve temperature away from the face below 29 C, even wth the above-mentoned hgh rock temperatures and wth ntensve machne operaton, e.g., part-face or full-face cutters. If other stes are set up n the area away from the face, these are also cooled to a drybulb temperature of below 28 C. In the longwall faces of German hard coal mnes the lower ar condtonng target of 28 C wth comparatvely hgh output s acheved only for a maxmum rock temperature of around 35 C. Wth hgher rock temperatures, ths ar condtonng target can be mantaned only at unreasonable expenses. It can not at all be acheved wth very hgh rock temperatures because of techncal reasons. In these cases the ar condtonng systems are desgned n such a way that the effectve temperature n the whole workngs does not exceed 29 C. The clmate plan can be adjusted to any other clmate lmt as maybe lad down n the dfferent natonal regulatons. AIR CONDITIONING SYSTEMS If t s not possble to comply wth specfed clmatc lmts by means of ventlaton measures alone, ar condtonng systems must be provded. About 6 % of the total coolng capacty of German hard coal mnng s nstalled n ar coolng systems wth a centralsed arrangement and the rest s found n decentralsed systems. Wth the support of the DMT clmate predcton program t s possble to desgn an optmum ar coolng system for a mne or parts thereof wth due regard to techncal and economc aspects, at the same tme takng account of local features. Decentralsed Coolng Decentralsed ar coolng systems are generally used only f the requred total coolng capacty of the mne s relatvely low or f merely wde-strewn, sngle separate workng faces or headngs have to be cooled. Usually ths holds for comparatvely small refrgeraton machnes wth a relatvely low average coolng capacty of 28 kw, nstalled sngly or n pars underground near the workng face that s to be cooled. A decentralsed ar coolng system normally conssts of an arcoolng machne (drect evaporator). In general the ar-

3 CONTROL OF HEAT AND HUMIDITY IN GERMAN MINES 359 coolng machne s dvded nto two parts to ncrease ts moblty and t s then suspended on an overhead monoral or stands on runners. The frst part of the machne contans the lquefer and the compressor. The second part comprses the drect evaporator. Both components are very compact (dmensons n each case are about 1m x 1m x 3m) and they are connected by short, renforced, flexble refrgerant lnes. The condenser heat s dscharged nto the servce water network f the machne does not have ts own coolng water system. I " = 12 t ' l.!' l Ar Condtonng Systems wth Centralsed Refrgeraton In the case of large total refrgeraton capactes, preference should be gven to an ar coolng system wth centralsed refrgeraton for economc and techncal reasons. Fgure 1 shows the man components of an ar coolng system wth centralsed refrgeraton. Up to mne depths of about 1,8 m water crcuts n shafts are closed and can be used as communcatng ppes. For economcal reasons the water crcuts n greater depths have to be opened (n ths case t could be an advantage to produce ce at surface lke n South Afrcan gold mnes) or a more economc three chamber ppe feeder has to be nterposed... Fgure 1. Ar coolng system wth centralsed refrgeraton. The central refrgeraton plant can be nstalled at the surface, underground or combned at surface and underground. The best locaton results from the clmate plannng and cannot be defmed generally. In German hard coal mnes the bggest refrgeraton plants of ar coolng systems ( capactes above 1 MW) are located at the surface, refrgeraton plants n medum ranges (between 5 and 1 MW) are not only located at surface but also underground and even combned at surface and underground. All smaller refrgeraton plants are nstalled underground. In Fgure 2 the bggest refrgeraton plants of German hard coal mnng are shown. Locaton of central refrgeraton plant: (whte) at surface (black) underground (grey) combned Fgure 2. The bggest ar condtonng systems wth centralsed refrgeraton plants n German hard coal mnng. A centralsed coolng nstallaton conssts manly of a number of chlled water machnes connected n seres wth ndvdual capactes of between 1 and 4 MW. Mnes coverng a very large area often have several ar coolng systems wth one centralsed coolng nstallaton at ther dsposal. The greatest cooler capacty that s nstalled n a German mne wth several ar condtonng systems amounts to around 31 MW. The central refrgeraton system can be located above ground or undergrmmd or combned above ground and underground. The selecton of the locaton s geared to the specfc condtons of each mne. If there s enough open space above ground then the central coolng system can be nstalled there (see Fgure 3). In ths case flameproofng of the electrc components wthn the refrgeraton system can be dspensed wth. Another advantage s a mnmum expense for montorng and mantenance, heat avalblty at a central pont (f heat recovery s demanded), applcablty of dfferent refrgerants and possblty of precoolng of ar at the ntake shaft n wntertme. But at least the chlled water flow lne n the shaft must be properly nsulated. In addton, n the area around the shaft landng one of the pressurereducton facltes descrbed later must be provded. If the condtons above ground are too confned, the centralsed coolng system can also be nstalled underground near a shaft landng f possble (see Fgure 4). To a certan extent, the dmensons of refrgeraton machnes can be chosen freely and can therefore be adapted qute easly to the spacal condtons underground. For example one can make use of compact or very narrow, drawn-out unts. In almost all coal mnes, flameproofng has to be consdered for refrgeraton systems nstalled underground. As a rule the heat emtted from the refrgeraton machnes s conveyed to the surface va a coolng water shaft crcut. Snce large

4 36 PROCEEDINGS OF THE 8TH US MINE VENTILATION SYMPOSIUM quanttes of water have to be conveyed n the coolng water crcut than n the chlled water crcut, accordngly the shaft crcut for coolng water must be of larger dmensons than that for chlled water. But the coolng water ppe normally does not need nsulaton. In the case of underground refrgeraton, pressure-reducng devces can be dspensed wth f hgh-pressure condensers are nstalled. Generally, the locaton of the central refrgeraton plant combned at the surface and underground (see Fgure 5) has the advantage of relatvely low chlled water volume flow wth large spread of temperatures between advance and return n the shaft (small ppe dameters n the shaft are possble) and of precoolng of ntake ar at the surface. As a rule, the heat emtted from the refrgeraton system s removed nto the atmosphere by means of a coolng water crcut and coolng tower or wet recooler. ll/1/11//111 refrgeraton plant 1/l//l/1/1// Fgure 4. Ar coolng system wth central refrgeraton p ant underground. Fgure 3. Ar coolng system wth central refrgeraton plant at the surface. Wthn the clmate plan the most practcal locatons as well as the desgn and number of the ar coolers have to be selected. Then the chlled water volume flows per cooler must be determned, takng nto account of the calculated, ar-sde cooler nlet condtons at the coolng locaton, the ar volume flow, the chlled water flow temperature and the refrgeraton losses n the chlled water ppng system, so that the coolng capactes requred at the cooler locatons can be transferred. DMT has a thorough knowledge of the performance characterstcs of a large varety of cooler types sutable for mnng as a functon of the respectve operatng condtons, because all these cooler systems were tested on DMT's own clmate test rg. The thermal characterstcs determned on the test rg are recorded n correspondng fles for each cooler type and are needed for the software part wth whch the performance of the cooler can be determned dependent on the operatng condtons. Fgure 6 shows that t s crtcal to have chlled water volume flows that pass through the ar coolers set correctly. Under otherwse constant operatng condtons the effcency of the ar cooler ncreases when the water volume flow rses. Should the water volume flow be set too low, t mght not be possble to meet the specfed ar condtonng target, to whch a certan mnmum coolng capacty has to be assgned. Fgure 7 shows the relatonshp between the cooler capacty and the ar volume flow whch flows through the cooler for a specfc cooler type sutable for use n mnes n otherwse constant condtons. It can be seen that wth an ncrease n the arflow, the cooler capacty also ncreases. Fgure 8 llustrates the dependency of the cocler capacty on the chlled water nlet temperature of a specfc cooler type under otherwse constant condtons. The curve makes clear how mportant t s for the water to reach the ar cooler as cold as possble to acheve the greatest cooler capacty.

5 CONTROL OF HEAT AND HUMIDITY IN GERMAN MINES 361 coolng tower 7111/111/ ,-----.! 2 :5'15 m a. C>1 (.).!. I, ! J I ; I I _ j r ,_. ;. I I ; - r r r r '(j!! 5 -- ; I ; 1 Mf ar volume flow [m 3 /s] Condtons: b = 28 oc; twb = 23 oc; te,h2 = 7 oc; VH2o = 12.4 m 3 1h Fgure 7. cooler capacty as a functon of ar volume flow 25, I I I. Fgure 5. Ar coolng system wth central refrgeraton plant combned at the surface and underground 2 b 1:5 15 ca Q.... Q) 1 8.!. 'j 5 j I MT water volume flow [m 3 /s] Condtons: = 28 C; twb = 23 C; te.mo = 7 oc; Yar= 6.3 m 3 /s Cooler capacty n relaton to chlled water vol Fgure 6. ume flow. [?;- 2 'u 15 ns a " ! t ' l -(j 5.. _ , : chlled water nlet temperature [ C] Condtons: = 28 oc; 1:wt, = 23 oc; v H2 = 12.4 m 3 /h; v ar= 6.3 m 3 /s Fgure 8. Cooler capacty as a functon of chlled water nlet. The dmensonng of the chlled water network s geared to the necessary volume flows. The flow lnes n the chlled water network are totally nsulated n order to feed the water to the ar coolers as cold as possble for reasons just mentoned. Then there are stable ppes wth water vapour-proof nsulaton wth heat transfer coeffcents of less than 2 W/(m) whch have proven sutable n rough underground operaton. Ths nvolves two steel ppes pushed over ' MT

6 362 PROCEEDINGS OF THE 8TH US MINE VENTILATION SYMPOSIUM one another (see Fgure 9). The cavty between the two ppes s ar-tght and flled wth fre-proof polyurethane foam. Snce the collar on the flanged connecton of the ppes was provded wth nsulatng materals, there s no longer any metallc,.e. no hghly heat-conductng connecton between the nsde ppe contanng chlled water and the flanges or metallc outer ppe. I L =--._... _J Fgure 9. Insulated chlled water ppes sutable for mnes. Pressure reducng facltes are used wth large statc pressure dfferences n the chlled water network, whch occur, for example, when chlled water lnes are lad n shafts. In general, such facltes are hgh-pressure/lowpressure heat exchangers, three-chamber ppe feeders or a Pelton turbne. For reasons of cost and safety, the pressure allowed n the underground chlled water system should not exceed 4 x 1 5 Pa (= 4 bar). The three-chamber ppe feeder s the most effectve pressure reducng faclty n closed chlled water crcuts because the chlled water s conducted from the hgh pressure to the low pressure sde of the ar coolng system - practcally wthout an ncrease n chlled water temperature. Fgure 1 shows the prncple of a three-chamber ppe feeder. The total capacty needed for a central coolng nstallaton s made up of the sum of the maxmum cooler capactes needed n future and the cold losses n the ppng system. In many cases only a fracton of the total cooler capacty needed later at ts maxmum s needed at the start of any ar condtonng measures. The coolng nstallaton ncludng pumps should therefore be of modular desgn so that the full nvestment costs for the ar condtonng system are not ncurred rght at the begnnng. As already mentoned above, the chlled water should be as cold as possble when fed nto the ar coolers. For ths reason chlled water machnes equpped wth tube evaporators should also be able to acheve chlled water flow temperatures of 3 oc n contnuous operaton wthout antfreeze havng to be added. Ths requres a well functonng power regulaton system wth correspondng montorng equpment. The chlled water machnes nstalled n the other ndustres produce flow temperatures around 6 C at most, whch are less sutable for mnng. When the more expensve plate-type evaporators are used, chlled water flow temperatures of 1 C are also acheved relably and wthout addtves. SUMMARY Wth the help of nternally developed software that has been tred out over many years t s possble to calculate n ad- Ste B, 5 s laler Fgure 1. Prncple of a three-chamber ppe feeder. Ste C, 1 s allej state A

7 CONTROL OF HEAT AND HUMIDITY IN GERMAN MINES 363 vance the expected clmatc condtons for mnes or parts of mnes lke panels or auxlarly ventlated headngs, and to desgn the requred ventlaton and ar condtonng equpment. Major clmate-affectng factors are the rock temperature, the machnery used for workng or headng, the face advance or the headng rate and the ar flow. If t s not possble to keep to the specfed clmatc lmts by takng ventlaton-related measures, then ar condtonng facltes must be planned, wth due regard to the techncal and economcal aspects. Decentralsed ar-coolng systems are only then used generally f the requred total refrgeraton capacty n the mne s relatvely low or, f only wdely strewn sngle workng faces have to be cooled. In the case of large total refrgeraton capactes, preference should be gven to an ar coolng system wth centralsed refrgeraton for economc and techncal reasons. REFERENCE "Klma-Bergverordnung - KlmaBerg V", Verlag G ltckauf GmbH, Essen, Germany, No (Central publsher for German mne regulatons)