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The ventilation and climate modelling of rapid development tunnel drivages
Tunnelling and Underground Space Technology 19 (2004) 139–150
The ventilation and climate modelling of rapid development tunnel drivages Ian S. Lowndesa,*, Amanda J. Crossleyb, Zhi-Yuan Yanga a
School of Chemical, Environmental and Mining Engineering, University of Nottingham, Nottingham, UK b School of Civil Engineering, University of Nottingham, Nottingham, UK Received 19 May 2003; received in revised form 18 September 2003; accepted 24 September 2003
Abstract The extraction of minerals and coal at greater depth, employing higher-powered machinery to increase production levels has imposed an increased burden on ventilation systems to maintain an acceptable working environment. A deterioration in the climate experienced within these workings may also adversely affect the health and safety of the workforce. In the UK, mineral extraction is now being practiced at depths of over 1000 m. In addition, the adoption of continuous miner and tunnel bolting support methods has permitted improved development rates to be achieved at the cost of increased emissions of dust, gas and heat and humidity. There is a recognized need to improve the efficiency in the design and operation of auxiliary ventilation systems to maintain an adequate underground environment and climate. Any improvement achieved in the quality, quantity and control of the delivered ventilation will assist in the provision of improved gas and dust dilution and climatic control. Due to the constraints imposed by the mining method, there may be an economic or practical limit to the climatic improvement that may be obtained by the sole use of ventilation air. Where this limit is identified, there may be the need to consider the selective application of air-cooling systems. The paper details the construction of a computer based climatic prediction tool developed at the University of Nottingham. This work builds upon earlier research (Ross et al., 1997, Proceedings of 6th International Mine Ventilation Congress, SME, Littleton, CO, pp. 283–288) that developed a prototype model for short tunnel developments. The current model predicts the psychrometric and thermodynamic conditions within long rapid development single entry tunnel drivages. The model takes into account the mass and heat transfer between the strata, water, machinery and the ventilation air. The results produced by the model have been correlated against ventilation, climatic and operational data, obtained from a number of rapid tunnel developments within UK deep coalmines. The paper details the results of a series of correlation and validation studies conducted against the ventilation and climate survey data measured within 105s district Tail Gate tunnel development at Maltby Colliery, UK. The paper concludes by presenting the results of a case study that illustrate the application of the validated model to the design and operation of an integrated mine ventilation and cooling system. The case study illustrates the effect that an increased depth and hence increased virgin strata temperature has on the climate experienced within rapid tunnel developments. Further investigations were performed to identify the optimum cooling strategy that should be adopted to maintain a satisfactory climate at the head of the drivage. 䊚 2003 Elsevier Ltd. All rights reserved. Keywords: Tunnel ventilation; Tunnel model; Climate control
1. Introduction The primary objective in the design of an auxiliary tunnel ventilation system is the delivery of an adequate quantity and quality of fresh air to the working face to support life and to rapidly dilute contaminants to below statutory threshold limits. The pollutants typically *Corresponding author.
include dust, gases, and heat and humidity (McPherson, 1993; Torano Alvarez et al., 2002). There is also a need to produce and adequate climate within the working areas, to maintain the health and safety of the workforce. For the purpose of this study, the effective temperature (ET) heat stress index was selected as the parameter to define the thermal condition of the ventilating air (Tuck et al., 1997).
0886-7798/04/$ - see front matter 䊚 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.tust.2003.09.003
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There is a recognized need to improve the efficiency in the design and operation of the auxiliary ventilation systems to maintain an adequate environment within deep, rapid tunnel developments. Any improvement achieved in the quality, quantity and control of the delivered ventilation will assist in the provision of improved gas and dust dilution and climatic control. To produce an economic solution to current and potential future underground climate problems it is pertinent to investigate the suitability of the adoption of the integrated air-cooling techniques with auxiliary ventilation systems within these rapid tunnel developments. Various models have been developed to predict the underground climate across a variety of underground workings. Earlier research work considered the heat flow into stopes (Starfield, 1966) and tunnels (Goch and Patterson, 1940; Starfield and Dickson, 1967; Gibson, 1976; McPherson, 1986). More complex situations such as short tunnel drivages (Voss, 1980; Kertikov, 1997; Ross et al., 1997), longwall coal districts (Voss, 1971; Middleton, 1979) and longwall coal faces (Longson and Tuck, 1985; Gupta et al., 1993) have also been considered. Advances in available computing power have led to an increase in the level of detail used to construct the models to represent the many contributing heat sources including the machinery, friction and autocompression. The paper introduces the physical basis behind the construction of the computational model. The conclusions drawn from a comparative analysis of the results predicted by the model with the climatic survey data collected from a number of underground tunneling operations are presented and discussed. The results of these exercises were used to establish design and planning guidelines. The further application of the correlated climate prediction model to identify the potential environmental benefits offered by alternative equipment layouts and duties is illustrated by the results produced by a case study. The case study was conducted to identify the optimal operational and practical limits involved in the application of purely ventilation techniques to ameliorate adverse climatic conditions within rapid development drivages operating at greater depth and hence higher virgin rock temperatures (VRTs). This section also summarizes the results of studies conducted to investigate the application of suitable integrated cooling systems to achieve adequate climatic conditions within a pre-defined climate control zone defined in the vicinity of the head end of the drivage. 2. Development of the climatic drivage prediction programme Within many deep, long and highly mechanized underground workings there is a need to investigate the
development of a range of efficient and flexible integrated ventilation and refrigeration cooling systems to maintain comfortable climatic conditions. The cyclical nature of mechanized cuttingybolting operations can produce periodic fluctuation in the climatic conditions created within these workings. The existence of this changing work and environmental loading cycle requires the development of sympathetic and adaptable ventilation and adaptable cooling system. It is therefore necessary to consider the optimal location, monitoring and control of these integrated refrigeration and ventilation systems, in order to produce both a flexible and cost effective solution. The ventilation costs can represent a significant proportion of the total energy cost of many underground UK coal mining operations. Thus, any small improvements that can be produced in the efficiency of the ventilation system can produce a significant power and cost saving. Within the UK coal mines, there is little operational and planning experience in the use of mine cooling systems. There is currently only one major mine that has a subsurface cooling plant capable of supplying chilled service and cooling water. To produce an economic solution to the current and potential future mine climate problems it is pertinent to investigate the suitability of the adoption of the integrated air-cooling and auxiliary ventilation systems within these drivages. Due to the absence at present of the surface cooling facilities it would be expedient to consider the suitability of the application and control of localized subsurface cooling plant. 2.1. Background behind the construction of the computer model The psychrometric, climatic and machinery heat source calculations used within the rapid development model are based on procedures used within the commercial software CLIMSIM娃 initially developed at the University of Nottingham (Gibson, 1976) and now supported by Mine Ventilation Services (MVS) Inc. (1997). The CLIMSIM娃 model was developed to simulate the climatic conditions within a through flow open ended tunnel, in which the ventilation air travels from one end of the tunnel to the other. The computational model divides the tunnel airflow domain into a linear series of interconnected discrete volume elements. The iterative calculation method requires the definition of either the measured or defined inlet airflow and psychrometric conditions for the element at the entry to the defined flow domain. By applying a successive series of calculations, based on the laws of the conservation of mass and energy across each volume element, the thermometric conditions of the airflow at the outlet to each element is determined. The calculations of each volume
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Fig. 1. The drivage and duct elements on a typical drivage schematic.
element are carried out sequentially from inlet of the tunnel to outlet in the direction of the airflow. However, in the construction of the computational model for the dead end tunnel drivage model, the air flow domain is divided into a series of linear interconnected discrete volume elements. It is necessary to construct two sets of integrated volume elements, one to represent the airflow in the main body of the tunnel drivage and the other to represent the air flowing within the ventilation ducts. This is illustrated in Fig. 1. In the case of a forcing duct, the direction of the airflow within the duct is counter to that flowing within the main body of the tunnel roadway. The iterative calculation method proceeds along each set of elements in a similar manner to that described for CLIMSIM娃 program. However, an additional set of iterative calculations is performed to evaluate the net heat transfer through the duct walls and the mass transfers of airflow due to the existence of any leakage between the duct and the tunnel. The calculations performed within the model involve the determination the sensible andyor latent (moisture) heat gainsylosses that occur within each element to evaluate the psychrometric conditions of the airflow leaving each element. The various thermodynamic effects simulated within the model include: 1. The heat sourceysink effects of the strata 2. The effects of the auto-compression of the ventilating air due to depth 3. The heat generated by the machinery and miscellaneous sources 4. The heat emitted from conveyed mineral 5. Water pools and floor dampness at head-end 6. The influence of dust suppression sprays 7. The influence of localized cooler units 8. The influence of ventilation fans 9. Interactions between drivage and duct air through leakage and heat transfer.
2.2. Construction of the drivage model UK coal mine rapid development drivages are normally advanced using a continuous miner or road header machine. There are principally two auxiliary ventilation systems used to ventilate these mining systems. The predominant auxiliary ventilation system employed is the forceyexhaust overlap system (Fig. 2). The second alternative auxiliary ventilation system used is the force with machine mounted exhaust scrubber duct system (Fig. 3). The tunnel climate model has been developed to simulate these two systems. However, should underground conditions require the use of a pure exhaust ventilation system, the model may be simply adapted to simulate this case. In Fig. 2 the iterative climatic calculations follow the predominant direction of the airflow though the force duct and within the drivage. As there may be an exchange of leakage air between the force ventilation duct and the drivage elements, together with heat transfer through the duct walls, an iterative approach has been used, whereby the calculations are repeated until a balanced and numerically converged solution is obtained. Fig. 2, also illustrates the various heat load zones identified within the drivage. Zone I represents the area in the immediate vicinity of the head end cutting area. This is defined to start from the outlet of forcing duct through to the face of the tunnel. In UK coal mines the outlet to the forcing duct is normally set at between 20–25 m to the face, and the inlet to the exhaust duct is maintained within 2–3 m of the head end. The major heat sources within the Zone I include the newly exposed rock faces (roof, floor, two side-walls, and the face of the head end), the broken rock, the cutting machine, and the water sprays. These heat sources will produce the greatest impact on the climate. The predominant airflow direction within this zone of the drivage follows that of the forcing jet towards the face of the heading.
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Fig. 2. Schematic of a conventional force-exhaust overlap configuration with the defined climatic zones.
Zone II lies beyond the immediate mining area and incorporates the region where the broken mineral is transferred to the conveyor belt or shuttle car. Zone II is defined as the overlap section of the forcing duct and the exhausting duct. The length of this overlap section is typically 15 m. The mineral transport equipment, the broken mineral and water sprays located within this region will produce a marked effect on the climatic conditions experienced by the ventilation air, as only a portion of the air delivered by the force fan to the head end will flow out through the Zone II. Typically in excess of 50% of the fresh air quantity delivered by the forcing fan is exhausted through the overlap duct. Zone III is defined to start from the outlet of exhaust duct to the entrance of the development drivage. The air exiting the exhaust duct mixes with the tunnel airflow leaving the overlap zone, and then this combined flow roadway air travels back towards the entrance to the drivage. Within this region of the tunnel, the conveyed broken mineral, any installed equipment, water sprays,
and the strata will produce the greatest impact on the climate. However, in the case of the application of a forcing duct with machine mounted exhaust scrubber fan system (Fig. 3), the air is delivered by the forcing duct to within of 5 m of the face of the heading. The exhaust scrubber fan draws air from the vicinity of the face and discharges this air to the rear of the cutting machine. Thus, in this case, the predominant flow direction and hence heat transfers are in a direction away from the headend of the drivage. The air returning from the face picks up the heat mainly from the newly exposed rock faces, the broken rock, the conveyed mineral, the cutting machine, the water sprays, the conveyor and the warm moist air exiting the exhaust scrubber fan at the rear of the machine. The following sections discuss the results of the validation exercises that were performed and the series of subsequent modifications made to the drivage climatic model.
Fig. 3. The simple forcing system with machine mounted exhaust dust scrubber fan.
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Fig. 4. Generic Measurement Schematic for a rapid development drivage employing Continuous Miner machine and a forceyexhaust overlap auxiliary ventilation system.
3. Validation and further development of the drivage model The results produced by the drivage climatic model have been validate against the ventilation and climate survey data collected from a number of underground rapid tunnel developments within UK Coal Ltd deep coal mine operations. Fig. 4 shows a generic schematic of the location of the various survey measurement locations within these rapid drivage developments. All of the developments surveyed employed a continuous miner and forcey exhaust overlap auxiliary ventilation system shown in Fig. 4. The dry and wet bulb temperatures were recorded outbye of the auxiliary force fan, in the main intake trunk airway. These data points were specified as the inlet flow conditions to the model. A dry bulb temperature reading was taken inside the force duct down stream of the fan to determine the temperature rise across the fan. As the moisture content of the air within the force duct was assumed constant only dry bulb measurements were recorded at regular intervals along the length of the duct. Two sets external temperature and flow measurements were made at the inlet and discharge points of the overlap exhaust fan duct. 3.1. Drivage model validations and modifications Four sets of the ventilation, climate and technical data have been used to validate and correlate the model predictions. They are from (1) the 190s Loader Gate Development at Thoresby Colliery; (2) the 190s Supply Gate Development at Thoresby Colliery; (3) the 312s Return Gate Development at Welbeck Colliery; and (4) the 105s Tail Gate Development at Maltby Colliery. Following a comprehensive analysis of the results produced by these validation exercises it was concluded that there was generally close agreement between the
measured and the predicted dry-bulb and wet-bulb temperatures. However, the model was unable to reproduce certain features observed from an analysis of the field measurements. In particular, it was observed that: (a) that the drop in the temperature of the air jet as it exited the force duct observed in the measured data, was not being reproduced by the model, and (b) the model did not fully account for the latent heat pick up in the headend region. Thus, to improve the predictions obtained from the model, a number of additional physical model features were developed and incorporated into the model. 1. Expansion cooling of the air as it exits the duct and enters the drivage. The procedure is based on the reversible adiabatic expansion of a fluid due to a change in pressure and the remaining physical model features were included in an attempt to account for additional sources of latent and hence moisture. 2. Small water pools whereby the heat loading is based upon the contact surface area and the water temperature. 3. Standing water at the head-end region of the drivage. The procedure is similar to the calculation performed to simulate a water pool, except in this case it is assumed that the floor is covered in water up to a point beyond a specified distance from the head-end. 4. The variation of the wetness factor observed along different sections of the roadway. This recognizes the greater concentration of dust suppression sprays, service water, wet shotcrete operations that may exist at the face end of the tunnel excavation. Thus, the drivage may be divided into two sections, and different wetness value can be specified at each end of two sections. Linear interpolation is used to calculate the intermediate values. 5. A re-entrainment of some of the air returning from the head-end by the momentum of the jet of air
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Table 1 Baseline input data for Maltby Collieries 105s tunnel development, as required by the Climatic Prediction Program Name
Data
Unit
Roadway length Roadway cross-section (width=height) Virgin Rock Temperature (VST) Rock thermal conductivity Coal thermal conductivity Average roadway thermal conductivity Rock thermal diffusivity Coal thermal diffusivity Average roadway thermal diffusivity Tonnage per shift Force fan power (nominal) Force fan ventilation flow, inlet to duct Force fan ventilation flow, outlet to duct Exhaust fan power (nominal) Exhaust fan ventilation flow, inlet to duct Dry-bulb temperature, force fan inlet Wet-bulb temperature, force fan inlet Conveyer belt drive (nominal) Continuous miner (nominal) Mineral transfer equipment (nominal)
1164 13.68 41.9 2.78 0.35 1.71 1.39=10y6 0.25=10y6 0.88=10y6 6.0 90 8.09 6.82 56 5.28 22.0 15.5 300.0 360.0 182.0
m m2 8C Wym 8C Wym 8C Wym 8C m2ys m2ys m2ys tyshift kW m3ys m3ys kW m3ys 8C 8C kW kW kW
exiting the force duct. A specified percentage of the return air may be combined with the air from the force duct. 6. The introduction of a mixing length in which the air exiting the exhaust overlap duct is assumed to mix with the air flowing from the face end of the drivage along the duct overlap zone. 3.2. An example of model validationsycorrelations against the measured data at Maltby Colliery The layout of 105s Tail Gate tunnel development at Maltby Colliery, UK, is similar to that shown in Fig. 2. The measured ventilation and climatic survey data com-
prised of a series of spot dry and wet bulb temperature readings taken within the drivage and several dry bulb measurements made within the auxiliary force ventilation duct. The data also included the geometrical and physical characteristics of the drivage and the type and power consumption of the equipment installed, and the quantity and type of water usage. The heat emitted from the conveyor drive motor was treated as a linear heat source, with the heat load distributed along the length of the conveyor. The input data of the inlet conditions and the geometrical and physical characteristics for the model calculations was based on the ventilation and climate survey data. Some other input parameter values were tested and varied within the climatic prediction model aiming to obtain the closest agreement to the measured outlet data. For example, the drivage was divided into two sections and the length of the section near the head end was set 60 m. The wetness factor value at the start line of the drivage, W1, was set 0.2; the value at the starting end of the head end section, W2, was set 0.2, and the value at the head end, W3, was set 0.5. Within the remainder of the drivage the wetness factor for the drivage faces (walls, roof and floor) is allowed to vary in a linear fashion. The input data for the drivage model is summarized and listed in Table 1. The predicted and measured temperature profiles within the tunnel drivage are plotted in Fig. 5. The predicted and measured temperature profiles within the forcing duct are shown in Fig. 6. The predicted temperature profiles within Zone I and Zone II are detailed in Fig. 7. Following an analysis of the results produced by these exercises it was concluded that the climatic model is able to adequately simulate the climatic conditions experienced within the Maltby Colliery 105s tunnel
Fig. 5. Measured and predicted temperatures along the drivage.
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Fig. 6. Measured and predicted dry-bulb temperature inside force duct.
drivage. The wet bulb temperature profiles within the drivage and the dry bulb temperature profiles inside the forcing duct were predicted to within "1 8C (Figs. 5 and 6). In Fig. 7, the dotted lines within the Zone I are the predicted air temperature profiles along the drivage as the predominant airflow in Zone I travels from the force duct outlet to the head end. The solid lines within the Zone I and Zone II are the predicted air temperatures along the drivage to represent the small proportion of the delivered air which travels away from the head end through the overlap zone, whilst the exhaust fan moves the remaining portion of the air from the head end and discharges it into Zone III. The solid lines within the Zone III are the predicted wet and dry air temperature profiles within this section of the drivage.
Following an analysis of the simulation and validation exercises performed on the model using the above data sets, it was concluded that the parameter that had the most significant influence on the production of a satisfactory correlation was the absolute value and spatial variation of the wetness factor applied to the tunnel surface. Fig. 8 illustrates the results of the sensitivity exercises performed to study the effects produced by a variation in the wetness factor. Fig. 8 illustrates a plot of both the measured and predicted the dry bulb and wet bulb temperatures for using different sets of wetness factors. Each combination (A–C) was obtained by using a different values of: W1 (wetness factor value at the entrance to the drivage), W2 (the value at the start of the head end section) and W3 (the value at the head end). It can be seen that the
Fig. 7. Predicted temperature profiles within the defined zones.
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Fig. 8. Predicted temperature profiles with different values of wetness factor.
combination C has obtained the closest agreement to the measured outlet data. 4. Case study: cooling design for Maltby Collieries 105s tunnel development To demonstrate the capabilities of the model to improve the efficiency of the design and operation of integrated mine ventilation and cooling systems for rapid development drivages the following case study was conducted. The drivage chosen for this case study was 105s Tail Gate tunnel development of Maltby Colliery, introduced in Section 3.1. 4.1. General cooling strategy for a rapid development drivage development Excessive temperatures and humidity are becoming more common in the highly mechanized districts of UK coal mines, especially where operations are performed at depth. The conventional approach to ventilation planning in UK collieries is to design an auxiliary ventilation system so that methane emissions are diluted to blow statutory threshold limit values at the minimum of cost. In the majority of cases to date, ventilation flows thus obtained have been sufficient to avoid uncomfortable climatic conditions. In situations within the main ventilation circuit where the conditions become unacceptable, it is the need to alleviate this problem, rather than the methane emission rate, which determines the air quantity required. However, within many workings, and single entry development workings in particular, the determined quantity is constrained by the need to avoid dust dispersion, and the flexibility of the existing auxiliary fan installations. Thus, in cases where the air quantity alone is insufficient in itself to achieve acceptable
climatic conditions, alternative methods of climate control are needed, including the application of mechanical cooling systems. The control of the thermal climate within mechanized developments is normally effected by the application of a staged air cooling strategy. The exact layout and duty of the cooling system used within a development will depend on: its length and advance rate, the method by which it is being driven, severity of the heat problem and the auxiliary ventilation layout employed. All these factors will influence the cooling strategy used. The following paragraphs present an overview of a general cooling strategy for a mechanized development employing a force-exhaust overlap auxiliary ventilation system (Fig. 4). 4.2. Identification of the coincidence of major heat loads and labour activity and definition of the climate control zone (CCZ) It is generally accepted that miners, who are undergoing heavy work activity under adverse climatic conditions, may experience an increased heat stress. Such adverse climatic conditions may often be present at the head end of rapid development drivages. These conditions are produced in part by the concentration of major sources of heat and humidity, which include mined mineral, machinery and water sprays. To develop effective ventilation and cooling strategy it is essential to identify the potential coincidence of major labour activity and heat loading within these mining operations. Typically, 7–8 miners and officials work within a UK rapid development drivage. 4–5 miners and officials are predominantly employed within the face end of the drivage. The remaining 2–3 miners are periodically employed within the overlap zone and further outbye in
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Fig. 9. Schematic of the cooling system proposed for the 105s Tail Gate Development at Maltby Colliery and the Climate Control Zone (CCZ).
the main body of the drivage. The major labour activities and heat loadings may be summarized as: 1. Major labour activities: ● Cutting operations ● Scaling, rock support, bolting and meshing ● Materials supply ● Advance of auxiliary ventilation system 2. Major Heat Loadings ● Strata heat in the vicinity of head end ● Newly cut mineral ● Electrical machine sources including, the continuous miner machine, conveyor, mineral breakery loader, and transformer ● Forceyexhaust auxiliary fans ● Water sprays. However, the majority of these heavy labour activities and heat sources are commonly concentrated within 60 m of the face end (cf. Figs. 1 and 2). Thus, this zone was subsequently used to define the establishment of a design climate control zone (CCZ) (Fig. 9), a zone within which the climate is to be maintained at or below a given effective temperature limit (Twort et al., 2002). An ET of 28 8C was set as the upper climatic design limit specified within the defined CCZ. Where the climatic conditions of the air exceed this limit, a number of cooling methods are employed to regulate the climate. The drivage development is driven by either a road header or a continuous miner machine, which is now predominately used within UK collieries. The cooling strategy employed to control the thermal climate of the development is sub-divided into two main distinct phases: Phase 1: Cooling the intake air within the force duct. A cooler is placed within the duct line after the force fan. It must cool the air, such that on delivery to the head end, the climatic conditions within a prescribed length of the heading will remain within the preset climatic limits. However, as the development advances
the relatively cool air within the forcing duct has an increased length of time in which to absorb sensible heat, through the ducting, from the warm air returning along the development. Under these circumstances, although the intake air ducted to the head end may be climatically acceptable, it can easily deteriorate and exceed climatic limits while applying for force-exhaust overlap ventilation system. The air is heated up by the sensible and latent heat generated by the newly cut minerals, water sprays, and the machinery within the Zone I as it reaches to the head end and it is further deteriorated after going through the exhaust fan. At this point Phase 2 of the cooling strategy may be initiated. Phase 2: Installation of an air cooler in the exhausting duct after the fan. This air cooler must re-cool the warm air exhausted off the head end, such that the ventilation air discharged by the exhaust fan remains within climate limits. 4.3. Climate prediction analysis with different virgin rock temperatures (VRTs) The validated computer model was employed to investigate the climatic conditions that would exist within a rapid development drivage as the excavation becomes deeper and hence experiences an increased virgin rock temperature. It was assumed in the following exercises that the ventilation quantities were optimal with regard to gas and dust dilution and control. The predicted dry-bulb, wet-bulb and effective temperatures within the drivage for the VRTs of 30 8C, 35 8C, 40 8C, 41.9 8C, 45 8C, 50 8C, 55 8C and 60 8C are given in Figs. 10–12, respectively. From an analysis of the predicted results shown in Fig. 12, it may be concluded: 1. The ET throughout the entire length of the drivage is maintained below 28 8C when the VRT is below 40 8C.
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Fig. 10. Predicted dry-bulb temperatures within the drivage with different VRTs.
2. When the VRT is between 40–45 8C, the ET within the CCZ remains under the 28 8C ET. However, the ET within the drivage outbye will exceed the 28 8C ET limit. 3. When the VRT is above 45 8C, the ET throughout the whole length of the drivage will exceed the 28 8C ET limit. 4.4. Cooling design with different VRTs Following the conclusions drawn above, a further investigation was performed to identify the cooling strategy to be adopted, and the minimum amount of cooling to be installed to maintain the ET within the head end CCZ below 28 8C.
The following conclusions were drawn: 1. For VRTs of up to 40 8C the climate within the entire drivage may be maintained below an effective temperature of 28 8C with the sole use of ventilation. 2. When the VRT is between 40–45 8C, the ET within the CCZ remains under the 28 8C ET. Thus, the ventilation flow is adequate to maintain the effective temperature within the CCZ at or below 28 8C 3. For VRTs in excess of 45 8C a cooler first needs to be first installed within the force duct to maintain the ET within the CCZ below the 28 8C ET limit. Table 2 presents the calculated minimum cooling requirements for VRTs of 50 8C, 55 8C and 60 8C, respectively. The following assumptions are inherent to
Fig. 11. Predicted wet-bulb temperatures within the drivage with different VRTs.
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Fig. 12. Predicted effective temperatures within the drivage with different VRTs.
these calculations: (a) following the application cooling and to avoid discomfort to the workforce the dry-bulb temperature at the outlet to the forcing duct should not be below 20 8C; (b) the cooler is positioned within the forcing duct at a position 150 m back from the head end. The cooler and force duct cassette can either be slung from a monorail or mounted on a sled that would be moved forward to follow the advance of the face. Where the cooler installed at a distance further back from the face, this would result in a reduction in the positional efficiency of the cooler. This would require the potential installation of additional cooling capacity to compensate for the increased heat flow that may experienced to the force duct from the drivage, due to the increased temperature differential. It was assumed in the calculations that a fan mounted internal to the cooler would handle the additional pressure drop afforded by the cooler unit within the forcing duct. From an analysis of the data contained in Table 2, it may be concluded that for a VRT of between 50–55 8C the application of a single indirect cooler unit may be able to maintain the climate within the CCZ below the required 28 8C ET limit. For a VRT of 60 8C and above, would require the installation of two indirect cooler units within the force duct to maintain the climate within
the CCZ below the required 28 8C ET limit. For a given cooling water supply temperature, adjusting the mass flow of the cooling water will modify the duty of each cooler unit. 5. Conclusions The paper documents the background behind the development and validation of a computer based model to predict the climatic environment in underground rapid development tunnel drivages. Following an analysis of the results obtained from the correlation exercises performed against ventilation and climatic data collected from a number of UK deep coal mine operations, it was concluded that there was close agreement between the model predictions and the measured dry-bulb, wet-bulb and effective temperatures. The paper details the results of a series of correlation and validation studies conducted against the ventilation and climate survey data measured within 105s district Tail Gate tunnel development at Maltby Colliery, UK. The paper presents the results of a case study that illustrate the application of the validated model to the design and operation of an integrated mine ventilation and cooling system. The case study illustrates the effect
Table 2 The calculated minimum net cooling duties required to maintain the ET in the CCZ below 28 8C VRT Total net cooling requirement Tws8 8C
50 8C 50 kW One cooler unit Ÿs1.05 lys
55 8C 100 kW One cooler unit Ÿs3.3 lys
Tws15 8C
One Cooler Unit Ÿs5.7 lys
NyA
Tw-water temperature,
Ÿ-water flow rate.
60 8C 140 kW Two coolers in series Cooler 1: Ÿs1.05 lys Cooler 2: Ÿs3.3 lys NyA
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that an increased depth and hence increased virgin strata temperature has on the climate experienced within rapid tunnel developments. Further investigations were performed to identify the optimum cooling strategy that should be adopted to maintain a satisfactory climate at the head of the drivage. Acknowledgments The authors would like to acknowledge the technical assistance of the Head Quarters Environmental and Safety Engineers, UK Coal in the collection of the underground survey data. The authors would also like to acknowledge the financial support of the ECSC research fund. References Gibson, K.L., 1976. Computer simulation of climate in mine airways. Ph.D. Thesis, University of Nottingham, UK. Goch, D.S., Patterson, H.S., 1940. Heat flow into tunnels. J. Chem. Metall. Min. Soc. S. Afr. 41, 117–121. Gupta, M.L., Panigrahi, D.C., Banerjee, S.P., 1993. Heat flow studies in longwall faces in India. In: R. Bhaskar, ed., Proceedings of 6th U.S. Mine Ventilation Symposium, SME, Littleton, CO, pp. 421– 427. Kertikov, V., 1997. Air temperature and humidity in dead-end headings with auxiliary ventilation. Proceedings of 6th International Mine Ventilation Congress, SMME, Littleton, CO, USA, pp. 269– 276. Longson, I., Tuck, M.A., 1985. The computer simulation of mine climate on a longwall coal face. In: P. Mousset-Jones, ed., Pro-
ceedings of 2nd U.S. Mine Ventilation Symposium, A.A.Balkema, Rotterdam, pp. 439–448. McPherson, M.J., 1986. The analysis and simulation of heat flow into underground airways. Int. J. Min. Geol. Eng. 4, 165–196. McPherson, M.J., 1993. Subsurface ventilation and environmental engineering. Chapman and Hall, London. Middleton, J.N., 1979. Computer simulation of the climate in underground production areas. Ph.D. Thesis, University of Nottingham, UK. Mine Ventilation Services Inc., 1997. CLIMSIM娃 for Windows version 1.0: Users manual and general theory. Ross, A.J., Tuck, M.A., Stokes, M.R., Lowndes, I.S., 1997. Computer simulation of climatic conditions in rapid development drivages. In: Ramani R.V., ed., Proceedings of 6th International Mine Ventilation Congress, SME, Littleton, CO, pp. 283–288. Starfield, A.M., 1966. The computation of air temperature increases in advancing stopes. J. Mine Vent. Soc. S. Afr. 19, 189–199. Starfield, A.M., Dickson, A.J., 1967. A study of heat transfer and moisture pick-up in mine airways. J. S. Afr. Inst. Min. Metall. 67, 211–234. Torano Alvarez, J., Rodriguez Diez, R., Cuesta Gutierrez, A., Diego Alvarez, I., 2002. A computer program for calculating ventilation in tunneling vorks based on an explicit method. J. Tunnelling Underground Space Technol. 17 (3), 227–236. Tuck, M.A., Stokes, M.R., Lowndes, I.S., 1997. Mine climate control options in underground working zones. Final Report on ECSC research Project No.7220 – ACy006. Twort, C.T., Lowndes, I.S., Pickering, S.J., 2002. An application of thermal exergy analysis to the development of mine coolong systems. Proc. Inst. Mech. Eng. Part C: Mech. Eng. Sci., Vol. 216. ¨ Voss, J., 1971. Prediction of climate in production workings. Gluckauf 107, 412–418. Voss, J., 1980. Mine Climate in Mechanised Drivages and Its Determination by Advanced Calculation. Methane, Climate, Ventilation in the Coalmines of the European Communities, Vol. 1. Colliery Guardian, pp. 285–305.
The ventilation and climate modelling of rapid development tunnel drivages Ian S. Lowndesa,*, Amanda J. Crossleyb, Zhi-Yuan Yanga a
School of Chemical, Environmental and Mining Engineering, University of Nottingham, Nottingham, UK b School of Civil Engineering, University of Nottingham, Nottingham, UK Received 19 May 2003; received in revised form 18 September 2003; accepted 24 September 2003
Abstract The extraction of minerals and coal at greater depth, employing higher-powered machinery to increase production levels has imposed an increased burden on ventilation systems to maintain an acceptable working environment. A deterioration in the climate experienced within these workings may also adversely affect the health and safety of the workforce. In the UK, mineral extraction is now being practiced at depths of over 1000 m. In addition, the adoption of continuous miner and tunnel bolting support methods has permitted improved development rates to be achieved at the cost of increased emissions of dust, gas and heat and humidity. There is a recognized need to improve the efficiency in the design and operation of auxiliary ventilation systems to maintain an adequate underground environment and climate. Any improvement achieved in the quality, quantity and control of the delivered ventilation will assist in the provision of improved gas and dust dilution and climatic control. Due to the constraints imposed by the mining method, there may be an economic or practical limit to the climatic improvement that may be obtained by the sole use of ventilation air. Where this limit is identified, there may be the need to consider the selective application of air-cooling systems. The paper details the construction of a computer based climatic prediction tool developed at the University of Nottingham. This work builds upon earlier research (Ross et al., 1997, Proceedings of 6th International Mine Ventilation Congress, SME, Littleton, CO, pp. 283–288) that developed a prototype model for short tunnel developments. The current model predicts the psychrometric and thermodynamic conditions within long rapid development single entry tunnel drivages. The model takes into account the mass and heat transfer between the strata, water, machinery and the ventilation air. The results produced by the model have been correlated against ventilation, climatic and operational data, obtained from a number of rapid tunnel developments within UK deep coalmines. The paper details the results of a series of correlation and validation studies conducted against the ventilation and climate survey data measured within 105s district Tail Gate tunnel development at Maltby Colliery, UK. The paper concludes by presenting the results of a case study that illustrate the application of the validated model to the design and operation of an integrated mine ventilation and cooling system. The case study illustrates the effect that an increased depth and hence increased virgin strata temperature has on the climate experienced within rapid tunnel developments. Further investigations were performed to identify the optimum cooling strategy that should be adopted to maintain a satisfactory climate at the head of the drivage. 䊚 2003 Elsevier Ltd. All rights reserved. Keywords: Tunnel ventilation; Tunnel model; Climate control
1. Introduction The primary objective in the design of an auxiliary tunnel ventilation system is the delivery of an adequate quantity and quality of fresh air to the working face to support life and to rapidly dilute contaminants to below statutory threshold limits. The pollutants typically *Corresponding author.
include dust, gases, and heat and humidity (McPherson, 1993; Torano Alvarez et al., 2002). There is also a need to produce and adequate climate within the working areas, to maintain the health and safety of the workforce. For the purpose of this study, the effective temperature (ET) heat stress index was selected as the parameter to define the thermal condition of the ventilating air (Tuck et al., 1997).
0886-7798/04/$ - see front matter 䊚 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.tust.2003.09.003
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There is a recognized need to improve the efficiency in the design and operation of the auxiliary ventilation systems to maintain an adequate environment within deep, rapid tunnel developments. Any improvement achieved in the quality, quantity and control of the delivered ventilation will assist in the provision of improved gas and dust dilution and climatic control. To produce an economic solution to current and potential future underground climate problems it is pertinent to investigate the suitability of the adoption of the integrated air-cooling techniques with auxiliary ventilation systems within these rapid tunnel developments. Various models have been developed to predict the underground climate across a variety of underground workings. Earlier research work considered the heat flow into stopes (Starfield, 1966) and tunnels (Goch and Patterson, 1940; Starfield and Dickson, 1967; Gibson, 1976; McPherson, 1986). More complex situations such as short tunnel drivages (Voss, 1980; Kertikov, 1997; Ross et al., 1997), longwall coal districts (Voss, 1971; Middleton, 1979) and longwall coal faces (Longson and Tuck, 1985; Gupta et al., 1993) have also been considered. Advances in available computing power have led to an increase in the level of detail used to construct the models to represent the many contributing heat sources including the machinery, friction and autocompression. The paper introduces the physical basis behind the construction of the computational model. The conclusions drawn from a comparative analysis of the results predicted by the model with the climatic survey data collected from a number of underground tunneling operations are presented and discussed. The results of these exercises were used to establish design and planning guidelines. The further application of the correlated climate prediction model to identify the potential environmental benefits offered by alternative equipment layouts and duties is illustrated by the results produced by a case study. The case study was conducted to identify the optimal operational and practical limits involved in the application of purely ventilation techniques to ameliorate adverse climatic conditions within rapid development drivages operating at greater depth and hence higher virgin rock temperatures (VRTs). This section also summarizes the results of studies conducted to investigate the application of suitable integrated cooling systems to achieve adequate climatic conditions within a pre-defined climate control zone defined in the vicinity of the head end of the drivage. 2. Development of the climatic drivage prediction programme Within many deep, long and highly mechanized underground workings there is a need to investigate the
development of a range of efficient and flexible integrated ventilation and refrigeration cooling systems to maintain comfortable climatic conditions. The cyclical nature of mechanized cuttingybolting operations can produce periodic fluctuation in the climatic conditions created within these workings. The existence of this changing work and environmental loading cycle requires the development of sympathetic and adaptable ventilation and adaptable cooling system. It is therefore necessary to consider the optimal location, monitoring and control of these integrated refrigeration and ventilation systems, in order to produce both a flexible and cost effective solution. The ventilation costs can represent a significant proportion of the total energy cost of many underground UK coal mining operations. Thus, any small improvements that can be produced in the efficiency of the ventilation system can produce a significant power and cost saving. Within the UK coal mines, there is little operational and planning experience in the use of mine cooling systems. There is currently only one major mine that has a subsurface cooling plant capable of supplying chilled service and cooling water. To produce an economic solution to the current and potential future mine climate problems it is pertinent to investigate the suitability of the adoption of the integrated air-cooling and auxiliary ventilation systems within these drivages. Due to the absence at present of the surface cooling facilities it would be expedient to consider the suitability of the application and control of localized subsurface cooling plant. 2.1. Background behind the construction of the computer model The psychrometric, climatic and machinery heat source calculations used within the rapid development model are based on procedures used within the commercial software CLIMSIM娃 initially developed at the University of Nottingham (Gibson, 1976) and now supported by Mine Ventilation Services (MVS) Inc. (1997). The CLIMSIM娃 model was developed to simulate the climatic conditions within a through flow open ended tunnel, in which the ventilation air travels from one end of the tunnel to the other. The computational model divides the tunnel airflow domain into a linear series of interconnected discrete volume elements. The iterative calculation method requires the definition of either the measured or defined inlet airflow and psychrometric conditions for the element at the entry to the defined flow domain. By applying a successive series of calculations, based on the laws of the conservation of mass and energy across each volume element, the thermometric conditions of the airflow at the outlet to each element is determined. The calculations of each volume
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Fig. 1. The drivage and duct elements on a typical drivage schematic.
element are carried out sequentially from inlet of the tunnel to outlet in the direction of the airflow. However, in the construction of the computational model for the dead end tunnel drivage model, the air flow domain is divided into a series of linear interconnected discrete volume elements. It is necessary to construct two sets of integrated volume elements, one to represent the airflow in the main body of the tunnel drivage and the other to represent the air flowing within the ventilation ducts. This is illustrated in Fig. 1. In the case of a forcing duct, the direction of the airflow within the duct is counter to that flowing within the main body of the tunnel roadway. The iterative calculation method proceeds along each set of elements in a similar manner to that described for CLIMSIM娃 program. However, an additional set of iterative calculations is performed to evaluate the net heat transfer through the duct walls and the mass transfers of airflow due to the existence of any leakage between the duct and the tunnel. The calculations performed within the model involve the determination the sensible andyor latent (moisture) heat gainsylosses that occur within each element to evaluate the psychrometric conditions of the airflow leaving each element. The various thermodynamic effects simulated within the model include: 1. The heat sourceysink effects of the strata 2. The effects of the auto-compression of the ventilating air due to depth 3. The heat generated by the machinery and miscellaneous sources 4. The heat emitted from conveyed mineral 5. Water pools and floor dampness at head-end 6. The influence of dust suppression sprays 7. The influence of localized cooler units 8. The influence of ventilation fans 9. Interactions between drivage and duct air through leakage and heat transfer.
2.2. Construction of the drivage model UK coal mine rapid development drivages are normally advanced using a continuous miner or road header machine. There are principally two auxiliary ventilation systems used to ventilate these mining systems. The predominant auxiliary ventilation system employed is the forceyexhaust overlap system (Fig. 2). The second alternative auxiliary ventilation system used is the force with machine mounted exhaust scrubber duct system (Fig. 3). The tunnel climate model has been developed to simulate these two systems. However, should underground conditions require the use of a pure exhaust ventilation system, the model may be simply adapted to simulate this case. In Fig. 2 the iterative climatic calculations follow the predominant direction of the airflow though the force duct and within the drivage. As there may be an exchange of leakage air between the force ventilation duct and the drivage elements, together with heat transfer through the duct walls, an iterative approach has been used, whereby the calculations are repeated until a balanced and numerically converged solution is obtained. Fig. 2, also illustrates the various heat load zones identified within the drivage. Zone I represents the area in the immediate vicinity of the head end cutting area. This is defined to start from the outlet of forcing duct through to the face of the tunnel. In UK coal mines the outlet to the forcing duct is normally set at between 20–25 m to the face, and the inlet to the exhaust duct is maintained within 2–3 m of the head end. The major heat sources within the Zone I include the newly exposed rock faces (roof, floor, two side-walls, and the face of the head end), the broken rock, the cutting machine, and the water sprays. These heat sources will produce the greatest impact on the climate. The predominant airflow direction within this zone of the drivage follows that of the forcing jet towards the face of the heading.
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Fig. 2. Schematic of a conventional force-exhaust overlap configuration with the defined climatic zones.
Zone II lies beyond the immediate mining area and incorporates the region where the broken mineral is transferred to the conveyor belt or shuttle car. Zone II is defined as the overlap section of the forcing duct and the exhausting duct. The length of this overlap section is typically 15 m. The mineral transport equipment, the broken mineral and water sprays located within this region will produce a marked effect on the climatic conditions experienced by the ventilation air, as only a portion of the air delivered by the force fan to the head end will flow out through the Zone II. Typically in excess of 50% of the fresh air quantity delivered by the forcing fan is exhausted through the overlap duct. Zone III is defined to start from the outlet of exhaust duct to the entrance of the development drivage. The air exiting the exhaust duct mixes with the tunnel airflow leaving the overlap zone, and then this combined flow roadway air travels back towards the entrance to the drivage. Within this region of the tunnel, the conveyed broken mineral, any installed equipment, water sprays,
and the strata will produce the greatest impact on the climate. However, in the case of the application of a forcing duct with machine mounted exhaust scrubber fan system (Fig. 3), the air is delivered by the forcing duct to within of 5 m of the face of the heading. The exhaust scrubber fan draws air from the vicinity of the face and discharges this air to the rear of the cutting machine. Thus, in this case, the predominant flow direction and hence heat transfers are in a direction away from the headend of the drivage. The air returning from the face picks up the heat mainly from the newly exposed rock faces, the broken rock, the conveyed mineral, the cutting machine, the water sprays, the conveyor and the warm moist air exiting the exhaust scrubber fan at the rear of the machine. The following sections discuss the results of the validation exercises that were performed and the series of subsequent modifications made to the drivage climatic model.
Fig. 3. The simple forcing system with machine mounted exhaust dust scrubber fan.
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Fig. 4. Generic Measurement Schematic for a rapid development drivage employing Continuous Miner machine and a forceyexhaust overlap auxiliary ventilation system.
3. Validation and further development of the drivage model The results produced by the drivage climatic model have been validate against the ventilation and climate survey data collected from a number of underground rapid tunnel developments within UK Coal Ltd deep coal mine operations. Fig. 4 shows a generic schematic of the location of the various survey measurement locations within these rapid drivage developments. All of the developments surveyed employed a continuous miner and forcey exhaust overlap auxiliary ventilation system shown in Fig. 4. The dry and wet bulb temperatures were recorded outbye of the auxiliary force fan, in the main intake trunk airway. These data points were specified as the inlet flow conditions to the model. A dry bulb temperature reading was taken inside the force duct down stream of the fan to determine the temperature rise across the fan. As the moisture content of the air within the force duct was assumed constant only dry bulb measurements were recorded at regular intervals along the length of the duct. Two sets external temperature and flow measurements were made at the inlet and discharge points of the overlap exhaust fan duct. 3.1. Drivage model validations and modifications Four sets of the ventilation, climate and technical data have been used to validate and correlate the model predictions. They are from (1) the 190s Loader Gate Development at Thoresby Colliery; (2) the 190s Supply Gate Development at Thoresby Colliery; (3) the 312s Return Gate Development at Welbeck Colliery; and (4) the 105s Tail Gate Development at Maltby Colliery. Following a comprehensive analysis of the results produced by these validation exercises it was concluded that there was generally close agreement between the
measured and the predicted dry-bulb and wet-bulb temperatures. However, the model was unable to reproduce certain features observed from an analysis of the field measurements. In particular, it was observed that: (a) that the drop in the temperature of the air jet as it exited the force duct observed in the measured data, was not being reproduced by the model, and (b) the model did not fully account for the latent heat pick up in the headend region. Thus, to improve the predictions obtained from the model, a number of additional physical model features were developed and incorporated into the model. 1. Expansion cooling of the air as it exits the duct and enters the drivage. The procedure is based on the reversible adiabatic expansion of a fluid due to a change in pressure and the remaining physical model features were included in an attempt to account for additional sources of latent and hence moisture. 2. Small water pools whereby the heat loading is based upon the contact surface area and the water temperature. 3. Standing water at the head-end region of the drivage. The procedure is similar to the calculation performed to simulate a water pool, except in this case it is assumed that the floor is covered in water up to a point beyond a specified distance from the head-end. 4. The variation of the wetness factor observed along different sections of the roadway. This recognizes the greater concentration of dust suppression sprays, service water, wet shotcrete operations that may exist at the face end of the tunnel excavation. Thus, the drivage may be divided into two sections, and different wetness value can be specified at each end of two sections. Linear interpolation is used to calculate the intermediate values. 5. A re-entrainment of some of the air returning from the head-end by the momentum of the jet of air
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Table 1 Baseline input data for Maltby Collieries 105s tunnel development, as required by the Climatic Prediction Program Name
Data
Unit
Roadway length Roadway cross-section (width=height) Virgin Rock Temperature (VST) Rock thermal conductivity Coal thermal conductivity Average roadway thermal conductivity Rock thermal diffusivity Coal thermal diffusivity Average roadway thermal diffusivity Tonnage per shift Force fan power (nominal) Force fan ventilation flow, inlet to duct Force fan ventilation flow, outlet to duct Exhaust fan power (nominal) Exhaust fan ventilation flow, inlet to duct Dry-bulb temperature, force fan inlet Wet-bulb temperature, force fan inlet Conveyer belt drive (nominal) Continuous miner (nominal) Mineral transfer equipment (nominal)
1164 13.68 41.9 2.78 0.35 1.71 1.39=10y6 0.25=10y6 0.88=10y6 6.0 90 8.09 6.82 56 5.28 22.0 15.5 300.0 360.0 182.0
m m2 8C Wym 8C Wym 8C Wym 8C m2ys m2ys m2ys tyshift kW m3ys m3ys kW m3ys 8C 8C kW kW kW
exiting the force duct. A specified percentage of the return air may be combined with the air from the force duct. 6. The introduction of a mixing length in which the air exiting the exhaust overlap duct is assumed to mix with the air flowing from the face end of the drivage along the duct overlap zone. 3.2. An example of model validationsycorrelations against the measured data at Maltby Colliery The layout of 105s Tail Gate tunnel development at Maltby Colliery, UK, is similar to that shown in Fig. 2. The measured ventilation and climatic survey data com-
prised of a series of spot dry and wet bulb temperature readings taken within the drivage and several dry bulb measurements made within the auxiliary force ventilation duct. The data also included the geometrical and physical characteristics of the drivage and the type and power consumption of the equipment installed, and the quantity and type of water usage. The heat emitted from the conveyor drive motor was treated as a linear heat source, with the heat load distributed along the length of the conveyor. The input data of the inlet conditions and the geometrical and physical characteristics for the model calculations was based on the ventilation and climate survey data. Some other input parameter values were tested and varied within the climatic prediction model aiming to obtain the closest agreement to the measured outlet data. For example, the drivage was divided into two sections and the length of the section near the head end was set 60 m. The wetness factor value at the start line of the drivage, W1, was set 0.2; the value at the starting end of the head end section, W2, was set 0.2, and the value at the head end, W3, was set 0.5. Within the remainder of the drivage the wetness factor for the drivage faces (walls, roof and floor) is allowed to vary in a linear fashion. The input data for the drivage model is summarized and listed in Table 1. The predicted and measured temperature profiles within the tunnel drivage are plotted in Fig. 5. The predicted and measured temperature profiles within the forcing duct are shown in Fig. 6. The predicted temperature profiles within Zone I and Zone II are detailed in Fig. 7. Following an analysis of the results produced by these exercises it was concluded that the climatic model is able to adequately simulate the climatic conditions experienced within the Maltby Colliery 105s tunnel
Fig. 5. Measured and predicted temperatures along the drivage.
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Fig. 6. Measured and predicted dry-bulb temperature inside force duct.
drivage. The wet bulb temperature profiles within the drivage and the dry bulb temperature profiles inside the forcing duct were predicted to within "1 8C (Figs. 5 and 6). In Fig. 7, the dotted lines within the Zone I are the predicted air temperature profiles along the drivage as the predominant airflow in Zone I travels from the force duct outlet to the head end. The solid lines within the Zone I and Zone II are the predicted air temperatures along the drivage to represent the small proportion of the delivered air which travels away from the head end through the overlap zone, whilst the exhaust fan moves the remaining portion of the air from the head end and discharges it into Zone III. The solid lines within the Zone III are the predicted wet and dry air temperature profiles within this section of the drivage.
Following an analysis of the simulation and validation exercises performed on the model using the above data sets, it was concluded that the parameter that had the most significant influence on the production of a satisfactory correlation was the absolute value and spatial variation of the wetness factor applied to the tunnel surface. Fig. 8 illustrates the results of the sensitivity exercises performed to study the effects produced by a variation in the wetness factor. Fig. 8 illustrates a plot of both the measured and predicted the dry bulb and wet bulb temperatures for using different sets of wetness factors. Each combination (A–C) was obtained by using a different values of: W1 (wetness factor value at the entrance to the drivage), W2 (the value at the start of the head end section) and W3 (the value at the head end). It can be seen that the
Fig. 7. Predicted temperature profiles within the defined zones.
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Fig. 8. Predicted temperature profiles with different values of wetness factor.
combination C has obtained the closest agreement to the measured outlet data. 4. Case study: cooling design for Maltby Collieries 105s tunnel development To demonstrate the capabilities of the model to improve the efficiency of the design and operation of integrated mine ventilation and cooling systems for rapid development drivages the following case study was conducted. The drivage chosen for this case study was 105s Tail Gate tunnel development of Maltby Colliery, introduced in Section 3.1. 4.1. General cooling strategy for a rapid development drivage development Excessive temperatures and humidity are becoming more common in the highly mechanized districts of UK coal mines, especially where operations are performed at depth. The conventional approach to ventilation planning in UK collieries is to design an auxiliary ventilation system so that methane emissions are diluted to blow statutory threshold limit values at the minimum of cost. In the majority of cases to date, ventilation flows thus obtained have been sufficient to avoid uncomfortable climatic conditions. In situations within the main ventilation circuit where the conditions become unacceptable, it is the need to alleviate this problem, rather than the methane emission rate, which determines the air quantity required. However, within many workings, and single entry development workings in particular, the determined quantity is constrained by the need to avoid dust dispersion, and the flexibility of the existing auxiliary fan installations. Thus, in cases where the air quantity alone is insufficient in itself to achieve acceptable
climatic conditions, alternative methods of climate control are needed, including the application of mechanical cooling systems. The control of the thermal climate within mechanized developments is normally effected by the application of a staged air cooling strategy. The exact layout and duty of the cooling system used within a development will depend on: its length and advance rate, the method by which it is being driven, severity of the heat problem and the auxiliary ventilation layout employed. All these factors will influence the cooling strategy used. The following paragraphs present an overview of a general cooling strategy for a mechanized development employing a force-exhaust overlap auxiliary ventilation system (Fig. 4). 4.2. Identification of the coincidence of major heat loads and labour activity and definition of the climate control zone (CCZ) It is generally accepted that miners, who are undergoing heavy work activity under adverse climatic conditions, may experience an increased heat stress. Such adverse climatic conditions may often be present at the head end of rapid development drivages. These conditions are produced in part by the concentration of major sources of heat and humidity, which include mined mineral, machinery and water sprays. To develop effective ventilation and cooling strategy it is essential to identify the potential coincidence of major labour activity and heat loading within these mining operations. Typically, 7–8 miners and officials work within a UK rapid development drivage. 4–5 miners and officials are predominantly employed within the face end of the drivage. The remaining 2–3 miners are periodically employed within the overlap zone and further outbye in
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Fig. 9. Schematic of the cooling system proposed for the 105s Tail Gate Development at Maltby Colliery and the Climate Control Zone (CCZ).
the main body of the drivage. The major labour activities and heat loadings may be summarized as: 1. Major labour activities: ● Cutting operations ● Scaling, rock support, bolting and meshing ● Materials supply ● Advance of auxiliary ventilation system 2. Major Heat Loadings ● Strata heat in the vicinity of head end ● Newly cut mineral ● Electrical machine sources including, the continuous miner machine, conveyor, mineral breakery loader, and transformer ● Forceyexhaust auxiliary fans ● Water sprays. However, the majority of these heavy labour activities and heat sources are commonly concentrated within 60 m of the face end (cf. Figs. 1 and 2). Thus, this zone was subsequently used to define the establishment of a design climate control zone (CCZ) (Fig. 9), a zone within which the climate is to be maintained at or below a given effective temperature limit (Twort et al., 2002). An ET of 28 8C was set as the upper climatic design limit specified within the defined CCZ. Where the climatic conditions of the air exceed this limit, a number of cooling methods are employed to regulate the climate. The drivage development is driven by either a road header or a continuous miner machine, which is now predominately used within UK collieries. The cooling strategy employed to control the thermal climate of the development is sub-divided into two main distinct phases: Phase 1: Cooling the intake air within the force duct. A cooler is placed within the duct line after the force fan. It must cool the air, such that on delivery to the head end, the climatic conditions within a prescribed length of the heading will remain within the preset climatic limits. However, as the development advances
the relatively cool air within the forcing duct has an increased length of time in which to absorb sensible heat, through the ducting, from the warm air returning along the development. Under these circumstances, although the intake air ducted to the head end may be climatically acceptable, it can easily deteriorate and exceed climatic limits while applying for force-exhaust overlap ventilation system. The air is heated up by the sensible and latent heat generated by the newly cut minerals, water sprays, and the machinery within the Zone I as it reaches to the head end and it is further deteriorated after going through the exhaust fan. At this point Phase 2 of the cooling strategy may be initiated. Phase 2: Installation of an air cooler in the exhausting duct after the fan. This air cooler must re-cool the warm air exhausted off the head end, such that the ventilation air discharged by the exhaust fan remains within climate limits. 4.3. Climate prediction analysis with different virgin rock temperatures (VRTs) The validated computer model was employed to investigate the climatic conditions that would exist within a rapid development drivage as the excavation becomes deeper and hence experiences an increased virgin rock temperature. It was assumed in the following exercises that the ventilation quantities were optimal with regard to gas and dust dilution and control. The predicted dry-bulb, wet-bulb and effective temperatures within the drivage for the VRTs of 30 8C, 35 8C, 40 8C, 41.9 8C, 45 8C, 50 8C, 55 8C and 60 8C are given in Figs. 10–12, respectively. From an analysis of the predicted results shown in Fig. 12, it may be concluded: 1. The ET throughout the entire length of the drivage is maintained below 28 8C when the VRT is below 40 8C.
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Fig. 10. Predicted dry-bulb temperatures within the drivage with different VRTs.
2. When the VRT is between 40–45 8C, the ET within the CCZ remains under the 28 8C ET. However, the ET within the drivage outbye will exceed the 28 8C ET limit. 3. When the VRT is above 45 8C, the ET throughout the whole length of the drivage will exceed the 28 8C ET limit. 4.4. Cooling design with different VRTs Following the conclusions drawn above, a further investigation was performed to identify the cooling strategy to be adopted, and the minimum amount of cooling to be installed to maintain the ET within the head end CCZ below 28 8C.
The following conclusions were drawn: 1. For VRTs of up to 40 8C the climate within the entire drivage may be maintained below an effective temperature of 28 8C with the sole use of ventilation. 2. When the VRT is between 40–45 8C, the ET within the CCZ remains under the 28 8C ET. Thus, the ventilation flow is adequate to maintain the effective temperature within the CCZ at or below 28 8C 3. For VRTs in excess of 45 8C a cooler first needs to be first installed within the force duct to maintain the ET within the CCZ below the 28 8C ET limit. Table 2 presents the calculated minimum cooling requirements for VRTs of 50 8C, 55 8C and 60 8C, respectively. The following assumptions are inherent to
Fig. 11. Predicted wet-bulb temperatures within the drivage with different VRTs.
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149
Fig. 12. Predicted effective temperatures within the drivage with different VRTs.
these calculations: (a) following the application cooling and to avoid discomfort to the workforce the dry-bulb temperature at the outlet to the forcing duct should not be below 20 8C; (b) the cooler is positioned within the forcing duct at a position 150 m back from the head end. The cooler and force duct cassette can either be slung from a monorail or mounted on a sled that would be moved forward to follow the advance of the face. Where the cooler installed at a distance further back from the face, this would result in a reduction in the positional efficiency of the cooler. This would require the potential installation of additional cooling capacity to compensate for the increased heat flow that may experienced to the force duct from the drivage, due to the increased temperature differential. It was assumed in the calculations that a fan mounted internal to the cooler would handle the additional pressure drop afforded by the cooler unit within the forcing duct. From an analysis of the data contained in Table 2, it may be concluded that for a VRT of between 50–55 8C the application of a single indirect cooler unit may be able to maintain the climate within the CCZ below the required 28 8C ET limit. For a VRT of 60 8C and above, would require the installation of two indirect cooler units within the force duct to maintain the climate within
the CCZ below the required 28 8C ET limit. For a given cooling water supply temperature, adjusting the mass flow of the cooling water will modify the duty of each cooler unit. 5. Conclusions The paper documents the background behind the development and validation of a computer based model to predict the climatic environment in underground rapid development tunnel drivages. Following an analysis of the results obtained from the correlation exercises performed against ventilation and climatic data collected from a number of UK deep coal mine operations, it was concluded that there was close agreement between the model predictions and the measured dry-bulb, wet-bulb and effective temperatures. The paper details the results of a series of correlation and validation studies conducted against the ventilation and climate survey data measured within 105s district Tail Gate tunnel development at Maltby Colliery, UK. The paper presents the results of a case study that illustrate the application of the validated model to the design and operation of an integrated mine ventilation and cooling system. The case study illustrates the effect
Table 2 The calculated minimum net cooling duties required to maintain the ET in the CCZ below 28 8C VRT Total net cooling requirement Tws8 8C
50 8C 50 kW One cooler unit Ÿs1.05 lys
55 8C 100 kW One cooler unit Ÿs3.3 lys
Tws15 8C
One Cooler Unit Ÿs5.7 lys
NyA
Tw-water temperature,
Ÿ-water flow rate.
60 8C 140 kW Two coolers in series Cooler 1: Ÿs1.05 lys Cooler 2: Ÿs3.3 lys NyA
150
I.S. Lowndes et al. / Tunnelling and Underground Space Technology 19 (2004) 139–150
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