Improved Climatic Modelling of Mine Ventilation Networks
UK Coal Ltd and the University of Nottingham have completed their contributions as partners in this ECSC supported project, led by Deutsche Montan Technologie GmbH (DMT) of Germany.
The current trends towards the adoption of retreat longwall mining methods and the associated rapid development of the access drivages have exacerbated the environmental conditions experienced within these workings. In particular, the increased working depth, levels of mechanisation and production have challenged the engineer to produce a satisfactory and cost effective solution to the adverse climatic conditions experienced within many deep mine workings.
To assist in the design and implementation of an integrated mine ventilation and climatic control strategy, the engineer needs to be able to predict the overall heat loads existing within alternative mine layouts and production configurations. The development of an effective mine network climate prediction and planning tool would aid the engineer to assess, quantify and cost the effectiveness of alternative climatic solution strategies, including ventilation, spot, linear and/or bulk cooling systems.
The UoN team developed integrated ventilation and climatic simulators to assist in the prediction of the potential heat loads that may be added to the ventilation air. The UoN team and UK Coal teams also accomplished the development and improvement of field-validated computational models to simulate the climatic conditions across roadways, rapid development drivages and high production longwall coalfaces.
The developed drivage model has been used in the identification of the operational and practical limits to the application of purely ventilation techniques to ameliorate adverse climatic conditions within mine workings and to investigate the adoption of high efficiency auxiliary fan and duct flow systems to increase the quality and quantity of mine air delivered to the drivage face ends.
The results obtained from a series of climate simulation exercises performed on a representative UK rapid development drivage, concluded that the application of an increased efficiency (from 50 to 60%) 90kW force ventilation fan, produced slight improvements to the climatic conditions experienced at the head end of the drivage (a decrease of 0.8 °C in the effective temperature). It is concluded that any additional improvements to the auxiliary fan performance would be expected to produce further improvements to the climatic conditions experienced at the head end of the drivage. This improvement would be achieved by the combination of the reduction in the total heat load imparted to the airflow by the fan and to the increase in the potential total airflow quantity delivered to the face end. Although a similar series of prediction exercises were not performed for a typical 57 kW exhaust ventilation fan, it is proposed that similar improvements in climate may be obtained by the application of a more efficient exhaust fan.
The longwall district model was developed to account for two different configurations: advancing longwall district and retreat longwall district. The district model is constructed by a combination of the roadway model and a previously developed face model.
The UK Coal research team facilitated a series of routine measured underground ventilation and climate data that has been used to validate the computer prediction codes. The University and UK Coal research teams have also collaborated on the development of improved and validated models of machine and cut mineral heat loads and both central and spot cooling systems.
The UK Coal research team has completed the work of development of user-friendly interface procedures for the computational models and the work of integration of the models with the VNET5 ventilation network analysis software.
The focus of the research project has been to further develop and validate district model designed to predict the climatic environment in underground longwall face area, and to incorporate the model into the existing VNET 5 ventilation network solver, to form an integrated, user-friendly ventilation and climatic network prediction tool.
Integrated High Efficiency Ventilation and Cooling Systems
Through another ECSC-supported project, the University of Nottingham has developed another computer based climatic prediction tool which can investigate the suitability of the adoption of the integrated air-cooling techniques with auxiliary ventilation systems within drivages.
The report documents the background behind the development and validation of a computer based model to predict the climatic environment in underground rapid development drivages. Following an analysis of the results obtained from the initial 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.
To develop effective ventilation and cooling strategies it is essential to identify the areas of coincidence of major labour activity and heat loading within these mining operations. The investigation concluded that the majority of the heavy labour activities and heat sources were concentrated within 60 metres of the head end of the drivage.
An analysis of the results obtained from a series of climate simulation exercises performed on a representative UK rapid development drivage, concluded that the development and application of an increased efficiency (from 50 to 60%) for a 90kW force ventilation fan, produced slight improvements to the climatic conditions (decrease 0.8 °C effective temperature) experienced at the head end of the drivage. Additional improvements to auxiliary fan performance would be expected to produce further improvements to the climatic conditions experienced in the head end of the drivage, by a combination of both reducing the total heat load delivered to the airflow and by the increase in the potential airflow quantity delivered by such fans. Although the corresponding simulation exercises have not been performed, it is proposed that similar climatic improvements could be obtained by the development and application of similarly improved efficiency 50 kW exhaust overlap auxiliary ventilation fans.
From the simulation exercises performed using forcing duct material of higher thermal insulation (hence lower thermal conductivity) it was concluded that this would reduce the heat transferred to, and hence the temperature gain experienced by, the airflow travelling along the forcing duct towards the head end of the drivage. This reduced heat gain would in turn affect better cooling at the face of the drivage. However, the improved thermal benefits gained may become less attractive due to the potentially high costs required to develop/purchase the lower conductivity fabric, or the additional capital and operational costs associated with the use of glass reinforced plastic ducting within such long development drivages.
The cooling strategy and amount of cooling power required to maintain adequate environmental and climate conditions within a rapid development drivage operating in virgin rock temperatures (VRTs) of 30 °C, 35 °C, 40 °C, 41.9 °C, 45 °C, 50 °C, 55 °C and 60 °C, were subsequently examined. An analysis of the results obtained from these studies concluded that:
It is concluded that for a VRT of between 50-55 °C the application of a single indirect cooler unit may be able to maintain the climate below the required 28 °C ET limit. For a VRT of 60 °C and above the installation of two indirect cooler units in the forcing duct may be able to maintain the climate below the required 28 °C ET limit.
Improving climate conditions in hot high performance workings
For this new ECSC project, the joint UoN and UK Coal research teams have been evaluating the use of thermal data loggers to collect continuous climatic data from a number of underground workings. Continuous climatic logging data have been obtained and collected from the 22's longwall district of Harworth Colliery. These record simultaneous dry bulb and relative humidity measurements. In addition to the collection of the continuous climatic record, the UK Coal researchers have undertaken a number of consecutive manual climatic surveys within the same underground workings.
In addition, the UK Coal research team have supplied the UoN researchers with the additional operational and engineering layout detail for 22's longwall district required to quantify the sensible and latent heat load source contributions that produce the resultant climatic conditions experienced across the district. An analysis of the individual shift reports has been conducted to give an assessment of both the pattern of total shearer usage and the total power consumption within the 22's longwall district across a typical shift. The durations of the shearer operation each day and hence indicative shearer power and water spray draw and mineral production were quantified. Preliminary comparative analyses have been conducted to identify any measure of cross correlation between the measured and computed dry/wet bulb temperatures in main gate and the operation of the shearer over a 48-hour period
The variation in the dry bulb temperature range was observed to be 2.1 °C between the period of a shearer cut and shearer stoppage. However, the range of wet bulb temperature variation observed was 5.65 °C between the period of a shearer cut and shearer stoppage. The computed standard deviation of the dry bulb temperature variation recorded was 0.59 °C whereas the standard deviation of the recorded wet bulb temperatures was1.78 °C. It was concluded that cutting activities and, in particular, the use of water sprays produce a significant influence on the variation of the wet bulb temperature experienced and a moderate influence on the dry bulb temperature change.