Coal mine ventilation systems must be designed so as to maintain at all times healthy and safe atmospheric working conditions. The main purposes of a coal mine ventilation system are to provide adequate quantities of fresh air to the miners in the workings and to render harmless toxic, noxious, and explosive gases and dusts and carry them out of the mine through dilution by fresh air.
Correct estimation of the required air quantity at each of the workings is vital. This quantity should be determined on the basis of number of workers in the workings, kinds of machinery used, and the make up of gases, dust, heat, and humidity. The required quantities of fresh air at the faces and other places must be increased in proportion to the amount of leakage anticipated in the airways. Leakage estimation may be problematical, but an allowance of 100% of the estimated quantities for faces is common. Quantity estimation is critical as head losses and power are proportional to the square and cube of quantity, respectively. Small errors in quantity estimates can therefore lead to large errors in pressure head and power estimates and affect the total
mine ventilation, health, safety, and production performance. The number of airways required to course the various quantities through the mine is important as this number influences the velocity of the air in the airway. Air velocities are critical from two points of view. From the safety viewpoint, inadequate air velocities can cause undesirable accumulations and layering of gases; very high velocities, on the other hand, can raise dust clouds. From the economic viewpoint, the head loss in a mine airway is proportional to the square of the velocity, and high velocities will entail large horsepower dissipation. Thus velocities must be carefully chosen so that the safety and economic factors are not compromised. Since velocity is a function of the area of an airway and of the number of airways in parallel, definition of the velocity and quantity requirements will automatically determine the number of airways once the shape and size of an airway are determined by mining machine and ground control conditions. The head loss in individual splits can be calculated once the resistances of the airways and the volumes of air circulating in them are known. The head loss in the individual splits can be accumulated using series or parallel circuit laws as applicable until the total head loss in the system is calculated. Knowing the quantity and head required for a mine, selection of a suitable mine fan can be made. This is not to imply that mine ventilation system planning and designing is a simple straightforward process but to emphasize that it is an ordered process with many interactions with other aspects of mine planning and designing (Stefanko, 1983; Suboleski and Kalasky, 1982; Luxbacher and Ramani, 1980).
Factors such as ground control, production requirements, and equipment limitations may often have great bearing on the mine design. In fact, mine ventilation planning is quite complicated when data on strata gases, mining methods, and mine openings are not readily available or estimates of these have large variances. Therefore, the final ventilation design selected must be flexible in order to adapt to changing conditions.
At the exploration stage, data must be collected on those specific geological factors that may affect the ventilation system. Mine design also includes many other geological data and, as indicated, is affected by rules and regulations on health and safety. The end result is the development of a mining method and a mine infrastructure. Mine ventilation considerations play an important role at this initial design stage. However, a more detailed ventilation analysis is required as more definite plans are made to mine the coal seam.
This analysis must be very specific with respect to quantity and quality control of the mine air, and should include a sensitivity analysis covering factors such as methane and leakage that cannot be accurately estimated. Once a suitable plan has been selected, it must be examined with relation to such factors as performance in case of emergencies (e.g., fires and explosions) and adaptability to changing mining plans (e.g., from room and pillar to longwall). On the basis of such an analysis, the plan may be accepted as presented or modifications may be required in the ventilation plan or even in mine design. Early liaison between mine planning and ventilation staffs can prevent many problems and shorten the length of planning time by revealing the need for additional investigations or new calculations on engineering revisions. In effect, mine development schemes should incorporate full details of ventilation arrangements and the means of achieving effective ventilation at each stage of the mine life. The design of the ventilation system, therefore, should be considered in relation to the long-, medium-, and short-range plans of the mining plan (Anon., 1971). While safety is the prime consideration, to maintain or to increase production and productivity levels, good ventilation planning is essential.