1 EFFECT OF AUTO COMPRESSION ON VENTILATION SYSTEM OF DEEP SHAFT COAL MINES IN JHARIA COAL FIELD – A CASE STUDY D. Mishra * and Dr. N. Sahay ** * Trainee Scientist, ACSIR, CSIR-CIMFR, Dhanbad **Sr. Principal Scientist & Head, Mine Ventilation Discipline, CSIR-CIMFR, Dhanbad 1.0 ABSTRACT The future prospect of underground coal mining in Indian mines is either from extensive mines or at depth (> 300 m). In this situation the intake air is expected to be influenced by various parameters, viz. auto- compression, surface air temperature (seasonal temperature variation), heat due to explosive detonation, heat from mechanized equipments, metabolic heat, heat from broken rock, wall rock heat flow, heat from other sources etc. Many mines in our country are receding towards lower horizon by taking the liability and responsibility of upper seams. In order to address the problem of oppressive climatic conditions at the workings, behavior of various parameters affecting the quality of intake are required to be studied for realistic ventilation planning of deep mines. The effect of auto compression is one of them. The paper deals with realistic estimation of heat addition to the intake air due to auto compression. 2.0 INTRODUCTION Many Indian coal mines have become extensive or receding towards greater depth. As a result in many mines work place environment has become oppressive and affecting the productivity and safety. The importance of ventilation has been realized since beginning of mining operation. It has been established that it has got direct relation with production, productivity and safety of the mines. In a study [1] the relation of wet bulb temperature at workplace environment and efficiency of the workers has been established. On the basis of literature, in US metal mines maximum efficiency is at or below 27 0c and economical efficiency is between 27 0 C to 29 0 C. In addition, the inspectorates of different coal producing countries have also stipulated the value of maximum permissible wet bulb temperature as per their climatic condition considering the miners health. These values are for coal mines India [2] , USA [3] , UK [4] are 33.5 0 C, 30 0 c, 33 0 C respectively. It has also been established that the temperature of the environment can be diluted by increasing the air quantity at the workings . For determination of optimum value of air quantity at particular workings depend on physical parameters of the openings and thermal properties of the virgin rock etc. For deep shaft mine heat due to auto compression plays an important role in adding enthalpy to the air flowing in the mine. Auto compression [5] is considered as a source of heat which can’t be diluted by increasing air circulation in mine. In case of shallow depth mines effect of heat due to auto compression is considered negligible. However in case of deep shaft mines auto compression of intake air in shaft raises the temperature affecting the workplace environment. This subject gets more complicated day by day as the Indian coal mines are receding towards a greater depth i.e. (>300m depth). Therefore consideration of auto compression on air current in deep shaft mines is necessary. The paper discusses the effect of auto compression on air in one of the mines in Jharia coal field of Tata Steel Ltd. 3.0 History of auto compression in Indian mines Value of [ 6] rise in dry-bulb temperature of air due to auto compression is 0.976 K per 100 m depth. The wet-bulb temperature of air also rises due to auto compression but its rate depends upon surface dry-bulb and wet-bulb temperature. For prevalent summer conditions in India the wet-bulb rises at the rate of 0.3-0.25 K for every 100 m depth in dry air, but as soon as the evaporation in shaft occurs then the dry-bulb temperature decreases sharply and wet-bulb temperature rises at a faster rate. In this condition the adiabatic index of the intake air can be represented by