Waste Heat Recovery Of Mine Exhaust And Applied Research

The general ventilation is adopted for underground mining. Air is extractedfrom the intake air shaft into the underground, and then discharged into theatmosphere. Air is heated by the geothermal energy. Mine exhaust inherent in a largenumber of low-temperature geothermal energy, and remains constant throughout theyear, this part of low-temperature heat has considerable value in use. By combiningwith the water source heat pump technology, the potential low-temperature heat canbe extracted. When the device is used for heating in winter, it can replace traditionalboiler of coal mining enterprises, reduce emissions and benefit environment. Whenused for cooling in summer, energy efficiency of the device can be improvedbecause the temperature of mine ventilation in the summer is lower than the ambientair. By using spray heat exchanger in the main fan diffuser, exhaust airflow can bepurified, and dust pollution can be reduced. This technology reduces environmentaldust and noise pollution.In this paper, a thermal calculation method analogous to spray chamber wasused for mine ventilation heat recovery device. The energy-saving potential wasanalyzed for the device by a. specific example. Using Newton’s second law, take astress analysis on the sprayed droplet in the main fan diffuser, four states thatdroplet may experience are obtained and the maximum drop height of the dropletunder each state were calculated. Droplet broken, suspension and blownphenomenon were also discussed to provide a sound theoretical basis for the designof spray device at different air velocities (3-12m/s), diameters (<4mm) and differentinitial drop velocities (4-20m/s). Using FLUENT software, take a numericalsimulation on the diffuser by different turbulence models and grid steps. Areasonable turbulence model and a separate grid step were determined. UsingMATLAB software, build a mathematical model for the mine spray heat exchanger.Using the classical fourth-order Runge-Kutta method, the numerical model iscalculated and the effect of diffuser installation parameters, working fluid initialparameters on the efficiency and the outlet droplet temperature were discussed. Thenumerical calculation results were used to take an exergy analysis. The exergyefficiency was calculated and impacts of various parameters on exergy efficiency were discussed. Numerical results show that latent heat transfer is the main type ofheat transfer in the device. As far as is the effects of aspects on the device heattransfer, the first is the computing-height of device, and the second is droplet size,air velocity, ratio of water-air, the last is initial droplet velocity. Air velocity has agreat impact on heat transfer of the device, which should be strictly controlled. Withthe decrease of droplet initial temperature, the decrease of air velocity orenvironmental reference temperature, and with the increase of droplet size or initialair temperature, exergy destruction both increase. The exergy efficiency of the minespray heat exchanger is72.1%. Finally, an up jet spray heat exchanger was designedto improve the efficiency of the device. The maximum droplet rise height wascalculated under different air velocities and different initial droplet velocities. Theresults shows that when initial droplet velocityu dis smaller than twice of the airvelocityu a, the maximum rise height of droplet z is mainly determined byu d,followed byu a, droplet diameter d has little effect on z. Whenu d>3u a, z is jointlydetermined byu a,u dand d. By contrast of down-jet spraying device, factors ofwater-saving, resistance, heat transfer and energy consumption of up-jet sprayingdevice were analyzed, the results show that up-jet spraying device has advantages ofwater saving, large diameter selecting range, low resistance, high thermal efficiency,low power consumption of water pump.