Design and Testing of Heat Exchanger for Waste Heat Recovery from Exhaust Air in Northern Coal Mines
In the field of waste heat utilization from exhaust air in coal mines,the insufficient utilization of the resistance of heat exchangers leads to generally low heat transfer coefficients.To address this issue,a design for a heat exchanger for waste heat recovery from exhaust air in coal mines was developed under the constraint that the pressure drop of the exhaust air does not exceed 200 Pa.A circular tube arrangement design method based on constraints of pressure drop in heat exchange tubes was proposed,and a heat exchanger with a vertical-horizontal tube spacing ratio of 5∶8 was analyzed.An automated decision-making tool for multi-variable optimization and multi-scheme comparison was further developed based on Excel VBA,enabling the selection of optimal design schemes from nearly a hundred design alternatives for three heat exchangers,including the heat exchanger for the No.2 air shaft of the Yulin Hongliulin Coal Mine in Shaanxi Province.Construction and installation were completed at the southern air shaft of the Ningtiaota Coal Mine and the No.2 air shaft of the Hongliulin Coal Mine.Data collection and analysis from the circular tube arrangement heat exchanger installed at the No.2 air shaft of the Hongliulin Coal Mine indicated that,compared to the heat transfer coefficient of 17 W/(m2·K)for the rectangular tube stacked heat exchanger at the Heyang Coal Mine,the heat transfer coefficient increased by nearly 76%,reaching 30 W/(m2·K).Additionally,compared to the annual energy consumption of 7.65×106 kWh for the original boiler at the No.2 air shaft of the Hongliulin Coal Mine,the system achieved a reduction of nearly 81%,resulting in only 1.47×106 kWh.The actual annual thermal recovery of the circular tube arrangement heat exchanger was 1.79×106 kWh,while the annual actual thermal recovery of the heat exchanger at the southern air shaft of the Ningtiaota Coal Mine was 1.16×106 kWh.With the widespread promotion of the circular tube arrangement heat exchanger across all coal mines in northern regions,it is expected that approximately 1.09×1010 kWh of thermal energy can be recovered annually,resulting in a reduction of emissions by 8.64×10⁶ tons of carbon dioxide,2.36×106 tons of carbon dust,2.6×105 tons of sulfur dioxide,and 1.3×105 tons of nitrogen oxides.
energy saving and emission reductioncoal mine exhaust airpressure drop limitwaste heat utilizationparameter optimization
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