Research And Application Of The Technological Process Of Intermittent Coal Dust Collection And Recovery

Coal still plays a leading role in China’s energy structure.Plenty of intermittent coal-bearing waste gas and coal-bearing waste water are produced in different production sections like coal mining,coal transportation and outdoor coal stacking,which poses a threat to the ecological environment and national health."National Occupational Disease Prevention and Control Plan(2016-2020)" and "Healthy China 2030" Planning Outline pointed out:it is essential to step up effort to solve health-affecting environmental problems.Therefore,building a clean,efficient,safe and sustainable modern industry is a must.The study is meant to explore the existing intermittent coal waste gas and coal waste water problems to come up with safer,energy-saving and effective intermittent coal dust control methods based on the various coal-pollution-control needs of Tianjin Coal Terminal of the National Energy Group.The formation of intermittent coal dust and the properties of coal dust are analyzed;different coal dust suppression and removal technologies are compared in terms of dust removal mechanism;some new ideas of coal dust collection and recovery are put forward based on dust removal technologies and objectives;new solutions to problems existing in the process are worked out and applied in the coal port.Site investigation and analysis reveals that dry electrostatic dust precipitators which are originally used have their problems as follows:(1)Safety problems:flammable and explosive particles can bring about safety hazards in the operating process of dry electrostatic precipitators which are originally used in the Coal Terminal transfer stations(T1 to T13).Secondary dust hazards exist when collected dust is manually unloaded and transported;(2)Waste gas pollution problems:the intermittent coal waste gas from the coal-unloading from the conveyor belts in T3 transfer station causes huge fluctuation of the coal dust concentration(5000～20000mg/m3)depending on the number of belts at work.The originally used dry electrostatic precipitators,with problems like insufficient output,aging and rust of air ducts,are underqualified for such working conditions;(3)Waste water pollution problems:the intermittent coal-bearing waste water from spray washing for coal dust suppression in the outdoor space and the dumper room is discharged into the rainwater pipe network,where it is diluted by rainwater and waste water from other port production sections to meet the discharge standard.The problem is that the pollutants in the water can still harm either the environment or the conventional sewage treatment facilities.Solutions to the above-mentioned three problems are put forward.To solve the safety problems,devices are reasonably optimized or replaced;to solve the gas pollution problems,a more efficient optimized dust removal system is applied;to solve the waste water problems,intermittent coal-bearing waste water is effectively treated,with both coal and water recycled.Through examination of the original system and experiment on main devices like dust removal devices and based on investigation and collected data and on the energy saving and emission reduction principles of related thermal equipment and environmental protection equipment,comparison is made between different technologies and the conclusion is reached that the coal dust collection and recovery system,which integrates circulating spray dust suppression,wet electrostatic precipitation and coal-bearing water treatment,has the best effect.The results obtained are as follows:(1)Intermittent coal-bearing pollutants are transferred into liquid state,eliminating the risk of coal-bearing gas explosion.Collected coal is dehydrated and made into coal cakes,with the secondary dust problem solved and coal dust recycled.(2)Application of the system reveals that after purification by the wet coal dust collection and recovery system,the concentration of exhaust particulate matter is less than 1mg/m3(close to zero emission)and less than 10 mg/m3 even under the rare worst working conditions,greatly improving the working environment;(3)After coagulation-sedimentation-filtration process,the coal-bearing water meets the standard of reclaimed water and fire water,and is partly recycled for the coal dust collection and recovery system and partly used for cleaning in the Coal Terminal,with annual water recovery of about 122316t.The result of nearly zero discharge greatly alleviates water pollution.(4)With the application of the new coal dust collection and recovery system,coal recycled from coal-bearing waste gas is about 1431 t/a annually,and coal recovered from coal-bearing waste water is about 243t/a annually,reaching 1674t/a totally per year.The economic benefits are substantial.