Ignition Characteristics of Lean Coal Used a Novel Alternating-Current Plasma Arc Approach

In order to achieve the target of reducing oil consumption to zero for pulverized coal(PC)boiler in power plant,the paper developed a novel coal pulverized ignition approach,called as Alternating-Current plasma(AC plasma)ignition,with the advantages of excellent PC combustion behavior and longer electrode life-span.The scientific principle of how to generate the AC plasma arc was elaborated in detail.First,the experiments on life-span of electrodes inside AC plasma generator had been conducted,finding a workable way to extend its life-span beyond 530 hours.Second,a new AC plasma burner specifically designed for lean coal according to the principle of PC staged combustion had been illustrated with diagrams and then used to ignite the PC-air stream under four kinds of conditions with a varying AC plasma power from 150 kW to 300 kW,focusing on analyses of the influence of AC plasma power on combustion behaver,such as combustion temperature,carbon burnout rate as well as PC combustion regime.The following results showed that in the case of the power of the AC plasma was P=300 kW,a satisfied PC combustion process could achieved,with the average PC combustion temperature of about 940°C,combustion flame length of 6.3 m,and the total carbon burnout rate of up to 52.2%.In addition,about 80%of the nozzle outlet section was filled with bright flame,while 81%of the PC was in zone of the cylindrical flame regime.The PC combustion modes were changed repeatedly during the process of combustion,which went from homogeneous combustion mode at initial ignition stage to combined combustion mode and heterogeneous combustion mode at middle stage,finally to combined combustion mode at later stage.The research conclusion in this paper has proved that the AC plasma ignition approach is feasible and effective to ignite low-rank coal without the present of fuel oil.