| With the strengthening of energy saving, emission reduction and strengthening ofdevelopment, utilization of natural gas resources, plus the increasing contradictionbetween national energy demand and environmental pollution, coal-fired boilerscannot meet the future development demand of our country. While, by using naturalgas and this kind of clean energy that is of low pollution and high-effectivecombustion, pollution can reduced effectively, so it is very helpful to build aenvironment-friendly society. Compared with buying a new gas-fired boiler,reconstructing existed coal-fired boilers to gas-fired ones is even cheaper, so forenterprises and companies, when needing to change coal-fired boilers to gas-firedboilers,“coal-to-gas” technology is practical and effective, and it should be the firstchoice.At present, researches on coal-to-gas technology mostly stay on experiencediscussion or partial research, and there are few theoretical and quantitative researcheson critical technology of “coal-to-gas” method, so quantitative data that used forguiding the coal-to-gas design scheme is lacking. Comparing with experimentalresearch, numerical simulation studies can not only lower the cost, but also can obtainthe thermal parameters of reconstructed boilers, it is very helpful for furtheroptimization to the boilers’ structure.In this paper, considering the SZL15-1.25-AⅡchain grate coal-fired boiler as theresearch object, the researches are carried out from the following aspects:First of all, the restructuring cost for coal-to gas technologies is analyzed andcompared. The results show that when the basic structure of the boiler isn’t changed,namely removing the coal-scuttle, the front arch and the rear arch, extending the frontwall to the forefront of the fire grate. After sealing, the gas boiler furnace is formed.The area of the radiant surface and the radiation ability are greatly increased, and therestructing cost is lowest at this time. So this scheme is chosen in this paper. For thechosen scheme, thermal calculation is done, and the results show it meets the thermalbalance condition.Second, Fluid flow, combustion, and heat transfer process in the furnace aresimulated and analyzed in computational fluid dynamics (CFD) method. Analysisresults agree well with relevant governing laws, theoretic thermodynamic calculation and the operation data provided by plant, and this also can prove the numericalsimulation method and the model in this paper are reasonable and reliable.Furthermore, combustion process in furnace under different excess air coefficientα and different air temperature is simulated; also, when the combustor is located ondifferent position, for each position, the combustion process is also simulated.Numerical results show that: when α is different, the tendency of averagetemperature on the cross section is generally the same, and the high temperature zonehas deviated from the center axis. If α=1.0, the temperature distribution gradientwill be minimum, nd the average temperature of furnace will be maximum; thevariation curves obtained by simulation between combustion temperature and excessair coefficient are generally consistent with the theoretical curves, but combustiontemperature of simulation are lower than theoretical results. With the increasing ofair’s preheating temperature, the maximum temperature in furnace doesn’t increaseobviously, but the high temperature zone area becomes larger, the temperaturegradient becomes smaller, and temperature distribution is more uniform. However,compared with preheating combustion condition, there exists obvious hightemperature zone while there is no combustion preheating. The installation position ofcombustor influences the combustion in furnace a lot. Generally speaking, when thecombustor is arranged symmetrically, the combustion is most effective.The research results of this paper provide important theoretical reference forcombustion adjusting experiments in the process of reconstructing coal-fired boiler togas-fired boilers. |
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