| Now,down-fired boiler combustion technology in China are mainly introducedfrom abroad, Haerbin Institute of Technology studied the four major down-firedcombustion technology and then raised the multi-injection multi-stage combustiontechnology, which has achieved good results in industrial demonstration and it has ahigh research value because the independent intellectual property rights of thecombustion technology.In this paper, a small cold test bench was designed based on a350MW superficialdown-fired boiler and its ratio was1:13. In the teat bench, smoke tracer experimentswas conducted to optimize the burner nozzle arrangement and the influence ofsecondary air to tertiary air,the tertiary air declination angle on the flow field in thefurnace was measured. The results are as follows:When the vent nozzles were arranged near to the center of the furnace singly,primary air was asymmetry, vent air swung in the furnace depth direction and appearedserious short-circuit. The flow field in the furnace was not sable, after increasing thevent air velocity, vent air still swung in the furnace depth direction and was short-circuit.When the vent and primary air nozzles were arranged together, arch air-air appeared noshort-circuit, the vent air and primary air were stable, front and rear air flow wassymmetrical. However, arch-air rigid was strong, had a deep penetration depth, mayerode the hopper. When primary air and vent air was alternative arrangement,meanwhile adopted multi-injection multi-stage combustion technology, symmetry andstability of the arch-air in the furnace was good and arch-air had a appropriatepenetration depth. Taking all factors, primary air and vent air which is alternativearrangement in the paper is more reasonable.In the cold single-phase experiments secondary air to tertiary air, it was found whenthe tertiary air enter the furnace at horizontal from the front and rear wall, flow filed inthe furnace was prone to deviation easily. In the condition secondary air was15%and25%, flow field in furnace skewed in cold ash hopper corner upper zone and cold ashhopper region, rear air dominated the flow field, this was extremely unfavorable tocombustion and safety operation of the boiler. As the secondary air increased to28.35%,it could reduce the flow field deviation, flow field in furnace only skewed in cold ashhopper region; when secondary air increased to35%, Flow deflection flow fieldeliminated basically, but this situation was not conducive to the regulation of boiler loadin practical operation and small tertiary air rate reduced classification of coalcombustion, was bad to reduce the NOx. So taking all factors, if the tertiary air enters the furnace at horizontal, it is advised secondary air is no less than28.35%, but no morethan35%.In the tertiary air declination condition, it was found when the tertiary air entered athorizontal, flow field appeared obvious asymmetry, rear air dominated the flow field,deflection flow field may cause pulverized coal combustion trip and residence timeshorter in the front wall, increased the carbon fly ash, reduced the boiler efficiency.When the tertiary air declination angle was20oand30o, flow field apperead “W” type.Front and rear air encountered tertiary air in the downstream process, two air flowsmixed and then turned up after continuing to go down a distance, this can make use ofmost of the furnace space and increase the pulverized coal combustion trip andresidence time, is beneficial to boiler efficiency. Considering a big tertiary airdeclination angle may cause the penetration depth of arch-air enter the bottom of thehopper, eroding the cold hopper. So the tertiary air declination angle is advised20o. |
PDF Full Text Request