Thermal Deviation Analysis of High-temperature Reheater for Single-tangential π Type Boiler

Abstract For some π type boilers with four-corner tangential and deep air staged low nitrogen combustion technology, under full load condition, the steam temperature deviation for both sides of reheater outlet can reach as high as 15 ℃. The left and right cross arrangement of steam between two stage reheaters increases the steam temperature deviation at the outlet, and the large amount input of desuperheating water makes the economic efficiency of the unit decrease. A flue gas residual rotation adjusting experiment for a 660 MW ultra-supercritical boiler was carried out by adjusting the level and up and down swing angle of the separated overfire air nozzle, and the grid method was applied to measure the radiation intensity for particles at the high-temperature reheater area according to the principle of radiation spectrum. The results show that there exists strong visible radiation in this area. Under the 600 MW-load condition, the radiation heat transfer of particle accounts for 25.95% of the total heat absorption of the high-temperature superheater and particle combustion still exists. In addition, the combustion share accounts for about 1.83% of the received carbon content of coal. The particle temperature and emittance data fitted from the Planck's law indicate that the high-temperature particles are enriched at single side due to the inertial effect of residual rotation of flue gas. The residual rotation momentum of the separated over-fire air is insufficient to balance the temperature rise of both sides of the low-temperature reheater. Therefore, a new type of combustion system rebuild principle of changing a five-layer Separated Over-fire Air (SOFA) nozzle to two-sections of six-layer SOFA nozzle is proposed to mitigate the combustion delay of pulverized coal particles and the wall-type tangent circle arrangement of the upper separated over-fire air nozzle, improving the residual rotation momentum of flue gas.