Thermal deviation analysis of high-temperature reheater for single-tangential pi type boiler

摘要

For some pi 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 degrees C. 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. The thermal deviation adjusting experiments of a 660 MW ultra-supercritical boiler were carried out by adjusting the level and up-and-down swing angle of the separated over-fire air nozzle, and the grid distribution of radiation intensity for particles at the high-temperature reheater area was measured by radiation spectroscopy. 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, whose 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 principle of reforming combustion system was proposed, which changes a five-layer Separated Over-fire Air (SOFA) nozzle to two-section of six-layer SOFA nozzle to mitigate the combustion delay of pulverized coal particles and sets the wall-type tangent circle arrangement of the upper separated over-fire air nozzle to improve the residual rotation momentum of flue gas.