| OCR Text |
Show In addition to the change in the heating value, changes in fuel flow can be anticipated. Fuel flow change can be significant due to equipment failure, and such failure can possibly lead to the total interruption of LFG supply. Flow fluctuation can be moderate, however, due to seasonal changes in the landfill yield of LFG. Due to reliability concerns associated with LFG supply, the low NOx system design was required to compensate in real time for any changes in LFG flow rate andlor composition. The City's operational goal was to minimize the total power generated while consuming all available LFG. Carrying out this goal to the extreme would limit the total power generation to 10 MW. Under these conditions, LFG would represent the sole source of fuel to the boiler. The low NOx system design was thus configured to approach this goal as closely as possible. The City's operational concerns were fully addressed by the simultaneous firing of natural gas and LFG at all loads. LFG was base loaded to consume, at all times, available LFG. Natural gas was used as the makeup fuel to accommodate the City's demand for electric power. The minimum burner header pressure for natural gas firing was initially set at 1 psig, which corresponded to electric power generation from natural gas fuing of only 3 MW. Subsequent adjustment and optimization of the combustion system resulted in reducing minimum gas pressure to 0.21 psig, which represents approximately 1.7 MW. Judging from the flame appearance, the burner appeared to accept further natural gas reduction: however, due to limitations of the existing flow control hardware, minimum natural gas pressure was left at 0.21 psig. The adopted design approach addressed the City's safety and reliability concerns. The continuous use of natural gas ensured flame stability. A flame, established with the combustion of natural gas, was always available in the boiler furnace. This ensured LFG ignition and safe combustion, in spite of fluctuations in composition and flow rate. A significant, abrupt change in the LPG supply due to partial or total equipment failure -7- |
