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Show Pipe blending offered the greatest degree of simplicity and provided a reduction in capital cost. The capital cost reduction is achieved by eliminating the redundancy in the fuel piping train. The elimination of piping and valve redundancy also offered system simplicity. At a 50/50 volumetric blend ratio, the fuel blend heating value was estimated at 678 Btu/hr. The fuel blending enhanced the flammability characteristics of LFG making it more suitable for the implementation of combustion modifications, such as combustion staging andlor the use of FGR. Generating more electricity than the City requires was the major drawback of pipe blending. At a 50/50 fuel blend, to consume all available LFG, electric power generation was estimated at 42 MW. Electricity produced from LFG alone was estimarM at 10 MW. As such, pipe blending would increase the total power generation required to consume LFG by 32 MW. Pipe blending posed a second major concern. If a blended fuel is fired, the burner's hardware must be sized to accommodate the flow of the fuel blend. At full-load conditions, for example, the flow rate of the fuel blend for Unit 3 would be approximately 143,000 scfh per burner. If the supply of LFG is interrupted, which is likely to be the case, the burner full-load fuel flow would drop to 63,000 seth. The fuel flow is reduced because the heating value of natural gas is three times that of LFG. Reducing fuel flow at the same load (full load conditions in this case) compromises fuel jet momentum and, in tum, its mixing eificiency with combustion air. Thus, poor burner performance would be anticipated. The deterioration in burner performance with interruption of LFG would be pronounced at lower loads due to the reduction, with load, in fuel and combustion air supply which reduces the total energy available to achieve efficient mixing between fuel and air. To document the impact of pipe blending, a burner design and an analysis of operating requirements were performed to determine the change in operating conditions with -5- |