The ability of the unit to operate at its absolute minimum is critical in today’s operating environment. Coal-fired assets must be able to rapidly adjust to changes in customer demand and to changing availability of wind and solar power.
Minimum load is generally driven by two major variables:
1. The SCR’s Minimum Operating Temperature
2. An NFPA driven need to maintain two pulverizers in service.
Cofiring substantial quantities of gas at low load can relieve both of these drivers. Replacing up to half of the total heat input with gas reduces the amount of SO3 by a base of 50%, essentially eliminating the SO3 factor in the MOT calculation.
From an NFPA standpoint, replacing half of the heat input with gas essentially replicates the presence of the heat input of one mill, eliminating the need for two.