The Gulf Power subsidiary of Southern Co. (NYSE: SO) is nearing an air construction permit approval that would allow it to co-fire larger amounts of natural gas in the coal-fired Crist Unit 7.
The Florida Department of Environmental Protection issued the draft permit on July 22 and is working on final approval.
Plant Crist consists of Units 4, 5, 6, and 7. All four boilers are fired primarily with coal, though all four have some capacity for natural gas, No. 2 fuel oil and used oil.
Units 4 and 5 each have a heat input capacity of 1,096.7 million British thermal units per hour (MMBtu/hr). Units 4 and 5 can be run at full capacity on either coal or natural gas. Unit 6 has a heat input capacity of 3,704.8 MMBtu/hr, again on coal or natural gas. Unit 7, the target of this permitting, has a heat input capacity of 6,406.4 MMBtu/hr, though this capacity can only currently be reached while firing coal.
While Unit 7 is also equipped to burn natural gas, its capacity on gas is currently just 848 MMBtu/hr. Gulf Power has requested to install additional natural gas burners in Unit 7, doubling its natural gas capacity to 1,696 MMBtu/hr. This does not entail increasing the overall capacity or output of the boiler, which will still be rated at 6,406.4 MMBtu/hr. This project simply increases the fraction of the overall boiler capacity that can consist of natural gas firing.
Boiler 7 is capable of burning coal, gas, or a combination of the two (a situation referred to as co-firing). Adding natural gas capacity to Boiler 7 would be expected to replace some firing of coal, the DEP noted. Additionally, low natural gas prices could lead to increased utilization of the boiler because of the increased natural gas capability.
The heat input rate assumed by the applicant in calculating both business-as-usual emissions and projected actual emissions was 28,355,474 MMBtu/yr. This is equivalent to 3,236.9 MMBtu/hr, which is 50.5% of the total boiler capacity (6,406.4 MMBtu/hr).
To determine whether or not the demand growth could have been accommodated by the boiler during the baseline period, the department analyzed information reported by the applicant to the U.S. Environmental Protection Agency Clean Air Markets Division (CAMD). For the five-year period from April 2011 to March 2016, the most recent five-year period for which CAMD data are available for this unit, the capacity factor for the unit was 40.8%, though it was much higher for some periods of time, and much lower for some periods of time.
It is clear, said the department, that the unit is capable of accommodating capacity factors greater than 50.5% on a monthly basis, depending on demand. For example, the capacity factor in July 2015 was 63.4%. It is quite likely that the fluctuations in boiler usage are due primarily to changes in power demand. Importantly, it is clear that periods of low capacity factor are not due to physical boiler constraints, since boiler usage increases when there is higher demand. There are many months, even as recently as 2014 and 2015, when the boiler capacity is greater than 50.5%. Therefore, an assumption of a 50.5% capacity factor for demand growth that the boiler could have accommodated is a reasonable one
The department has made a preliminary determination that the proposed project will comply with all applicable state and federal air pollution regulations as conditioned by the draft permit. Gulf Power would be authorized to replace one row of coal-only burners with one row of four dual-fuel (coal and natural gas) burners. The nominal design capacity of each burner for natural gas would be approximately 212 MMBtu/hr. Permitted associated equipment includes four center-fired gas guns, four coal spreader assemblies, four modified burner receiving chamber end plates, four ceramic-lined protective sleeves for the spreader support tubes in the burner receiving chamber, additional natural gas piping, gas supply skids and valves, and auxiliary air piping with isolation valves.