The Florida Department of Environmental Protection on Sept. 28 approved an extension of time for JEA to complete a project to reburn lime-rich ash in the two fluidized-bed combustion units at the Northside Generation Station (NGS) to get further SO2 control out of the plant’s flue gas.
On Sept. 16, the department received a request to extend a December 2014 permit, with an expiration date of Dec. 31, 2015. The air construction (AC) permit objective is to temporarily reintroduce a mixture of bottom ash and fly ash into two boilers at Northside. This bottom ash/fly ash byproduct, all of which is generated and stored on site, contains lime because of the use of limestone in the boilers as a control strategy for SO2 emissions. Therefore, the reintroduction of the byproduct is expected to aid in SO2 control, likely decreasing the amount of limestone needed. The reuse of bottom ash is already permitted, but the reuse of fly ash required that December 2014 permit.
The construction permit did not contain a best available control technology (BACT) determination that would require reassessment. Based on the circumstances and the rational provide in the attached Technical Evaluation and Preliminary Determination (TEPD) document, the department granted the extension, from Dec. 31, 2015, to June 30, 2016, to allow JEA adequate time to complete the byproduct reuse project.
The Northside plant and St. Johns River Power Park (SJRPP), both of which fire coal and are located near each other Duval County, are considered one air emissions source under DEP permitting.
NGS consists of three boilers and four combustion turbines. Units 1 and 2 are circulating fluidized bed boilers (CFB Boilers), fired by coal, coal coated with latex, petroleum coke, biomass, natural gas, and landfill gas. NGS Unit 3 is a pre-NSPS boiler fired by natural gas, landfill gas, No. 6 residual fuel oil, and used oil. The four NGS combustion turbines are fired with low-sulfur fuel oil. SJRPP consists of two boilers, fired with pulverized coal, a blend of petroleum coke and coal, natural gas, No. 2 distillate fuel oil, and used oil.
The control equipment for multi-pollutant control for NGS consists of the injection of limestone in the boilers, a spray dryer absorber (SDA), a fabric filter (FF) baghouse, and selective non-catalytic reduction (SNCR). This control equipment reduces emissions of SO2, acid gases, nitrogen oxides (NOx), particulate matter (PM), and HAP.
Mercury accumulation not expected to be an issue
This project permits the reinjection of a mixture of fly ash and bottom ash into the boilers. Since there is no change in the type or amount of fuel to be combusted in the boilers, and no change in the pollution control requirements at the boilers, emissions changes are expected to be minimal for all pollutants. No changes in emissions limits were requested by the permittee.
One pollutant which may possibly be affected by this project is mercury. If reintroduced fly ash were being recycled from the boiler, to the bag house, back to the boiler, etc., in an indefinite cycle, mercury would gradually accumulate in the system, possibly leading to mercury breakthrough of the baghouse system, the DEP noted. However, in this project, a mixture of bottom ash and fly ash will be reinjected into the boilers; due to its volatility, mercury accumulation could occur through the fly ash route, but likely not the bottom ash route. Bed ash may cycle repeatedly through the system (as JEA is already permitted to reintroduce bed ash into the boilers), but fly ash will not be subsequently reintroduced again. The only fly ash that will be reintroduced into the boilers is fly ash that was generated prior to the beginning of the project. Therefore, a runaway mercury cycle is highly unlikely.
In order to better understand how mercury emissions are affected by by-product reintroduction, JEA will perform at least three Method 30B mercury stack tests over the course of this project. In addition to a baseline test before reintroduction begins, mercury stack tests will be performed about one month, three months, and six months after ash reintroduction begins. These tests will show how byproduct reintroduction affects mercury over the course of several months.
It is also possible that SO2 emissions may be affected by this project. The ash byproduct to be reintroduced into the boilers contains lime, which may reduce SO2 emissions (or reduce the amount of limestone needed to achieve the same SO2 emissions rate). Therefore, increased SO2 emissions from this project are unlikely. This project would also be unlikely to appreciably affect emissions of NOx or carbon monoxide. Any changes in emissions of these pollutants will be apparent in the continuous monitoring data, which would allow JEA to terminate or adjust the project in the unlikely event of an appreciable increase in SO2, NOx, or CO emissions.