APCD grants 90-day variance for Orange Grove Energy plant

The San Diego County Air Pollution Control District Hearing Board granted a 90-day variance to Orange Grove Energy, LP, for tuning activities at its Pala generation plant.

The hearing board’s 4-0 vote April 11 approves the variance which began that day and will expire on July 11, 2013, or when the tuning is complete. The variance allows for up to 20 hours of tuning. During the variance Orange Grove will be limited to a nitrogen oxides (NOx) concentration of 3.0 parts per million volumetric dry (ppmvd) at 15 percent oxygen, emissions of 5.2 pounds of NOx per hour, and an ammonia concentration of 6 ppmvd.

“They have to really fix these problems to plug up the holes,” said APCD civil action investigator Heidi Gabriel-Pack. “They wanted to take these measures before they ended up really violating their permit conditions or harming their turbines.”

The Orange Grove Energy plant in the 35400 block of Pala Del Norte Road generates energy using two 49.8 megawatt natural gas fired combustion turbines. The turbines were designed to be peaking turbines and were commissioned in 2010. Emissions are controlled initially by water injection and then by a selective catalytic reduction (SCR) system which controls NOx by injecting ammonia into the exhaust gases.

Condition No. 16 of the APCD permit for the Orange Grove Energy plant limits NOx concentration to 2.5 ppmvd corrected to 15 percent oxygen except for startup and shutdown operations. Condition No. 19 limits hourly emissions of each turbine during normal operations to 4.2 pounds of NOx, 6.1 pounds of carbon monoxide (CO), and 1.3 pounds of volatile organic chemicals (VOC) while Condition No. 20 limits daily emissions for each turbine to 141.2 pounds of NOx, 182.2 pounds of CO, and 36.5 pounds of VOC. Condition No. 24 limits ammonia emissions from each turbine to 5 ppmvd corrected to 15 percent oxygen except during startup and shutdown. Orange Grove’s petition did not ask for a variance from CO or VOC limits.

The APCD hearing board previously granted an emergency variance in November 2010 after Orange Grove Energy found problems with the insulation and the catalyst; the exhaust duct had areas where the insulation was exposed and during turbine operations the insulation was deposited on the surface of the catalyst and thus compromised the catalyst’s performance. The emergency variance allowed Orange Grove to conduct data gathering and testing to determine the reasons behind the higher NOx and ammonia emissions, although during the variance period Orange Grove did not have any excess emissions.

Orange Grove has since changed the ammonia injection headers and installed additional catalyst. Although the NOx levels are lower with the additional catalyst, the values are higher than expected and the ammonia values are also higher than expected. In order to lower the NOx emissions, Orange Grove has been using more water in the water injection than is recommended.

The continuous emissions monitoring system indicated NOx emissions which exceeded the clock hour limit on July 29, 2012, and September 2, 2012. In October 2012 Orange Grove requested a 90-day variance to allow for up to 20 hours of tuning over two days. Having new catalyst blocks in place would allow Orange Grove to adjust the ammonia injection nozzles to fine-tune the amount of ammonia sprayed in each section of the catalyst, which is approximately 30 feet wide and 50 feet high. That adjustment would allow an even distribution of ammonia across the catalyst, maximizing the SCR performance and minimizing NOx and ammonia emissions. Orange Grove withdrew the October request for a variance on November 7, as the completion of testing without exceeding any permit condition eliminated the need for that variance. The ammonia injection headers were not tuned during the 2012 testing.

The most recent request also sought a variance for up to 20 hours of tuning over two days. After Orange Grove installs seal plates and additional insulation to cover existing holes, adjustment of the ammonia injection nozzle will be necessary to fine-tune the amount of ammonia sprayed in each section of the catalyst. Orange Grove does not plan to perform a complete tuning of the injection headers but will collect test data and make necessary adjustments to match ammonia flow highs and lows to the exhaust flow highs and lows.

In order to grant a variance, the APCD hearing board must make findings that the petitioner would be in violation of an APCD rule or permit condition without the variance, that due to conditions beyond the petitioner’s control requiring compliance would result in an arbitrary or unreasonable taking of property or the practical closing or elimination of a lawful business, and that the petitioner will take measures to reduce emissions as much as possible and will monitor emissions during the variance period.

The APCD board agreed that the SCR system has not performed adequately despite Orange Grove’s attempts to remedy the problems. The current water/fuel mixture of approximately 1.1 compared to the recommended operation mixture of 0.95 reduces efficiency of the facility while long-term water injection above the recommended level could damage a turbine and shorten its operating life. The estimated replacement cost of a turbine’s core engine is $6-8 million while the estimated cost to replace the catalyst and exhaust duct is $1.5-2 million per turbine. Orange Grove’s potential financial costs if a variance wasn’t granted also included fines and staff time for violations which would occur. Curtailing business operations would not only deprive Orange Grove of revenue but would also jeopardize San Diego Gas & Electric’s reliability and limit grid capacity.

During the variance period Orange Grove will attempt to limit emissions above the permit amount by planning testing in advance, minimizing test duration, and maintaining water injection and SCR operations throughout the testing.

Because the adjustments will alter the emissions concentration profile in the stack, Orange Grove will also need to recertify its continuous emissions monitoring system with a relative accuracy test audit (RATA). Orange Grove has scheduled RATA testing with the APCD for June 4 and June 6.