VOC Control Technologies

The NSPS regulations for combustion turbines and duct burners provide no VOC emission limits. The following sections assess the control strategies that are potentially feasible for decreasing VOC emissions from the facility.

Catalytic Oxidation

The formation of VOC in combustion units depends primarily on the efficiency of combustion. Inefficient combustion leads to the formation of aldehydes, aromatic carbon compounds, and various other organic compounds by several mechanisms. Catalytic oxidation decreases VOC emissions by facilitating the complete combustion of organic compounds to water and carbon dioxide. Prior to entering the catalyst bed where the oxidation reaction occurs, the exhaust gas must be preheated to about 400–800 °F.

The RBLC database shows few instances of catalytic oxidation being selected as BACT for VOC at any gas‐fired turbine power plant nationwide. An economic analysis for the catalytic oxidation of VOC emissions based on vendor information estimates the cost at $30 811/T of VOC removed. This cost level is economically infeasible for VOC removal. Thus, catalytic oxidation would not be selected as BACT for VOC emissions from turbines and duct burners proposed in the present time frame.

Good Combustion Practices

All the RBLC database BACT determinations for VOC outside California and New York show the use of combustion control or good combustion practices. Thus, in most areas good combustion practices are acceptable as BACT for VOC, with limits of 7.25 ppmvd at 15% O₂, as methane.

BACT Evaluation for SO₂ and H₂SO₄ Emissions

Control techniques available to reduce SO₂ and H₂SO₄ emissions include FGD systems and the use of low‐sulfur fuels. Although FGD systems are common in boiler application, the RBLC database shows no known FGD systems on combustion turbines. Thus, the use of an FGD system is not warranted and an FGD system should be rejected as a BACT control alternative.

Another available technique is the use of low‐sulfur fuels. There are no adverse environmental or energy impacts associated with the properly specified use of pipeline natural gas with low‐sulfur content, and this control alternative should be acceptable as BACT. NSPS Subpart GG requires that either SO₂ emissions from a gas turbine be limited to 0.015% by volume (or 150 ppmvd) at 15% O₂, or that the turbine fuel contain less than 0.8% sulfur by weight.

The power plant proposes to combust only low‐sulfur fuel (i.e. pipeline quality natural gas or diesel with a sulfur content < 0.05% by weight) in the proposed units, which is a widely accepted BACT determination for SO₂. By firing low‐sulfur fuels, the turbines will meet the NSPS emission standard of 150 ppm at 15% O₂.

Step 1: Identify Potential Control Technologies

The first step in the BACT analysis is to identify all potential control technologies available for the control of SO₂ emissions. The technologies identified for the control of SO₂ emissions are as follows:

• FSD
• Spray dryers
• Fuel specification: low‐sulfur fuels

Step 2: Eliminate Technically Infeasible Options

Neither FGD systems nor spray dryers have been applied to the exhaust gases from turbines, and significant technological difficulties are envisioned to apply to either of these technologies with high exhaust temperatures. The high temperature of the turbine exhaust deems FGD units and spray dryers infeasible. Thus, both FGD systems and spray dryers are eliminated for the control of SO₂ emissions from the proposed PSE turbines.

Step 3: Ranking of Remaining Control Technologies by Control Effectiveness

All add‐on control options for the control of SO₂ emissions have been eliminated due to technical unfeasibility. For the control of SO₂ emissions, the use of low‐sulfur fuels is the only control method determined to be technically feasible.

Step 4: Evaluation of the Most Effective Emissions Controls

As stated above, all add‐on control options for the control of SO₂ emissions have been eliminated due to technical unfeasibility. Thus, the use of low‐sulfur fuels containing less than 0.05% by weight of sulfur is the most effective means for reducing SO₂ emissions.

Step 5: Select BACT for the Control of SO₂ Emissions

The low SO₂ emissions levels inherent with low‐sulfur fuel in a turbine constitutes BACT. Thus, the permittee proposes that BACT for the proposed turbines is the firing of low‐sulfur fuels.