How Combustion Improvements Help Meet Requirements
A new EPA ruling came out April 29, 2010 and is to be finalized by the end of 2010. Boiler MACT refers to rulings to limit hazardous air pollutants from industrial, commercial, and institutional boilers and heaters.
What is Boiler MACT?
One outcome of the 1990 Clean Air Act (CAA) was the formation of National Emissions Standards for Hazardous Air Pollutants (NESHAP) to regulate air pollutants that are not covered by the National Ambient Air Quality Standards (NAAQS). There are 188 Hazardous Air Pollutants (HAPs) that are covered. The EPA is tasked with determining the Maximum Achievable Control Technology (MACT) and establishing permit limits for HAPs control for each source category (Boilers, Kilns, Dry Cleaning Units, etc.). Boiler MACT is for industrial, commercial, and institutional boilers and process heaters that have the potential to emit more than 10 tons per year of any one HAP or 25 tons per year of any combination of HAPs, have a heat input rating of >10 MMBtu/hr, and can burn solid, liquid, or gaseous fuels.
The EPA promulgated the initial Boiler MACT rules in 2004 with a 3-year compliance period
However, on June 8, 2007, the US Court of Appeals vacated the ruling on the basis of complaints
that portions of the ruling were not stringent enough, not inclusive enough, and required better definition of fuel classifications. A new ruling came out for comment on April 29, 2010, and is to be finalized by the end of 2010.
What Pollutants are Covered?
Considering the complexity of monitoring 188 pollutant species (ranging from Acetaldehyde to Xylenes), a handful of surrogate species have been selected for regulation in boilers, including emissions of particulate matter (PM) for heavy metals, carbon monoxide (CO) for organic compounds, and hydrochloric acid (HCl) for acid gases. Regulations for emissions of mercury (Hg) and dioxins/furans have also been proposed. These are in addition to existing NAAQS limits that may exist for PM2.5, PM10, sulfur dioxide (SO2), CO, nitrogen oxides (NOx), ozone (O3), and lead (Pb).
What Pollutant Emission Limits were Proposed?
The EPA has reviewed available data to determine the top 12% emission level performances for each surrogate pollutant on which to base future limits. The critical emissions limits that have been proposed that may be difficult for biomass-fired boilers to comply with are CO (560 ppm at 3% O2; or 0.465 lb/MMBtu), PM (0.02 lb/MMBtu or 0.01 grains/dscf at 7% O2), and dioxins/furans (0.004 ng/dscm at 7% O2).
How Can Combustion Improvements Help Biomass Boilers?
Intense mixing of fuel and combustion air, as well as improved control of fuel-to-air ratios and air distribution can drastically lower CO emissions. Installation of Jansen air system upgrades on existing biomass-fired boilers typically results in at least a 50% reduction in CO emissions. Improved combustion also reduces the total PM that exits the furnace from entrainment of ash and unburned fuel. Lower excess air operation due to improved combustion air delivery also reduces flue gas volumetric flow to the PM emissions control equipment, resulting in improved PM collection efficiency. Jansen has seen reductions in PM emissions of 30% or greater as a consequence of combustion air system upgrades. Care must be taken in the combustion system design to avoid increasing NOx emissions beyond permit limits as a
consequence of more intense fuel and air mixing. Reductions in excess air operation may be required to compensate for the greater availability of oxygen to react with nitrogen when mixing is enhanced.
What are CISWI Requirements and What Boilers Qualify?
Another EPA ruling to be aware of and that may impact owner/operators of biomass-fired boilers is for Commercial and Industrial Solid Waste Incinerators (CISWI). There is the potential that boilers burning certain solid fuels, such as paper mill sludge, construction and demolition (C&D) wood, tire-derived fuels (TDF), old corrugated container (OCC) rejects, etc., could be classified as solid waste incinerators and be required to meet a different set of air pollutant regulations. CISWI rules have additional emission limits for NOx, SO2, cadmium (Cd), and lead (Pb) that are not covered by Boiler MACT rules. Combustion improvements will also likely be required on these units that are classified as solid waste incinerators since the CO limit is lower than required by Boiler MACT.
How Can Jansen Help?
If operational improvements are not sufficient to meet the new emissions requirements, Jansen can provide combustion system upgrades and team with pollution control equipment providers to help comply with the new regulations.
Refer to our Project Capabilities (no. 22) Boiler MACT & CISWI Compliance Review & Implementation for more information.