Industrial/Commercial/Institutional Boilers
and Process Heaters NESHAP Summary

4. What Type Units Have Emission Limitations and Work Practice Standards under the Boiler MACT?

Large units are:
Watertube boilers and process heaters with heat input capacities greater than 10 million British thermal units per hour (MMBtu/hr).

Small units are:
Any firetube boilers or any boiler and process heater with heat input capacities less than or equal to 10 MMBtu/hr.

Limited use units are:
Large units with capacity utilizations less than or equal to 10 percent as required in a federally enforceable permit. If a new or existing boiler or process heater is permitted to burn a solid fuel (either as a primary fuel or a backup fuel), or any combination of solid fuel with liquid or gaseous fuel, the unit is in one of the solid subcategories. If a new or existing boiler or process heater burns a liquid fuel, or a liquid fuel in combination with a gaseous fuel, the unit is in one of the liquid subcategories, except if the unit burns liquid only during periods of gas curtailment. If a new or existing boiler or process heater burns a gaseous fuel not combined with any liquid or solid fuels, or burns liquid fuel only during periods of gas curtailment or gas supply emergencies, the unit is in the gaseous subcategory.

Emission Limits & Work Practice Standards for Boilers & Process Heaters
(Pounds per million British thermal units (lb/MMBtu)

Source	Subcategory	Particulate Matter (PM)	Total Selected Metals (TSM)	Hydrogen Chloride (HCl)	Mercury (Hg)	Carbon Monoxide (CO) (ppm)
Existing Boiler or Process Heater	Solid Fuel, Large Unit	0.07 or	0.001	0.09	0.000009	------------
	Solid Fuel, Small Unit	-----------	----------	----------	---------	-----------
	Solid Fuel, Limited Use	0.21 or	0.004	----------	---------	-----------
	Liquid Fuel, Large Unit	-----------	----------	----------	---------	-----------
	Liquid Fuel, Small Unit	-----------	----------	----------	---------	-----------
	Liquid Fuel, Limited Use	-----------	----------	----------	---------	-----------
	Gaseous Fuel	-----------	----------	----------	---------	-----------
New or Reconstructed Boiler or Process Heater	Solid Fuel, Large Unit	0.025 or	0.0003	0.02	0.000003	400 (@7% oxygen)
	Solid Fuel, Small Unit	0.025 or	0.0003	0.02	0.000003	-----------
	Solid Fuel, Limited Use	0.025 or	0.0003	0.02	0.000003	400 (@7% oxygen)
	Liquid Fuel, Large Unit	0.03	----------	0.0005	---------	400 (@7% oxygen)
	Liquid Fuel, Small Unit	0.03	----------	0.0009	---------	-----------
	Liquid Fuel, Limited Use	0.03	----------	0.0009	---------	400 (@7% oxygen)
	Gaseous Fuel, Large Unit	-----------	----------	----------	---------	400 (@7% oxygen)
	Gaseous Fuel, Small Unit	-----------	----------	----------	---------	-----------
	Gaseous Fuel, Limited Use	-----------	----------	----------	---------	400 (@7% oxygen)

For solid fuel-fired boilers or process heaters, sources may choose one of two emission limit options:
(1) Existing and new affected units may choose to limit PM emissions to the level listed in the table above, or
(2) Existing and new affected units may choose to limit total selected metals (TSM) emissions to the level listed in the table above. Sources meeting the emission limits must also meet operating limits.
The US EPA has provided several compliance alternatives in the final rule. Sources may choose to demonstrate compliance based on the fuel pollutant content if the calculated emission rate is below the emission limit. Sources are also allowed to demonstrate compliance for existing large solid fuel units using emissions averaging.


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