SACAQMD RULE 411 BOILER NOx
LAST REVISED 01/09/97



RULE 411

BOILER NOX

Adopted 02-02-95

(Amended 11-7-96, 1-9-97)


INDEX

100 GENERAL

200 DEFINITIONS

300 STANDARDS

400 ADMINISTRATIVE REQUIREMENTS

500 MONITORING AND RECORDS


100 GENERAL

101 PURPOSE: To limit NOX and CO emissions from existing industrial, institutional, and commercial boilers, steam generators, and process heaters.

102 APPLICABILITY: The requirements of this rule shall apply to boilers, steam generators and process heaters with rated heat inputs of 5 million Btu per hour or greater, used in industrial, institutional, and commercial operations.

110 EXEMPTION - EQUIPMENT RATING: The requirements of this rule shall not apply to any unit with a rated heat input capacity of less than 5 million Btu per hour.

111 EXEMPTION - ELECTRIC UTILITY BOILERS: The requirements of this Rule shall not apply to any unit that is exclusively used by an electric utility to generate electricity.

112 EXEMPTION - PROCESS HEATERS, KILNS, AND FURNACES: The requirements of this Rule shall not apply to process heaters, kilns, and furnaces where the products of combustion come into direct contact with the material to be heated.

113 EXEMPTION - WASTE HEAT RECOVERY BOILERS: The requirements of this rule shall not apply to waste heat recovery boilers used to recover heat from the exhaust of combustion turbines or reciprocating internal combustion engines.

114 EXEMPTION - REMOVAL FROM SERVICE: The requirements of Sections 301 through 307 and 502.2 shall not apply to any unit that is expected to be taken out of service on or before May 31, 1997 provided that the owner or operator complies with one of the requirements listed in Sections 308 and 401.5.

115 EXEMPTION - LOW FUEL USAGE: The requirements of Sections 301 through 307 shall not apply to any unit that uses less than 90,000 therms per year of fuel provided that the owner or operator complies with one of the requirements listed in Sections 308 and 401.4.

200 DEFINITIONS

201 ANNUAL HEAT INPUT: The total input of fuels burned by a unit in a calendar year, as determined from the higher heating value and cumulative annual usage of each fuel.

202 BEST AVAILABLE RETROFIT CONTROL TECHNOLOGY (BARCT): Best available retrofit control technology as defined in Section 40406 of the California Health and Safety Code is "an emission limitation that is based on the maximum degree of reduction achievable, taking into account environmental, energy, and economic impacts by each class or category of sources." These limits are specified in Sections 304, 305, and 306.

203 BIOMASS: Any solid, organic material used as a fuel source for boilers or steam generators including, but not limited to, wood, almond shells, or agricultural waste.

204 BIOMASS BOILER OR STEAM GENERATOR: Any unit used in any institutional, commercial, or industrial operation that is designed to burn biomass fuel to produce steam, heat water and/or other fluids, and/or generate electricity. For the purpose of this rule, a unit that simultaneously burns multiple fuels including biomass fuel shall be considered a biomass boiler or steam generator.

205 BOILER OR STEAM GENERATOR: Any unit fired with any fuel used to produce steam or heat water that is not used exclusively to produce electricity for sale. Boiler or Steam Generator does not include any waste heat recovery boiler that is used to recover sensible heat from the exhaust of a combustion turbine or reciprocating internal combustion engines.

206 BRITISH THERMAL UNIT (BTU): The amount of heat required to raise the temperature of one pound of water from 59 oF to 60 oF at one atmosphere.

207 HEAT INPUT: The chemical heat released due to fuel combustion in a combustion unit, using the higher heating value of the fuel. This does not include the sensible heat of incoming combustion air.

208 GASEOUS FUEL: Any fuel which is a gas at standard conditions.

209 HIGH HEATING VALUE (HHV): The total heat liberated per mass of fuel burned (Btu per pound), when fuel and dry air at standard conditions undergo complete combustion and all resultant products are brought to their standard states at standard conditions. If certification of the HHV is not provided by the third party fuel supplier, it shall be determined by one of the test methods specified in Section 501.2.

210 MALFUNCTION: Any sudden and unavoidable failure of air pollution control equipment or process equipment or of a process to operate in a normal or usual manner. Failures that are caused entirely or in part by poor maintenance, careless operation, or any other preventable upset condition or preventable equipment breakdown shall not be considered malfunction.

211 NITROGEN OXIDES (NOX): The sum of nitric oxide and nitrogen dioxide in the flue gas.

212 NONGASEOUS FUEL: Any fuel which is not a gas at standard conditions.

213 PARTS PER MILLION BY VOLUME (PPMV): The ratio of the number of gas molecules of a given species, or group, to the number of millions of total gas molecules.

214 PROCESS HEATER: Any unit fired with any fuel which transfers heat from combustion gases to water or process streams. Process heater does not include any dryer in which the material being dried is in direct contact with the products of combustion, cement or lime kilns, glass melting furnaces, or smelters.

215 RATED HEAT CAPACITY: The heat input capacity in million Btu per hour specified in the nameplate of the combustion unit. If the combustion unit has been altered or modified such that its maximum heat input is different than the heat input capacity specified on the name plate, the maximum heat input shall be considered as rated heat input.

216 REASONABLY AVAILABLE CONTROL TECHNOLOGY (RACT): The lowest emission limitation that a particular unit is capable of meeting by using measures that are reasonably available in terms of technological and economic feasibility. These limits are specified in Sections 301, 302, and 303.

217 RETROFIT: Any physical change to an emissions unit necessary for reducing NOx and CO emissions to comply with the NOx and CO emissions limits specified in Sections 301 through 307 of this rule, including, but not limited to, burner replacement, addition of emissions control equipment, and addition of oxygen trim systems. Changes in the method of operation shall not be considered as retrofit.

218 SHUTDOWN: The period of time a unit is cooled from its normal operating temperature to ambient temperature. The shutdown period shall be limited to two hours.

219 STANDARD CONDITIONS: For the purpose of this rule, standard conditions are 68 oF and one atmosphere.

220 STARTUP: The period of time a unit is heated from ambient temperature to its operating temperature as specified by the unit manufacturer.

221 THERM: One hundred thousand (100,000) Btu's.

222 UNIT: Any boiler, steam generator, as defined in Section 205, or process heater, as defined in Section 214.

223 WOOD: Wood, wood residue, bark, or any derivative fuel or residue thereof, in any form, including but not limited to sawdust, dust from sanding, wood chips, scraps, slabs, millings, shavings, and processed pellets made from wood or other forest residues.

300 STANDARDS

301 RACT EMISSIONS LIMITS - GASEOUS FUEL FIRING

302 RACT EMISSIONS LIMITS - NONGASEOUS FUEL FIRING

303 RACT EMISSIONS LIMITS - BIOMASS FUEL FIRING

304 BARCT EMISSIONS LIMITS - GASEOUS FUEL FIRING

305 BARCT EMISSIONS LIMITS - NONGASEOUS FUEL FIRING

306 BARCT EMISSIONS LIMITS - BIOMASS FUEL FIRING

307 EMISSION LIMIT - EMERGENCY STANDBY NONGASEOUS FUEL FIRING

308 LOW FUEL USAGE\REMOVAL FROM SERVICE: Any unit with an annual heat input of less than 90,000 therms per year, or any unit that will be operated with annual heat input of less than 90,000 therms, or any unit which will be removed from service by May 31, 1997 shall meet one of the following conditions:

309 EQUIPMENT REQUIREMENT - FUEL CONSUMPTION

400 ADMINISTRATIVE REQUIREMENTS

401 COMPLIANCE SCHEDULE

500 MONITORING AND RECORDS

501 TEST METHODS

502 RECORDKEEPING


ATTACHMENT A

Tuning Procedure1

Nothing in this Tuning Procedure shall be construed to require any act or omission that would result in unsafe conditions or would be in violation of any regulation or requirement established by Factory Mutual, Industrial Risk Insurers, National Fire Prevention Association, the California Department of Industrial Relations (Occupational Safety and Health Division), the Federal Occupational Safety and Health Administration, or other relevant regulations and requirements.

  1. Operate the unit at the firing rate most typical of normal operation. If the unit experiences significant load variations during normal operation, operate it at its average firing rate.
  2. At this firing rate, record stack gas temperature, oxygen concentration, and CO concentration (for gaseous fuels) or smoke-spot number2 (for liquid fuels), and observe flame conditions after unit operation stabilizes at the firing rate selected. If the excess oxygen in the stack gas is at the lower end of the range of typical minimum values3 and if the CO emissions are low and there is no smoke, the unit is probably operating at near optimum efficiency - at this particular firing rate. However, complete the remaining portion of this procedure to determine whether still lower oxygen levels are practical.
  3. Increase combustion air flow to the furnace until stack gas oxygen levels increase by one to two percent over the level measured in Step 2. As in Step 2, record the stack gas temperature, CO concentration (for gaseous fuels) or smoke-spot number (for liquid fuels), and observe flame conditions for these higher oxygen levels after boiler operation stabilizes.
  4. Decrease combustion air flow until the stack gas oxygen concentration is at the level measured in Step 2. From this level gradually reduce the combustion air flow, in small increments. After each increment, record the stack gas temperature, oxygen concentration, CO concentration (for gaseous fuels) and smoke-spot number (for liquid fuels). Also, observe the flame and record any changes in its condition.
  5. Continue to reduce combustion air flow stepwise, until one of these limits is reached:
    1. a. Unacceptable flame conditions - such as flame impingement on furnace walls or burner parts, excessive flame carryover, or flame instability.

      b. Stack gas CO concentrations greater than 400 ppm.

      c. Smoking at the stack.

      d. Equipment-related limitations - such as low wind box/furnace pressure differential, built in air-flow limits, etc.

  6. Develop an O2 /CO curve (for gaseous fuels) or 02/smoke curve (for liquid fuels) similar to those shown in Figures 1 and 2 using the excess oxygen and CO or smoke-spot number data obtained at each combustion air flow setting.
  7. From the curves prepared in Step 6, find the stack gas oxygen levels where the CO emissions or smoke-spot number equal the following values:
    Fuel Measurement Value
    Gaseous CO Emissions 400 ppm
    #1 and #2 smoke-spot number number 1
    #4 Oil smoke-spot number number 2
    #5 Oil smoke-spot number number 3
    Other oils smoke-spot number number 4

    The above conditions are referred to as the CO or smoke thresholds, or as the minimum excess oxygen levels.

    Compare this minimum value of excess oxygen to the expected value provided by the combustion unit manufacturer. If the minimum level found is substantially higher than the value provided by the combustion unit manufacturer, burner adjustments can probably be made to improve fuel and air mix, thereby allowing operations with less air.

  1. Add 0.5 to 2.0 percent to the minimum excess oxygen level found in Step 7 and reset burner controls to operate automatically at this higher stack gas oxygen level. This margin above the minimum oxygen level accounts for fuel variations, variations in atmospheric conditions, load changes, and nonrepeatability or play in automatic controls.
  2. If the load of the combustion unit varies significantly during normal operation, repeat Steps 1-8 for firing rates that represent the upper and lower limits of the range of the load. Because control adjustments at one firing rate may affect conditions at other firing rates, it may not be possible to establish the optimum excess oxygen level at all firing rates. If this is the case, choose the burner control settings that give best performance over the range of firing rates. If one firing rate predominates, setting should optimize conditions at the rate.
  3. Verify that the new settings can accommodate the sudden load changes that may occur in daily operation without adverse effects. Do this by increasing and decreasing load rapidly while observing the flame and stack. If any of the conditions in Step 5 result, reset the combustion controls to provide a slightly higher level of excess oxygen at the affected firing rates. Next, verify these new settings in a similar fashion. Then make sure that the final control settings are recorded at steady-state operating conditions for future reference.


1 This tuning procedure is based on a tune-up procedure developed by KVB, Inc. for the EPA.

2 The smoke-spot number can be determined with ASTM test method D-2156 or with the Bacharach method. ASTM test method D-2156 is included as Attachment 3 to this determination.

3 Typical minimum oxygen levels for boilers at high firing rates are:

  1. For natural gas: 0.5 - 3%
  2. For liquid fuels: 2 - 4%