SAN JOAQUIN VALLEY UNIFIED AIR POLLUTION CONTROL DISTRICT

RULE 4304 - EQUIPMENT TUNING PROCEDURE FOR BOILERS, STEAM GENERATORS, AND PROCESS HEATERS
(Adopted October 19, 1995)

1.0 Purpose

The purpose of this rule is to provide an equipment tuning procedure for boilers, steam generators and process heaters to control visible emissions and emissions of both nitrogen oxides (NOx) and carbon monoxide (CO).

2.0 Applicability

This procedure applies to any boiler, steam generator, or process heater that requires tuning pursuant to District regulations or permit conditions.

3.0 Incorporation by Reference

The provisions of Attachment 4304-A and Attachment 4304-B are hereby adopted by reference and made a part hereof.

Attachment 4304-A

Equipment Tuning Procedure(1)

for Mechanical Draft Boilers, Steam Generators, and Process Heaters

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.

A different tuning procedure may be used if it produces equivalent results. Should a different tuning procedure be used, a copy of this procedure should be kept with the unit records for two years and made available to the District personnel on request.

  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 number(2) (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 values(3), and if 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:

    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 windbox/furnace pressure differential, built in air-flow limits, etc.

  6. Develop an O2/CO curve (for gaseous fuels) or O2/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 oils

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 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 is included in a tune-up kit that can be purchased from the Bacharach Company.
  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%

Attachment 4304-B

Equipment Tuning Procedure

for Natural and Induced Draft-Boilers, Steam Generators, and Process Heaters.

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.

A different tuning procedure may be used if it produces equivalent results. Should a different tuning procedure be used, a copy of this procedure should be kept with the unit records for two years and made available to the District personnel on request.

  1. Preliminary Analysis

    a. Check the Operating Pressure or Temperature. Operate the boiler, steam generator, or process heater at the lowest acceptable pressure or temperature that will satisfy the load demand. This will minimize heat and radiation losses. Determine the pressure or temperature that will be used as a basis for comparative combustion analysis before and after tuneup.

    b. Check Operating Hours. Plan the workload so that the boiler, steam generator, or process heater operates only the minimum hours and days necessary to perform the work required. Fewer operating hours will reduce fuel use and emissions. For units requiring a tuneup to comply with the rule, a totalizing non-resettable fuel meter will be required for each fuel used and for each boiler, steam generator, and process heater to prove fuel consumption is less than the heat input limit in Btu per year specified in the rule.

    c. Check Air Supply. Sufficient fresh air supply is essential to ensure optimum combustion and the area of air supply openings must be in compliance with applicable codes and regulations. Air openings must be kept wide open when the burner is firing and clean from restriction to flow.

    d. Check Vent. Proper venting is essential to assure efficient combustion. Insufficient draft or overdraft promotes hazards and inefficient burning. Check to be sure that vent is in good condition, sized properly and with no obstructions.

    e. Combustion Analysis. Perform an "as is" flue gas analysis (O2, CO, CO2, etc.) at high and low fire, if possible. In addition to data obtained from combustion analysis, also record the following:

      i. Inlet fuel pressure at burner (at high and low fire)

      ii. Draft above draft hood or barometric damper

      1. Draft hood: high, medium, and low
      2. Barometric damper: high, medium, and low

      iii. Steam pressure, water temperature, or process fluid pressure or temperature entering and leaving the boiler, steam generator, or process heater.

      iv. Unit rate if meter is available.

      With above conditions recorded, make the following checks and corrective actions as necessary:

  2. Checks and Corrections

    a. Check burner Condition. Dirty burners or burner orifices will cause boiler, steam generator, or process heater output rate and thermal efficiency to decrease. Clean burners and burner orifices thoroughly. Also, ensure that fuel filters and moisture traps in place, clean , and operating properly, to prevent plugging of gas orifices. Confirm proper location and orientation of burner diffuser spuds, gas canes, etc. Look for any burned-off or missing burner parts, and replace as needed.

    b. Check for Clean Boiler, Steam Generator, or Process Heater Tubes and Heat transfer Surfaces. External and internal build-up of sediment and scale of the heating surfaces creates an insulating effect that quickly reduces unit efficiency. Excessive fuel cost will result if the units is not kept clean. Clean tube surfaces, remove scale and soot, assure proper fluid flow, and flue gas flow.

    c. Check Water Treatment & Blowdown Program. Soft water and the proper water or process fluid treatment must be uniformly used to minimized scale and corrosion. Timely flushing and periodic blowdown must be employed to eliminate sediment and scale build-up on a boiler, steam generator, or process heater.

    d. Check for Steam Hot Water or Process Fluid Leaks. Repair all leaks immediately since even small high pressure leaks quickly lead to considerate fuel, water and steam losses. Be sure there are no leaks through the blow-off drains, safety valve, by-pass lines or at the feed pump, if used.

  3. Safety Checks

    a. Test primary and secondary low water level controls.

    b. Check operating and limit pressure and temp. controls.

    c. Check safety valve pressure and capacity to meet boiler, steam generator, or process heater requirements.

    d. Check limit safety control and spill switch.

  4. Adjustments

    While taking combustion readings with a warmed up boiler, steam generator, or process heater at high fire perform checks and adjustments as follows:

    a. Adjust unit to fire at rated capacity. Record fuel manifold pressure.

    b. Adjust draft and/or fuel pressure to obtain acceptable, clean combustion at both high, medium and low fire. Carbon monoxide value should always be below 400 ppm at 3% O2. If CO is high make necessary adjustment. Check to ensure boiler, steam generator, or process heater light offs are smooth and safe. A reduced fuel pressure test at both high and low fire should be conducted in accordance with the manufacturers instructions and maintenance manuals.

    c. Check and adjust operation of modulation controller. Ensure, proper efficient and clean combustion through range of firing rates. When above adjustments and corrections have been made, record all data.

  5. Final Test

    Perform a final combustion analysis with a warmed up boiler, steam generator, or process heater at high, medium, and low fire, whenever possible. In addition to data from combustion analysis, also check and record:

    a. Fuel pressure at burner (High, Medium, and Low).

    b. Draft above draft hood or barometric damper (High, Medium, and Low).

    c. Steam pressure or water temperature entering and leaving boiler, steam generator, or process heater.

    d. Unit rate if meter is available.

    When the above checks and adjustments have been made, record data and attach combustion analysis data to boiler, steam generator, or process heater records indicating name and signature of person, title, company name, company address and date the tuneup was performed.