The burners covered by this specification are intended for use in packaged steam boilers or hot water generators. The burner class should be determined in accordance with the availability or economics of the fuel supply and the intended application. Multi-fuel burners should be specified in order to ensure economic and reliable operation within the constraints of fuel availability and applicable environmental regulations.

Selection factors and the best choice of options will vary depending on the size of the boiler that the burner is to be installed in. A spare burner should not be procured without knowing the specific boiler that it is intended to be used in. Variable fuel composition and boiler configuration information needed when specifying a burner must be known. The following boiler sizes are listed for decision purposes: size 2 boilers are defined as having a thermal output capacity between 320,001 and 10,000,000 Btu/hr (93 783 and 2 930 711 W); size 3 boilers are defined as having a thermal output capacity between 10,000,001 and 35,000,000 Btu/hr (2 930 712 and 10 257 489 W); size 4 boilers are defined as having a thermal output capacity between 35,000,001 and 125,000,000 Btu/hr (10 257 490 and 36 633 888 W). The following items should be considered in the selection of the burner and the exercise of options herein:

a. Size 2 and larger heavy oil fired boilers are usually capable of burning fuel oil grades no. 2, no. 4, no. 5 and no. 6 without difficulty. The pump and motor drive selected for each burner should be sized based on firing all fuel grades to be used (see 3.1).

b. This specification can be used for replacement or conversion installations to specify the procurement requirements for the burner. However, it should remain the responsibility of the contractor who is performing the boiler modifications to make the retrofitted boiler operate satisfactorily (see 3.1).

c. The break between ASME CSD-1 and NFPA 8501 requirements is at 12,500,000 Btu/hr (3 663 389 W) input firing rate. This corresponds to 10,000,000 Btu/hr (2 930 711 W) output boiler with an 80-percent thermal efficiency. Therefore, the break between ASME CSD-1 and NFPA 8501 requirements is about the same as the break between size 2 and size 3 boilers (see 3.3).

d. Propane is the preferred alternate pilot fuel compared to light oil. Oil igniters with direct spark ignition should be used only where natural gas or propane is unobtainable or unfeasible (see 3.6.2).

e. Steam atomization is recommended only for boilers operating at greater than 100 pounds per square inch gage (689 kilopascals (gage)) pressure (see 3.6.4.1.1).

f. When No. 5 and no. 6 oil is to be fired, the burner should be provided with a preheater to reduce the oil viscosity. Preheaters are sometimes required for oil burners firing no. 4 oil (see 3.6.4.5).

g. The selection of a combustion control system should be based on anticipated fuel savings from the increased boiler efficiency. An approximate guideline for selection of a combustion control system is: Size 2 boilers can either be on-off, high-low-off, or positioning, size 3 boilers should be positioning, and size 4 boilers should be modulating or parallel metering (see 3.6.10).

h. Burner turndown ratios higher than those required for the combustion controls should not be specified. Pressure atomizing burners are usually limited to a minimum firing rate of 33 percent of the maximum firing rate and are generally used for size 2 or size 3 boilers fired on light oil. Most air atomizing burners equipped with modulating controls have minimum firing rates of 20 to 25 percent of the maximum firing rates. Size 3 and 4 boilers can be readily obtained with minimum firing rates of 20 percent of the maximum firing rate. In general, burner turndown ratios can only be controlled by controlling the excess air and this should change with alternate fuels (see 3.6.10).

i. The cost of flue gas analyzers for oxygen and unburned combustibles should be justified based on the anticipated fuel savings they should produce. They tend to be more economic on larger boilers with constantly changing loads and fuel quality and should be used only on size 3 or size 4 boilers. Typical excess air on a boiler without analyzers is from 10 to 25 percent. An oxygen compensator will reduce excess air to between 3 and 5 percent. A combination oxygen and carbon monoxide analyzer may reduce excess air up to between 1.5 to 5 percent (see 3.6.10.6 and 3.6.10.6.1).

j. Fungus resistant varnish conforming to MIL-V-173 should be used to coat electrical components and circuit elements, including terminal and circuit connections, when the boiler is to be installed in humid conditions. Components and elements inherently inert to fungi or in hermetically sealed enclosures or current carrying contact surfaces should not be coated.

k. Electromagnetic interference suppression (EMI), when required, should conform to the EMI suppression requirements and test limits for Class C3, Group I equipment as specified in MIL-STD-461. The boiler should be subjected to tests to determine conformance in accordance with MIL-STD-462.

The performance requirements specified herein may be based on other fuels providing the quantity on-site is sufficient for testing specified in section 4 and a guaranteed ultimate analysis and higher heat content available at time of testing the burners. Corrections between the values of the analysis in section 3 of this specification and the guaranteed analysis and heating value should be made in accordance with ASME PTC-4.1. Referenced below are some of the most commonly used gas fuels with their average specific gravity and higher heat content:

Average Average higher Fuel Specific gravity heat content Natural gas 0.65 1,075 Btu/ft³ (1 220 kJ/m³) Manufactured gases 0.38 535 Btu/ft³ ( 607 kJ/m³) Mixed gas 0.50 800 Btu/ft³ ( 908 kJ/m³) Liquefied petroleum gas 1.66 2,500 Btu/ft³ (2 837 kJ/m³)