I.- Ping Chung, PhD, is a senior development engineer in the Technology and Commercial Development Group at
1.6 Pilot Burners
1.6.1 Premix Pilots
1.6.1.1 John Zink ST-1-S Premix Gas Pilot
The most common pilot supplied by John Zink is pres- ently the ST-1-S, which is shown in Figure 1.60. This pilot is a manually ignited, premix gas pilot, designed for high
(a) (b)
Figure 1.59
(a) DEEPstar oil flame and (b) gas flame.
efficiency on natural gas fuels. The pilot mixer is gener- ally located external to the burner housing, making the combustion air for the pilot ambient air. The gas/air mix- ture tube is 1 in. (25 mm) sch. 40 pipe allowing a high per- centage of stoichiometric air. The tip is a multiport premix tip utilizing impinging ports for initial flame stabiliza- tion. The tip also has a high-alloy cast shield providing additional stabilization and protection from variations in directional external flows (wind or draft effects).
The standard ST-1-S pilot utilizes a 1.59 mm (0.0625 in.) diameter fuel orifice. It has a normal operating pressure range of 0.5–1.1 barg (7–16 psig). On most methane-rich natural gas fuels, its capacity would be 21.4–31.6 kW (73,000–108,000 Btu/h). The ST-1-S pilot has a proven operational range from 0.2 to 1.75 barg (3 to 25 psig).
This pilot’s standard configuration will handle fuels ranging from LPG (liquefied petroleum gas, which usu- ally consists of vaporized butane and propane) to 30%
hydrogen with a single-tip design. There are two (2) additional reduced area tips, designed for progressively higher hydrogen content of up to 75 mol%. As each of the smaller area tips, suitable for higher hydrogen, is used, the pilot becomes less suitable for heavier pilot fuels.
The ST-1-S pilot is available with high-tension (trans- former powered) electric ignition, the ST-1-SE (see Figure 1.61). It is available with frame rectification rods for flame proof, the ST-1-S-FR. It is available configured for both electric ignition and flame proof via rectification, ST-1-SE-FR (see Figure 1.62).
1.6.1.2 John Zink KE-1-ST Premix Gas Pilot
The KE-1-ST pilot, shown in Figure 1.63, is a variation on the ST-1-S pilot with an internal electric ignition rod sup- plied standard. This pilot is a high-tension (transformer powered) electrically ignited, premix gas pilot, designed for high efficiency on natural gas fuels. The pilot mixer is generally located external to the burner housing, mak- ing the combustion air for the pilot ambient. The electric ignition rod is housed within the gas/air mixture tube,
giving a self-contained package. The gas/air mixture tube is 1 in. (25 mm) sch. 40 pipe allowing a high percent- age of stoichiometric air. However, owing to the obstruc- tion created by the electrode and insulators, the mixer efficiency is less than that of the ST-1-S. The tip is a multi- port premix tip utilizing impinging ports for initial flame stabilization. The tip also has a high-alloy cast shield pro- viding additional stabilization and protection from varia- tions in directional external flows (wind or draft effects).
The standard KE-1-ST pilot utilizes a 1.59 mm (0.0625 in.) diameter fuel orifice. It has a normal operating pressure range of 0.5–1.1 barg (7–16 psig). On most methane-rich
Figure 1.60
ST-1-S manual pilot. Figure 1.61
ST-1-SE electric ignition pilot.
Figure 1.62
ST-1-SE-FR electric ignition pilot with an integral flame rod.
Figure 1.63
KE-1-ST electric ignition pilot.
natural gas fuels, its capacity would be 21.4–31.6 kW (73,000–108,000 Btu/h). This pilot is capable of handling fuels ranging from LPG to 30% hydrogen with a single- tip design. Higher levels of hydrogen content can be accommodated, but the range of operating pressure and capacity are restricted. Owing to the required configu- ration for internal electric ignition sparking, there are no variations in tip areas available for higher-hydrogen- content fuels.
1.6.1.3 John Zink ST-2 Premix Gas Pilot
The John Zink ST-2 pilot is a manually ignited, premix gas pilot, designed for high efficiency on a broad range of refinery or chemical plant fuels (see Figure 1.64). The pilot mixer has been redesigned following ASME design crite- ria. The venturi is generally located external to the burner housing, making the combustion air for the pilot ambient.
The gas/air mixture tube is 1½ in. (38 mm) sch. 40 pipe (2 in. or 51 mm nominal outside diameter) allowing even higher percentages of stoichiometric air. The tip is a multi- port premix tip utilizing impinging ports for initial flame stabilization. The tip also has a high-alloy cast shield pro- viding additional stabilization and protection from varia- tions in directional external flows (wind or draft effects).
The standard ST-2 pilot can be designed to utilize a 1.59 mm (0.0625 in.) diameter or a 1.99 mm (0.0785 in./#47 MTD) diameter fuel orifice. It has a normal oper- ating pressure range of 0.35–1.38 barg (5–20 psig). On most methane-rich natural gas fuels, the pilot’s capac- ity using the smaller standard orifice would be 18.25–
35.75 kW (62,300–122,000 Btu/h). The pilot’s capacity using the larger standard orifice would be 28.8–56 kW (98,250–191,000 Btu/h). Test stand operation of the ST-2 pilot has shown an operational range from 0.2 to 1.75 barg (3 to 35 psig). This pilot has shown the ability to handle fuels ranging from LPG (vaporized butane and propane) to 85% hydrogen with a single-tip design. The higher levels of hydrogen content are accommodated by operating at greater than 0.7 barg (10 psig).
The ST-2 pilot is available with high-tension (trans- former powered) electric ignition or high-energy (capac- itance discharge) electric ignition, the ST-2-E or ST-2-EI. It is available with frame rectification rods for flame proof, the ST-2-FR. It is also available supplied with a modified flame shield for flame proof via optical or digital scan- ner. It is available configured for both electric ignition and flame proof via rectification, ST-2-E-FR/ST-2-EI-FR.
1.6.1.4 John Zink KE-2-ST Electric Ignition Premix Gas Pilot
The standard KE-2-ST pilot (Figure 1.65) utilizes a 1.59 mm (0.0625 in.) diameter fuel orifice. It has a nor- mal operating pressure range of 0.5–1.1 barg (7–16 psig).
On most methane-rich natural gas fuels, its capacity is 21.4–31.6 kW (73,000–108,000 Btu/h). The KE-2-ST pilot has a proven operational range from 0.2 to 1.38 barg (3 to 20 psig). This pilot is capable of handling fuels rang- ing from LPG to 30% hydrogen with a single-tip design.
Higher levels of hydrogen content can be accommo- dated, but the range of operating pressure and capacity are restricted. Owing to the required configuration for internal electric ignition sparking, there are no varia- tions in tip areas available for higher hydrogen content at normal operating pressure ranges.
The ignition system utilizes a fixed spark gap igniter.
Those units supplied with flame rods utilize a fixed surface area ionization rod. Both elements, the igniter and flame rod, are encapsulated inside a stainless steel tube to help eliminate problems with moisture and dirt, which can result in shorting out the electronics.
The KE-2-ST pilot is available with high-tension (trans- former powered) electric ignition KE-2-HT (high ten- sion) or high-energy (capacitance discharge) electronic ignition KE-2-HE (high energy). It is available with flame rectification rods for flame proof, KE-2-HT-FR and KE-2- HE-FR. This pilot can also be supplied with a modified flame shield for flame proof via optical or digital scan- ner. This modified flame shield is angled, restricting the
Figure 1.65
KE-2-ST electric ignition pilot.
Figure 1.64 ST-2 manual pilot.
scanner’s view to the pilot flame only. Scanners are also available, KE-2-HT-SC and KE-2-HE-SC. The KE-2-ST series pilot can be engineered to fit most existing pilot mounting systems.