Ignition pilot

Calculate the time to ignite (piloted) for the materials listed below if the irradiance is 30 kW/ m2 and the initial temperature is 25 °C. The materials are thick and the convective heat transfer coefficient is 15 W/m2 K. Compute the critical flux for ignition as well. 

In the ASTM E84 25-foot tunnel furnace test (34) for measuring flame spread of building materials, an igniting pilot flame is applied to the underside of a horizontally mounted specimen. The flame heats the combustible material to pyrolysis, and the flammable gases given off are ignited by the pilot flame. 

This method is based on the Ohio State University Release Rate Apparatus. The specimen is injected into the environmental chamber through which a constant flow of air passes. The exposure of the specimen is determined by a radiant-heat source adjusted to produce the desired total flux on the specimen, which may be tested horizontally or vertically. Combustion may be initiated by non-piloted ignition, piloted ignition of evolved gases, or by point ignition of the surface. The changes in temperature and optical density of the gas leaving the chamber are monitored, and from the resultant data the release rate of heat and visible smoke are calculated. This aj aratus is also used to measure the rate of toxic gas release and consumption. 

To make the flame stable against the flow in a thin annular region near the rim, the flow velocity p should be made equal to the burning velocity at some radius r. This annulus serves as a pilot and ignites the main flow of the mixture, ie, the flame gradually spreads toward the center. In most of the mixture flow, which results in a stable flame. With increasing mixture flow, the height and area of the flame increase. Measurement of the area of a... 

Flare systems are subject to potential flashback and internal explosion since flammable vapor/air mixtures may be formed in the stack or inlet piping by the entry of air, and the pilot constitutes a continuous ignition source. Flares are therefore always provided with flashback protection, which prevents a flame front from travelling back to the upstream piping and equipment. Design details are described later. 

In the consideration of elevated flare pilots and igniters, proprietary flare tips are normally provided with the manufacturer s recommended igniter and pilot system. Usually, one to four pilots are used depending on the flare tip type and diameter. The forced air supply type of igniter system (described below) is normally preferred. Controls should be located at a distance from the base of the... 

Smokeless Coanda Gas releases at base of elevated tulip create low pressure region. Gas film follows Coanda profile mixes with air and is ignited by pilot. 

Pilots and Igniters - Duplicate continuous gas pilots are required at each side of the flare, corresponding to the split burner grid layout. Selection of pilot and igniter systems follows the guidelines described below, and the controls should be located 15 m to 30 m from the windbreaker. 

Pilots and Igniters - Two gas-fired pilots with igniters are installed adjacent to the inlet distributor. The igniter assembly and pilot gas valves must be located remote from the flare for protection of personnel and equipment. This restricts igniter selection to the forced air supply type. Location of these components should be such that the calculated radiant heat density at maximum load does not exceed permissible levels for personnel exposure. Because of the potential hazard of release of unignited hydrocarbons at ground level, a flame scanner (suitably shielded and aircooled and cotmected to an alarm in the control house), is provided for each pilot. 

Figure 6. Typical elevated flare pilot and igniter.

Preferably, the HjS flare system should consist of a segregated header and separate line routed up the side of a conventional elevated flare stack, sharing the same structure, pilots and igniters. However, the HjS header may be tied into the regular flare seal drum if there are special mechanical design problems associated with the separate stack e.g., in the case of a flare which is to be dismantled for overhaul. Flare elevation must be sufficient to meet atmospheric pollution and ground level concentration requirements for the sulfur dioxide produced. 

The flare tip assembly shall be furnished complete with smoke suppression system, pilot and igniter assemblies, windshield, and flame retention assembly. 

The flare tip assembly shall be provided with at least two pilot assemblies to assure complete ignition of gases leaving the flare tip. 

Each pilot shall be spark operated complete with a windshield, pilot tip and pilot tube. It shall also have an igniter tube, thermocouple and remote venmri, if applicable. 

Ignition controls shall include upstream (in flare header prior to knockout drum) dual flow sensing equipment which shall start the automatic flare purge, pilot ignition and the flare ignition cycle. N P Refinery will be responsible for the wiring between the flow sensors and the ignition control panel. 

All pilot and igniting piping shall be provided with break flanges located just below the burner tip flange. If the pilot is equipped with an air inspirator, the latter shall be located as low as practicable but not within 500 mm of the burner tip flange. Screwed connections shall not be used for pilot and ignition piping. 

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