Combustion – Flash-back controlling or preventing structure
Reexamination Certificate
2001-09-06
2004-03-02
Basichas, Alfred (Department: 3749)
Combustion
Flash-back controlling or preventing structure
C048S192000, C222S189010, C220S088200
Reexamination Certificate
active
06699035
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the field of flame arrestors in pipe line applications.
2. Background of the Invention
A detonation flame arrestor is designed to extinguish a flame front resulting from an explosion or detonation of the gas in the line. However, in addition to extinguishing the flame, the flame arrestor must be capable of dissipating (attenuate) the pressure front that precedes the flame front. The pressure front (shock wave) is associated with the propagation of the flame front through the unburnt gas toward the flame arrestor. The flame induced pressure front is always in the same direction as the impinging flame travel. The pressure rise can range from a small fraction to more than 100 times the initial absolute pressure in the system.
A flame arrestor apparatus usually comprises flame extinguishing plates, ribbon and/or some type of fill media which includes very small gaps of a small diameter, typically less than the MESG of gases, media with passages that permit gas flow but prevent flame transmission by extinguishing combustion. This results from the transfer of heat from the flame to the plates and/or fill media which effectively provides a substantial heat sink.
Two very common flame arrestor element designs are of a crimped ribbon type such as described in U.S. Pat. Nos. 4,909,730, 5,415,233 as well as parallel plate type as described in U.S. Pat. No. 5,336,083 and Canadian Patent No. 1,057,187. The above is referred to as straight path flame arrestors because the gas flow takes a straight path from the channel entrance to the exit.
Flame arrestors are often used in installations where large volumes of gas must be vented with minimal back pressure on the system. It is generally understood that even small deviations in channel dimensions can compromise flame arrestor performance.
A known conflict results from the fact that gas line pressure is frequently maintained at atmospheric pressure or higher. Pressure drop resulting from a flame arrestor or back pressure created as a result of gas passage through the flame arrestor are undesirable. However, pressure drop resulting from passage of the flame through the plates, ribbons, or fill media in the flame arrestor assists in effectively extinguishing the flame. As a result, a need, therefore, exists for a detonation flame arrestor design which includes a large pressure drop per unit volume but a small aggregate pressure drop over the entire apparatus.
The extinguishing process (flame arrestment) is based on the drastic temperature difference between the flame and fill media material. As such, this is a process that not only depends on the temperature gradient, but also on the hydraulic diameter of the passages and the thermal conduction properties of the gas and the fill media.
The level of turbulence significantly affects the rate of heat loss of the flame within the flame arrestor passages. Turbulence is desirable to facilitate the level of heat loss within the flame arrestor. However, straight path flame arrestors of the currently known designs are inefficient in maximizing the amount of turbulence for effective flame arrestment. This is partly because the path of the flame front is unaltered through the flame arrestor. In addition, known straight path flame arrestor designs are inefficient in dispensing the initial shock wave or reflective shock wave. A need exists for a flame arrestor design which alters the flow of the flame front as it passes through the flame arrestor.
In addition, the fill media commonly used for detonation flame arrestors commonly include ceramic beads. Although ceramic beads have useful thermal characteristics, they are relatively fragile and cannot be compacted without crushing to minimize the space between adjacent beads, thereby maximizing surface area of the fill media and varying the path of travel of the flame creating additional turbulence. The ceramic media could also be crushed by the shock wave thereby leaving gaps larger than the MESG of the gas which would compromise the performance (flame stopping capabilities) of the flame arrestor. A need, therefore, exists for a flame arrestor including a fill media which can be compacted to minimize air space and surface area, thereby maximizing the heat sink properties of the fill media as well as increase turbulent flow through the spaces between adjacent components of the fill media.
A detonation flame arrestor must also be capable of attenuating a reflective pressure front in addition to the initial pressure front (shock wave). Initial shock waves impacting flame arrestor elements have been known to cause significant structural damage (element breach) causing the flame arrestor element to fail.
Prior art devices have been known to fail due to the pressures encountered in connection with a reflection pressure front. Although the flame is extinguished within the flame arrestor, a high pressure wave front may exit the outlet side of the flame arrestor as a result of the pressure rise from the initial shock wave. This high pressure wave front continues to travel along the pipe line in the direction of flow. This high pressure wave front, however, will be reflected by any discontinuity located in the pipe line. Discontinuities are the result of bends, stubs, valves, reducers, and the like. As a wave front strikes such a discontinuity, a reflection front is created which travels back towards the flame arrestor. Reflections from many objects along a pipe line can cause transient pressure increases many times the initial pressure. When these reflections enter the outlet side of the flame arrestor, the pressure within the flame arrestor can become many times that for which it was designed. While these pressure increases are of extremely short duration and transient in nature, they nonetheless are known to cause failures in flame arrestors.
A need, therefore, also exists for a flame arrestor that includes the capability of attenuating an initial shock wave and a reflection pressure front.
Another important factor in flame arrestor design relates to cleanability. Presently known parallel plate, ribbon, and/or fill media designs are known to become blocked or clogged as a result of collection of contaminant particles carried in the gas stream. Once significant clogging occurs which restricts flow and increases pressure drop, the entire flame arrestor must be removed for cleaning or replacement. A need exists for a flame arrestor design which can be cleaned in stream and/or easily accessed for cleaning and/or replacement of the fill media.
Detonation flame arrestors known presently in industrial applications are not known to be effective for low Maximum Experimental Space Gap (MESG) gases, such as Group B gases. In particular, known detonation flame arrestors are not effective for hydrogen gas or enriched oxygen and hydrogen applications. Ribbon or parallel plate detonation flame arrestor constructions cannot be cost effectively produced to meet the requirements of low MESG applications. A need, therefore, exists for a detonation flame arrestor design which can be manufactured in a cost effective manner which is capable of operation in low MESG gas environments.
SUMMARY OF THE INVENTION
The detonation flame arrestor of the present invention includes, generally, an outer member or cylinder secured to a canister flange, an inner member or cylinder secured to the canister flange and a fill media retained between the outer and inner cylinders. Both the outer cylinder and inner cylinder, while being secured to the canister flange on one end, include a domed face on their other end. The outer cylinder, inner cylinder, and canister flange together form a canister. The canister is secured within an outer housing bolted to a bulkhead which is welded to the inside of the outer housing. The outer housing is then fitted in the pipeline flow path such that the flow of gas passes into the outer housing and through the canister.
Both the outer cylinder and the inner cylinder include a spiral wo
Basichas Alfred
Enardo, Inc.
Fellers Snider Blankenship Bailey & Tippens, P.C.
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