Liquid bubble screen seal for controlling combustible gases

Abstract

This abstract describes a burner system in which gas is flowed into a combustion chamber through a water barrier in such a way that the gas is forced to bubble up through the overlying water through perforations in a horizontal plate. The gas proceeds as a series of isolated bubbles without having a continuous flow channel, thread or column of gas, so as to prevent the flash back of a flame front from the combustion chamber to the source of gas. The apparatus comprises essentially three parts. In the lower part is the water seal structure which comprises a shallow tank of water communicating through its bottom plate to a source tank of water. The gas is introduced under pressure through the water seal by passing downward through an annular passage surrounding the water seal tank. The gas enters the water seal tank through a series of perforations on the circumference near the bottom of the tank and is forced to bubble up through perforations in a horizontal plate, and up to the surface of the water. The gas then passes upwardly through a central cylindrical passage where it meets air at the top of the passage. The air is drawn into the bottom of a cylindrical column or tower which supports the water lock apparatus and permits air to enter the bottom of the tower and pass through an annular space around the combustion chamber apparatus, and to meet and mix with the rising gas column. The mixture is ignited by a pilot flame. The gas mixture then burns and passes upwardly through ceramic covered portion of the tower to whatever apparatus to utilize the hot gases or to the atmosphere.

Description

BACKGROUND OF THE INVENTION

This invention lies in the field of gas flaring apparatus. Still more particularly, it is concerned with the flaring of gases which are highly detonatable, when mixed with air in the proper proportion. Still more particularly, it concerns the design of a water trap system interposed between the entering gas line and the combustion zone, where the gas meets an entering air supply. The purposes of the water trap is to prevent the formation of a continuous column or thread of gas from the inlet pipe to the combustion zone, through which a detonation wave or flame front can progress backwardly along this thread or column of gas, and into the gas line and back to the source of the gas.

In the prior art there are examples of apparatus which has been designed to provide water trapped systems. Some of these are described in the following U.S. Patents: No. 3,231,252; No. 3,331,194; No. 3,606,985; and others. These are unique in that they cause gas flow through liquid to be as a series of separated bubbles, with a liquid interval between successive bubbles, rather than as a continuous flow in the form of a thread or column of gas. When there is a single dip leg tubular device through which the gas flows there is danger, on maximum gas flow, that the gas in passage from the dip leg through the water to the surface will provide a continuous column of gas through which a detonation wave may progress countercurrent to the gas flow direction downwardly and ultimately to the source of gas. With highly detonative gases flowing through the seal, and if downstream of the liquid surface there is an ignition source such as the pilot flame, the flame front can travel countercurrent to the gas flow when there is uninterrupted flow of gas through the liquid to reach the source of the gas. However, if there is a liquid interval between each successive bubble that passes through the liquid, the flame front cannot pass through the liquid interval, and burning is confined to the space downstream of the liquid surface.

A characteristic of liquid seals as in the prior art is that gases in progress toward the liquid through tubular means must provide for the tubular entry at a point above the liquid surface. This is because liquids seek their own levels and if tubular gas entry is below the liquid level the liquid will flow back into the tubular means in such quantity as to prevent a liquid seal above the tubular entry through drain away of liquid.

Because of the demand for air pollution abatement it is frequently necessary to burn highly detonative gas mixtures such as carbon disulfide and air, or ethylene oxide and air. Also, these gases mixed with oxygen. The standard pilot equipped flare cannot be employed in this case because of the violent detonative action of the entire flame system which could result.

However, these gas mixtures can be safely burned off the liquid surface in the liquid seal if the passage of the gases through the liquid is as a series of bubbles. In this device there is structure and gas flow porting means for creation of a state of gas flow through liquid as bubbles, and means for protection of flowing gas from flame created high temperature. Also, means are provided for entry of gases significantly below the level of contained seal liquid.

This device can be used safely for burning of discharged detonatable gases either with no appurtenant apparatus or in conjunction with a refractory lined vertically projecting structure for discharge of combustion products significantly above grade level, through indraft of adequate air for burning. The combustion gases discharged are products of complete combustion. In the application of this device it is optional to provide adequate pilot means to ignite the gases as they depart the liquid surface.

SUMMARY OF THE INVENTION

It is a primary object of this invention to provide a system for combustion and flaring of highly detonative gases with safety, by passing the gas through a water trap, of large horizontal cross sectional area, where the gas is forced to pass through a large plurality of small perforations, and to pass up through the water column as a train of water-separated bubbles of gas. The gas passage is formed as a pair of concentric annular spaces, the gas passing up through the outer space, over a barrier, and down through the inner space, from which it flows into the bottom of the water chamber through a plurality of gas flow ports at the lower level of the water chamber. While the operation is described in terms of water, any other suitable liquid can, of course, be used.

A large supply of water at controlled level is provided so as to replenish the water in the trap which will be normally evaporated by being intermixed with the passage of gas, and evaporated due to the heat of the flame above its surface. There will also be loss of water due to the bubbling and turbulence of the water itself. The construction of the water trap provides means for minimizing the turbulence. This comprises two baffles, one being an annular horizontal ring of selected radial width, and a large central opening, through which the major portion of the gas is directed. The central opening is covered by an overhanging sheet of perforated metal through the perforations of which the gas must pass to be carried upward through the water to its surface.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention and a better understanding of the principles and details of the invention will be evident from the following description taken in conjunction with the appended drawings in which:

FIG. 1 shows in vertical cross section one embodiment of the water trap portion of the apparatus.

FIG. 2 shows a vertical cross section of the complete flaring combustion apparatus, including the water trap portion of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and particularly to FIG. 1, there is shown a water trap system for the passage of gas into a combustion chamber. It is indicated generally by the numeral 10 and comprises an outer cylindrical wall 12 and a circular plate base 14 with a pipe 16 at the axis of the cylinder for the introduction of the gas. There is a second horizontal plate 40 spaced above the bottom plate 14. This supports a cylindrical shell 37 which is welded to the plate 40 and forces the incoming gas to flow upwardly through the annular space 31, between the wall 37 and the outer wall 12 in accordance with the arrows 21 and 22. There is a second cylindrical wall 38 welded to the plate 40 and spaced so as to provide a second annular space 33 through which the incoming gases having traveled up through the space 31 now proceed down through the annular space 33, and through a circumferential series of perforations 36 near the bottom of the wall 38 close to the plate 40.

There is a tank 52 of liquid, which will be described as water for convenience, connected by a pipe 56 which passes up through the bottom plate 14 and is welded through the plate 40 at point 60. Water is maintained at a level 62 in the tank 52, and therefore, seeks its own lever 61 which is the same as 62 inside of the inner wall 38. Water also rises to the level 61 in the space between the two walls 38 and 37 when no gas flows.

Gas flows in accordance with the arrows 18, 20, 21, 22 and 23. The gas flowing into the water at a selected depth below the surface is controlled by a pair of baffles, one of which, 25, is in the form of an annular flat ring with a central opening 67 supported on legs 28 at a selected level above the bottom plate 40. There is a second circular plate of larger diameter than the opening 67 in the plate 25. This upper plate 30 has a plurality of small openings 32 distributed over its area. The plate 30 is supported by legs 34 above the annular plate 25. The water level 61 is maintained at a selected height above the level of the plate 30, so that gas flowing in accordance with arrows 23 progress toward the center of the water space in accordance with arrows 24 and up through the perforations in accordance with arrows 64 until they break through the surface 61 and pass upwardly within the cylindrical wall through the space 66.

It is important that the flowing gas be maintained at all times below a temperature at which it would spontaneously combust and therefore, since there will be hot gas and flame in the space 66, the space between the wall 46 and the outer wall 38 is filled with ceramic insulation 44 and also, if preferred, with a thin layer of ceramic wool insulation 42. This combination, or other suitable combination of insulation, serves to maintain the entering gas at a low enough temperature that it will not spontaneously combust but will flow in the space 33 inside the wall 38 and pass through the baffles and upward through the liquid as trains of water-separated bubbles.

It is thus seen in FIG. 1 there is a design of a water trap that provides

a. A water leg of large cross-sectional area, and of sufficient vertical height to maintain a water seal.

b. There is a large surface area of water through which the gas can pass upwardly in the form of bubbles, to ensure that there will not be a continuous thread of column of gas.

c. There is a plurality of small bubbles which minimize the turbulence of the water which could provide opportunity for momentary large columns of gas to break through to the surface. This forces the gas to pass through the small cross section of the individual ports 32 so that it is forced to break up into bubbles and therefore the entering gas is isolated from the flame by means of a water barrier at all times.

d. An adequate supply of water is provided to maintain a positive level of water in the trap apparatus.

e. Sufficient thermal insulation is provided over the area where the gas passes through the trap so that the gas will not be heated to the point of detonation.

Referring now to FIG. 2 there is shown a flare tower indicated by the numeral 70 which comprises an outer vertical cylinder 72 which rests on a flange 75 on the earth. The water trap apparatus 10 described in FIG. 1 is installed in the bottom end of this tower 70, with an annular space 87 between the water trap 10 and the outer wall of the tower. Air enters the bottom of the tower through a plurality of openings 74. The water trap apparatus can be supported from the outer wall of the tower by means of welded braces 76 or other suitable means.

Air enters the bottom of the tower through a series of openings 74 and passes up through the annular space 87 as indicated by arrows 89, over the top of the water trap 10 in the form of arrows 90. Here the air meets the rising gas column in accordance with arrows 92 and they are mixed and ignited by the flame 50 of the pilot light 48. The burning gases pass upward in accordance with the arrows 93 through a portion of the flare tower that is lined by ceramic means 88. Containment of hot gases as 93 within the flare tower develops "draft" or less-than-atmospheric pressure above 10 to cause inflow of air as recited. The burning gases are completely combusted and pass into the atmosphere through the top, which is not shown.

The water supply can conveniently be provided in the form of an annular tank 78 welded to the outside of the tower 72 near the base thereof. Water enters through the inlet 80 through a control orifice 79 in the outer wall of the tank. A pipe 81 is welded in the bottom of the tank of a vertical dimension such as to ensure that there will be adequate water level and that the level will be maintained at or near the top of the overflow pipe 81. A pipe 56 is welded into the bottom of the tank and passes into the water trap assembly 10 in accordance with the pipe 56 of FIG. 1. The pipe 16 provides the gas flow as indicated by the arrow 18.

While the upper portion of the tower above the plate 86 could be dispensed with and the gas passing upwardly through the space 66 could be burned at the mouth of the wall 12 this would not be entirely satisfactory because of the possibility of pollution of the air at low levels. Therefore, the combination of the water trap and combustion device 10 with a continuing lined tower 72 provides a taller high-temperature passage for the burning gases to ensure complete combustion. Also the tower 70 ensures the dispersal of the products of combustion at a high level, so that there would be a distribution over a wide area, and therefore lower concentration of contaminants at any point at ground level.

While the invention has been described with a certain degree of particularlity it is manifest that many changes may be made in the details of construction by the arrangement of components. It is understood that the invention is not to be limited to the specific embodiment set forth herein by way of exemplifying the invention, but the invention can be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element or step thereof is entitled.

Claims

What is claimed:

1. Apparatus for controlled burning of combustible gases, comprising:

a. a cylindrical tank, and means for maintaining a selected level of non-combustible liquid in said tank;

b. a first wall outside of said tank wall forming first annular space surrounding said tank for the downflow of said combustible gases;

c. a plurality of circumferentially spaced small openings in the wall of said tank near its base communicating with said first annular space;

d. baffle means inside said tank above said openings but below the surface of said liquid, said baffle means including at least a first horizontal plate with a plurality of spaced small openings;

e. cylindrical shell means inside of said tank above the surface of said liquid, and thermal insulation means between said shell and the wall of said tank;

f. means to supply said gas to the top of said annular space, and means to ignite said gas above the level of said liquid.

2. The apparatus as in claim 1 including a second wall outside of said first wall forming a second annular space communicating with the top of said first annular space, and means to supply said gas to the bottom of said second annular space.

3. The apparatus as in claim 2 including a circular plate welded to the bottom of said second wall, and spaced below the bottom of said cylindrical tank, the space between said plate and said bottom communicating with said second annular space, and means to inject said gas into said space.

4. The apparatus as in claim 1 including a second baffle in the form of an annular plate of outer diameter greater than the diameter of said first plate, with a central opening of lesser diameter than said first plate, said second baffle mounted between said first plate and the bottom of said tank.

5. The apparatus as in claim 1 including a supply tank of said liquid and means to maintain the level of liquid in said cylindrical tank and said supply tank the same.

6. The apparatus as in claim 1 in which said liquid is water.

7. The apparatus as in claim 1 including a cylindrical tower of larger diameter than, and surrounding, said apparatus for burning and means to pass air upwardly through the annular space between said apparatus for burning and said tower.

8. The apparatus as in claim 6 including the ceramic lining means on the inside surface of said tower above said apparatus for burning.

9. The apparatus as in claim 1 where said maintained level of non-combustible liquid is below the upper level of flow of said combustible gases.