US2087031A - Ingition apparatus for closed-system fluid-combustible burners - Google Patents

Description

July 13, 1937. J. w. HAYS 2,087,031

IGNITION APPARATUS FOR CLOSED SYSTEM FLUID COMBUSTIBLE BURNERS Filed March 18, 1935 L Mt DH INVENTOR WITNESSES Patented July 13, 1937 resin PATENT oFFicE IGNITION APPARATUS FOR CLOSED-SYS- TEM FLUID-COIVIBUSTIBLE BURNERS Joseph W. Hays, Tulsa, Okla.

Application March 18,

2 Claims.

My invention relates particularly to igniting device for that form of gas, oil, vapor or powdered fuel burner in which all of the air utilized is taken as primary air and mixed with the combustible element either prior to or at the time of ignition, the structure of the burner and the conditions under which it operates being such that no secondary air can be taken after ignition occurs and such that the entire combinaing and firing continuously an uninterrupted stream of explosive.

My invention applies in an especial manner to' that particular form or process of combustion which has been variously called surface, or flameless, or catalytic combustion, in which a fluent explosive mixture is burned within a bed or packing of refractory material, and under a pressure, either positive or negative, other than that of the atmosphere, the heat being yielded very largely in the radiant form.

Immediately after ignition the mixture burns in the interstices of the refractory packing and in a short time the refractories .become heated to a point of incandescence, whereupon the mixture burns without flame and a very high temperature is reached, the heat being produced, very largely if not entirely, in the radiant form. Combustion is practically instantaneous. This being so, the capacity limits of such a combustion tube are fixed by the free area of the interstitialspaces of the refractory packing and by the pressures used to force the gases into and through the tube.

In prior devices, the air gas mixture has been ignited at the discharge outlet of the combustion tube, relying upon the balancing of the velocities of mixture flow and of flame propagation to fix the location of the combustion zone. The com,- bustion zone, however, is likely to remain fixed at, or close to, the spot where it is first established. The tendency of the combustion zone to remain stationary is influenced to some extent by the state of the refractory packing, as to coarseness or fineness, by the length of the tube and by the temperatures attained in the combustion zone as well as by the velocities. There is an enormous increase in gas volume in the combustion zone, due to the high temperature, and this acts as a brake upon the flow of the gases through the tube.

The positioning of the combustion zone is a very important consideration in all cases where 1933, Serial No. 661,628

such combustion tubes are employed. The advantages of counter-flow in effecting heat exchanges are well known. The fluid to be heated should, in all cases where possible, fiow in a direction contrary to that of the hot gases. This is best accomplished by fixing the location of the combustion zone at the extreme end of the combustion tube and approximately adjacent to the place where the heated fluid reaches its outlet. In this Way the fluid, when in its hottest state, is exposed to the highest temperature and, when in its coolest state, on entering the heater, is exposed to the lowest temperature. Thus the highest heater capacities and efficiencies are obtained.

It can easily be seen that if the combustion zone should be established at the opposite end of the combustion tube, or midway of the tube, there would be a marked loss of heat energy with the waste combustion gases, and this would be reflected adversely upon the heating device, both as to its efficiency and its capacity.

An object of the invention is to provide an ignition device which is positive in operation in igniting the combustible mixture and in establishing a zone of combustion at the desired place.

A further object of the invention is'to provide an ignition device of suitable type which will operate under the conditions found at a preferred zone of combustion.

A still further object of the invention is to provide an ignition device which may be suitably used in a surface combustion system in which the fuel and combustion supporting gas are fed by forced draft.

The objects of the invention have been achieved by the use of an igniting device, the operation of which is unaffected by the passage of large volumes of relatively cool gases thereover.

More specifically, the igniting device may suitably consist of a spark plug of known type. A spark plug, because of the fact that relatively low or high temperatures have no effect on its ability to produce a spark, is capable of igniting the combustible mixture whether the volume of gas passing thereover and thereby be a few hundred or several thousand feet per minute.

The spark plug must be in the path of flow of the mixture to positively ignite it and preferably is located at or closely adjacent the desired zone of combustion in order that it. may establish the zone at the desired place. The spark plug, in such a location, will then be exposed to direct radiations from the incandescent zone of refractory material while the heating system is operating. Unless some means are provided for shielding the spark plug it will be destroyed by the intense heat radiations.

I have overcome this difficulty by providing a screening layer of refractory material of relatively low heat conductivity which intercepts the direct radiations from the combustion zone. This layer of refractory material is preferably situated so that the combustion mixture directed upon it and due to the relative coolness of the mixture maintains the mass at a comparatively low temperature.

For a better understanding of my invention, reference may be had to the accompanying drawing in which the figure discloses a view in section of a surface combustion heater including one embodiment of my igniting device.

A typical embodiment of my invention may suitably be described in conjunction with a heater of the type disclosed in my copending application, Serial No. 653,468, filed January 25, 1936, which includes a combustion tube or chamber CT containing a mass of refractory material Re retained therein by means of a grid Gr and a Venturi plate V containing a series of Venturi-type orifices through which a fluid such as for example gas, liquid or finely divided solid combustible matter may be injected from a series of injecting nozzles N. The injecting nozzles are connected to a common fuel chamber C formed by a housing DH fed by an inlet pipe P and having a baffle B located therein in order to equalize and distribute the fuel to the injection nozzles N. Encircling and spaced from the combustion chamber is a jacket J having suitable gaskets and plates R therein in alignment with the ends of the combustion tube to form a jacket Sp through which fluid Fd may be circulated from an inlet conduit I11. downwardly toward the inlet end of the combustion tube and outwardly through an outlet conduit Ot. The jacket J preferably is extended below the end of the combustion tube forming a wall H of a chamber M for receiving and distributing a combustion-supporting gas passing into the chamber through an inlet conduit A. The combustion supporting gas is forced into the chamber M, circulates about the fuel injection nozzles N through a straightener plate St which reduces turbulence of the gas and causes it to flow parallel to the nozzles N and passes with the fuel through the orifices O in the Venturi plate V to impinge upon and mushroom over the surface of the refractory Re thereby producing an intimate mixture of the fuel and combustion supporting gas. The tips N1 of the injecting nozzles N are preferably restricted in size so that concentrated jets of fuel may be produced. The Venturi plate V may be suitably adjusted by means of shims or washers S, spacer sleeves SI and rods to regulate its distance from the tips of the injecting nozzles in order to produce a slight premixing of fuel. These shims S, spacer SI and rods may be suitably affixed by means of nuts N15 and additional shims SW to a base plate TP in which the nozzles N are mounted. Gaskets W may also be provided for preventing leakage around the rods. The fuel cham ber C, nozzle base plate TP may be affixed by means of suitable bolts L to an internally extending flange FZ aflixed to the jacket J thereby producing a rigid assembly. Suitable gaskets GI and G may be inserted between the various elements consisting of the flanges Fl, base plate TP and flange F on the fuel chamber to produce a gas tight construction.

In operation, fuel is forced unde press through the chamber C, nozzles N and nozzle tips Nl, against the refractory Re and at the same time a combustion supporting gas passes through conduit A into chamber M to travel, with the fuel, onto the surface of the refractory Re in the combustion chamber CT where it mushrooms and mixes.

In the construction shown, it is preferable to ignite the mixture and establish a combustion zone CZ near the fuel inlet and mixing zone. The purpose of this construction and location of the combustion zone is to produce countercurrent heating of the fluid passing from the inlet In to the outlet 0t in the fluid jacket J. This type of heating, as is well known, is the most efficient, in that the incoming cool fluid is gradually heated by passage from the part of the combustion zone heated by hot gases HG to the hottest part, adjacent the combustion zone CZ thereby tending to withdraw the greatest amount of heat possible from the combustion zone.

To establish the combustion zone at the inlet end of the combustion tube CT, it is desirable to initially ignite the mixture of fuel and combustion supporting gas at the inlet end. To do this I have inserted a housing or nipple WJ through the jacket J and combustion tube CT immediately above the plate V. The housing WJ is preferably internally threaded to receive a spark plug ID which extends through and presents its points within the combustion tube CT closely adjacent the outer surface of the refractory material Re defined by the line DL. The

points of the spark plug are thus located in the path of flow and at the point of mixture of the fuel and combustion supporting gas so that when the spark plug is excited by means of current passing therethrough the combustible mixture will be ignited and will gradually heat the refractory material to incandescence. refractory material in the zone CZ has become incandescent the fuel supply may be temporarily stopped and only air passed into the combustion tube, thereby clearing the combustion tube of any excess fuel. Fuel may then be directed along with the combustion supporting gas into the combustion tube whereby the mixture produced will ignite and burn without flame on the surface of the refractory mass Re.

Injury to the spark plug points is prevented during operation of the heating system by placing a layer of refractory material Ref of relatively low heat conductivity, for example, fused magnesia, between the Venturi plate V and the line DL defining the rear surface of refractory Re and opposite the spark plug ID. The incoming fuel and combustion supporting gases will impinge upon the mass of refractory material and being relatively cool will gradually cool the near surface of the refractory layer Ref below the temperature in the combustion zone. The portion of the refractory layer Ref adjacent the combustion zone CZ will be heated highly by radiations but due to loW conductivity, the greater portion of the heat will not be con-ducted to the spark plug. The screen of refractory material Ref also intercepts radiations from the combustion zone directed toward the spark plug and will prevent excessive heat from radiation.

It will thus be seen that I have produced a construction which will positively ignite combustible mixtures fed into a combustion tube, will locate the combustion zone in the desired place and will have great length of operating life under most extreme operating conditions.

When the 1 I through for passage of gases, fuel and combustion It will also be understood thatvariations, readily occurring to those skilled in the art, may be made in the construction disclosed and there fore the embodiment disclosed should be considered as illustrative only and not as limiting the scope of the following claims.

I claim:

1. In a water-cooled tubular furnace, the combination of a combustion tube, a mass of refractory material therein, having openings theresupporting gas inlets for impinging the fuel and the gas on a surface of the refractory mass to thoroughly mix them, a spark-plug extending into the combustion tube adjacent the surface of the refractory mass and means for exciting the spark-plug to ignite the mixture at the point of mixing, the refractory mass adjacent the sparkplug being of lower heat conductivity than the remainder of the mass, whereby the spark-plug is shielded from heat radiations during operation of the furnace.

2. In a water-cooled tubular furnace, the combination of a combustion tube, a fluid jacket encircling said tube, a mass of refractory material in said combustion tube having apertures therethrough for passage of gases, fuel and combustion supporting gas inlets for impinging the fuel and gas on a surface of said mass to thoroughly mix them, a spark-plug extending through the fluid jacket into said tube adjacent the surface of the refractory mass and means for exciting the spark-plug to ignite the mixture at the point of mixing, the refractory mass adjacent the sparkplug being of lower heat-conductivity than the remainder of the mass, whereby the spark-plug is shielded from heat radiations during operation of the furnace.

JOSEPH W. HAYS.

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