US2113426A - Method of automatic control for gas burning apparatus - Google Patents

Description

A ril 5, 1938. E. OpENGELS 2,113,426

METHOD OF AUTOMATIC CONTROL FOR GAS BURNING APPARATUS Filed Feb. 16, 1934 BURNER I Juuuuuu gwumtoz EUGENE OSCAR Evans enough suction in the combustion chamber to Patented Apr. 5, 1938 unmen STATES.

PATENT OFFICE 2,113,426 mn'rnon-or AUTOMATIC con'rnor. FOR

GAS BURNING APPARATUS Eugene Oscar Engels, Saginaw, Mich, assignor to Baker Perkins Company, Inc.,

Saginaw,

Mich, a corporation of New York Application February 16, 1934, Serial No. 711,526 2 Claims. 01. I ins-117.5)

This invention relates to gas burning furnaces notwithstanding fluctuations of suction, flame magnitude, and furnace duty. Industrial heating Systems that use furnaces of this character include bake ovens, enameling ovens and the like.

Objects of the invention are, to prevent gasair pocketing, back-firing, belching, and explosion;

' To cause the burner to send forth appropriately varying volumes of flame by using the suction fluctuations in the combustion chamber as an automatic regulator for the fuel supply;

To prevent any-gas from entering the burner and combustion chamber except while there is overcome a predetermined degree of sub-atmospheric pressure that is permanently maintained in the gas supply at the burner, accomplishing this result automatically and without employing valves or other mechanical shut-off devices;

To scavenge the furnace and heating system by automatically haltingthe 'gas flow in the manner stated and circulating fresh air-throughthe passages whenever the degree of partial vacuum in the combustion chamber approaches closely to atmospheric, as for example in starting and shutting down;

To exercise such control without disarranging the optimum gas-air rate for which the burner inlets may have been set,.even though the furnace duty were to vary much more widely than is permissible with earlier systems; and

To attain all these desirable results by a novel method that is capable of being carried out with a new combination of known devices, simple to operate, relatively inexpensive, compact and mechanically eflicient.

other objects will appear later in the specification and the method steps and the structural 'features appertaining to the invention will be recited in the "claims. The accompanying drawing shows a preferred embodiment of the invention. g

Fig. 1 is a fragmentary side view partly in section showing a furnace embodying my invention, together with a diagrammatically indicated heat circulating system.

Fig. 2 is a view in front elevation of the furnace and burner;

A combustion chamber l is provided with a burner adapted to mix gas and air and to discharge the' mixture into the chamber. Preferably the burner is of the type known in the trade as a nozzle-burner because it simultaneously com-' pletes the mixture, discharges it from the nozzle 7 and gives a long, soft flame that does not damage the furnace lining.

- The air supply enters the burner intake 2 at atmospheric pressure.

The primary gas supply for the burner may be any source of gas, say, a service main-3 with a conduit ,4 leading to the burner.

Alsuitable pressure reducer 5 of known construction is installed inthe conduit and delivers to the burner a supply of gas which is permanently maintained at slightly below atmospheric pressure, say, in the order of minus two-tenths of an inch, water column.

During the operation of the burner a suction device I, such as an exhaust fan or impeller, maintains inthe combustion chamber a partial vacuum, lower than the previously mentioned slight sub-atmospheric pressure which is maintained permanently at the, gas intake of the burner by the reducer 5. The" burner stops operating when the suction in the combustion chamber is not lower than that of the gas sup plied by the reducer.

Numerals 8, 8 designate the conduits of a heat circulating system and are to be considered as representing ovens, heaters or the like. A flow regulating damper 9, a vent III for escape of excess gases, and a damper ll therein indicate diagrammatically the usual auxiliaries of such a system. An annular jacket l2 may enclose the.

and no suction is then produced in combustion chamber l or in the burner even though the fan operates at full speed; but by opening vent Ill more or less at damper II, a corresponding degree of suction will be created around the burner nozzle. As soon as a very slight amount of suction develops in the combustion chamber fresh air is drawn in through the burner, but no gas,

since regulator ,5 keeps the gas supply at less than atmospheric pressure. When suction increases, as by wider opening of damper l I, or else by change of fan speed, or by changing damper 9, gas will be released. from the somewhat reluctant regulator '5 and mixing starts in the burner at .whatever gas-air ratio may have been 2 determined by the setting of its gas intake and air intake. It will be clear to those skilled in the art that even while the fan is running full speed,

gives ample scope for practical attainment of the desired automatic control and regulation, and further that the arrangement gives extreme sensitivenes's of control at unusually low rates of fuel consumption and low furnace duty.

A typical burner structure, shown in Fig. 1, has a tubular shell ll projecting into the combustion chamber. Fixed air swirling vanes l5 are provided in shell I! near one end and an air nozzle i5 is fitted in the other end. The shell has a longitudinally adjustable sleeve IT by which the size of the air intake can be fixed. Air nozzle I6 is formed to present a jacket space l8 for gas, and holes IS in the wall of the nozzle allow gas to go from the jacket space into the air nozzle. Numeral 20 designates the gas intake to jacket space 18 from gas conduit 4. The fiow of gas passing from pressure reducer 5 to the burner is adjustable by valve. 2|, Fig. 2,.and its fastener A typical pilot light system is shown diagrammatically, 23 indicating the pilot nozzle, and 24 its gas supply pipe. In pipe I a shut-off valve 25 is also provided.

The operation is as follows. When the system is to be started the fan is caused to circulate air through the heating system at a rate corresponding to the normal speed of the fan, then if vent I0 is opened so that some of the circulating air can escape, a correspondingly slight suction will develop in the combustion chamber l, but not suiiicient to bring in gas, hence scavenging is effected in the heating system.

Ifthe suction is increased so as; to overcome the negative pressure for which the reducer 5 has been set, then gas will enter the burner in whatever quantity is permitted by the setting of valve 2| and air will enter in quantity determined by the setting of sleeve IT, these two adjustments determining the optimum gas-air ratio appropria e to the kind and quality of fuel. When the heatingsystem warms up underthe increased temperature of the circulating gases the latter becomes less dense and the suction in the combustion chamber will decrease.v

In practice it has beenobserved that without anychange in fan speed the suction at the bum-- er will be half as much at six hunderd degrees Fahrenheit as it was when the circulating gases were at room temperature, so it is seen that when the heating system is at its maximum temperature and less fuel is required to keep it in that condition, then the suction in the combustion chamber will have dropped automatically and in consequence less mixture will be drawn to the burner, yet the optimum gas-air ratio will stay constant. If anything should occur to stop the fan the suction in the combustion chamber will disappear and the pressure therein will become atmospheric, but the gas supply will stop first, the air supply later.

It is now apparent that under no circumstances can gas enter the burner or the combustion chamber or the heating system unless the fan is running and is producing a degree of suction in the combustion chamber that is greater than the degree of negative pressure maintained in the gas supply at the burner. No levers, thermoa. predetermined sub-atmospheric pressure, and

maintaining pressures around the delivery end of said burner less than said sub-atmospheric gas pressure, thereby drawing gas into e burner to produce a combustible mixture, and varying the said pressures, the range of variation extending static valves or other devices are required to profrom pressures less than the said sub-atmos EUGENE OSCAR- ENG-ELS.

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