US3310096A - Apparatus for securing burners - Google Patents

Description

March 21, 1967 G. M. B. DE LIVQIS APPARATUS FOR SECURING BURNERS Filed July 8, 1965 mwbmrmmm E w NEE zozoom United States Patent T 3,310,096 APPARATUS FOR SECURING BURNERS Guy M. Baudelet de Livois, Paris, France, assignor to Coutrole Bailey (Societe Auonyme), a company of France Filed July 8, 1965, Ser. No. 470,413 Claims priority, application France, Aug. 5, 1964, 984,257 8 Claims. (Cl. 158-1) This invention relates to a method and apparatus for operating burners. More particularly the invention relates to a method and apparatus for securing one or more of the burners delivering fuel and air to a furnace.

One object of my invention is to provide an arrangement for safely and economically firing a furnace under partial load conditions with one or more of the burners supplying fuel and air thereto secured.

Another object of my invention is to provide a simple, economical arrangement for cooling the secured burners.

A further object of my invention is to provide an arrangement for maintaining the proper distribution of air for combustion in a furnace when one or more burners supplying fuel and air thereto are secured.

Still another object of my invention is to provide an arrangement whereby a furnace having a plurality of burners may be operated with one percent or less of free oxygen in the flue gas at partial load with one or more of the burners secured.

A further object of my invention is to provide an arrangement preventing the leakage of air through a secured burner into a furnace.

In accordance with my invention when a burner is secured, concurrently with the fuel and air thereto being shut off an inert gas such as recirculated flue gas is substituted for the normal air supply. Thus leakage, if any, through the burner merely introduces an inert gas into the furnace. The normal or desired excess air is then maintained at the opearting burners and in the furnace which is not the case with presently available burners wherein a certain amount of air leakage necessarily occurs through any secured burners.

Until recently the increase in excess air caused by air leakage into a furnace through a secured burner or burners could be tolerated as it was and is customary under present practice to operate a furnace at a fairly high excess air in the order of 15% or more. Little or no effect is felt by slightly reducing the air-fuel ratio to the operating burners to compensate for the air leakage through the secured burners. Or in the alternative, by maintaining the same air-fuel ratio in the opearting burners and permitting the furnace as a whole to operate at a slightly greater excess air. Recent studies have shown, however, that in addition to increasing efficiency, the formation of delterious compounds in the flue gas is retarded by operation at approximately zero excess air, that is to say operation at an excess air of or less. To accomplish this it is essential that the correct air-fuel ratio be maintained at all operating burners and air leakage through any burners which are secured be eliminated. It is to a method and apparatus for accomplishing these and other objects that my invention is directed.

Referring to the drawing, I show a furnace having a wall 64 in which are mounted a plurality, in the specific embodiment shown, three burners 57, 58 and 59 supplied with air through individual windboxes 61, 62 and 63 respectively. The air for combustion is supplied the burner 57 through a register 66 positioned to the open or closed position by any suitable device such as a control drive 67 through linkage 68. A shut-off damper 69 is mounted within a duct 71 through which air to the windbox 61 is 3,3 10,096 Patented Mar. 21, 1967 supplied. The damper 69 is positioned to an open or closed position by a control drive 72. In a similar manner combustion air to the burners 58 and 59 is supplied through registers 73 and 74 which are positioned to the open or closed position by a control drive 76 and 77 respectively. A shut-off damper 78 positioned by a control drive 79 is provided in duct 80 through which air to the windbox 62 is supplied. Similarly, combustion air supplied the burner 59 may be shut off by a damper 81 mounted within a duct 83 and positioned by a control drive 82.

The air ducts 71, 80 and 83 are connected to a supply duct 84 which in turn is connected to one or more force draft fans, not shown, as conventional in the art. Disposed in'the fuel supply lines to burners 57, 58 and 59 are shut-off valves 43, 42 and 41 respectively. Fuel and air to burners 57, 58 and 59 may be regulated by positioning a damper 47 by means of a control drive 48, and a fuel valve 20 from a control signal derived from a conventional combustion control system, as common in the art; or in the alternative, the dampers 69, 78 and 81 may be used as combination control and shut-off dampers. Similarly valves 43, 42 and 41 may be used both to control the flow of fuel and act as shut off valves. In the latter case dampers 69, 78 and 81 as well as the valves 43, 42 and 41 would be controlled from a signal derived from a conventional combustion control system and damper 47, control drive 48 and fuel valve 20 omitted.

During normal operation more or less equal fuel flows to the burners 57, 58 and 59 are maintained and variations in heat release obtained by adjusting in substantially equal amounts the fuel flows to all of the burners. Simultaneously with changes in fuel flow, corresponding changes in air flow are made by parallel adjustment of the individual dampers 69, 78 and 81 or in the alternative by adjustment of the force draft damper 47. With the latter form of control, as previously explained, the individual dampers 69, 78 and 81 are held in a wide open position. As with burners presently available, whether for firing oil, gas or coal, the required range in heat release cannot be obtained, it is customary practice to operate with all burners in service from max heat release to some predetermined lesser heat release when one or more burners are secured to permit a further reduction in heat release. At such time the fuel flow to the burner or burners being secured is shut-off and the associated air registers closed. Certain auxiliary operations may also be required such as withdrawing the burner tip, in case of oil firing, to prevent overheating, carbonizing of the fuel remaining in the burner, etc.

As heretofore explained air registers such as shown at 66, 73 and 74 are not tight closing and accordingly air, while the burner is secured, passes through the burner and escapes into the furnace. Such air does not ordinarily enter into the combustion process as it is not properly mixed with the fuel discharged from the burners remaining in service. Also as it is customary to ratio total fuel to total air, the air actually unavailable for combustion at the burners in operation may decrease. To avoid the consequence of operating with a defiiciency of air and to provide a factor of safety, ordinarily the total air to total fuel ratio is maintained higher than would otherwise be required. Recent tests have indicated that a high air-fuel ratio in addition to decreasing eificiency also results in the formation of harmful substances in the products of combustion which rapidly deteriorate any surfaces with which they are in contact and polute the atmosphere upon being wasted.

In accordance with my invention the leakage of air through a secured burner is eliminated by sealing the inlet side of the closed air register with an inert gas. In

some cases the inert gas may be the products of combustion discharged from the furnace which are composed largely of nitrogen and carbon dioxide. If the furnace is used to supply heat to a boiler or other heat absorbing apparatus, preferably the products of combustion (flue gas) are diverted to the air register after having passed through such apparatus as the gases are then sufliciently cooled to avoid the necessity for auxiliary cooling, which might otherwise be required. Thus referring to the drawing I show the inert gas as being drawn from a gas pass 46 of a boiler (not shown) just before the flue gases are wasted to the atmosphere. At such a point the temperature of the gases may be in the order of 350 degrees F. or less and relatively free of solids particularly if the gases have passed through a dust precipitator as is now common in the art. While I have shown the gas pass 46 as forming the outlet of an economizer and air pre heater 45, it is evident that the inert gas may be obtained at any desired point in the gas stream as, for example, after a dust precipitator.

The diverted gas is passed through a duct 85 to a blower 86 which discharges into three branch ducts 88, 89 and 91 by way of a duct 87. Branch duct 91 discharges into the air supply duct 71 between damper 69 and register 66. Similarly, branch duct 89 discharges into duct 80 between damper 78 and register 73. Branch duct 88 discharges into duct 83 between damper 81 and register 74. The diverted gas is pressurized by the blower 86 and maintained positive with respect to the forced draft air by a differential pressure controller such as shown at 92 operating a damper 94 through a control drive 93. Disposed in ducts 88, 89 and 91 are shut-off dampers 99, 97 and 98 respectively, which are arranged to be operated by control drives 102, 103 and 101 respectively.

When burners 57, 58 and 59 are in operation, dampers 97, 98 and 99 are closed thus shutting off the flow of inert gas to the burner registers. When however a burner is secured as, for example, the burner 57, damper 98 is opened simultaneously with the closing of air register 66 and damper 69. Thus the flow of combustion air is shut off and the register 66 sealed with the inert gas. Similarly, when burner 58 is secured air register 73 and damper 78 are closed and damper 97 is opened and when burner 59 is secured air register 74 and damper 81 are closed and damper 99 is opened.

I show dampers 97, 98 and 99 arranged to be operated by control drives 103, 101 and 102 respectively. As evident to those skilled in the art, the teachings of my invention may advantageously be incorporated in an Automatic Burner Management System so that the operations I have described in securing a burner may be performed automatically. Thus I show such an arrangement schematically for burner 57 wherein a control signal, transmitted through a line 44, from a signal generator such as shown at 31 is arranged to operate fuel shut-off valve 43, register 66, damper 69 and damper 98. Such a control signal may be originated by an operator or automatically. Further, I show schematically a system whereby an overriding signal for securing a burner may be generated by a flame failure detector, such as shown at 32, so that upon loss of ignition to the burner 57 the fuel flow thereto is shut off and concurrently register 66 and damper 69 are closed and damper 98 opened, thereby impressing on the inlet side of register 66 the inert gas, which being above the pressure of the forced draft, effectively seals the leakage of air through the register and into the furnace. Burners S and 59 may be similarly provided. I have not shown circuit details nor components as their inclusion is presumed and forms no part of my invention. Thus it is obvious that a lock out device in the circuit from the flame failure detector would be provided to allow igniting of the burner, etc.

As is evident from the preceding description, leakage l of air into the furnace through a secured burner is completely eliminated by the introduction at the proper point into the air supply system of an inert gas such as pressurized recirculated flue gas. All secured burners are prevented from overheating by such leakage of the pressurized inert gas as may pass through the closed register. In certain instances it may be desirable to provide for a predetermined amount of leakage of the inert gas through the register to provide for such cooling. Obviously many such changes can be made both in equipment and arrangement without departing from the scope of my invention as set forth in the accompanying claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Burner control apparatus comprising, in combination, a fuel burner, a windbox for supplying air to said burner, an air supply duct connected to said windbox, a first shut-off damper in said duct, an inert gas supply duct connected to said air supply duct between the burner and shut-otf damper, a second shut-off damper in said inert gas supply duct and signal responsive means for closing said first damper and concurrently opening said second damper and means responsive to failure of flame from said burner generating the signal to which said signal responsive means responds.

2. Burner control apparatus comprising, in combination, a fuel burner, a windbox for supplying air to said burner, a register for admitting air to said burner from said windbox, an air supply duct connected to said windbox, a first shut-off damper in said duct, an inert gas supply duct connected to said air supply duct between the register and first shut-off damper, a second shut-off damper in said inert gas supply duct, and signal responsive means for simultaneously closing the air register and first shut-ofl? damper and opening said second shut-off damper and vice versa.

3. The combination of claim 2 including a fuel supply means for the burner having shut-off means and means for operating said shut-off means simultaneously with the closing of the register.

4. The combination of claim 3 wherein the inert gas supply duct is connected to a gas passage for the flue gases exhausted from the furnace.

5. The combination of claim 3 including means responsive to failure of flame from the burner for generating the signal to which said signal responsive means responds.

6. Burner control apparatus comprising, in combination, a burner supplied with fuel and combustion supporting air, a windbox enclosing said burner and supplying combustion air thereto, means within said windbox for shutting off the supply of air to said burner, an air duct connected to said windbox for supplying pressurized combustion air thereto, a damper operatively mounted within said duct thereby providing a means for shutting off the flow of combustion air to said windbox, a flue for carrying away the gases produced by the combustion of fuel at said burner, means for diverting a portion of the gas from said flue, means connected to said diverting means for increasing the pressure of the flue gas over the pressure of the combustion air supplied to said windbox, means responsive to flame failure at said burner for supplying the pressurized flue gas to said windbox upon flame failure and concurrently operating said first named means and said damper to shut ofl? the flow of combustion air to said burner.

7. Burner control apparatus comprising, in combination, a burner supplied with fuel and combustion supporting air, a windbox enclosing said burner and supplying combustion air thereto, an air duct connected to said windbox for supplying combustion air thereto, a first damper operatively mounted within said duct to provide a means for shutting off the flow of combustion air to said burner, a flue for carrying away the gases produced by the combustion of fuel at said 'burner, a flue gas duct for diverting a portion of the flue gas from said flue to said windbox when said first damper shuts off the flow of combustion air, a compressor connected to said flue gas duct for pressurizing the diverted flue gas, a second damper operatively mounted within said flue gas duct for controlling the pressure of the diverted flue gas, means responsive to the pressure of the combustion air and the pressurized flue gas to control the position of said second damper to maintain the pressure of the pressurized flue gas above the pressure of the combustion air and a third damper operatively mounted within said flue gas duct for shutting off the flow of flue gas to said WindboX.

8. Burner control apparatus comprising, in combination, a plurality of burners individually supplied with fuel and combustion supporting air, a plurality of windboxes each enclosing one of said plurality of burners and supplying combustion air thereto, a plurality of air ducts individually connected to said Windboxes for supplying combustion air thereto, a damper for each of said ducts and operatively mounted therein thereby providing a means for shutting off the flow of combustion air to a burner, a flue for carrying away gas produced at said burners by the combustion of fuel thereat, means for diverting a portion of the gas from said flue, means for pressurizing the gas diverted from said flue and a plurality of flue gas ducts individually connected to said windboxes and collectively connected to said pressurizing means for supplying the pressurized flue gas to said windboxes, a shut-off damper in each of said flue gas ducts, a flame failure detector associated with each of said burners, and means under the control of each of said detectors for closing the damper in the air duct and concurrently opening the shut-01f damper in the flue gas duct connected to a burner upon detection of flame failure at the burner by the flame failure detector associated with that burner.

References Cited by the Examiner UNITED STATES PATENTS 2,800,175 7/1957 Sharp 158117.5

3,146,821 9/1964 Wuetig 158-1 FOREIGN PATENTS 1,119,245 4/1956 France.

FREDERICK L. MATTESON, IR., Primary Examiner.

E. G. FAVORS, Assistant Examiner.

Claims (1)

1. BURNER CONTROL APPARATUS COMPRISING, IN COMBINATION, A FUEL BURNER, A WINDBOX FOR SUPPLYING AIR TO SAID BURNER, AN AIR SUPPLY DUCT CONNECTED TO SAID WINDBOX, A FIRST SHUT-OFF DAMPER IN SAID DUCT, AN INERT GAS SUPPLY DUCT CONNECTED TO SAID AIR SUPPLY DUCT BETWEEN THE BURNER AND SHUT-OFF DAMPER, A SECOND SHUT-OFF DAMPER IN SAID INERT GAS SUPPLY DUCT AND SIGNAL RESPONSIVE MEANS FOR CLOSING SAID FIRST DAMPER AND CONCURRENTLY OPENING SAID SECOND DAMPER AND MEANS RESPONSIVE TO FAILURE OF FLAME FROM SAID BURNER GENERATING THE SIGNAL TO WHICH SAID SIGNAL RESPONSIVE MEANS RESPONDS.

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