Oil Gasification Burner

Abstract

In a burner in which oil is gasified by the heat of the incoming air for combustion, that air is heated upon start up by an electric heater and after the burner is running by heat from the products of combustion. Should the combustion air be inadequately heated during operation a lower limit switch actuates controls to energize the electric heater and simultaneously reduce the amount of air supply by a predetermined increment. This action is repetitious until there is sufficient change thereby caused in the oil/air ratio (due to the decreased air flow) to result in the temperature not dropping below the lower temperature limit. Should the combustion air be excessively heated an upper limit switch actuates controls which shut off the flow of oil and simultaneously increase the amount of air supply by a predetermined increment. When the temperature is reduced to within the normal range, the oil supply turns back on. Again, this action is repetitious until there is sufficient change thereby caused in the oil/air ratio (due to the increased air flow) to result in the temperature not exceeding the upper temperature limit.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to an automatic control system for an oil-gasifying burner, in which fuel oil is sprayed into a gasifying chamber, preheated air is blown into said chamber by means of a blower to form oil gas, which is burned on a burner plate closing the gasifying chamber, the incoming air for combustion being heated by the burning gas, which burner comprises an auxiliary electric heater adapted to be energized by first switch means when a sensor provided in the gasifying chamber indicates that the temperature drops below a lower limit.

Such oil-fired water heater burner provided with a blower must be adjusted at the place of installation to have a predetermined fuel-air ratio. This adjustment at the place of installation is required, e.g., in view of variations in the desired heat load and the local chimney draft or in view of the local atmospheric pressure, which depends on the altitude of the place of installation, or in view of an intended or unintended change of the fuel supply rate. In some areas it is required by law that the efficiency of combustion be checked from time to time in order to ascertain any adverse effect on the combustion by a soiling of the air flow path or the exhaust gas flow path or by a change of the draft conditions. Because such check can be made only in relatively large intervals of time, changes in the draft conditions may result during long periods of time in an incomplete combustion and in a formation of exhaust gases which do not meet the specified requirements.

It is an object of the invention to provide means which, during the combustion, automatically correct for any deviations from the specified values and control the supply of air in response to the set heat load. The corrections affect the air-to-fuel ratio, the formation of soot and the CO content.

The invention is based on the recognition that the combustion can be automatically controlled in response to the gasification temperature because the gasification temperature in the burner installation is a measure of the ratio of fuel to air. If the gasification temperature is automatically controlled, e.g., by a control of the air rate, whereas fuel is supplied at a constant rate, the maintenance of a constant gasification temperature will result in the maintenance of an almost constant fuel-air-ratio. If the air supply rate is reduced for any reason whatever, the air supplied at such reduced rate will be heated to a higher temperature by the exhaust gases during a counterflow movement with reepect to the exhaust gases, the result being that the gasification temperature is increased. If the air rate is increased, the inflowing air will be heated to a lower temperature and the gasification temperature will be decreased.

In a control system for an oil-gasifying burner of the kind defined first hereinbefore, the invention resides in that an air control valve is connected in series with the air flow of the blower and by a servomotor, adapted to be operated in conjunction with temperature limit switch means, the valve is adjustable to effect a two-position control of the gasification chamber temperature by controlling the input oil/air ratio of the burner.

When during a steady-state operation of an arrangement according to the invention the sensor frequently detects a temperature drop below the lower limit so that the auxiliary heater is energized, each of these energizations results also in an energization of the servomotor for a predetermined time so that the air supply rate is reduced by a predetermined amount. This control sequence is repeated until the sensor no longer detects a temperature drop below the lower limit. Also, second switch means are provided, which energize the servomotor for the opposite sense of rotation to increase the air supply rate when the sensor detects a temperature rise above an upper limit.

The first switch means may comprise a thermostat change-over switch controlled by the sensor and which in one switch position energizes a relay for energizing the auxiliary electric heating and also energizing the servomotor by means of a switch which is closed by a timer after a predetermined time, whereas in a second switch position, corresponding to the higher gasification chamber temperature, the change-over switch energizes a self-holding energizing relay for energizing the means for the normal operation of the appliance and for simultaneously triggering the timer. This arrangement ensures that the throttle valve will be readjusted only when, during normal operation after a heating-up period, the temperature drops below the predetermined lower limit whereas such temperature drop will not result in a readjustment during the heating-up period.

The second switch means may comprise a second thermostat change-over switch, which is controlled by the sensor and in a first switch position energizes a solenoid valve, which controls the supply of oil, in a sense to open said valve.

DESCRIPTION OF THE DRAWING

The drawing diagrammatically shows a heater for a hot water-circulating heating system, which heater comprises an oil-gasifying burner according to the invention, together with the associated circuit diagram.

The following disclosure is offered for public dissemination in return for the grant of a patent. Although it is detailed to ensure adequacy and aid understanding, this is not intended to prejudice that purpose of a patent which is to cover each new inventive concept therein no matter how others may later disguise it by variations in form of additions or further improvements.

A heater 1 communicates with a return conduit 2 of a heating circuit. The cooled heating water coming from radiators 4 of the heating circuit is discharged by a pump 3 to a finned body 5. The body 5 is a heat exchanger in which the water is reheated by the products of combustion from a burner 6 of the heater. From the body 5 the hot water is supplied through a forward flow conduit 7 to the radiators 4.

The heater 1 is connected to an electric supply system by electrical terminals 50 and 51 (Mp, R) and is grounded by a terminal 52. To put the heater into operation, a master switch 8 is closed so that the power supply system is connected to a circuit which includes a contact 9 of a controller 10, a temperature limiter 11, a room thermostat 12 (connected to terminals 53 and 54), a forward flow thermostat 13, a flow control switch 14, a lower-limit switch 15 and the solenoid of a contactor 16. Contactor 16 has contacts by which an electric preheater 17 can be energized from switches 8 and 9.

The temperature in a gasification chamber 27 of the oil-gasifying burner is sensed by a sensor 18, which controls a lower-limit switch 15, 15' and an upper-limit switch 25. When the master switch 8 is closed and the electric preheater 17 is energized by the contactor 16, the temperature in the gasification chamber 27 will soon reach the lower limit which is required. Under the control of the sensor 18, the lower-limit switch 15 then opens the circuit to the solenoid of the contactor 16. This de-energizes the preheater 17. It also makes a circuit through its second contact 15' so that a self-holding relay 19 is energized to operate the controller 10. Via an output 10' the controller 10 energizes a motor 20 for driving a blower 21 and an oil pump 22. At the same time, via an output 10" the controller 10 energizes an ignition transformer 23 so that igniting sparks are produced at igniting electrodes 24.

After a prescavenging time, the controller 10, via an output 10'" and the upper-limit switch 25, energizes a solenoid-controlled oil valve 26 so that oil is sprayed into the gasification chamber. The oil then is gasified in the hot air to form oil-gas, which emerges through the plate of burner 6. The emerging oil-gas is ignited by the igniting electrode 24. It burns in a combustion chamber 28. Heat from the hot gases is transferred through the heat exchanger 5 to the circulating water, and the gases then flow through an exhaust hood 29 to the chimney. The hot products of combustion also heat the wall 34 of the combustion chamber.

When the solenoid-controlled oil valve 26 opens to allow an inflow of oil but the oil-gas is not ignited on the plate 6 of the burner after a predetermined time delay, an ionization detector 30 responds and subsequently the contact 9 interrupts the circuit. At the same time a fault lamp 31 is turned on. A fault may be due to the fact, for example, that the supply of oil is exhausted.

The air for combustion delivered by the blower 21 is heated as it flows through concentric annular ducts 32 and 33. As the air is so heated it cools the chamber wall 34 of the combustion chamber 28. The heated air enters the gasification chamber 27 from a conical annular duct 35 partly through openings 36 of the gasification chamber wall 37 and partly through a lower opening 39 in the gasification chamber wall, which is opposite to an oil nozzle 38.

The heat which is delivered by the burning oil-gas to the combustion chamber wall 34 results in a corresponding temperature rise of the air for combustion supplied through the annular ducts 32 and 33. That combustion air will be heated to a larger extend and will result in a higher gasification temperature sensed by the sensor 18 if the rate of combustion air is decreased relative to the rate at which fuel is supplied. It has been found that this automatic control of the gasification temperature sensed by the sensor 18 enables the maintenance of a substantially constant fuel-air ratio.

When the temperature of the forward flow water has reached the predetermined value, the forward flow thermostat 13 opens to shut down the appliance. When the preset room temperature reaches its preset value, the room thermostat 12 also shuts down the appliance. When the water temperature in the heater exceeds its preset value for any reason whatever, the safety thermostat 11, 11' operates to de-energize the heater.

When the heater is put into operation by the switch 8, the electric heater 17 is energized. The gasification temperature in the gasification chamber 27 will be reached soon. Thereafter the sensor 18 causes the lower-limit switch 15 to assume its switch position 15'. The controller 10 is put into operation and after a prescavenging time a timer 43 is energized. After a predetermined time delay the timer closes its contact. During an initial period, the sensor 18 can energize and de-energize the heater 17 by means of the lower-limit switch 15. The switch of the timer 43 closes after this initial period.

When air is then delivered at an undesirably high rate, the air entering the combustion chamber 27 and the lower-limit switch 15 continually energizes and de-energizes the heater 17. Whenever the lower-limit switch 15 assumes the switch position shown in the drawing, a servomotor 41 is energized via the closed contact of the timer 43, the contact of a timer 44 and a contact of the picked-up relay 45. The servomotor 41 adjusts a throttle valve 42 in the air supply duct so as to reduce the rate at which air is drawn into the blower. The timer 44 controls the time for which the servomotor 41 is energized. With switch 43 closed, the timer 44 is energized when the lower-limit switch assumes the lower switch position 15. When energized it closes its contact to re-open it after a predetermined, short time. The switch of solenoid 45 is moved to its lower position as a result of that solenoid being energized. This connects the switch of timer 44 to the line to motor 41 which line controls the motor in valve closing direction. As a result, whenever the heater 17 has been energized by the lower-limit switch 15 and an initial period set at the timer 43 has elapsed, the air rate is reduced by a predetermined fixed amount. This control sequence is repeated until the lower-limit temperature causing a response of the lower-limit switch 15 is reached and maintained at the sensor 18.

When the temperature in the gasification chamber exceeds its upper limit, the upper-limit switch 25 responds to open the circuit to the solenoid-controlled oil valve 26 with the result that the valve closes. The movement of switch 25 to its other contact energizes timer 44. However, the switch of solenoid 45 remains in the illustrated position. Such switching operation causes the servomotor 41 to be energized for the opposite sense of rotation by means of the timer 44 and the upper contact of the relay 45. As a result, the throttle valve 42 in the blower 21 is turned in the opening sense so that the combustion air rate is increased by a predetermined amount (determined by the opening of the switch of timer 44). Because the upper-limit switch 25 shuts off the supply of oil through the solenoid-controlled oil valve 26 at the same time, the gasification temperature will drop below its upper limit in any case. With the drop in temperature the switch 25 returns to its lower position to open the solenoid-controlled oil valve. If the temperature then again rises above the upper limit in spite of the higher air rate, the solenoid-controlled oil valve 26 will be closed yet another time and the air rate will be increased once more by the movement of upper-limit switch 25. This control sequence will be repeated until the temperature no longer rises above its upper limit.

The response time of the upper-limit switch 25 for shutting down the oil supply is within the time delay of the controller 10 so that the latter does not indicate a fault. The controller 10 will indicate a fault, however, when the upper-limit switch 25 responds several times within short intervals.

Claims

I claim:

1. In an oil-gasifying burner apparatus having a gasifying chamber into which oil is sprayed, a combustion chamber having ducts for preheating the air for combustion, an air supply device including said ducts, an electric heater and a blower to deliver heated air to said gasifying chamber, oil supply means to spray oil into said gasifying chamber, and control means including a temperature sensor for shutting off the fuel supply when the temperature rises above an upper limit and for turning on said heater when the temperature is below a lower limit, the improvement comprising:

said air supply device includes valve means for varying amount of air delivered to said gasifying chamber, and motor means connected to said valve means for adjusting the valve means in an opening sense and in a closing sense, said control means being connected to said motor means for, when said burner is operating, moving said valve means in the closing sense when the temperature drops below said lower limit and for moving said valve means in the opening sense when the temperature exceeds the upper limit.

2. In an apparatus as set forth in claim 1, wherein said control means includes a sensor means exposed to the temperature in the gasifying chamber, an upper limit switch means connected to said sensor to be actuated thereby, a lower limit switch means connected to said sensor means to be actuated thereby, a timer including a switch and means connecting the switch to the motor means for operating the motor means in one sense or the other for a period of time determined by the setting of the timer, means connecting the lower limit switch means to the timer and to the electric heater for energizing said electric heater and said motor means when the temperature drops below the lower limit after the burner has been running, and means connecting the upper limit switch means to the timer when the temperature exceeds said upper limit.

3. In an apparatus as set forth in claim 2 including a solenoid control oil valve in said oil supply means, said upper limit switch means being connected to said solenoid control valve to close the valve and thereby shut off the flow of oil when the upper temperature limit is exceeded.

4. In an apparatus as set forth in claim 3, wherein the means connecting the timer switch and the motor includes a relay having two positions, in one of said positions the motor being connected for operation in one sense and in the other of said positions said motor being connected for operation in the other sense.

5. In an apparatus as set forth in claim 2, wherein the means connecting the timer switch and the motor includes a relay having two positions, in one of said positions the motor being connected for operation in one sense and in the other of said positions said motor being connected for operation in the other sense.