EP0211913B1 - Device for a fire installation - Google Patents

Abstract

The burner (1) has a suction pipe (9) with a blower (16) and a regulation member (10) which varies the cross-section of the suction pipe (9). A flow measuring apparatus (12) provided with a sensor (14) measures the air stream circulating in the suction pipe (9). On one hand it is necessary to supply a predetermined air amount (vo) for an optimum combustion of the fuel and on the other hand the natural chimney draught which determines the air flow rate is subjected to strong variations due to weather conditions which may be so important that in extreme cases the direction of the chimney draft may even be reversed. The sensor (14) is connected to a regulating device (16) which on one hand acts on the member (10) and/or on the control (7) of the blower (16) so as to maintain the optimal air flow independently from atmospheric influences. As a function of those influences and therefore of the natural chimney draugth, the cross-section of the passage of the member (10) is enlarged or reduced by the regulating device (15), or the blower (16) is switched on or off or its rotational speed is modified or its orientation is reversed.

Description

The invention relates to a device for eliminating atmospheric influences on the draft behavior of a chimney of a combustion system, the latter being provided with a burner for a constant supply of liquid or gaseous fuels, an intake duct and a fan connected to the latter for supplying air to the burner is, the blower has a controllable drive and the latter is connected to a control device for its control, and that a control member regulating its flow cross-section and also connected to the control device is provided in the intake duct.

From Patent Abstracts of Japan, Vol. 7, No. 106, (M-213) (1251), 10 May 1983 JP-A-5828921 a firing system is known in which both the cross section of the intake duct and the blower are regulated in order to keep the furnace pressure constant. However, keeping the furnace pressure constant is unusable for domestic combustion systems with their constant fuel supply when strong air turbulence occurs at the chimney outlet mouth and thus often suddenly in the chimney from suction to congestion or vice versa alternating draft changes in the chimney. If a chimney outlet, e.g. in the case of normally extremely turbulent blow-ins in mountain valleys, such that an extreme negative pressure is suddenly generated in the interior of the chimney, the chimney draft increases and the pressure in the combustion chamber of the heating boiler is also suddenly reduced. If one were to immediately increase the pressure in the combustion chamber of the heating boiler by means of a blower in accordance with this prior art, the gas throughput in the chimney and thus the amount of combustion air supplied would be increased further instead of correctly reduced. If, on the other hand, the chimney outlet in the case of falling winds is flown in such a way that an overpressure is generated in the interior of the chimney in a pulsating manner, then the chimney draft which normally prevails may be reduced to zero and the pressure in the combustion chamber of the boiler suddenly increases at the same time. If, according to this state of the art, the pressure in the combustion chamber from the air intake side were to be further reduced in order to keep the furnace pressure constant, then the gas throughput in the chimney and thus also the quantity of combustion air supplied would be reduced even more instead of being necessary in terms of combustion technology in the case of constant fuel supply to a house combustion system, increased, ie there would be a severe sooty burn. Such a regulation is therefore not expedient in combustion plants of the type mentioned at the beginning.

A boiler system with a gasification burner is known from German Offenlegungsschrift 31 25 513, in which the required and required burner output is determined from the outside air temperature and the boiler flow temperature. The air mass flow and the heating oil mass flow are then controlled in a stoichiometric ratio as a function of this burner output, and deviations in the air mass flow from the setpoint are recorded and regulated in the total air flow by means of an air mass flow sensor. To achieve the latter, a valve is arranged between a compressor and the burner in the air supply line, which divides the total air flow according to the corresponding control variables into a gasification air flow and a combustion air flow, both of which are fed to the burner in separate lines.

According to German Offenlegungsschrift 32 02 425, a device for pendulum-free power regulation in combustion systems is also known. This consists of a temperature or pressure-controlled regulation of the angular position of a throttle valve in the combustion air supply system and a regulation of the fuel supply controlled by the air flow setting. The throttle valve is angularly adjusted via one or more temperature or pressure-controlled regulators and the downstream control of the fuel supply is controlled by the angular position of the throttle valve or a probe for measuring the combustion air flow in the supply system. The control variables for the angle setting of the throttle valve (pressure and / or temperature) are taken from the heat-dissipating medium.

The purpose of these known measures is to optimize the combustion in the heating systems or to operate the power control with as little fluctuation as possible. The known regulating and control devices described above require a tremendous amount of equipment, since according to these suggestions both the air flows and the fuel flows are influenced by the respective control variables and have to be constantly coordinated with one another in a stoichiometric ratio by means of a complicated and very expensive electronic computer. An expense of this kind may be justified in industrial plants, but is neither expedient nor usable, for example, for heating systems in residential and residential construction due to the high investment costs and the associated maintenance. On the other hand, it should be borne in mind that the domestic fire contributes a very considerable and by no means negligible part to the generally complained air pollution.

In order to operate a combustion system with high efficiency, the combustion chamber must have a certain optimal amount of air per combustion unit are fed. The amount of air supplied is determined by the chimney draft. This must generate the pressure difference required for the supply of combustion air and removal of the flue gases. As a rule, this pressure difference is not constant, rather it depends to a large extent on the prevailing temperature and wind conditions and often even strongly pulsates. The chimney crowns are flown by winds of different strengths and in different directions. This fact can result in the pressure differential on the chimney being optimally disturbed for the particular combustion system. These disturbances can go so far that the chimney even creates an overpressure in relation to the outside atmosphere. Chimney caps have already been used to counteract these interfering influences. Such chimney caps of the most varied types are generally used when there is a risk of excess pressure forming in the chimney due to the occurrence of falling winds, for example in mountainous regions or in the case of narrow buildings. In addition, they can prevent backflow in various cases even with horizontal wind. This is the case if the boiler room is located in such a way that a negative pressure generated by the wind on the building walls can be impressed on it.

With horizontal wind inflows, pressures occur inside the chimney, which also depend on the design of the chimney head and are generally lower than the undisturbed ambient pressure. While negative pressure remains with rising winds, i.e. wind coming from below, the pressure in the chimney increases with falling winds, which may be the case with larger angles of incidence. leads to overpressure and backflow.

Firing systems with oil or gas burners in residential and residential construction are regulated in such a way that when the burner is switched on, a constant amount of fuel per unit of time is always supplied, but the burner is operated intermittently. With these burners it is not possible to intervene in a regulating manner in the fuel supply line, except that it is opened or closed, i.e. the fuel flow has a free cross-section when switched on, and the line is completely blocked when the burner is switched off. Despite these unfavorable conditions for regulating optimal combustion, it is now the object of the invention to counter the influences resulting from the chimney behavior described above as far as possible in order to achieve optimal combustion, i.e. combustion, regardless of the external pressure and wind conditions in the combustion system with as little pollution as possible, a goal that is also in the interest of the national economy, since it enables the plant to be operated with constant and the highest possible efficiency, which undoubtedly amounts to considerable fuel savings.

This object is achieved in a device of the type mentioned in the invention according to the characterizing part of patent claim 1.

Extensive tests have clearly shown that e.g. in the event of a sudden vacuum in the chimney after an immediately preceding congestion, in which the combustion air had to be introduced into the heating boiler with considerable excess pressure with the aid of the fan, a considerable, also sudden and nevertheless extremely precise reduction of the supply air volume due to the large moment of inertia of the fan can only be achieved with an immediate simultaneous reduction of the blower drive power to the subsequently desired value in combination with a regulating member regulating the flow cross-section, both regulated by a common regulating device depending on the current air flow rate.

The problem to be solved according to the invention in a burner with a constant fuel supply can be solved perfectly with the combination of a speed-controlled fan with a control element regulating the flow cross-section of the intake duct to a constant flow rate value, controlled with the aid of a sensor that senses the current air flow rate in the intake duct. Such a combination of regulating means according to the invention enables a simple, extremely rapid and nevertheless very precise elimination of even a chimney draft that changes rapidly in a pulsating manner. The slow coarse regulation by the blower and the immediately responsive fine regulation by the flow cross-section regulating means is accomplished, and has proven itself excellently in fire-critical areas of application such as mountain valleys, i.e. under all atmospheric conditions influencing the chimney draft, soot-free, i.e. environmentally friendly combustion.

The known systems described at the beginning do not suggest this measure, since they are based on fundamentally different control variables, namely control variables that result directly from the requested heating output (flow temperature of the heating system, outside temperature, pressure), whereas, according to the proposal according to the invention, the requested heating output is the controlled variable as such not directly and directly touched. The measure according to the invention also offers the advantage that an intake duct with the organs and control elements required for regulation and control can be retrofitted as a compact structural unit on conventional and operating burners, since the proposed measures according to the invention do not interfere with the existing one and existing burner system. The large-scale use of the inventive Construction is therefore suitable for contributing a considerable portion to the improvement of the complained air quality. For the sake of completeness, it should only be mentioned that brand-new burners can also be equipped with the control system according to the invention. It is equally important to offer the measure according to the invention on the market as a compact structural unit which can be retrofitted to all conventional burner types with the interposition of a suitable adapter.

The drawing schematically illustrates the invention in connection with an oil burner.

Of the furnace, only the oil burner 1 is shown here with the oil supply line 2, the ignition transformer 3, the ignition electrode 4, the atomizer nozzle 5 and the burner fan 6.

An intake duct 9 having an enlarged inflow opening 8 leads to the burner 1. The inflow opening 8 is expediently equipped with a grille or a flow straightener 17. In this intake duct 9, a cross-section of the exhaust duct, which can be changed, is installed in the manner of an iris diaphragm and can be actuated with the aid of a motor 11. Furthermore, a blower 16 is arranged in this intake duct 9 and can be driven by a controllable motor 7. It is expedient to design the blower 16 so that it can be driven in both directions of rotation, that is to say clockwise and counterclockwise. In the area of the inflow opening there is a flow meter, here designed as an impeller 12. This impeller 12 is loaded by a spiral spring and is, for example, in direct connection with a tap of a potentiometer 14. This potentiometer with its central tap serves as a transmitter for a control device 15, which in turn is in operative connection with the drive motor 7 for the fan 16 and / or with the drive motor 11 for the diaphragm 10.

Other relevant devices can also be used as flow meters here, for example an impeller which is connected to a dynamo loaded with high impedance, the disturbance variable being the voltage generated by the dynamo, which increases with increasing speed. The dynamo can be designed so that the terminal voltage of the dynamo increases linearly with its speed.

A freely flowable measuring nozzle would also be conceivable in connection with a differential pressure measurement in the inflow and outflow area of the nozzle, in which case the directly measurable differential pressure can be used as a disturbance or manipulated variable for the control loop. Instead of an iris diaphragm, as described above, a simple slide could also be used, but such a flow valve makes the flow conditions in the intake duct extremely asymmetrical and very turbulent, which should be avoided in view of the optimization of the device as a whole. Flaps can also be used here.

For a given firing system, the optimal air flow v _o is determined by calculation and / or experiment when there is _no wind. This air flow v _o flowing through the intake duct, the burner, the boiler and the chimney causes the impeller 12 to rotate by a predetermined angle a _o when the orifice 10 is set, which here as b. referred to as. Under these conditions and settings, the combustion process runs optimally, i.e. shows its highest possible efficiency. The control element 10 is in a middle position, the fan 16 is stationary. Under these conditions described above, there is a pressure difference of p _o at the chimney.

If, due to the weather, disturbances act on the chimney, which increase the chimney draft, i.e. increase the pressure difference prevailing at it, the air flow rate also increases, v _{o increases} . This increasing air flow additionally rotates the impeller 12 so that a _{o also} grows. This increase in angle now serves as a disturbance or manipulated variable, which acts on the control loop and which subsequently results in the aperture opening b. reduced by the motor 11 until the optimal air flow rate v. again is achieved. This optimal air flow rate v _o corresponds to the optimal pressure difference p _o at the furnace. If the fan 16 is already running under normal weather conditions in order to maintain the optimum air flow rate v _o , then in this case (increasing air flow rate) the speed of the fan 16 is also reduced via the control device 15. In this case, the aperture 10 and the fan 16 can be subjected to such a control process either simultaneously, individually or in succession.

However, the weather-related disturbances can also cause the chimney draft to decrease, so the optimum air flow rate v _o is reduced. This also reduces the deflection a _{o of} the impeller 12 and this decrease in angle now acts as a disturbance or control variable on the control circuit, with the result that the blower 16 or its drive motor 7 is switched on or the speed of the running blower 16 increases and / or the aperture b. is increased until the air flow rate again reaches the value _Vo at which the pressure difference p _o prevails on the combustion system and on the chimney.

What has been explained here in connection with an oil burner can also be used for gas burners in the same way. In all cases, the fuel is provided with the air quantity necessary for its optimal combustion, irrespective of the pressure conditions at the chimney which are disturbed by environmental influences, at which, thanks to the measures according to the invention, the optimum pressure difference _{Po is} forcibly maintained, so to speak.

For the design of the control loop, conventional devices are used which are available to the skilled person in various embodiments without restricting the invention to a particular type of control; In addition to simple electrical control loops, electronic control loops can also be used. Modern electronics offer an abundance of circuits for such control loops.

In the exemplary embodiment shown and described, the fan 6 in the oil burner 1 serves to atomize the oil emerging from the nozzle 5 and to regulate the air flow rate, an additional fan 16 is provided in the intake duct 9. If oil burners with controllable blowers 6 are offered by the trade, the blower 16 can be saved, the control device then acting directly on the drive motor of the blower 6 of the burner 1.

The device is expediently designed so that at optimal air flow _Vo, the blower 16 stands still, its speed is therefore zero and the blower 16 is only switched on when the air flow drops due to the reduction in the pressure difference at the chimney and / or if the airflow is increased Opening width at the aperture 10, the required air flow can no longer be achieved.

The device according to the invention can be used in combustion plants which are used in continuous operation but also in those which work intermittently. The latter way of working is the usual one, especially with house combustion systems. The control and regulating circuit is then designed such that the chimney is ventilated for the time being when the burner is switched on. Oil is only injected into the combustion chamber and ignited after the ventilation process has been completed. From this point in time, the control device described then begins to operate as described above. In addition, a flap can be provided in the intake duct 9, which releases the flow cross-section of the intake duct 9 when the burner is switched on, but which, as soon as the burner has switched off, closes the intake duct in order to avoid cold air from the chimney when the burner is stopped and switched off flows through and cools it. Such controlled flaps are known for oil and gas burners, for which reason this flap was not shown in the drawing.

If the invention has now been explained above with the aid of an oil burner or a gas burner, it should be mentioned in conclusion that the measure according to the invention can also be used successfully if the combustion system is designed for solid fuels. Then the burner 1 shown in the drawing is missing, the intake duct 9 for the combustion air then opens directly into the combustion chamber of the boiler without the interposition of such a burner.

Thanks to the invention, it is possible, regardless of the external pressure and wind conditions of the firing system, to provide a constant, optimal air quantity for the respective system, which is also in the primary interest of the national economy, since the system is operated with constant and maximum efficiency can be. This also results in considerable fuel savings, which in turn result in a significant reduction in pollutant emissions. For heating systems, this means that once the optimal air ratio Lambda (= 1.0 ₅ --1.1) has been set, perfect combustion is always achieved. This allows full use of the fuel to be achieved. The toxic exhaust gases carbon monoxide and hydrocarbons, as well as soot, which are produced when combustion is incomplete, do not occur and therefore cannot reach the atmosphere. This greatly reduces the environmental impact and makes a very significant contribution to air hygiene and thus to environmental protection.

Claims (1)

1. Apparatus for the elimination of atmospheric influences on the draught behaviour of a chimney of a furnace, the latter being provided with a burner for supplying a constant quantity of liquid or gaseous fuels, an intake channel and a fan connected to the latter for supplying air to the burner, the fan (16) having a regulable drive (7) and the latter being connected to a regulating apparatus (15) to control it, and in that there is provided in the intake channel (9) a regulating member (10, 11) regulating the through-flow cross section of the intake channel and also connected to the regulating apparatus (15), characterized in that the regulating apparatus (15) is connected to a transmitter (14) sensing the present throughput quantity of air in the intake channel (9) and the regulating apparatus (15) is constructed for the purpose of obtaining a constant supply of air to the burner such that, on a decrease in the chimney draught and thus a shortfall in the constant throughput quantity (v_o) of air required for optimum burning, the regulating apparatus actuates the regulating member (10) so as to widen the through-flow cross section and where appropriate switches.on the fan (16) or increases its speed, and on an increase in the chimney intake draught and thus an overstepping of the constant throughput quantity (v_o) of air required for optimum burning the regulating apparatus actuates the regulating member (10) so as to reduce the through-flow cross section and where appropriate switches off the fan (16) or reduces its speed.

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