EP2005066A1

EP2005066A1 - Method for starting a firing device in unknown general conditions

Info

Publication number: EP2005066A1
Application number: EP07703333A
Authority: EP
Inventors: Ulrich Geiger; Martin Geiger; Rudolf Tungl
Original assignee: Ebm Papst Landshut GmbH
Current assignee: Ebm Papst Landshut GmbH
Priority date: 2006-02-14
Filing date: 2007-02-07
Publication date: 2008-12-24
Anticipated expiration: 2027-02-07
Also published as: WO2007093312A1; US8721325B2; EP2005066B1; US20090148798A1; DE102006006964B4; DE102006006964A1; CA2641352A1

Abstract

The invention relates to a method for starting a firing device, in particular for first-time non-ignition of a gas burner, in unknown general conditions, a characteristic curve of a start air coefficient known from empirical calculations, being stored for the firing device in a memory in conjunction with the burner temperature. According to the invention, a calibration of the start profile is carried out. The ratio of opening of the gas valve (w) to the amount of air M<SUB>L</SUB>, required for ignition, is determined in an iterative manner by varying the amount of gas and/or air, and in the event of ignition, the firing device is started and the relevant air coefficient (?)<SUB>IGNITION</SUB> is recorded.

Description

Method for starting a firing device under unknown conditions

The invention relates to a method for starting a firing device, in particular a gas burner, under unknown conditions and in particular at first igniting, wherein for the firing device in a memory from a known empirical investigations characteristic of a starting air ratio depending on the burner temperature is stored.

Gas heaters are used for the preparation of hot water in a boiler, for the provision of heating heat or similar. In different operating phases, different requirements are placed on the device. Specifically, the starting process of the device requires a quick ignition of the burner flame and a subsequent, adapted to the heat demand, power output. Due to the normally irregular use of the gas burner over the day and the night, the starting conditions for the gas burner are mostly unknown. Important parameters for these start conditions are above all the burner temperature, the type of gas, the gas pressure, the ambient pressure of the air and the humidity. The decisive factor for igniting the burner is the starting air ratio, which describes the ratio of the actual amount of air supplied to the burner to the amount of air theoretically required for optimal stoichiometric combustion. To an Op- Excess air operated, ie the setpoint for the air ratio for the hygienically optimal combustion during operation is about 1, 3. Burners ignite in different gas-air conditions depending on the conditions.

The output of a gas burner depends on the regularly changing heat demand. Essentially, the power output is determined by the adjustment of the supply of air and fuel gas and by the set mixing ratio between air and gas. The mixing ratio can be specified, for example, as the ratio of the mass flows or the volume flows of the air and the gas.

DE 100 45 270 C2 discloses a firing device and a method for controlling the firing device with fluctuating fuel quality. In particular, when the gas quality changes, the fuel-air ratio is changed accordingly. In this case, the mixture composition is adjusted for each suitable type of fuel until the desired flame core temperature is reached. In addition, characteristic maps are used for various fuels, from which a new, suitable fuel-air ratio is read out whenever the performance requirements change. A method for starting the burner is not disclosed.

GB 2 270 748 A shows a control system for a gas burner. The regulation takes place here using a temperature measured at the burner surface. Since the surface temperature depends on the flow rate of the air-gas mixture, falls below a certain temperature, the speed of the fan rotor is lowered, whereby the air flow and thus the air-gas ratio is lowered. The starting process of the burner and the associated procedural steps are not dealt with individually.

From AT 411 189 B a method for controlling a gas burner is known, in which the CO concentration in the exhaust gases of the burner flame is detected by an exhaust gas sensor. A certain CO value corresponds to a certain gas-air ratio. Starting from a known, for example experimentally determined, gas-air ratio at a certain CO value, a desired gas-air ratio can be set. For starting, the burner regulates the air-gas mixture according to a standard specification adapted to a certain type of gas. However, it does not take into account the fact that conditions are changing or that the startup procedure fails.

EP 770 824 B1 shows a regulation of the gas-air ratio in the fuel-air mixture by measuring an ionization current which depends on the excess air in the exhaust gases of the burner flame. In stoichiometric combustion, a maximum of the ionization current is known to be measured. Depending on this value, the mixture composition can be optimized. The starting process is carried out by an automatic start, which generates by means of a setpoint generator, a start speed of the blower, in which an ignitable mixture is present. Also ignored is the case of a failed start attempt.

A disadvantage of the last-mentioned methods is that, in order to execute them, it is assumed either that the burners have already been started, or that insufficient starting methods adapted to fixed framework conditions are used. A disclosure integrates in the description the starting process of a burner, solved with a start-up automatic, which uses only the blower as a controlled variable. This is not enough to consider different, unknown framework conditions and to react to non-ignition.

The object of the present invention is to provide a method for starting a firing device under unknown conditions.

This object is achieved in a generic method in that a calibration of the start-up process is carried out in several steps, wherein the necessary for ignition ratio of opening of the gas valve to air quantity is iteratively determined by varying the gas and / or air quantity, and in the case the ignition is started the firing device and the correct air ratio is stored.

According to the invention, in a method according to claim 1, the calibration is carried out in the following steps:

• feeding too lean a fuel-air mixture to the burner, that no ignition can take place;

• steady, slow enrichment of the fuel-air mixture by opening the gas valve during continuous ignition attempts; - A -

• for ignition: calculation of the air ratio (λ) to _DU N _G from the burner temperature using the stored characteristic curve;

«Calculation of the nominal mass flow of the combustion air m _L , _s for the nominal air ratio (λ) _s from the size of the measured actual mass flow and the calculated airflow (λ) zύN _DU N _G at the time of ignition;

• storing the starting air number (X) _Z O _NDUNG for future _starts ;

• Determination of a corridor on the characteristic curve resulting from the calibrations.

When you first commission a gas burner, the general conditions are completely unknown. Both the composition of the gas and the environmental conditions play a crucial role in the start-up and operation of the burner. In order to ensure a safe starting process, it is advantageous according to the invention to carry out a calibration in which the decisive influencing factors are determined and taken into account. However, the starting procedure must always be able to be carried out reliably even after the first startup in everyday operation, depending on the heat requirement. For this purpose, a calibration is also advantageous because in this way it can be responded to different needs situations accordingly. The storage of the air numbers determined during the calibration for the different starts offers the possibility of using these numbers for future starts. This is beneficial in terms of a safe and quick start of the gas burner. An automatic start, as disclosed in the prior art, can not have these advantages, since it must be set exclusively to exactly specific conditions and can not respond to unknown conditions. Calibration is performed by a multi-step procedure. The supply of too lean a fuel-air mixture to the burner and the steady slow enrichment of the gas-air mixture by opening the gas valve brings the great advantage that it can come to any deflagration explosion of an accumulated, unburned gas-air mixture , In principle, it would also be possible to approximate the mixture from a gas-containing, rich to more air-containing, lean mixture until a combustible fuel-air mixture is present at the burner, but such an approach would be extremely disadvantageous in terms of safety. The calculations during the calibration process are easy and fast to execute. During ignition, the air ratio and the target mass flow of the combustion air are calculated with the aid of a characteristic curve which can be interrogated in a memory, so that the burner can be transferred directly into the operating state. The storage of the calculated results has the advantage of a faster start-up in the future.

Furthermore, it is advantageous if the individual results are not only stored, but used to develop a characteristic around which a corridor is determined. This corridor is a crucial tool for every subsequent start-up and operation because it delimits an area in which the burner can be safely started and operated in the various power spectra. This has the great advantage that any malfunctions, which are shown by operation of the gas burner outside the corridor, are detected safely and the burner is switched off after a set period of time for safety reasons. It is also advantageous to carry out the change in the opening of the gas valve by the modulation of a pulse width, by the variation of a voltage or current of a valve coil, or by actuation of a stepping motor of a valve. In this way, the gas valve can quickly and safely realize the required openings.

Furthermore, it is advantageous that an empirically determined characteristic curve of starting air numbers to known framework conditions is stored in a memory for the firing device for calculating the actual starting air ratio. At different burner temperatures, different starting air numbers are pre-determined, which describe the stored characteristic curve. With the aid of the characteristic curve, the actual starting air ratio can simply be calculated during the calibration procedure by measuring the burner temperature.

Further features and advantages of the method according to the invention will become apparent from the following description. Show it:

Fig. 1 is a flowchart of the calibration process;

FIG. 2 shows a characteristic curve which is stored from empirical investigations for the firing device; FIG. Fig. 3 is a graph with a corridor calculated during the calibration process.

Figure 1 shows a flowchart illustrating the individual steps of the calibration process.

The flow chart should be read incrementally from top to bottom according to the arrows shown. Steps mapped to one another are executed one after the other, and steps shown next to one another are executed simultaneously. Each step corresponds to a rectangular box.

At the beginning of the calibration process, gas is mixed with a constant amount of air. The initially resulting fuel-air mixture is deliberately too lean, i. the proportion of gas is too low to be ignited. In this way, an initial situation is ensured, in which there can be no unexpected ignition, which could give rise to an explosion hazard.

By slowly, steadily opening the gas valve at a constant mass air flow, the fuel-air mixture flowing to the burner is greased, i. the ratio of the amount of gas supplied to the amount of air supplied increases. At the same time, the ignition system continuously attempts to ignite it with the continuously gas-containing mixture.

When the unknown ratio necessary for the ignition between gas quantity and air quantity for the respective boundary conditions is reached, the mixture ignites and the gas burner is started. Exactly at this time of ignition, the burner temperature is measured. Using this measured temperature and the stored in the memory characteristic of the relationship between the starting air ratio and the burner temperature, the actual air ratio is calculated at the time of ignition.

The result of this calculated air ratio at the time of ignition, at the corresponding measured burner temperature, is stored, so that the air ratio is available for future starting operations.

Furthermore, the desired mass flow of the air quantity to be supplied is calculated from this air ratio. Then, with a known constant opening of the gas valve, the amount of air supplied can be converted from a measured actual value to a calculated one Setpoint value can be changed so that the setpoint air ratio is reached. The setpoint air ratio is based on the setpoint characteristic which describes the desired ratio of air volume to gas volume or m _{L actual} _ch / m _{L mm} for different heat / power requirements Target characteristic, a corridor is generated that is at least as large / wide that the calculated start air number within this corridor holds the characteristic and the corridor generated are stored in the memory, so that future starts, according to the different heat / power demands , be carried out according to this corridor The previously unknown for the gas burner framework conditions have been converted by the Kalibπerungsvorgang for the following launches in known conditions

The control of a desired air ratio of the calculated starting air ratio can be done by changing the supplied air flow at a constant held Gasoffnung

By forming a corridor above the air mass flow, it is possible to ignite in a parameter range adapted to the heat / power requirement. Firing at high power, although there is only a small heat requirement, much energy was introduced into the heating system Therefore, with low power requirements, a certain small gas opening and a corresponding amount of air can be controlled. In the case of a fast demand for high power, eg for service water operation, the maximum heat / power output is provided by a controlled large opening of the gas valve corresponding amount of air directly to the disposal, without having to approach slowly from a limited Zundleistung the maximum power

Due to the generated corridor, there are also limits to normal operation within which the gas burner is operated. If these limits are exceeded or fallen short of over a certain period of time, an indication of a malfunction is given. This may, for example, be a deviation gas pressure from the allowable inlet pressure range, gas deviation, or malfunction of sensors The gas burner automatically shuts off after a set period of time FIG. 2 shows a detailed sketch of the characteristic stored in a memory for the firing device. This characteristic results from a function of start-air ratio and combustor temperature - f (T Enner _Br) = λ.

Burner temperature is a crucial parameter in terms of the starting air ratio needed to start. From several preliminary tests carried out in advance, a characteristic curve can be developed which determines a starting air ratio as a function of the burner temperature and which is stored in a memory of the firing device. To determine this characteristic, a fuel-air mixture which is too lean is slowly enriched in continuous ignition tests until ignition occurs. The air ratio at the moment of ignition is recorded. By repeating this process at different burner temperatures results from the individual results of the sought characteristic. By storing in a memory, the characteristic curve can be accessed at any time.

FIG. 3 shows a detailed sketch of the characteristic curve generated by the calibration process and the corridor determined for this purpose (shown in dashed lines).

The decisive influencing factors for the mixture formation are the supplied gas quantity m _G and air quantity m _L. The amount of gas m _G is dependent on the opening (w) of the gas valve. In order to ensure hygienic operation, the furnace is operated at an air ratio of about λ = 1, 3. The characteristic curve lies in the diagram shown, depending on the framework slightly shifted towards the top or bottom. In the upper part of the fuel-air mixture is fatter, leaner at the bottom. The corridor is determined around the characteristic curve, which specifies the limits for operation and a safe range for the air ratio for the following starting procedures. The upper limit limits the combustibility of the fuel-air mixture to the rich, the lower limit to the lean range.

Claims

claims

1. A method for starting a firing device, in particular at first non-ignition, in particular a gas burner, under unknown conditions, wherein for the firing device in a memory known from empirical investigations characteristic a starting air ratio depending on the burner temperature is deposited, characterized in that

a) is performed a calibration curve of the starting, wherein the igniter to the necessary ratio of opening of the gas valve (w) amount of air m _L iteratively by varying the gas and / or the amount of air is determined, and

b) in the case of ignition, the firing device is started and the applicable air ratio (λ) _Z _D UNG stored.

2. Method, in particular according to claim 1, characterized in that the calibration is carried out in the following steps:

Supply of an excessively lean fuel-air mixture to the burner, that no ignition can take place,

continuous, slow enrichment of the fuel-air mixture by opening the gas valve (w) and / or reducing the amount of air supplied during continuous ignition tests,

with ignition: calculation of the air ratio (λ) to N _D UN _G from the burner temperature with the aid of a stored characteristic curve,

Calculation of the desired mass flow of the combustion air m _L , s for the desired air ratio (λ _s ) from the variables of the actual mass flow of the combustion air and the calculated air ratio (λ) to N _DU NG at the time of ignition.

Storage of the starting air ratio (λ) _ZUNDU N _G for future _starts

3. The method according to claim 1 or 2, characterized in that by appropriate calibrations, a characteristic curve is formed at which a corridor is determined within or at the limits of the firing device is operated.

4. The method according to claim 3, characterized in that the characteristic curve by the function w = f (m _L ), with w = opening of the gas valve and m _L = air mass, is described.

5. The method according to claim 2, characterized in that the calculation of the desired mass flow of the combustion air m _LS for the desired air ratio (λ _s ) an immediate

Activation of the calculated setpoint operating state by means of the calculated setpoint values is followed.

6. The method according to claim 5, characterized in that the driving of the operating state with respect to the desired values by adjusting the amount of gas and / or air is performed.

7. The method according to claim 5 or 6, characterized in that the process of Ansteuems follows a control of the combustion operation.

8. The method according to claim 3, characterized in that an exceeding of the upper or an undershooting of the lower limit of the corridor is detected.

9. The method according to claim 7, characterized in that an operation of the firing device outside the limits of the corridor, after the lapse of a predetermined period of time, leads to the switching off of the device.

10. The method according to any one of the preceding claims, characterized in that the adjustment of the gas valve opening by the variation of a voltage or a current of a valve spool, the modulation of a pulse width, or by regulating a stepping motor of a valve is performed.

11. A method for igniting a gas-air mixture in known conditions after passing through the method according to one of claims 1 to 3, characterized in that

an empirically determined and stored in a memory for the firing device characteristic is used as start air number (X) _START for the start.

12. firing device, in particular gas burner, characterized in that it is ignited and started by the previous claims.

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