EP0375494B1 - Automatic regulation method and apparatus for a discontinuously solid fuel-fired boiler using forced draft, particularly for a wood-fired boiler - Google Patents

Abstract

Automatic regulation method for a solid-fuel boiler (1), with discontinuous firing with fuel and using a forced draft from an electric fan (8, 9), characterised in that use is made of a fan (8, 13), with continuously variable output, regulated on the basis of the simultaneous measurement of the temperature of the water in the boiler and the temperature of the flue gases, with the aid of a suitable regulation. <IMAGE>

Description

The invention relates to solid fuel boilers with discontinuous fuel loading and forced draft by electric fan, and more particularly to boilers of this type operating on wood and commonly called "Turbo wood".

These boilers are distinguished from natural draft boilers in that they are equipped with an electric fan which, most often, blows the air necessary for combustion, or less often sucks combustion fumes.

This type of boiler, whose appearance on the market is relatively recent, see for example the document DE-A-3 402 787, generally has the advantage of appreciably improving the combustion efficiency and allowing the user to operate the boiler at a higher power range. Numerous comparative trials conducted in particular by the French Agency for Energy Management (AFME) confirmed the indisputable advantages brought by the electric fan.

Unfortunately, we have also seen many disadvantages of these boilers, most often related to the control of these same fans which are driven by an electric motor at a single speed, operating therefore all or nothing, or more rarely, at two speeds, either following only a water temperature setpoint given by a thermostat mounted in the central heating water circuit, or for other types only a flue gas temperature setpoint given by a thermostat mounted on the smoke circuit.

In the case of boilers with fluid fuel, or with granular or pulverulent fuel with continuous supply, a room thermostat is used to control the temperature prevailing in the room to be heated by the more or less significant supply of fuel , the combustion air flow being then adapted to the fuel debris, so that the power of the boiler constantly follows the needs of the use. On the contrary, for solid fuel boilers, such as wood boilers, the loading of which is necessarily discontinuous, the power of the boiler is determined either by the temperature of the fumes or by the temperature of the body water. heats up, so that one or the other of the two temperature sensors orders the shutdown or the start of the fan in all nothing, or according to a discrete number of regimes, and this independently of the mass of the fuel in the presence. However, the instantaneous power of the boiler being dependent on the more or less harmonious mixture between the air which passes and the fuel present in the boiler, the All or nothing fan operation results in variations in air flow, which in turn results in changes in boiler output.

This results in great instability of the ambient temperature of the living room and poor quality of combustion. This results in an increase in the level of carbon monoxide in proportions completely incompatible with the standards relating to atmospheric pollution, or in combustion with excess air. In addition, the permanent instability of combustion compromises the life of the boiler to a more or less short term.

Indeed, during periods of cooling of the flame due or operation with excess air, we observe inside the heating body the formation of tars which come from the condensation of the compounds resulting from the combustion of wood and which attack quickly the sheet steel. Conversely, when there is a lack of air, there is the formation of fumes and unburnt gases which are released into the atmosphere as well as the formation of polyaromatic molecules of which we know all the drawbacks.

Despite all the precautions that installers take to try to curb the discomfort and instability of combustion, for example by recycling the return water, by suppressing parasitic air inlets in the boiler and by installing a buffer tank to limit slow speeds, the litigation is numerous and perfectly reflects the current difficulty of properly regulating a solid fuel boiler of the type indicated.

The aim of the invention is to eliminate the above drawbacks, that is to say to control the power of the flame of a solid fuel boiler, and more particularly of a wood boiler, by eliminating the transient regimes and by treating in a particular way the abnormal operating cases which can occur and which affect the quality of combustion of this type of boiler, in order to conform the boiler to the most severe standards while ensuring a correct operation and longevity, compatible with the expectations of users concerned with a level of thermal comfort regular and constant.

• que le ventilateur est à régime variable en continu,
• que la régulation est basée sur la mesure simultanée de la température de l'eau de la chaudière et de la température des fumées sortant de celle-ci, et
• que la régulation comporte, au cours d'une phase de fonctionnement normal, la détermination d'une température théorique des fumées sensiblement proportionnelle à l'écart entre une température de consigne et la température de l'eau mesurée, la détermination d'un régime théorique du ventilateur sensiblement proportionnel à l'écart entre la température théorique des fumées et la température des fumées mesurée, enfin l'adaptation progressive du régime imposé au ventilateur par incrémentation ou décrémentation de la valeur imposée à ce régime selon le signe de l'écart entre le régime théorique calculé et le régime actuel au cours de cycles successifs définis par une temporisation.

The invention resides above all in a method of automatic regulation of a solid fuel boiler, with batch loading of fuel and forced draft by electric fan, distinguished mainly by the fact:

• the fan is continuously variable speed,
• that the regulation is based on the simultaneous measurement of the temperature of the water in the boiler and the temperature of the fumes leaving it, and
• that the regulation includes, during a normal operating phase, the determination of a theoretical flue gas temperature substantially proportional to the difference between a set temperature and the measured water temperature, the determination of a speed theoretical fan substantially proportional to the difference between the theoretical smoke temperature and the measured smoke temperature, finally the gradual adaptation of the speed imposed on the fan by incrementing or decreasing the value imposed on this speed according to the sign of the difference between the theoretical regime calculated and the current regime during successive cycles defined by a time delay.

In fact, the two proportionality coefficients can be variable over time or according to parameters measured to take account of a differential or integral action of the regulation.

• une phase d'allumage ou chargement en combustible, initialisée automatiquement à la mise sous tension et après chaque fermeture de la porte dont l'état d'ouverture est détecté par un contact, cette phase comprenant une incrémentation très progressive du régime du ventilateur à partir d'une valeur initiale définie et au cours de cycles successifs définis par une temporisation, ces cycles provoquant le passage à ladite phase de fonctionnement normal, soit lorsque la température de l'eau dépasse une valeur définie, soit lorsque le régime dépasse une valeur finale définie et après une autre temporisation,
• ladite phase de fonctionnement normal, laquelle prévoit d'une part, lorsque la température des fumées atteint une valeur très basse, d'arrêter complètement le ventilateur, d'autre part, lorsque l'écart entre le régime théorique calculé et le régime actuel est positif et conduit à une incrémentation du régime, de comparer la température des fumées avec celle mise en mémoire au cycle précédent, et de provoquer le passage automatique à une phase de fonctionnement anormal si cette température est en décroissance, et
• ladite phase de fonctionnement anormal prévoyant une décrémentation plus importante du régime et une temporisation plus importante avant de repasser en phase de fonctionnement normal pour un nouvel essai, le nombre d'essais étant limité à une valeur définie.

In a preferred embodiment, the method according to the invention comprises several operating phases which are linked automatically, including

• an ignition phase or fuel loading, initialized automatically when power is applied and after each closing of the door, the opening state of which is detected by a contact, this phase comprising a very gradual incrementation of the fan speed from of a defined initial value and during successive cycles defined by a time delay, these cycles causing the transition to said normal operating phase, either when the water temperature exceeds a defined value, or when the speed exceeds a final value defined and after another timeout,
• said normal operating phase, which provides on the one hand, when the flue gas temperature reaches a very low value, to stop the fan completely, on the other hand, when the difference between the calculated theoretical speed and the current speed is positive and leads to an increase in the speed, to compare the temperature of the fumes with that stored in the previous cycle, and to cause the automatic transition to an abnormal operating phase if this temperature is decreasing, and
• said abnormal operating phase providing for a greater decrement of the speed and a longer time delay before returning to the normal operating phase for a new test, the number of tests being limited to a defined value.

Naturally, the boiler according to the invention comprises the necessary elements, in particular the smoke and water temperature sensors, as well as the door closing detection contact, and also a microprocessor receiving the various data and actuating the fan control with continuous variation of the speed, this microprocessor being programmed for the implementation of the method according to the invention.

• la figure 1 est un schéma d'ensemble de la chaudière;
• la figure 2 représente un bloc diagramme de relation des divers éléments; et
• les figures 3, 4 et 5 représentent les organigrammes des phases principales du procédé.

Other particularities of the invention will appear in the following description of an embodiment and implementation taken as an example and shown in the attached drawing, in which:

• Figure 1 is an overall diagram of the boiler;
• FIG. 2 represents a block diagram of the relationship of the various elements; and
• Figures 3, 4 and 5 show the flowcharts of the main phases of the process.

The boiler 1, represented in FIG. 1, usually comprises an inverted hearth 2 arranged inside the heating body 3 comprising a connection 4 for the hot water departure and a water return 5, this hearth 2 being supplied with fuel from a loading door 6 located in the upper part and on the front of the appliance, while at the rear there is at 7 the flue evacuation pipe by forced draft under the effect of a fan 8 blowing air through an upper distribution plate 9.

According to the invention, the boiler includes both a probe 10 for measuring the temperature of the flue gases in the flue 7, a probe 11 for measuring the temperature of the water in the heating body, a contact 12 for detection of the closed state of the door 6, as well as an electric motor 13 with variable speed for driving the fan 8, this motor being controlled for example by chopped current modulated in power from a housing of control 14 placed on or near the boiler and applying the method according to the invention.

In addition to the essential elements that are the smoke temperature probe 10, the water temperature probe 11 and the door opening contact 12, the boiler can advantageously include a bulb 15 controlling a dilation thermometer 16 placed on the housing 14 available to the user, a safety probe 17, a button 18 for starting and stopping, a button 19 for resetting the safety and a button 20 for setting the temperature of the water, all these elements being available to the user.

The box may also include various other members at the sole disposal of the installer, for example a button 21 for adjusting the minimum smoke temperature, an inverter 22, manual / automatic, making it possible to switch to manual during an intervention. finally, on the electronic card, a multi-pin connection plug 23 to which a test box or any other control and data entry device can be connected.

Found on the block diagram of Figure 2, the door contact 12, the smoke temperature probe 10, the water temperature probe 11, the safety probe 17 which controls the safety block 24, which receives at 25 the mains supply and in turn ensures the general supply 26 when it has been reset by the reset button 19, this box, on the contrary, triggering to cut off the supply under the effect of the probe 17 when the latter ci detects the appearance of an abnormal temperature, finally the automatic / manual reverser 22.

Among the controls accessible by the user, there is also the on-off button 18 and the temperature setpoint button 20. the water. Also, inside the housing, that is to say not accessible to the user, there is button 21 for setting the minimum temperature of the fumes.

We also see at 27 the chopper for controlling the motor 13 of the fan 8.

For the implementation of the method according to the invention, the control unit 14 comprises a microprocessor 28 which receives the various information via the appropriate interfaces, in particular analog / digital converters 29, 30, 31 and 32, for convert the analog values from the measurement interfaces 33 and 34 of the smoke and water temperatures to digital and the set values from 21 and 20. 35 represents the time base input from the network for synchronization of chopper 27, and 36 the command of the self-test.

Naturally, the processor 28 is programmed for the implementation of the method according to the invention, that is to say essentially the determination of the speed Q to be imposed on the fan as a function of the various data, essentially the temperature of the fumes TF, the TE water temperature, minimum smoke temperature setpoint Cmf and CE water temperature setpoint, as well as other constant values defined by the manufacturer or set by the installer.

In the following, it is assumed that the fan speed is controlled from a numerical value Q expressing this speed in arbitrary units, so that the value 100 corresponds to the maximum speed.

We will now examine the operation of the complete device with reference to the flowcharts in Figures 3, 4 and 5.

• le fonctionnement à régime ou débit d'air réduit à une valeur initiale faible définie Q1 durant par exemple 3 minutes,
• l'augmentation progressive du débit d'air jusqu'à une valeur finale dfinie Q2 correspondant au maximum permis pour l'allumage, et ceci par incrémentations successives de la valeur Q au cours de cycles définis par une temporisation de 20 secondes dans l'exemple choisi, et
• le fonctionnement à ce débit d'air constant Q2 durant par exemple 5 minutes, ce temps, ainsi que celui pratiqué précédemment de 3 minutes, étant éventuellement raccourci comme indiqué plus haut si la température de l'eau TE vient à dépasser 90°C.

The program P1 in Figure 3 corresponds to ignition and fuel loading. It is initialized at the time of power-up after reset, or after loading with fuel after closing the loading door, the opening state of which is detected by contact 12. During the course of this operating phase, the TE water temperature is constantly monitored, and as soon as it exceeds 90 ° C, the fan is stopped and we go to the main program P2 of figure 4. On the contrary, as long as this temperature remains below 90 ° C, the program is divided into three successive periods:

• operation at reduced speed or air flow to a defined low initial value Q1 lasting for example 3 minutes,
• progressive increase of the air flow to a final defined value Q2 corresponding to the maximum allowed for ignition, and this by successive increments of the value Q during cycles defined by a time delay of 20 seconds in the example chosen, and
• the operation at this constant air flow Q2 lasting for example 5 minutes, this time, as well as that previously practiced by 3 minutes, possibly being shortened as indicated above if the temperature of the water TE comes to exceed 90 ° C.

It can thus be seen that the regulation according to the invention makes it possible to light the boiler in forced draft, and not in natural draft, which is particularly advantageous. We indeed know that in a forced draft boiler with reverse combustion, the ignition operation is done thanks to an ignition start valve that the invention saves by very gradually metering the combustion air as and as the actual evolution from the ignition to the normal operating phase P2 towards which in any event it ends.

After each fuel loading, we know that the fuel supply tends to cool the store considerably, which has the effect of degrading the combustion by excess air if the regulation does not take this new state into account. We therefore understand the advantage of the regulation according to the invention of metering the combustion air so as to obtain a very gradual increase in the flame to the desired value during normal operation.

During the phase P2 of normal operation, corresponding to FIG. 4, the water temperature TE and the temperature of the fumes TF are continuously read. The objective sought is to avoid all the transitional periods mentioned above by seeking the most regular operation possible. For this, the flame power is continuously adapted to the need programmed by the user.

The exchange surface between the flame and the water of the boiler being constant, the temperature of the fumes TF is taken as an indicator of the power of the flame at an instant. Furthermore, it is considered that the difference between the actual temperature of the water TE and the set temperature of the water CE set by the user expresses the calorie requirement at the same time to satisfy the user.

dans laquelle K1 est un coefficient déterminé expérimentalement et qui est fonction de la géométrie du corps de chauffe de la chaudière et de ses caractéristiques d'échange.In accordance with the invention, a theoretical temperature of the TTF fumes is calculated by the following relation:

$\text{TTF = K1 (CE - TE)}$

in which K1 is a coefficient determined experimentally and which is a function of the geometry of the heating body of the boiler and of its exchange characteristics.

As explained above, this coefficient K1 can in fact be variable over time or according to measured parameters to take account of a differential or integral action of the regulation.

However, if the calculated value TTF is lower than the minimum smoke setpoint Cmf set by the installer, the fixed program TTF = Cmf. Likewise, if TTF is greater than the maximum CMF smoke setpoint programmed by the manufacturer in the microprocessor, the fixed program TTF = CMF.

dans laquelle K2 est un coefficient déterminé expérimentalement et qui peut lui aussi être fixe ou variable dans le temps pour tenir compte de l'importance de l'écart entre TTF et TF.From this value of the theoretical flue gas temperature TTF, the theoretical air flow QT is calculated, i.e. the fan speed required for combustion as a function of the actual flue gas temperature from the following relationship:

$\text{QT = K2 (TTF - TF)}$

in which K2 is a coefficient determined experimentally and which can also be fixed or variable in time to take account of the importance of the difference between TTF and TF.

However, the calculated QT theoretical speed is not suddenly applied to the fan, but on the one hand a minimum speed Qmin and a maximum speed Qmax are fixed, and if QT is less than Qmin, it is fixed at this value, while if QT is greater than Qmax, we set it to this last value, and on the other hand, we modify the variable Q defining the flow rate by progressive incrementation during successive cycles, with a new delay of 20 seconds and a return to the top of phase P2 to restart the measurements and calculations.

It is important to note that in the middle of the unfolding of phase P2, after having measured TF and before calculating QT, we test the value TF, and if it is less than 40 °, we produce the total stop of Boiler.

On the other hand, between the comparison test between QT and Q and the final time delay of 20 seconds, there are three parallel branches, one direct central corresponding to the equality of the two values, the other to the right of the figure corresponding to QT lower than Q, and consequently to a decrementation of Q, and the third on the left, particularly interesting, corresponding to QT higher than Q. In the latter case, we increment Q as it should be, but we compare the temperature of the fumes TF at the temperature of the TFP fumes stored in the previous cycle, and in the case where TF is less than TFP, that is to say in the case where an increase in the air flow leads to a decrease in smoke temperature, we conclude that we are in an abnormal operating phase and we go to phase P3 corresponding to the diagram in FIG. 5.

This phase P3 of abnormal operation, where the temperature of the fumes drops when the air flow increases, generally corresponds to the existence of an excess of air, due either to the formation of a vault, consequently by example of a bad load which does not allow the wood to descend correctly on the hearth, that is to say a lack of fuel.

To manage this new situation, a variable is used which is the number of trials, which is constantly fixed at a determined value, for example 3 in the example chosen, each time the left branch of the organization chart of the Figure 4, that is to say for QT greater than Q, but for normal operation, that is to say when the temperature of the fumes is not decreasing. When this anomaly occurs, we therefore go to phase P3 with the variable number of tests loaded to 3. Phase P3 in Figure 5 therefore begins with a decrementing this variable number of tests followed by a comparison test to the value 0. As long as the number of tests has not reached the value 0, we go through a time delay of 20 seconds before starting phase P2 again for a new try. If, during these successive tests, the roof collapses, the boiler resumes normal operation. It is only if we go back three times through the branch P3 of phase P2 that we arrive at the zero value for the number of tests, which then leads to a larger decrementation of Q, by example of 5, by not going below a minimum value, for example of 25, this decrementation being followed by a time delay, for example of 5 minutes, followed by a significant new decrementation before returning to phase P2 .

In this way, if the abnormal operating phase is perpetuated, either because the roof has not collapsed, or because the fuel runs out, we end up arriving at a smoke temperature below 40 ° in the center of P2, which leads, as we have seen, to a general shutdown of the boiler.

The last flowchart X in FIG. 5 corresponds to an interruption of the program for each opening of the door, which has the effect of stopping the fan (Q = 0) and of a detector if the closing contact of the door is in position closed to return to phase P1. Indeed, the opening of the door normally corresponds to a refueling.

We have been able to verify that the application of the process according to the invention makes it possible to ensure very precise and very stable regulation of a boiler of this type, with variations in water temperature not exceeding more or less 1 ° around of the set point. This operation is therefore very flexible and very safe.

In addition, the regulation can signal operating anomalies and give a complete diagnosis of its operating state, either on the control panel 14 of the boiler, or via an independent test box connected to the socket 23 , which considerably simplifies maintenance.

Claims (7)

1. Method for automatically regulating a solid fuel-fired boiler (1) which is loaded discontinuously with fuel and which has a draught forced by an electric fan (8, 13) which is used in a continuously variable speed, in which the regulation is based on simultaneously measuring the temperature (TE) of the water of the boiler and the temperature (TF) of the smoke, characterized in that the regulation includes, during a normal operational phase (P2), determining a theoretical temperature of (TTF) of the smoke which is substantially proportional (K1) to the difference between a set temperature (CE) and the measured temperature (TE) of the water, determining a theoretical speed of the fan (QT) which is substantially proportional (K2) to the difference between the theoretical temperature (TTF) of the smoke and the measured temperature (TF) of the smoke, and progressively adapting the speed of the fan by incrementing or decrementing the value (Q) imparted to this speed according to the sign of the difference between the theoretical speed calculated (QT) and the actual speed (Q) during successive cycles defined by a time delay.
2. Regulation method according to Claim 1, characterized in that, during the normal operational phase, when the difference between the calculated theoretical speed (QT) and the actual speed (Q) is positive and leads to incrementation of the speed, the temperature (TF) of the smoke is compared with that (TFP) stored in the preceding cycle, and automatic transfer to an abnormal operational phase (P3) is caused if this temperature (TF) is decreasing, and the said abnormal operational phase (P3) causes a larger decrement of the speed (Q) and a larger time delay before returning to the normal operational phase (P2) for a new test, the number of tests being limited to a defined value.
3. Method according to Claim 2, characterized in that the said normal operational phase (P2) provides, when the temperature of the smoke reaches a very low value, for complete shut down of the fan.
4. Regulation method according to any one of the preceding claims, characterized in that it includes, in addition, an ignition or fuel-loading phase, automatically initialized on powering up and after each closure of the fuelling door (6), the state of opening of which is detected by a contact (12), this phase comprising a highly progressive incrementation of the speed (Q) of the fan from a defined initial value (Q1) and, during successive cycles defined by a time delay, these cycles causing transfer to the said normal operational phase (P2), either when the temperature (TE) of the water exceeds a defined value, or when the speed (Q) exceeds a final defined value (Q2) and after another time delay.
5. Solid fuel-fired boiler with intermittent fuelling and forced ventilation, including an electric motor (13) with variable speed for driving a fan (8), a probe (10) for measuring the temperature (TF) of the smoke, and a probe (11) for measuring the temperature (TE) of the water, characterized in that it comprises a contact (12) for determining the state of opening of the fuelling door (6), a member (20) for adjusting the set temperature of the water (CE), and a microprocessor (28) programmed for implementing the method according to any one of the preceding claims.
6. Boiler according to Claim 5, characterized in that it includes, in addition, a safety probe (17), a button (19) for repriming the safety, a button (18) for starting up and a directly read thermometer (15, 16), all these members being available to the user.
7. Boiler according to one of Claims 5 and 6, characterized in that it includes, in addition, adjustment or connection members available to the user, in particular adjustment (21) of the minimum set value (Cmf) of the smoke, a manual or automatic inverter (22) and a multipin plug (23) for connection to a diagnostic appliance.

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