FR2640732A1 - METHOD AND DEVICE FOR AUTOMATIC REGULATION OF A SOLID FUEL BOILER WITH DISCONTINUOUS LOADING AND FORCED DRAFT, IN PARTICULAR A WOOD 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.

Description

Method and device for automatic regulation of a boiler

  solid fuel with batch loading

  and forced draft, in particular from a wood boiler.

  The invention relates to solid fuel boilers with batch loading of fuel and forced draft by electric fan, and more particularly to boilers of this type operating on wood and commonly called "Turbo wood". These boilers differ 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, generally has the advantage of appreciably improving the combustion efficiency and allowing the user to operate the boiler at a greater power range. Numerous comparative trials conducted in

264073?

  by the French Agency for Energy Management (AFME) confirmed the benefits

  indisputable 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, therefore operating 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 flow, so that the power of the boiler constantly follows the needs of the user. 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

264073?

  fan operation - all or nothing causes variations in air flow, which in turn

  changes in boiler power.

  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 lifetime

  of the boiler at a more or less close date.

  In fact, during periods of cooling of the flame due to operation with excess air, the formation of tar is observed inside the heating body, which results from the condensation of compounds resulting from the combustion of wood and which attack quickly the steel sheet. 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 disadvantages.

  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 slowed-down regimes, the litigation is numerous and perfectly reflects the current difficulty in properly regulating a

  solid fuel boiler of the type indicated.

  The object of the invention is to eliminate the preceding drawbacks, that is to say to control the flame power of a solid fuel boiler, and more particularly of a wood boiler, by eliminating the transient and by treating in a particular way the abnormal operating cases which may arise and which affect the combustion quality of this type of boiler, in order to conform the boiler to the most stringent standards while ensuring correct operation and longevity, compatible with the expectations of users concerned with a regular and constant level of thermal comfort. 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: - that the fan is at 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 smoke temperature substantially proportional to the difference between a set temperature and the measured water temperature, determination of a theoretical fan speed 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 increment or decrement of the value imposed on this regime 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

264073?

  or according to parameters measured to take into account a

  differential or integral action of regulation.

  In a preferred embodiment, the method according to the invention comprises several operating phases which are linked automatically, including - an ignition or fueling phase, initialized automatically when the power is turned on and after each closure 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 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 defined final value and after another delay, - said normal operating phase, which provides on the one hand, when the smoke temperature reaches a very low value, stop the fan completely, on the other hand, when the screen t between the calculated theoretical regime and the current regime is positive and leads to an incrementation of the regime, to compare the temperature of the flue gases 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 probes, 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. Other features of the invention

  will appear in the following description of a mode

  of embodiment and implementation taken as an example and shown in the appended drawing, in which: FIG. 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

  flow diagrams of the main phases of the process.

  The boiler 1, shown 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, 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 control unit 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 can also include various other organs 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 device can be connected

  control and input of information.

  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 triggering on the contrary to cut the supply under the effect of the probe 17 when the latter this detects the appearance of an abnormal temperature, finally

the automatic / manual reverser 22.

Among the commands accessible by

  user, there is also the power button

  stop 18 and the water temperature setpoint button 20. Also, inside the case, that is to say not accessible to the user, there is the button 21

  set point for the minimum smoke temperature.

  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 boot 14 includes a microprocessor 28 which receives the various information via the appropriate interfaces, in particular analog / digital converters 29, 31 and 32, for converting the analog values from the measurement interfaces 33 and 34 of the smoke and water temperatures to digital, and the reference values from 21 and 20. represents the input of the time base coming from the network for the synchronization of the 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 defined constant values

  by the manufacturer or adjusted by the installer.

  It is assumed, in the following, that the fan speed is controlled from a numerical value Q expressing this speed in arbitrary unit, such

  so that the value 100 corresponds to the maximum speed.

  We will now examine the operation of the complete system with reference to the flowcharts of the

Figures 3, 4 and 5.

  The program Pl in FIG. 3 corresponds to the ignition and the 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 C, the program breaks down into three successive periods: - operation at reduced speed or air flow to a defined low initial value Q1 lasting for example 3 minutes, - gradual increase in air flow to a defined final value Q2 at 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 - operation at this flow t of constant air 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

  TE water temperature exceeds 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 effective evolution of the ignition towards the normal operating phase P2

  towards which we end up in any event.

  After each loading of fuel, it is known that the supply of fuel tends to cool the store considerably, which has the effect of degrading 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 up to the

  desired value during normal operation.

  During 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. To do this, we continuously adjust the power

  flame if necessary programmed by the user.

  The exchange surface between the flame and the boiler water 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 water temperature TE and the set water temperature CE set by the user expresses the calorie requirement at the same time for

satisfy the user.

  In accordance with the invention, a theoretical temperature of the TTF fumes is calculated by the following relation:

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 its

exchange characteristics.

  As explained above, this coefficient KI can in fact be variable over time or according to parameters measured to take account of an action

  differential or integral regulation.

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

  microprocessor, the fixed program TTF = CMF.

  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:

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

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 the latter 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 for

  repeat 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 fumes TFP 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 rate leads to a decrease in smoke temperature, we conclude that we are in an abnormal operating phase and we pass

  in 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,

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, i.e. for QT greater than Q, but for normal operation, i.e. when the

  smoke temperature 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 decrementation of 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 20-second patch before repeating phase P2 for a new test. 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

return to phase P2.

  In this way, if the abnormal operating phase is perpetuated, either because the roof has not collapsed, or because the fuel is running out, we end up arriving at a smoke temperature below 40 in the center of the P2, which leads, as we have seen, to the 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 = O) and of detecting if the closing contact of the door is in position closed to return to phase P1. Indeed, opening the door

  normally corresponds to refueling.

  We have been able to verify that the application of the method 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 plus or minus 1 around 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 automatic regulation of a boiler (1) with solid fuel, with discontinuous loading of fuel and forced draft by electric fan (8,13), characterized in that - a fan (8,13 is used) ) with continuously variable speed, - that the regulation is based on the simultaneous measurement of the water temperature (TE) of the boiler and the flue gas temperature (TF), and - that the regulation includes, during '' a phase (P2) of normal operation, the determination of a theoretical smoke temperature (TTF) substantially proportional (K1) to the difference between a set temperature (CE) and the measured water temperature (TE) , the determination of a theoretical fan speed (QT) substantially proportional (K2) to the difference between the theoretical smoke temperature (TTF) and the measured smoke temperature (TF), finally the progressive adaptation of the fan speed by increment or decrement tion of the value (Q) imposed on this regime according to the sign of the difference between the calculated theoretical regime (QT) and the current regime (Q) during successive cycles defined by a time delay. 2. A control method according to claim 1, characterized in that during the normal operating phase, when the difference between the calculated theoretical regime (QT) and the current regime (Q) is positive and leads to a incrementing the regime, the temperature of the fumes (TF) is compared with that (TFP) stored in the previous cycle, and the automatic transition to an abnormal operating phase (P3) is caused if this temperature (TF) is decreasing, and said abnormal operating phase (P3) provides for a greater decrementation of the regime (Q) and a greater delay before returning to the normal operating phase (P2) for a new test, the number of tests being limited to one defined value.   3. Method according to claim 2, characterized in that said normal operating phase (P2) provides, when the temperature of the fumes reaches a very low value,   stop the fan completely.   4. Method of regulation according to one   any of the preceding claims, characterized   by the fact that it further comprises an ignition phase or loading with fuel, initialized automatically on power-up and after each closing of the loading door (6), the opening state of which is detected by a contact (12), this phase comprising a very 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 the transition to said phase normal operation (P2), either when the water temperature (TE) exceeds a defined value, or when the speed (Q) exceeds a final value   defined (Q2) and after another time delay.   5. Solid fuel boiler with intermittent loading and forced ventilation, characterized in that it comprises a. variable speed electric motor (13) for driving its fan (8), a probe (10) for measuring the flue gas temperature (TF), a probe (11) for measuring the water temperature ( TE), a contact (12) for determining the opening state of the loading door (6), a member (20) for adjusting the set water temperature (CE) and a microprocessor (28 ) programmed for the implementation of the method according to any one of previous claims.   6. Boiler according to claim 5, characterized in that it further comprises a safety probe (17), a safety reset button (19), a start button (18) and a direct reading thermometer (15,16), all these organs   being available to the user.   7. Boiler according to one of claims 5 and   6, characterized by the fact that it further comprises adjustment or connection members available to the installer, in particular an adjustment (21) of the minimum smoke setpoint (Cmif), an inverter (22) automatic manual and multispindle socket (23)   of a diagnostic device.