EP2362146B1

EP2362146B1 - A control method for a pellet and/or biomass combustion apparatus and a pellet and/or biomass combustion apparatus operating according to such a method

Info

Publication number: EP2362146B1
Application number: EP11155550.4A
Authority: EP
Inventors: Alessandro Bertoncello; Stefano Salvatico
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-02-23
Filing date: 2011-02-23
Publication date: 2015-07-15
Anticipated expiration: 2031-02-23
Also published as: IT1398456B1; SI2362146T1; ES2550519T3; ITVI20100042A1; EP2362146A1; HUE027936T2

Description

The present invention concerns a method for controlling and adjusting the operating parameters of a pellet and/or biomass combustion apparatus.
The present invention also concerns a pellet and/or biomass combustion apparatus suited to implement said method.
Different types of combustion apparatuses are known, in which the adjustment of the operating parameters is carried out only in advance, and precisely during testing of the apparatus, establishing, for example, the smoke temperature or the static and dynamic vacuum suitable for ensuring good combustion results.
Substantially, the adjustment is an initial setting based on pre-set parameters. However, when changes take place in the environmental conditions and/or in the combustion process, the operator cannot correct said parameters that were previously set.
The necessary modifications can be carried out only by specialised technical staff that, taking action on the control and programming electronic system, modifies the parameters based on programming logics initially defined by the manufacturer.
In the combustion apparatuses of known type it is therefore rather complex to modify the pre-set operating parameters concerning vacuum inside/at the level of the combustion chamber, smoke temperature and reference ambient temperature when the environmental conditions are affected by changes that make it necessary to modify said values.
The complex procedure required to modify said parameters often leads the user to omit said modifications, also to avoid expenses, which results in the inefficiency of the apparatuses and in increased atmospheric pollution and operating charges.
In order to eliminate the above mentioned drawbacks, combustion apparatuses have been designed that are provided with vacuum sensors, smoke temperature sensors and ambient temperature sensors that during the operation of the combustion apparatus can be managed through a feedback control carried out by means of an electronic unit.
Patent documents regarding this last solution are, for example, patent application WO 2006/120717 A1 or patent application EP 1 219 899 A1 or patent application DE 10 2007 055168 A1 .
According to these patent documents, the type of control that is obtained concerns the individual operating parameters and is carried out through sensor measurements and individual variation curves of said parameters.
In other words, the individual parameters are adjusted via a feedback control of their conformity with the set reference values.
A drawback that is observed in these apparatuses lies in that each parameter is adjusted independently of the others.
Consequently, in these combustion apparatuses the adjustment of vacuum inside/at the level of the combustion chamber as measured by the vacuum sensor is carried out independently of the adjustment of the smoke temperature measured by the smoke temperature sensor and of the ambient temperature measured by the ambient temperature sensor.
This means that the efficiency of the combustion apparatus is not always optimal.
Patent document WO 2006/120717 A1 is about an air-gas regulation system applied to a heating plant with radiant tubes. This regulation system is not applicable to a pellet and/or biomass combustion apparatus.
Patent document DE 10 2007 055168 A1 is about a regulation method of the fuel-comburent mixture according to the water quantity measured at the outlet of the combustion chamber.
Patent document EP 1 219 889 A1 claims a combustion apparatus in which the combustion regulation is made through the regulation of the oxygen quantity using a fan regulating the air flux.
In pellet and/or biomass stoves/boilers it is not possible to vary the oxygen quantity through the variation of the air quantity, because it is necessary to have a combustion with an air excess in order not to block the burner with clinkers and unburnt residues. Clinker and unburnt residues would block the burner reducing the autonomy of pellet and/or biomass stoves/boilers.
The above-mentioned regulation systems for gas stoves/boilers do not function in pellet and/or biomass stoves/boilers. In fact, if there is an oxygen sensor in gas stoves/boilers, it is put directly at the smoke discharge outlet, while in pellet and/or biomass stoves/boilers oxygen sensors are put into decantation chambers.
If the oxygen located in pellet and/or biomass stoves/boilers is measured directly at the smoke discharge outlet, the oxygen sensors would be neutralized by the ashes and by the thin powders produced by the pellet and/or biomass combustion.
Further, the methods used to control the parameters of gas stoves/boilers are different from the parameters used to control pellet and/or biomass stoves/boilers. This is demonstrated by EN 14785, which is a standard specific for pellet and/or biomass stoves/boilers and is different from the standard of gas stoves/boilers.
The object of the present invention is to eliminate the above mentioned drawbacks.
In particular, it is the object of the present invention to provide a method for controlling and adjusting the operating parameters of a pellet and/or biomass combustion apparatus that constitutes an integrated system, that is, a system in which all the operating parameters can be adjusted automatically and are correlated so that modifying one of them means modifying all the others.
It is a further object of the present invention to provide a pellet and/or biomass combustion apparatus that operates according to the above mentioned method.
The objects mentioned above are achieved by the present invention that concerns a method for controlling and adjusting the operating parameters of a pellet and/or biomass combustion apparatus, whose main characteristics are in accordance with the contents of claim 1.
The objects mentioned above are also achieved by a pellet and/or biomass combustion apparatus that is suited to implement the above mentioned method and whose main characteristics are in accordance with claim 9.
Advantageously, the control and adjustment method of the pellet and/or biomass combustion apparatus and the pellet and/or biomass combustion apparatus according to the invention make it possible to implement an integrated system the minimises wastes and enhances the efficiency of the apparatus.
Still advantageously, the increased efficiency of the pellet and/or biomass combustion apparatus according to the invention reduces environmental pollution.
To further advantage, the pellet and/or biomass combustion apparatus according to the invention makes it possible to reduce consumption and atmospheric pollution by recovering the unburnt gases present in the exhaust gases and re-introducing them in the combustion chamber.
The objects and advantages described above will be highlighted in greater detail in the description of a preferred embodiment of the invention that is supplied as an indicative, non-limiting example with reference to the enclosed drawings, wherein:

Figure 1 shows a block diagram illustrating the operation of the pellet and/or biomass combustion apparatus according to the invention;
Figure 2 shows a block diagram of a variant embodiment of the diagram of Figure 1;
Figure 3 shows a schematic view of the pellet and/or biomass combustion apparatus according to the invention;
Figures from 4 to 11 show a series of graphs in a logic sequence that illustrate the control and adjustment method according to the invention suited to adjust the operating parameters of the pellet and/or biomass combustion apparatus according to the invention.

The pellet and/or biomass combustion apparatus of the invention is indicated as a whole by 1 in Figure 1 and by 20 in Figure 2, and comprises:

a combustion chamber 2 fed with a fuel and a comburent;
an exhaust circuit with fan for the forced extraction of smokes connected to the combustion chamber 2;
a plurality of sensors suited to detect the operating conditions of the apparatus 1, 20;
a unit CPU 3.

According to the present invention, the CPU 3 is provided with one or more ports for the input of signals emitted by the sensors, which
are connected to the input ports, and with one or more ports for the output of signals for controlling the means for supplying the fuel-comburent mixture into the combustion chamber 2 and the means for extracting the smokes let out by the combustion chamber 2.
The control carried out by the CPU 3 includes the presence of feedback controls emitted based on a series of curves of correlation with the values measured by the sensors.
In particular, the CPU 3 comprises an electronic unit managed by means of input data processing software.
In particular, the CPU 3 is provided with programmable means for processing and adjusting with feedback the input and output signals according to the above mentioned correlation curves.
The pellet and/or biomass combustion apparatus 1, 20 comprises, as mentioned above, a plurality of sensors for detecting the operating conditions of the pellet and/or biomass combustion apparatus, including the following:

a first sensor 8 for measuring the internal room temperature;
a second sensor 25 for measuring the external room temperature;
a third sensor 6 for measuring the smoke temperature;
a fourth sensor 4 for measuring depression inside/at the level of the combustion chamber 2;
a fifth sensor 21 for measuring the atmospheric pressure.

Regarding depression, it is important to specify that it can be measured at the entrance of the combustion chamber or inside the combustion chamber.
If necessary, it can also be measured at the outlet of the combustion chamber, in which case the measurement will concern pressure and not depression.
However, in all of the three cases the purpose of the measurement is the same.
Regarding the smoke temperature, this can be measured both at the outlet of the combustion chamber and inside the combustion chamber, at the level of the burner.
In particular, the first and the second sensor are temperature probes for the generation of a climatic curve 26.
The third sensor, instead, is a temperature probe for the generation of a fuel supply curve 7.
The fourth and fifth sensors are depression sensors for the generation of a flue gas extraction curve 22.
Always according to Figure 2, the CPU 3 is connected to means for detecting the percentage of oxygen present in the smokes, that comprise a lambda sensor 27 for measuring the smoke emissions and intervene in the processing of the flue gas extraction curve 22 and in the modulation of the by-pass valve 29.
Furthermore, the lambda sensor 27 if necessary activates an electrostatic filter 28 for reducing the particulate matter (the so-called PM10), so as to respect the pre-fixed emission values.
With reference to Figure 1, the pellet and/or biomass combustion apparatus 1 comprises a depression sensor 4 that measures the static and dynamic depression in the combustion smoke exhaust circuit of the stove/boiler and generates a flue gas extraction curve 5 that is obtained based on the input data.
The depression is preferably but not exclusively measured by means of a depression sensor provided with a Venturi pipe.
The output data according to the flue gas extraction curve 5 are processed by the CPU 3 that, in case of deviation from the pre-set values, emits output electric signals that are conveyed to a fan (not illustrated) suited to adjust the quantity of comburent, that is, air.
Always with reference to Figure 1, the pellet and/or biomass combustion apparatus 1 also comprises a sensor 6 for measuring the temperature of the smokes let out by the combustion chamber 2.
The signals of the sensor 6 generate a fuel supply curve 7 that takes in consideration the ratio between the smoke temperature and the quantity of fuel supplied per unit of time.
The output data according to the curve 7 are processed by the CPU 3 that, in case of deviation from the pre-set parameters, emits electric signals suited to adjust the quantity of fuel that is supplied.
The pellet and/or biomass combustion apparatus 1 shown in Figure 1 also comprises an room temperature sensor 8 that measures the temperature in the room to be heated and generates a climatic curve 9.
The output data of the climatic curve 9 are processed by the CPU 3, which also in this case emits electric signals for the adjustment of the quantity of fuel supplied to the stove/boiler through the electric motors that operate the fuel supply unit, or for the adjustment of the comburent air (not illustrated in the figures).
Both types of adjustment take place according to the temperature difference to be compensated for with respect to the pre-set data.
Figure 2 shows a different embodiment of the pellet and/or biomass combustion apparatus according to the invention, indicated now by 20, which differs from the one illustrated in Figure 1 due to the fact that there are further sensors.
In fact, an atmospheric pressure sensor 21 is provided in the room to be heated and connected to the CPU 3, and interacts with the depression sensor 4 described above in order to generate a flue gas extraction curve 22.
A humidity sensor 24 intervenes in the generation of the flue gas extraction curve 22 and of the fuel supply curve 23, and measures the humidity present in the room where the stove/boiler has been installed, considering to what extent the combustion process is affected by the relative humidity.
The pellet and/or biomass combustion apparatus 20 of Figure 2 also comprises an external temperature sensor 25, which measures the temperature of the environment outside the building where the stove/boiler has been installed and calculates the difference between the measured temperature value and the pre-set temperature value, adjusting the quantity of fuel and/or comburent according to the temperature difference to be compensated for.
Furthermore, a motorised by-pass throttle valve 29 is provided, visible in Figure 3, which serves to recycle part of the exhaust smokes containing unburnt substances in the combustion chamber.
From an operational point of view, the pellet and/or biomass combustion apparatus of the invention operates according to the method described here below, illustrated in Figures from 4 to 11 and comprising:

a first step for determining the heating power of the apparatus 1, 20 based on the internal room temperature set and the external room temperature measured;
a second step for determining the number of rpm of the smoke extraction fan motor;
a third step for determining the number of rpm of the fuel supply unit motor;
a fourth step for determining the percentage of oxygen present in the smokes.

All the steps described above are connected to each other and take place simultaneously, continuously over time and through a feedback control.
In particular, as shown in the graph of Figure 4, during the first step the operator sets an initial value of the temperature to be obtained in the room (thermostat temperature), after which it is possible to determine on the x-axis the power modulation coefficient C _m of the pellet and/or biomass combustion apparatus, obtaining it according to a first correlation curve A, which expresses the values of the climatic curve, and based on the value of the external temperature.
The values of the external temperature are indicated on the y-axis in the Cartesian graph of Figure 4.
Each value of the power modulation coefficient defined in the x-axis of the graph of Figure 4 defines in its turn a single curve belonging to the bundle of curves shown in the graph of Figure 5.
The graph of Figure 5 shows on the x-axis the value of the heating power P_t of the pellet and/or biomass combustion apparatus according to the second correlation curve B, selected among the curves of the bundle, representing the power modulation coefficient C_m, and based on the difference ΔT between the set temperature and the temperature of the air/water circulating in the pellet and/or biomass combustion apparatus 1, 20.
The values of the difference between the temperature set and the temperature of the air/water circulating in the pellet and/or biomass combustion apparatus can be read on the y-axis in the Cartesian graph of Figure 5.
The first step, consisting in fact in the determination of power based on the difference in temperature, is thus concluded.
The heating power value obtained from the graph of Figure 5 is then included among the values indicated on the x-axis of the graph of Figure 6, where the second step of the method according to the invention begins.
During the second step the depression p inside/at the level of the combustion chamber is determined according to a third correlation curve C, visible in the graph of Figure 6, and based on the value of the heating power P_t .
The third correlation curve is actually represented by several curves, among which it is possible to identify an optimal depression curve D included between two minimum and maximum depression curves. Successively, with reference to the graph of Figure 7, the number of rpm of the fan motor N_f is determined on the y-axis according to a fourth correlation curve and based on the value of the depression p in Pascal, measured on the x-axis and calculated based on the values obtained from the graph of Figure 6.
The second step intended to determine the heating power according to the optimal rpm is thus concluded.
The third step of the method according to the invention is illustrated in the graphs of Figures 8 and 9.
From the graph of Figure 8 it is possible to obtain the value of the smoke temperature according to a fifth correlation curve E of the smoke temperature T_f and based on the heating power P_t required by the pellet and/or biomass combustion apparatus.
The values of the heating power are indicated on the x-axis of the graph of Figure 8 and are calculated based on the values obtained from the graph of Figure 5.
From the graph of Figure 9 it is possible to obtain, on the y-axis, the number of rpm N_c of the fuel supply unit motor according to a sixth correlation curve F, representing the fuel supply curve, and based on the smoke temperature T_f inside/at the level of the combustion chamber, indicated on the x-axis.
The values of the smoke temperature of the graph of Figure 9 are obtained based on the values obtained from the graph of Figure 8.
The fourth step of the method according to the invention includes the determination of the percentage of oxygen present in the smokes inside/at the level of the combustion chamber and is illustrated in the graphs of Figures 10 and 11.
In normal operating conditions and with reference to the graph of Figure 11, the x-axis shows the difference ΔT_f between the smoke temperature measured and the smoke temperature actually calculated in the graph of Figure 8.
From the graph of Figure 11 it is possible to obtain, on the y-axis, the value of the voltage V_dc to be applied to the motor of the by-pass valve 29.
Said value is obtained on the x-axis of the graph of Figure 10 according to an eighth correlation curve H of the valve motor voltage V_dc and based on the difference ΔT_f between the smoke temperature measured and the smoke temperature actually calculated in the graph of Figure 8.
The value just obtained can be accepted only in the case where there are no excess quantities of oxygen in the exhaust smokes of the pellet and/or biomass combustion apparatus 1, 20.
In the case where, instead, there is an excess quantity of oxygen in the exhaust smokes, the value of the voltage V_dc to be applied to the by-pass valve 29 is obtained from the x-axis of the graph of Figure 10 according to a ninth correlation curve G of the voltage for the regulation of the valve motor and based on the percentage of oxygen O₂% present in the exhaust smokes. The adjustment of the parameters aimed at maintaining the correct percentage of oxygen has priority over all the other adjustments. This means that when an excess quantity of oxygen is detected, first of all it is necessary to pilot the various parameters in order to lower the quantity of oxygen below the required values.
Furthermore, this last adjustment and all the other adjustments described herein are carried out at the same time, in order to maintain the operation of the apparatus 1, 20 under control, so that it always works in optimal conditions. This adjustment is managed by the CPU 3.
All the operation and control logics of the apparatus, including in particular the shapes of the correlation curves, are stored and managed in the CPU 3.
In this regard, all the curves described in these graphs have a linear trend, except for the graph of Figure 9 which shows a broken line with a saw-tooth profile.
It is clear, however, that the graphs illustrated up to now may also have a different shape compared to the one shown, for example they can be represented with curves having their concave or convex part facing towards the x-axis of each graph.
As can be understood from the description provided above, the pellet and/or biomass combustion apparatus and the control and adjustment method of the invention achieve all the set objects.
In particular, with the pellet and/or biomass combustion apparatus according to the invention it is possible to provide for continuous monitoring of the stove/boiler, thus obtaining very high efficiency and reducing costs by approximately 60% compared to the combustion apparatuses of known type. Furthermore, all the operating parameters are maintained under control to reduce environmental pollution.
As a whole, therefore, the invention achieves the object to provide a pellet and/or biomass combustion apparatus and a method for controlling and adjusting its operating parameters that make up an integrated system.
In this regard, all the operating parameters can be adjusted automatically and are correlated, so that modifying one of them means modifying all the others. The pellet and/or biomass combustion apparatus and the control and adjustment method according to the invention can be subjected to modifications that must all be considered protected by the present patent, provided that they fall within the scope of the following claims.
Where technical features mentioned in any claim are followed by reference signs, those reference sings have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the protection of each element identified by way of example by such reference signs.

Claims

A method for controlling and adjusting the operation of a pellet and/or biomass combustion apparatus (1; 20) of the type comprising:
- a combustion chamber (2) with a fuel charge unit operated by a fuel charge motor;

- an exhaust circuit with a fan for the forced extraction of smokes, connected to said combustion chamber (2) and operated by a fan motor;

- a motorized by-pass throttle valve for recirculating part of the exhaust smokes;

- a CPU (3),
the method comprising the following steps:
i) determining the temperature difference (ΔT) between the set temperature and the temperature of the air/water to be heated circulating in said combustion apparatus (1; 20);

ii) determining the heating power (P_t) of said apparatus (1; 20) according to said temperature difference (ΔT) and through a curve (B), selected among a bundle of curves, representing the power modulation coefficient (C_m) and based on said temperature difference (ΔT) between the set temperature and the temperature of the air/water to be heated circulating in said combustion apparatus;

iii) determining the depression (p) inside/at the level of the combustion chamber according to said heating power (P_t) and through a curve (C) which is based on the value of the heating power (P_t);

iv) determining the number of rpm (N_f) of said fan motor for the extraction of smokes, according to said depression (p) and through a curve (D) of the optimal depression which is included between two minimum and maximum depression curves;

v) determining the value of the smoke temperature (T_f) according to the heating power (P_t) and through a curve (E) of the smoke temperature (T_f) based on the heating power (P_t)required by said apparatus (1; 20);

vi) determining the number of rpm (N_c) of the motor of said fuel charge unit according to said smoke temperature (T_f) and through a curve (F) representing the fuel supply curve based on the smoke temperature (T_f) inside/at the level of said combustion chamber;

vii) determining the oxygen percentage (O₂%) present in the smokes;

viii) regulating the oxygen percentage (O₂%) determined in the preceding phase,
characterized in that said oxygen percentage (O₂%) regulation phase is made by regulating the voltage value (V_dc) of the motor of the by-pass valve (29) for the recirculation in the combustion chamber of at least part of the smokes,
said voltage value (V_dc) being determined according to the following alternative ways:
a) if the oxygen percentage value (O₂%) in the smokes is not in excess, said voltage value (V_dc) is obtained according to a curve (H) of the by-pass valve motor voltage value (V_dc) based on the difference of temperature (ΔT_f) between the smoke temperature measured and the smoke temperature actually calculated;
or

b) if the oxygen percentage value (O₂%) in the smokes is in excess, said voltage value (V_dc) is obtained according to a curve (G) of the voltage for the regulation of the valve motor based on the oxygen percentage (O₂%) present in the exhaust smokes;
all said phases of said method being made continuously and automatically through a feedback control made through said CPU (3).
A method according to claim 1), characterized in that said phase of determining the heating power (P_t) comprises the following operations:
- measuring the external room temperature (T_e);

- individuating the power modulation coefficient (C_m) according to said external room temperature and through a climatic curve (A);

- individuating the single curve (B) relating to said power modulation coefficient (C_m) belonging to said bundle of curves of the graphic of the thermal power selection curve;

- determining the heating power (P_t) of said apparatus (1; 20) according to said temperature difference (ΔT) through said single curve (B) relating to said power modulation coefficient (C_m).
A method according to any of the preceding claims, characterized in that said depression curve (C) is represented by a bundle of curves from which said optimal depression curve (D) is obtained.
A method according to any of the preceding claims, characterized in that one or more of said curves (A, B, C, D, E, F) is a straight line represented in a Cartesian graph.
A method according to any of the preceding claims, characterized in that one or more of said curves (A, B, C, D, E, F) has its concave part facing towards the X-axis.
A method according to any of the preceding claims, characterized in that one or more of said curves (A, B, C, D, E, F) has its convex part facing towards the X-axis.
A pellet and/or biomass combustion apparatus (1; 20) of the type comprising:
- a combustion chamber (2) with a fuel charge unit operated by a fuel charge motor;

- an exhaust circuit with a fan for the forced extraction of smokes, connected to said combustion chamber (2) and operated by a fan motor;

- a motorized by-pass throttle valve for recirculating part of the exhaust smokes;

- a CPU (3),
characterized in that the control and the adjustment of said combustion apparatus are carried out through a method according to any of the preceding claims.