EP4058727B1 - Method for controlling the combustion in furnace systems - Google Patents

Description

The invention relates to a method for controlling the combustion of solid fuels in combustion plants, for example in single-room combustion plants or manually fed single-room combustion plants
Various measures are known for improving combustion and emissions performance in single-room combustion systems. Combustion-related, design-related, and control-related measures, as well as integrated technologies based on catalytic and thermal effects, can be used to improve combustion and emissions performance in single-room combustion systems.

The combustion principle in single-room combustion systems plays a major role in combustion and emission behavior. Optimization of combustion and emission behavior can be achieved through automatic feeding, where the fuel throughput and the corresponding combustion air quantity can be precisely and accurately adjusted. Automatic feeding of logs is technically possible, but due to the The framework, application, and operating conditions of single-room combustion systems cannot be implemented. Manual feeding through a lock system without opening the combustion chamber door, thus abruptly cooling the combustion chamber, is technically feasible and can also be implemented in single-room combustion systems. The lock system not only keeps the combustion chamber warm but also stabilizes the pressure conditions there so that no flue gas or pollutant contamination can occur in the installation room, regardless of the pressure and flow conditions in the combustion system. Furthermore, the lock system enables uniform feeding (loading regime), which significantly reduces emissions.

Depending on the type of combustion air supply to the combustion chamber and its flow direction and shape to the fuel, the combustion process (drying, degassing, gasification, combustion of the fuel gas) takes place differently. A combustion process can be described as favorable if it produces a fuel gas with favorable combustion properties and sufficient heat for oxidation. Both high-energy (strong) and low-energy (weak) fuel gases lead to unfavorable combustion with numerous pollutants. For example, supplying combustion air to the lower area of the ember bed leads to uncontrolled gasification, which requires a regulated, precise supply of secondary air. Without an appropriately regulated secondary air supply, incomplete combustion occurs. A better design of the combustion process also includes staging the combustion air, so that not only controlled gasification but also rapid cooling of the active reaction zone can be avoided.

The design and flow-related measures are measures that ensure favorable flow conditions with optimal oxidation conditions in the active reaction zone over a longer period of time during the burnup. During the oxidation, the The shape, volume, and geometry of the combustion chamber and the afterburner chamber with the downstream exhaust flues play a major role. Furthermore, the correct positioning and distribution of the primary and secondary air openings contributes significantly to stabilization and, consequently, to improving combustion quality. An optimal design can be calculated and determined using flow simulation.

Combustion can also be controlled by control engineering measures.

The combustion process in single-room combustion systems is controlled exclusively by regulating the combustion air, which must ensure controlled thermal conversion of the fuel with proper combustion. The control is intended to prevent the combustion process from experiencing either oxygen deficiency or excess oxygen. Furthermore, it is intended to ensure more controlled heat release, thus achieving high heat utilization efficiency with a high level of thermal comfort.

So-called integrated technologies are also known. These are usually installed in the combustion plant upstream of the heat exchanger or heat dissipation system. Their main function is to support the oxidation process. Integrated technologies can be divided into thermal and catalytic processes:
In the catalytic oxidation process, the exhaust gas is fed into the catalytically coated structure (granulate bed, foam structure made of oxide and non-oxide ceramics, honeycomb, wire mesh or wire mesh). The combustible pollutants contained in the exhaust gas, such as carbon monoxide (CO) and hydrocarbons (C _n H _m , VOCs, PAHs), come into contact with the catalytically active surface of the catalyst. In the presence of oxygen, the oxidation reactions can take place through the catalyst at temperatures exceeding 300°C. These pollutants are converted into Substances such as water and carbon dioxide are converted into oxidizing agents, thereby reducing their toxicity. The catalyst is not consumed during the oxidation process. It simply ensures that the reactions take place at a lower temperature (as low as 300°C instead of 500°C).

Catalytic oxidation processes, when used in biomass combustion, have the disadvantage that catalytic poisoning occurs during the combustion of unsuitable fuels due to high levels of undesirable pollutants (such as halogens, sulfur, polymers, tar, soot, and other aerosols). This steadily reduces the catalytic effect and eventually completely eliminates it. Furthermore, the catalytic coating (including the washcoat) is damaged during operation or after several hours of operation due to high thermal and mechanical stress (erosion by dust or high exhaust gas velocities) as well as significant temperature changes (from approximately 250°C to approximately 900°C). It is important to note that part of the catalytic coating and heavy metals such as platinum, rhodium, and palladium are removed over time and can enter the environment via the exhaust gas, causing health and environmental problems [according to Beebe et al. Heterogeneous Catalysis I, Heidelberg 1943 , Janbozorgi et al. Handbook of Combustion, Vol. 1, Weinheim, 2010 ].

• Aleysa, M.; Leistner, Ph.: Verbesserung des Verbrennungs- und Emissionsverhaltens in biomassebetriebenen Einzelraumfeuerungsanlagen durch den Einsatz spezieller Einbauten, Abschlussbericht eines von der Fachagentur Nachwachsende Rohstoffe (FNR) geförderten Projekts, FKZ: 13NR104, Stuttgart 2016, 162 S;
• Aleysa, M., Leistner, Ph.: Low-Emission-Verbrennungssystem (LEVS) für die Verbrennung von festen Brennstoffen in Vergaserkesseln, Abschlussbericht über ein Forschungsprojekt gefördert vom Bundesministerium für Wirtshaft und Energie, FKZ: 03KB093A, Stuttgart 2017, 168 S; und
• Aleysa, M.: Konzeptionelle, konstruktive und regelungstechnische Maßnahmen zur Schadstoffminderung und Effizienzerhöhung von Scheitholzfeuerungen im Praxisbetrieb, Vortrag im 7. Fachkolloquium Maßnahmen und Technologien zur Feinstaubminderung aus Biomassefeuerungen, Stuttgart, 18. Mai 2017.

The internal technology (for thermal oxidation processes) represents a technology developed by the Fraunhofer Institute for Building Physics IBP as part of a project funded by the FNR. The operating principle of the internal technology is based on the provision of favorable oxidation conditions during combustion within a defined internal module. This module stores sufficient energy in the form of heat during combustion and automatically makes it available for thermal oxidation when temperatures during combustion fall below certain limits (exhaust gas temperature < module temperature). Due to its special architecture, the internal module ensures intensive Mixing of the combustible exhaust gas components with the combustion air and extending the active residence time through multiple redirection or swirling of the exhaust gases. The stored energy (heat) is intended to enable the oxidation of unburned components in the exhaust gas during unfavorable operating phases, such as when adding wood, and to lead to a stable combustion process independent of the dynamics of the combustion process. Compared to the technologies currently used for pollutant reduction in small combustion systems, the built-in technology offers a number of technical and conceptual advantages, ensuring its practical feasibility. These advantages include, above all, ensuring safe operation without the need for intensive maintenance (once every two years), longevity (at least 5 years), low specific costs (less than €1.50 per kilowatt of system output), high technical integration capability, technical flexibility with regard to design and operation, and no operating energy requirement. The built-in technology has demonstrated particularly stable performance in both single-room combustion systems and biomass boilers. Detailed results on this technology can be found in: Aleysa, M.; Weclas, M.; Leistner, Ph.: Correlation of the filter-reactor architecture with thermophysical functional conditions for the research and development of a non-catalytic 3D porous filter-reactor system for biomass-fired small combustion plants, final report of a project funded by the German Federal Foundation (DBU), AZ 30550, Stuttgart 2015, 59 p.

• Aleysa, M.; Leistner, Ph.: Improvement of combustion and emission behavior in biomass-fired single-room combustion systems through the use of special internals, final report of a project funded by the Agency for Renewable Resources (FNR), FKZ: 13NR104, Stuttgart 2016, 162 pp.
• Aleysa, M., Leistner, Ph.: Low-Emission Combustion System (LEVS) for the combustion of solid fuels in Gasification boilers, final report on a research project funded by the Federal Ministry of Economics and Energy, FKZ: 03KB093A, Stuttgart 2017, 168 p.; and
• Aleysa, M.: Conceptual, constructive, and control-related measures for pollutant reduction and efficiency improvement of log-fired combustion systems in practical operation, presentation at the 7th Expert Colloquium on Measures and Technologies for Particulate Matter Reduction from Biomass Combustion Systems, Stuttgart, May 18, 2017.

Combustion control of manually fired single-room combustion systems is a current topic requiring further research. Controlling the combustion process in such combustion systems is very difficult due to their primitive design and the non-automatable fuel feeding, and requires the development of novel control philosophies.

The initial situation for the use of controllers in single-room heating systems is presented here from a normative, technical and sales perspective, which are of great importance for the successful development and implementation of controllers in practice.

To date, there are no normative regulations for the testing of manually fired single-room combustion systems with controllers in accordance with DIN EN 13240, DIN EN 13229, DIN EN 15250, etc. For the development of the control system, the parent procedure or the EC Machinery Directive 2006/42/EC will be used first. The approval of single-room combustion systems with controllers can be carried out in testing laboratories such as the Test Laboratory for Fireplaces and Flue Gas Systems of the Fraunhofer Institute for Building Physics IBP, which have flexible accreditation in the field of fireplaces. Within the framework of flexible accreditation (Category II), the testing laboratories are authorized to develop new test procedures and offer them to manufacturers without any further coordination with the German Accreditation Body (DAkkS). It should be noted that the The basis for the normative regulation of the use of controllers in single-room combustion systems is currently being developed and is to be taken into account in the new series of the DIN EN 16510 standard.

From a technical perspective, the implementation of the control system in single-room combustion systems is feasible. The safety-related application and framework conditions still need to be determined. To achieve high practical feasibility, concepts for a uniform combustion air supply should be developed that can be used regardless of the construction and design of the single-room combustion systems. Individual controller developments are not cost-effective or, for many medium-sized and small companies, cannot afford them.

The integration of controllers in manually operated single-room heating systems leads to a corresponding increase in acquisition costs and requires a new warranty concept. For large numbers of single-room heating systems, controllers prone to failure lead to adverse economic consequences. The use of sensitive sensors such as lambda sensors should therefore be avoided.

A key consideration for controllers is the need for a power supply. The dependence of manually operated single-room heating systems on electricity has so far been undesirable for both manufacturers and users. Therefore, for marketing reasons, such fireplaces should be independent of electricity or supply themselves with the necessary electricity. Current technology offers two technical options. The first option generates electricity (up to 250 watts) using thermal energy (thermoelectrics), while the second option uses solar panels. Both options require a storage unit. When using lambda sensors or similar sensors with high power consumption, the use of household electricity is unavoidable.

The EP 2 208 938 A2 discloses measuring the ember bed temperature, the exhaust gas temperature and the residual oxygen in the exhaust gas and then regulating primary and secondary combustion air by a control module depending on the measured values.

From the US 2007/0100502 A1 It is known to measure combustion emissions and influence combustion using predictive models. This allows the selection of fuels from several options that can provide the current heat demand most cost-effectively.

The EP 0 624 756 A1 shows the measurement of the exhaust gas temperature and the control of the combustion so that a specified target value of the exhaust gas temperature is reached and maintained.

Based on the prior art, the invention is therefore based on the object of providing a method for controlling combustion in a single-room combustion system and a device therefor, which does not have the disadvantages of the prior art and with which, in particular, a safe and sustainable reduction of pollutant emissions, heat production suitable for mining and an increase in efficiency can be achieved.

The object is achieved according to the invention by a method according to claim 1. Advantageous developments of the invention can be found in the subclaims.

According to the invention, a method for controlling the combustion of solid fuels in combustion plants, for example single-room combustion plants, such as manually fed single-room combustion plants, is proposed, which is characterized in that an oxygen co-value is determined from the temperature in a combustion chamber area and/or in the exhaust gas flues of the combustion plant and possibly in the exhaust gas as well as via an energy balance of the combustion process in the combustion plant, the combustion air and the exhaust gas, with which the primary and secondary combustion air flows and thus the thermal Performance and combustion quality can be regulated. This regulation can be done quickly.

In this context, an oxygen coefficient is to be defined as a value that provides direct information about the oxygen content in the active oxidation zone or the oxygen requirement for proper combustion.

When measuring temperature, the earlier and further away from the radiation zone the temperature is measured, the more accurate and reproducible the oxygen value calculation will be. The optimal temperature measurement area for control purposes is the first flue after the flue baffle plate in the combustion chamber. This reduces the influence of the ember bed's heat radiation on the temperature measurement and protects the temperature sensors from thermal stress, especially when using unsuitable fuels.

The control concept is technically designed to serve as a cross-manufacturer standard application or a universal standard solution. It can therefore be used not only for new but also for existing single-room heating systems with reasonable effort.

The control principle and function of the method according to the invention can be illustrated as follows: For the successful development of a universally applicable control system, the combustion process has a standardized combustion air supply (primary (SSL-PL + RL_PL) + secondary air SL).

In particular, the method according to the invention achieves a safe and sustainable reduction of pollutant emissions, an increase in the efficiency of the thermal conversion of the fuel, and an improvement in the efficiency through demand-oriented heat production by permanently monitoring the ambient temperature: By controlling the combustion process, low-pollutant and efficient combustion is ensured through a more precise supply of combustion air. Furthermore, by presenting and Operational monitoring allows operators to digitally explain optimal operation of the combustion system in an intuitive and simple way, and combustion quality can be detected and evaluated. The optimal operation of the combustion system is determined by evaluating combustion quality thanks to the intelligent control system. It is possible to collect statistical data and evaluate the functionality of the combustion systems in practice.

The method according to the invention is based on an energy balance method. This involves comparisons of the energies of the components before and after combustion. A detailed description follows below. In contrast to the controllers according to the prior art (see above), robust temperature sensors can be used in the combustion chamber area and, if applicable, in the exhaust gas system. With these sensors, an oxygen signal and thus an oxygen coefficient can be generated via an energy balance in the combustion chamber with the aid of parameterizable algorithms. This signal can be used for rapid/immediate control of the combustion process. For the method according to the invention, it is advantageous to record the temperatures in the combustion chamber area and/or in the first exhaust gas flue of the first exhaust gas baffle plate at at least one point for the energy balance and in the installation room for demand-oriented heat production in order to increase utilization efficiency and to use this for control purposes.

In addition, the signals generated by the temperature sensor can be used to generate a virtual signal (the so-called emissions reference value: ERW signal) using additional intelligent algorithms, which is used to evaluate operation. The integral and differential development of the ERW value over time describes a process behavior that can be used to draw conclusions about combustion quality and the causes of both negative and positive cases.

In one embodiment, the temperature in the combustion chamber can be measured at at least one, for example two different locations. In another embodiment, the The temperature in the combustion chamber and, if necessary, the temperature in the flue gas can also be measured at two locations. The temperature sensors mentioned above can be used for these measurements. This makes it possible to determine the temperatures particularly reliably.

In one embodiment, the combustion is controlled by supplying primary air (which may include or consist of primary air from the grate air and primary air from the window purge air (PL = RL-PL + SSL-PL)) and/or by supplying secondary air.

The regulation of primary air, such as grate air and/or glass purge air, can be adjusted in relation to the desired combustion output or to set favorable temperatures in the combustion chamber area for efficient and low-emission combustion. The amount of primary air supplied to the combustion process determines the intensity of the thermal conversion of the fuel and thus the thermal output of the combustion system. When adjusting the primary air, the heat requirement of the installation room can also be taken into account and the primary air adjusted accordingly, allowing heat to be produced according to demand. Consequently, the heat can be not only produced but also used efficiently. Grate air can be supplied in addition to the glass purge air if the latter is insufficient for combustion, such as when burning damp or very thick logs or when burning coal.

In one embodiment, the secondary air can be supplied in such a way that the oxygen content in the combustion chamber area is as close to a favorable range as possible, such as approximately 7 vol.% to approximately 10 vol.%, for example, approximately 8 vol.% to approximately 9 vol.% for optimal post-oxidation. The virtual oxygen signal can be used for control, which can be generated every second by the algorithms based on the measured temperatures.

The advantages of temperature-based control include not only low production costs and longevity, but also the parameterizable algorithms, which allow for easy programming adjustments and universal use of the controller without any software changes. The parameterization factors take all relevant process specifications into account.

The following is a detailed description of the energy balance method for determining the oxygen surplus in the combustion chamber area as well as the parameterizable algorithm:
A combustion can be represented schematically as follows:

C + O ₂ -> CO ₂ + heat

This process produces exhaust gases. Heat losses may also occur. Under adiabatic conditions, these losses are zero.

The fuel can be described as follows: $${\dot{\mathrm{m}}}_{\mathrm{A}}\times {\mathrm{H}}_{\mathrm{u}}+{\dot{\mathrm{m}}}_{\mathrm{B}}\times {\mathrm{c}}_{\mathrm{B}}\times {\vartheta }_{\mathrm{L}}$$

The combustion air can be represented as follows: $${\dot{V}}_L\times c_{P,L}\times {\vartheta }_L$$

The exhaust gas can be represented by the following formula: $${\dot{V}}_R\times c_{P,R}\times {\vartheta }_R$$

A simplified energy balance for a combustion process is given above. The energy supplied to the combustion process via the fuel is equal to the energy generated during thermal conversion and carried as heat via the exhaust gas. Adiabatic means that the thermal conversion occurs without any heat loss. This assumption results in Formula 1: $${\dot{m}}_A\times H_u+{\dot{V}}_L\times c_{P,L}\times {\vartheta }_L={\dot{V}}_R\times c_{P,R}\times {\vartheta }_R$$

Where:
ṁ _A : fuel mass flow [kg/s], H _u : calorific value of the fuel, V̇ _L : specific combustion air quantity [Nm ³ /kg fuel], ϑ _L : temperature of the combustion air, V̇ _R : specific flue gas quantity [Nm ³ /kg], c _P,L : specific heat capacity of the air under constant pressure, c _P,R : specific heat capacity of the flue gas under constant pressure, ϑ _R : flue gas or combustion chamber temperature after completion of combustion, c _B : specific heat capacity of the fuel, ϑ _m : fuel temperature during feeding.

The combustion chamber or exhaust gas temperature ϑ _v described in formula 1 represents the maximum temperature that can be achieved in the combustion chamber area during the thermal conversion or combustion of the fuel, which is produced under adiabatic conditions or without any heat losses and with the supply of stoichiometric combustion air quantity (lambda: 1).

The energy transferred with the combustion air and fuel is very small compared to the energy produced during combustion and can be neglected. This means that Formula 1 can be reduced to the following form: $$\begin{array}{l}{\dot{m}}_A\times H_u={\dot{V}}_R\times c_{P,R}\times {\vartheta }_R\\ \mathrm{oder}\mathrm{für}\mathrm{ein}\mathrm{Kilogramm}\mathrm{Brennstoff}\mathrm{gilt}:\\ H_u=V_R\times c_{P,R}\times {\vartheta }_R\end{array}$$

The specific exhaust gas quantity V _R [Nm ³ /kg fuel] is calculated from formula 3: $$V_R=V_{R,\mathit{min}}+\left(\mathrm{\lambda }-1\right)\times L_{\mathit{min}}$$

Inserting formula 3 into formula 2 results in formula 4: $$H_u=c_{P,R}\times {\vartheta }_R\times \left[V_{R,\mathit{min}}+\left(\mathrm{\lambda }-1\right)\times L_{\mathit{min}}\right]$$

The specific minimum flue gas quantity V _R,min and the minimum specific stoichiometric combustion air quantity L _min can be calculated approximately according to formula 5 and formula 6 or according to the Rosin-Fehling approximations: $$L_{\mathit{min}}=0,241\times H_u/1.000+0,5\left[{\mathit{Nm}}^3/\mathit{kg}\right]$$ $$V_{R,\mathit{min}}=0,217\times H_u/1.000+1,67\left[{\mathit{Nm}}^3/\mathit{kg}\right]$$

The calculation in formula 5 can also be done using the elemental composition of the fuel.

Inserting formula 5 and formula 6 into formula 3 results in formula 7 for calculating the specific exhaust gas quantity [Nm ³ /kg fuel]: $$V_R=0,217\ast H_u/1.000+1,67+\left(\mathrm{\lambda }-1\right)\times \left[\left(0,241\ast H_u\right)/1.000+0,5\right]$$

When formula 4 is transcribed to lambda, formula 8 is used to determine lambda or the excess air number: $$\mathrm{\lambda }=H_u/\left[c_{P,R}\times {\vartheta }_R\times L_{\mathit{min}}\right]-V_{R,\mathit{min}}/L_{\mathit{min}}+1$$

The specific heat capacity c _P,R of the exhaust gas depends on the exhaust gas temperature and is approximately calculated from formula 9: $$c_{P,R}=0,995+0,0002\times {\vartheta }_R$$

When Formula 5, Formula 6 and Formula 9 are used in Formula 8, the result is Formula 10 for determining lambda or the excess air number: λ = H _u /[[0.995 + 0.0002 × ϑ _R ] × ϑ _R × [0.241 × H _u / 1,000 + 0.5 ]] Formula - [0.217 × H _u /1,000 + 1.67] / [0.241 × H _u / 1,000 + 0.5] + 1 10

The combustion air supply can be controlled directly by the oxygen coefficient. Determining or calculating the oxygen excess or oxygen coefficient is not mandatory in this case.

Lambda is a function of, among others, H _u , K _B , K _F and K _S : $$\mathrm{\lambda }=\mathrm{f}\left({\mathrm{H}}_{\mathrm{u}},{\mathrm{K}}_{\mathrm{B}},{\mathrm{K}}_{\mathrm{F}}\mathrm{und}{\mathrm{K}}_{\mathrm{S}},{\mathrm{L}}_{\min },{\mathrm{V}}_{\mathrm{r},\min }\right)$$ where:
L _min : the minimum amount of air required for stoichiometric combustion and:
V _{r, min} : the minimum flue gas or off-gas quantity produced during stoichiometric combustion or at lambda = 1. L _min and V _{r, min} depend on the fuel properties, especially the elemental composition, and are calculated directly from them.

• K_B: Korrekturfaktor des Brennstoffs. Dieser Faktor berücksichtigt die Abweichung des eingesetzten Brennstoffs von dem Idealbrennstoff.
• k_F: Korrekturfaktor zur Hochrechnung der bei der Verbrennung existierten nicht adiabatischen Energieumwandlungsbedienungen zu adiabatischen Energieumwandlungsbedienungen. Der Faktor kF berücksichtigt also die thermischen Verluste durch die Feuerstätte bis zur Temperatur Messstelle im Feuerraumbereich. k_S berücksichtigt das Verhältnis: Primärluft (SSL-PL)/Sekundärluft (SSL-SL), welches sich aus der Scheibenspülluft einstellt und in der Regel von der Höhe der Sichtscheibe H_s abhängt. Hier gilt, je höher die Sichtscheibe der Feuerstätte bzw. H_s ist, umso mehr kann die Scheibenspülluft als Primärluft wirken. In der Regel nimmt k_S einen Wert zwischen 0,93 und 1,07 und wird in der Berechnungsgleichung des Sauerstoffs und nicht von Lambda wie folgt in der Gleichung eingesetzt: $$\mathrm{oder}\mathrm{Sauerstoffbeiwert}=\left(21*\mathrm{\lambda }*{\mathrm{k}}_{\mathrm{s}}-21\right)/\mathrm{\lambda }*{\mathrm{k}}_{\mathrm{s}}$$

Lambda (after integrating the correction factors K _B , K _F and K _{S ,} Lambda can be called the lambda coefficient) is a function of three correction factors _{k B} , k _F and k _s :

• K _B : Fuel correction factor. This factor takes into account the deviation of the fuel used from the ideal fuel.
• k _F : Correction factor for extrapolating the non-adiabatic energy conversion conditions existing during combustion to adiabatic energy conversion conditions. The factor k F therefore takes into account the thermal losses through the fireplace up to the temperature measuring point in the combustion chamber area. k _S takes into account the ratio: primary air (SSL-PL) / secondary air (SSL-SL), which is established from the pane purge air and generally depends on the height of the viewing pane H _s . Here, the higher the viewing pane of the fireplace or H _s , the more the window purge air can act as primary air. Typically, k _S takes a value between 0.93 and 1.07 and is used in the oxygen calculation equation, not lambda, as follows: $$\mathrm{oder}\mathrm{Sauerstoffbeiwert}=\left(21*\mathrm{\lambda }*{\mathrm{k}}_{\mathrm{s}}-21\right)/\mathrm{\lambda }*{\mathrm{k}}_{\mathrm{s}}$$

It should be noted that the calculation presented above can be converted to the _CO2 value. The combustion-related relationship between _CO2 and _O2 is derived from the following formula:

CO ₂ = CO _2max - O ₂

CO _2max : 19 vol.% to 21 vol.% (depending on the carbon content of the fuel)

• k_b: y = f (x) [x_min = 500, x_max = 1000, y_min = 0,75, y_max = 1,2]
• k_f: y = f (x) [x_min = 50, x_max = 1000, y_min = 1, 0, y_max = 2,5]
• k_s: y = f(x) [x_min = <20, x_max = >60, y_min < 0,93, y_max = 1,07]

The correction factors k _f , k _{b ,} and k _s are explained in more detail below. The specific values are not fixed; they can be calculated using the following mathematical functions:

• k _b : y = f (x) [x _min = 500, x _max = 1000, y _min = 0.75, y _max = 1.2]
• k _f : y = f (x) [x _min = 50, x _max = 1000, y _min = 1, 0, y _max = 2.5]
• k _s : y = f(x) [x _min = <20, x _max = >60, y _min < 0.93, y _max = 1.07]

The calculations or factors for the mathematical function are determined by the system limits (maximum achievable temperature during real, proper combustion, temperature trends and changes during operation).

A further explanation of these correction factors is provided below. Non-adiabatic combustion conditions in the furnace can be taken into account using the correction factor k _F :
During combustion in fireplaces, heat losses occur due to the heat dissipation through the fireplace into the room, and therefore no adiabatic conditions exist. To adjust the non-adiabatic to adiabatic conditions, the correction factor k _F is defined, which calculates the heat dissipation. (unwanted heat losses) through the fireplace during the thermal conversion of fuel are taken into account. Depending on the type of single-room combustion system and operating condition, this factor can have a value between one and four. This value is determined by a function. The greater the heat emission or heat losses in the combustion chamber area (from the flame zone to the end of the post-oxidation chamber) before oxidation is complete, the higher the value of this factor.

The functional parameters of the factor _kF can, for example, be automatically determined in the software of a control unit by simply entering the technical data of the fireplace type. The size (area and height) of the combustion chamber, the fireplace lining, the size and type of glazing of the combustion chamber door, etc., play a crucial role here.

Furthermore, the type and properties of the fuel as well as the quality of the condition can be taken into account by the correction factor k _B as follows:
The correction factor k _B takes into account the variation in fuel properties. The value of this factor varies and is calculated during combustion by an integrated function analogous to the factor k _F , for example in an appropriately programmed control device, and changed in the control algorithms. The function of the correction factor k _F is based on the combustion behavior or the changes in temperature over time in the combustion chamber area (dϑ _F /dt). In large order, the faster the combustion chamber temperature rises, the higher the value of the factor k _B . Furthermore, the slower the combustion chamber temperature rises, the lower the value of the factor k _B . k _B can have values from 0.80 to 1.2. The factors k _F and k _B are also dependent on each other. This dependency is also determined and taken into account, for example by being integrated into the software of a control device.

Furthermore, the quality of the operation of the fireplace can be taken into account by the correction factor k _q as described below:
The factor k _q plays only a minor role in regulating the combustion air supply and is not relevant for calculating the excess oxygen in the combustion chamber. The values of this factor are variable and result from an integral calculation or temporal change in the combustion chamber temperature with respect to a specific combustion operating point (dϑ _F /dt)/dτ), where τ describes a point in time or a time range from which or in which the evaluation of the combustion chamber temperature change dϑ _F /dt takes place. In contrast to the factor k _B , which exclusively takes the energy content of the fuel into account, the factor k _q provides direct conclusions about the feeding regime (fuel quantity, number of logs fed, fineness of the fuel, etc.).

According to the consideration introduced above and when using the correction factors defined above or an average value of the lower calorific value of 17,000 [kJ/kg], formula 11 results, with which the excess air factor can be calculated parameterized by the factors k _F and k _B or by the temperature measurement in the combustion chamber area. $$\mathrm{\lambda }=1+\left[17.000\times k_B/\left[\left[\begin{array}{l}0,995\\ +0,0002\times {\vartheta }_R\times k_F\end{array}\right]\times {\vartheta }_R\times k_F\times \left[\begin{array}{l}0,241\times 17.000\times k_B\\ /1.000\end{array}\right]+0,5\right]\right]-\left[\begin{array}{l}0,217\times H_u\times k_B/1.000\\ +1,67\end{array}\right]/\left.\left[0,241\times H_u\times k_B/1.000+0,5\right]\right]$$

The excess oxygen in the combustion chamber area is calculated from the formula 12 Oxygen in the combustion chamber area: $${\mathrm{O}}_2=\left(21*\lambda -21\right)/\mathrm{\lambda }$$

Equation 12 can be supplemented by the correction factor k _s . It takes into account the ratio of primary air (SSL-PL) to Secondary air (SSL-SL), which is generated from the pane purge air and generally depends on the height of the viewing pane H _s . The following applies: the higher the viewing pane of the fireplace (H _s ), the more the pane purge air can act as primary air. ks can have a value of 0.93 to 1.07 and can be used in equation 12 as follows: $${\mathrm{O}}_2=\left(21\cdot \lambda \cdot {\mathrm{k}}_{\mathrm{s}}-21\right)/\lambda \cdot {\mathrm{k}}_{\mathrm{s}}:$$ Formula 11 and formula 12 respectively form the basis for controlling combustion plants using temperature measurement in the combustion chamber area and the energy balance method according to the method according to the invention. The parameters specified above (temperature measurement, energy balance method) are used to determine the oxygen demand and supply it accordingly to the process, as well as to adjust the optimal oxidation temperatures in the active reaction zone so that proper combustion and consequently operation of the combustion plant can be ensured.

The calculation of the oxygen coefficient by the energy balance method can be carried out not only for the secondary air supply, but is also useful for identifying the limits of the primary air actuator and reducing the primary air (gasification air regardless of how it is supplied to the fireplace - through the grate, from the side, or via the fuel)) accordingly and in a timely manner, thus preventing the combustion from falling into oxygen deficiency.

The normative combustion calculations can be taken into account or used for the regulations.

In one embodiment, the method according to the invention can be carried out automatically. The control interventions can therefore be carried out automatically. This can be done, for example, by means of a control unit in which the above formulas are stored in appropriate software, including the correction parameters that may need to be entered. The temperature values from the combustion chamber area and/or the exhaust gas are then transmitted to this control unit. By calculating the oxygen in the combustion chamber, the supply of primary and/or secondary air can be automatically regulated by a controller. The present invention further provides a device with which this control of the supply of primary and/or secondary air can be carried out in a particularly advantageous manner, in particular with which the advantages described above can be achieved in a particularly favorable manner.

The device according to the invention for supplying combustion air into the combustion chamber of a single-room combustion system is characterized in that it has a chamber which, on a first side, has a main duct for supplying ambient air and/or air from the chimney system and, on a second side, a pane purge air duct and a secondary air duct through which primary and/or secondary air can be conducted into the combustion chamber, wherein both the pane purge air duct and the secondary air duct are provided with a flap so that the pane purge air duct and the secondary air duct can be closed independently of one another, wherein the flaps are connected to a stepless motor so that the flaps can be moved continuously.

Depending on the height of the viewing window of the combustion plant, the window purge air functions as primary (SSL-PL) and secondary air (SSL-SL).

For example, the first side of the chamber can be located opposite the second side of the chamber. Other configurations are also possible.

In one embodiment, the flaps can be designed as discs mounted at the air inlet of the primary duct and/or the secondary air duct. In another embodiment, the flaps can regulate both the window purge air via the window purge air duct and the grate air via the grate air duct. For an opening of 0% to x%, the window purge air can be regulated, and from 100% to x%, the grate air can be regulated, where x is the percentage. Opening width of the flaps and is generally between 70% and 90% for an adequate design of the air supply ducts.

In a further embodiment, the device can comprise at least one solar panel and/or a device for thermoelectric power generation and/or a regular power supply via a household socket. In the three variants mentioned, an intermediate power storage device, e.g., a rechargeable battery, can be provided to ensure a secure power supply for the entire control system. In this way, the required power requirement of the device can be provided without great effort.

In one embodiment, the device may further comprise a control or regulating unit adapted to automatically control or regulate the air supply.

The following is a detailed description of the device: Air dampers with stepless motors can be used to regulate the combustion air supply. The dampers regulate defined opening widths via two dampers, which can be designed, for example, as discs, installed at the air inlet of the separate air chambers or ducts. The two dampers are installed in a box or pipe system, which draws all combustion air via a main duct from the environment or, in the case of room-air-independent operation, from the chimney system. The negative pressure and boiler temperature in single-room combustion systems with water-bearing components, as safety-relevant variables, can be recorded using a built-in pressure switch or temperature sensor and integrated into the software accordingly.

Due to the very low energy consumption of the hardware and the control actuators (control valves), no domestic power supply is required to operate the control system. In contrast to other systems, the power consumption is very low and lies in the wattage range. This power consumption can be a solar panel, thermoelectric during combustion, or with a domestic power socket, each possibly with a corresponding simple power storage unit (see also above).

In the event of a power failure or technical defect, the primary air damper is technically rotated to the zero position, where the primary air opening is 100% closed. In order to prevent dangerous conditions such as heavy smoke formation in the living space or deflagrations due to a lack of oxygen in the combustion chamber, as can occur when feeding the fire in the presence of a bed of embers, a mechanism for regulating the combustion air is provided. With this mechanism, when the primary air damper is moved back from a 40% position to 0% position, a mechanically locked safety air damper is simultaneously actuated. This creates a correspondingly large opening and thus supplies the combustion process with a sufficient amount of combustion air for safe combustion. This is only an example description of a technical possibility. It can also be implemented with other technical possibilities.

The primary air damper can be controlled in normal operation over 60% (between 40% and 100%) of the total opening width of the primary air, while the secondary air can be controlled from 0% to 100% of the opening width.

• Die Regelung kann mit preiswerten, robusten und langlebigen Sensoren durchgeführt werden, welche stabile Signale liefern bzw. keine Wartung und Kalibrierung im Praxisbetrieb benötigen. Hier können beständige Temperaturfühler eingesetzt werden, die eine einfache Elektronik für die Verwertung der Signale benötigen.
• Die automatische und mit der Einstellung von Parametern anpassbare Steuerung ermöglicht es, eine schnelle Anpassung der Regelung an alle Arten von Feuerungsanlagen unabhängig von ihrer Konstruktion ohne Bedarf einer Änderung der Software ermöglicht wird.
• Die Soft- sowie die Hardware mit dem Verbrennungsluftverteilungssystem sind universell einsetzbar und berücksichtigen alle normativen Anforderungen sowie Zulassungsregelungen des DIBt (Deutsches Institut für Bautechnik) für eine technische Zulassung bzw. einen sicheren Betrieb in der Praxis.
• Die Hardwarekomponenten mit den Sensoren sowie den Regelakteuren können so ausgesucht werden, dass sich das Regelungssystem ohne jeglichen Starkstrom bzw. häusliche Stromversorgung betreiben lässt. Dabei liegt der gesamte Stromverbrauch im Wattbereich. Ein einfaches Solarmodul kann das Regelungssystem mit dem nötigen Strom versorgen.
• Die technische Kombination aus dem Luftverteilungssystem mit dem erfindungsgemäßen Verfahren ermöglicht einen universellen Einsatz in neuen Feuerungsanlagen sowie eine sichere Nachrüstbarkeit von vielen in der Praxis bestehenden Einzelraumfeuerungsanlagen.
• Durch die intelligente Regelung wird die Wärme nicht nur effizient produziert, sondern auch effizient genutzt, wodurch nicht nur Ressourcen- sondern bedeutsame CO2-Ersparnisse erreicht werden können.

The method and device according to the invention achieve a number of advantages:

• Control can be implemented using inexpensive, robust, and durable sensors that provide stable signals and require no maintenance or calibration during operation. Durable temperature sensors can be used here, requiring simple electronics for signal processing.
• The automatic control system, which can be adjusted by setting parameters, enables rapid adaptation of the control system to all types of combustion plants regardless of its design without the need to change the software.
• The software and hardware with the combustion air distribution system are universally applicable and take into account all normative requirements and approval regulations of the DIBt (German Institute for Building Technology) for technical approval and safe operation in practice.
• The hardware components, including the sensors and control actuators, can be selected so that the control system can be operated without any high-voltage current or household power supply. The total power consumption is in the wattage range. A simple solar module can supply the control system with the necessary power.
• The technical combination of the air distribution system with the method according to the invention enables universal use in new combustion systems as well as safe retrofitting of many existing single-room combustion systems.
• Thanks to intelligent control, heat is not only produced efficiently but also used efficiently, which not only saves resources but also significantly reduces CO2 emissions.

• Fig. 1 eine Darstellung einer handbeschickten Einzelraumfeuerungsanlage.
• Fig. 2 zeigt eine Draufsicht auf die erfindungsgemäße Vorrichtung.
• Fig. 3 stellt die paramagnetisch gemessene und mit der Modellgleichung berechnete Sauerstoffkonzentration in einer Einzelraumfeuerungsanlage dar.
• Fig. 4 stellt Sauerstoff, Feuerraumtemperatur und Kohlenstoffmonoxid beim Betrieb einer Einzelraumfeuerungsanlage dar.

The invention will be explained in more detail below with reference to figures without limiting the general inventive concept.

• Fig. 1 a representation of a manually fired single-room heating system.
• Fig. 2 shows a plan view of the device according to the invention.
• Fig. 3 represents the oxygen concentration measured paramagnetically and calculated using the model equation in a single-room combustion system.
• Fig. 4 represents oxygen, combustion chamber temperature and carbon monoxide during operation of a single-room combustion system.

Fig. 1 shows a manually fed single-room combustion system 10. It has a combustion chamber area 11 in which a fuel is burned. For example, a pane purge air (SSL) and/or grate air (RL) can be introduced into the combustion chamber area 11 via a pane purge air duct 3, and secondary air (SL) can be introduced into the combustion chamber area 11 via a secondary air duct 4. The air flows are in Fig. 1 shown with arrows. Grate air can be introduced if the oxygen content of the pane purge air is not sufficient to initiate combustion sufficiently intensively to reach favorable temperatures for the oxidation reactions, such as in the case of the combustion of moist and/or thick logs or coal. The grate air can enter the combustion chamber area 11 from below through the grate. The path of the grate air is in Fig. 1 shown with an arrow. Both the window purge air duct 3 and the secondary air duct 4 can be closed independently of one another using flaps 5, whereby these flaps can be continuously adjusted using motors 6, 7 to ensure precise control of the air supply. In the combustion chamber area 11 there are two temperature sensors T ₁ , T ₂ , which can be provided, for example, on the baffle plate. In addition or alternatively, temperature sensors can be mounted in the first flue after the flue baffle plate. However, this is only an example of a location where the temperature sensors T ₁ , T ₂ can be provided. They can of course also be located at other points in the combustion chamber area, such as in the flue pass. There can also be another temperature sensor T _Ab in the flue gas area, which measures the temperature in the flue gas. Furthermore, the ambient temperature T _U in the installation room can be measured and taken into account for the control. Measuring the temperature of the flue gas provides more information, but it is not mandatory; it is optional. The measured temperature values are transmitted to the control unit 12 (control unit/microcontroller) (see dashed lines). Formulas and parameters are used to calculate the oxygen. Depending on the result obtained, the supply of primary air and/or secondary air can then be regulated by issuing appropriate commands to motors 6 and 7. The combustion air flows are as follows: SSL-SL: window purge air as secondary air; SSL-PL: window purge air as primary air; RL-PL: grate air as primary air; SL: secondary air.

In Fig. 2 The device according to the invention is shown in plan view, with which the supply of primary and/or secondary air into the combustion chamber area can be controlled. The device has a chamber 1, which has on a first side a main duct 2 for the supply of air and/or air from the chimney system (combustion air) (shown as an arrow) and on a second side a pane purge air duct 3 (SSL: pane purge air) and a secondary air duct 4 (SL: secondary air, such as O ₂ ), wherein both the pane purge air duct 3 and the secondary air duct 4 are provided with a flap 5 (in Fig. 2 (only indicated schematically) so that the windshield scavenging air duct 3 and the secondary air duct 4 can be closed independently of one another, with the flaps 5 each being connected to a stepless motor 6, 7 so that the flaps 5 can be moved continuously. Furthermore, a grate air duct 13 is provided, with the grate air being regulated via the flap 5, which is connected to the motor 6 for the windshield scavenging air duct 3.

The device further comprises a solar panel 8 with which the required power for operating the device can be generated.

In the Fig. 3 The oxygen concentrations calculated according to the model equation and measured with a paramagnetic oxygen analysis during the combustion of beech logs in a prototype of a single-room combustion system from Hase are shown. Fig. 3 It can be seen that the oxygen concentrations in the exhaust gas calculated and measured on the basis of the model equation correlate and Thus, the model equation is very well suited for determining the oxygen content in the exhaust gas.

Using a simple test facility, the control concept was implemented using the energy balance method of the Fraunhofer Institute for Building Physics IBP and a PLC (programmable logic controller). Pollutant emissions such as carbon monoxide were reduced by 62% and particulate matter by approximately 43% compared to operation without control (see Figure 1). Fig. 4 ). Furthermore, efficiency was increased by approximately 16% compared to real-world operation. Further improvements can be achieved through further software development.

The diagram of the Fig. 4 It can be seen that when using the controller, the combustion chamber temperature remains above a favorable or average combustion chamber temperature of more than 550 °C for an extended period of combustion. The same applies to the oxygen content in the exhaust gas, which allows clear conclusions to be drawn about the controlled combustion.

According to the invention, the targeted control of the secondary air (SSL-SL + SL) is carried out by an oxygen coefficient calculated using the energy balance method.

Furthermore, the oxygen coefficient can be used to operate the primary air actuator within its optimal limits, thus preventing combustion from experiencing oxygen deficiency. This means that if the secondary air actuator reaches its maximum limit (flap 5 of stepper motor 6 (or secondary air actuator) 90% open; here, 10% as a reserve) and the calculated oxygen coefficient is still below the oxygen setpoint stored in the program, the primary air (RL-PL + SSL-PL) is reduced in time to prevent oxygen deficiency and thus incomplete combustion. As an alternative to stepper motor 6, a servo motor can also be used.

The targeted control of the primary air (SSL-PL + RL-PL) is carried out to set a favorable temperature in the active reaction zone (combustion chamber + post-oxidation chamber) for an effective implementation of the oxidation reactions or a complete combustion.

• Verwendung von feuchten Brennstoffen
• Verwendung von trocknen Brennstoffen in großen Mengen
• Beschickung großer Brennstoffmenge
• Illegale Verbrennung von Abfällen wie z. B. Plastik, Altöl usw.
• Erkennung von ungünstigem bzw. sehr hohem oder sehr niedrigem Kaminzug.

The description and evaluation of combustion quality (completeness of combustion) and the operational quality of the fireplace are carried out through differential and integral evaluations of the recorded temperatures, the calculated oxygen coefficient, and the behavior of the control actuators, i.e., the stepper motors or servomotors (6 and 7) for controlling the combustion air supply. This provides the following information, and users are informed accordingly or digitally trained for better operation of the fireplace:

• Use of wet fuels
• Use of dry fuels in large quantities
• Feeding large quantities of fuel
• Illegal burning of waste such as plastic, waste oil, etc.
• Detection of unfavorable or very high or very low chimney draft.

Of course, the invention is not limited to the embodiments illustrated in the figures. The above description is therefore not to be considered restrictive, but rather explanatory. The following claims are to be understood as meaning that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the description or the claims define "first" and "second" features, this serves to distinguish similar features without establishing a priority.

Claims (8)

1. Method for controlling the combustion process of solid fuels in a single-room furnace, characterized in that an oxygen coefficient is determined from a temperature in a combustion chamber and/or a temperature in a waste gas flue of the single-room furnace, an energy balance of the combustion process in the single-room furnace, an amount of combustion air and an amount of waste gas, wherein said oxygen coefficient is used to control a primary combustion air flow and/or a secondary combustion air flow and thus a thermal output and a combustion quality.
2. Method according to claim 1, characterized in that an oxygen demand for the combustion is determined using an oxygen surplus in the combustion chamber area, the oxygen surplus being calculated according to the following formula $${\mathrm{O}}_2=\left(21\times \mathrm{\lambda }-21\right)/\mathrm{\lambda }$$ where λ is determined as follows λ = 1 + [17.000 × k_B /[[0,995 + 0,0002 × ϑ_R × k_F ] × ϑ_R × k_F × [0,241 × 17.000 × k_B / 1.000] + 0,5 ]] = [0,217 × H_u × k_B /1.000 + 1,67] / [0,241 × H_u × k_B / 1.000 + 0,5 ]] where k_B has a value of 0.80 to 1.2, ϑ_R is the waste gas and/or combustion chamber temperature, k_F has a value of 1 to 4, and H_U is the calorific value of the fuel.
3. Method according to any one of the preceding claims,
   characterized in that the temperature in the combustion chamber and/or in the waste gas flue is measured at least at one point.
4. Method according to any one of the preceding claims,
   characterized in that the temperature in an installation room of the furnace system is measured for a heat production in accordance with demand.
5. Method according to any one of the preceding claims,
   characterized in that the primary air is pane-flushing air and/or grate air.
6. Method according to any one of the preceding claims,
   characterized in that the supply of secondary air is effected in such a way that the oxygen content in the combustion chamber area is about 7 vol.% to about 10 vol.% or about 8 vol.% to about 9 vol.%.
7. Method according to any one of the preceding claims,
   characterized in that the control of the combustion takes place automatically.
8. Use of the method according to any one of claims 1 to 7 for monitoring the operation of a single-room furnace system for its optimum operation and for ensuring the quality of the combustion.