DE102020124544A1 - Process and system for the thermal utilization of solid fuel in a reaction chamber - Google Patents

Abstract

The invention relates to a method and a system for the thermal utilization of solid fuel in a reaction chamber, the process of thermal utilization of the fuel being controlled by a control unit (5) as a function of the water content of the fuel. The water content of the fuel is determined before it is introduced into the reaction chamber. For this purpose, a gas flow is passed through a fuel bed and the humidity of the gas flow is measured after it has exited the fuel bed. The water content of the fuel is determined by means of an evaluation unit (4) from the measured value representing the humidity of the gas flow. The plant also has a container (1) upstream of the reaction chamber for receiving the bulk fuel and a device (2) for generating the gas stream conducted through the bulk fuel.

Description

The invention relates to a method and a system for the thermal utilization of solid fuel in a reaction chamber according to the preamble of patent claim 1 or according to the preamble of patent claim 14.

"Thermal recycling" is understood here to mean a heat-generating process such as firing, gasification or pyrolysis. The "solid fuel" mentioned here includes thermally usable biomass such as e.g. B. wood chips, wood shavings, pellets, and biogenic residues such. B. corn cobs or olive stones, but also thermally usable waste.

• - die Unterschiedlichkeit der Brennstoffe (Holzhackschnitzel, Späne, Pellets, biogene Reststoffe wie z. B. Maisspindel, Olivenkerne etc.);
• - Unterschiede in der Brennstoffaufbereitung, denn selbst Brennstoffe mit gleicher Einordnung variieren oft drastisch in der Qualität; z.B. besteht ein signifikanter Unterschied bei Heizwert und Wassergehalt für naturbelassenes Holz als Frischholz oder getrocknet aus der Nutzung von Abwärme einer Biogasanlage;
• - Schwankungen in der Qualität des Brennstoffes bedingt durch Jahreszeit, Lagerbedingungen und Standort.

For plants for the thermal utilization of biomass and biogenic residues, the large heterogeneity and range of fluctuation of the characteristics of the fuel represents a considerable procedural challenge. Important parameters in this context include the water content and the bulk density of the fuel, as well as the particle size distribution and the fines content in the fuel . Reasons for varying these parameters are e.g. e.g.:

• - the variety of fuels (wood chips, shavings, pellets, biogenic residues such as corn cobs, olive pits, etc.);
• - Differences in fuel processing, because even fuels with the same classification often vary drastically in quality; For example, there is a significant difference in calorific value and water content for natural wood as fresh wood or dried from the use of waste heat from a biogas plant;
• - Fluctuations in fuel quality due to season, storage conditions and location.

If the fuel parameters mentioned vary without prior knowledge when it reaches the combustion chamber of a furnace, temperature fluctuations occur in the combustion chamber, with the result of emission peaks, sintering of mineral components and damage to the system technology.

In order to prevent this and to do justice to the heterogeneity of the fuel, various measures are used in practice. For example, strict specifications are made for the quality of the fuel, which ultimately requires comprehensive management and monitoring of the fuel quality with the corresponding high expenditure on personnel and costs, or leads to higher expenditure in the area of maintenance and support of the system. Other measures are of an organizational nature and consist of limiting the range of fuel and operating quality assurance, whereby the effort required for this can be considerable because it requires e.g. fuel certification, incoming and quality control as well as the definition of permissible parameters by the plant manufacturer. These organizational measures limit the flexibility of the systems. In addition, the monitoring effort required to comply with clearly defined fuel bands is considerable and associated with high costs.

Other concepts can also be used to avoid the disadvantages associated with the measures described above. One of these concepts is to draw conclusions about the fuel moisture by recording the flue gas moisture and to control the firing system with this knowledge. This concept is described in more detail, for example, in DE 19917572 A1 . A control of a solid fuel firing device based on the water content in the flue gas is in DE 102007055168 A1 described. Furthermore, the control of a combustion system by drawing conclusions about the fuel quality from the flue gas in the DE 19547258 A1 described.

Another one in the DE 4446022 A1 The concept described is based on the knowledge that the incineration of waste can only be carried out best if the composition or the nature of the waste to be incinerated is determined before incineration and its incineration is coordinated with this determined information, so that a forward-looking driving style is possible the incineration of waste is possible. For this purpose, the water content of the waste to be incinerated is determined before incineration in the allocation shaft using microwave signals. Signal weakening and/or phase changes in these microwave signals are caused by the water content of the waste. These are evaluated to determine the water content in the waste. The information signals obtained in this way are forwarded to a process control unit which is provided for controlling the supply of air for the combustion of the waste taking place on the grate. The measurement technology based on microwave signals requires a high level of installation effort and is also relatively expensive. In addition, measurement is only available at discrete points.

From the AT 15458 U1 a method for burning solid fuel, in particular lignin and agricultural biomass, is known, in which the water content of the fuel is detected and taking into account the energy content for a selected output, the supply of fuel is increased with a higher water content and decreased with a low water content. In addition, the proportion of primary air and/or secondary air in the combustion air is selected depending on the detected water content of the fuel. The ratio in the combustion air between primary air and secondary air on the one hand and recirculation gas on the other is selected as a function of the water content of the fuel. Furthermore, the water content of the fuel is recorded continuously or discontinuously during its storage or its supply through a fuel feed channel. However, it is not specified how the water content of the fuel is recorded.

Against this background, the object of the invention arises in the method and the system for the thermal utilization of solid fuel in a reaction chamber in which or in which the water content of the fuel is determined before it is introduced into the reaction chamber and the process of thermal utilization of the fuel is controlled as a function of the water content of the fuel, to carry out or indicate measures which allow a simple and inexpensive determination of the water content of the fuel and any other parameters useful for controlling the process of thermal utilization.

With regard to the method, the object of the invention is achieved in that, in the method according to the preamble of patent claim 1, a gas flow is passed through the fuel and the humidity of the gas flow is measured after it has exited the fuel and from the measured value representing the humidity of the gas flow Water content of the fuel is determined.

With regard to the system, the object of the invention is achieved in that the system according to the preamble of claim 14 has a device for generating a gas flow that can be guided through a fuel bed in a container, and a measuring device for measuring the humidity of the gas flow whose exit from the fuel bed is provided, and an evaluation unit for determining the water content of the fuel from the measured value determining the moisture of the gas flow is provided, and that the water content of the fuel determined in this way can be communicated to the control unit so that it can be taken into account in the process control.

Advantageous developments of the invention can be found in the dependent claims.

The invention allows information about the fuel to be provided before it is transported into the reactor space. As a result, changes in fuel quality can be identified and fuel properties important for efficient and targeted combustion can be derived from the data. This includes in particular information about the water content, the bulk density, the fines content, the ash content and the calorific value. This information can be made available to the operator of the system or the controller of the system.

• - es findet ein Wärmeübergang vom Gasstrom auf den Brennstoff oder umgekehrt statt; infolgedessen erfolgt z. B. eine Abkühlung des Gasstromes und Aufheizung der Brennstoffschüttung;
• - es findet ein Trocknungsprozess des Brennstoffs und eine Aufnahme von Wasser in den Gasstrom statt;
• - es findet ein Druckverlust über die Schüttung statt;
• - es werden bei höheren Temperaturen flüchtige Bestandteile freigesetzt, welche z. B. über einen Flammenionisationsdetektor, kurz FID, analysiert werden können.

According to the invention, a gas flow, which can be air, nitrogen, recirculation gas, exhaust gas or air enriched with oxygen, and can have a temperature between -10° C. and 200° C., is fed through a fuel bed in a container, which is a storage container, a lock, a chute, an auger or a receptacle separate from a fuel supply device. Various physical processes take place when the bulk material flows through:

• - there is a heat transfer from the gas flow to the fuel or vice versa; as a result z. B. cooling of the gas stream and heating of the fuel bed;
• - There is a drying process of the fuel and an absorption of water in the gas flow instead;
• - There is a pressure drop across the bed;
• - Volatile components are released at higher temperatures, which z. B. can be analyzed using a flame ionization detector, FID for short.

• - Messung der Temperatur, des Druckes und der relativen Luftfeuchte in der Umgebung (Standardmesstechnik: z. B. Umgebungstemperatur [°C] und relative Umgebungsluftfeuchtigkeit [%] Temperatur/RH Almemo^®-Stecker; Messbereich: -50°C ...+200°C; 0% ... 100% RH);
• - Messung von Temperaturen in der Schüttung sowie vor Eintritt und nach Austritt des Gases aus der Schüttung (Standardmesstechnik z. B. Messfühler: Thermoelemente; NiCr-Ni Almemo^®-Stecker Typ K; Messbereich: -200°C ... +1370°C);
• - Messung des Druckes vor und nach der Schüttung (Standardmesstechnik: z. B. Messfühler: Silikonschlauch + Metallrohr; Staudruck/Strömung Almemo^®-Stecker; Messbereich 0Pa ... 6800Pa);
• - Messung des Wassergehaltes auf der Abluftseite (Standardmesstechnik: z. B. Gasanalysator Dr. Födisch MCA 04) ;
• - Messung des Umgebungsdruckes (Standardmesstechnik:
  • digitales Manometer Modell Leo 2 der Firma Keller (Messbereich: 0 bar...300bar; 0°C...50°C).

These processes lead to a change in the nature of the gas, which can be determined with comparatively simple, standardized metrological instruments and methods, such as e.g. e.g.:

• - Measurement of temperature, pressure and relative humidity in the environment (standard measurement technology: e.g. ambient temperature [°C] and relative ambient humidity [%] temperature/RH Almemo ^® connector; measuring range: -50°C ...+ 200°C; 0% ... 100% RH);
• - Measurement of temperatures in the bed and before the gas enters and exits the bed (standard measuring technology, e.g. sensors: thermocouples; NiCr-Ni Almemo ^® plug type K; measuring range: -200°C ... +1370° C);
• - Measurement of the pressure before and after the filling (standard measuring technology: e.g. measuring sensor: silicone hose + metal tube; dynamic pressure/flow Almemo ^® plug; measuring range 0Pa ... 6800Pa);
• - Measurement of the water content on the exhaust air side (standard measurement technology: e.g. gas analyzer Dr. Födisch MCA 04);
• - Measurement of the ambient pressure (standard measurement technique:
  • digital manometer model Leo 2 from the company Keller (measuring range: 0 bar...300bar; 0°C...50°C).

The change in the parameters of the gas after it has been poured can be recorded in a time-resolved manner. Characteristic values or functions (f _Δp (t), f _w (t), ƒ' _w (t), f _T (t), f _ΔT (t)) are formed from the measurement curves. Changes in parameters or in the curves indicate a changed fuel quality or a different fuel. In this way, changes in the fuel quality can be recorded. On this basis, warnings can be issued to the user and/or direct technical control interventions can be made.

The bulk fuel can include a partial flow from the entire fuel mass flow or the entire fuel mass flow.

The flow through the fuel bed can be from top to bottom or from bottom to top.

The bulk fuel and the gas stream can preferably have a ΔT of at least 15 K.

The exhaust air from the bulk fuel can be integrated into the thermal utilization process, e.g. B. as primary air or secondary air.

The inventive measures can be retrofitted to existing systems or taken into account from the outset in new systems.

Coupling with other metrological devices is possible (process data of the system, fuel scales, acquisition of image data from the fuel, etc.).

An upstream drying of the gas stream can, for. B. done by directing the gas flow through a silica gel bed, so as to eliminate ambient air-related fluctuations. This shows differences in the exhaust air even more clearly and further improves the process.

• - Änderungen relevanter Brennstoffparameter, insbesondere Wassergehalt und Eigenschaften der Schüttung erfasst, so dass der Anlage die Information zur Verfügung gestellt werden kann, dass ein anderer Brennstoff eingesetzt und/oder sich die Qualität des Brennstoffes geändert hat;
• - mit Hilfe des Druckverlusts unterschiedliche Schüttungen differenziert (Pellets, Hackgut, Späne etc.) und Informationen zum Feinanteil ermittelt;
• - mit Hilfe des Wassergehaltes im Gasstrom Rückschlüsse auf den Wassergehalt des Brennstoffes ermöglicht;
• - Informationen über die „Richtung“ der Änderung bereitgestellt, also Informationen darüber ob eine Erhöhung oder eine Absenkung des Wassergehaltes stattgefunden hat oder sich die Partikelgröße erhöht oder vermindert hat;
• - an Hand der Daten und durch den Abgleich von Datensätzen Brennstoffe und Brennstoffqualitäten Gruppen zugeordnet;
• - basierend auf der Detektion des Brennstoffes bzw. der Brennstoffeigenschaften die Betriebsweisen der Anlage angepasst, z. B. durch Erhöhung oder Reduzierung des Brennstoffmassenstromes, Erhöhung oder Reduzierung des Anteils an Rezirkulationsluft, Verstärkung oder Reduzierung der Vorwärmung der Brennstoffluft.

The invention makes it possible to provide information about the fuel before it enters the reaction space. In detail will

• - Changes in relevant fuel parameters, in particular water content and properties of the fill, are recorded so that the system can be provided with the information that a different fuel has been used and/or the quality of the fuel has changed;
• - With the help of the pressure loss, different bulk materials are differentiated (pellets, wood chips, shavings, etc.) and information on the fines is determined;
• - With the help of the water content in the gas flow, conclusions can be drawn about the water content of the fuel;
• - Information provided about the "direction" of the change, i.e. information about whether there has been an increase or decrease in the water content or whether the particle size has increased or decreased;
• - assigned fuels and fuel qualities to groups on the basis of the data and by comparing data sets;
• - Based on the detection of the fuel or the fuel properties, the operating modes of the system are adapted, e.g. B. by increasing or reducing the fuel mass flow, increasing or reducing the proportion of recirculation air, increasing or reducing the preheating of the fuel air.

An exemplary embodiment of the invention will now be described below with reference to the accompanying drawing, which shows the basic structure of a system according to the invention and the basic sequence of a method according to the invention in a schematic manner.

As can be seen from the drawing, a plant for the thermal utilization of solid fuel has a container 1 for receiving a bulk fuel. The container 1 is connected upstream of a reaction chamber, not shown, into which the fuel can be introduced after leaving the container 1 in order to be thermally utilized there by combustion. The container 1 is preceded by a hot air blower 2 which accelerates and heats a gas stream which has previously flowed through a drying device in the form of a silica gel bed 3 . The gas stream leaving the hot-air blower 2 flows through the bulk fuel in the container 1. Various physical measuring devices are used for thermal utilization, which are not shown relevant parameters such as B. pressure and temperature of the gas stream before entering and after exiting the fuel bed and the moisture content of the gas stream measured especially after it exits the fuel bed. These measured values are fed to an evaluation unit 4, which allows conclusions to be drawn about the water content and other parameters relevant to thermal utilization, such as the density of the bed and the proportion of fines in the bed. The data determined by the evaluation unit 4 are supplied to a control unit 5, which controls the thermal utilization process taking this data into account. When evaluating the measured values supplied to it, the evaluation unit 4 can access a database 6 in which certain data relevant to the thermal utilization process are stored.

• - Bei der datenbasierten Auswertung erfolgt ein Abgleich zwischen hinterlegten Daten bzw. Profilen und den erzeugten Messwerten. Durch Verfahren wie z. B. eine Kreuzkorrelation oder andere vergleichbare mathematische Methoden werden Ähnlichkeiten bzw. Abweichungen ermittelt und auf dieser Basis entschieden, um welche Art von Brennstoff es sich handelt.
• - Bei dem analytischen Ansatz ist eine Information über die Masse des Brennstoffes zumindest zu Beginn erforderlich. Vereinfachend wird bei diesem Ansatz der Brennstoff als eine Mischung aus Anteilen von Wasser, Asche und Brennbarem unterschieden. An Hand der Masse und weiterer Messwerte (insbesondere Wassergehalt in Zu- und Abluft) wird eine Massen- und Energiebilanz des Trocknungsprozesses aufgestellt. So wird zunächst die Menge an Wasser berechnet, die ausgetrieben wurde und so analytisch auf den Wassergehalt zurückgerechnet. Über die Messwerte der Temperaturen wird die Aufheizung des Schüttgutes bewertet und erfasst.

When evaluating the measured values and data supplied to the evaluation unit, two approaches are followed and combined in order to achieve the best possible results:

• - In the data-based evaluation, a comparison is made between the stored data or profiles and the measured values generated. Through methods such as B. a cross-correlation or other comparable mathematical methods, similarities or deviations are determined and on this basis decided what kind of fuel it is.
• - With the analytical approach, information about the mass of the fuel is required at least at the beginning. To simplify matters, this approach distinguishes the fuel as a mixture of water, ash and combustibles. A mass and energy balance of the drying process is drawn up based on the mass and other measured values (in particular the water content in the supply and exhaust air). First, the amount of water that was expelled is calculated and then analytically calculated back to the water content. The heating of the bulk material is evaluated and recorded via the measured temperature values.

Of course, the invention is not limited to the illustrated embodiments. The foregoing description is therefore not to be considered as limiting but as illustrative. It is to be understood in the following claims that a specified feature is present in at least one embodiment of the invention. This does not exclude the presence of other features. If the claims and the above description define “first” and “second” embodiments, this designation serves to distinguish between two similar embodiments without establishing a ranking.

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 19917572 A1 [0006]
• DE 102007055168 A1 [0006]
• DE 19547258 A1 [0006]
• DE 4446022 A1 [0007]
• AT 15458 U1 [0008]

Claims (20)

Process for the thermal utilization of solid fuel in a reaction space, the water content of the fuel being determined before it is introduced into the reaction space, and the process of thermal utilization of the fuel depending on the water content of the fuel being controlled, characterized in that a gas flow is passed through the fuel and the humidity of the gas flow is measured after it has exited the fuel and the water content of the fuel is determined from the measured value representing the humidity of the gas flow. procedure after claim 1 , characterized in that the humidity of the gas flow is also measured before it enters the fuel and is taken into account when determining the water content of the fuel. procedure after claim 1 or 2 , characterized in that the temperature of the gas flow is measured before it enters the fuel and/or exits the fuel and is taken into account in the process control Procedure according to one of Claims 1 until 3 , characterized in that the pressure of the gas stream is measured before it enters the fuel and/or before it exits the fuel and is taken into account in the process control. Procedure according to one of Claims 1 until 4 , characterized in that the temperature of the gas stream is measured while it is in the fuel. Procedure according to one of Claims 1 until 5 , characterized in that the gas flow before it enters the fuel has a higher or lower temperature than the fuel at the point where the gas flow enters the fuel. procedure after claim 6 , characterized in that the temperature difference between the gas stream and the fuel is at least 15 K. Procedure according to one of Claims 1 until 7 , characterized in that the gas stream has a temperature in the range between -10°C and 200°C before it enters the fuel. Procedure according to one of Claims 1 until 8th , characterized in that the gas stream is used after its exit as primary air and / or secondary air in the thermal utilization of the fuel. Procedure according to one of Claims 1 until 9 , characterized in that the gas stream is dried before it enters the fuel. procedure after claim 10 , characterized in that the gas stream is passed through a silica bed to dry it. Procedure according to one of Claims 1 until 11 , characterized in that the gas stream consists of one of the following gases: air, nitrogen, recirculation gas, exhaust gas, oxygen-enriched air. Procedure according to one of Claims 1 until 12 , characterized in that the fuel through which the gas stream flows is the entire quantity or only part of the fuel introduced into the reaction space. Plant for the thermal utilization of solid fuel in a reaction space, which is preceded by a container (1) for receiving a bulk fuel, the water content of the fuel being able to be determined before it is introduced into the reaction space, and the process of thermal utilization of the fuel dependent on it can be controlled by the water content of the fuel by means of a control unit (5), characterized in that a device (2) is provided for generating a gas flow which can be guided through a fuel bed in the container (1), and a measuring device for measuring the moisture of the gas stream after it has exited the fuel bed, and an evaluation unit (4) for determining the water content of the fuel from the measured value representing the moisture in the gas stream, and that the control unit (5) receives the water content of the fuel determined in this way so that it can be taken into account ng can be communicated in the process control. plant after Claim 14 , characterized in that the device for generating the gas flow has a hot air blower (2). plant after Claim 14 or 15 , characterized in that it comprises a drying device (3) for the gas flow. plant after Claim 16 , characterized in that the drying device (3) contains a silica gel bed through which the gas stream can be guided before it enters the fuel bed. Plant after one of Claims 15 until 17 , characterized in that the silica gel bed (3) is connected upstream of the hot air blower (2). Plant after one of Claims 14 until 18 , characterized in that the container (1) is a storage container, a lock, a chute, or a screw or is a separate container from a fuel supply device. Plant after one of Claims 14 until 19 , characterized in that the container (1) and the reaction chamber are connected by a line through which the gas stream can be guided into the reaction chamber after it has exited the fuel bed, in order to be usable there as primary air and/or secondary air.

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