METHOD AND PLANT FOR THE THERMAL UTILIZATION OF SOLID FUEL IN A REACTION ROOM

Description

[0001] The invention relates to a method and a plant for the thermal utilization of solid fuel in a reaction chamber according to the preamble of claim 1 or according to the preamble of claim 11. Such plants are shown in EP 2 770 255 A2.

[0002] Here, "thermal utilization" refers to a heat-generating process such as combustion, gasification, or pyrolysis. The "solid fuel" mentioned here includes thermally usable biomass such as wood chips, wood shavings, pellets, as well as biogenic residues such as corn cobs or olive pits, but also thermally usable waste.

[0003] For plants that thermally utilize biomass and biogenic residues, the significant heterogeneity and variability of the fuel's characteristics poses a considerable process engineering challenge. Important parameters in this context include the fuel's moisture content and bulk density, as well as its particle size distribution and the proportion of fines. Reasons for varying these parameters include, for example: The diversity of fuels (wood chips, shavings, pellets, biogenic residues such as corn cobs, olive pits, etc.); differences in fuel processing, as even fuels with the same classification often vary drastically in quality; for example, there is a significant difference in calorific value and moisture content for untreated 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.

[0004] If the aforementioned fuel parameters vary without prior knowledge upon reaching the combustion chamber of a furnace, temperature fluctuations occur in the combustion chamber, resulting in emission peaks, sintering of mineral components, and damage to the plant technology.

[0005] To prevent this and address the heterogeneity of the fuel, various measures are employed in practice. For example, strict specifications are imposed on fuel quality, which ultimately requires comprehensive management and monitoring of fuel quality with correspondingly high personnel and cost expenditures, or leads to increased maintenance and servicing of the system. Other measures are organizational in nature and consist of limiting the range of fuel types and implementing quality assurance. The effort required for this can be considerable, as it necessitates, for example, fuel certification, incoming and quality control, and the definition of permissible parameters by the system manufacturer. These organizational measures restrict the flexibility of the systems.Furthermore, the monitoring effort required to comply with clearly defined fuel bands is considerable and involves high costs.

[0006] To avoid the disadvantages associated with the measures described above, other concepts can also be applied. One such concept involves inferring the fuel moisture content from the flue gas moisture content and using this knowledge to control the combustion system. This concept is described in more detail, for example, in DE 19917572 A1. A control system for a solid fuel combustion plant based on the water content in the flue gas is described in DE 102007055168 A1. Furthermore, the control of a combustion plant by inferring the fuel quality from the flue gas is described in DE 19547258 A1.

[0007] Another concept, described in DE 4446022 A1, is based on the understanding that waste incineration can only be carried out optimally if the composition or properties of the waste to be incinerated are determined before incineration and its combustion is adjusted to this information, thus enabling predictive operation of the waste incineration process. For this purpose, the water content of the waste to be incinerated is determined in the allocation shaft before incineration using microwave signals. The water content of the waste causes signal attenuation and / or phase changes in these microwave signals. These are evaluated to determine the water content in the waste.The information signals obtained are transmitted to a process control unit, which regulates the air supply for the waste combustion taking place on the grate. The microwave-based measurement technology requires significant installation effort and is also relatively expensive. Furthermore, the measurement is only available at discrete points.

[0008] From Austrian patent AT 15458 U1, a process for burning solid fuel, in particular lignin and agricultural biomass, is known in which the moisture content of the fuel is measured and, taking into account the energy content for a selected output, the fuel supply is increased at higher moisture content and decreased at lower moisture content. Furthermore, the proportion of primary and / or secondary air in the combustion air is selected depending on the measured moisture content of the fuel. The ratio in the combustion air between primary and secondary air on the one hand and recirculation gas on the other is also selected depending on the moisture content of the fuel. The moisture content of the fuel is also measured continuously or discontinuously during its storage or its supply through a fuel conveying channel. However, it is not specified how the moisture content of the fuel is measured.

[0009] Against this background, the object of the invention is to implement or specify measures for the process and plant for the thermal utilization of solid fuel in a reaction chamber, in which the water content of the fuel is determined before it is introduced into the reaction chamber and the thermal utilization process is controlled depending on the water content of the fuel, that allow for a simple and cost-effective determination of the water content of the fuel and possibly other parameters useful for controlling the thermal utilization process. JP 2003 028407 A and JP S52 113065 A disclose further processes for the thermal utilization of solid fuel in a reaction chamber.

[0010] With regard to the method, the problem of the invention is solved by a method according to claim 1.

[0011] With regard to the system, the problem of the invention is solved by a system according to claim 11.

[0012] Advantageous further developments of the invention can be found in the dependent claims.

[0013] The invention enables the provision of information about the fuel before it is transported into the reactor chamber. As a result, changes in fuel quality can be identified, and fuel properties relevant for efficient and targeted combustion can be derived from the data. This includes, in particular, information about the water content, bulk density, fines content, ash content, and calorific value. This information can be made available to the plant operator or the plant control system.

[0014] According to the invention, a gas stream, which can be air, nitrogen, recirculated gas, exhaust gas, or oxygen-enriched air, and which can have a temperature between -10°C and 200°C, is passed through a fuel bed in a container, which can be a storage container, a lock, a chute, a screw conveyor, or a container separate from a fuel supply device. Various physical processes occur as the gas flows through the bed: Heat transfer occurs from the gas stream to the fuel or vice versa; as a result, for example, the gas stream cools and the fuel bed heats up; the fuel dries and water is absorbed into the gas stream; pressure drops across the fuel bed; and volatile components are released at higher temperatures, which can be analyzed, for example, using a flame ionization detector (FID).

[0015] These processes lead to a change in the properties of the gas, which can be determined using relatively simple, standardized measuring instruments and methods, such as: Measurement of ambient temperature, pressure, and relative humidity (standard measurement technology: e.g., ambient temperature [°C] and relative humidity [%], Almemo®< connector; measuring range: -50°C to +200°C; 0% to 100% RH); measurement of temperatures within the packed bed as well as before and after the gas enters and exits the packed bed (standard measurement technology, e.g., sensors: thermocouples; NiCr-Ni Almemo®< connector type K; measuring range: -200°C to +1370°C); measurement of pressure before and after the packed bed (standard measurement technology: e.g., sensors: silicone tubing + metal tube; dynamic pressure / flow, Almemo®< connector; measuring range: 0 Pa to 6800 Pa). Measurement of the water content on the exhaust air side (standard measuring technology: e.g. gas analyzer Dr. Födisch MCA 04); measurement of the ambient pressure (standard measuring technology: digital manometer model Leo 2 from Keller (measuring range: 0 bar...300 bar; 0°C...50°C)).

[0016] The change in the gas parameters after the gas is packed can be recorded with temporal resolution. From the measurement curves, characteristic values ​​or functions (f Δp (t), fw (t)) are derived. f ' w (t) , fT(t) and fΔT(t)) are calculated. Changes in these parameters or their curves indicate a change in fuel quality or a different fuel altogether. This allows for the detection of fuel quality changes. Based on this information, warnings can be issued to the user and / or direct control interventions can be implemented.

[0017] The fuel feed can capture a partial flow from the total fuel mass flow or the entire fuel mass flow.

[0018] The fuel can flow through the fuel bed from top to bottom or from bottom to top.

[0019] The fuel bed and gas flow can preferably have a ΔT of at least 15 K.

[0020] The exhaust air from the fuel bed can be integrated into the thermal recovery process, e.g. as primary air or as secondary air.

[0021] The inventive measures can be retrofitted to existing plants or taken into account from the outset in new plants.

[0022] Coupling with other measuring devices is possible (process data of the plant, fuel scale, acquisition of image data of the fuel, etc.).

[0023] Pre-drying of the gas stream can be achieved, for example, by passing the gas stream through a silica gel bed to eliminate fluctuations caused by ambient air. This makes differences in the exhaust air even more apparent and further improves the process.

[0024] The invention makes it possible to provide information about the fuel before it enters the reaction chamber. Specifically, Changes in relevant fuel parameters, in particular water content and properties of the fuel bed, are recorded so that the system can be informed that a different fuel has been used and / or the fuel quality has changed; different fuel beds (pellets, wood chips, shavings, etc.) are differentiated using pressure drop, and information on the fines content is determined; the water content of the fuel can be inferred from the water content of the gas stream before it enters the fuel and after it exits the fuel; information on the "direction" of the change is provided, i.e., information on whether there has been an increase or decrease in water content or whether the particle size has increased or decreased; fuels and fuel qualities are assigned to groups based on the data and by comparing data sets; based on the detection of the fuel or...The operating modes of the plant are adapted to the fuel properties, e.g. by increasing or reducing the fuel mass flow, increasing or reducing the proportion of recirculated air, or increasing or reducing the preheating of the fuel air.

[0025] An embodiment of the invention will now be described with reference to the attached drawing figure, which schematically shows the basic structure of a system according to the invention and the basic sequence of a method according to the invention.

[0026] As can be seen from the drawing, a plant for the thermal utilization of solid fuel has a container 1 for receiving a fuel bed. The container 1 is located 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. Upstream of the container 1 is a hot air blower 2, which accelerates and heats a gas stream that has previously flowed through a drying device in the form of a silica gel bed 3. The gas stream exiting the hot air blower 2 flows through the fuel bed in the container 1.

[0027] Various physical parameters relevant to thermal utilization, such as the pressure and temperature of the gas flow before entering and after exiting the fuel bed, and, according to the invention, the moisture content of the gas flow before entering and after exiting the fuel bed, are measured using various measuring devices (not shown). These measured values ​​are fed to an evaluation unit 4, which provides information about the water content and other parameters relevant to thermal utilization, such as the density of the fuel bed and the proportion of fines in the fuel bed. The data determined by the evaluation unit 4 are fed to a control unit 5, which controls the thermal utilization process taking this data into account.The evaluation unit 4 can, when evaluating the measured values ​​supplied to it, refer to a database 6 in which certain data relevant to the thermal recycling process are stored.

[0028] Optionally, in addition to the fuel properties determined from the change in gas flow as it passes through the fuel bed, further fuel parameters can be recorded. These additional parameters can serve to further refine and / or validate the fuel properties determined from the gas flow changes as it passes through the fuel bed. For this purpose, additional measuring devices may be available. These may be selected from process data of the plant and / or a fuel scale for determining the fuel mass and / or a device for determining the bulk density and / or a device for acquiring image data of the fuel. The moisture content can also be determined from the change in fuel mass, resulting in redundant and therefore more reliable data acquisition.

[0029] Two approaches are used and combined to evaluate the measured values ​​and data supplied to the evaluation unit in order to achieve the best possible results: Data-based analysis involves comparing stored data or profiles with the generated measurements. Using methods such as cross-correlation or other comparable mathematical techniques, similarities and deviations are identified, and the type of fuel is determined based on these findings. This analytical approach requires information about the fuel's mass, at least initially.

[0030] For simplicity, this approach defines the fuel as a mixture of water, ash, and combustible material. Based on the mass and other measured values ​​(according to the invention, the water content in the supply and exhaust air), a mass and energy balance of the drying process is established. First, the amount of water driven off is calculated and then analytically derived back to the water content. The heating of the bulk material is assessed and recorded using the measured temperatures.

[0031] Naturally, the invention is not limited to the embodiments shown. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Where the claims and the foregoing description define "first" and "second" embodiments, this designation serves to distinguish between two similar embodiments without establishing any hierarchy.

Claims

1. Method for thermally recycling solid fuel in a reaction chamber, the water content of the fuel being determined before it is introduced into the reaction chamber, and the process of thermally recycling the fuel being controlled on the basis of the water content of the fuel, characterized in that a gas stream is passed through the fuel and the humidity of the gas stream after it leaves the fuel is measured and the water content of the fuel is determined from the measured value representing the humidity of the gas stream, the humidity of the gas stream being also measured before it enters the fuel and taken into account for determining the water content of the fuel.

2. Method according to claim 1, characterized in that the temperature of the gas stream is measured before it enters the fuel and / or after it leaves the fuel and is taken into account in the process control and / or in that the pressure of the gas stream is measured before it enters the fuel and / or after it leaves the fuel and is taken into account in the process control.

3. Method according to any one of claims 1 or 2, characterized in that the temperature of the gas stream is measured while it is in the fuel.

4. Method according to any one of claims 1 to 3, characterized in that the gas stream, before it enters the fuel, has a higher or lower temperature than the fuel at the point of entry of the gas stream into the fuel.

5. Method according to claim 4, characterized in that the temperature difference between the gas stream and the fuel is at least 15 K.

6. Method according to any one of claims 1 to 5, characterized in that the gas stream, before it enters the fuel, has a temperature which is in the range between -10°C and 200°C.

7. Method according to any one of claims 1 to 6, characterized in that the gas stream, after its exit, is used as primary air and / or secondary air in the thermal recycling of the fuel.

8. Method according to any one of claims 1 to 7, characterized in that the gas stream is dried before it enters the fuel or in that the gas stream is passed through a silica gel bed (3) in order to dry it.

9. Method according to any one of claims 1 to 8, characterized in that the gas stream consists of one of the following gases: air, nitrogen, recirculation gas, exhaust gas, air enriched with oxygen.

10. Method according to any one of claims 1 to 9, characterized in that the fuel through which the gas stream flows is the entire quantity or only a part of the fuel introduced into the reaction chamber.

11. Installation for thermally recycling solid fuel in a reaction chamber, upstream of which a container (1) is arranged in order to receive a fuel bed, the installation further containing a device for determining the water content of the fuel before it is introduced into the reaction chamber, and the installation further containing a control unit (5) which is designed to control the process of thermally recycling the fuel on the basis of the water content of the fuel, characterized in that the device for determining the water content contains a device (2) for generating a gas stream which can be passed through the fuel bed in the container (1), and furthermore a measuring apparatus for measuring the humidity of the gas stream before it enters the fuel bed and a measuring apparatus for measuring the humidity of the gas stream after it leaves the fuel bed, and an evaluation unit (4)) for determining the water content of the fuel from the measured value representing the humidity of the gas stream and in that the device for determining the water content is designed to transmit the thus determined water content of the fuel to the control unit (5) for it to be taken into account in the process control.

12. Installation according to claim 11, characterized in that the device for generating the gas stream includes a hot air blower (2) and / or in that the device for generating the gas stream includes a drying apparatus (3) for the gas stream.

13. Installation according to claim 12, characterized in that the drying apparatus (3) contains a silica gel bed through which the gas stream can be passed before it enters the fuel bed and / or in that the silica gel bed (3) is arranged upstream of the hot air blower (2).

14. Installation according to any one of claims 11 to 13, characterized in that the container (1) is a collection container, a lock, a chute, a screw or a container separate from a fuel supply apparatus.

15. Installation according to any one of claims 11 to 14, characterized in that the container (1) and the reaction chamber are connected by a line through which the gas stream can be passed after it leaves the fuel bed into the reaction chamber where it can be used as primary air and / or secondary air.