Measurement method for determining the amount of organic constituents in a wood ash

Abstract

The present invention relates to a measurement method for determining the amount of organic constituents in a wood ash, the method comprising the steps of: - providing ash samples, each having different quantitatively defined amounts of organic material, as reference samples; - recording at least one NIR spectrum of each of the reference samples using at least one NIR measurement head in a wavelength range between 1300 nm and 1800 nm, preferably between 1400 nm and 1650 nm; - assigning the different quantitatively defined amounts of organic material in the reference samples to the recorded NIR spectra of said reference samples; and - generating a calibration model for the correlation between the spectral data of the NIR spectra and the corresponding quantitatively defined amounts of organic material in the reference samples by means of multivariate data analysis; - providing at least one ash sample to be measured having an unknown amount of organic material; - recording at least one NIR spectrum of the provided ash sample using the at least one NIR measurement head in a wavelength range between 1300 nm and 1800 nm, preferably between 1400 nm and 1650 nm; and - determining the quantitative amount of organic material in the ash sample to be measured by comparing the NIR spectrum recorded for the ash sample to be measured with the calibration model generated from the reference samples.

Description

[0001] Measurement method for determining the amount of organic components in wood ash

[0002] The present invention relates to a measuring method for determining the amount of (unburned) organic components in wood ash, the use of the data determined by the measuring method for controlling the operating parameters of a combustion plant, and a combustion plant.

[0003] Description

[0004] Biomass, especially wood, has been used since ancient times to generate heat and energy through combustion. During the combustion process, most of the substances contained in the wood are oxidized. This produces heat energy as the main product and oxides as a byproduct. The carbon and nitrogen oxides escape into the atmosphere as gases (CO, CO2, NOx), while other unburned components remain as ash. The ash that remains in the combustion furnace is called grate ash or coarse ash and constitutes the largest fraction by volume. The resulting wood ash has a high pH value (i.e., it is alkaline) and must be disposed of as waste.

[0005] The ash content of the wood varies depending on the type of wood, the growing conditions, the felling time, etc., and averages between 0.3 and 0.6%; bark, fine twigs, needles and leaves have a higher ash content than the wood.

[0006] Wood ash comprises the mineral components of wood that remain as non-combustible inorganic components after the combustion of wood, as well as unburned organic components, particularly lignin, cellulose and hemicellus, depending on the combustion conditions.

[0007] The predominant inorganic components in wood ash are alkali and alkaline earth carbonates (14 to 19% K₂O, Na₂O; 30 to 40% CaO; 5 to 11% MgO). Other constituents include iron (1 to 3% Fe₂O₃), phosphates (0.4 to 5% P₂O₃), silicates (1.8 to 3% SiO₂), and sulfates (3 to 5% SO₃).

[0008] When operating boiler houses primarily fueled by biomass (wood waste, pellets, green waste, seedlings, sewage sludge, etc.), a key focus is on the complete combustion of organic components. Depending on the combustion technology and fuel used, problems can arise. Complete combustion is essential for the ash to be landfilled. However, depending on the landfill classification, the ash must contain less than a certain percentage of unburned material. Ideally, this percentage is less than three percent. Ash containing higher percentages of unburned material may not be accepted at certain landfills, or thermal post-treatment may be required before landfilling. All of these measures increase the landfilling costs.

[0009] Due to efforts at the European level to minimize waste and reuse residual materials, increasingly stringent quality requirements are being placed on combustion ash. These requirements must be ensured through close monitoring and control. The previously mentioned parameter of unburned components is particularly important for ash, as unburned material used in road construction, for example, can contaminate groundwater upon contact.

[0010] The content of organic / unburned components is determined by measuring the loss on ignition. In this process, the ash sample is heated to temperatures above 800°C for a defined period, and the mass loss is then measured. This procedure is complex, starting with sampling, weighing, ashing, and weighing, and can take hours. This is particularly critical for combustion systems that use lumpy wood waste, as combustion can be negatively affected by various parameters. Furthermore, only isolated values ​​can be obtained, which do not provide information about the overall situation. In addition, personnel and technical equipment must be procured for this monitoring.

[0011] This results in various disadvantages, such as a lack of continuous monitoring, a complex procedure involving high costs and time delays.

[0012] The invention is therefore based on the technical objective of providing a simple and rapid method to solve the problems described above. It should, if possible, enable continuous monitoring of the ashes. Furthermore, it should ensure the immediate transmission of values ​​so that an immediate reaction is possible in the event of changing values. The method should eliminate the need for time-consuming and expensive internal or external analyses of ashes. This objective is achieved according to the invention by a method with the features of claim 1.

[0013] Accordingly, a measurement method for determining the amount of (unburned) organic components in wood ash is provided, the method comprising the following steps:

[0014] - Providing wood ash samples with different (known, conventionally determined by loss on ignition) quantitatively defined amounts of organic material as reference samples;

[0015] - Recording of at least one NIR spectrum of each of the reference samples using at least one NIR measuring head in a wavelength range between 1300 nm and 1800 nm, preferably between 1400 nm and 1650 nm,

[0016] - Assigning the different quantitatively defined amounts of organic material in the reference samples to the recorded NIR spectra of the aforementioned reference samples; and

[0017] - Creating a calibration model for the relationship between the spectral data of the NIR spectra and the corresponding quantitatively defined amounts of organic material in the reference samples using a multivariate data analysis;

[0018] - Providing at least one wood ash sample to be measured, containing an unknown amount of organic material,

[0019] - Recording at least one NIR spectrum of the provided wood ash sample using the at least one NIR measuring head in a wavelength range between 1300 nm and 1800 nm, preferably between 1400 nm and 1650 nm, and

[0020] - Determining the quantitative amount of organic material in the wood ash sample to be measured by comparing the NIR spectrum recorded for the wood ash sample with the calibration model created from the reference samples. The present method thus enables the determination of the unburned organic components in the wood ash using NIR spectroscopy. The analysis is preferably carried out continuously directly downstream of the ash discharge point of the boiler house. For this purpose, an NIR measuring head is installed above the ash transport device. As explained in detail later, the NIR measuring head can control the boiler house parameters (fuel supply, grate speed, air supply, etc.) via feedback.

[0021] Furthermore, it is advantageously provided that the at least one NIR measuring head records several spectra per minute, preferably up to eight spectra per minute or more, typically between 8 and 30 spectra, preferably between 10 and 20 spectra, from which an average is formed over the number of recorded spectra.

[0022] The NIR measuring head used should also be insensitive to temperature fluctuations, dust and emissions of wood components.

[0023] This method enables the rapid provision of measurement data (online, preferably without disruptive delays). The measurement data can be used for quality assurance, research and development, process control, process regulation, process management, etc. The measurement process does not reduce production speed or other factors. In principle, it improves production monitoring. Furthermore, it also reduces downtime due to quality control and equipment adjustments.

[0024] The present method utilizes the fact that NIR radiation is reflected or scattered at the particle surface. The reflected or scattered NIR radiation is detected by the NIR detector, and the resulting NIR spectrum is used to determine the desired parameters (here, the proportion of organic material in wood ash).

[0025] The general possibility of using NIR spectroscopy to determine the ash and carbonization content of various biomasses is known from Labbe et al. (Bioresource Technology 99, 2008, 8445-8452). This study investigates various calibration models for evaluating NIR spectra recorded from different biomasses. The biomasses studied include woods such as oak or poplar, grasses, corn stalks, and bagasse. To cover all the different biomasses, NIR spectra are recorded in a wavelength range between 350 and 2500 nm.

[0026] In contrast, the focus of the present application is on the investigation of wood ash, in particular wood ash from coniferous trees, preferably pine, deciduous trees, preferably oak, or mixtures thereof. This requires an adaptation of the spectroscopic investigations, especially the selected wavelength range.

[0027] In a preferred embodiment of the present measurement method, it is therefore provided that spectral data from the recorded spectral range between 1300 and 1800 nm, in particular between 1400 and 1650 nm, are used to determine the amount of organic material contained in the wood ash.

[0028] According to the inventive method, reference samples of wood ash containing known amounts of organic material are first provided. The amount of unburned organic material is then determined using conventional methods (re-ashing and loss on ignition).

[0029] The amount of organic material in the reference samples is between 0 and 25 wt%, preferably between 1 and 20 wt%, particularly preferably between 2 and 15 wt%, most preferably between 3 and 10 wt%, and even more preferably between 4 and 8 wt% (based on the total amount of wood ash). In a particularly preferred embodiment, the content of unburned wood is below 10 wt%, preferably below 8 wt%, and even more preferably below 6 wt% (based on the total amount of wood ash).

[0030] At least one NIR spectrum is recorded from these reference samples in a wavelength range between 1300 nm and 1800 nm; in particular preferably between 1400 nm and 1650 nm.

[0031] The varying quantities of organic material in the reference samples are then assigned to the respective recorded NIR spectra of these reference samples. A calibration model is created for the relationship between the spectral data of the NIR spectra of the reference samples and the corresponding quantities of organic material in the wood ash as parameter values ​​using multivariate data analysis; that is, each parameter value of the reference sample corresponds to a specific NIR spectrum of the reference sample. The calibration models created for the various parameters are stored in a suitable data repository.

[0032] Subsequently, at least one ash sample containing an unknown amount of organic material is provided for measurement, and at least one NIR spectrum of this ash sample is recorded. The quantitative amount of organic material contained in the ash sample can be determined by comparing the NIR spectrum recorded for the sample with the established calibration model.

[0033] A comparison and interpretation of the NIR spectra is best performed across the entire recorded spectral range. This is advantageously carried out using a well-established multivariate data analysis (MDA). Multivariate analysis methods typically examine several statistical variables simultaneously in a well-established manner. These methods usually reduce the number of variables contained in a dataset without diminishing the information it provides.

[0034] In this case, multivariate data analysis is performed using partial least squares regression (PLS), which allows for the creation of a suitable calibration model. The evaluation of the obtained data is preferably carried out using appropriate analysis software, such as SIMCA-P from Umetrics AB or The Unscrambler from CAMO.

[0035] The significance of a wavelength for predicting parameters, such as the amount of organic material, from the NIR spectrum is illustrated using regression coefficients. Regions with large coefficient values ​​have a strong influence on the regression model. For example, the representation of regression coefficients in a PLS regression model shows that the wavelength range between 1400 nm and 1650 nm is most important for the model calculation, as the regression coefficient values ​​are highest in this range. While other regions of the spectrum contain less information related to the NIR measurement, they nevertheless contribute to incorporating and minimizing other information and interfering factors.

[0036] To eliminate interfering influences, it may be necessary to process the spectral data using mathematical pretreatment methods (e.g., derivative data pretreatment, standardization according to SNVT (Standard Normal Variate Transformation), multiplicative signal correction (EMSC, Extended Multiplicative Signal Correction, etc.). As already mentioned above, the organic material contained in the wood ash includes lignin, cellulose and / or hemicellulose, as well as their degradation products.

[0037] The amount of organic material to be determined in the wood ash is between 0 and 25 wt%, preferably between 1 and 20 wt%, particularly preferably between 2 and 15 wt%, most preferably between 3 and 10 wt%, and even more preferably between 4 and 8 wt% (based on the total amount of wood ash). In a particularly preferred embodiment, the content of unburned wood is below 10 wt%, preferably below 8 wt%, and even more preferably below 6 wt% (based on the total amount of wood ash).

[0038] The wood ash to be measured contains, in particular, calcium, magnesium, potassium, iron, phosphates, silicates, and sulfates as inorganic components. Typical inorganic components are alkali and alkaline earth carbonates (14 to 19% K₂O, Na₂O; 30 to 40% CaO; 5 to 11% MgO), iron (1 to 3% Fe₂O₃), phosphates (0.4 to 5% P₂O₃), silicates (1.8 to 3% SiO₂), and sulfates (3 to 5% SO₃).

[0039] The present measurement method for determining the amount of (unburned) organic components in wood ash is preferably carried out continuously online or offline after the wood ash has exited a combustion plant.

[0040] The ash to be analyzed can be continuously extracted as a partial stream from the total amount of ash or taken as a single sample at regular intervals (e.g., 1-2 per hour).

[0041] Preferably, the wood ash, in particular a partial stream of the discharged wood ash, is spread onto a continuously running conveyor belt after exiting the combustion plant and measured on the conveyor belt.

[0042] Prior to NIR measurement, the wood ash is ground after exiting the combustion system. After grinding, the wood ash to be measured has an average particle size of 10 to 1000 pm, preferably 30 to 700 pm, particularly preferably 50 to 500 pm, and even more preferably 100 to 300 pm. The layer thickness of the ash spread onto the conveyor belt is determined by the installed belt. Typical layer thicknesses of spread wood ash are between 1 mm and 100 mm, preferably between 10 and 80 mm, and particularly preferably between 30 and 50 pm.

[0043] In a further embodiment of the present method, it is provided that the at least one NIR measuring head moves transversely to the direction of travel of the conveyor belt sprinkled with wood ash and traverses over the entire width of the conveyor belt.

[0044] This provides a method in which the amount of unburned organic material in wood ash can be determined from a single NIR spectrum or from the reflection or scattering of NIR radiation using a non-contact measurement with an NIR measuring head. In an advantageous embodiment of the invention, the data obtained with the measuring head(s) are used directly for plant control or regulation.

[0045] In particular, the data determined using the present measurement method are used to control the operating parameters of a combustion plant (e.g. a boiler house) in which wood ash is obtained by burning wood.

[0046] The data on the amount of organic components in wood ash, determined using the measurement method described above, are thus used to control operating parameters of a combustion plant in which the wood ash is obtained by burning wood, especially wood waste.

[0047] Wood waste materials used include lump recycled wood, wood chips, shredded coated fiberboard, as well as wood dust, wood fibers, and wood shavings. The wood fibers, wood shavings, and wood dust are waste products generated during the production process of wood-based panels. Wood dust is produced particularly during the further processing of panels through mechanical machining (grinding and milling dust). The parameters for controlling the operating parameters of a combustion system are preferably selected from fuel supply, grate speed, air supply, and other factors.

[0048] The advantages of the present method are manifold: Non-contact multi-parameter determination ("real time" or "real-time" measurement) with significantly reduced time delay in the evaluation of the measured parameter values; improved plant control and regulation, reduction of scrap, improvement of the quality of the products manufactured on the plant, cost reduction and improvement of plant availability.

[0049] According to the invention, a combustion plant for burning biomass, in particular wood, is also provided, wherein the combustion plant is connected with the following elements:

[0050] At least one NIR multi-sensor head for recording at least one NIR spectrum of wood ash leaving the combustion plant in a wavelength range between 1300 nm and 1800 nm, particularly preferably between 1400 nm and 1650 nm,

[0051] - at least one control system for controlling the combustion plant, wherein the control system of the combustion plant comprises at least one computer-aided evaluation unit and a database,

[0052] - wherein at least one NIR multi-measuring head is connected to at least one control system with evaluation unit and database for processing and storing the recorded NIR data,

[0053] - wherein the evaluation unit is configured to determine the amount of organic material in the wood ash sample to be measured by an automated comparison of the NIR spectrum recorded for the wood ash sample with a created calibration model, wherein the calibration model is determined using reference samples (as described above);

[0054] - where the database is configured to store the data specified in this way, and

[0055] - whereby the specified data are used to control operating parameters, in particular fuel supply, grate speed, air supply, of the combustion system.

[0056] The NIR multi-measuring head is configured so that the measured parameters (actual values) are delivered to the evaluation unit, which, if the measured parameters (actual values) deviate from the corresponding target values ​​of these parameters, regulates the production process accordingly or controls it predictively.

[0057] Furthermore, the control system is configured to automatically adjust the system control in case of deviations of the measured parameters (actual values) from the target values ​​of these parameters.

[0058] For the calibration and control of the respective system, a computer-implemented procedure and a computer program comprising commands are provided. These commands, when executed by a computer, cause the computer to carry out the computer-implemented procedure. The computer program is stored in a memory unit of the control system of the respective production line.

[0059] The invention is explained in more detail below using exemplary embodiments with reference to the figures. The figures show:

[0060] Figure 1 NIR spectra recorded from a sample of wood ash with different proportions of organic material (0 wt%, 4 wt%, 11 wt% and 17 wt%)

[0061] Example 1:

[0062] Various boiler ash samples, whose content of unburned organic material was initially determined by post-combustion in a muffle furnace (800°C, 4 h), were analyzed using a NIR measuring head. Three individual samples were produced from each ash sample and measured. The post-ashing revealed values ​​of 0 wt%, 4 wt%, 11 wt%, and 17 wt% for unburned organic material.

[0063] The NIR spectra (see Figure 1) showed clear differences depending on the organic material content: 0 wt%, 4 wt%, 1 wt%, and 17 wt%. A regression line was calculated from these spectra using calibration software.

[0064] Subsequently, re-ashed samples were mixed with boiler ash samples whose organic material content was known and measured again with an NIR measuring head.

[0065] It was found that the measuring head determined the expected measured value with an error of less than 10%. Example 2:

[0066] Re-ashed boiler ash was homogeneously mixed with grinding dust from the grinding of HDF boards. 5, 10, 15, and 20 wt% grinding dust were added to the ash.

[0067] Then, using the NIR measuring head, measurements were taken on unburned organic material. The following values ​​were obtained:

[0068] The reduced results may be due to the glue content in the grinding dust, which should be lower in the boiler ash.

[0069] Example 3:

[0070] In a boiler house that uses various types of wood waste (lump recycled wood, wood chips, shredded coated fiberboard, etc.), it was to be tested at what fuel throughput the boiler ash reliably meets landfill class 1. Due to the heterogeneous fuel and the variable quantities of the different wood waste used, fluctuations in the loss on ignition occurred repeatedly.

[0071] For this purpose, the maximum fuel input of 10.2 tons of wood / hour was reduced in 2% increments.

[0072] The fuel mix was within the usual range. After approximately one hour, an ash sample (1 kg) was taken, homogenized in a mill under cooling, and the ash content of a portion of the sample was determined via loss on ignition (duplicate determination, muffle furnace, 800°C, 24 h). The fuel quantity was then further reduced. The ash content of another portion of the ash was determined using NIR spectroscopy (duplicate determination).

[0073] As can be seen from the table, the values ​​for the loss on ignition are always lower than those determined via NIR. However, the deviation is very small. Therefore, determining the loss on ignition via NIR allows for a significantly faster result. A 6% reduction in fuel throughput can reliably achieve a loss on ignition of less than 3%.

[0074] This results in advantages:

[0075] - Continuous monitoring

[0076] - Cost reductions

[0077] - Faster analysis

[0078] - Boiler house control

Claims

Patent claims 1. Measurement method for determining the amount of organic components in wood ash, comprising the steps - Providing wood ash samples with different, quantitatively defined amounts of organic material as reference samples; - Recording of at least one NIR spectrum of each of the reference samples using at least one NIR measuring head in a wavelength range between 1300 nm and 1800 nm, preferably between 1400 nm and 1650 nm - Assigning the different quantitatively defined amounts of organic material in the reference samples to the recorded NIR spectra of the aforementioned reference samples; and - Creating a calibration model for the relationship between the spectral data of the NIR spectra and the corresponding quantitatively defined amounts of organic material in the reference samples using a multivariate data analysis; - Providing at least one wood ash sample to be measured, containing an unknown amount of organic material, - Recording at least one NIR spectrum of the provided wood ash sample using the at least one NIR measuring head in a wavelength range between 1300 nm and 1800 nm, preferably between 1400 nm and 1650 nm, and - Determining the quantitative amount of organic material in the wood ash sample to be measured by comparing it to the amount of organic material used in the sample. Ash sample recorded NIR spectrum compared with the calibration model created from the reference samples.

2. Method according to claim 1, characterized in that spectral data from the entire recorded spectral range between 1300 nm and 1800 nm, in particular between 1400 and 1650 nm, are used to determine the amount of organic material contained in the wood ash.

3. Method according to one of the preceding claims, characterized in that the amount of organic material to be determined in the wood ash is between 0 and 25 wt%, preferably between 1 and 20 wt%, particularly preferably between 2 and 15 wt%, most preferably between 3 and 10 wt%, even more preferably between 4 and 8 wt% (based on the total amount of wood ash).

4. Method according to one of the preceding claims, characterized in that the content of unburned wood is below 10 wt%, preferably below 8 wt%, more preferably below 6 wt% (based on the total amount of wood ash).

5. Method according to any of the preceding claims, characterized in that the organic material contained in the wood ash comprises lignin, cellulose and / or hemicellulose, 6. Method according to one of the preceding claims, characterized in that the wood ash to be measured contains inorganic components, in particular calcium, magnesium, potassium, iron, phosphates, silicates, sulfates.

7. Method according to one of the preceding claims, characterized in that the determination of the amount of organic material contained in the wood ash is carried out continuously online or offline after the wood ash has exited a combustion plant.

8. Method according to one of the preceding claims, characterized in that the wood ash is ground after exiting the combustion plant.

9. Method according to one of the preceding claims, characterized in that the wood ash to be measured has an average particle size of 10 to 1000 pm, preferably 30 to 700 pm, particularly preferably 50 to 500 pm, more preferably 100 to 300 gm.

10. Method according to one of the preceding claims characterized in that the wood ash is scattered onto a continuously running conveyor belt after exiting a combustion plant and is measured on the conveyor belt.

11. Use of the data determined by the method according to the preceding claims for controlling the operating parameters of a combustion plant (e.g. a boiler house) in which the wood ash is obtained by burning biomass, in particular wood.

12. Use according to claim 11, characterized in that the parameters for controlling the operating parameters of a combustion plant are selected from fuel supply, grate speed, air supply.

13. Combustion plant for the combustion of biomass, in particular wood, combined with At least one NIR multi-sensor head for recording at least one NIR spectrum of wood ash leaving the combustion plant in a wavelength range between 1300 nm and 1800 nm, preferably between 1400 nm and 1650 nm, - at least one control system for controlling the combustion plant, wherein the control system of the combustion plant comprises at least one computer-aided evaluation unit and a database, - wherein at least one NIR multi-measuring head is connected to at least one control system with evaluation unit and database for processing and storing the recorded NIR data, - wherein the evaluation unit is configured to determine the amount of organic material in the wood ash sample to be measured by an automated comparison of the NIR spectrum recorded for the wood ash sample with a generated to determine a calibration model, wherein the calibration model is determined using reference samples according to claim 1; - where the database is configured to store the data specified in this way, and - wherein the specified data are used to control operating parameters, in particular fuel supply, grate speed, air supply, of the combustion system, 14. Combustion plant according to claim 13, characterized in that the NIR multi-measuring head is configured to supply the measured parameters (actual values) to the evaluation unit, which, in the event of deviations of the measured parameters (actual values) from the corresponding target values ​​of these parameters, regulates the production process accordingly or controls it predictively.

15. Combustion plant according to claim 13 or 14, characterized in that the control system is configured to make an automatic adjustment by the plant control in the event of deviations of the measured parameters (actual values) from the target values ​​of these parameters.

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