Thermogravimetric analyzer for large-size solid pyrolysis

Abstract

The invention discloses a thermogravimetric analyzer for large-size solid pyrolysis. The thermogravimetric analyzer comprises a furnace body, an electromagnetic heating device, a gas supply device, a measuring and recording device and a computer control and post-processing device, the furnace body is fixed by two bases, the upper part and the lower part of the furnace body are respectively provided with a smoke exhaust hole and an air inlet hole, the furnace body is made of a stainless steel material with high temperature resistance and high corrosion resistance, and a high-temperature-resistant and antioxidant coating is arranged in the furnace body; the electromagnetic heating device comprises a fixed bracket, an insulating layer, an electromagnetic heating coil and an electromagnetic heating controller; the gas supply device comprises a plurality of gas supply sources, a gas flow meter and a gas mixer; the measuring and recording device comprises a crucible, a temperature sensor, a pulley block, a weight and an electronic balance; the computer control and post-processing device is a high-performance computer and is mainly used for controlling the power of the electromagnetic heating device and realizing sample quality and temperature data processing and visualization. The system is simple in structure, reasonable in design, convenient to implement, capable of being effectively applied to a large-size solid pyrolysis simulation test in combination with a test method, rich in function, easy and convenient to operate, remarkable in effect and convenient to popularize, and simulation data can accurately reflect thermal weight loss and thermal conversion characteristics of a sample.

Description

Technical Field

[0001] The present invention relates to the technical field of thermogravimetric analysis, and particularly to a thermogravimetric analyzer for pyrolysis of large-sized solids. Background Art

[0002] A thermogravimetric analyzer is based on the principle that the mass of a sample changes with temperature and is used to study the thermal properties and pyrolysis behavior of materials. This instrument is widely used in the fields of materials science, chemistry, biology, etc. Traditional thermogravimetric analyzers have strict requirements for the mass, size, etc. of samples. The mass of samples is usually dozens or even thousands of milligrams, and the thermal properties of samples are mainly measured in the form of powders. At present, the mass of samples used in some engineering technology experiments has reached several hundred grams or even larger, far exceeding the mass of samples used in traditional thermogravimetric analyzers, and existing thermogravimetric analyzers cannot fully meet the requirements of engineering technology experiments.

[0003] Currently, the heating methods used in thermogravimetric analyzers mainly include resistance heating, radiation heating, and convection heating, etc. Heating samples by resistance has disadvantages such as poor heating uniformity, high energy consumption, and relatively slow response speed; the method of using a radiation source to send thermal energy to the heated sample has the problem that the non-uniformity of the sample receiving radiation will lead to non-uniform temperature distribution; while the convection heating method is limited by the shape and size of the sample and is difficult to meet the needs of large-sized samples. In contrast, electromagnetic heating, as an emerging heating method, has advantages such as high thermal efficiency, fast heating speed, energy conservation and environmental protection, high temperature control accuracy, safety and reliability, and simple maintenance, showing obvious advantages in thermogravimetric analyzers. Electromagnetic heating can achieve more uniform heating of samples, improve heating efficiency, and is more suitable for the pyrolysis of large-sized samples. Its non-contact feature also helps to reduce the influence of external factors on samples and improve the accuracy of experiments.

[0004] Based on the defects of existing thermogravimetric analyzers, it is necessary to provide a thermogravimetric analyzer for pyrolysis of large-sized solids. Summary of the Invention

[0005] The present invention mainly aims at the problems that existing thermogravimetric analyzers cannot measure and record the dynamic changes of mass and temperature with time during the pyrolysis process of large-volume solid samples and have low thermal efficiency, and provides a thermogravimetric analyzer for pyrolysis of large-sized solids with safe heating and high thermal utilization rate.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a thermogravimetric analyzer for pyrolysis of large-sized solids, including a furnace body, an electromagnetic heating device, a gas supply device, a measurement and recording device, and a computer control and post-processing device.

[0007] The furnace body is configured as an enclosed space with an opening door. There are a smoke exhaust hole and an air inlet hole respectively provided at the upper and lower parts of the furnace body. The furnace body is fixed by two bases. The furnace body is made of stainless steel material with high temperature resistance and high corrosion resistance to ensure the stability and durability of the furnace body under high temperature and corrosive atmosphere, and at the same time meet the pyrolysis conditions of solids containing corrosive products. The inner wall of the furnace body can be coated with a high temperature resistant and antioxidant coating to improve its service life.

[0008] The electromagnetic heating device consists of a fixed bracket, an insulating and heat-preserving layer, an electromagnetic heating coil, and an electromagnetic heating controller. The fixed bracket is made of high-temperature alloy steel material for metal with high temperature resistance and high strength, installed inside the furnace body, connected to the insulating and heat-preserving layer, and used to fix the insulating and heat-preserving layer. The insulating and heat-preserving layer is made of aluminum silicate fiber material with high temperature resistance and low thermal conductivity. The electromagnetic heating coil is made of nickel-chromium alloy material with high temperature resistance and good electrical conductivity, wound outside the insulating and heat-preserving layer, and responsible for converting the electrical energy of the electromagnetic heating controller into heat energy. The frequency converter uses an industrial-grade frequency converter with high stability and high precision to meet the precise control requirements of the electromagnetic heating coil. It is installed outside the furnace body and connected to the electromagnetic heating coil to convert direct current into alternating current. The frequency conversion control device is connected to an external power supply and connected to the frequency converter and the computer, and controls the frequency converter to output alternating current with different frequencies through the computer or directly through the frequency conversion control device.

[0009] The gas supply device consists of multiple gas cylinders, a gas flow meter, and a gas mixer. The gas cylinders are high-pressure gas cylinders to adapt to the storage requirements of different gases. The gas flow meter uses a flow measurement instrument with high precision and high stability to ensure the precise control of the gas flow. The gas mixer is made of stainless steel material with corrosion resistance and high temperature resistance to adapt to the working environment of high temperature and corrosive atmosphere. Each gas cylinder is respectively connected to the gas mixer through the gas flow meter to provide different atmospheres; the gas mixer is connected to the air inlet hole at the bottom of the furnace body to mix different gases and make the air flow uniform.

[0010] Measuring and recording device, consisting of a crucible, a temperature sensor, a pulley block, weights, and an electronic balance. The crucible is made of quartz material that is resistant to high temperatures and corrosion. The temperature sensor uses a high-temperature thermocouple sensor to measure the temperature change of the sample in real time. The pulley block is made of high-strength and high-temperature-resistant materials to ensure stability and safety in a high-temperature environment. The weights are high-precision and high-stability mass measuring instruments. The electronic balance uses a high-precision and high-stability industrial-grade electronic balance to meet the precise measurement requirements for the mass change of the sample. The crucible is located inside the furnace body, used to place the sample to be measured, and is connected to the weights by a rope; the temperature sensor is located above the crucible, and the other end is fixed to the computer through a pulley, uploading and recording the temperature change of the sample in real time; the pulley block is fixed above the furnace body; the weights are placed on the electronic balance, and the mass of the weights should be the same as that of the sample; the electronic balance is used to monitor the mass change of the sample and is connected to the computer, uploading and recording the mass change of the sample in real time.

[0011] Computer control and post-processing device, mainly used to control the frequency converter to output alternating current of different frequencies and process and visualize the sample mass and temperature data, realizing the automatic calculation of the kinetic parameters of the sample to be measured. Through the temperature sensor and the electronic balance, the temperature and mass change data during the pyrolysis process of the sample are collected in real time. The collected data is preprocessed, including steps such as Butterworth data filtering, wavelet denoising, and Savitzky-Golay data smoothing, to ensure the accuracy and reliability of the collected temperature and mass data. The Coats-Redfern integral method is used to calculate the reaction kinetic parameters of the sample under non-isothermal conditions, obtain information such as the apparent activation energy and frequency factor of the sample, and clarify the thermokinetic characteristics of the sample.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The present invention provides a thermogravimetric analyzer for the pyrolysis of large-sized solids, mainly used to measure the dynamic changes of temperature and mass over time during the pyrolysis process of large-sized solids. Compared with traditional heating devices, the present invention uses electromagnetic heating to heat the sample. It mainly directly physically heats the object through the action of a magnetic field, with high thermal utilization efficiency and uniform heating of the sample. At the same time, by controlling the frequency converter to output alternating current of different frequencies to control the magnetic field size, the temperature control accuracy is high, and combined with the measuring and recording device to collect the dynamic data of the mass and temperature during the pyrolysis process of the sample in real time, and through the computer control and post-processing device to process and visualize the pyrolysis data of the sample, realizing the measurement and recording of the thermogravimetric and thermal conversion characteristics of large-sized solid samples. Description of the Drawings

[0014] Figure 1 Front view of the structural schematic diagram of the thermogravimetric analyzer of the present invention with the furnace door open

[0015] Figure 2 It is an oblique rear view of the structural schematic diagram of the furnace door of the thermogravimetric analyzer of the present invention in the open state.

[0016] Figure 3 It is a graph showing the change rules of TG and DTG of the experimental sample.

[0017] Figure 4 It is the TG graph after Butterworth low-pass filtering, wavelet denoising and Savitzky-Golay smoothing processing.

[0018] Figure 5 It is the functional relationship between ln(-ln(1-α) / T2) and 1 / T of the experimental sample.

[0019] Figure 1 , 2 In the figures: 1. Furnace body; 2. Furnace door; 3. Door handle; 4. Base; 5. Air inlet hole; 6. Smoke exhaust hole; 7. Gas cylinder; 8. Flowmeter; 9. Gas mixer; 10. Fixed bracket; 11. Electromagnetic heating coil; 12. Insulating and heat-preserving layer; 13. Inverter; 14. Frequency conversion control device; 15. Computer; 16. Electronic balance; 17. Weights; 18. Pulley block; 19. Crucible; 20. Temperature sensor. Specific embodiments

[0020] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0021] As Figure 1 , 2 shown, a thermogravimetric analyzer for pyrolysis of large-sized solids includes a furnace body 1, an electromagnetic heating device, a gas supply device, a measurement and recording device, and a computer control and post-processing device.

[0022] The furnace body 1 is an internally hollow structure with an openable side, a furnace door 2 is installed on the open side, a door handle 3 is installed on the outer side of the furnace door 2, a smoke exhaust hole 6 and an air inlet hole 5 are respectively arranged at the center positions of the inner top and bottom of the furnace body 1, fixed brackets 10 are installed on the inner walls of the two sides adjacent to the furnace door 2 inside the furnace body 1, an insulating and heat-preserving layer 12 is installed inside the furnace body, the insulating and heat-preserving layer 12 is installed inside the furnace body through the fixed brackets 10, a crucible 19 for carrying large-sized solids is arranged at the top inside the furnace body, and bases 4 for fixing the furnace body are arranged at both ends of the outer side of the furnace body bottom.

[0023] The electromagnetic heating coil 11 is wound around the outside of the insulating and heat-preserving layer 12. Both ends of the electromagnetic heating coil 11 pass through the inside of the furnace body 1 and are connected to the opposite side of the side of the furnace door 2, and then connected to the frequency converter 13 outside the furnace body 1. The frequency conversion control device 14 is connected to the frequency converter 13, the external power supply, and the computer 15. The frequency conversion control device 14 adopts a closed-loop control mode. The measured solid is placed in the crucible 19. During the experiment, the crucible 19 is lowered into the insulating and heat-preserving layer 12. The frequency conversion control device 14 controls the frequency converter 13 to change the supply frequency and voltage, and the measured solid realizes the heating process with different heating rates by cutting the alternating magnetic field lines.

[0024] The measurement and recording device consists of an electronic balance 16, weights 17, a pulley block 18, a crucible 19, and a temperature sensor 20. The crucible 19 is arranged at the inner top of the furnace body 1, the temperature sensor 20 is arranged above the crucible, the electronic balance 16 and the weights 17 are arranged outside the furnace body 1, the pulley block 18 is arranged above the furnace body. The tail end of the temperature sensor 20 passes through the smoke exhaust hole 6 and is connected to the computer through the first pulley in the pulley block 18. The top of the crucible 19 is connected to a rope, the rope passes through the smoke exhaust hole 6 at the top of the furnace body 1 and successively bypasses the two pulleys of the pulley block 18 and is connected to one end of the weight 17. The mass of the weight 17 needs to be the same as the mass of the measured large-sized solid. The weight 17 is placed on the electronic balance 16. One end of the electronic balance 16 is connected to the computer 15. The measured large-sized solid is placed in the crucible 19. The temperature sensor 20 is inserted into the measured solid. The temperature and mass changes during the pyrolysis process of the measured solid are measured by the temperature sensor 20 and the electronic balance 16 and recorded by the computer 15.

[0025] The gas supply device consists of multiple gas cylinders 7, a flowmeter 8, and a gas mixer 9. The gas cylinders 7 are connected to the gas mixer 9 through pipelines. The gas mixer 9 is connected to the air inlet hole 5 at the center of the bottom of the furnace body 1 through a pipeline. The flowmeter 8 is arranged on the pipeline near the outlet of the gas cylinder 7 to detect the gas flow rate.

[0026] The number of gas cylinders 7 is multiple. The outlet of each gas cylinder 7 is connected to the inside of the gas mixer 9 through a pipeline. A flowmeter 8 is arranged on the pipeline near the outlet of each gas cylinder 7. Different atmospheres are set in different gas cylinders 7. By controlling the flow rate of different gas cylinders 7, the pyrolysis of the measured solid under different atmospheres can be realized.

[0027] Computer control and post-processing system, the core of which is dominated by a highly integrated state-of-the-art computer 15 that can control the thermogravimetric test bench and automatically calculate the thermokinetic parameters of the sample. The end of the temperature sensor 20, the end of the frequency conversion control device 14, and the end of the electronic balance 16 are all connected to the host computer 15 through USB cables. Through the cables, the measured solid mass and temperature data measured in real time by the temperature sensor 20 and the electronic balance 16 can be recorded into the computer 15. Through the computer 15, the collected temperature and mass data are preprocessed, and the changes in the temperature and mass of the measured solid are displayed in real time. At the same time, combining the sample temperature and mass data, using the Coats-Redfern integration method, the automatic calculation of the sample kinetic parameters is realized. The computer 15 can also directly control the frequency conversion control device 14 through the USB cable to make the frequency converter 13 change the power supply frequency and voltage, so as to achieve the purpose of changing the heating rate.

[0028] The computer control and post-processing device of the present invention can not only measure and record the temperature and mass changes of the sample during pyrolysis in real time, but also realize the automatic calculation of the sample kinetic parameters by using computer control and post-processing technology based on the collected relevant data. The specific implementation method is as follows: 1. Data collection Through the temperature sensor 20 and the electronic balance 16, the temperature and mass change data during the pyrolysis process of the sample are collected in real time. The temperature sensor 20 transmits the real-time temperature data of the sample to the computer 15 through the USB cable, and the electronic balance 16 transmits the real-time sample mass change data to the computer 15. Taking pulverized coal as the experimental sample, Figure 3 shows the thermogravimetric data graph of pulverized coal at a heating rate of 10K / min. 2. Data preprocessing The purpose of data preprocessing is to ensure the accuracy and reliability of the collected temperature and mass data, including steps such as data filtering, noise removal, and data smoothing. Users can select the data preprocessing method according to their needs. The specific method is as follows: (1) Data filtering Use a low-pass filter to remove high-frequency noise. Commonly used filters include Butterworth filters, Chebyshev filters, etc. Select the type and parameters of the filter to ensure that the useful signal is retained while the noise is removed. The design formula of the Butterworth low-pass filter is: In the formula, ω c is the cut-off frequency, and n is the filter order. Such as Figure 4As shown, it shows the effect of the Butterworth low-pass filter on TG data processing. Through bidirectional filtering (filtfilt function), phase distortion is effectively avoided, ensuring the integrity of the signal shape. The data after filtering is smoother, which helps with subsequent analysis. (2) Data denoising ① Use wavelet transform for denoising. Select a suitable wavelet basis (such as Daubechies wavelet), perform multi-scale decomposition, and decompose the signal into different frequency levels. Perform threshold processing (such as soft threshold or hard threshold) on the high-frequency layer, and then reconstruct the signal to remove noise. ② Basic steps of wavelet denoising: 1) Select the wavelet basis function and the number of decomposition levels. Select the Daubechies wavelet (db4), which has good local characteristics and frequency resolution ability when processing thermogravimetric analysis data. 2) Perform wavelet decomposition to obtain detail coefficients and approximation coefficients. Use the wavelet decomposition algorithm to decompose the original signal into detail coefficients and approximation coefficients at different scales. 3) Perform threshold processing on the detail coefficients. In the formula, N is the data length, coeffs are the detail coefficients obtained by wavelet decomposition, and median(|coeffs|) is the median of the absolute values of the detail coefficients. 4) Reconstruct the signal. Use the processed detail coefficients and the original approximation coefficients to perform inverse wavelet transform to reconstruct the denoised signal. Figure 4 It shows the effect diagram of wavelet denoising on TG data. Since wavelet transform has the ability of multi-scale analysis, it can extract signal features at different scales. The data after db4 can remove high-frequency noise, ensure the optimization of the denoising effect, and at the same time retain the important features of the signal. (3) Data smoothing processing ① Use the Savitzky-Golay filter, which performs smoothing processing through local polynomial fitting and can better retain the characteristics of the signal. ② The formula of the Savitzky-Golay filter is: In the formula, is the smoothed data point, c j is the convolution coefficient, m is the order of the fitting polynomial, and y i+j is the original data point. Figure 4Shows the effect after smoothing the TG data. After smoothing, the trend of the data becomes clearer, which is helpful for subsequent analysis and calculation. 3. Data Processing Analyze the preprocessed data, and use the basic principle of thermogravimetric analysis (TGA) to calculate the pyrolysis rate of the sample. The calculation formula for the pyrolysis rate is as follows: In the formula, Δm is the mass change, and Δt is the time change. 4. Activation Energy Calculation (Using Coats-Redfern Integration Method) (1) The Coats-Redfern integration method is used to solve the reaction kinetic parameters under non-isothermal conditions. Its integration formula is as follows: In the formula, α is the conversion rate, T is the absolute temperature, A is the frequency factor, β is the heating rate, E a is the activation energy, and T is the gas constant. (2) Conversion Rate Calculation ① The calculation formula for the conversion rate α is: In the formula, m0 is the initial mass, m t is the mass at any time, and m f is the final residual mass. ② Using the collected mass data, calculate the conversion rate α during the pyrolysis process point by point. (3) Plot the Linear Fitting Graph ① Under different heating rates β, conduct multiple thermogravimetric analysis experiments, and collect the temperature and mass data under different heating rates. ② Process the experimental data under different heating rates, and calculate the conversion rate α at each temperature point. ③ According to the Coats-Redfern integration formula, plot the graph line of. (4) Linear Fitting and Parameter Solving ① Use the least squares method to linearly fit the plotted graph line to obtain the slope and intercept of the fitting straight line. ② The slope is Calculate the activation energy E a through the slope: E a = - slope × R (7) In the formula, the gas constant R = 8.314 J / (mol·K). ③ The intercept is Calculate the frequency factor A through the intercept: As Figure 5 shows the function relationship between ln(-ln(1-α) / T 2 ) and 1 / T from the accelerating temperature when the TG data of the pre-treated experimental sample rapidly decreases to the burnout temperature when the sample mass drops to the lowest. By linearly fitting the plotted curve, it can be seen that R 2 reaches 0.958, and the fitting effect is good. The apparent activation energy E a of the sample is calculated to be 86.6788 kJ / mol, and the frequency factor A is 175362.1. Therefore, the present invention can preferably display the changes in the temperature and mass of the sample in real time, and at the same time, automatically calculate the kinetic parameters of the sample with high quality.

[0029] The present invention provides a thermogravimetric analyzer for pyrolysis of large-sized solids, which is mainly used to measure the dynamic changes of temperature and mass with time during the pyrolysis process of large-sized solids. Physical heating of the object is directly carried out through the action of a magnetic field, which has a high thermal utilization rate. The dynamic changes of mass and temperature during the pyrolysis process of large-sized solids are recorded by a temperature sensor and an electronic balance, and data processing and visualization are carried out through a computer control and post-processing device, so as to measure and record the thermogravimetric and thermal conversion characteristics of large-sized solid samples under different atmospheres, different heating rates and different gas flow rates.

[0030] The above content is only to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the present invention.

Claims

1. A thermogravimetric analyzer for pyrolysis of large-size solids, characterized in that: The invention comprises a furnace body (1), wherein an electromagnetic heating device is arranged in the furnace body (1), the bottom of the furnace body (1) is connected to a gas supply device through a pipeline, and a computer control and post-processing device is arranged outside the furnace body (1); a crucible (19) is also arranged inside the furnace body (1), and the crucible (19) is connected to a weight (17) outside the furnace body (1) through a rope, and the weight (17) is arranged on an electronic balance (16), and the mass of the weight (17) is the same as the mass of the solid to be measured, and a temperature acquisition device for measuring the temperature of the solid is also arranged on the crucible (19).

2. The thermogravimetric analyzer for large-size solid pyrolysis according to claim 1, characterized in that: The furnace body (1) is a rectangular parallelepiped with a hollow structure that can be opened on one side. Circular smoke exhaust holes (6) and air inlet holes (5) are provided at the center positions of the upper and lower parts of the furnace body (1). Fixed brackets (10) are provided twice on the left and right inside the furnace body (1) for fixing the insulating and heat-preserving layer (12).

3. The thermogravimetric analyzer for large-size solid pyrolysis according to claim 1, characterized in that: The gas supply device comprises a flow meter (8), a plurality of gas cylinders (7) and a gas mixer (9), each gas cylinder (7) is connected to the gas mixer (9) via a flow meter (8), and the gas mixer (9) is connected to the gas inlet (5) at the bottom of the furnace body (1).

4. The thermogravimetric analyzer for large-size solid pyrolysis according to claim 1, characterized in that: The electromagnetic heating device comprises an electromagnetic heating coil (11), an insulating and heat-preserving layer (12), a frequency converter (13) and a frequency conversion control device (14); the insulating and heat-preserving layer (12) is fixed inside a furnace body (1) through a fixing bracket (10), the electromagnetic heating coil (11) is wound around the outside of the insulating and heat-preserving layer (12), two ends of the electromagnetic heating coil (11) are connected to the frequency converter (13) outside the furnace body (1), and the frequency conversion control device (14) is electrically connected to an external power supply and is connected to the frequency converter (13) and a computer (15).

5. The thermogravimetric analyzer for large-size solid pyrolysis according to claim 1, characterized in that: The temperature sensor (20) is arranged above the crucible (19) through the smoke exhaust hole (6) at the top of the furnace body (1), and the other end of the temperature sensor (20) is connected to the computer (15) via a USB connection line to measure and record the temperature of the solid being measured in real time.

6. The thermogravimetric analyzer for large-size solid pyrolysis according to claim 1, characterized in that: The electronic balance (16) is connected to the computer (15) via a USB connection line to measure and record the mass of the solid being measured in real time.

7. The thermogravimetric analyzer for large-size solid pyrolysis according to claim 1, characterized in that: The computer control and post-processing device is composed of a computer (15), which is installed outside the furnace body (1) and connected to an electronic balance (16), a temperature sensor (20) and a frequency conversion control device (14). It can display the changes in the mass and temperature of the solid being measured in real time and can also display and adjust the state of the electromagnetic heating device.

8. The thermogravimetric analyzer for large-size solid pyrolysis according to claim 1, characterized in that: A fixed pulley is arranged on the outer side of the top of the furnace body (1), and a section of the rope passes through the fixed pulley and the smoke exhaust hole (6) in sequence to be connected to the crucible (19).

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