CN109030768B - Method for measuring shortest spontaneous combustion period of coal experiment - Google Patents
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- 239000001301 oxygen Substances 0.000 claims description 51
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
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Abstract
The invention relates to a method for measuring the shortest natural ignition period of a coal experiment, which belongs to a coal testing method and solves the problems of complex measuring method, low measuring accuracy and long period of the shortest natural ignition period of the existing coal experiment.
Description
Technical Field
The invention relates to a coal testing method, in particular to a method for measuring the shortest natural ignition period of a coal experiment.
Background
China is the most serious country of spontaneous combustion of coal in the world, and according to statistics, mines with more serious spontaneous combustion of coal in important coal mines in China account for about 56 percent. The natural ignition period of coal is an important parameter for guiding the on-site production of coal mines.
At present, the test method of the natural ignition period comprises the following steps: statistical method, analog method, large-scale experiment table method, small sample adiabatic experiment method, ignition model establishing method and the like. The results obtained by a statistical method and a comparison method are obtained according to the existing basic data, and experience errors exist; the large-scale laboratory bench method is to simulate the process of spontaneous combustion ignition of underground coal in a laboratory by establishing a large-scale ignition platform, and the method has the advantages of long experimental period, large coal consumption and high cost although the obtained result is high in accuracy; the small sample heat insulation experiment method simulates the spontaneous combustion process by establishing a small sample heat insulation spontaneous combustion device, and although the method has low cost and short period, the small sample experiment is difficult to explain the spontaneous combustion and ignition characteristics of a large amount of coal; the ignition model method is established by capturing main factors influencing coal spontaneous combustion and neglecting secondary factors, and the obtained result is poor in accuracy.
Disclosure of Invention
In view of the above analysis, the present invention aims to provide a method for measuring the shortest spontaneous combustion period in a coal experiment, so as to solve the problems of the existing method for measuring the shortest spontaneous combustion period in a coal experiment, such as complexity, large coal consumption, low measurement accuracy and long period.
The purpose of the invention is mainly realized by the following technical scheme:
the method for measuring the shortest natural ignition period of the coal experiment comprises the following steps:
a method for measuring the shortest spontaneous combustion period of a coal experiment comprises the following steps:
step S1: performing a temperature programming experiment on a coal sample, including a water evaporation stage and an oxygen uptake weight gain stage, and obtaining a series of thermogravimetric change data of the coal sample at different temperature rise rates in the stages;
step S2: calculating and obtaining a series of conversion rates of the stages according to the thermogravimetric change data; calculating to obtain apparent activation energy under different conversion rates according to the conversion rate, and fitting to obtain a function of the apparent activation energy and the conversion rate; acquiring a most probable mechanism function; according to the intercept and the most probable mechanism function under each conversion rate, obtaining the pre-pointing factor under the corresponding conversion rate, and obtaining the pre-pointing factor and the conversion rate function of the stage by the dynamic compensation effect;
performing a constant temperature experiment, respectively selecting a plurality of experiment temperatures in the stage as constant temperature experiment temperatures, obtaining the final residual thermogravimetry of the coal sample reaction at each constant temperature in the stage, calculating the conversion rate according to the thermogravimetry, and fitting to obtain a function of the temperature and the conversion rate in the stage;
step S3: and obtaining a natural ignition period solving formula by integrating and changing an Arrhenius rate equation, respectively bringing the stage apparent activation energy and conversion rate function, the most probable mechanism function, the pre-exponential factor and conversion rate function and the temperature and conversion rate function into the solving formula to obtain the reaction time of a moisture evaporation stage and an oxygen absorption weight gain stage, and adding the reaction times to obtain the shortest natural ignition period of the coal sample experiment.
On the basis of the scheme, the invention is further improved as follows:
further, according to a common solid-phase reaction kinetic mechanism function and temperatures corresponding to different conversion rates, a probable activation energy corresponding to each mechanism function at each conversion rate is obtained, and a mechanism function corresponding to a probable activation energy closest to the apparent activation energy value is a most probable mechanism function.
Further, the temperature programming experiment comprises the following steps: in the step S1, air flows with set oxygen concentration are respectively introduced into the temperature-programmed meters, and the flow rate is 100 ml/min; setting the initial temperature as the environment temperature, the heating rates as 1 deg.C/min, 2 deg.C/min, 4 deg.C/min and 8 deg.C/min, the experiment end temperature as 400 deg.C, and taking 10mg coal sample for each experiment.
Further, the calculation formula of the stage conversion rate in the temperature programming experiment is as follows:
wherein α is the conversion rate, α is more than 0, m0Initial thermal weight, mg; m is the thermal weight value in mg during the reaction; m is total change of stage thermogravimetry, mg.
Further, the conversion rate of the stage is between 0.05 and 0.95, the interval of the conversion rate is 0.05, the temperature corresponding to the conversion rate and the corresponding temperature rising rate are put into a Starink equation, and the apparent activation energy of the stage and the conversion rate function E (α) are obtained by fitting:
wherein, C is a constant term, and the calculation formula of C is as follows:
wherein β is the temperature programming rate, DEG C/min, T is the temperature of the reaction process, K, E is the apparent activation energy, kJ/mol, g (α) is the most probable mechanism function, A is a pre-factor;
the most probable mechanism function g (α) for the stage-to-conversion is:
the solution formula of the pre-pointing factor is as follows:
further, the relationship between the pre-factor and the conversion rate is as follows:
lnA＝aE+b
wherein a and b are dynamic compensation coefficients;
the kinetic compensation coefficients a and b are obtained by fitting apparent activation energy and pre-exponential factors under different conversion rates;
and obtaining a pre-exponential factor and conversion function A (α) according to the apparent activation energy and conversion function E (α).
Further, the most probable mechanism function is obtained by fitting and solving data within the conversion rate range of α +/-0.025, and when the shortest spontaneous combustion period of the coal experiment is calculated, the same most probable mechanism function is used within the conversion rate range of α +/-0.025.
Further, the natural ignition period solving formula is as follows:
calculating the natural ignition period t of the water evaporation stage by using the natural ignition period solving formula1And the natural ignition period t of oxygen uptake weight increasing stage2The shortest natural ignition period of the experiment for obtaining the coal sample is t1+t2。
Further, before the step S1, selecting fresh raw coal to grind, and screening coal particles with a particle size of 120-160 meshes as a coal sample to be detected.
Further, the coal sample is placed in a cool and dry position for sealed preservation; the temperature in the constant temperature experiment is an integer.
The invention has the following beneficial effects:
a) the method for measuring the shortest natural ignition period in the coal experiment provided by the invention utilizes a TG-DSC combined synchronous thermal analyzer to carry out program constant temperature test and constant temperature test, the experiment operation is convenient, the coal sample dosage in each experiment is only 10mg, the coal dosage is small, and the experiment period is short.
b) According to the method for measuring the shortest natural fire period of the coal experiment, provided by the invention, the temperature programming experiment comprises a moisture evaporation stage and an oxygen uptake weight gain stage, formula transformation derivation is skillfully performed through a series of experimental data, the method for obtaining the shortest natural fire period of the coal experiment is simple, the shortest natural fire period of the coal experiment is the total time of the moisture evaporation stage and the oxygen uptake weight gain stage, the measurement accuracy is high, the cost is obviously reduced under the condition of ensuring the measurement accuracy, and the method has wide practicability.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
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The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a flow chart of the method for testing the shortest spontaneous combustion period in a coal experiment.
Detailed Description
The present invention is described in detail with reference to the following drawings, which form a part hereof, and which are included to illustrate and not to limit the scope of the invention, the names and notations of the functions in the present invention are defined as conversion α, apparent activation energy E, apparent activation energy and conversion function E (α), and probable activation energy E for each mechanism functionxPre-exponential factor A, pre-exponential factor and conversion function A (α), most probable mechanism function g (α), most probable mechanism function differential form f (α), and commonly used several solid phase reaction mechanism functions g (α)xA reaction process temperature T, a temperature and conversion function T (α).
The invention discloses a method for testing the shortest natural ignition period of a coal experiment, which comprises the following steps:
step S1: performing a temperature programming experiment on a coal sample, including a moisture evaporation stage and an oxygen uptake weight gain stage, and obtaining a series of thermogravimetric change data of the moisture evaporation stage and the oxygen uptake weight gain stage (which can be simply referred to as 'each stage') at different temperature rise rates;
step S2: calculating a series of conversion rates of a water evaporation stage and an oxygen absorption weight increasing stage according to the series of thermogravimetric change data in the step S1; calculating to obtain apparent activation energy under different conversion rates according to the series of conversion rates, and fitting to obtain a function of the apparent activation energy and the conversion rate; according to a common solid-phase reaction kinetic mechanism function and temperatures corresponding to different conversion rates, obtaining a probable activation energy corresponding to each mechanism function under each conversion rate, wherein the mechanism function corresponding to the probable activation energy closest to the apparent activation energy value is the most probable mechanism function; according to the intercept and the most probable mechanism function under each conversion rate, obtaining the pre-exponential factor under the corresponding conversion rate, and obtaining the pre-exponential factor and the conversion rate function of the stage by the dynamic compensation effect;
carrying out constant temperature test, respectively selecting a plurality of test temperatures as constant temperature test temperatures in a moisture evaporation stage and an oxygen absorption weight increasing stage, obtaining the final residual thermogravimetry of the coal sample reaction at each constant temperature in the moisture evaporation stage and the oxygen absorption weight increasing stage, calculating the conversion rate according to the thermogravimetry, and fitting to obtain the temperature and conversion rate functions of the moisture evaporation stage and the oxygen absorption weight increasing stage;
step S3: obtaining a natural ignition period solving formula by integrating and changing an Arrhenius rate equation, respectively bringing apparent activation energy and conversion rate functions, most probable mechanism functions, pre-indication factors and conversion rate functions and temperature and conversion rate functions of a moisture evaporation stage and an oxygen absorption weight increasing stage into the natural ignition period solving formula to obtain reaction times of the moisture evaporation stage and the oxygen absorption weight increasing stage, and adding the reaction times of the two stages to obtain the shortest natural ignition period of the coal sample experiment.
The method comprises the following specific steps:
step S1:
the method comprises the following steps of carrying out a programmed heating experiment on a coal sample by utilizing a TG-DSC combined synchronous thermal analyzer, wherein the programmed heating experiment comprises a moisture evaporation stage and an oxygen absorption weight increasing stage, the low-temperature oxidation stage of the coal is a process that the thermogravimetric change of the coal sample obtained by the programmed heating experiment is firstly reduced and then increased, the end point temperature of the thermogravimetric increase process is approximately the ignition point temperature, the moisture evaporation stage is a thermogravimetric reduction process, and the oxygen absorption weight increasing stage is a thermogravimetric increase process. Obtaining a series of thermogravimetric change data, an initial thermogravimetric value, a thermogravimetric value at a corresponding temperature and a total thermogravimetric change amount at a research stage under different temperature rise rates at a water evaporation stage and an oxygen absorption weight increasing stage through a temperature programming experiment; the temperature programming experiment comprises the following steps: respectively introducing airflow with set oxygen concentration into a temperature programming instrument, preferably, the oxygen concentration is 8-21%, and the flow of the introduced airflow is 100 ml/min; the initial temperature is set as the environmental temperature in the experiment, the heating rates are respectively 1 ℃/min, 2 ℃/min, 4 ℃/min and 8 ℃/min, the temperature of the end of the experiment is 400 ℃, 10mg of coal samples are taken in each experiment, and thermogravimetric change data under different temperature rates are obtained.
Before step S1, selecting fresh raw coal to grind, screening coal particles with a particle size of 120-160 meshes as a coal sample to be tested, and placing the coal sample to be tested in a cool and dry position for sealed storage to avoid the influence on the experimental result caused by water absorption or oxidation of the coal sample to be tested.
Step S2:
the low-temperature oxidation stage of the coal spontaneous combustion period research is divided into two stages of water evaporation and oxygen uptake weight increment. Calculating a series of conversion rates corresponding to each stage at a certain temperature according to the thermogravimetric change data obtained at each stage of the temperature programming experiment in the step S1, wherein the conversion rates are positive numbers, and the calculation formula of the conversion rate corresponding to each stage in the temperature programming experiment is as follows:
wherein α is the conversion rate, α is more than 0, m0Initial thermal weight, mg; m is the thermal weight value in mg during the reaction; m is total change of stage thermogravimetry, mg.
Calculating to obtain apparent activation energy under different conversion rates, and fitting to obtain a function of the apparent activation energy and the conversion rate, wherein the conversion rate of each stage in a temperature programming experiment is 0.05-0.95, the intervals of a series of selected conversion rates are 0.05, the temperature corresponding to the conversion rate and the corresponding temperature rise rate are introduced into a Starink equation, and the function E (α) of the apparent activation energy and the conversion rate of each stage obtained by fitting is as follows:
in the process of solving the apparent activation energy, the value of a constant term C corresponding to each conversion rate is obtained at the same time, and the calculation formula of the constant term C is as follows:
wherein β is the temperature programming rate, DEG C/min, T is the temperature of the reaction process, K, E is the apparent activation energy, kJ/mol, and g (α) is the most probable mechanism function;
according to the expression formula of the constant term C and the most probable mechanism function corresponding to each conversion rate, the formula is substituted into an index factor solving formula shown as follows:
obtaining the pre-factor of the conversion rate within the range of 0.05-0.95 at every 0.05, obtaining the pre-factor and the conversion rate function by using the kinetic compensation effect, namely the internal relation of lnA and E, wherein the expression is shown as the following formula,
lnA＝aE+b
in the formula, a and b are kinetic compensation coefficients, the kinetic compensation coefficients are obtained by fitting apparent activation energy and pre-exponential factors obtained by taking conversion rate every 0.05 within the range of 0.05-0.95, and then the pre-exponential factors and conversion rate function A (α) is obtained according to the obtained functional relation formula E (α) of the apparent activation energy and the conversion rate.
Specifically, 20 common solid-phase reaction kinetic mechanism functions in the attached table 1 and the temperature corresponding to the value of the apparent activation energy at every 0.05-0.95 intervals of a value of the conversion rate in each stage are taken into a deformation formula of a Starink equation to obtain the probable activation energy corresponding to the mechanism functions at different conversion rates, and compared with the apparent activation energy value corresponding to each conversion rate obtained in the above step, the function corresponding to the closest probable activation energy is the most probable mechanism function g (α) at each stage corresponding to the conversion rate,
when the most probable mechanism function with the conversion rate of 0.05-0.95 every 0.05 is obtained, the most probable mechanism function is subjected to fitting solution through data in the conversion rate range of α +/-0.025, if the most probable mechanism function with the conversion rate of 0.05 is obtained, the range of 0.025-0.075 needs to be fitted, and similarly, the most probable mechanism function with the conversion rate of 0.9 needs to be fitted, the range of 0.875-0.925 needs to be fitted, and correspondingly, when the shortest spontaneous combustion period of the coal experiment is calculated, the corresponding most probable mechanism function is used in the conversion rate range of α +/-0.025.
Table 1 section commonly used solid phase reaction kinetics mechanism function
Since the Arrhenius rate equation is used for calculating the natural ignition period of the coal sample, the function T (α) of the temperature T relative to the conversion rate α in the reaction process needs to be known, and the expression of T (α) is difficult to be deduced according to the heat flow and thermogravimetric curves by the existing consulted reference and knowledge capacity, therefore, the function T (α) of the temperature T relative to the conversion rate α in the reaction process is obtained by performing constant temperature experiments.
When the constant temperature test is carried out, a plurality of test temperatures are respectively selected as constant temperature test temperatures in a moisture evaporation stage and an oxygen absorption weight increasing stage, the reaction is fully carried out at a fixed temperature, the final residual thermogravimetry of the coal sample reaction at each constant temperature in the moisture evaporation stage and the oxygen absorption weight increasing stage is obtained, the conversion rate is calculated according to the final residual thermogravimetry, and a function T (α) of the temperature and the conversion rate of each stage is obtained through fitting.
Step S3:
obtaining a natural ignition period solving formula for the integral change of the Arrhenius rate equation, wherein the solving formula is as follows:
respectively introducing the apparent activation energy and conversion rate functions, the most probable mechanism function, the pre-indicator factor and conversion rate function and the temperature and conversion rate function of the water evaporation stage and the oxygen absorption weight gain stageObtaining the time t of the water evaporation stage in the solving formula1And time t of oxygen uptake weight gain stage2Adding the reaction time of the water evaporation stage and the oxygen absorption weight increasing stage to obtain the shortest natural ignition period t of the coal sample experiment1+t2。
The apparent activation energy in the moisture evaporation stage and the oxygen uptake weight gain stage is the same as the method for solving the function E (α) of the conversion rate, the function g (α) of the most probable mechanism, the function a (α) of the index factor and the conversion rate, the function T (α) of the temperature change with the conversion rate, and the experimental shortest spontaneous combustion period time of the coal sample in each stage.
Compared with the prior art, the method for measuring the shortest natural ignition period of the coal experiment provided by the embodiment has the advantages of simple method for obtaining the shortest natural ignition period of the coal experiment, convenience in experiment operation, less coal consumption, high measurement accuracy and short period, obviously reduces the cost under the condition of ensuring the measurement accuracy, and has wide practicability.
The following will further explain this embodiment by taking the natural ignition period of raw coal in a certain mining area of Xinjiang as an example:
taking raw coal of a certain mining area in Xinjiang, grinding the raw coal, screening out particles with the particle size of 120-160 meshes as an experimental test coal sample, taking 10mg of coal sample thermal analyzer which is an SDT-Q600 type TG-DSC combined synchronous thermal analyzer produced by American TA company, introducing gases with oxygen concentrations of 21%, 16%, 12% and 8% into each experiment, and carrying out the experiment at each oxygen concentration at 4 heating rates (1 ℃/min, 2 ℃/min, 4 ℃/min and 8 ℃/min) until the end of the experiment at 400 ℃; the water evaporation stage is carried out at constant temperature of 30 deg.C, 40 deg.C, 50 deg.C, 60 deg.C and 70 deg.C, and the oxygen absorption weight increasing stage is carried out at constant temperature of 90 deg.C, 110 deg.C, 120 deg.C, 140 deg.C and 160 deg.C.
Converting thermogravimetric data obtained from temperature programming experiments into conversion rate, wherein the conversion rate is ln (β/T) at a value of every 0.05 in the range of 0.05-0.951.92) Regarding a scatter diagram of (-1.0008/RT), fitting to obtain the apparent activation energy E and the intercept C under each conversion rate, namely a constant C, and performing linear fitting in stages to obtain a function of the apparent activation energy and the conversion rate to obtainSpecific results of the functions of the activation energy and the conversion rate of the coal sample in the water evaporation stage and the oxygen absorption weight increasing stage of a certain mining area in Xinjiang are shown in tables 2 and 3;
ln [ g (α) for a fixed conversion according to the general 20 solid phase theory functions listed in Table 1x/T1.92]Obtaining the probable activation energy E under each mechanism function by fitting a scatter diagram of (-1.0008/RT)xBy comparing the apparent activation energies E and ExThe most probable activation energy corresponds to the most probable mechanism function g (α) at the conversion.
For any reaction stage, making lnA scatter diagram about E and fitting to obtain values of kinetic compensation coefficients a and b, and then obtaining the pre-exponential factor and conversion rate function A (α) according to the apparent activation energy and conversion rate function E (α);
converting the thermogravimetric value at the corresponding temperature obtained in the constant temperature experiment into a conversion rate according to the thermogravimetric change value at each stage of the temperature programming experiment, and fitting to obtain a function T (α) of the temperature changing along with the conversion rate;
in the process of obtaining the natural ignition period of raw coal in a certain mining area in Xinjiang, the apparent activation energies of the moisture evaporation stage and the oxygen-absorbing weight-increasing stage are the same as the conversion rate function E (α), the most probable mechanism function g (α), the pre-factor and conversion rate function A (α), the temperature-dependent conversion rate function T (α), and the solving method of the experimental shortest natural ignition period time of the coal sample in each stage, and the obtained correlation functions are listed in tables 2 to 9, wherein tables 2 to 4 are correlation function lists of the moisture evaporation stage under different oxygen concentrations, tables 5 to 8 are correlation function lists of the oxygen-absorbing weight-increasing stage under different oxygen concentrations, and table 9 is a T (α) function list corresponding to the temperature and the conversion rate.
TABLE 2 function list of moisture evaporation stage E (α) at different oxygen concentrations
TABLE 3 list of the most probable mechanism function g (α) corresponding to each conversion in the water evaporation stage with different oxygen concentrations
TABLE 4 list of functions of evaporation stage A (α) for water with different oxygen concentrations
TABLE 5 tabulation of oxygen uptake gain stage E (α) function at different oxygen concentrations
TABLE 6 tabulation of the most probable mechanism function g (α) corresponding to each conversion rate at different oxygen concentration oxygen uptake weight gain stages
TABLE 7 oxygen uptake weight gain stage A (α) function for different oxygen concentrations
TABLE 8T (α) function of temperature at each stage versus conversion
And substituting the obtained solving results of the kinetic parameters, the temperature and the pre-exponential factors into a natural ignition period solving formula to obtain the shortest experimental natural ignition period under different oxygen concentrations, wherein the specific results are shown in a table 9.
TABLE 9 natural ignition period solution of raw coal in certain mining area of Xinjiang
According to the experimental results in table 9, the laboratory shortest spontaneous combustion period of the coal sample in a certain mining area in Xinjiang increases with the decrease of the oxygen concentration, the experimental shortest spontaneous combustion period is 16.65d under the condition of 21% oxygen concentration, the experimental shortest spontaneous combustion period is 16.56d under the condition of 16% oxygen concentration, the experimental shortest spontaneous combustion period is 18.71d under the condition of 12% oxygen concentration, and the experimental shortest spontaneous combustion period is 26.94d under the condition of 8% oxygen concentration.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (7)
1. A method for measuring the shortest spontaneous combustion period of a coal experiment is characterized by comprising the following steps:
step S1: performing a temperature programming experiment on a coal sample, including a water evaporation stage and an oxygen uptake weight gain stage, and obtaining a series of thermogravimetric change data of the coal sample at different temperature rise rates in the stages;
step S2: calculating and obtaining a series of conversion rates of the stages according to the thermogravimetric change data; calculating to obtain apparent activation energy under different conversion rates according to the conversion rate, and fitting to obtain a function of the apparent activation energy and the conversion rate; acquiring a most probable mechanism function; according to the intercept and the most probable mechanism function under each conversion rate, obtaining the pre-pointing factor under the corresponding conversion rate, and obtaining the pre-pointing factor and the conversion rate function of the stage by the dynamic compensation effect;
performing a constant temperature experiment, respectively selecting a plurality of experiment temperatures in the stage as constant temperature experiment temperatures, obtaining the final residual thermogravimetry of the coal sample reaction at each constant temperature in the stage, calculating the conversion rate according to the thermogravimetry, and fitting to obtain a function of the temperature and the conversion rate in the stage;
step S3: obtaining a natural ignition period solving formula by integrating and changing an Arrhenius rate equation, respectively bringing the stage apparent activation energy and conversion rate function, the most probable mechanism function, the pre-exponential factor and conversion rate function and the temperature and conversion rate function into the solving formula to obtain reaction times of a moisture evaporation stage and an oxygen absorption weight gain stage, and adding the reaction times to obtain the shortest natural ignition period of a coal sample experiment;
according to the solid-phase reaction kinetics mechanism function and the temperatures corresponding to different conversion rates, obtaining the probable activation energy corresponding to each mechanism function under each conversion rate, wherein the mechanism function corresponding to the probable activation energy closest to the apparent activation energy value is the most probable mechanism function;
the temperature programming experiment comprises the following steps: in the step S1, air flows with set oxygen concentration are respectively introduced into the temperature-programmed meters, and the flow rate is 100 ml/min; setting the initial temperature as the ambient temperature, the heating rates of 1 ℃/min, 2 ℃/min, 4 ℃/min and 8 ℃/min respectively, the end temperature of the experiment is 400 ℃, and taking 10mg of coal samples in each experiment;
the natural ignition period solving formula is as follows:
in the above formula, α is a conversion rate, α > 0, E (α) is a function of stage apparent activation energy and conversion rate, A (α) is a function of prespecified factors and conversion rate, f (α) is a derivative form of a function of the most probable mechanism, and T (α) is a function of temperature and conversion rate;
calculating the natural ignition period t of the water evaporation stage by using the natural ignition period solving formula1And the natural ignition period t of oxygen uptake weight increasing stage2The shortest natural ignition period of the experiment for obtaining the coal sample is t1+t2。
2. The method for measuring the shortest spontaneous combustion period in a coal experiment according to claim 1, wherein the calculation formula of the stage conversion rate in the temperature programming experiment is as follows:
wherein α is the conversion rate, α is more than 0, m0Initial thermal weight, mg; m is the thermal weight value in mg during the reaction; m is total change of stage thermogravimetry, mg.
3. The method of claim 1, wherein the stage conversion rate is 0.05-0.95, the conversion rate interval is 0.05, the temperature and the temperature rise rate corresponding to the conversion rate are put into a Starink equation, and the stage apparent activation energy and conversion rate function E (α) is obtained by fitting:
wherein, C is a constant term, and the calculation formula of C is as follows:
wherein β is the temperature programming rate, DEG C/min, T is the temperature of the reaction process, K, E is the apparent activation energy, kJ/mol, g (α) is the most probable mechanism function, A is a pre-factor;
the most probable mechanism function g (α) for the stage-to-conversion is:
the solution formula of the pre-pointing factor is as follows:
4. the method of claim 3, wherein the pre-exponential factor as a function of conversion is:
lnA＝aE+b
wherein a and b are dynamic compensation coefficients;
the kinetic compensation coefficients a and b are obtained by fitting apparent activation energy and pre-exponential factors under different conversion rates;
and obtaining a pre-exponential factor and conversion function A (α) according to the apparent activation energy and conversion function E (α).
5. The method as claimed in claim 3, wherein the most probable mechanism function is calculated by fitting data with a conversion rate of α ± 0.025, and the same most probable mechanism function is used with a conversion rate of α ± 0.025 in calculating the shortest spontaneous combustion period of the coal experiment.
6. The method as claimed in any one of claims 1 to 5, wherein before the step S1, fresh raw coal is selected and ground, and the coal particles with particle size of 120-160 meshes are selected as the coal sample to be tested.
7. The method for measuring the shortest spontaneous combustion period in the coal experiment according to any one of claims 1 to 5, wherein the coal sample is placed in a cool and dry position for sealed preservation; the temperature in the constant temperature experiment is an integer.
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