CN113670980B - Method for determining shortest natural ignition period of coal - Google Patents
Method for determining shortest natural ignition period of coal Download PDFInfo
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- CN113670980B CN113670980B CN202110846680.9A CN202110846680A CN113670980B CN 113670980 B CN113670980 B CN 113670980B CN 202110846680 A CN202110846680 A CN 202110846680A CN 113670980 B CN113670980 B CN 113670980B
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Abstract
The invention mainly discloses a method for determining the shortest natural ignition period of coal, which comprises the following steps: acquiring the ignition temperature of coal; acquiring a shortest firing period model of the coal, wherein the shortest firing period model is used for reflecting the mapping relation between the exposure time and the coal temperature from the time of exposing the coal to air; determining a rapid heating stage of coal in the shortest ignition period model, wherein the temperature of the coal in the rapid heating stage and the exposure time are approximately in a linear relation, and the ignition temperature is in a range of the temperature of the coal corresponding to the rapid heating stage; and determining the shortest natural ignition period corresponding to the ignition temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage. According to the invention, the calculation of the shortest ignition period can be realized by combining data such as ignition temperature, chemical reaction activation energy and the like with the shortest ignition period model, and meanwhile, the influence of links such as oxidization, heat accumulation and temperature rise of the residual coal in the underground goaf is considered, so that compared with the prior art, the method has the advantages of short detection time consumption and more accurate and reliable result.
Description
Technical Field
The invention relates to the field of determination of a natural ignition period of coal, in particular to a method for determining the shortest natural ignition period of coal.
Background
The natural ignition period refers to the time that elapses from the time when the coal seam is mined and exposed to air to the time when natural ignition occurs. The prior natural ignition period is mostly measured by adopting a temperature programming or adiabatic oxidation method in the adiabatic environment of a laboratory, the prior methods consume long time, and the goaf coal leakage under the coal mine is influenced by other factors such as air leakage and different heat storage conditions of the goaf, and the method is greatly different from the adiabatic environment of the laboratory, so that the natural ignition period measured by the laboratory has errors from the actual natural ignition period of a mine, cannot be used as effective reference data, and is used in the fields of coal mine management and the like.
Disclosure of Invention
Aiming at the problems in the prior art, the invention can determine the shortest natural ignition period of the coal only by measuring the ignition temperature and other data in a laboratory, and has the advantages of high prediction accuracy, short required time and the like.
The invention discloses a method for determining the shortest natural ignition period of coal, which comprises the following steps:
acquiring the ignition temperature of coal;
acquiring a shortest firing period model of coal, wherein the shortest firing period model is used for reflecting the mapping relation between exposure time and coal temperature from when the coal is exposed to air;
determining a rapid heating stage of coal in the shortest firing period model, wherein the coal temperature in the rapid heating stage and the exposure time (approximately) form a linear relation, and the ignition point temperature is in the range of the coal temperature corresponding to the rapid heating stage;
and determining the shortest natural ignition period corresponding to the ignition temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage.
Further, the obtaining a shortest firing period model of the coal comprises: the shortest firing period model obtained is shown as the following expression:
wherein eta is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in air when t=0, and k 0 Is the factor before finger, q is the heat of chemical reaction, E is the activation energy of chemical reaction, E is the constant, R is the ideal gas constant, T is the temperature, C p The specific heat capacity is constant pressure, and ρ is density;
the chemical reaction activation energy was measured based on experiments.
Further, the obtaining the shortest firing period model of the coal further comprises:
establishing a two-dimensional coordinate system, wherein an X axis and a Y axis of the two-dimensional coordinate system respectively represent the exposure time and the coal temperature;
determining a corresponding visual curve of the shortest firing period model in the two-dimensional coordinate system;
the step of determining the rapid heating stage of the coal in the shortest firing period model comprises the following steps:
and determining a rapid heating line segment corresponding to the rapid heating stage in the visual curve.
Further, in the visual curve, determining a rapid heating line segment corresponding to the rapid heating stage includes:
and selecting a line segment with the largest slope from the visual curve as a rapid heating line segment.
Further, the determining the shortest natural ignition period corresponding to the ignition point temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage includes:
selecting a first coal temperature and a second coal temperature on the rapid heating line segment, wherein the ignition temperature is between the first coal temperature and the second coal temperature;
determining a first exposure time and a second exposure time of the first coal temperature and the second coal temperature corresponding to the rapid heating line segment;
the shortest natural ignition period is determined based on the first coal temperature, the second coal temperature, a first exposure time, a second exposure time, and the ignition point temperature.
Further, the determining the shortest natural fire period based on the first coal temperature, the second coal temperature, a first exposure time, a second exposure time, and the ignition point temperature includes:
determining the shortest natural fire period based on the following expression:
t c ＝t 1 +(t 2 -t 1 )*(T c -T 1 )/(T 2 -T 1 )
wherein T is 1 And t 1 Respectively, a first coal temperature and a first exposure time, T 2 And t 2 Respectively, a second coal temperature and a second exposure time, T c And t c The ignition temperature and the shortest natural ignition period are respectively.
The invention also discloses a system for determining the shortest natural ignition period of coal, which comprises:
the experimental data acquisition module is used for acquiring the ignition temperature of the acquired coal;
acquiring a shortest ignition period model of the coal, wherein the shortest ignition period model is used for reflecting the mapping relation between the exposure time and the coal temperature from the time of exposing the coal to air;
the selecting module is used for determining a rapid heating stage of the coal in the shortest ignition period model;
and the calculation module is used for determining the shortest natural ignition period corresponding to the ignition temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage.
Further, the obtaining a shortest firing period model of the coal comprises: the shortest firing period model obtained is shown as the following expression:
wherein eta is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in air when t=0, and k 0 Is the factor before finger, q is the heat of chemical reaction, E is the activation energy of chemical reaction, E is the constant, R is the ideal gas constant, T is the temperature, C p The specific heat capacity is constant pressure, and ρ is density;
the experimental data acquisition module is also used for acquiring the chemical reaction activation energy measured by experiments.
Further, the obtaining the shortest firing period model of the coal further comprises:
establishing a two-dimensional coordinate system, wherein an X axis and a Y axis of the two-dimensional coordinate system respectively represent the exposure time and the coal temperature; determining a corresponding visual curve of the shortest firing period model in the two-dimensional coordinate system;
the step of determining the rapid heating stage of the coal in the shortest firing period model comprises the following steps:
selecting a line segment with the largest slope from the visual curve as a rapid heating line segment corresponding to the rapid heating stage;
the determining the shortest natural ignition period corresponding to the ignition temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage comprises the following steps:
selecting a first coal temperature and a second coal temperature on the rapid heating line segment, wherein the ignition temperature is between the first coal temperature and the second coal temperature; determining a first exposure time and a second exposure time of the first coal temperature and the second coal temperature corresponding to the rapid heating line segment;
determining the shortest natural fire period based on the following expression:
t c ＝t 1 +(t 2 -t 1 )*(T c -T 1 )/(T 2 -T 1 )
wherein T is 1 And t 1 Respectively, a first coal temperature and a first exposure time, T 2 And t 2 Respectively, a second coal temperature and a second exposure time, T c And t c The ignition temperature and the shortest natural ignition period are respectively.
The present invention also discloses a computer readable storage medium having instructions stored therein, which when run on a computer, cause the computer to perform comprising: a method of determining the shortest natural fire period of coal as hereinbefore described.
The invention has at least the following beneficial effects:
according to the invention, the calculation of the shortest ignition period can be realized by matching the data such as the ignition temperature, the chemical reaction activation energy and the like of the coal measured in a laboratory with the shortest ignition period model, and meanwhile, the influence of links such as oxidization, heat accumulation and temperature rise of the residual coal in the underground goaf is considered, so that compared with the prior art, the method has the advantages of short detection time consumption and more accurate and reliable result.
Other advantageous effects of the present invention will be described in detail in the detailed description section.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method of determining the shortest natural fire period of coal as disclosed in a preferred embodiment of the present invention.
FIG. 2 is a schematic view of a portion of a visual curve of a two-dimensional coordinate system of a method of determining the shortest natural fire period of coal as disclosed in a preferred embodiment of the present invention.
FIG. 3 is a schematic illustration of a portion of a rapid heating line segment of a two-dimensional coordinate system of a method for determining a shortest natural fire period of coal, as disclosed in a preferred embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, based on the examples herein, which are within the scope of the invention as defined by the claims, will be within the scope of the invention as defined by the claims.
As shown in fig. 1, the invention discloses a method for determining the shortest natural ignition period of coal, which mainly comprises the following steps:
s1: the ignition temperature of the coal is obtained. The ignition temperature of the coal can be obtained by collecting a coal sample and carrying out related experiments in a laboratory.
S2: and acquiring a shortest ignition period model of the coal, wherein the shortest ignition period model is used for reflecting the mapping relation between the exposure time and the coal temperature from the time of exposing the coal to the air, and the data of any exposure time has the unique corresponding coal temperature. The model should fully consider the influence of links such as oxidation, heat accumulation, temperature rise and the like of the underground goaf on the model. The shortest firing period model can also be pre-established and stored, and the model is directly called and applied in the process of actually calculating the shortest firing period.
S3: determining a rapid heating stage of coal in the shortest ignition period model, wherein the coal is spontaneously combusted in the rapid heating stage, so that the temperature of the coal is rapidly increased in a short time, the temperature change is severe, and the temperature of the coal is relatively stable and the change is relatively gentle after the combustion is started; the coal is not burnt before the temperature is stable and the change is gentle. Based on the above characteristics, it is possible to accurately determine the rapid temperature rise phase, for example, the smaller the value of the unit exposure time is, the more accurate the rapid temperature rise phase is determined, when the temperature difference value of the coal at the exposure time per unit time before/after a certain exposure time (time point) is larger than a specified threshold value, that is, when it is judged that the exposure time corresponds to the exposure time. The coal temperature in the rapid heating stage and the exposure time are approximately in a linear relation, namely, the coal temperature is increased along with the increase of the exposure time as a whole until combustion is stabilized, and the ignition point temperature is in the range of the coal temperature corresponding to the rapid heating stage.
S4: and determining the shortest natural ignition period corresponding to the ignition temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage. In the rapid heating stage, the rising rate of the coal temperature is relatively stable and shows a certain regularity on the whole, so that the exposure time corresponding to the ignition point temperature, namely the shortest natural ignition period, can be calculated based on the regularity between the exposure time in the rapid heating stage and the coal temperature.
In some embodiments of the present invention, the shortest firing period model obtained in step S2 is represented by the following expression:
wherein eta is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in air when t=0, and k 0 Q is the chemical reaction heat, E is the chemical reaction activation energy based on experimental measurement, E is a constant, R is an ideal gas constant, T is temperature, cp is a constant pressure specific heat capacity, ρ is density.
The establishment process and principle of the shortest ignition period model are as follows:
in the closed space, the coal mainly generates CO 2 Reaction of gases, assuming that CO gas generated in the reaction is continuously oxidized to CO 2 The gas emits heat q, and the expression is shown as%1) As shown.
C+O 2 ＝CO 2 +q (1)
According to the theory of chemical reaction kinetics, the chemical reaction rate of the reaction is as follows:
wherein r is 1 The chemical reaction rate is expressed in mol/(m) 3 *S)；c_co 2 、c_o 2 Respectively represent CO 2 、O 2 In mol/m 3 The method comprises the steps of carrying out a first treatment on the surface of the t represents the reaction time in seconds.
At the same time, reactant O for chemical reaction rate 2 The concentration of (2) can also be expressed as:
wherein k is 1 Is a chemical reaction rate constant, and has the unit of s -1 The method comprises the steps of carrying out a first treatment on the surface of the Negative (-) indicates O 2 As a reactant, the concentration gradually decreases as the chemical reaction proceeds.
Equation (3) is a differential equation, and the integral operation is performed on equation (3) to obtain C_O 2 Analytical expressions as a function of reaction time t. First, the formula (3) is modified into
The dC_O is respectively paired with the two sides of the equation (4) 2 Integrating dt to obtain
lnc_o 2 ＝-k 1 t+C 1 (5)
Performing exponential operation on both sides of the equation (5) by taking e as a base to obtainLet->Can obtain
C in the formulas (5) and (6) 1 And C are constant.
Thus, c_o is obtained 2 Analytical expressions as a function of reaction time t. It was found that as the reaction proceeded, O 2 The gas concentration gradually decreases in a substantially negative exponential fashion. When t=0, c_o 2 Is the concentration of oxygen in the air, is 9.33mol/m 3 . Thus, it was found that C was 9.33mol/m 3 。
At the same time of chemical reaction of coal and oxygen, heat transfer phenomenon also occurs in the coal body. The heat generated by the chemical reaction is accumulated in the coal body to gradually increase the temperature of the coal body. The relationship between the amount of heat generated by the chemical reaction per unit time and the change in the temperature of the coal can be expressed by the following formula:
wherein C is p The specific heat capacity is the constant pressure, and the unit is J/(Kg.K); ρ is density in Kg/m 3 The method comprises the steps of carrying out a first treatment on the surface of the T is the temperature in K.
From the arrhenius empirical formula:
k 1 ＝k 0 ·e -E/RT (8)
wherein E is chemical reaction activation energy, and the unit is KJ/mol; r is an ideal gas constant, 8.314J/(mol.k);
substituting the formula (3) into the formula (7) to obtain
Substituting the formula (8) and the formula (6) into the formula (9) can obtain
The formula is a coupling equation of a chemical reaction field and a temperature field at a certain point in a space in a coal body.
However, due to the influence of air leakage factors of the goaf, the heat generated by oxidation of residual coal in the goaf is not stored in the coal body, most of the heat acts on the air leakage and surrounding rock of the goaf under the mechanism of heat convection and heat conduction, and only a small part of the heat is stored in the coal body, so that the temperature of the coal body is increased continuously. Equation (10) is therefore optimized to equation (11), the shortest firing period model.
Wherein eta is the heat storage coefficient and the unit is percent.
In the formula (11), parameters eta and C, K 0 、q、E、e、R、ρ、C p Are constant, only T and T are variables. And, among the variables, T is an dependent variable and T is an independent variable. And (3) constructing a solving model by using a differential equation of the formula (11) through a corresponding calculating module, and solving to obtain a visual curve reflecting the relation between the time T and the coal temperature T.
In some embodiments of the present invention, the above-mentioned expression of the shortest firing period can accurately reflect the relationship between time and temperature, and in order to reduce the complexity of subsequent analysis, the present invention adopts a two-dimensional coordinate system to represent the relationship between time and temperature, so after determining the shortest firing period model, the present invention further includes the following steps:
establishing a two-dimensional coordinate system, wherein an X axis and a Y axis of the two-dimensional coordinate system respectively represent the exposure time and the coal temperature, and determining a visual curve corresponding to the shortest firing period model in the two-dimensional coordinate system, wherein the visual curve can clearly and intuitively show the mapping relation between the exposure time and the coal temperature.
When the rapid heating stage of the coal in the shortest ignition period model is determined, the various link stages including the rapid heating stage can be clearly distinguished through a visual curve, and the corresponding part of the rapid heating stage in the visual curve becomes a rapid heating line segment which is a straight line segment or an approximate straight line segment. Further, since the coal in this stage is rapidly heated, the inclination of the line is large in the two-dimensional coordinate system relative to the line corresponding to the other stage, and the line is easily recognized and determined, and therefore, the line with the largest inclination is selected from the visualized curve as the rapid heating line.
Because the ignition temperature of the coal falls on the rapid heating line segment, the exposure time corresponding to the ignition temperature, namely the shortest natural ignition period, can be calculated. As known from the general knowledge of mathematics, in a two-dimensional coordinate system, the slope of a straight line can be obtained by two points on the straight line, and because a rapid heating line segment can be regarded as having a fixed slope, the method for determining the shortest natural ignition period corresponding to the ignition point temperature based on the mapping relationship between the exposure time and the coal temperature in the rapid heating stage according to the invention preferably comprises the following implementation steps:
two different points are selected from the rapid heating line segment, and the two points are respectively expressed as (t 1 ,T 1 ) And (t) 2 ,T 2 ). Specifically, the first coal temperature T on the rapid heating line segment can be selected 1 And a second coal temperature T 2 Preferably, the ignition temperature is between the first and second coal temperatures. Then, determining a first exposure time t corresponding to the first coal temperature and the second coal temperature on the rapid heating line segment 1 And a second exposure time t 2 。
Finally, the shortest natural fire period is determined based on the first coal temperature, the second coal temperature, a first exposure time, a second exposure time, and the ignition point temperature. Due to (t) 1 ,T 1 )、(t 2 ,T 2 ) The points corresponding to the combustion temperature-the shortest natural ignition period are all on the rapid heating line segment with fixed leakage, so that the following equation can be obtained: (t) c -t 1 )/(T c -T 1 )＝(t 2 -t 1 )/(T 2 -T 1 ). Further optimization can be achieved by:
t c ＝t 1 +(t 2 -t 1 )*(T c -T 1 )/(T 2 -T 1 ) (12)
and because of t selected therein 1 、T 1 、t 2 、T 2 Is known, therefore, the time t required for spontaneous combustion of goaf residual coal from the underground real environment temperature through the oxidation, heat accumulation and temperature rise links can be obtained through the formula (12) c This is the shortest natural ignition period of the goaf residual coal.
The invention also discloses a system for determining the shortest natural ignition period of coal, which comprises:
the experimental data acquisition module is used for acquiring the ignition temperature of the acquired coal;
acquiring a shortest ignition period model of the coal, wherein the shortest ignition period model is used for reflecting the mapping relation between the exposure time and the coal temperature from the time of exposing the coal to air;
the selecting module is used for determining a rapid heating stage of the coal in the shortest ignition period model;
and the calculation module is used for determining the shortest natural ignition period corresponding to the ignition temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage.
Further, the obtaining a shortest firing period model of the coal comprises: the shortest firing period model obtained is shown as the following expression:
wherein eta is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in air when t=0, and k 0 Is the factor before finger, q is the heat of chemical reaction, E is the activation energy of chemical reaction, E is the constant, R is the ideal gas constant, T is the temperature, C p The specific heat capacity is constant pressure, and ρ is density;
the experimental data acquisition module is also used for acquiring the chemical reaction activation energy measured by experiments.
Further, the obtaining the shortest firing period model of the coal further comprises:
establishing a two-dimensional coordinate system, wherein an X axis and a Y axis of the two-dimensional coordinate system respectively represent the exposure time and the coal temperature; determining a corresponding visual curve of the shortest firing period model in the two-dimensional coordinate system;
the step of determining the rapid heating stage of the coal in the shortest firing period model comprises the following steps:
selecting a line segment with the largest slope from the visual curve as a rapid heating line segment corresponding to the rapid heating stage;
the determining the shortest natural ignition period corresponding to the ignition temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage comprises the following steps:
selecting a first coal temperature and a second coal temperature on the rapid heating line segment, wherein the ignition temperature is between the first coal temperature and the second coal temperature; determining a first exposure time and a second exposure time of the first coal temperature and the second coal temperature corresponding to the rapid heating line segment;
determining the shortest natural fire period based on the following expression:
t c ＝t 1 +(t 2 -t 1 )*(T c -T 1 )/(T 2 -T 1 )
wherein T is 1 And t 1 Respectively, a first coal temperature and a first exposure time, T 2 And t 2 Respectively, a second coal temperature and a second exposure time, T c And t c The ignition temperature and the shortest natural ignition period are respectively.
The present invention also discloses a computer readable storage medium having instructions stored therein, which when run on a computer, cause the computer to perform comprising: a method of determining the shortest natural fire period of coal as hereinbefore described.
The invention also discloses a preferred embodiment aiming at the technical scheme disclosed above.
Examples
By means of the simulation function of COMSOL Multiphysics, a mathematical solution model is built based on the above formula (11) by using a differential equation interface, and parameters set in the simulation process are shown in the numerical simulation set parameter values and sources shown in table 1.
| Physical quantity | Description of the invention | Parameter value |
| E | Activation energy | 41.2kJ/mol |
| k 0 | Factor before finger | 8.97×10 2 s -1 |
| k 1 | Rate constant of chemical reaction | 9.24×10-5s -1 |
| C p | Constant pressure specific heat capacity | 1.26kJ/(kg·K) |
| ρ | Density of | 1.3×103Kg/m 3 |
| T | Ambient initial temperature | 298.15K |
| q | Heat of chemical reaction | 393.5kJ/mol |
| η | Coefficient of heat storage | 0.3(given value) |
TABLE 1
And after the parameter setting is completed, starting calculation. The calculated visualization curve between time T and temperature T is shown in fig. 2.
The ignition point of the coal was measured at 325℃in the laboratory by an ignition point measuring instrument for the coal (i.e., 598.15K), and the vicinity of 598.15K was partially enlarged in FIG. 1, as shown in FIG. 3.
Selecting an approximate straight line segment in the partial enlarged view (figure 3), wherein the end point coordinates of the straight line segment are (573.3, 552) and (573.6, 636), and t is calculated by the formula (12) c 573.46h.
That is, the shortest natural fire period of the coal is 573.5 hours, about 24 days, taking into consideration the oxidation properties of the coal itself and the actual conditions in the downhole site.
It should be noted that the activation energy and ignition temperature of the coal in the present invention are obtained by experimental determination in a laboratory, and the existing experimental methods, processes and equipment can be specifically adopted, which are not described herein.
The steps S1 to S4 are only a preferred implementation sequence, and those skilled in the art should understand from the description herein that the step sequence may be changed according to actual needs, for example, the shortest ignition period model is built in advance, and then the ignition temperature of the coal is obtained, which can also solve the technical problem to be solved by the present invention, and achieve the expected technical effect.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention.
Claims (3)
1. A method of determining a shortest natural fire period of coal comprising:
acquiring the ignition temperature of coal;
acquiring a shortest firing period model of coal, wherein the shortest firing period model is used for reflecting the mapping relation between exposure time and coal temperature from when the coal is exposed to air;
determining a rapid heating stage of coal in the shortest ignition period model, wherein the coal temperature in the rapid heating stage and the exposure time are in a linear relation, and the ignition point temperature is in the range of the coal temperature corresponding to the rapid heating stage;
determining the shortest natural ignition period corresponding to the ignition point temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage;
the obtaining of the shortest firing period model of the coal comprises the following steps: the shortest firing period model obtained is shown as the following expression:
wherein eta is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in air when t=0, and k 0 Is the factor before finger, q is the heat of chemical reaction, E is the activation energy of chemical reaction, E is the constant, R is the ideal gas constant, T is the temperature, C p The specific heat capacity is constant pressure, and ρ is density;
the chemical reaction activation energy is measured based on experiments;
the method for obtaining the shortest firing period model of the coal further comprises the following steps:
establishing a two-dimensional coordinate system, wherein an X axis and a Y axis of the two-dimensional coordinate system respectively represent the exposure time and the coal temperature;
determining a corresponding visual curve of the shortest firing period model in the two-dimensional coordinate system;
the step of determining the rapid heating stage of the coal in the shortest firing period model comprises the following steps:
in the visual curve, determining a rapid heating line segment corresponding to the rapid heating stage;
in the visual curve, determining a rapid heating line segment corresponding to the rapid heating stage includes:
selecting a line segment with the largest slope from the visual curve as a rapid heating line segment;
the determining the shortest natural ignition period corresponding to the ignition temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage comprises the following steps:
selecting a first coal temperature and a second coal temperature on the rapid heating line segment, wherein the ignition temperature is between the first coal temperature and the second coal temperature;
determining a first exposure time and a second exposure time of the first coal temperature and the second coal temperature corresponding to the rapid heating line segment;
determining the shortest natural fire period based on the first coal temperature, the second coal temperature, a first exposure time, a second exposure time, and the ignition point temperature;
the determining the shortest natural fire period based on the first coal temperature, the second coal temperature, a first exposure time, a second exposure time, and the ignition point temperature, comprising:
determining the shortest natural fire period based on the following expression:
t c ＝t 1 +(t 2 -t 1 )*(T c -T 1 )/(T 2 -T 1 )
wherein T is 1 And t 1 Respectively, a first coal temperature and a first exposure time, T 2 And t 2 Respectively, a second coal temperature and a second exposure time, T c And t c Respectively are provided withIs the ignition temperature and the shortest natural ignition period.
2. A system for determining a shortest natural fire period of coal, comprising:
the experimental data acquisition module is used for acquiring the ignition temperature of the coal;
acquiring a shortest ignition period model of the coal, wherein the shortest ignition period model is used for reflecting the mapping relation between the exposure time and the coal temperature from the time of exposing the coal to air;
the selecting module is used for determining a rapid heating stage of the coal in the shortest ignition period model;
the calculation module is used for determining the shortest natural ignition period corresponding to the ignition temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage;
the obtaining of the shortest firing period model of the coal comprises the following steps: the shortest firing period model obtained is shown as the following expression:
wherein eta is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in air when t=0, and k 0 Is the factor before finger, q is the heat of chemical reaction, E is the activation energy of chemical reaction, E is the constant, R is the ideal gas constant, T is the temperature, C p The specific heat capacity is constant pressure, and ρ is density;
the experimental data acquisition module is also used for acquiring the chemical reaction activation energy measured by experiments;
the method for obtaining the shortest firing period model of the coal further comprises the following steps:
establishing a two-dimensional coordinate system, wherein an X axis and a Y axis of the two-dimensional coordinate system respectively represent the exposure time and the coal temperature; determining a corresponding visual curve of the shortest firing period model in the two-dimensional coordinate system;
the step of determining the rapid heating stage of the coal in the shortest firing period model comprises the following steps:
selecting a line segment with the largest slope from the visual curve as a rapid heating line segment corresponding to the rapid heating stage;
the determining the shortest natural ignition period corresponding to the ignition temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage comprises the following steps:
selecting a first coal temperature and a second coal temperature on the rapid heating line segment, wherein the ignition temperature is between the first coal temperature and the second coal temperature; determining a first exposure time and a second exposure time of the first coal temperature and the second coal temperature corresponding to the rapid heating line segment;
determining the shortest natural fire period based on the following expression:
t c ＝t 1 +(t 2 -t 1 )*(T c -T 1 )/(T 2 -T 1 )
wherein T is 1 And t 1 Respectively, a first coal temperature and a first exposure time, T 2 And t 2 Respectively, a second coal temperature and a second exposure time, T c And t c The ignition temperature and the shortest natural ignition period are respectively.
3. A computer-readable storage medium having instructions stored therein that, when executed on a computer, cause the computer to perform comprising:
a method of determining the shortest natural fire period of coal as recited in claim 1.
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