CN113670980A - 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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- CN113670980A CN113670980A CN202110846680.9A CN202110846680A CN113670980A CN 113670980 A CN113670980 A CN 113670980A CN 202110846680 A CN202110846680 A CN 202110846680A CN 113670980 A CN113670980 A CN 113670980A
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
- G01N25/22—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures
- G01N25/28—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures the rise in temperature of the gases resulting from combustion being measured directly
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/02—Investigating or analyzing materials by the use of thermal means by investigating changes of state or changes of phase; by investigating sintering
- G01N25/12—Investigating or analyzing materials by the use of thermal means by investigating changes of state or changes of phase; by investigating sintering of critical point; of other phase change
Abstract
The invention mainly discloses a method for determining the shortest natural ignition period of coal, which comprises the following steps: obtaining the ignition temperature of coal; obtaining 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 of the coal from the time of exposure to the air; determining a rapid temperature rise stage of the coal in the shortest ignition period model, wherein the coal temperature in the rapid temperature rise stage is approximately in a linear relation with the exposure time, and the ignition point temperature is in a coal temperature range corresponding to the rapid temperature rise 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 shortest ignition period can be calculated by matching 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 oxidation, heat storage, temperature rise and the like of the left coal in the underground goaf is considered, so that the detection time is short, and the result is more accurate and reliable compared with the prior art.
Description
Technical Field
The invention relates to the field of coal spontaneous combustion period determination, in particular to a method for determining the shortest spontaneous combustion period of coal.
Background
The spontaneous ignition period is the time that elapses from the day when the coal seam is mined and exposed to air until the day when spontaneous ignition occurs. At present, the natural ignition period is mostly measured by adopting a temperature programming method or an adiabatic oxidation method in an adiabatic environment of a laboratory, the existing methods are long in time consumption, and the residual coal in the goaf under the coal mine is influenced by other factors such as goaf air leakage and different heat storage conditions, so that the difference from the adiabatic environment of the laboratory is large, so that the natural ignition period measured in the laboratory has an error with the actual natural ignition period of the mine, and the natural ignition period cannot be used as effective reference data for the fields of coal mine management and the like.
Disclosure of Invention
Aiming at the problems in the prior art, the shortest natural ignition period of the coal can be determined only by measuring data such as ignition temperature and the like in a laboratory, and the method 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:
obtaining the ignition temperature of coal;
obtaining 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 of the coal from the time of exposure to the air;
determining a rapid heating stage of the coal in the shortest ignition period model, wherein the coal temperature in the rapid heating stage is in a linear relation with the exposure time (approximately), 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 point temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage.
Further, the obtaining of the shortest fire period model of the coal comprises: the obtained shortest ignition period model is shown as the following expression:
where η is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in the air when t is 0, k0Is a pre-factor, q is the heat of chemical reaction, E is the activation energy of chemical reaction, E is a constant, R isIdeal gas constant, T is temperature, CpIs the specific heat capacity at constant pressure, and rho is the density;
the activation energy of the chemical reaction is determined based on experiments.
Further, the obtaining of the shortest ignition period model of the coal further includes:
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 ignition period model in the two-dimensional coordinate system;
the step of determining the rapid temperature rise of the coal in the shortest ignition period model comprises the following steps:
and determining a rapid heating line segment corresponding to the rapid heating stage in the visual curve.
Further, the determining a rapid temperature rise line segment corresponding to the rapid temperature rise stage in the visualized curve includes:
and selecting a line segment with the maximum 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 relationship 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 burning point temperature is between the first coal temperature and the second coal temperature;
determining first exposure time and second exposure time corresponding to the first coal temperature and the second coal temperature on the rapid temperature rise line segment;
determining the shortest spontaneous ignition period 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 ignition 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:
tc＝t1+(t2-t1)*(Tc-T1)/(T2-T1)
wherein, T1And t1First coal temperature and first exposure time, T, respectively2And t2Second coal temperature and second exposure time, T, respectivelycAnd tcRespectively the ignition temperature and the shortest spontaneous combustion period.
The invention also discloses a system for determining the shortest natural fire period of coal, which comprises the following steps:
the experimental data acquisition module is used for acquiring the ignition temperature of the obtained coal;
obtaining a shortest ignition period model of the coal, and reflecting the mapping relation between the exposure time and the coal temperature from the time when the coal is exposed to the air;
a selecting module for determining the rapid temperature rise 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 point temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage.
Further, the obtaining of the shortest fire period model of the coal comprises: the obtained shortest ignition period model is shown as the following expression:
where η is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in the air when t is 0, k0Q is the heat of chemical reaction, E is the activation energy of chemical reaction, E is a constant, R is the ideal gas constant, T is the temperature, CpIs the specific heat capacity at constant pressure, and rho is the density;
the experimental data acquisition module is also used for acquiring the chemical reaction activation energy measured by the experiment.
Further, the obtaining of the shortest ignition period model of the coal further includes:
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 ignition period model in the two-dimensional coordinate system;
the step of determining the rapid temperature rise of the coal in the shortest ignition period model comprises the following steps:
selecting a line segment with the maximum slope from the visual curve as a rapid heating line segment 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, wherein the determining comprises the following steps:
selecting a first coal temperature and a second coal temperature on the rapid heating line segment, wherein the burning point temperature is between the first coal temperature and the second coal temperature; determining first exposure time and second exposure time corresponding to the first coal temperature and the second coal temperature on the rapid temperature rise line segment;
determining the shortest natural fire period based on the following expression:
tc＝t1+(t2-t1)*(Tc-T1)/(T2-T1)
wherein, T1And t1First coal temperature and first exposure time, T, respectively2And t2Second coal temperature and second exposure time, T, respectivelycAnd tcRespectively the ignition temperature and the shortest spontaneous combustion period.
The present invention also discloses a computer-readable storage medium having instructions stored therein, which when executed on a computer, cause the computer to perform operations comprising: the method for determining the shortest spontaneous combustion period of the coal is described above.
The invention has at least the following beneficial effects:
according to the invention, the shortest ignition period can be calculated by matching data such as the ignition temperature of coal, chemical reaction activation energy and the like measured in a laboratory with a shortest ignition period model, and meanwhile, the influence of links such as oxidation, heat storage, temperature rise and the like of the left coal in an underground goaf is considered, so that the detection time is short, and the result is more accurate and reliable compared with the prior art.
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 present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flow chart of a method for determining a shortest spontaneous combustion period for coal as disclosed in a preferred embodiment of the present invention.
FIG. 2 is a schematic view of a visualized curve part of a two-dimensional coordinate system of the method for determining the shortest spontaneous combustion period of coal, which is disclosed by the preferred embodiment of the invention.
FIG. 3 is a schematic diagram of a portion of a rapid temperature rise line segment of a two-dimensional coordinate system of a method for determining a shortest spontaneous combustion period of coal according to 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 is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.
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 performing 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 of the coal from the time of exposure to the air, and the data of any exposure time has the unique corresponding coal temperature. The influence of links such as oxidation, heat storage, temperature rise and the like on the model in the underground goaf is fully considered. The shortest ignition 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 ignition period.
S3: determining a rapid temperature rise stage of the coal in the shortest ignition period model, wherein in the rapid temperature rise stage, the coal is spontaneously combusted, so that the temperature of the coal is rapidly raised in a short time, the temperature is changed violently, and the temperature of the coal is relatively stable and relatively gentle after the coal is combusted; before the combustion, the coal is not combusted, the temperature is also stable, and the change is smooth. Based on the above features, the rapid temperature rise stage can be accurately determined, for example, the coal temperature difference value of the exposure time unit time before/after a certain exposure time (time point) is larger than a specified threshold value, that is, the selected value of the unit exposure time is smaller and the determined rapid temperature rise stage is more accurate corresponding to the exposure time. The coal temperature in the rapid heating stage and the exposure time are approximately in a linear relationship, namely the coal temperature can be increased along with the increase of the exposure time until stable combustion is achieved, 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 point 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 rule between the exposure time in the rapid heating stage and the coal temperature.
In some embodiments of the present invention, the shortest ignition period model obtained in step S2 is expressed by the following expression:
where η is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in the air when t is 0, k0In order to indicate a preceding factor, q is the heat of chemical reaction, E is the activation energy of chemical reaction based on experimental measurements, E is a constant, R is an ideal gas constant, T is the temperature, Cp is the specific heat capacity at constant pressure, and ρ is the density.
The establishment process and the principle of the shortest ignition period model are as follows:
in the enclosed space, the coal mainly generates CO2Reaction of gases, provided that CO gas formed in the reaction is continuously oxidized to CO2Gas and heat q is released, and the expression is shown as (1).
C+O2＝CO2+q (1)
According to the chemical reaction kinetics theory, the chemical reaction rate of the reaction is as follows:
wherein r is1The chemical reaction rate is expressed in mol/(m)3*S)；c_co2、c_o2Respectively represent CO2、O2In mol/m3(ii) a t represents the reaction time in seconds.
At the same time, the chemical reaction rate is determined by the reactant O2The concentration of (d) can also be expressed as:
wherein k is1Is a chemical reaction rate constant in units of s-1(ii) a Minus sign (-) denotes O2As the reactant, the concentration gradually decreases as the chemical reaction proceeds.
The formula (3) is a differential equation, and the C _ O can be obtained by integrating the formula (3)2Analytical expressions as a function of the reaction time t. Firstly, the formula (3) is modified into
The two sides of equation (4) are respectively paired with dC _ O2Dt is integrated to obtain
lnc_o2＝-k1t+C1 (5)
Performing exponential operation on two sides of equation (5) by taking e as a base number at the same time to obtain
Order to
Can obtain
C in the formulae (5) and (6)1And C are both constants.
Thus, c _ o is obtained2Analytical expressions as a function of the reaction time t. It was found that as the reaction proceeded, O2The gas concentration gradually decreases approximately in a negative exponential form. When t is 0, C _ O2The concentration of oxygen in the air is 9.33mol/m3. Thus, it was found that C was 9.33mol/m3。
While the coal chemically reacts with oxygen, heat transfer also occurs within the coal body. The heat generated by the chemical reaction is accumulated in the coal body to gradually raise the temperature of the coal body. The relationship between the amount of heat generated by the chemical reaction per unit time and the temperature change of the coal body can be represented by the following formula:
wherein, CpThe specific heat capacity at constant pressure is J/(Kg.K); rho is density and is Kg/m3(ii) a T is temperature in K.
From the arrhenius empirical formula:
k1＝k0·e-E/RT (8)
wherein E is chemical reaction activation energy, and the unit is KJ/mol; r is an ideal gas constant, and 8.314J/(mol · k) is taken;
by substituting formula (3) for formula (7), the compounds are obtained
By substituting formula (8) or formula (6) for formula (9), a compound having the formula
The formula is a chemical reaction field and temperature field coupling equation of a certain point in the space in the coal body.
However, under the influence of the factors of air leakage of the goaf, the heat generated by the oxidation of the residual coal in the goaf cannot be completely stored in the coal body, most of the heat acts on the air leakage and surrounding rocks of the goaf under the heat convection and heat conduction mechanisms, and only a small part of the heat is stored in the coal body to continuously raise the temperature of the coal body. Equation (10) is therefore optimized to equation (11), the shortest firing period model.
Wherein eta is the heat storage coefficient, and the unit is%.
In the formula (11), the parameters eta, C, K0、q、E、e、R、ρ、CpAre both constants, only T and T are variables. In the variables, T is a 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 calculation 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 expression of the shortest ignition 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, and therefore, after determining the shortest ignition period model, the present invention further includes the following steps:
and establishing a two-dimensional coordinate system, wherein the X axis and the Y axis of the two-dimensional coordinate system respectively represent the exposure time and the coal temperature, and determining a corresponding visual curve of the shortest ignition period model in the two-dimensional coordinate system, wherein the visual curve can clearly and intuitively embody 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 stages of all links including the rapid heating stage can be clearly distinguished through a visual curve, the corresponding part of the rapid heating stage in the visual curve becomes a rapid heating line segment, and the line segment is a straight line segment or an approximate straight line segment. And because the coal is rapidly heated at the stage, the inclination of the line segment is larger than that of the line segment corresponding to other stages in the two-dimensional coordinate system, and the line segment is easy to identify and determine, so that the line segment with the largest gradient is selected from the visual curve as the rapid heating line segment.
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 is known from the common general knowledge of mathematics, in a two-dimensional coordinate system, the slope of a straight line can be obtained from two points on the straight line, and a rapid temperature rise line segment can be regarded as having a fixed slope, so that the shortest spontaneous ignition period corresponding to the ignition temperature is determined based on the mapping relationship between the exposure time and the coal temperature in the rapid temperature rise stage, and the method is preferably implemented as follows:
two different points are selected from the rapid temperature rise line segment, and the two points are respectively expressed as (t)1,T1) And (t)2,T2). Specifically, the first coal temperature T on the rapid heating line segment may be selected1And a second coal temperature T2Preferably, the ignition temperature is between the first coal temperature and the second coal temperature. Then, determining that the first coal temperature and the second coal temperature are in the emergencyCorresponding first exposure time t on rapid heating line segment1And a second exposure time t2。
Finally, the shortest natural fire period is determined based on the first coal temperature, the second coal temperature, the first exposure time, the second exposure time, and the ignition point temperature. Due to (t)1,T1)、(t2,T2) And the combustion temperature-the point corresponding to the shortest spontaneous combustion period is all on a rapid temperature rise line segment with fixed leakage, so that the following equation can be obtained: (t)c-t1)/(Tc-T1)＝(t2-t1)/(T2-T1). Further optimization can obtain:
tc＝t1+(t2-t1)*(Tc-T1)/(T2-T1) (12)
and because of t selected therein1、T1、t2、T2As is known, the time t required for the residual coal in the goaf to reach spontaneous combustion from the underground real environment temperature through the oxidation heat storage temperature rise link can be obtained through the formula (12)cThis is the shortest natural fire period of the coal left in the goaf.
The invention also discloses a system for determining the shortest natural fire period of coal, which comprises the following steps:
the experimental data acquisition module is used for acquiring the ignition temperature of the obtained coal;
obtaining a shortest ignition period model of the coal, and reflecting the mapping relation between the exposure time and the coal temperature from the time when the coal is exposed to the air;
a selecting module for determining the rapid temperature rise 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 point temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage.
Further, the obtaining of the shortest fire period model of the coal comprises: the obtained shortest ignition period model is shown as the following expression:
where η is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in the air when t is 0, k0Q is the heat of chemical reaction, E is the activation energy of chemical reaction, E is a constant, R is the ideal gas constant, T is the temperature, CpIs the specific heat capacity at constant pressure, and rho is the density;
the experimental data acquisition module is also used for acquiring the chemical reaction activation energy measured by the experiment.
Further, the obtaining of the shortest ignition period model of the coal further includes:
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 ignition period model in the two-dimensional coordinate system;
the step of determining the rapid temperature rise of the coal in the shortest ignition period model comprises the following steps:
selecting a line segment with the maximum slope from the visual curve as a rapid heating line segment 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, wherein the determining comprises the following steps:
selecting a first coal temperature and a second coal temperature on the rapid heating line segment, wherein the burning point temperature is between the first coal temperature and the second coal temperature; determining first exposure time and second exposure time corresponding to the first coal temperature and the second coal temperature on the rapid temperature rise line segment;
determining the shortest natural fire period based on the following expression:
tc＝t1+(t2-t1)*(Tc-T1)/(T2-T1)
wherein, T1And t1First coal temperature and first exposure time, T, respectively2And t2Second coal temperature and second exposure time, T, respectivelycAnd tcRespectively the ignition temperature and the shortest spontaneous combustion period.
The present invention also discloses a computer-readable storage medium having instructions stored therein, which when executed on a computer, cause the computer to perform operations comprising: the method for determining the shortest spontaneous combustion period of the coal is described above.
Aiming at the technical scheme disclosed above, the invention also discloses a preferred embodiment.
Examples
With the aid of the analog simulation function of COMSOL Multiphysics, a mathematical solution model is established based on the above equation (11) by using a differential equation interface, and parameters set in the simulation process are shown in the parameter values and sources set by numerical simulation shown in table 1.
| Physical quantity | Description of the invention | Parameter value |
| E | Activation energy | 41.2kJ/mol |
| k0 | Factor of premodial finger | 8.97×102s-1 |
| k1 | Rate constant of chemical reaction | 9.24×10-5s-1 |
| Cp | Specific heat capacity at constant pressure | 1.26kJ/(kg·K) |
| ρ | Density of | 1.3×103Kg/m3 |
| T | Initial temperature of the environment | 298.15K |
| q | Heat of chemical reaction | 393.5kJ/mol |
| η | Coefficient of heat storage | 0.3(given value) |
TABLE 1
And starting calculation after parameter setting is finished. The calculated visualization curve between time T and temperature T is shown in fig. 2.
The ignition point of coal was determined to be 325 c (i.e., 598.15K) in the laboratory by a coal ignition point tester, and a portion around 598.15K was enlarged in fig. 1, as shown in fig. 3.
In the partially enlarged view (fig. 3), an approximate straight line segment is selected, and the coordinates of the end points of the straight line segment are (573.3, 552) and (573.6, 636), and t is calculated by the above equation (12)c573.46 h.
That is, the shortest spontaneous ignition period of coal is 573.5h, about 24 days, under the combined consideration of the oxidation properties of the coal itself and the actual conditions at the site downhole.
It should be noted that the activation energy and the 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 again.
The above steps S1 to S4 are only a preferred implementation sequence, and it should be understood by those skilled in the art from the description herein that the above steps may be changed according to actual needs, for example, a shortest ignition period model is established in advance, and then the ignition temperature of the coal is obtained, etc., so as to solve the technical problems to be solved by the present invention and achieve the expected technical effects.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention.
Claims (10)
1. A method of determining a shortest spontaneous combustion period for coal, comprising:
obtaining the ignition temperature of coal;
obtaining 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 of the coal from the time of exposure to the air;
determining a rapid heating stage of the coal in the shortest ignition period model, wherein the coal temperature in the rapid heating stage is in a linear relation with the exposure time, and the burning 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 point temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage.
2. The method for determining the shortest spontaneous combustion period of coal according to claim 1, wherein the obtaining of the shortest spontaneous combustion period model of coal comprises: the obtained shortest ignition period model is shown as the following expression:
where η is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in the air when t is 0, k0Q is the heat of chemical reaction, E is the activation energy of chemical reaction, E is a constant, R is the ideal gas constant, T is the temperature, CpIs the specific heat capacity at constant pressure, and rho is the density;
the activation energy of the chemical reaction is determined based on experiments.
3. The method for determining the shortest spontaneous combustion period of coal according to claim 1 or 2, wherein the obtaining of the shortest spontaneous combustion period model of 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 ignition period model in the two-dimensional coordinate system;
the step of determining the rapid temperature rise of the coal in the shortest ignition period model comprises the following steps:
and determining a rapid heating line segment corresponding to the rapid heating stage in the visual curve.
4. The method for determining the shortest natural fire period of coal according to claim 3, wherein the determining the rapid temperature rise line segment corresponding to the rapid temperature rise stage in the visualization curve comprises:
and selecting a line segment with the maximum slope from the visual curve as a rapid heating line segment.
5. The method for determining the shortest natural fire period of coal according to claim 4, wherein the determining the shortest natural fire period corresponding to the ignition temperature based on the mapping relationship between the exposure time and the coal temperature in the rapid heating stage comprises:
selecting a first coal temperature and a second coal temperature on the rapid heating line segment, wherein the burning point temperature is between the first coal temperature and the second coal temperature;
determining first exposure time and second exposure time corresponding to the first coal temperature and the second coal temperature on the rapid temperature rise line segment;
determining the shortest spontaneous ignition period based on the first coal temperature, the second coal temperature, a first exposure time, a second exposure time, and the ignition point temperature.
6. The method of determining a shortest natural fire period for coal according to claim 5, wherein said determining said shortest natural fire period based on said first coal temperature, said second coal temperature, first exposure time, second exposure time, and said ignition point temperature comprises:
determining the shortest natural fire period based on the following expression:
tc＝t1+(t2-t1)*(Tc-T1)/(T2-T1)
wherein, T1And t1First coal temperature and first exposure time, T, respectively2And t2Second coal temperature and second exposure time, T, respectivelycAnd tcRespectively the ignition temperature and the shortest spontaneous combustion period.
7. A system for determining a minimum spontaneous combustion period for coal, comprising:
the experimental data acquisition module is used for acquiring the ignition temperature of the obtained coal;
obtaining a shortest ignition period model of the coal, and reflecting the mapping relation between the exposure time and the coal temperature from the time when the coal is exposed to the air;
a selecting module for determining the rapid temperature rise 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 point temperature based on the mapping relation between the exposure time and the coal temperature in the rapid heating stage.
8. The system for determining the shortest natural fire period for coal according to claim 7, wherein said obtaining the shortest fire period model for coal comprises: the obtained shortest ignition period model is shown as the following expression:
where η is the heat storage coefficient, t is the exposure time, C is the concentration of oxygen in the air when t is 0, k0Q is the heat of chemical reaction, E is the activation energy of chemical reaction, E is a constant, R is the ideal gas constant, T is the temperature, CpIs the specific heat capacity at constant pressure, and rho is the density;
the experimental data acquisition module is also used for acquiring the chemical reaction activation energy measured by the experiment.
9. The system for determining the shortest natural fire period of coal according to claim 7 or 8, wherein the obtaining the shortest fire period model of 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 ignition period model in the two-dimensional coordinate system;
the step of determining the rapid temperature rise of the coal in the shortest ignition period model comprises the following steps:
selecting a line segment with the maximum slope from the visual curve as a rapid heating line segment 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, wherein the determining comprises the following steps:
selecting a first coal temperature and a second coal temperature on the rapid heating line segment, wherein the burning point temperature is between the first coal temperature and the second coal temperature; determining first exposure time and second exposure time corresponding to the first coal temperature and the second coal temperature on the rapid temperature rise line segment;
determining the shortest natural fire period based on the following expression:
tc＝t1+(t2-t1)*(Tc-T1)/(T2-T1)
wherein, T1And t1First coal temperature and first exposure time, T, respectively2And t2Second coal temperature and second exposure time, T, respectivelycAnd tcRespectively the ignition temperature and the shortest spontaneous combustion period.
10. A computer-readable storage medium having stored therein instructions that, when executed on a computer, cause the computer to perform operations comprising:
the method of any one of claims 1 to 6 for determining the shortest spontaneous combustion period of coal.
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