DESC:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(See section 10 and rule 13)

AN APPARATUS FOR MULTIPARAMETER COAL SPONTANEOUS COMBUSTION & QUASI-STEADY STATE ASSESSMENT AND METHOD THEREOF

TECHNOLOGY INNOVATION IN EXPLORATION & MINING FOUNDATION
a company incorporated in India, having address at
3rd Floor, i2h Tower (Institute Innovation Hub), IIT(ISM) Dhanbad, Jharkhand - 826004

The following specification particularly describes the invention and the manner in which it is to be performed.
FIELD OF THE INVENTION
The present invention relates to the development of apparatus and methodology for multiparameter coal spontaneous combustion and quasi-steady state assessment. More particularly, the present invention provides a comprehensive apparatus designed to assess the thermal behavior of pulverized coal under controlled conditions, employing advanced features such as programmable temperature control, multi-gas analysis, and precise data acquisition.
BACKGROUND OF THE INVENTION
The coal mining industry worldwide faces the critical issue of recurrent fires in mines, posing serious safety risks and causing the loss of coal, a non-renewable resource. These fires can swiftly escalate, resulting in health problems and accidents. They carry extensive consequences, encompassing economic losses, health risks, environmental damage, safety concerns, legal liabilities, and societal impacts. A notable case is the persistent coal mine fire in India's Jharia Coalfield, which has been burning for over a century and is one of the world's largest. This ongoing fire emits toxic gases and particulate matter, causing respiratory issues and displacing numerous residents. The Indian government has allocated $1.2 billion to extinguish the fire and relocate affected individuals (Bose, 2018). The fundamental cause of coalmine fires is spontaneous combustion, also known as "Spon-comb." This phenomenon occurs when the heat produced in the coal pore lattice exceeds the thermal dissipation rate, increasing the temperature.

The risk of spontaneous coal combustion is elevated in damp or inadequately ventilated environments due to the influence of moisture content and oxygen availability on the oxidation process. Self-heating in coal comprises multiple exothermic stages. The initial trigger for self-heating occurs during low-temperature coal oxidation, typically at temperatures below 100ºC. Subsequent phases involve pyrite oxidation, microbial metabolism, and heat transfer resulting from the wetting and drying of coal (Banerjee et al., 1990; Nelson & Chen, 2007).

Coal from various locations primarily contains surface moisture and moisture within its internal pore structure. The presence of water in coal is a critical factor as it significantly influences heat and mass transfer processes when coal interacts with the surrounding air. When dry air flows through coal with higher moisture content, the self-heating capacity of coal diminishes. This is primarily because the evaporation process absorbs heat from the coal. Contrarily, when moist air is introduced to extremely dry coal, it enhances the heat associated with wetting. Still, this heat is typically less than the heat generated by coal oxidation. Achieving equilibrium between the moisture content in coal and the relative humidity of the surrounding air is essential. The competition between oxygen and water molecules for adsorption sites on coal surfaces is a crucial aspect of coal-oxygen reactivity. When water molecules occupy these adsorption sites, they restrict the access of oxygen molecules, affecting the oxidation process. This phenomenon has significant implications for the combustion efficiency and kinetics of coal combustion reactions. Furthermore, moisture within coal's internal pore matrix requires additional vaporisation energy. This energy requirement affects the spontaneous combustion kinetic parameters, influencing coal's ignition and combustion behaviour.

The present invention relates to the development of apparatus and methodology for multiparameter coal spontaneous combustion and quasi-steady state assessment. The present invention relates to a high-temperature-resistant, multi-parameter analysis apparatus designed to determine the susceptibility of coal towards spontaneous combustion within a short period. It is characterized by its exceptional operational efficiency, necessitating merely a modest quantity of coal specimen for comprehensive analysis. It excels in reliability and ruggedness, offering high repeatability and reproducibility in its results. The present invention primarily serves as a closed-system apparatus for simulating, predicting, and detecting spontaneous combustion, distinct from the naturally transpiring self-heating processes observed in real-life underground coal mines or the coal stored as a stockpile.

SUMMARY OF THE INVENTION
According to an embodiment of the present invention, a coal thermal stability determination device for determining the spontaneous combustion susceptibility of coal is disclosed. The coal thermal stability determination device comprises an insulated cubicle heating cavity with a programmable temperature controller, a reaction control module comprising a humidifier unit and a multi-gas manifold comprising a nitrogen gas cylinder, an oxygen gas cylinder, and an air compressor with a tank, a coal reaction vessel encapsulating the pulverized coal undergoing oxidation, a data acquisition module to capture the tempo-thermal data of the spatial points along the geometric center of the coal reaction vessel and a multi-gas analyzer for measuring index gas composition.

According to the embodiment of the present invention, the reaction control module comprises three independent carrier gas movement loops capable of intercommunication for executing both purging and oxidizing medium phases in multiple modes.

According to the embodiment of the present invention, the insulated cubicle heating cavity is equipped with the programmable temperature controller comprising a Universal Input Process Controller (UIPC) is configured for handling thermocouples, RTD Pt100, and DC Linear mA/mV/V sensors, providing programmable input ranges, digital filtering, zero offset, Self-Tune PID, and On-Off control modes for precise temperature control.

According to the embodiment of the present invention, the coal reaction vessel is constructed from SS-316 grade stainless steel, with an internal diameter of 100 mm and a thickness of 6 mm, and comprises an upper lid, a holding middle column, and a removable base with a 20 mm depth serving as buffer void zones. Further two stainless steel wire woven meshes with 75-micron circular discs separated by 100 mm for coal containment and a pressure gauge attached to the bottom void zone to measure the pressure of the inlet gas discharged at the second gas discharge.

According to the embodiment of the present invention, wherein the device employs five K-type thermocouples for temperature monitoring within the coal reaction vessel. Further, thermocouple T1 is positioned vertically with a radial alignment at a positioning coordinate of (50) and is 50 mm from the geometric centroid, thermocouple T2 is positioned vertically with a radial alignment at a positioning coordinate of (100) and is 100 mm from the geometric centroid, thermocouple T3 is positioned centrally at the geometric centre with a positioning coordinate of (0,0) and is 0.01 mm from the geometric centroid, thermocouple T4 is positioned horizontally with an axial alignment at a positioning coordinate of (0, -5) and is 50 mm from the geometric centroid and thermocouple T5 is positioned horizontally with an axial alignment at a positioning coordinate of (0, -10) and is 100 mm from the geometric centroid.

According to the embodiment of the present invention, the data acquisition module is configured to record thermal data from K-type thermocouples in both vertical and horizontal orientations, comprises a 4×20-line alphanumeric LCD, supporting J/K/R thermocouples and PT100 sensors, allowing user-selectable scanning rates from 1 to 99 seconds, and offering digital offset adjustments for individual channels with date and time information.

According to the embodiment of the present invention, the multi-gas analyzer is configured for accurate quantification of oxygen (O2), carbon dioxide (CO2), and carbon monoxide (CO) volume concentrations in emissions, employing a diaphragm peristaltic pump to induce pressure, to enable the flow of oxidizing gases through a plurality of electrochemical sensors, with the results visualized on a digital display unit.

According to the embodiment of the present invention, the humidifier unit is constructed from stainless steel of 304-grade material, resulting in a cylindrical enclosure with an internal diameter of 150 mm and a depth of 300 mm, comprising bossed ends at both extremities and incorporating an overflow protection valve to prevent water spillage.

According to the embodiment of the present invention, the humidifier unit employs a 1500-watt heating element constructed from cupronickel alloy, submerged in distilled water, with a rheostat for precise temperature control, and integrates two ball valves connected to distinct pathways for discharging from both the humidifier unit and the moisture trap, facilitating the introduction of water vapor saturation into the carrier gas.

According to the embodiment of the present invention, wherein the mixing tank is equipped with a differential pressure gauge and a digital thermo-hygrometer, provides real-time data on the pressure, relative humidity, and temperature of the carrier gas, which is displayed through a digital readout unit.

According to the embodiment of the present invention, wherein the mixing tank consists of a rotameter with a capacity of 0-2 lpm and a needle valve in the bypass line to control the carrier gas flow rate to the coal reaction vessel. The carrier gases pass through a pre-heated copper conduit, a ten-foot-long coiled copper pipe, allowing the gases to reach the desired temperature before entering the coal reaction vessel. The vessel features an inlet at the bottom where the pre-heated copper coil terminates. Carrier gas feed wires have independent loops with isolation ball valves and connectors to divert the gases from the humidifier or the moisture trap.

According to an embodiment of the present invention, a method for determining the susceptibility parameter for coal towards spontaneous combustion using the coal thermal stability determination device is disclosed. The method comprises determining the equilibrium moisture, inherent moisture, and total moisture of coal's apparent porosity. Next introducing 500 grams of selected pulverized coal meeting size criteria into the coal reaction vessel. Further inspecting the hermetic integrity of the coal reaction vessel to ensure gas-tight seals. Next activating nitrogen gas discharge to test for air leakage, monitoring pressure drop at the humidifier over 15 minutes, and continuously monitoring the pressure in the coal reaction vessel for leaks. Then heating the coal reaction vessel using a programmable temperature controller and an electric heater, ensuring uniform heating with a circulating fan, following a specified heating ramp rate. Next simultaneously activating the pressure-reducing valve to control the flow of oxygen gas from the cylinder, directing gas to the humidifier and the gas conduit connected to the moisture trap. Further introducing the humidified oxygen and dry gas from the moisture trap into the mixing tank, adjusting the relative humidity, temperature, and total pressure of the gas mixture. Next pre-heating the carrier gas within the insulated heating cavity before it enters the coal reaction vessel. Next recording the temperature distribution of the coal using the data acquisition module during various oxidation phases. Further employing the diaphragm pump within the multi-gas analyzer to aspirate the exhaust gases at specified intervals and collecting data for index gases after every 10°C rise in the average temperature of the coal reaction vessel. Finally closing the oxygen cylinder supply and powering off the insulated heating cavity when the average coal body temperature reaches 250°C, allowing the coal reaction vessel to cool naturally to room temperature.

BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, example of which may be illustrated in the accompanying figure(s). These figure(s) are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

Figure 1 illustrates a schematic overview of the coal thermal stability determination device according to the embodiments of the present disclosure.

Figure 2 illustrates a schematic overview of the coal reaction vessel according to the embodiments of the present disclosure.

Figure 3 illustrates a graph showing the average coal body temperature (red line) and the programmable heating cavity temperature (23) (blue line) over the oxidation period according to the embodiments of the present disclosure.

Figure 4-(i) illustrates a graph showing variation in conduction gradient with oxidation time for axial (T4) and radial (T1) thermocouples relative to the central thermocouple (T3) according to the embodiments of the present disclosure.

Figure 4-(ii) illustrates a graph showing the time derivative of the thermal conduction gradient for axial and radial directions according to the embodiments of the present disclosure.

Figure 5 illustrates a graph showing the relationship between the average coal body temperature and the concentrations of critical gases at the outlet during the coal oxidation process according to the embodiments of the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention disclose the development of apparatus and methodology for multiparameter coal spontaneous combustion and quasi-steady state assessment. More particularly a coal thermal stability determination device for determining the spontaneous combustion susceptibility of coal.

According to an embodiment of the present invention, the coal thermal stability determination device comprises an insulated cubicle heating cavity with a programmable temperature controller, a reaction control module comprising a humidifier unit and a multi-gas manifold comprising a nitrogen gas cylinder, an oxygen gas cylinder, and an air compressor with a tank, a coal reaction vessel encapsulating the pulverized coal undergoing oxidation, a data acquisition module to capture the tempo-thermal data of the spatial points along the geometric center of the coal reaction vessel and a multi-gas analyzer for measuring index gas composition.

According to the embodiment of the present invention, the reaction control module comprises three independent carrier gas movement loops capable of intercommunication for executing both purging and oxidizing medium phases in multiple modes.

According to the embodiment of the present invention, the insulated cubicle heating cavity is equipped with the programmable temperature controller comprising a Universal Input Process Controller (UIPC) is configured for handling thermocouples, RTD Pt100, and DC Linear mA/mV/V sensors, providing programmable input ranges, digital filtering, zero offset, Self-Tune PID, and On-Off control modes for precise temperature control.

According to the embodiment of the present invention, the coal reaction vessel is constructed from SS-316 grade stainless steel, with an internal diameter of 100 mm and a thickness of 6 mm, and comprises an upper lid, a holding middle column, and a removable base with a 20 mm depth serving as buffer void zones. Further two stainless steel wire woven meshes with 75-micron circular discs separated by 100 mm for coal containment and a pressure gauge attached to the bottom void zone to measure the pressure of the inlet gas discharged at the second gas discharge.

According to the embodiment of the present invention, wherein the device employs five K-type thermocouples for temperature monitoring within the coal reaction vessel. Further, thermocouple T1 is positioned vertically with a radial alignment at a positioning coordinate of (50) and is 50 mm from the geometric centroid, thermocouple T2 is positioned vertically with a radial alignment at a positioning coordinate of (100) and is 100 mm from the geometric centroid, thermocouple T3 is positioned centrally at the geometric centre with a positioning coordinate of (0,0) and is 0.01 mm from the geometric centroid, thermocouple T4 is positioned horizontally with an axial alignment at a positioning coordinate of (0, -5) and is 50 mm from the geometric centroid and thermocouple T5 is positioned horizontally with an axial alignment at a positioning coordinate of (0, -10) and is 100 mm from the geometric centroid.

According to the embodiment of the present invention, the data acquisition module is configured to record thermal data from K-type thermocouples in both vertical and horizontal orientations, comprises a 4×20-line alphanumeric LCD, supporting J/K/R thermocouples and PT100 sensors, allowing user-selectable scanning rates from 1 to 99 seconds, and offering digital offset adjustments for individual channels with date and time information.

According to the embodiment of the present invention, the multi-gas analyzer is configured for accurate quantification of oxygen (O2), carbon dioxide (CO2), and carbon monoxide (CO) volume concentrations in emissions, employing a diaphragm peristaltic pump to induce pressure, to enable the flow of oxidizing gases through a plurality of electrochemical sensors, with the results visualized on a digital display unit.

According to the embodiment of the present invention, the humidifier unit is constructed from stainless steel of 304-grade material, resulting in a cylindrical enclosure with an internal diameter of 150 mm and a depth of 300 mm, comprising bossed ends at both extremities and incorporating an overflow protection valve to prevent water spillage.

According to the embodiment of the present invention, the humidifier unit employs a 1500-watt heating element constructed from cupronickel alloy, submerged in distilled water, with a rheostat for precise temperature control, and integrates two ball valves connected to distinct pathways for discharging from both the humidifier unit and the moisture trap, facilitating the introduction of water vapor saturation into the carrier gas.

According to the embodiment of the present invention, wherein the mixing tank is equipped with a differential pressure gauge and a digital thermo-hygrometer, provides real-time data on the pressure, relative humidity, and temperature of the carrier gas, which is displayed through a digital readout unit.

According to the embodiment of the present invention, wherein the mixing tank consists of a rotameter with a capacity of 0-2 lpm and a needle valve in the bypass line to control the carrier gas flow rate to the coal reaction vessel. The carrier gases pass through a pre-heated copper conduit, a ten-foot-long coiled copper pipe, allowing the gases to reach the desired temperature before entering the coal reaction vessel. The vessel features an inlet at the bottom where the pre-heated copper coil terminates. Carrier gas feed wires have independent loops with isolation ball valves and connectors to divert the gases from the humidifier or the moisture trap.

According to an embodiment of the present invention, a method for determining the susceptibility parameter for coal towards spontaneous combustion using the coal thermal stability determination device is disclosed. The method comprises determining the equilibrium moisture, inherent moisture, and total moisture of coal's apparent porosity. Next introducing 500 grams of selected pulverized coal meeting size criteria into the coal reaction vessel. Further inspecting the hermetic integrity of the coal reaction vessel to ensure gas-tight seals. Next activating nitrogen gas discharge to test for air leakage, monitoring pressure drop at the humidifier over 15 minutes, and continuously monitoring the pressure in the coal reaction vessel for leaks. Then heating the coal reaction vessel using a programmable temperature controller and an electric heater, ensuring uniform heating with a circulating fan, following a specified heating ramp rate. Next simultaneously activating the pressure-reducing valve to control the flow of oxygen gas from the cylinder, directing gas to the humidifier and the gas conduit connected to the moisture trap. Further introducing the humidified oxygen and dry gas from the moisture trap into the mixing tank, adjusting the relative humidity, temperature, and total pressure of the gas mixture. Next pre-heating the carrier gas within the insulated heating cavity before it enters the coal reaction vessel. Next recording the temperature distribution of the coal using the data acquisition module during various oxidation phases. Further employing the diaphragm pump within the multi-gas analyzer to aspirate the exhaust gases at specified intervals and collecting data for index gases after every 10°C rise in the average temperature of the coal reaction vessel. Finally closing the oxygen cylinder supply and powering off the insulated heating cavity when the average coal body temperature reaches 250°C, allowing the coal reaction vessel to cool naturally to room temperature.

Figure 1 illustrates a schematic overview of the coal thermal stability determination device (100) according to the embodiments of the present disclosure. The coal thermal stability determination device (100) comprises (101)-nitrogen cylinder, (102)-oxygen cylinder, (103)-compressed air source, (104) pressure gauge of the gas sources, (105)-pressure reducing valve, (106)-four-way connector, (107)-two-way split connector, (108)-pressure gauge for the humidifier, (109)-heating element, (110)-humidifier, (111)-moisture trap, (112)-ball valve, (113)-mixing tank, (114)-digital thermo-hygrometer, (115)-digital readout unit, (116)-mixing tank differential pressure gauge, (117)-rotameter, (118)-pre-heated copper conduit, (119)- first gas discharge, (120)-coal reaction vessel, (121)-insulated cubicle heating cavity programmable temperature controller with the heating element, (122)-circulation fan, (123)-insulated heating cavity, (124)-data acquisition module, (125)-gas analyser, (126)-second gas discharge, (127)-pressure gauge of coal reaction vessel.

According to an embodiment of the present invention, the coal thermal stability determination device (100) relies primarily on quasi-steady-state phase evaluation of oxidising coal under controlled experimental conditions. Input factors consider flexible carrier gas flow rate ramped temperature settings to induce thermal stress, oxygen concentration and relative humidity in carrier gas and coal moisture content.

Insulated Heating Cavity with A Programmable Temperature Controller

According to an embodiment of the present invention, the device comprises an insulated heating cavity, which is a cubical enclosure working as an air bath having an inner void dimension of 500 mm (W) x 500 mm (D) x 550 mm (H); the outer casing structure is made of powder-coated steel. The front door of the insulated heating cavity (124) houses an 8 mm thick transparent borosilicate glass. Fibreglass is an insulation material between the inner and outer casing to trap the air pockets and prevent the heat from escaping. The insulated housing cavity attaches a programmable temperature controller with the heating element (121), preferably made of high-resistance nickel-chromium wire. The circulation fan (122) ensures even temperature distribution throughout the cavity's interior.

The programmable temperature controller (121) has a Universal Input Process Controller (UIPC) that receives input signals from sensors, including thermocouples, RTD Pt100, and DC Linear mA/mV/V. It utilises programmable input ranges, digital filtering, and zero offset capabilities to ensure precise measurements. The controller offers versatile control modes, including Self-Tune PID and On-Off, facilitating precise process control. Its universal control output options, as in the Relay, SSR, and mA/Volts output, make it adaptable to regulate the heating rate of coal reaction vessels (120) at different time stages. The Self-Tune PID mode offers extensive control parameters, including Proportional Band, Integral Time, Derivative Time, Cycle Time, Relative Cool Gain, Power Low, Power High, and Overshoot Inhibit, enabling fine-tuning and optimisation of control loops. Additionally, the controller supports manual control with seamless bump-less transfer between auto PID and manual control modes, enhancing operational flexibility and precision. With a wide supply voltage range (85~264 VAC) and compliance with DIN standard dimensions.
Reaction Control Module
Gas Station Manifold
According to an embodiment of the present invention, the reaction control module consists of two main components: a humidifier unit (110) and a multi-gas manifold, including a nitrogen gas cylinder (101), an oxygen gas cylinder (102), and an air compressor with a tank (103). The nitrogen gas cylinder assesses the overall equipment's integrity. It plays a crucial role during the purging phase, effectively removing inherent moisture from the coal. Additionally, it aids in releasing trapped methane and carbon dioxide from the coal's pore structure, making these spots accessible for subsequent oxygen molecule adsorption during the oxidation phase. The carrier gas is split using a two-way split connector (107), with one outlet connected to the humidifier unit (110) inlet and the other to the moisture trap (111). The high purity (99% UHP grade) oxygen gas cylinder (102) provides the most favourable conditions for the shortest oxidation of coal. It is important to note that the oxygen consumption rate is directly related to the reaction rate during the oxidation phase. Meanwhile, the compressed air from the compressor emulates real-world oxidation conditions of coal, as mine air typically contains a minimum of 19 % oxygen. The gas manifold enables studying coal's oxidation behaviour under contact with aerial oxidation conditions that closely mimic those encountered in practical scenarios of spontaneous combustion zones of large stockpiles or silos, virgin coal seams, coal pillars, coal goaf areas, spoil heaps, abandoned mine workings and waste dumps.
Humidifier
According to an embodiment of the present invention, the humidifier unit (10) comprises a stainless-steel 304-grade cylindrical enclosure with a 150 mm internal diameter and 300 mm depth, featuring bossed ends at both extremities. It is equipped with an overflow protection valve to prevent water spillage. The unit has a 1500-watt heating element (109) crafted from cupronickel alloy submerged in distilled water. Precise water temperature control is achieved by regulating the heating element through a rheostat. The rheostat allows for finely tuned power adjustments to ensure gradual and controlled heating, effectively serving as a constant-temperature water bath. The pressure gauge (108) measures water vapour pressure in the humidifier tank. Incorporated within the system are two ball valves (112), which are connected to distinct pathways of discharge from both the humidifier unit (110) and the moisture trap (110), which is a columnar glass body of 42.6 mm outer diameter and a column length of 255 mm consisting of granules of silica gel and calcium chloride. The ball valves (112) are affixed to both in-lets of the mixing tank (113), inlets serving as a discharge gas of the humidifier and the moisture trap; the gas is mixed in the mixing tank (113), enabling the saturation of the carrier gas with water vapour. The degree of saturation of the carrier gas in the mixing tank depends upon the pivot action of the ball valves (112) across an extensive range using the lever action mechanism.
Mixing tank
According to an embodiment of the present invention, the mixing tank (113) contains a differential pressure gauge (116) and a digital thermo-hygrometer (114), providing real-time data on the pressure, relative humidity and temperature of carrier gas in the mixing tank. The data is fittingly displayed through a digital readout unit (115). The rotameter (117) of capacity 0-2 lpm and the needle valve in the bypass line to the volumetric flow controller. It controls the carrier gas flow rate to the coal reaction vessel (120). Carrier gases enter the pre-heated copper conduit (118), which is affixed to the sidewall of the insulated cavity; it also bridges the connection between the terminal of the rotameter outlet and the first gas discharge (119). The pre-heated copper conduit (118) comprises a ten-foot-long 8 mm ID copper pipe coiled to transfer heat to the coal reaction vessel (120), allowing carrier gases to reach the desired temperature. The coal reaction vessel (120) features carrier gas discharge or first gas discharge as an inlet (119) at the bottom, where the pre-heated copper coil (118) terminates. The carrier gas feed wires have independent intercommunicable loops using the isolation ball valves and two split connectors to deviate the carrier gases from the humidifier (110) or the moisture trap (111). The coal reaction vessel (120) features carrier gas discharge as an inlet (119) at the bottom, where the pre-heated copper coil (118) terminates. The carrier gas feed wires have independent intercommunicable loops using the isolation ball valves and two split connectors to deviate the carrier gases from the humidifier (110) or the moisture trap (111).
Coal reaction vessel
According to an embodiment of the present invention, the upper lid of the coal reaction vessel (120) is sealed tightly by a screw mechanism. It includes the carrier gas exhaust outlet as the second gas discharge (126) connected to the multi-gas analyser (125).

Figure 2 shows that the coal reaction vessel (200) is made up of SS 316 grade, the internal diameter is 100 mm and has a thickness of 6 mm, and the material is corrosion and heat-resistant. It is separated by two stainless steel woven wire mesh discs with 75-micron (203), separated by a vertical distance of 100mm, and the coal body resides within them. The whole reaction vessel has three detachable units. The upper lid is a screw lid-on mechanism with the vessel neck extended up to 2cm above the top layer of coal, which works as the top buffer void zone (205). Also, the base is detachable and has a depth of 20mm, which acts as a bottom buffer void zone (205) for the carrier gas discharge at the vessel inlet from the copper conduit terminal (118). The pressure gauge (127) of the coal reaction vessel, which has a range of 0-3 bar pressure, is attached to the bottom void zone (205) to measure the pressure of the inlet gas discharged at the second gas discharge (126); the carrier and gas pass through a gas buffer zone (204) within the coal reaction vessel (120) to curtail turbulence. The bottom base part is flanged to the mid part using screw clamps (208). A silicone airtight ring (204) provides the hermetic integrity of the vessel body. The NPT Elbow brass ¼ inch ID elbow valves (207) and (208) are connected at the vessel gas inlet and the outlet. Temperature monitoring within the coal reaction vessel (120), encompassing the coal, is conducted radially and axially from the geometric centre. This is achieved using five K-type plurality of thermocouples (201 & 202) with one central, two vertical (201) and two horizontal (202) orientations. The plurality of thermocouples (201 & 202) -related information is given in Figure 2.
Thermocouple ID Positioning coordinate Alignment in the reaction vessel Temperature variation Euclidian distance from the geometric centroid ?(r?_i) in mm
T_1 (5,0) Vertical Radial 50
T_2 (10,0) Vertical Radial 100
T_3 (0,0) Central Geometric Centre 0.01
T_4 (0, -5) Horizontal Axial 50
T_5 (0, -10) Horizontal Axial 100

Type K (Ni Cr-Ni) thermocouples element has an extension cable denoted as TT-465-2K-0.22L. The insulation is single and joint, utilising Teflon material. The cable features a copper-meshed screen and a cross-sectional area of 2 x 0.22 mm² to ensure reliable performance. The cable length (212) extends to 2 meters for flexible installation. Additionally, the thermocouple includes six AL-sleeves, each measuring 50 mm in size, with a material designation of 1.4305. The sheath of the thermocouple is constructed from Inconel 600, featuring a 1.0 mm diameter and a nominal length of 100 mm. It complies with IEC 584 standards, specifically meeting Class 1 deviation requirements. The thermocouples (201 & 202) are aligned to sense the temperature variation in and around the geometric centre of the vessel, as shown in Figure 2. The centre-to-centre distance between any two adjacent thermocouples is 5mm. Thermocouples (201 & 202) are aligned and welded to an external holder-aligner (210); they consist of thin hollow tubes tapered from one end and filled with glass wool (211). They hold the thermocouple wires and have symmetrical alignment to the geometric centre.

Data acquisition system
Temporal-thermal data from the K-type plurality of thermocouples (201 & 202) in vertical and horizontal directions were logged through a data acquisition module (126). The data acquisition module features a 4×20-line alphanumeric LCD, accommodating J/K/R thermocouples and PT100 sensors with wide temperature ranges and high accuracy. The system accommodates a maximum of 16 channels, user-selectable scanning rates from 1 to 99 seconds, and digital offset adjustments for individual channels, including date and time information. The system ensures precise measurements with an accuracy of ±1°C (± 1 Least Significant Digit) for K-type plurality of thermocouples and ±0.1°C (± 1 Least Significant Digit) for PT100. It operates on a 230V AC ± 15% power supply, adopts a panel-type mounting, and features a 96mm x 192mm front facia. It has a built-in microprocessor, a real-time clock, and the ability to store data in an MS Excel-compatible format on a USB drive.
Index gas analyser
The self-contained gas emission analyser, known as the gas analyser, provides temperature-controlled sensors that measure O2 and carbon oxide levels. It operates on a rechargeable nickel hydride battery that can be utilised with a 220 V, 50 Hz power source. The device is designed to measure positive and negative pressures within the range of -200 mbar to +50 mbar, featuring an integrated diaphragm pump with a flow rate of 0.6 LPM. The body of the multi-gas analyser has a condensate trap where the fill level of the moisture is present in the exhaust gas.

In terms of its measurement capabilities, the multi-gas analyser provides the following information:

Oxygen (O2): It offers a measurement range from 0 to 100% by volume, with a resolution of 0.1% by volume. The accuracy of O2 measurements is within 0.2% of the reading ± 0.2%, and it exhibits a prompt response time of less than 10 seconds. The oxygen sensor is the zirconium oxide sensor involving a solid-state electrochemical cell; a solid electrolyte separates the two electrodes. The diffuse oxygen molecules are reduced, generating an electrical current proportional to the oxygen concentration.

Carbon Monoxide: The measurement range for CO extends from 0 to 10,000 ppm, with a resolution of 10 ppm. The accuracy of CO measurements is within ± 2% of the reading ± 5 ppm. The sensor composition comprises a platinum noble metal electrode, and the counter electrode includes carbon and a proton-conducting membrane. The proton-conducting membrane is typically made of a perfluorosulfonic acid (PFSA) polymer. The diffused CO molecule gets diffused and oxidised to carbon dioxide. It gives away current, which is proportional to carbon monoxide concentration.

Carbon Dioxide (CO2): The CO2 measurement range spans from 0 to 10,000 ppm, with a resolution of 10 ppm. The accuracy for CO2 measurements is 0.2% of the reading ± 0.2%. The sensor used for carbon dioxide detection is NDIR, a non-dispersive infrared sensor; it is principled to work by emitting the infrared light of a specific wavelength. The CO2 absorbs the IR to a particular wavelength, creating the magnitude of proportionality to the concentration of the CO2.
Mode of operation of the apparatus
According to an embodiment of the present invention, the data for the equilibrium moisture, inherent moisture, and total moisture of the apparent porosity of coal is determined as the basis for suitable standards of practice. Before this step, the coal's apparent porosity was accurately estimated through appropriate analytical methods.

Assuming the inherent moisture content of coal (m) is the ratio of the water mass existing in the coal unit mass. The presence of moisture affects the reaction kinetics of coal by influencing the apparent porosity of the coal in the reaction vessel and accounting for the fact that water molecules can compete with oxygen molecules for adsorption sites on the coal surface. The adjusted porosity of coal can be deduced as:

A sample weight of 500 grams of pulverised coal, carefully selected to meet the desired size fraction criteria, is meticulously measured and placed within the coal reaction vessel (120).

The coal reaction vessel (120) undergoes an initial inspection to verify its hermetic integrity. This meticulous examination guarantees the absence of any gas leakage from all interconnected pipe joints and the coal reaction vessel (120). All valves on the gas flow branches connecting the compressed air source (Figure 1, 3) and oxygen cylinder are closed to restrict the intermixing of gas.

Nitrogen gas discharge is made active for unidirectional flow through the pressure-reducing valve (105) and the release via the route (Figure 1, a-b-d-e-g-h) and (Figure 1,e-f-i) to check the air leakage of the humidifier (110), the moisture trap (111) and the gas mixing chamber (113). The humidifier's gauge pressure (Figure 1, 8) (110) is monitored for 15 minutes to check the pressure drop due to leakage. The rotameter valve (116) activates the gas route (Figure 1, j-k-l-m-n). To assess the hermetic integrity of the subsequent components, a pressure gauge is affixed at the outlet valve of the coal reaction vessel (120). For Next 15 minutes, continuous monitoring of the pressure buildup within the vessel is conducted, enabling the detection of any pressure drop, which could suggest the presence of leaks within the experimental setup.

The coal reaction vessel (120) is heated by the programmable temperature controller (121). The electric heater (121) is engaged with the necessary electrical load to begin heating. Concurrently, the circulating fan (122) is switched on to heat the air inside the cavity (123) and provide an air bath to heat the coal reaction vessel (120) uniformly. The heating ramp rate, determined following the prescribed experimental design, is specified as the input parameter. Within the initial pre-oxidation ramped heating (Figure 3), the temperature of the coal samples was raised from ambient temperature to 40°C over a period of 10 minutes. Following this, the heating rate was increased to 14°C/min, bringing the samples to an isothermal temperature of 140°C. This isothermal oxidation phase was maintained for 3 hours to ensure a stable thermal environment, allowing the coal to reach a quasi-steady state in temperature distribution. After completing the isothermal phase, the programmable temperature controller's (Figure 1, 121) thermal settings were switched to dynamic heating, with the programmable heating increasing at 1°C/min.

Simultaneously, the pressure-reducing valve (105) controlling the flow of the oxygen gas cylinder (102) is activated, allowing the gas to bifurcate through two distinct pathways denoted as (Figure 1, b-d-e-g-h) and (Figure 2, e-f-i). A portion of the gas stream is directed towards the inlet of the humidifier (110). In contrast, the remainder is directed into the gas conduit connected to the moisture trap (111).
Subsequently, the oxygen gas, having undergone humidification, and the remnant gas free from moisture, discharged from the outlet of the moisture trap (111), is introduced into the mixing tank (113).

Assume the carrier gas stream towards the mixing tank has relative humidity (?). The relative humidity affects the intermediate inlet concentration of the oxygen gas leaving the mixing tank (13) as mol/cm3. According to Dalton's law of partial pressure, the gas mixture exerts the total pressure in the tank .

Where the partial pressure of the oxygen gas is in Pascal , is the water vapour pressure in Pascal.

The oxygen and water vapour gas composite, characterised by its relative humidity, temperature, and total pressure attributes, as measured within the mixing tank (113), is meticulously adjusted following the requisites of the experimental setup. The precise control of vapour saturation within the carrier gas is achieved by manipulating the ball valve (112) positioned at the exit terminals of the humidifier and the moisture trap (111).

The partial vapour pressure of water depends upon the relative humidity (?) of the carrier gas at a given temperature as well as the saturation pressure of water vapour at the given temperature (Pa) as:

The Clausius Clapeyron equation determines the changes in saturated vapour pressure of water vapour at a given temperature (T).

The mixture gas enters the insulated heating cavity (123) from the outlet of the rotameter to the pre-heated copper conduit (118) of copper pipe; within the confines of the insulated heating cavity (123) cavity, the heat exchange mechanism efficiently pre-heats the mixture gas before it enters the inlet of the coal reaction vessel (120). The concentration of the mixture gas changes as it enters the coal reaction vessel.

Substitution into the equation with an equation for determining the oxygen concentration at the outlet of the mixing tank by the ideal gas equation mol/cm3, which is also the oxygen concentration of the inlet of the coal reaction vessel.

Or
[6]
Here, R is the universal gas constant as 8.314 J/mol-1K-1, and T is the temperature in Kelvin.
The data acquisition module records the spatial temperature distribution of the coal undergoing different oxidation phases (124).

At time t=0, at the beginning of the experiment, the temperature of the coal body in the vessel will be the same. After the start of the experiment, Elevated-temperature carrier gas flows from the conduit discharge beneath the coal body, inducing heat transfer through gas convection and conduction due to temperature disparities between the coal body and the carrier gas. This reaction initiates at the bottom surface boundary layer. It progresses upwards, permeating through the coal matrix with minimal diffusional resistance. The comprehensive thermal data acquired every 15-second intervals is crucial for accurately determining the average coal body temperature, defined as the mean temperature readings from all thermocouple positions.

Here:
T_avg is the average coal body temperature.
n is the total number of thermocouples, which is 5 in this case.
T_i is the temperature reading of the i th thermocouple.

The collected thermal data shown in Figure 3 suggests the variation of average temperature with oxidation time. The results are illustrated through a graph showing the average coal body temperature (red line) and the programmable heating cavity temperature (23) (blue line) over the oxidation period. The experiment begins at room temperature, progresses through the initial pre-oxidation ramped-up stage, and enters the isothermal heating zone at approximately 140°C. The transition from the isothermal heating zone to the non-isothermal heating zone occurs around the 200th-min mark, indicating the coal transition temperature.

Simultaneously, the walls of the coal reaction vessel heat up due to the surrounding air bath, leading to heat conduction from the lateral surface boundary layer towards the longitudinal axis of the vessel. It's important to note that the coal reaction vessel is an equicylinder, characterised by an "h/D" ratio of 1, resulting in heat transfer occurring in both directions.

Therefore, the energy conservation model for the transient method suggests that coal conduction plays a role in heat dissipation, as indicated in the studies of Sondreal and Ellman (1974)

Alternatively, in the cylindrical conduction derivative term, equation [7] reference here can be simplified as:

In this context, ? represents the coefficient of thermal conductivity of the loose coal in Wm-1K-1, ? is the density of coal in kg/cm3, and c is the specific heat capacity of coal in J/kg-k. r is the cross-over position of the temperature node point from the axis, S is the heat source term incorporated as the sum of exothermic heat, which denotes the heat liberated by the composite reaction between the coal particles with oxygen and the phase transition enthalpy due to moisture vaporisation present in coal pore matrix. As the reaction progresses, the temperature at the geometric centre of the coal reaction vessel is higher than that near the boundary layer, primarily because the oxygen sorption sites become more active further away from the vessel wall boundary layer. This leads to a relatively steady temperature distribution.

The quasi-steady state is accomplished at different time junctures along the axial and radial directions. The system is designed to monitor quasi-thermal equilibrium states, where the temperature gradients within the coal sample approach a minimum value, indicating a near-balance between heat generation and heat adsorption. This quasi-thermal equilibrium is crucial for understanding the thermal behaviour of coal under oxidation as it marks the transition to a nearly stable thermal regime. The steady-state conditions observed in the isothermal phase and the dynamic thermal transitions during ramped-up heating are pivotal in identifying critical thermal management points.

We can use the following to discretise the conduction term from the equation using the central difference method.

Here,T_ijk is the temperature at the grid point which is dynamically changing due to the time-dependent variability of the heat source mentioned in Eq [9]. The ?r is the uniform radial grid spacing and ?z = uniform axial grid spacing.

This model assumes that the temperature field distribution changes per unit of time due to oxidation. The heat conduction in the spatial arrangement, as monitored by the thermocouples, is the sum of the conduction gradients of axial and radial components. The thermal conduction gradient varies with space along the radial and axial directions , respectively. These thermal parameters demonstrate the temperature change at a specific location inside the reaction vessel. So, the conduction derivative / thermal gradient in the radial direction is represented by

The corresponding axial conduction derivative term is

To measure the tendency or liability towards spontaneous combustibility of coal under a given experimental design, the association between versus time (t) is plotted to determine when the derivative terms are acquired to be zero and intersect the abscissa (t).

This quantitative stability time parameter changes from unsteady to quasi-steady state can be determined from the temporal thermal data obtained in step 8.

In Figure 4-(i). The results illustrate the graphical representation of the variation of with oxidation time observed at the thermocouple (T4) position for axial conduction gradient measurement and thermocouple (T1) for the radial thermocouple location concerning central thermocouple (T3). The graphs reflect the variation in heat transfer dynamics within the coal sample due to oxidation. The increase in the conduction gradient is evident in both the axial and radial directions during the initial ramp-up stage to 140°C, creating initial thermal instability. The oxidation sequence is followed by a decrease in the gradient in the isothermal heating zone due to the balance between heat generation and dissipation rates within the coal reaction vessel. This balance maintains the isothermal heating condition, and the state of coal oxidation is in quasi-thermal equilibrium. After the programmable heating enters the non-isothermal zone, uniform dynamic heating of the coal sample induces thermal changes, leading to the corresponding departure of the curve from the axis of the temporal steady state.

In Figure 4-(ii). The result illustrates the time derivative of the thermal conduction gradient depicted in the graphical representation of Figure 4-(i). The gradient of heat conduction at the thermocouple locations changes with oxidation time. Peaks of conduction fluctuation in both the axial and radial directions indirectly indicate the heat generated by coal oxidation, suggesting that the heat from the surroundings is not in equilibrium—consequently, the thermal gradient changes. Second peaks are observed in the non-isothermal oxidation phase, where the thermal stress induced by dynamic heating leads to further gradient changes, indicating that the coal is reaching the thermal runaway stage.

The diaphragm pump integrated within the multi-gas analyser (25) is employed to aspirate in the exhaust column's index/exhaust gases emanating from the outlet. The composition of the index gases is analysed at designated intervals, the data for index gases is collected after every ten °C rise for the average temperature of coal reading of the coal reaction vessel (120). The experiment was concluded when the average coal body temperature reached 250°C.

As represented in (Figure 5) ,The green line represents the concentration of carbon dioxide (ppm), the red line indicates the oxygen concentration (%), and the blue line denotes the concentration of carbon monoxide (ppm). The left vertical axis corresponds to the carbon dioxide concentration, the right vertical axis corresponds to the carbon monoxide concentration, and the horizontal axis represents the average coal body temperature (°C). Notably, as the coal body temperature increases, the oxygen concentration decreases.

In contrast, carbon dioxide and carbon monoxide concentrations significantly increase, particularly beyond 150°C. This is evident as the heating shifted to isothermal dynamic heating. The shaded area indicates the region where measurements were taken at room temperature.

Once the coal temperature has attained the maximum temperature per the experimental design of 250 °C, the oxygen cylinder supply is closed with the insulated heating cavity (123) power load shut-off. When the insulated heating cavity (123) door is opened, the coal reaction vessel (120) cools off naturally until the vessel reaches room temperature. Hence, the methodology concludes.

The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the disclosure.
,CLAIMS:We Claim:
1. A coal thermal stability determination device (100) for determining the spontaneous combustion susceptibility of coal, comprising:
an insulated cubicle heating cavity (123) with a programmable temperature controller (121);
a reaction control module comprising a humidifier unit (110) and a multi-gas manifold comprising a nitrogen gas cylinder (101), an oxygen gas cylinder (102), and an air compressor with a tank (103);
a coal reaction vessel (120) encapsulating the pulverized coal undergoing oxidation;
a data acquisition module (124) to capture the tempo-thermal data of the spatial points along the geometric centre of the coal reaction vessel (120); and
a multi-gas analyser (125) for measuring index gas composition.
2. The coal thermal stability determination device (100) as claimed in claim 1, wherein the reaction control module comprises three independent carrier gas movement loops capable of intercommunication for executing both purging and oxidizing medium phases in multiple modes.

3. The coal thermal stability determination device (100) as claimed in claim 1, wherein the insulated cubicle heating cavity is equipped with the programmable temperature controller (121) comprising a Universal Input Process Controller (UIPC) is configured for handling thermocouples, RTD Pt100, and DC Linear mA/mV/V sensors, providing programmable input ranges, digital filtering, zero offset, Self-Tune PID, and On-Off control modes for precise temperature control.

4. The coal thermal stability determination device (100) as claimed in claim 1, wherein the coal reaction vessel (120) is constructed from SS-316 grade stainless steel, with an internal diameter of 100 mm and a thickness of 6 mm, and comprises:
an upper lid, a holding middle column, and a removable base with a 20 mm depth serving as buffer void zones;
two stainless steel wire woven meshes with 75-micron circular discs separated by 100 mm for coal containment; and
a pressure gauge (127) attached to the bottom void zone to measure the pressure of the inlet gas discharged at the second gas discharge.

5. The coal thermal stability determination device (100) as claimed in claim 1, wherein the device (100) employs five K-type thermocouples for temperature monitoring within the coal reaction vessel (120), wherein:
thermocouple T1 is positioned vertically with a radial alignment at a positioning coordinate of (50) and is 50 mm from the geometric centroid;
thermocouple T2 is positioned vertically with a radial alignment at a positioning coordinate of (100) and is 100 mm from the geometric centroid;
thermocouple T3 is positioned centrally at the geometric centre with a positioning coordinate of (0,0) and is 0.01 mm from the geometric centroid;
thermocouple T4 is positioned horizontally with an axial alignment at a positioning coordinate of (0, -5) and is 50 mm from the geometric centroid and
thermocouple T5 is positioned horizontally with an axial alignment at a positioning coordinate of (0, -10) and is 100 mm from the geometric centroid.

6. The coal thermal stability determination device (100) as claimed in claim 1, wherein the data acquisition module (124) is configured to record thermal data from K-type thermocouples in both vertical and horizontal orientations, comprises a 4×20-line alphanumeric LCD, supporting J/K/R thermocouples and PT100 sensors, allowing user-selectable scanning rates from 1 to 99 seconds, and offering digital offset adjustments for individual channels with date and time information.

7. The coal thermal stability determination device (100) as claimed in claim 1, wherein the multi-gas analyzer (125) is configured for accurate quantification of oxygen (O2), carbon dioxide (CO2), and carbon monoxide (CO) volume concentrations in emissions, employing a diaphragm peristaltic pump to induce pressure, to enable the flow of oxidizing gases through a plurality of electrochemical sensors, with the results visualized on a digital display unit.

8. The coal thermal stability determination device (100) as claimed in claim 1, wherein the humidifier unit (110) is constructed from stainless steel of 304-grade material, resulting in a cylindrical enclosure with an internal diameter of 150 mm and a depth of 300 mm, comprising bossed ends at both extremities and incorporating an overflow protection valve to prevent water spillage.

9. The coal thermal stability determination device (100) as claimed in claim 8, wherein the humidifier unit (110) employs a 1500-watt heating element constructed from cupronickel alloy, submerged in distilled water, with a rheostat for precise temperature control, and integrates two ball valves (112) connected to distinct pathways for discharging from both the humidifier unit and the moisture trap, facilitating the introduction of water vapor saturation into the carrier gas.

10. The coal thermal stability determination device (100) as claimed in claim 1, wherein the mixing tank is equipped with a differential pressure gauge (116) and a digital thermo-hygrometer (114), provides real-time data on the pressure, relative humidity, and temperature of the carrier gas, which is displayed through a digital readout unit.

11. The coal thermal stability determination device (100) as claimed in claim 10, wherein the mixing tank (113) consists of a rotameter (117) with a capacity of 0-2 lpm and a needle valve in the bypass line to control the carrier gas flow rate to the coal reaction vessel (120), wherein the carrier gases pass through a pre-heated copper conduit (118), a ten-foot-long coiled copper pipe, allowing the gases to reach the desired temperature before entering the coal reaction vessel (120), wherein the coal reaction vessel (120) comprises an inlet at the bottom where the pre-heated copper coil terminates, wherein the carrier gas feed wires have independent loops with isolation ball valves (112) and connectors to divert the gases from the humidifier (110) or the moisture trap (111).

12. A method for determining the susceptibility parameter for coal towards spontaneous combustion using the device of claim 1, comprising:
determining the equilibrium moisture, inherent moisture, and total moisture of coal's apparent porosity;
introducing 500 grams of selected pulverized coal meeting size criteria into the coal reaction vessel;
inspecting the hermetic integrity of the coal reaction vessel to ensure gas-tight seals;
activating nitrogen gas discharge to test for air leakage, monitoring pressure drop at the humidifier over 15 minutes, and continuously monitoring the pressure in the coal reaction vessel for leaks;
heating the coal reaction vessel using a programmable temperature controller and an electric heater, ensuring uniform heating with a circulating fan, following a specified heating ramp rate;
simultaneously activating the pressure-reducing valve to control the flow of oxygen gas from the cylinder, directing gas to the humidifier and the gas conduit connected to the moisture trap;
introducing the humidified oxygen and dry gas from the moisture trap into the mixing tank, adjusting the relative humidity, temperature, and total pressure of the gas mixture;
pre-heating the carrier gas within the insulated heating cavity before it enters the coal reaction vessel;
recording the temperature distribution of the coal using the data acquisition module during various oxidation phases;
employing the diaphragm pump within the multi-gas analyzer to aspirate the exhaust gases at specified intervals and collecting data for index gases after every 10°C rise in the average temperature of the coal reaction vessel; and
closing the oxygen cylinder supply and powering off the insulated heating cavity when the average coal body temperature reaches 250°C, allowing the coal reaction vessel to cool naturally to room temperature.