Future approaches to cope with spontaneous combustion

Prepared By : Sujit Surendran

Saroj Raj Kumar Ramnaresh

Katariya Prashant Rameshbhai

Future Approaches To Cope with Spontaneous Combustion

Government Engineering College - Bhuj


Prepared Under the guidance ofN.N. Mupkalwar

Mining Department

Government Engineering College -Bhuj

Theme Of Our Project

Fires in coal mines can be categorised into two groups, Viz. – A) Fires resulting from spontaneous combustion of coal and B) Open fires – which are accidental in nature and are caused because of ignition of combustion materials. Here, in this paper we are going to discuss for –

“Group A)” kind of fires – its detection, prevention techniques and newly developed ideas which can bring about a revolutionary change in the face of Safety in Mines.

SPONTANEOUS COMBUSTION IN OPENCAST MINES

What Is Spontaneous Combustion ?

“SPONTANEOUS COMBUSTION OF COAL DEFINED AS THE PROCESS OF “SELF-HEATING” RESULTING EVENTUALLY IN ITS IGNITION WITHOUT THE APPLICATION OF EXTERNAL HEAT.”

MAINLY CO, CO2, WATER VAPOR ALONG WITH THE EVOLUTION OF HEAT DURING THE CHEMICAL REACTION. THE PROCESS TAKES PLACE AT NORMAL TEMPERATURE, BUT IT IS SLOW AND THE HEAT EVOLVED IS NOT PERCEPTIBLE AS IT IS CARRIED AWAY BY AIR UNLESS AIR IS STAGNANT.

How Spontaneous Combustion Leads to fire

The Fire Triangle

OXIDATION OF COAL (FUEL) AND HENCE – PRODUCTION OF HEAT

IF HEAT NOT DISSIPATED, TEMPERATURE OF COAL INCREASES

OXIDATION INCREASES AT HIGHER TEMPRETURE- IGNITION POINT REACHED

FIRE


MAJOR DETECTION TECHNIQUES :

“Radon Detection Technique”

“Thermal Remote Sensing”

“Infrared Technique”

“Installing Smell Sensors & Thermal Survey”

PREVENTION AND CONTROL BY :

“Colloid Injection Technique”

Radon Detection Technique

Principle of Radon-Detection Technique

U-238 is a common rare element in rock strata, as is its decay product Rn-222 (radon) and radon progeny.

Radon has a strong diffusion ability. Activated carbon, silica gel, polyethylene and some other materials can easily adsorb radon and its progeny.

This property enables radon and its progeny to be easily collected from the surface with a container coated with these adsorbents and analyzed.

Experimental test data show that when the coal is heated up, the emanation rate of radon from overlying strata will increase.

This relationship, combined with radon radioactive and its unique properties form the fundamental principle of radon-based detection techniques for coal sponcom.


KEY INSTRUMENTS USED :

Adsorbents :

Activated charcoal silica gel and polyethylene

Alpha Cup

Radon Detector

Alpha Cup Radon Detector

Ionization Chamber inside a Radon Detector which takes the readings of a Radon-222 Emanations.


OPERATION AND ANALYSIS :

After the survey area is decided the grid pattern is designed.

Measurement spacing point can be 20 m×20 m, 15 m×15 m or 10 m×10 m, depending on site conditions.

An auger machine is used to dig holes for placing alpha cups. Hole is 30 cm in diameter and 30-40 cm in depth.

Cups are analyzed and radon detectors is used to take the CPM values.

A program used produces a 3D map of abnormal.CPM values, and the location of “high-temperature” area.

Detection Point and Collection Cup

Hot spots detected with the radon technique.

Sample of Grid Pattern


Merits of Radon Detection Technique :

It can remotely locate abnormal temperature areas. Its accuracy for locating the sponcom center is 90%. Detection depth is up to 800 m.

It is of high suitability, low cost and easy to operate

It has a high reliability and is largely unaffected by external factors.

Thermal Remote Sensing and Infra-Red Techniques

Principle of Infrared Detection Techniques

All warm (warm defined as being above “0 Kelvin” in temperature) objects’ atoms, molecules, and electrons are always in motion, vibrating and radiating (emitting) infrared waves, forming in infrared radiation field.

As the object’s temperature increases, the intensity of the radiation increases. The radiation field can be characterized by its energy, momentum, direction and other information.

Like any other objects, a coal seam is also emitting infrared waves. If there is a spontaneous combustion in the coal seam, this should be reflected in the characteristics of its infrared radiation field.

“Thermal infrared remote sensing systems” record thermal infrared images that can be used to determine the type of material in certain instances based on its thermal emission characteristics and evaluate if significant changes have taken place in the thermal characteristics of these phenomena over time. It is obvious that coal fires will heat the ground around them even when they are located underground, provided that they are not at a great depth.


The process of remote sensing can be briefly described by the following steps: Energy source illuminates/provides electromagnetic energy to

the target. Radiation energy travels from the source to the target. Interaction with target – depending on the properties of both

target and radiation.

Within the overall thermal infrared region, the 3-5μm and 8-14μm regions are used in thermal remote sensing as in the intervening part of the electromagnetic spectrum the energy is greatly absorbed by the atmospheric gases.


Thermal infrared radiation of an object is controlled mainly by several factors: i.The emissivity of the object, ii. Its geometry and iii. Its temperature.

Why acquire data at night ?

Coal fires on the surface, when present as flaming combustion, emit significant thermal energy that is easy to detect by any remote sensing scanner. Some of these may be at a high enough temperature to become visible in wavelengths. In the case of a subsurface coal fire the surface heating is comparatively subdued and may be masked by the solar heating or reflected solar thermal radiation during the day. In that case it is necessary to use night-time remote sensing data to reveal and measure the extent of heating. Coal fire detection using remote sensing has three major steps: Acquire a thermal image (preferably night) of the area under investigation using remote sensing and process digitally to

create a surface temperature map to reveal the temperature anomalies, Acquire information about local geological setting, temperatures of coal fire vents and different land covers through

field survey, A final temperature map calibrated with field collected temperatures to reveal the coal fires.


Use of Handheld Infrared camera /Infrared detector in a localized area of a mine.

A thermal imaging camera works similar to a normal video camera. The glass of a normal video camera doesn’t transmit infrared radiation well. The infra-red camera is equipped with germanium glass which is a good transmitter of infra-red radiation.

Sensor Electronics

LCD SCREEN

Infrared radiations coming from an object

Infrared detector

transforming a infrared image into radiometric

Calculated temperature values from the image. Note : Before capturing a

thermal image the camera is to be set with correct emissivity. The camera is preloaded with “Emissivity table” for certain

objects.


A thermal Image of Stockpile

A thermal imaging camera


1.Layout of measurement points :

Measurement stations are set along the gate road to be surveyed. Each measurement station covers a number of adjacent measurement points in the ribs, roof and floor.

Schematic layouts of measurement stations and points with the infrared technique 2.Field Measurement: An infrared camera is used to measure the strength of the energy field of infrared radiation and surface temperatures of the measurement points. If a zone of abnormal strength is recorded, then repeated measurements in that zone are undertaken.

3.Data Analysis. A program is used to process measurement data. The program has three main functions: (1) Graphic outputs of strength profiles of infrared radiation, (2) Identifying any abnormal strength of radiation caused by sponcom, and (3) Determining the position and temperature of the spontaneous combustion by the inverse calculation of heat conduction based on the heat conduction mechanism of coal strata.


Merits of the Infrared Detection Technique: It is remote and requires no direct contact to detect spontaneous

combustion of coal.

Maximum detection depth of 10 m in a coal pillar.

90% accuracy for detecting the location of a sponcom.

It can detect a coal sponcom with temperature at 130º C and above.

Suitable for detecting “hot spots” in coal pillars and areas adjacent to roadways.

Smell Sensor & Thermal Survey

This invention not only detect heating by smell like a human nose but also measure the degree of smell. It makes use of piezoelectricity to calculate the amount of odorant present on the mine atmosphere.

What is piezoelectricity? Piezoelectricity is the electric charge that accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure.

Working :

The sensor component employs synthetic bilateral membrane like human lipid membrane.

For quantifying the odorants a piezoelectric crystal device that can oscillate several million per second is used.

Upon absorbing the odorants the weight of the membrane increases and the frequency of the oscillator is changed.

The magnitude of frequency changes an electrical signal which enables measurement of frequency.

Structure of Smell Sensor

Thermal Survey : The thermal survey can be categorized as : 1. Direct Method2. Indirect Method

The direct measuring instruments operate making use of following principles:

Expansion of confined volume of materials e.g. Hg in glass type maximum thermometers, bimetallic strips.

Melting point of suitable material fire alarms operated by relays with fusible plugs (made of alloys/agents of suitable melting points).

Thermoelectric effect e.g. thermocouple type sensors commonly marketed.

Transducer of different types continuously measuring temperature differential.

Smell Sensor & Thermal Survey

Colloid Injection Technique

What is a colloid?

A colloid is a substance microscopically dispersed throughout another substance. A colloid is a solution that has particles ranging between 1 and 1000 nanometres in diameter, yet are still able to remain evenly distributed throughout the solution.

Colloids developed for the control of spontaneous combustion can be broadly divided into three categories :

Gels, Large -molecule colloids, Compound colloids.


Water solidification

Cooling effect due to two processes:

Gelatinization and Vaporization

Block air leakage paths

Control of formation time of

gelatinization

Thermally stable

Low content

High Elasticity

Low Viscosity

Low cost

Better control of spontaneous combustion.

HIGH MECHANICAL STRENGTH LARGE -MOLECULE COLLOIDSGELS

SPECIAL PROPERTIES COLLOIDS :


Two systems have been developed for the colloid injection technique for sponcom control:

An underground based system suitable for controlling small-scale spontaneous combustion.

A surface-based method suitable for controlling large-scale spontaneous combustion.

The main equipment used in the underground-based system includes i. A movable colloid mixer and ii. pumping station.

An underground-based system for colloid injection

Required materials are fed into the station and mixed to make the colloid and then pumped into the area of sponcom via pipelines.


To control large-scale sponcom, a surface-based system should be used. A surface-based mixer blends base materials with water.

A pipeline is then used to deliver colloids from surface to underground, the pipeline is connected to a number of borehole drilled from underground workings into the area(s) of sponcom.

A small mixer and pumping station located underground is used to mix water with the additive for fast gelatinization and pump the mix into the pipeline. Figure shows the flow chart of the system. The system is capable of delivering 30-100 m³/h of colloids into sponcom spots. A surface-based system for colloid

injection

A surface-based method for Large scale spontaneous combustion.


Merits of the Colloid Injection Technique:

Speedy control of sponcom. For a small-scale e sponcom in a coal pillar it may take only a few hours to control, even for a large -scale sponcom in goaf it may take a couple of days at maximum.

Colloid can be solidified in fragmented coal, resulting in the blockage of leakage passes and hence stopping poisonous gases flowing out from the passes. At high temperatures a colloid gives off a very small amount of water steam (unlike water injection technique) and therefore there is no possibility of explosion of water gas and no risk of injuries resulted from high temperature water steam.

To date there has been is no reoccurrence of sponcom in an area treated with colloid.

Any Questions???

Thank You !!!

Technology

Future approaches to cope with spontaneous combustion