Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech III MINE ENVIRONMENTAL ENGINEERING - II Previous Question Paper (September - 2021 - R18)
Answer any five questions. All questions carry equal marks.
Main
What is spontaneous heating in coal? Mention the factors that contribute towards spontaneous heating in a coal mine.
Answer
Spontaneous heating is the process of self-heating of coal due to the oxidation of coal at ambient temperatures, which, if left unchecked, can lead to spontaneous combustion and mine fires. It occurs when the heat generated by the oxidation of coal exceeds the rate at which heat is dissipated into the surrounding environment.
The factors contributing to spontaneous heating include:
- Intrinsic factors: Rank of coal (lower rank coals like lignite are more susceptible), moisture content, pyritic content (which promotes oxidation), and the physical state of coal (finely divided coal has a larger surface area).
- Extrinsic factors: Rate of air leakage through the goaf or coal pillars, ventilation pressure differences, presence of geological disturbances like faults or folds, and the method of mining (e.g., caving methods often increase air leakage).
What is the use of “pressure balancing chamber”? Discuss the constructional details of a pressure balancing chamber. Give the drawing.
Answer
A pressure balancing chamber is a ventilation control structure used to minimize the pressure differential across a sealed area or a goaf. By equalizing the pressure between the intake and return sides of a sealed zone, it significantly reduces the leakage of oxygen-rich air into the area, thereby preventing or suppressing spontaneous heating.
Constructional details involve creating a series of chambers or airlocks equipped with regulating doors and fans. These are designed to maintain a neutral pressure zone. The chamber typically consists of two or more sets of airlocks to allow passage without disrupting the pressure balance, and a bypass duct with a small auxiliary fan to adjust the pressure precisely to match the pressure inside the sealed area.
Drawing description: The system consists of a main ventilation roadway divided by two air-tight doors forming a chamber. A pressure-equalizing pipe connects the space behind the seal to the chamber. A manometer is installed to monitor the pressure difference, and a small fan is placed in the bypass line to inject or extract air to nullify the pressure gradient across the seal.
What steps should be taken in a coal mine to prevent fire damp explosion?
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A sample taken from a sealed off area shows the following composition: Oxygen = 19.50%, Nitrogen = 78.50%, Methane = 1.67%, Carbon Dioxide = 0.40%, Carbon Monoxide = 0.03%. Assess the condition of the sealed off area and whether it is advisable now for re-opening?
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Discuss the method of fire fighting by high expansion foam in an underground coal mine and its applicability. What are its merits and demerits?
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Why stone dust barriers are used in mines and what are the different types of stone dust barriers? A gate roadway in a long wall panel of dimension 4.8m (width) × 3.0m (height) is to be provided with stone dust barrier near to the face. What type of barrier you recommend? Calculate the quantity of stone dust required, number of shelves, loading per shelf and per meter run of the same. Also where it should be located from the face?
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How to approach safely water logged workings in an u/g mine workings? Explain with sketches.
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State the factors considered for selection of site and type of water dam in a mine. Mention a formula for deciding thickness of water dam with representing notations.
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What is the principle of a Self Contained breathing apparatus and what are its main components?
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What are the places to be illuminated in a mine? Mention the standard of lighting at (i) Pit bottom, (ii) Roadways, (iii) Depillaring areas in an U/G Mine.
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Explain the explosibility limits of fire damp air mixture.
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Where burn-side boring apparatus is used in mines? Explain briefly the principle of operation of such apparatus.
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How the thickness of a water dam is determined? Mention the formula for the calculation of thickness of a flat dam.
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Explain the caution and preventive measures of Ground Vibrations.
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Why and where self-contained breathing apparatus is used? What are the essential requirement of such apparatus for use in mines?
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Define and briefly discuss the concepts of: (i) Luminous flux, (ii) Luminous intensity.
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