MINISTRY OF SCIENCE AND TECHNOLOGY DEPARTMENT OF TECHNICAL AND VOCATIONAL EDUCATION GOVERNMENT TECHNOLOGICAL COLLEGE B.E. (Mining Engineering) Sample Answer Final Examination Date: 24 -10-2006 (Tuesday) Time: 08:30 - 11:30 Min. 05048 Mine Safety and Environmental Engineering Answer All Questions ============================================== Q1. Describe the important aspects of a land use plan of the mining areas that should be prepared before the exploitation of a mineral deposit. Answer: Land Use Planning It is important to prepare land use plan of the mining areas along with the project report for exploitation of a mineral deposit. Such a plan is aimed to achieve the minimization of adverse environmental impacts. Preparation The land use plan must encompass pre-operational, operational and post-operational phases of a mine. It should clearly indicate the planned post-operational land use for the area, with details of measures required to achieve the intended purpose. It is necessary to conduct a general survey that takes into account broad features of proposed or actual mining operations, and the surrounding terrain conditions. Such a survey includes: 1 .Present land use pattern in the area 2. Main features of the human settlements in the area 3. Characteristics of local ecosystem 4. Climate in the area 5. Relevant terrain information. For this, exploration should include: (i) Geomorphological analysis (topography and drainage pattern) (ii) Geological analysis (structural features) (iii) Hydrogeological analysis (permeable formation, surface-ground water link) (iv) Analysis of natural soil and water to assess pollutant absorption capacity. (v) Availability and distribution of topsoil. 6. Communication and transport 7. Details concerning the mining plans (i) Minerals to be worked (ii) Method of working (iii) Details of fixed plants (iv) Nature and quality of wastes and disposal facilities (v) Possibility of subsidence and landslides (vi) Transportation facilities , Action clan Important aspects are: 1. Pre-operational phase (i) Raise vegetational barriers for prevention of soil erosion and arresting mine wash (ii) Vegetate the banks of streams in the mining area 2. Operational phase (i) For opencast working, construct banks of soil in the peripheral zone (ii) Construct vegetation barriers along the periphery of a mining area. The tree or soil screen preserves soil, lessen adverse visual impact, baffle noise and suppress dust. 3. Post-operational phase Once the mining operations are over, rehabilitate the land for productive use like agriculture, forestry, recreation, wildlife habitats etc. Q2. Social, cultural, economic, and political impacts should be integrated into the feasibility study because they could potentially mean major costs/delay to the project, thereby impacting profits. Give a short account on "Socio-Cultural Feasibility" for mining companies. Answer: Socio-Cultural Feasibility A company cannot impose its will on a community and expect positive relations; it must work in harmony with that community. Working together means that it is mandatory to understand the values, goals and aspirations of the community and the beliefs and positions of various constituencies. Therefore, along with ongoing company programs of education and communications, socio-cultural research is necessary. What is now lacking is the perception and understanding that societal feasibility is as important to the project as any technical feasibility study or EIS. It is important that the social, cultural, economic, and political impacts be integrated into the feasibility study because they could potentially mean major costs/delay to the project, thereby impacting profits. Therefore, during the prefeasibility process, factors need to be identified and a preliminary assessment made of their impact on the project so that these issues become included and integrated into the feasibility. This process is termed as "Socio-Cultural Feasibility". Socio-Cultural Feasibility identifies the socio-cultural issues and political risks. Currently the mining industry fails to consider fully the social, cultural, and political environment where they develop properties. Those companies who have been successful in the United States have grasped the social and political elements at the earliest stages of the projects. It is to the mining company's benefit to research socio-cultural feasibility during pre- feasibility because this is the stage when it is easiest and cheapest to make changes on the project. The further the project gets along, the more expensive and difficult changes become. As the process proceeds, social impact assessment should be performed in conjunction with the environmental impact assessment. Q3. (a) Define the followings: - Network Branch Junction Mesh Kirchhoff s laws Answer: Network A network is any closed system of branches. Branch A branch is any airway connecting two junctions. Junction A junction is the meeting point of three or more branches. Mesh A mesh is a series of consecutive branches forming a closed loop within the network. Kirchhoff' s laws Kirchhoff 's law 1 Q 0 at each junction Kirchhoff s law 2 ( P - Pfan - nVp ) = 0 for each closed mesh. [ nVp = natural ventilating pressure ] Q3. (b) Two airways are connected in parallel across a downcast and upcast shaft. The airways have a resistance of 0.6 Ns2/m8 and 0.7 Ns2/m8. Calculate the equivalent resistance of these airways in parallel. If the downcast shaft has a resistance of 0.2 Ns2/m8 and the upcast shaft of 0.3 Ns2/m8, Calculate the fan pressure required circulating 30 ni3/s of air around the network. Calculate the airflow in each of the two parallel branches connected across the shaft. Answer: Total resistance Rt = Rl + Rp + R2 = 0.3 + Rp + 0.2 Where 1/VRp = 1/V0.6 + 1/V0.7 l/VRp = 1/0.7746+1/0.8367 = 1.2909 + 1.1952 = 2.4861 VRp = 0.4022 Rp = 0.1618 Rt = Rl +Rp + R2 = 0.3 + 0.1618 + 0.2 = 0.6618 P = RQ2 P = 0.6618 x 30 x 30 P =595.62 Pa Air flow at R0.6 branch = 30 x 7/13 = 16.15 m3/s Air flow at R0.7 branch = 30 x 6/13 = 13.85 m3/s Q4. Describe the construction of an axial flow fan and adjustable pitch axial How impeller with the neat sketches. Answer: An axial flow fan consists of a shaft with a hub or boss to which is attached a number of blades. These blades can be fixed, which means that they are permanently attached to the hub at a certain angle, they can have adjustable pitch, which means that the angle of the blades can be changed by undoing the nuts and lock screws at their bases, or they can be of the variable pitch type, which means that the angle of all the blades can be altered by operating a suitable mechanism whilst the fan is in motion. Inlet cone Diffuser Blade Guide vane Nose piece Shaft Supports Hub streamlining Housing Impeller When an axial flow fan is removed, the blades scoop up air on the one side of the impeller (the hub together with the blades) and push it to the other side, thereby causing a flow of air parallel to the shaft, or axis, from which fact it derives its name. At the same time the air is given a twist, which causes it to leave the impeller with a spiral motion. To counteract this motion and to improve the efficiency of the fan, a set of stationary blades is usually installed on either the inlet or outlet side of the impeller. These fixed blades are the inlet or outlet guide vanes. Some fans have two or three impellers, one behind the other, each with its own set of guide vanes. They are called two-stage or three stage fans. Others have two impellers driven by separate motors and revolving in opposite directions, thereby obviating the need for guide vanes. These are called contra-rotating fans. Except in the case of small fans used purely for stirring up the air in a room, axial flow fans also have casings. In large, efficient fans, these normally consist of three parts ~ a cylindrical section round the impeller, an inlet section with a bell mouth to reduce the entrance losses, and a diverging outlet section or evase to reduce shock losses by allowing the air to slow down gradually. Finally, to improve the efficiency of the fan by ensuring smooth flow of the air through it, the fan has a short snub-nosed inlet fairing on the upstream side of the hub and along, pointed outlet fairing on the downstream side. The fan blades can be made from the flat steel plate, in which case they are called laminar blades, or they can be cast or otherwise formed into a special aerodynamic shape in which case they are called aerofoil blades. In an aerofoil blade the leading edge is rounded and thick while the trailing edge is much thinner and sharp. It is obvious that when the direction of rotation of an axial flow fan is reversed, the direction of the air current will also be reversed. However, because the trailing edges of the blades now become the leading edges and the evase and outlet fairing are now on the inlet side, etc., the fan will naturally handle less air and be less efficient. Q5. Describe the construction of a centrifugal fan and backward, radial and forward curve blades with the neat sketches. Answer: A centrifugal fan works on an altogether different principle to an axial flow fan. The word "centrifugal" means, "fleeing from the centre". Anything, which is revolved tends to leave the centre and will do so if allowed to. Thus a stone attached to a string and swung around by a man will move in circles around his hand, but the moment the string is released it will fly away. Scroll casing Impeller Blade Rotation Inlet Shaft Exposure Clearance Discharge The impeller of a centrifugal fan consists of two rings with blades fitted between them. The rings are attached to the shaft by means of spokes. When the fan is revolved, air is drawn parallel to the shaft into the open ends of the impeller (or eyes) and thrown out in a radial direction through the blades. If the air can enter on both sides of the impeller, it is called a double-inlet fan. If air entry is from one side only, it is called a single-inlet fan. Two blades can be either laminar or of aerofoil shape. They can be either radial, backward or forward inclined or curved as shown in following figures. It is obvious that when a centrifugal fan is rotated in the wrong direction the air will still enter at the eye and leave in a radial direction. Thus the air continues flowing in the same direction as before, but the air quantity and the efficiency of the fan are reduced. Normally, a centrifugal fan does not have guide vanes or fairings, but it does have an evase and usually a short inlet cone or ring. The casing around the impeller is shaped like a spiral curve and is called the scroll or volute of the fan. The point where the scroll is nearest to the impeller is called the cut-off. In some special cases adjustable inlet control vanes are fitted. The angle of these vanes can be altered in order to change the output of the fan. Centrifugal fans are not made with variable pitch blades in the same sense as axial flow fans, but in special cases variable tip-length blades are used to give flexibility of performance. These consist of short fixed blades to which extensions of different lengths can be bolted as required. While the air passes through an axial flow fan in a straight line unless a bend is specially added to it on either side, air is turned through ninety degrees on passing through a centrifugal fan. This is generally a nuisance because it increases the amount of space required for the installation, but sometimes it is an advantage when it happens to fit in with the reminder of the layout. The intake is invariably horizontal, but the discharge direction can easily be arranged to suit the customer. The most common cases are called: Top Horizontal Discharge, bottom horizontal discharge, top vertical and bottom vertical discharge. Centrifugal fans are also classed as either left or right-hand drive. This expression indicates on which side of the fan the motor is situated. When one stands behind the fan and faces the direction in which the air is discharged, it is a left-hand drive fan if the motor is on one's left and vice versa. The fans on modern mines are nearly all driven by driven by electric motors, but some old units are still driven by steam engines while standby units are driven by diesel engines The fan can be direct driven, i.e. the motor shaft is in line with and directly connected to the fan shaft, or it can be indirectly driven through gears, belts or a friction clutch.
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