Fluids in Mining PDF

Lecture 8 Fluids in Mining COMMON FLUIDS ENCOUNTERED IN MINING OPERATIONS Drainage is done to remove excess water generated in mining operations. The expelled “water” is a fluid. In ore preparation facilities, enrichment is made with water + solid mixture pulp. Here, “pulp” is a fluid. Some hydra...

Lecture 8 Fluids in Mining COMMON FLUIDS ENCOUNTERED IN MINING OPERATIONS Drainage is done to remove excess water generated in mining operations. The expelled “water” is a fluid. In ore preparation facilities, enrichment is made with water + solid mixture pulp. Here, “pulp” is a fluid. Some hydraulic machines (crusher, etc.) are operated with compressed oil. This oil is a fluid. In machines working with compressed air (martopicator, filter, etc.), the air is compressed in the compressor and used. “Air” is a fluid. Drainage in an Thickener in Martopicator and Hydraulic Crusher Open Pit Processing similar equipments WATER PROBLEM IN MINING OPERATIONS The most important problem in mining operations is the invasion of rain or groundwater into the production area and its removal. Drainage (water disposal) is the process of collecting underground and surface water and removing it from the operating area. Drainage is done with pumps. In open pit mines, drainage is necessary for the continuity of production. In underground mining, as the work progresses, the disposal of water leaking into the opened space becomes a significant problem. WATER PROBLEM IN MINING OPERATIONS Before preparing the mining operation project, a detailed hydrogeological survey of the area where the deposit to be operated is located must be carried out. According to the results of this study, the most appropriate water disposal project should be prepared. The suitability of the water disposal facility for operation, both technologically and economically, will affect the continuity and cost of production. WATER AND SLURRY IN MINERAL PROCESSING PLANTS Water is the preferred medium for operations such as grinding, classification and enrichment in mineral processing plants. Therefore, solid particles are stored in the facility and transported from one operation to another in slurry (pulp) form. Ore pulp is transported within the facility many times for short distances by pumping it in pipelines or by flowing it in pipelines and troughs using gravity. WATER AND SLURRY IN MINERAL PROCESSING PLANTS Tailings (processing wastes) are also pumped into tailings dams or underground mines to be used as fill material. In some cases, concentrated ores are transported long distances in pipelines with water. The water transported through pipes in mines and ore preparation facilities often contains solid particles. PUMPS WHAT IS A PUMP? It is the general name of the machines used to transmit fluids from one place to another or to raise them to a higher level. Today, there are many pumps called by different names (centrifugal pump, submersible pump, piston pump, etc.). The first pump known in history is the "Archimedes Screw", developed by the Greek mathematician Archimedes. By rotating an inclined spiral, the fluid can be transported to higher levels. Archimedes Screw Modern Archimedes screws which have replaced some of the windmills used to drain the polders at Kinderdijk in the Netherlands WATER RAM PUMP (HYDRAULIC/NATURAL PUMP) Mechanisms that create a "pressure difference" with water in a pipeline with a height difference and convert this pressure difference into kinetic energy to transport water meters (50-150 m) up are called "water ram pumps". In this mechanism, there is no need for external energy and the compression energy is produced naturally. Water ram pumps have been used in Europe for 200 years and in our country for 60 years. No energy is consumed for the pump. The aim is to press some of the water into a much higher water tank with the pressure of the water higher than the pump level. For this process, there are valves in the mechanism that can be opened and closed by the pressure of the water. ALTERNATIVE PUMP TYPES Pumps can also be used to compress gases or move them from one place to another. Pumps used to transport gases or increase their pressure are called compressors. The pump provides kinetic or potential energy to the fluid it draws in. There are many types of pumps with different mechanical structures and operating principles. Generally, pumps are divided into two main classes. PUMPS Positive Displacement Pumps Centrifugal Pumps (Volumetric Pumps) (Rotodynamic Pumps) Piston Gear Screw Single Stage Multi Stage POSITIVE DISPLACEMENT PUMPS Pumps in which displacement is carried out mechanically are called positive displacement or volumetric pumps. In general, positive displacement pumps move Piston Pump small amounts of fluid with high pressure. In other words, they move a certain amount of liquid for each pump cycle and do not change the flow rate despite the pressure resistance it encounters. The most known types are piston, gear and Gear Pump screw types. Positive displacement pumps are generally used in systems with very high pressure loads (higher than 4MPa). For example, piston type pumps in this class are used to transport pulp in long-distance pipelines. Screw Pump PISTON PUMPS The liquid is moved by a piston moving back and forth. The liquid moves intermittently. The most important feature of piston pumps is that they have high output pressure. They provide high pressure to the fluid, but they pump small amounts of liquid. As the viscosity of the pumped fluid increases, the effective flow rate of piston pumps decreases. These pumps work horizontally or vertically and their capacity can go up to 500 t/h. While gear pumps try to reach pressure levels of 15–20 MPa, radial piston pumps can easily reach pressure levels of 65 MPa. GEAR PUMPS The gear pump consists of a pair of gears and a pump body, working to create minimum radial and axial clearance. While one of the gears is driven by the motor, the other rotates freely and rotates in opposite directions, transferring the liquid from one environment to another. As the number of teeth increases, the discharge becomes continuous and uniform. If the number of teeth is reduced, the capacity increases, but the discharge will be pulsed. It is generally used for the transportation of viscous liquids/hydraulic oils and fuels. SCREW PUMPS It is also defined as the Archimedes screw. It consists of a spiral blade rotor that rotates at a low speed. It is used to provide very small amounts of potential energy to high flow rates. Like gear pumps, screw pumps are also used to transport viscous liquids such as lubricating oil, hydraulic fluid, and fuel. CENTRIFUGAL PUMPS Centrifugal pumps are the most frequently used pumps all over the world and in the mining industry. It is also known as slurry pump. In the centrifugal pump, the liquid is taken to the fan center by gravity and circulated around the fan by centrifugal forces and pushed to the outlet pipe. Centrifugal pumps provide a continuous flow of liquid and the fluid is delivered at a constant pressure. It can be connected directly to the motor shaft. CENTRIFUGAL PUMPS Centrifugal pumps are more suitable for low viscosity (maximum 50 cSt) liquids due to their high speed. Air may have accumulated in the suction line and may need to be filled with fluid before starting. Nominal dimensions are expressed by the diameters of the pump's inlet and outlet pipes. For example, an 8/6 pump means a pump with an inlet diameter of 8 inches and an outlet diameter of 6 inches. Nominal Dimensions Inlet Diamater: 8 inches Outlet Diamater:6 inches 8/6 Pump  Outlet/Discharge COMPONENTS OF CENTRIFUGAL PUMPS Pipe Snail Shell Inlet/Suction Pipe Fan (Open or Enclosed) Electric Motor Power = ? kW Centrifual Pump Q= ? m3 CALCULATING THE ENGINE POWER OF THE CENTRIFUGAL PUMP Correct selection of drive motor power is important. Choosing a motor that is smaller than necessary creates problems such as not reaching the desired hydraulic capacity in operation and frequent thermal tripping, while choosing a motor that is larger than necessary causes unnecessary electricity consumption in the operation and therefore high electricity costs. It is possible to use the following formula to correctly select the engine power. Q (m3/h): Flow rate of the pump at the operating point H (m): Discharge head, 𝑸×𝑯×𝒒 q (t/m3): Density of the slurry 𝒑= × 𝑺. 𝑭. 𝟑𝟔𝟕 × 𝒏 n (%): Efficiency value taken from the pump curve [usually between 50%-60%] P (kw/h): Minimum engine power When pressurized feeding of liquids is required (to a cyclone, tank, etc.), 20% more of the pump power is taken. (S.F.: safety factor).  4/3 CENTRIFUGAL PUMP CURVE Efficiency Rates If we press 150m3 at 30 meters, the efficiency will be in the range of 65-68% EXAMPLE In a coal washing facility, heavy medium liquid with a density of 1.4 t/m3 will be fed under pressure into a cyclone located 20 meters above at a rate of 500 m3 per hour. Accordingly, calculate the motor power required for the selected 8/6 centrifugal pump. [Take pump efficiency as 60%]. 𝑸×𝑯×𝒒 𝟓𝟎𝟎 × 𝟐𝟎 × 𝟏. 𝟒 𝒑= × 𝑺. 𝑭. 𝒑= × 𝑺. 𝑭. 𝟑𝟔𝟕 × 𝒏 𝟑𝟔𝟕 × 𝟎. 𝟔 P= 63.57 kW If a 20% safety factor is added because the cyclone will be fed; P = 63.57+12.65P = 76.22 kW. CALCULATION OF PUMP SHAFT SPEED IN ENGINES WITH BELT-PULLEY SYSTEM The amount of the water that will pumped is adjusted by the speed of the pump fan (shaft). As the speed of the engine or pump increases, the amount of water pumped increases, and if the speed decreases, the amount of water pumped decreases. MOTOR Small Pulley Diamater = d cm Rotation = n rpm Large Pulley D = D cm PUMP Rotation = N rpm Circumferential Speed of Small Pulley Should Be Equal to Circumferential Speed of Large Pulley 2лdn=2лDN EXAMPLE There is a 10 cm diameter pulley on a motor shaft rotating at 1200 rpm, and this pulley will be connected to the centrifugal pump with a belt-pulley system. In order to pump 100 m3 of water per hour, the speed of the pump is required to be 400 rpm. Determine the diameter of the pulley that will be attached to the pump shaft so that the pump shaft speed is 400 rpm. SOLUTION Using the equation 2 л d n = 2 л D N Pulley1 x Revolution1 = Pulley2 x Revolution2 10cm x 1200 rpm = ? cm x 400 rpm The diameter the pulley that will be attached to the pump shaft = 30 cm.