Week 10.pdf

TRANSPORTATION AND METERING OF FLUIDS PUMPS Week # 10 Dr. Zohaib Atiq Khan Assistant Professor [email protected] Department of Chemical, Polymer & Composite Materials...

TRANSPORTATION AND METERING OF FLUIDS PUMPS Week # 10 Dr. Zohaib Atiq Khan Assistant Professor [email protected] Department of Chemical, Polymer & Composite Materials Engineering (New Campus) 1 CHAPTER 8 Week 9 Summary 1. ABOUT PUMPS 2. BASIC COMPONENTS OF PUMPS UET 2 LAHORE Copyright ® Dr Zohaib Atiq Khan CHAPTER 8 TRANSPORTATION AND METERING OF FLUIDS 1. HOW PUMP WORKS 2. PUMP OPERATION 3. PUMP MAINTENANCE UET 3 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Pump Basic Principle Head is the height of liquid Suction Lift exists when the source of supply is below the center line of the pump. Static Suction Lift is the vertical distance in feet from the centerline of the pump to the free level of the liquid to be pumped. Suction head exists when the source of supply is above the centerline of the pump. Static suction head is the vertical distance in feet from the centerline of the pump to the free level of the liquid to be pumped. UET 4 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Pump Head Static discharge head is the vertical distance in feet between the pump centerline and the point of free discharge or the surface of the liquid in the discharge tank. Total static head is the vertical distance in feet between the free level of the source of supply and the point of free discharge or the free surface of the discharge liquid. UET 5 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS LIFT & HEAD CONCEPT UET 6 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Question: Will Different Density Liquids Pump to the Same Level (As Shown Here) or: ? S.G.- 1.2 S.G.- 1.0 S.G.- 0.7 UET 7 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Or Will They Pump to Different Levels as Shown Here? S.G.- 1.2 S.G.- 1.0 S.G.- 0.7 UET 8 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Answer: They Will Pump to the Same Height (Head) but Will Show Different Pressure Gauge Readings. H=115ft H=115ft 60 psi 50 psi 35 psi S.G.- 1.2 S.G.- 1.0 S.G.- 0.7 UET 9 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS NPSH Liquids can flash into vapor near boiling point which depends on pressure. In the suction of the pump impeller eye, there may be lower pressure (or vacuum) Ps created due friction losses and sucking by the impeller. S If the liquid flashes, pump performance will be affected NPSH is a related subject to solve this problem. UET 10 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Net Positive Suction Head (NPSH) NPSH Available: Absolute pressure at the pump suction, changed into head minus the vapor pressure of the liquid being pumped, changed to head. NPSH Required: Minimum head needed at the suction to get the liquid into the impeller without vaporizing NPSHa > NPSHr NPSH = Ha ± H – H – HfZ v Ha Absolute pressure head at reservoir surface Hz Elevation head/lift at pump suction Hv Vapor Pressure head of liquid at pump suction Hf Friction Head in inlet pipe UET 11 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS NPSH of Vacuum System In the vacuum system like surface Vacuum condensers, you will find either the level is high/the equipment is elevated and some cases the pump is S M under the ground to meet the required NPSH. Example: condensate pump UET 12 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Net Positive Suction Head Available Case 1 Positive Suction from an open tank. UET 13 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Net Positive Suction Head Available Case 2 Suction lift from a reservoir below pump 15’ UET 14 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS To Increase the NPSHa Raise the suction tank (or level in the tank). Lower the pump. Increase the pressure in the suction tank. Cool the liquid to reduce vapor pressure. Modify the suction piping. - Increase pipe diameter Reduce the length - change fittings - modify valve type - reduce number. UET 15 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Power and Efficiency Brake horsepower (bhp) Actual horsepower delivered to the pump shaft Hydraulic horsepower (whp) The liquid horsepower delivered by the pump UET 16 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS PUMP WORK b’ Wp a b Zb’ PUMP Za Zb a’ Reservoir UET 17 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Performance Curve/System Curves The performance curve is actually four curves resulting with each other on a common graph. These four curves are: The Head-Flow Curve The Efficiency Curve The Energy Curve The Pump’s Minimum Requirement Curve UET 18 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Performance Curve/System Curves 265 mm 20% 60 40% 245mm 50 40% 225 mm Best Efficiency 20% 40 85% Head (m) 265mm 20 245 mm 15 225 mm 10 kW 6 NPSH 4 NPSHR 2 0 5 10 15 20 25 30 35 40 45 Capacity (m3/hr) UET 19 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS System Curve It defines Capacity & Pressure needs of any system graphically. It represents the relationship b/w flow and hydraulic losses in a system graphically. A pumping system operates at the intersection of System Curve & Pump Performance Curve. UET 21 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Performance Curve/ System Curve 50 Pump Curves 40 Head - Meters 30 20 10 0 5 10 15 20 25 30 35 40 45 50 UET Capacity m3/hr LAHORE 22 Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Performance Curve/ System Curve Run Out Point Operating Point TOTAL HEAD, H PUMP CURVE BHP CURVE EFFICIENCY SYSTEM CURVE CURVE FLOW RATE, Q UET 23 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS UET 24 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS AFFINITY LAWS The affinity laws express the mathematical relationship between the several variables involved in pump performance. They apply to all types of centrifugal and axial flow pumps. UET 25 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS With Impeller Diameter (D) Held Constant A. Capacity (flow rate) is proportional to speed of impeller. B. Discharge head is proportional to square of the speed of impeller. C. Power required is proportional to the cube of speed of impeller. UET 26 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Pumps – Operation: Start Up Pump lubricating mechanism must be checked Surface of mechanical seals are cooled A pump that is to handle hot liquid should be warmed before it is started to prevent damage from unequal expansion of parts. UET 28 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS PUMP STARTUP Startup of Centrifugal Pump Start lube oil circulation. Close pump vents and drains. Prime the pump and open the suction valve fully. Slightly open the discharge valve. Start motor or other drive mechanism and bring the pump up to the required speed. As the pump comes up to speed, fully open the discharge valve. UET 29 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS PUMP STARTUP Startup of Positive-displacement Pump Start the pump cooling water system. Close vents and drains. Prime the pump (if the system requires). Verify valve line-up in system is correct. Fully open suction and discharge valves. Start the motor or other drive mechanism and bring the pump up to the required speed. UET 30 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS PUMP SHUTDOWN Shutdown of the Centrifugal Pump Shut down the drive mechanism. Shut the discharge and suction valves. Allow the pump to cool down. Stop the cooling and oil circulating systems. Open the vents and drains, and drain pump to approved location. UET 31 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS PUMP SHUTDOWN Shutdown of the Positive-displacement Pump Shut down the driver. Shut the suction and discharge valves. Allow the pump to cool down. Stop the cooling system. Open vents and drains, and drain pump to approved location. UET 32 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Pumps - operation Operational Problems UET 33 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Cavitation Cavitation can be termed as: “The Heart attack of the pump” Heart: The Engine of Life UET 34 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Cavitation means Different Things to different people It has been described as A reduction in pump capacity A reduction in the head of the pump The formation of bubbles in a low pressure area of the pump A noise that can be heard when the pump is running Damaged that can be seen on the pump impeller and volute UET 35 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Concept of Cavitation In summary, cavitation is an abnormal condition that can result in loss of production, equipment damage and worst of all, personnel injury. UET 36 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Concept of Cavitation Steps In Cavitation UET 37 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS Mechanism of Cavitation Formation of bubbles Vaporization of Liquid Increase in Temperature of Liquid Decrease in Pressure Growth of bubbles Operating Conditions Collapses of bubbles Implosion Liquid Micro Jet Impeller Pitting UET 38 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS MECHANISM OF CAVITATION UET 39 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS UET 40 LAHORE Copyright ® Dr Zohaib Atiq Khan TRANSPORTATION AND METERING OF FLUIDS UET 41 LAHORE Copyright ® Dr Zohaib Atiq Khan  Suction Cavitation Suction Cavitation occurs when the pump suction is under a low pressure/high vacuum condition where the liquid turns into a vapor at the eye of the pump impeller. This vapor is carried over to the discharge side of the pump where it no longer sees vacuum and is compressed back into a liquid by the discharge pressure. This imploding action occurs violently and attacks the face of the impeller. UET 51 LAHORE Copyright ® Dr Zohaib Atiq Khan UET 52 LAHORE Copyright ® Dr Zohaib Atiq Khan  Discharge Cavitation Discharge Cavitation occurs when the pump discharge is extremely high. It normally occurs in a pump that is running at less than 10% of its best efficiency point. The high discharge pressure causes the majority of the fluid to circulate inside the pump instead of being allowed to flow out the discharge. As the liquid flows around the impeller, it must pass through the small clearance between the impeller and the pump cutwater at extremely high velocity. UET 53 LAHORE Copyright ® Dr Zohaib Atiq Khan UET 54 LAHORE Copyright ® Dr Zohaib Atiq Khan