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## Piping and Pumping

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**Chemical Engineering and Materials Science**Syracuse University Piping and Pumping Process Design CEN 574 Spring 2004**Outline**• Pipe routing • Optimum pipe diameter • Pressure drop through piping • Piping costs • Pump types and characteristics • Pump curves • NPSH and cavitation • Regulation of flow • Pump installation design**Piping and Pumping Learning Objectives**At the end of this section, you should be able to… • Draw a three dimensional pipe routing with layout and plan views. • Calculate the optimum pipe diameter for an application. • Calculate the pressure drop through a length of pipe with associated valves. • Estimate the cost of a piping run including installation, insulation, and hangars.**List the types of pumps, their characteristics, and select**an appropriate type for a specified application. • Draw the typical flow control loop for a centrifugal pump on a P&ID. • Describe the features of a pump curve. • Use a pump curve to select an appropriate pump and impellor size for an application. • Predict the outcome from a pump impellor change. • Define cavitation and the pressure profile within a centrifugal pump. • Calculate the required NPSH for a given pump installation. • Identify the appropriate steps to design a pump installation.**References**• Appendix III.3 (pg 642-46) in Seider et al., Process Design Principals (our text for this class). • Chapter 12 in Turton et al., Analysis, Synthesis, and Design of Chemical Processes. • Chapter 13 in Peters and Timmerhaus, Plant Design and Economics for Chemical Engineers. • Chapter 8 in McCabe, Smith and Harriott, Unit Operations of Chemical Engineering.**Pipe Routing**• The following figures show a layout (looking from the top) and plan (looking from the side) view of vessels. • We want to rout pipe from the feed tank to the reactor.**piping chase**reactor Plan View steam header 40 ft feed tank 60 ft 35 ft 50 ft**Layout View: Looking Down**steam header 40 ft feed tank piping chase 45 ft 30 ft reactor 10 ft reactor 35 ft 50 ft**Plan View**piping chase reactor = out = in steam header 40 ft feed tank 60 ft 35 ft 50 ft**Layout View**steam header 85 ft 30 ft feed tank 20 ft 35 ft 60 ft 10 ft 10 ft reactor**Pipe Routing Exercise**• Form groups of two. • Draw a three dimensional routing for pipe from the steam header to the feed tank on both the plan view and the layout view.**Size the Pump**• Determine optimum pipe size. • Determine pressure drop through pipe run. 200 ft globe valve check valve 150 ft 100 gpm**Optimum Pipe Diameter**The optimum pipe diameter gives the least total cost for annual pumping power and fixed costs. As D , fixed costs , but pumping power costs .**Optimum**Optimum Pipe Diameter Total Cost Annualized Capital Cost Pumping Power Cost**Example**• Two methods to determine the optimum diameter: Velocity guidelines and Nomograph. • Example: What is the optimum pipe diameter for 100 gpm water.**Using Velocity Guidelines**• Velocity = 3-10 ft/s = flow rate/area • Given a flow rate (100 gpm), solve for area. • Area = (/4)D2, solve for optimum D. • Optimum pipe diameter = 2.6-3.6 in. Select standard size, nominal 3 in. pipe.**3.3 in optimum diameter**Nomograph -Convert gpm to cfm 13.4 cfm. -Find cfm on left axis. -Find density (62 lb/ft3) on right axis. -Draw a line between points. -Read optimum diameter from middle axis.**Practice Problem**• Find the optimum pipe diameter for 100 ft3 of air at 40 psig/min. • A = (s/50ft)(min/60 s)(100 ft3/min) = 0.033 ft2 • 0.033 ft2 = 3.14d2/4 • d = 2.47 in**Piping Guidelines**• Slope to drains. • Add cleanouts (Ts at elbows) frequently. • Add flanges around valves for maintenance. • Use screwed fitting only for 1.5 in or less piping. • Schedule 40 most common.**Calculating the Pressure Drop through a Pipe Run**• Use the article Estimating pipeline head loss from Chemical Processing (pg 9-12). • P = (/144)(Z+[v22-v12]/2g+hL) • Typically neglect velocity differences for subsonic velocities. • hL = head loss due to 1) friction in pipe, and 2) valves and fittings. • hL(friction) = c1fLq2/d5**c1 = conversion constant from Table 1 = 0.0311.**• f = friction factor from Table 6 = 0.018. • L = length of pipe = 200 ft + 150 ft = 350 ft. • q = flow rate = 100 gpm. • d = actual pipe diameter of 3” nominal from Table 8 = 3.068 in . • hL due to friction = 7.2 ft of liquid head**Loss Due to Fittings**• K= 0.5 entrance • K = 1.0 exit • K=f(L/d)=(0.018)(20) flow through tee • K=3[(0.018)(14)] elbows • K=0.018(340) globe • K=0.018(600) check valve Sum K = 19.5**hL due to fittings = c3Ksumq2/d4 = 5.7 ft of liquid head**loss due to fittings. • hLsum=7.2 + 5.7 ft of liquid head loss • Using Bernoulli Equation P = (/144)(Z+[v22-v12]/2g+hLsum) P = ( /144)(150+0+12.9)= 70.1 psi due mostly to elevation. Use P to size pump. elevation velocity friction and fittings**Find the Pressure Drop**400 ft 50 ft check valve 400 gpm water 4 in pipe**Estimating Pipe Costs**Use charts from Peters and Timmerhaus. Pipe Fittings (T, elbow, etc.) Valves Insulation Hangars Installation**Note: not 2003 $**$/linear ft**Pumps – Moving Liquids**• Centrifugal • Positive displacement • Reciprocating: fluid chamber stationary, check valves • Rotary: fluid chamber moves**Positive Displacement: Reciprocating**• Piston: up to 50 atm • Plunger: up to 1,500 atm • Diaphragm: up to 100 atm, ideal for corrosive fluids • Efficiency 40-50% for small pumps, 70-90% for large pumps**Positive Displacement: Rotary**• Gear, lobe, screw, cam, vane • For viscous fluids up to 200 atm • Very close tolerances**Comparisons: Centrifugal**• larger flow rates • not self priming • discharge dependent of downstream pressure drop • down stream discharge can be closed without damage • uniform pressure without pulsation • direct motor drive • less maintenance • wide variety of fluids**Comparisons: Positive Displacement**• smaller flow rates • higher pressures • self priming • discharge flow rate independent of pressure – utilized for metering of fluids • down stream discharge cannot be closed without damage – bypass with relief valve required • pulsating flow • gear box required (lower speeds) • higher maintenance**Advantages**simple and cheap uniform pressure, without shock or pulsation direct coupling to motor discharge line may be closed can handle liquid with large amounts of solids no close metal-to-metal fits no valves involved in pump operation maintenance costs are lower Disadvantages cannot be operated at high discharge pressures must be primed maximum efficiency holds for a narrow range of operating conditions cannot handle viscous fluids efficiently Centrifugal Pumps**Moving Gases**• Compression ratio = Pout/Pin • Fans: large volumes, small discharge pressure • Blowers: compression ratio 3-4, usually not cooled • Compressors: compression ratio >10, usually cooled. • Centrifugal (often multistage) • Positive displacement**Pump Curves**For a given pump • The pressure produced at a given flow rate increases with increasing impeller diameter. • Low flow rates at high head, high flow rates at high head. • Head is sensitive to flow rate at high flow rates. • Head insensitive to flow rate at lower flow rates.**Pump Curve- used to determine which pump to purchase.-**provided by the manufacturer.**Low flow at high head**Pressure increases with diameter Head sensitive to flow at high flow rates Pump Curve**NPSH and Cavitation**• NPSH = Net Positive Suction Head • Frictional losses at the entrance to the pump cause the liquid pressure to drop upon entering the pump. • If the the feed is saturated, a reduction in pressure will result in vaporization of the liquid. • Vaporization = bubbles, large volume changes, damage to the pump (noise and corrosion).**NPSH**• To install a pump, the actual NPSH must be equal to or greater than the required NPSH, which is supplied by the manufacturer. • Typically, NPSH required for small pumps is 2-4 psi, and for large pumps is 22 psi. • To calculate actual NPSH… NPSHactual= Pinlet-P* (vapor pressure) Pinlet = P(top of tank, atmospheric) + gh - 2fLeqV2/D**What if NPSHactual < NPSHrequired?**INCREASE NPSHactual • cool liquid at pump inlet (T decreases, P* decreases) • increase static head (height of liquid in feed tank) • increase feed diameter (reduces velocity, reduces frictional losses) (standard practice)