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Design Process

Design Process. Understand the Problem Develop the underlying issues, constraints (i.e. cost, standards, patents, user needs, physical properties, chemical reactions, ..)

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Design Process

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  1. Design Process • Understand the Problem • Develop the underlying issues, constraints (i.e. cost, standards, patents, user needs, physical properties, chemical reactions, ..) • What is the big picture? – How does the project/process fit in to the business , social, marketing, strategy of the company and society? • Generate Alternatives • Employ the action of using synthesis and apply engineering science • Document with standard engineering documents • Analyze the Alternatives and choose the best one • Use decision making tools • Prepare final design and recommendations • Knowing your audience and their needs, presenting the facts and making a recommendation

  2. An Example • A local construction company is creating a large pit that keeps filling up with water whenever it rains. This is delaying excavation and construction. Provide a solution.

  3. Understand The Problem • What’s the issue here? • Water filling a hole, or • The water becoming contaminated and affecting the health of the workers, or • The cost of construction, or • The schedule delays of construction impacting the availability and costs of cranes and material being delivered to site, or…

  4. Understand The Problem • Constraints • Cost • Where can we send the water (environ standards, city municipal standards) • How long do we have to provide a workable solution • Design issues • How long do we allow to pump the hole out? • What pump capacity do we need? • How will they be powered? • How much water can we leave behind? • Do we need a spare in case the pump breaks down? • Background research • Talk to construction company – needs, power, portability (weight, wheels, ..) • What don’t we know about pumps to provide a workable solution? • How much time do we have to provide a solution (to what problem?) and how much money is available for the solution?

  5. Background Research • Design Research / Assumptions : • rainfall is 60 mm / day – state basis of this • (Link) to weather office • Drainage basin is: • 200m x 100m • Volume = 1200 m3 • Pump in 1 hr to limit construction delays

  6. Background Research • Clarify with the people that sell pumps what is required • They tell us they need to know the pump capacity and the differential pressure • Realize that the differential pressure is the difference between the liquid level and the street where we’re going to pump it to • Whoaa… can we pump it to the street? Is this allowed? Who do we ask? • The liquid level will go down as the hole gets deeper. How deep is the hole going to be? • What else affects the differential pressure? (piping, foot valve) • Where do we want to locate the pump? At street level the pump will need to suck the liquid up. At bottom of pit level the pump will need to be able to withstand being immersed in water. How do we make a decision?

  7. Generate Alternatives • Back to problem statement… • Prevent delays in construction • Alternatives: • Do nothing – accept the delays • Put a dome over the area • Call a pump rental company whenever we need it to be pumped out • Design a stationary pump system • Design a portable pump system

  8. Options • Fishbone Diagram Do nothing – accept the delays stationary pump system Put a dome over the area portable pump system Call a pump rental company whenever we need it to be pumped out

  9. Decision Making • Create a decision making matrix • Weighted Evaluation Matrix Pros / Cons / Costs

  10. Process Industry Decisions • Meets all applicable standards • Safe to Operate • Performs the necessary function • Minimal / Acceptable environmental impact • Reliable • Cost (Initial and operating) • Meets Schedule Requirements

  11. Design Detail • Upon knowledge of how you will evaluate the various options now you can begin generating the data required • Engineering calculations • Cost estimates • Equipment quotes • …

  12. Design Documentation • Option 2 - Design our own pump system • Make a Process Flow Diagram & Material balance 2 Pump City Sewer 1 Pit

  13. FC PFD Construction Site Pit Pump By: D. Mody Date: Sept /08 PFD with Controls Pump City Sewer Pit

  14. FC FC TC PC LC PFD with Controls

  15. Piping & Instrumentation Diagramaka P&ID Line dia = ? “ • Thoughts: • - Most pumps have some sort of a shut off when there is no feed (this prevents overheating and/or damaging the pump) • A lot of pumps have some sort of control on the flow rate. Do we need something too? • Is it possible to pump water in the sewer so fast that the sewer can’t take it away (flood someone’s basement) • Preliminary Safety Analysis - Are there other ‘hazards’ we might be causing? Line dia = ? “ Pump City Sewer M ----Concept Sketch---- HS From Pit

  16. Line dia = ? “ Line dia = ? “ Pump City Sewer M I FIT 100 FV 100 HS LSH FIC 100 P&ID Construction Site Pit Pump By: D. Mody Date: Sept /08 LSL Pit P&ID

  17. Other Design Documents • Pump Data Sheet • Provides a summary of the performance requirements & the essential mechanical details – • Used as a central document for purchasing the pump • Requires that we state the pump differential pressure • Thus begins … Engineering Calculations • To determine the pump pressure differential we must first determine the piping line losses. • This requires we know the length of lines, elevations and any fittings • or make assumptions based on engineering judgment

  18. Calculations • To determine the pipe (or flex hose) pressure drop we first size the lines using a heuristic. • Our table of flow vs piping pressure drop heuristics indicates that should be using about a 18” diameter line. • This seems excessive. Rethink plan to let the liquid build up over a day • run the pump whenever it rains. It only has to handle the normal rain rate. • 60 mm/ 24 hours = 2.5 mm /hr = 50 m3/hr • We only need 4” diameter pipe • Now ask yourself is this reasonable? What assumptions are you making and would these always be right? How likely/often would you be wrong? What are the implications of being wrong?

  19. Preliminary Line Sizing • We decide on the 4” pipe and we find the pressure drop is 1.2 psi/100 ft for pipe • We now need to know how long the piping is. For the more accurate calculation we need a ‘plan’ and ‘elevation’ drawing. For an initial assessment (i.e. we’re tossing around lots of options and we just need a comparison number) we can make an assumption by reviewing the site plan.

  20. Plan and Elevation Drawings 200 ft 75 ft 15 ft 20 ft 25 ft 50 ft Construction Site Pit Pump Plan Dwg 2 ft Ground 25 ft Construction Site Pit Pump Water Surface Elev Dwg

  21. Pump Calculations • To Determine the Pump differential Pressure, subtract the pump discharge pressure from the pump suction pressure • Pump discharge pressure = destination pressure + line & fitting losses + (or -) static head (elevation) losses • Disch Press = 0 psig + 367 ft * 1.2psi/100 ft * 4 (account for pipe fittings) – 2 ft = 16.7 psig • Suction pressure = 0 psig - 27 ft * 4 * 1.2psi/100 – 25 ft * 0.43352 psi/ft = -12.1 psig • Pump differential pressure is: DP = 16.7 psig – (-12.1 psig) = 28.9 psi DP = 28.9 / 0.43352 psi/ft = 67 ft of liquid head

  22. Calculations Horsepower = GPM * DP (psi) / 1714 / efficiency HP = (50 m3/hr *4.4 GPM/ m3/hr) * 15.5 psi / 1714 / 50% Motor HP = 7.4 hp

  23. Documentation – Pump Data Sheet We can now start to fill in our equipment data sheet and send it out for quotes to our pump vendors.

  24. Whew.. Is that it? Every engineering project must look at the societal impact and the costs. A process hazards analysis for this system is relatively straightforward, since were pumping cold water from a hole to another hole, but… • What if Hazard Methodology: • The water were contaminated with machine oil, diesel fuel, foul water? • What If a pipe ruptures and sprays a worker, other equipment? • Could we end up sending a toxic fluid into the sewer system (Environmental)? • Do we require a water treatment or oil catch basin prior to discharging it to the sewer? • What are we powering the pump with? If it’s gasoline then we need to concern ourselves with the hazards of handling gasoline safely.

  25. Process Economics • Often we look at the cost of goods sold minus the cost to produce the goods (and include the equipment costs) • In this case we’re not really selling or buying anything, but we might have the option to rent or buy the unit C

  26. Risk Analysis • Notice there is some risk in our economics, depending on whether we use the pump more or less the rent/buy decision is affected. • A risk analysis of the economics is usually a good idea. • Ultimately a recommendation/decision needs to be made

  27. Decision Making • Overall Decision making • And.. We make a recommendation to buy The END!

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