Multiple effect evaporator with vacuum
- For a desalination plant which has a multiple effect evaporator as its main fresh water production system, determine:
- The temperature and enthalpy of the steam/vapour and the condensate at each step
- The energy used in each evaporator vessel to evaporate water and the quantity of water evaporated in one hour
- The minimum quantity of cooling sea water required to fully condense the No. 5 vapour if the initial water temperature is 25 C and a temperature rise of 8 C is allowed for a contact condenser
- The quantity of total fresh water produced for two cases (do not count the LP steam condensate): 1. use of a non-contact condenser, 2. use of a contact condenser
- Draw an schematic of the setup with flows and conditions
- Information: simplify by using fresh water properties. Salt water inflow is 600 t/h at 100 C (a preheater has been used), LP saturated steam flow is 100 t/h.
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Steam conditions
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Pressure (kPaabs)
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LP steam
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220
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No.1 vapour
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180
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No.2 vapour
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140
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No. 3 vapour
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100
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No. 4 vapour
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60
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No. 5 vapour
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15
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P&ID for boiler and steam turbine system
- Prepare a P&ID diagram for a boiler and steam turbine system with a steam flow of 100 t/h, 20 bar, 350 C. Feedwater at 25 bar and 95 C.
Use the standards given in the lecture notes. Please include:
- turbine, condenser, condensate tank, subcritical boiler, feed water pump, feedwater control valve, feed pressure control valve with excess return to condensate tank, level control for condensate tank, level control for steam drum, attemperation control for steam temperature
- You can use a software package such as autocad, or submit it neatly hand drawn (or a combination). This is an assignment to show that you understand how to put together a P&ID diagram, not on how to use software.
Perforated plates in a clarifier
Two concentric perforated plates are separated by a 200 mm launder and form the flow exit for a clarifier (Figure 1). The inlet water flow of 1200 m3/h into the clarifier is through a 300 mm peripheral launder. The perforated plate information is in Table 1.
1. Determine the water flow rates through each plate by assuming the water flow rate is proportional to the plate area.
2. Determine the Reynolds number for the main body of the clarifier , compare it to the lower limit given on slide 4 and comment.
3. Determine the number of holes necessary in the inner plate to achieve the same pressure drop through both plates, state the value of the pressure drop.
4. Change the inner plate outlet flow to 400 m3/h, and while keeping other geometry the same, determine the hole diameter required for the outer plate to have the same pressure drop as the inner plate, state the value of the pressure drop.
- Use water properties at 20 C and atmospheric pressure. Sketch the side view and plan view with all dimensions. Use the equation for zeta. Hints: use an excel spreadsheet and the goal seek function. Detail the main variables and their values on paper. Submit your excel spreadsheet.
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Table 1 Perforated plate details
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Inside diameter(m)
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Outside diameter (m)
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No of holes
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Diameter of holes (mm)
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Inner plate
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0.5
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2.5
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?
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20
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Outer plate
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2.4
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4
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900
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20
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