Abu Dhabi
Men’s College / EMC-4923 Desalination & Power
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Abu Dhabi
Men’s College / EMC-4923 Desalination & Power
Project / / Page | 1

Background

  • Cogeneration or combined heat and power (CHP) is the use of a power station to generate electricity and useful heat at the same time from the combustion of a fuel or an alternate thermal energy source.
  • In separate production of electricity, some energy must be discarded as waste heat, but in cogeneration this thermal energy is put to use. All thermal power plants emit heat during electricity generation, which can be released into the surroundings through cooling towers, flue gas, or by other means. In contrast, CHP captures some or all of the by-product for heating, either very close to the plant, or—especially in cold climates —as hot water for district heating with temperatures ranging from approximately 80 to 130C. This is also called combined heat and power district heating (CHPDH). Small CHP plants are an example of decentralized energy. The process heat at moderate temperatures (100–180C) can also be used in absorption refrigerators for cooling.[ref: Wikipedia].
  • With respect to desalination, cogeneration is the process of using excess heat from electricity generation, or useful process heat, for another task: in this case the production of potable water from seawater or brackish groundwater in an integrated, or "dual-purpose", facility where a power plant provides the energy for desalination.
  • Cogeneration takes various forms, and theoretically any form of energy production could be used. However, the majority of current cogeneration desalination plants use fossil fuels andnuclear power as their source of energy. Most desalination plants located in the Middle East or North Africause their petroleum resources to offset limited water resources. The advantage of dual-purpose facilities is they can be more efficient in energy utilization, thus making desalination a more viable option for drinking water. [ref: Wikipedia].

Project Problem Statement

  • This mini-project is to be completed in partial fulfillment of the course “Desalination & Power, EMC-4923”; Student will work individually and submit a MS word report documenting the solution and results, and a PPT presentation of the results highlights – Parts k, l.
  • In this mini-project, you will consider the study of a hypothetical cogeneration-desalination problem in order to gain some insight into the process, the calculations involved, and the behavior of the various outputs. This should bring together the different fragments of the process covered in the [Desalination and Power, EMC-4923] course at ADMC.
  • The purpose of the report is to document the solution to the given cogeneration-desalination problem using what you learned in class. A discussion of the results is to be documented and presented.
  • In the project problem description statement given below, the process heat generated is used as the heating load to a single-effect evaporator (SEE) to generate a distillate product. The SEE process hardware is described by figure 1a. Figure 1b shows a general profile of the temperature variation across the hardware. Detailed description of the SEE process and the mathematical model can be found in the class notes [EMC-4923] for learning outcome 4.
  • Help for the treatment of a cogeneration problem can be found in the class notes for learning outcome 5.


  1. SEE Schematic Diagram [EMC 4923]


b. Apparent temperature variation
Figure 1. Single Stage Evaporation Process [EMC 4923]

The above SEE desalination configuration is common to all the projects. The following set of specifications is to be used in the solution of the SEE process:

  • The seawater temperature, Tcw, varies over a range of 5°C to 30°C.
  • The feed water temperature, Tf, is less than the brine boiling temperature by 4 to 15 °C.
  • The steam temperature, Ts , is higher than the brine boiling temperature by 4 to 15°C.
  • The seawater salinity, Xf, range is 32,000 to 42,000 ppm.
  • The salinity of the rejected brine, Xb, is 70000 ppm.
  • The boiling temperature, Tb, varies over a range of 55 to 100 °C.
  • The heat capacity of seawater, distillate, and reject brine are assumed constant and equal to 4.2 kJ/kg °C.
  • You must first solve the cogeneration problem, and use the results to continue the solution of the SEE process. The connection between the two processes (power generation and desalination) is through the process heater block (left to students), where you will use your understanding of the individual processes that make up the overall problem.
  • While the cogeneration process is well defined and fixed, the desalination of seawater via SEE can be analyzed by varying some key operating parameters (the cooling water temperature, seawater and brine salinity, and feedwater temperature) in order to investigate the behavior of the SEE process based on the mathematical model formulated in class. This means that you will rely on the same formula sheets provided for SEE (LO4) and CHP (LO5) in order to develop your solution. The analysis should shed light at the behavior of key output and control parameters (such as the cooling water mass flow rate, the performance ratio, and the evaporator and condenser heat transfer areas.)
  • You may use MS Excel, Matlab, EES, or similar tools to help you do the calculations… But I would encourage everyone to first do the work on scratch paper, and then type your report when done. If you need help, do not hesitate to see me immediately…
  • You will need to use the steam tables A4 – A7 (Y. Cengel’ s Thermodynamics textbook)
  • Your report should include the material presented above to begin with. Add sections under the headings: Calculations (for parts a, b, c, d, e, f, g, h, i, j, k, l);Discussions (for parts a, b, c, d, e, f, g, h, i, j, k, l);
  • Marking: See Rubric for Report and Presentation…

Cogeneration Plant & Single Effect Evaporation (SEE) Desalination

A desalinationSEE plant requires 4 kg/s of saturated steam at 2 MPa, which is extracted from the turbine of a cogeneration plant. A schematic of the hardware and a T-s diagram are shown in figure 2 for the cogeneration plant. Steam enters the turbine at 8 MPa and 500°C at a rate of 11 kg/s and leaves at 20 kPa. The extracted steam leaves the process heater as a saturated liquid and mixes with the feedwater at constant pressure. The mixture is pumped to the boiler pressure. Assuming an isentropic efficiency of 88%for both the turbine and the pumps, determine

a.temperature of the process heater steam.

b. the rate of process heat supply.

c. the net power output.

d. the utilization factor of the plant.


a. Cogeneration plant hardware /
b. T-s Diagram
Figure 2. Cogeneration plant

Based on the results of the cogeneration system, choose proper SEE operating parametersaccording to general specifications given earlier, and produce plots of the following output and control parameters against variations of key input parameters (here we consider only the cooling temperature, Tcw, and salinity, Xf as inputs) in the proper range suggested at the beginning of this problem statement. In each case, interpret and discuss your plots… Explain in simple terms the meaning of the variables you are plotting, and then explain the behavior based on the plot and the physics of the process..

e. The distillate product mass flow rate.

f. The performance ratio.

g. the specific heat transfer area of the evaporator.

h. the specific heat transfer areas of the condenser.

i. thespecific cooling seawater mass flow rate, .

IMPORTANT: In each case above, show the formulation, and a sample calculation. But for plots, you must use the Excel workbook provided.

Effect of seawater temperature

Consider a range of Tcw = 5 oC to 30 oC. Calculate and tabulate as follows, then plot.

Tcw (oC) / Md (kg/s) / PR / Ae/Md / Ac/Md / Mcw/Md
5
10
15
20
25
30

1. Calculation and Plot of the product mass flow rate vs seawater temperature: Md vs Tcw.

2. Calculation and Plot of performance ratio vs seawater temperature: PR vs Tcw.

3. Calculation and Plot of specific heat transfer area vs seawater temperature: Ae/Md vs Tcw

4. Calculation and Plot of specific heat transfer area vs seawater temperature: Ac/Md vs Tcw.

5. Calculation and Plot of specific cooling water flow rate vs seawater temperature: Mcw/Md vs Tcw.

Effect of seawater salinity

Consider a range of Xf = 32000 ppm to 42000 ppm. Calculate and tabulate as follows, then plot.

Xf (%) / Md (kg/s) / PR / Ae/Md / Ac/Md / Mcw/Md
3.2
3.4
3.6
3.8
4.0
4.2

6. Calculation and Plot of the product mass flow rate vs seawater salinity: Md vs Xf.

7. Calculation and Plot of performance ratio vs seawater salinity: PR vs Xf.

8. Calculation and Plot of specific heat transfer area vs seawater salinity: Ae/Md vs Xf

9. Calculation and Plot of specific heat transfer area vs seawater salinity: Ac/Md vs Xf.

10. Calculation and Plot of specific cooling water flow rate vs seawater salinity: Mcw/Md vs Xf.

Report RubricName: ……………………………………… Section ………….

Scale / A / B / C / D / F
Cover page / 5 / 5 / 4 / 3 / 2 / 1
Background / 10 / 10 / 8 / 6 / 4 / 2
Problem Statement / 10 / 10 / 8 / 6 / 4 / 2
Calculations
& Discussions / 100 / A / B / C / D / F
1.Assumptions
2. Formulas,
3. Solutions,
4. Plugins,
5. Results,
6. Discussions / A / 10 / 8 / 6 / 4 / 2
B / 10 / 8 / 6 / 4 / 2
C / 10 / 8 / 6 / 4 / 2
D / 10 / 8 / 6 / 4 / 2
E / 10 / 8 / 6 / 4 / 2
F / 10 / 8 / 6 / 4 / 2
G / 10 / 8 / 6 / 4 / 2
H / 10 / 8 / 6 / 4 / 2
I / 10 / 8 / 6 / 4 / 2
J / 10 / 8 / 6 / 4 / 2
Excel Plots
& Discussions / 30 / A / B / C / D / F
1. Excel sheet
2. Tables
3. Plots
4. Discussions / 30 / 24 / 18 / 12 / 6
Report Quality / 15 / A / B / C / D / F
Organization,
Proper format / 5 / 4 / 3 / 2 / 1
Neatness, Relevancy / 5 / 4 / 3 / 2 / 1
Clear discussions & conclusions / 5 / 4 / 3 / 2 / 1
Report Total / 170

Report mark

Total from above / ………………… / . / Percent: ……………

Presentation Rubric Name: ……………………………………… Section ………….

Excel Plots / A / B / C / D / F
Assumptions / 5 / 4 / 3 / 2 / 1
Plot 1 / Data / Plot / 5 / 4 / 3 / 2 / 1
Discussion / 5 / 4 / 3 / 2 / 1
2 / Data / Plot / 5 / 4 / 3 / 2 / 1
Discussion / 5 / 4 / 3 / 2 / 1
3 / Data / Plot / 5 / 4 / 3 / 2 / 1
Discussion / 5 / 4 / 3 / 2 / 1
4 / Data / Plot / 5 / 4 / 3 / 2 / 1
Discussion / 5 / 4 / 3 / 2 / 1
5 / Data / Plot / 5 / 4 / 3 / 2 / 1
Discussion / 5 / 4 / 3 / 2 / 1
6 / Data / Plot / 5 / 4 / 3 / 2 / 1
Discussion / 5 / 4 / 3 / 2 / 1
7 / Data / Plot / 5 / 4 / 3 / 2 / 1
Discussion / 5 / 4 / 3 / 2 / 1
8 / Data / Plot / 5 / 4 / 3 / 2 / 1
Discussion / 5 / 4 / 3 / 2 / 1
9 / Data / Plot / 5 / 4 / 3 / 2 / 1
Discussion / 5 / 4 / 3 / 2 / 1
10 / Data / Plot / 5 / 4 / 3 / 2 / 1
Discussion / 5 / 4 / 3 / 2 / 1
Total / 105

Presentation mark

Total from above / ………………… / . / Percent: ……………

Summary: Report + Presentation mark(255 max)

Report (10%) / Presentation (5%) / Total Mark %
………………… / …………………. / …………………… / ……………………

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