Environmental Engineering Reference
In-Depth Information
TABLE 27.2
Energy Consumption and Capacity for Various Commercially Implemented
Desalination Methods
Process
MSF
MED/TVC
RO
ED
a
Heat consumption (kJ/l)
290
145-390
-
-
Electricity consumption (kJ/l)
10.8-18
5.4-9
6.5-25.2
4.32-9
Total energy consumption (kJ/l)
300.8-308.8
150.9-399
6.5-25.3
4.32-9
Production capacity (m
3
/day)
<76,000
<36,000
<20,000
<19,000
Conversion to freshwater
10%-25%
23%-33%
20%-50%
80%-90%
Total capacity (m
3
/day)
304,000
109,091
40,000
21,111
Pretreatment required
Little
Little
Demanding
Moderate
Source:
Data from Trieb, F., ed.
Concentrating Solar Power for Water Desalination
. ed. G.A.C. (DLR) and
I.O.T. Thermodynamics. Federal Ministry for the Environment, Nature Conservation and
Nuclear Energy: Stuttgart, Germany, 2007.
a
Electrodialysis, for brackish water. All other technologies for seawater desalination.
Thermal processes such as MED and MSF consume between 150.9 and 399 kJ/l of energy;
thus, they may not be practical for high-eficiency implementation unless coupled with a
process that produces a large amount of waste heat such as a power plant. Furthermore, it
should be noted that all major processes listed in Table 27.2 operate at signiicantly higher
energy consumption than theoretical limits. Examples of combined generation plants and
energy savings for the desalination process are listed in Table 27.3, with a more detailed
description reported previously [8,20].
The energy consumption estimates listed in Table 27.2 often do not account for energy or
material consumption for source water treatment. For example, the pretreatment require-
ments for RO units are very stringent to permit lower-energy operation of the desalina-
tion process and include scale control, usually managed by pH adjustment or an addition
of a chemical antiscalant, thus preventing irreversible scaling damage to the membrane.
Preiltration is also employed for particulate removal, and disinfection is used to prevent
biofouling when the disinfectant is compatible with the membrane material. The RO pro-
cess can also require post-treatment, depending on the initial water quality to remove
dissolved gases and adjust the pH and alkalinity [21]. Furthermore, most RO units operate
at ~40% or lower water recovery for seawater desalination. It should be noted that scaling
and corrosion are also major problems for MSF and MED desalination methods, as contin-
ued scaling decreases the eficiency of the desalination plant over time.
TABLE 27.3
Potential Energy Savings for Thermal Desalination Using Cogeneration Plants
Plant Type
Energy Savings Range
Backpressure steam turbine
5%-40%
Extraction/condensing steam turbine
0%-30%
Gas turbine/HRSG
20%-30%
Combined cycles
30%-40%
Source:
Data from El-Nashar, A.M.,
Desalination
, 134, 7, 2001.
