Power engineering 2A3, Chapter 8 Exam Questions And Answers 100% Pass
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Course
Power Engineering
Institution
Power Engineering
Power engineering 2A3, Chapter 8 Exam
Questions And Answers 100% Pass
Using simple sketches, explain the difference between osmosis and reverse
osmosis. - answerWhen two solutions, one dilute and one concentrated, are separated by a
semipermeable
membrane, the solvent (water) from the dilute s...
Power engineering 2A3, Chapter 8 Exam
Questions And Answers 100% Pass
Using simple sketches, explain the difference between osmosis and reverse
osmosis. - answer✔When two solutions, one dilute and one concentrated, are separated by a
semipermeable
membrane, the solvent (water) from the dilute solution diffuses through
the membrane into the concentrated solution. This phenomenon is called osmosis. If
pressure is applied to the concentrated solution, the solvent (water) diffuses through
the membrane into the dilute solution. This phenomenon is called reverse osmosis.
What are two RO membrane types? Describe the construction of each type. - answer✔The
spiral-wound construction the membranes are produced in flat sheets. The
membranes and the spacers are wound around the permeate or outlet collection tube
in the middle. The membrane and the spacers create the flow channels for the
permeate and the reject water.
Hollow fibre RO membranes are composed of bundles of tine hair-like membrane
tubes. The pressured feedwater tries to pass through the outside of the tube walls into
the centre of the tube. The permeate is collected form the hollow centre of the fibre or
tubes. The concentrate remains in the module housing on the outside of the tubes.
Why must the water fed to an RO unit be filtered? What other types of
pretreatment are commonly used? - answer✔Filtration is important in RO because the
feedwater must pass through very narrow
passages during the process. Suspended solids must be removed and the water pretreated
so that salt precipitation or microorganism growth does not occur on the
membranes. Usually the pretreatment consists of fine filtration and the addition of
acid or other chemicals to inhibit precipitation. Sometimes a sodium zeolite softener
is used upstream of the RO filters. The softener removes the calcium and magnesium
hardness replacing them with sodium ions. The sodium does not foul or scale the
membranes as the calcium and magnesium do.
What are the variables that may cause operating problems in a hot process
softener? Explain. - answer✔Temperature variations of more than 4
C may cause carry-over out of cold or warm
process units. In hot process units, poorly operating inlet sprays reduce the
temperature of the reaction. This reduces the hardness reduction and increases the
dissolved gases in the outlet water.
Flow variations can upset the systems. They cause carry-over in cold units and added
hardness to both cold and hot processes.
Chemical control is necessary for control of all softening processes. Accurate control
involves frequent testing and adjustments of chemical feeds. For well waters the
quality of the makeup water changes little. Surface waters, especially rivers, change
with the seasons. The operator must anticipate changes and make the proper
adjustments to the chemical feeds.
Systems that feed powdered lime can require a lot of maintenance. Most often the
chemicals are fed in direct proportion to the raw water flow.
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