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10 Cards in this Set
- Front
- Back
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S.P.8.1a Define capex and opex and describe their role in the choice of softening techniques |
Capex = Capital Expense; Opex = Operation Expense Choice of unit operations is based on smallest (Capex + Opex) per Liter of Water Produced |
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S.P. 8.2c. List three methods used to manage scale by the removal of ions. |
1. LS (Which includes LS, WLS and HLS) 2. IX 3. NF |
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S.P. 8.3b Lime softening is also sometimes called “basic precipitation”. a. explain why lime is used instead of caustic soda (NaOH) in this technique. b. Use reactions to show why adding lime (CaO) ends up removing calcium hardness |
a. NaOH costs much more than lime b. |
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S.P. 8.3j: Shown below is a figure of a sludge contact softener. First make a bloc flow diagram showing the following components a. addition of slaked lime and soda ash b. sludge contact basin c. separation of sludge and clarified water d. sludge removal e. treated water. and then using kinetic parameters explain why the water is recirculated through the sludge contact basin. |
The Sludge is recirculated to improve the contact between the unprecipiated and precipitated carbonates so as to speed up the precipitation process (4 kinetics parameters, Temperature, Catalyst, SA, [Reactants]) |
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S.P. 8.4c i. Explain why a WAC can be regenerated with acid but a SAC cannot, ii. Explain why a WAC, regenerated with HCl, is then regenerated again with NaOH (given the very high cost of HCl and NaOH). iii. Consider the answer to S.P. 8.4b, and explain why the Capex for a WAC is increased because of the need to contain concentrated HCl. |
i. When the pH is below the pKa of a resin, H+ will replace the cations on the column. The pKa of a WAC is within the operating pH range of the equipment. The pKa of a SAC is much lower than the operating pH range. ii. The HCl is corrosive, and so the NaOH is used to remove this in a controlled way. iii. Any use of HCl will lower the pH increasing corrosion. Corrosion results in iron (III) which cannot be removed from a column by regeneration. Therefore any pipes carrying the HCl upstream from the column must be coated to prevent corrosion. This will increase the capex. |
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S.P. 8.4f There are a few idiosyncrasies to IX columns. Explain each of the following: 1. A given operation must always have more than one IX column on site. 2. Regeneration must be done carefully to avoid channels. 3. SACs do not work well with water of a high TDS 4. Regeneration of a WAC is much more expensive than for a SAC 5. The waste stream is not continuous but when it flows it has a very high TDS |
1. IX columns must be removed from the stream when regenerated 2. channels mean that water will flow through the column without contacting beads 3. the equilibrium [NaCl] will be very high, therefore a much higher [NaCl] will be needed to regenerate the column to drive off any divalent cations on the column 4. It requires both NaOH and HCl which are both expensive in pure form. In addition, pipes must be coated to prevent corrosion 5. During the regeneration, the hardness removed from the water is removed from the column using water with a high TDS. Much of this TDS passes through the column unused and therefore ends up in the waste stream. |
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S.P. 8.5c: i. Draw a sketch that distinguishes between cross flow and through flow configurations.
ii. Are the “film tech” membranes used in RO units designed to have a cross flow or a through flow configuration? iii. Why is there a limit to the pressure that can be exerted on a “film tech” membrane? iv. Is the main expense for RO capex, or opex? Explain. |
1. Section 10 notes 2. Cross flow 3. The membranes will become unseated causing leaks between the permeate and the concentrate streams 4. OPEX, paying for the pump pressure is the main cost |
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S.P. 8.6b: Explain how each of the following are used in evaporators to improve the efficiency of water removal: Temperature, the ratio of the surface area of the water to the volume of water being purified, and dryness of the air. |
- Temperature, the T is High to improve evaporation rates and equilibria. - The ratio of the surface area of the water to the volume of water being purified; The water is run as thin films down pipes - Dryness of the air: when possible, the air passing over the thin films is kept as dry as possible |
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S.P. 8.7b Draw a sketch of a hot process softener showing each of the following: Influent lines, steam inlet, and chemical inlet lines Sludge Blanket Sludge recirculation lines and pump Sludge removal Treated water effluent |
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S.P. 8.8a Give the three options available in Alberta for the disposal of sludge from a sludge contact softener, and give the main compounds that will be present in the sludge. |
Solid land fill Pumping down a well swan hills In all cases there will be salts, mostly calcium and magnesium carbonates. When the waste is wet, it will also contain the salts (Sodium and Bicarbonate ions( id soda lime softening is used. |
