Technical Manual
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- Bu səhifədəki naviqasiya:
- Average Flux
- Particulate Fouling
- Organic Fouling
Fundamentals
9 | 37
Form-No: TM-WW002 // Revision: A // Date: Oct. 10, 17
If there is any height difference between the locations of the feed pressure and permeate pres- sure sensors than this shall be compensated in the above calculation of TMP indicated as Cor- rection Factor (CF). For example if the feed pressure sensor is 50 cm higher located than the permeate pressure sensor then CF = + 0.05 bar. In the event the permeate pressure sensor is located 80 cm higher than the feed pressure sensor then CF = - 0.08 bar.
The flux presents the absolute hydraulic flow in relation to the active membrane area that is used for filtration. Increasing the flow also increases the flux. Reducing the active membrane area (e.g. by isolating a module) also increases the flux. See the formula below. ?????????????????????????????? ???????????????????????? = ???????????????????????? ???????????????????????? [ ?????? ℎ
???????????????????????????????????????????????? ???????????????????????? [?????? 2 ] [ ??????
?????? 2 ⋅ ℎ ???????????? ??????????????????]
The gross flux is the instantaneous, “real” flux through the available membrane surface area. For feed pump flow rate sizing the gross flux shall be used multiplied by the total (maximum) membrane area that this particular feed pump is feeding to.
Net Flux The net flux (NF) is the average flux with consideration of water consumption and no permeate production time during back flush and chemical cleaning periods. The net flux depends on the filtration time, (air scouring) (AS), the back flush flow, the back flush time and cleaning interval and duration. The formula below can be used to calculate the net flux: ?????????????????? ???????????????????????? = ?????????????????? ???????????????????????????????????????????????? ???????????????????????????????????????????????????????????? ???????????????????????? [ ??????
ℎ ] ???????????????????????????????????????????????? ???????????????????????? [?????? 2 ] [ ?????? ??????
2 ⋅ ℎ
???????????? ??????????????????]
Average Flux The average flux is defined as the specific flux over a longer period, e.g. over a week, month or even a year. It can be calculated by the following formula (as example for a period of one week):
?????????????????????????????????????????? ???????????????????????? (????????????????????????) = ???????????????????????????????????????????????? ?????????????????????????????? ???????????????????????????????????? ?????????????????? ???????????????????????? ?????????????????????????????? ???????????????????????????????????????????????? ???????????????????????? ???????????????????????? ⋅ 168 ℎ???????????????????????? [??????????????????]
The permeability expresses the ratio of gross flux to the transmembrane pressure (TMP). Per- meability is an important factor for evaluation of the membrane performance. ???????????????????????????????????????????????????????????????????????? = ?????????????????????????????? ???????????????????????? ?????????????????? [ ??????
?????? 2 ⋅ ℎ ⋅ ?????????????????? ]
Normalized permeability The permeability is strongly related to the viscosity of the medium which in turn depends on the temperature. Usually, the permeability is normalized to a temperature of 20˚C for better com- parison of membrane modules operated at different temperature conditions. The following equation can be used for that purpose. T is the actual temperature of the medium:
Fundamentals
10 | 37
Form-No: TM-WW002 // Revision: A // Date: Oct. 10, 17
?????????????????????????????? ???????????????????????? ?????????????????? ⋅ 1.024 (20−??????) [ ??????
?????? 2 ℎ ?????????????????? ]
Recovery The recovery or recovery rate is the ratio of the usable product flow to the total feed water flow during a certain time period. The longer the time frame the more accurate the recovery calcula- tion is due to factoring in all water losses and non productive time for backflushes and chemical cleanings. ???????????????????????????????????????????????? = ?????????????????? ?????????????????????????????????????????? ???????????????????????? ???????????????????????? ???????????????????????? ?????? 100%
Membrane Fouling 3.3 Fouling and fouling control is an inevitable topic in all membrane filtration processes. Fouling describes the process of particulate and solutes accumulating on the feed side of the mem- brane due to the membranes selectivity. There are three
general types of fouling: Particulate Fouling Particulate fouling is caused by suspended solids, colloids and turbidity in the feed water. This fouling is controlled by hydraulic cleanings through regular air scouring and back flushing.
Most inorganic fouling occurs when filtering ground water or alkaline industrial waste water. In- organics may precipitate onto the surface of the membrane and create a solid layer at certain circumstances when certain solubility limits are reached at certain concentration, pH and tem- perature. This type of fouling can be removed by using acid for cleaning. In general, the use of citric acid is sufficient. The concentration dependents on the exact nature of the inorganic pre- cipitate and how severe and long the fouling has been present on the membrane surface area.
Organic fouling occurs when filtering water containing a certain amount of organics. Alginates, humic acids and fatty acids are the most common ones. Bacteria growth on the membrane is also a common cause. Alkaline solutions, such as sodium hypochlorite (NaOCl), are commonly used for removal of organic fouling.
All three types of fouling will occur during the lifetime of a membrane module, which fouling type will be seen predominantly depends on the feed water characteristics. Unfortunately, not all fouling is easy to remove and some fouling types are not able to remove at all.
1) Reversible fouling can be fully removed by hydraulic cleaning, performance may
be substantially recoverable. 2) Irreversible fouling can be fully removed by chemical cleaning, performance may
not be entirely recoverable, with gradual deterioration over time. 3) Irrecoverable fouling cannot be removed, performance is compromised and non-
recoverable.
Irrecoverable fouling will permanently reduce the performance of the membrane and can only be recovered by replacing the affected membrane module(s). Yüklə 1,67 Mb. Dostları ilə paylaş:
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