Erosion of Membrane...!!!!
One of the India's leading power generation company used to rely more on traditional water treatment tools for boiler feed water treatment. So, system and setup was developed in accordance to that. The company's power generation setup in South India had tried reverse osmosis + EDI treatment on boiler feed water for the first time. Within first few months they started facing a problem of rise in a feed pressure and high differential pressure. Frequent cleaning was supporting to control the condition upto certain limit, but again trend of rise in feed pressure was maintained.
After few cleaning cycles, deterioration of product quality and quantity was also observed. This all actions, and costly down time and replacement cost of membrane turn up to the panic situation.......
We received the call for autopsy from this OEM. Based on our recommendation, they have selected the RO membrane for autopsy and sent it to us with recommended packing. We studied this case and came up with very interesting facts.
So, let's see the case and it's findings.
The principle effluent treatment flow diagram is as follows :
Chemical used for Raw water treatment :
2. Ferric Chloride
Chemical used for RO feed treatment :
After receipt of membrane while carrying out autopsy we came up with very valuable observations and findings as follows :
Aberration / Erosion observed
Delamination of polyamide layer
Each of the above picture reveals some condition and understandng of this and exact interpretation of the same is required
Some of our analytical findings and interpretation of foulants deposited on membrane leaf are as follows:
1. In chemical analysis silica deposition was prominently observed followed by iron.
2. There was very less microbial deposition.
3. Fujiwara test and Dye test was positive at various locations.
4. The spiking of colloidal silica, which has not been highlighted in routine analysis was the major culprit. Sharp crystals of silica has scratched and erode the membrane.
5. Uncontrolled or excessive dose of ferric chloride has reflected in terms of deposition on a membrane sheet.
6. Inadequate doses of SMBS or high spiking of chlorine dose has oxidised the membrane.
Although power company is confident, well aquainted in water chemistry, they were using traditional demineralisation technique for water purification / treatment. Analysis of colloidal silica was missing in their monitoring plan and also in raw water treatment laboratory.