Pollution of metal compounds
Metal compound pollution is mainly metal oxides, metal hydroxides, etc., especially iron pollution. The main causes are pretreatment defects, pipeline corrosion, etc. The symptoms are decreased water production and salt rejection rate, and increased pressure difference of membrane elements. Cleaning can be carried out according to the following formula:
| Main pollutants | Recommended cleaning fluid | Remark ; |
| Metal compound ; | 1% Sodium metabisulfite Na2S2O5 ; | Na2S2O5，PH=5，Max temperature：30℃ |
2%Citric acid（C6H8O7） | C6H8O7，PH>2,Max temperature:45℃ |
The total amount of cleaning fluid includes the volume of pressure vessels, cleaning pipes, high-pressure pipes and filters, and a margin of 20%. The cleaning fluid calculation includes two methods: rough estimation and accurate calculation.
Calculation of the amount of cleaning fluid
1. Roughly estimate the cleaning solution: it depends on the type of membrane element and the degree of pollution.
2. For general pollution conditions:
Each 4040 type membrane element needs to prepare 10 liters of cleaning solution;
Each 8-inch membrane element needs to prepare 40 liters of cleaning fluid.
3. For severe pollution:
Each 4040 type membrane element needs to prepare 18 liters of cleaning fluid;
Each 8-inch membrane element needs to be prepared with 55 liters of cleaning fluid.
4. Example of accurate calculation:
see Table 2 and Table 3 for the volume estimation of pressure vessel and cleaning pipeline
| Pipe diameter（inch） | Volume rate |
| 2 | 0.16 gallon/inch,2.0 liter/meter |
| 3 | 0.37 gallon/inch,4.6 liter/meter |
| 4 | 0.65 gallon/inch,8.1 liter/meter |
Table 2 Volume rate of commonly used pipelines
| Pressure vessel volume rate | |
| Membrane size | Volume rate of membrane (pcs) gallon(liter) |
| 2540 | 0.8(3) |
| 4040 | 2(8) |
| 8040 | 8(320 |
Table 3 Volume of pressure vessel
Taking 36 8040 membrane elements as an example, the calculation is as follows:
The membrane system is arranged in a 4:2 arrangement, each pressure vessel is equipped with 6 8040 membrane elements, which are cleaned in sections.
The cleaning pipeline with a nominal diameter of 3 inches is 15 meters long, and the volume of the cleaning pipeline = 15x4.6=69L;
The security filter can store 60 liters of water;
The volume of a pressure vessel=4x6x32=768L;
The total amount of cleaning fluid is =69+60+768=897 liters, that is, 81076 liters of cleaning fluid needs to be prepared for the first stage of cleaning.
In the same way, 615 liters of cleaning fluid is also required for the subsequent cleaning.
| Estimation of the total volume of cleaning fluid | ||
| volume（liter） | ||
| first stage | second stage | |
| Pressure vessel | 4*6*32=768 | 2*6*32=384 |
| Cleaning pipes | 15*4.6=69 | 15*4.6=69 |
| Safty filter | 60 | 60 |
| 20% margin | 180 | 102 |
| Total volume | 1076 | 615 |
Table 4 Total amount of cleaning solution required
Note:
1. When performing chemical cleaning, please pay attention to prevent chemical agents from harming operators, especially when using some highly corrosive chemical agents (such as fluorine-containing agents when cleaning silicon pollution). It is recommended to clean under the guidance of professionals.
2. The calculation example of the amount of cleaning fluid is for reference only.
