Reverse osmosis unit failure and chemical cleaning analysis

Analysis of reverse osmosis equipment malfunctions generally involves three aspects

First, system design aspects

Second, installation and commissioning aspects

Third, operation and maintenance aspects

1. System design aspects

（ 1) Raw water quality and special ions—Complete water quality analysis and special ions such as iron, manganese, and silicon;

（ 2) Water temperature—Design calculations based on actual operating water temperature;

（ 3) Recovery rate—Determine the optimal recovery rate based on the arrangement of membrane elements to prevent exceeding the water flux of individual membrane elements;

（ 4) Number of membrane elements—Ensure that the average water production of each membrane element is less than 1 ton/hour;

（ 5) Product water backpressure—Calculate the product water backpressure appropriately based on the product water transportation conditions;

（ 6) Operating years—Simulate at least 3 years of operation to ensure reliable and sufficient high-pressure pump selection, extending the operating life of the reverse osmosis system.

Ignoring the above 6 key points can easily lead to serious malfunctions and adverse effects:

A. As the operating years of reverse osmosis increase and the water temperature changes, the water production still does not reach the initial design value when the high-pressure pump reaches its full output;

B. The high pressure on the product water side causes the water production to still not reach the initial design value when the high-pressure pump reaches its full output;

C. The number of membrane elements configured in the reverse osmosis is small, so a higher inlet pressure is required to maintain a stable water production as the operating years increase;

D. The reverse osmosis recovery rate exceeds the normal value, accelerating the pollution.

2. Installation and commissioning aspects

（ 1) Safety filter—Strictly control the tightness and compaction of the safety filter cartridge installation;

（ 2) Instruments and meters—The flow probe should be kept 1.5 meters from the inlet and 1 meter from the outlet, and equipped with a saddle-shaped probe base;

（ 3) Flushing pipeline system—Install the safety filter cartridge when flushing the pipeline system to prevent large particles from accumulating in the reverse osmosis equipment and related pipelines;

（ 4) Membrane installation—Use medical glycerin when installing membrane elements, and avoid using detergents and other lubricants as much as possible;

（ 5) Scale inhibitor addition—Ensure the normal addition of scale inhibitors and other chemicals during initial commissioning to prevent membrane element pollution and scaling after prolonged commissioning time;

（ 6) Brine seal—Check the installation direction of the brine seal when installing membrane elements;

（ 7) Pollution index SDI—Keep the system inlet SDI value below 3.

Ignoring the above 7 key points can easily lead to serious malfunctions and adverse effects:

A. Severe mechanical fouling, especially membrane elements easily scratched by sharp impurities;

B. Unstable flow meter readings, unable to play a monitoring role;

C. Wear and tear of O-rings and brine seals, resulting in decreased product water quality and high recovery rate;

D. Large pressure difference causes the membrane elements to produce a telescope effect, including abnormal pressure difference due to scaling and fouling.

3. Operation and maintenance aspects

（ 1) Instruments and meters—Regular calibration of flow meters and regular cleaning of probes;

（ 2) Pressure gauge—Regular calibration of pressure gauges;

（ 3) Pressure vessel—Correct disassembly and installation of pressure vessel end plates;

（ 4) Concentrate stop ring—Correct placement of the concentrate stop ring;

（ 5) Upper limit of operating data—Determine the upper limit of operating parameters, such as inter-stage pressure difference, and take timely action when the upper limit is reached;

（ 6) Manual cleaning—For severe mechanical fouling, avoid using excessively strong water jets for flushing.

Ignoring the above 6 key points can easily lead to serious malfunctions and adverse effects

A. The brine seal is installed in reverse, resulting in a high recovery rate;

B. The pressure vessel thrust ring overlaps or partially overlaps with the concentrate outlet, resulting in high recovery rate operation;

C. The mixed use of new and old membrane elements or different types of membrane elements accelerates the pollution rate;

D. The flow meter shows a large or small deviation, affecting the adjustment of the system recovery rate;

E. Excessive pressure difference causes the membrane elements to be mechanically fractured, resulting in irreversible losses;

F. Inaccurate operating pressure easily causes the system to operate under overload, accelerating the pollution rate.

Chemical cleaning and sterilization

Chemical cleaning and maintenance is the fundamental means for reverse osmosis systems to recover their performance after degradation. Therefore, both the cleaning principles and the cleaning process must match the actual on-site conditions.

In addition to having a good cleaning plan, a more complete cleaning system is also the key to restoring the performance of the reverse osmosis system.

1. Chemical cleaning principles

（ 1) Multi-stage systems can be cleaned in series when the pollution is not serious;

（ 2) Multi-stage systems must be cleaned section by section when the pollution is serious;

（ 3) When the cleaning solution turbidity is too high, it needs to be re-prepared for cleaning;

（ 4) During the initial cleaning process, some concentrate should be discharged to prevent the cleaning solution from being diluted;

2. Eight Essential Functions of a Chemical Cleaning System

（ 1) Heating - Electric heating, steam heating, or hot water mixed heating

（ 2) Chemical circulation pipeline - The chemicals are mixed evenly through self-circulation before entering the reverse osmosis device;

（ 3) Cleaning flow meter - Observe the changes in cleaning flow rate to adjust the cleaning operation in real time;

（ 4) Cleaning pressure - Observe the changes in cleaning pressure to adjust the cleaning operation in real time;

（ 5) Cleaning pump and lift - Must ensure a minimum cleaning flow rate of 9 tons/hour for each container (calculated by multiplying the number of pressure vessels in one section by 9) heating;

（ 6) Cleaning pipeline - Relatively ample chemical cleaning pipeline diameter to ensure a flow rate of less than 2 m/s;

（ 7) Cleaning chemical tank - Relatively ample cleaning capacity;

（ 8) Cleaning safety filter - Prevents pollutants from transferring during cleaning, causing more serious clogging.