1. Standardized Data Recording
Accurate and detailed recording of operational data and standardized processing of system performance are crucial for early detection and prompt handling of potential problems, effectively preventing the escalation of faults. Therefore, when recording data daily, it is essential to standardize parameters using formats such as project tables and graphs, ensuring the recorded parameters are accurate and detailed, and avoiding frequent changes to the recording method. These measures play a key role in fault analysis and troubleshooting.
2. System Diagnosis
Upon discovering performance degradation, the first step in troubleshooting is to pinpoint the location of the problem and identify its cause. This can be achieved more effectively by utilizing test data from the system’s designed sampling points or monitoring instruments. In-depth data analysis allows us to pinpoint the root cause of the failure. The following are routine checks:
(1) Have all instruments, sensors, and displays been calibrated?
The calibration of the instrument can be checked against the following equilibrium equation:
Influent flow rate = Product water flow rate + Concentrate flow rate
(2) Has the system entered a period of stable operation and performance?
To read the system’s parameters, it must have been running continuously for approximately 24 to 72 hours. If the system has been running for longer, the trend of changes in the system’s standardized performance data must be studied and analyzed.
(3) Has the water production pressure been taken into account?
Sometimes, when the system is running, the permeate pressure is high. Ignoring the influence of the permeate pressure can lead to a low flow factor value, resulting in a result that does not conform to the actual performance of the membrane.
(4) Is there a high pressure drop from the inlet to the outlet of the concentrated water?
Inspect the piping and instrumentation process flow diagram of the system:
- Are there any measures to prevent back pressure in the produced water?
- Does the design take into account the requirement of easy troubleshooting?
- Are there any measures to prevent siphoning inside the pressure vessel?
(5) Check the prescribed sequence of start-up and shutdown.
In view of phenomena such as water hammer, product water back pressure (back pressure is defined as product water pressure being higher than feed water or concentrate pressure) and product water backflow (backflow is defined as product water seeping back to the feed water or concentrate side; when the feed water is seawater or high salinity, product water backflow is very obvious), is the membrane system still safe?
(6) Check the cleaning steps and cleaning chemicals used to determine if the cleaning steps are effective and whether the cleaning chemicals will damage the membrane elements.
(7) How frequently should the system be cleaned?
Excessive cleaning frequency indicates poor pretreatment performance, and frequent use of strong cleaning will shorten membrane life.
(8) Was a water quality analysis conducted?
The conductivity value is insufficient for calculating TDS removal rate, especially since CO2 in the raw water can completely permeate through the membrane into the product water and be converted into carbonic acid, which will lead to an increase in the conductivity of the product water.
(9) Inspecting the use of chlorine or other oxidizing chemicals indicates a potential oxidation problem.
(10) Check the replacement rate of the security filter; an excessively high replacement rate indicates a potential risk of fouling in the membrane system.
(11) Check the SDI data; the SDI of the influent should be consistently maintained at <5 or <3, as required by the design specifications.
(12) Check the scaling calculation sheet and confirm whether the amount of scale inhibitors and other chemicals added meets the requirements.
3. Pressure Vessel Diagnosis
Analyzing the performance parameters of individual pressure vessels is crucial for troubleshooting system-wide failures. Pressure vessels are vital components of the system; damage to connectors, seals, or membrane elements can all lead to performance degradation. Measuring the permeate flow rate of a single pressure vessel is generally difficult; therefore, the permeate conductivity of an individual vessel becomes an important parameter for fault analysis.
To pinpoint the location of a malfunction in a membrane element within a pressure vessel, probe and extraction methods can be used.
4. Membrane Element Analysis
If the system data is insufficient to determine the cause, individual membrane elements must be removed from the system for analysis. This analysis of membrane element performance includes both non-destructive and destructive analyses.
(1) Visual inspection and weighing
Visual inspection of the components can reveal information about physical damage or organic adhesion failures, whether the membrane element exhibits a “telescope” phenomenon or damage to the outer winding layer, whether there is mechanical damage to the permeate pipe, whether the brine seal ring is intact, and whether the installation orientation is correct.
The weight of a component is an important indicator for analyzing its degree of contamination, and can provide a rough estimate of the amount of contaminants.
(2) Performance test
Standard element performance tests are used to compare the desalination rate and permeate flow rate of membrane elements under standard test conditions with the performance data of elements in question. Element performance tests should be conducted once before and once after the cleaning test to determine the cleaning method and evaluate the cleaning effect.
(3) Anatomical analysis
The ultimate method for determining the cause of performance degradation is destructive analysis of the membrane element. By removing the element’s end caps and outer casing, the membrane blades inside can be rolled open. Carefully open the membrane element, being careful not to scratch the membrane surface. Examine the membrane surface thoroughly, cut a sample, and collect the contaminants for chemical analysis. Analytical methods include infrared spectroscopy, scanning electron microscopy, and ion analysis of dissolved substances, among others.
