Do you know how to properly flush your MED water desalination plant to extend the life of your equipment and reduce energy consumption?

Proper chemical flushing of multi-stage desalination plants (MEDs) not only maintains system efficiency, but also prevents corrosion, scaling, and reduced heat flow. In this practical guide, we will review the detailed and systematic steps for chemically flushing a MED water desalination plant, step by step, taking into account industry best practices.

1. Why is MED chemical flushing necessary?

MED (Multi-Effect Distillation) systems produce fresh water by successively evaporating water in multiple stages. However, over time, mineral deposits (such as calcium carbonate, calcium sulfate, silica), biofilms, and corrosion products accumulate on the surfaces of the pipes and heat exchangers. These layers:

• Reduce heat transfer
• Increase system pressure
• Increase steam and energy consumption
• Severely shorten equipment life

If you observe symptoms such as reduced water production, increased outlet temperature, or pressure fluctuations, the system probably needs flushing. To identify these symptoms more accurately, read the article [Symptoms of Needing Chemical Flushing of MED Water Desalination Plant].

2. Before you start: Identify the scale type and plan

Laboratory or guesswork? Never guess!

Choosing the right chemicals without knowing the exact scale type is like prescribing medication without diagnosing a disease. Professionals should:

• Take a scale sample
• Perform an XRD or SEM-EDS analysis
• Check the pH, hardness, TDS, and concentrations of specific ions (e.g.₂SiO,²₄SO⁻)

To learn about the common types of scale in MED systems, read the article [Scales Types and Corrosion in MED Desalination].

Determine the cleaning goal

• Is the goal to completely remove scale or just reduce surface layers?
• Is the system in operation or out of circuit?
• Is biofouling also present?

These decisions determine the type of detergent, concentration, temperature, and contact time.

3. MED Desalination Chemical Flushing Procedures

Step 1: System Preparation

• Remove the system from the circuit and cool it down.
• Flush all units with clean water (preferably RO) to remove floating particles and dissolved salts.
• In case of biofilm, perform a pre-treatment with a biocide (such as glutaraldehyde or DBNPA).

Technical Note: In MED systems, due to susceptibility to corrosion, the use of non-oxidizing biocides is preferred.

Step 2: Selecting the appropriate chemical detergent

Depending on the type of sediment, one of the following detergents is used:

Warning: The use of strong acids (such as HCl) is prohibited in aluminum or copper systems and can cause severe corrosion.

Abrizan Company, under the brand name “Mitreh”, produces specialized detergents for every type of scale in desalination systems — from mild acid cleaners to advanced descalers for silica.

Step 3: Set the washing parameters

• Detergent concentration:Typically 2 to 5% by weight
• Solution temperature:40 to 60°C (above 70°C may damage polymers)
• Contact time:2 to 8 hours (depending on scale thickness)
• Flow rate:At least 1.5 m/s to prevent the formation of dead zones

Step 4: Perform the cleaning (Circulation Cleaning)

1. Prepare the detergent solution in a separate tank (CIP Tank).

2. Use a pump to pass the solution counter-currently from the last effect to the first effect.

3. Monitor the temperature and pH of the solution continuously.

4. If the pH drops (in acid wash), add fresh acid to continue the reaction.

❓Frequently asked question: Why countercurrent?

Because the sedimentation is higher in the end effects (with lower temperature) and this method avoids excessive detergent consumption.

Step 5: Final rinse and neutralization

• After the main rinse, rinse the system with RO water to remove any chemical residue.
• If acid is used, perform a mild alkaline rinse (pH ≈ 8.5) to neutralize.
• Finally, fill the system with an anti-corrosion protection solution (such as nitrite or molybdate) to prevent corrosion when restarting.

4. After rinsing: validation and documentation

• Perform a visual or endoscope inspection.
• Effluent analysis: Checking the reduction of the concentration of ionsCa²⁺, Fe³⁺, SiO₂ 
• Comparison of performance: water production, steam consumption, effects temperature
• Recording of the report: including detergent type, time, temperature, pH, analysis results

This data is vital for planning future washes.

5. Common mistakes in MED cleaning and how to avoid them?

• ❌Using acid without corrosion inhibitor → Severe pipe corrosion
• ❌Washing at very high temperatures → Destruction of O-Rings and gaskets
• ❌No final rinsing → Re-deposition due to remaining ions
• ❌One-way rinsing (not counter-current) → Failure to clean end effects

6. When do you need expert help?

If:

• You have mixed deposits (e.g. silica + carbonate)
• Your system is aluminum or made of special alloys
• Previously cleaned but without results
• You need on-line cleaning

In these cases, expert advice is essential.

For a deeper understanding of the chemical challenges of MED systems, read the article [Introduction to the MED System and Its Chemical Challenges].

✍️ Conclusion: Smart cleaning = cost and energy savings

Properly performing the chemical cleaning steps of the MED desalination plant not only prevents expensive breakdowns, but also increases the efficiency of the system by up to 20%. This process is not a “cost”, but a strategic investment in your operational sustainability.

If you plan to do your next cleaning without guesswork and with scientific accuracy, use data-driven and laboratory expertise.

If you need expert advice...

If you need expert advice to identify the type of scale or the optimal selection of chemicals, Abrizan Company specialists, with over 20 years of experience in advanced laboratories, are ready to provide customized solutions to various industries. The specialized products of the "Mitreh" brand — from anti-scale to membrane cleaners — are formulated according to the exact conditions of each system.

☎️Free call and consultation with Abrizan specialists☎️