Chemical vs. Mechanical Washing in MED: Which Method is Better?

Is chemical MED cleaning better than mechanical cleaning?

Is your MED machine experiencing reduced efficiency, increased steam consumption or abnormal pressure? Internal fouling is likely to be the culprit — but what is the solution? Chemical or mechanical cleaning?

In this article, we will transparently examine the key differences between the two methods from a technical, economic and operational perspective. The goal: to help you choose the smartest solution to preserve the life of your equipment and optimize maintenance costs.

Why do MEDs scale easily?

MED (multi-effect) thermal desalination systems operate by heating graded water in a series of effects at reduced pressure. These relatively low temperature conditions (usually below 70°C) but continuous evaporation lead to the formation of deposits such as:

• Calcium carbonate (CaCO₃)
• Calcium sulfate (CaSO₄)
• Silicates
• Magnesium hydroxide (Mg(OH)₂)

These deposits settle on the surfaces of the heat transfer tubes and provide a natural thermal insulation. The result? Reduced heat transfer, increased energy consumption, and ultimately reduced produced fresh water flow.

Three main factors that exacerbate scaling in MED:

1. High feed water hardness

2. Longer maintenance-free operation periods

3. Lack of appropriate anti-scaling agents

Mechanical washing in MEDs: When is it appropriate?

Mechanical cleaning involves physically dismantling the units and using tools such as wire brushes, sand blasting, or high-pressure water jetting to remove hard layers.

Advantages of mechanical cleaning

• Removal of very hard and old layers that are no longer resistant to chemicals
• Ability to visually inspect and detect mechanical defects (such as holes or localized corrosion)
• No need for chemicals—suitable for units with severe environmental constraints

Major disadvantages of mechanical cleaning

• Requires complete system shutdown (typically 7 to 14 days)
• High labor and transportation costs
• Risk of physical damage to pipe surfaces (scratches → new corrosion initiation)
• Incomplete cleaning of inaccessible points (e.g., in bends or parallel pipes)

Common question: “Does mechanical cleaning solve the problem immediately?”

No. If the root cause of scale formation (e.g. feed water quality or lack of anti-scale agents) is not addressed, the scale will form again within a few months, this time at a faster rate.

Chemical cleaning in the MED system: the smart solution for preventive maintenance

In chemical cleaning, specialized solutions are used to dissolve the scale without opening the system. This process is usually carried out in a closed circuit: the solution circulates through the MED pipes via a pump and removes the scale in a controlled manner.

How does chemical cleaning work?

Modern formulations are based on mild acids + corrosion inhibitors + permeability agents. For example:

• Organic acids (such as glutaric or citric) to dissolve CaCO₃
• Chelating agents (such as EDTA) for sulfate scale
• Corrosion inhibitors to protect 316L stainless steel or titanium

These compounds are formulated to remove scale, not the underlying metal.

Key benefits

✅No disassembly required — system stays in place

✅Short turnaround time (typically 2-6 days)

✅Uniform cleaning of all circulation points

✅Ability to be implemented during scheduled maintenance periods

✅Reduced risk of physical damage to equipment

Potential challenges (and how to manage them)

Need for accurate scale type analysis:

Without knowing the scale composition, it is impossible to select the right solution.

→Solution: Laboratory analysis of scale samples before starting operations.

Risk of corrosion if unsuitable formulations are used

→Solution: Use of materials containing corrosion inhibitors with compatibility testing.

Limitation against very hard and old deposits

→Solution: Intelligent combination of chemical cleaning with a gentle mechanical step (e.g. pre-rinsing with medium pressure water)

Direct comparison: chemical vs. mechanical cleaning

Key point: Chemical flushing is ideal for preventive maintenance and early scale management. However, in cases where scale is embedded in ceramic layers, a combination of both methods is sometimes necessary.

When to use which method? Decision-making guide

✅Use chemical flushing if:

• Freshwater flow reduction is less than 20%
• System still operates within acceptable pressure and temperature ranges
• A short-term shutdown is possible
• Sediment sampling and analysis have been performed

Consider mechanical flushing if:

• Deposits are so hard that even strong acids are not effective
• System has already suffered from under-deposit corrosion
• Concurrent NDT (non-destructive testing) is to be performed

Is chemical flushing suitable for all MED metals?

No — and this is where formulation selection becomes critical.

• 316L stainless steel: Fully compatible with mild organic acids and appropriate inhibitors.
• Titanium: Sensitive to mineral acids (e.g. HCl), but safe with chloride-free formulations.
• Copper and copper alloys: Require higher pH and specific inhibitors.

Never use a “generic” chemical solution for MED flushing. Each system requires a customized solution.

Frequently Asked Questions (FAQ)

Will chemical flushing corrode pipes?

No — if the formulation contains appropriate inhibitors and the pH is controlled. Compatibility tests are essential before implementation.

What is the difference between chemical flushing in MED and RO?

MED deals with mineral deposits (carbonates, sulfates), while RO deals more with biofilm and organic contaminants. Therefore, completely different chemicals are required.

Can we do this process ourselves?

Only if you have the necessary safety equipment, parameter monitoring software, and technical know-how. Otherwise, the risk of costly errors is high.

How many times a year should we flush?

It depends on the quality of the feed water. With effective anti-scale control, some units only need to be cleaned every 3–4 years.

Conclusion: Smart maintenance = long-term savings

Chemical and mechanical flushing are both valid tools — but their application areas are different.

In most cases, chemical flushing is the more efficient, safer, and more cost-effective solution for restoring the performance of MED devices, especially when done proactively and data-driven.

If you are still hesitating between the two methods, the first step is to collect a sediment sample and have it analyzed in the laboratory. Without this step, any decision will be a matter of chance.

If you need expert advice to identify the type of sediment or select the optimal chemical, Abrizan Company's specialists, with more than 20 years of experience in advanced laboratories, are ready to provide customized solutions to various industries.

☎️Free call and consultation with Abrizan specialists☎️