New product
High-melting ceramic-metal composite coating
A report on successfully protecting waste-incineration boilers against corrosion and slagging caused by high-temperature molten-salt fly ash. Issued 18 August 2026.
Request a technical consultation90%
Reduction in deposit thickness on the rear arch
155 m²
Sprayed across #1 and #2 boilers
>15 months
Waterwall service life proven on hazardous waste
>0.45 mm
Applied coating thickness
1. Solving slag blockage and unplanned shutdowns at Xinyi Gaoneng
Background: two waste-incineration boilers of 400 t/day each, co-firing sludge. During 2025 the plant was forced to shut down twice because severe slag build-up on the front and rear arch side walls blocked the furnace, causing serious losses.
#1 boiler — trial spray, 14 Jan 2026
Area: 40 m². Sprayed sections:
- Replaced castable at the bottom of the rear arch
- Partially replaced castable at the bottom of the front arch
- 1 m height of the side wall connecting the front and rear arches
- Waterwall around the ammonia-injection port
#2 boiler — spray, 5 Apr 2026
Area: 115 m². Sprayed sections:
- Front and rear arches and side walls below the auxiliary burner port (rear arch relined with new castable; other areas already flat)
- Waterwall around the ammonia-injection port
Operating results, 6 March 2026
Shutdown inspection, 21 June 2026 (grid maintenance outage)
#1 boiler: rear arch covered by a 20–30 cm deposit layer in uncoated areas; after cleaning those areas were left uneven, while the coated areas stayed flat and the deposit fell away easily. The coating itself was undamaged.
#2 boiler: rear arch covered by only a 2–3 cm deposit. Side walls and front / rear arches were flat and needed no de-slagging; the coating under the thin scale was intact.
Conclusions from the case
- Deposit thickness cut dramatically — comparing the rear arches of #1 and #2 boilers over the same period, a 90% reduction.
- The nature of the slagging changed: the mineralisation reaction between high-temperature molten-salt fly ash and the refractory is blocked, so the deposit layer is easy to clean.
- Refractories and boiler tubes are effectively protected against corrosion.
- Unplanned shutdowns caused by slag blocking the combustion chamber were completely eliminated.
2. The corrosion and slagging mechanism
The culprit is high-temperature molten-salt fly ash — fly ash carrying alkali metal ions, chloride ions and sulphate ions. With chlorine as the director, corrosion and slagging work hand in hand, accelerating attack on the substrate while the deposit layer sinters, hardens and thickens:
- 1Initial deposition: fly ash adheres physically and the deposit layer starts to grow.
- 2The deposit thickens, thermal resistance rises, and the outer tube-wall / interface temperature increases.
- 3Chlorides concentrate at the deposit–substrate interface.
- 4A liquid molten-salt film forms.
- 5Tubes: electrochemical corrosion accelerates and consumes wall metal. Refractories: Cl penetrates and destroys the structure.
- 6Tubes: corrosion product FeCl₂ is released into the deposit. Refractories: mineralisation reactions begin.
- 7Tubes: reaction with KCl / NaCl forms eutectic salts of even lower melting point. Refractories: Cl keeps migrating deeper.
- 8The deposit sinters, becoming denser and far harder to remove — then the cycle returns to step 2 and accelerates.
Corrosion and slagging therefore occur together and reinforce each other. The root of the solution is to stop chlorine from directing the process.
3. Validation data for the coating technology
1. Salt-bath validation
A 4:6 mixture of sodium chloride and calcium chloride, melting point 500 °C. At this temperature a liquid molten-salt film forms and adheres to the tube surface, reproducing the conditions of a high-temperature superheater in service.
2. Dense refractory-brick 'crucible' validation
A 4:6 sodium chloride / calcium chloride mix was held inside a dense refractory crucible at 1100 °C for 10 hours. Both the salt-bath and crucible tests confirmed that the coating can stop chlorine from driving the corrosion–slagging cycle.
3. Hazardous-waste rotary kiln and waste-heat boiler validation
Dezhou Zhengshuo project. The waterwall sections at the ammonia-injection and ash-drop openings have exceeded 15 months in service, proving corrosion and erosion resistance. In the rotary kiln, the castable in the combustion zone was sprayed; after five months the coating had prevented any mineralisation reaction between the hazardous waste and the castable.
After six months of operation the rotary kiln lining had not thinned by the usual 10 cm or more; instead, a thicker protective kiln coating reduced the internal diameter by 20 cm.
Conclusion: the high-melting ceramic-metal composite coating ends chlorine's role as director. It protects tubes and refractories from molten-salt fly-ash corrosion and changes the nature of the deposit — from bonded, mineralised and sintered slag to simple physical adhesion that is easy to remove.
Expected life in waste boilers: because the corrosive media in hazardous-waste incineration are far more aggressive than in municipal or industrial waste, and rotary-kiln tumbling with scraping scrap is far harsher than boiler service, the expected life in a waste-incineration boiler is one full overhaul cycle — so the return on this technology comfortably exceeds the investment.
4. Application
Process
- Surface preparation of tubes and refractories (sand blasting, cleaning)
- Spraying of the ceramic-metal composite coating
- Hot-air curing — spraying and curing repeated 4–5 times until the coating exceeds 0.45 mm
- Inspection and acceptance
- Sintering
Method
Waterwalls and the front / rear arches and side walls of the combustion chamber are coated on site, then sintered during start-up along the normal heat-up curve. High-temperature superheaters must be sintered off-line at our production base.
Thermal-conductivity performance has also been verified, so the coating does not penalise heat transfer.
5. Value: energy saving, emission reduction, lower cost, higher output
- Longer service life for castables, refractory bricks and boiler tubes, lowering replacement and overhaul costs.
- Eliminates unplanned shutdowns from tube bursts and slag blockage.
- Less de-slagging work in the combustion chamber, reducing the safety risk of cleaning.
- Higher heat-exchange efficiency and lower flue-gas exit temperature, increasing power and heat output.
- Longer campaign length between outages and higher operating revenue.
- Restores superheaters that had to be de-rated because of corrosion — or whose heat transfer dropped after cladding or overlay welding — raising power generation.
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