Corroded switches and damaged cable trays

Severe corrosion in a waste incineration plant due to flue gas and steam leakage

Ton de Weijer and Wally Huijbregts (paper 55)

Anti-Corrosion Methods and Materials, Vol. 50, No. 5, (2003), pg 334-340.

Ton de Weijer is based at ARN B.V., Weurt, The Netherlands

Wally Huijbregts is based at Huijbregts Corrosion Consultancy, Renkum, The Netherlands

Paper available as pdf

Summary.

In a new build waste incinerator, the waste (Refuse Derived Fuel) was burned on a discontinuous moving grate. Frequent furnace overpressure peaks occurred because of this firing method and as a result, flue gas and flyash were pushed out of the boiler and into the building. During the plant start up period, a seal in a water-feed pipeline broke, and a large amount of condensed steam was discharged into the boiler house.

Shortly thereafter, very severe corrosion was noticed on the galvanised gangways, steel building components, the boiler aluminium sheeting and on processing lines.

The following calculations were made:

1. Estimation of the flue gas concentration in the boiler house;

2. Prediction of the dew points of the gases at the isolation wall and within the boiler house;

3. Estimation of the pH value of condensed moisture after the steam leakage;

4. Estimation of the expected corrosion which might result from the condensed acidic moisture.

A theoretical study of the condensation of the flue gas indicated that sulphuric acid would condense before it reached the external aluminium sheeting and that, under normal conditions, dry hydrochloric acid fumes would be removed by the boiler house ventilators. However, the steam leakage had caused the hydrochloric acid to be dissolved in the condensed water and that had resulted in the severe corrosion damage, which had become evident subsequently.

Conclusions

1. Corrosion damage to external walls, boiler sheeting and galvanised gangways was the result of the steam leakage: hydrochloric acid from the leaking boiler made the condensed moisture very acidic in a short time.

2. Under conditions of normal operation, any dry hydrochloric acid that escaped from the boiler would be removed from the boiler house by means of the boiler house ventilators.

3. The SO3 gas in the flue gas, leaking from the boiler, condensed as sulphuric acid inside the aluminium sheeting on the inside of the isolation void.

4. ARN B.V. began an arbitrage to appeal the claim-refusal of insurance in 1997. (The CAR-policy prescribed arbitrage in case of parties not reaching agreement)

5. In early 2002, the arbiters concluded that damage that had been sustained by the plant was covered by the CAR policy.

Some Figures from the paper