New models for predicting corrosion risk

In recent decades, the global drive to convert power plants from coal to biomass has brought its own problems. Biomass contains high levels of corrosive species and is also associated with huge build-ups of ash deposits on superheaters, known as fouling. Minimising corrosion and fouling could therefore save power plants considerable maintenance and replacement costs as well as improving boiler efficiency and reducing unintended shutdowns.

In order to address these problems, FORCE Technology has developed new models for corrosion risk prediction in biomass-fired plants. It has subsequently been able to validate these new models at Verdo Combined Heat and Power Plant, where the recent conversion to 100% biomass firing had resulted in a major increase in the rate of corrosion of the superheater directly above the grate, significantly shortening its lifetime.

FORCE Technology’s new corrosion modelling process focused on the main topics: high-temperature corrosion in biomass ash deposits; chemical reactions in the deposits and flue gas; release of critical species from the biomass combustion; and deposition mechanisms. This resulted in three main models for the simulation: a BED model for simulating the release of corrosive species from the grate; a coarse ash deposition model; and a model of the risk of corrosion of the metal surfaces of the boiler.

By incorporating these new models into the CFD simulations at the Verdo plant, FORCE Technology was able to predict high-risk corrosion areas and consequently offer Verdo an appropriate solution strategy to enable more efficient utilisation of its boiler.