Optimizing the use of variable quality feedstock

Over the last few months there have been frequent enthusiastic references to the optimization of processes to cater for variations in available raw materials, mostly coming from the Invensys board after their purchase of the Spiral Software business, which builds on a database of crude oil properties.  A similar optimization approach can be supplied to many processes, particularly where most raw materials are now available from many and varied sources, or might come with variable composition.

Co-fired biomass fuels

The Metso Corrosion Management solution is a package for corrosion monitoring and control that has been developed in close cooperation with customers and help from various of the Metso business segments: last month it won the award for the best paper presented at Power-Gen Europe 2013 in Vienna.

Their Fuel Diet Corrosion Management solution tackles the effects of corrosion, optimizes the fuel diet and extends equipment lifetime, based on the long Metso experience of working with various fuels and boilers. It gives relevant information for fuel diet optimization to control the amount of corrosive gases in the boiler, and helps plan preventive maintenance and replacement operations. Online measurement and corrosion rate calculation, based on wide material know-how, together with information and control applications, ensure higher plant efficiency in parallel with wide fuel flexibility. Power producers no longer need to avoid inexpensive, lower-quality fuels due to risks of corrosion. A concrete case example was presented, with results, in an application where recycled and biomass fuels are co-fired.

Biomass water content monitoring

Another approach to improving power plant combustion efficiency on biomass fuelled plants comes from the Emerson Ovation expert control system: this is said to help reduce maintenance costs and boost net yearly MWh production. Biomass fuel with a high moisture content will generate far less heat than dry fuel: traditionally the control would be based on flue gas monitoring to control the combustion air supply.

The ovation system takes a biomass sample from the fuel transport system, measures the moisture content using microwave absorption, and sends the measurement to the Ovation system as an input to the thermal cycle control logic, on a 2-3 minute cycle.

“The variable moisture content of biomass fuels presents a challenge for operators who are under pressure to maximize performance from their power plants,” said Bob Yeager, president of Emerson Process Management’s Power & Water Solutions business. “With continuous moisture monitoring data incorporated into the Ovation control system, operators can make rapid adjustments to the combustion process to help enable an increase in net yearly MWh production.”

The system has been applied to a 15 MWe – 50 MWh power station in Italy fuelled by wood chips with variable moisture content. The system has helped improve plant efficiency and reduce maintenance costs.

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