Effect of primary air maldistribution due to nozzle wear on CFBC performance

As in any fluidized bed application, the nozzle grid of a CFBC riser has the task of supplying fluidization/primary combustion air to the combustion chamber with a uniform distribution and at the same time retaining the coarse ash to form a dense bed at the riser bottom. A typical issue in large scale CFBs is a maldistribution of primary air caused by either excessive nozzle wear in certain grid regions or clogging and blocking on the other hand. The contribution presents a joint method of grid nozzle measurement and CFB combustion simulation for plant performance assessment. Results of erosion patterns and their effect on primary air maldistribution and subsequent combustion issues for a 105MWth CFBC are shown. The method of nozzle grid field measurements combined with detailed flow and combustion computations provides the CFBC operator with information on required number of nozzles to be changed in order to ensure uniform air distribution and at the nozzle grid. As a prerequisite for burn-out quality, boiler efficiency and emission control, the nozzle grid assessment is an effective measure to reduce boiler maintenance costs. •Joint method of grid nozzle measurement and CFB combustion simulation for plant performance assessment•Internal and external erosion on CFBC primary air nozzles•Primary air maldistribution