A General Description of a CFBC Boiler

 The CFBC boilers in India are mostly top-supported boilers with a single drum, natural circulation, and balanced draft type. These boilers are designed to operate with coal as a major fuel. 

The combustor will be provided with a number of openings for fuel feeding and bed material feeding. A bunker will be provided for storing fuel and a separate bunker will also be used for storing the bed material. Drag chain feeders will mostly be used for fuel feeding and a rotary airlock valve (RAV)  will be used for bed material feeding.

 A set of burners for Heavy furnace oil (HFO) or LDO firing will be provided for the start-up of the boiler. The burners will be mounted on the sidewalls of the combustor. The boiler will have Primary Air (PA) fan and  Secondary Air (SA) fan for supplying the required air for fluidization and combustion. 

The flue gas coming out of the combustor passes through the ‘hot loop’ cyclone (water-cooled) where the coarser particles are separated and returned to the combustor. A  Loop seal blower will be provided for fluidizing the solids in the seal pot and returning the coarser particles back to the combustor. The flue gas with fine ash will be carried over to the back pass through the steam cooled cyclone outlet chamber (COC). The back pass will also be of steam-cooled wall enclosure construction housing the primary and final superheaters. 

The superheater will consist of three stages namely primary convective superheater, the Radiant superheater in the upper portion of the combustor, and the final convective superheater. Double stage fixed nozzle spray type desuperheater will be located in between primary to radiant superheater and radiant to final superheater to maintain the rated superheated steam temperature between 60% and 100% MCR loads of the boiler. 

The economizer will be located below the superheaters in the gas path within the duct casing. Tubular air pre-heater will be located after the economizer in multi blocks for heating both primary and secondary air. The Bed ash coolers will provide one on each side of the combustor for cooling the bed ash to facilitate further handling.

What are the advantages of a CFBC Boiler?

• Water Cooled ‘Hot’ Cyclone separator
• A higher degree of fuel flexibility
• High combustion Efficiency
• Low SOx Emissions
• Low NOx Emissions
• Good Turn Down Ratio
• No Need for In-Bed Tubes, which are Subject to Erosion
• Smaller Combustor Cross Section
• Fewer Fuel Feed Points
• Elimination of Slagging
• High Availability
• Easy to Operate and Maintain