What are Bi-Drum Boilers? How Do They Work?

Bi-drum boilers are used for purposes of power generation and as process steam generators. This type of boiler is used up to 100MW for generating power. Bi-drum boilers are non-reheat units which are getting wiped out due to high heat rate of the plant. These boilers are used for generating high steam pressure which is used for power generation owing to their ability to accommodate high load of fluctuation and respond to load changes with more agility compared a single drum boiler.

The two drums in the bi-drum boiler are connected using a large number of convective heat transfer tubes known as bank tubes or boiler bank tubes. These tubes are about one thousand in number. The bank tubes and the drum at the bottom that contains water will have a water level that will be up to the normal working level of water in the upper drum.

The water availability in the bi-drum boiler makes it very adoptable for large load changes. Flue gases enter the bank tubes which are placed towards the furnace side and the tubes act like raisers to contain the mixture of steam and water. The load impacts the number of rows of bank tubes that act like raiser tubes. The remaining rows of bank tubes act as downcomer tubes between the upper and lower drum.

The boiler bank must maintain a temperature such that the flue gas exiting the bank tubes remains constant at all operating loads. During load changes that are fast or slow, the number of raiser tube rows increase and the downcomer tubes decrease to ensure that more steam in the steam drum surges upward almost instantaneous.

Bank tubes are placed in the upper and lower drum holes, and expand as operating pressure changes.

Boilers are classified on many factors such as usage, fuel fired, fuel firing system, and type of arrangement. Commonly known boiler types are pulverized coal fired boilers, super critical boilers, oil and gas fired boilers. All of these cater to industrial and power generation.

Boilers can be designed as two pass boilers and tower boilers. The tower type boiler is adopted for highly erosive high ash coal.

Carbon emissions are a major concern today. It is natural for super critical pressure units to be preferred as they increase plant cycle efficiency. This will make once through type boilers take over from drum type boilers.

Thermax provides the best quality boiler drums in the India and is a global leader in the heat treatment process sector. Powermax, one of Thermax’s two-drum water tube boiler is used to combust a wide variety of fuels. It is suited for applications that need uninterrupted boiler operation even on fuel which have a high fouling tendency. Thermax also provides bi-drum boilers which are rugged in nature and can operate all throughout the year. To learn more about the best heat treatment equipment visit https://www.thermaxglobal.com/.