D-type boiler

A package boiler is a factory-made boiler that consists of a range of standard designs. Package boilers are used for heating and act as a steam generator for small power purposes such as self-powered industrial plants. They cannot be used for large-scale power plants such as co-generation plants due to their size and lack of efficiency. Advantages of package boilers are that they can be brought in as a whole assembly, perfect for tight spaces, and easily installed. They require steam pipes, water pipes, fuel supply, electrical connections and can be made ready almost immediately. Because of their compact design, these boilers are cheaper to operate due to their automatic burner management system as well as maintenance cost.

A great cost-saving for package boilers is their simple need for draughting. The chimney may either use an existing masonry chimney, or else a simple steel tube stack is provided, just sufficient to clear the nuisance of the exhaust fumes. As the burner provides its own draught from a fan, they do not require the tall brick chimneys needed to provide the draught for a coal-fired.

Package boilers are commonly called water or fire tube Boilers. Water tube boilers use convection heating, which draws the heat from the fire source, and passes against the generating tubes of the boiler, causing water inside those tubes to boil off into steam. The fire tube boiler arrangement utilizes conduction heating which transfers heat from physical contact. Fire tube boilers are not commonly used due to their method of conduction heating because pipes in direct contact with fire and cold water could damage the pipes. The package boiler is usually a two or three-pass fire-tube boiler with an internal furnace tube. This is similar to the much earlier Scotch boiler.

Generating tubes filled with water are in direct contact with the heat source inside the boiler, causing damage to the pipes as well as scaling. These boilers however are great with steam production due to the large volume inside the boiler and the surface area of the steam output. In order for these boilers to operate properly, they require a long warm-up process, and are prone to thermal shock of the boiler. These boilers can be rated up to 500,000 lb/hr. The wall membrane of the boiler are dual welded, (welded on either side of the wall membrane) to provide extra reinforcement for high loads.

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Wikipedia