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Package boilers

Package boilers are commonly called water or fire tube Boilers.

The packaged boiler is so-called because it comes as a complete package. Once delivered to a site, it requires only the steam, water pipework, fuel supply, and electrical connections to be made to become operational. Package boilers are generally of a shell type with a fire tube design so as to achieve high heat transfer rates by both radiation and convection.

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. The 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.

The features of packaged boilers are:

Small combustion space and high heat release rate resulting in faster evaporation.
A large number of small diameter tubes leading to good convective heat transfer.
Forced or induced draft systems resulting in good combustion efficiency.
A number of passes resulting in better overall heat transfer.
Higher thermal efficiency levels compared with other boilers.

Construction of three pass packaged type boiler :

The packaged boiler is so-called because it comes as a complete package with burner, level controls, feed pump, and all necessary boiler fittings and mountings. Once delivered to the site it requires only the steam, water, and blowdown pipework, fuel supply, and electrical connections to be made for it to become operational. This type of boiler having a capacity of 50 tons per hour. It consists of three stages of the tube in which flue gases are flowing. It has maximum structural rigidity and safety. Presently these types of boilers are also designed to burn wood, coal, and process waste also.

Working of three pass packaged type boiler:

In this boiler pulverized coal is used as a fuel. Hot gases are produced by burning coal. The flue gases coming from the first pass or combustion chamber pass through a number of tubes in different passes. Tubes are surrounded by water. The heat released by flue gases is absorbed by water and gets converted into steam. After passing through all tubes flue gases exhausted to the atmosphere through chimney and steam is collected in the upper part of the boiler.

Package boilers are fired from fuel oil in the form of liquid or gas. Fuel is ignited in the burners which creates an explosion within the boiler. Such a package boiler does not require purifiers (filters) because they burn consistently removing all contaminants within the fuel. To create constant combustion within the boiler, the forced draft fan forces air into the burner, causing a tornado effect creating turbulence to keep the flame ignited and the furnace pressurized.

Types of Package Boilers

The D-type Package Boiler

The D-type boiler has a water drum, steam drum, and generating tubes. Water flows into the steam drum, flows down the downcomers and into the water drum. Water is then sent from the water drum through the generating tubes, where the fire is located around causing water molecules to boil off into steam. Steam rises up more generating tubes and finally back into the steam drum where the dry pipe is located then into the plant. This configuration shaped the package boiler into a D-shape, hence the name D-type package boiler. These boilers are mostly used for plants that allow greater clearances.

The A-type Package Boiler

The A-type package boiler has two water drums and one steam drum compared to the D-type package boiler. Water boils off in the water drums shared by a common header, then sent up the generating tubes, into the steam drum and up the dry pipe. Just like the D-type package boiler, fire heats the tubes surroundings causing the tubes to increase in temperature thus boiling off water molecules to steam. A-type package boilers were designed to improve package boiler reliability and reduce tube replacements. A-type package boilers are smaller than D-type therefore will fit smaller plants, but does not have the same power output as D-type package boilers.

The O-type Package Boiler

O-Type Package boiler. The boiler has two drums, one water drum, and one steam drum. The combustion chamber is in the middle surrounded by downcomers and generating tubes.
The O-type boilers are a little simpler compared to D-type and A-type. They consist of one water drum and one steam drum. Generating tubes are lined up from either side of the steam and water drums. When water boils due to convection heating, steam rises up through the tubes and into the steam drum. This is an asymmetrical design for restrictive plant layouts. O-type boilers are mainly used for their fast steam production and reduced maintenance cost.

Advantages of a packaged boiler :

Advantages of package boilers are as follows,

Compact design capable to fit tight engineering spaces
Utilizes forced or induced draft system to provide greater efficiency and better airflow
Many tube passes which provide greater heat transfer.
High thermal wear levels.
Inexpensive maintenance.
Ease of installation.
Less costly than a water tube boiler erected on site of the same capacity.
Less manpower is required.