1. Packaged boilers can be water tube or fire tube. These boilers are classified single pass 2 pass and 3 pass boilers. based on the number of times the hot combustion gases pass through the tubes of the boiler.
2. Package boilers can be further classified to Wet back boiler and dry back boilers.
3. Water tube packaged boiler mostly come in the form of “D” type “A” and “O” type configurations.
1. The packaged boiler is so called because it comes as a complete factory-assembled Package with all mountings, accessories and control instrumentation are installed on it.
2. Once it delivered to site, boiler requires only the steam, feed water pipe line. fuel supply connections and electrical connections to be made for package boiler to become operational and produce steam.
3. Package boilers are generally of a shell type internally fired furnace with fire tube design so as to achieve high heat transfer rates from both radiation heating surface and convection heating surface.
The D-type Package Boiler
1. 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.
2. 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
1. 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.
2. 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.
3. 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
1. 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.
2. 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 sides of the steam and water drums.
3. When water boils due to convection heating, steam rises up through the tubes and into the steam drum. This is a symmetrical design for restrictive plant layouts. O-type boilers are mainly used for their fast steam production and reduced maintenance cost.