Efficient Use of Watertube Boilers

In today’s world of high fuel costs there has never been a more important time to insure your boiler is working efficiently. Obviously the more efficiently the boiler works the lower your fuel costs will be and the lower per unit cost for your final product. There are many areas where boilers can be made more efficient and we will outline these areas in the following list.

Efficiency Saving Strategies

1. Boiler design: This area is often overlooked when buying a new boiler, but can be critical in determining the fuel usage of such a boiler. Good designs should provide a thermal efficiency of approximately 8% on natural gas with exit temperatures around 240°C with a boiler running at approximately 1000kpa pressure.
2. Boiler Sizing: This is also an area where not enough time is put into ensuring the boiler is correctly sized for the load it will feed. An over-sized boiler will cycle way too much, putting stress on the pressure parts due to continuous changes in temperature as the boiler cycles through start and stop. Under sizing the boiler will cause problems at the supply end.
3. Boiler Cleanliness: The efficiency losses on a boiler when tubes are either scaled on the waterside, or sooty on the fireside is quite considerable and if left unchecked, either of these conditions will lead to increased fuel usage and higher fuel costs.
4. Feed Water: The importance cannot be overstated of the adherence to well monitored and well thought out feed water treatment plan. Poor water quality leads to not only lower efficiency from the boiler due to scaling, but in severe cases to total failure of the boiler tubes and thus the boiler.
5. Heat Recovery: There are several areas in the process where heat can be recovered thus making the boiler more efficient. These can be broken down into two areas.
6. Economisers: For every 22°C lowering of flue gas exit temperature 1% efficiency gain to the boiler.

Example – if the boiler was running at 1000kpa with an exit temperature of 230°C on natural gas

Efficiency gains = 230 – 130

22

= 4.5%

Note: This is a simple approximation as other factors govern this gain, but you get the thrust of this point.

1. Blowdown Recovery: Depending on the amount of blowdown associated with a boiler’s water quality, there may be sufficient energy in this blowdown to enable feed water heating in the feed tank. Where blowdown is considerable due to poor water quality the savings that can be made are considerable.
2. Regular Maintenance: The observation and tuning of a boiler should be done on a regular basis. Temperatures in all areas should be monitored regularly to ensure the boiler is operating to its capacity and efficiently. The setting up of the burner during commissioning is also important as this sets the stage for future reporting.
3. Energy-saving: The fitting of VDSs to both the blower motor and the feed water pups will ensure that the maximum electrical energy savings. These are becoming standard fitments on most boilers.
4. Burner Efficiency: The fitting of the latest microprocessor based burner controls will aid the tuning of the boiler and when used in conjunction with oxygen trim, will guarantee the best and most efficient burner possible.