When calculating industrial boiler efficiency, one needs to account for stack losses, radiation losses, and convection losses. But what are the factors that affect these readings and, ultimately, boiler efficiency?
An obvious answer is the design of the industrial boiler itself. But there are also a host of environmental factors that can impact boiler efficiency calculations. Knowing what they are will help you identify shortcomings in your boiler system so you can resolve them and put your system on the path to optimization.
1. Flue Gas Temperature
Flue gas temperature, also known as “stack temperature,” measures how hot the combustion gases are as they exit the boiler. If the temperature of the flue gas is high, it indicates that heat produced by the boiler is not being used to create steam and is therefore being lost.
Addressing heat loss through high flue gas temperatures often involves installing economizers or combustion air heaters to recoup heat for the boiler system. In the case of boilers that depend on solid fuels (e.g., coal, biomass), it’s also important to implement a regular maintenance program to make sure that the heat transfer surfaces in the boiler are clean and operating efficiently.
2. Fuel Specification
It shouldn’t come as any surprise, but boiler fuel specification can also have a dramatic effect on efficiency. Addressing this issue is simply a matter of establishing the right fuel specification and ensuring that actual fuel meets the documented criteria.
Fuel specification should be of particular concern for industrial boilers that rely on natural gas, due to the typically high hydrogen content. Some of this hydrogen inevitably becomes water during combustion, which monopolizes energy that could otherwise be used in the combustion process.
The main combustible in “natural gas” is methane (CH4) but there are also often lesser traces of ethane (C2H6), propane (C3H8), butane (C4H10) and pentane (C5H12). The greater the hydrogen content in the gases being burned, the more water produced by combustion. This means that natural gas with higher methane content and the lower proportions of the other gases will burn more efficiently.
3. Excess Air
Some boiler burners require excess air because their combustion process would be too fuel rich otherwise. In ultra low-emission burners, excess air is also used to reduce the production of carbon monoxide and NOx by controlling the temperature of the flame.
Whatever the reasons for the use of excess air, it inevitably absorbs some of the combustion heat, reducing the efficiency of the heat transfer to the boiler water. This issue can be addressed by calibrating a boiler regularly, and at multiple firing levels.
4. Ambient Temperature
Ambient temperature is the temperature of the combustion air that enters the boiler — basically the temperature of the air impelled by the forced draft fan. It can have a noticeable effect on industrial boiler efficiency and boiler efficiency calculations because it affects the net stack temperature, which is the difference between the ambient temperature and the flue gas temperature.
While it may be tempting to try to reduce ambient temperature to lower flue gas temperature, every 40-degree change in ambient temperature can affect industrial boiler efficiency by 1 percent or more. Finding the right balance is a delicate give-and-take that requires careful evaluation. Most industrial boiler efficiency calculations assume an ambient temperature of 70° or 80° Fahrenheit.
5. Radiation and Convection Losses
Radiation and convection losses are the heat losses that emanate from a boiler during operation. They’re inevitable, so you can’t do anything to eliminate them. But you can minimize them.
The two basic strategies for reducing radiation and convection losses are insulation and the control of any airflow over the surface of a boiler. Properly insulating an industrial boiler will reduce its surface temperature and lower heat losses. Shielding an industrial boiler from outdoor winds or indoor drafts will prevent heat from being lost due to air flow over the surface of the boiler.
Once you’ve determined if your industrial boiler is operating inefficiently, the next step is to try to determine the underlying causes. While it’s important to look at the efficiency of your industrial boiler equipment itself, there are also a number of environmental factors that can affect boiler operation. Addressing them is often more manageable and less capital intensive that considering new equipment.
Source - national boiler