Last updated on 03/27/2020
How does a steam boiler work?
A boiler is a closed vessel in which a liquid, typically water, has heat energy applied to create steam. Boilers of the nineteenth century were usually made with very expensive, high-quality wrought-iron. Modern boilers, on the other hand, are made of steel or steel alloys to combat higher-temperature characteristics and for better strength-to-weight ratios. Heat energy is provided to the boiler chamber by burners fueled by natural gas, oil, coal, or electric heaters. While boilers are widely used in many industries, some typical applications of steam boilers are:
- Steam power generators
- Hot water applications
- Food preparation
- Water sanitation purposes
When discussing boiler design, safety is paramount. Even though modern industrial steam boilers must adhere to strict regulatory standards, catastrophic explosions still occur. This is one application where pressure switches absolutely must work and is a reason why CCS has focused on making sure our switches work reliably and repeatedly.
Two Main Types: Fire-Tube and Water-Tube Steam Boilers
There are two main types of Industrial Steam Boilers: Fire-Tube and Water-Tube Boilers. Fire-Tube boilers consist of a series of straight tubes housed inside a water-filled outer shell. In fire-tube boilers, hot combustion gases pass through inside the tubes to heat the water that surrounds the outside of them causing steam. This construction is more straightforward with less rigid treatment requirements for the water used in the outer shell. This design is well suited for space heating and low pressure hot-water industrial applications, but not for high power steam generation. Applications for Fire-Tube Boilers
- Home heating systems
- Trains
- Small Factories
Fire-Tube Boiler and Water-Tube Boiler Differences
The main difference between fire-tube and water-tube boilers is that fire-tube boilers send fire through tubes to heat water on the outside of the tubes and water-tube boilers send water through tubes to be heated by burning gases on the exterior of the tubes. These tubes extend between an upper header, called a steam drum, and one or multiple lower headers or drums. Water-tube boilers produce steam much more quickly and allow for the generation of lower weight-per-pound of steam. Generally, both these types of boilers can handle pressures up to 5,000 PSI with the steam generated reaching very high temperatures. Proper controls of these high pressures and temperatures are necessary to prevent catastrophic events from happening. Two drums are needed for water containment, making water-tube boilers extremely large and bulky with a typically much higher initial capital cost. Applications of Water-Tube Boilers
- Paper manufacturing
- Chemical and oil refining
- Steam power generation
How do you control the pressure and temperature of a steam boiler?
Every boiler requires proper control of the pressures and temperatures during the steam generation process. A team of pressure and temperature switches strategically placed throughout the system facilitates this control to maintain proper operation. A boiler pressure switch’s primary function is to protect the system from overpressure while boiler temperature switches help to control and maintain the appropriate temperature range. The pressure and temperature switches used need to be specially designed to endure the extremely high pressures and temperatures found within steam and gas boilers. Here are some of the most commonly used boiler switches:
Steam & Gas Boiler Pressure Switches & Controls
High Steam Pressure Switch
This switch triggers when the steam pressure inside the vessel reaches too high a point and triggers the burner to stop firing. If the switch did not work correctly and the burner continued firing, the pressure would build higher and higher causing the vessel to explode. Common CCS switches used for this type of steam application are CCS 604G or 6900G models. These are standard non-hazardous CCS pressure switches that can easily handle the pressure levels seen in boilers and are suitable for steam conditions.
High Gas Pressure Switch
This switch concerns industrial boilers where the heat is powered by natural gas combustion. If too much natural gas flows to a combustor, the burner could go out due to improper fuel mixture or the flame could be too large and could cause boiler overheating. When the flame goes out, a combustible mixture could fill the boiler combustion chamber. When the flame turns back on, an explosion would occur. CCS Models used for natural gas combustion are 6900GE and 646GE. These are standard switches to be used in hazardous areas and are compatible with applications using natural gas.
Low Gas Pressure Switch
Like the High Gas Pressure Switch, this switch is triggered when the natural gas inlet pressure is too low. This is still likely to be considered a hazardous environment so 646GE or 6900GE switches are commonly used here.
Oil Temperature Switches for Steam Generation
Oil Low-Temperature Switch
To burn oil properly, the oil needs to be heated to a proper degree to ensure the proper vaporization for the fuel/air mix. A temperature switch is used here to monitor if the oil is falling below the needed level. This temperature switch can be located in hazardous areas, therefore a CCS 646TE or 6900TE temperature switch is used for these applications.
Oil High-Temperature Switch
Likewise, a temperature switch is used for the same purpose, but this time if the oil reaches too high of a temperature then the proper oil/air mixture will be incorrect. The 646TE or 6900TE temperature switch makes sense here. Without these pressure and temperature switches, both fire-tube and water-tube boilers could not be operated properly. Switches help to monitor and maintain both the temperature and pressure within a system to ensure the safety of the system and the people operating it. For more information take a look at our selection of pressure switches and temperature switches or contact us directly.