Firetube boilers are a boiler design in which hot gasses from the combustion of fuel pass through tubes running through a sealed pressure vessel of water. They are compact in construction, cost-effective, and can meet fluctuating steam demand when sized properly. Firetube boilers are sometimes referred to as Scotch Marine Boilers due to their common use on ships in a horizontal configuration.
Firetube boilers are very durable, easy to service, and work well with consistent and predictable loads. Firetube boiler characteristics include:
- 2, 3, and 4 pass configurations
- Design pressures from 15 PSIG to 300 PSIG
- Capacities up to 2,500 BoHP in a single boiler
- Can be used to produce steam or hot water
- Vertical firetube boilers – have a single pass and reduced capacities, under 150 BoHP
- Firebox boilers – offer reduced capacities, under 150 BoHP and pressures of 15 PSIG or less
Superior Boiler Firetube Boilers
Koch Applied Solutions works with Superior Boiler to offer our customers optimal firetube boilers engineered for maximum efficiency, excellent performance, and complete reliability.
Our team has the expertise and experience to help our customers design safe and compliant boiler applications. Request a quote to get started.
Wetback Firetube Boilers
The wet back design has a water-cooled, rear face of the combustion chamber heating surface. Benefits of the wetback design include:
- Great heat transfer to the water
- Higher efficiency
- Lower maintenance costs
- Longer life expectancy
- Less stress on the rear tube sheets, prolonging the boiler life
- Less maintenance clearance required
- Capacity: 50 to 1,500 HP
- 4-pass design with smooth tubes
- Steam pressures: 15 to 300 PSIG
- Hot water pressures: 30 to 160 PSIG
- Fuel options: Natural gas, propane, hydrogen, #2 oil, bio-diesel, digester gas, and syngas
- Capacity: 80 to 200 HP
- 3-pass design with smooth tubes, available with or without turbulators
- Steam pressures: 15 to 300 PSIG
- Hot water pressures: 30 to 160 PSIG
- Designed to meet Ohio code with less than 360 sq. ft. of ASME heating surface
- Capacity: 50 to 1,800 HP
- 3-pass design with smooth tubes
- Steam pressures: 15 to 300 PSIG
- Hot water pressures: 30 to 160 PSIG
- Fuel options: Natural gas, propane, hydrogen, bio-diesel, heavy oil, and syngas
- Capacity: 50 to 1,800 HP
- 3-pass design with rifled tubes
- Steam pressures: 15 to 300 PSIG
- Hot water pressures: 30 to 160 PSIG
- Fuel options: Natural gas, propane, hydrogen, and #2 oil
- Capacity: 100 to 2,500 HP
- 2-pass design with rifled tubes
- Steam pressures: 15 to 300 PSIG
- Hot water pressures: 30 to 160 PSIG
- Fuel options: Natural gas, propane, hydrogen, and #2 oil
Dryback Firetube Boilers
The dryback design has an open box rear combustion area, backed or surrounded by a refractory. The benefits of the dryback design include:
- Lower first cost
- Simplistic design that is easier to service
- Capacity: 10 to 2,500 HP
- 2-pass design with smooth tubes and turbulators
- Steam pressures: 15 to 300 PSIG
- Hot water pressures: 30 to 160 PSIG
- Fuel options: Natural gas, propane, hydrogen, and #2 oil
- Capacity: 30 to 1,000 HP
- 2-pass design with smooth tubes and turbulators
- Steam pressures: 15 to 300 PSIG
- Hot water pressures: 30 to 160 PSIG
- Fuel options: Natural gas, propane, hydrogen, #2 oil
- Capacity: 100 to 2,500 HP
- 2-pass design with rifled tubes
- Steam pressures: 15 to 300 PSIG
- Hot water pressures: 30 to 160 PSIG
- Fuel options: Natural gas, propane, hydrogen, #2 oil
- Capacity: Customized for job-specific applications, with experience designing units over 40,000 lb/hr
- 1-pass design with smooth or rifled tubes
- Steam pressures: 150 to 300 PSIG
- Hot water pressures: 150 to 250 PSIG (Section I vessels)
- Fuel options: Customized based on application
- Capacity: 30 to 1,000 HP
- 3-pass design with smooth tubes
- Steam pressures: 15 to 300 PSIG
- Hot water pressures: 30 to 160 PSIG
- Fuel options: Natural gas, propane, hydrogen, #2 oil, bio-diesel, digester gas, syngas
- Capacity: 80 to 225 HP
- 2-pass or 3-pass design with smooth tubes (with or without turbulators)
- Steam pressures: 15 to 300 PSIG
- Hot water pressures: 30 to 160 PSIG
- Fuel options: Natural gas, propane, hydrogen, #2 oil
Vertical Firetube Boilers
Vertical firetube boilers are designed to fit in smaller spaces than traditional horizontal configurations and can be fired from the top or bottom depending on the model and the space available. They are limited in size but can be great for small loads in tight spaces.
- Capacity: 14 to 48 HP
- Steam design pressure: Up to 150 PSIG
- Tube type: Smooth tubes with turbulators for maximum heat transfer
- Fuel options: Natural gas, propane, hydrogen, #2 oil
- Capacity: 7 to 48 HP
- Hot water design pressure: 30 to 125 PSIG
- Tube type: Smooth tubes with turbulators
- Fuel options: Natural gas, propane, hydrogen, #2 oil
- Designed for applications up to 15 PSIG
- Used for space heating or industrial process heat applications
- Typically available as a packaged system with all steam boiler controls pre-installed
Understanding State Specific Boiler Requirements
In certain areas of the country, there are state-specific laws regarding the design of boilers. Firetube manufacturers have adjusted their designs accordingly. For example, in Ohio, there are restrictions on the amount of heating surface that can be used to run a boiler without an operator. A firetube boiler for such an application is commonly referred to as an “Ohio Special Boiler.”
Recently, however, the laws in Ohio have changed to allow boilers that exceed the heating surface requirement to be run without an operator by providing some additional monitoring and documentation.