What are the differences between fire-tube boilers and water-tube boilers?

What are the differences between fire-tube boilers and water-tube boilers? These are two common types of boilers with distinct differences in their structure and working principles.

Generally, what is termed a "smoke tube boiler" is essentially a "fire-tube boiler."
So, what are the differences? A fire-tube boiler is one where high-temperature flue gases flow inside the tubes, and the boiler water surrounds the tubes externally. Heat is transferred from the flue gases through the tube walls to the water. This type is often called a "smoke tube boiler" or "horizontal fire-tube boiler" in Chinese contexts.

In contrast, a water-tube boiler is one where water/steam flows inside the tubes, and the hot flue gases sweep over the external surfaces of the tubes. This design is more suitable for higher pressures and larger capacities.

What are the key differences? ZOZEN Boiler summarizes the main distinctions below:

Difference 1: Structural Design

What are the differences in design? In ZOZEN's fire-tube boilers, the combustion chamber and flue passages are formed by fire tubes. The combustion chamber is typically located in the lower part. Flue gases pass from the combustion chamber through the fire tubes and are then released into the atmosphere. Water surrounds the outside of these tubes, absorbing heat from the gases inside. A prime example is ZOZEN's WNS series gas-fired boiler.

WNS Series Oil/Gas Fired Steam Boiler

Capacity: 1 - 20 t/h

Working Pressure: 0.7 - 2 MPa

Applicable Fuels: Natural gas, coke oven gas, biogas, and other gaseous fuels; Diesel, heavy oil, light oil, residual oil, and other liquid fuels.

Application Industries: Heating, chemical, food, tobacco, textile, printing & dyeing, feed, pharmaceutical, building materials, brewing, rubber, hospitals.

What about water-tube boilers? In ZOZEN's water-tube boilers, the furnace and convection sections feature banks of water tubes. These tubes are located within the furnace enclosure. Flue gases flow around the outside of these tubes, transferring heat to the water circulating inside them. The water absorbs heat and converts to steam. ZOZEN's SZS series gas-fired boiler is a typical example of this structure.

Difference 2: Heat Transfer Method

How do they transfer heat differently? In ZOZEN's fire-tube boilers, heat transfer occurs primarily through convection between the hot gases inside the tubes and the water outside them. The combustion gases flow through the tubes, heating the surrounding water to produce steam.

In ZOZEN's water-tube boilers, heat transfer involves both convection and radiation. The hot combustion gases flow outside the tubes, transferring heat through the tube walls to the water/steam mixture circulating inside.

Difference 3: Pressure Handling Capacity

What about pressure capabilities? ZOZEN's fire-tube boilers generally have a lower pressure containment capacity, making them suitable for lower-pressure and smaller-scale applications.

ZOZEN's water-tube boilers are designed with a higher pressure containment capacity, making them suitable for high-pressure and large-scale applications, such as power plants or heavy industries.

What are the differences between fire-tube and water-tube boilers? ZOZEN Boiler remains committed to research, development, and innovation, providing tailored solutions that leverage the distinct advantages of each boiler type to meet diverse customer needs. For further details on the differences between fire-tube and water-tube boilers, please visit our official website or contact our customer service team. We are dedicated to offering you professional service and support.