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(Small) once-through boiler

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Unlike conventional flue and smoke tube boilers, once-through boilers have the characteristic technologies listed below.
· The basic structure has no steam drum and is a simple structure mainly composed of the header and water tube. The water content is very small, at approximately 1/20 to 1/30 that of conventional boilers.
· Special heat transfer fins are positioned at the appropriate places to enable compact boiler structure with high heat transfer performance.
· Optimized economizers can be included in a package to provide high efficiency.
· Some models are equpped with higher performance economizers, making it possible to recover the latent heat of the water vapor in the exhaust gas.
· Some models are also equipped with additional energy saving technologies such as inverter control for the fan.
· Sensors with failsafe functions and multi-level safety control are used.
· The devices such as the burner, fan, and control equipment are supplied as a package.

Organisation providing the technology:
Ministry of Economy, Trade and Industry
Endorsing entity:

Ministry of Economy, Trade and Industry.


Relatively high performance gas-fired flue and smoke tube boilers installed worldwide demonstrate an average boiler efficiency of around 90%. If these are replaced with once-through boilers, then it is possible to expect roughly 8% efficiency improvement and coresponding emission reduction.


· The water content is extremely small and the amount of energy held inside is also small, leading to extremely high safety regarding destruction.
· Short startup time (i.e. the time required for boiler to generate steam) about 10 minutes or less.
· Low NOx specification (NOx<25 ppm) models of gas fired boiler are also in the market.
· On models containing boiler controllers, when a minor failure occurs, safety is checked and then the control is switched and the operation is continued, leading to reduced production losses.
· The product is supplied as a package, so installation is easy and it is possible to expect shorter installation work time and reduced expenses.


· The maximum boiler efficiency is 98% for gas fired boilers. Boilers equipped with economizers which recovers latent heat can perform at efficiency of 100% or higher, depending on the situation of operation.
· Furthermore, the burner turn-down ratio on those models is increased to 1:5 to reduce the combustion cycles and heat losses.

Succes factors and requirements:

It is necessary to check the laws and regulations related to boilers in the country of installation and also the characteristics of the fuel and the water, etc.

Investments required:




Countries where implemented:
South Korea

Ministry of Economy,Trade and Industry, JAPAN

Technology owners:

Ministry of Economy, Trade and Industry.