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.
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.
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.
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Ministry of Economy,Trade and Industry, JAPAN
meti_low-carbon-technology@meti.go.jp
Ministry of Economy, Trade and Industry.