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Electric and gas hybrid-type superheated steam generator



Superheated steam is steam which has been heated to higher than 100℃ which, because of its ability to enhance the taste of food by creating an anoxic cooking environment which seals in flavor, as well as its ability to rapidly heat both metals and nonmetals like plastic and ceramic, is widely used in factories, home ovens and elsewhere.
Commercial superheated steam generators typically rely on either electricity or gas combustion. Electrical superheated steam generators allow for precise temperature control, but they also consume a tremendous amount of power. On the other hand, gas combustion-powered generators have lower running costs but also more imprecise temperature control. 
Tokyo Gas has developed a generator which utilizes a hybrid system combining the superior temperature control of electric systems with the highly efficient heating capacity of gas combustion to overcome the conventional challenge of controlling power consumption while also achieving precise temperature control.
This generator was developed in conjunction with Chubu Electric Power Co., Inc. and Naomoto Corporation, and it is being marketed by the Naomoto Corporation to food production factories, automobile factories and others who will have use of such a device in their ovens or other commercial heating systems.



(1) Reduced power consumption 

The generator is able to limit power consumption thanks to the combined use of gas burners and electric heaters. 

 (2) Superior temperature control 

Through optimized load sharing between electricity and gas, power consumption can be kept down while also enabling sufficiently precise temperature control to within ±5℃ for preset temperatures (up to 400℃). 

 (3) Improved energy efficiency  

Primary energy consumption is roughly 35% less than that of a fully electric superheated steam generator. 

 (4) Compact size 

Thanks to its compact size, the generator can easily be incorporated into ovens, driers and other such devices.

Generator specifications

〔Fig. 1 External view of the generator〕
〔Generator specifications〕
Gas Unit Gas supplied City gas (13A) @2.0kPa
Rated gas flow 1.9m3/h
Dimensions 330×910×660㎜
Electricity unit  Electricity supplied  Three-phase AC 200V
Electric heater capacity 7.2kW(1.8kW ×4)
Dimensions 185×610×80mm×4
Superheated steam Temperature 160~400℃
Maximum pressure 0.2MPaG
Maximum steam volume 120kg/h
※ Saturated steam should be supplied from another boiler.

【Development key points】


(1) Development technology 

① Gas unit development 
  • Introduces a novel concept involving the use of metal knit burners* arranged in a burner configuration enabling efficient heat exchange between combustion exhaust gas and saturated steam**. 
  • Adopts a double helix arrangement for the steam pipes within the gas unit, thereby making it possible to reduce the overall size while still ensuring sufficient heat transfer surface area. 

② Control system development 
  • By ensuring an optimal operational balance appropriate to the preset temperature, such as using only the electric heater for low-load operation and a combination of gas burner and electric heater for medium and high-load operation, the generator is able to provide highly precise temperature control while limiting power consumption.
〔System overview〕
 *A highly efficient surface combustion gas burner of which the combustion surface is made of woven fabric of heat-resistant metal fiber.
This burner can be processed to the optimum shape according to any heated object, and its short flame can make the combustion chamber more compact.

**Steam generated by the boiling water, where gas (water vapor) and liquid (water) coexist.
Such steam becomes at the saturation temperature (boiling point) under a certain pressure and at 100°C under atmospheric pressure.

(2) Examples of industrial-use applications 

① Food processing...Locks in flavor for a remarkably improved taste.  
② Heating metals...Significantly reduces heating time compared with conventional systems. 
〔An image of a large scale unit
for a food plant〕
〔An image of food superheated〕

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