Direct Hot-air Tumbler

Overview

Linen supply factories and other similar facilities often use batch-type large rotary drying ovens (hereinafter referred to as tumblers) to dry items such as towels and standard bedding after washing. For that purpose, the indirect steam heating system, which uses steam as a heat source to generate hot air, is widely used. Although the direct gas heating system has advantages such as lower running costs and less disturbance from the outside temperature than the steam system, the system’s introduction has been limited due to concerns over the discoloration (yellowing) of dyes attributed to NOx in combustion exhaust gas.
We addressed this challenge by developing an ultra-low NOx lean premixed burner (PHL burner), which features 10 ppm (O2 = 0%) or less NOx concentration, and establishing a design method for the duct to uniformly inject the burner combustion gas. Thus we have developed a compact, gas-fired direct hot-air tumbler with an elegant finish.

Operating Principle/Features

■ Development of ultra-low NOx lean premixed burner (PHL burner)
One of the causes of the yellowing of textile fabrics during drying is anthraquinone dyes used to produce bluish colors. The dyes react with NO2 and their blue colors fade, resulting in yellowish discoloring. Osaka Gas has developed an ultra-low NOx lean premixed burner (PHL burner), which features less than 10 ppm (O₂ = 0%) NOx concentration, causing no yellowing, and applied it to a tumbler.
In terms of combustion performance, the tumbler has achieved the target NOx concentration of 10 ppm (O₂ = 0%) or less by a large margin.
The PHL burner comes with combustion capacity options of 150 kW, 300 kW, and 600 kW according to tumbler capacity.

■ Safety design
The direct hot-air tumbler lets the combustion exhaust gas enter the tumbler drum directly from the gas burner. Accordingly, various safety measures are implemented to function in the event of failure.