Open-flame kilns

Open Flame kiln. A kiln in which the ware being fired is exposed directly to the burning gases of the flame. 

Lignocellulosics reach temperatures around 80 C in many ways besides. For example, planer shavings and peat insulation around hot pipes or in walls of dry kilns easily attain 100 C, and forest product industries stack still hot wood-base panels at temperatures around 80 C. In many cases the temperatures of the hot materials later on rose above the initial 80 or 100"C, first to levels of smoldering combustion, and finally to those of open flames. In air-exposed and ventilated materials oxidation could cause the heating above 80 or 100 C, but inside tight packs of panels pyrolysis must have been the heat source. 

In view of the cheaper building costs, modern kilns are more likely to be rectangular than round, the air will be heated either by an open-flame oil burner or by a closed stove and either forced or drawn through the bed of hops with a powerful fan. Air speeds of about 15 m/min (50 ft/min) are normal, although up to 30 m/min (100 ft/min) have been used. Above this speed dried bracts may be blown off the kiln. Using these higher air speeds much... 

In addition to the use of nitrite and nitrate as additives, a second general mechanism by which foods may become contaminated with NA is through the drying of foods in air which has been directly heated in an open flame. The highest levels of VNA resulting from this common method of food processing have been in the kilning of malted barley. Concentrations of NDMA in the dried malt of over 100 yg/kg have been reported (Hotchkiss et al. 1980 Preussmann et al. 1981). 

---