Effect of air volume flow rates on pyrolysis temperatures and flue gas compositions to control smoldering smoke generation

Smoking is an important process unit operation used for preservation, as well as flavor, color and texture modifications of many foods. Currently, wood pyrolysis temperatures in industrial smoke generators cannot be systematically adjusted, thus process outcomes can only be controlled by varying smoke exposure time and environmental conditions in the adjacent product chamber. In this study, we investigated changes in pyrolysis temperature and flue gas composition in a redesigned smoldering smoke generator in which air intake could be adjusted. Air volume flow rates were set at 5.6 m³/h, 7.7 m³/h, 10.2 m³/h, 12.1 m³/h and 15.7 m³/h. Ember bed temperatures and flue gas compositions were determined as a function of these rates. Mean ember bed temperatures were affected by both the air volume flow rate as well as the smoke generation time i.e. a higher volume flow rate and/or a longer smoke generation time increased mean ember bed temperatures. Increasing air volume flow rates also led to decreases in oxygen concentration and increases in carbon monoxide concentration. Furthermore, frequential supply of fresh wood chips from the storage container to the site of the pyrolysis led to an increase in oxygen concentration, which decreased again upon ignition. The results suggest that - contrary to current practice - smoke composition and amount may be altered by controlling the pyrolysis process itself, thereby providing new possibilities to modify quality attributes of smoked foods such as meat, seafood or dairy products.