From the article:
A mathematical model of a gasifier-combustor was developed and validated with experimental data. The observed and predicted thermal efficiencies differed by an average of 5.8%. The model was used to analyze the effects of biomass moisture, unit size, and degree of insulation on turndown ratio. Turndown ratio was defined as the ratio of design to minimum thermal output and was calculated for a specific updraft biomass gasifier-combustor configuration. Turndown ratio decreased from approximately 8 to 2 as moisture content increased from 10 to 50% (w.b.). The effect of insulation was more significant for smaller gasifier-combustors than for larger ones.