A normal experiment started with preheating the grate and the combustion chamber using a propane torch placed under the grate. When the temperature in the combustion chamber (2 cm above the grate) reached 800°C (after ~2 hours), the torch was turned off and biomass was added to the gasifier. The addition continued until the bed height attained 17cm; afterwards, the fuel port was closed and the flows of steam and air were adjusted to the desired experimental conditions. As the biomass was pyrolyzed and the char was burned the bed height started decreasing and the ash accumulated. Thus, biomass was added every 10 minutes and in batches as required. In the earlier batch experiments reported by Priyadarsan et al. (2004), there was no ash disposal system; as such the temperature peak moved towards the bed surface due to ash accumulation at the bottom. In the current experiments, the ash was disposed of continuously and a quasi-steady state was assured by maintaining the peak temperature at the same location in the ash disposal system. When the peak temperature achieved a steady state (~1.0 hours) the gas sampling unit was turned on and the gas analysis was performed continuously during 20 minutes by the mass spectrometer (MS).

The flowrate of dairy biomass was maintained constant at 1 kg/h and the flows of air (0.56-2.26 SATP m3/h (standard ambient temperature and pressure meter cube per hour)) at 15°C and steam (0.19-0.43 kg/h) at 100°C were changed in order to obtain the desired experimental conditions: ER = 1.59, 2.12, 3.18, 4.24, and 6.36 and S:F = 0.35, 0.56, 0.68, and 0.80. An air drier was used to dry the air before it was supplied to the gasifier. The gasifier was operated at 98 Pa vacuum pressure during all the experimentation. Temperatures along the gasifier were monitored at every 60 seconds by type K thermocouples located at 0.02, 0.04, 0.07, 0.13, 0.20, 0.24, and 0.28 m above of the grate. Samples were taken at the top of the gasifier at the rate of 0.14 SATP m3/h and conditioned by the sampling unit in order to remove tar and particulate material. The mole fractions of CO2, CO, CH4, C2H6, O2, H2, and N2 were measured every ten seconds by the MS. The same procedure used for the air gasification was again employed for enriched air gasification with little changes.