Determination of Absorption Capacity and Mass Transfer Coefficient of Several Oils as Solvents for Biomass Gasification Cleaning System

With the aim to find an absorbing liquid suitable for the gas cleaning system in the application of gasification unit in a remote area, three types of oil were tested using a bubble column and a wetted wall column. Air streams containing toluene vapour with flowrates of 13.6 mL·min -1 or 27.6 mL·min -1 were bubbled through a 50 mL static oil in a glass tube at a temperature of 30 o C or 60 o C. In experiments using the wetted wall column, air streams containing toluene were contacted with a falling thin film of oil on the outer wall of a column with a diameter of 6.4 cm and two different contacting heights of 60 cm or 80 cm. Toluene concentrations in the air stream were adjusted in the range of 700-3000 ppm corresponding to a typical tars concentration in the producer gas. The phase equilibrium of toluene was represented as values of 1/H of 326, 220 and 182 respectively for lubrication oil, palm oil and sunflower oil (H is Henry's constant with the toluene concentrations in g·L -1 for liquid phase and g·Nm -3 for gas phase). From experiments using the bubble column, it was found that the overall mass transfer coefficient (KGa) was in the order of 10 -3 cm 3 ·min -1 and the overall liquid phase mass transfer coefficient (KLa) was about 10 -3 cm 3 ·min -1 . Although lubrication oil had a slightly better absorption capacity than the other two tested oils, it had a lower mass trasfer coefficient than that of palm oil. All three proposed oils had a much better absorption capacity and absorption rate than that of water used conventionally as a scrubbing liquid in a small biomass gasification plant.