I am an Associate Professor in the department of Thermal Engineering and Fluid Mechanics of the Universidad Carlos III de Madrid (UC3M). My research is focussed on the fields of fluidization and thermochemical conversion of biomass, thus the BRISK2 project was an excellent opportunity for combining these two fields in an experimental work concerning gasification of biomass in a bubbling fluidized bed reactor. I decided to send my proposal to TUGraz where a versatile fluidized bed gasifier capable of using steam as fluidization agent was available.
During my 2 weeks research stay in TUGraz I have always been working together with my hosts Andrés Anca-Couce and Lukas Von Berg. They have always been available for experimental work and discussion of the results, showing a great enthusiasm for the research work. The system in TUGraz was ready for starting the tests at my arrival in Graz, so we could start with the measurements from the first day.
The experimental campaign in TUGraz started with a basic fluid-dynamic characterization of the fluidized bed employed at high temperature, including the measurement of the gas distributor pressure drop and the minimum fluidization curve of the bed material. This first experimental measurements were also used to set the limits of the setup in mass flowrate of steam to determine the operating conditions selected for the gasification tests. The gasification tests were conducted using two different materials to conform the fluidized bed: olivine and sepiolite. The particle size distribution of both materials was similar, with an average particle size of 250 mm. The main difference between the bed material tested is their particle density, which is 3350 and 1550 kg/m3 for olivine and sepiolite, respectively. Therefore, the lower density of sepiolite will result in a more vigorous fluidization of the bed compared to the olivine bed, enhancing the mixing of biomass particles and increasing their heating rate, which is beneficial for the gasification of biomass with steam.
The gasification tests were conducted at two different steam mass flowrates for each bed material to quantify the effect of the fluidization velocity in the bed on the gasification products. Furthermore, the same steam mass flowrates were used for both olivine and sepiolite to determine also the effect of the bed material. During the gasification tests, the composition of the permanent gases generated, i.e., H2, CO, CH4, CO2, O2, and N2, were monitored and tars were collected according to the tars protocol. The tars content was also measured during the research stay by the gravimetric method. Samples of the tars generated during each test were also collected and will be send to Madrid to determine the composition in a GC-MS equipment. Each gasification test, i.e., the two different steam velocities tested in both the olivine and the sepiolite beds, was conducted twice to check the repeatability of the process. Also, a long-term gasification experiment for the sepiolite bed was run to evaluate if any degradation of the material occurred during the test.
The results obtained during the research stay shows an increase of the concentration of combustible gases (H2 and CO) in the syngas produced during the gasification process in the bed conformed by sepiolite particles, which confirms that the gasification performance is improved using a lower density bed material due to the more vigorous fluidization produced in the bed. Therefore, the heating value of the producer gas obtained in the bed conformed by sepiolite particles is higher than that obtained in the olivine bed. Furthermore, the sepiolite bed contributes to reduce the amount of tars generated during the gasification compared to the bed of olivine particles.