# Steam Gasification of Lignite in a Bench-Scale Fluidized-Bed Gasifier Using Olivine as Bed Material
## 2 Materials and Methods  
### Experimental Test Rig  
The bench-scale gasification reactor represented in Figure 1 was used to carry out the experimental tests. The gasifier consisted of a cylindrical stainless steel reactor (internal diameter of 100 mm and height of 850 mm) externally heated with a 6 kW electric furnace. Steam was used as a gasification agent and a flow of nitrogen was added in order to fluidize the bed; they were sent to a wind-box to be mixed and pre-heated, and then fed from the bottom of the gasifier through a porous ceramic distribution plate. In order to investigate the effect of an increase of temperature in the freeboard, in some tests, a small stream of air was injected in the freeboard through a steel tube of a 6 mm diameter. The bed material used was sintered, calcined olivine particles provided by Magnolithe GmbH [19] with a d\({}_{3,2}\) diameter of 317 \(\upmu\)m and density of 3000 kg/m\({}^{3}\), with the following composition by weight: MgO, 48%-50%; SiO\({}_{2}\), 39%-42%; and Fe\({}_{2}\)O\({}_{3}\), 8%-10%. As reported in the literature, calcination at high temperatures (around 1100 \({}^{\circ}\)C or higher) allows the iron oxides contained in the olivine particles to emerge at the surface, and thus to be available for catalytic reactions [20; 21; 22]. The height of the bed in the reactor was approximately 200 mm. The feedstock consisted of WTA lignite, and Rhenish lignite from a process of fluidized-bed drying with internal waste heat utilization [23], supplied by RWE Power AG. Lignite was continuously fed to the bed of the reactor by means of a screw feeder and a feeding probe that delivered the material directly to the fluidized bed. The feeding probe was purged with a small N\({}_{2}\) flow, in order to help the fall of the feedstock and to avoid the material from clogging the tube. The reactor was designed to host a ceramic filter candle in the freeboard above the bed, through which the product gas was forced to pass to exit the gasifier; in this way, the solid particulate remained on the external surface of the candle and the dust-free gas could exit the reactor. The product gas downstream of the gasifier was sent to heat exchangers for gas cooling and condensation of the residual steam. Circulation of the gas was granted by a vacuum pump. The flow of the dry product gas was measured with a mass flow controller, and its composition was analysed by online gas analyzers; a slipstream of the gas produced, about 1 NI/min, was sent to the tar sampling unit, carried out following the specification of the standard CEN/TS 15439. The gas passed through five impinger bottles containing 2-propanol and kept in a cold bath at \(-20^{\circ}\)C, to help the condensation of tars. The gas stream was moved by a vacuum pump and its flow rate was controlled by a mass flow controller. Finally, the main gas stream and the slipstream used for tar sampling were both sent to the vent. Temperatures were measured by means of three K-type thermocouples: one was positioned in the reactor bed (T1); one was located in the freeboard (T2); and the other was situated at the exit of the candle, just at the outlet of the filter (T3). The operating temperature was considered the average of the values measured from T1, T2, and T3. Differential pressures were measured by means of pressure probes through the candle (\(\Delta\)P1) and through the reactor (\(\Delta\)P2). The pressure probes were connected to U-tube manometers, and were able to measure in the range of 0.5-90 mbar. The fluidized-bed bench-scale reactor was equipped with a vertical probe in its freeboard, for acquisitions of pressure fluctuation signals. The probe was connected to a piezoelectric pressure transducer, in turn transmitting its signal to a charge amplifier KISTLER 5019A, and the operation parameters were tuned so as to obtain the highest amplification, without overloading. The resulting amplified voltage signal was then digitally converted and stored on a PC, provided with a tailored LABVIEW(r) routine.