# Steam Gasification of Lignite in a Bench-Scale Fluidized-Bed Gasifier Using Olivine as Bed Material
## 3 Results and Discussion
### Gasification Results  
The results obtained are summarized in Table 3. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Test** & **\#1** & **\#2** & **\#3** & **\#4** & **\#5** & **\#6** \\ \hline Bed Temperature (\({}^{\circ}\)C) & 752 & 813 & 841 & 757 & 800 & 850 \\ Avg Temperature (\({}^{\circ}\)C) & 757 & 825 & 842 & 741 & 786 & 818 \\ Air Injections (Nl/min) & - & - & - & 8 & 8 & 8 \\ Steam/Fuel & 0.61 & 0.64 & 0.65 & 0.65 & 0.65 & 0.66 \\ Length test (min) & 120 & 120 & 120 & 121 & 66 & 50 \\ H\({}_{2}\)O conversion (\%) & 38.91 & 57.86 & 56.07 & 28.14 & 32.92 & 35.04 \\ C conversion (\%) & 66.12 & 68.52 & 75.41 & 62.50 & 67.51 & 90.17 \\ Gas yield (Nm\({}^{3}\)/kg) & 1.35 & 1.41 & 1.37 & 1.03 & 1.15 & 1.46 \\ H\({}_{2}\) (\%) dry N\({}_{2}\)-free & 55.11 & 54.28 & 53.16 & 49.78 & 49.38 & 48.48 \\ CO (\%)dry N\({}_{2}\)-free & 22.75 & 27.91 & 31.03 & 19.93 & 23.01 & 30.69 \\ CO\({}_{2}\) (\%) dry N\({}_{2}\)-free & 18.56 & 13.53 & 12.87 & 26.92 & 24.73 & 17.76 \\ CH\({}_{4}\) (\%) dry N\({}_{2}\)-free & 3.58 & 4.28 & 2.95 & 3.37 & 2.89 & 3.08 \\ NH\({}_{3}\) (ppm) dry N\({}_{2}\)-free & 1094 & 1355 & 761 & 902 & 957 & 886 \\ H\({}_{2}\) (Nl/min) & 10.12 & 9.65 & 10.07 & 7.63 & 7.80 & 10.06 \\ Char yield (\%) & 17.06 & 8.93 & 8.00 & 14.91 & 7.86 \\ \(\eta_{\rm CC}\) (\%) & 57.11 & 61.27 & 58.21 & 44.58 & 42.17 & 58.94 \\ Tar content (mg/Nm\({}^{3}\)) & 2461 & 938 & 481 & 2259 & N.A. & 305 \\ Mass balance (err \%) & 1.25 & 6.11 & 4.95 & 3.25 & 5.62 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of lignite gasification tests. Figure 3: Particle size distribution of olivine. The length of tests #5 and #6 was shorter compared to the previous tests; however, the gas composition analysed online during the tests reached a steady state after around 10 min, giving stable values for the entire length of the test; a 60 min period was therefore considered sufficient for an evaluation of the results. The amounts of char and ash produced during gasification were evaluated in relation to the total amount of lignite fed during the experimental run. Consequently, the evaluation of their content was not affected by the length of the test. From the comparison of the results obtained in the first three tests, it is possible to observe that, in general, at higher temperatures, the product gas has a higher quality in terms of the H\({}_{2}\)O and C conversions and gas yield. Moreover, the gas composition in the tests carried out at 850 \({}^{\circ}\)C displays an increase in CO and decrease in CO\({}_{2}\), probably caused by the higher extent of steam gasification reactions that takes place for higher temperatures, and the lower extent of the WGS reaction, enhanced at lower temperatures (\(\sim\)600 \({}^{\circ}\)C). Starting from the syngas compositions obtained in the six experimental runs, the equilibrium contents of CO and CO\({}_{2}\) were calculated with the software Aspen Plus, in order to compare the experimental and equilibrium compositions. The equilibrium compositions calculated were approximately equal to the gas compositions obtained in the experimental tests, meaning that the WGS reaction had reached equilibrium. For higher temperatures, the char yield is also lower, which is proof of the higher conversion of carbon and thus lower amount of solid un-reacted residual char. Furthermore, the amount of tar produced at higher temperatures is lower compared to the cases with lower temperatures. In the tests conducted at 750 \({}^{\circ}\)C, the tar content is around 2.5 g/Nm\({}^{3}\), while at 850 \({}^{\circ}\)C, it reduces to 0.5 g/Nm\({}^{3}\). Regarding the tar content in general, it was observed that in tests with lignite, the amount of tar produced is lower compared to in similar tests carried out with biomass in the same experimental reactor with olivine as bed material [27; 29; 30].