# Steam Gasification of Lignite in a Bench-Scale Fluidized-Bed Gasifier Using Olivine as Bed Material
## 2 Materials and Methods
### Analysis of Products  
Downstream of the steam condensers and the vacuum pump, a slipstream of the product gas was sent to online gas analyzers for an evaluation of the composition. Online analyzers allowed H\({}_{2}\), CO, CO\({}_{2}\), CH\({}_{4}\), H\({}_{2}\)S, and NH\({}_{3}\) to be detected (ABB URAS, LIMAS, CALDOS, and ULTRAMAT 6 Siemens).  
The water content in the product gas was calculated from the quantity of water collected in the flasks connected to the steam condensers. The water conversion \(\eta_{vac}\) (\(\%\)) was thus calculated as  
\[\eta_{vac}=\frac{\dot{m}_{water,\ in}-\dot{m}_{water,\ out}}{\dot{m}_{water,\ in}}\times 100, \tag{1}\]  
where \(\dot{m}_{water,\ in}\) and \(\dot{m}_{water,\ out}\) are the mass flows of the water input and output, respectively.  
The quantity of dry product gas, measured by means of a mass flow controller, allowed the gas yield \(Y_{gas}\left(Nm^{3}/kg_{residual}\right)\) to be calculated:  
\[Y_{gas}=\frac{F_{gas,\ out}}{F_{feedstock,\ in}}, \tag{2}\]  
where \(F_{gas,\ out}\) is the total dry N\({}_{2}\)-free volume of gas flow produced, and \(F_{feedstock,\ in}\) is the mass flow of the input feedstock.  
From the analysis of the gas composition and the carbon content in the feedstock, it was possible to calculate the carbon conversion \(X_{C}\) (\(\%\)):  
\[X_{C}=\frac{n_{CO}+n_{CO_{2}}+n_{CH_{4}}}{n_{C_{in}}}\times 100, \tag{3}\]  
where \(n_{i}\) represents the moles of the \(i\) carbonaceous species in the product gas (CO, CO\({}_{2}\), and CH\({}_{4}\)), and \(n_{C_{in}}\) represents the total moles of C in the feedstock input.  
Post-combustion was carried out after gasification: an air stream was fed to the reactor and the gaseous products (CO and CO\({}_{2}\)) were analysed and quantified, in order to evaluate the amount of the residual un-reacted char in the reactor. From this result, it was possible to calculate the char yield \(Y_{char}\) (\(\%\)):  
\[Y_{char}=\frac{m_{char}}{m_{fedstock}}\times 100, \tag{4}\]  
where \(m_{char}\) is the mass of the residual char estimated by the post-combustion in the gasifier, and \(m_{feedstock}\) is the mass of the total feedstock fed.  
The cold gas efficiency \(\eta_{CG}\)(\(\%\)) was calculated as  
\[\eta_{CG}=\frac{LHV_{gas}F_{gas,\ out}}{LHV_{Bignite}F_{feedstock,\ in}}, \tag{5}\]  
where \(LHV_{gas}\) and \(LHV_{lightite}\) are the lower heating values of the gas produced and lignite, expressed in MJ/Nm\({}^{3}\) and MJ/kg, respectively.  
The liquid tar samples collected in the impinger bottles were analysed offline by means of HPLC (Hitachi \"Elite LaChrom\" L-2130) for the detection and quantification of heavy hydrocarbons in the product gas. The tar compounds chosen as representative of a typical tar composition [28] were as follows: phenol, toluene, styrene, indene, naphthalene, acenaphthylene, fluorene, phenanthrene, anthracene, fluoranthene, and pyrene.  
After each test, the bed material was extracted from the reactor and sieved, in order to separate the fly-ashes accumulated in the bed during the experimental run from the olivine particles; samples of ashes were thus collected for analysis after tests. Afterwards, the ashes were analysed by means of SEM/EDS and XRD analyses, in order to study their morphology and the present elements and compounds.