## 3 Results and Discussion  
### Impact of Moisture Content on Tar Formation  
The drying of biomass is required for thermal gasification to achieve higher efficiency. Drying of the biomass is achieved by using solar energy or waste heat. Moreover, biomass is hygroscopic, and therefore, even after it is dried, it can still absorb moisture from the atmosphere. [PERSON] et al. studied the effect of moisture content level in fuel. The study established that a fixed air-flow rate and drier fuels have higher burning rates in comparison to wetter fuels [19]. When utilizing biomass as fuel, its high moisture content affects tar formation in the syngas. Moreover, steam gasification involves the reaction of steam with solid carbonaceous feedstocks such as wood pellet biomass, or carbon-containing wastes to produce syngas. Syngas is a gas mixture fuel consisting primarily of hydrogen, carbon monoxide, and very often some carbon dioxide. In order to reduce undesired product including tar formation, the steam gasification of biomass is one alternative way to produce syngas with a high flammable gas production [20; 21; 22]. The gasification process can be classified as an incineration technology. During the process, combustion is the chemical reaction of biomass gasification and tar production. Homogeneous and heterogeneous reactions are displayed in reaction R1 to R16 as shown in Table 4. The distributed air in the oxidation zone moves with the feedstock to the gasifier. All the products are driven to pass through the oxidation zone, resulting in the effect of tar production. In case water (H\({}_{2}\)O) is present in the reaction, CO\({}_{2}\) can be produced by the water gas shift reaction (WGS) to generate more production of the gas H\({}_{2}\) (reaction R10). Additionally, the aqueous-phase reforming through bimetallic catalysts can generate the production of the gases CO\({}_{2}\) and H\({}_{2}\). The steam reforming process needs to be carried out at high temperatures, where the increasing temperature drives the endothermic reaction from hydrocarbons (reaction R13). The temperature increases in the steam reforming process, enhancing tar removal and increasing H\({}_{2}\) and CO concentration [23]. The reaction can be seen in the Table 4.  
Even though tar problem is lately a primary concern, the terminology of tar is not well defined. According to [PERSON] et al., different compounds with a molecular weight more than 78 (benzene) can be found and be defined as tar compounds [9; 10]. The tar sample was quantified using gas chromatography analysis and yielded the tar formation. Additionally this research has focused on the nine tar compounds including phenol (C\({}_{6}\)H\({}_{5}\)OH), toluene (C\({}_{7}\)H\({}_{8}\)), indene (C\({}_{9}\)H\({}_{8}\)), naphthalene (C\({}_{10}\)H\({}_{8}\)), biphenyl (C\({}_{12}\)H\({}_{10}\)), fluorene (C\({}_{13}\)H\({}_{10}\)), phenanthrene (C\({}_{14}\)H\({}_{10}\)), fluoranthene (C\({}_{16}\)H\({}_{10}\)), and pyrene (C\({}_{16}\)H\({}_{10}\)). This research focused on the nine tar compounds because all of them appeared in every experiment's results. These nine tar compo  
Figure 3: **(a)** Shimadzu GC-MS QP2010 Plus (b) Dryer–evaporation machine (IRIS OHYAMA) (c) Tar-weight measurement machine (Chyo JL-200). All nine compounds were measured through tar concentration using Equation (2) shown below:  
\[C_{t}=\frac{W_{t}}{V_{s}} \tag{2}\]  
where \(C_{t}\) is the concentration of tar in the syngas (g/Nm\({}^{3}\)), \(W_{t}\) is the weight of tar in the syngas (g), and \(V_{s}\) is the normal volume of syngas (Nm\({}^{3}\)). Additionally, the result of tar formation and concentration with a variation of moisture content was calculated, and the results are shown in Figure 4.  
Tar formation on air-flow rate 80 L/min with 2 wt. %, 4 wt. %, and 6 wt. % is shown in Figure 4 and the graph is displayed with an error bar chart. The concentration in tar formation in descending order includes phenol, naphthalene, phenanthrene, fluorene, biphenyl, fluoranthene, pyrene, toluene, and indene.