## 3 Results and Discussion
### Impact of Moisture Content on Tar Classification  
A method for analysis of tar classification in syngas from biomass gasification has been actively studied. The purpose of this analysis was to separate the tar classification into two categories, including light and heavy tar. Light tar is mainly composed of volatile and semi-volatile aromatic and phenolic compounds, while heavy tar contains polar non-volatile compounds. Light tar may pass through a capillary gas chromatography (GC) column while heavy tar might damage the operation of the equipment. According to [PERSON] et al., the differentiation of tar classification based on molecular weight can be determined by gas chromatography [25].  
The biomass gasification generated syngas and tar, though the feedstock with higher moisture content was difficult to ignite. Its gasification resulted in low gas yield and higher tar production. In the downdraft gasifier, higher moisture content reduced the temperature of the reaction zone, leading to the deposition of tar in the gasifier. In the experiment, tar was divided as light and heavy, with phenol as the standard parameter. If the compounds have a molecular weight less than that of phenol, they  
Figure 4: Tar formation on air-flow rate at 80 L/min with variation of moisture content 2 wt. %, 4 wt. %, and 6 wt. %.  
are included as light tar. Otherwise, if the chemical compounds have a molecular weight more than that of phenol, they are included as heavy tar.  
Figure 5 shows the formation of light and heavy tar in the biomass gasification process with variation in moisture content. In Figure 5a, the tar formation in moisture content 2 wt. % with an air-flow rate of 80 L/min shows different results. The tar concentration of light tar is 13.18 g/Nm\({}^{3}\), which is equal to 15.70% of the total tar. The heavy tar has a concentration of 70.77 g/Nm\({}^{3}\), which is equal to 84.30% of the total of 83.95 g/Nm\({}^{3}\). Figure 5b shows the tar classification with a moisture content of 4 wt. % and light tar 2.81 g/Nm\({}^{3}\), which is equal to 3.42%. The heavy tar is 79.41 g/Nm\({}^{3}\), which is equal to 96.58% of the total concentration of 82.22 g/Nm\({}^{3}\). Figure 5c shows the same parameter with the moisture content of 6 wt. %, where the concentration of light tar is 1.55 g/Nm\({}^{3}\) or 2.16%, while heavy tar is 70.32 g/Nm\({}^{3}\) or 97.84% of the total 71.87 g/Nm\({}^{3}\). This result shows that the production of light tar decreased along with an increase in moisture content while the heavy tar increased along with an increase in moisture content. This is the evidence to show that the lowest moisture content of 2 wt. % is better for the biomass gasification process due to a lower yield of heavy tar. More production of heavy tar leads to extensive failure and plugging of the valve and reduces the performance of the biomass operating system. The light tar was much more easily burnt compared to the heavy tar. This was due to the more volatile chemical composition of light tar, such as the hydrocarbon compounds.  
Figure 5: **(a)** Tar formation in light and heavy tar in moisture content 2 wt. % **(b)** Tar formation in light and heavy tar in moisture content 4 wt. % **(c)** Tar formation in light and heavy tar in moisture content 6 wt. %