**3.4.2 Overall results**

This section shows the overall results of experiments with pelletized PEFB at different air flow rates in term of producer gas yield, feedstock consumption rate and cold gas efficiency. Table 9 presents the overall results for pelletized PEFB at different air flow rates.


Table 9. Overall results for pelletized PEFB at different air flow rates

From Table 9, although the maximum heating value of 4.77±0.29 MJ/Nm3 is taken place at the air flow rate of 33 Nm3/hr, the maximum cold gas efficiency of 55.76 % occurs at the air flow rate of 18 Nm3/hr. In additional to heating value, the ratio of producer gas yield to fuel consumption plays an important role on cold gas efficiency, as clearly seen from Equation 2. At the air flow rate of 33 Nm3/hr, 1 kg of pelletized PEFB can produce 1.83 Nm3 of producer gas, whereas 1 kg of pelletized PEFB can produce 2.34 Nm3/hr of producer gas at the air flow rate of 18 Nm3/hr which is the condition that the maximum producer gas can be yielded from 1 kg of feedstock.

#### **3.4.3 Temperature distribution**

To identify the temperature distribution in each reaction zone, the gasification process of pelletized PEFB is only investigated and the result is shown in Figure 14.

The reaction zone for the experiments with different air flow rates is almost identical. Drying zone for moisture removal taking place at the top of gasifier (a height of 70-80 cm) has the temperature of less than 200 °C for all air flow rates. Next reaction zone is pyrolysis zone, 50-70 cm high, which has the pyrolysis temperature of 200-600 °C for all air flow rates. At the height of 30-50 cm, where air is introduced into gasifier, the combustion process occurs and the combustion temperature is 600-1000 °C. At the bottom of a downdraft gasifier (10-30 cm), where the reduction process is taken place, the temperature in the reduction zone is considerable reduced to 400-800 °C.

Fig. 14. Temperature distribution along the height of gasifier at different air flow rates

#### **3.5 Conclusion**

142 Renewable Energy – Trends and Applications

value of 4.20±0.31 MJ/Nm3 and the lower heating value increases to 4.77±0.29 MJ/Nm3 at the air flow rate of 33 Nm3/hr. The increase in the lower heating value is resulted from the

From the experiments with both as received PEFB and pelletized PEFB, it can be concluded that using pelletized PEFB can provide more stable gasification process than using asreceived PEFB and the relevant reactions can approach their equilibriums; hence, pelletized PEFB is more proper to be used as fuel in gasification process than as-received PEFB. Since the producer gas will further be used as fuel in a combustion engine generator for electricity production, the heating value of producer is the major parameter to be concerned. The maximum heating value of 4.77±0.29 MJ/Nm3 is achieved from gasification of pelletized

This section shows the overall results of experiments with pelletized PEFB at different air flow rates in term of producer gas yield, feedstock consumption rate and cold gas efficiency.

15 24.50 10.74 4.20±0.31 49.71 18 28.70 12.24 4.58±0.29 55.76 21 34.80 15.65 4.60±0.26 53.15 27 41.24 21.64 4.73±0.55 46.80 33 48.89 26.66 4.77±0.29 45.42

From Table 9, although the maximum heating value of 4.77±0.29 MJ/Nm3 is taken place at the air flow rate of 33 Nm3/hr, the maximum cold gas efficiency of 55.76 % occurs at the air flow rate of 18 Nm3/hr. In additional to heating value, the ratio of producer gas yield to fuel consumption plays an important role on cold gas efficiency, as clearly seen from Equation 2. At the air flow rate of 33 Nm3/hr, 1 kg of pelletized PEFB can produce 1.83 Nm3 of producer gas, whereas 1 kg of pelletized PEFB can produce 2.34 Nm3/hr of producer gas at the air flow rate of 18 Nm3/hr which is the condition that the maximum producer gas can be

To identify the temperature distribution in each reaction zone, the gasification process of

The reaction zone for the experiments with different air flow rates is almost identical. Drying zone for moisture removal taking place at the top of gasifier (a height of 70-80 cm) has the temperature of less than 200 °C for all air flow rates. Next reaction zone is pyrolysis zone, 50-70 cm high, which has the pyrolysis temperature of 200-600 °C for all air flow rates. At the height of 30-50 cm, where air is introduced into gasifier, the combustion process occurs and the combustion temperature is 600-1000 °C. At the bottom of a downdraft gasifier (10-30 cm), where the reduction process is taken place, the temperature in the

Lower heating value (MJ/Nm3)

Cold gas efficiency (%)

Table 9 presents the overall results for pelletized PEFB at different air flow rates.

Table 9. Overall results for pelletized PEFB at different air flow rates

pelletized PEFB is only investigated and the result is shown in Figure 14.

reduction zone is considerable reduced to 400-800 °C.

Fuel consumption rate (kg/hr)

increase in combustible gases, e.g. H2 and CO with increasing air flow rate.

PEFB at the air flow rate of 33 Nm3/hr.

Producer gas yield (Nm3/hr)

yielded from 1 kg of feedstock.

**3.4.3 Temperature distribution** 

**3.4.2 Overall results** 

Air flow rate (Nm3/hr)

> From the experiments in a laboratory scale downdraft gasifier, it can be implied that both as received and pelletized PEFB has a potential to be used as fuel for producer gas production. However, pelletized PEFB is more suitable than as received PEFB because their reactions in gasification process are more stable and can approach equilibrium. The producer gas obtained from gasification of pelletized PEFB at the air flow rate of 33 Nm3/hr which is the most suitable operating condition consists of 19.02 % wt. CO, 13.32 % wt. H2, 2.78 % wt. CH4 and 16.58 % wt. CO2. It heating value of 4.77 MJ/Nm3 can be achieved with the cold gas efficiency of 45.42 %. The reaction temperature has been classified on 4 different zones; less than 200 °C for drying zone, 200-600 °C for pyrolysis zone, 600-1000 °C for oxidation zone and 400-800 °C for reduction zone.
