03.08.2015   Pretreatment Techniques for Biofuels and Biorefineries

Experi2ental Results

Figure 12.7 and Table 12.2 represent the experimental and calculated data of investigation of the plasma gasification of biomass using wood waste as the example.

Fig. 12.7 Time dependence of main experimental parameters: a Temperature (1 wall in pyrolysis zone; 2 wail in oxidizing zone; 3 wall in reduction zone; 4 syngas at the outlet); b Dry syngas composition (5 H2; 6 CO; 7 N2; 8 CO2; 9 the others); c Mass flows (10 fuel; 11 air; 12 syngas; 13 steam); d Energy flows. (14 energy losses; 15 fuel LHV; 16 plasma; 17 syngas LHV; 18 sensible heat)

Feedstock consumption was determined by differences of mass streams of major elements (carbon, hydrogen, oxygen, and nitrogen) assuming that ash content and the nitrogen content in wood are negligibly small. The fuel element composition was determined by mean values of flow rates of carbon, hydrogen, and oxygen of fuel for two intervals. The lower heating value (LHV) was estimated by this composition (by formula for an estimation of heating value of biomass [92]).

The mode of wood plasma gasification was observed on the interval 9:43-16:30. About 606.34 kg of wood was processed during this period according to the estimates, and actually about 609.98 kg of wood was loaded into the reactor in the course of the experiment. That validates the technique of experimental data processing.

The experimental results were compared with calculations for two regimes with constant air plasma flow rate and powers of plasma torches (see Table 12.2). The comparison showed that the data agreed well for the chemical energy yields and are satisfactory for syngas composition.

Calculations were carried out assuming adiabatic process and thermodynamic equilibrium of gasification products composition. On these modes, the composition of raw materials which matches to wood with moisture of 8-10 % also had been

Table 12.2 Comparison of averaged experimental data with the calculation results

Parameter

Time period of experiment (hh:mm) 9:30-11:36 13:36-15:12 Exp. Calc. Exp. Calc.

Mass balance per 1 kg of Inlet

Wood waste

1.000

1.000

1.000

1.000

feedstock (kg)

Air plasma

1.538

1.538

1.692

1.692

Total

2.538

2.538

2.692

2.692

Outlet

Syngas

2.428

2.402

2.549

2.536

Steam

0.110

0.136

0.142

0.155

Total

2.538

2.538

2.692

2.692

Syngas yield (Nm3/kg of feedstock)

2.633

2.484

2.726

2.571

Syngas composition, (%vol)

H2

20.01

19.45

18.25

19.01

CO

30.87

35.26

26.92

30.78

N2

40.25

40.82

43.39

43.40

O2

0.01

0.00

0.22

0.00

Ar

0.48

0.49

0.54

0.52

CO2

7.33

3.98

9.15

6.28

CH4

1.05

0.00

1.53

0.00

Syngas LHV (MJ/Nm3)

5.558

6.001

5.036

5.440

Energy balance per 1 kg Inlet

Wood waste

16.79

16.79

16.62

16.62

of feedstock (LHV basis)

Air plasma

3.21

3.21

1.46

1.46

Total

20.00

20.00

18.08

18.08

Outlet

Syngas

14.63

14.91

13.73

13.99

Sensible heat

3.27

5.09

2.89

4.09

Heat losses

2.10

—

1.46

—

Total

20.00

20.00

18.08

18.08

Syngas LHV/Plasma energy ratio

4.565

4.651

9.381

9.555

determined. Well data agreement on the chemical energy yields was explained by the fact that the air plasma flow rate was more than stoichiometric in 2.8-3.0 times. It led to a considerable shortening of a reduction zone, therefore heat losses did not significantly affect syngas composition. More considerable difference in composition is caused by high methane stability and water-gas shift reaction at weak reaction rates and branch pipe sampling zones. As a whole, comparison results confirm usability of equilibrium approach for the estimation of plasma gasification key parameters.

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