11.08.2015   BIOFUELS FROM ALGAE

YIELDS AND CHARACTERISTICS OF PYROLYSIS OF ALGAL BIOMASS

The microalga used in this experiment is a nongenetially modified organism (non-GMO) adapted to a culture medium containing vinasse from an ethanol distillery. The culture was carried in open ponds (Figure 7.4) at an Ourofino Agronegcicio biofuels facility.

After being cultured, the biomass was flocculated, centrifuged, and dried. Dried algal bio­mass containing about 12% moisture was used in a fast pyrolysis system (see Figure 7.5).

The conditions of fast pyrolysis were:

Reactor temperature: 485 ± 15

Reactor pressure: 1.2 atm

Mass flow: 17kg/h

Air flow: 1.7 kg/h

The results achieved from fast pyrolysis with algal biomass are shown in Table 7.3. Elemental analyses of each fraction were carried out and are presented in Table 7.4.

To analyze the potential of fuel use, the lower heating value (LHV) was determined according to the method ABNT/NBR11956. Results are shown in Table 7.5.

Bio-oil was the fraction with higher LHV, presenting values very near some vegetable oils. For example, soy oil has an LHV of 9,500.00 kcal/kg, and babassu oil (a typical Brazilian coconut) has around 9,140 kcal/kg.

The obtained algal coal was also superior to some solid fuels, of which the LHV is around

4,0 kcal/kg.

FIGURE 7.4 Open ponds for microalgae cultivation at Ourofino Agronegocio, Brazil.

FIGURE 7.5 Fast pyrolysis equipment.

TABLE 7.3 Yields of Algal Biomass Fast Pyrolysis Experiments Carried Out at Ourofino AgronegOcio Biofuels Facilities (DalmasNeto, 2012).

Product

Yield (%) (m/m)

Bio-oil

17.4

Acid extract

32.3

Coal

10.8

Gases

39.5

TABLE 7.4 Elemental Analysis of Each Product Generated by Fast Pyrolysis of Algal Biomass. Acid Extract Values are in Terms of Dry Base; The others are in Terms of Wet Base (DalmasNeto, 2012).

Material

Carbon (%)

Hydrogen (%)

Nitrogen (%)

Sulfur (%)

Oxygen (%)

Ash (%)

Moisture (%)

Biomass

45.32

6.85

3.93

0.25

34.35

4.12

5.20

Coal

52.16

3.14

6.86

0.17

15.44

19.08

3.11

Bio-oil

65.49

10.17

1.58

0.07

19.70

0.15

2.73

Extract

64.30

10.44

2.08

0.08

20.31

0.28

0.00

TABLE 7.5 Lower Heating Value (LHV) of Each Product from Fast Pyrolysis (DalmasNeto, 2012).

Fraction

LHV (kcal/kg)

Biomass

5,060

Coal

5,167

Bio-oil

8,071

Acid extract

7,323

It is important to consider the high mass density of the bio-oil: 1,230.00 kg/m3. Volumetric energetic density was then calculated as 9,927.33 kcal/L, which means the amount of energy that 1 liter of bio-oil is capable of providing. This value is 15% higher than diesel oil (8,620 kcal/L) (DalmasNeto, 2012).

The average cost of one tonne of microalgal biomass is about US$310; one liter of bio-oil produced by this technology in pilot scale is near US$1.20 per liter. This production cost will probably lower as technology scales up. Bio-oil can provide 85% of the energy that diesel oil can provide (7,922 kcal/US$ from diesel versus 6,746 kcal/US$ from bio-oil), which costs around US$1.28/L. This comparison shows the competitiveness of such bio-oil technology.

7.2 CONCLUSIONS

The technology of fast pyrolysis of algal biomass for the production of bio-oil presented very interesting results, which, combined with low cost and simplicity of operation, make this technology a potential alternative carbon-free-emission fuel process.