**6. Results and discussion**

#### **6.1. Characterization of the raw and torrefied biomass**

#### *6.1.1. TGA*

TGA is very important in the torrefaction of renewable biomass to establish the thermal properties of the dried biomass [4].

The thermogravimetry profile of dried coconut leaves in **Figure 4** shows an onset temperature of 245°C that denotes the temperature at which weight loss begins. Starting from 5.679 g, a weight loss of 7.436% was observed. After which the weight drastically falls down until a temperature of 350°C is reached when a weight loss of 53.33% of its weight was recorded. This is called the first derivative peak temperature, also known as the inflection point. This indicates the point of greatest rate of change on the weight loss curve. It was reported that the higher the cellulosic content of the dried coconut leaves, the higher was the thermal degradation rate and the initial degradation temperature [4].

The TGA results for dried coconut leaves [4, 5], cogongrass [5] and rice husks [5] shown in **Table 1** provided the basis for the optimum operating temperatures (between 245 and 298°C) that were utilized in the torrefaction experiment.

**Figure 4.** Thermogravimetric profile of dried coconut leaves.

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**Figure 5.** Fuel characteristics of the raw and torrefied biomass.

#### *6.1.2. Heating value, proximate analysis*

The heating value obtained in a bomb calorimeter test represents the gross heat of combustion for the sample. This is the heat produced when the sample burns, plus the heat given up when the newly formed water vapor condenses and cools to the temperature of the [4].

The results of the experiments showed that torrefaction can improve the fuel properties of the biomass. The fuel characteristics of the raw and torrefied biomass are shown in **Figure 5**. **Figure 5(b)** shows the moisture content was reduced by an average of 67%. The heating values were increased to 20–26 MJ/kg, see **Figure 5(a)**. The fixed carbon was increased to 44–46%, see **Figure 5(d)**. The ash content increased to 9–28%, see **Figure 5(c)**. These values approach that of subbituminous coal that coal contains 42–52% carbon (on a dry, ash-free basis) and has calorific values ranging from about 19 to 26 MJ/kg.

The raw biomass low heating values are due to low fixed carbon content of about 45% and relatively high moisture content, typically about 50% [25]. Torrefaction significantly improved the heating values of the biomass (see **Figure 5a**). Improvement of heating value is due to increased fixed carbon. The fixed carbon content of torrefied biomass is high (25–40% depending on reaction conditions) [12, 15, 26]. The combustion property also improved; torrefied biomass burns longer due to larger percentage of fixed carbon [27]. Torrefaction reduces the O/C ratio and this makes the biomass better suited for gasification [26]. Gasification also produces less smoke during the process since smoke causing volatiles are driven off during torrefaction [28, 29].

Development of Torrefaction Technology for Solid Fuel Using Renewable Biomass http://dx.doi.org/10.5772/intechopen.76100 51

**Figure 4.** Thermogravimetric profile of dried coconut leaves.

**6. Results and discussion**

50 Gasification for Low-grade Feedstock

erties of the dried biomass [4].

and the initial degradation temperature [4].

*6.1.2. Heating value, proximate analysis*

that were utilized in the torrefaction experiment.

calorific values ranging from about 19 to 26 MJ/kg.

*6.1.1. TGA*

[28, 29].

**6.1. Characterization of the raw and torrefied biomass**

TGA is very important in the torrefaction of renewable biomass to establish the thermal prop-

The thermogravimetry profile of dried coconut leaves in **Figure 4** shows an onset temperature of 245°C that denotes the temperature at which weight loss begins. Starting from 5.679 g, a weight loss of 7.436% was observed. After which the weight drastically falls down until a temperature of 350°C is reached when a weight loss of 53.33% of its weight was recorded. This is called the first derivative peak temperature, also known as the inflection point. This indicates the point of greatest rate of change on the weight loss curve. It was reported that the higher the cellulosic content of the dried coconut leaves, the higher was the thermal degradation rate

The TGA results for dried coconut leaves [4, 5], cogongrass [5] and rice husks [5] shown in **Table 1** provided the basis for the optimum operating temperatures (between 245 and 298°C)

The heating value obtained in a bomb calorimeter test represents the gross heat of combustion for the sample. This is the heat produced when the sample burns, plus the heat given up when

The results of the experiments showed that torrefaction can improve the fuel properties of the biomass. The fuel characteristics of the raw and torrefied biomass are shown in **Figure 5**. **Figure 5(b)** shows the moisture content was reduced by an average of 67%. The heating values were increased to 20–26 MJ/kg, see **Figure 5(a)**. The fixed carbon was increased to 44–46%, see **Figure 5(d)**. The ash content increased to 9–28%, see **Figure 5(c)**. These values approach that of subbituminous coal that coal contains 42–52% carbon (on a dry, ash-free basis) and has

The raw biomass low heating values are due to low fixed carbon content of about 45% and relatively high moisture content, typically about 50% [25]. Torrefaction significantly improved the heating values of the biomass (see **Figure 5a**). Improvement of heating value is due to increased fixed carbon. The fixed carbon content of torrefied biomass is high (25–40% depending on reaction conditions) [12, 15, 26]. The combustion property also improved; torrefied biomass burns longer due to larger percentage of fixed carbon [27]. Torrefaction reduces the O/C ratio and this makes the biomass better suited for gasification [26]. Gasification also produces less smoke during the process since smoke causing volatiles are driven off during torrefaction

the newly formed water vapor condenses and cools to the temperature of the [4].

**Figure 5.** Fuel characteristics of the raw and torrefied biomass.

In some plant species, a significant fraction of the total biomass is not combustible and is recovered as ash from bioenergy processes. The amounts range from about 6% of dry weight in dried coconut leaves to about 9% in torrefied coconut leaves. Generally, the ash content of herbaceous biomass is higher than that of woody biomass. While ash weight content (in dry basis) values of less than 1% are expected for wood, different herbaceous biomass types have reported values ranging from less than 2% up to 8–10% or even up to 25% for rice husks. In waste fractions, the ash content may often be as high as 30–50% and is only scarcely less than 10% [30].

#### **6.2. The torrefaction process design**

#### *6.2.1. Feedstock grinding*

Standard-sized pellet mills generally require biomass that is ground to particles that are no more than 3 mm in size. Several types of equipment are available to carry out this task.

Above measures will make biomass technologies as an attractive option to potential users [36].

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53

Torrefaction can convert low-grade biomass to solid fuel with properties similar to subbituminous coal that can be used for industrial and domestic applications. Torrefaction results on coconut leaves showed that the moisture content was reduced by 67% compared to the raw material, and the heating values, fixed carbon, and ash content were increased from 20 to 26 MJ/kg, 44 to 46%, and 9 to 28%, respectively. These values approach that of typical subbituminous coal with calorific values ranging from about 19 to 26 MJ/kg. The proposed torrefaction process is cheaper, less complicated, and more convenient to handle compared to the

pyrolysis or gasification. It is appropriate and suitable for application with biomass.

1 Department of Chemical Engineering, University of Santo Tomas, Manila, Philippines

[1] Brožek M, Nováková A, Kolářová M. Quality evaluation of briquettes made from wood.

[2] Karunanithy C, Wang Y, Muthukumarappan K, Pugalendhi S. Physiochemical characterization of briquettes made from different feedstock's. Hindawi Publishing Corporation

[3] Bioenergy Consult. Biomass Energy Potential in the Philippines [Internet]. May 12, 2015. Available from: https://www.bioenergyconsult.com/tag/biomass-energy-in-philippines/

2 Department of Chemical Engineering, National Graduate School of Engineering,

**7. Conclusion**

**Figure 6.** The complete torrefaction process.

**Author details**

**References**

Lola Domnina B. Pestaño1,2\* and Wilfredo I. José2

\*Address all correspondence to: lbpestano@ust.edu.ph

University of the Philippines, Quezon City, Philippines

Research Agriculture Engineering. 2012;**58**(1):30-35

[Accessed: Sept. 13, 2017]

Biotechnology Research International. 2012;**2012**:165202. 12 pages

#### *6.2.2. Moisture control*

Maintaining an appropriate moisture level in your feedstock is vital for overall quality of the final pellets. For wood, the required moisture level of the feedstock is at or near 15%. Other types of biomass have other requirements—you may need to experiment a bit. Moisture can be removed from the feedstock by oven-drying or by blowing hot air over or through the particles. If the feedstock is too dry, moisture can be added by injecting steam or water into the feedstock [31].

#### *6.2.3. Torrefaction*

Torrefaction is usually performed in inert atmosphere at temperature below 300°C that aims to remove mostly the major hemicellulose contents from biomass structure [32, 33].

A typical torrefaction process is presumed to comprise drying of the biomass feedstock to have a biomass feed of constant moisture content to torrefaction, which also implies a more or less constant heat duty to be delivered to the torrefaction reactor. Furthermore, it is expected that the best destiny for the liberated torrefaction gas is to combust it to generate heat for the drying and torrefaction processes, which requires a combustible torrefaction gas [34].

#### *6.2.4. Pulverizing and pelletizing*

Torrefied biomass can be subjected to pulverizing and pelletizing to produce fuel pellets. A roller is used to compress the biomass against a heated metal plate called a "die." The die includes several small holes drilled through it, which allow the biomass to be squeezed through under high temperature and pressure conditions. If the conditions are right, the biomass particles will fuse into a solid mass, thus turning into a pellet [35].

The torrefaction process is quite simple as **Figure 6** shows. Our pre-feasibility study for a commercial plant shows an investment of USD 1 million, whereas a Belgian company offers USD 25 million. We are designing small-scale units that can be operated by Local Government Units (LGUs) at subsidized cost.

In order to promote the wider use of biomass resources for energy generation, three A's have to be satisfied: A—appropriate to varying local conditions, A—affordable to a wide sector of the population and A—available along with the necessary support services and program back-up.

Development of Torrefaction Technology for Solid Fuel Using Renewable Biomass http://dx.doi.org/10.5772/intechopen.76100 53

**Figure 6.** The complete torrefaction process.

Above measures will make biomass technologies as an attractive option to potential users [36].

#### **7. Conclusion**

In some plant species, a significant fraction of the total biomass is not combustible and is recovered as ash from bioenergy processes. The amounts range from about 6% of dry weight in dried coconut leaves to about 9% in torrefied coconut leaves. Generally, the ash content of herbaceous biomass is higher than that of woody biomass. While ash weight content (in dry basis) values of less than 1% are expected for wood, different herbaceous biomass types have reported values ranging from less than 2% up to 8–10% or even up to 25% for rice husks. In waste fractions, the

Standard-sized pellet mills generally require biomass that is ground to particles that are no more than 3 mm in size. Several types of equipment are available to carry out this task.

Maintaining an appropriate moisture level in your feedstock is vital for overall quality of the final pellets. For wood, the required moisture level of the feedstock is at or near 15%. Other types of biomass have other requirements—you may need to experiment a bit. Moisture can be removed from the feedstock by oven-drying or by blowing hot air over or through the particles. If the feedstock is too dry, moisture can be added by injecting steam or water into the feedstock [31].

Torrefaction is usually performed in inert atmosphere at temperature below 300°C that aims

A typical torrefaction process is presumed to comprise drying of the biomass feedstock to have a biomass feed of constant moisture content to torrefaction, which also implies a more or less constant heat duty to be delivered to the torrefaction reactor. Furthermore, it is expected that the best destiny for the liberated torrefaction gas is to combust it to generate heat for the

Torrefied biomass can be subjected to pulverizing and pelletizing to produce fuel pellets. A roller is used to compress the biomass against a heated metal plate called a "die." The die includes several small holes drilled through it, which allow the biomass to be squeezed through under high temperature and pressure conditions. If the conditions are right, the bio-

The torrefaction process is quite simple as **Figure 6** shows. Our pre-feasibility study for a commercial plant shows an investment of USD 1 million, whereas a Belgian company offers USD 25 million. We are designing small-scale units that can be operated by Local Government

In order to promote the wider use of biomass resources for energy generation, three A's have to be satisfied: A—appropriate to varying local conditions, A—affordable to a wide sector of the population and A—available along with the necessary support services and program back-up.

to remove mostly the major hemicellulose contents from biomass structure [32, 33].

drying and torrefaction processes, which requires a combustible torrefaction gas [34].

mass particles will fuse into a solid mass, thus turning into a pellet [35].

ash content may often be as high as 30–50% and is only scarcely less than 10% [30].

**6.2. The torrefaction process design**

*6.2.1. Feedstock grinding*

52 Gasification for Low-grade Feedstock

*6.2.2. Moisture control*

*6.2.3. Torrefaction*

*6.2.4. Pulverizing and pelletizing*

Units (LGUs) at subsidized cost.

Torrefaction can convert low-grade biomass to solid fuel with properties similar to subbituminous coal that can be used for industrial and domestic applications. Torrefaction results on coconut leaves showed that the moisture content was reduced by 67% compared to the raw material, and the heating values, fixed carbon, and ash content were increased from 20 to 26 MJ/kg, 44 to 46%, and 9 to 28%, respectively. These values approach that of typical subbituminous coal with calorific values ranging from about 19 to 26 MJ/kg. The proposed torrefaction process is cheaper, less complicated, and more convenient to handle compared to the pyrolysis or gasification. It is appropriate and suitable for application with biomass.
