**2. Biomass upgrading as energy source**

In future energy supply scheme, biomass can play an important role in supplying renewable energy [6]. Biomass is an attractive energy source as a renewable energy, especially as a sustainable carbon carrier.

#### **2.1. Biomass**

In the last four decades, researchers have been focusing on alternate fuel resources to meet the

Among different sources of renewable energy, biomass residues are the most potential raw material due to their inherent capability to store solar energy and amenability to subsequent conversion to convenient solid, liquid and gaseous fuels. Further, biomass is a renewable source of carbon through a global carbon cycle and can be a source to make

With serious concern about deforestation as one of the causes of global warming, especially in developing countries, and need for reforestation to maintain global ecological balance, increasing demand is being made for proper utilization of agro and forestry biomass residues

Torrefaction is a recently well-known technology which can change biomass properties to become a higher energy quality biofuel. From a viewpoint of chemical components, torrefaction process comprises mainly the removal of oxygen to yield a final solid product. The torrefied biomass product contains a lower O/C ratio compared to the original raw

Torrefaction occurs through the heating of biomass below 300°C in the absence of oxygen, where moisture and volatile materials are lost. It was first applied in 1939, then in 1984 but forgotten until recently. Published papers and patents issued were from late 2000s to present.

The Philippines is mainly an agricultural country with a land area of 30 million hectares, 47% of which is agricultural. The total area devoted to agricultural crops is 13 million hectares distributed among food grains, food crops and non-food crops. Among the crops grown, rice, coconut and sugarcane are major contributors to biomass energy resources. The most common agricultural residues are rice husk, rice straw, coconut husk, coconut shell and

In order to utilize agricultural crop residues and to improve its biomass properties, there is a need to create new knowledge and apply it to be more productive focusing on creativity and innovation. Agricultural crop residues that are abundant in the Philippines such as coconut leaves [4, 5], cogongrass [5], and rice husk [5], were utilized to produce solid fuel by torrefaction for use as alternative source of energy. The design of the torrefaction process based on the

In future energy supply scheme, biomass can play an important role in supplying renewable energy [6]. Biomass is an attractive energy source as a renewable energy, especially as a sus-

It can convert biomass wastes to solid fuel affordably without complications.

ever increasing energy demand and to avoid dependence on crude oil [2].

many chemicals.

44 Gasification for Low-grade Feedstock

biomass.

bagasse [3].

tainable carbon carrier.

to play the role previously carried out by wood.

biomass characteristics was researched and developed.

**2. Biomass upgrading as energy source**

Biomass can generally be defined as any hydrocarbon material which mainly consists of carbon, hydrogen, oxygen and nitrogen. Sulfur is also present in less proportion. Biomass resources include many natural and derived materials such as woody and herbaceous species, wood wastes, bagasse, agricultural residues, waste paper, municipal solid wastes, sawdust, biosolids, grass, food wastes, animal wastes, aquatic plants, and algae, etc. Woody materials are preferred among biomass resources because they contain much higher energy value. Most important feature of biomass is its inherent climate neutral behavior. When biomass is grown in a sustainable way, during the life cycle of biomass production and application, no net amount of CO2 emits into the atmosphere. The CO2 released during the utilization of biomass is stored in return in the biomass resource through photosynthesis, which means a climate neutral carbon cycle of CO2 . Biomass is considered as an environmentally friendly alternative energy source replacing fossil fuels because it is produced in nature by photosynthesis from CO2 and H<sup>2</sup> O [7].

On the other hand, some biomass properties are inconvenient, particularly its high oxygen content, a low heating value, a hydrophilic nature and high moisture content. Also, the energy accumulation to biomass through photosynthesis has known to be a process of low energy efficiency. The overall energy efficiency from solar energy to biomass energy is 1–3% [8]. Typical disadvantages of biomass are its tenacious and fibrous structure and its heterogeneous composition that makes process design and process control more complicated.

Biomass has unique characteristics that necessitate pre-processing before it can be stored, transported or used in various applications. Unlike fossil fuels which are mined at one location, biomass is often available seasonally in small quantities scattered over many locations [9]. Biomass is highly heterogeneous in quality and nature, and is available in low energy density form [10]. It has relatively high moisture content and consequently lower heating value compared to fossil fuels [11]. It is therefore often needs to be pre-treated to improve handling [12].

#### **2.2. Thermal conversion processes**

Burning biomass in an oxidative environment is the oldest conversion process practiced by man. Combustion, however, does not intend to produce value-added products in the form of fuels, chemicals or materials, as other thermochemical conversion technologies, but only heating value [13].

Thermal conversion processes can be categorized into combustion, gasification, pyrolysis and the emerging torrefaction technology according to the operating conditions. The products of the thermochemical processes are divided into a volatile fraction consisting of gases, vapors and tar components and a carbon rich solid residue [4].
