**7. Biomass conversion**

Biomass feedstock can be converted into useful forms of energy using a number of different processes. This is possible in the country because there is potential biomass that could be used for the process. However, before conversion processes can be initiated, factors that in‐ fluence the choice of conversion [17] have to be established. The critical factors are:-


Biomass can be converted into three main products [18].Two related to energy i.e. power or heat generation and transportation, and one as a chemical feedstock. Conversion of biomass to energy is usually undertaken using two main technologies: Thermo – chemical and biochemical. Within thermo-chemical conversion four process options are available. The proc‐ esses are: Direct combustion, Gasification, pyrolysis and liquefaction. Thermo-chemical conversion route is given in Figure 14.

*Direct combustion* is the process of burning biomass in air. It is used to convert the chemical energy stored in biomass into heat, mechanical power, or electricity using items such a stoves, furnaces, boilers steam turbines, turbo-generators, etc. However, direct combustion

*Liquefaction* is a process, which tries to clear the large biomass feedstock macro molecules by applying high pressure and how level of heat. Common process parameters of temperature

faction are liquid fuels with similar consistency like that of pyrolysis processes. Given that Liquefaction require high pressure reactor there are only a few commercially available Liq‐

Table 9 summarizes the findings of performance of thermo-chemical conversion technology and ranking the applicability. The assessments vary from very poor (-), good (+) and very

From Table 9, it can be concluded that Gasification process has very good conversion level and applicability. Hence, the process is suitable biomass conversion technology in the country.

Water diluted biomass such as sludge, manure, vegetable waste are difficult to be converted by thermo- chemical conversion process due to difficulties in vaporizing the water present in the biomass. Hence, for feed stock with significantly more than 50% moisture content, it is usually not to apply thermo-chemical technology at comparatively at low temperature is an

Two main processes are employed: anaerobic digestion, where biomass is converted by bac‐ teria, and fermentation using yeast to convert biomass. Anaerobic digestion is the standard solution for treating very high dilution levels of biomass, fermentation is used to biomass

C and pressure ranges of 50-200 bar [19, 22], the main products of lique‐

Biomass Conversion to Energy in Tanzania: A Critique

http://dx.doi.org/10.5772/ 52956

261

**Gasification Pyrolysis Other conversion**

does not a fuel suitable for use in gas turbine, etc.

*Ranking of thermo-chemical conversion technology*

**Table 9.** Ranking of thermo-chemical conversion Technology

**7.2. Bio-chemical conversion**

economic alternative solution.

containing lower amount of water. [20].

**ACTION PROCESS**

Conversion level +++ ++ ++ Simplicity ++ ++ - Plant cost ++ ++ - Applicability to scale +++ ++ - Conversion time + + +

in the range 200-4000

good (+++).

uefaction processes. [22].

**Figure 14.** Biomass thermo-chemical conversion route

#### **7.1. Thermo-Chemical conversion**

#### *7.1.1. Gasification*

Gasification is the conversion of biomass into a combustible gas mixture by the partial oxi‐ dation of biomass at high temperature [19] resulting in production of (CO), H2, and trace of Methane (CH4). The mixture of these gases is called producer gas. Producer gas can be used to run internal combustion engine, also it can be used as substitute for furnace oil in direct heat applications. The gas can be used to produce methanol-an extremely attractive chemi‐ cal which is used as a fuel for heat engines as well as chemical feed stock for industries. Since any biomass material can undergo gasification, this process is much more attractive than ethanol production or biogas where only selected materials can produce the fuel. Gasi‐ fication conversion is suitable for Tanzanian environment.

#### *7.1.2. Pyrolysis*

Pyrolysis is the process of converting biomass to liquid termed bio-oil, solid and gaseous fraction, by heating the biomass in the absence of air to around 500o c. Pyrolysis is used to produce predominantly bio-oil. The product i.e. bio-oil can be used in engines and turbine. Obstacle of Pyrolysis is the water dilution [20] of the bio-oil and it's corrosively due to the broad range of organic and inorganic compounds. Hence, the application of bio-oil as a raw material for electricity generation technology is difficult [21].

#### *7.1.3. Other conversions*

Other conversions include direct combustion of biomass and liquefaction.

*Direct combustion* is the process of burning biomass in air. It is used to convert the chemical energy stored in biomass into heat, mechanical power, or electricity using items such a stoves, furnaces, boilers steam turbines, turbo-generators, etc. However, direct combustion does not a fuel suitable for use in gas turbine, etc.

*Liquefaction* is a process, which tries to clear the large biomass feedstock macro molecules by applying high pressure and how level of heat. Common process parameters of temperature in the range 200-4000 C and pressure ranges of 50-200 bar [19, 22], the main products of lique‐ faction are liquid fuels with similar consistency like that of pyrolysis processes. Given that Liquefaction require high pressure reactor there are only a few commercially available Liq‐ uefaction processes. [22].

### *Ranking of thermo-chemical conversion technology*

to energy is usually undertaken using two main technologies: Thermo – chemical and biochemical. Within thermo-chemical conversion four process options are available. The proc‐ esses are: Direct combustion, Gasification, pyrolysis and liquefaction. Thermo-chemical

Gasification is the conversion of biomass into a combustible gas mixture by the partial oxi‐ dation of biomass at high temperature [19] resulting in production of (CO), H2, and trace of Methane (CH4). The mixture of these gases is called producer gas. Producer gas can be used to run internal combustion engine, also it can be used as substitute for furnace oil in direct heat applications. The gas can be used to produce methanol-an extremely attractive chemi‐ cal which is used as a fuel for heat engines as well as chemical feed stock for industries. Since any biomass material can undergo gasification, this process is much more attractive than ethanol production or biogas where only selected materials can produce the fuel. Gasi‐

Pyrolysis is the process of converting biomass to liquid termed bio-oil, solid and gaseous

produce predominantly bio-oil. The product i.e. bio-oil can be used in engines and turbine. Obstacle of Pyrolysis is the water dilution [20] of the bio-oil and it's corrosively due to the broad range of organic and inorganic compounds. Hence, the application of bio-oil as a raw

c. Pyrolysis is used to

conversion route is given in Figure 14.

260 New Developments in Renewable Energy

**Figure 14.** Biomass thermo-chemical conversion route

fication conversion is suitable for Tanzanian environment.

material for electricity generation technology is difficult [21].

fraction, by heating the biomass in the absence of air to around 500o

Other conversions include direct combustion of biomass and liquefaction.

**7.1. Thermo-Chemical conversion**

*7.1.1. Gasification*

*7.1.2. Pyrolysis*

*7.1.3. Other conversions*

Table 9 summarizes the findings of performance of thermo-chemical conversion technology and ranking the applicability. The assessments vary from very poor (-), good (+) and very good (+++).


**Table 9.** Ranking of thermo-chemical conversion Technology

From Table 9, it can be concluded that Gasification process has very good conversion level and applicability. Hence, the process is suitable biomass conversion technology in the country.

#### **7.2. Bio-chemical conversion**

Water diluted biomass such as sludge, manure, vegetable waste are difficult to be converted by thermo- chemical conversion process due to difficulties in vaporizing the water present in the biomass. Hence, for feed stock with significantly more than 50% moisture content, it is usually not to apply thermo-chemical technology at comparatively at low temperature is an economic alternative solution.

Two main processes are employed: anaerobic digestion, where biomass is converted by bac‐ teria, and fermentation using yeast to convert biomass. Anaerobic digestion is the standard solution for treating very high dilution levels of biomass, fermentation is used to biomass containing lower amount of water. [20].
