**1.1 Hydrogen fuel**

228 Sustainable Growth and Applications in Renewable Energy Sources

socio-economic position of the Malaysian rural population that involves 80,000 households. About 63% of coconut production, coconut fronds and shells represent the largest amount as residues (about 8%) (Ninth Malaysia Plan 2006-2010). Table 1 summarize the estimations of the current and potential selected agicultural wastes (biomass) utilizations in annual energy

Thermo-chemical conversion processes, including gasification, pyrolysis and combustion have been proven the best available technology to convert these renewable materials into valuables fuel (hydrogen) and fine chemical feedstock. However gasification process offers technologically more attractive and useful options for medium and large scale applications due to presence of non–oxidation conditions and lower green house gases emission. Fluidized bed gasifier is proven to be a versatile technology capable of burning practically any wastes combination with low emissions. The significant advantages of fluidized bed gasifier over conventional gasifiers include their compact furnaces, simple designs, effective gasification of wide variety of fuels, relatively uniform temperatures and ability to reduce

> **Current Annual Amount Used for Energy Purposes**

29.5 Wood 4.967 Wood

23.609 13.630 0.022

1.578

Fruit shells Fruit fibres Effluents

plants 11.54 Rice husks

Shells

Sugarcane 54.9 Bagasse 0.421 Leaves and

waste

Logging - - Residues 19.060

Table 1. Estimates of the energy productivity and biomass production and utilization (Ninth

**Current Annual Energy Potential of Utilised Biomass (million boe)** 

> 77.665 11.444 2.928 12.94

3.707 0.210

1.025 2.541

16.850 0.085 0.630

0.298

Pruned fronds EFB Effluents Replanting wastes

Effluents

Rice straws

0.785 Fronds 0.164

Pruning wastes Pod husks Replanting wastes

tops

sawdust 1.0

3.733 Tree bark and

emissions of carbon dioxide, nitrogen oxides and sulfur dioxides.

28.21 Fronds

Cocoa trees 80.33 N.A. N.A.

processing - Sawdust &

**Energy productivity (boe/ha/year)** 

productivity in Malaysia.

**Crops/ Activities** 

> Rubber trees

Paddy

Coconut trees

Timber

Malaysia Plan 2006-2010)

Oil Palms 88.7

Technology development for conversion of waste feedstock to hydrogen has an economical potential. Depletion of fossil fuel source such as oil, gas and coal is going to become the biggest problem in the near future. Therefore, hydrogen fuel from the biomass waste is the best supersede for fossil fuels. Hydrogen is not widely used today but it has a great potential as an energy carrier such as fuel cell that can be applied to power cars and factories and also for home usages in the future. In comparison with fossil fuels, 9.5 kg of hydrogen produce energy equivalent to that produced by 25 kg of gasoline (Mirza et al., 2009).

Hydrogen has the highest energy content of any common fuel by weight (about three times more than gasoline). Hydrogen is an odorless, tasteless, colorless and non-poisonous gas. It is a renewable resource found in all growing things. Hydrogen is an important raw material for chemical, petroleum and agro-based industries. The demand for hydrogen in the hydrotreating and hydrocracking of crude petroleum is steadily increasing (Min et al., 2005). Hydrogen is catalytically combined with various intermediate processing streams and is used in conjunction with catalytic cracking operations to convert heavy and unsaturated compounds to lighter and more stable compounds. Large quantities of hydrogen were used to purify gases such as argon that contain trace amounts of oxygen. Furthermore, in the food and beverages industry, hydrogen was used for hydrogenation of unsaturated fatty acids in animal and vegetable oils, to produce solid fat and other food products. While in manufacturing of semi conducting layers in integrated circuits, hydrogen were used as a carrier gas. The pharmaceutical industries use hydrogen to make vitamins and other pharmaceutical products. Hydrogen is mixed with inert gases to obtain a reducing atmosphere that is required for many applications in the metallurgical industry such as heat treating steel and welding (Delgado et al., 1997 and Dupont et al., 2008).

In 2005, the overall U.S. hydrogen market is estimated at \$798.1 million and it is expected to rise to \$1,605.3 million for U.S. and \$740 million for European in 2010 (Keizai, 2005). However, hydrogen production is not enough to uphold this value. The hydrogen technology had been intensively studied to find a variety of hydrogen source with different treatment processes because hydrogen has great potential as an environmentally clean energy fuel and as a way to reduce reliance on imported energy sources. In Asian region, the biomass from agriculture sector is the largest source of hydrogen production. Many experts predict that hydrogen will eventually power tomorrow's industries and thereby may replace coal, oil and natural gas. However, it will not happen until a strong framework of hydrogen production, storage, transport and delivery is developed.

### **1.2 Biomass gasification**

According to Xiao et al. (2007), it is generally reported by different authors that the process of biomass gasification occurs through main three steps. At the first step in the initial heating and pyrolysis, biomass is converted to gas, char and tar. Homogeneous gas-phase reaction resulted in higher production of gaseous. High bed temperature during this phase allowed further cracking of tar and char to gases. Second step is tar-cracking step that favours high temperature reactions and more light hydrocarbons gases such as Hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2) and methane (CH4). Third step is char gasification step that is enhanced by the boudouard reaction.

The gasification mechanism of biomass particles might be described by the following reactions:

Air Gasification of Malaysia Agricultural Waste in a

4 Biomass two-step process

5 Palm kernel Fluidized bed

6 Biomass downdraft

biomass Fixed bed

8 Biomass Fixed bed

10 Biomass catalytic fluidized bed

gasifier

gasifier

Integrated gasifier

down draft gasifier

applied air-blown gasification

Raw

sawdust

<sup>2</sup>Pine wood block

<sup>3</sup>Hazelnut shell

<sup>7</sup>Woody

<sup>1</sup>Wood

Fluidized Bed Gasifier: Hydrogen Production Performance 231

materials Gasifier design Gasification performance References

Fuel gas yield:

Hydrogen yield:

Hydrogen yield:

biomass

Efficiencies: > 87.1% LHV: of 5000 kJ/Nm3.

(0.82-0.94) Nm3/kg biomass,

(21.18- 35.39) g/kg biomass LHV : (4.76-5.44) MJ/Nm3

24 g/kg hazelnut shells.

Hydrogen content : 60% Hydrogen yield : 65 g/kg

Hydrogen yield : 67 mol % LHV : 1.482 - 5578 MJ/Nm3

The product gas composition: a)cellulose : 35.5% mol CO, 27% mol CO2 and 28.7% mol H2. b) Xylan and lignin were

approximately 25% mol CO, 36%

mol CO2 and 32% mol H2.

(increasing trend from 600 to

and 83% mol % (steam)

Hydrogen yield: 28.7% Conversion efficiencies79%.

H2 concentration: air- 59% mol steam – 87%

1050K)

Table 2. Selected review on biomass gasification performance for hydrogen production.

9 Biomass updraft gasifier H2 composition: 22.3 mol% (air)

LHV: 9.55 MJ/Nm3 H2 yield : 52.19-63.31% Cao et al. (2006)

Pengmei et al. (2007)

Midilli et al. (2001)

Zhao et al. (2010)

Wan Ab Karim Ghani et al.,(2009)

LV et al. (2007)

Hanaoka et al. (2005)

Florin and Harris (2007)

Lucas et al. (2004)

Miccio et al. (2009)

$$\text{Biomass} \rightarrow \text{Gas} \dagger \text{Ts} \star \text{Char} \tag{1}$$

**The Combustion reactions:** 

$$\text{C} \vdash \forall \text{-} \mathcal{O}\_2 \rightarrow \text{CO -111 MJ/Kmol} \tag{2}$$

$$\text{CO} + \text{V}\_2\text{O}\_2 \rightarrow \text{CO}\_2\text{-}283 \text{ MJ/Kmol} \tag{3}$$

$$\text{H}\_2 + \text{M}\_2\text{O}\_2 \rightarrow \text{ H}\_2\text{O} \cdot \text{242 MJ/Kmol} \tag{4}$$

**The Boudouard reaction:** 

$$\text{C} + \text{CO}\_2 \rightleftharpoons 2\text{CO} + 172\text{ MJ/Kmol} \tag{5}$$

**The Water gas reaction:** 

$$\text{C} + \text{H}\_2\text{O} \rightleftharpoons \text{CO} + \text{H}\_2 + 131 \text{ M} / \text{Kmol} \tag{6}$$

**The Methanation reaction:** 

$$\text{C} + 2\text{H}\_2 \rightleftharpoons \text{CH}\_4\text{-75 M}/\text{Kmol} \tag{7}$$

#### **The Water gas shift (CO shift) reaction:**

$$\text{CO} + \text{H}\_2\text{O} \rightleftharpoons \text{CO}\_2 + \text{H}\_2\text{-}41 \text{ MJ/Kmol} \tag{8}$$

The gasification performance for optimized gas producer quality (yield, composition, production of CO, H2, CO2 and CH4 and energy content) depends upon feedstock origin, gasifier design and operating parameters such as temperatures, static bed height, fluidizing velocity, equivalence ratio, oxidants, catalyst and others which are summarized in Table 2.

In summary, most of performed researches have explored the effect of different gasifying agent (air or steam) and applied different types of catalysts on gasification or pyrolysis process. Temperature and equivalence ratio of biomass with fuel (either air or steam) is the most significant parameter to contribute to the hydrogen production. However, less emphasis has been given to experimental investigation on the optimization of pyrolysis and gasification processes integration for the conversion of low value biomass into hydrogen and value-added products, which is the focus of this paper.

### **2. Materials and experimental**

#### **2.1 Raw materials**

Three types of agricultural residues were investigated in this research namely palm kernel shell, coconut shell and bagasse as they are abundantly available in the agriculture sector in Malaysia. The samples were open air dried for 2 to 3 days to remove moisture and to ease crushing. Both of these samples were pulverized into powder and were sieved into specific particle size of (0.1-0.3 mm). Sieving was accomplished by shaking the ground biomass samples in a Endecotts Shaker Model (EFL2 MK3) for 30 minutes and dried in a vacuum oven at 80°C overnight and were kept in a tightly screw cap bottle. Table 3 summarized fuel properties investigated in this research.

Biomass Gas+ Tars + Char (1)

 *H2 + ½ O2 H2O -242 MJ/Kmol* (4)

The gasification performance for optimized gas producer quality (yield, composition, production of CO, H2, CO2 and CH4 and energy content) depends upon feedstock origin, gasifier design and operating parameters such as temperatures, static bed height, fluidizing velocity, equivalence ratio, oxidants, catalyst and others which are summarized

In summary, most of performed researches have explored the effect of different gasifying agent (air or steam) and applied different types of catalysts on gasification or pyrolysis process. Temperature and equivalence ratio of biomass with fuel (either air or steam) is the most significant parameter to contribute to the hydrogen production. However, less emphasis has been given to experimental investigation on the optimization of pyrolysis and gasification processes integration for the conversion of low value biomass into hydrogen

Three types of agricultural residues were investigated in this research namely palm kernel shell, coconut shell and bagasse as they are abundantly available in the agriculture sector in Malaysia. The samples were open air dried for 2 to 3 days to remove moisture and to ease crushing. Both of these samples were pulverized into powder and were sieved into specific particle size of (0.1-0.3 mm). Sieving was accomplished by shaking the ground biomass samples in a Endecotts Shaker Model (EFL2 MK3) for 30 minutes and dried in a vacuum oven at 80°C overnight and were kept in a tightly screw cap bottle. Table 3 summarized fuel

*C + ½ O2 CO -111 MJ/Kmol* (2)

CO + ½ O2 CO2 -283 MJ/Kmol (3)

C + CO2 2CO +172 MJ/Kmol (5)

C + H2O CO + H2 +131 MJ/Kmol (6)

CO + H2O CO2 + H2 -41 MJ/Kmol (8)

C + 2H2 CH4 -75 MJ/Kmol (7)

**The Combustion reactions:** 

**The Boudouard reaction:** 

**The Water gas reaction:** 

**The Methanation reaction:** 

in Table 2.

**The Water gas shift (CO shift) reaction:** 

**2. Materials and experimental** 

properties investigated in this research.

**2.1 Raw materials** 

and value-added products, which is the focus of this paper.



Air Gasification of Malaysia Agricultural Waste in a

Fluidized Bed Gasifier: Hydrogen Production Performance 233

Gas

Chromatography

Fig. 1. Schematics diagram of biomass air gasification in fluidized bed reactor

the product gas leaving the cooler for off line gas analysis.

feeding rate (0.78 kg/h) and equivalence ratio(ER)(0.26).

**3. Results and discussion** 

**3.1 Effect of gasification temperature** 

Prior each experiment, the reactor was charged with 20 g of silica beads as the bed material to obtain a better temperature distribution, to stabilize the fluidization and to prevention coking inside the reactor. The solenoid valve (S.V) was turned on and a pre-heated air flow passed through the bed and the reactor when the temperatures in the bed (pyrolysis zone) and in the gasification zone reached the desired temperature. The feeder was turned on once the temperatures of these two parts stabilized. Typically, each test took about 20 to 25 minutes to stabilize and measurements were taken at intervals of 2 minutes. During each experiment, the air stream and the biomass feedstock were introduced from bottom and top of the gasifier, respectively. The clean gas was then sent to a water cooler to separate the condensed and un-condensed tars and steam. Sampling gas bags were employed to collect

The gasification performance mainly will be evaluated based on the gas production quality (hydrogen yield and carbon conversion efficiency) and quantity (gas composition).

The product yields (hydrogen, ash and oil) and detail gas composition of studied biomass at different gasification temperature are summarized in Table 4 and Figure 2, respectively. In this study, reactor temperature is increase from 700 to 1100 °C in 50°C and at constant

Furthermore, the ash and oil yield will also be determined and quantified.


Table 3. Proximate and Ultimate Analysis of Feedstock Sample

### **2.2 Experimental set up and procedures**

The schematic diagram of the experimental facility used in this study is shown in Figure 1. The reactor was made of stainless steel pipe and the total high of reactor is 850 mm with an internal diameter of 50 mm, directly heated via electrical furnace equipped with Temperatures Indicator Controller (TIC) and thermocouples that those installed in two different zones of reactor, screw feeder, condenser, gas cleaning, gas drying and sampling section, gas chromatograph (GC).

**Palm Kernel shell** 

Volatile matter 30.53 51.10 43

Fixed carbon 48.5 26.4 32.40

Ash 8.97 12.50 10.20

Moisture 12 10 14.40

Hydrogen 5.52 5.40 5.30

Carbon 51.63 50.20 43.80

Oxygen 40.91 43.40 47.10

Nitrogen 1.89 1.46 1.20

Sulfur 0.05 0.06 0.03

Cellulose 20.80 28.60 30

Hemicellulose 22.70 28.60 23

Lignin 50.70 24.40 22

Table 3. Proximate and Ultimate Analysis of Feedstock Sample

**2.2 Experimental set up and procedures** 

733 24.97

The schematic diagram of the experimental facility used in this study is shown in Figure 1. The reactor was made of stainless steel pipe and the total high of reactor is 850 mm with an internal diameter of 50 mm, directly heated via electrical furnace equipped with Temperatures Indicator Controller (TIC) and thermocouples that those installed in two different zones of reactor, screw feeder, condenser, gas cleaning, gas drying and sampling section, gas chromatograph (GC).

661 21.50

111 16.70

**Proximate Analysis (wt% wet basis)** 

**Ultimate Analysis (wt% dry basis)** 

Bulk Density (kg/m3) HHV (MJ/kg)

**Coconut** 

**shell Bagasse** 

Fig. 1. Schematics diagram of biomass air gasification in fluidized bed reactor

Prior each experiment, the reactor was charged with 20 g of silica beads as the bed material to obtain a better temperature distribution, to stabilize the fluidization and to prevention coking inside the reactor. The solenoid valve (S.V) was turned on and a pre-heated air flow passed through the bed and the reactor when the temperatures in the bed (pyrolysis zone) and in the gasification zone reached the desired temperature. The feeder was turned on once the temperatures of these two parts stabilized. Typically, each test took about 20 to 25 minutes to stabilize and measurements were taken at intervals of 2 minutes. During each experiment, the air stream and the biomass feedstock were introduced from bottom and top of the gasifier, respectively. The clean gas was then sent to a water cooler to separate the condensed and un-condensed tars and steam. Sampling gas bags were employed to collect the product gas leaving the cooler for off line gas analysis.
