Briquettes & Pellets:forms of solid fuel

biomass briquetting

2Fuel derived from compacting the biomass into dense block is known as Briquette. It is cheaper and requires no other raw material and produce heat equivalent to other fuel. Now a days biomass briquetting is used by the same industries where the low-density biomass is produced. Jute waste, groundnut shell, coffee husk, coir pith and rice husk is used for Briquetting.

What is Biomass Briquetting?

3to fight the deforestation

To reduce the dependence of the forest as a resource for energy, the Dept of Energy (DoE) in Malawi [Africa] launched a project called Promotion of Alternative Energy Sources Programme(PAESP) in 2006, to encourage the use of energy sources other than firewood and charcoal.

Alternative energy source considered in this project is the biomass briquette (seeillustration 1).

Illustration 1: A typical biomass briquette made of compressed paper and sawdust.

4biomass briquettes in Malawi.

The briquette evaluation was made in terms of physical and chemical characteristics (like material content, size, weight, energy content), costs for the fuel and usability in household cooking stoves. The feasibility of the production method for each briquette type was also evaluated.

The briquettes were compared with the characteristics of firewood and charcoal.

5Agro-residues and agro-industry residues-1

Agricultural or agro-industrial biomass is

generally difficult to handle because of its

bulky and scattered nature, low thermal

efficiency and copious liberation of smoke

during burning. It will be useful to

compress them into manageable and

compact pieces, which have a high thermal

value per unit weight.

6Agro-residues and agro-industry residues-2

Biomass residues and by products are

available in abundance at the agro

processing centres (rice husk,

bagasse, molasses, coconut shell,

groundnut shell, maize cobs, potato

waste, coffee waste, whey), farms

(rice straw, cotton sticks, jute sticks).

7marketing base for biomass briquettes

Small-scale industries are the major

marketing base for biomass briquettes.

Rubber industries, textile dyeing units,

leather processing units, small boiler units,

tobacco processing units, brick kilns and

the domestic sector are potential market.

Users of huge amount of wood and loose

biomass can switch over to briquettes

profitably.

8briquetting or pelleting

The process is called

biomass briquetting or pelleting.

Compressed biomass briquettes are usually cylindrical in shape with a diameter between 30 to 90 mm and length varying between 100 to 400mm.

Briquetting consists of applying pressure to a mass of particles with or without a binder and converting it into compact aggregate. Ram type and screw type machinery are used for the manufacture of

briquettes.

9Briquetting technology

Ram type consists of a plunger or rod which forces the material received from a hopper into a die, which is not usually heated by external means.

The screw type machine employs a screw auger which forces the material into a pipe heated by electricity.

The choice of the type of machinery depends on many factors.

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Ram type [piston type] briquetting machine

Ram type consists

of a plunger or rod

which forces the

material received

from a hopper into

a die, which is not

usually heated by

external means.

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Ram type briquetting press

Common in India, alternate to screw type.

Material is compressed in horizontal press, made into a cylindrical continuous log; Cut to pellets later.

Log diameter is 50 mm for a 500 kg per hour machine and 90 mm for a 1500 kg / hr machine

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Screw type briquetting machine

The screw type

machine employs a

screw auger which

forces the material

into a pipe heated

by electricity.

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Screw type briquetting Press

The material is extruded under compression continuously in the form of a log, under screw.

These logs are partially carbonized and free of volatile compounds.

They can supplement charcoal / lignite as solid fuel for small scale uses.

Wear of screw is a problem and designers of machine have solved this.

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Preparing biomass for pellet making

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PELLETISING

Biomass material is compressed through

many holes by giving very high pressure

from rollers to the material.

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PELLETISING: High pressure, smaller size

In pelletising, the biomass material

is compressed through many holes by giving very high pressure from rollers to the material.

The stick is continuous but the size of pellet is smaller (6-25 mm in diameter) than briquettes.

Pelletizing is more efficient and recognized as a good method because of low investment.

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Pelletizing, though introduced very

recently, is considered to be most wanted

method due to its high bulk density.

Ring and Flat Die are two types found in

this category.

The Ring die method is mostly used for

making animal feed, which has high bulk

density.

The flat die is used for low bulk density.

PELLETISING: Ring and Flat Die

Muthaiya Chettiar Research Centre, Chennai

charcoal briquetting

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Muthaiya Chettiar Research Centres method of charcoal briquetting

1. Locally available biomass (e.g.,

casuarina leaf litter, sugarcane trash,

rice husk, coir pith, groundnut shells,

etc)

2. Carbonizing chamber (furnace )

3. Binder (starch or cassava flour)

4. Mini Briquetting machine (10kg/hr)

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1.Collection of biomass: Collect the locally available biomass, sort them, chop the large-size raw materials into smaller pieces and dry at sunlight.2. Carbonization: i. Designing the Furnace Outer drum : A 200lits. metal oil drum with the top cut out and a 12" width x 10" height hole cut in the lower side Two iron rids (8) has to be fixed at the bottom of the metal drum running parallel from one side to the other side. This iron rods act as base to support the stainless steel inner drum. Inner drum : A 100lits stainless steel drum with proper lids and six (3/8") holes at the bottom. The inner drum is placed into the larger drum.

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MCRCs method of charcoal briquetting [continued]

ii. Carbonizing the biomass The biomass is tightly packed into the inner drum and fired for 45minutes to 1hr (Depending upon the biomass) using biomass. After firing, the carbonized biomass in the inner drum has to collected and weighed. In this method 30 % of carbonized char can be obtained.

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3. Preparation of binderThe binder material is used for strengthening the briquettes For every 100 kg of total weight of carbonized charcoal powder, prepare a binder mixture by adding 5 to 6 kg of starch or cassava flour to 60 - 100 litres of water (based on the weight of the raw materials)4. MixingMix such that every particle of carbonised charcoal material is coated with binder. It will enhance charcoal adhesion and produce identical briquettes.

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5. Briquetting. The charcoal mixture is made into briquettes either

manually or using machines. Pour the mixture directly into the briquetting mould / machine to form uniform-sized briquettes.

6. Drying and PackagingCollect the briquettes in a tray, dry them under the sunlight, pack them in plastic bags and seal

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General Characteristics of briquettes

Moisture : 7.1%-7.8%

Volatile Matter : 13.0%-13.5%

Fixed Carbon : 81.0%-83.0%

Ash : 3.7%-7.7%

Sulfur : 0.0%

Heating Value : 7,100-7,300 kcal/kg

Density : 970kg/m3