Part 2 CCT Overview
Multi-purpose Coal Utilization Technologies (Powdering, Fluidization, and Co-utilization Technologies)

4C3. Briquette Production TechnologyTechnology Overview

1. Background
Global warming, caused by CO2 and other substances, has

substitute fuel for charcoal is necessary. Briquette production

become an international concern in recent years. To protect

technology, a type of clean coal technology, can help prevent

forestry resources, which act as major absorbers of CO2,

flooding and serve as a global warming countermeasure bycontrolling the ever-increasing deforestation, along with theconserving forestry resources through the provision of a stable

increase in the consumption of wood fuels, such as firewood andsupply of briquettes as a substitute for charcoal and firewood.

charcoal, is an urgent issue. Given this, the development of a

2. Carbonized briquettes(1) Process overview(2) Carbonization stage

The coal briquette carbonization production process consists of a

The raw coal (10% or lower surface water content, 5-50mm

carbonization stage and a forming stage. Figure 1 shows theparticle size) is preliminarily dried in a rotary dryer. The gas

basic process flow.

exhausted from the dryer passes through a multi-cyclone to

In the carbonization stage, an internal-heating, low-temperature

remove the dust before venting the gas to the atmosphere. Figure

fluidized-bed carbonization furnace (approximately 450oC)

2 shows a cross-sectional view of the internal-heating, low-produces smokeless semi-coke containing approximately 20%

temperature fluidized-bed carbonization furnace, the mostvolatile matter. The carbonization furnace has a simple structure,efficient process for carbonizing semi-coke and one which retains

with no perforated plates or agitator, making it easy to operate

approximately 20% of theand maintain.

volatile matter in the semi-

In the forming stage, the smokeless semi-coke and auxiliary raw

coke.

materials, hydrated lime and clay, are thoroughly mixed at a

The preliminarily dried raw

predetermined mixing ratio. After pulverizing, the mixture iscoal is charged to theblended with a caking additive while water is added to adjust themiddle

water content of the mixture. The mixture is kneaded to uniformly

furnace, and is subjected to

distribute the caking additive, and to increase the viscosity influidization

order to make the forming of the briquettes easy. The mixture is

The semi-coke is discharged

then introduced into the molding machine to prepare thefrom the top of the furnace

briquettes. The briquettes are dried and cooled.

together with the carbonization

sectionof

thecarbonization.

gas. Thesemi-coke

isseparated

from

thecarbonization gas by the
primary cyclone and thesecondary cyclone.

Raw Coal

After cooled, the semi-cokeFig. 2 Cross-sectional view ofcarbonization furnace

is transferred to a stockyard, and the carbonization gas isDrying

supplied to the refractory-lined combustion furnace, where theCoalite

Crushing

carbonization gas is mixed with air to combust. The generated hot
CycloneCarbonizing

Kneading

gas is injected into the raw coal dryer and to the succeeding
briquette dryer to use as the drying heat source for theDesulfurizer
Binderpreliminary heating of the raw coal and the drying heat source ofWater

the formed oval briquettes.
(3) Forming stage

Mixing

The semi-coke (Coalite) produced in the carbonization stage isthe raw material for the briquette, containing adequate amounts

Briquetting

Briquetteof volatile matter, little ash and sulfur, and emitting no smoke orodor. The semi-coke, as the primary raw material, is mixed withDrying

hydrated lime (sulfur fixing agent), clay (to assist forming), and aFig. 1 Process flow of briquette production

caking additive.

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Clean Coal Technologies in JapanTo attain uniform composition and improved formability, theblended raw materials are fully kneaded. The forming of themixture is carried out using a roll-molding machine at normal
temperatures and under approximately 1,000 kg/cm (300-500kg/cm2) of line pressure. Photo 1 shows the forming state.
In the final stage, the formed briquettes are dried in thecontinuous dryer. Since semi-coke is used as a raw material forthe briquettes, they are highly ignitable and can readily ignite in
the furnace if the dryer is not operated at low temperatures. The
dryer was designed with this temperature-sensitive concern inmind.
Photo 1 Formed briquettes

3. Bio-briquettes
Bio-briquettes are a type of solid fuel, prepared by blending coal

which permeates the coal particles, assuring the combustion ofwith 10-25% biomass, such as wood, bagasse (fibrous reside ofvolatile matter at low combustion temperatures. As a result, theprocessed sugar cane stalks), straw, and corn stalks. A

amount of generated dust and soot is significantly reduced.

desulfurizing agent, Ca(OH)2, is also added in an amount

2. Bio-briquettes prepared by blending biomass with coal have acorresponding to the sulfur content of the coal. Owing to the highsignificantly shorter ignition time. In addition, because of the lowpressure briquetting (1-3 t/cm2), the coal particles and the fibrousexpansibility and caking property of bio-briquettes, sufficient air

biomass material in the bio-briquette strongly intertwine andflow is maintained between the briquettes during continuous

adhere to each other. As a result, they do not separate from each

combustion such as in a fireplace. As a result, the bio-briquettes

other during combustion, and the low ignition temperature

have superior combustion-sustaining properties, and do not diebiomass simultaneously combusts with the coal. The combinedout in a fireplace or other heater even when the air supply is

combustion gives favorable ignition and fuel properties, emits

decreased. This makes it easy to adjust the combustion rate.

little dust and soot, and generates sandy combustion ash, leaving

3. Since fibrous biomass is intertwined with the coal particles,

no clinker. Furthermore, since the desulfurizing agent also

there is no fear of the fused ash in the coal adhering and forming

adheres to the coal particles, the agent effectively reacts with theclinker-lumps during combustion. Instead, the ash falls in a sandy

sulfur in the coal to fix about 60-80% of the sulfur into the ash.

form through the grate. Therefore, aeration is maintained toMany coal ranks can be used, including bituminous coal, sub-stabilize the combustion state. Furthermore, since no clinker isbituminous coal, and brown coal. In particular, the bio-briquettes

formed, the ash contains very small amounts of unburned coal.

produced with low grade coal containing large amounts of ash

4. The bio-briquettes are formed under high compressive force.

and having low calorific value combust cleanly, thus the bio-Because of this, the desulfurizing agent and the coal particles

briquette technology is an effective technology to produce clean

strongly adhere to each other, and they effectively react during

fuel for household heaters and small industrial boilers.

combustion. With the addition of a desulfurizing agent at a ratio of(1) Bio-briquette production process

approximately 1.2-2 of Ca/S, 60-80% of the sulfur in the coal isFigure 3 shows the basics of the bio-briquette production

fixed in the ash.

process. The raw materials, coal and biomass, are pulverized to asize of approximately 3 mm or smaller, and then dried. The driedmixture is further blended with a desulfurizing agent, Ca(OH)2.
The mixture is formed by compression molding in a high-pressure
briquetting machine. Powder coal may be utilized without being
Coal

pulverized. A small amount of binder may be added to some coalranks. The

production

processdoes

notinvolve

Biomass

hightemperatures, and is centered on a dry, high-pressure briquetting

DryingPulverization

machine. The process has a simple flow, which is safe and which
does not require skilled operating technique. Owing to the high-Drying
Pulverizingpressure briquetting process, the coal particles and the biomass
Deodorant

strongly intertwine and adhere to each other, thus the process

Caking additive

produces rigid formed coal, which does not separate during

Caking additive may berequired depending on
coal rank.

combustion.
(2) Bio-briquette characteristics

Mixing

1. Bio-briquette combustion decreases the generation of dust andHigh-pressure briquettingsoot to one-fifth to one-tenth that of direct coal combustion. Direct
coal combustion increases the generation of dust and sootbecause the volatile matter released at low temperatures (200-Bio-briquettes

400oC) does not completely combust. To the contrary, biobriquettes simultaneously combust the low ignition point biomass,

Fig. 3 Basic process flow for bio-briquette production72