Currently Vietnam ranks as the world’s second largest coffee producer behind only Brazil. Coffee is the second most important export commodity in Vietnam in value and quantity. There are around 600,000 hectares of coffee plantations with 1600,000MT in Vietnam. This is made up of 90% Robusta concentrated in the central highlands and 10% Arabica grown in the north. The majority of Vietnamese coffee is harvested between the months of October and January. Coffee turns from green to red or yellow when fully ripe. It is harvested by selective picking in Vietnam: workers passing from plant to plant, hand-picking only the bright red ripe cherries, one by one, which ensure higher quality coffees. Coffee husk is the residual product from qualified coffee processing industry. It represents 15% of the cherry weight when dried. Average coffee yield per hectare is 1.8 ton, thus there is 270kg of husks per hectare resulting in 162,000 ton total in Vietnam.
In Vietnam, current practices of husk disposal are similar to those of rice husk. Either burned out in the open or disposal along ways and countryside, either as fertilizers and livestock feed or just left on the road. Coffee husks are mostly underutilized and gradually become the "waste products". Therefore there is vast materials in Vietnam for pellet production!
Coffee Husk Main Locations in Vietnam
85% of the coffee production is carried out by small holders (typically less than 2 hectare land tenure) and 15% is state-owned (larger farms). There are about 500,000 smallholders supplying 1500-2000 small traders and primary collectors, who provide their goods for:
* 5-6 multinationals
* 140-150 domestic private firms and
* 5-6 joint stock companies
The residues like coffee husks are produced mainly on these final destinations.
Coffee Hull Merits as Raw Material for Pelletizing
a. Coffee Husk is a fibrous sub-product obtained during the processing of raw coffee beans. It is rich in organic nature: 50%cellulose, 38%hemicelluloses, pectin and lignin, which makes it an ideal raw material for the production of value-added pellets.
b. Coffee husk contains 1.50%lipids and 6.80%protein which will improve its calorific value.
c. Coffee husk has the similar element with wood sawdust: dense, high calorific value and easy to process and etc., which is good for making pellets. Coffee husk pellets can be used as a renewable fuel, with combustion characteristics very similar to firewood.
Advantages of Coffee Husk Pellets
a. Coffee husk pellet compressed from coffee husk materials is cylindrical with uniform shape, which can improve ease of transportation and storage and lower the cost.
b. The pellet has a uniform size usually with diameter of 6-12mm and high density energy, which is ideal for automatic combustion heating systems such as pellet stoves and boilers.
c. The moisture content of pellets is substantially lower. Less moisture means that very little of the energy produced is needed to evaporate water. Compared with raw materials direct combustion, pellets can be burnt at high temperature with high combustion efficiency.
d. Coffee hull pellets have a wide range of application like heating, cooking and industrial steam furnace or boiler.
e. The environment will benefit noticeably because the pellets combustion reduces the amount of burned residue in open spaces and consequently the pollution.
Coffee Husk Pellet Production
Coffee processing removes husk and flesh form the cherry, which in turn becomes the coffee bean. In Vietnam three different processing technologies are used: wet processing for Arabica, semi-wet or dry processing for Robusta. These release solid waste such as coffee husk.
The different processing technologies produce coffee husk with different characteristics in regard to moisture and composition. So before pelletizing, coffee husk properties should be understood as follows:
Moisture content% on wet basis: 10-12
Net heating value of wet matter(mj/kg): 15.4-15.8
Bulk density, wet (kg/m3): 185-300
Gross calorific value of dry matter(mj/kg): 16.1-18.2
Net calorific value of dry matter(mj/kg): 17.8
Collecting raw materials for your production. For large production, you need a car to transmit the material. To lower the transmission fee, you can choose a place which is close to raw material production area (refer to No. 2 in Part I: main locations in Vietnam).
Collected materials first are crushed by crushing machine. The length should be less than 5mm. The particle size effect the efficiency of pellet making.
3. Drying and blending
Dry crushed materials by drying machine to lower moisture content to aound 15% to prepare for pellitizing. If your material moisture is between 12-14%, the drying process is not necessary.
Different biomass materials are with different calorific value. To get a higher burning calorific value, crushed materials will fall into the blender to evenly mix with other materials. Please see the following Material Blending Formulas. (The blending procedure can be operated based on customers' demands.)
4. Pelletizing by pellet machine
Ring die pellet mill is the significant part of large scale pellet production line, and has reliable and stable performance. Start the biomass pellet machine and wait a few minutes for heating up the pellet die. The heat could help the lignin in out of the coffee husks, and bonding the husk as the pellets. When materials go into the pellet, pellet making machine compress rice husk into pencil sized pellets.
5. Cooling, sieving and packing
Cool down the pellets by cooler or nature before you handle them.
Then sieve pellets that did not form properly. Some pieces will fall apart or break during the pressing process. Separate the improperly formed pieces by shaking or sifting them through a screen.
Store pellets in bags in a dry place.
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