Coffee husk is a residual product from coffee cultivation. It is widely used for extracting caffeine and tannin, composting. Besides these, it is also a suitable material for pellet making machine to replace coal and fossil fuel. Brazil is the biggest coffee production area around the world and there are several and increasing number of power plant is using coffee husk pellets for electricity generating.
Analysis on the project of making burning pellets from coffee husk
As we all know, dense,high calorific value and easy to process, wood sawdust is the most suitable material for biofuel pellet plant. Coffee husk has the similar element with wood sawdust. Although not as good as wood sawdust, coffee husk is still a good materials for making pellets. Coffee husk is in uniform size and shape, so it's easy to be processed into biomass pellets.
For proper analysis, the materials were dried in the sun to reduce their moisture content to at least less than 12% (w/w). The sizes were then reduced to a uniform particle of 1 mm diameter. The proximate analysis parameters included moisture andash contents, volatile matters, and fixed carbon. The result of the analysis was as presented in table 1 below.
|Type of Analysis||Parameters||Result (%)|
Table 1: The proximate analysis of raw materials of coffee husk.
The moisture content and volatile substances reduced during carbonization process. Contrastingly, fixed carbon content and the calorific values increased. Besides, the moisture content evaporated at high temperature even during storage. This was attributed to environmental conditions due to its hygroscopic nature.
|m1 (g)||m2(g)||m3(g)||Moisture Content (%)|
Table 2: The moisture content.
The moisture content has influence on net calorific value, combustion efficiency, temperature, and its equilibrium. Moreover, the ambient moisture content was affected by storage conditions. The results of moisture content analysis were as presented in table 2. It is prudent to note that the moisture content of the biopellet ranged from 8.30% to 8.90% (Figure 1).
Figure 1: The ratio of moisture content biopellet coffee husk.
There was a difference in the initial moisture content of the coffee husk briquette and biopellet. The preliminary value of briquettes in the hot air chamber when using drying machine was much lower compared to the solar drying sample. While using moisture analyzer, the content was 8.67%. This was different from the one in briquettes within the hot chamber air that had 6.34%. Moreover, the difference in value between biopellet and briquettes of coffee husk was 4.62%. It is imperative to note that the moisture value of biopellet was meant to fulfill the New Europe Pellet Standard-EN 14961-1. Notably, the higher moisture content required more energy to evaporate water. The needed energy to ignite the biopellet increased, causing the fuel to react during combustion. With a higher moisture content, the quality of biopellet decreases.
To determine ash content,it is important to analyze the unburned part without carbon element after the combustion of the biopellet (Table 3).
|Replication||W1 (g)||W2 (g)||Ash (%)|
Table 3: The ash content of biopellet coffee husk.
The gross calorific value is an important parameter when determining the fuel quality. Its values in the biopellet was 16.897MJ kg-1, established using the LECO AC-350. This was considerably lower than the European Pellet Standard-EN 14961-1 required for the production of commercial biomass. It is required to range between 17.500 and 19.500MJ kg-1 (Table 4).
|Fuse wire 1 (cm)||9.80||10.01||10.01|
|Δ Fuse wire (cm)||6.41||7.22||7.51|
|Δ T (pre-fire) (° C)||1.68||1.62||1.70|
|Calorific value (cal/g)||3951.50||3932.90||4230.10|
Table 4: The calorific value of coffee husk biopellet.
The lower calorific value was brought about by high moisture content which slowed down the rate of combustion. This is essentially because it had to evaporate water, thereby lowering the calorific value.
While using the furnace method, the value of ash content in coffee husk biopellet was 8.071%. During production the pellet is expected to have the lowest ash content. Nevertheless, the value obtained in the study did not satisfy the set requirement, 0.5%, by the New Europe Pellet Standard-EN14961-1. Further, high ash content (beyond 4%) could corrode the burners and abrade equipment. Since heat from the sun alone was not enough to produce the product that satisfies the set standards, the highwater content of the material affected the value of ash content.
Coffee husk pelletizing is similar to other biomass materials, including: drying, crushing, pelletizing, cooling, and packing. However, to process premium coffee husk pellets, we have two tips of guidance for coffee husk pellets starters.
A. To cutting down the production cost, you should choose a place which is close to raw material production area to processing coffee husk pellets.
B. As different biomass materials are with different component content, the pellets calorific value are also different. To get a higher burning calorific value.
These pellets are advantageous in comparison to the other biomass pellets because of numerous factors. These factors include:
These pellets are capable of producing a high heat value in comparison to the pellets of agricultural waste.
The cost of production of these pellets is low as the materials are available in abundance due to the huge production of coffee in various places. The machines that are used for the process of pelletizing the coffee husks and coffee grounds are also not very expensive.
The agricultural wastes and the forestry residues are collected from the paper plants, croplands, sawmill, and furniture factory, whereas coffee husks and grounds are the leftovers of the cultivated land or brewed coffee. This product does not cause any harm to the human body.
With a large market demand, coffee has a broad production area around the world. One of the famous coffee cultivation countries is Brazil. Brazil country's availability of land, water and labor has allowed coffee increased production and exports. Annually, Brazil could produce upwards of 150,000 tons of coffee husk. Besides Brazil, Coffee also has a wide planting in Colombia, Indonesia, Vietnam, etc. Coffee husk can be transformed into a value-able fuel -- coffee husk pellets and becoming an important local energy source. In Brazil coffee husk is mainly used in power plant for the purpose of electricity generating. There are still a amount of coffee husk pellets used for home heating etc.
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