Making Paper Mill Residues into Wood Pellet Fuel

The High Potential of Paper Factory Residues

Paper is made from raw materials containing cellulose fibers, generally wood, recycled paper, and agriculturalresidues. In developing countries, about 60%6 of cellulose fibers originate from non-wood raw materials,including bagasse, cereal straw, bamboo, reeds, esparto grass, jute, flax, and sisal. The main steps in paperproduction are raw material preparation, like wood debarking and chip making; pulp manufacturing; pulpbleaching, paper manufacturing; and fiber recyeling. In the paper factory, the generation of residues isunavoidable. Pulp and paper manufacturing is characterized by different cycles, both internal and external, andrespects the hierarchy of reusing, recycling and what can not be recycled any longer is sent to energy recoverysuch as wood residues, bark residues, etc.

Different Types of Residues Generated in Different Paper Production Process Phases

• Raw Material Preparation：The wood raw material used by the paper factory mainly comes from forests or by-products from the sawmill.
• Pulp Manufacturing：Wood used for pulping is first debarked, leaving amount of bark residues. There are mainly two types of pulpingmethod, namely kraft pulping(the dominant chemical pulping method) and mechanical pulping. Differentpulping processes generate different residues.
• In kraft pulping, wood chips are cooked with chemicals. Cooking removes lignin breaking up the wood intofibers. The residues from chemical pulping are green liquor dregs, lime mud, and lime sludge.In mechanical pulping fibers are separated from each other either by grinding logs against a rotating stone or byrefining woodchips between a rotating disc and a fixed plate. The residues from mechanical pulping are mainly a mixture of fbers and bigger wood components.
• Paper Manufacturing：Residues from paper production include wood fibers and minerals.

Fuel Pellets Production

• Equipment for Making Fuel Pellets From Paper Mill Residues

The basic equipment includes:

Wood Hammer Mill: to crush large size paper mill residues into powder with the size of less than 6mm.

Sawdust Dryer: to lower the moisture content and make the materials suitable for direct pelletizing

Wood Pellet Machine: the core equipment in the wood pellet production line. Pellet machine can be classifiedinto flat die pellet mill and ring die pellet mil. Flat die pellet mill is suitable for small and medium wood pelletplant while ring die pellet mill is suitable for large scale wood pellet plant.

Fuel Pellets Cooler: to cool the hot pellets to the temperature similar to room temperature.

Pellets Sieve: to remove the residual fines in the pellets.

Biopellets Packaging Machine: weight and package the pellets automatically, especially for large scale pellet production line.

Technology of Pellets Manufacturing

• Collecting residues：The collected biomass is usually of different size and so it has to be sorted and prepared for further process ofpellet production.
• Grinding：The large biomass materials should be reduced to the size ofless than 6mm by wood hammer mill.
• Drying：The moisture content of the material for producing fuel pellets is about 1296-15%. Drying of the powdery materialcan be carried out by rotary dryer or pipeline dryer.
• Pelleting：The materials with the proper size and moisture content are fed into the wood pellet machine to make fuelpellets. There are two kinds of wood pellet machine, namely ring die wood pellet machine and flat die woodpellet machine.
• Cooling：The temperature of pellets after compression is very high, about go'(, so that cooling is an essential step in pelletmanufacturing. By cooling, pellets are stabilized, hardened and finally shaped.
• Sieving：Pellets are sieved to remove the residual fimes. Fines are harmful in use and they are generally reused in theprocess and re-pelletized.、
• Packaging and storage：Pellets are packaged automatically by the biopellets packaging machine in bags. Because pellets are highly proneto moisture, it is very important to provide enough storage of fnished pellets. Pellets also can be stored in theclosed silos.

Benefits for Paper Factories

Worldwide, the pulp and paper industry is the fifth largest consumer of energy, accounting for four percent ofthe entire world’s energy use. Around 20% of the manufacturing costs of paper are energy costs. Thus it is crucialfor paper factory to reduce the energy cost by finding a new clean and cheap fuel to substitute expensive fossilfuels. Fuel pellet is the one. One ton of wood pellets has the energy equivalent of 120 gallons of heating oil. Byproducing densified fuel pellets at the mill from mill residues and other waste wood to produce steam andelectricity for papermaking, the paper factory can reduce coal use to a certain percent and thus reduce energycost.

Benefits for Environment

Fuel pellets are considered carbon neutral, meaning that the amount of carbon dioxide released when burningpellets are consumed is the same as carbon dioxide consumed from the atmosphere while a tree grows in theforest. So fuel pellets reduce pollution to the air in a large extent. It is a sustainable and environmental-friendlyto dispose paper factory residues.

In order to reduce energy costs and protect the environment, it is a trend for paper mills to process paper residues in a sustainable, efficient, and environmentally friendly manner. The pellet machine produced by Zhengzhou Fude Machinery can produce fuel pellets from paper mill residues, which is a validated and effective method.