Straw for Pellets Fuel Production

Straw for Pellets Fuel Production

Straw pellets are widely used in daily life. Typically, straw pellets are used as animal bedding, animal feed, and heating fuel for domestic and industrial use.

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Introduction of straw

Straw is a general term for the stem and leaf (ear) part of a mature crop. Usually refers to the remainder of wheat, rice, corn, potatoes, rape, cotton, sugar cane and other crops (usually coarse grains) after the seeds are harvested. More than half of the products of crop photosynthesis exist in straw, which is rich in nitrogen, phosphorus, potassium, calcium, magnesium and organic matter, etc. It is a multi-purpose renewable biological resource. It is characterized by high crude fiber content (30%-40%), and contains lignin and so on. Although lignocellulose cannot be utilized by pigs and chickens, it can be absorbed and utilized by livestock such as ruminants, cattle and sheep.

Worldwide use of straw

In the United States

there are 24 agricultural states that can collect about 45 million tons of straw each year, which is used as feed, or used to build houses, and the whole bales of straw are extruded with high strength to fill the walls of new houses; in addition, the United States is also actively promoting In the renewable energy business, straw is used as an emerging alternative fuel, especially biofuel.

In Europe

it has created a new way of straw power generation.

In Japan

people mainly turn the straw into the soil layer and return it to the field as fertilizer, and also use the straw as roughage to feed livestock.

In China

In 2017, China's total theoretical straw resources reached 1.02 billion tons, an increase of nearly 400 million tons compared with the early 1990s. Among them, the straws of corn, rice and wheat were 430,240,000,000,000,000,000,000,000,000,000,000 tons respectively, and the proportion of straw of the three major crops reached 83.3%. The amount of straw that can be collected in China is 840 million tons, and the utilized amount is about 700 million tons. The comprehensive utilization rate of straw (the ratio of utilized amount to the amount that can be collected) exceeds 83%. The utilization rates of fuel, base, and raw materials are 47.3%, 19.4%, 12.7%, 1.9%, and 2.3%, respectively, and a comprehensive utilization pattern of fertilizer and feed has been formed.

Main characteristics of straw

Generally, straw consists of 80-90% cell and 10-20% lumen, the inside substance, consisted of 5-10% silica and 5-15% extractives, most of which are water soluble. In the terms of molecular aspect, straw cell walls is just like woody cell walls, consisting of cellulose, hemi-celluloses, and lignin. Cellulose is aggregated in fibril which are surrounded by molecules. Lignin is the “glue” which links individual cells to form plant tissues and fibrils to form the cell wall. The straw is differentiated from the wood in terms of content of celluloses, hemi-celluloses and lignin. Straw has lower portion of cellulose and lignin but higher portion of hemi-celluloses.

Due to its wood-like composition, straw can be used to make straw pulp or converted into straw pellets. According to the particularity of straw, the granulation process of straw can be summarized as follows:

1. Raw materials preparation:

Straws usually has a high potential of dust, which is affected by the way of harvesting. Thus, straw needs to be screened from contaminants, such as, dust that may influence straw pellet quality and other alien materials, such as, stones, metals, and those that may damage the pellet mill in the following procedures.


Straw biomass is a tube-like or pipe-like material with a diameter of 4 to 8 mm, and wall thickness around 0.3-0.6mm. With the tube/pipe-like structure, straw can be easily processed and get the desire particle size. Generally, the grinding of straws including cutting and chopping of the straws.

3. Drying stage:

Usually, the straw is transported in the form of air-dried bales with a moisture content of about 15%, which is suitable for the production of straw pellets. Therefore, the drying process of the straw pellets is omitted. But if the straw moisture is large, the drying step is necessary.

4. Conditioning:

Straw requires special conditioning to achieve desirable hardness. Straw conditioning includes the application of steam(and /or water) and the addition of binding agents or additives. Conditioning is required to achieve the necessary temperature and moisture to get the malleability and to melt the lignin to act as binding agent. Binding agents are needed to strengthen the hardness of the pellets and also to decrease abrasion during pelletizing.

5. Pelletizing:

During pelletizing, it is necessary to consider the factors such as, materials moisture content, density, particle size, fiber strength, and the natural binder for they can influence the pellet quality.Common problems in the straw pelleting process are blockage and breakage of pellet molds, overheating, high energy costs or poor pellet quality, and high pelletizer maintenance. To avoid the above problems, a high-quality granulator is required.

6. Cooling and screening:

The newly extruded straw particles are hot and soft, and need to be cooled to obtain the desired hardness. At the same time, the screen on the cooling machine is used to screen out the particles that do not meet the standard forming effect.

Application range of straw pellets:

Straw pellets are widely used in daily life. Typically, straw pellets are used as animal bedding, animal feed, and heating fuel for domestic and industrial use. Straw pellet technology is now widely used and straw pellet machines are available worldwide, which makes straw pellets popular in heat and power production.

Straw pellet production process:

The straw solidification molding technology uses agricultural wastes such as straw, wheat straw and corn straw as raw materials, and is pressed into solid biomass fuel that can be directly burned through special equipment straw pellet machine, crushing treatment, compression treatment and other processes.

1. Broken and pulverized.

Broken and crushed. Cut or pulverize the straw to be pressed, and control its length to be less than 30mm.

2. Drying

The crushed straw is sent to the dryer through the conveyor, and the moisture content is controlled within the range of 10-15%.

3. Storage of materials after drying

After drying, the raw materials are stored in piles after unloading Cyclone, or stored in silos.

4. Pressed pellets

The material is fed into the feed port of the biomass pellet machine through the feeding conveyor, and the machine rotates through the main shaft to drive the pressure roller to rotate. Through the rotation of the pressing roller and the interaction force with the ring die , the material is forced to be extruded from the die hole.

5. Cooling of pellets

Then the pellets are fed by a special conveyor and sent to the pellet cooler.

6. Packing

After the pellets are cooled, the pellets are sent to the packing scale or the ton packer for bagging and packaging.`

The solidified biomass pellet fuel has a large specific gravity and a small volume, which is convenient for storage and transportation. It is a high-quality solid fuel with a calorific value of 3200-4500 kcal. It has the characteristics of flammability, less ash and low cost, and can replace firewood. And raw coal and other fuels. Particles are widely used in heating, living stoves, industrial boilers, biomass power plants, etc. As a new commercial energy, straw pellet fuel has been widely used in various industries. And because of its high density, high calorific value, regular shape and good fluidity, it is very convenient to realize automatic combustion control, which can save a lot of energy costs for enterprises.

Notes in Pellet Processing:

  1. Before the worker gets on the machine, the operator must read the instruction manual carefully to understand the various technological processes of the equipment.

  2. In the production process, strictly follow the procedures and operation sequence, and carry out the installation operation as required.

  3. The main equipment needs to be installed and fixed on a flat concrete floor and fixed with screws.

  4. Smoking and open flames are strictly prohibited at the production site.

  5. After each boot, it needs to be idle first. After the equipment runs normally without abnormality, the material can be fed evenly.

  6. It is strictly forbidden to add hard impurities such as stones and metals into the feeding device. In order to avoid damage to the granulation chamber, iron should be removed before granulation.

  7. It will be dangerous, if the material is moved by hand or other tools during the operation of the equipment.

  8. If abnormal noise occurs during the production process, the power supply should be cut off immediately. After checking and handling the abnormal situation, the production can continue.

  9. The feeding must be stopped first, and then the machine should be shut down. After the raw materials of the feeding system are processed, the power supply should be cut off.

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