I. Abstract
Switchgrass is a tall-growing, perennial, warm season grass. It generally needs relatively little herbicide, fertilizer, lime or water, So switchgrass has attracted many peoples’ attention. The market value of switchgrass pellet is considerable. The preprocessing of making switchgrass pellet including Chopped Hay, Fine grinding, Drying, Pelleting, Cooling, Screening and Packing.
II. Introduction of Switchgrass
Switchgrass has been identified as an important biomass energy crop. It is a native grass to North America and can grow up to 2.7 m high, it is high yielding, has low input, grows long fibrous root system, is a perennial and is beneficial to water quality and wildlife. It is compatible with conventional farm practices and equipment, and can be sold as forge for livestock. Switchgrass is also a significant carbon sink, sequestering carbon in its extensive root system that remains buried after harvest.
Switchgrass is a source of low-quality fodder for animals, and with hay prices expected to be in the $80-per-ton range (at 15% moisture), switchgrass might be more valuable as livestock feed than as a cellulosic feed stock. There are other potential markets for switchgrass as an energy crop: 1) Pellets for fuel. This market is too new to reliably determine the value of switchgrass for use as fuel pellets. 2) Co-firing in steam boilers, usually with coal. However, switchgrass bales will not be price-competitive with coal, except perhaps in areas that have renewable-fuel portfolio mandate requirements. In these situations, marginal substitution of switchgrass for coal might be cheaper than substitution of other renewable fuels.
III. The Market value of Switchgrass Pellet
Switchgrass in particular has attracted attention as a fiber source for bio fuel since it will typically result in lower ash content than other fiber sources. It has been estimated that switchgrass pellets can be produced and marketed for a price of $150/MT. This price could include $50/MT paid to switchgrass producers for new baled switchgrass product, $50 for transportation and pellets, and $50 for packaging and marketing of the pellets. Switchgrass pellets have been observed to produce in the size of 18.5 GJ/MT for late fall harvested switchgrass and 19.2 GJ/MT for overwinter switchgrass. As a comparison wood has been reasoned as producing 19.8 GJ/MT and wheat straw at 19 GJ/MT. If a final pelleted price of $150/MT is considered, switchgrass pellets as source of energy would cost in the range of $7 to $8 per GJ. Furthermore, if a comparison energy source of natural gas is priced at $17/GT (late January price according toenergyshop.com), then it has been estimated that an average homeowner would recoup the costs of a pellet stove purchase in three to four years.
IV. The Preprocessing of Making Switchgrass Pellet
Before pelletizing there are several preprocessing step need to be considered.
1. Chopped Hay
When you harvest the material, the switchgrass should be baled and transported to the plant. There is a straw breaker to cut the swichgrass into pieces, this machine can process both dry and fresh materials, so the swichgrass can be chopped directly. And then transported to the slicer and hammer machine.
2. Fine Grinding
The Slicer and hammer mill is used to reduce the size of feed stock particles in preparation for pelleting. This machine is suitable for biomass pellet industry to pelletize such materials as straw, corn stalk, peanut shell, weed and tree branches and twigs, etc. It’s used for cutting Switchgrass into smaller pieces of 2-5mm, Material after conveyed into the crushing chamber will be pulverized by the swiftly rotating hammer plates. Then smashed pieces will be tossed out of the machine via centrifugal force from the rotor and suction force from the fan. Particles failing to pass through the sieve meshes will be re-pulverized as same as the process above.
3. Drying
Rotor drum dryer is normally used to reduce feed stock moisture to levels suitable for pelleting. Moisture levels in swichgrass usually contain between 12-20% moisture. Feed stock at the rotor drum dryer is dried to between 10-12% after fine grinding.
Rator drum dryer is normally used to reduce feed stock moisture to levels suitable for pe
4. Pelletizing
A pellet mill extrudes material under high pressure through a die using a configuration of rollers. Through experimenting, we found that moisture content of the material fed into the pellet mill is very important. Initially when we fed dry feed stock material into the pellet mill it would either plug the die or would make non-durable, unacceptable pellets. Initially the pellets were very low in density, looked like shredded wheat, without the sheen typically seen in a high quality pellet. We realized after talking to industry experts that we needed steam.
5. Cooling
Pellets exit from the pellet machine at high temperature and are cooled with forced air to prevent “sweating”. A cooling chamber is place where the pellets can be rapidly cooled, we uses cooling system of pellet machine including two cyclone separators and sedimentation box wit soft pipes and hoop.
6. Screening
A screening process is used to separate fines from the finished pellets before bagging. This step is essential for producing high quality, user-friendly pellets. Fines can be redirected to the pellet mill by conveyor or auger for reprocessing.
7. Packing
The final step in the production process is packing, there is an Automatic packing weigher, this machine consists of a weighting system, conveying system, packing system and intelligent controller. The package specification is 10kg~80kg (22.065lbs~176.52lbs).
V. Conclusion
Switchgrass pellets are environmental friendly and some even consider it carbon negative-meaning that the grass growing in fields remove more carbon from the air that is expelled from equipment used to plant, harvest, and process it. Switchgrass pellets have a high BTU output (16,020,000/ton). It requires less energy to plant, manage and harvest over a number of years compared to corn. This may give native grasses an advantage when comparing your energy investment to energy return.
