Abstract
Introduction
Materials and methods
Equipment
Results and discussion
Conclusion
Paper No.9401
Shen Zonglin* Han Baoqi** Yuang Hongyin** Liu Guoxi** Gou Zhijian* Li Changhai* Li Hongtao*
* Jilin Engineering Institute, Changchun, 130000, China
** Jilin Agricultural University, Changchun, 130118, China
|
Biomass energy is a natural transformation form of solar energy. It is the main fuel for life in the countryside of our country. But the technology of transformation is lagging behind, so there is much waste during transformation. The purpose of this article is to introduce a new technology for transforming biomass energy, that is, using the solidifying and charring method to increase the utilizing rate of biomass energy and to open up a new area of energy resources in the country. |
Energy shortage is a prominent problem in the world, which restricts the development of agriculture and industry. In the near future, the energy consumption structure of our country will not change, that is, its dependence mainly on coal. But in the countryside (there are about 900 million farmers in our country), people basically use agricultural plants, straw and cortical hulls as living fuel. They burn more than 200 million tons of biomass fuel each year by the direct ways. The average thermal efficiency is only about 10%. At the same time, such burning results in a great waste of fuel.
Biomass energy amounts to 61% of the energy in the countryside. If we change the traditional form of burning and apply the solidifying and charring technology to convert it into shaped fuel, the utilizing rate will increase up to four times, and it will have special burning characteristics which coal and charcoal do not have.
There will be a bright future if we apply solidifying and charring technology to develop biomass energy resources.
1. Our country has a large area and is rich in resources. It also has very rich biomass energy resources. If collected, these will reach to about 400 million tons, which can be converted into 200 million tons of solid fuel. That is a great amount of substitute energy.2. In the areas where coal and natural gas are used, people do not burn agricultural straw at the side of the fields and roads any more. Thus they can produce solid fuel to increase economic benefits.
3. Solidifying can increase the utilizing efficiency of the fuel, and the remaining straw can become humus fertilizer in the fields, which does a great deal for agricultural production and can also help maintain ecological balance.
4. Solidified and charred fuel has exceedingly good characteristics. It can mitigate the contradiction of energy tension of our country, can be used for domestic heating and as fuel in industry instead of coal, for metallurgy, textile, active carbon and food industry fuel instead of charcoal.
Biomass is a common material in nature, for example, agricultural straw: corn straw, wheat stalks, rice stalk, cotton stalks and straw, etc, cortical hulls, rice hulls, corncobs, husks of sunflower seeds and melon seeds, peanut husks and cotton seed hulls, etc. All green plants belong to the category of biomass. The basic tissue of biomass is cellulose, hemicellulose and lignite. In addition, there are some resins, fats, enterpanes and other materials.
Cellulose is a kind of macromolecular polysugar which has colloidal characteristics. Its molecular formula is C6H10O5, which is a microcolloid long-chain structure. Hemicellulose contains polypentose, polyhexose and polyuronic acid glycoside, etc. and is a macromolecular compound. Its molecular formula is C5H8O4. Lignin contains aromatic and hydrocarbon compounds, its empirical molecular formula is C22H20O7 and C40H42O16, etc. The three elements mentioned above have a characteristic in common, that of malacia at adequate temperature. In addition, they can plasticize at the same time. Plasticilization may produce stickiness, if pressure is applied simultaneously. The unsolidified biomass, through stickiness, pressure and its force of friction, can cohere together tightly and be formed into any size and shape, to form solid materials after natural cooling.
The mechanism of biomass suits not only the farm waste materials mentioned above and cogongrass, etc., but also forest waste materials such as sawdust, wood shavings, wood powder, branch, bark, leaves etc. as well as hard cortical shells such as coconut shells, walnut shells and pine nut shells; also waste residues such as bagasse, wine residue, traditional Chinese medicine residues and uronic residue, etc. Therefore many materials which contain the three elements mentioned above can become resources for solid, shaped fuel.
During the process of heating biomass to solidifing temperature, moisture, carbon dioxide, methane, acetic acid and tar are produced in the form of gas. The amount of gas varies according to the type of biomass and solidifying temperature.
Besides temperature and pressure, moisture is also a major factor influencing solidifying and shaping of the fuel. When the moisture contained in biomass goes beyond 10% to 13%, solidifying and shaping cannot be carried out. In the contracting room, when biomass is contracted, some moisture is retained. The rest of the moisture is extracted through vents. When moisture is less than or equal to 10% to 13%, vapour pressure in shaped fuel is equal to the cohering force. When moisture is more than 13%, vapour pressure will become larger than cohering force. Under this condition, once the shaped fuel leaves the contracting room, its vapour will be released. This makes shaped fuel unsolidated and disintegrated. Therefore, the moisture of raw materials for solidifying and shaping biomass varies from 10% to 13%.
The technology of converting biomass energy into shaped fuel is to be carried out by making the use of the mechanism of solidifying biomass. By the use of contracting and shaping equipment, crushed and porous biomass can be heated to 250 to 350°C, and the pressure can be raised to 0.5 to 1 t/cm2. Under such conditions, biomass can be extruded into a new type of fuel with specific sizes and shapes. Here is the technological process: raw material ->| crushed -> dried ->| contracted ->| packed
The equipment used in making the biomass shaped fuel are grinder, desiccator and formatore. Of these, the formatore is the most important. It can be screw, cylinder or piston type, although the screw type is the most common. It has the following shape and structure.
This type of formatore, compared with the same kind of equipment made by other factories, has the advantage of being small and convenient, it has less parts and produces more. It can produce up to 200 kilos of shaped fuel per hour. In Liaoning and Jilin province some factories, which have been using this type of formatore, have reported that the cycloidal pinwheel reduction gear of this type has greater strength, and its fuel is dense and works quite powerfully. At the same time the belt pulley reduction gear made by other factories has less strength, it idles from time to time and does not save electric energy. Thus, even when using the same motor, this equipment seems to be much better than others.
Fig. 1. Screw-type formatore
1. motor
2. reduction gear
3. bearing
4. compression room
5. hopper
6. chillroom
7. heating ring
8. contracting room
9. mount
The leading end of the screw of the screw-type formatore gets comparatively great abrasion. The life span of screws made by other factories is between 40 and 50 hours. Although we also use similar materials to make screws, since we use the best wearproof-treated method, reasonable screw distance angle height and other factors, and adjustable ration of the contracting room, the life-span of the screw can be up to 300 hours, thus solving this problem.
There are various types of biomass in nature. Which types are suitable for solidifying into shaped fuel must be verified through experiment. The following are such experimental data:
1. Some materials available in Jilin province for solidifying and shaping fuel are listed in Table 1 .
Table 1. Materials available in Jilin province
|
materials |
thermal value kJ/kg |
moisture % |
ash % |
real specific weight Kg/m2 |
yield kg/h |
|
sawdust |
23500 |
10 |
5--7 |
1.42 |
125 |
|
corn cob |
23020 |
10--11 |
4--7 |
1.39 |
120 |
|
rice hulls husk of sunf |
16640 |
10--12 |
8--10 |
1.36 |
124 |
|
lower seeds |
2300 |
8--10 |
5--7 |
1.37 |
120 |
|
peanut husk |
22820 |
9--11 |
5--7 |
1.39 |
118 |
2. Solidifying temperature
Solidifying temperature is listed in Table 2
Table 2. Solidifying temperature characteristics
|
materials solidifying temperature (°C) |
heating-power KW |
temperature-rising time h |
|
corn cob 250 - 300 |
4.5 - 6 |
0.5 - 1 |
|
sawdust 280 - 350 |
4.5 - 6 |
0.5 - 1 |
|
rice hulls 280 - 330 |
4.5 |
0.5 |
|
husk of sun |
||
|
-flower seeds 250 - 300 |
4.5 |
0.5 |
|
peanut husk 250 - 290 |
4.5 |
0.5 |
|
straw 270 - 320 |
4.5 - 6 |
0.5 - 1 |
|
corn stalk 280--330 |
4.5 - 6 |
0.5 - 1 |
3. Solidifying pressure
In the screw-type formatore, the solidifying pressure is generated through the contracting thrust which is created by the rotation of screws driven by the motor.
Table 3 lists the data acquired from experiments:
4. The temperature of shaped fuel
Fuel produced by the screw-type formatore is bar-shaped. Its external radius is 67mm and the diameter of the interior hole is 20mm. When the fuel bar leaves the contracting room and contracting cylinder/its temperature is:
edge temperature: 250--280°C
central temperature: 280--470°C
Table 3. Lists the data acquired from experiments
|
motorpower |
ration of deceleration* |
belt pulley deceleration |
note |
|
|
1: 11 |
1: 17 |
|||
|
7.5kW |
0.5 - 1t/cm2 |
0.5 - 1.3t/cm2 |
0.5 - 0.8t/cm2 |
belt pulley deceleration occurs sometimes |
|
10 kW |
0.5 - 2t/cm2 |
0.5 - 2.2t/cm2 |
0.5--1.3t/cm2 |
idling phenomenon |
* Decelerating machine is belt pulley reduction gear.
Shaped fuel, also known as man-made coal or fuel bars, has many advantages: high thermal value (about 21, 0 00kJ/kg); small bulk and high specific weight (easy to preserve and transport); clean and healthy to use, no polluting effects on the environment (a clean fuel); easy to ignite, its fire roaring and its thermal efficiency great (45%). On the other hand, uncontracted straw, cortical hulls and so on, have low specific weight and low thermal efficiency. From this point of view, contracting these agricultural wastes into shape is a very good means. It opens up a hopeful way for the utilization of rural energy resources. Shaped fuel, besides the use in our families and in the catering trade, can also be used in industry. It can replace boiler coal, and can be dried into carbon bars.
Fuel bars pressed from rice hulls can also be used to keep the surface temperature of molten steel and to anti-oxidize in the metallurgical industry.
In short, wherever coal is used, fuel bars can take its place.
China is a large agricultural country. Crops are grown year after year. It is these numerous crops that become the treasure-house of raw materials to be used for making shaped fuel.
Burning straw and cortical hulls in the countryside pollutes the environment, wastes energy resources and has low thermal efficiency. That is, this method is quite unreasonable. If the technology suggested here can be adopted, shaped fuel will certainly become a commercialized "clean energy resource" and the substituting energy for many activities. It will play an important role in improving farmers' lives and speeding up rural development. It can help save energy, protect the environment and keep an ecological balance. That is, its utilization will prove to have economical and social benefits.
References
1. Practical Energy Sources, Issue 3, 1990 The Energy Institute of Jilin Province
2. Drying Equipment Design, the Editorial Board of the Great Books of Chemical Equipment Design, Press of Science and Technology of Shanghai
3. Wood pyrolysis Technology, Book One, B.H.Kozlov, Press of Jilin Industry
