List of contents
List of Tables
List of Figures
List of Plates
List of Abbreviations and Symbols
II REVIEW OF LITERATURE
2.1 Harvesting and transporting of wastes
2.2 Handling and storage of wastes
2.3 Cutting energy and moisture content
2.4 Industrial use of agricultural wastes
2.5 Use in the production of organic manure
III MATERIALS AND METHODS
3.1 Physical properties of agricultural wastes
3.2 Design and constructional details
3.3 Working principle
3.4 Economics of machine
3.5 Performance evaluation
Chapter PARTICULARS Page No.
IV RESULTS AND DISCUSSION
4.1 Physical properties of agricultural wastes
4.2 Design of main components
4.3 Selection of standard assembly
4.4 Cost of construction
4.5 Performance evaluation
V SUMMARY AND CONCLUSIONS
VI SCOPE FOR FUTURE WORK
LIST OF TABLES
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LIST OF FIGURES
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LIST OF PLATES
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LIST OF PLATES
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LIST OF ABBREVIATIONS AND SYMBOLS
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It is seen that large quantity of agricultural crop residues is being wasted. The annual production of crop residues (including industrial waste) in India is estimated as 347.2 million tonnes (Anon., 1992). The manurial value and quantity of plant waste available vary from crop to crop and variety to variety.
Usually plant residues collected while preparing fields are thrown in nearby nalahs or burnt. Some material is utilized in farmyard manure along with dung and other waste, which turns in to manure after a long time. Therefore only a small proportion of such waste is thus put to use. A major disadvantage of most recyclable waste is their bulk i.e. it requires large space for accommodation. It is said that the annual stalks production of Castor, Cotton, Pigeon pea, Sesamum & Mustard crops in Gujarat is estimated 8.735 million tonnes (census, 1993-’98) and in India it is 59.007 million tonnes (census, 1991-’96) as given in Appendix I & II.
It has been observed by bio-scientists that if the waste is burnt, that affects on soil microflora, loss of nitrogen and organic matter but the phosphorus and potassium are retained in the ash. Theoretically at least they are returned to soil but again it depends on wind, rain and time. Therefore certainly there is no guarantee that they will remain in situ. Thus the burning of crop wastes results in the loss of organic matter. Also the process itself is hazardous, disturb the biological equilibrium, creates pollution problems, reduce nitrogen fixing bacteria and other organisms which are required to improve the soil fertility through decomposition of organic matter.
If the farmers collect stalks and throw in nearby nalahs or other place which requires more space for storing or it will take one to two years for decomposition and the resultant organic matter may not be completely useful after two years. Therefore in order to have adequate disposal, size reduction of the crop residues is an important step for recycling of agricultural waste. Most bulky residues need some type of pre incorporated physical processing or shedding to facilitate their rapid decomposition and mixing in the soil.
It has been established fact that finer particles (4 to 5 cm) decompose faster as compared to large particles. This needs pulverizing, which increase the surface area of the waste materials several thousand folds, thus exposing very large areas for micro organic reaction.
Shredder is ideal for disposal of course leaves, garden and agricultural wastes. Such as twinges, small branches, flower stalks straw, tree pruning etc. The finally ground wastes mixed with grass, logs and leaves, produce a light compost that encourages improvement of soil. It provides more oxygen and more energy for all the organisms involved in soil fertility process. The building blocks of any plant are the nutrients it absorbs from the soil through its roots system. Therefore the best way to dispose off farm waste is to turn it into compost. This scientific way returns the nutrients back to the soil in natural ways. Therefore the efforts must be concentrated towards effective utilization of all the wastes.
On the scientific background there are no materials in the world, which can be called a waste. Most of these materials can be used in one or in the other form like fuel, manure, mulcher, cattle feed and industrial uses but the efficient use of the wastes in the byproducts may be emphasized only based on their maximum utilization. Utilization of indigenously available organic resources for meeting the shortage of raw materials for related industries and inputs for agriculture is an important aspect of our national economy.
Serious efforts in this direction provide rich dividends to the farmers as well as solve the disposal problems, minimize pollution effects, open up evens for starting rural industries and self-employment or gainful employment for rural youth. It is more relevant way to avoid migration of youth from villages to the urban area in search of employment.
Despite their potential economic uses, the valuable natural resources have remained, more or less commercially unexploited. If the technologies developed are properly adopted particularly in the rural area of our country, it will provide supplementary occupation and means of uplift of the financial conditions and living standards of our villages.
India has the largest area under cotton cultivation in the world and therefore generates a huge quantity of cotton stalks, which is an agricultural waste. It is said that presently every year about 15 million tonnes of cotton stalks is available in the country (Anon., 1996). Mostly the bulk of these stalks are disposed off by burning in the field after harvesting of the cotton crop. It is obvious that much attention has not been paid to their various utilization.
After picking of cotton bolls, plants are usually left in the field. They are likely to harbour certain pests and insects, which may spread to the next crops. On the a limited scale, cotton plant stalks are used by the rural people as a source of as domestic fuel for cooking but the bulk of the stalks normally burnt in the field. Unlike most other agricultural residues, cotton plant stalk is comparable to the common species of hardwood with regard to fibrous structure and dimensions.
This stalk contains about 79 % holocellulose, 27 % lignin and 7 % ash (Anon., 1996). Therefore besides use as fuel, it can utilized for the production of boards, filler, pulp & paper, microcrystalline cellulose, sugars, furfural, lignin, animal feeds, corrugated boards & boxes, cellulose derivatives, as a cellulose substrate for growing edible mushrooms etc.
By using different chemicals and additives, the board can be made water proof, fire proof, termite resistance etc. Those boards meet BIS specifications and can be used for interior decoration, false ceiling, partitioning, paneling, etc. These boards are cheaper than those made from wood, as mechanical processing of cotton stalk consumes less power as compare to that for wood. The process there by is cheap and most ideally suitable for setting up of particleboard industry in rural areas.
The hard board prepared from cotton stalks is useful in furniture, partitioning, false ceiling, false ceiling, tabletops, paneling, building materials etc. Good quality Kraft paper as well as superior grade writing and paper sheets can be produced as compared to those produced from bamboo and hard wood. Cost wise, the paper production for cotton stalks in comparatively cheaper than those produced from conventional raw materials. The Kraft paper produced from cotton stalks can be conveniently used for the preparation of good quality 3 ply and 5 ply corrugated boards. Corrugated boxes of various dimensions can be prepared by using the boards. These boxes confirm to the BIS specifications and can be used effectively for the packaging of various types of fruits and vegetables, canned food, glassware etc.
Since cotton, castor, pigeon pea, sesamum & mustard stalks and other agricultural wastes production are seasonal. Where as requirement to industries based on it is continuous, a safe and economical storage must be provided, so that the greater part of the wastes can be available for future and continuous requirements of industries. Safe storage must maintain wastes in quality and quantity.
Bulk density of agricultural wastes are very low hence for the industries based on it there is a problems of handling and transportation as this increases the cost of final products. Hence the size reduction or volume reduction is very much important for effective utilization of all these sort of wastes.
Looking all these aspects and to utilize agricultural waste in industries as well as in manure effectively, the research work on “Design and development of agricultural wastes shredder” was carried out with the following objectives.
1. To study the crop parameters of castor, cotton, pigeon pea (tur) etc. for the design of shredder.
2. To design, fabricate and develop the agricultural wastes shredder.
3. To test and evaluate the machine performance.
II REVIEW OF LITERATURE
The review of literature helps the researcher to get aquatinted with the subject matter and canalize efforts in desirable direction. This chapter deals with the review of physical and mechanical properties of various agricultural wastes including relevant work on these aspects. Determination of shear strength, size, bulk density, moisture content of different waste are important technical parameters with reference to harvesting, transporting, handling, storage, size & volume reduction, industrial use and recycling of agricultural waste. These informations are basically required in the design and development of agricultural wastes shredder.
2.1 Harvesting and Transporting of Wastes
Ahlgren (1974) and Raison (1979) reported that, open fire of agricultural wastes/residues could be hazardous. Burning of residue cause in decrease of soil organic matter and water stable aggregates. Burning leads to loss of N and S by volatilization and rapid conversion of nutrients in the organic matter to inorganic forms. The nutrients appear in the ash, can also be lost rapidly by leaching or erosion. Burning also causes rapid soil desiccation and reduces the microbial population.
Sumner, et al. (1983) reported about cotton plant residue yielded 3 to 7 t/ha of dry material with 23 per cent of the material in plant roots.
Varshney (1987) reported that the low initial density and poor compaction characteristics of waste reduce carrying capacity and thus contribute to the high cost of collection and transportation. Compaction is frequently required to reduce volume and to increase the density of waste to reduce the transportation costs and the storage space required for final product.
Bajaj (1988) reported that chopping of any materials could increase the bulk density. Volume reduction of 65 to 70 % was observed that due to chopping when loosely filled, the bulk density increases approximately more than one and half times due to tight filling of chopped material. However in comparison to raw materials also reported that the carrying capacity of truck or trolley is almost doubled due to chopping and recommended that handling and transport of cotton stalks will be easier and economical by collecting and bailing of cotton stalks at certain stations, transporting them to chopping station and transporting the chopped materials to industry site.
Bhoi and Varshney (1988) studied the different parameters of castor stalk and estimated the stalk production as 1900kg/ha. They observed that the length and diameter of castor stalks vary from 63 cm. to 166 cm. and 1.44 to 2.52 cm. respectively. The tensile strength is 300.49 kg / cm2.
It is seen from above studies that the stalk production per hectare of cotton and castor crops as 3.0 to 7.0 t. and 1.9 t respectively. The length and diameter of castor stalks varied from 63.0 to 166.0 cm and 1.44 to 2.52 cm respectively. Due to chopping of cotton stalks volume reduction as 65 to 70 % in case of loosely filled and carrying capacity of truck or trolley is almost doubled. It is clearly seen that shredding of any materials can increase the bulk density, which is mostly required for handling, storage and effective utilization of bulky wastes.
2.2 Handling and Storage of Wastes
Hassan, et al. (1980) studied the compaction of wood chips for physical and pulping characteristics. They observed temperature of the containerized compacted and uncomplicated chips for 236 days of outdoor storage. Temperature of the uncomplicated chips was higher than those of compacted chips. The moisture content of the compacted chips after the storage period was the same as the green chips. Pulping results indicated that the compaction process neither damaged wood fibbers nor altered the chip response to conventional pulping.
Chepurnol, et al. (1985) conducted a test through cylinder choppers for chopping the cotton stalks. Tests were conducted on a rig set to a 5 mm chop length at a cutting speed of 27 m/s and the perforated hexagonal shear plates where spaced at 32, 35 and 70 mm intervals. They observed that a perforated shear plate reduced the mean weighted particle length and improved the homogeneity of the chopped materials.
Varshney (1987) reported that most agricultural crop residues have a bulk density less than 100 kg/m3. This requires densification of the residues and a large holding capacity of the reactor or frequently continuous feeding of the reactor. The first step of densification is the size reduction of waste by a shredder. The material is reduced in size, but not into a uniform size distribution. The densification facilitates bulk storage, handling, conveying and automatic feeding.
A test was conducted by Bajaj (1988) on locally fabricated chaff cutter, Sardar chaff cutter and ‘ROM’ machine developed by Shri Shivaji College, Amravati. He observed that performance of ‘ROM’ machine was found to be best in all respects amongst the three machines tested for cotton crop. With ‘ROM’ machine the uniformity index was found to be highest i.e. 71.15 % with an average size of the chips being 7.82mm. Having capacity of cotton stalk chopping as 0.30 t/h.
He also studied that the moisture migration was fast in open treatments as compared to the cover treatments. Moisture migration was more in unchopped substrate rather than chopped one amongst the covered treatments. The initials increase and subsequent decrease in the moisture content was maximum in unchopped open stacks, optimum in chopped materials in open stacks and minimum in go down or covered stacks which might be due to less lose of moisture in later case.
Anap, et al.(1996 ) observed that the bulk density of loosely packed cotton stalks was about 50 kg/m3 and that of densely packed stalks was almost double i.e. 95 kg/m3. The cotton stalks are very bulky, difficult to handle and transport without chopping. The bulk density of chopped cotton stalk is about 200 kg/m3. The chopping of cotton stalk gives a definite particle size. The definite chop size is very important while selecting suitable time - temperature combinations during thermal processing of chops. Using the laws of size reduction, definite particle size can be obtained by selecting suitable knives, shear plates and feeding mechanism. They concluded that the proper ratio of the speed of roller to fly wheel (1:11) and peripheral speed of knives (30m/s) yields as an average chop size of 6.50 cm. with 75% uniformity index.
From above studies, it can be concluded that the required proper ratio of the speed of feed roller to flywheel as 1:11 and cutter head speed as 27 to 30 m/s for an average chop size of 7.82 and 65.0 mm respectively for cotton stalks. The bulk density of chopped cotton stalks is about 200 kg/m3. The capacity of stalks chopping is about 0.3 t/h desired.
2.3 Cutting Energy and Moisture Content
Nagpal and Aggarwal (1973) reported that the energy consumed in cutting napier grass decreased with the increase in moisture content of the crop for a given throat size.
Zohns and Jenkins (1985) studied the energy and force requirements for shearing moduled Almond pruning. They reported that the cross cut shearing energy for almond tree pruning in influenced by moisture content and the size of individual branches. Energy ranged from 25.6 to 34.9 J/cm2 for green wood (34 % (w.b.) moisture content) and from 20.0 to 53.1 J/cm2 for dry wood (16% (w.b.) moisture content) for bundles made of uniformly sized stems in the range of 1.3 to 5.1 cm diameter. Bundles made of randomly sized stems averaged 33.0 J/cm2 for green wood and 40.0 J/cm2 for dry wood. Energy per unit area tends to increase with diameter for dry wood up to the maximum size (5.1 cm) tested, but tends to level off green wood in the range from 2.5 to 5.1 cm. Peak force during cutting is higher for dry wood than for green wood, although energy per unit area may be higher for small diameter (1.3 cm) green wood than same diameter dry wood. No discernible effects from blade thickness or tip angle on energy or peak force were observed in the size range tested. Power requirements for cross cut shearing entire modules are low (2.3 kW) but minimum force requirements are high (1152 kN ).
Bajaj (1988) observed that the cutting energy for cotton stalk decreased with increase in moisture content up to 40 % moisture level and then increased with further increase in moisture level. He concluded that the optimum moisture level for minimum cutting energy is around 40 %.
From above studies it can be concluded that the cutting energy per unit area tends to increase with diameter for dry wood but tends to level of green wood of almond tree pruning. Peak force for cutting almond tree pruning is higher for dry wood than for green wood. The thickness for tip angle of cutting blades does not effect on cutting energy or peak force. The optimum moisture level for minimum cutting energy is around 40 per cent for cotton stalk.
2.4 Industrial Use of Agricultural Wastes
Several million tonnes of castor, pigeon pea, and cotton plant stalk are currently available in the country, and particularly in Gujarat state. Cotton stalk can be utilized for following industrial uses (Bajaj, 1988; Pandey and Mehta, 1979; Sundaram and Pandey, 1976). Cotton plant stalk contains about 79 % holo cellulose, 27 % lignin and 7 % ash. In comparison with other agricultural wastes, cotton stalk is closer hardwood in respect of its fibrous structure, evincing good potential for the manufacture of particle boards, pulp and paper, hard board, corrugated board & boxes, micro crystalline cellulose, sugar and lignin. Agricultural wastes also useful as filler, in animal feed and making organic manure.
2.4.1 Use in the production of boards
Cotton plant stalk contains about 46 % a Cellulose and about 26 % lignin and can be used as a raw materials for preparing composite boards. The stalk cuts in to small chips and mixed with natural or synthetics resins can be made into particle boards for different end uses. The same materials can be ground to different particle sizes or can be separated into fibbers to produce hard boards. In the presents of adequate moisture, lignin present in the material helps in binding the particles together (Anon., 1977). It has been reported from the laboratory scale work has shown that various types of boards confirming to ISI specifications can be prepared from cotton plant stalk. Boards prepared from the stalk can be further improved by a hardening process.
2.4.2 Use in pulp and paper making
Varshney (1987) reported that most of the crop residues have cellulose as major constituent, their effective utilization may be in paper and pulp industries. The cellulosic material with low lignin content is the desired raw material for pulp production. Depending upon the properties, the crop residues may be used for the preparation of different types of papers like fine paper, blotting paper, filter paper, packing and file board, straw board, greeting card, album paper and cover paper etc.
Bajaj (1988) reported that the cotton stalk is much cheaper than wood, which is the conventional raw material for pulp and paper making. Quality paper grade pulp can be made from debarked cotton plant stalk by the conventional process. The resulting pulp will be good for making newsprint.
Cotton stalk can be converted into pulp by a cheap chemico-mechanical process. The pulp from these process thus obtained can be used as such or after bleaching to improve brightness for making newsprint and printing paper as well as a variety of paper boards.
Two types of pulps, viz. Soda and Kraft can be prepared from cotton plant stalks (Anon.1996). The soda pulp can be used as such for making wrapping paper of after bleaching using a two steps hypochlorite process for making writing and printing grade paper. Kraft pulp can be used for making good quality Kraft paper as well as superior grade writing papers and paper sheets can be produced in comparison to those produced from bamboo and hardwood. Coastwise, the paper produce from cotton stalks is comparatively cheaper than those made from confessional raw materials.
Cotton stalk, wood flour, ground to fibrous form, can be used as filler for linoleum and moldable plastics like Urea- formaldehyde and Phenol formaldehyde plastics. The light colour and bulkiness are it’s special advantages. Moulding powder can be prepared by impregnating the filler particles with a suitable resin and compounding it with pigments lubricants and catalysts. It can be used as filler for rubber and in the production of explosives (Reynolds, 1953). It also acts as a mordant for colours (Grant, 1958).
2.4.4 Source of lignin
It is reported that lignin present to the extent of about 27% in cotton stalks can be easily obtained as a by-product during pulping process (Anon. 1996). The industrial applications of lignin include preparation of Lignin Sulphonic acid, which is used as raw material in ion exchange resins, as a grinding aid in cement concrete productions, in insecticides, fungicide formulations, an important ingredient of oil well-drilling muds, etc. Useful products like Vanillin, Dimethyl-Sulphide, etc. can also be obtained after degradation of lignin.
2.4.5 Production of micro-crystalline cellulose
Due to high contents of alpha cellulose in cotton stalk, it can be a suitable substrate for the preparation of micro-crystalline cellulose, which find a number of industrial application. Micro-crystalline cellulose has various uses in pharmaceutical industry and also in preparation of low calories food (Anon., 1996)
2.4.6 Production of sugars
Cotton plant stalks, after delignification and purification, can be utilized for the production process of sugars.
2.4.7 Production of furfural
Through a sequence of hydration and dehydration reactions, pentosans present in cotton plant stalk can be converted into furfural. Which is an important industrial chemical. Several methods for the production of furfural from agricultural products have been reported (Bajaj, 1988).
2.4.8 Animal feeds
The cellulose of woody; plants is unsuitable as cattle feed because of the highly crystalline nature of it’s molecules and the existence of lignin carbohydrate complex. By chemical treatments the availability of wood cellulose to enzymatic or microbial systems can be enhanced. The stalk, which is similar to wood in many respects, can be hydrolyzed to produce concentrated sugar solutions or molasses for use as animal feed. Wood sugar molasses has been reported to be a highly digestible carbohydrate feed (Anon. 1955). It can also be used as roughage. It is reported that cotton plant stalk after hydrolysis, is a suitable substrate for proteins (yeast) which is useful cattle feed because of it’s high protein and vitamin B content. One tone of cotton stalk is reported to yield 200 kg of yeast protein. The digestibility of cotton plant stalks increases on delignification (Salyamora and Bronovitskil, 1970).