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§ 1.2 The role of the pneumatic transport system in the delivery of raw cotton to the technological process by air flow
After harvesting the raw cotton grown in the fields, it is transported to the ginnery by trailers, and then placed in warehouses and bales, depending on the type and variety.
A variety of vehicles can be used to deliver raw cotton to the technological processes of primary processing on the territory of ginneries. That is done using a belt conveyor, augers and pneumatic conveyors. Transportation of raw cotton to processing plants and equipment, from nearby mills and warehouses, mainly by pneumatic transport are given. The pneumatic transport system is characterized by high efficiency in the supply of raw materials throughout the enterprise, as well as the simplicity of construction and, most importantly, the ability to easily move from one place to another. Another advantage of pneumatic transport is that during the transportation of cotton in the air stream, the raw material becomes thinner and a certain amount of dust and dirt is released. Also, the process of transporting cotton by air has a direct effect on reducing the moisture content of cotton. It is also easy to repair and reconstruct.
The pneumatic transport system is the main equipment in the supply of raw materials for technological processes in ginneries, as well as in the interconnection of technological equipment. There are several types depending on its processing. That is, they are suction, spray, and suction-spray types.
The suction type of pneumatic transport equipment is widely used in cotton ginning enterprises and it is an integrated system consisting of several shears.
Figure 1. Pneumatic transport system and devices located in it.
1st chamber, 2nd chamber spoiler, 3rd air duct, 4th stone holder, 5th separator, 6th centrifugal fan, 7th cyclone, 8th dust chamber.
It is known that raw cotton imported from the fields at the ginnery depends on the variety and variety at the enterprise placed on the stakes. The raw material from the cotton bales is removed using a bale breaker RP-1, which supplies it to the air-suction pipe in the same way as the raw bale.
The pneumatic transport system works as follows: when the fan moves, a strong air flow inside the pipes and devices is directed to one side, resulting in an air flow along the pipe, which attracts the raw cotton, which is supplied by means of a spool. Thus, there is a flow of cotton in pneumatic transport. When the flow of cotton in the pipe occurs, a certain part of the dust and dirt mixture in it moves away from the cotton.
The reason for the occurrence of dirty mixtures in the cotton is that during the picking, transportation to the enterprise and its ginning, various foreign compounds are added to its composition. Mixtures that are foreign to such cotton are called contaminants. They are mineral and organic according to their origin. The mineral includes soil, rock and sand, while the organic mainly includes cotton and its residues as well as organic compounds. It is also divided into two types, depending on the size of the impurities in cotton, ie small and large impurities. If the size of the impurities is less than 10 mm, it is called minor pollution, if the size is more than 10 mm, it is called large pollution. It is also divided into passive and active types, depending on the method of separation of contaminants. Passive mixtures are located on the surface of the cotton pieces, which are easily separated when shaken lightly. Passive mixtures, on the other hand, are more difficult to separate because they are deeply attached to the cotton pieces.
When cotton is moved in an air stream, the heavy impurities (rock and metal fragments) attached to it are separated in stone trapping devices located in the pneumatic transport system. There are two types of stone handles according to the principle of operation. That is, there are horizontal and vertical types. However, cotton gins mainly use a vertical stone holder. This is due to its high stone-holding efficiency and that it is easy to release the accumulated foreign matter into the external environment. The vertical stone holder is installed in the middle of the pipe where the horizontal pipes rise, i.e. in the vertical direction. As the cotton raw material coming in with the air flow through the horizontal pipe moves in a vertical direction, the air pressure inside the pipe changes and objects heavier than the cotton mass fall into the stone holding hopper unable to rise.
Also, the main device that is part of the pneumatic transport system is the separator device. This is because the separator allows the product to be separated from the air flow being transported in order to drop the product at the desired point during air transport from one place to another. In addition, cotton separators also slightly remove dust and fine contaminants found in cotton. The separator device lowers the cotton raw material to the desired position using a vacuum valve after it is separated from the air stream.
The air flow sucked from the separator device goes to the fan and the air flow is directed from the fan to the cyclone device. In a cyclone device, dust and fine particles are trapped by centrifugal force. Since the air from the cyclone also contains a small amount of aerosol particles, it is directed to the dust chamber, and after entering the air chamber, the particles in it settle under the chamber and the air is cleaned and released into the atmosphere.
The location and capacity of pneumatic transport equipment in ginneries is determined by the volume of cotton received by the enterprise, the capacity of the enterprise's cotton processing equipment and the distance between the shops and gins. Typically, the established distance for transporting cotton by pneumatic transport in the enterprise can be 200 m and more. If the transport distance is high, additional devices will need to be added to the system. The average capacity of the device is 15 tons per hour. The effect of the installed length of pneumatic transport on air productivity during air transportation of raw cotton was studied in the study [17], which showed that the connection of additional equipment to the system and moisture content of cotton reduces labor productivity by 10-15%.
Also, in the process of air transportation of raw cotton, the devices in the system have a sharp impact on the quality of raw materials due to the working conditions and high humidity. That is, an increase in the moisture level in the cotton causes mechanical damage to the seed when the cotton is exposed to the working bodies of the device, which in turn causes the fiber to separate with the seed coat during ginning and to be added to the waste during cleaning.
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