Summary: The working principles and characteristics of several commonly used filters for micro-irrigation are introduced. The history of the research and development of filters for micro-irrigation is briefly described. Aiming at the needs and trends of micro-irrigation development. The development trend of filters is discussed. Points out the topics that need further research in the future. It has certain positive significance for the promotion and application of micro-irrigation technology and the research and development of filters.
Micro-irrigation is an advanced water-saving irrigation method. However, due to the water flow aperture of the emitter in the micro-irrigation system is generally very small. It is required that the irrigation water does not contain dirt and impurities that cause the blockage of the emitter. Therefore, it has relatively high water quality requirements.
In fact, any water source such as well water, river canal water, rainwater, and pond water contains various dirt and impurities to varying degrees. Therefore, sediment treatment for irrigation water sources is essential. The filter for micro-irrigation is the key equipment of the first hub in the irrigation system. The quality of the filter is not up to standard, or the design and use are unreasonable, which will increase the operating cost of the system or reduce the quality of irrigation water, and even cause the entire micro-irrigation system to be paralyzed and scrapped. Therefore, the development of micro-irrigation technology requires advanced filters.
wedge wire screen for Micro-irrigation
Wedge wire screen filter is mainly used for irrigation in areas with good water quality. When the water quality is poor, it can be used in combination with other types of filters in a single stage or combination.
It can be installed in primary water filter equipment. There are various forms of cleaning, including vertical and horizontal installation methods, and manual and automatic cleaning methods. This type of screen is beneficial for removing fine sand and organic matter from the water. Mainly used for filtering water quality containing organic matter and sediment in reservoirs, dams, ditches, rivers, and other open water sources.
Working Principle And Characteristics Of Micro Irrigation Filter
Commonly used filters in micro irrigation systems:
- Hydrocyclone filter.
- Sand filter.
- Mesh filter.
- Laminated filter.
Hydrocyclone filter: A device that uses the centrifugal force of water circulation to accelerate the settling of heavy phase particles and enhance separation.
The flow of its internal fluid is a special three-dimensional strong rotational shear turbulent movement. This vortex motion consists of two basic swirling fluid flows. That is, the external swirl flow moving downward along the helix and the internal swirl flow moving upward along the helix. They rotate in the same direction but have opposite directions of axial movement.
The external swirling flow carries sand or particles heavier than water down into the sand storage tank. The internal swirling flow pushes the clear water out of the overflow port to achieve the effect of water and sand separation.
The head loss under normal operating conditions should be within the range of 3.5-5.0m. If the head loss is less than 3 m, it means that there is not enough centrifugal force to effectively separate the impurities in the water. And as long as the flow rate is constant, its head loss also remains constant.
The advantage of the hydrocyclone filter is that it is easy to maintain and maintain, and it can continuously and automatically discharge sand during work. The disadvantage is that when the pump starts and stops for a while, the filtering effect decreases.
As a result, impurities will enter the downstream system, therefore, hydrocyclone filters can only be used for primary filtration. It needs to be used in conjunction with other filters to reduce the burden on the secondary filter.
The sand filter uses physically and chemically stable quartz sand or granite sand as the filter medium to intercept various dirt in the water.
Because it is three-dimensional filtering. It is most effective in treating organic and inorganic impurities in water. It has a strong ability to intercept dirt and is often used as a fine filter for water sources.
And as long as the organic matter content in the water exceeds 10 mg/L, sand and gravel filters should be used.
But its disadvantage is that it requires a high level of management. Due to improper operation during backwashing, the filter sand will be washed away. After long-term use, the sand and gravel medium will wear out due to friction. The surface of the particles becomes smooth, the dirt-holding capacity decreases, and some new sand needs to be refilled.
Mesh filter is a device that relies on sieve filtration to physically purify irrigation water. The filter element is nylon mesh or wedge wire filter.
When the water flows through the sieve, impurities larger than the mesh size of the sieve will be retained. Therefore, the quality of the filtering effect mainly depends on the mesh number of the filter screen used.
Its advantages are simple structure, small size and low price. But when the organic content is slightly higher. A large amount of organic dirt will squeeze the filter screen and enter the downstream pipeline to cause blockage of the emitter.
However, surface water sources used as irrigation water sources always contain various organic matter or thread-like pollutants. Therefore, screen filters are generally used to filter dirt such as silt, sand and scale in irrigation water, and are used as final filter devices.
In addition, as the screen is gradually clogged with sediment, the pressure difference increases. If the screen is not cleaned in time, it will cause the screen to break, and the cleaning of the screen is also very troublesome.
The laminated filter uses a large number of plastic ring discs with grooves to lock and stack together to form a cylindrical filter element. As water flows through the laminations, the walls and grooves are used to collect and trap debris.
The composite internal cross-section of the slots provides three-dimensional filtration similar to that produced in sand filters. Therefore, its filtration efficiency is very high. Like the mesh filter, its filtering capacity is also expressed in mesh. Moreover, laminations of different meshes are usually made into different colors. The laminations are locked tightly during normal operation. When flushing, the filter element can be removed and the compression nut can be loosened to flush with water. It can also be automatically flushed, and the laminations must be able to loosen by themselves during automatic flushing. Therefore, flushing is very convenient, and the number of flushing and water consumption are relatively small.
Historical Overview Of The Development And Research Of Filters For Micro-Irrigation
Overview Of Filter Development
The earliest filter used in the micro-irrigation system was the Lewis filter. That is, single tank backwash sand filter.
Pot type pottery tube filter, which is the prototype of screen filter. Since then, a special sand filter for micro-irrigation and a double-tank backwash sand filter have been developed.
This type of filter connects two canisters in parallel. Water can still be supplied to the system during backwashing. Its characteristic is that the filter is a horizontal structure, thereby increasing the effective filtering area.
The screen filter has appeared in the form of direct flushing and backwashing. There are also filters made of plastic. Solved the problem of anti-corrosion and anti-rust. The design of the laminated flow channel of the new laminated filter adopts a curved surface. Increased filtration area and reduced head loss.
Research on Hydraulic Performance of Filter
The hydraulic performance of the filter directly affects the quality of the micro-irrigation system. Therefore, many experts have conducted special research on this issue. The law of filtering and clogging of gravel filter is analyzed. The rule of intercepting dirt by filter layer, the change of head loss and the factors affecting head loss are introduced.
At the same time, according to the principle of hydraulics, a design calculation method for determining the size and hydraulic performance of the screen filter is proposed.
The empirical formula of the local head loss coefficient of the filter under different clogging conditions. The water passing area of the filter element and the flushing performance of the filter are discussed. It is proposed that the screen area can be reduced, the structure of the filter can be improved, and the filter can be made compact.
Development Trend and Discussion of Filters for Micro-irrigation
Large Complete Filter Station System
In general micro-irrigation system engineering. In modern field micro-irrigation systems, the water demand can reach 1000 m³/h.
Therefore, it is difficult for general filters to meet the requirements in terms of filtering effect and flow rate. The large-scale filter station system is rationally configured and combined in multi-stage parallel series through different types of filters.
In order to achieve the purpose of good filtering effect and large flow.
Combined configurations can be made according to different needs. However, this type of filtration system has a large head loss and complicated pipe network installation. Equipment costs are high. How to optimize system combination and design to reduce head loss. Finding the best operating parameters and how to select and configure them needs further in-depth research.
Generally for mesh and laminated filters. After filtering a certain amount of sewage, a certain amount of dirt must be retained. Thus occupying the space of the filter.
Therefore, filter clogging is inevitable. Theoretically, the composite filter uses some additional devices to generate favorable water flow patterns in the filter body to reduce the movement speed of solid particles in a certain direction.
Such as the direction perpendicular to the mesh surface. The solid particles are always suspended in the water instead of being pressed on the mesh surface. This reduces clogging of the filter element. Reduce flushing frequency, save labor and energy and water.
Another example is the torpedo filter. Add a shuttle-shaped cylinder at the water inlet to change the cross-sectional area of the flow. High-speed water flow is generated in the direction parallel to the mesh surface. Make solid particles unable to stay on the mesh surface. The purpose of reducing clogged filter elements is also achieved. However, this type of filter has a larger head loss than ordinary filters.
The development of micro-irrigation technology requires the development of its supporting equipment. As a filter for water treatment equipment in micro-irrigation systems. Compared with water treatment equipment used in other industries.
The development requirements should be: simple structure, convenient installation and use, durable and cheap. And its hydraulic performance should be excellent to ensure the normal and reliable operation of the irrigation system.
Therefore, research and investment in micro-irrigation filtration equipment should be increased. In particular, attention is paid to the experimental research of its hydraulic performance. Increase the technological content of micro-irrigation filtration equipment. Improve the quality of water supply and ensure the application and promotion of micro-irrigation technology.