Main machines for screening aged waste

Aged waste refers to household waste that has been stored for more than 3 years. After long-term anaerobic fermentation, it exhibits characteristics such as high moisture content (40%-60%), severe material adhesion, complex composition (containing incompletely degraded organic matter, inert impurities, leachate, plastic film, etc.), and low particle strength. Traditional household waste screening equipment is difficult to adapt to its processing needs. The core objective of aged waste screening is to separate recyclable resources (such as plastics and metals), usable organic matter (for composting or anaerobic fermentation), and inert landfill materials (such as bricks and slag). This requires specialized equipment with targeted modifications. Currently, the mainstream aged waste screening machines in the industry include five main categories: modified drum screens, dual-shaft shear screens, wet screens, air-separation-bounce composite screens, and integrated magnetic separators. These machines, through structural optimization and functional integration, address the screening challenges of the "sticky, wet, and mixed" characteristics of aged waste. This article will systematically analyze the technical characteristics, application scenarios, and practical points of various types of equipment to provide technical support for aged waste resource utilization projects.

1. Improved Rotary Cylinder Screen: Core Equipment for Large-Scale Screening of Aged Waste

The improved rotary cylinder screen, based on an optimized design of the traditional rotary cylinder screen, is the core screening equipment for centralized aged waste treatment plants (daily processing capacity of over 500 tons). Specifically designed for high-moisture, high-viscosity materials, it can achieve preliminary grading and impurity separation.

Its core improvements are reflected in three aspects: First, the screen cylinder structure is optimized, adopting a "segmented screen aperture" design (large aperture of 50-80mm in the front section and small aperture of 20-40mm in the rear section), first separating large, inert impurities (such as bricks, stones, and waste furniture), and then grading finer materials, reducing the risk of clogging; second, a powerful cleaning device is added, with alloy scrapers and elastic brushes inside the screen cylinder that scrape away adhering materials on the screen surface in real time during rotation. The cleaning frequency is linked to the screen cylinder rotation speed, adapting to materials with high moisture content; third, a sealing and corrosion-resistant design, with the screen cylinder made of stainless steel and an outer shell fitted with a leak-proof cover to prevent secondary pollution caused by leachate leakage. The working principle is the same as that of a traditional drum screen. Material grading is achieved through the rotation of the inclined screen cylinder and the throwing of materials by the lifting plates. A single unit can process 40-250 tons/hour, with a screening efficiency of 75%-85%.

A typical application scenario is in landfill waste excavation and treatment projects. One landfill uses a modified Φ3.6×8m drum screen to process 1200 tons of aged waste per day, separating the material into three categories: >80mm (inert landfill material), 40-80mm (recyclable plastics and metals), and <40mm (organic matter + fine soil). Further purification is then achieved through air separation and magnetic separation, with an organic matter recovery rate exceeding 60%. It is important to note that pretreatment is required before processing to remove large metal pieces and sharp impurities to avoid damaging the screen and cleaning device.

2. Twin-Shaft Shear Screen: Specialized Equipment for Breaking and Screening High-Viscosity Materials

The twin-shaft shear screen (also known as an integrated shredder and screener) integrates crushing and screening functions. It uses twin shear blades to break up clumps of aged waste, simultaneously grading the material. It is suitable for processing aged waste with high viscosity and high moisture content (>50%), and is particularly suitable for small to medium-sized projects (daily processing capacity 100-500 tons).

Working principle: The twin blades rotate at high speed (30-60 r/min), and the interlocking blades shear, breaking up clumps of aged waste to below 50mm. A fixed screen is installed below the blades; material smaller than the screen openings is discharged directly, while material larger than the screen openings continues to be sheared until it meets the particle size requirements. The core advantages include: First, excellent breaking effect, with a shearing force of 50-100kN, effectively breaking up organic clumps and plastic film entanglements, solving the "wall sticking and hole clogging" problem of traditional equipment; second, integrated operation, combining crushing and screening, simplifying the process flow, and occupying only half the area of a "crusher + drum screen" combination; third, wear-resistant and corrosion-resistant, with blades made of hard alloy material and a corrosion-resistant coating sprayed on the blade shaft surface, suitable for corrosive leachate in aged waste.

A county-level aged waste treatment project uses the SSJ-800 dual-shaft shear screener, processing 300 tons of waste per day. After crushing and screening the clumped aged waste, organic matter <30mm is sent to the composting system, while plastics and metals are subsequently sorted and recycled. The moisture content of the processed material is reduced by 10%-15%, and the composting fermentation cycle is shortened by 20%. Its limitations lie in its relatively limited processing capacity and rapid wear of the blades, requiring regular sharpening and replacement (lifespan approximately 3-6 months).

3. Wet Screening Machine: Specialized Equipment for Deep Purification of Fine Materials

The wet screening machine employs a combined "water washing + screening" process. Through water flow impact and screen separation, it achieves deep purification of fine materials (<40mm) from aged waste. It is particularly suitable for separating organic matter from fine slag and is a key piece of equipment for the resource utilization of aged waste.

Working principle: After the material enters the screening tank, high-pressure water flow (0.3-0.5MPa) impacts the material, breaking up adhering organic matter and slag. Simultaneously, the screen vibrates at a low frequency (5-10Hz), discharging fine slag smaller than the screen openings (10-20mm) with the water flow, while the organic matter remains on the screen surface and is conveyed to subsequent processing stages by a scraper. The core advantages are: First, high separation purity. Water washing removes surface slag and contaminants from organic matter, increasing organic matter purity to over 85%, meeting the requirements for composting or anaerobic fermentation. Second, extremely strong anti-clogging properties. The combination of water flow scouring and vibration completely prevents material from sticking to the screen holes, making it suitable for extreme working conditions with a moisture content >50%. Third, wastewater is recyclable. Equipped with a sedimentation tank and filtration system, the treated wastewater (SS <100mg/L) can be reused for water washing, achieving a water resource utilization rate of over 80%.

A certain aged waste composting project uses a WS-1000 wet screening machine to process <40mm fine materials pretreated by a modified drum screen, with a daily processing capacity of 200 tons. The separated organic matter is dewatered and then composted, with an organic matter content of over 35%. The fine slag is solidified and used for roadbed backfilling. It should be noted that the equipment requires a wastewater treatment system to avoid environmental pollution from washing wastewater, and its energy consumption is higher than that of dry screening equipment (single unit power 30-50kW).

4. Air Separation - Bounce Composite Screen: High-Efficiency Separation Equipment for Light and Heavy Materials

The air separation - bounce composite screen integrates bounce screening and air separation functions. Based on the differences in material density and elasticity, it simultaneously separates organic matter, inert matter, and light matter (plastics, paper). It is suitable for the recycling of recyclable resources and component classification in aged waste and is often used in conjunction with a drum screen.

Its structural design is as follows: The upper layer is a bounce screen plate (inclination angle 15°-20°), which separates inert matter (bricks, glass) with poor elasticity and organic matter + light matter through high-frequency bounce (frequency 50-80Hz); the lower layer is an air separation channel, where airflow blows from bottom to top (wind speed 15-25m/s), blowing light matter (plastics, foam) to the collection bin, while organic matter, due to its higher density, falls, achieving triple separation. The core advantages include: First, high separation efficiency, capable of classifying "inert matter + organic matter + light matter" in a single operation with a separation efficiency exceeding 80% and a light matter recovery rate exceeding 90%; second, strong adaptability, capable of handling aged waste with a moisture content of 30%-50%, with the self-cleaning function of the bouncing screen preventing material blockage, and the air separation speed adjustable according to material characteristics; third, low energy consumption, with the composite design reducing the number of devices, and a single unit power of only 15-30kW, resulting in lower operating costs than the "bouncing screen + air separator" combination.

A waste recycling plant uses the FT-1200 air separator-bouncing composite screen to process 40-80mm aged waste pre-treated by a drum screen, with a daily processing capacity of 400 tons. The separated plastics are washed, crushed, and recycled into granules, the organic matter is used for anaerobic fermentation, and the inert matter is landfilled, generating an annual recycled resource value exceeding 1.5 million yuan. When applying this type of magnetic separator, it is necessary to control the uniformity of the feed to avoid large impurities impacting the screen plate, and to regularly clean the dust accumulated in the air separation channel.

5. Integrated Magnetic Separator: Precise Metal Impurity Separation Equipment

Metals mixed in aged waste (such as steel bars, iron wire, and aluminum cans) not only affect the safety of subsequent processing equipment but also have recycling value. The integrated magnetic separator is a dedicated separation device for these metals, often used as an auxiliary device in the screening process, installed after a drum screen or composite screen.

Based on the installation method, it is divided into drum-type magnetic separators and suspended magnetic separators: Drum-type magnetic separators are linked to a conveyor belt. The magnetic drum contains permanent magnets (magnetic field strength 8000-12000Gs). When material passes through, metals are attracted to the surface of the drum and fall into the collection box as the drum rotates, escaping the magnetic field. Suspended magnetic separators are suspended above the material conveyor, adsorbing flowing metal impurities, and are suitable for separating large pieces of metal. The core advantages include: First, strong adsorption capacity and a long service life of the permanent magnet (5-10 years), effectively adsorbing metal particles ≥5mm in diameter with an adsorption efficiency exceeding 95%; second, flexible installation, adaptable to various screening production lines without significant equipment modifications; and third, convenient maintenance, requiring only periodic cleaning of metal impurities in the collection box, with no easily damaged parts.

A landfill's aged waste treatment line uses a drum-type magnetic separator, processing 800 tons of waste daily and recovering approximately 500kg of scrap metal daily. After baling and recycling, this generates over 300,000 yuan in additional annual revenue, while also preventing damage to the subsequent dual-shaft shearing machine and wet screening machine from metal impurities. It is important to note that large non-metallic impurities must be removed before treatment to avoid obstructing the magnetic field and affecting the adsorption effect.

6. Key Considerations for Selecting Screening Equipment for Aged Waste

The selection should be based on a comprehensive assessment of the characteristics of the aged waste, the processing scale, and the resource recovery goals:

* Large-scale projects (daily processing capacity > 500 tons): Prioritize the combination of a "modified drum screen + air-separation-bounce composite screen + magnetic separator" to balance processing capacity and separation efficiency.

* High-moisture, high-viscosity waste treatment (moisture content > 50%): Utilize a dual-shaft shear screen or wet screen to overcome adhesion issues.

* Organic matter resource recovery projects: Employ a combination of a "modified drum screen + wet screen" to improve organic matter purity.

* Recyclable resource recovery projects: Focus on configuring an air-separation-bounce composite screen and a magnetic separator to improve the recovery rate of plastics and metals.

* Small to medium-sized decentralized projects (daily processing capacity 100-500 tons): Select a dual-shaft shear screen, integrating crushing and screening functions to control investment and land area.

The core requirement for aged waste screening equipment is to solve the problems of "stickiness, wetness, and impurities." Various specialized equipment, through structural improvements and functional integration, achieve targeted processing: the improved drum screen is the "main equipment" for large-scale processing; the dual-shaft shear screen is a "powerful tool" for breaking up highly sticky materials; the wet screen is a "precision tool" for purifying organic matter; the air-separation-bounce composite screen is the "core equipment" for separating light and heavy materials; and the integrated magnetic separator is a "supporting guarantee" for metal recovery. With the increasing demand for aged waste excavation and processing, future equipment will develop towards "multi-functional integration" (such as integrated crushing-screening-air separation-magnetic separation), "intelligent control" (real-time monitoring of moisture content and adjustment of operating parameters), and "environmental protection and energy saving" (low energy consumption and zero wastewater discharge), providing more efficient technical support for the "reduction, harmlessness, and resource recovery" of aged waste.

Author:Fiona Fan

Fiona Fan is a contributor to the blog and news column of the Zhongcheng Machinery website. She has several years of work experience in the machinery industry, has a deep understanding of crushing machinery and screening equipment, and shares useful knowledge about environmental protection machinery.