Plastic pneumatic conveying is a way of moving plastic materials through a pipeline using air flow, and it has become a standard part of modern recycling equipment. In a lithium battery recycling plant, for example, the separator film and plastic casing separated from waste batteries have to be collected and carried to a briquetting station without manual handling. A well-designed plastic pneumatic conveying system keeps the whole line clean, enclosed and easy to arrange, which is why more and more plant owners are asking about it.
When engineers talk about pneumatic conveying, the first question is almost always the same: dilute phase or dense phase? These two modes describe how the material actually travels through the pipe, and the difference between them affects everything from energy consumption and pipe wear to the kind of material you can handle. Understanding the difference between dilute phase and dense phase plastic pneumatic conveying systems helps you choose the right setup for your recycling plant instead of simply copying what a neighbour plant bought.
Dilute phase conveying, also called lean phase conveying, carries material by fully suspending it in a high-velocity air stream. The plastic particles or film pieces stay dispersed evenly through the pipe and travel along with the air. Typical air velocity is around 15 to 30 metres per second, and the system usually runs at low pressure, below about 1 bar. Because the material is fully suspended, the design is relatively simple and the upfront cost is lower than a dense phase system. Dilute phase can handle almost any material, which makes it a flexible choice for many applications.
The high velocity, however, comes with trade-offs. Fast-moving particles hit the pipe wall and each other, which causes more wear on the pipeline and can break fragile materials. The large volume of air needed to keep the material suspended also means higher energy consumption for each tonne moved. For lightweight plastic film and granules, these drawbacks are usually acceptable, which is why dilute phase remains the more common choice in plastic conveying.
Dense phase conveying moves material at low velocity and higher pressure. Instead of being fully suspended, the material travels in concentrated slugs, plugs or slow-moving dunes. Air velocity is typically between 3 and 10 metres per second, and the system operates at higher pressure, usually between 2 and 10 bar. Because the material moves gently, dense phase causes far less particle breakage and pipe wear, making it well suited to abrasive, fragile or high-value materials.
The lower air velocity also means less air is needed to move the same amount of material, so the energy cost per tonne is lower, especially over long distances. The trade-off is that dense phase systems are more complex and more expensive to build. They need pressure vessels or blow tanks, extra valves and controls, and more floor space. Not every material can be conveyed reliably in dense phase either; coarse, granular or sticky materials can cause blockages.
| Parameter | Dilute phase | Dense phase |
|---|---|---|
| Air velocity | 15-30 m/s | 3-10 m/s |
| Operating pressure | Low, below about 1 bar | High, about 2-10 bar |
| Material flow | Fully suspended in the air stream | Concentrated slugs, plugs or dunes |
| Solids-to-air ratio | Low, typically below 10:1 | High, often above 10:1 and up to 25:1 |
| Energy consumption | Higher per tonne moved | Lower per tonne moved |
| Pipeline wear | Higher due to particle speed | Lower, gentler material movement |
| Upfront cost | Lower, simpler design | Higher, more complex equipment |
| Conveying distance | Short to medium, up to about 300 m | Longer, up to about 600 m |
| Material suitability | Almost any material | Abrasive, fragile, coarse or fine air-retentive materials |
In practice, most plastic pneumatic conveying systems used in recycling plants are dilute phase. Plastic separator film from lithium battery crushing and separation is light and flexible, so a high-velocity air stream can carry it easily over the short distances typical inside a plant. For example, San Lan's plastic pneumatic conveying system collects the plastic film separated from waste lithium batteries and feeds it into a hydraulic briquetter, which presses the film into compact blocks for easy handling and storage. This kind of dilute phase arrangement keeps the process simple, reliable and low in maintenance.
Dense phase becomes attractive when the conveying distance is long, when the material is fragile or abrasive, or when you want to cut energy consumption and pipe wear. If you are moving plastic granules over several hundred metres, or handling a material that degrades easily, dense phase is worth serious consideration even though the initial investment is higher.
- Material: light, free-flowing plastic film or pellets usually work well with dilute phase; fragile, abrasive or high-density materials favour dense phase.
- Distance: short to medium runs suit dilute phase; long-distance conveying suits dense phase.
- Energy and wear: if running cost is your main concern, dense phase saves energy and reduces pipe wear over time.
- Budget: dilute phase costs less to install; dense phase costs less to operate per tonne over the long term.
- Plant layout: dilute phase is compact and easy to integrate; dense phase needs space for pressure vessels and controls.
There is no single best system for every plant. The right choice depends on your material, your layout and your budget. For most plastic conveying tasks in lithium battery recycling plants, a dilute phase system offers a simple, cost-effective solution. For long-distance or fragile-material applications, dense phase delivers better protection and lower running costs.
If you are planning a lithium battery recycling plant or upgrading an existing plastic conveying line, San Lan Technologies can help you ｓｅｌｅｃｔ and design the right plastic pneumatic conveying system for your material and process. With over 15 years of experience in e-waste recycling machines and a full range of recycling equipment, the team can advise you on the best solution and provide a complete plant design. Contact San Lan for a free consultation and quotation.
