When deciding to adopt a pneumatic conveying system, there is usually a critical technical crossroads: should we choose dilute phase conveyingor dense phase conveying?
In the world of pneumatic conveying, the core of this trade-off lies in two physical parameters: airflow velocity and conveying pressure.
- Dilute phase transportis like a gust of wind sweeping up fallen leaves, relying on high speed to suspend the material.
- Dense phase transportationis like waves pushing a beach, relying on high pressure to push materials to move in clusters.
If fragile coffee beans are transported in dilute phase, you will receive coffee powder; If using dilute phase to transport highly abrasive quartz sand, your pipeline elbow may need to be replaced every week. This article will delve into these two technologies to help you find the most suitable solution for your materials.
What is Dilute Phase Conveying?
Working Principles and Characteristics
Dilute phase conveying is currently the most common and technologically mature form of pneumatic conveying in industrial applications. Its core feature is * * “suspension” * *.
In this mode, in order to prevent material settling and blockage of the pipeline, we must maintain a high airflow velocity (usually between 15-35 meters per second). Due to the large amount of air and relatively small amount of material, the gas-solid ratio is usually low.
- Power source: Roots blower or centrifugal blower is usually used.
- Feeding device: The most common is the rotary feeding valve (wind shutter).
- Pressure range: Belongs to low-pressure systems, usually below 1 bar.
Pros and Cons of Dilute Phase Conveying
- Advantages:
Low initial investment: The equipment structure is simple and does not require expensive pressure vessels.
Easy to operate: The airflow control is relatively simple and does not require high demands on the operator.
Strong flexibility: Very suitable for feeding from one point to multiple points, or sucking from multiple points.
- Disadvantages:
Material damage: High speed impact can cause brittle materials to break.
Pipeline wear: If the material hardness is high, high-speed friction will quickly wear through the elbow like a sandblasting machine.
High energy consumption: requires moving a large amount of air to maintain suspension speed.
Typical Applications
Suitable for non abrasive, non fragile, and low-density materials, such as:
- Flour, corn starch.
- Plastic pellets: resin and catalyst that are not easily broken; Polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), etc.
- Calcium carbonate powder, activated carbon powder.
What is Dense Phase Conveying? (Plug Flow)
Working Principles and Characteristics
Dense phase transport is designed to address the pain points of dilute phase transport. Its core feature is * *”embolism” or “sand dune like movement” * *.
In this mode, the airflow velocity is deliberately reduced (usually below 10 meters per second, even as low as 2-3 meters per second). The material is no longer suspended, but fills the entire cross-section of the pipeline, forming “material plugs” that are
pushed forward like pistons by high-pressure gas at the back.
- Power source: Usually requires a high-pressure air compressor.
- Feeding device: High pressure resistant sending tanks (bin pumps) must be used instead of ordinary rotary valves.
- Pressure range: belongs to high-pressure systems, usually above 1 bar, and can even reach 4-6 bar.
Pros and Cons of Dense Phase Conveying
- Advantages
Extremely gentle: Low speed conveying means that the material has almost no intense impact, greatly protecting the integrity of the material.
Ultra low wear: The speed is reduced by half, and the degree of wear may be reduced by more than 4 times. The service life of pipelines has been significantly extended.
Preventing segregation: For well mixed materials, dense phase transportation can prevent components of different densities from layering.
High energy efficiency: Although the pressure is high, the volume of compressed air used is small, and the overall operating energy consumption is usually lower.
- Disadvantages
High initial investment: The cost of sending tanks and high-pressure gas source equipment is higher than that of Roots blower systems.
Intermittent work: Sending tanks requires a “feeding inflation conveying” cycle, usually batch conveying (although quasi continuous conveying can be achieved
through parallel connection of two tanks).
Typical Applications
Suitable for fragile, high wear, or mixed high-value materials, such as:
- Fragile items: instant coffee, cereal, rice, nuts, sugar, milk powder, PBS and other materials in the chemical industry.
- Wear resistant materials: glass mix, silica sand, ceramic powder, cement, positive and negative electrode materials for lithium batteries.
How to Choose Based on Material Properties?
| Characteristic dimension | Dilute Phase Transport | Dense Phase Transportation |
| conveying speed | High speed (>15 meters/second) | Low speed (<10 meters/second) |
| delivery pressure | Low pressure (<1 bar) | High pressure (>1 bar) |
| Gas-solid ratio | Low (more air, less material) | High (more materials, less air) |
| Material damage rate | high | extremely low |
| Pipeline wear degree | high | extremely low |
| equipment cost | lower | higher |
| Suitable for materials | Flour, plastic pellets, lightweight powder;
Plastic pellets: resin and catalyst that are not easily broken; Polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), etc. |
Coffee beans, sand, lithium battery materials;
Fragile items: instant coffee, cereal, rice, nuts, sugar, milk powder, PBS and other materials in the chemical industry. |
Scenario 1: Fragile Materials
Conclusion: Dense phase transport must be selected. If the appearance of your product directly affects the selling price (such as intact cashews or instant coffee granules), the high-speed impact of dilute phase transportation will cause your product to turn into powder before reaching the packaging machine. The ‘soft landing’ of dense phase transportation is the key to protecting product profits.
Scenario 2: Abrasive Materials
Conclusion: It is recommended to choose dense phase transportation. Wear and speed have a geometric relationship. When transporting quartz sand or glass fragments, the bends of the dilute phase system may wear through within two weeks, resulting in frequent shutdowns for maintenance. Although dense phase transportation equipment is expensive, it can save huge pipeline replacement costs and downtime losses.
Scenario 3: Standard Materials
Conclusion: Choose dilute phase transportation. For materials such as flour, starch, or ordinary plastic particles that are neither fragile nor worn, dilute phase conveying provides the highest cost-effectiveness. It is a time proven and cost-effective industrial standard.
Technical Diagram: The Importance of Saltation Velocity
When designing pneumatic conveying systems, our engineers rely not only on experience, but also on precise fluid dynamics calculations. The most important parameter among them is the Saltation Velocity.
This refers to the critical velocity at which material particles fall from the suspended airflow and begin to accumulate at the bottom of the pipeline.
- In the designing of dilute phase conveying, we must ensure that the gas velocity is always higher than the jump velocity, otherwise the pipeline will be instantly blocked.
- In the designing of dense phase conveying, we intentionally keep the speed lower than the jumping speed and use pressure waves to push the material plug.
Accurately calculating this value is the core technical capability to ensure that the system neither blocks pipes (avoiding underspeed) nor wastes energy (avoiding overspeed).
Find the Best Answer Through Material Testing
Theory belongs to theory, but in practical working conditions, many materials are in a “gray zone”. For example, is a specific modified plastic particle considered fragile? Will a certain chemical powder wear down pipelines?
Don’t guess, speak with data.
As a professional manufacturer, we have an advanced pneumatic conveying testing laboratory. You can send us your material samples, and we will simulate the actual conveying distance and number of bends, and conduct separate tests on the conveying of dilute and dense phases.
We will provide you with a detailed Material Handling Test Report, including:
- Comparative analysis of material crushing rate.
- Monitoring of actual energy consumption data.
- Customized suggestions for your factory layout.
Contact our engineers now and schedule your free material testing.
