Dilute Phase Pneumatic Conveying

Dilute Phase Pneumatic Conveying

One of the most popular methods of moving solids in the chemical industry is pneumatic conveying. Pneumatic conveying refers to the moving of solids suspended in or forced by a gas stream through horizontal and/or vertical pipes. Pneumatic conveying can be used for particles ranging from fine powders to pellets and bulk densities of 16 to 3200 kg/m3 (1 to 200 lb/ft3).

Considering designing a pneumatic conveying system yourself? Probably not a good idea. There's as much art involved as there is science and such a design should be left to professionals. Consider that even different grades of the same material have been known to convey differently. Testing is a must (as you'll see from the method below). Before you can even make any good judgements from the method presented here, you need to know solid friction factor for your solids (which we'll discuss later) and the minimum gas velocity required to move your particles. So, if you're involved in designing a system from the ground up, seek assistance from reputable people in the field of conveying. If you're already familiar with your solids, the method below can be used to examine the pressure loss expected in your system. The method presented here is very good and has been stood the test of real systems over time.

Read the full white paper (courtesy of Process Systems & Design) below:

Dilute Phase Conveying from Process Systems & Design

Pneumatic Conveying: Dense Phase Conveying Vs. Dilute Phase Conveying

Dense Phase Conveying

A pneumatic conveying system transfers powders, granules, and other dry bulk materials through an enclosed horizontal or vertical conveying line. Controllable air is used to transport either vacuum or pressure materials through piping at a controlled rate. This system has quite a few advantages. It can be configured with bends to fit around existing equipment, which gives it much more flexibility. The pneumatic conveying also takes up less space, is totally enclosed, which allows the system to contain dust, and typically has fewer moving parts than other systems. Pneumatic conveying systems are grouped by their operating principle into two types: dilute phase and dense phase, which both can be run under a vacuum or pressure.

Dilute phase conveying the particles being transported are at low pressure and high velocity and will be fully suspended in the conveying air. Dense phase conveying transports the particles are at a high pressure and low velocity, while they are not being suspended. Much larger distances may be accomplished compared to dilute phase conveying.

Dilute Phase Conveying

Dilute phase conveying with pressure is one of the most common conveying methods for powders or granules, as well as fibrous materials. This system relies heavily on the air stream's velocity. The air stream's velocity picks up and draws each particle along, keeping them in suspension as they go through the conveying line. Dilute phase vacuum conveying is suitable for conveying materials that usually pack or compress under pressure. This system is usually used to transport materials over short distances at low capacities.

In dense phase pressure conveying, the system conveys the materials at a lower speed to limit materials degradation, air consumption, and abrasion on pipeline, bend, and diverter contact surfaces. This system also has the ability to start or stop with the conveying line being full with material. In dense phase vacuum conveying fragile or abrasive materials are conveyed much more gently. Minimal damage, reduced erosion in the conveying line and being traveled longer distances are all advantages of this low velocity process.