Page 38 - FoodFocusThailand No.144_March 2018

SMART PRODUCTI
SMART PRODUCTIONON

8 Things to Know

When Specifying Vacuum Conveying Systems

for Powders

Vacuum conveying systems for powders and 4. Know How You Recevie The Raw Materials
other bulk materials involve a starting point and a When designing a vacuum-conveying system, it is important to clearly
destination, avoiding many hazards along the way. define how the materials are received and introduced to the process.
Powders are transferred from various sources to the There are many ways of introducing materials into a vacuum- conveying
system; some are more manual, while others are more suitable to
processing line using vacuum or negative pressure. automation—and all require attention to control dust. Material can
The number one advantage of vacuum conveying is be received in various types and sizes or upstream process
dust control. equipments.
5. Know Your Upstream Process
To properly design a vacuum conveying system, you must define the
System controls allow material to convey and discharge on demand, upstream process that is supplying the material. Find out if the material
ideal for larger applications requiring movement of bulk materials from is coming from a loss-in-weight feeder, volumetric feeder, mixer, or
larger containers such as bulk bags, totes, railcars, and silos without any other equipment used to move material. These all influence the
a lot of manual intervention, reducing frequent container changes. To conveying process. Additionally, the frequency of material coming out
properly design a pneumatic conveying system, it is important to define of these vessels, whether batch or continuous, affects the conveying
the following 8 key criteria in your process: process and how the material will behave when it comes out of the
process. Upstream equipment affects downstream equipment. It is
1. Know Your Bulk Density important to know everything about the source.
As a first step, it is important to know more about the powder that is
being conveyed, specifically its bulk density. This is typically described 6. Know Your Headroom Requirements
in pounds per cubic feet (PCF) or grams per cubic centimeter (g/cc).
This is a key factor in calculating the size of the vacuum receiver. For This is an important consideration when installing equipment in an
example, lighter-weight powders need larger receivers in order for the existing plant. What may have been designed for manual operation
material to fall out of the air stream. Bulk density of the material is also may not offer enough room for an automated process. Even the smallest
a factor in calculating the size of the conveying line, which in turn conveying system for powder handling will require at least 30 in. of
determines the vacuum producer and conveying velocity. Higher-bulk- head- room over your pro- cess, taking into consideration maintenance
density materials require faster transport velocity. requirements for filter access, discharge-valve inspection, and access
to equipment below the conveyor. Applications requiring high
2. Know Your Conveying Distance throughput rates, which require large headroom, can use a filterless
Conveying distances comprise both horizontal and vertical factors. A vacuum receiver.
typical “up-and-in” system offers a vertical lift from floor-level, conveying
up to a receiver over an extruder or loss-in-weight feeder. It is important
to know the number of 45° or 90° sweep elbows. “Sweep,” in general, 7. Is Your Process Batch Or Continuous?
refers to a large centerline radius that is typically 8-10 times the diameter It is important to define the type of operation that you are feeding: batch
of the tube itself. It is important to keep in mind that one sweep elbow or continuous. For example, small conveyors discharging into a surge
is equivalent to 20 ft of linear tubing. Reducing the number of elbows bin is a batch process. Know whether a batch of material will be received
in your system should be an important goal. Powders do not flow like in the process via a feeder or an intermediate hopper, and whether
liquids, and vacuum conveying systems should minimize the number your conveying process can handle the surge of material from a batch.
of back-to-back elbows. If vertical vacuum conveying runs exceed
12-15 ft in batch mode, the material in that line will stop conveying and 8. Know Your Geographic Or Atmospheric Conditions
fall back down. For this scenario, it is important to design a “line-clearing Geographic and atmospheric considerations are important design
valve” to make sure that the vertical leg is clear before the batch process
stops. considerations, particularly where altitude plays an important part in
sizing the system. The higher the altitude, the more air is required to
3. Know Your Conveying Rate convey the material. Additionally, consider plant environmental
When calculating conveying rates, it is important to know how many conditions and temperature/humidity control. Certain powders that are
pounds or kilograms per hour will be conveyed. Additionally, define hygroscopic can have discharge problems on humid days.
whether the process is batch or continuous. It is important to know the
demands of the process in order to properly size the system to
determine the conveying rate.

38 FOOD FOCUS THAILAND MAR 2018