Quadro has supplied a number of Comils complete with Nitrogen (N2) purge/Oxygen (O2) Analyzing Systems recently to its customers around the world.
Who Requires an N202 System?
The requirement for this type of system typically stems from the ignition characteristics of the powder that the customer is sizing. Customers send their products to independent Labs to have the product’s ignition characteristics investigated. If inerting is recommended by the lab, then an N2/02 system is applied. Inerted mills can range from a very simple design to a more intricate controlled, closed loop system. The selection of which design to use is determined by the end-user.
Option 1 - Customer Supplied Inerting System
The Comil is configured with a small port (usually ½" or 13 mm) in the infeed chute, and a vent port either in the lower portion of the mill or further downstream. When the N2 gas enters the mill, it naturally flows downward through the mill. This design is the most economical and straightforward solution. However, there are no controls on the amount of N2, the amount of O2 displaced, and whether or not there is N2 flowing through. The end-user is responsible for such controls. Option 2 - Open Loop Inerting System
Type 1:Without O2 Monitoring
The flow of Nitrogen is monitored and timed at the inlet port on the Comil. If the flow at the N2 inlet falls below a particular pre-set point, then the mill is stopped. This ensures that N2 is purged into the mill before and during the operation of the mill. Calculations are done prior to set-up to determine the purge time and flow required for displacing the O2 in the mill prior to start-up. This system ensures there is N2 in the mill. However, it does not measure the amount of O2 in the mill/system.
Type 2:With O2 Monitoring
The N2 flow into the mill is monitored with a pressure regulator, flowmeter and flow switch. The oxygen level in the mill is also monitored. The gas sample is taken from the mill on a continuous basis. If the O2 level reaches the MOC (Maximum Oxygen Content) level, then a signal sent to the mill controller to shut down the mill.
Option 3 - Closed Loop Inerting System
In this option, the control of the N2 purge is based on the level of O2. There may be multiple O2, target /alarm and warning levels set in this system. If the O2 in the mill increases to the warning level, a flashing light alerts the operator. The system is then automatically purged with N2.
If the level of O2 in the mill increases to the target/alarm stage, the mill automatically shuts down and (if equipped) an alarm will sound.
Summary
N2/O2 systems can substantially reduce the risk of explosion of the combustible material being size reduced by a mill. The right system for a particular application is a factor of the hazardous nature of the product, the present production system in place and the degree of protection desired by the company. A Quadro representative can help you determine the right equipment for your application
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Photograph of Option 3
Control box for Inert Comil
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Comil