Hammer mill systems have known challenges that include fires, explosions in the system and explosions propagating through equipment through the hammer mill. Jim Peters, regional manager at Boss Products, LLC, has years of experience working with these systems and came on the podcast to share some tips, insights, and recommendations for dust safety measures.
Hammer Mill Systems- an Overview
Hammer mills appear in a wide range of industries. From a configuration perspective, they consist of a rotor, which is a series of hard-tipped ‘hammers’ rotating inside a screen cylinder. In rotating the cylinder, the hammers essentially create a low-efficiency fan that draws air into the inlet and tries to force it out through the discharge and through the holes in the screen.
With grain handling, hammer mills act as a size reduction system. When material is introduced into the grinding zone, it is repeatedly impacted until the particles pass through a perforated mesh screen or a perforated plate. Other operational and safety devices include:
- Drop boxes and magnetic separators.
- A feeder that keeps an even flow of feed coming into the grinding zone
- A pneumatic or mechanical system for taking the material away as fast as it’s being ground so that it doesn’t build back up into the grinding zone
“It’s really indiscriminate grinding, compared to a roller mill, where you can determine the particle size and you can grind or roll or do the flake or different things,” Jim says. “But a hammer mill is going to reduce everything to a certain maximum size and that’s it.”
Basic Safety Checks for Hammer Mills
In terms of safety checks, Jim recommended the following:
- Using a magnetic separator to ensure that tramp metal doesn’t come into the mill itself.
- Prevent build-up in the grinding chamber, so that heat doesn’t create a source of ignition.
- Checking to make sure that the bearings are not running hot.
- Listening for unusual sounds.
- Making sure that nothing is blocking the inlet.
- Checking plenums to confirm that the hopper is not backing up.
NFPA 61 requires temperature sensors on bucket elevators, and Jim recommended them for hammer mills too. “Monitoring systems for all your critical bearings is a really good idea,” he says.
Common Challenges for Hammer Mills
Jim explained that there were two setups for a hammer mill discharge.
Pneumatic Airlifts
Pneumatic airlifts that drop directly from the bottom of the mill into a negative dilute convey system that goes up into either a cyclone or a cyclone and pneumatic receiver. With this system, operators need to be alert for pressure drops or signs of backing up into the cyclone.
Jim said that for these systems, he was putting back-blast dampers or flap valves into the inlet so that if an event occurs in the mill itself or another receiver, it doesn’t come back through the ducting and out of the system through the air inlet.
Plenum Systems
With plenum systems, the mill drops into an elongated hopper. The material goes from a screw conveyor to the opposite end of the grinder and is discharged through an explosion-proof airlock that isolates the system from passing on an explosion. Operators need to make sure that the plenum isn’t building up material, that the discharges are all operating properly and that whatever’s upstream from the mill and the plenum is conveying and doing its job.
With plenums, explosion venting needs to be applied because the system has all the elements of the explosion pentagon: fuel, air, ignition, dispersion and confinement.
“We recommend thermal probes for fire and spark detection right below the grinder to catch sparks coming out,” Jim says. “If there’s anything coming out, you want to be able to trigger alarms. If you have a high temperature rise, you need to shut down the system. If you have an event, you need to stop the airlock, stop the fans and trigger either a dry chemical deluge or CO2, some suppression system. So you treat it just like you would a dust collector, with venting and suppression.”
Dust Safety Training for Hammer Mills
Jim emphasized the importance of training facility employees on how hammer mills work.
“In my own experience, I don’t think I totally understood what was going on until I had some time with the maintenance crew to dig into it and change hammers and look at the inside and see how it works. (There should also be) training on the fire triangle and the explosion pentagon as well as the safety measures that are in place. I think that will go a long way.”
Conclusion
Jim’s final piece of advice for hammer mill safety was knowing who to contact for advice or help if an issue arises.
“A flour miller knows how to grind grain, a carpenter knows how to build houses. Talk to people like us or talk to people at your university and get our opinion or get the expert’s opinion on what you need for safety. You don’t need to know everything about it, but then take their advice. Also train your people. How do you respond when there is an event? What does it mean and how do you react quickly, who to call? When to call and who to call. I think that’s good advice.”
If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Jim Peters directly:
Email: [email protected]
Website: https://www.bossproductsamerica.com/
LinkedIn: https://www.linkedin.com/in/jim-peters-93185813/
If you have questions about the contents of this or any other podcast episode, you can go to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.
Resources mentioned
Dust Safety Science
Combustible Dust Incident Database
Dust Safety Science Podcast
Questions from the Community
Dust Safety Academy
Dust Safety Professionals
Organizations
NFPA
Standards
NFPA 61
Companies
Boss Products, LLC
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DSS113: Hammer Mill Fire and Explosion Safety with Jim Peters
