Improving feed mill performance
September 1, 2008
Editor’s note: This is the first in a three-part series in which ways to improve feed mill performance will be examined. The remaining two articles will be published in upcoming issues of World Grain.
A feed mill cannot be run without an organized supply of raw materials, yet it is easy to overlook the importance of the intake system, particularly when it comes to the costs of running this area of the mill.
Regarding the intake system, feed millers everywhere ask the same questions: Can we run our intake system without supervision? Will rogue parcels of raw materials get into our mill without our knowledge if we don’t have someone there? Will suppliers and merchants take advantage of our lack of supervision? Will we have problems with cross-contamination if we rely on remote control?
The answer to all of these questions is probably “yes.” But the same answer applies in several instances, whether you choose to operate your intake system remotely or employ someone specifically to address the area and its operation.
Much depends on how your facility is set up. If you are a small mill with few ingredients, large silos and no real automation, then you are most likely to stick with what you already have since the capital cost of automating your intake system, retrofitting electro-pneumatic slides and valves and linking the whole system to a PC that still needs an operative, albeit one who is also doing another job, is probably not economically viable.
If you have a complex raw material supply system with a plethora of small silos, most of which already have automatically and centrally controlled slides and valves in the inlets and a system of elevating and conveying that is part of an overall mill control system, then the decision to remove the operative and go “hands free” is probably easier and one that can be justified on economic grounds.
Irrespective of whether or not the cost of supervision is warranted, the costs of raw materials focuses your attention on making sure you only buy quality ingredients and make full use of them in the blends you put together for the various types of mills you run and the classes of livestock you feed.
Making sure your silo intake system has no leaks, your slides and valves shut properly, and there is no cross-contamination from one ingredient’s storage point to another are all key issues in both your maintenance programs and the daily management of your mills.
The benefit of a daily inspection by the observant mill manager or operative who can pick up on the small points that have a big impact on your bottom line cannot be overemphasized. Intake is an extremely important area in which you receive ingredients that amount to some 80% of your total costs. It is an area where you should demonstrate due diligence when it comes to evaluation of raw materials and selection of storage point.
Grinding is the second key area within your mill that requires attention. Grinders have been traditionally housed separately from the other milling machinery due to insurance companies insisting they be enclosed and housed against an outside wall in case they explode and do damage to the rest of the mill. Fortunately, most insurers today recognize the reduced risk that hammermills present and that they need not be stuck in a small, old concrete house that is virtually impossible to access. Whether you choose to be a post- or pre-grind miller, your choice of hammermill is critical to your operation. Power-to-throughput ratio, screen size selections, method of feed and means of discharge are all areas you will take into account when selecting the appropriate grinder.
Areas not always addressed when operating hammermills are the grist spectrum and the maximum size of particle you can effectively utilize through the subsequent press facilities in combination with the correct die size and specification.
Mixing and matching screen sizes, beater tip speeds, and die tapers and thicknesses have all led to improved pellet durability and enhanced on-farm performance. But this varies tremendously from mill to mill and from one type of animal to another. Ruminant animals obviously can consume larger diameter pellets, but that doesn’t necessarily mean the granulation of the meal used to produce those pellets needs to be correspondingly larger than an early-stage pig diet, post-weaning. You need to do some work within your own mill and with your major throughput customers to establish the optimum. But generally, obtaining and evaluating plenty of data on a regular basis will indicate which areas show the most benefit.
As millers, you are seeking to minimize power consumption, reduce spare costs, and maximize throughput and mill efficiency. It is easy to look at grinding in isolation, but you must remember that the only reason you grind ingredients is in respect to further processing, liquid addition and absorption through the mixing phase and pellet mill performance later.
Obtaining the right blend of particle sizes within the grist is important, but so is maintaining that blend or grist spectrum. It is surprising how this can change on a daily basis if you do not pay attention to beaters and screens, hammermill speeds and airflow through the hammermill. Filters that become soiled or blocked can reduce airflow dramatically. When this happens, the dwell time in the hammermill also increases and particle sizes of ground product can change significantly. Power consumption also increases, and before long you can have quite a different type of finished product leaving the mill.
So what do you need to do to make sure your intake and grinding systems are up to standard? First, you must be certain that the raw materials you purchased are the quality that you actually receive. Buying from trusted suppliers will help, but you must be diligent and sample and inspect each load that arrives.
Secondly, you must be sure that what you buy is stored appropriately and that conveying equipment is properly maintained — electrically, physically and mechanically. You must be certain that silos are always weatherproof and that slides and valves are fully functional. Checking that compressed air systems are fully operational with no leaks will prove beneficial. A quiet walk around the mill when everything else is stopped will audibly highlight any compressed air leaks.
For those millers who buy grain well in advance of use and who store ingredients for any length of time, it is important that regular checks are done on storage silos and sheds, particularly when weather presents a risk. Making sure that marine unloaders are ready for use is important, as is verifying that trucks are in good order. Rail intakes need to be examined after each train has been through to make sure any damage done to hoppers is rectified before the next rail shipment arrives.
In the mills you need to have daily checks on your grinder installations to ensure that hammers and screens are in good order without excessive wear and with no damaged screens.
Setting the parameters for beater reversal and change is a critical issue if you want to maintain grist spectrum regularity. Some millers reverse rotation of the hammermill every day, some every shift, while some base their decision on tonnage throughput. Whichever you choose, make sure you stick with your choice until you see something within the mill that causes you to make a change. Constantly chopping and changing small parameters of machine settings is a sure way to lose control of your mill technical performance, since you will not know what aspect has affected another if there is constant change. Using the correct screen size or mixture of sizes is crucial to good throughput and appropriate grist spectrum. Where you make a wide range of feeds, including coarse poultry mashes, your screen selection will be broad and you will probably utilize auto screen changers at your hammermills. Prescreening of product prior to hammer milling and extracting the smaller particles will assist with protected vitamin survival and subsequent on-farm utilization of such vitamins. It will also reduce your power consumption as you will not be processing product unnecessarily. Providing you have the proper height over the hammermill, a screen will pay for itself rapidly in both existing and new installations.
As previously mentioned, airflows and inspection of filters is important. The use of magnohelic gauges will pay dividends, provided they are checked regularly and action is taken when they show increased resistance across the filter.
And finally, that all important daily walk through the plant — more often if you can do it — will probably be the most effective thing you can do to ensure that you have an efficient mill.
Jonathan Bradshaw is a consultant to the agribusiness and food processing industries, specializing in project management and bespoke training programs through his company, J B Bradshaw Ltd. He has extensive experience in flour and feed milling in Africa, the Americas, Europe and the Caribbean. He may be contacted at: firstname.lastname@example.org .