Process control systems

by Jonathan Bradshaw
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Editor’s note: This is the final part in this series of three articles on the subject of automation. Part 1 of the series was published in the February issue of World Grain and part 2 of the series was published in the March issue.

The pellet mill is the area of the feed production facility where millers can intervene and exert their influence the most, whether it involves improving pellet quality or power consumption. It is also the area where automation can be used to regularize the process and assist milling operatives.

There is a wide range of pellet mill controllers available these days. There are some excellent devices on the market which are all tried and tested, and good sound pieces of equipment with a wealth of experience behind them. Unfortunately, there are also a range of controllers — invariably on the floor below the pellet press, usually switched off and which I doubt will ever be put into use — that were the brainchild of the engineer whose concepts were good but whose practical engineering skills did not match their ambition to revolutionize the press control and automation market.

The best pellet mill controllers operate independently of the rest of the mill. These controllers take information from a range of sensors which draw data strategically from around the pelleting press, including steam volume and pressure, valve settings, meal temperature, motor loadings, including cooler fan motor loadings, throughput per hour, feeder settings, etc. Having gathered this information, it is then the time taken to react to fluctuations in the most significant of these readings that is important. Some parameters require a swift response, such as when steam pressure builds up, while others may require a slow response, as would be the case with meal temperature. Part of the quality of the controller is the ability each one has to allow input data response time to be adjusted, and part is the way in which the press controller is used or the way in which the operative finds the controller easy to adjust.

Some pellet mill controllers restrict the scope of the activity to just the pelleting press itself, while others take into account the ability to influence and control pellet temperature as product enters the bulk load out bins. After all, there is no point in maximizing pellet press throughput only to have the pellets deteriorate in storage before they get a chance to be put in front of the animals. On this subject, I cannot emphasize enough the need to have a good airflow through finished product bins, especially when large diameter pellets are being made. Mold can develop within 12 hours inside a load out bin purely due to the lack of air flow. Modern day cooling plants are made to cool feed down to ambient temperature, but this is based on 6 millimeter pellets, not 20 millimeter nuts where the core temperature still remains high even after 24 hours. When this is compounded with a lack of air flow, the results are catastrophic. Always provide a good air throughput for large-diameter product when placing it into storage at the mill. Also, always use open topped tote bags when delivering in bags.


Moving on from pellet mill controllers to control of routing through to bulk out loading and finally to farm, it has now become commonplace to use the mixing and blending computer to set up the finished-product routes. This may seem odd, but it really isn’t when one considers the need to have a destination and a farmer’s name for record-keeping purposes so that drug batch numbers have somewhere to be allocated and test results can be identified on a select batch from a supplier. This does, in practice, keep life relatively simple.

With bagging records a similar situation arises, and I have been in the practice of, for accounting purposes, manufacturing into a bulk load out bin and then transferring product to the packing station for filling bags. Effectively, this makes the bagging line an independent customer, and it is treated as such for all intents and purposes of batch record-keeping. This has worked well for me, although I appreciate that other millers may well have their own preferred means of dealing with such internal record-keeping.

This article refers in part to “storage and automation” either directly or by inference, but there is little room for these two topics to work hand in hand in a feed mill. Many hours can be wasted trying to reconcile physical and theoretical inventory, and as far as I know there are still people arguing the subject now. My view is to take theoretical inventory for all bulk ingredients and finished feeds and use physical stock counts for all bagged inventory. Again, while I have found this works well, readers will each have their own preferred choice and much depends on time available and size of the inventory to be counted.


When using a throughput-based program, it is not difficult to add on a small

program that can deal with simple routine maintenance tasks such as lubrication and regular checks on belt and chain tension, sprocket wear, elevator belt alignment, etc. Major services to mixers and presses can also be scheduled. But obviously the longer the task, the more difficult it is to find a slot to accommodate such major work during normal running hours. Some large items, such as off loaders, are easy to accommodate, but they can easily be serviced following their own vessels.

Other items such as lab analyses can be built into statistical analyses programs, and the use of statistics to enhance the accuracy and effectiveness of data recall is something which nutritionists have looked at from time to time.

The feed miller has a lot to be thankful for by way of having today’s software programs available to him. There are many programs which make millers’ lives simpler, easier and more cost effective. You can control your environment and monitor and record emissions into the atmosphere and water courses. You can control your haulage fleets much more effectively and derive economics which until recently neither management nor operatives thought possible and practical.

When it comes to fully integrated units, particularly pig and poultry operations, there are many areas where the computer application possibilities are wide ranging. Given that birds can rapidly utilize energy in feed, you can easily bring forward or slow down weight-for-age figures in most flocks. Thus, in the case of a 16-piece, cutup bird wanted for an imminent bank holiday, you can increase the numbers of ready birds that you can make available. There are obviously compromises to be made with other areas, but the principles are now well accepted that you can greatly influence the profitability of an integrated unit to such an extent that you no longer have to simply accept a given growth rate utilizing a fixed formula each month.

There is much to be learned yet from the application of technology, perhaps more from a marketing standpoint than anything. But there are also areas where batch records can be easier traced and data retrieval made simpler.

Printouts of plant performance can be useful to the diligent mill manager as he goes about his daily walk around his mill. The saying that the camera doesn’t lie is rather quickly being taken over by the phrase the computer only gives true data. You know that is not the case and that computer data being generated is only as good as the quality of the data which is being input. This being the case, however, you should learn to respect the data generated and apply it as best you can to enhance the performance of your mills, ingredients and transport fleets. That walk around the mill, which I preach as being key to a good operation, may soon be with a laptop under your arm. But anything which will enhance your milling performance and yield has to be core to your success and that of your customers.

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