Technological recommendations when using methionine sources in the feed mill
by Marc Perel, Solution Application Manager, Adisseo
Methiopedia 2, the technical reference guide for methionine edited by Adisseo at the end of 2018 has a full part dedicated on the application of methionine sources in feed. In this article, we will investigate these technological aspects for an accurate and safe use of methionine sources in feed production.
Indeed, liquid and powder methionine products (liquid OH-Methionine, DL-Methionine or L-Methionine) require proper equipment and use in the process. To obtain an optimum feed quality, main process stages need to be managed regarding this methionine addition.
Main vigilance points at the feed production when adding methionine sources
Specific equipment is available for the distribution of powder and liquid methionine sources in feed. This addition is performed in the mixer, but the transfer from the storage point till the mixer and the supplementation in the right quantity need to be mastered to achieve the expected quality of the feed. Indeed, methionine products have to be added at the quantity defined by the formulator and this, for every single batch.
Three main process steps require a right equipment implementation and settings, and a regular monitoring: storage, dosing and distribution.
Safety comes first when speaking about the use of additives or raw material in process. For powder and liquid methionine sources, the safety data sheets have to be accessible easily and quickly in the plant in case of any accident. Before any maintenance intervention, everyone from the plant staff or any external company - maintenance contractor for instance - should be aware of the risks and wear the appropriate PPE (Personal Protective Equipment) such as mask, goggles, plastic gloves, covering suit, etc.
During regular control visits, the presence of these PPE, of risks labelling and spill kits will be verified. One will also check the proper functioning of the shower and eye wash station if any, for the liquid installations.
Powder sources of methionine (L-Methionine or DL-Methionine) can also be packed in bags or big-bags, that will be stored inside the warehouse protected from humidity and weather. These forms are directly used by the feed mill or come through the premixes.
Liquid OH-Methionine (OH-Met) is packaged in drums or IBCs that can be stored outside to save internal space in the feed mill. The product is also delivered in bulk for a storage in tanks before use. According to the local regulation, a containment pool may be needed.
Preferred tank materials are:
- Poly Ester reinforced by fiberglass
- PEHD Poly Ethylene High Density
- Stainless steel 316L
Tanks can be insulated according to the temperature conditions and wind exposure. Heating the product by a coil inside the tank is not preferred, and a double-jacket heating system (thermal oil) at the daily-tank is far better.
A pump allows to bring the methionine product to the dosing step. Pumps used for liquid OH-Methionine are volumetric gear pumps or screw pumps designed for viscous liquids. For powders, the most common dosage device is the screw, generally equipped with a speed variator for better accuracy. Dosing slides is a very fast and accurate interesting alternative.
For the dosage itself, a weighing scale can be used. The scale has the same principle for solid and liquid methionine forms except for emptying: simple gravity cannot ensure a proper pressure in the case of liquid.
For liquid methionine, the working principle involves the continuous automatic filling of the product in a weigher hopper to pre-set mass
Using 'loss in weight' methodology, the dosing pump will draw a precise amount of liquid OH-Met from the weigher hopper to be sprayed onto the feed in mixer. General dosing accuracy can be achieved around (+/-) one percent error tolerances against set point for these applicators. As an example: at 2kg/tonne, the error is (+/-) 20 g.
Another option to achieve dosage of liquid OH-Met is by flow-metering. For flowmeters, three types are possible: mechanical flowmeter, mass flowmeter and electromagnetic flowmeter. The water content of OH-met gives a high conductivity, which allows the use of an electromagnetic ﬂowmeter.
These systems have the advantage of working without a pressure drop and do not need any maintenance. Dosing accuracy is made by the chain of measurement from pulse control to valve closing, and ﬂowmeter accuracy. It is important that the entire chain is built consistently to obtain the highest precision, with a high reliability of the entire dosing operation.
The precision of the dosing system is commonly 0.5 percent. As an example, at 2kg per tonne, a dosing error is (+/-) 10 g. The flowmeter, whatever its type, is placed between the pump and the injection point.
If the plant is using a scale, its metrology will be included in the global program, with the other scales. It mainly consists on a verification with calibration masses, calibration of the zero and span adjustment if needed.
Concerning the flowmeters, the principle is to run the pump in standard working conditions and to collect the product before the mixer thanks to a calibration valve, in a bucket. The accuracy of the dosage is assessed by comparing the value measured by the flowmeter and the quantity that is weighed in the bucket. In case of a slight deviation, parameters such as number of pulses per litre or density have to be rectified. The suitable frequency for these controls is one-to-two times per year.
Apart from the efficiency of the mixer to mix solid ingredients and the specific maintenance program of this key machine in the feed plant, the most important feature is the way (where? when? how?) that the methionine sources are applied to the macro-ingredients.
A collector or manifold feeds the mixer through different nozzles, which are key points for application systems for liquid methionine. The right type is a calibrated flat-bed spray nozzle in stainless steel with different sizes and numbers. It allows liquid methionine to be sprayed in small droplets without mist emission, which avoids build-up inside the mixer. Nozzle specifications are defined according to the size and the shape of the mixer. Generally, three-to-five nozzles are used to spray liquid OH-Met.
Mixability depends on droplet size. This right droplet size (250 μm) is obtained by taking care of some parameters of the spraying equipment itself and liquid methionine characteristics:
- Liquid methionine viscosity
- Working pressure in pump
- Nozzle selection and positioning
Nozzle positioning is defined according to the size and the shape of the mixer and added quantity. Spraying must be done on the moving surface of feed, and liquid must be absorbed before reaching the wall of the mixer to avoid any build-up.
The quantity of feed within the mixer should never cover the mixer's ribbons (i.e. the working capacity of the mixer). If the ribbons are covered, then a quasi-motionless dead space forms over the ribbons; this in turn does not allow dry or liquid methionine sources to homogeneously mix throughout the feed.
Formation of lumps can occur if there are issues with the system settings: nozzles not of the right size, leakage in the mixer, pump not of the right size or a defect in the heating system of liquid methionine leading to a too low temperature and a too high viscosity.
Plus, liquid methionine is added in a low amount compared to some other liquids (oils for example) in formula, so there is no risk of agglomeration.
Working pressure in the nozzles is the second key factor to monitor, as it will influence the spray angle and the droplets size and, ultimately, the contact between the liquid and the solid phases. This pressure can be altered by the abnormal wear of the pump or by some leakages in the liquid system. Therefore, it is important to check it regularly and react in case of any deviation. In most cases, it should be between two-to-five bars.
The methionine sources, like other additives must be added to the right place and at the right time in the mixer. The powder methionine should be added from the beginning of the mixing time, preferably in the center of the mixer, and after or in the middle of the macro ingredients.
For the liquid methionine, the arrangement of nozzles must be such that the liquid hits the feed in an area where mixing is vigorous. Liquid OH-Met can be sprayed from the beginning of the mixing time. The addition of liquid methionine does not require any increase in mixing time.
Optimal feed quality: mixability and homogeneity:
If done properly, the distribution of the methionine sources leads to a satisfying mixability in feed. For example, for a DLM incorporation rate of 2kg/t, 12.2g of feed should be eaten by the animal to have 95 percent probability to find the expected level of methionine +/-10 percent.
When mixing powder, the main issue is segregation between the fines and the big particles. When working on very heterogeneous feed in terms of particle size, like coarse ground layer feed for example, it is very difficult to mix everything intimately, and segregation can occur after mixing. The risk of particle segregation is much lower with liquid methionine because it will be adsorbed on the feed particles.
Homogeneity (dispersion of methionine in feed) is independent of the nature and inclusion rate of methionine source when equal conditions are applied, as assessed on the field. Both forms of methionine will give equivalent mixing performances.
Even at a rather low incorporation rate (<0.1%), liquid and powder methionine are generally well dosed (recoveries between 90 and 110%) and evenly spread (coefficient of variation below 10%).
With respect to the general requirements for an accurate dosing, a full transfer to the mixer and an appropriate spraying, most of the equipment is suitable for low quantities.
In general, liquid and powder methionine sources lead to same quality of feed. Equipment for the distribution of these forms are well-designed to have targeted mixability and homogeneity of the product in feed. These installations have to be monitored through time. There is no heavy maintenance operation linked to liquids but mainly inspections.
With liquid methionine, there is no dust, which means no risk explosion, no particles breathed by workers and a better hygiene in the plant. The liquid packaging is also convenient as it does not need to be stored inside the warehouse and can be recycled or sold.
For a same feed quality, powder methionine is suitable for plants using an annual low volume of methionine, as this product in bags or big-bags offers flexibility. On the other hand, liquid methionine is convenient for medium and large feed mills because this product can be transferred from the tank, dosed and distributed in the feed automatically.