Post-Pelleting Liquid Application: A Practical Guide: Part 1

Introduction And Background

In most cases, post-heat liquid application treatment has been limited to fat additions of 1-10 percent. Equipment to apply fat is present in many mills and in some cases can be adapted to apply other liquid ingredients. In the past five years, several hundred pellet lines globally have been retrofitted to dispense enzymes. This increasing trend in Asia has been mostly in high capacity integrated operations. However, today, benefits can be realized in most mills as technology has changed to offer more cost effective solutions.

When determining equipment needs for heat-sensitive liquid ingredients such as enzymes, every effort should be made to ensure that these products are applied with precision and accuracy. Systems to apply liquids post-heat treatment work in a continuous flow setting in most instances. The aim is to apply the liquid after the fines are returned and before the feed goes to the feed truck. Parameters must be defined to monitor the equipment's efficiency. The installation of a liquid addition system can add a number of requirements to the feed process and existing equipment. These will be discussed in this paper.

The accuracy of a liquid application system should be determined by its ability to consistently deliver precise amounts at the feedmill. It should not be measured by animal or bird performance after consumption of the finished feed.

The Problem

High temperatures are used to satisfy requirements of quality feed and hygiene. Most pelleting mills operate at temperatures between 70 - 80 c. Health issues, such as salmonella have created the need for pelleting temperatures in excess of 90 c. Thermal treatment provides the following advantages:
- Gelatization of starch
- Enhancing the pellet quality
- Enhancing digestibility
- Hygiene treatment

Typically, the pelleting process involves conditioning, pressing and then cooling. Those mills utilizing expanders, process at higher temperatures and pressure. Heat, moisture, pressure and friction, reduction and oxidation reactions and light are stress factors which can negatively influence additives (Schwartz, 1998; Putnam and Taylor, 1997; Perry, 1997; Blair, 1996) Therefore, heat sensitive feed stuffs such as enzymes, vitamins, amino acids, probiotics and antibiotics, may require optional processing equipment.

Getting Started

The application of well-defined feed additives is becoming an indispensable tool for feed producers. There is a constant drive to produce low cost feed with maximum nutritional availability. In fact, postpelleting application can increase profitability.

As mentioned previously, post-pelleting application is not entirely new to the industry. However, enzymes and other heat-sensitive concentrates have changed the paradigm for post-pelleting addition. Inclusion rates of 40 to 250 grams per ton of finished feed have created the need for precision equipment and have raised some notable concern within the feed industry.

Following are some factors that influence the success of any post-pelleting application system:
1. Coefficient of Variation - the additive must be presented with uniformity to pellets
2. Accuracy - over-dosing or under-dosing is undesirable
3. Precision - the system must provide consistent and repeatable dosing

The answers to the following questions will provide some basic information to consider when making equipment changes and adapting new processes to the mill. The answers will also assist in successfully achieving the above points.

1. Where is it possible to add liquid ingredients in the feed process? Heat-sensitive ingredients must be added after cooling/sieving and prior to load-out.
2. Where is it possible to measure or calculate the flow of feed pellets or crumbles? In order to accurately dose precise amounts of liquids, the rate of dry flow must be accurately determined.
3. How much automation is needed to meet quality control requirements? To ensure repeatability and guarantee the application, a means of implementing both robust hardware and controls/software is necessary.

Some Useful Resources in Helping to Evaluate Equipment Needs:
1. The liquid supplier may have feed engineers or technicians available
2. The liquid equipment supplier will have varied experience
3. Consulting or engineering firms may help assess mill needs

Equipment suppliers in conjunction with nutritionists, mill managers and maintenance personnel can all provide input to creating a well-defined system. In short, if you do your homework, your application will be successful.