Post-addition technology for liquid feed

As more and more hot processing equipment is used in feed mill equipment, such as extruders, extruders or other types of accelerating equipment and high-temperature short-term processing equipment, the feed is subjected to granulation, extrusion and expansion. The strong effects of temperature, pressure and moisture lead to the inactivation of anti-nutritional factors in the feed, denaturation of the protein, gelatinization of the starch, which is conducive to the digestion and absorption of livestock and poultry, but also brings many negative effects.

1. The necessity of liquid post addition

1.1 loss of vitamins

Temperature, pressure, friction and moisture will lead to the loss of vitamins, especially the effects of high temperature (94 ~ 104 ° C, average temperature of 100 ° C) on the destruction of vitamins. Especially VC, VK and VB1 losses are the most serious.

1.2 loss of enzyme preparation

Since the enzyme is a protein, the feed processing process has an important influence on the activity of the enzyme preparation. The optimum temperature of the general enzyme is between 35 and 40 ° C, and the maximum temperature is not more than 50 ° C. However, the temperature during the granulation process sometimes reaches above 120 ° C, accompanied by high humidity and high pressure. Under such conditions, the loss of activity of most enzyme preparations is exhausted.

1.3 loss of microbial preparations

Microbial preparations currently use more Lactobacillus, Streptococcus, Bacillus and Yeast. These microorganisms are particularly sensitive to high temperatures, and all of the activity is lost when the granulation temperature exceeds 85 °C.

Since the above three types of substances will have different degrees of loss during the expansion or granulation process, and with the continuous development of feed resources, the use of liquid components in animal feed is greatly increased. Today, the liquid feed components commonly used in feeds include various fat-soluble vitamins, minerals, antibiotics, amino acids and enzyme preparations, which provide the impetus for the study of liquid feed post-addition technology. More scholars have carried out research on post-expansion granulation and post-addition techniques.

2. Advantages of post addition

2.1 The heat sensitive trace components can be protected from the thermal processing, and the addition amount of these components can be reduced, thereby reducing the production cost. For example, the use of liquid post-addition technology greatly increases the activity retention of vitamins (see Table 1).

2.2 Adding the drug to the back instead of adding it to the mixer will help reduce the drug residue in the mixer and the back-end equipment and reduce cross-contamination. For example, some antibiotics used in pig feed are not allowed in chicken feed. Thereby improving product quality and safety.

2.3 The addition of some trace components is set after granulation or puffing, which is beneficial to be added according to the needs of users, so as to meet the requirements of users.

3. Substituting liquid materials and their advantages

The liquid materials that can be obtained at the end are:

(1) Vitamins, including water-soluble vitamins (VC, etc.) and fat-soluble vitamins (VE, etc.).

(2) Enzyme preparations such as phytase, amylase and protease.

(3) Growth promoters, including antibiotics such as monensin and probiotics such as lactic acid bacteria and yeast.

(4) Others such as antioxidants, flavors, colorants, flavoring agents, vegetable oils, organic acids and amino acids.

The use of liquid raw materials has the following advantages over powdered raw materials:

(1) The drying process is omitted. Many trace components such as enzymes are produced in a liquid state and then dried. The production cost of the drying process is high, and if a liquid trace additive is used, drying is not required, thereby saving costs.

(2) Reduced cross-contamination Trace additives can be directly pumped from the supplier's container when used, thus reducing cross-contamination and potential environmental pollution.

(3) Reduced packaging, transportation and storage costs Liquids can be packed in plastic drums or iron drums, which can be reused, thus reducing packaging costs and reducing residual losses.

Table 1 Effect of vitamin addition form on its activity Vitamin activity retention rate /%

Powdery liquid

VA6079

VB151144

VB21278

VB64771

VB12086

VE6689

VK3038

Niacin 46105

Biotin 061

4. Liquid post addition technology

4.1 Direct addition of suspension or colloid

Kvanta (1987) reported the incorporation of small amounts of biologically active substances (including vitamins, hormones, enzymes, bacteria, etc.) into processed feed. It is first mixed with an inert carrier to form a slurry, and then a homogeneous suspension is formed. The suspension is converted into a form which can act on the pellets by a device to form a uniform film covering the pellets. s surface. Lavery (1996) also reported a method of adding certain ingredients to the granules: mixing the added material with a viscous colloid and then mixing with the feed granules. The colloid-coated particles are substantially uniform and have little contamination to the mixer, and are added in an amount of about 2 to 40 kg per ton of feed. These two methods of addition are more suitable for small batch production of feed or farm processing.

4.2 spray adding liquid

At present, there are not many companies researching liquid post-addition technology in feed at home and abroad, and these companies are mainly concentrated in several industrialized countries in Europe and America. Due to the different requirements of spray accuracy, accuracy, liquid feed type and dosage, there are certain differences in the post-addition systems of various countries and companies. Nowadays, several representative liquid addition systems are introduced as follows:

Germany's Amandus Kahl is a pioneer in the development of post-addition and dosing technology. The core of its liquid addition system is the rotary spray adder Rotospray Type RS350. The center of the machine is equipped with a set of high-speed rotating rotating discs. When the rotating disc rotates at a high speed, 1ml of liquid feed material can be separated into 10 million fog particles, and the top-down particles or puffing can be sprayed around the rotating disc. On the feed. The machine has a simple structure, good spray effect and even distribution. According to the data, when adding phytase, the coefficient of variation of the uniformity of liquid distribution is less than 10%; when the flow rate of pellets is 5-20t/h, more than 98% of the liquid material is sprayed on the pellet feed. .

Schranwen of Belgium and Finnfeads International of the United States have jointly developed a new spray-addition system. The system delivers the liquid enzyme preparation to a gas-assisted atomizing nozzle at a metered flow rate through a pump, the nozzle being located above a rotating disc that receives pellet feed from an impact weighing device. And the material can stay on it for about 30s. Due to the rotation of the disc, and the fact that there is a paddle wheel that constantly flips the pellet feed, all the particles can be sprayed.

Novo Nordisk (1993) has developed a liquid spray system that meets the requirements of liquid enzyme preparations after feed granulation. It consists mainly of a high-precision metering pump that dispenses a precise amount of liquid enzyme preparation through a pneumatic nozzle and the output of the pump can be adjusted to suit the feed.

Daniso has also developed an enzyme spray system that sprays liquid enzyme preparations onto the surface of pelleted feed. This spray system ensures the accuracy and safety of the addition of liquid enzyme preparations, and the company also produces a range of products. Liquid enzyme preparation.

Chevita (1998) invented a new spray application system that can simultaneously spray up to four liquid or colloidal additives on processed feed at a dose of 0.1 to 5 kg/t.

In 1999, the Sprout-Matador company in Denmark developed the MicroFluid System MFS, which is used to add trace amounts of liquids such as vitamins, amino acids, aromas and enzymes to the granules. The system can be sprayed at a dose of 10 g/t and has a coefficient of variation (CV) of less than 10%. Since the MFS system can adjust the spray according to the different feed types and recipe changes, it saves time. Its liquid addition accuracy can reach more than 98%.

In March 1999, BASF and ProMinent developed a new advanced liquid enzyme preparation application system (PPA system). The system focuses on its accuracy, while the system can spray up to 83 ml per ton of feed. The system features precise spray (±1.5%) and small coefficient of variation (cv<10%). In order to avoid blockage and dust problems, the system uses features such as airtightness, self-cleaning and self-removal of faults. The PPA system is controlled by PLC control panel for automatic feeding or individual control.

The KOF&G (KoldingOmegnsFoderstofOgingsforening) company in Denmark developed a liquid spray system in the early summer of 1999. The application method is mainly based on the famous rotating disc law and the control system of Amandus Kahl. The system has five spray system pumps that are responsible for different traces of liquid components. Two rotating discs made of nylon rotate at a high speed around the apex of the cone at a speed of 2800 r/min. The spouts on the two rotating discs are injected into the cone at the center of the first disc. The notch around the cone and the notch at the edge of the disc serve as a passage for the droplets to be ejected. Once the dimples on the surface of the second disc are encountered, the notches release tiny particles that are immediately sprayed into the falling pellets.

In 2000, China Agricultural Mechanization Science Research Institute developed a liquid spray system LC50S. The core equipment of the system is a liquid sprayer. During operation, the material tray and the liquid tray are simultaneously started, and the dry matter remaining on the material tray is thrown out in the range of 360° under the action of centrifugal force and gravity, and forms a uniform dry material curtain flowing downward. At the same time, the liquid in the liquid tank is pumped into the liquid tray which is rotated at a high speed, and then is thrown upward by the centrifugal force to form an upward liquid curtain. The two kinds of reverse-moving curtains are sprayed into the mixing chamber after being fully contacted with the help of the blades, and further mixed in the mixing chamber and then flow out from the nozzle.

Most of these systems consist of six parts: control cabinet, sprayer, liquid metering system, liquid tank, liquid pump and feeder. Due to the different types of sprayers and liquid metering systems, the systems developed by companies around the world are also different. The liquid spraying machine is the core equipment of the system. At present, the spraying machines mainly used in the world have the following types:

(1) The ordinary spraying machine mainly includes a rotary spray adding machine and two disc rotating adding machines.

(2) The vacuum sprayer includes a dual-shaft paddle vacuum sprayer, a rotary vacuum sprayer (RVC), and a vertical vacuum sprayer (VAC).

According to the different liquid metering systems, they are divided into the following categories:

(1) The Amandus Kahl system developed by Amandus Kahl, Germany, a combination of liquid ingredients and post-additions.

(2) DWRobot system developed by AdvancedAutomations of Canada. The system contains three metering methods: weight loss from the liquid tank, positive pressure press from the bulk tank control time, and flow from the bulk tank through the pulse flow meter.

(3) The Liquidmaster system developed by BetaReven of the United States, which consists of liquid scales.

5. Main factors affecting the quality of liquid addition

5.1 temperature

The change in temperature affects the characteristics of the liquid, which affects the metering accuracy. In general, the lower the temperature, the greater the density of the liquid. For example, when the temperature is raised by 50 ° C, the density of most amino acids is increased by 3% to 5%, and when the temperature of the animal and vegetable fats is 84 ± 5 ​​° C, the density change rate is ± 5%.

5.2 Feed processing

For post-addition, the feed should be uniformly vortexed and a large curtain width formed so that the liquid can fully contact the solid feed to improve spray uniformity. However, it is virtually impossible to inject liquid additives onto the surface of all feed pellets. Therefore, the granulated feed after granulation comprises two parts: one is the portion to which the additive has been sprayed; the other is the portion to which the additive is not sprayed.

5.3 feed size

The larger the feed particle size, the smaller the number of particles in the same heavy sample, and the larger the particle size, the more difficult it is to spray droplets on the surface of the feed, and the worse the uniformity. Conversely, the larger the particle, the greater the proportion of particles that are sprayed when a certain volume of feed particles is sprayed. This in many cases compensates for the above-mentioned factors that cause the uniformity to deteriorate due to the large particles. Since the coefficient of variation is more dependent on the ratio of being sprayed to the feed than the particle size, it can be said that the particle size can be expected to obtain better uniformity, so care must be taken to minimize the particles in the pellet feed. During the spraying process, the liquid additive will diffuse as much as possible onto the surface of the feed, and the ratio of surface area to weight of the particles is relatively large, so the smaller the particles, the higher the proportion of additives. Due to the high content of additives in the small particles, the stratification of the fine particles will greatly affect the uniformity of the additives in the feed.

5.4 additive amount

Since many liquid additives are concentrated and account for a small proportion of the formulation, some occupies only a few tens to a few millionths, for ease of metering and atomization, small doses of liquid need to be diluted. It is best to dilute to 1% by flow metering; it is best to use 0.1% by weight.

5.5 Mixing quality after spraying

The sprayed and unsprayed feeds need to be mixed evenly after spraying. But the importance of fully mixing this step throughout the process is often overlooked.

5.6 droplet size

In order to make the additive more evenly distributed in the feed, it is best to contain a large number of small droplets, but many too small droplets will float forward in the direction of the feed stream instead of falling on the feed, causing the additive to eventually disappear. In the air, the adjustment of the spray structure should be enhanced to control the droplet size within a narrow logarithmic distribution.

5.7 pellet feed strength

Even if the spraying and mixing are uniform, in the subsequent process and during storage and transportation, if the pellet feed strength is not high, more powder is produced, which causes the concentration of the additive in the powder to be large and the concentration in the particles to be small. Therefore, it is necessary to increase the pellet feed strength for post-addition.

6. Problems

6.1 Post-add system problems

Post-addition systems typically consist of receiving, processing, storage, pressure sources, metering, and spraying, while receiving, processing, and storing portions are easily overlooked.

6.1.1 Inaccurate measurement

There are two types of liquid metering, flow metering and weight metering, most of which use a lower cost metering method. The flow metering is triggered by the control system to start the spray pump and open the spray solenoid valve. When the liquid passes through the flowmeter, the pulse signal generator of the flowmeter sends a pulse to the control system, one pulse represents a certain amount of liquid, and the cumulative number of pulses of the control system When the set number of pulses is reached, the control system sends a signal to close the spray solenoid valve. However, the frequency of reading pulses by most control systems is not high, and the accuracy of the flowmeter is generally ±0.25% to ±0.5%. At the same time, the calibration of the flowmeter is usually to set a bypass after the flowmeter to detect the flow, but the calibration is time-consuming because the resistance of the actual spray pipe and the resistance of the bypass used for detection are inconsistent. At the same time, the factors of inaccurate measurement are: the gear pump itself has large flow pulsation and pressure pulsation; when the flow metering is used, if the gas in the pipeline is not completely separated, the air will be metered as “liquid”; the flowmeter and gear The wear and corrosion of the pump running parts will reduce the stability of the system; the control part of the metering system will be affected by its own noise and environmental clutter, which will cause the pulse signal to be distorted.

6.1.2 Poor atomization effect

With accurate metering systems, poor atomization can also greatly reduce the accuracy of the entire liquid addition. Commonly used atomization methods include pressure atomization, centrifugal atomization, air flow atomization, ultrasonic atomization, etc. Among them, pressure atomization and centrifugal atomization are the most extensive. In the production process, the flow rate is not well controlled, the pressure at the end of the atomization is significantly reduced, the uniformity of the spray is affected, and the liquid is easily clogged when the liquid containing the impurities is sprayed.

6.2 Post-adding problems

Generally, after the addition, the liquid is sprayed on the surface of the pellet feed. During the subsequent packaging, storage and transportation, the pellets will rub and collide with each other, and the liquid wrapped on the surface of the pellet can easily peel off from the surface to form a powder, which is reduced. The amount of liquid additives in the pellet feed results in loss of nutrients and distortion of the formulation. Studies have shown that almost 80% of the added ingredients in the traditional liquid post-added pellet feed are in the powder, which greatly affects the performance of the ingredients.

7. Summary

Adding liquid to the feed can reduce transportation, handling and storage costs. It can use more flexible processing technology to improve feed quality and protect the active ingredients in the feed. Therefore, many large foreign feed mills use liquid addition technology, especially post-addition technology. Gradually recognize and start using post-add technology. At the same time, as a new process of feed processing, there are still different views on the selection of liquid carriers, the interaction between trace elements, the influence of droplet size distribution on uniformity and the measurement of accuracy. However, there are some shortcomings in the post-addition method. For example, the absorption capacity of the feed particles to the liquid additive directly affects the additive effect; there is a possibility of cross-contamination or chemical reaction when adding a plurality of liquids. However, as a new thing in the feed industry, post-addition technology has undoubtedly opened up a vast world for the feed industry and will play a huge role in the future feed industry.