3, steam quenching procedures and feed granulation efficiency
There are many factors that affect the quality of the pellets:
Feed formulations are generally considered to have the greatest impact on particle quality, but our argument is that steam conditioning can play a greater role in formulation. In warmer tropical regions, higher material temperatures are required. When the combined water content of the raw material is high, the feed granulation effect is increased, because correspondingly, the high moisture mixed material will enter the conditioner, but this does not necessarily result in stable particle quality.
Steam conditioning plays a huge role in ripening raw starch, especially amylose.
Condensed steam provides the principle of efficient operation (sufficient latent heat and micro moisture - 2257 kj/kg + 419 kj/kg = 2676 kj/kg). Therefore, it is instructive to make the saturated steam temperature entering the conditioner close to the condensation temperature (102-105 ° C) is the most ideal solution.
However, the actual understanding of the industry is often the opposite. Usually, a very high steam temperature (130-140 ° C) and a large steam pressure are used, which in turn leads to poor quenching and tempering effects and incomplete starch ripening (see below for specific reasons). ). It should be noted that the application of high heat and moisture in the steam conditioning process may cause chemical changes, which may be harmful to the utilization of nutrients, which may reduce or completely obliterate the benefits of granulation.
The only solution is to redesign the traditional steam piping setup to generate enough low temperature saturated steam (102-105 ° C) into the conditioner and maintain consistency throughout the workload. To succeed in this, we must understand steam thermodynamics. The entire steam piping layout is designed so that the steam meets its thermodynamic behavior. Do not have any condensed water at the low pressure setting or steam that affects sufficient flow into the conditioner.
Saturated steam provides less sensible heat and more latent heat and water... Latent heat and moisture are released when saturated steam begins to condense at 100 °C. What we really need is "latent heat and moisture", which can effectively soften and penetrate into the starch granules, and ripen the raw starch - especially the amylose fraction can provide gelation.
Achieving a high level of starch gelatinization, it is very important to bond the internal particles together to form a good particle. In addition, this will effectively improve feed granulation efficiency and reduce energy consumption.
Ideally, steam conditioning for quenching and tempering will be developed to another level on an existing basis – various forms of steam (superheated steam, unsaturated steam, saturated steam) can be produced from the same redesigned steam line. . This is very useful for feed production in some countries, such as China and South Korea, which determine the base temperature of the material due to differences in extreme weather in the four seasons. We need to design different steam temperatures for the difference in material base temperature in feed production due to seasonal temperature differences. The new method of steam pipeline engineering is very flexible and efficient. Depending on the material temperature (5-48 ° C), the feed granulation process can be fully controlled.
Steam conditioning has a greater impact on particle quality than any other processing technology!
PDI (Particle Durability Index) problems:
PDI is customarily used in feed production to determine the quality standards for the granules. However, even a finished pellet with a high powder rate can still have an acceptable PDI reading. Therefore, the criteria for evaluating the quality of pellets by PDI do not mean that the raw starch has matured and the amylose fraction in the matrix is ​​fully ripened.
PDI is very subjective. This can be improved by slowing the discharge rate and increasing the ring mode compression ratio, but this will inevitably affect production capacity and increase production costs.
The most important determinant of the quality of the feed pellets is the degree of starch gelatinization, which represents the actual ripening of the raw starch. The surface of the feed granules with high durability will lose powder due to poor tempering, inefficient cooking, low level of starch gelatinization and insufficient internal particle binding. Insufficient internal binding of the particles means that the ripening of the amylose fraction is a huge failure.
Experience has shown that 4-5% moisture absorption should be achieved during steam conditioning, which is achievable in cold regions. However, in the warm tropical regions, very low water absorption can only be obtained from steam, with an average of only 2%.
To understand an important concept: the base temperature of the material has a huge impact on the absorption of steam and moisture. If the base temperature of the mixed material is too high, it will greatly affect the steam conditioning. There are four seasons in East Asia, but the summer weather conditions are much hotter than in Europe, and the base temperature of the materials is 8-45 °C. Southeast Asia has a tropical climate with a base temperature range of 38-42 °C. All of these differences in temperature, combined with changes in the moisture of the mixture at different times of the year, have a significant effect on steam conditioning. Therefore, we need to have the ideal steam quality to participate in the work.
retention time
The purpose of steam conditioning is to fully form the pellet feed and soften the interior of the dried fine powder.
This is done in three stages: heating, moisturizing and mixing. The absorption of heat and the increase in moisture are the key to the quality of the particles, and good mixing is also necessary, which will allow the surface of the particles to be in full contact with the added steam. Longer conditioning times result in more uniform moisture penetration and heat transfer.
Increasing the residence time of the material in the steam conditioner (by adjusting the structure of the blade, slowing the speed of the blade, or using a longer conditioner) will improve the particle quality. Briggs et al. (1999) showed that increasing the time of the material in the conditioner by changing the pitch of the mixture increased the PDI by 4.5 percentage points. It has been shown that the feed granules require a longer hydration time than the heating time, and the tempering time of the feed should be based on the hydration time required rather than the heating time.
Superheated steam only provides enough heat but not enough water. Therefore, only very low moisture is absorbed after conditioning. With a higher quenching and tempering temperature, only a small amount of moisture can be obtained from the steam.
Saturated steam balances the three elements of ripening (temperature, heat, moisture) to provide adequate moisture and heat. . . . . . Saturated steam is associated with a low pressure setting and a lower flow rate into the conditioner. This is why we recommend using a saturated steam tempering time that must be close to 60 seconds.
4, the problem of feed granulation in a warm climate environment
Because feed producers are in different environmental and climatic conditions, their huge differences determine that a single parameter standard cannot be used. (As we all know, in China, when the summer ambient temperature is high, the moisture absorption rate of the material steam after quenching and tempering is very low, only 1.5-2% on average, and the industry has accompanied this daunting problem until today.--Translator's Note For example: the following situations occur frequently:
Poor steam quenching and tempering, poor starch ripening, very poor starch gelatinization, poor powder-to-particle combination, high-returning powder, poor pellet quality, poor crushing quality, low production efficiency,
5. Why does the feed industry still face granulation problems?
Here are some very disturbing facts and issues impede progress feed pelleting efficiency of
Question 1: Most feed mills in the industry have been working in the wrong way. Try to increase the quenching temperature and increase the moisture absorption by providing high-pressure high-temperature steam. But this concept is wrong from the beginning!
Superheated steam provides mainly sensible heat, but not enough latent heat and moisture.
The use of superheated steam results in higher temperature steam (130-140 ° C or higher) entering the conditioner. The superheated steam has a high sensible heat (steam temperature) and can reach the temperature signal sensor very quickly, reaching a set temperature of 85 ° C. The sensor sends a signal to the automatic flow control valve to adjust the steam flow into the conditioner. . Therefore, the amount of steam entering the conditioner is compromised. Less steam means less latent heat and moisture.
It must be noted that steam granulation is mainly a close relationship between moisture, heat and temperature, and can not only focus on one but ignore others. In fact, people tend to ignore the important factor of moisture, and the high temperature and temperature of the region.
Question 2: Too short a quenching time is a common problem.
Many people have not noticed the problem of steam conditioning time. Some conditioners have only 3-5 seconds of conditioning time, which has a very negative impact on the ideal relationship between steam and materials. It should be emphasized that reaching the set quenching and tempering temperature before the material is transferred from the conditioner to the controller is a great concern for ripening raw starch. The total retention time of the pre-conditioner and the time inside the conditioner are attributed to “total conditioning timeâ€, which is incredible because it ignores all the logic of food science.
Question 3: The problem caused by insufficient conditioning is the cause of less water absorption after steam conditioning.
â— The negative impact of imperfect steam quenching and tempering on the processing of pellet feed
Feeding poultry in the form of granules increases the economics of production by improving feed efficiency and broiler performance. These improvements are mainly due to reduced feed wastage, greater volume and nutrient concentration, no selective feeding, reduced time and effort spent on feeding, reduced segregation of ingredients, destruction of feed pathogens, thermal denaturation of starch and protein, Improve palatability and inactivation of enzyme inhibitors.
However, if a suitable temperature is not used during the quenching and tempering process, the particles will result in poorer production performance.
Studies have shown that granulation can cause changes in starch traits and is not susceptible to enzymatic hydrolysis (resistant starch). Bedford (2006) reported that broilers fed a basal diet with a tempering temperature of 93 °C significantly reduced weight gain and increased feed consumption compared to 85 °C. Lysine and arginine are lost due to Maillard reaction, starch aging into anti-enzymatic starch leads to loss of available energy, due to increased solubilization viscosity of non-starch polysaccharides and loss of thermolabile vitamins, exogenous enzymes and crystalline amino acids These are the negative effects of known high temperature conditioning. Heating the starch may also cause a decrease in starch digestibility if not handled properly. After heating, the amylose may recrystallize (reverse reaction) and become less digestible than before heating. Superheated starch causes a caramelization reaction, mainly by condensation of amino acids with sugars to produce indigestible Maillard products. Increasing the tempering temperature increases the PDI of the wheat based diet, but has no effect on the maize based diet. This finding can be explained by the difference in gelatinization properties between wheat and corn starch, which has a lower gelatinization temperature (52-65 °C) than corn (65-77 °C) (Lund, 1984).
Tempering of wheat starch at 90 °C may provide more heat than the gelatinization temperature, which leads to an increase in wheat-based diet PDI compared to corn starch. However, it should be noted that in the process of quenching and tempering, the degree of gelatinization during granulation is usually relatively low due to the low moisture content, and the components are mainly used to improve the physical quality of the granules in addition to gelatinized starch. It is worth noting that with the improvement of the quenching and tempering temperature, although the PDI of the wheat-based diet has improved, the weight gain and the absorption and utilization of the feed have a negative impact. Therefore, although it is generally believed that the durability of the particles is related to better production performance, it is obvious that high particle durability does not overcome the negative impact of high temperature quenching on production performance. Since the feed processing involves mechanical shear, heat, quenching time and water, it may cause denaturation of proteins in the feed, and their solubility decreases but the digestion efficiency increases. In general, heating increases the protein digestibility by inactivating enzyme inhibitors, and additionally denatures the protein to allow more sites to be exposed to the action of the enzyme. Improper steam conditioning will greatly affect the digestible protein value.
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