Troubleshooting The Pelleting Process

The benefits of producing good quality pellets are well documented and accepted. This article will deal specifically with production matters and pelleting technique for supplying consistently good quality pellets.
The “Troubleshooting” strategy is to investigate the major factors which influence pellet quality and production efficiency, i.e. feed formulation, specific power consumption (pellet press) and conditioning, which results in better pellet quality, production rate and profitability.
Pellet Quality/Production Rate Problem
A pellet quality problem occurs when pellet durability falls below your level of acceptability while a production rate problem occurs when it falls below your level of acceptability relative to pellet quality and design capacity. Level of acceptability varies from country to country depending on a number of factors such as technical production ability, feed raw materials and market pressures. However, better pellet quality or better overall efficiency is widely accepted, particularly by integrated feed producers.
Development of Pellet Quality
For better quality pellets, engineering process technology suggests to apply greater amounts of electrical energy per ton of pelleted feed, more so for ruminant and pig than for poultry. Fundamental Requirements for good pellet quality and production rate are adequate grinding and conditioning.
The first two stages that are recommended to investigate troubleshooting either Pellet Quality or Production Rate problems are: a good feed formulation and Sufficient Specific Energy (kWh/ton) used by the pellet press motor:
Stage 1
Determination Of The Formulation’s “Feed Pellet Quality Factor” (FPQF)
If FPQF is higher than level of acceptability, then the problem is in the feedmill. If it is lower, then discuss it with the nutritionist or feed formulator.
Determination of FPQF can be used:
A. as a formulating tool to predict pellet quality
B. as a production tool to maximize production rate
A. Feed raw materials and their influence on physical pellet quality needs to be understood. Knowing that some raw materials pellet well while others are very difficult. Each raw material should be given a Pellet Quality Factor; 0 for bad, 10 for good.
Pelleting each raw material as a straight and ascribing a value to it in order to calculate the pelletability of a mixture, does not always work out correctly. There is a synergy between raw materials which we is not yet fully understood.
The values listed for various raw materials are given in the table on page 40 of “The Pelleting Handbook” , published by Borregaard Ligno Tech. Clearly, if a feed formulation can be identified as potentially difficult before it gets into production, then a great deal of time and money can be saved. However, it should be stressed that the results from calculations should only be used as guidelines.
pleTables 1, 2 and 3 show the FPQF calculation of a ruminant, duck and Tilapia feed formulation, respectively. The process of calculating the Feed Pellet Quality Factor (FPQF) for any given formulation is straightforward. List the raw materials used in the formulation with their respective % inclusion and Pellet Quality Factor (taken from The Pelleting Handbook or your own modified version). Then, multiply the PQF by the % inclusion of the raw material e.g., Wheat meal: PQF 8: Inclusion 30%. Therefore, its contribution to the overall FPQF = 8 x 30% = 2.4. Add all the FPQF’s together and their total represents the Feed Pellet Quality Factor for that particular feed formulation.
When using a conventional pelleting line with no expander, if the result is below 5, there could be a pellet quality problem, if it is below 4.7, then the probability of a problem is very high. The tolerance between 4.7 and 5 takes into account the effectiveness and pelleting technique of the feed mill, some mills need to be “5” or over to make good pellets, while others could tolerate a lower level. It is suggested, therefore, that producers of pelleted feeds set their own FPQF level based on nutritional production circumstances and raw materials in relation to the level of pellet quality acceptability. When using an Expander, lower FPQF can be tolerated.
B. Calculating FPQF also provides a means of deciding production strategy. If FPQF is 5 or over, it generally indicates that the formulation will be easy to condition, therefore more steam can be added. It also indicates that Pellet Quality should be good, therefore, production rate can be maximized.
Stage 2
Determination Of Specific Energy (kWh/T Pellet Press Motor)
If good quality pellets are to be produced, then the pellet press has to impart a given quantity of energy. Studies suggest higher pellet quality requires greater energy input. To produce poultry, pig and ruminant pellets of acceptable durability at an acceptable production rate, then at least 10, 12/15 and 20/25 kWh/T, respectively must be used by the pellet press motor. For fin fish and shrimp feed, around 12 kWh/T is required.
The second stage, therefore, in a trouble shooting effort to solve a pellet quality/production rate problem is to determine the kWh/T of the feed formulation in question. But first check the die to ensure that the holes are not blocked or rolled over. If the kWh/T value is found to be lower than that required, it suggests that the die is not working hard enough. Possibly, it is worn out or simply that its compression length is insufficient. If the value is equal to, or higher than that required, then the fault must lay somewhere else in the plant, such as grinding or conditioning.
To determine kWh/T (units of electrical energy used by the pellet press motor to produce one tone of pellets) the production rate in ton/hour must be known as well as voltage and the average amperage used by the pellet press. To calculate production rate, determine the amount of time it takes to produce a given quantity of feed and calculate tons/hour. Then apply the following formula to calculate power (kW) being taken by the pellet press motor.
kW = Average pellet press motor amperage x Voltage x 1.73 x Power Factor / 1000
Assume a Power factor of 0.93 unless known.
Specific Energy Consumption (kWh/T) = kW / T/h
A “Troubleshooting” route in block form provides a summary to help direct you to a speedy solution of pellet quality/production problems you may encounter.
Measuring/monitoring the performance of your plant will enable you to manage it effectively and provide a means of speedily troubleshooting production or pellet quality problems.
Source: Borregaard Ligno Tech