Global Solution Application Manager
In the feed mill, pellet production is generally the most energy consuming step. Therefore, any potential area of optimization is beneficial to pursue. Adisseo several studies have shown that the addition of a liquid source of methionine (OH-Methionine) may lead to power savings of up to 13% compared to the powder form (DL-Methionine) when pelleting.
Power consumption is one of the key points that must be monitored when managing a feed mill as it directly affects the feed production cost. The manufacturing step that contributes the most is pelleting, as it can account for up to 60% of the electricity consumption (Tecaliman, 2016). Thus, even the smallest source of savings should be considered as it will improve the feed mill performance. This is even truer when we deal with high production volumes. This translates concretely in economic terms, but also in terms of the impact on the environment.
Methionine is an amino acid added to feed in either powder or liquid form. It has been reported that customers, using liquid methionine instead of powder, experience energy savings when pelleting. To confirm this statement, Adisseo conduct trials in a pilot pellet mill in controlled conditions and collect field measurements.
[box type="shadow" align="" class="" width=""]
• Mixing without methionine
• Methionine addition in the mixer: spraying of liquid methionine or addition of powder methionine
• Final mixing
• Start phase of pelleting in a Kahl flat-die pellet mill, die 4 x 24 mm (equivalent to 4 x 85 mm for an industrial ring-die)
• Pelleting of all batches at a rate of 40 kg/h and addition of steam at 80°C (a cycle of production then few minutes of rinsing)
• Decrease of temperature and moisture of the pellets in a cooler
4. Storage & Analysis
• Storage of pellets at room temperature
• Analysis of pellets quality[/box]
Two trials were conducted in Tecaliman, the French technical center for Feed, in their pilot pellet mill: a first one in 2016 and a second one in 2020. They assess the pelleting behavior of complete feed by varying formula and methionine sources (liquid or powder). The quality of pellets and energy use at pellet mill are measured.
The process for each test is summarized in Figure 1.
All process variables (steam addition, throughput, die characteristics, pellet length, etc.) are at fixed values to limit the variability.
Electricity consumption is obtained by measuring the instantaneous power absorbed (kW) by the motor of the press each second. Only the values in which pelleting conditions (production rate and temperatures) are stable are used. This amount is then divided by the real output rate (t/h) to calculate the specific energy consumption (kWh/t). In the second trial, the results are expressed in net specific consumption by deducing the idle operation of the machine (which represents about 10% of total energy consumption).
Powder DL-Methionine (DL-Met) and liquid OH-Methionine (OH-Met) are used as methionine sources and are added in feed on equimolar basis given the concentrations of each methionine product (DL-Met at 99% concentration and liquid OH-Met at 88% concentration).
Additionally, pellet quality, which is a major parameter to consider when looking at power consumption, is assessed:
- A hardness test is carried out on 36 pellets for each sample. This test measures a pellet’s resistance to crushing by imitating the effect of an animal chewing. For the first test, we use a Schleuniger machine (results in Newton) and for the second one a MT50 Easy TDH SOTAX (results in MegaPascal).
- A durability test (or PDI) is carried out on two 500 g different samples. This test consists in measuring pellet shock resistance levels, with a EUROTEST device from Sabe. It is expressed in %.
- The rate of fines is assessed by weights before and after sieving on a 3.15 mm grid. It is expressed in %.
A first trial at pilot pellet mill shows electricity consumption at pelleting decreased by
2.5% to 7% and investigates formula moisture & oil content impact.
For this test, thirty-two feed batches of 7 kg are prepared using the same diet (Table 1). DL-Met, OH-Met, oil and/or water are added at different inclusion rates. DL-Met and liquid OH-Met are first added at a standard dose on equimolar basis (0.20% for DL-Met and 0.23% for liquid OH-Met), then liquid OH-Met is added at higher doses to highlight the effect of the additive. Three sub-trials are performed.
The first sub-trial points to an effective reduction in energy consumption with liquid OH-Methionine. In general, the addition of high levels of liquid OH-Met (more than 0.23%) diminishes the power consumption in all cases. When standard doses (0.23%) of liquid methionine are used, the reduction phenomenon is particularly observed when no other liquids are added to the formulation (Figure 2 – Dry feed). Here, a 7% reduction is obtained. As expected, the addition of oil reduces the overall energy consumption. When 3% is added (Figure 2 – Oil 3%), savings when using liquid OH-Met instead of DL-Met account for 4%.
These results also lead us to believe that a possible slight increase in energy consumption is caused by the addition of powder methionine.
A second sub-trial set is performed in order to confirm these findings. The negative control is prepared without additives, oil nor water. The positive control does not contain additives and is prepared with oil and/or water according to the different tested conditions.
Results show that, on one hand, there is no significant difference between the positive control and feed with liquid methionine. On the other hand, a significant increase in energy consumption, when DL-Met is used instead of liquid OH-Met, is confirmed. Although the addition of oil alone show only a tendency for lower power usage (Figure 3 – Oil 3%), savings range from 3% when feed is dry (Figure 3 – Dry feed) to 4% when feed contains additional free oil and water (Figure 3 – Oil 3% + Water 1%).
The effect of water alone is also explored in a third sub-trial, and three levels of water are tested (0.5% – 1%
– 2%). The addition of water alone does not permit to differentiate the control from DL-Met and liquid OH- Met (Table 2). Therefore, in this case, benefits for OH-Met are not clear. However, a tendency of lower power consumption is observed in each case.
For all sub-trials, the pellet quality is generally maintained. Values range at 91% ± 0.8% for durability and at 34 N/pellet ± 3.3 N/pellet for hardness for feed without oil.
They demonstrate that liquid OH-Met has the capacity to reduce power consumption from 2.5% to 7% when pelleting formulations without water addition.
A second trial explores various type of formula and demonstrates again a decrease of energy consumption at pellet mill, when using liquid methionine compared to powder methionine.
For this trial conducted in 2020 in TECALIMAN, different types of formula (wheat-based formula and one based on corn) are produced, as displayed in Table 3.
Each formula is supplemented either by liquid OH-Methionine or DL-Methionine on an equimolar basis to obtain 2.5 kg of active substance per ton of feed. The objective is to see the impact of methionine sources on net energy consumption at pellet mill for a same formula.
Each configuration (composition & methionine source) is repeated 3 times.
The specific net electricity consumptions at pellet mill obtained for each formula and methionine source are shown in Figure 4.
For formula A, C and D, a significant decrease of net energy consumption of respectively: 8%, 13% and 12% is observed when methionine is brought as liquid OH-Methionine vs DL-Methionine.
No significant effect has been determined between methionine sources on specific net electricity consumption for formula B and E. As the formula E contains the highest contents in oil & water, its composition leads to soften the potential differences, thus the effect of methionine sources may be negligible. We cannot explain why no significant difference is observed on formula B.
With the formula A, B, C and E, there is no significant difference observed between the methionine sources and the Control on pellet hardness, durability and rate of fines. Only statistically significant differences on pellet hardness for 2 formula are observed but with no practical impact, as these differences are imperceptible (hardness of formula C: with liquid OH-Met: 1.79 MPa vs 1.67 MPa with DL- Met and for formula D: with liquid OH-Met: 1.29 MPa vs 1.44 MPa with DL-Met).
As a conclusion, a decrease of up to 13% of net energy consumption at pellet mill is assessed in this test, without affecting the physical characteristics of the pellets produced (durability, hardness, % of fines).
Power saving trends showed in the field
Same conclusions are drawn in the field with trials in two different Malaysian feed mills comparing the two sources of methionine in 2015. Liquid OH-Met and DL-Met are added in the mixer in 2 independent batches of the same formulation and tonnage. First trials demonstrate savings up to 3% in favor of liquid OH-Met. In a second feed mill (Figure 5), a formulation composed of a corn and soybean base with 0.25% of water and water-based liquids and 3% of palm oil is used. Pelleting is conducted according to the feed mill current practices and power consumption measured with a power analyzer Lutron DW-6093. The specific energy consumption is obtained by doing the ratio between the mean power absorbed by the press (kW) during the trials and the real production rate (t/h). The data showed power consumption when pelleting to be 2.5% inferior when using liquid OH-Met instead of DL-Met.
The general mechanisms that cause the energy reduction observed between usage of liquid OH-Met versus DL-Met are still unknown. However, as the main power drain in the pellet press comes from the effort needed to overcome the friction force in between the interface feed/die, it is possible that the DL-Met effect originates from an increase of this force. The apparent balancing effect when moisture is added leads us to believe that the phenomenon may be caused by hydrophilic particle interactions between the die walls and among themselves. Because liquid OH-Met is a water-soluble liquid, these interactions may not take place which could justify the power savings observed. These savings are a common trend overall, but they are variable. Indeed, one must be aware that the coefficient of friction which affects energy usage is impacted by an important number of parameters making it difficult to obtain a precise number.
Overall, feed mill and pilot trials show an advantage in power consumption for liquid OH-Met with values up to 13% less compared to DL-Met. This advantage is not seen in every case, but the electricity consumption for pelleting is a least the same than for feed with DL-Met or even lower, i.e. better. Seeing this advantage from another angle, it means that, at a constant power, the flowrate of the pellet mill may be increased by a few percent when using liquid methionine compared to DL-Met.
[box type="shadow" align="" class="" width=""]
For example, assuming that:
- Annual production of pelleted broiler feed: 100 000 tons
- Specific electrical consumption at pellet mill: 15 kWh/ton
- Cost of electrical energy: 0.13 $ per kWh
- Estimated energy savings at pellet mill: 10% - CO2 emission: 0.5 kg CO2 -eq per kWh Estimated annual savings =100000×15×0.13×10%=19 500$
Estimated annual CO2 emission savings =100000×15×0.5×10%=75 000 kg CO2−eq (That is the equivalent of the emissions of 28 round trip flights Paris-Bangkok)[/box]
For the feed miller, these potential savings will reflect on the cost of feed production.
These amounts are only an example. Each production manager can adapt it to his own situation.