08 Jan Energy efficiency in feed factories
Possibility to reduce energy consumption in the feed pelleting process without impacting pellet quality.
Oriane Guerin, Zetadec bv, Wageningen, the Netherlands; email@example.com
In the last years, according to a global feed survey (Koeleman, 2019), more than 1 billion metric tons of compounds feed have been produced by about 30,000 feed mills distributed over the world. Top 8 countries produced 55% of this compound feed. About 40 % of the feed is produced for poultry, 30 % as pig feed, 20 % as ruminant feed and 10% for other species (as for example pet food or aqua feed). During feed production, a lot of attention is given to feed formulation in order to optimise the nutrient composition required by the target animal. Processing techniques affect nutrient availability and the physical characteristics of feed products (Kaushik et al., 2000). However, effects of the processing parameters on these nutrients are often neglected or underestimated (Behnke, 2001). Concurrently, there is a desire to improve the energy efficiency of the feed production process to decrease its CO2 footprint (Liang et al., 2011).
As for other production process industry, energy use in the manufacture of feed is high: based on different estimations and depending on the formulations, the production of one ton of compound feed usually requires 40 to 60 kWh/t of energy. Pelleting is the process requiring the most energy with up to 25 kWh/t (Redecker and Thoben, 2012). Consequently, attention to the processing parameters could help optimizing the energy consumption of the pelleting process without degrading pellet quality.
Determination of energy consumption
As illustrated in Figure 1, feed manufacturing is characterized by the requirement of mechanical energy for milling, mixing, pre-conditioning, pelleting and cooling. Mechanical energy and thermal energy, in the form of steam, is used for pre-conditioning and pelleting the feed.
Consequently, in order to determine energy consumption, several known parameters can be used to calculate the input of energy used in the feed pelleting process, which is defined in two forms (Guerin and Thomas, 2013):
- Specific Mechanical Energy (SME): this represents the level of energy transfer from the main drive motor to the compounding process, measured by mass of material (Dreiblatt and Carnedo, 2012). It also corresponds to electrical energy.
- Specific Thermal Energy (STE): this represents the energy transfer from heat sources (via steam injection) to the material (Janssen et al., 2002). This is thus related to the amount of head added via steam.
By knowing the SME and STE values of the produced feed formulations, it is possible to analyse the variability present in the process. These specific indicators are thus useful to maintain good control of the critical processing parameters.
Incidence of processing variability
From previous work performed at Zetadec, it is indeed known that differences in processing conditions between lines and feed formulations are present. For example, temperature of the feed and capacity of the production lines may vary a lot for a same formulation (see the examples given in Figure 2). Consequently, SME and STE values will also vary. From the figure, it appears that the production capacities of the different formulations have a large variation. In order to produce the same feed, capacities of 8 to 12 t/h are mostly measured. Because lower energy consumptions are measured with higher capacities, it is interesting on an energy and technical point of view, to optimise the process by producing at higher capacities.
From these observations, it can be deduced that by registering detailed data, calculations of the SME and STE may yield relevant information to be able to optimize the process, and consequently the energy use of a process in the future (Liang et al., 2011). Nowadays, with the help of online meters instruments, real-time optimisation can be performed, which will hopefully help to catch the opportunities present to reduce energy consumption in feed manufacturing.
To conclude, with an appropriate evaluation of current STE-SME values, it is possible to reduce the pelleting variability while decreasing electrical and thermal energy consumption. Consequently, energy can be saved in the pelleting process without impacting pellet quality.
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