A feed mill's electricity bill has risen clearly over the last two years. The production manager has reviewed motor efficiency, compressors and lighting and made some improvements. But the manager cannot explain why the bill swings so much from month to month. When the records are compared, the months with high bills turn out to be the months when the share of barley and fibrous by-products in the formulas went up and the share of pelleted feed rose.
Where does the energy go?
In a compound feed mill, most of the electricity goes to two processes: grinding and pelleting. Mixing, conveying and cooling use energy too, but their share is smaller. The steam used for conditioning is a separate energy item and is usually raised with natural gas or another fuel.
The energy needed for grinding depends on the hardness and moisture of the ingredient and the target fineness. Corn, barley and wheat take different amounts of energy to grind. Fibrous ingredients usually need more. Grinding finer raises energy use per tonne quickly. In pelleting, the make-up of the formula, the die thickness and the quality of conditioning decide the result. A formula that binds well and is well conditioned goes through the die with less energy.
An example
The numbers are illustrative. Assume a mill uses 8 kWh per tonne of feed for grinding, 15 kWh for pelleting and 7 kWh for other processes, 30 kWh in all. At 4 TRY per kilowatt-hour, energy costs 120 TRY a tonne. In a mill producing 10,000 tonnes a month, that is 1.2 million TRY a month.
Assume that when the share of barley and fibrous by-products in the formula rises, grinding energy goes up to 10 kWh a tonne and pelleting energy to 18 kWh a tonne because of a harder, less binding mix. The total becomes 35 kWh and energy cost rises to 140 TRY a tonne. The difference is 20 TRY a tonne, or 200,000 TRY a month. If that formula change saved 30 TRY a tonne in ingredient cost, the energy difference takes back two-thirds of the saving.
This shows that formula decisions should not be made on ingredient price alone. The cost of processing an ingredient inside the mill is part of its real cost.
Bringing processing cost into the formula
A practical way to reflect this in formulation is to add a processing cost to each ingredient. For example, a hard grain can carry a grinding cost per tonne, while an ingredient used without grinding carries none. When these costs are added to ingredient prices, ingredients are compared at their real cost to the mill.
Writing pelleting cost directly onto ingredients is harder, because how a mix pellets depends on how the ingredients behave together. This is where the scoring system used for pellet quality can help. Formulas that bind well mean both better pellets and lower pelleting energy. Setting a minimum for pellet quality indirectly keeps energy use in check as well.
Grinding fineness
Grinding fineness is a balance point between energy and animal performance. A more finely ground feed usually gives better pellet quality and, in some species, better digestibility. But energy cost rises, and in poultry very fine grinding can weaken gizzard development. In ruminant feeds, very finely ground grain ferments quickly in the rumen and raises the risk of acidosis.
So the target grinding fineness should be set separately for each type of feed and the screen size chosen to match. Grinding every feed through one screen is usually the worst compromise for both energy and performance.
Production planning
Production planning is another factor in energy cost. In regions where electricity tariffs vary by time of day, moving energy-heavy grinding to cheaper hours brings serious savings. That needs enough bin capacity for ground ingredients. Frequent formula changes also raise energy use per tonne by adding time when the line runs empty or is being cleaned.
A plan that solves a mill's feeds together under shared limits can also treat pellet line capacity and grinding capacity as constraints. The formulas are then thought through together with the load the line can carry and the cost of energy.
Steam and conditioning
Besides electricity, the cost of the steam raised for conditioning is also linked to the formula. Some mixes, those high in grain for example, need a higher conditioning temperature for a good pellet. Mixes high in fat take up less steam. Boiler efficiency, condensate return and insulation of the lines also decide fuel use per tonne. Keeping conditioning temperature higher than needed raises fuel cost and speeds up the loss of some vitamins and enzymes.
Measuring and recording
The first step in managing energy use is measuring it. Fitting separate meters to the grinding and pelleting lines and recording use per tonne, formula by formula, shows which formulas are expensive in energy terms. Over time, that data also makes it possible to set more accurately how much processing cost should be written onto each ingredient.
In OptiFormula, processing costs can be taken into account by adding them to ingredient prices, constraints can be defined for pellet quality, and in the Premium edition a mill's formulas can be solved together with capacity limits. As energy prices rise, bringing the costs inside the mill into the formula is the way to make sure the least-cost formula really is the least-cost one.
