When blending animal feeds, closely controlling the feed blend ensures proper taste and nutrition while keeping production costs down. Additives, such as fats and vitamins, are added to base feed products for taste and nutrition. If not enough additives are blended, the animals may not receive proper nutrition or eat the feed because of the taste. As some additives can be costly, adding more than necessary will increase the cost of the feed.
For example, consider a feed mill that requires blending 5% of its nutrient; this would be 100 lbs of nutrient per ton. Now consider if instead of adding the required 5%, an additional 10 lbs of nutrient per ton were added. If the cost of the nutrient were $0.25 per lb. the cost of the feed would increase $2.50 per ton. In a mill that produces 15,000 tons per year the cost would be an additional $37,500 per year.
Using a solids flow meter to measure the flow rate of the base feed product and a Coriolis mass flow meter to measure the flow rate of the additives, a PID control loop can be used to add the correct amount of additives for the amount of base feed product.
How the system works
A Siemens solids flow meter measures the flow of the base feed product as it is moved into the mixing drum. The Siemens Coriolis mass flow meter measures the amount of additives being pumped into the mixing drum. The Siemens SF500 solids flow integrator calculates the rate the base feed is moving into the mixing drum. The built-in PID controller of the SF500 uses the flow rate of the base feed product and the programmed ratio to calculate the amount of additives needed to provide the correct feed blend. The SF500 compares the additive flow rate from the Coriolis mass flow meter to the calculated ratio set point. After comparing the flow rates, the SF500 then adjusts its control output to speed up or slow down the additive pump so that the pump is delivering the correct amount of additives for the blend.
There is a maximum rate that can be put through a mixing drum. If the maximum rate is exceeded, the mixing drum will not properly mix the product. The SF500 has two built-in PID control loops. In the system described above, a speed control could also be added to the conveyor moving the product into the solids flow meter. The second PID control loop could be set up to control the flow rate of the base feed product into the mixing drum, which allows the mixing drum to operate at maximum efficiency.
Feed products are often made-to-order in a specific batch size. The SF500 accumulates the total pounds moved into the mixing drum and has a batch controller built-in. This would allow the batch controller to move a specified amount of base feed product into the mixing drum and provide an output that would stop the flow of material going into the mixing drum, enabling tight control of the batch size.