Continuous mixing in feed mill with advantages and limitations

1. Continuous Mixing
in Feed Mill
K.GURU MOHAN REDDY
TVM/2016-13
DEPARTMENT OF ANIMAL NUTRTION
COLLEGE OF VETERINARY SCIENCE, TIRUPATI
SRI VENKATESWARA VETERINARY UNIVERSITY

2. Introduction
• continuous mixing operations.
• The concepts of continuous mixing system and continuous mixers are
explained.
• Continuous mixing- applications,
- advantages,
- disadvantages are discussed in detail.

3. Material Flow
• In continuous mixing,
• material flows steadily from an upstream process into the mixer,
• Then retained in the mixing vessel for a specified mixing time,
• And discharges at the same flow rate for downstream handling.

4. Continuous Mixing Operation
• Continuous mixing is used to mix ingredients continuously in a mixer
in a single pass.
• In a continuous mixing process, the weighing, loading, mixing, and
discharge steps occur continuously and simultaneously.
• The materials to be mixed are continuously charged into the mixer as
per the formulation.

5. • The process of charging the material in a continuous mixer is
extremely critical and can significantly affect quality of the final mix.
• Radial and axial mixing takes place as the material travels from the
feeding point to the discharge point.
• The time taken by the material to travel from the feeding point to the
discharge point is known as the Retention time of the material in the
mixer.

6. • Retention time is not uniform and can be directly affected by mixer
speed, feed rate, mixer geometry, and the design of mixer internals.
• Material is continuously discharged at a constant rate which is
generally termed as the capacity of the continuous mixer.
• This capacity is measured in kg/hr of mixed product.

7. • To keep track of the mix quality, a well defined sampling and material
testing procedure is to be defined and observed.
• While discharging from the mixers, segregation can be reduced by
positioning the discharge closer to the packing units or as an integral
part of it.

8. Continuous Mixers & Mixing Systems
• The construction of continuous mixers requires that the charging of
materials is from one end of the mixer and discharge from the
opposite end.
• Adequate residence time within the mixer is required for
homogenous mixing of the material.
• This is achieved through controlled movement of material from the
feeding point to the discharge point.

9. • The controlled movement of material is caused because of the
rotation of mixer vessel as in the case of a Zig-Zag continuous mixer
• Or by rotating mixing elements that result in motion of material in
the direction of discharge, like in a continuous paddle mixer.
• Material handling equipment and instruments like feeders, rotary
valves, belt scales, etc. are provided at the feeding point of the mixers

11. Applications of Continuous Mixing
• Continuous mixing is preferred for applications where:
Large quantities of a single product are to be mixed.
In a continuous process line requiring high production rate.
Strict batch integrity is not critical.

12. Advantages of Continuous Mixing
• The advantages of the continuous mixing is as follows:
High Capacity -
• Compared to batch type mixers, continuous mixers of smaller
volumes and power can be used to produce large quantities of
uniform mix. Hence for a given capacity they are more compact than
batch mixers.

13. Lower Mixing Time -
• The residence time in continuous mixers is lower than in batch mixers.
Consistent Mixing Performance –
With proper feeding arrangements, online instrumentation and operation
controls, a consistent mixing performance and uniform product quality can
be achieved.
Suitability for Automatic Control -
• Operation of continuous mixers can be automated using online monitoring
and measuring instruments.

14. Minimum Segregation –
• Continuous mixers can reduce and control segregation of products as they
can be located in proximity of the next processing station.
Lower Cost of Mixers -
• Continuous mixers tend to be cheaper than the equivalent batch mixers
because they are compact and require less space.
• However the cost of feeders for metering the product into the mixer,
instrumentation and control may result in a higher overall cost of the
system.

15. Minimum Labor –
• Since material feeding and discharging processes are automated,
minimal labor is required for continuous mixing.

16. Disadvantages and Limitations
Lack of Flexibility –
• Continuous mixing systems are designed for a particular application and cannot
be easily tailored to mix different formulations.
• Even if a new ingredient is to be introduced, it calls for a change in the protocol,
and the system has to be recalibrated.
Component Limitations –
• When a large number of ingredients are to be added, continuous mixers have
limitations with respect to mixing uniformity when compared to batch mixers.

17. Higher Overall Maintenance Cost –
• Continuous mixers heavily depend on feeders, instrumentation and online
control systems.
• Failure, malfunction in any one component can lead to complete stoppage.
• Hence, overall maintenance costs for continuous mixers are higher compared
to batch mixers.
Calibration and Checking –
• The feeding devices in a continuous mixing require careful calibration and
frequent checking for accuracy

18. Critical Applications –
• Continuous mixers are not suited for critical applications where product
formulations need to be exact.
• Batch mixers are better suited to processes that require a very tight
product formulation, uniform composition.
• Continuous mixers are generally dedicated to a single high volume
product.
• Continuous mixers can be designed for capacities as high as 500
Tons/hour.

19. • Even though continuous mixing is gaining popularity, selection of
continuous mixers is much more complicated than batch mixers.
• For some applications, continuous mixing has distinct advantages over
batch mixing.
• For example, mixing in batch often leads to variation in the mixing quality
amongst batches. This variation can be controlled or eliminated in
continuous mixing.
• For higher processing capacities, continuous mixers are more compact than
batch mixers.