Which key figures determine the energy efficiency of a mixer, and how do they affect the TCO?
The energy efficiency of an industrial mixer is not determined by a single metric. What is decisive is the interplay of energy input, mixing time, mixing quality achieved, product throughput, drive efficiency and the energy demand of the auxiliary equipment. For an economic assessment, these values must always be considered in connection with the product, recipe, fill level, process objective and plant concept.
Specific energy input
Specific energy input describes the energy required per kilogram, tonne or cubic metre of product for a mixing process. This metric can be expressed, for example, as kilowatt-hours per tonne or as kilowatt-hours per cubic metre. It is particularly suitable for comparing different batches, process parameters or mixing systems, provided the same mixing task and the same target quality apply.
A low specific energy input is only an advantage if the required mixing quality, product protection and reproducibility are achieved. A mixer with very low energy demand can be unsuitable if it requires excessively long mixing times or fails to reliably achieve the recipe's homogeneity.
Power consumption and specific power
Power consumption shows how much electrical power the drive draws during operation. Specific power relates this power to the mixing volume or the product mass. It can be expressed in kilowatts per cubic metre or kilowatts per kilogram.
With highly viscous, cohesive or heavily compacted products, specific power is often an important design value. It influences the sizing of the motor, gearbox, shafts, mixing tools and electrical infrastructure. However, a high installed power does not automatically mean high energy consumption per batch. What matters is power, mixing time and load profile together.
Mixing time and batch time
Mixing time describes the duration until a defined mixing quality is achieved. It influences the energy per batch, the throughput and the plant's availability. A short mixing time can lower energy consumption and cost per batch, provided it is achieved without excessive power input, product damage or segregation.
In addition to the actual mixing, the total batch time comprises filling, dosing, temperature control, discharging, cleaning and, where applicable, drying. For TCO, this total time is often more important than mixing time alone. Long changeover, cleaning or discharge times can cancel out the economic advantage of a short mixing phase.
Mixing quality and reproducibility
The energy efficiency of a mixer must always be measured against the product quality achieved. Relevant criteria include, for example, concentration distribution, particle distribution, moisture distribution, agglomerate breakdown, temperature uniformity or viscosity. There is no universally valid mixing-quality metric, because the assessment method depends on the respective mixing task.
What is decisive is the ratio of energy input, mixing time and reliably achieved mixing quality. A process is particularly economical if it repeatably achieves the required homogeneity without unnecessarily stressing the product or using more energy than required.
Hydraulic metrics for liquids and slurries
With liquid, pasty or slurry-type products, hydraulic metrics can be important. These include circulation rate, delivery volume, flow velocity and shear stress. Pumping capacity here describes a mixing tool's ability to circulate product within the vessel.
A high circulation rate can speed up homogenisation. However, it is not automatically energy-efficient if the high flow leads to product damage, air entrainment, foaming or unnecessary energy input. The appropriate flow and shear action depends on viscosity, particle content and the sensitivity of the product.
Newton number and other dimensionless numbers
The Newton number describes the power requirement of an agitator as a function of tool geometry, rotational speed, fluid density and flow regime. It is an important design and comparison variable, above all with liquid media and classic stirring processes. Its informative value for dry powders, on the other hand, is limited, because gravity, wall friction, cohesion and particle contacts there strongly influence mixing behaviour.
Other metrics such as the Reynolds number or the Froude number can be relevant for design and scale-up. However, they do not replace trials with the actual product, particularly with cohesive, moist, abrasive or segregation-prone bulk materials.
Efficiency of the drive train
The overall efficiency of the drive train comprises the motor, frequency inverter, gearbox, bearings and seals. Efficient motors, suitable gear ratios and low mechanical losses reduce electricity demand. However, the selection should not be based on the highest efficiency class alone. Part-load behaviour, load changes, torque requirement, maintenance effort and process safety are also relevant.
Frequency inverters enable a controlled start and the adaptation of rotational speed to the product and process phase. This can save energy and reduce mechanical loads. However, the frequency inverter's own consumption and the actual mode of operation should be included in the assessment.
Auxiliary equipment and thermal energy demand
With heated, cooled, vacuum-operated or inerted mixers, the mixing drive is not the only factor determining energy demand. Heating and cooling circuits, vacuum pumps, condensers, filters, compressed air and inert gas supply can account for a considerable share of total consumption.
Lower power losses and an appropriate energy input can reduce heat generation in the product. This can lower cooling demand. With drying processes, however, the entire energy balance must be considered. Vacuum can lower the required product temperature, but it does not automatically reduce the total energy demand of vacuum generation, condensation and evaporation.
Effect on total cost of ownership
Energy metrics influence TCO directly through electricity, heat, cooling, compressed-air and inert-gas consumption. With high utilisation or energy-intensive processes, even comparatively small improvements in specific energy consumption can become economically relevant over many years.
The indirect effect can be even greater. A product-appropriate energy input reduces the risk of product damage, scrap, rework and unplanned downtime. Lower dynamic loads can reduce wear on bearings, seals, gearboxes and mixing tools. This can extend maintenance intervals and improve plant availability.
Short and reproducible batch times increase the throughput of the existing plant. This lowers the fixed costs per unit produced. High mixing quality with low scrap can be economically more important than the pure saving of electrical energy, particularly with high-value raw materials or quality-critical products.
A robust TCO assessment therefore compares not just motor power or energy per tonne. It considers the entire process chain of energy consumption, mixing time, throughput, product quality, scrap, cleaning effort, maintenance, plant availability and the cost of the required peripherals.
How amixon® assesses energy efficiency, cleaning performance, TCO and payback of an industrial mixer
The energy efficiency of a mixer is not determined by motor power alone. What is decisive is whether the required mixing quality, product protection and reproducibility are achieved with a product-appropriate energy input. For total cost of ownership, product losses, cleaning and changeover times, maintenance, spare-parts supply, plant availability and the plant's long-term usability are also relevant.
amixon® views these factors as a connected overall system. The most important metrics are specific energy input, mixing time, total batch time, achievable mixing quality, residual discharge, cleaning effort, plant availability and the energy demand of the required auxiliary equipment.
Energy input and mixing time
General figures for energy consumption per tonne of product are of only limited value for industrial mixers. The real energy demand depends on the recipe, batch size, fill level, bulk density, viscosity, mixing time, temperature and the required energy input.
Depending on the design and mixing task, amixon® mixers operate at low circumferential speeds. The low-speed mode of operation can reduce friction, impact stress and dynamic loads. With sensitive, free-flowing or segregation-prone powders, a large-volume product circulation can achieve the required mixing quality with a comparatively low energy input.
A short mixing time does not automatically lower energy consumption. A short mixing time is economical when the required homogeneity is achieved without excessive rotational speed, unnecessary shear action or product damage. Mixing time and energy input must therefore be assessed for each recipe with the original product.
The Gyraton® silo mixer GM is designed for large-volume batches of up to approximately 100 cubic metres. The mixing principle enables the homogenisation of large product quantities with a comparatively low installed drive power. This can limit energy demand per batch, particularly with large quantities of free-flowing bulk material. The actual power consumption is assessed with the specific product, fill level and process objective.
Residual discharge and product loss
Product loss is a major TCO factor, especially with high-value raw materials, active ingredients, additives or small batches. Every residual quantity remaining in the mixer causes not only a direct loss of material. It can also extend cleaning, affect subsequent batches and increase the risk of cross-contamination.
The amixon® AM and KS series are designed for extensive residual discharge. ComDisc® discharge tools support the removal of residual product from the mixing chamber. The discharge rate achievable always depends on product properties such as moisture, particle shape, cohesion, bulk density, abrasiveness and adhesion tendency. Dischargeability should therefore be trialled with the original product.
Extensive residual discharge can reduce raw-material loss, shorten cleaning time and increase the plant's productivity. As a result, it often has a greater influence on TCO than a small difference in the mixing drive's electrical power consumption.
Programmable target-jet cleaning
Cleaning and changeover times are a major part of total operating costs with multi-product plants. Particularly in the food, pharmaceutical, chemical and specialty chemical industries, the duration between two batches determines how much productively usable plant time is available.
amixon® can equip mixing plants with programmable target-jet cleaning nozzles. The nozzles are directed specifically at product-contact surfaces, mixing tools, mixing chamber geometries and discharge areas. Cleaning programs can activate the nozzles in defined sequences, thereby supporting reproducible wetting of the relevant surfaces.
Programmable target-jet cleaning can reduce water, cleaning agents and cleaning time if it is designed to match product build-up, vessel geometry and the cleaning task. It can reduce manual cleaning work and speed up the changeover between different recipes. However, the required cleaning performance must be validated for the product, the cleaning medium and the release criteria.
Rapid drying after wet cleaning
After wet cleaning, drying the mixing chamber is often a decisive step. Remaining moisture can compromise subsequent products, delay release and extend the plant's downtime. This applies particularly to hygroscopic powders, moisture-sensitive recipes or applications with stringent product-purity requirements.
amixon® can design mixing plants so that the cleaned, wet mixing chamber is dried in a very short time. The mixing chamber is purged with specifically directed process air or inert gas. The mixing tool supports the distribution of the flow within the interior and can speed up the drying of product-contact surfaces.
Rapid drying can also be possible with cold cleaning water, if air routing, volumetric flow, temperature, vacuum, pressure level and condensate removal are appropriately matched to each other. The drying time achievable depends on vessel size, surfaces, residual water, air humidity, temperature and the intended drying method. The benefit lies in reduced downtime, shorter product changes and higher availability of the mixing plant.
Maintenance and long-term availability
amixon® mixing technology is designed for robust construction, low dynamic loads and good accessibility for inspection and cleaning. The mixing tool is supported exclusively at the top. This means a product-contacted lower shaft passage can be dispensed with. This reduces a potentially maintenance-intensive area within the mixing chamber.
The combination of low-speed operation, low-wear construction and long-term available design documentation can reduce maintenance effort and spare-parts risks. Selected wear parts can already be provided with the initial delivery. For spare-parts needs, conversions or modernisation, amixon®'s design, manufacturing and service support the plant's long-term use.
Robust trial data instead of catalogue values
A robust TCO, ROI or payback calculation should be based on documented data obtained with the original product. In the amixon® pilot plant, mixing time, power consumption, mixing quality, product protection, dischargeability, cleaning effort, drying time and changeover time can be assessed under realistic conditions.
The amixon® pilot plant at the Paderborn site has more than 30 test units in different sizes available. Additional pilot plants exist in Japan, India, Thailand, China, South Korea and the USA. The trials can be carried out with realistic fill levels, batch sizes and the intended temperature and pressure conditions.
The results are documented and form a basis for selecting the size, defining process parameters and the economic assessment. amixon® therefore does not assess energy efficiency in isolation as the drive's power consumption. What is decisive is the overall process comprising mixing time, energy input, product loss, cleaning, drying, maintenance, plant availability and long-term usability.