Which criteria help to reliably compare the total cost of ownership of different mixing technologies?
A robust comparison of total operating costs, also known as total cost of ownership or TCO, must take into account all relevant costs over the entire life cycle of a mixing plant. The purchase price or the mixer's energy consumption alone are not sufficient. What is decisive is assessing different technologies under comparable process conditions and relating the costs to a uniform reference unit.
Suitable reference units are, for example, cost per tonne of saleable product, cost per batch with defined mixing quality, or cost per production hour. The precondition is that all compared technologies meet the same recipe, the same target quality, comparable batch sizes and the same requirements for hygiene, safety and documentation.
Investment and integration costs
Investment costs include not only the mixer, but also the drive, control system, sensors, safety equipment and required peripherals. These include feeding, dosing, discharge, conveying technology, extraction, filters, cleaning systems, temperature control and, where applicable, vacuum or inerting.
Further costs arise from foundations, structural engineering, electrical infrastructure, piping, building modifications, engineering, assembly, commissioning and acceptance. In regulated industries, qualification, validation and documentation are added. A cheaper core machine can therefore become more expensive overall if it requires significantly more peripherals, space, personnel or special equipment.
Energy and utility consumption
Energy efficiency should be assessed for the entire process. Relevant factors are not only the electrical power consumption of the mixing drive, but also mixing time, energy per batch, energy per tonne of product and the drive's part-load behaviour.
Auxiliary equipment can account for a considerable share of total energy consumption. This includes heating and cooling systems, vacuum pumps, condensers, filters, compressed-air supply, extraction and inert-gas supply. With temperature-controlled, vacuum-operated or inerted processes, the energy demand of the peripherals can exceed the energy demand of the mixing drive.
The consumption of cleaning media, water, cleaning agents, process gases, barrier gases, lubricants and auxiliary materials should also be assessed. These costs can be considerable, particularly with frequent product changes, stringent hygiene requirements or toxic products.
Process performance and productivity
Process performance should be compared on the basis of the total batch time, not just the pure mixing time. Batch time includes filling, dosing, mixing, temperature control, discharging, cleaning, drying, sampling and release. A mixing technology with a very short mixing time can be economically disadvantageous if discharge or cleaning takes a long time.
Important metrics are throughput, the number of possible batches per shift, usable fill volume, mixing time, changeover time and productively available plant time. With continuous processes, start-up losses, product changes, cleaning, minimum run times and the stability of steady-state operation must also be considered.
The achievable mixing quality and its reproducibility are central comparison criteria. Depending on the mixing task, concentration distribution, moisture distribution, particle integrity, agglomerate breakdown, temperature uniformity or viscosity can be relevant. The coefficient of variation can be a suitable value for certain recipes, but it is not the sole quality metric for every mixing task.
Product quality, yield and scrap
A mixing technology must not only homogenise, it must also preserve the product properties. Particle breakage, abrasion, temperature rise, shear stress, segregation tendency and the stability of sensitive recipe components must therefore be assessed.
Product losses arise from residual quantities, build-up, dead spaces, cleaning losses and failed batches. With high-value raw materials, the economic importance of residual discharge can be greater than a small difference in electricity consumption. Scrap, rework, laboratory analysis and release times must also be included in the TCO analysis.
Cleaning and changeover
Cleaning and product changes are important cost factors, particularly with multi-product plants. Time, personnel effort, water consumption, cleaning agents, wastewater, energy for heating or drying, and the effort for inspection and release must be assessed.
Constructions with minimal dead space, readily accessible mixing chambers, extensive residual discharge and suitable cleaning methods can significantly reduce changeover times. Depending on the application, dry cleaning, manual wet cleaning, WIP, CIP or automated cleaning systems can be used. The required cleaning performance must always be measured against the specific products and the permissible residual limits.
Maintenance, upkeep and spare parts
Maintenance costs comprise planned inspections, preventive maintenance, repairs, spare parts, consumables and external service work. Relevant wear parts, depending on the mixer type, are seals, bearings, gearboxes, mixing tools, linings, discharge elements and sensors.
In addition to the direct spare-parts costs, maintenance duration, the accessibility of components, spare-parts availability and the necessary qualification of personnel are important. Metrics such as mean time between failures and mean time to repair help to compare the reliability of different concepts. However, they should be based on comparable operating data and conditions of use.
Availability and downtime costs
Plant availability often has a greater influence on TCO than small differences in the purchase price. Unplanned downtime causes repair costs, lost production, personnel waiting time, delivery delays, scrap and, where applicable, contractual penalties.
For a robust comparison, cost per hour of downtime, planned maintenance windows, redundancy requirements and the mixer's position within the overall plant should be assessed. If the mixer is a bottleneck, high availability can be economically particularly valuable.
Personnel, compliance and environment
Personnel effort comprises operation, feeding, cleaning, changeover, maintenance, training, sampling, analysis and documentation. A high degree of automation can reduce direct operating effort, but may require greater engineering, maintenance and qualification effort.
Depending on the industry, further costs arise from GMP, ATEX, pressure equipment law, hygiene requirements, dust protection, emission reduction, occupational safety and environmental regulations. Relevant items are, for example, filter technology, extraction, disposal of cleaning residues, inspections, calibrations, audits and documented change processes.
Service life, modernisation and residual value
A comparison should include the expected technical and economic service life. Relevant factors are the robustness of the construction, the availability of spare parts, the modernisability of the control system and drive, and suitability for new products or changed regulatory requirements.
At the end of the service life, costs arise for dismantling, decontamination, cleaning and disposal. These can be offset by residual values from resale, repurposing, modernisation or the material value of high-grade materials.
Methodological recommendation
A robust TCO comparison should relate all costs to the same reference unit and the same time period. A present-value analysis is particularly meaningful. It captures investment, operating costs, maintenance, downtime, modernisation and residual value while taking the time value of money into account.
In addition, sensitivity analyses should be carried out. They show how energy prices, utilisation, raw-material values, cleaning effort, spare-parts prices, downtime risks and maintenance intervals affect the result. This is particularly important when comparing different mixing principles, batch and continuous processes, or plants with substantially different peripherals.
A robust TCO comparison therefore does not assess the mixing machine alone. It considers its effect on product quality, yield, cleaning, availability, personnel effort, process stability and the entire production line.
How amixon® assesses energy efficiency, TCO and payback of an industrial mixer
The purchase price of an industrial mixer is only one part of the economic assessment. What is decisive are the costs and losses over the entire planned service life. This includes investment and integration, energy and utility consumption, product loss, cleaning and changeover times, maintenance, spare parts, personnel effort, downtime risks, modernisation and a possible residual value.
amixon® therefore views total cost of ownership as an overall process. The focus is on factors that can be influenced through the choice of mixing principle, the design and the process layout. This includes a product-appropriate energy input, high mixing quality, extensive residual discharge, short changeover times, good cleanability, long service life and plannable maintenance.
A robust comparison is only possible if different mixing technologies are assessed under the same conditions. This includes the same recipe, comparable batch sizes, the same target homogeneity, identical safety and hygiene requirements, and a comparable degree of automation. Meaningful reference units are, for example, cost per tonne of saleable product, cost per batch or cost per productive operating hour.
Energy consumption and process performance
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, mixing time, product condition, temperature, viscosity 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 or free-flowing powders, a large-volume total product circulation can achieve the required mixing quality with a comparatively low energy input.
The goal is not the lowest motor power, but achieving the required mixing quality with the lowest technically sensible energy input. Too little energy can lead to insufficient homogeneity. Too much energy can stress the product, raise the temperature and unnecessarily increase energy consumption.
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 means that energy demand per batch can be limited, particularly with large quantities of free-flowing bulk material. The actual power consumption is always assessed with the specific product, fill level and process objective.
Short mixing times can improve the energy demand per batch and productivity. What is decisive, however, is the total batch time. This comprises not only mixing, but also feeding, dosing, discharge, cleaning, drying and the release of the plant. A mixing technology with a short mixing time is only economical if the subsequent process steps also run efficiently.
Product loss, discharge and cleaning
With high-value raw materials, small batches or frequent recipe changes, product loss and cleaning effort are important TCO factors. Every remaining residual quantity 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, however, always depends on the product properties. Moisture, particle shape, cohesion, bulk density, abrasiveness and adhesion tendency significantly influence the residual quantity.
Mixing chambers with minimal dead space, product-appropriate discharge elements and readily accessible product-contact surfaces support efficient dry or wet cleaning. amixon® can also equip mixing plants with programmable target-jet cleaning nozzles. These are directed specifically at the mixing chamber, mixing tool 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, personnel effort and changeover time if it is matched to product build-up, vessel geometry and the required release criteria. After wet cleaning, the mixing chamber can be dried with a coordinated air or inert-gas flow. A short drying time reduces downtime and increases the plant's productively usable time.
Maintenance, availability and service life
amixon® mixing technology is designed for robust construction, low dynamic loads and good accessibility. 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 in the mixing chamber.
Low-speed operation, low-wear construction and the targeted selection of product-contact materials can reduce maintenance effort. Selected wear parts can already be provided with the initial delivery. The long-term availability of design documentation facilitates the identification, assessment and, where necessary, re-manufacture of individual components.
For conversions, modernisation, control system adaptations or spare-parts needs, amixon®'s design, manufacturing and service support the plant's long-term use. Good modernisability can extend the technical and economic service life and reduce the need for replacement investment.
Robust data from the pilot plant
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, residual quantities, 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 the basis for selecting the size, defining the process parameters and the economic assessment. Scale-up to the target size is carried out on the basis of the respective mixing task and, for critical processes, should be confirmed through further trials.
TCO as a decision criterion
amixon® does not assess energy efficiency in isolation as the mixing drive's power consumption. What is decisive is the mixing technology's effect on the entire production process. This includes energy, utility consumption, mixing time, product loss, residual discharge, cleaning, drying, personnel effort, maintenance, plant availability and long-term usability.
An economical mixing plant is therefore not necessarily the one with the lowest purchase price. It is the plant that achieves reproducible mixing quality for the specific product, limits raw-material losses, speeds up product changes, reduces downtime costs and enables plannable operating costs over its entire service life.