Plant report
A new unparalleled mixing plant from BHS-Sonthofen has been in operation of late at
Nikolaus Müller Kalkwerk-Natursteinwerke (Müllerkalk) in Üxheim-Ahütte in RhinelandPalatinate close to the Belgian border: It combines the continuous moistening of agricultural
lime and the batch production of mixed binders for ground stabilization measures. The new
plant opens up new markets for Müllerkalk, thereby compensating for the somewhat
seasonally fluctuating lime market. The fully automatic loading is a special feature: it is
available approximately 24 hours a day, 7 days a week.
TEXT Ludwig Bechteler, Head of Sales, Mixing and Crushing Technology, BHS-Sonthofen GmbH, Sonthofen/Germany
Sebastian Kneppel, Plant Manager, Nikolaus Müller Kalkwerk-Natursteinwerke GmbH & Co. KG, Üxheim-Ahütte/Germany
A bird’s eye view of the Müllerkalk works
BHS-SONTHOFEN GMBH/NIKOLAUS MÜLLER KALKWERK-NATURSTEINWERKE GMBH & CO. KG
Twin mixing plant: Two different mixing
procedures in one system
1 Introduction
Müllerkalk supplies both special binders for
ground stabilization and agricultural lime from
the Üxheim-Ahütte plant. The raw materials required for this mainly come from the lime works’
own quarries.
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The company was founded in 1834 and has
recently developed “Müllermix”, the new product
for ground stabilization; it consists of a mixture
of various lime products and Portland cement. It
avoids several work steps in road construction,
thereby cutting costs: “Müllermix” is milled into
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All BHS-Sonthofen
the ground and hydraulically bound – the ground
no longer has to be excavated.
Apart from standardized products, Müllerkalk
also offers customized mixtures: The customers
sample their ground and receive individually configured mixtures from Müllerkalk depending on
its composition. Although both product lines have
only been on offer for a short time, the demand
for the products has been steadily growing in the
meantime.
The second product line consists of earth-moist
agricultural limes for agriculture and forestry.
They are used to neutralize the pH value of the soil.
The moist – and therefore heavier – particles of
the agricultural lime spread evenly over the ground
and thereby have a direct effect.
Müllerkalk has used a single-shaft continuous
mixer of the type MFKG 0520 from BHS-Sonthofen
to moisten agricultural lime for more than ten years.
With a throughput rate of around 50 t/h, it could no
longer cope with the continuously growing demand
and the requisite shortest possible truck loading
times. The company management therefore planned
a ­major expansion of the production capacity.
2 The goal: Exploitation of synergy effects
Since the sale of the various lime products is subject to seasonal fluctuations, Müllerkalk was also
looking for solutions which enable constant utilization of the production facilities as far as possible.
The expansion of the product range with the
new special binders finally tipped the scales in
favor of investment in a new mixing system. It
includes both product lines – both dry mixing in
batches as well as continuous moistening. Another
synergy effect for the company as a whole was
provided by using the cement products of the parent company, Portlandzementwerk “Wotan”.
The homogeneity of the products and a consistent quality were of prime importance in the selection of the mixers.
Since the plant had grown over decades from
small beginnings, the extremely cramped conditions and the space requirement for the construc-
Single-shaft continuous mixers of the MFKG series
A special feature of the MFKG mixers, which BHS-Sonthofen manufactures for throughput rates between 10
and 700 t/h, is the pulsating rubber trough. It prevents mixed material from caking on the inner wall – the mixer
continuously cleans itself during operation. The wear of the mixing arms and the power consumption of the
drive thereby decrease compared with machines with a steel mixing trough.
Single-shaft continuous mixers are used for all “difficult” mixing tasks – also outside the construction industry –
starting from the lump-free moistening of dust to the conditioning of sludges of all kinds.
The mixed material is accelerated to a high speed by the mixing arms in the MFKG. The centrifugal force creates
a ring of material along the inner wall of the rubber trough with high turbulence. The mixing arms generate a very
intense relative movement. This results in optimum mixing and prevents undesired agglomerations at the same
time. Special spiral jets, which generate an extensive, finely distributed mist, optimally wet the infeed goods in
the loading chamber.
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Plant report
that the dry powder batch mixers of the type DMX
were the perfect solution for the planned special
binders. These mixers were therefore “set” for the
project, irrespective of the potential suppliers of
the overall mixing system.
However, the discussions were gradually extended from the mixers to the complete plant, because the concept was so far from a standard solution that the special application and engineering
know-how of BHS was needed for the special plant
technology.
1 Precision is essential
here: One of the two
binder scales on the
weighing platform on
the dry side
tion of the new mixing system were a particular
challenge.
Owing to the excellent experience with the
existing single-shaft mixer, Müllerkalk contacted
BHS-Sonthofen, but only on the subject of “mixing
technology” to begin with. It quickly became clear
3 Mixers in a twin-package
In the course of the project, the specialists at BHSSonthofen developed a concept for a twin mixing
plant together with the personnel of Müllerkalk. It
combines the fundamentally different mixing procedures for agricultural lime and mixed binders in
two mixers:
»» The engineers from Sonthofen recommended
the dry powder batch mixer of the type DMX
2600 for the mixed binders; this provides an
output of 2.2 m³ per batch, which corresponds
to an hourly output of approximately 100 t.
»» The MFKG 0728 single-shaft continuous mixer,
which achieves an output of between 80 and
90 t/h, was planned for the earth-moist agricultural lime.
2 Five silos were
­recently added
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3 Dry powder batch mixer of type DMX 3600
with open double flaps for complete discharge
of the mixer
4 The three-dimensional mixing principle
with the BHS spiral-blade mixing mechanism for more intense material exchange
and shorter mixing times
Apart from the BHS mixers, the system includes two
binder scales for the batch process and a volume
weighing unit for continuous metering. Both systems are supplied from ten 150 m³ silos. The silos are
filled with raw products via a newly installed pneumatic conveying plant – firstly, directly from the
lime plant and, secondly, with high-quality cement
products from the adjoining Wotan cement plant.
The experience of the operators was also incorporated in this special construction. For example,
a wide stairway was built up to the filters of the
binder silos to provide optimum accessibility for
maintenance and service work.
4 Just-in-time delivery
This overall package was the key to awarding the
contract to BHS-Sonthofen in December 2013. The
construction and assembly phase began in July
2014, the first mixture was produced as early as
November.
The engineering and project planning experts
at BHS planned and implemented the complete
mixing plant with the exception of the binder silos,
as well as the weighing terminal and the associated automated loading. Apart from the mixers, the
scope of the project therefore included the weighing, metering and materials handling technology of
the mixing system right up to the loading bellows
and the dust removal. Owing to the cramped space
conditions mainly caused by the works traffic and
the continuous production, the individual components were delivered “just-in-time” depending on
the progress of the construction work.
The control of the two independent production
lines was one of the challenges for the concept of
the new mixing plant. It constitutes both dry mixing in batches as well as continuous wet mixing including the complete metering systems. The precise
proportional control of limestone powder and water
is of critical importance particularly in continuous
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5 The DMX can be equipped with agitators
as an option­, in order to break up undesired
­agglomerations
mixing, because the mixing ratio must be configured to provide a dust-free, moistened, lump-free
final product at all times. Both driving lanes have
calibrated vehicle weighbridges which provide the
control system with the precise loading quantities
for optimum filling of the trucks, in order to systematically exclude the danger of overloading.
5 Loading 24/7
The two mixing lines work in parallel, so that loading can take place simultaneously on the wet and
the dry side.
Apart from the customized plant concept, the
loading process is also user-friendly: The re­spective
material can be loaded virtually on a 24/7 ­basis
owing to the complete automation of the system.
This means that the customers of Müllerkalk can
also flexibly collect urgently needed material at
short notice at night and at weekends.
6 Single-shaft continuous mixer of the type MFKG 0520
with a possible throughput rate of 20-50 t/h
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Dry powder batch mixers of the DMX series
BHS-Sonthofen has especially tailored the twin-shaft batch mixers of the DMX series to the particular requirements for mixing a variety of dry materials such as lime, cement or dry mortar. With the unique modular system,
all the mixers are individually configured and tailored to the respective task, no matter whether it concerns fine
materials such as binders or mortar mixes with particle sizes up to 8 mm. The dry powder batch mixer series at
BHS extends from 20 t/h to currently approximately 300 t/h.
The mixers have a mixing mechanism whose arms are in the form of an interrupted spiral arranged on two
counter-rotating mixing shafts. They generate a circular, three-dimensional movement with intense material
exchange in the turbulent overlap area of the two mixing circuits. Counter paddles on the shaft ends redirect the
material, so that the entire material is always in the mixing process.
They achieve a higher mixing effect than comparable single-shaft or intensive mixers even at lower speeds. This
significantly reduces the energy requirement. The mixer is emptied with hardly any residues and within a very
short time via two large bottom discharge flaps in a dust-proof discharge hopper.
Twin-shaft batch mixers can be filled to a considerably higher level in comparison with other mixer systems, so
that they are more compact with a comparable throughput. The mixers therefore score points with their low
dimensions in the new-build plants, and a more powerful mixer can be accommodated in an existing installation
space for conversions.
Loading is basically carried out by the truck drivers themselves. The truck driver is briefed on the
overall loading process by an employee of ­Müllerkalk
at the first visit. The drivers also receive a smart card
for independent loading, on which the customer
and order data is stored. A weighing terminal with
a touchscreen is located at the mixing system. The
driver uses this to start the job and single-handedly
control it via the respective loading area of the two
product lines. Owing to the uncomplicated operation,
acceptance of the automatic loading is very high, also
among non-German speaking drivers.
6 Initial experience
The new plant enables Müllerkalk to occupy new
market niches and strengthen the position of the
company as a whole: With Müllermix, Müllerkalk
now offers a unique product over a wide area.
The excellent homogeneity of the mixed ­binders
and earth-moist agricultural limes is repeatedly
praised by the end customer. Apart from scheduled maintenance work and plant extensions, the
twin mixing plant has operated stably since being
­commissioned. Unscheduled downtimes have not
occurred so far.
The short mixing times enable rapid loading
of the silo vehicles and semitrailers. The loading
of approximately 25 t of finished product takes
around 20 minutes on average.
Müllerkalk will additionally offer “Müllermix”
in Big Bags in the near future, in order to be able to
serve customers with smaller construction projects.
An individual filling station for this is already
­under construction.
www.bhs-sonthofen.de
www.muellerkalk-wotan.de
7 Mixing principle and machine design of the MFKG, in which the mixed
material is accelerated to a high speed by the mixing arms
8 Cross-section: The self-cleaning rubber trough
prevents caking on the trough wall through slight
­vibrations and kneading effects during operation
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