Title | Author | 2005
Unloaders
Selecting the right system
Vincent van der Wijk
2 | © Bühler |
Agenda
Unloaders | Vincent van der Wijk | 2014-01-22
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Practical implications
Functional principles and technical configuration
Energy consumption
Active working range
Rest unloading of product out of the hatch
Selecting the right ship unloading system
Operational handling & Maintenance costs
Product protection
3 | © Bühler |
Selecting the right ship unloading system.
For efficient unloading of grain and other free flowing bulk goods, several continuous ship
unloading systems (CSU) such as a vertical chain, pneumatic, and belt conveyer are employed
worldwide. Each of these systems is founded on sophisticated, powerful technology and can be
the perfect instrument for a specific area of application. An often-used rule of thumb is that
pneumatic unloaders are an option with lower unloading capacities up to 600 t/h, while
mechanical unloaders show off their strengths at higher capacities.
Unloaders | Vincent van der Wijk | 2014-01-22
4 | © Bühler |
All continuous ship unloaders serve the same basic
purpose: to unload grain or other bulk goods as efficiently
as possible. But each system possesses specific
advantages that make it the preferable choice for certain
areas of application. To make an informed and well-
founded decision on which unloader is the best solution
for your terminal, basic issues have to be considered and
evaluated, such as costs, energy consumption,
availability, safety, etc.
With unloading vessels of more than 10.000 DWT, the
average capacity for the total unloading process, in
combination with the reliability of the unloader during
operation, are the key functions. Because the unloader is
the backbone of a terminal and its overall operation,
fluctuations in capacity or breakdowns have a direct,
significant impact and create high overall costs.
Moreover, several regulatory specifications relating to
personnel and environmental safety are influencing the
choice and level of investment for new unloaders. The
Technical University of Munich has compared the three
unloading systems shown below. Safety and regulations
for the unloader applies not only to the operating
personnel, but also to the equipment itself. For the owner
of a port terminal, it is inadvisable to try to save on safety
factors, and inadequate performance with regard to these
criteria can have a serious impact on running the
business.
Chain Belt Pneumatic
Availability ++ - +
Material breakage ++ + --
Ease of operation ++ - +
Safety of unloader +++ - +
Dust emission ++ - ++
Noise emission ++ ++ -
5 | © Bühler |
Selecting the right unloader
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Practical implications.
Key investment criteria are the operational expenditures
(OPEX) in combination with the capital expenditure
(CAPEX). For an optimal customer solution, these criteria
should be in balance. As shown in the figure, the Buhler
system featuring a highly efficient vertical chain conveyer
has the lowest OPEX value of the available CSUs. With
lower overall efficiency and relatively high replacement
costs, the belt conveyer and pneumatic systems have a
higher OPEX and are therefore less favourable unloading
options in this case.
To show the bottom line implications of the study made by the TU Munich, Buhler has prepared a
comparison between the three continuous unloading systems based on a customer project
developed in Central Europe which projects to unload grain. The project details are in the
customer profile.
Customer profile
Yearly Unloading volume 600.000 t
Energy costs € 0.15 kWh
Daily operating hours 22
Daily tie-up costs € 25,000
Nominal capacity 600 t/h
Demanded availability 90 %
Daily personnel costs € 247.5*
* € 5 p/h= Ø 2.25 m.p
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System comparison
Chain Belt Pneumatic
Average efficiency 75 % 65 % 65 %
Annual unloading days 67 77 77
Annual personnel costs 16.600 19.230 19.230
Energy (kWh/t) 0,4 0,3 0,8 – 1,0
Annual energy costs 36.000 27.000 76.500
Annual tie-up costs 1.683.500 1.942.500 1.942.500
Annual wear & tear costs 48.000 96.000 96.000
Annual operating costs 1.785.000 2.084.000 2.134.200
Unloading costs per ton € 2,97 € 3,47 € 3,56
Profit lost € - 300.000 € - 350.000
8 | © Bühler |
Functional principles and technical configuration.
Mechanical:
Buhler's Portalink mechanical ship unloading system transports
bulk material to the pier at low speed using two independent
high-performance chain conveyors, one in the vertical conveying
arm, the other in the boom. The Portalink has a standardized
design based on years of experience and is optimally configured.
The advantages of this design principle with few wearing parts
and low conveying velocity include high dependability, low
energy costs and reduced maintenance requirements. Low wear
also ensures a constant conveying capacity with no losses in
performance over the entire life cycle. Thanks to the minimal
maintenance requirements, the amount of downtime of the entire
installation decreases while system availability increases.
9 | © Bühler |
Functional principles and technical configuration.
Pneumatic:
Pneumatic ship unloading systems include several additional
components such as telescopable spouts, airlocks, filter systems
and the suction nozzle. These parts require more maintenance
and thus also lead to higher maintenance costs. The high
conveying velocity of the bulk material also contributes
significantly to the high level of wear – unexpected failures of the
installation are more probable with this system.
Additionally, many of the parts must be designed to be
particularly resistant to wear in order to withstand great forces.
The frequency at which parts must be replaced is naturally
greater, which increases the amount of downtime of the
installation and reduces the availability of the system.
10 | © Bühler |
Functional principles and technical configuration.
The higher amount of wear also automatically causes a loss in
capacity that reduces the overall efficiency of the unloader. The
berthing times of ships can also increase due to sudden
stoppages in operation, leading to higher berthing fees.
These disadvantages are less critical at lower conveying
capacities and low annual throughput, since wearing parts do not
need to be replaced as often and maintenance requirements are
lower as a result.
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Overall efficiency
While the Portalink unloading system continues to unload at
constant full capacity as the level of bulk material sinks, the
throughput of the pneumatic unloading system decreases
by at least 10 % with a decreasing bulk material level and
the suction pipes fully extended. The overall efficiency of
the mechanical Portalink system is 87 %, whereas with the
pneumatic system, efficiency is only 66 %. The result is
astonishing!
There are various reasons for the time savings offered by
the mechanical unloader, all influencing the efficiency, such
as the use of heavy bucket loaders to unload the material
residues and the difference in throughput.
For a customer with an unloading capacity of 600 t/h and
mainly having Panamax size vessels the unloading time for
the Panamax vessel comes to only 99 hours using the
mechanical unloader, where a pneumatic unloader
completes the process in a total of 131 hours. This
represents roughly a 25 % increase in time for unloading a
single ship!
12 | © Bühler |
Active working range.
Together with ease of operation, the working range and flexibility of the unloader is important. With a larger
effective working range, the unloader can unload a broader area without moving, and thus increase the overall
efficiency of the operation. Two persistent myths exist regarding unloading systems. The first myth is that
pneumatic unloaders have a greater reach in the hatch than mechanical systems. The second myth is that with
pneumatic unloading, the material left in the hatch after the main unloading phase is removed more efficiently
and without the deployment of bulldozers.
13 | © Bühler |
Mechanical:
Mechanical unloading systems like the Buhler Portalink use
the so-called "kick-in/kick-out system" to move the unloader
arm through the hatch to unload with optimal coverage. In
this process, the conveying arm moves through the bulk
material in a curve. In this manner, it reaches the bulk
material below the rim of the cargo hold without requiring
repositioning of the ship (with stationary systems) or the
Pneumatic:
Pneumatic solutions are often compared with the vacuum
cleaners used at home. In theory, this sounds logical, since
both systems have a flexible hose and can move around
easily – but nothing is farther from the truth. In practice,
bulldozers and bucket loaders are used to effectively
remove all the bulk material residues from the cargo hold.
Pneumatic unloaders can only adjust the position of the
unloader (with mobile systems).
This flexibility significantly
speeds up the unloading
process and minimizes the
need for bulldozers for removal
of bulk material residues.
conveying arm vertically or
horizontally. The bulk material
below the rim of the cargo hold
cannot be reached, requiring
bulldozers to be used earlier
and leading to longer unloading
times.
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Rest unloading of product out of the hatch.
Mechanical:
Many modern unloading systems with mechanical technology are
equipped with a winch integrated in the boom for moving large
bulldozers into the cargo hold for highly efficient rest unloading.
Depending on the capacity of the unloading system, they can
offer a high load-bearing capacity up to 15 tons.
In this case, the use of a single heavy bucket loader is sufficient
to remove all cargo residues. The last remaining product in the
hatch can conveniently be placed in the bulldozer's bucket and
simultaneously lifted onto the pier.
15 | © Bühler |
Rest unloading of product out of the hatch.
Pneumatic:
Pneumatic unloading systems have a lighter construction and are
equipped with winches with a limited maximum load-bearing
capacity of 3.5 tons. If winches capable of bearing heavier loads
are preferred, larger steel constructions are required, leading to
increased costs compared to standard systems.
Often, several smaller bulldozers or bucket loaders are moved
into the hold to remove the remaining bulk material. Increased
unloading time and berthing time of the ships results in an
increase in costs.
The basic advantage pneumatic systems offer, i.e. being able to
remove literally every grain from the hold, is countered by their
(physically determined) low residue unloading capacity.
16 | © Bühler |
Operational handling.
Mechanical:
With the mechanical Buhler Portalink unloading system,
operating staff only occasionally has to intervene in operation.
The conveying arm automatically sinks into the bulk material and
discharges large amounts of cargo at a constant throughput level
before repositioning becomes necessary.
The static construction of mechanical unloading systems does
however have a disadvantage in that the water level can vary
significantly during unloading. In this case, additional
repositioning is required to adjust the unloader to the water level
difference.
17 | © Bühler |
Operational handling.
Pneumatic:
Without the benefit of the automatic "sink-in" function, operators
of pneumatic unloading systems have to manually adjust the
position of the conveying arm depending on the height of the bulk
material and reposition the suction nozzle accordingly.
The disadvantage of this flexibility: As the length of the
telescopable spout increases, throughput decreases.
18 | © Bühler |
Energy consumption.
Mechanical unloaders have a lower energy
consumption per ton compared to pneumatic
unloading systems. Thanks to a reduced design with
few components and a lower conveying speed, the
energy consumption of mechanical unloading systems
like the Buhler Portalink is significantly lower.
By comparison, the energy consumption of mechanical
unloaders is approximately 0.35 – 0.4 kWh per ton. where
pneumatic systems average roughly 0.85 – 0.9 kWh/t; older
systems even require more than 1 kWh/t.
Depending on conveying capacity and local energy prices,
mechanical unloading systems can save the user tens of
thousands of Euros each year.
In light of the continuing trend toward higher energy prices,
it stands to reason that in the future, mechanical unloading
systems may also become more attractive for lower
capacities – above all in countries where energy is
expensive.
High levels of specific energy consumption also have a
negative impact on the overall power supply of an
installation – and on costs for the provision of energy. The
necessary investment costs, as well as the annual
increases in electricity rates, are often overlooked in
calculating the overall costs of a system. In this regard,
mechanical unloading systems are clearly superior to
pneumatic solutions.
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Energy usage throughout the hatch
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Product protection.
Mechanical:
Mechanical solutions like the Buhler Portalink/Portalino
unload bulk material at a constant low velocity. This not only
Pneumatic:
The physical properties of pneumatic solutions require the
conveying speed to be higher than that of mechanical
The overall high product quality leads to higher margins than with pneumatic unloading
systems – a financial aspect that shouldn't be underestimated in light of increasing grain prices.
reduces wear and the
maintenance costs of the
system, but also ensures that
especially sensitive grain is
unloaded in an exceedingly
gentle manner. In this way,
damage to the product is
minimized and financial losses
caused by high reject rates are
avoided.
systems. The resulting higher
maintenance costs are not the
only disadvantage; critical
disadvantages also include
higher reject rates and lower
product quality, which in turn
leads to lower market prices.
Additionally, greater system
wear results in reduced
unloading throughput.
21 | © Bühler |
www.buhlergroup.com