P.A. van Gaelen en N. Kuijken
Meten van mors bij de overslag van stortgoed - deel II
Experiment,
Report 2007.TEL.7186, Transport Engineering and Logistics.
Introduction
Recently more and more attention is asked for the protection of the
environment. As a big polluter, the stevedore industry also has to live up
to stricter regulations, concerning the loss of coal during transshipment
and substance - and noise nuisance.
Due to obscurity concerning the new regulations and the lack of reliable
numbers about the degree of coal lost during transshipment, Delft University
of Technology started a project together with 12 bulk handling corporations,
Rijkswaterstaat, NIEMA, Syntens and the Erasmus University Rotterdam. This
experimental study is the third paper in this cooperation.
The aim of this research is to quantify the amount of coal lost in the
surface water during transshipment. Besides this the paper focuses on the
differences of the particle size distribution of the coal loaded and the
distribution of coal that is spilled.
In the period from august 2007 till September 2007, 13 measurements have
been carried out at 5 cooperating stevedores. To get a good understanding of
the loss of coal during transshipment a logical combination of stevedores
and crane types is chosen.
Methodology
During a measurement it is strived for to measure for 2-3 hours during
constant circumstances at full ships' holds. Depending on the situation and
the trajectory the gripper of the crane made, areas were outlined on the
ship, the pontoon, the quay and/or the barge. After a certain period of
time, in which the number of cycles of the gripper is registered, the mass
of the coal spilled on the outlined area's is measured. The measured mass of
the spilled coal is divided by the area of the outlined area and the total
mass of coal that passed over this area during the transshipment. This gives
a specific number expressed in kg/(m2.kton). This
number is called the GaKu. The GaKu of the different areas are plotted and
the GaKu above the surface water is interpolated. By multiplying the GaKu
above the surface water with the area of the surface water and with the total
mass of transshipped coal, the mass of the coal that is spilled in the water
becomes known. With the same method the total mass of coal spilled per year
is calculated.
During the measurements the factors that have influence on the spilled are
registered. These factors are wind power and wind direction, the experience
of the crane operator, the filling degree of the gripper and the ship's
hold, the construction of the cranes, damage and delays.
Conclusions
From the data of the thirteen measurements the following conclusions can be
formulated.
- The percentage of the annual transshipment of coal that is spilled at
the different companies is very small. It's in the order some
10-6 percents.
There is also no relation between the transshipment on an annual basis and
the spillage per fixed amount of transshipped coal.
- There has been shown that at measurements with larger water surface not
automatically more spillage occurs. At these measurements the transshipment
was done with floating cranes and generally even less was spilled.
- The ratio in transshipment capacity per hour between the kinds of cranes
is proportionate with the differences in spillage. De capacity per hour is
1,5 times as large with portal cranes with respect to floating cranes. In
situations with portal cranes spillage is two times higher than with
floating cranes.
- More measurements are needed to be able to draw plain conclusions. With
these few measurements there is too much variation in the variables. If some
measurements are left out of the comparison of a specific factor, to little
data remains to draw a conclusion. comparison material for an analysis is
important.
- The appraisals of the data of the measurements per company do not lead
to the conflicting conclusions and give no new insights concerning the
measurements overall.
Because of the large number of factors that influence the spillage of coal,
the fact that the data comes from several sources and that some assumptions
have been made, the reliability of the measurement and calculations has been
examined. The reliability of the calculations at portal cranes is around
14%. For floating cranes this is around 16%. The main reason for this
difference is that, for floating cranes, the trajectory of the gripper from
the ship's hole to the barge or quay wall can't be determined precisely.
With the reliability of the calculations between 14% and 16% there can be
concluded that the reliability and punctuality of the stated mass of spilled
coal is admissible.
In addition to the mass of the spilled coal, the relation of the particle
size of the loaded coal and the spilled coal is examined. At five
measurements the particle size distribution is determined with the help of a
sieve analysis. Based on the results the following can be concluded.
- The particle size of the spilled coal is generally smaller then the
particle size of the transshipped coal. This means that smaller coals are
being spilled.
- The particle size distribution of the spilled coal generally becomes
larger when the outlined areas are themselves positioned further away of
the ship's hole.
- The combination of crane, operator and gripper seems to spill a certain
own particle size. There is therefore no specific coal particle size which
is commonly spilled more than others.
All three these conclusions became clear from the available data. Further
research must lead to a more elaborated substantiating.
Recommendations
Due to the experiences of this research recommendations for following
researches have been formulated.
- During following measurement the height difference is between the ship
and the quay needs to be registered. This has influence in the way the coal
falls, on the calculation of spillage in water and also on the particle
size distribution.
- Measurements are preferably planned at a ship which is not yet
discharged. This way the measurement can be started more rapidly.
Furthermore are all the holds full in this way, which ensures a more
constant condition during the discharging.
- Data of the circumstances and factors which are of influence on the
spillage must be obtained during the measuring day.
- More measurements are needed to ensure analysis can be worked out
properly. If there are measurements left out and there is zoomed in on a
specific point, enough information has to be left to make viable
conclusions.
Reports on Transport Engineering and Logistics (in Dutch)
Modified: 2008.01.26;
logistics@3mE.tudelft.nl
, TU Delft
/ 3mE
/ TT
/ LT.