Breakthrough performance with the Helix Dumper system B. M. Bolsöy Kiruna Wagon, Kiruna, Sweden
ABSTRACT: The unloading processes of rail based logistic systems for dry bulk, currently are either complex or have relatively low capacity. It should therefore be possible to increase the logistic performance by re-designing this process. The unloading process of the relatively new Helix Dumper Solution (HD) offers low complexity and extreme capacity. Therefore, its logistic performance has been compared with the traditional and most popular Rotary Car Dumper Solution (RCD). The comparison was performed by analyzing and evaluating a set of key performance indicators, selected for a like comparison. The results show that the HD system significantly outperforms the RCD system in every aspect with significantly higher reliability, availability, and safety. In addition, the HD solution emits significantly less noise, dust and a stunning 57 % less CO₂ per transported tonne of commodity. For annual volumes from 10 Million tonnes, the logistic cost of the HD system per unit volume is 15 to 35 % lower and, in contrast to the RCD system, almost unaffected by the annual volume. While this is an advantage for larger mines, it makes many smaller mineral deposits worthwhile to develop. In addition, the great unloading capacity enables direct loading of ships, allowing additional significant savings. 1 INTRODUCTION For transports of large volumes of heavy dry bulk, rail freight is many times the only costeffective alternative. The logistic process involves loading, transport and unloading of trains and requires rail wagons and unloading stations. There are effective, established solutions to load dry bulk and to pull rail wagons. There are also several established solutions for unloading for example side dumpers, bottom dumpers, and rotary car dumpers and excavator unloading. None of these, however, combine low total complexity with high capacity. This means that there is a potential for improving the performance of the unloading part of the logistic process. The unloading process of the relatively new Helix Dumper, HD, system, shows low complexity and extreme capacity. A question therefore is if this system has higher over-all performance than traditional systems. A study has therefore been made to compare this system with the traditional and globally dominating Rotary Car Dumper system. First, the two systems are briefly presented. Then a set of key performance indicators, KPI’s, are selected to give an over-all picture of the performance of the systems. Then these KPI’s are evaluated for each system and compared with each other.
2 DEFINITIONS Unloading station t Mt tph Mtpa
a device that moves rail wagons to unload them metric tonnes million metric tonnes metric tonnes per hour million metric tonnes per annum
3 SYSTEM PRESENTATION 3.1 The Rotary Car Dumper system 3.1.1 Wagon The Rotary Car Dumper (RCD) systems use the simplest possible type of wagons – the gondola wagon - which basically is a rectangular box with wheels, see the figure below.
Figure 1. Gondola wagon.
3.1.2 Unloading Since complexity adds cost, this should be the most cost-effective wagon type to use. The simplicity of the gondola wagons, however, makes the unloading challenging. In some cases they are unloaded with excavators, which is time-consuming. In RCD systems, the unloading is made by a machine that grabs the wagons one by one with the rail they stand on, rotate them almost upside down and then back. In a simpler version of RCD machines, the wagons are rotated around an axis through the center of gravity of the loaded wagons, see the figure below. This requires, however, each wagon to be decoupled from the rest of the train to be unloaded, which takes time.
couplers, the wagon that is unloaded, has to be rotated with a minimum of swaying. The large and shifting forces in combination with the required stability, put hight demands on the presicion and stability of the RCD machines. In addition, the excentric motion of the wagons makes the rotational movement wider, increasing the machine size and the height to hoist the commodity back to surface. Each wagon to be unloaded also has to be carefully positioned. For this purpose, special machines, indexers, are used for moving the entire wagon set. In order to keep up the efficiency, this positioning is made at high speeds, causing high fatigue loads on wagons and their couplers. The largest RCD machines commonly in use, handle two wagons at a time and have a capacity of about 8,000 metric tonnes per hour. The practical annual limit is about 50 Mt. For larger volumes, additional stations must be installed. 3.2 The Helix Dumper system 3.2.1 Wagon The Helix Dumper (HD) wagons consist of a rounded body that is connected to the chassis via a hinge on one side. On the opposite side, a tipping wheel is positioned on the top of the body, see the figure below.
Figure 2. Smaller RCD – The loaded wagons are rotated around their center of gravity.
A more effective kind of RCD system unloads the wagons without the need of decoupling, which saves time. In this case, the wagons are rotated around an axis through their couplers, see the figure below. This requires the wagon couplers to be swiveling, see the picture below.
Figure 4. Helix Dumper wagon
Compared to the RCD wagons, these wagons have a somewhat higher complexity and about 10 % higher tare weight. 3.2.2 Unloading
Figure 3. Larger RCD – The loaded wagons are rotated around their coupler axis.
With this design, the rotation is, however, made offset from the center of gravity of the loaded wagons, wich leads to large and shifting forces on the RCD machine. In order not to damage the
The unloading process is made with the complete train set intact, including the locomotive, in a continuous, smooth movement. Depending on the capacity of the receiving system, the unloading rate that is controlled by the train speed, can be up to 25,000 tph at a speed of 0.5 m/s. The unloading station consists of a relatively long helix spiral above and on the side of the rail track, the center line coinciding with the pivot line of the wagon hinges. As the wagons enter the unloading station, the tipping wheels enter the spiral which forces them to be lifted up, sideways to an almost upside-down position and then back in a slow, smooth movement, see the figure below. During the unloading process, the chassis remain on the tracks and kept stable by the aid of support wheels.
4 KEY PERFORMANCE INDICATORS In order to give an all-round picture of the performance of the two logistic systems, a set of relevant key performance indicators, KPI, have been selected. Reliability, availability and safety cover a large part of the picture. To these is added system performance in the form of cost as well as environmental impact in the form of CO₂-emissions per transported unit volume. Below, the first KPI’s are qualitatively investigated while system performance and environmental impact are quantitatively evaluated and compared for a selected case. Figure 5. End view of a Helix Dumper wagon in the unloading station
The unloading process is initially powered by the locomotive, but as soon as the first wagon body is tipped a little bit, its center of gravity starts to descend. The resulting reduction of potential energy powers the forward motion and the unloading of the next wagon, and so on until all the wagons are unloaded. The resulting coupler forces during the unloading process is the same or lower than during regular transports. The figure below shows a side view of HD wagons unloaded. The high unlaoding capacity makes the unloading process quick and the time per round trip short. In many cases this allows for an extra round trip per day compared to RCD systems, thus reducing the required number of locomotives and wagons. It also allows for loading of ships directly from the trains, saving handling and buffer storage. A single HD unloading station has an annual capacity of over 100 Mtpa. The HD unloading station comes in two versions – a basic version entirely without moving parts, except the stabilizing rollers, and a version that allows for locomotive passage.
5 RELIABILITY Reliability is the probability that an item can perform a required function under given conditions for a given time interval. (EN 50126). In this case, reliability could be translated as the probability that the system will work during the planned production time. In general, the simpler the system, the less effort is required to keep up the reliability. 5.1 Wagon reliability Since the wagons of the RCD system are so simple, they should have a high reliability. However, as previously mentioned, the many and fast start-stop motions of the unloading process wear heavily on the couplers. Since it is quite a challenge when couplers crack and break during transport, frequent effort is put into coupler inspections in order to avoid this. Still the couplers do break occasionally. Compared to the RCD wagons, the added complexity of the HD wagons is a hinge and a tipping wheel. The function of these is based on bearings. With high-quality, maintenance free bearings, the added maintenance is minimal and the wagon reliability very high.
Figure 6. Side view of Helix Dumper wagons in the unloading station
With proper maintenance, the reliability of the HD wagons is likely to be higher than for the RCD wagons.
Hence, the availability of the HD wagons is higher than for the RCD wagons. 6.2 Unloading station availability
5.2 Unloading station reliability The RCD unloading station is large and complex, with many moving parts that are exposed to frequent, heavy and shifting loads. Even with wellfunctioning maintenance, the risk of unplanned failure is relatively high. The basic version of the HD unloading station on the other hand, has no moving parts except chassis stabilizing wheels. In addition, the unloading movement is very smooth. In some other version of the unloading station that allows for locomotive passage, hinges are added to the list of moving parts. The wear and maintenance of these are, however, very low. The reliability of the HD unloading stations is significantly higher than for the RCD ones. 5.3 System reliability Since the reliability of the HD wagons are higher, and for the HD stations, significantly higher, the combined reliability is significantly higher for the HD system. 6 AVAILABILITY Availability is the ability of a product to be in a state to perform a required function under given conditions at a given instant of time or over a given time interval assuming that the required external resources are provided. (EN 50126). In this case, availability is translated as the part of the time that a system does not have to be maintained or repaired. Again, the simpler the system, the less maintenance is required and the greater portion of the total time it can be available. 6.1 Wagon availability The wagons of the two systems mainly consists of the same parts – wheels, brake system, couplers etc. with the same need of maintenance. As earlier mentioned, the couplers of the RCD-wagons need to be frequently inspected for cracks. Some types of commodities tend to stick to the sharp inner corners of the RCD wagon bodies. When that happens, the risk is that commodity keeps building up every time they are loaded. Therefore they have to be cleaned every time they are unloaded. In such cases, this further decrease the availability. The additional complexities of the HD wagons are basically maintenance free and do not affect the availability. The rounded shape of the HD wagon bodies minimizes the risk of sticking commodities.
The HD unloading stations are basically maintenance free. Due to their simplicity, they are also not likely to break down and fail. The RCD stations, on the other hand, require relatively much maintenance and are also more prone to unplanned needs of repair. Hence, the availability of the HD unloading stations is significantly higher than for the RCD stations. 6.3 System availability Since the availability of the HD wagons are higher, and for the HD stations, significantly higher, the combined availability is significantly higher for the HD system. 7 SAFETY Safety is freedom from unacceptable risk of harm. (EN 50126) 7.1 Wagon safety The wagons of the two systems are very safe. 7.2 Unloading station safety The main risks involved in the unloading process are squeeze injuries from moving parts and hitting by falling commodity. The unloading process of the HD system involves one smooth movement of the train through the unloading station where the only moving parts are the train and wagon bodies. In a version that allows for locomotive passage, the row of chassis stabilizer wheels tilt back and forth, causing a risk of squeeze injuries. The unloading process of the RCD system involves more movements, for example of the indexer arm that moves back and forth, up and down as well as the many starts and stops of the wagon sets and rotations back and forth of the RCD machine. All of these movements create additional risks for serious injuries. In the case when material sticks to the body of the RCD wagons, the commodity may fall on employees that must go underneath the tipped wagons in order to clean them. They risk injuries and even death. If, on the other hand, commodity happens to stick to the HD wagon bodies, the train can be stopped to allow for convenient access to the body interior from the side of the unloading station for safe cleaning operation.
Hence, the HD unloading process involves much fewer and less severe risks than that of the RCD one, and is hence significantly safer. 7.3 System safety Since the safety of the two different wagon types is high, while the HD unloading stations are significantly safer, the combined safety is significantly higher for the HD system. 8 LOGISTIC COSTS In this section, the performances of the two systems are compared as cost per transported unit volume for a selected logistic case. The costs include capital expenditure, CapEx and operational expenditure, OpEx. In the calculations, CapEx includes the cost of the trains and unloading stations with civil works. OpEx includes transport, unloading and hoisting of the commodity back to surface level. 8.1 Transport costs For the cost of transport, the same standard AAR cost for haulage is used for both systems, and it is 0.01 USD/ton-km. It includes CapEx as well as OpEx - locomotive as well as maintenance cost. It can be argued that the HD wagons, due to their higher complexity, should have a slightly higher CapEx and hence a higher haulage cost than the simple RCD wagons. It is, however assumed that the lower need for coupler inspections of the HD wagons weighs up for their higher CapEx per wagon. As will be shown later, the shorter unloading time of the HD trains, shortens the transport cycle. In many cases, this reduces the number of active trains which drastically decreases the system CapEx. 8.2 Unloading costs 8.2.1 CapEx The CapEx of the RCD unloading stations is relatively high. For the installation of the stations, relatively deep ground penetration is required and since they are normally placed in ports, costly measures must be taken against ground water penetration. The indexers and RCD machines are very large, complex and powerful. In contrast, the HD station is very simple and the ground penetration relatively small. In total, the CapEx is about 10% of that of a large RCD unloading station including civil works. Due to its low cost, the system is cost-effective even with smaller annual volumes, yet the capacity of a single HD unloading station exceeds that of two large RCD stations.
8.2.2 OpEx The operation and maintenance of each RCD unloading station requires several full-time staff members. The powerful indexer consumes high quantities of energy. The large dumping depth results in higher hoisting height to bring the commodity back to surface, which consumes energy. The operation of the HD station can basically be managed by the locomotive driver alone. This saves costs for wages. The only powered devices in the unloading station are for the adaption of locomotive passage and the commodity hoisting from the shallow hopper. The energy consumption of the HD system is hence relatively low. Since the unloading station is basically maintenance free, the maintenance cost is very low. Due to the simplicity not many things can break, keeping also the repair cost to a minimum. In addition, the HD system allows for another saving, not included in the calculation. The large unloading allows for loading of ships directly from the trains, without intermediate storage. The cost of putting down and picking up commodity is by standard counted as one dollar per metric tonne, which hence is an additional potential saving of the HD system. 8.3 Case input and calculation A logistic case has been selected in order to compare the performance of the two systems. It consists of a 200 km A to B transport of 50 Mtpa. The input parameters of the case are shown in the tables below. Table 7. Logistic input parameters Description Distance pit-port Annual transport volume Number of wagons per train set Number of wagons per locomotive Axle load Number of wheels per wagon Max wagon weight Average speed loaded Average speed empty Travel time per round trip Work days per year Work hours per day Haulage cost* Diesel power cost Electrical power cost *Incl. loco and wagon maintenance
Value 200 50 235 47 40 4 160 70 80 2,50 320 24 0,01 1 0,3
Unit km Mtpa psc. psc. t psc. t km/h km/h h days h USD/ton-km USD/kWh USD/kWh
Table 10 Unloading station power consumption
Table 8. Input parameters for wagons and unloading Description RCD HD Unit Wagon tare weight 22 24 t Wagon load capacity 138 136 t Average loading rate 95 95 % Average wagon load 131 129 t Loading capacity 12 000 12 000 tph Unloading capacity 8 000 16 000* tph Staff number per station 5 1 pers. * Reduced to keep down the cost of the receiving system
Description
RCD
HD
Unit
260
130
h
Avg. power consumption
6,232
4,186
Annual power need
1 623
545
MWh
Total power cost
78,534
164
USD/yr
Total power cost
0.0097
0.0033
Operative hours/year
kW
USD/t
The resulting logistic costs are shown, first in the table and then in the graph below.
9 RESULTS Table 11. Logistic costs (USD/t)
The table below shows the resulting, basic logistic parameters for the selected case. Table 9. Resulting logistic data Description
RCD
HD Unit
Loading time per train set
2.6
2.5 h
Unloading time per train set
3.9
1.9 h
0.78
0.78 h
Time per round trip
9.9
7.9 h
Time per round trip
0.41
0.33 days
2
3 psc.
Shunting & brake check
Possible No. of daily round trips Average train load
30,809
30,362 t
1,623
1,647
Required daily No. of train loads
5.1
5.2
Resulting annual capacity
50
51 Mtpa
Required annual No. of round trips
Required No. of active train sets Required number of locos Required number of wagons Annual travel distance per wagon
3
2 psc.
15
10 psc.
705
470 psc.
649
659 km
Annual station 24 hour days
260
130 days
1
1 psc.
Station utilization
RCD
HD
Diff
Diff
CapEx station
1.111
0.067
-1.044
-94%
Haulage
4.671
4.743
0.072
2%
Unloading staff
0.041
0.004
-0.037
-90%
Station power
0.010
0.003
-0.006
-66%
Station maintenance
0.040
0.002
-0.038
-95%
5.87
4.82
-1.05
-18%
Sum
206,000 314,000 km
Annual travel distance per train Required No. of stations
Category
81 %
41 % Figure 12. Logistic costs for the selected case.
It is worth to notice that since the unloading process of the HD system and hence the time per round trip is shorter, each HD train manages an extra round trip per day compared to the RCD system. The HD system can therefore manage the annual volume with 33 % fewer locomotives and wagons than the RCD system. The table below shows the calculation of the amount and cost of power.
The result is that the logistic cost of the HD system is about 1 USD/metric tonne, or 18 % lower than for the RCD system, mainly due to the difference in capital cost of the unloading stations. With the other factors fixed, but with increased annual volumes, the RCD system would soon require another unloading station, which increases the logistic cost. Even with lower annual volumes, the logistic cost increases for the RCD system. In contrast, the logistic cost of the HD system remains relatively constant, see the figure below.
Figure 13. Total logistic cost for different annual volumes.
10 ENVIRONMENT
unloading of the HD system, the noise emissions are also significantly lower than from the RCD system.
The environmental impact of the logistic operations is, to begin with, quantified as CO₂ emissions for the logistic case that was first evaluated. The table below shows the input parameters for the calculation of the CO₂ emissions. Table 14. Input parameters Description Value Loco diesel consumption 0.0115 CO2-emissions/l diesel 3 CO2-emissions/kWh 0.291* * electrical power of unspecified source
Unit litre/ton-km kg/litre kg/kWh
The resulting CO₂ emissions per transported metric tonne of commodity are shown in the table below. Table 15. CO₂-emissions (kg/tonne) Description Transport Unloading Sum
RCD 1.56 9.45 11.00
HD 1.59 3.17 4.76
Difference +0.03 +2 % -6.28 -66 % -6.24 -57 %
As the table shows, the emissions are almost the same for the transport part of the logistic operations of the two systems. The emission from the unloading process, however, is almost 60 % lower per unit volume for the HD system. Dusting is another environmental issue. Mainly due to the lower dumping height, the HD solution dusts less than the RCD solution. Due to the smooth
11 DISCUSSION The purpose of the study was to investigate whether the performance of the relatively new Helix Dumper system for rail freight of heavy dry bulk is higher than established solutions. As the established solution, the Rotary Car Dumper system was selected. The result shows that, in spite of the slightly heavier and more complex wagons, the HD system significantly outperforms the RCD system in every aspect. Due to the large cost of the RCD unloading stations, the unit logistic cost for the RCD system varies relatively much with annual volume. Since each station manages about 50 Mtpa, it is crucial for the logistic cost to transport volumes close to, but not more than this amount, for each installed station. This causes a stress on the mines to match the capacity of the unloading station and to push the capacity of each station, in order for the CapEx to be distributed on as large annual volume as possible. For new mines, it is also essential to quickly increase the production up to the capacity of the unloading station. It is also likely that mineral deposits that are judged not to yield large enough volumes to fill the capacity of an unloading station, won’t be developed. Since most of the rich mineral deposits in the world are already found, and in the process of being extracted, most of the remaining deposits are smaller. This means that in the future, the conventional
RCD system for mineral logistics will become increasingly ineffective. The HD system, on the contrary, has 1-2 USD/t lower logistic cost per metric tonne than the RCD system. In addition, this logistic cost is relatively constant from annual volumes of 10 Mt and up. For large mines, the lower logistic cost of the HD system is an advantage and they wouldn’t be so sensitive to variations in annual volumes either. New as well as smaller mines would benefit from as low logistic cost as larger mines. The HD system also opens up possibilities for smaller deposits to be worth-wile to be extracted. An added advantage of the great unloading capacity of the HD system is the possibility of direct loading of ships from the trains. To the degree this is logistically possible, this part of the volumes don’t have to be put in intermediate storages. A standard cost for intermediate storage is 1 USD per metric tonne. For these volumes, another USD/ton of logistic cost could hence be saved. 12 CONCLUSIONS The HD system significantly outperforms the RCD system in every aspect with significantly higher reliability, availability, and safety. In addition, the HD solution emits significantly less noise, dust and 57 % less CO₂ per transported tonne of commodity in the selected case. For annual volumes from 10 Million tonnes, the logistic cost of the HD system per unit volume is 15 to 35 % lower and, in contrast to the RCD system, almost unaffected by the annual volume. While this is an advantage for larger mines, it makes many smaller mineral deposits worthwhile to develop. In addition, the great unloading capacity enables direct loading of ships from the trains, allowing additional significant savings.