Bryan Reid is a mechanical engineer. He led the mechanical and material handling design of the steelmaking coal terminal expansion at Neptune Bulk Terminals, including the implementation of a new tandem rotary railcar dumper system to maximize the railcar unloading rate and overall terminal throughput.
In the below interview, Bryan breaks down rotary railcar dumpers and describes the unique considerations associated with their design, maintenance and integration into a live rail system.
What is a rotary railcar dumper and how does it work?
A rotary railcar dumper is a piece of equipment used to unload open-top railcars by placing the railcars inside this piece of equipment and rotating the car about one-hundred seventy degrees to allow the material to empty from the railcar. The entire system that is usually comprised of the dumper, which rotates the car, an indexer, and wheel grippers.
The indexer is used to move the train. It’s a large carriage with an mechanical arm on it that travels parallel to the rail track to move the train one or more cars at a time, depending on how many dumper barrels you have. The indexer arm comes down and grabs the railcar knuckles and moves the train along the rails into the dumper.
To time the indexer, sensors are placed along the rail tracks that monitor the position of the wheels on the railcars. Those sensors determine where the wheels are and control the indexer, telling it when to move and when to stop, so that it knows if it’s moved the car into the dumper.
The wheel grippers are just like they sound. They grip the wheels of the railcars, so when the indexer is moving the train it’s got the arm holding the train and that’s controlling it, but when the arm releases you need to use the wheel grippers to hold the train in place. The number of wheel grippers used in a system depends on the application, how long your trains are, and whether or not there are inclines or slopes on the rails. Typically you have at least one set on either side of the dumper — four wheels in total — and in most applications you have more. Additional wheel grippers are used to provide redundancy in case one of the wheel grippers fails and also to provide enough capacity, based on the forces that need to be considered.
What are some of the advantages of rotary railcar dumpers over other railcar unloading methods?
There are really two common methods for unloading railcars: the first method that we’re talking about now, rotary dumpers, and the other method would be bottom-dump railcars. That’s where they’ll just position a railcar over a hopper, open the gates at the bottom of the railcars, and all the material will pour out.
One advantage of the rotary railcar dumper is that it provides a very high throughput, because turning a railcar upside down tends to empty it faster than unloading it through the bottom.
It also depends on the material you’re handling. Bottom unloading doesn’t work well with sticky materials such as coal, some iron ores, bauxite, and sulphur, because the railcar hoppers simply aren’t steep enough for that material to pour out of the bottom efficiently. So, the rotary dumper really is the best way to unload cohesive materials.
Are there unique design or installation considerations associated with rotary railcar dumpers?
Yes, one of the biggest challenges with a rotary railcar dumper is that it requires a relatively deep pit to be built under it that contains the receiving hoppers, feeders, and take-away conveyors. And because a lot of these rotary railcar dumpers are located at ports that can have relatively poor soil conditions, building these large, deep foundations can be challenging; because you’re performing a large excavation that’s below the water table, so you have to deal with all the complications of digging a very deep pit and keeping it dewatered. From a mechanical materials handling standpoint, you can always optimize the design and layout of the equipment to minimize the depth of the pit, which will reduce the civil work challenges.
Earlier you touched on the importance of the indexer’s timing and the control sensors. Can you elaborate?
Typically, they’ll get the timing down during commissioning. The indexer’s timing is an important factor because of how it controls the in-train forces. Because, as you know, trains are extremely heavy, and as the train moves with the indexer it creates a lot of force on the indexer arm that’s moving the train, as well as in between all the railcar couplers. So you have to be very careful with how you accelerate the indexer and slow it down to maintain those in-train forces. If you accelerate or decelerate too fast, you risk breaking the indexer arm, derailing railcars, or breaking the knuckles between railcars.
How are rotary railcar dumpers integrated into live rail systems?
When a rotary railcar dumper is built at an existing terminal, generally clients can’t afford the lengthy shutdown and the interruption to their rail operations that would be required to install that system. Operators can build a bypass track so that their systems can continue to operate and operational trains can bypass the rotary dumper while it’s being built. If you didn’t have a bypass track, you would have to shut down your rail system for a fairly long time. Most terminals can’t afford such costly shutdowns.
Are there any other concerns associated with the operation of rotary railcar dumpers and how can they be addressed?
We’ve already talked about the importance of the indexer. The other concern when you’re dumping a railcar upside down is that the material can generate a large amount of dust as it rapidly exits the railcar. There are usually two ways to address that: the first is a dust collection system, with either a baghouse or a wet scrubber connected to the dumper system that pulls out all the dust from the dumping area. Clients typically use a baghouse for drier materials, and then the wet scrubber will be used for wetter, more cohesive materials. Another way to address the dust is with a type of misting system that sprays a curtain of water. Typically, one or the other of these methods is used.
Maintaining worker safety is also a very important concern. You have to be diligent, because it’s a massive piece of moving equipment. Operations staff need to be properly trained on how it’s going to operate, how to ensure everything is properly guarded, and how access to the dumping area will be restricted.
Are there unique maintenance requirements or considerations for rotary railcar dumpers?
One of the most difficult parts of the rotary dumper to maintain are the trunnion wheels located at the bottom of the dumper barrel. Those are the huge steel wheels that the dumper barrel sits on for support and that allow it to rotate. Typically, a rotary dumper will consist of two end-rings and those end-rings sit on the trunnions. Like I said earlier, because the dumper is located in a deep pit, these trunnions will be about half-way down that pit, which typically puts them in a very difficult area to access. And theses trunnions typically weigh anywhere from about two to four tonnes.
It’s important to be thinking about these difficult maintenance issues from the very start of a project, so that you can put in place the infrastructure that‘s required to ensure there’s adequate space to maintain the equipment safely. The maintenance of trunnion wheels requires a design that makes them accessible by either an overhead crane or ground-level crane, allowing them to be easily and safely pulled out of the pit. You have to consider how much room will be required to perform the crane maneuver at the start of a project and then design all the foundations and equipment around the trunnions to make this possible. The crane system can either be build into the dumper system itself for items that you know are difficult to maintain and require a permanent crane in place or, alternatively, mobile cranes can be used.
Is car derailment a particular concern of rotary dumper systems? What measures can be taken to mitigate or avoid derailment?
When a railcar comes off the rail tracks it creates downtime and can damage the equipment around the railcar if it falls onto some other piece of equipment. It’s also a serious safety issue for some of the personnel working around the rail tracks.
The risk goes up when you’re handling the train through a rotary railcar dumper system. But you mitigate these risks, as I mentioned earlier, through your control system. Calibrating the speed of the indexer, proper placement of the wheel grippers, building redundancy into the design, and using sensors to monitor the position of the railcars to ensure all the railcars end up in the right spot and are properly positioned in the dumper — these are all factors that mitigate the risk of derailment.
Positioning tolerances are only a couple of inches. You’re talking about moving a train that’s a few kilometers long, so accurate and precise controls are very important. That’s why, even though an optimized control system can be quite an investment for the client, in the end it’s something that will help to avoid accidents and costly downtime.