Bossing the Black Stuff: How to Transfer Coking Oil Safely and Cleanly

Editor: Charles Butcher

Tricky fluids handling with viscous and hazardous media? The right pump technology can make all the difference – Even after decades of experience, a carbon black manufacturer still encountered challenges when unloading coal tar. The problem was solved through collaboration between the operator, the contractor and pump experts.

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For tar to become soot, viscous and critical raw materials must first be unloaded.
For tar to become soot, viscous and critical raw materials must first be unloaded.
(Source: Bungartz)

What do mascara, printer toner and car tires have in common? An important ingredient in these products — as well as many others — is soot. More precisely: industrial soot, also known as carbon black. This material, which contains 80–99.5 percent carbon, differs from the “shiny soot” that clogs domestic chimneys mainly through its very high ratio of surface area to volume, making carbon black valuable as a filler and pigment.

One company that has mastered the “black art” of soot production since 1936 is Deutsche Gasrußwerke (DGW) in Dortmund, Germany.

“Several processes are used to produce carbon black,” explains DGW Managing Director Harald Baumgart. In Dortmund, the company produces about 100,000 tons a year of carbon black in a staged combustion process. Most of this is used as a “reinforcing filler” for tire production and other applications, but DGW also manufactures pigment-grade carbon black for lacquers, paints and plastics.

Although the carbon black business is highly traditional, production has seen changes over the years. Waste heat from the combustion process, for instance, is used to raise steam that is fed into the local district heating network. More recently, to remain efficient in the delivery of raw materials DGW has invested in train unloading for the delivery of coking oil, which is used as a raw material.

And that’s where the pumping difficulties started. Coking oil, otherwise known as coal tar, is hard to handle because it is both toxic and highly viscous. Even the seemingly simple task of unloading railcars presented the soot experts with a tricky challenge.

Working Together to Solve a Tricky Transfer Task

In complex situations like this, the co-operation of planners, operating experts and equipment suppliers is crucial to success. This was certainly the case at DGW, where the engineering contractor entrusted with the job is known for its flexibility in developing creative solutions to tricky problems. The team from centrifugal pump specialist Bungartz, meanwhile, has the expert know-how needed to pump demanding media, gained from long experience across a wide range of customer projects.

The plant operator attached great importance to combining a high level of safety with low investment and operating costs — aspects already familiar to both the engineering company and the pump supplier. “Especially important for Deutsche Gasrußwerke was the ability to empty the tank cars completely,” explains Bungartz project manager Michael Hucklenbruch. “Thanks to our previous experience with coal tar, we were able to reassure the client that our pump could do the job.”

To reduce capital costs the team decided to use a single pump to empty all four tank cars on the incoming train. The ability to empty each tank completely is also important to the economics of the project.

Reliable Pumps Developed Through Experience

For more than ten years, Bungartz has relied on its MPCV magnetically coupled pumps for difficult materials like coal tar. These combine the characteristics of the company’s V-AN vertical pumps with those of the horizontal MPCH dry-run series.

These pumps are able to run dry for indefinite periods because they operate without bearings in the pumped liquid. Instead, a gas barrier in the form of a frictionless throttling bush protects the grease-lubricated roller bearings from the product vapors. The complete shaft sealing system has three main principles: hydrodynamic relief of the bearing and seal unit from the pump delivery pressure; backflow vanes and a gas barrier that prevent vapors from entering the bearing unit; and the eddy-current-free magnetic coupling that seals the pump from the environment.

Thanks to the vertical alignment of the pump, the bearing and seal unit runs completely without product contact, even in the event of a seal gas failure. In this way, the bearings can achieve a service life of more than five years in continuous operation, the pump developers explain proudly. The fact that the MPCV pump requires no special control or monitoring systems saves costs in both investment and operation.

For the Dortmund plant Bungartz supplied an almost complete fluids handling system, leaving only the piping to be completed by DGW. The temperature of the coking oil is raised to around 90 °C to reduce the viscosity and make pumping easier. To ensure safety, the pump is certified for use in hazardous atmospheres.

Specialist Centrifugals Make Life Easier

With the new coking oil handling system in place, the process of unloading an incoming train is straightforward. Discharge valves are opened on each tank car and the pump is started. The pump is mounted at the mid-point of the tank cars, so the ones furthest away take a little longer to unload; however, each tank is always emptied completely, regardless of its initial filling level.

The DGW project shows in a very practical way how special-purpose centrifugal pumps can provide reliable, affordable service even with very challenging fluids such as coking oil. Bungartz’s experience with difficult media includes toxic wastewater, other hazardous and outgassing liquids, and media containing solids, sludge, crystallizing or corrosive substances.


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