Process Equipment Fast, safe, efficient


Emptying of tanker trucks and railway tank cars without risk and residue


For companies from the chemical sector, refineries and fertilizer industry, the emptying of vessels and tanks poses a challenge in terms of both the technical and efficient implementation. Plant engineers and operators rely on functioning safety concepts as well as the lowest possible investment and operating costs, when it comes to media such as liquid gases, heavy substances such as sulfuric acid, or preheated materials such as tar and heavy oil. Standards such as safety and environmental protection provisions, legal regulations and guidelines have to be observed and complied with.


The unloading of dangerous, toxic and so-called heavy media (such as sulfuric acid) is a complex process requiring sophisticated pumping technology. Common pumps such as normal suction centrifugal pumps quickly reach their limits. Liquid gases such as propane and butane are stored in vessels with volumes of a few hundred liters to several thousand cubic meters. Tanker trucks deliver the liquid gases, which have to be unloaded on-site. These gases are media at boiling point. For this reason, the tank is emptied from below. The usual unloading process involves so-called barrel-type pumps being installed in recesses in the floor. Gravity causes the medium to flow into the underground storage tank from which it is then pumped out of by means of a submersible pump. Disadvantages: A long unloading time and high infrastructure effort increase the costs. And residual material remains in the tanker truck.


Normal pumps also have this problem with residual material. These standard pumps are vented via an empty pressure line during standstill. When the pump is switched on, the liquid immediately starts being pumped. As the process progresses, the liquid level falls and an increasing amount of gas is drawn in by the pump. These gas bubbles reduce the performance and cause irregular running. In the event of even more gas entering, the flow rate sinks completely down to zero. The flow stops despite the pump still running. Operating faults are inevitable! It is therefore necessary to constantly monitor the pump at all times. On top of this, the pumps have to be vented regularly and are often designed to be product-lubricated. Thus, the functioning of the slide bearings and the seal is reliant on the pumping medium. A contaminated medium or


MARCH/APRIL 2018


insufficient venting inevitably lead to faults. This pump type can only be used to a limited extent, in particular for liquids which are outgassing or have critical boiling points. Similar difficulties arise when unloading media with a self-priming pump. This pump often uses a small reservoir volume at the impeller inlet, in order to ensure the flooding of the pump. When the pump is started, it can suck in some media, as a small amount of negative pressure builds up in the feed tank. A minimum volume flow has to be observed as is the case with normal suction pumps.


pressure reduction without cavitation up to the boiling point, the complete emptying of liquid gases is also unproblematic.


Ideal tanker truck emptying with heavy media


Media such as oleum, sulfuric acid and tin tetrachloride with densities of between 1800 and 2300 kg/m3


are difficult to


unload. During unloading from above, the pressure at the highest point of the loading arm drops almost to the boiling point. Common magnetic coupling or canned motor pumps are not normally safe to run dry. The problem: the pumps need to be switched off in time before gas starts getting drawn in. This requires continuous monitoring. And a lot of residual material remains in the tanker truck. The disadvantages predominate: personnel assignments, wasting and disposal of residual material are cost factors!


Figure. Ideal for the complete emptying of tanker trucks and railway tank cars, the self-regulating centrifugal pump


V-AN, in this case as space-saving pumping system.


Intrinsically safe solution through self-regulating behavior Bungartz, the manufacturer of special centrifugal pumps in its third generation, offers a safe, easy and efficient alternative for emptying tanker trucks, railway tank cars and other vessels. The pumping process is achieved with self-regulating pumps of the V-AN range. They adjust independently to changing feed rates and do not require any suction.


Here is the principle in simplified terms: When a medium flows into a vessel, the liquid level rises until the inflow and outflow of the vessel balance out – without any type of mechanical or electrical regulation equipment. In addition to the feed and pressure port, the V-AN is equipped with a gas compensation port. It is connected to the gas phase of the feed tank. Thus, the pump loses its suction characteristics. Compared to normal suction centrifugal pumps, where the typical drop in pressure always occurs systemically at the impeller inlet, the V-AN has one advantage: It has a low NPSH value (<0.1 m) and pumps every medium in every operating state without cavitation. The pump has no problem pumping acids or alkali – from sulfuric acid, through sodium hydroxide solution to substances such as acrylamide, propylene, isopropanol, ammonia or maleic anhydride – down to the very last drop. Due to the


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In the case of the self-regulating centrifugal pump V-AN, the suction vessel is only filled manually before the first start-up. The return volume of the pressure line refills the vessel after shutdown. A principle both easy and efficient: during the start of the pump, negative pressure forms due to the surface drawdown in the suction vessel. Once a certain negative pressure in relation to the suction height is reached, the liquid siphons to the suction vessel. The vessel fills up and the pumping rate reaches its maximum capacity. The accompanying gas in the final phase is extracted via the pressure compensation line of the pump. An online animation illustrates the process: www.bungartz.de/ flash/german/tankwagen/tankwagen. htm


Advantage: The system even recovers from faults in the suction line (flow rate sinks to zero), because the negative pressure in the suction vessel is preserved. The result: fault-free and complete emptying of tanker trucks and railway tank cars.


Bungartz offers a space-saving pumping system for emptying tanker trucks. It consists of the V-AN self-regulating centrifugal pump, a pump stand and feed vessel. The system does not require a control/regulating unit and does not need any additional monitoring. It is only connected directly to the power supply and the pipeline.


A functioning model of the V-AN pump will be shown at ACHEMA 2018, in order to visualize the emptying process of railway tank cars: Hall 8, Stand C 1.


For more information please contact: pumpen@bungartz.de www.bungartz.de


ENQUIRY NO. 11


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