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HENZE Double-Wall-Tanks with tank-heating

HENZE is one of the market-leading manufacturer of large diameter plastic pipes. The pipes, made out of Polyethylene or Polypropylene are used for applications in water- and sewage systems and as industrial application as well. The spiral wound pipes can be produced either with a solid or profiled wall as structured pipes.

Especially the double wall structures enables HENZE to provide a high quality and security standard for industrial applications and interesting solutions for process-engineering (double wall tanks, heat- exchanger etc.)

The following brief-report shows the special application of storage- and treatment tanks, made of Polypropylene, for a bitumen-emulsion in road constructing.


HENZE Double Walled Tanks for the suspension of Bitumen emulsionHENZE Double Walled Tanks for the suspension of Bitumen emulsion

The storing and maintained suspension of a bitumen-emulsion for further production steps depends largely on whether the temperature of approximately 70 degree Celsius can be constantly held inside the storage tanks. Additionally to the fine distribution of bitumen in the watery liquid, emulsifiers stabilize the temperature inside the mixture. In case the temperature drops below a certain degree, the emulsion is broken and the bitumen will fall out and become sticky. Therefore, the constant temperature is of major importance.

Since thermal discharge arises in terms of hot water during the production, it stands to reason to use this for the intended purpose. Thanks to the know-how in process engineering and design of plastic pipes a constant temperature, proper storage as such as an adequate treatment could be achieved.

The double-walled construction allows beside its usual purpose (the storage of media) also a leakage test. The test can be carried out via electric resistance measurement using probes to detect over- or under pressure.
The spirally wound profiles inside the pipe wall can additionally be used for cooling of process media. However, in this specific case the storage medium (bitumen-emulsion) was heated up by passing a heat-medium through the profiles. Thus, the heating-water (thermal discharge from production) was pumped into the spiral profile of the double-walled wounded pipes of the vertically tanks.

HENZE Double-walled tanks, unique in material and construction

The Double-Wall-Tanks for this application are produced out of Polypropylene Homopolymer PP-H,

“Daplen BE 60” by Borealis. This material is known for its outstanding thermal and mechanical characteristics. According to graduate engineer Michael Florin, who is HENZE’s responsible project manager, it is:”… the first choice for the present case”.

HENZE Double Wall Structure, designed for perfect flow of heating mediumHENZE Double wall Structure, designed for perfect flow of heating medium

The pipe was produced according to DIN 16961 with an inner diameter of 2000 x 5900 mm cylindrical height.  The general approval Z-40.21-209 by DIBT served as the base for the structural dimensioning. Additionally, the following important parameters were calculated by the manufacturer in order to guarantee the maintenance of warmth in the inside: energy yield, isolation and heat loss. The effective volume amounts to 15 m³ per tank during unpressurized storage and treatment of media. A design temperature of 70 degrees based on a lifetime of 25 years was chosen. Standardly, a safety factor of 2 was taken.

Lateral connection pieces are included in the structural view. The tanks consist of a flat bottom and a cover each. Agitators run on top of the covers fixed by traverses.

Performance guidelines perfectly fulfilled

If there are nozzles installed in the cylinder wall of the tank, a bridging piece / bypass has to be used to avoid any disturbance for the flow of the heating media. The pinpointed redirection of heating media into the bypass was realized through special connection pieces. The connection pieces seal hermetically the complete wall cross-section by welding. The bridging pieces were connected respectively before and after each “water-stop-nozzle” (see Pic. 3).
To achieve the greatest heat transfer, the wall thickness base (Inliner) was chosen to be small. Correspondingly, the wall thickness of the top layer was constructed greater to achieve a better isolation and meet the structurally required overall-wall-thickness.

Tank Design with Special Bridging Piece / Bypass
Tank Design with Special Bridging Piece / Bypass

To know exactly what is needed

The storage- and treatment tanks for bitumen-emulsion called for a particular specification of the wall. Moreover, an exclusive design was demanded which could flexibly adapt itself according to its use. “This was the only way to save all heating costs for the tanks operation. Precisely this individuality, the responding to problems and its solutions such as the choice of wall thickness according to its required design, are strengths which we can retrieve at any time for any case” says Florin after the successfully completed case.

Dipl.-Ing. Michael Florin
HENZE GmbH, Germany
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