HK1082484A - Method for packing bitumen - Google Patents

Description

Method for packaging asphalt

Technical Field

The invention relates to a method for packaging bitumen, in particular road bitumen, in a large-volume disposable transport unit for transporting the bitumen in the cold state.

Background

The processing of bitumen is highly temperature dependent, since bitumen is a liquid at high temperatures and a hard solid at low temperatures; the physical state of the asphalt has a wide transition range between high temperature and low temperature, including viscous state and pasty state, and the viscoelastic asphalt has great change of performance while the physical state is changed from solid to liquid.

For transporting asphalt over long distances, it is inefficient to use heated trucks to achieve this goal, as it requires maintaining the asphalt permanently at a temperature above its softening point. Moreover, these vehicles require careful safety precautions to protect the environment from the hazards of asphalt leakage. In view of the environmental hazards and high energy consumption in transportation, a tendency has arisen to reduce the transportation of bitumen in liquid form.

If it is necessary to transport the asphalt over long distances, it is common to fill the asphalt in hot liquid form into a thin metal drum and let it cool, and then either cut the drum open on site in order to remove the cold asphalt from the drum, or heat the asphalt to a liquid form and pour it out. Both of these methods are unsatisfactory because the disposable containers are waste materials and are extremely difficult to dispose of because they are contaminated with asphalt.

In the case of specific asphalts, such as roofing asphalt and industrial asphalt, it has therefore been a practice to pack the asphalt into small units having a capacity of 30 kg, which are filled in plastic films which are later melted and processed together with the asphalt inside. These films are placed in special moulds and then subjected to hot bitumen to cure. However, this method is difficult to employ for large quantities of bitumen (as is the case with road asphalt) as it requires a number of vessels in which such bitumen can be cooled. Furthermore, the plastic films generally used cannot be applied to road asphalt due to the high softening point of road asphalt.

Due to the large amount of asphalt required, particularly in road construction, efforts have been made to develop packaging units that are larger than conventional portable packaging. In addition to being easier to fill, such large packaging units have the advantage that the ratio of molten plastic to bitumen in the large packaging unit is significantly more favorable for bitumen than in conventional small packaging units. Large packaging units typically fail due to the following: filling large-volume plastic containers with bitumen having viscoelastic properties does not avoid the risk that the plastic materials are melted off or softened to such an extent that they lose their shape stability and expand and start to tear.

It is known how to package road asphalt in multi-layer plastic bags which are then melted off together with the asphalt. The known package (U.S. Pat. No. 5,452,800A) is small-unit and no mention is made in this publication of the type of filling or the specific filling parameters. Such small packages are efficient only when used for packaging small quantities of bitumen, since a relatively large amount of packaging material is required for packaging and transporting large quantities of bitumen. Furthermore, there is a considerable portion of packaging material in the bitumen after melting.

In the processing of bitumen, it should basically be taken into account that it has no defined melting point, but rather a very broad thermal transition range from the solid via paste-like state to the viscous state and finally to the liquid state, as mentioned at the outset, which makes the viscoelastic properties of the bitumen highly temperature-dependent.

Disclosure of Invention

The invention is based on the task of: a method is created as described at the outset, i.e. a package for a large quantity of bitumen can also be selected, which can be melted together with the bitumen without adversely affecting the quality of the bitumen.

According to the invention, this task is achieved in that: a disposable packaging unit made of flexible plastic having a melting point between 20-50 degrees above the softening point of the bitumen is manufactured and the bitumen is cooled to a temperature close to the softening point of the bitumen being processed before filling. This leaves the bitumen in a state: it is already viscous but can still be pumped. In this state, the bitumen cools down quickly on contact with the cold plastic outer layer, which is a good heat conductor, which brings the bitumen to ambient temperature quickly; this allows a layer of bitumen immediately adjacent to the plastic film to have cooled. In this way, on the one hand, the disposable packaging unit is not damaged, and on the other hand, the bitumen forms a stable blank on the sides soon after it has been filled into the cold packaging material. Inside it, the bitumen is also slowly cooled down.

In road construction, bitumen qualities are generally used which have different softening points RaB, ranging between 45 ℃ and up to 60 ℃, such bitumens being generally stored in liquid form at temperatures of about 140-. Each quality of bitumen used is cooled to a precisely specified filling temperature, defined as the respective actual softening point of each bitumen, at which the bitumen, although already viscous, is still pumpable. Furthermore, there is a clear relationship between the melting point of the plastic material used as packaging and the processing temperature or softening point of the bitumen to be processed, and observing this relationship between the melting point of the plastic material and the temperature of the bitumen being pumped enables this desired "cooling" effect to be achieved, thereby protecting the packaging unit by means of the bitumen.

The packaging material is typically selected from plastics having a melting point of about 115 ℃ @and130 ℃, and which still have sufficient dimensional stability to accept the bitumen without being damaged at the filling temperature. In selecting a plastic, it is also considered that it will completely melt at normal processing temperatures (at about 140-.

The bitumen can be cooled by hot oil, which has the advantage that the temperature of the oil can be chosen such that it is exactly equal to the final bitumen temperature and stabilizes at this value during processing.

In summary, the method according to the invention has the advantage that a precisely defined temperature regime is present during filling, since the average temperature is constant within the pitch mass, with a tolerance within ± 2 ℃. Thus, for various bitumen qualities, the constancy of the filling temperature can be maintained throughout the filling process, which is generally continuous for several days; thus, on the one hand, by using a controlled low temperature, the risk of unfavourable melting of the packaging plastic is minimized and the safety of the work is achieved; on the other hand, the continuous filling is not interrupted by overcooling and thus solidification of the material. This enables the realization of economical automated packaging of large volumes (e.g. 50,000 and 100,000TPA) in large volume packaging units (about 1 m 3).

In a preferred embodiment of the method of implementation, a plate heat exchanger is provided for cooling the bitumen, the temperature difference between the cooling medium and the bitumen at the outlet of the heat exchanger being between 10 ℃ and 25 ℃, preferably between 15 ℃ and 20 ℃. The temperature across such a plate heat exchanger can be kept well at a constant temperature, which allows an efficient and fast temperature adaptation due to the large heat transfer area. For constant temperature, recent heat exchangers may be equipped with heating systems (e.g. electrical heating elements). This can be used as a precaution to prevent the pitch from becoming consolidated within the heat exchanger during short periods of plant downtime and, if consolidation occurs, to completely disassemble the plate heat exchanger before the pitch process can be resumed. Furthermore, a return tube may be provided on the filling head, which branch off near the filling valve and back to the storage tank. In this way, the bitumen continues to circulate even if the filling process is interrupted, so that solidification can be avoided. The filling head can be kept at the filling temperature by using heating elements, in particular electrical heating elements, so that the bitumen in the filling head always remains in a liquid state and does not solidify even when the filling process is stopped.

Drawings

Fig. 1 is an overall layout of a filling plant.

Detailed Description

Referring to FIG. 1, 1 is a storage tank in which the bitumen can be maintained at a storage temperature of about 140 ℃ and 160 ℃ by means of a heating device 2. A feed pump 3 pumps bitumen from the storage tank 1 into a bitumen pipe 5, and if no bitumen can be withdrawn, the bitumen is pumped back into the storage tank via a return pipe 4. Pitch pipe 5 passes to a heat exchanger 6 where pitch is cooled and then fed through a filling pipe 7 to a filling head 8. Bitumen is filled into a container 9 through a filling head 8 for transport.

Through a coolant circulation pipe 10, a coolant (in this case hot oil) is fed to the heat exchanger by a pump 11, the temperature of which is maintained at the desired value by a cooler 12, the temperature difference between the coolant and the bitumen at the outlet of the heat exchanger being between 10 ℃ and 25 ℃, preferably between 15 ℃ and 20 ℃.

13 represents an empty transport container before filling and 14 a full transport container after filling. The temperature throughout the plant was monitored by conventional thermocouples and controlled by a central computer. The thermocouples and control computer are not shown in the figure.

Filling is performed under electronic control through a filling valve on a filling scale. The pallets, in particular steel pallets, have special suspension means for receiving the lifting lugs of the disposable transport unit. The disposable transport unit is supported by the support means until the asphalt has been sufficiently stabilized that support is no longer required. The filled container 14 is then stopped in a roofed but well ventilated place, allowing the bitumen and its interior to cool to ambient temperature as well. Since bitumen is a good insulator, the cooling process may take 4-7 days for a vessel of about 1 cubic meter volume, depending on the ambient temperature.

The containers filled in this way can then be transported by conventional alternative means, such as by train, ship or truck without any thermostatic device, and after reaching the destination the bitumen can be melted together with the disposable packaging and further processed.

Claims (6)

1. A method of packaging bitumen, in particular road asphalt, in a large-volume disposable transport unit for transporting the bitumen in the cold state, characterized in that the disposable packaging unit is made of a flexible plastic material having a melting point of between 20 and 50 ℃ above the softening point of the bitumen, and that the bitumen is cooled to a temperature close to the softening point of the bitumen being processed before filling.

2. The method of claim 1 wherein the bitumen is cooled by heat exchange with hot oil.

3. A plant for carrying out the method according to claim 1 or 2, characterized in that a plate heat exchanger is provided for cooling the bitumen, wherein the temperature difference between the coolant and the bitumen at the outlet of the heat exchanger is 10-25 ℃, preferably 15-25 ℃.

4. Plant according to claim 3, characterized in that said plate heat exchangers are provided with heating means for maintaining a constant temperature, such as electric heating elements.

5. Plant according to claim 3 or 4, characterized in that a return pipe is provided on the filling head, which branch off close to the filling valve and lead back to the storage tank.

6. Plant according to claim 5, characterized in that the filling head is kept at a constant filling temperature by using heating elements, in particular electric heating elements.