METHOD AND APPARATUS FOR FOAMING OF BITUMEN

Abstract: Liquid bitumen at a temperature of 120 - 160<o>C is mixed with 1-3% by weight of water in a mixing device (8) at a pressure which is higher than the saturation pressure of water vapor at the temperature of the hot bitumen. From the mixing device the mixture is allowed to expand through a valve (10) such as a throttle valve, the resulting evaporation of the water in the mixture causing the desired foaming of the bitumen.

Description: METHOD AND APPARATUS FOR FOAMING OF BITUMEN The invention relates to a method and an apparatus for foaming of bitumen to be used e.g. as a coating or film on road materials such as gravel, crushed rock and the like. To this end the bitumen is heated to a temperature at which it t exists in a liquid state. The purpose of the foaming is to increase the volume of the bitumen and thus provide a thinner coating and a better utilization of the bitumen material than would be possible by spraying the liquid bitumen without any kind of foaming. Conventionally foaming of bitumen is carried out by flowing the hot liquid bitumen, which normally has a tempera¬ ture of 120 - 160 C, through a pipe, and permitting it to meet a water flow immediately before the pipe outlet, the instantane¬ ous evaporation of the water which then occurs causing foaming of the bitumen as it discharges from the pipe to be mixed with the road material to be coated. Generally a certain amount of amine is added to the bitumen to enhance its adhesion. Amines are unstable at the temperatures to which the bitumen is heated, and the amines therefore can not be added to the bitumen until immediately before discharging the bitumen, in order to avoid substantial deterioration of the adhesion effect. Also, from the same reason, only relatively limited amounts of bitumen at a time can be mixed with amines. The object of the invention is to provide a more effective method for foaming of bitumen than the conventional method, and an apparatus to carry out the new method. This object is achieved according to the invention by mixing water with hot liquid bitumen at a pressure which is higher than the saturation pressure of water vapor (steam) at the temperature of the bitumen, and then allowing the mixture to expand at a pressure which is lower than said saturation pressure. According to a preferred embodiment amines are added to \ the water before the latter is mixed with the bitumen. The apparatus according to the invention comprises a container for hot liquid bitumen and a container for water to be mixed with the liquid bitumen and a mixing device adapted to mix the bitumen and water at a pressure which is higher than the saturation pressure of water vapor at the temperature of the bitumen, ' metering pumps adapted to rise the pressure of the bitumen and water to the desired value, and a valve through which the bitumen/water mixture will expand under reduced pressure while developing water vapor. The invention is more fully explained below with reference to the drawing which diagrammatically shows an apparatus for foaming- of bitumen according to the invention. Iϊr the drawing 1, 2 and 3 refer to containers or reser¬ voirs for bitumen, water and aminerespectively. The bitumen in reservoir 1 is heated to a temperature between 120 - 160 C and therefore is present in a relatively easy-flowing liquid state. Bitumen and water are pumped via metering pumps 4 and 5 respectively and non-return valves 6 and 7 respectively into a closed chamber of a mixing device 8 provided with stirring means, at a pressure which always is higher than the saturation pressure for water vapor at the above mentioned temperature of the bitumen. Owing to the high pressure prevailing in the mixing device 8 the water is not boiling while being effectively mixed with the bitumen. The amount of water added to the bitumen will normally be from 1 to 3 % by weight as is conventional, depen¬ ding on the desired degree of foaming. However, the water content may, if desired, of course be higher, favourable re¬ sults having been reached with a water content as high as 30 %. According to a preferred feature of the invention amine is added to the water before the water pump 5 via a metering pump 9. The aminewill be of a kind that is conventionally used for such purposes, for example diamine, and in usual quantities, for example 0,2 - 1,5 % by weight of the amount of bitumen. From the mixing device 8 the mixture of bitumen, water and amine is lead to an adjustable valve 10, preferably a throttle valve, through which the mixture is allowed to expand at a pressure lower than the above defined saturation pressure, into an expansion chamber in the form of a hollow spraying beam 11 provided with a plurality of outlet nozzles 12. Under the pressure drop on the low pressure side of the valve 10 the water in the hot bitumen mixture will instantly start boiling and thus cause foaming of the bitumen when flowing into the expansion chamber and discharging through the nozzles 12. As mixing device 8 any convenient conventional apparatus may be used. An apparatus which has been found particularly useful for this purpose is an ultrasonic ho ogenization or emulsification unit, e.g. of the type "Reson-Heat" as disclosed in US patent 4 302 112 and delievered in various standard capacities from Reson Systems ApS, Hillerød, Denmark. The pressure in the mixing device 8 is adjusted by means of the valve 10 depending on the temperature of the bitumen, such that the pressure at any time is sufficiently high to prevent boiling of the water on the high pressure side of the 2 valve 10. Normally a pressure of about 10 kp/cm will be used, corresponding to a water boiling point of about 180 C. The pressure on the low pressure side of the valve 10 2 will be 1 - 3 kp/cm above atmospheric pressure, sufficient to force the bitumen foam out through the nozzles 12 at a desired rate. The nozzles 12 may be ordinary spraying nozzles when the apparatus according to the invention has a modest capacity, for example up to 10 litre bitumen pr. minute, while for larger capacities they may advantageously be slit nozzles with adjustable nozzle apertures.

Claims: WHAT WE CLAIM IS: 1. A method for foaming of hot liquid bitumen, in which the foaming is caused by evaporation of water in contact with the hot liquid bitumen, c h a r a c t e r i z e d by mixing the water with the hot liquid bitumen at a pressure which is higher than the satura¬ tion pressure of water vapor at the temperature of the bitumen, and then allowing the mixture to expand at a pressure lower than, said saturation pressure. 2.. A method according to claim 1, in which the bitumen has a" temperature of 120 - 160 C, c h a r a c t e r i z e d by mixing the bitumen and water 2 at a pressure of about 10 kp/cm . 3. A method according to claims 1 or 2, c h a r a c t e r i z e d by adding amine to the water before the latter is mixed with the bitumen. 4. An apparatus for carrying out the method according to claim 1, for foaming of hot liquid bitumen by adding water thereto, comprising a container (1) for bitumen and a container (2) for water to be mixed with the hot liquid bitumen, c h a r a c t e r i z e d by said apparatus further compris¬ ing a mixing device (8) adapted to mix the bitumen and water at a pressure which is higher than the saturation pressure of water vapor at the temperature of the hot bitumen, metering pumps (4, 5) adapted to rise the pressure of the bitumen and water to the desired value, and a valve (10) through which the bitumen/water mixture can expand at a reduced pressure while developing water vapor. 5. An apparatus according to claim 4, c h a r a c t e r i z e d in that said valve (10) is a throttle valve. 6. An apparatus according to claim 4 or 5, c h a r a c t e r i z e d in that said mixing device (8) is an ultrasonic homogenisation or emulsification unit, e.g. of the type "Reson-Heat" . 7. An apparatus according to one of the preceding claims 4 - 6, c h a r a c t e r i z e d by a foam spraying device (11) connected to the outlet (low pressure) side of the valve (10) . 8. An appataus according to claim 7, c h a r a c t e r i z e d in that said foam spraying device (11) is a hollow spraying beam provided with a plurality of outlet nozzles (12) . 9. An apparatus according to claim 8, c h a r a c t e r i z e d in that said outlet nozzles (12) are formed with an adjustable slit aperture. 10. An apparatus according to one of claims 4 - 8, comprising a container (3) for ' amineto be added to the bitumen to be foamed, c h a r a c t e r i z e d by a metering pump (9) for adding the amine to the water before the water pump

Inventors: AUNE EINAR, WENTZEL JARLE, AUNE, EINAR, WENTZEL, JARLE
Applicants: NODEST VEI AS, NODEST VEI A/S
Application year: 1986
Main classification: C10C3
IPC codes: C08J9, C10C3, E01C19