Bitumen Blowing

Industrial grades of bitumen with industrial uses, such as road paving, waterproofing, insulation, are manufactured from heavy crudes, either by vacuum reduction alone or air blowing of vacuum resids. However, the vacuum resids from all crudes are not suitable for making bitumen.

Vacuum distillation of some crudes under specified conditions may yield resid that meets the specifications of a bitumen for certain paving grades, but for low penetration and higher softening point grades, air blowing the vacuum resid under specified operating conditions is required. Pilot plant tests are generally necessary to establish whether a given crude can yield good-quality bitumen and determine the optimum operating conditions for a given bitumen grade. Subjecting the bitumen to high temperatures during processing can affect the ductility of the product and care is taken not to subject asphalt to more than approximately 750°F.

In the air blowing operation, the aromatic and polar compounds in the feed are condensed to form higher-molecular-weight chemical species. The process increases the asphaltene level, while the level of aromatics and polar aromatics are reduced. The change is also indicated by a significant increase in the average molecular weight of the blown asphalt. The saturates in the feed, consisting mainly of cyclosaturates, are not affected by the air blowing step.

When certain additives, such as ferric chloride, are added to the air blowing step, the cyclosaturates are dehydrogenated. There is increase in the level of aromatics, which is a major contributor to higher penetration values. These aromatics, in turn, are converted to asphaltenes.

It has been shown that the weight percentage of material with molecular weight 490 is related to the softening point of the asphalt, while the weight percent of material at molecular weight 2160 is related to penetration. The relationship between the softening point and lower-molecular-weight material (490) contained in asphalt and also between high molecular weight (2160) and penetration has been presented by Dark.5 A balance of material at these two molecular weights is required to obtain air blown asphalts with desired final characteristics. Composition of asphalts, however, is also important. The ratio of saturates to asphaltenes determines the weathering characteristics of asphalts. Good-quality asphalts generally have a saturates/asphaltene ratio of between 2 and 3.

ASPHALT CONVERTER

WASTE GASES

WASTE GASES

Asphalt Blowing Unit Process
Figure 6-7. Bitumen blowing unit.

THE BITUMEN BLOWING PROCESS

Vacuum resid from the vacuum distillation unit is charged to asphalt converters V-101 and V-102 through steam-jacketed gear pump P-101 and charge heater H-101 (see Figure 6-7). The temperature of the feed to asphalt converters is controlled at 390-410°F. Compressed air at 100 psig mixed with HP steam is bubbled at a controlled rate through the vacuum resid using an internal sparger, causing exothermic reactions in the asphalt converter. The temperature of the bed is controlled by the air/ steam injection rate in the range of 500-520°F. Approximately 2% of the charge is carried overhead as fumes and vapor. The waste gases pass through knockout drum V-104, where any condensed liquid separates out and is sent to slop. The vapors from V-104 are scrubbed with water in absorber V-105 and sent to refinery flare.

Finished blown asphalt from the asphalt converter is pumped through E-101, where its temperature is brought down to approximately 250°F by heat exchange with a closed-circuit diesel stream. The diesel stream, in turn, is cooled in an air cooled exchanger. The asphalt stream at 250°F is sent to storage through steam-jacketed pump P-102.

The typical operating conditions for a bitumen blowing unit processing a 24 API Middle Eastern crude are listed in Table 6-15. The properties of the feed and product from the bitumen blowing unit are shown in Table 6-16. The overall yields from the unit and utility consumption are listed in Tables 6-17 and 6-18. The product specifications for various end uses and test methods used are shown in Tables 6-19 and 6-20.

OPERATING CONDITIONS

Table 6-15

Bitumen Blowing Unit Operating Conditions

OPERATING VARIABLE

UNITS

VACUUM RESID (FEED) TEMPERATURE BED TEMPERATURE CONVERTER PRESSURE AIR BLOWING RATE*

390-410 500-520 95 166

for 60/70 pen. asphalt.

Table 6-16 Properties of Feed and Products

PROPERTY FEED PRODUCT

PENETRATION 220 60-70

SPECIFIC GRAVITY 1.016 1.028 KINEMATIC VISCOSITY

210, Cst 800-1100 6400

250, Cst 1400

300, Cst 335

400, Cst 35

520, Cst 5

Table 6-17 Bitumen Blowing Unit Yields

STREAM WT FRACTION

FEED

VACUUM RESID 1.0000

TOTAL FEED 1.0000

PRODUCTS

BITUMEN, 60/70 PEN. 0.9800

LOSSES 0.0200

TOTAL PRODUCT 1.0000

Table 6-18

Bitumen Blowing Unit Utility Consumption (per Ton Feed)

CONSUMPTION

Table 6-18

Bitumen Blowing Unit Utility Consumption (per Ton Feed)

UTILITY

UNITS

60/70 PEN.

40/50 PEN.

ELECTRICITY

kWhr

7

10

FUEL

mmBtu

0.04

0.06

STEAM

mmBtu

0.09

0.09

AIR

scft

1500

2300

DISTILLED WATER

MIG*

0.11

0.11

COOLING WATER

MIG*

1.3

1.3

*MIG = 1000 IMPERIAL GALLONS.

*MIG = 1000 IMPERIAL GALLONS.

Table 6-19

Properties of Penetration Grade Bitumens

PROPERTY

TEST METHOD

GRADE

15 PEN. 25 PEN. 35 PEN. 40 PEN. 50 PEN. 70 PEN. 100 PEN. 200 PEN. 300 PEN. 450 PEN.

PENETRATION AT 25'C IP 49

SOFTENING POINT, MEM. IP 58

MAX.

LOSS ON HEATING FOR IP 45

SOLUBILITY IN TRICHLORO IP 47

ETHYLENE % BY MASS, MIN. PERMITTIVITY AT 25° C AND 1592Hz, MIN.

10-20 20-30 63

76 69

99.5

99.5

28-42 57 64

99.5 2.630

30-50 52 68

40-60 58 58

60-80 47 54

80-120 170-230 255-345 385-515

44 51

99.5

99.5

33 39

99.5

30 34

99.5

Table 6-20 Properties of Cutback Bitumen

GRADE

PROPERTY

TEST METHOD

50 SEC.

100 SEC.

200 SEC.

VISCOSITY (STV)* AT 40°C, 10 mm CUP

IP 72

40-60

80-120

160-240

DISTILLATION

(A) DISTILLATE AT 225°C (vol%, MAX.)

IP 27

1

1

1

DISTILLATE AT 360° C (vol%, MAX.)

8-14

6-12

4-10

(B) PENETRATION AT 25 °C OF RESIDUE

ASTM D5-73

100-350

100-350

100-350

FROM DISTILLATION TO 360°C

IP 49

SOLUBILITY IN TRICHLORO ETHYLENE, % MASS, MIN.

IP 47

99.5

99.5

99.5

* STANDARD TAR VISCOMETER

* STANDARD TAR VISCOMETER

+1 -1

Responses

  • larry
    What is bitumen blowing?
    8 years ago
  • trahand headstrong
    How does bitumen blowing vessel operate?
    7 years ago
  • rosemarie henry
    How to obtain bitumen?
    7 years ago
  • lassi niskavaara
    What is bitumen blowing unit?
    7 years ago
  • carla
    What is the process for asphalt blowing?
    6 years ago

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