Introduction
Bitumen blowing unit consists of a bitumen converter in which
Vacuum Residue from High Sulphur Persion Gulf Crudes is polymerized
using air, to form bitumen. The reaction is essentialy a condensation
polymerization reaction. A dedicated two stage air compressor
was used for blowing air. Bitumen produced is further cooled
to run down temperature of 80 – 900C in a heat exchanger
circuit prior to routing it to storage.
Background
Air for Fluidized Catalytic Cracking Unit regenrator is supplied
by the Main Air Blower (MAB) unit. Of late the air requirement
in the regenrator has increased due to
a) Higher conversion and
b) Increased feed thru put of the unit.
To meet the increased demand and to limit the regenerator
superficial velocity for higher run length of the FCC unit
at higher flow rate, the Main Air Blower (MAB) is operated
at a higher discharge pressure.
The operating pressure of the regenerator was increased from
2.65 kg/cm2. to 3.05 kg/cm2 to limit the superficial velocity
below 1m/sec. On doing so the compressor operating condition
was near to the surge limit curve. The suction flow is kept
at a higher value than required in the FCC unit regenerator
and the excess flow of 5-6 T/Hr is vented to atmosphere. The
vent to the atmosphere is through snort valve and a fine control
valve.
Modification
The scheme has been conceived and implemented for energy
saving and reliable operation of bitumen unit. The excess
air (difference between the suction flow of MAB and the air
flow to FCCU catalyst regenrator) is vented to atmosphere
through the snort control valve for stable operation of compressor
since the operation point of the compressor is near the surge
regime.
In the scheme, part of this excess air is routed to Bitumen
Unit to replace the air supply form dedicated compressor and
hence stoppage of compressor. A new line was connected from
snort control line to the air supply line to Biutmen Unit
through a flow transmitter and control valve as per the schematic
diagram below : |
