Monday, December 18, 2017

Routing of FCC main air blower vent air to bitumen blowing unit.Print


To encourage “Energy Conservation & Environment Protection” in the industrial sector PCRA has been continuously upgrading the energy conservation knowledge through energy audits and sharing the experience of energy efficiency improvement and achievement of industries. Based on these information developing case studies for dissemination of information to various industrial groups and organizations. The case study detailed below is one of the modification carried out by Kochi Refineries Ltd, Kochi which is being reproduced for the benefit of petroleum sector, industries dealing with bitumen process for any purpose.

 

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 :

 

Cost Analysis

Total investment Rs. 3 lac

Reduction in power 345 KW

Savings due to reduction in power intake Rs. 55 lac/Annum

Annual maintenance cost of old compressor Rs. 15 lac/Annum

Recurring saving Rs. 70 lac/Annum

 

Conclusion

Total investment for implementation of scheme was Rs. 3 lac and expected benefit is Rs. 70 lac/Annum. Overall benefits realized are

a) Reduction is operating cost of bitumen unit.
b) Reduction in power consumption by 345 KW, thereby savings in fuel consumption.
c) Reduction in environmental pollution due to reduction in emissions.