Produce On-Specification Ethylene within 8-12 hours of Hydrocarbon Feed Introduction to the Cracking Furnaces with Minimal or No Flaring
Publication Date: 2012-May-04
The IP.com Prior Art Database
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PRODUCE ON-SPECIFICATION ETHYLENE WITHIN
8 -12 HOURS OF HYDROCARBON FEED INTRODUCTION TO THE CRACKING FURNACES WITH
MINIMAL OR NO FLARING.
Process Manager The M. W. Kellogg Co.
C. J. Lee
Chinese Petroleum Corporation
The Chinese Petroleum Corporation, commissioned its No.5 Naphtha Cracking Plant at the Kaohsiung Refinery, in February 1994. The plant has a nominal capacity of 400,000 MTPA and utilizes M. W. Kellogg's Millisecond technology. The initial startup of this facility was accomplished with virtually no flaring and on- specification ethylene was produced within 17 hours of hydrocarbon feed introduction to the cracking furnaces which exceeded CPC's past experiences and expectations. Subsequent startups have produced on-specification ethylene within 8-10 hours of feed introduction to the cracking furnaces.
Traditionally, the startup of an ethylene plant is associated with flaring for an extended period because the Demethanizer Feed System and the cold train must be chilled with the cracked gas from the Pyrolysis Furnaces before the operation of the Deethanizer can be lined out. Furthermore, the Deethanizer and downstream Acetylene Removal Unit must be operating satisfactorily before on- specification ethylene can be produced.
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The chilling process for the cold train generally takes 12-24 hours in an established plant. In a new plant, where the equipment has not yet been tested at operating pressures and temperatures, this process could take longer if any leaks are detected in the system as the temperature is brought to operating levels. These leaks must be fixed before forward feed flow can be established. Each time a leak is detected, the system must be depressured, the leaks fixed and the chilling restarted, adding to the total flaring time.
The flaring time can be further extended if high pressure steam is not available from auxiliary sources to start the major compressor turbine drivers. In such cases, several cracking furnaces must be brought online to produce sufficient high pressure steam to start the major compressor turbine drivers.
Figure-I shows the duration and flaring rates during the startup of a typical ethylene plant.
1 Six Furnaceson line I
Four Furnaces on line
4 8 12 16 20 24
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Generally, the startup of an ethylene plant with a front-end Demethanizer entails the following major steps:
0 Auxiliary boilers are started or availability of imported steam is confirmed before start up of the refrigeration compressors.
0 Propylene Refrigeration Compressor (PRC) is started and its operation stabilized at minimum governer speed. Propylene refrigerant is required to condense the discharge vapors of the Ethylene Refrigerant Compressor (ERC), therefore its operation must be stable before the ERC can be commissioned. The speed control is pu...