Control of a cracking furnace

A method for operating a cracking furnace comprising the steps of:

• combining a feed stream provided to said cracking furnace with a diluent fluid;
• supplying fuel to said cracking furnace, the combustion of said fuel supplying heat to said cracking furnace;
• removing a gaseous mixture, containing the cracked components of said feed stream and containing said diluent fluid, from said cracking furnace;
• establishing a first signal representative of a prediction of the heat required by said cracking furnace to maintain a desired percent conversion;
• establishing a second signal representative of said desired percent conversion;
• establishing a third signal representative of the actual percent conversion;
• comparing said second signal and said third signal and establishing a fourth signal responsive to the difference between said second signal and said third signal;
• combining said first signal and said fourth signal to establish a fifth signal representative of a corrected prediction of the heat required by said cracking furnace to maintain said desired percent conversion;
• establishing a sixth signal representative of the heating value of said fuel;
• establishing a seventh signal in response to said fifth signal and said sixth signal, said seventh signal being representative of the flow rate of said fuel required to supply the heat required by said cracking furnace to maintain said desired percent conversion;
• establishing an eighth signal representative of the actual flow rate of said fuel;
• comparing said seventh signal and said eighth signal and establishing a ninth signal responsive to the difference between said seventh signal and said eighth signal;
• and
• manipulating the flow rate of said fuel in response to said ninth signal.

Apparatus comprising:

• a cracking furnace means;
• means for supplying a feed stream to said cracking furnace means;
• means for supplying a diluent fluid to said cracking furnace means, said diluent fluid being combined with said feed stream;
• means for supplying a fuel to said cracking furnace means, the combustion of said fuel supplying heat to said cracking furnace means;
• means for removing a gaseous mixture, containing the cracked components of said feed stream and containing said diluent fluid, from said cracking furnace means;
• means for establishing a first signal representative of the flow rate of said diluent fluid required to maintain a desired ratio of said diluent fluid to said feed stream;
• means for establishing a second signal representative of the flow rate of said diluent fluid required to maintain a desired total flow to said cracking furnace means to prevent damage to said cracking furnace means;
• and
• means for controlling the flow rate of said diluent fluid in response to the higher of said first and said second signals.

A method for

• controlling the flow rate of a diluent fluid which is combined with a feed stream before said feed stream is cracked in a cracking furnace comprising the steps of:
• establishing a first signal representative of the flow rate of said diluent fluid required to maintain a desired ratio of said diluent fluid to said feed;
• establishing a second signal representative of the flow rate of said diluent fluid required to maintain a desired total flow to said cracking furnace to prevent damage to said cracking furnace;
• and
• controlling the flow rate of said diluent fluid in response to the higher of said first and said second signals.