to ethylene typically have a temperature of 800 950 u00b0 c the high grade heat retained in the product gases can be recovered and utilized as the heat sources for various process schemes downstream as well as upstream of the reactor the simplest scheme for utilizing the available heat is the one contrived for preheating the feeds of methane oxygen and ethane to the combustion pyrolysis and in situ hydrogenation zones to 600 u00b0 c by using an in line multiple stage heat exchanger as a feed pre heater as shown in fig3 preheating of the feeds to this temperature is necessary in order to achieve efficient combustion and pyrolysis reactions while it is still below the temperature of ignition which occurs at 645 u00b0 c a computer simulation result table 1 for a hypothetical ethylene plant capacity of 167 000 t y shows that the waste heat recoverable from the in situ hydrogenation could easily provide the required preheating energy without recycling and burning of hydrogen and co that are by products of the pyrolysis this simplifies the process while adding by product credit to the process economics part of the quench water is used for cooling down the hot pyrolysis gas to required in situ hydrogenation temperature while other part of water quench is introduced as low pressure steam using the available gas heat to moderate the reaction temperature of the in situ hydrogenation zone the use of thermal expansion combined with partial quench can.