Delayed coker furnace tubes

There is little danger, in injecting a controlled amount of water into a furnace inlet, when using a properly designed metering pump. Such pumps typically have a capacity of 1 to 10 GPM and provide a set flow, regardless of the discharge pressure. The injected water flashes immediately to steam inside the furnace tubes. Vfe have retrofitted several vacuum and delayed coker heaters with condensate injection systems, with no adverse downstream effects. Water from the hot well of a vacuum ejector system is our normal source of condensate for this environmentally friendly modification. 

After the reactions have occurred in the catalytic crackers, cokers, and alkylation plants, the effluents are separated by fractionation to obtain the various products desired. The materials for the fractionation equipment are selected using basically the same criteria as those used for crude units, as discussed in Chapter One [i.e., carbon steel below 550 to 600°F (288 to 315°C) and 5Cr-V6Mo piping and 12Cr clad vessels above]. However, there are some slight differences from crude units. An example is furnace tubes in delayed cokers, which are usually 9Cr-t Mo (because of the high-fluid temperatures) rather than 5Cr-V Mo. 

Visbreaking is a relatively mild thermal (noncatalytic) cracking process that is used to reduce the viscosity of residua. A visbreaker reactor may be similar to a delayed coker with a furnace tube followed by a soaker drum. However, the drum is much smaller in volume to limit the residence time with the entire liquid product flowing overhead. Alternatively, the entire visbreaker may be a long tube coiled within a furnace. Coke formation can occur and the coke accumulates on visbreaker walls periodic decoking (cleaning) is necessary. 

Flue gas temperature is usually 650-820 °C leaving the radiant section and 260-425 °C leaving the convection section. To minimize the thermal cracking inside tubes in a fired furnace, use 600 kg/s.m for lube oils, crude and vacuum desulfurizer and 1200 kg/s.m for delayed coker and visbreaker. Keep tube temperatures < 760 °C. Specify the highest fuel gas pressure that is consistently available. 

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See also in sourсe #XX -- [ ]

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