What Happens in a Reaction-Type Heater?

In the case of a visbreaker heater, thermal energy is applied to the heavy hydrocarbon feed like short residue, which breaks down the larger molecules into smaller molecules. This reaction results in the reduction of viscosity. The main objective here is to reduce feed viscosity.

In a thermal cracker heater, the feed is heated to a much higher temperature (480 490 C), which results in thermal cracking reaction (thermal conversion). This produces lighter products like cracked gas, naphtha, gas oil, and fuel oil. This is a time-temperature reaction.

In a coker heater, the feed is heated to around 500 C which results in severe thermal cracking and ultimately in coking. Note that in all the reaction-type heaters, the rate of reaction is a function of energy input (coil outlet temperature).

Visbreaker Heater Layout

In a visbreaking operation, feed has to be heated from 350 C to 450 C to 480 C to achieve reduction in viscosity of heavy residues. This is achieved by a heater as shown in figure E-2. Feed enters at 350 C and leaves at 450 480 C as shown by the arrows in figure E-2. Figure E-3 shows various major parts of a vertical heater used in process industries.

Figure E-2: Visbreaker...