Injecting steam into a pyrolysis process may seem counter-intuitive. Although the presence of water in fuels is highly undesirable (reducing its calorific value), with a proper product separation system, it is possible to remove the water from the products, while reaping many benefits.

 
In terms of safety, the injection of steam near the beginning of the process will dilute the flammable vapors downstream and help prevent against fires in the case of a leak.

 
Another key role of steam is to prevent any unwanted secondary reactions (over-cracking). When steam is fed into the reactor at the same time as the feedstock, the water molecules mix with the produced hydrocarbon vapors. This provides the hydrocarbons with a protective barrier and increases their flow rate, making sure that the valuable products exit the reactor as soon as possible without any further degradation.

 
Lastly, steam plays an important role for the optimal function of various equipment:

• Injecting steam in the feedstock before it enters the reactor makes spraying much easier;
• Steam also improves cyclone performance, making the removal of solids from the vapors more effective;
• The presence of steam in the vapors improves the sorting of the vapors; and
• Steam also helps prevent fouling.

Although other gasses (such as nitrogen) would also do the trick for most of these applications, the low cost and high temperature of steam makes it the best option.