Burners. Before the 1990s, it was common to install multiple rows of wall burners
in olefins furnaces, with a typical firing rate of 1 MBtu/h per burner. Wall burners are
premix burners, with air coming in with the fuel. It was difficult to control excess air in a
furnace with over 144 burners at multiple levels, as shown in Figure 9.10a . Since the
mid-1990s, the wall burners have mostly been replaced by floor burners, with each floor
burner firing in excess of 10 MBtu/h capacity. For a big furnace, each firebox typically
has 24–32 floor burners, as shown in Figure 9.10b, leading to much easier control of excess air. In addition, many modern furnaces are fitted with a jack-shaft arrangement to
control excess air through the floor burners. This makes it easier to control the excess air
over a wide range of operating conditions, including decoke and turn down.