Furnace Capacity. In the 1970s and 1980s, it was common to see an 800 million
lb/year capacity ethylene plant with 10–12 furnaces. Over the years, plant capacities have
grown and so have furnace capacities. Today, an ethylene plant capacity in excess of
3 billion lb/year is very common. Correspondingly, the furnace capacities have grown
with current capacities exceeding 400–450 million lb/year (200+kta) of ethylene per
furnace. The radiant coils of each furnace could be in two medium-length radiant boxes
with a common convection section or in one long radiant box. Today, it is common to see
a 3.0 billion lb/year (1500 kta) ethylene plant with only six to seven operating furnaces.
Figure 9.8 shows how furnace capacity has grown over time [4].