The new vertical boiler building from around 1960 is to the left and the older from 1949 is to the right. A fair guess is that the new one was built to be optimized for oil firing whereas the old one was designed only with coal firing in mind.

Where coal was still in short supply after WWII, the market was flooded with low-cost oil in the early 1950s. Bunker oil then became an economical alternative for industrial boilers and together with the lower labor requirements and higher energy density, the demand for coal fell drastically during the late 1950s.