Using steam at the lowest possible pressure for indirect heat exchange reduces the steam required and thus the fuel consumption. This is because latentheat increases with a decrease in steam pressure.
Most of the energy content of steam is the latent heat of evaporation. In indirect heating applications in a process, it is this latent heat of evaporation that is actually utilized. The condensate which leaves the plant equipment contains a portion of heat termed “sensible heat”.
Seen from the illustration below, latent heat of evaporation increases as steam pressure decreases i.e. more usable heat for the process and thus lower steam consumption translating into lower fuel bills.