Page 391 - Compression Machinery for Oil and Gas

Drivers Chapter 7 369

Hot Gas Expanders
The idea of converting the energy in combustion exhaust gas to power has been
in practice for a century. Energy costs, environmental regulations, emissions
control, and carbon management have driven interests in employing hot gas
expanders in modern plants.
There are fundamental challenges to design a reliable expander operation:
the extreme high temperatures, chemical corrosion, and kinetic erosion caused
by the hot, particulate laden flue gas caused the rapid erosion of critical rotating
and stationary components such as the rotor disk, blades, and stator vanes. Dras-
tic thermal differentials also imposed substantial stress on the structural ele-
ments of the machine.
Corrosion is another critical consideration in expander operations. Corro-
sion is related to the high temperatures at which expanders operate. The effects
of creep and gaseous corrosion increase at elevated temperatures. The nature of
the corrosive attack is primarily influenced by the feedstock and the additives
injected during the cracking process. If not addressed, hot corrosion can lead to
rotor blade or disc failure (Fig. 7.54).

Exhaust
casing
Expansion joint

Inlet casing

Gas
inlet
Shaft

Bearing support
Trunnion support
pedestal

FIG. 7.54 Basic components of a hot gas expander (Hydrocarbon Engineering, August 2013).