Unless the load (generator or pump etc.) can operate at high speeds, the associated turbine normally connects to the load via a reduction gearbox. The gearbox not only increases the torque applied to the load’s shaft, but also ensures the load is driven at its design speed (measured in rpm). From an efficiency perspective, a gearbox is an added weight, represents additional maintenance, additional financial expense (both initially and operationally), and it increases friction (which causes an overall reduction in machinery efficiency). If a gearbox is installed, it is not possible to operate the turbine without the gearbox, thus failure of either the gearbox or turbine will result in a total failure of the unit. For this reason, a gearbox represents an additional potential failure mode.

If using a steam turbine to drive/rotate a ship’s propeller, there needs to be some way of driving it astern (reverse direction). This is normally achieved with a separate turbine mounted on the back of the low pressure (LP) turbine; this setup causes efficiency losses due to condenser conditions during heavy or prolonged operation.

In many applications, steam turbines have been replaced by diesel engines. Diesel engines are favoured because they do not require the large supporting water and steam systems that steam turbines require. However, steam turbines have a high operating efficiency, and this can be further increased if they are utilised within a favourable industrial setting. For example:

1. Steam turbines are ideal for liquid natural gas (LNG) carries/ships because onboard boilers can burn any natural gas that does not remain in condensed form; this gas is known as ‘boil off’. The boilers provide the necessary steam for the steam turbine(s).
2. Combined cycle power plants reclaim waste heat from combustion turbines or from industrial processes that generate significant waste heat e.g. nitric acid plants. Waste heat is reclaimed using heat recovery steam generators (HRSGs). HRSGs provide the necessary steam for the steam turbine(s).
3. Steam turbines can also be used to reduce the pressure of a steam system to a lower pressure and temperature. This is useful if other parts of the industrial plant require service steam for heating and sterilisation purposes.
4. Large boiler feedwater pumps are also often steam driven, which reduces the electrical load of the power plant whilst increasing the overall plant efficiency.