Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

Hydraulic Power Recovery Turbines 273
actor is still at high pressures, however, so that much of this energy can
be recovered if an HPRT is incorporated in the drive train.
• In the gas processing industry where crude gas is scrubbed by a high
pressure fluid medium such as potassium carbonate or amine in order
to remove unwanted components. For the purpose of regeneration and
recycling, the pressure has to be reduced; in other words, possible energy
recovery has been made available.
The pressure can be reduced by using pressure breakdown valves;
however, the differential pressure will be converted into thermal energy,
which is either wasted or very uneconomical to recover. A relatively efficient
method for pressure reduction and energy recovery is by the use of
HPRT's.
HPRT's will convert the differential pressure into rotational energy,
which can be utilized in helping to drive the centrifugal pump that returns
the regenerated medium to the absorber. Both major types, namely, the
reaction and impulse types, are used in the gas processing industry. Figure
14-19 shows the operational system using a reverse-running purnp
with fixed guide vanes. Since in a recycle system the recovered energy is
smaller than the required energy to drive the pump, an electric motor or
steam turbine on the other side of the pump is used to cover the energy
difference and to maintain as a second function a constant RPM of the
entire train.
The desired flow can be obtained either by changing speed of the assembly
(steam turbine drive) or by throttling the pump output (motor
drive), which means loss of energy. Unfortunately, the operating behavior
of the standard reverse-running pump with fixed guide vanes requires
a controllable throttling inlet valve for reduced capacity and a bypass line
for increased capacity. Both represent additional energy losses (see
Curve "A" and "B" in Figure 14-20).
Figure 14-21 illustrates the system using an HPRT with variable guide
vanes.
The losses of the system in Figure 14-19 are avoided. The function of
the inlet throttling valve (reduced capacity) and the bypass (increased capacity)
are served by the variable inlet guide vanes installed in the HPRT,
which satisfy the following purposes:
• Regulation of the capacity by varying the cross-section area of the
guide vanes depending on the level in the absorber.
• Feeding the medium to the runner in a definite direction.
• Complete or partial conversion of the differential pressure into kinetic
energy.