Hydrocarbon Processing - October 2021 - 81

Valves, Pumps and
Turbomachinery
K. BRASHLER, Y. ALSHAHRANI and S. KHAN,
Saudi Aramco, Dhahran, Saudi Arabia
Pump recycle line optimization and energy savings
The objective of this article is to demonstrate the benefits
of optimizing the pumping system through pump recycle line
evaluations. Excessive use of pump recycle lines can be a key
indicator of pump oversizing-subsequently, hydraulic re-rating
of the pump can result in significant energy savings. The
focus of this article will be on detection and quantification of
pump recycle line leakage or passing conditions. These efforts
require very little effort and are considered low-hanging fruit,
resulting in significant savings potential. This article includes
a relevant case study related to recycle line leakage detection,
along with the resulting energy and maintenance cost savings.
Pump recycle line. Energy conservation efforts are becoming
an important area of focus for many industries that are
looking to improve operating efficiency and profit margins.
U.S. industry estimates indicate that approximately 20% or
more of industrial electricity consumption is used by pumping
systems; therefore, pumping systems are an ideal area of focus
to realize energy conservation opportunities. This article discusses
pumping system recycle or bypass system optimization.
There are two main purposes for a pump recycle line, and
these include:
1. Protecting the pump from low-flow conditions, where,
in this case, the recycle valve will open to maintain
pump flow above minimum continuous stable flow
2. Facilitating pump startup and shutdown
conditions, or hydraulic performance testing
utilizing the recycle or bypass line.
Under normal operating conditions, the pump recycle valve
should be closed. In some cases, the pump may operate with
a continuous or frequent opening of the recycle valve. These
conditions are a clear sign of pump oversizing, and they can
be addressed by considering a hydraulic re-rate of the pump to
better match actual system requirements. This article is concerned
with a less-obvious pumping system deficiency, which
is often overlooked, related to pump recycle valve leakage or
passing conditions.
Typically, pump recycle lines do not incorporate a flow element
(FE), which results in recycle valve passing conditions
going undetected. These conditions can go undetected until
the severity of the leakage either results in the inability to meet
process flow demands or results in high noise and vibration
levels. The objective of this article is to demonstrate the importance
of human intervention and to ensure proper function
of these systems. Valve passing conditions are often difficult
to identify without a careful survey of these systems to detect
passing valves. Typically, the flow element is upstream of the
recycle line take-off; therefore, there is no flow indication to
indicate any bypass control valve leakage.
Benefits. Very simple plant surveys can be conducted to evaluate
shut-off integrity of these recycle valves to identify passing
conditions and subsequent energy savings potential. At a
minimum, these surveys should target higher energy pumping
systems to realize the greatest benefit. Among the benefits of
identifying passing recycle valve conditions are the following:
* Significant energy savings potential
* Reduced noise and vibration, since continuous leakage
flow through recycle lines can induce vibration and noise
* Reduced maintenance costs, as passing valves
will result in the erosion of valve seats, leading to
reduced valve life and higher maintenance costs
* Excessive recycle valve leakage can result in the
inability to meet process flow demand; in extreme
cases, this may require operating an additional
pump in parallel to meet system demand.
Methods of detection. When implementing pump recycle
valve integrity surveys, there are three primary methodologies
to consider:
* Differential temperature
* Acoustic emission (AE) or ultrasound measurements
* Portable ultrasonic flow measurement.
Differential temperature. If there is a large difference between
process temperature and ambient temperature, then differential
temperature across the recycle valve can be a good indicator
of a passing condition. Different techniques can be utilized
to detect the temperature differential, including the following:
* The easiest method is by feel or touch;
however, care should be taken to avoid burns
from high piping skin temperatures
* Single-point thermal point temperature gun
* Thermal imaging cameras allow for a quick scan
of the valves to obtain the temperature profile.
For high-temperature applications, the recycle line may be
insulated; therefore, the temperature differential can usually be
measured in between the valve flanges. FIG. 1 shows an example
of a thermal image of a recycle valve without a passing condiHydrocarbon
Processing | OCTOBER 2021 81
Hydrocarbon Processing - October 2021

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