Motorized Turbochargers - Much More Than Energy Recovery White Paper - FEDCO
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White Paper
Motorized Turbochargers
Much More Than Energy Recovery
MK-WP-09
Fluid Equipment Development Company, LLC www.fedco-usa.com
Offices in USA, Singapore and Dubai sales@fedco-usa.com
Reverse Osmosis Pumps and ERDs The Right Choice for Off-shore Platforms and Marine Service
Executive Summary focus on motorized turbocharged ERDs - the Hydraulic
Energy Management Integration or HEMI.
Energy Recovery Devices (ERDs) are widely used in
seawater reverse osmosis (SWRO) systems with turbo-
Flow Control and RO Systems
chargers and rotary ceramic isobaric chambers or CICs
dominating the market. The White Paper ERD Efficiency To better understand the HEMI, consider that the per-
– What Systems Builders and Consultants Need to Know formance of a given membrane array depends on feed
explores in detail ERD potential to reduce SWRO energy salinity, feed temperature, flux rates and fouling levels.
consumption in realistic field conditions with a focus Feed flow and pressure are adjusted to accommodate
on mega-scale systems. The results show that both changing membrane performance through one of these
types of ERDs are approximately equal in the potential means:
to reduce net energy consumption. Feed Control Valve - The simplest means but requires
a high-pressure pump (HPP) and motor sized for the
This paper will focus on the motorized turbocharger ERD highest-pressure membrane condition (a combination
or HEMI (Hydraulic Energy Management Integration) for of fouling, high salinity and low feed temperature).
SWRO applications. The HEMI can often have the lowest The control valve throttles excess pressure (and wastes
SEC value any commercially available ERD. However, its energy) at all other duty conditions. Motor control is
most unique and advantageous features are the ability provided by a direct online (DOL) starter. Please refer to
to provide complete control of feed flow and pressure Figure 1.
and brine flow and pressure. In short, the HEMI pro-
vides RO membrane control as well as effective energy Variable Frequency Drive on the HPP – A VFD controls
recovery in a compact and relatively low-cost package. HPP speed to regulate membrane pressure without
wasteful throttling. Please refer to Figure 2.
The HEMI reduces CAPEX by eliminating the multiple mega-
watt variable frequency drive (VFD) on the high-pres- Jockey Pump with VFD – To mitigate the very high
sure pump (HPP) and reducing the size and cost of the VFD CAPEX on the HPP, a smaller “jockey” pump may be
HPP, motor and power supply system. These savings can placed in series with the HPP. Using a relatively small
pay for the cost of the entire HEMI installation in many VFD, the jockey pump provides variable pressure to
cases. A low net CAPEX and superior energy savings meet membrane requirements with the bulk of the total
means a significant reduction in the cost of permeate. pressurization from an HPP operating at constant speed
and ∆P using a low cost DOL starter. A feed throttle
Reverse osmosis (RO) systems reject a portion of the valve may still be required to better regulate pressure
high pressure (HP) feed as HP brine. Energy Recovery during systems startup and shutdown.
Devices (ERDs) recover brine hydraulic energy there-
by reducing net energy consumption. This paper will
Figure 1 RO with Feed Control Valve Figure 2 RO with Variable Frequency Figure 3 RO with Jockey Pump and VFD
Drive on HPP
Fluid Equipment Development Company, LLC www.fedco-usa.com
Offices in USA, Singapore and Dubai sales@fedco-usa.com
Motorized Turbochargers — Much More Than Energy Recovery
What ERDs Do Turbos come in all sizes – from 8 m3/h to the largest
RO ERD in the world rated to over 3,000 m3/h (shown
ERDs transfer hydraulic energy from the brine stream
in Figure 7).
to the feed stream. Some ERDs are fully integrated in a
single unit such as turbochargers. Others ERDs such as
Feedback Effect
isobaric chambers and Pelton turbines consist of multi-
ple interconnected components. Turbochargers transfer brine hydraulic energy to pres-
sure energy in the feed. When more brine energy is
ERD performance is explored in the White Paper ERD available then there is more boost in the feed.
Efficiency – What System Builders and Consultants Need
to Know. Why this is good – if feed TDS increases or feed tem-
perature decreases, recovery decreases. However, the
What Turbochargers Do resulting higher brine flow and pressure generates a
Turbos convert brine hydraulic energy to mechanical greater pressure boost in the feed thereby minimizing
energy and then back to hydraulic energy in the feed the change in recovery. The converse is true as well.
stream within a single casing. The separation of flu-
id energy transfers permits the Turbo to handle brine In some cases, hydraulic feedback eliminates the need
and feed flows that differ in pressures and flow rates. for all flow control devices such as feed control valves
The Turbo boosts feed pressure between the HPP and or VFDs on the HPP. To be clear, recovery will vary but
membranes per Figure 4. Figure 5 shows the HEMI (mo- less so than without a Turbo ERD. For applications with
torized turbo). The versality of the Turbo is illustrated relatively stable salinity and temperature, the Turbo
in Figure 6 where one Turbo provides pressure boosting may provide sufficient recovery control.
between membrane stages and a HEMI recovers remain-
ing brine energy and provides 1st stage flow control. Adding a Motor Changes Everything
This particular arrangement, the Multi Stage Multi Turbo Recalling that the Turbo converts brine hydraulic energy
(MSMT), allows 60% recovery in seawater applications into mechanical energy (RPM and torque), mechanical
and is the subject of the White Paper MSMT – A Major energy can be easily added by attaching a motor to the
Process Improvement for SWRO. Turbo shaft. To motorize the Turbo involves extending
the Turbo shaft through the brine discharge coupled to
the motor. As will be explained later, the HEMI:
• Eliminates the feed control valve and VFD on the HPP
• Provides control of feed flow and pressure
• Reduces the size of HPP and motor
Figure 4 Turbo as Feed Pressure Figure 5 Motorized Turbo as
• Provides control of brine flow
Booster feed presssure booster
• Provides highly efficient brine energy recovery.
Thus, the HEMI provides all control functionality
required for operation and brine energy recovery of the
membrane array.
Figure 6 Turbo as feed and as interstage pressure booster,
MSMT arrangement
Fluid Equipment Development Company, LLC www.fedco-usa.com
Offices in USA, Singapore and Dubai sales@fedco-usa.com
Motorized Turbochargers — Much More Than Energy Recovery
Brackish Water Applications Figure 8 shows a smaller HEMI installation at a BWRO
facility in the United States.
Brackish water RO systems (BWRO) use brine stag-
ing with interstage pressure boosting to improve flux
Seawater RO
balance between stages. Flux balance minimizes fouling
and as well as reduces transmembrane pressure resulting Turbochargers are also used for interstage boosting in
in pumping energy savings. SWRO systems. Figure 9 shows a large scale turbocharger
in a desal plant with total capacity 1,282,000 m3/day.
Turbochargers are well-suited for interstage boosting In SWRO applications, HEMI advantages include superior
as the boost function is combined with brine energy SEC, reduced CAPEX, simplified operation and increased
recovery and brine flow control. The resulting package reliability.
provides a significant CAPEX and OPEX savings com-
pared with separate components. Several hundred BWRO
installations use interstage Turbos.
The HEMI provides a broader operating range than
Turbos as the boost pressure can be greater than the
available brine energy would otherwise permit.
Figure 7 shows a BWRO HEMI (1 of 10) at a 228,000
m3/day water recycle facility in Singapore. The HEMI
provides pressure boosting between the first and second
stages as well as brine energy recovery. The motor al-
lows the optimal boost amount regardless of the avail-
able brine energy. These unit have been operating since
2012 without downtime or maintenance.
Figure 9 Large Turbo in SWRO as interstage pressure booster
Motor
Superior SEC – Based on realistic field conditions, the
HEMI matches or is superior to isobaric performance
as discussed in ERD Efficiency – What Every OEM and
Consultant should Know.
Turbine
The key takeaways are that, in mega-scale systems, the
HEMI has the same energy savings potential (expressed
as Specific Energy Consumption or SEC) as isobaric
chambers, with turbochargers also competitive. More-
over, the CAPEX and OPEX advantages strongly favor
Pump Module both the Turbo and HEMI.
The SWRO HEMI illustrated in Figure 10 is fully cus-
tomized for each installation to achieve best efficiency
point operation at the field duty point operating con-
ditions. This involves an extensive computational fluid
Figure 7 Large capacity Figure 8 Small capacity
motorized Turbo in Singapore. motorized Turbo. dynamics analysis (CFD) and advanced computer-aided
Fluid Equipment Development Company, LLC www.fedco-usa.com
Offices in USA, Singapore and Dubai sales@fedco-usa.com
Motorized Turbochargers — Much More Than Energy Recovery
manufacturing (CAM) with 5-axis milling machines to provides programmable HPP speed control to allow grad-
produce optimized flow path components. ual pressure ramps. These units are more compact than
VFDs, more robust and with a cost from 25% to 33% of
Motor Brine out
a VFD of equivalent rating. Once up to speed, the sol-
Feed out
id-state control is electrically by-passed thus providing
Brine in
lossless power flow to the HPP motor free of electrical
harmonics typical of VFDs.
The HEMI motor requires a VFD of about 10-15% of the
Feed in rating of the HPP motor. This VFD is low voltage and
may be located adjacent to the HEMI or in a separate
enclosure. Figure 11 compares a medium voltage VFD
otherwise needed for the HPP and a low voltage VFD
Nozzle actuator suitable for the HEMI.
Figure 10 HP-HEMI or SWRO motorized turbocharger
Per Table 1, the HEMI has the lowest SEC (largest en-
ergy savings) yet also has the lowest published effi-
ciency. Published efficiency claims, when no industry
standard for “ERD efficiency” exists, are worthless and
should not be used in ERD selection.
Figure 11 Medium voltage VFD compared to low voltage VFD
HPP and Motor Size – The HPP and motor is sized to
handle the worst-case membrane pressure requirements.
For example, if the expected feed pressure range is
from 64 to 70 bar, the HPP must be sized for the 70 bar
condition.
Table 1 ERD SEC comparison
With the HEMI, the HPP and motor are sized for the
HPP Motor Drive – A medium voltage VFD in the mega- lowest pressure condition. From the above example, it
watt class is an expensive beast – climate-controlled would be 64 bar; about a 10% reduction in size. Note
motor control room, large floor space, special cabling that HEMI takes care of pressures above the minimum.
and line reactors plus the VFD itself can exceed 250,000
USD per train. Field Installation – The HEMI is factory tested at full
power conditions prior to shipment on a test loop rated
The HEMI entirely regulates feed flow and pressure to 2.7 megawatts. A complete performance map cover-
during operation thereby allowing the HPP to oper- ing all duty points is generated as well as SEC calcula-
ate at constant speed. To accommodate the need for tions – thus no surprises during field commissioning.
slow pressure ramps at system startup and shutdown, The HEMI is plug-and-play. Make pipe joints for feed
a solid-state soft starter is recommended. This starter and brine, bring power to the HEMI VFD, check motor
Fluid Equipment Development Company, LLC www.fedco-usa.com
Offices in USA, Singapore and Dubai sales@fedco-usa.com
Motorized Turbochargers — Much More Than Energy Recovery
alignment and make a connection to the plant SCADA.
Installation and commissioning can be completed in
just a few days.
Safety – Pipe joint failure is considered a prime safety
hazard in SWRO facilities. The HEMI has four (4) pipe
connections which may be groove-type pipe joints or
ANSI 600# flanges. Isobaric ERDs may involve up to one
hundred (100) pipe joints per train.
HEMI System Operation
The HEMI adjusts permeate flow via pressure boost in
the feed via adjustment of the Turbo shaft RPM. The Figure 13 HEMI response during annual changing membrane
variable area turbine nozzle adjusts brine flow per sys- conditions
tem requirements.
The HEMI control philosophy may be implemented in
Figure 12 provides a summary of the control philosophy. the facility SCADA system or with a small PLC provided
Figure 13 illustrates how the HEMI responds annually by FEDCO dedicated to HEMI operation. The PLC I/O and
to changing membrane conditions. Note that the HPP functions include:
operates at a constant ∆P with the HEMI providing feed • Input signals for run and stop and alarm outputs
pressure modulation. The power contribution by the
• Outputs to the HEMI VFD and turbine flow control
HEMI motor varies from near zero in summertime to a
maximum in winter conditions. actuator
• Monitoring of vibration and motor temperatures
Main process inputs (bearing and windings)
to PLC
• FM1 - Permeate
• Data logging.
• FM2 - Brine
• Set point values The Complete Package
Main process inputs
to PLC The HEMI equipment and documentation package in-
• VFD reference Hz to Turbo cludes:
• Turbine nozzle actuator
• Turbocharger custom designed to duty range conditions
• Compatible HEMI motor drive package
• Common baseplate
• Monitoring instrumentation
• PLC with programming for HEMI control and monitoring
Figure 12 HEMI control philosophy • Full power testing prior to shipment (may be witnessed)
• Quality and test documentation
• Field commissioning services.
Motorized Turbochargers — Much More Than Energy Recovery
HEMI Motor The HEMI takes further
strides toward simplicity
In small HEMIs, the rotor speed is up to about 10,000 by eliminating the multiple HEMI
RPM and larger HEMI; run at about 4,500 RPM. Evalu- Motor
megawatt medium voltage
ating motor suppliers and performing motor endurance VFDs. Centralization of all
testing has taken several years. The selected motors membrane and flow control
are standard induction design, 380 to 460 volt power, in a single compact device
grease lubricated hybrid bearings and totally enclosed move plant design toward
using either fan or blower cooling. Motor maintenance/ the goal of design and oper-
repair may be performed by any motor shop with EASA ational simplicity.
accreditation or equal.
Simplicity also means reduc-
Some Thoughts on Complexity Turbo
ing the number of vendors,
Industry observers have noted that large scale RO sys- negotiations, contracts,
Figure 15 HEMI on test stand
tems are becoming more complex and expensive. Much warranty administration
of that complexity and added expense is driven by ERD overhead and general project
selection. complexity. The HEMI, from a single supplier, replaces a
multitude of suppliers, personnel training for operation
Please refer to Figure 14 to gain a sense in the differ- and maintenance as well as spare parts inventory.
ence in complexity between an isobaric chamber ERD
system and a Turbo. Both units are illustrated to scale, Final Thoughts
both have the same capacity and both have approxi-
mately the same energy savings potential. The HEMI represents that next phase of RO equipment
optimization – equipment specifically designed for RO
Figure 15 shows a HEMI under test with feed and brine service with hydraulic characteristics tailored to achieve
piping placed horizontally for ease in testing. Such lower cost permeate.
flexibility of installation provides options for system de-
signs in limited space such as offshore platforms. Note Please contact FEDCO with comments, objections or
that the pictured (figure 15) unit has approximately the clarifications on any data or calculation presented in
same capacity as the ERDs illustrated in Figure 14. this paper.
HP-HEMI,
ERD System
Isobaric Chamber
ERD System
Figure 14 - Isobaric ERD and HEMI — same capacity and drawn to scale
Fluid Equipment Development Company, LLC www.fedco-usa.com
Offices in USA, Singapore and Dubai sales@fedco-usa.com
Motorized Turbochargers — Much More Than Energy Recovery
Addendum I - HEMI Performance
The HEMI core is a turbocharger. The Turbocharger has a single stage centrifugal pump using a multi-vane diffuser on
a common shaft with a single stage radial inflow turbine. A suitable motor under VFD control is coupled to the turbo
shaft. The best efficiency points of the pump and turbine need to match, and power balance must be obtained.
Advanced CFD, CAD and CAM are used to manufacture flow components from forgings and bar stock. Performance
is validated on high precisions test systems at the FEDCO facility. As can be seen in the performance map below,
pump efficiency exceeds 90% in this relatively small HEMI. In larger HEMI’s, pump efficiency can exceed 92%.
Note that HEMI motor power is returned to the RO system through the HEMI pump thus providing a significantly
higher energy return than provided by the HPP.
The turbine section includes a variable area nozzle to maintain constant flow at variable pressure. The performance
map below shows the pressure range at a fixed brine flow. Careful readers may note that the HEMI functions like a
jockey pump, but a pump of unusually high efficiency driven by a high efficiency brine turbine that provides the
bulk of the power input with a small motor and VFD for pressure boost adjustment.
The shaded area below is defined by the available HEMI motor power. For this installation, a 100 hp motor input
covers the high pressure condition. However, the motor and VFD are rated to 150 hp to provide a large safety
margin in the event of unexpected membrane pressure requirements. The pump power input is mostly supplied by
the turbine with the motor providing incremental power input as required (from zero to about 12% of the turbine
power). If there is potential that the required pressure boost drops below the zero-motor power input, one of
these options can be used:
1. The HEMI VFD may include a regeneration function allowing the motor to act as a generator thus absorbing
excess turbine power, reducing boost and returning electrical energy to the facility power supply;
2. Install resistors on a standard VFD to burn off excess turbine power;
3. Install a small brine bypass line to reduce brine flow through the turbine.
The likelihood of the above is low in a well-designed system with a well understood operating environment.
Option 1 is likely the lowest cost and highest energy efficiency if such precautions are judged necessary.
Fluid Equipment Development Company, LLC www.fedco-usa.com
Offices in USA, Singapore and Dubai sales@fedco-usa.com
Motorized Turbochargers — Much More Than Energy Recovery
About FEDCO
Founded in 1997 as a pump and ERD development partnership with a large RO system builder, Fluid Equipment Devel-
opment Company, LLC, evolved to a vertically integrated design, manufacturing and global sales/marketing company.
FEDCO holds numerous patents in pump and turbine design and reverse osmosis system design. FEDCO is a privately held
company with a proven commitment to its customers, suppliers, end users, its community and the environment.
Manufacturing and Head Office - Monroe Michigan U.S.A.
Fluid Equipment Development Company, LLC www.fedco-usa.com
Offices in USA, Singapore and Dubai sales@fedco-usa.com
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