resistance to the magnetic flux generated from the magnet. This gap resistance
decreases as the reed blades come closer together. The magnetic force produced by
permanent magnets or electromagnets is inversely proportional to the square of
this distance gap. Therefore, the reed-switch-blade closure will accelerate as the
tips approach each other. The larger the magnetic field, the faster the blades snap
together. (See Fig. C-417.)
Control Valves
A number of process valves are simple hand-turned valves. They include:
Globe valves: Fluid flow through this valve changes direction. Fewer turns are
required to move this valve than with a gate valve. It is useful for throttling service.
If extremely close regulation is required, a needle globe valve should be used.
Ball valves require a 90° turn to shut off flow completely. They are much lighter
for a given size than either a globe or a gate valve. Maintenance is simple; however,
this valve type is not suitable for throttling.
Plug valves can be either lubricated or nonlubricated. They are like ball valves,
except instead of the ball there is a plug, often shaped like a truncated cone. These
valves do not seize or gall as might be the case with some gate valves.
Diaphragm valves have a flexible diaphragm that closes the pipe against the flow
of the liquid. Isolation of the working parts from the fluid stream prevents product
contamination and corrosion. Maintenance requires the occasional diaphragm
change.
Pinch valves are more for laboratory-type application as they stop flow through
small-diameter rubber tubing.
Some valves operate either manually or automatically.
Controls, Retrofit C-391
FIG. C-414 Reed switch. (Source: Demag Delaval.)
FIG.
C-415 Single-pole–single-throw (SPST) reed switch. (Source: Demag Delaval.)
FIG.
C-416 Single-pole–double-throw (SPDT) reed switch. (Source: Demag Delaval.)

FIG.
C-417 Magnetic activation of reed switch. (Source: Demag Delaval.)
resistance to the magnetic flux generated from the magnet. This gap resistance
decreases as the reed blades come closer together. The magnetic force produced by
permanent magnets or electromagnets is inversely proportional to the square of
this distance gap. Therefore, the reed-switch-blade closure will accelerate as the
tips approach each other. The larger the magnetic field, the faster the blades snap
together. (See Fig. C-417.)
Control Valves
A number of process valves are simple hand-turned valves. They include:
Globe valves: Fluid flow through this valve changes direction. Fewer turns are
required to move this valve than with a gate valve. It is useful for throttling service.
If extremely close regulation is required, a needle globe valve should be used.
Ball valves require a 90° turn to shut off flow completely. They are much lighter
for a given size than either a globe or a gate valve. Maintenance is simple; however,
this valve type is not suitable for throttling.
Plug valves can be either lubricated or nonlubricated. They are like ball valves,
except instead of the ball there is a plug, often shaped like a truncated cone. These
valves do not seize or gall as might be the case with some gate valves.
Diaphragm valves have a flexible diaphragm that closes the pipe against the flow
of the liquid. Isolation of the working parts from the fluid stream prevents product
contamination and corrosion. Maintenance requires the occasional diaphragm
change.
Pinch valves are more for laboratory-type application as they stop flow through
small-diameter rubber tubing.
Some valves operate either manually or automatically.
Controls, Retrofit C-391
FIG. C-414 Reed switch. (Source: Demag Delaval.)
FIG.
C-415 Single-pole–single-throw (SPST) reed switch. (Source: Demag Delaval.)

FIG.
C-416 Single-pole–double-throw (SPDT) reed switch. (Source: Demag Delaval.)
FIG.
C-417 Magnetic activation of reed switch. (Source: Demag Delaval.)
Butterfly valves operate with the movement of a wing-like disk that works at right
angles to the fluid flow. This valve type can be operated manually or using
pneumatic, electrical, hydraulic, or electronic actuation.
Nonreturn or check valves prevent the reversal of flow in piping. In a swing check
type the hinged disk is held open with the flow of liquid. When flow stops, gravity
causes the disk to fall into closed position. With lift check–type valves, the closure
disk is raised by the fluid flow. When flow stops, the disk falls back into closed
position.
Current-to-Pressure Converters for Precise Steam and Fuel Valve Control*
The source for the information in this subsection is Voith Turcon who designate
their current-to-pressure converters “I/P” (“I” for current and “P” for pressure).
I/P converters offer control of steam and fuel valve actuators. Although designed
for turbine applications, these converters can also be effective in other process
control situations.
This converter quickly and precisely changes a current input signal into a
proportional fluid output pressure to regulate steam or fuel flow.
I/P converters are built to a solid, compact design. All of the control electronics
are safely housed within the unit for reliable functioning—even in harsh environments.
With just three moving parts, this I/P converter is reliable and durable (“low-wear”).
(See Figs. C-418 through C-421 and Table C-33.)
Operating principles
The I/P converter reliably converts a 4–20 mA input signal into a proportional
output hydraulic pressure and double-checks for supremely accurate valve positions
and turbine speeds.
At the core of the I/P converter is an electromagnet. A 24-volt DC current
energizes the magnet, which in turn creates a force on the actuating rod. A 4–

20 mA input signal works with the unit’s controller and amplifier to regulate this
force. Any variation in the 4–20 mA input signal affects the pressure being exerted
by the magnet onto the actuating rod. The force applied to the actuating rod is used
to precisely control a hydraulic piston, which opens and closes the consumer and
drain ports. (See Figs. C-422 through C-425.)
The sequence of operations is as follows:
1. When the 4–20 mA signal reaches the converter, its controller and amplifier
adjust the magnetic force to a pressure directly proportional to the input signal.
2. This force is measured by a semiconductor that serves as the unit’s magnetic
force sensor/flux detector. Magnetic force lines penetrating this element produce
a proportional output voltage (the Hall effect).
3. The output voltage is looped back to the converter’s controller and compared to
the set value, W. If the unit senses a difference between the input signal and the
feedback signal, the controller and amplifier correct the magnetic force so that
the difference is zero.
4. The magnetic force adjusts the actuating rod to the appropriate position with up
to 90 lb (400 N) of pressure.
5. As a result of this precise control technology, the I/P converter’s output line
always contains the exact pressure needed to position the steam or fuel valve.
C-392 Controls, Retrofit
*Source: J.M. Voith GmbH, Germany.
Controls, Retrofit C-393
FIG. C-418 “I/P” converters. (Source: J.M. Voith GmbH.)
FIG.
C-419 A typical installation of an I/P converter in a cogeneration plant. (Source: J.M. Voith
GmbH.)
C-394 Controls, Retrofit
FIG.
C-420 Minimum and maximum output pressures of an I/P converter can be set externally.
(Source: J.M. Voith GmbH.)

TABLE C-33 Selection Table
Manual Piston
Maximum Flow Rate Flow Rate
Regulating
Actuation Damping I/P Converter Type
Input to Consumer to Drain
Range With Without With Without Standard EExd Pressure (Dp = 1 bar) (Dp = 1 bar)
0–72.5psi ᭿᭿DSG-B05102 DSG-B05202 101.5psi 4.9GPM 5.4GPM
0–5 bar ᭿᭿DSG-B05112 DSG-B05212 7 bar 18.6l/min 20.5l/min
᭿᭿ DSG-B05103 DSG-B05203
᭿᭿DSG-B05113 DSG-B05213
14.5–101.5psi ᭿᭿DSG-B07102 DSG-B07202 101.5psi 4.9GPM 5.4GPM
1–7bar ᭿᭿DSG-B07112 DSG-B07212 7 bar 18.6l/min 20.5l/min
᭿᭿ DSG-B07103 DSG-B07203
᭿᭿DSG-B07113 DSG-B07213
0–145psi ᭿᭿DSG-B10102 DSG-B10202 219psi 4.4GPM 4.9GPM
0–10 bar ᭿᭿DSG-B10112 DSG-B10212 15 bar 16.8l/min 18.8l/min
᭿᭿ DSG-B10103 DSG-B10203
᭿᭿DSG-B10113 DSG-B10213
14.5–203psi ᭿᭿DSG-B14102 DSG-B14202 219psi 4.4GPM 4.9GPM
1–14 bar ᭿᭿DSG-B14112 DSG-B14212 15 bar 16.8l/min 18.8l/min
᭿᭿ DSG-B14103 DSG-B14203
᭿᭿DSG-B14113 DSG-B14213
0–290psi ᭿᭿DSG-B20102 DSG-B20202 655psi 2.5GPM 2.1GPM
0–20 bar ᭿᭿DSG-B20112 DSG-B20212 45 bar 9.8l/min 12.0l/min
᭿᭿ DSG-B20103 DSG-B20203
᭿᭿DSG-B20113 DSG-B20213
0–430psi ᭿᭿DSG-B30102 DSG-B30202 430psi 5.4GPM 5.8GPM
0–30 bar ᭿᭿DSG-B30112 DSG-B30212 30 bar 20.5l/min 22.3l/min
᭿᭿ DSG-B30103 DSG-B30203

᭿᭿DSG-B30113 DSG-B30213
NOTES
1. Further pressure ranges available upon request.
2. Consult factory for FM-certified explosion-proof designs which meet Class I, Divisions 1 and 2, Groups B, C, and D service.
3. I/P converter weight: approximately 22 lb (10 kg) for all models.
FIG. C-421 Applications of an I/P converter. (Source: J.M. Voith GmbH.)
C-395
C-396 Controls, Retrofit
FIG. C-422 Internals of a typical I/P converter. (Source: J.M. Voith GmbH.)
Controls, Retrofit C-397
FIG. C-423 Typical dimensions of an I/P converter. (Source: J.M. Voith GmbH.)
FIG. C-424 I/P converter uses industry standard connections. (Source: J.M. Voith GmbH.)
FIG. C-425 Schematic of I/P converter connections. (Source: J.M. Voith GmbH.)
Advantages of this basic design
᭿
The unit’s magnetic drive and the hydraulic section’s pressure-reducing valve
work together to function as a pressure-regulating valve.
᭿
Dynamic and hysteresis-free
᭿
Resolution is better than 0.1 percent
᭿
Accuracy is not affected by air-gap, magnetic hysteresis, temperature, or
fluctuations in supply voltage.
᭿
Recommended oil contamination to NAS 1638 Class 7, or ISO 4406 Class 16/13.
᭿
Short conversion time from mA input signal to proportional, stationary pressure
(t < 35 m).
᭿

Few electronic and mechanical parts ensure full functionality in harsh
environments.
᭿
All electronics for the I/P converter are integrated in the housing.
᭿
Design withstands higher input pressure (pressure ranges available from 0 to
3000 psi).
᭿
Standard and explosion-proof designs are available. (See Figs. C-426 and C-427.)
᭿
In the version incorporating a PID controller, you can compensate for pipeline
pressure losses. This optional design also allows for control of valve positions and
turbine rpm.
᭿
Uses turbine oil as hydraulic fluid with no additional filter required.
C-398 Controls, Retrofit
FIG.
C-426 Explosion-proof design (for EExD IIC T4, PTB No Ex-90, C, 1065). (Source: J.M. Voith GmbH.)
Speed and accuracy
᭿
Reproducibility <0.1 percent
᭿
Accuracy <1 percent
᭿
No drift
᭿
Resolution is better than 0.1 percent
᭿
Hysteresis-free
᭿

Does not generate static friction during operation.
᭿
Accuracy is not affected by air-gap, magnetic hysteresis, temperature, or
fluctuations in supply voltage.
᭿
Fast response time
᭿
Short conversion time for proportional stationary pressure (t < 35 ms)
᭿
Rapid closedown, which includes internal oil circulation (£0.1 s)
Performance and frequency response
See Figs. C-428 and C-429.
Knife-gate valve*
Depending on what flows through (process) pipe, the cause of costliest wear on one
line could be heat or corrosion, while abrasiveness is the key concern in another
Controls, Retrofit C-399
FIG. C-427 Explosion-proof design (for Class I, Divisions 1 and 2, Groups B, C, and D service). (Source: J.M. Voith GmbH.)
*Source: Adapted from extracts from “Controlling the Flow,” Mechanical Engineering, ASME, December
1998.
FIG.
C-428 Performance and frequency response curves for different I/P converters. (Source: J.M. Voith GmbH.)
C-400
FIG. C-429 Performance and frequency response curves for different I/P converters. (Source: J.M. Voith GmbH.)
C-401
system. Each mining, power, or paper company has to choose parts for its pipeline
that offer the best balance of performance characteristics for its particular load.
Knife-gate valves control the flow in many process piping systems.
Mining companies use piping systems to transport newly mined minerals, such
as gold, ore, and coal, to processing plants. The excavated materials are crushed
and suspended in a liquid slurry. An efficient slurry handling system is crucial to

timely mineral processing, which is necessary for fast delivery.
The slurry flow can be very abrasive and corrosive to the hundreds of valves
directing its materials. In mining, newly crushed ore has a sharp surface, can be
quite hot, and flows quickly, constantly, and often at high pressure. A slurry valve
must be designed for these conditions to reduce maintenance time and replacement
costs. (See Fig. C-430.)
Power companies, meanwhile, transport different materials, putting their own
set of demands on the line’s components.
One valve OEM, Clarkson Co., USA, has simulated its valve in action to test
how variations in material and design of the product will hold up under different
pipeline stresses.
This OEM designs and manufactures knife-gate and control valves that can
halt and isolate sections of a slurry flow. Efficient control is necessary when the
slurry must be delayed, inspected, or redirected. Knife-gate valves are also used in
other applications, including industrial scrubber systems, waste-water treatment
systems, and industrial process water systems.
This OEM’s latest knife-gate designs are referred to as wafer-type valves
because they are lighter and thinner than their predecessors, although they can
handle higher pressures. The narrower valve fits tighter spaces and gives pipeline
designers more flexibility. Wafer-type valve dimensions meet a nationwide
standard, providing greater flexibility in choice of supplier because the valves are
interchangeable.
The knife-gate valve has a blade-like steel gate that lowers into the slurry flow
to create a bubble-tight seal. See Fig. C-431. The valve has two matching, smooth
elastomer sleeves that seal the blade when the gate is closed and seal each other
when the valve is open, so the slurry can flow through unobstructed. The elastomer
sleeves are designed to resist abrasion and corrosion and to cover the valve’s metal
par´ts to shield them from wear.
FIG.
C-430 Computer simulation software was used to simulate the valve in action on a computer,

reacting to the severe pressure and temperature of the slurry piping system’s flowing materials.
(Source: Clarkson Co.)
C-402 Controls, Retrofit
Controls, Retrofit C-403
The knife-gate valve was a new concept when it was introduced because it
replaced conventional metal seats and gate guides with easily replaceable snap-in
elastomer sleeves, which are more durable and versatile, and handle higher
pressure and temperature. Conventional metal seats and gate guides can fill with
hardened slurry and then fail to open or close.
Pipeline operators value the elastomer’s long life because each seal costs between
$75 and $500 to replace. More important, they lose revenue when they suspend the
slurry system for maintenance repairs.
This OEM wants to develop a greater variety of elastomer seals for the wafer-
type valve to increase its efficiency and reliability in different applications. For
example, power companies prefer synthetic types of elastomers like neoprene, butyl
or viton, which handle high temperatures and corrosive materials, while mining
companies prefer elastomers like natural gum rubber for abrasive slurries.
Control, of (Fuel) Manifold Flow*
Stepper motor–driven valve
In the control of fuel flow to fuel manifolds in a gas turbine, the advent of the stepper
motor–driven valve has brought about more accurate control of fuel supply to a gas
turbine, with increased safety of operation, simplicity of piping design (see Fig. C-
432), and reduced time between overhauls for the gas turbine.
This is by no means the only application for a stepper motor–driven valve, which
is popular now in many processes and also in aviation applications.
Case study: stepper valve usage. The Petrochemical Corporation of Singapore (PCS)
was initially discouraged from producing independent power in excess of its needs.
Singapore Power (SP) has preferred to continue to receive the high tariffs paid
by its consumers rather than administrate the buyback of small amounts of
FIG. C-431 To increase its efficiency in different applications, a greater variety of elastomer seals

for the wafer-type knife-gate valve were developed. (Source: Clarkson Co.)
* Source: Claire Soares, adapted from 1998 article written on “stepper” valves, PCS, and turbine fuel
flexibility for Asian Electricity.
power from several small power producers (SPPs). However, now the move toward
deregulation is changing that. “Pool rules for small generators,” which covered
generators of less than 10 MW and industrial in-house generators (“autogenerators”),
were instituted in Singapore as of April 1, 1998.
An SPP such as PCS does not have the benefit of steady load, and the quality,
type, and heating value of their fuels will vary. This is because they use process
gases and fluids for fuel whenever they can, especially if that is the most cost-
effective use for a process fluid. Due to the variations in the different characteristics
of these fuels, which are in essence different process streams, a very fast response
valve is required. Without such a valve, the exhaust gas thermocouples on the gas
turbine would note larger swings in turbine exhaust temperature. The key to PCS’s
successful use of process fluids—which it didn’t have much other use for—as fuel
is valve response time and actuation characteristics. An ideal valve for this type of
application is a “stepper” valve or its equivalent.
C-404 Controls, Retrofit
BEFORE
AFTER
GAS
SUPPLY
SHUT
OFF
VALVE
SPEED
RATIO
VALVE
GAS FLOW
CONTROL

VALVE
SRV
GCV
SOV
HYDRAULIC
PRESSURE
GAS
SUPPLY
ELECTRIC
SHUT
OFF
VALVE
STEPPER
GAS FLOW
CONTROL
VALVE
ENGINE
MANIFOLD
ENGINE
MANIFOLD
FIG.
C-432 “Before” and “after” schematics showing how retrofit of a stepper value can simplify the piping and control
system into a gas-turbine engine fuel manifold. (Source: HSDE.)
Controls, Retrofit C-405
The stepper valve and functional equivalents. The stepper (short for stepper motor–
driven) valve is a fast-response, electrically operated valve that was pioneered by
Vosper Thornycroft (HSDE, UK) in the mid-1960s. Now this valve type is made by
other well-known manufacturers too, such as Moog, in Germany. The term stepper
actually refers to the motor type that drives the valve as opposed to the valve itself.
The motor is a stepper motor, as opposed to a torque or AC or DC motor. Its self-

integrating function ensures that the valve will proceed to a desired position and
then the motor will stop. With other motors, the motor has to continue to run in
order to keep the valve in that position—such valves need signals to cue them: run,
stop running, then start running again, and so forth. If something were to happen
causing the valve to fail, the stepper-type valve position would still lock and the
system would continue running. The valve then makes the system fault tolerant,
which is critical in applications such as emergency power-supply generators. It also
provides the fast response required by aeroderivative and some industrial gas
turbines. This is useful for both power generation and mechanical drive service.
Before the stepper valve was introduced in the mid-1960s, hydraulic and pneumatic
actuation valves were used to provide the required response time. This increased
the overall complexity of the fuel system. As always, with instances where system
complexity is heightened, system cost increased but mean time between failures
(MTBF) and availability decreased.
The valve takes up very little space on the installation and service people unused
to this new design spend frustrated time looking for the extensive “old” equivalent
control system.
Development of valves that could compete with HSDE’s original stepper arose
from competition with that early design. As a result, there are now many
manufacturers who produce functional equivalents on the market for use in gas-
turbine fuel systems, high-resolution controls for robots, automatic machining
controls, and so forth. In PCS’s application, they use a Moog (German manufacturer)
valve that has a DC motor. To get the same “stay in position” feature as a stepper-
type valve would have, manufacturers typically use a spring to hold a position.
Design aims of fast response valves. The original design aims of the stepper-type
valve and its equivalents generally include the following safety considerations:
᭿
A fail-freeze or fail-closed option, depending on whether the operator is a power-
generation facility (“freezing” at the last power setting is then required) or a
pipeline (in which case turbine shutdown on valve failure is required).

᭿
The liquid fuel version of the valve incorporates a pressure-relief valve protecting
the system against overpressure and the fuel pump running on empty or
“deadheading,” caused by closure of valves downstream of the fuel valve during
system operation.
᭿
High-speed response of less than 60 ms required by aeroderivative gas turbines
to prevent overspeed in block off-load conditions.
᭿
Explosion-proof actuation to appropriate specification standards allows operation
in hazardous methane service.
᭿
Resistance to fuel contaminants, including tar, shale, water, sand, and so forth.
᭿
Twenty-four volts DC is the maximum drive voltage that ensures personnel safety
᭿
Corrosion resistance in components exposed to wet fuel and to all parts if the
service is sour gas.
Operational objectives of fast-response valves. Other operational objectives that
dictate design features are operator’s requirements for:
᭿
Low mean time to repair (LMTR). The target of 1 h, achieved with modular
design, together with the target MTBF provided an availability of 99.998 percent
for HSDE’s original stepper.
᭿
Higher MTBF. (In HSDE’s case, an initial development target of 50,000 h was set
and achieved.)
᭿
Low maintenance costs, since the modular design can be repaired by an individual
with relatively little experience. Service intervals are 12 months.

᭿
Large control ratio that allows control over the ignition to full load as well as
full-speed ranges to be possible with one fuel valve. Fuel pressure variation
compensation is provided. The additional speed ratio–type control valve found in
many other industrial gas fueled installations is not required here.
᭿
Low power consumption since an electric motor of less than 100 W is used.
This also eliminates the need for additional hydraulic or pneumatic systems. Also,
black starting is more reliable if the fuel system is powered by the same batteries
as the controller.
A generic stepper valve system can consist of the following items:
᭿
Transformer
᭿
Power supply
᭿
Controller
᭿
A rack
᭿
A DC motor
The motor, a brushless servomotor, is generally an electronically commutated three-
phase motor with permanent magnet excitation on a low-inertia rotor. The stator’s
three-phase windings have thermistor protection. Sinusoidal back electromotor force
(emf) provides improved low-speed performance and higher efficiency. The integral
brushless resolver provides position feedback so no tachogenerator, mechanical
commutator, or electronics within the motor are required. Bearings are preloaded
and sealed with high-temperature grease. A static load holding brake is an option.
Applications experience. Power production in phase II of the Petroleum Corporation
of Singapore was commissioned in June 1997. PCS is part of a massive

petrochemical plastics conglomerate in Singapore. Power production was an
afterthought, since when they were built, its design did not include provision
for becoming an SPP. PCS chose a nominally 25-MW (23 MW in their normal
ambient conditions) Alstom GT10, although their power needs are roughly
26 MW. This was because while SP were pleased to sell them their residual
requirement, they would not buy any power from SPPs at the time of original power
plant design.
The turbine is fueled by three different types of fuel, depending on the state of
the plant. The British thermal units for each type varies, so again the fast response
time for the stepper valve is critical.
As PCS operations found, the fast response valve proved as useful as the
stepper valve has been for power generation on the North Sea oil and gas
platforms. The fast response time of the stepper valve design helps the valve avoid
the sudden burst of excess temperatures that accompany higher heating value fuel.
(North Sea platform users frequently operate gas, liquid, or gas and liquid fuel
mixtures.)
Not all gas turbines are tolerant of a wide range of fuel types in a single
application. Some of them require a whole different fuel system—nozzles, lines, and
C-406 Controls, Retrofit
all components—to be able to handle a totally different heating value fuel. In this
application in Singapore, the Alstom machine shows no sign of distress, which is
interesting since the heating value of the fuel types varies as much as 50 percent.
The exact fuel composition data are proprietary to PCS only; however, the GT10
operational data chart, figures, and curves here provide data for typical power
output with light oil and natural gas fuel. The rest of the data is typical for the
GT10.
PCS’s GT10 heat-recovery steam generator (HRSG) provides a reliable source of
steam. The plant exports steam to the nearby Seraya Chemicals plant in addition
to fulfilling its own needs.
The turbine. The relatively low turbine-inlet temperature of the GT10 is one of

the keys to being able to use three different fuel streams that exhibit a divergence
of 50 percent in terms of heating value, without any noteworthy surges in
performance or reductions in hot section component lives. As already described,
valve-response speed is another critical feature for ensuring the stability of this
application.
Emissions and steam supply. The Alstom EV burner—a low NO
x
burner that can
be fitted and retrofitted on the GT10, fuel types permitting—was not fitted in this
case. The EV burner will handle clean natural gas and clean diesel fuel. It was
not suitable for the high hydrogen content and variations in fuel composition that
this application involves. Such fuels need a more forgiving fuel system, as well
as water or steam injection to keep the NO
x
down. The PCS Singapore application
uses steam for NO
x
reduction purposes. The steam is piped in through nozzles that
are adjacent to the fuel nozzles on the fuel manifold of the GT10’s annular
combustor.
The source of the steam is the HRSG that is packaged as part of the GT-10 system.
If and when required, the plant also can draw high-pressure steam from its process
cracker.
In PCS’s case, one boiler has been found to suffice. This is noteworthy as in
applications such as this, a redundant “packaged boiler” (running hot and on
minimum load) is often found essential. This is so that it is possible to pick up the
steam load should the turbine trip or be unavailable due to maintenance. A common
subject for debate is whether uninterrupted steam supply during the switch
from HRSG mode to fresh-air firing is possible without flameout on the boiler
supplementary burners.

The PCS plant is part Japanese owned, so the specifications the installation had
to meet matched those of environmentally particular Singapore, as well as the
Japanese, who are the most environmentally strict practitioners in Asia. Steam
injection reduces NO
x
levels from 300 to 400 mg/MJ fuel to just below 100 mg/MJ
fuel.
(Note: As the upstream company PCS’s main role is to supply high-quality
ethylene, propylene, acetylene, and butadiene, as well as utility services such as
water, steam, and compressed air, to downstream companies, PCS directly produces
and exports benzene, toluene, and xylene for global markets.)
Future potential for power generation in Singapore. The pressure for accelerated
deregulation is increasing in Singapore as well, if not as fast as in the rest of
southeast Asia. Singapore Power is gradually seeing more IPP contracts let in
the country. SPC’s experience with the GT10 they operate has been positive in
terms of availability and maintainability. Just as important is this gas turbine’s
ability to use three different “waste” petrochemical fluids as fuel, despite the 50
Controls, Retrofit C-407
percent difference of these three fluids in terms of heating value. That it can do this
while maintaining NO
x
emissions below legislated limits for countries as
environmentally strict as Singapore, speaks well for its continued use in similar
applications.
Conversion Tables (see Some Commonly Used Specifications, Codes, Standards,
and Texts)
Conveyors* (see also Drives; Power Transmission)
With numerous process plants employing conveyors of one type or another, it
was felt that this text should give at least an introduction to this type of
machinery by focusing on one of the more sophisticated executions: steel-belt

conveyors.
The use of steel-belt conveyors has spread throughout the processing industries.
Applications of steel-belt conveyors include cooling/solidification, drying, pressing,
freezing, baking, and materials conveying.
The steel belt is made from flat strip steel from a rolling mill, prepared through
special techniques that straighten, flatten, and make the ordinary strip suitable for
welding into endless bands continuously running around two terminals. The
conveyors based on this specialized technology are designed for the processing
industries according to the needs of the product and the special needs of the steel
belt.
Table C-34 summarizes a wide variety of steel-belt applications and the important
steel-belt properties that make the applications successful. The general categories
that are shown in Table C-34 are material handling, food processing, industrial
processing, and presses for particle boards, plastics, and rubber. Table C-34 also
indicates the four major steel-belt grades that are in common use.
The following discussions describe the applications and processes for which steel-
belt conveyors have been selected as the best of competing alternatives, including
the types of materials used for conveyor belts.
Reference and Additional Reading
1. Bloch, H., and Soares, C. M., Process Plant Machinery, 2d ed., Butterworth-Heinemann, 1998.
Coolant; Engine Coolant
The number of coolants available on the market is large. For illustrative purposes,
the common one chosen here is propylene glycol. The discussion that follows
†
indicates the characteristics sought in most coolants.
Circulation of Coolant through a Typical Engine
Coolant circulates through passages in the engine block surrounding the cylinders.
Coolant also flows through the cylinder head to cool the valves and combustion
chamber area. The heated coolant then flows through a thermostat to either the
radiator to be cooled or to the coolant pump for circulation back to the engine. (See

Fig. C-433.)
C-408 Conversion Tables
* Source: Sandvik Process System, Inc., USA.
†
Source: ARCO Chemical, USA.
Propylene glycol (PG) is a recent innovation in improved antifreeze formulations.
Its key advantage over more traditional engine coolants made with ethylene glycol
(EG) is lower toxicity to people, pets, and wildlife.
PG coolants have been extensively tested in both heavy-duty and automotive
service. Laboratory, engine dynamometer, and fleet tests all prove that PG is an
Coolant; Engine Coolant C-409
TABLE
C-34 Areas of Steel-Belt Application
Possible
Important Steel-Belt Properties Steel Belt
Steel Belt
Installation Type
Conveyors,
general • (•) • X X
Sorting systems • (•) (•) • • X X
Work tables,
general (•) (•) (•) X X X
Meat cutting
tables • • (•) X
Bottle headling • (•) • • X X
Bake ovens (•) (•) • • (•) (•) X
Contact freezers • (•) (•) (•) X
Belt coolers/food (•) (•) (•) (•) X X
Belt coolers/
chemicals (•) (•) (•) (•) X X

Steel-belt dryers (•) (•) (•) • (•) (•) X X
Flow-through
belt unit (•) (•) (•) X X X
Double belt
presses • • (•) • (•) X X X
Belt skimmers • X
Single opening
presses • (•) • • • X X
Multiopening
presses • (•) X X
Rotation presses • • (•) • • X X
Rotation presses • • • (•) X X
Rotation presses • • • • (•) X X
(•) = property sometimes of importance
• = property always of importance
SOURCE: Sandvik Process System, Inc.
Strength—High Temperature
Strength—Cryogenic Temperature
Austenitic (SA)
Carbon (C)
Surface Finish
Straightness
Flatness
Hygienic
Wear Resistance
Corrosion Resistance
Stability against Temperature
Difference
Strength—Ambient Temperature
Martensitic (SM)

Strength Martensitic (SM)
Material
HandlingFood Industry
Particle
Board Industry
Rubber
Industrial Process
Applications
Plastics
excellent base fluid for engine coolants, providing the necessary heat transfer
characteristics, boilover prevention, freeze protection, and, when adequately
inhibited, corrosion protection.
PG coolants may be recycled using the same methods used by many maintenance
facilities to recycle traditional EG coolants, and similar additives can restore the
recycled product to meet requirements for virgin coolants.
Commercial antifreeze formulations based on PG are readily available for
both heavy-duty fleet and automotive uses. In service, PG/water or PG/EG/water
antifreeze compositions and freeze protection may be easily measured using
inexpensive, commercially available devices.
Results of comparison tests have demonstrated that propylene glycol is as
effective an engine coolant as ethylene glycol. The testing program included
laboratory bench-scale testing, engine dynamometer studies, and fleet tests on both
heavy-duty and light-duty vehicles. Both high- and low-load conditions were studied
at ambient temperature extremes of -43 to 49°C (-46 to 120°F).
The effectiveness of a heat transfer fluid in modern gasoline and diesel engines
depends on two factors—the removal of heat from the engine as the liquid circulates
through the cylinder head and engine block, and the transfer of heat to the air by
the radiator. Detailed studies and analysis of the mechanisms of heat transfer have
shown that although there are very slight differences between the heat transfer
properties of propylene glycol and the more traditional ethylene glycol coolants,

these make no difference in operating vehicles.
C-410 Coolant; Engine Coolant
FIG. C-433 Coolant flow through an engine. (Source: ARCO Chemical.)
Engine Cooling Effectiveness
PG has proven to be as effective a coolant as EG. Removal of heat from the engine
depends on heat transfer coefficients, which are dependent on the mechanism of
heat transfer. At low heat flux (heat transfer rates), forced convection (heat transfer
between a solid metal surface of the engine and the liquid coolant) is the
predominant mechanism of heat transfer. In this regime, the Prandtl number,
which is dependent upon coolant physical properties, is the controlling factor in
heat transfer. At higher heat flux, the metal temperature increases and nucleate
boiling (formation of some vapor bubbles at the heat transfer surface) occurs,
increasing the efficiency of the heat transfer. Under nucleate boiling conditions, the
Prandtl number is no longer the controlling factor in heat transfer.
At still higher heat flux, the surface temperature continues to rise, and too much
vaporization occurs for an efficient transfer of heat. A vapor film may form that
blocks direct contact between the liquid coolant and metal surface. At this point, a
dramatic drop in the heat-transfer coefficient occurs, causing a concurrent dramatic
rise in the cylinder metal temperature and possible engine failure. Ideally, a coolant
will operate in the convective and nucleate boiling regions and never reach film
boiling stage.
Theory predicts that, because a PG/water coolant mixture has different physical
properties than an equal solution of EG/water (e.g., slightly higher viscosity and
slightly lower density), convective heat transfer will be 5–10 percent lower, while
heat transfer in the nucleate boiling range will be 5–10 percent higher. Figures C-
434 and C-435 show the calculated heat-transfer coefficients for 50 percent solutions
of PG/water and EG/water. Data for water is included for comparison. Detailed
laboratory and engine dynamometer studies of heat-transfer coefficients have
confirmed these predictions. These differences in the heat transfer over the
combination of low and high loads seen in normal vehicle operation approximately

offset each other.
With all else being comparable, the major difference between propylene and
ethylene glycol is their toxicities. Two ounces of ethylene glycol antifreeze can be
lethal to a dog, while a teaspoonful may kill a cat.
When ingested by humans and animals, EG is metabolized to glycolic and oxalic
acids, which may cause acid-base disturbances, kidney damage, and possibly death.
Coolant; Engine Coolant C-411
FIG. C-434 Forced convection heat transfer. (Source: ARCO Chemical.)
In 1994, 4200 incidents of EG poisoning were reported by the American Association
of Poison Control Centers, resulting in 29 deaths. EG is also a major source of
poisonings of dogs and cats. According to an ASPCA survey of veterinarians, over
100,000 pets were poisoned in 1995 by accidentally ingesting EG antifreeze,
resulting in more than 90,000 deaths.
In contrast, propylene glycol and its metabolites, lactic and pyruvic acid, account
for its low toxicity in both acute and long-term exposures. Many of the harmful
consequences of accidental antifreeze poisonings could be avoided by replacing EG-
based coolant with PG coolant.
Because of this clear difference in toxicity, ethylene glycol is regulated by
numerous federal and state health environmental acts in the United States, as
summarized in Table C-35. These include the 1990 U.S. Clean Air Act Amendments
and CERCLA. The U.S. Federal Health and Safety Administration also requires a
specific label on ethylene glycol coolants warning of the toxicity.
In the European Union, ethylene glycol is classified as a hazardous product and
must be handled according to strict regulations. In Switzerland, Austria, and the
Czech Republic, it is classified as a poison and its sale to the general public is
carefully regulated.
Coolers, Dairy
Glycol is an effective and fast coolant, commonly used in the food and agriculture
industry. Often used in large-scale industrial systems, glycol can also be used in
smaller customized designs. One example is a system designed in Hawaii’s dairy

sector for chilling the milk from cows on a small farm (300 to 900 cows). Milk
temperature is lowered from 98 to 38°F. The standard coolers available worked well
in competitive dairies in the rest of the United States, as the ambient temperatures
there do not impose as much of a heat load as in Hawaii. Milk typically takes 2 h
to cool in a large modern industrial dairy.
A standard air conditioner was fitted with an 800-gal glycol tank. The milk was
found to cool in 30 s (the time for milk to flow through the system). A variable speed
motor moves the milk through the cooler. The refrigeration unit incorporates two
scroll compressors and brazed plate evaporators.
C-412 Coolers, Dairy
FIG. C-435 Nucleate boiling heat transfer. (Source: ARCO Chemical.)
Adjustable speed vacuum pumps replaced the constant speed milking pumps for
further energy conservation. Overall about $6000 in 1997 prices was saved in
energy costs with these modifications for a cooler handling output from 1000 cows.
See Figs. C-436 and C-437.
Cooling; Cool, Products That (Air Conditioners); Liquid-Cooled Air Conditioners
(see also Chillers)
Cooling (Using) Solid-State Technology
A key requirement among cooling products in the process engineers’ world is that
they adhere to environmental safety standards. Existing coolers may have “old”
refrigerants, such as chlorofluorocarbons (CFCs), corrosive liquids, and gases, in
their cooling circuitry. What follows is a summary of design environment
specifications and standards, product selection charts, information on how to size
an air conditioner, typical mounting configuration, theory of operation, and some
example application illustrations.
Typical design environment (NEMA, Mil-Std, NED, UL/CSA) specifications* (see Figs. C-438 through C-441)
Typical NEMA
(Source: NEMA Publication No. 250, Part 1, Page 1)
NEMA-12 Type 12 enclosures are intended for indoor use primarily to provide
a degree of protection against dust, falling dirt, and dripping

noncorrosive liquids.
NEMA-4X Type 4X enclosures are intended for indoor and outdoor use
primarily to provide a degree of protection against corrosion,
windblown dust and rain, splashing water, and hose-directed
water.
Cooling; Cool, Products That (Air Conditioners); Liquid-Cooled Air Conditioners C-413
TABLE
C-35 U.S. Statutes Relating to Glycols
Propylene
U.S. Regulation Glycol Ethylene Glycol
1990 Clean Air Act Amendments (CAAA) None “Hazardous Air Pollutant”
42 U.S.C. § 7412 (b)
CERCLA (Superfund) None “Hazardous Substance”
HAPs from 1990 CAAA are included into
42 U.S.C. § 9601 (14)
Superfund Amendments & Reauthorization Act (SARA) None “Toxic Chemical”
42 U.S.C. § 11023
42 C.F.R. § 372.65
Safe Drinking Water Act (SWDA) None Health Advisory Issued
Occupational Health & Safety Administration (OSHA) None 50 ppm PEL
29 C.F.R. § 1910.1000
American Conference of Governmental Industrial Hygenists (ACGIH) None 50 ppm TLV
Federal Health & Safety Administration (FHSA) None “Warning, Harmful or Fatal if Swallowed”
16 C.F.R. § 1500.132
* Source: Thermoelectric Cooling America Corporation (TECA), USA.