Process Engineering Equipment Handbook Episode 2 Part 2 pot

They include: Globe valves: Fluid flow through this valve changes direction.. They include: Globe valves: Fluid flow through this valve changes direction.. Current-to-Pressure Converters

resistance to the magnetic flux generated from the magnet This gap resistancedecreases as the reed blades come closer together The magnetic force produced bypermanent magnets or electromagnets is inversely proportional to the square ofthis distance gap Therefore, the reed-switch-blade closure will accelerate as thetips approach each other The larger the magnetic field, the faster the blades snaptogether (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 Thesevalves 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 productcontamination and corrosion Maintenance requires the occasional diaphragmchange

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 resistancedecreases as the reed blades come closer together The magnetic force produced bypermanent magnets or electromagnets is inversely proportional to the square ofthis distance gap Therefore, the reed-switch-blade closure will accelerate as thetips approach each other The larger the magnetic field, the faster the blades snaptogether (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 Thesevalves 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 productcontamination and corrosion Maintenance requires the occasional diaphragmchange

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 usingpneumatic, 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 closedposition

Current-to-Pressure Converters for Precise Steam and Fuel Valve Control*

The source for the information in this subsection is Voith Turcon who designatetheir 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 designedfor turbine applications, these converters can also be effective in other processcontrol situations

This converter quickly and precisely changes a current input signal into aproportional fluid output pressure to regulate steam or fuel flow

I/P converters are built to a solid, compact design All of the control electronicsare 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 proportionaloutput hydraulic pressure and double-checks for supremely accurate valve positionsand turbine speeds

At the core of the I/P converter is an electromagnet A 24-volt DC currentenergizes 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 thisforce 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 anddrain 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 amplifieradjust 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 magneticforce 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 tothe set value, W If the unit senses a difference between the input signal and thefeedback signal, the controller and amplifier correct the magnetic force so thatthe 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 linealways 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.)

Actuation Damping I/P Converter Type

Input to Consumer to Drain Range With Without With Without Standard EExd Pressure ( D p = 1 bar) ( Dp = 1 bar)

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 valvework 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 harshenvironments

 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 pipelinepressure losses This optional design also allows for control of valve positions andturbine 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

 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 oneline 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 pipelinethat 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 crushedand suspended in a liquid slurry An efficient slurry handling system is crucial totimely mineral processing, which is necessary for fast delivery

The slurry flow can be very abrasive and corrosive to the hundreds of valvesdirecting its materials In mining, newly crushed ore has a sharp surface, can bequite hot, and flows quickly, constantly, and often at high pressure A slurry valvemust be designed for these conditions to reduce maintenance time and replacementcosts (See Fig C-430.)

Power companies, meanwhile, transport different materials, putting their ownset 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 differentpipeline 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 theslurry must be delayed, inspected, or redirected Knife-gate valves are also used inother applications, including industrial scrubber systems, waste-water treatmentsystems, 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 canhandle higher pressures The narrower valve fits tighter spaces and gives pipelinedesigners more flexibility Wafer-type valve dimensions meet a nationwidestandard, providing greater flexibility in choice of supplier because the valves areinterchangeable

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, smoothelastomer sleeves that seal the blade when the gate is closed and seal each otherwhen the valve is open, so the slurry can flow through unobstructed The elastomersleeves are designed to resist abrasion and corrosion and to cover the valve’s metalpar´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 itreplaced conventional metal seats and gate guides with easily replaceable snap-inelastomer sleeves, which are more durable and versatile, and handle higherpressure and temperature Conventional metal seats and gate guides can fill withhardened 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 theslurry system for maintenance repairs

This OEM wants to develop a greater variety of elastomer seals for the type valve to increase its efficiency and reliability in different applications Forexample, power companies prefer synthetic types of elastomers like neoprene, butyl

wafer-or viton, which handle high temperatures and cwafer-orrosive materials, while miningcompanies 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 steppermotor–driven valve has brought about more accurate control of fuel supply to a gasturbine, 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 towardderegulation is changing that “Pool rules for small generators,” which coveredgenerators 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 processgases 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 responsevalve is required Without such a valve, the exhaust gas thermocouples on the gasturbine would note larger swings in turbine exhaust temperature The key to PCS’ssuccessful 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 ofapplication is a “stepper” valve or its equivalent

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 byVosper Thornycroft (HSDE, UK) in the mid-1960s Now this valve type is made byother well-known manufacturers too, such as Moog, in Germany The term stepperactually 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 andthen the motor will stop With other motors, the motor has to continue to run inorder 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 happencausing the valve to fail, the stepper-type valve position would still lock and thesystem would continue running The valve then makes the system fault tolerant,which is critical in applications such as emergency power-supply generators It alsoprovides the fast response required by aeroderivative and some industrial gasturbines This is useful for both power generation and mechanical drive service.Before the stepper valve was introduced in the mid-1960s, hydraulic and pneumaticactuation valves were used to provide the required response time This increasedthe overall complexity of the fuel system As always, with instances where systemcomplexity 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” equivalentcontrol system

Development of valves that could compete with HSDE’s original stepper arosefrom competition with that early design As a result, there are now manymanufacturers who produce functional equivalents on the market for use in gas-turbine fuel systems, high-resolution controls for robots, automatic machiningcontrols, 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-typevalve and its equivalents generally include the following safety considerations:

 A fail-freeze or fail-closed option, depending on whether the operator is a generation facility (“freezing” at the last power setting is then required) or apipeline (in which case turbine shutdown on valve failure is required)

power- The liquid fuel version of the valve incorporates a pressure-relief valve protectingthe system against overpressure and the fuel pump running on empty or

“deadheading,” caused by closure of valves downstream of the fuel valve duringsystem 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 theservice is sour gas

Operational objectives of fast-response valves. Other operational objectives thatdictate design features are operator’s requirements for:

 Low mean time to repair (LMTR) The target of 1 h, achieved with modulardesign, together with the target MTBF provided an availability of 99.998 percentfor HSDE’s original stepper.

 Higher MTBF (In HSDE’s case, an initial development target of 50,000 h was setand achieved.)

 Low maintenance costs, since the modular design can be repaired by an individualwith 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 variationcompensation is provided The additional speed ratio–type control valve found inmany 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

Applications experience. Power production in phase II of the Petroleum Corporation

of Singapore was commissioned in June 1997 PCS is part of a massivepetrochemical plastics conglomerate in Singapore Power production was anafterthought, 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 normalambient conditions) Alstom GT10, although their power needs are roughly

26 MW This was because while SP were pleased to sell them their residualrequirement, they would not buy any power from SPPs at the time of original powerplant design

The turbine is fueled by three different types of fuel, depending on the state ofthe plant The British thermal units for each type varies, so again the fast responsetime 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 avoidthe sudden burst of excess temperatures that accompany higher heating value fuel.(North Sea platform users frequently operate gas, liquid, or gas and liquid fuelmixtures.)

Not all gas turbines are tolerant of a wide range of fuel types in a singleapplication Some of them require a whole different fuel system—nozzles, lines, andC-406 Controls, Retrofit

all components—to be able to handle a totally different heating value fuel In thisapplication in Singapore, the Alstom machine shows no sign of distress, which isinteresting 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 GT10operational data chart, figures, and curves here provide data for typical poweroutput with light oil and natural gas fuel The rest of the data is typical for theGT10.

PCS’s GT10 heat-recovery steam generator (HRSG) provides a reliable source ofsteam 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 inperformance or reductions in hot section component lives As already described,valve-response speed is another critical feature for ensuring the stability of thisapplication

Emissions and steam supply. The Alstom EV burner—a low NOx burner that can

be fitted and retrofitted on the GT10, fuel types permitting—was not fitted in thiscase 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 thatthis application involves Such fuels need a more forgiving fuel system, as well

as water or steam injection to keep the NOxdown The PCS Singapore applicationuses steam for NOxreduction purposes The steam is piped in through nozzles thatare adjacent to the fuel nozzles on the fuel manifold of the GT10’s annularcombustor

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 processcracker

In PCS’s case, one boiler has been found to suffice This is noteworthy as inapplications such as this, a redundant “packaged boiler” (running hot and onminimum load) is often found essential This is so that it is possible to pick up thesteam load should the turbine trip or be unavailable due to maintenance A commonsubject for debate is whether uninterrupted steam supply during the switch from HRSG mode to fresh-air firing is possible without flameout on the boilersupplementary 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 theJapanese, who are the most environmentally strict practitioners in Asia Steaminjection reduces NOxlevels from 300 to 400 mg/MJ fuel to just below 100 mg/MJfuel

(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 aswater, steam, and compressed air, to downstream companies, PCS directly producesand exports benzene, toluene, and xylene for global markets.)

Future potential for power generation in Singapore. The pressure for acceleratedderegulation is increasing in Singapore as well, if not as fast as in the rest ofsoutheast 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’sability 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 thiswhile maintaining NOx emissions below legislated limits for countries asenvironmentally strict as Singapore, speaks well for its continued use in similarapplications.

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-beltconveyors

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 throughspecial techniques that straighten, flatten, and make the ordinary strip suitable forwelding into endless bands continuously running around two terminals Theconveyors based on this specialized technology are designed for the processingindustries according to the needs of the product and the special needs of the steelbelt

Table C-34 summarizes a wide variety of steel-belt applications and the importantsteel-belt properties that make the applications successful The general categoriesthat are shown in Table C-34 are material handling, food processing, industrialprocessing, and presses for particle boards, plastics, and rubber Table C-34 alsoindicates the four major steel-belt grades that are in common use

The following discussions describe the applications and processes for which belt conveyors have been selected as the best of competing alternatives, includingthe types of materials used for conveyor belts

steel-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 combustionchamber area The heated coolant then flows through a thermostat to either theradiator to be cooled or to the coolant pump for circulation back to the engine (SeeFig 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 automotiveservice 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

(•) = property sometimes of importance

• = property always of importance

SOURCE : Sandvik Process System, Inc.

excellent base fluid for engine coolants, providing the necessary heat transfercharacteristics, boilover prevention, freeze protection, and, when adequatelyinhibited, corrosion protection.

PG coolants may be recycled using the same methods used by many maintenancefacilities to recycle traditional EG coolants, and similar additives can restore therecycled 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/waterantifreeze compositions and freeze protection may be easily measured usinginexpensive, commercially available devices

Results of comparison tests have demonstrated that propylene glycol is aseffective an engine coolant as ethylene glycol The testing program includedlaboratory bench-scale testing, engine dynamometer studies, and fleet tests on bothheavy-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 enginesdepends on two factors—the removal of heat from the engine as the liquid circulatesthrough the cylinder head and engine block, and the transfer of heat to the air bythe radiator Detailed studies and analysis of the mechanisms of heat transfer haveshown that although there are very slight differences between the heat transferproperties 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 enginedepends on heat transfer coefficients, which are dependent on the mechanism ofheat transfer At low heat flux (heat transfer rates), forced convection (heat transferbetween a solid metal surface of the engine and the liquid coolant) is thepredominant mechanism of heat transfer In this regime, the Prandtl number,which is dependent upon coolant physical properties, is the controlling factor inheat transfer At higher heat flux, the metal temperature increases and nucleateboiling (formation of some vapor bubbles at the heat transfer surface) occurs,increasing the efficiency of the heat transfer Under nucleate boiling conditions, thePrandtl number is no longer the controlling factor in heat transfer

At still higher heat flux, the surface temperature continues to rise, and too muchvaporization occurs for an efficient transfer of heat A vapor film may form thatblocks direct contact between the liquid coolant and metal surface At this point, adramatic drop in the heat-transfer coefficient occurs, causing a concurrent dramaticrise in the cylinder metal temperature and possible engine failure Ideally, a coolantwill operate in the convective and nucleate boiling regions and never reach filmboiling stage

Theory predicts that, because a PG/water coolant mixture has different physicalproperties than an equal solution of EG/water (e.g., slightly higher viscosity andslightly lower density), convective heat transfer will be 5–10 percent lower, whileheat 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 Detailedlaboratory and engine dynamometer studies of heat-transfer coefficients haveconfirmed these predictions These differences in the heat transfer over thecombination of low and high loads seen in normal vehicle operation approximatelyoffset 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 belethal to a dog, while a teaspoonful may kill a cat

When ingested by humans and animals, EG is metabolized to glycolic and oxalicacids, 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 ofpoisonings of dogs and cats According to an ASPCA survey of veterinarians, over100,000 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, accountfor 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 bynumerous federal and state health environmental acts in the United States, assummarized in Table C-35 These include the 1990 U.S Clean Air Act Amendmentsand CERCLA The U.S Federal Health and Safety Administration also requires aspecific label on ethylene glycol coolants warning of the toxicity

In the European Union, ethylene glycol is classified as a hazardous product andmust be handled according to strict regulations In Switzerland, Austria, and theCzech Republic, it is classified as a poison and its sale to the general public iscarefully regulated

Coolers, Dairy

Glycol is an effective and fast coolant, commonly used in the food and agricultureindustry Often used in large-scale industrial systems, glycol can also be used insmaller customized designs One example is a system designed in Hawaii’s dairysector for chilling the milk from cows on a small farm (300 to 900 cows) Milktemperature 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 temperaturesthere 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 wasfound to cool in 30 s (the time for milk to flow through the system) A variable speedmotor moves the milk through the cooler The refrigeration unit incorporates twoscroll 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 forfurther energy conservation Overall about $6000 in 1997 prices was saved inenergy 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 thatthey adhere to environmental safety standards Existing coolers may have “old”refrigerants, such as chlorofluorocarbons (CFCs), corrosive liquids, and gases, intheir cooling circuitry What follows is a summary of design environmentspecifications and standards, product selection charts, information on how to size

an air conditioner, typical mounting configuration, theory of operation, and someexample 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 drippingnoncorrosive 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-directedwater

Cooling; Cool, Products That (Air Conditioners); Liquid-Cooled Air Conditioners C-413

TABLE C-35 U.S Statutes Relating to Glycols

Propylene

1990 Clean Air Act Amendments (CAAA) None “Hazardous Air Pollutant”

42 U.S.C § 7412 (b)

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

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.