Process Engineering Equipment Handbook Episode 2 Part 8 pps

Releases of VOCs lead to ground-level ozone pollution when theseemissions occur in the presence of nitrogen oxides Fig.. The federal government has provisionally adopted the number of da

deceptively simple and is often misused Surface preparation is particularlyimportant because defects can easily be masked by overpeening.

In the analysis of service-exposed components such as discs and blades, ajudicious compromise is often required on the surface preparation Light glass beadcleaning is often effective in removing surface deposits with minimal loss insensitivity; however, care must be taken not to overpeen the surface Whereoptimum sensitivity is required, such as in rotating blades, the parts should bechemically etched after glass bead cleaning to remove metal peened over thediscontinuities

LPI is designed to locate only discontinuities that are open to the surface When

a penetrant is applied to the surface of a component, it is drawn into surfacediscontinuities by capillary forces After the excess penetrant has been removedfrom the surface, the penetrant trapped by the defects is drawn back out bycapillary action and forms a detectable outline of the defect

Over the years, many penetrants have been developed that vary in sensitivityand application As indicated in the enclosed information sheets from themanufacturers, the penetrants are divided into water washable and post-emulsifiable (solvent remover) types Commonly used penetrants include ZL-17B orArdrox 970-P10 (water washable) and ZL-22A (solvent type) Care must be taken

to ensure that the correct combinations of penetrants, removers, and developers areused In addition, a test should never be repeated using a different penetrant typebecause complete masking of the defects will occur

Field inspections are particularly challenging because the inspection conditionsare generally not ideal and often the operator does not have all the equipmentdesired Although some compromises are often required, the inspector must ensurethat the sensitivity and validity of the test are not jeopardized

Laser techniques. These can be used for inspection, calibration, and resolution surface mapping

highest-Computer-aided topography (CAT) scan. CAT scanners locate internal defects inengine components It is particularly useful for sophisticated components such asblades and airfoils with internal passages and cavities

 Laser welding: Extremely accurate and much less heat intensive thanconventional repair, laser welding is particularly useful for turbine blades,compressor blade leading edges, and other sensitive components

Metallurgy; Metallurgical Repair; Metallurgical Refurbishment M-37

 Weld repair using robotics*: The automation of turbine blade welding providesboth metallurgical benefits and production advantages Heat-affected zonecracking in sensitive superalloys, such as IN738 and IN100, can be eliminated

or greatly reduced by optimizing process control, and higher production yields can be achieved when welding jet engine blades However, the successfulimplementation of automated processes requires careful consideration andengineering of the technology package In particular, the equipment packagermust be experienced in the technology associated with turbine blade welding andincorporate appropriate tooling, measurement system, power source and roboticcontrols

 Superalloy welding at elevated temperatures (SWET): OEMs often develop theirown proprietary process for this technology that is commonly used on superalloy

or directionally solidified materials such as turbine blades

 Dabber TIG (tungsten inert gas): A slightly older process that uses TIG to rebuildknife edge seals with minimal heat warpage

 Plasma transfer arc: Similar to dabber TIG and used for the same components.The exception to the “land-based turbine design approaches aircraft enginetechnology standards” is evident in certain OEM models, such as Alstom’s GT11N2and GT35 However, that is because both these models are designed to take thepunishment meted out by vastly inferior fuels or just be conservative enough torequire less training for end-user operators and maintenance staff Alstom alsomakes sophisticated models with metallurgy that will match those of the “dual”(both aircraft engine and land-based engine) OEMs for users with differentrequirements and less punishing fuels However, Alstom also contracts powdermetallurgy repair, for instance

All OEMs can enhance their “benefits to end user” objectives from some for the preceding techniques, such as the ultimate time-saver laser machining Itultimately depends on the specifics of an end user’s application The potentiallyusable repair techniques on any end user’s selection play a huge role in determiningthe turbine model’s overall maintenance costs and therefore the ultimate crux ofgas turbine selection, called “total costs per fired hour.”

Basic Fundamentals of Materials

The properties of the materials used in gas turbines are determined by theircomposition and their prior processing and service history To understand how thesefactors work to govern alloy behavior, a basic understanding of some fundamentalprinciples of materials engineering is useful This is largely a question ofunderstanding some of the terms used by metallurgists in describing materialbehavior

Turbine materials are governed by the laws of thermodynamics, which basicallymeans that changes that take place in the materials result in a reduction of the

energy state in the material We often speak of the equilibrium or stable condition

of a material; this simply means the condition of lowest energy

Given infinite time, all materials would end up in their equilibrium condition In

* Source: Adapted from extracts from Lownden, Pilcher, and Liburdi, “Integrated Weld Automation for Gas Turbine Blades,” Liburdi Engineering, Canada, ASME paper 91-GT-159.

practice, there are kinetic barriers to achieving equilibrium and most materials are used in a metastable condition The most common kinetic barrier is the rate of

diffusion (i.e., the speed at which atoms in a solid material can rearrange

themselves) Almost all of the metallurgical reactions that occur in turbinematerials occur at rates governed by the speed of diffusion Examples include therate at which a coating interdiffuses with the base metal or the rate at whichstrengthening particles grow in an alloy

All of the materials used in gas turbines are crystalline in nature This means

that the atoms of the elements that make up the alloy are arranged in regularperiodic arrays or lattices, with each atom occupying a site in the array When we

refer to grain or crystal orientation, we are referring to the direction relative to this

crystal lattice The mechanical and physical properties of materials depend on theirorientation

In real materials, the crystals are not perfectly periodic, but contain various

lattice defects Two of the most important of these are dislocations and grain

boundaries Dislocations are an important class of planar defects, since their

presence within crystals leads to plastic deformation behavior Most materials arenot used as a single crystal, but as polycrystals that consist of many individual

crystals with different orientation called grains The interfaces between the individual grains are grain boundaries The size and degree of orientation between

grains and the nature of the grain boundaries are important in determining theproperties of a material

Metallurgists control the nature of grains by the processing performed duringmanufacture In a polycrystalline material, grains will increase in size at elevated

temperatures and thus grain growth will occur during high temperature heat

treatments Grain sizes can be reduced by introducing plastic work into a material

At high temperatures, the resulting strain energy drives the process of

recrystallization, which results in the formation of smaller grains during heat

treatments or hot-working operations

Engineering materials are almost exclusively mixtures of two or more elements,

which are called alloys Alloying elements can dissolve in the matrix of the principal elements to form a solid solution, in which the dissolved element is randomly

distributed in the crystal lattice The alloying elements can also react with the

matrix to form a compound that has a specific arrangement of atoms of each

element

Commonly both solid solutions and compounds will coexist within the same

material as different phases The stability of specific phases within a given alloy

system varies with the composition and the temperature Kinetics also determinewhich phases form within an alloy Many reactions are sluggish enough that the stable phase may not form initially and the alloy may exist in metastablecondition for some length of time By using chemistry and heat treatment to control the phases formed by an alloy, metallurgists can alter the strength ofmaterials

Three principal types of deformation take place upon the application of loads

to turbine materials Elastic deformation is instantaneous reversible deformation that results from the distortion of the crystal lattice Plastic deformation is the

irreversible deformation that takes place instantaneously through the movement

of dislocations through the crystal matrix Creep deformation takes place by a

variety of diffusion-controlled processes over time, resulting in continuing strainunder the applied load

At sufficiently high loads or after a critical amount of deformation has taken

place, fracture of a material will occur Fracture can be broadly classed as ductile

or brittle In turbine materials under most conditions, fracture occurs by the

Metallurgy; Metallurgical Repair; Metallurgical Refurbishment M-39

formation and linkage of internal cavities formed either by creep or plastic deformation.

When cyclic loads are applied to a material, cracking and fracture may occur by

the process of fatigue On a microscopic scale, fatigue occurs by localized plastic

deformation, resulting in the initiation and growth of macroscopically brittle cracks.The resistance of a material to deformation and fracture depends on its

composition and microstructure The size of grains, the size and distribution of

second phases, and the effects of alloying elements on the crystal lattice of thematrix all influence the mechanical behavior of the alloy

Exposure of alloy surfaces to operating conditions results in surface reactions

between the alloy and the environment Oxidation and hot corrosion occur at

elevated temperatures through direct reaction with oxygen and other environmental

contaminants Aqueous corrosion occurs in wet environments through dissolution

reactions

Material Selection for Gas Turbines

This subsection is with specific reference to gas turbine materials, the most severethermal application in a plant

The materials used in gas turbines or jet engines span the range of metallurgicalalloys from high-strength steel, to lightweight aluminum or titanium, to temperature-resistant nickel or cobalt superalloys In a gas turbine, the temperatures can varyfrom ambient to gas temperatures in excess of the melting point of superalloys and,therefore, the materials in the different sections must be selected on the basis oftheir capability to withstand the corresponding levels of stress and temperature.The following summary outlines the materials used in the different components ofthe gas turbine, along with a rationale for their selection

Compressor rotor

The temperature in a typical compressor will range from ambient to approximately800°F (425°C) The discs and blades rotate at high-speed and are, therefore, highlystressed and subjected to aerodynamic buffeting or fatigue In industrial turbines,the discs are generally made from high strength alloy steel and the blades frommartensitic stainless steel However, in jet engine derivatives, lighter materialssuch as aluminum and titanium are used for the blades and vanes in the front ofthe compressor In some cases, the last stages of the compressor can runsignificantly hotter and more creep-resistant materials must be used such as A286and IN718

Turbine discs

Turbine discs are highly stressed in the rim area where the blade root attachmentoccurs and in the hub of bored discs where high burst strength is required Thediscs are forged from high-strength steels in advanced industrial turbines and iron

or nickel base superalloys such as A286 and Inconel 718 for the jet engines Thedisc rim is generally isolated from the hot gas path and cooled to as low as 600°F(315°C) for alloy steel discs to ensure adequate material strength and creep resistance

Combustion cans

The flame temperature in a burner generally exceeds 3000°F (1650°C) Thetemperature is moderated by mixing with cooler compressor discharge air that flows

around the combustion chamber and through the slots in the walls to keep metalrelatively cool [approximately 1500°F (815°C)] The combustor cans are generallyfabricated from nickel base sheet superalloys such as Hastelloy X, Nimonic C263,and Inconel 617 These alloys have good weldability and oxidation resistance.

Turbine vanes

The stationary vanes in a turbine act as guides for the hot gas to ensure that itenters the blade’s airfoil at the right angle and with minimal pressure loss Theapplied stresses are generally low; however, they are subjected to turbine inlet gastemperatures which, in some engines, exceed the melting point of the material[2500°F (1370°C)] The vanes are generally made from cobalt base alloys such

as FSX414 and X45, which have good castability and excellent oxidation andthermal shock resistance In advanced designs, the vanes are cast with integralcooling passages to reduce the metal temperature The cobalt base alloys aregenerally weldable and minor weld repairs are often allowed In some designs, the cobalt base alloys have been replaced with more creep-resistant nickel basealloys such as IN738, Rene 80, and IN939, which are significantly harder to weldrepair

Turbine blades

Turbine blade airfoils are subjected to the most severe combination of appliedstresses due to centrifugal and bending loads and high temperatures The bladematerials must have excellent strength and creep resistance, as well as oxidationresistance In advanced units, the blades are cooled by internal passages tomoderate the metal temperature and improve blade life The blades are generallyprecision forged or cast from nickel base alloys such as Udimet 520, IN738, Rene

80, and Mar M247 and can be manufactured as either equiaxed, directionallysolidified, or single crystal castings These materials have poor weldability andrepairs must be approached with extreme caution

Service life for turbine components

Once in service, critical gas path components require care and attention to optimizetheir life potential Often, turbine users choose to abdicate their responsibility inthis critical area and elect to rely solely on the manufacturer for guidance However,this can lead to premature component replacement of failures if components areneglected or improperly assessed

A gas path component management program basically involves the detailedcharacterization of components at established intervals For example, during majoroverhauls, representative blades are removed and destructively tested for corrosion,microstructure, and remaining creep life The data are tabulated and a life trendcurve established for the material This will provide the user with specificinformation on how the engines are standing up rather than rely on someone else’s data and provide advance warning of impending problems with corrosion orcreep

Creep damage can be detected in turbine blades by judicious testing of samplesfrom the airfoil and by metallurgical inspection With prolonged service exposure

at high temperature and stress, cavities are formed at the grain boundaries of thematerial that, with time, will grow in number and size and eventually join to form

a crack However, if creep voiding can be detected prior to surface crack formation,the parts can be rejuvenated by hot isostatic pressing (HIP)

Metallurgy; Metallurgical Repair; Metallurgical Refurbishment M-41

During HIP, the parts are subjected to a combination of pressure and temperaturethat collapses any internal cavities and diffusion bonds the surfaces back together.Tests have shown that, in most materials, HIP is capable of fully restoring theproperties and, therefore, offers the opportunity to recycle and extend the life ofserviced blades.

Steam-turbine metallurgy

Steam turbines operate in far less demanding service than gas turbines as thefollowing list of typical steam turbine materials illustrates

Typical steam turbine materials

Manufacture

Superalloys

The term superalloy is popularly used to define a material having structuralstrength above 1000°F (540°C) The development of these temperature-resistantmaterials in the early 1940s was a primary catalyst for jet engine development Thetwo technologies have been interrelated ever since and, as the temperaturecapability of materials was improved, so did the turbine efficiency The enclosedgraph illustrates the strength improvements obtained through alloy developmentand how the chemistry and microstructure became more complex with eachevolution

Basically, superalloys can be categorized into three chemical families: iron base,nickel base, and cobalt base All alloys contain additions of chromium andaluminum for oxidation resistance and variations of aluminum, titanium,molybdenum, and tungsten for strength The nickel base superalloys offer thehighest strength and are generally chosen for rotating blade applications Thecobalt base alloys, although weaker, offer better environmental resistance and aregenerally chosen for stationary vane applications

From a metallurgical point of view, all superalloys exhibit an austenitic or gmicrostructure that, unlike steel, does not undergo any transformation as it isheated to its melting point The alloys derive their strength from three principalmechanisms:

1 Solid solution hardening of the g matrix resulting from the coherency strains orstiffening effect or larger atom elements such as chromium, molybdenum, andtungsten.

2 Precipitation of small g ¢ particles Ni3 (Al, Ti) throughout the matrix act asobstacles to dislocations or strain flow The g ¢ phases precipitate on cooling fromthe solution temperature and during aging treatments

3 The formation of blocky carbides at the grain boundaries act to pin the grainboundary and prevent grain boundary sliding during creep

Manufacture: Castings and Forgings

There are two main routes by which superalloys are manufactured into turbinecomponents: casting and forging

Forged parts are made by hot-working cast ingots or powder metallurgy compactsinto billet or bar and eventually into the final shape Since it involves significantplastic deformation, considerable refinement of grain size can be achieved throughrecrystallization; however, the alloy must also have good ductility at the forgingtemperature Consequently the higher strength superalloys cannot be manufactured

by forging Turbine discs, some turbine blades, and compressor components aremade by forging

Cast parts are formed by pouring molten alloy into near-net-shape molds andallowing them to solidify The investment casting process used allows extremelycomplex shapes, including cooling passages, to be cast in Molds are made bydepositing a ceramic layer around a wax form and melting the wax to form a cavity,while ceramic cores are used to cast internal passages Because the process doesnot involve the deformation of the alloy, ductility is not an important consideration.Turbine blades and vanes are commonly made by casting

A modification of the investment casting process is used to produce directionallysolidified and single crystal components To produce components in these forms,alloy is cast into molds that are subsequently withdrawn from a furnace at acontrolled rate By controlling the solidification of the casting, the grains are forced

to grow in one direction and by using a crystal selector at the base of the casting,the casting can be made as a single crystal Such components have improved creepand thermal fatigue resistance because there are no grain boundaries orientedperpendicular to the principal stress direction Because of their high cost, such partsare typically limited to first-stage turbine blading

Metering, Fluids; Metering Pumps (see Fuel Systems)

Mist Eliminators (see Separators)

Mixers (see Agitators; Centrifuges)

Monitoring (see Condition Monitoring)

Motors (see Electric Motors)

Motors M-43

Noise and Noise Measurement (see Acoustic Enclosures, Turbine)

Noise Silencing and Abatement (see Acoustic Enclosures, Turbine)

Nondestructive Testing (FP1, MP1, X Ray) (see Metallurgy)

Nozzles

Nozzles can mean nozzles in the airfoil sense, i.e., inlet guide vanes on gas turbines

or steam turbines See Metallurgy.

Nozzles can also be used to eject (see Ejectors) or spray Spray-nozzle applications

are too numerous to itemize and must be customized for each application Spraynozzles in gas-turbine fuel systems, for instance, are typically for one-, two-, or dual-phase fuel streams (gas; gas and liquid; or gas, liquid, and a mixture of gas andliquid) Spray nozzles can also be used extensively in metallurgical processes such

as plasma coating

Increasingly, for uniform flow distribution, spray patterns are CNC systemcontrolled A robot that sprays plasma is one such example This robotic CNC orPLC control system is generally customized for most applications

N-1

O Oil Analysis

Some plants have oil-sample analysis done on oil samples taken from oil drains ontheir turbomachinery packages Metallic particulate content is trended for a clue

as to what problems may occur For instance, rising content of babitt may indicate bearing wear and/or incipient bearing failure The problem of using thistechnique with rotating machinery is that most of this machinery turns so fast, themachine may fail between sampling analyses Oil analysis has a far better chance

of detecting deterioration in slower reciprocating machines, provided the samplesare analyzed expeditiously

Oil Sands; Synthetic Crude; Tar Sands; Shale

Oil sands and tar sands are synonyms for the same material Synthetic cruderesults from processing oil sands Shale is similar to oil sand in that it is a category

of soil/rock that contains oil that can be extracted

Certain areas of the world have large deposits of oil sands (northern Alberta,Canada) or shale (China and the United States) that oil can be extracted from,either by mining the soil and processing it or directing leaching steam into theground The latter process recovers only about 60 percent of the oil The formerprocess can recover more oil but is expensive to design and build because of thehigh level of corrosion and erosion problems experienced

This technology is significant to process engineers in that it provides usefulinformation on what equipment can survive the harshness of this process: suchequipment would be suitable for similarly demanding processes elsewhere FigureO-1 is a simplified line diagram of synthetic crude manufacture from processing oilsands

Reference and Additional Reading

1 Soares, C M., Environmental Technology and Economics: Sustainable Development in Industry,

Butterworth-Heinemann, 1999.

Oxygen Analysis

Oxygen analyzers used to have applications in turbine and boiler design; theymonitored fuel/air ratios Now the zirconium oxide probe for oxygen analysis isfound to have applications in process operations as well, where turbines areinvolved These applications give the probe some predictive solving potential, whichmost rotating machinery engineers might depend on other indicators (such asvibration analysis) for

O-1

Oxygen Analysis Produces Profitable Power Plants*

A recent survey of instrument engineers from European power companies has indicated that many have expanded the utility of the ZrO2oxygen probe beyond itstraditional use as a tool to optimize fuel/air ratios

Most operators of large boilers have come to realize that significant stratificationcan exist in the ductwork carrying flue gases (See Fig O-2.) By installing an array

of O2 probes, and averaging the outputs, an average signal is generated that issuitable for use in automatically trimming fuel/air ratios

While averaging for control purposes is increasingly common, many operatorsdemand a trend display of each individual probe By watching the relative O2values,many operators feel that they can detect problems with fouling at individualburners, slag accumulation, or even problems with coal fines at a pulverizer TheO2measurement is increasingly taking on a “predictive maintenance” function

 Air heater leakage. An increasing number of customers are utilizing the O2measurement to detect seal leakage at air preheaters This is particularlyeffective when utilized with rotating units Air leakage at the preheater is notonly a strong indicator that maintenance is required, it negatively affects thermalheat rate efficiency See Fig O-3

FIG O-1 The production of synthetic crude oil (Source: Syncrude Canada Limited.)

* Source: Adapted from extracts from Simmers, “Oxygen Analysis Produces Profitable Power Plants,”

IPG, January 1998.

 Flue gas recirculation. One NOxreduction strategy is to mix some flue gas intothe combustion air prior to the burner, preventing the formation of thermal NOx.

An O2analyzer placed downstream of the mixing point can be utilized to maintain

a specific final O2set-point (See Fig O-4.)

It should be noted that the ZrO2 sensing cell is mildly sensitive to pressurechanges, whereby each 10 mm of H2O pressure = 1 percent change in reading(not a 1 percent change in O2) Some windboxes may experience pressures highenough to require a pressure balancing accommodation to compensate

 NO x predictor. Thermal NOx is dependent in great part on the amount of O2available, as well as temperature at the burner Increasing numbers of stationsare watching O levels as an indication of NO production (See Fig O-5.)

Oxygen Analysis O-3

FIG O-2 Most operators realize that significant stratification can exist in ductwork carrying flue gases (Source: Simmers.)

FIG O-3 Oxygen measurement can be used to detect seal leakage in air heaters (Source:

Simmers.)

Industrial activity and motor vehicle emissions produce ozone, a greenhouse gas

As desired ozone levels are legislated toward, its effects need to be familiar toprocess and industrial engineers

Two problems to be considered are ground-level and stratospheric ozone (As asample country for data comparisons, Canada has been selected.)

It is important not to confuse the problem of ground-level ozone pollution with

FIG O-4 Using O 2 measurement to control NO x formation (Source: Simmers.)

FIG O-5 Using O 2 to predict NO x formation (Source: Simmers.)

* Source: Environment Canada Adapted with permission.

the thinning of the stratospheric ozone layer About 90 percent of atmospheric ozoneoccurs in the stratosphere, a layer that extends from about 15 to 50 km above theEarth’s surface There it performs the critical function of absorbing harmfulultraviolet (UV) radiation emitted by the sun At present the stratospheric ozone isthinning and providing plants and animals with less protection from the harmfuleffects of excess UV radiation than in the past This is an urgent problem; however,

it is not the topic of the fact sheet

The ozone problem at the Earth’s surface is accumulation rather than depletion.The normal state of affairs at ground level is for ozone to form and almostimmediately break down, at the same rate at which it is being produced, byreleasing one oxygen atom Figure O-1 shows the chemical cycle involving oxygen(O2) and two of the nitrogen oxides (NOx) (in this case, nitric oxide and nitrogendioxide), sunlight, and high temperatures that governs the formation andbreakdown of ground-level ozone Problems arise when volatile organic compounds(VOCs) (see “Chemical precursors of ground-level ozone” for a description of VOCs)are added to the mix (Fig O-6)

Because the buildup of ozone at ground level depends upon the concentration ofother pollutants, as well as temperature and sunlight, ozone levels usually peak inthe late afternoon of hot summer days and can persist into the evening and night.Just how much ozone builds up varies considerably from year to year and fromregion to region, but summers that are hotter than normal generally produce moreepisodes of ozone pollution

Chemical Precursors of Ground-Level Ozone

Ozone is a secondary pollutant in that it is not emitted directly to the atmosphere.Nitrogen oxides and VOCs, both of which are emitted by natural processes andhuman activities, are called ozone precursors because they must be present forozone to form (Fig O-7)

and bacterial action in the soil About 95 percent of human-caused emissions ofnitrogen oxides come from the combustion of gasoline, diesel fuel, heavy fuel oil,natural gas, coal, and other fuels, notably in motor vehicles, heavy equipment,turbines, industrial boilers, and power plants (Fig O-8).

Volatile organic compounds

The term volatile organic compounds (VOCs) is used to describe carbon-containing

gases and vapors that are present in the air, with the major exceptions of carbondioxide, carbon monoxide, methane, and chlorofluorocarbons VOCs are given off bytrees and other vegetation, particularly in heavily forested areas The combustion

of fossil fuels, especially in cars and trucks; certain industrial processes; and theevaporation of some liquid fuels and solvents found in cleaning solvents, oil-basedpaints, varnishes, stains, and thinners are important sources of human-causedVOCs (Fig O-9) Releases of VOCs lead to ground-level ozone pollution when theseemissions occur in the presence of nitrogen oxides (Fig O-7)

Effects of Ground-Level Ozone

Effects on human health

Ozone is a very irritating and harmful gas It adversely affected lung function inyoung, normal subjects who exercised for 6 h in concentrations as low as the presentCanadian 1-h objective of 82 parts per billion (ppb) (A part per billion is a unit ofmeasure used to describe the concentration of atmospheric gases In this case, theunit represents one molecule of ozone in one billion molecules of all gases in the

FIG O-7 In unpolluted air, ground-level ozone forms and breaks down in a steady cycle Scenario b shows one way that

pollutants disrupt the natural equilibrium (Source: Environment Canada.)

air.) When lung function is affected, ozone has probably caused inflammation in the lung.

Scientific studies show that after a few days of continuous exposure to ozone,respiratory discomfort disappears However, although little is known of the long-term effects of repeated ozone exposure on humans, recent research on animalssuggests that it may lead to irreversible changes in lung function

When ozone levels exceed 82 ppb, there is evidence that more people are admitted to hospitals with acute respiratory diseases In 1987 it was reported thathigh ozone levels coincided with increased admission of patients with acuterespiratory disease to 79 hospitals in southern Ontario However, it is difficult toseparate the effects of ozone from those of sulfate in these epidemiological studies.Furthermore, the health effects of individual pollutants may be intensified whentwo or more pollutants occur together

High concentrations of ozone may affect the health of people and vegetation and corrode materials.

Heavy exercise for 2 hours at an exposure of 120 ppb may lead to coughing,shortness of breath, and pain on deep inhalation in healthy adults Exposures above

120 ppb have resulted in dryness of the throat, shortness of breath, chest tightnessand pain, wheezing, fatigue, headache, and nausea

People working or exercising outdoors inhale larger quantities of air and maysuffer more during episodes of ozone pollution Children are more susceptiblebecause they spend more time outside than adults Studies showed that children

at summer camps in Canada and the United States where they were exposed to atypical summer mix of pollutants, including ozone, experienced a measurabledecline in lung function

Ozone causes similar decreases in lung function in people who have asthma as

in those who do not, but the loss is more likely to be serious in those whose lungsare already unhealthy In clinical studies, people with asthma do not respond toozone differently than any other population However, there is recent evidence thatwhen asthmatics are exposed to ozone their sensitivity to allergens is heightened.Lung function is known to decline with age Studies of the exposure of humanpopulations to ozone have noted an increase in the rate at which lung functiondeclines Scientists are researching whether long-term exposure is causing changes

in human cells and tissues

The savings that could be achieved by cutting ground-level ozone pollution are likely considerable.

Effects on vegetation

Ozone is now viewed as the most important pollutant affecting vegetation Canadian research on the impact that ozone is having on farming has focusedmainly on southern Ontario, where ozone levels are typically highest Estimates ofthe cost of reduced yields in southern Ontario range from $17 to $70 million,depending on the number of ozone events Ozone damage to crops also occurs inother regions Value of lost production in the Fraser Valley has been estimated as

$8.8 million annually

Ozone damages leaf tissue Leaves may become mottled with yellow, exhibit smallblack or white spots, develop larger bronze-colored, paper-thin areas, or exhibitother visible symptoms Inside the leaf, ozone can inhibit metabolic activity, destroythe walls of cells, damage chlorophyll, and reduce photosynthesis The plant as awhole may grow 10–40 percent more slowly, age prematurely, lose its leaves duringthe growing season, and produce pollen with a shorter life span

The effects of ozone on ecosystems are difficult to measure, because species vary

in their susceptibility In forest ecosystems, exposure to ozone may lead to increasedvulnerability to disease and other stresses, increased mortality of individuals, andeventually to overall decline of affected species Both the degree of, and reasons for,the decline in forest health in eastern North America are still debatable, but ozone

is believed to be partly responsible for the reported decline of red spruce, sugarmaple, and white birch (See Fig O-10.)

Damage to materials

Ozone can lead to the development of cracks in products made of rubber or syntheticrubber, such as tires, boots, gloves, and hoses Continued exposure to high levels ofozone can cause these products to disintegrate completely Ozone accelerates thefading of dyes; damages cotton, acetate, nylon, polyester, and other textiles; andaccelerates the deterioration of some paints and coatings

It is difficult to pin down the costs of this type of ozone damage The economicimpact in the United States has been estimated at $1 billion, but a similar estimatehas yet to be prepared for Canada

Ambient Air Quality Objective for Ozone

An air quality objective is a statement of the concentration of a specified airpollutant that should not be exceeded beyond a specified length of time, in order toprovide adequate protection against adverse effects on humans, animals, plants,and materials Pollution control agencies routinely monitor the levels of airpollutants and compare the levels with air quality objectives This allows them tomeasure their progress in controlling air pollution

The maximum acceptable level for ground-level ozone in Canada is set at 82 ppbover a 1-h period (see Fig O-11) An “episode” occurs when the average ozoneconcentration exceeds 82 ppb for 1 h or more Ozone episodes in Canada typicallylast from one to a few days It is considered that natural levels of ozone inunpolluted conditions would range between 15 and 25 ppb

Ozone O-9

FIG O-10 Grape leaf with ozone exposure damage (Source: Environment Canada.)

The federal government has provisionally adopted the number of days per yearwhen ozone concentrations exceed the 1-h air quality objective as its indicator forground-level ozone (Environment Canada, Indicators Task Force 1991) Theobjective of the National Environmental Indicators Project is to develop credible,understandable indicators of environmental conditions These numbers will helpdecision-makers to make choices consistent with sustainable development and toevaluate the country’s progress toward that goal.

Emission Control Options

Measures to control ground-level ozone concentrations focus on the reduction of emissions of nitrogen oxides and VOCs.

Because ground-level ozone is a secondary pollutant, formed by the reaction ofprimary pollutants, measures to control ground-level ozone concentrations focus

on the reduction of emissions of nitrogen oxides and VOCs The amount of ozoneformed depends on the ratio of nitrogen oxides to VOCs in the atmospheric mixture.Under certain conditions, ozone formation could be limited more effectively bycontrolling nitrogen oxides more than VOCs, and under other conditions the reversecould be true The complex nature of the problem has made evaluation of controlstrategies difficult Computer models are needed to predict the degree of ozoneformation based on particular atmospheric conditions As warm temperatures and

FIG O-11 Maximum 1-h ozone concentrations for Canadian cities, based on an average of the three highest years during 1983–90 (Source: Environment Canada.)

Ozone O-11

sunlight are needed for ozone formation, it is especially important to reduce summerdaytime emissions

International focus for the control of nitrogen oxides and VOCs

International protocols: In 1988, Canada and 24 other countries signed a protocol

to stabilize emissions of nitrogen oxides at 1987 levels by 1994 Canada, the UnitedStates, and 19 European countries signed another protocol in November 1991 toreduce the emission of VOCs and their transport across international boundaries.The protocol commits Canada to a 30 percent reduction in annual VOC emissions

in the Lower Fraser Valley and Windsor–Quebec Corridor by 1999 based on 1988levels Canada is also committed to a national freeze on VOC emissions at 1988levels by 1999 (United Nations Economic Commission for Europe 1991)

The Canada–U.S Air Quality Accord: In March 1991, Canada and the United

States signed an Air Quality Accord This agreement addresses the acid rainproblem and provides for the study and control of those air pollutants thatcommonly move across the Canada–U.S border Annexes will be developed tospecifically address urban smog

International Joint Commission recommendations on air quality in the Detroit– Windsor–Port Huron–Sarnia Region: In March 1992, the International Joint

Commission (IJC) highlighted the need for governments to phase out emissions ofair toxics in the region Among 19 recommendations, the IJC promoted development

of a joint regional ozone control strategy that includes emission controls for mobile and stationary sources, including coke ovens A common ground-level ozonestandard has also been recommended for the region

Canada’s management plan for nitrogen oxides and VOCs

A national plan has been developed for the management of nitrogen oxides and VOCs.

A national plan for the management of nitrogen oxides and VOCs has beendeveloped by federal and provincial governments through the Canadian Council

of Ministers of the Environment Initiated in 1988 as a coordinated approach

to reducing levels of ground-level ozone throughout the country, the plan wasdeveloped in consultation with industry, public interest groups, and environmentalgroups It aims for consistent attainment of the 1-h ground-level ozone air qualityobjective of 82 ppb by the year 2005 Implementation is occurring in several phases:Phase I (in place by 1995):

a National Prevention Program: The program outlines 31 initiatives that willreduce emissions of nitrogen oxides and VOCs, including the following:

 Energy-conservation and product-improvement measures:

 Energy efficiency standards in equipment and appliances

 Energy audits by industry

 Reductions in emissions when surface coatings are applied and whenadhesives, sealants, and general solvents are used

 Public education to promote informed consumer choice and an environmentally responsible lifestyle including:

 Energy-conserving driving habits and alternative transportation modes,such as cycling, walking, and ridesharing

 Energy conservation

 The use of energy-efficient products

 The construction of energy-efficient homes and businesses

 Improved solvent use and recycling

 Source control initiatives:

 New emission standards for cars and light trucks

 Caps on emissions of nitrogen oxides from trains

 Emission guidelines for new sources, i.e., power plants, industrial boilers,and compressor engines, as well as for storage tanks for volatile liquids,chemical processes used by industry, commercial and industrial coatingapplications, printing, degreasing, and dry cleaning

b Remedial programs: The plan identifies 27 sample regional initiatives for reducing ozone, which could be implemented in the three ozone problem areas:the Lower Fraser Valley, the Windsor–Quebec Corridor, the Southern AtlanticRegion Most initiatives involve the installation, retrofit, or enhancement ofemission-control technologies for existing sources

c Study initiatives: The plan outlines 24 research initiatives aimed at determiningthe most effective control strategies for limiting the formation of ground-levelozone Ambient air monitoring, modeling, and studies of industrial processes andemission sources will help to determine what controls on emissions of nitrogenoxides and VOCs will be necessary in Phases II and III of the plan

d Federal–provincial agreements: Federal–provincial agreements will establishthe responsibilities of the respective governments for specific remedial actionsrequired to reduce ground-level ozone concentrations The agreements will alsoset out interim targets for emission reductions

Phases II and III: Phase II of the management plan will establish emission capsfor problem areas for the years 2000 and 2005 To meet these caps, it is likely thatadditional steps, over and above the initiatives laid out in Phase I, will be needed.Phase III will make final adjustments to emission caps and control programs.Implementation of Phase I of the NOx/VOC management plan should be asignificant step toward solving the country’s ground-level ozone problem by 2005.Maximum ground-level ozone concentrations should be reduced by 15–35 percent

as a result of predicted Canadian and U.S emission reductions In addition, jointCanada–U.S emission reductions will lead to a 40–60 percent reduction in the timeduring which the maximum acceptable ground-level ozone objective (82 ppb) isexceeded in the regions of greatest concern

Some regional remedial measures already underway

 The Montreal Urban Community has passed regulations that require dry cleaning

and printing facilities, surface-coating applications, and metal degreasingoperations to control emissions Substantial reductions have been achieved

 The B.C Motor Vehicle Branch is implementing mandatory vehicle emission

testing starting in late 1992 under the Air Care Program As a condition of annual

license renewal, all light-duty vehicles in the province’s Lower Mainland will beinspected for exhaust emissions and emission-control systems Those not meetingthe standards will undergo repairs

Global efforts to address stratospheric ozone depletion have been underway since

1981 The Vienna Convention for the Protection of the Ozone Layer entered intoforce on September 22, 1988 As of March 1, 1989, thirty-seven countries,representing the vast majority of the industrialized nations of the world, hadratified this Convention The Convention provides the framework for cooperativeactivities, including the exchange of data or information related to the ozone layer.This Convention provides for the subsequent creation of protocols (free-standing

treaties) for matters such as control of specific pollutants or families of pollutants.The first such protocol created was the Montreal Protocol on Substances thatDeplete the Ozone Layer.

The Montreal Protocol was signed in Montreal, Canada on September 16, 1987

It is clearly a watershed in cooperative and collaborative international undertakings

It introduces many new features never before established in international law.The Montreal Protocol had two requirements for entry into force; namely, 11signatures of ratification by countries and these countries must represent at leasttwo-thirds of global consumption of the controlled substances The MontrealProtocol entered into force on January 1, 1989, and as of March 1989 had alreadyattained 33 ratifications, again representing most of the industrialized states of theworld

On May 1988, Environment Canada published its first Control Options Report,titled: “Preserving the Ozone Layer: a first step.” This report set out a series ofoptions to implement regulations to meet Canada’s obligations under the MontrealProtocol

The Montreal Protocol calls for a 50 percent cutback in the 1986 levels ofconsumption of five chlorofluorocarbons (CFC 11, 12, 113, 114, and 115) and a freeze

at 1986 consumption levels of three brominated fluorocarbons called Halons (Halon

1211, 1301, and 2402) At a series of United Nations Environment Programme(UNEP) meetings held in The Hague, Netherlands, in October 1988, the world’sleading scientists expressed the consensus viewpoint that the Antarctic hole willremain unless the emissions of controlled CFCs are reduced by at least 85 percentfrom 1986 levels The target reductions contained in the Montreal Protocol arecurrently undergoing international review This review is expected to culminate inamendments that will tighten the Montreal Protocol Canada contributed to boththe organization and conduct the UNEP meeting in The Hague and fully supportsthe notion of reducing consumption further

On February 20, 1989, the Federal Government of Canada announced that it hadset as its objective the complete elimination of controlled CFCs within the next 10years It also called on the rest of the world to set as its common target a reduction

of no less than 85 percent by no later than 1999 The Minister of the Environmentfurther announced that the following actions would be taken to achieve theCanadian objective

1 Implement the protocol

As a first step, regulations will be enacted under the Canadian EnvironmentalProtection Act to implement the current control requirements set out in the protocol.These are a freeze in consumption at 1986 levels (CFCs on July 1, 1989, and Halons

on January 1, 1992) and a two-step reduction in annual consumption of CFCs to 50percent of 1986 levels by 1999

2 Regulate a reduction in chlorofluorocarbon consumption of at least 85 percent

Draft regulations recently released call for at least an 85 percent reduction of thecontrolled CFCs by no later than 1999 Consultation on what is achievable isexpected to increase the percentage reduction and tighten the time frame

3 Prohibit specific CFC uses

As a third step, draft regulations have been released for discussion purposes thatwould prohibit the use of ozone-depleting substances for nonessential uses or wheresubstitutes are available For example, the import, manufacture, and sale of aerosol

Ozone O-13

products containing controlled CFCs (with the exception of certain medical andindustrial applications for which alternatives are not yet available or for which firesafety is a particular concern); food packaging foam including food and beveragecontainers containing or manufactured with controlled CFCs; portable handheldfire extinguishers for home use containing Halons; and small pressurized canistersthat contain CFCs, including refrigerants, air horns, and party streamers, will beprohibited by January 1, 1990 As safe alternatives become available, a similarprohibition will apply to the following aerosol products: release agents for moldsused in the production of plastic and elastomeric materials, cleaners and solventsfor commercial use on electrical or electronic equipment, and products used inmining applications where fire hazard is critical.

4 Further control measures

As a fourth step, this comprehensive control options report has been prepared tofocus discussion on the earliest possible prohibition dates for remaining CFC uses.Some examples of prohibition dates proposed in this report are as follows:

a New refrigeration and air-conditioning equipment (1994–1999)

b Existing equipment maintenance (as replacements are available)

a Hospital sterilants, optical coatings (1990–1994)

As these remaining uses are prohibited, the total allowable quantities of controlledCFCs produced and consumed in Canada will be lowered

This Control Options Report, “Preserving the Ozone Layer: A Step Beyond theMontreal Protocol,” describes the most promising options to control ozone-depletingsubstances for each process group and product group including rigid and flexiblefoams, refrigeration and air conditioning, solvents, sterilants, aerosols, and firesuppression systems in which controlled CFCs and Halons are used The controloptions comprise three main categories:

 Emission controls

 Chemical and process substitutes

 Product substitutes

Depletion of Ozone in the Stratosphere

As excess ozone at lower atmospheric levels is a problem, reduced ozone in thestratosphere is also dangerous to life Industry is therefore being pressured to takesteps to alleviate this problem Some background information follows

Figure O-12* describes effects of ozone on vegetation and health

Benefits and costs †

The benefits of the Montreal Protocol consist of two components For benefitsassociated with reduced damage to materials, reduced damage to agriculturalproductivity, and reduced damage to fish stocks, estimates of the dollar amounts ofbenefits are shown For health impacts, including reduced incidence of skin cancers,reduced fatal skin cancers, and reduced cataract incidence, estimates of avertedhealth effects are shown In both cases, the framework for producing the estimates

is the same Effects are estimated for the scenario in which no controls on theconsumption of ozone-depleting substances are implemented relative to thealternative scenario represented by the introduction of the Montreal Protocol.The overall benefits of the Montreal Protocol are shown in summary form in TableO-1 This table shows quantified dollar benefits of $459 billion plus a reduction inskin cancer cases of 3.4 million, 129 million fewer cataract cases, and more than330,000 reduced fatalities

Montreal Protocol costs are also substantial but small relative to benefits Thepresent discounted value of protocol costs over the time period from 1987 to 2060total $235 billion Although substantial, these costs are less than the quantifiablebenefits from reduced damages to agriculture, fishing, and materials The benefitsfrom averted health effects are extremely large in relation to the costs If reducedfatalities from skin cancers alone are considered, the number of cases averted from

1987 to 2060 is 333,500

Costs of Replacing Ozone-Depleting Substances ‡

Overview and methodology

The methodology for assessing the costs of implementing the Montreal Protocolfocuses on the economic costs of the controls that have been introduced In theeconomics literature, this is frequently referred to as assessing the real resourcecosts of the policy See Table O-2

As an example, consider refrigeration and air-conditioning services Assume inthis example that a constant quantity of these services will be produced—that is,there are no price impacts on this quantity Prior to the regulation, CFCs are used

as refrigerants throughout this sector As a result of the introduction of the MontrealProtocol, a number of changes are made in this sector to reduce and then eliminate CFCs The economic cost of the regulation is the difference in the cost

of producing these outputs prior to the control and after it is introduced

In this cost methodology, the real resource costs that are relevant consist of theadditional quantity of resources needed to produce this constant level of output

Ozone O-15

* Source: Environment Canada, “Preserving the Ozone Layer: A Step Beyond,” April 1989 This report was written with specific reference to Canada, but provides applications information for readers anywhere.

† Source: Adapted from extracts from Environment Canada, “Montreal Protocol 1987 to 1997: Global Benefits and Costs of the Montreal Protocol on Substances That Deplete the Ozone Layer.”

‡ Source: Environment Canada SOE Sheet 92-1, written with specific reference to the U.S.–Canada Air Quality Agreement and Ozone Levels in Canada.

Other private sector costs may be incurred that are not reflected in the economiccosts described above If the price of CFCs increases, for example, due to regulatoryrestrictions on quantity, some private sector users will register this as an increasedcost This is not a economic cost, however, because no additional input resourcesare required to produce the output in question Viewed somewhat differently, theprice increase is not an economic cost because the additional costs of the purchasersare exactly offset by the additional revenues of the producers.

In any regulatory scenario, we would expect to observe both real resource costimpacts and price impacts as described above Economists refer to the price effects

as transfers in that they involve transfers from one group in society to another In

FIG O-12 Effects of ozone on vegetation and health (Source: Environment Canada.)