ED 086 492

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Air Pollution, Causes and Cures.Manufacturing Chemists Association, Washington,D.C.[73]24p.Manufacturing Chemists Association, 1825 ConnecticutAvenue, N.W., Washington, D. C. 20009 (Free)

MF-$0.65 HC-$3.29*Air Pollution Control; Diagrams; *Environment;*Environmental Influences; Industry; *InstructionalMaterials; *Pollution; Resource Materials;Technology

ABSTRACTThis commentary on sources of air pollution and air

purification treatments is accompanied by graphic illustrations.Sources of carbon monoxide, sulfur oxides, nitrogen oxides, andhydrocarbons found in the air are discussed. Methods of removingthese pollutants at their source are presented with cut-away diagramsof the facilities and technical processes. Car pollution controls andfactory flue air-filtering systems are among these illustrated.(JP)

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CAUSES & CURES

MANUFACTURINGCHEMISTS

ASSOCIATION1825 CONNECTICUT AVENUE, N W. WASHINGTON. D C. 20009

Founded in 1872,

the Manufacturing Chemists Association

is the oldest chemical trade organization

in the Western Hemisphere.

Its member companies

represent more than 90 percent

of the production capacity

of basic Indust; al chemicals

within the United States and Canada.

When the canary dies,it's time to

get our of the mine!

AIRPOLLUTION

That expression was all too true a few generationsago. Miners took a canary underground to monitorthe air. Its death warned of potential disaster dueto an accumulation of carbon monoxide since thebird's size and metabolism rate would cause it tosuccumb quicker than man.

1 ortunately, such heartless detection methods arenot needed today. We have sophisticated devicesto detect air pollutants resulting from a variety ofsources.

The truth that, regardless of recent dramati-zation, man's pollution of toe air is not new. In61 A.D., the statesman, Seneca, complained aboutthe soot and stink of the heavy air of Rome. Eng-land's Queen Eleanor moved away from Notting-ham 700 years ago because of the unendurablesmoke. And, in the 17th Century, it was written thatLondoners breathed nothing but impure thick mist.

Eons before man added his contribution, naturewas putting foreign matter into the airfor goodreason. It is essential to earth's life cycle. For in-stance:

Volcanic ash and dust provide the nuclei for rain-fall.

Pollens propagate plant life.

Various gases and mists, resulting from reactionscaused by sunlight, humidity and decompositionof plant and animal life are essential to the con-CAUSEStinuing renewal of life sources.

In fact, nature constantly emits a far greater quan-tity of so-called air contaminants than does man.Her recycling processes, however, are uncannily

CURES self-cleansing. Given time, nature maintains a tol-erable balance between polluted and acceptably-clean air, even with man's input.

Therefore, today's air pollution problems resultfrom our persistent overwhelming of nature's self-cleansing capabilities in densely populated and in-dustrialized areas, thus creating a temporary or con-tinuing imbalance in nature's process.

Although the analysis is simple,.the effects arenot. Therefore, the purpose of this booklet is tobring better understanding to this complex subject.It describes the major causes of those aspects of airpollution for which man is responsible, and someof the cures he has devised for its abatement orprevention.

William I. DriverPresidentManufacturing Chemists Association

1

THE ATMOSPHEREClean dry air, by volume, is composed of slightly

more than 78 percent nitrogen and nearly 21 per-cent oxygen. The less-than-one-percent remainderis made up of carbon dioxide and such rare gases asargon, neon, helium, krypton and xenon. Normalatmospheric air also contains water vaporfromtrace amounts up to three percent, depending onlocale. It is important to understand, however, thatan atmosphere composed solely of these gases andmoisture is really not natural.

Natural atmosphere also contains a variety ofother substancesgaseous, liquid and solidalbeitin very mall amounts when compared to the entireair mass. These substances may react among them-selves, chemically or physically, ar are transported'br,air currents. For the most part, they do not

,,,re,Malk in the atmosphere indefinitely. Some, like...heljuni; escape to outer space. Most are neutralized

40V-4orried to the earth by rainfall to take part in,,recycling processes.idely-held misconception is that some sub-

e entering the atmosphere at a faster rata.are removed. The fact is that nature's

step up her removal processes to01:input. Therefore, although

some s*ta9os may jempoTarily.,that

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PHOTOSYNTHESIS

Some understanding of this natural phenomenonis essential to a discussion of air pollution becauseof its effect on certain man-made contaminants.

Photosynthesissynthesizing by lightis one ofnature's most important recycling processes. it usessolar energy to recover oxygen from carbon dioxide,thereby setting off a chain of chemical reactionswhich produce the basic food for all living things.Its unbelievably complex mysteries are not com-pletely unraveled and will not be ..until scientistsfully understand the effects of sunlight on chloro-phyll, the pigment in green. leaves and plants, andon chloroplasts, the microscopic michines in chlo-rophyll.

Each chloroplast contains chlorophyll nliSq.which absorb the orange-red .(Iong)and,:,..:ih.blue (short) rays 'of :.00ight;:.141"t: reflexgreen (middle), rays Thin is Jwhyleaves}

mole y

gain or lose atoms or electrons with lightning speed.In the process, oxygen is produced, which is re-leased to the atmosphere, and sugars are synthe-sized. Some of the sugar feeds the leaf itself; moreflows as a nourishing stream of sap throughout thetree; some is converted into starches, proteins andoilscreating fruits, seeds, flowers and the like.

Nor is photosynthesis limited to tree leaves. Everygreen growing plant carries on the process, andmust do so to survive. This is true of aquatic plantsas well Microscopic algae called .draiiitns'.;cr-olIy onthe bulk of aquatic photOSyntheSiTinyi.;::.OnirrialsCalled;*Popla nkton ;fee

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CAUSES

Nature emits air contaminants in far greateramounts than does man. Problems arise, however,

when nature's self-cleansing capabilities areoverwhelmed by man's excessive input from densely

populated and industrialized areas.

According to the U. S. Public Health Service, thefive man-made contaminants emitted in the largest

quantities are:Carbon monoxide,

Sulfur oxides,Nitrogen o) ides,

Hydrocarbons andParticu'ates.

Mo5t of these result from combustion man's useof fire to provide heat, power, transportation, and

to dispose of refuse.

Combustion is the rapid combination of oxygenwith other substances, notably those containing

carbon, and the consequent release of energy.Perfect combustion is achieved only through theproper mixture of pure oxygen and pure carbon.Its harmless byproducts are carbon dioxide and

water vapor. However, under day-to-day conditions,the materials used in combustion are neither pure

nor the process ideal and potential air pollutantsare produced.

Let us consider the five major man-mad7contaminants in more detail:

4

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CARBON MONOXIDERecent studies at the Argonne National Labora-

tory reveal that nature is the source of about 90 per-cent of this contaminant, mostly through photo-chemical oxidation of methanea gas resultinglargely from decomposition of organic matter inmarshes, forests and the like.

Man's input of some 10 percent is attributed toimperfect or incomplete combustion of gasoline,oil, coal and wood. The most familiar source is theautomobile exhaust. (Note: Auto exhaust odor iscaused by other ingredients such as aldehydes, acidsand ketones, not by carbon m,)noxide.)

When carbon monoxide is released into open airand dispersed by wind, it is not troublesome sincenature gradually converts it to carbon dioxide. How--ever, during climatic inversionswhen there is littleor no wind and the air aloft is tco warm for heatedsurface air to risecarbon monoxide may tempo-rarily accumulate in urban communities, thus creat-ing problems. Also, when vehicles are left runningin tunnels or enclosed areas, carbon monoxide canreach dangerous concentrations since, when in-haled, it acts on the blood stream to preventabsorption of life-giving oxygen.

SULFUR OXIDESAccording to the National Industrial Pollution

Control Council, nature is responsible for abouttwo-thirds of the sulfur emitted into the atmos-phere. Major sources are volcanoes and fumarolesholes in or near volcanoes.

Man's input is mostly in the form of sulfur diox-ide, with minor amounts of sulfur trioxide, resultingfrom combustion of sulfur-containing fuelscoal oroilby power plants. Smelting sulfide ores andsome chemical operations, such as sulfuric acidmanufacture, also produce modest amounts of sul-fur oxides.

Both sulfur dioxide and sulfur trioxide are solublein water and can be washed from the air by rainfall.This is part of nature's design, since sulfur is essen-tial to plant nutrition. However, large amounts canbe harmful if the soil is low in alkali.

Also, photoche,oical reactions can convert sulfurdioxide to sulfur trioxide which avidly combineswith water vapor in the atmosphere to form acidmists. In the absence of rain over an extended pe-riod, such mists can accelerate the deterioration ofpaints, metals, building materials and textiles, espe-daily some man-made fibers used in stockings,dresses and the like.

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NITROGEN OXIDES

As stated earlier, nitrogen comprises nearly four-fifths of the atmosphere. Although it is relativelyinert, under high temperatures and through variousbiological reactions it can combine with oxygen toform several different oxides of nitrogen. Naturalcauses include lightning, volcanic eruptions and de-composition of organic matter. This, too, is part ofnature's design since nitrogen is essential to plantgrowth but cannot be utilized by green plants in itselemental atmospheric form.

Only two nitrogen oxides are of concern as airpollutantsnitric oxide and nitrogen dioxide. It hasbeen estimated that their production through natu-ral causes is perhaps 10 times greater than fromman-made sources. While the latter includes somechemical manufacturing processes, the bulk of ni-trogen oxide emissions is mostly in the form ofnitric oxide resulting from high-temperature com-bustion in furnaces and in transportation vehicles.

Nearly half of man's input comes from so-calledstationary sources, utility plants which provide elec-tricity or steam and manufacturing operations whichproduce essential high-grade metals such as stain-less steel, chromium and nickel.

Transportation accounts for a large portion of thisman-made contaminant and gasoline engines are byfar the largest source. Diesels and non-transporta-tion us( ; of motor fuels contribute lesser amounts,wHe aircraft emissions, contrary to wide-spreadbelief, contain negligible quantities. Home heatingunits, municipal incinerators and even forest firesalso produce nitric oxide. It is a problem because:

When released to the atmosphere in the presenceof sunlight and certain organic vapors such as re-active hydrocarbons, nitric oxide combines withoxygen in the air to create nitrogen dioxideabrownish gas. While much of this gas is washedfrom the air by rainfall, this benefiting soil andplants, it does play a major role in photochemicalsmogthe hazy mixture of eye, nose and throatirritantswhich is prevalent in many urban areas.

HYDROCARBONSOn a global scale, nature produces about five

times as many airborne hydrocarbons as does man,mostly through decomposition of organic matterin forests and vegetation. The primary man-madesources are:

Unburned or partially-burned fuels, and

Evaporation of industrial solvents.

As the word implies, hydrocarbons contain onlyhydrogen and carbon. There are several classes ofthese compounds. Some contribute to photochemi-cal smog far more than others. For instance: Un-saturated hydrocarbons, which contain fewer hy-drogen atoms than the corresponding saturatedmolecule (e.g.: Ethylene, in which each moleculecontains two carbon and four hydrogen atoms ascompared to the corresponding saturated com-pound, ethane, which has two carbon and six hydro-gen atoms per molecule).

Hydrocarbons are essential to the life cycle. Somehave an odor, such as terpenes in a pine forest.As they occur in the atmosphere, nearly all of themare transparent gases or vapors and are involved innatural photochemical processes. In fact, the GreatSmoky Mountains, part of the Appalachian systemin North Carolina and Tennessee, were so namedbecause of the characteristic haze generated byphoto emical reactions involving terpenes releasedby pi 2 trees. And, "Bahia de Humos y Fuegos"(Bay cf Smokes and Fires) was the name given towF.;.-.t is now Los Angeles Harbor in 1542 by itsSpanish discoverer, Juan Rodriguez Cabrillo. Nodoubt he attributed the haze to smoke from primi-tive Indian fires when, actually, it was a naturalphotochemical phenomenon.

This is not to say that man does not contribute toconditions which cause photochemical smog. In ur-

ban and highly industrialized areas he certainlydoes, and scientists have been battling for years tosolve this exceedingly complex problem. Perhapsthis over-simplified description indicates just howcomplex it is:

As stated in the prevrous chapter, when nitric ox-ide is released into the presence of sunlight andcertain hydrocarbon compounds, nature converts itto nitrogen dioxide, which readily absorbs ultra-violet light from the sun. This causes it to breakdown into nitric oxide and atomic oxygensingleoxygen atoms. (Normal air oxygen is moleculartwo atoms bound together). Atomic oxygen may re-act with molecular oxygen to form ozonethreeoxygen atoms bound together. Ozone can then re-act with nitric oxide to create molecular oxygen andmore nitrogen dioxide.

In turn, atomic oxygen can react with some hy-drocarbons to form chemical species called radicals.They may take part in further reactions to createmore radicals which can react with molecular oxy-gen, other hydrocarbons or nitric oxide. In someinstances, more nitrogen dioxide is generated; inothers, nitric oxide disappears, causing ozone toaccumulate and further react with hydrocarbons.Some of the resulting compounds are potent irri-tants to eyes, nose and throat. Others may form par-ticulates whit.'. hamper sunlight reaching the earth.

If you are confused, it is perfectly natural, be-cause the entire process is far from being fullyunderstood and can vary tremendously, thus creat-ing an equally varying potential for smog.

While these reactions are part of nature's air-cleansing process, their immediate effects are obvi-ously much less desirable than natural green-plantphotochemistry whereby oxygen is recovered fromcarbon dioxide.

7

1

PARTICULATES

Storms, winds and volcanoes put far more par-ticles into the air than does man. A man-made per-centage is nearly impossible to estimate, but par-ticles result from grinding, spraying and combustionoperations.

Although particulates are last in the U.S. Govern-ment's list of the five most prominent man-made aircontaminants, they are perhaps highest in publicconcern due to their visibility. In this regard, onemajor misconception is that all white plumes issuingfrom stacks are pollutants. In many cises, they are

8

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only steamoften resulting from a pollution con-trol process.

Particles range in size from something micro-scopic (less than a millionth of an inch) to coarsegrit. They may react in endless waysgrowing bycondensation, adsorbing or absorbing vapors andgases, coagulating or dispersing, and absorbing andscattering light. Because of these variables, as wellas their real or esthetic effect on individuals, theirimportance to air pollution cannot be overesti-mated.

CURES

In considering air pollution control, eitherpreventive or remedial, it is important to keep

man-made emissions in perspective. For, as hasbeen established, natural causes of the five major

air contaminants far exceed, in total amount, thosefrom man-made sources and are one aspect of

nature's life cycle.

The natural presence of such materials, then,provides background concentrations which must be

taken into account. Where they are substantial,there is less leewa./ for man-made emissions if

objectionable levels are to he avoided.

However, every step in controlling man-madeemissions adds to the cost of consumer goods.

Therefore, it is far more reasonable to let nature dothe job for which it is highly qualified wherever

satisfactory results can be achieved.

PROCESS CHANGE

It is apparent that most man-made contaminantsstem from his use of fireto cook and heat, to gen-erate electricity, to provide power for transportationand manufacturing.

As a result, extensive efforts have been under wayfor many years to control the combustion processso as to minimize potentially polluting by-products.For instance:

To the extent they are available and in relationto economic factors, low-sulfur fuels are usedto reduce the emission of sulfur oxides.

Improvements in carburetion, engine design,recycling and catalytic devices will ultimatelycontrol emissions of carbon monoxide, hydro-carbons and nitrogen oxides.

Sanitary landfills and municipal incinerators arerapidly supplanting yard and apartment houseincinerators.

These illustrate the most desirable type of emis-sions controlprocess changewhich can include:

The choice of raw materials or their modifica-tion prior to use,The manner in which they are processed orused,

The design of equipment, andOperating procedures.

However, because there are practical limits towhat can be achieved by process change, emissionsmay need to be controlled by one or a combinationof these three methods:

Dispersion . . .

. . . whereby emissions are diluted by the --r-rounding atmosphere. Tall stacks are generally used,their height being determined by the volume, thechemical/physical nature of the emission, topog-raphy and meteorological conditions.

Debate continues as to the acceptability of stacksfor pollution control because they do not decreasethe quantity of the emission. However, it is wellestablished that, in many instances, properly engi-neered stacks do accomplish control objectives bydecreasing the environmental impact of emissions.

Destruction . . .

. . . which generally consists of burning the emis-sion, either with a smokeless flare, in a special in-cinerator, in the combustion chamber of a boiler orin an afterburner.

Destruction may also be carried out catalytically,that isbringing the emission into contact with asL,5stance which speeds up beneficial chemicalchange. In some instances, catalysis is used to con-trol pollution while recapturing useful products.

Collection . . .

. . . which is probably the most widely usedmethod of Lir pollution control. There are a varietyof techniquesemploying the use of screens, filters,mechanical devices, electricity, water, chemicalsand absorbing or adsorbing materials.

Let us explore how one or a combination of thesethree methods may be used to control pollution bythe five major man-made contaminants.

CARBON MONOXIDEThe primary man-made cause of this contaminant

is the internal combustion engine and its cure lieswith more complete use of ;iiels, as does thecontrcl of hydrocarbon emissions from the samesource. Therefore, this will be subsequently coveredunder hydrocarbons.

9

Hot Flue GasFrom Boiler

10

Flue Gas WithSulfur Dioxide

Flue Gas WithSulfur Trioxide Hot Air Fed

To Fire Box

Sulfuric AddTrapped By Mit.tEliminatorTrickles Down FilterFor Collection.

Clean GasFlow Out

Dust

SULFUR OXIDES

Cooled Flue Gas

Some Sulfuric AcidAlready Produced

Since these are predominantly caused by burningsulfur-bearing fuels, it would appear that use oflow-sulfur fuels would provide for a cure. However,such a prucess change has its limitations:

Sources of natural gas are rapidly diminishing.Propane gas (derived from crude oil) is costlyfor large-scale operations.Sulfur removal from crude oil is also expensiveand would raise the price of heating and manu-facturing.

Low-sulfur coal is in short supplyinadequatefor future needs.

Since atomic power plants are embroiled in con-troversy, their immediate capacity is far behindknown energy requirements and may never meetthem entirely.

Therefore, to meet energy needs in the imme-diate future, we need to rely on coal with a fairlyhigh sulfur content. Most experts agree there is

enough of it in the earth to last another 500 years.Can sulfur be removed from coal before it is

used? . . . or . . . Can a process change in burningreduce the effects of sulfur content?

The answer to both is yes ... through gasificationand liquefaction. However, improvement of theseprocesses on a large scale, in order to meet the re-

ater

Gas With

Sulfuric Acid Mist

Sulfuric Acid

FibersInAnnularSection

quirements of sulfur control laws, is still under way.None are low enough in cost to compete with exist-ing procedures to remove sulfur from stack gases.

As a result, various methods which remove sulfurfrom flue gasesof which there is a bewilderingarraywill probably be employed for some time,with improvements being developed and tested inplant operations. Among them:

Limestone or dolomite .. . . is relatively cheap and plentiful. Either is pul-

verized and injected into the furnace along withthe fuelpulverized coal. As the latter burns, theheat decomposes the minerals into carbon dioxide(a harmless end-product of any combustion process)and into:

Calcium oxide, it limestone is used, orCalcium oxide and magnesium oxide, if dolo-mite is used.

Either of these, in turn, react with the sulfur con-tent in the fuel to form solid mattersulfites orsulfateswhich can be removed for disposal by oneof the particle cures described later.

This dry system, however, has certain drawbacks.The injected limestone or dolomite has a tendencyto coat boiler tubes and, under certain conditions,to partially plug the boiler. Therefore, test opera-tions am under way with a wet system wherein flue

SCHEMATIC OF A CATALYTIC OXIDA-hON PROCESS

REMOVES SULFUR FROM STACK GASESRECAPTURES SULFURIC ACID,

gas from the boiler is scrubbed with water contain-ing limestone particles or with water containinglime. Such scrubbing processes, also described later,show considerable promise and large scale applica-tions are expected.

The recovered calcium sulfite or calcium sulfateis ordinarily disposed of as landfill. However, suchlandfill procedures are not simple and, becauseof the quantities involved, the potential pile up ofthese materialsshould all power-generating sys-tems use this methodis tremendous. In addition,such landfills can lead to water pollution problemsdue to leaching, particularly by magnesium salts re-sulting from the use of dolomite.

Catalytic Conversion . . .

. . . requires passing the flue gas over a specialvanadium-containing catalyst where sulfur dioxidecontent is further oxidized to sulfur trioxide. Uponsubsequent cooling, it reacts with moistureaddedin a scrubber processto form a sulfuric-acid mistwhich is trapped in a filter and recovered.

This method, an extension of conventional sul-furic-acid technology, duplicates under controlledconditions the chemical steps that would occur ifthe sulfur dioxide were released into the atmos-phere where it would combine with rain or mois-ture. However, the process is expensive, with cor-responding impact on consumer prices since, even

though a saleable product is produced, its value isinsufficient to offset the cost of recovery.

Molecular Sieves . . .

. . . belong to a class of compounds known aszeolites. They occur in nature and are unique in thatthey release moisture when heated and readsorl, itwhen cool. In addition, they can selectively adsorband release molecules other than water. Meanwhile,their crystalline structure remains unchanged.

Chemical research during the last several yearshas developed methods to not only synthesize zeo-lites but to tailor-make their crystalline structures sothey will adsorb only certain molecules. Once sucha mass of material has adsorbed all it will hold, itcan be purged for repeated reuse.

Molecular Sieves have been employed for manyyears in various gas and other purification proce-dures. Now, a highly-specialized sievea crystallinemetal alumino-silicateto call it by the correctnamehas been devised to remove sulfur from thevent gas of a sulfuric acid manufacturing plant and,through purging, turn it into a marketable product.Success of the pilot project thus far indicates thatMolecular Sieves may eventually be used on a largescale to remove sulfur from stack gases.

Another sulfur recovery process is described inthe postscript to this booklet.

11

NITROGEN OXIDESAs stated earlier, high temperature combustion is

the major man-made source of the two pollutantsin this categorynitric oxide and nitrogen dioxide.The prime means of their control is preventive, thatisavoiding their formation rather than trying torecapture or neutralize them after-the-fact. This in-volves carrying on combustion at the lowest possibletemperatures and the lowest excess oxygen consist-ent with complete oxidation.

However, this is not always compatible with re-gard to utility and industrial furnaces, so-called sta-tionary sources, or to gasoline engines, since heatreduction is reflected in loss of power. As a result,other procedures are necessary to reduce emissionsto acceptable levels so that nature can complete thejob. The technology to do this is known. However,the primary obstacles are:

Establishing standards for all categories;

Time and money to complete the monumentaltask of replacing or modifying the vast numberof furnaces and engines which were not de-signed to meet such standards.

Stationary Sources

Utility plants now under construction are beingdesigned to reduce nitrogen oxide emissions tostandards which have been established by the Envi-

lower Temper

To complete cair only entersthrough top bi

(

High Temperature Zone

Fuel-rich mixture offuel and air entersfire box through lowerburners.

Burners

ronmental Protection Agency (EPA). Flue gas recir-culation and staged combustion are the methodsbeing applied. They may be used independently orin conjunction, depending on need. However, manyexisting facilities will continue to be used until themoney, space and other related factors make it pos-sible to modify or replace them.

As yet, EPA has not established standards for in-dustrial furnacesthose in refineries, cement andlime kilns, glass manufacturing and metallurgicaloperations. Most of these are smaller than theirutility cousins and represent a special class sincethey must function at extremely high temperatures.

Control technology for home-heating units andmunicipal incinerators is known and EPA is ex-pected to ultimately establish standards. However,due to the vast number of installations, conversionor replacement will take many years.

AutomobilesFederal standards for nitrogen oxide emissions

from gasoline engines were established through theClean Air Act Amendments of 1970. They are dueto become effective in 1976, except in California,where state regulations will apply in 1975.

Methods of controlling such emissions are di-rectly related to the control of carbon monoxideand hydrocarbon emissions.

tHot Flue Gas -..

GasRecirculation

Fan

Heat Exchanger

Stack

Cooled Flue Gs

Hot Air Fed ToBoiler Fire Box

Fan

SCHEMATIC OF COMBINED "STAGED COMBUSTION" AND "FLUE GAS RECIRCULATION"TO CONTROL NITROGEN OXIDE FORMATION IN STEAM BOILERS

12

Air

Exhaust Manifold

Exhaust Pipe

Tail Pipe

Air Compressor-Source Of Secondary Air

HYDROCARBONS

As stated earlier, the primary man-made sourcesof hydrocarbon emissions are:

Evaporation . . .

. . . which is generally under control. At one timelarge amounts of hydrocarbons escaped from stor-age tank vents, during transfer to and from vehicles,through safety devices in manufacturing plants andfrom automobiles. Today:

Floating roofs on storage tanks are widely used,eliminating the need for vents.

Closed systems prevent vapors from escapingduring transfer operations.

Plant safety procedures effectively burn suchsolvents if they must be vented during manu-facture or use and,

In late-model cars, fuel vapors are captured incharcoal-filled canisters to be burned whenthe engine is running.

Combustion .... which must be carefully controlled in order to

avoid emitting unburned or partially-burned fuels.To achieve this, two methods are now in use:

Positive Crankcase Ventilation (PCV)whichrecycles vapors and gases to the engine forburning with the fuel.

Air injection into the manifoldwhich inducesmore complete combustion prior to the exhaust.

An additional method, which U.S. automotivemanufacturers seem to prefer, is:

Catalytic Conversion .... . . which calls for passing exhaust gases through

two muffler-like chambers in the exhaust system.

LCatalytic Converters

The first chamber would be filled with an inerthoneycomb structure which is plated with a thinfilm of a noble metal, such as platinum or palla-dium, or a base metal catalyst containing such ele-ments as cobalt or manganese. These materialswould accelerate the complete-burning of fuelsthrough high temperature so as to decrease carbonmonoxide, and hydrocarbon emissions.

However, since high temperature increases nitricoxide production, a second chamber, containing adifferent catalyst, is required to dissociate it intoelemental nitrogen and oxygen prior to emissionthrough the tailpipe.

Technology in this second stage is far less ad-vanced. However, as this booklet was written, itappeared the second-stage catalyst would compriserare earths, perhaps of the lanthanum type. Thestate-of-the-art in this phase is still undergoing ex-tensive research.

Other methods receiving intensive considerationinclude:

Improved carburetionto control the fuel-airratio and thus achieve more complete burningwhile reducing peak temperatures in cylindercombustion chambers.

Vortex combustion chambersa means ofburning the fuel-air mixture an unusually longtime inside the engine so that potential pollut-ants are used up.

Additional control methods may include rede-signed or completely new types of engines andimproved or different fuels.

Ultimately, a combination of the processes nowin use or being investigated will solve the nitro-gen oxide/hydrocarbon/carbon monoxide emissionsproblem. The cost, however, will be reflected in theconsumer price of fuel and automobiles.

13

PARTICULATES

Rainfall and earth's gravity are the prime mecha-nisms for removing particles from the aft. Theirefficiency, however, varies considerably in relationto the size of the particles and to the processes ofcoagulation and absorption of vapor. Particles arealso removed when they impinge on buildings, treesor other objects.

Such natural removal is usually sufficient in iso-lated regions but not for densely populated and in-dustrialized areas. As a result, several processes anddevices are in use and are being improved. Eachadds to the cost of consumer goods, since theyeither require large capital investments, or are ex-pensive to operate. The four methods are:

Cyclones.. .

. . . that turn suspended particles in smoke or gasinto a man-made whirlwind inside a containerwhich throws out the larger particles so they canbe collected.

While there are many variations, most cyclonesare cone-shaped with a tube center. Dust-ladensmoke or gas is forced in tangentially at the topwhich makes it spiral downward. Larger particles areblown against the side and fall to the bottom wherethey can be removed. Cleaner air flows upwardthrough the center tube.

Cyclones are relatively inexpensive to buy and tooperate, but they are efficient only for larger par-ticles.

Wet Scrubbers .... . . that capture particles too small to be col-

lected in a cyclone.The smoke or gas is fed into a chamber or a stack

where, depending on need, water or a specially-formulated scrubbing liquid runs down the sides,flows over a series of baffles like a waterfall, or issprayed like a shower. This duplicates rainfall andwashes particles out of the smoke or gas.

There are also high-energy wet scrubbers whichturbulently mix the gas and the scrubbing liquid.These are highly efficient, but cost considerablymore to operate due to their high energy demands.

Electrostatic Precipitators .... . . that work on the principle of static electricity

and are widely used.A strong electrical charge is placed on the par-

ticles which are attracted to plates with an oppositeelectrical charge placed inside a chamber. Thismethod is highly efficient and can achieve 99 per-

14.

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ELECTROSTATIC PRECIPITATOR

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cent removal of part:Hes in most situations. Gen-erally, the plates are'clecined With a rapping devicewhich causes the particles ci fail off for collection.

Compared to high-energy wet scrubbers, elec-trostatic precipitawrs are more expensive to install,but less costly to operate.

The only instances where they are not efficient iswith certain particles which create electrically-con-ductive films that short-circuit the high voltages re-quired, or those which are so insulating that thefirst thin layer prevents the electrically-chargedplates from attracting further dust.

Filters .... . . that may be used to clean the air in both wet

and dry systems.However, like those used in automobiles, home-

heating units and coffee makers, filters must bedesigned for the specific need, taking into con-sideration the high volumes involved in large in-stallations, the velocity of the gas, its temperature,chemical reactions and clogging.

One widely-used filtering technique is the BagHouse. It can be compared to a series of giantvacuum cleaners which filter particles from thesmoke or gas. This method is very efficient and maybe used alone or following one of the previously-described dry systems.

It is necessary, however, to provide up to onesquare foot of filter area for every cubic foot perminute of gas flow to .be treated. Therefore, theprice of installation is generally high while operat-ing costs vary, depending on the type of bag re-quired, the nature of the captured material and thefrequency of replacement.

RESIDUE

Every method of air pollution prevention collectssomething which must be disposed of. Sometimesit is useful, such as sulfur removed from smoke-stack gases. In some instances, ashes can be con-verted into building materials. More often, how-ever, the leftovers have no value and are generallyused as landfill or, in the case of wet scrubbingprocesses, are either treated before release into asewer system or pumped into holding ponds wherethe captured material settles, permitting the waterto either evaporate or overflow into a sewer orstream.

15

, ::;;;

V

16

OTHER ODORS. . . result from natural as well as man-made

PROBLEMScauses. Among the latter: Fertilizing, tanning, brew-ing; manufacturing chemicals, textiles and pharma-ceuticals; ore smelting, petroleum refining and foodprocessing; sewers, dumps, lagoons and settlingponds.

Odors are extremely prominent as a source ofpublic resentment and, although most are not healthhazards, nuisance laws to control them have beenpassed by a number of states.

While considerable progress has been made tomeasure odors mechanically, the final and mostreliable device is the nose. As a result, all in-depthodor research is conducted by odor panelsgroupsof individuals whose responses to smells help toevaluate odor thresholdsthe point of concentra-tion where they can either be detected or becomeoffensive.

Although many odors result from liquid solu-tions, they are gaseous in nature and variations ofseveral processes described earlier can be employedto control them. Depending on the nature of eachindividual odor problem, they include one or acombination of the following:

Combustion .

. . . whereby the odorous gas is burned in a

special incinerator or destroyed by a specific cata-lyst,

Ventilation .... . . which dilutes the gas with air,

Absorption .... . . wherein the gas is assimilated by a liquid,

which may then be treated,

fp!

Adsorption .. .

. . . whereby the odor-containing molecules aregathered by a particular substance (such as activatedcharcoal),

Masking .... . . which smothers a bad smell with a stronger,

better smell, and,

Counteraction .... .. which employs the discovery that many odors

have a counter odor and that when proper ratiosof each are brought together, they tend to neutralizeeach other.

The brevity of the above may cause some to as-sume that the elimination of offensive industrial ormunicipal odors is simple.

However, nothing could be .farther from thetruth. Each problem must be approached on anindividual basis involving numerous facets such astype, volume, degree of concentration, topography,prevailing winds and tolerance threshold.

In turn, every step in odor controlalong withall forms of pollution preventionadds to the costof the product and must be based on the fine linebetween social and economic benefits.

LEAD . . .

. . . in gasoline can cause heated debate amongthe most respected experts even though evidenceof its deleterious effects is inconclusive. Most dis-cussion concerns:

Its possible influence on human health,

The problems it creates in controlling otheremissions, andIts possible impact on ecology and climate.

EPA announced regulations calling for one gradeof lead-free gasoline to be generally availablethroughout the country by July 1974. (This may bedelayed due to the one-year postponement of Fed-eral auto-emission standards.) The purpose is toprovide a fuel compatible with catalytic converterssince, as presently designed, lead would interferewith their efficiency. Meanwhile, several chemicalcompanies have exhaust-system lead traps in variousstages of development.

DIESEL POWERED...

. . . vehicles have been the target of considerablecriticism because of smoke and odor. While someolder buses and trucks may still be in use, newerengines are built to meet Federal standards whichwent into effect January 1, 1970. They employ rela-tively high fuel injection pressures and producelittle smoke or odor when properly maintained andoperated. Also, barium additives in diesel fuel candramatically reduce smoke.

Diesel engines produce only about one-tenth asmuch carbon monoxide as do gasoline engines.Hence, it is not considered a problem since dieselspower less than one percent of the vehicle popula-tion.

However, diesel hydrocarbon emissions are aboutthe same as gasoline engines and nitric oxide pro-duction is slightly higher. These can be controlledin the same manner as those resulting from gasolineengines.

17

CONCLUSIONTo anyone who has read this booklet thus far it

is obvious that clean air, as well as the food we eatand the water we drink is the result of an endlessprocess of chemical change. True, some of it is bad.However, Most of it is good, as exemplified by ourcontinuing enjoyment of life.

The mere fa'ct that photochemistry, the first linkin the chemical chain that binds us together as in-dividuals, also induces unwanted effects in ourmodern atmosphere means that air pollution prob-lems can and will be solved through the applicationof chemical technology. This, however, involvesthree key powersmoney, mind and man.

In three separate surveys during the past fewyears, the Manufacturing Chemists Association hasattempted to determine the extent to which thesepowers have been and will be committed to airpollution control in the chemical manufacturing in-dustry. In 1962, 125 member companies participatedin the survey; in 1967, 129 and in 1':72, 137. Theresults showed that:

In Moneypower ... . . more than half a billion dollars have been in-

vested in air pollution control equipment, with thesum due to more than double by 1976 to a total ofmore than a billion dollars.

This compares with $212 million invested up to1962 and $288 million by 1967.

In addition, annual operating and maintenancecosts for air pollution control have reached $77 mil-lion. In 1962, it was $24 million and in 1967, $42million.

In Mindpower. . . research expenditures for air pollution con-

trol have reached $18.6 million a year.This more than doubles the 1967 figure of $9.1

million. in 1962, it was $2.8 million.

In Manpower .... . . the equivalent of 2,255 full-time personnel

is devoted to air pollution control activity, as com-pared to 1,624 in 1967 and 1,340 in 1962.

18

ACTUALAND PROJECTEDCAPITAL INVESTMENTFOR AIRPOLLUTION CONTROL

$288

million

$587

million-

1962 1967 1972

Humber of reporting companies:1962 -125 1967-129 1972-137,

Source: Manufacturing Chemists Association

$1,178

million

1976

OPERATION ANDMAINTENANCE COSTSFOR AIR POLLUTIONCONTROL EQUIPMENT

$77million

1962 1967 1972

RESEARCHEXPENDITURESFOR AIRPOLLUTION CONTROL

$18.6million

1962 1967 1972

MANPOWERASSIGNEDTO AIRPOLLUTIONCONTROL

2,255people

1962 1967 1972

19

POSTSCRIPT

The preceding statistics for the chemical manu-facturing industry, impressive as they are, representonly a fraction of the total money, mind and man-power that will be required to control air pollutionso that nature's self-cleansing ability is not over-whelmed. Ultimately, every citizen will be calledupon to bear his share of the cost in terms of taxes,goods and services.

Consequently, the Federal Clean Air Act takesinto consideration both the urgent need and theeconomic factors involved. Some standards foremissions have been established by the Environ-mental Protection Agency, others are in variousstages of being set. In the process, there have beenand will be pro and con arguments. But, agreementis unanimous that the goal of clean air must be at-tained. To this end, scientific genius and chemicaltechnology will be further challenged. That we canbe confident of results is perhaps typified by a re-cent case history:

As 1972 began, an innovative effortone of manywithin the chemical industrywas under way toeffectively remove sulfur dioxide from the smoke-stacks of two large electric power plants and turn itinto a marketable product. It is unique since it is

the first effort to be undertaken on a regional basis,the first involving both oil-fired and coal-fired utilityfurnaces and is another method for recovering sulfurfrom flue gas. Participants in the venture are: TheBoston Edison Company, the U.S. EnvironmentalProtection Agency, the Chemical Construction Cor-poration and an MCA member company. This ishow it works:

Flue gas from Boston Edison's oil-fired boiler atEverett, Massachusetts is scrubbed with a slurry ofmagnesium oxide in water. The magnesium oxide,a non-combustible, reactive granular material, ab-sorbs and reacts with at least 90 percent of thesulfur dioxide in the flue gas before the washed gas

20

is sent up the smokestack. The product of this reac-tion is magnesium sulfite, which is recovered fromthe system as a granular crystalline material.

The crystalline magnesium sulfite is transportedby bulk trailer to a regeneration facility adjacent tothe chemical company's sulfuric-acid plant in Rum-ford, Rhode Island. There, the crystals are heated torelease sulfur dioxide which is converted to saleablesulfuric acid, a valuable industrial commodity. Thecalcining step also converts the crystals back tomagnesium oxide, which is transported back toEverett for re-use in the scrubber at the powerplant.

This demonstration project is now under way.Construction for a similar project at a coal-firedboiler of Potomac Electric Power Company, not farfrom Washington, D.C., is now proceeding. In thisplant, a preliminary scrubbing step is being pro-vided for removal of fly-ash particles.

The economics of these demonstration plants isrecognized to be poor. Full-scale application of thistechnology, however, is expected to provide aneconomical means of accomplishing the goal oflow-sulfur emissions from powerhouse stacks, sincethere is no solid waste to be disposed of and theproduct is sulfuric acid of normal commercialstrength and quality.

As the Boston operation began, the chemicalcompany's President called the process "a majorbreakthrough in industry's efforts to curb air pollu-tion in an economically practical manner." And, inMarch 1972, W. Reid Thompson, Chairman of theBoard and President of the Potomac Electric PowerCompany, emphasized the significance of chemicalrecovery of sulfur products since there is a seriousdisposal problem of the waste byproducts fromthrowaway scrubbing operations. "Most importantof all," Mr. Thompson stated, "the area benefits bycleaner air."

Air PollutionCauses & Cureswas written, edited and published

by theCommunity Relations Department

of theManufacturing Chemists Association,

Al lin G. Robinson, Manager.

Single copies are free.Requests for additional-free copies

are considered, based on aletter describing distribution.

Art, design and printing byHennage Creative Printers

Washington, D.C.

Technical Advisors:

George E. BestVice President andTechnical Director

Manufacturing Chemists Association

Kenneth D. Johnson, Ph.D.Assistant Technical Director

Manufacturing Chemists Association

And the following members of MCA'sAft Quality Committee:

J. H. Huguet (Chairman)Ethyl Corporation

Max B. Tohline (Vice Chairman)Mobil Oil Corporation

W. Bailey BartonBorden, Inc.

Paul L. McDanielUnion Carbide Corporation

T. H. RhodesExxon Chemical Company

L. W. RoznoyOlin Corporation

W. R. TaylorDiamond Shamrock Chemical Company

Jerome WilkenfeldHooker Chemical Corporation

and by:

John C. LaneEthyl Corporation

Irwin S. ZonisEssex Chemical Corporation

MANUFACTURING CHEMISTS ASSOCIATION1825 CONNECTICUT AVENUE, N. W. WASHINGTON, D. C. 20009