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T H E J O U R T A L O F I X D G S T R I A L A N D ENGIMEERIiVG C H E M I S T R Y
will resulc and t h e low discharge is t h e one which must be expected. H a d the sinuous formula given the lower value of v, the result b y the formula for viscous flow would have been rejected.
T‘ol. 8, NO. 7
since .the earliest ages, if not by name a t least b y its characteristic properties. The first authentic record t h a t we possess of t h e manufacture of this gas was in 1783 when Van Marum: a Dutch scientist, termed it ‘la smell of electricity,” as a result of its production S I Z E O F P I P E F O R VISCOUS LIQUIDS by this means. Liquids of even moderate viscosity flowing under I t was not, however, until t h e exhaustive studies of lorn heads follow viscous motion unless the pipes be Schoenbein in 1840 t h a t t h e active properties of ozone very large. It is very important t o keep in mind were well understood or a n y analytical methods were the fact t h a t , so long as t h e motion is viscous, doubling devised for measuring this gas. Schoenbein recognized the size of t h e pipe increases t h e velocity 4-fold a n d this active oxidizing agent as a distinct gas t o which the discharge 16-fold for t h e same pressure drop. he gave t h e name of ozone. For t h e same discharge a pipe twice t h e size requires For more than fifty years after Schoenbein’s reonly one-sixteenth t h e pressure drop and therefore but one-sixteenth t h e power. If a pipe is carrying searches nothing was accomplished in placing ozone liquid in viscous motion, increase in size of the pipe within. the scope of a commercial possibility, although its active and oxidizing power was well known. With IS always well worth consideration, owing t o this very great effect on carrying capacity and power consump- t h e development of t h e alternating current generators tion. Decrease in size will ultimately result in con- and transformers, which so materially reduced the cost verting the flow into sinuous motion, after which of production, and t h e increasing knowledge of the bacteriology and chemistry of water, ozone T?”S recogthe effect of size is greatly lessened, being inversely nized as a water purification agent of great value. proportional t o only t h e first power of t h e diameter. Berthelot, a French chemist, in 1890 undertook, with S C XM A R Y some degree of success, t o apply this method of water Liquids flowing through pipes flow either in straight purification, and from then on Europe, as well as line motion in which case they follow Poiseuille’s America, has been practically flooded with numerous 8 ,ulz designs of generators and patented appliances for formula, p = , or in sinuous motion. t h e pressure g1.2 v a t e r treatment. All t h e ozonizers t h a t have been devised are based drop being represented by p = J1pv2. The flow will upon t h e same genera! principle, ziz., t h e production gr follow t h a t formula which requires t h e higher pressure of t h e allotropic form of oxygen, 03,from the oxygen drop, t h e higher radius, or gives t h e lower velocity, of the atmosphere. This is accomplished by passing as the case may be. Both formulae must therefore a current of air over a brush discharge u-hich takes be employed and t h e result chosen according t o t h e place between electrodes connected t o a high volabo77-e rule. T o obtain the coefficient j of the formula’ tage alternating current circuit; these usually ha\-e for sinuous motion: look up, in suitable hydraulic a solid dielectric interposed between them. There tables, t h e value of t h e coefficient for water flowing are, of course, many other ways of generating this in the same size pipe a t t h e same velocity a n d multi- gas, b u t none of these processes other t h a n the one 0 . oqjz) ply this coefficient b y t h e expression (0.95j described has proven a commercia! success. wherein z is the viscosity relative t o water of t h e liquid Numerous theories h a r e been advanced t o account flowing. for t h e production of ozone in this manner b u t t h e one These formulae have been experimentally substan- generally accepted is based on the theory of molecular tiated only for use in pipes u p t o 2 in. in diameter m0tion.l This theory, as stated b y Dr. C. P. Steinand for t h e flow of liquids of viscosity (relative t o metz, regards the chemical effect of all ether radiations water a t zoo) of 20. They are probably safe for use recognized b y light, heat and electrical waTTes as more in larger pipes and a t higher viscosities, b u t more or less specific for various compounds t o definite exact expressions for these conditions must be de- frequencies of their movement setting up resonance termined b y further experimentation. effects upon t h e natural molecular or atomic motion. RESEARCH LABORATORY OF APPLIED CHEMISTRY Pure ozone is colorless, has a distinct and peculiar INSTITUTE OF TECHXOLOGY MASSACHUSETTS odor and instantly decomposes a t 260’ C. I t can be BOSTON liquefied b y a pressure of 1840 lbs. per sq. in. and a t a THE DESIGN AND OPERATION OF OZONE WATER C. I n this condition it is temperature of -103’ PURIFICATION SYSTEMS highly magnetic b u t is not so powerful an oxidizing By SHEPPARDT. POW ELL^ agent as t h e gas. Received February 7 , 1916 The great affinity of ozone for organic matter renders Although t h e first attempt t o purify water on a it peculiarly suited for water purification, in t h a t it practical scale b y means of ozone was made less t h a n not only removes the bacteria by direct oxidation b u t thirty years ago, still this gas was generated and its will eliminate t o a considerable degree other organic chemical and physical properties have been studied substances ‘contained therein. b y many investigators for more t h a n a century. In A11 ozonation plants for the purification of water all probability ozone has been recognized by scientists ozone generator and consist of two distinct parts-the
+
1 Chemist and bacteriologist of the Baltimore County Water and Electric Company, 100-102 West Fayette Street, Baltimore, Md.
1
Engineering S e w , 65 (1910). 488.
T H E J O C R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
July, 1916
the mixing chamber or emulsifier. If the design or operation of either appliance is a failure then t h e failure of t h e system as a whole is a certainty, as t h e success of t h e plant depends equally upon both parts. I t would be impossible at this time t o give descriptions of the numerous designs of all ozonizers t h a t have been introduced within t h e past few years, b u t brief mention of a few of t h e more important types may be of interest.
633
T H E VOSMAER SYSTEM
The Vosmaer system as originally designed was unique in t h a t no solid dielectric was used. This t y p e of generator, although a failure from t h e standpoint of efficiency, is of value t o t h e engineer in designing
T H E S I E 31A N- D EF R I S E S Y S T E RI
The Sieman-DeFrise ozone generator, which has proved a commercial success at t h e S t . Maur plant for t h e purification of t h e water supply of Paris, is shown in Fig. I . The generator consists of a n iron box divided into three sections b y horizontal metal plates having t h e center compartment pierced b y glass tubes which are made water-tight, so t h a t there is a water jacket above these tubes. Within these glass cylinders are placed aluminum tubes of smaller diameter so t h a t there is a n annular space of about in. between the surface of t h e electrodes and t h e dielectric. The aluminum tubes are thoroughly insulated in a metal case, and are connected t o a high
F I G . 8-VOSMAER
SYSTEX FOR OZOXIZINO
WATER
t h e generator in t h a t it has proved,.even t o the mind of t h e originator, t h e futility of building a n ozonizer without t h e use of a solid dielectric medium interposed between t h e electrodes. This generator (Fig. 3), as described by Don and Chisholm,' consists of iron tubes provided with strips of metal fused along their length inside and insulated on porcelain supports. The width of t h e strips was such t h a t t h e free edges did not reach t h e central line towards which they were directed. These edges were cut saw-shaped and each strip was connected t o one pole of t h e high tension transformer while t h e tubes were connected t o the other pole. T H E OTTO S Y S T E N
h,,
,
LA. ,
0
'7'8
FIG.~-SIEMAN-DEFRISE SYSTEM
tension circuit. and as t h e case is grounded t h e brush discharge is given off from t h e aluminum electrode. Cnder these conditions t h e oxygen of t h e air drawn through t h e tubes is converted into ozone, which is drawn off from the top of the generator b y means of a pump and is then forced into and mixed with t h e water t o be treated in a tower designed for this purpose. Each generator contains eight tubes, and t h e voltage used is said t o be between 36,000 and 40,000 volts. The mixing or sterilizing tower is cast iron lined with enamel, and is 2 j ft. high and I ft. in diameter. Within this tower is a set of perforated celluloid discs for the purpose of thoroughly mixing the gas and water. Dr. Samuel Rideal in 1908 approved of this system and pronounced i t a thorough success, not only from a bacteriological standpoint but on account of t h e high reduction of organic matter, which was over 4 0 per cent as measured b y t h e required oxygen tests. The general arrangement of the generators and mixing tower of t h e Sieman-DeFrise system is shown in Fig. 2 .
The Otto system, which was used in ozonizing the water supply a t Nice, France, differs quite materially from t h e other systems t h a t have been described. This generator is composed of a series of metallic plates upon which is coated a metallic foil. I n each pair of plates a different potential is maintained and the plates are so spaced as t o generate a maximum con-
F I G . 4 - 0 ~ T o SYSTEX
centration of ozone b y the electrical discharges as the air is drawn through the space betu-een each pair of plates (Fig. 4). A feature of this system is a sterilizing chamber where the ozone is thoroughly and efficiently mixed with water. THE GERARD
OZOXIZER
The Gerard ozonizer, although based upon t h e same general principle as t h e other types, has an additional 1
Don and Chisholm, 1913, p . 219.
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feature in t h a t t h e stream of air during t h e process of ozonization is subjected t o t h e electrical discharge twice instead of once. This is accomplished (Fig. 5 ) b y drawing t h e air down t h e inside of t h e tubes a n d back again through t h e annular space between t h e inner and outer set of electrodes. These tubes are of glass with tinfoil coated UDOn t h e m . a n d are housed in a
sheet iron box o n t o p of which is a marble slab; over t h e slab is a n aluminum case having a glass t o p so t h a t t h e discharge can be seen a t all times. The ozonized air is mixed with water b y a spraying system (Fig. 6) permitting three separate applications by means of chambers in t h e mixing device. The air used in these generators is treated b y refrigeration and the generators are cooled by oil.
VOI.
a,
NO.
7
T h e generators proper are cylindrical iron d r u m s 33 in. high by 36 in. in diameter, within which are 109 aluminum tubes (Fig. 7 ) . These tubes are rolled into t h e head of t h e d r u m in much t h e same manner a s t h e tubes in a tubular boiler, so a s t o be water-tight. Within these tubes are micanite dielectrics, a n d within t h e dielectrics are another set of aluminum electrodes. T h e case of each generator is connected t o one pole of t h e transformer and is grounded, while t h e inner electrodes are connected to t h e other pole. Discharge takes place between t h e electrodes and ozonizes the air as i t is drawn through t h e annular spaces o n either side of t h e dielectrics. The air is refrigerated and t h e drums are cooled b y artesian well water. The ozonized air is sucked through t h e generators b y means of t h e aspirators and delivered t o t h e bottom of t h e mixing well. T h e Herring R u n plant is quite flexible in operation and has demonstrated the fact t h a t ozone generators can be so constructed as t o be capable of continuous operation under varying atmospheric conditions for long periods without serious breakdowns. I t might be of interest t o s t a t e briefly the reason for t h e particular character of dielectrics a n d electrodes t h a t have been used in the construction of these gcnerators. It is well known t h a t many other metallic electrodes could be used in place of aluminum,
THE H O W A R D B R I D G E SYSTEM
In the Howard bridge system aluminum electrodes and micanite dielectrics are used, and are of either the cylindrical or flat plate design. T h e plant built at Lindsay, Canada, was constructed of flat plates, while the Ann Arbor, Michigan, a n d the Herring R u n , Maryland, plants made use of the tubular design. A feature of this original patent consisted in perforated electrodes, t h e object of which was t o increase t h e o u t p u t b y bringing t h e air into more intimate contact with t h e brush discharge: theoretically t o have each jet of air as i t was drawn through t h e perforations completely surrounded b y t h e discharge. Also t h e air is not forced into t h e ozonizers, a s is the procedure a t t h e majority of plants of this character, b u t is aspirated through t h e generators b y means of the raw water flowing through specially designed nozzles; the object of this is t o reduce t h e cost of pumping the ozone into t h e water and t o obtain a more intimate mixture a s t h e ozone is drawn into the aspirator tubes. T h e Herring R u n plant was originally constructed under t h e Bridge patents, and similar in design t o the plant a t Ann Arbor. Owing t o certain minor defects and t o local conditions this plant was not a success, so it became necessary t o redesign the system. The plant a t Herring R u n as it exists to-day, although it embodies t h e general features of the Bridge design, has many additional features a s a result of t h e experimental work carried on b y t h e Water Company under t h e supervision of Mr. A. E. Walden.
a t a much less first cost. Aluminum. however, is t h e only metal of which we are aware, other t h a n gold or platinum, t h a t will withstand t h e corrosive action of t h e ozone. Vosmaer and others have claimed t h a t t h e choice of material for electrodes is immaterial, b u t this is contrary t o our experience during t h e past six years. The main objection t o t h e use of aluminum
J u l y , 1916
T H E J O C R N A L O F I N D U S T R I A L :l.VD E N G I N E E R I N G C H E M I S T R Y
for this purpose is t h a t sooner or later aluminum nitrate is formed upon t h e surface of t h e tubes, a n d as this compound is deliquescent it creates disastrous arcs. This condition, however, can be overcome by removing t h e electrode and cleaning t h e surface. T h e production of nitrate on t h e electrodes would indicate t h a t some nitrous compounds are formed. a n d undoubtedly this is so hut from careful tests we have not been able t o determine this, so t h e quantities formed must be infinitesimal. 4 numher of dielectrics of various materials were tried h u t u p t o t h e present time none of t h e m have, under actual tests in this particular generator, proven
63s
imported, they would probably he prohihitory on account of breakage. The aspirators in use to-day are not the result of a chance design h u t t h e logical result of several months of experiments with various types of nozzles dcsigned b y Mr. Walden. They are of cast iron lined with porcelain a n d so constructed as t o furnish the maximum velocity of air with comparatively l o a liead of water over t h e throats, I n t h e operation of ozonizers for water puritiration many factors must be taken into consideration. a n d it is due t o a lack of comprehension of this fact t h a t so many failures, in this country a t least, have been
....~... ".."...
as satisfactory as t h e micanite tubes in use. T h e objection t h a t has been raiscd against t h e use of micanite is t h a t under continuous use t h c mica sheets separate, causing unevenness in thickncss. I t has been demonstrated in our experience t h a t this can be overcome by careful manufacture of t h e micanite. At t h e prcsent time we have in t h e generators a t Herring R u n dielectrics of this material t h a t have been in constant usc for sis years without failure. Glass dielectrics have been tried in a n experimental way a t this plant a n d are quite satisfactory, h u t our results tend t o show t h a t , as these tubes h a r e t o he
experienced. The operator must l
