CONSERVATION? KENNETH HICKMAN Aquastills, Inc., Rochester, New York
Tm:
water shortages, local and general, that arise in various parts of the world are being brought increasingly to public attention and receiving correspondmgly greater allotments of research funds. Scientists and inventors are encouraged to devise ways of converting foul water to pure and creating new water where none yet exists. The most insistent demands are for irrigation water in spite of the probability that currently the most acute need is for potable water in a few localities. Not the least pressing need, therefore, appears to he mutual education-of the technologist concerning what is needed, and of the public and its administrators in regard to what is feasible or even within the realm of technical possibility. These notes have been compiled by a technologist searching for hydro-political education. Source material has been papers collected in the volume "The Future of Arid Lands" and a companion volume "Water for Industry" which covers the Boston symposium held by the American Association for the Advancement of Science on December 29, 1953 ( 1 ) . Together with Professor Gilliland's article on means for water conversion (16) and a collection of papers on industrial and regional water problems published in December, 1953 ( I S ) , these books outline many of the problems and remedies so far recognized. Other recommended reading is an article by A. P. Black in a hrochnre from the Southern Research Institute (5), the survey by Richard Hoak (S), and the reports issued annually since 1953 by the Salime Water Conversion officeof the United States Department of the Interior. The most recent collection of papers is in press for the National Academy of Sciences as the "Proceedings of the First International Water Conversion Symposium," held in Washington, D. C., November 4-6, 1957. The writer's first written attack on the water problem appeared in Industrial and Engineering Chemistry (4) and this, the second, starts from conclusions reached in the first. The Water Problem Has Come to Stay. Together with care for the atmosphere, the conservation and repurification of water will grow in urgency with the passing years and may well become the limiting factor to population on this earth and a major cause of strife. Water Will Be Expensive. In prodigal supply from nature and often of negative value (as flood victims will testify), delivered water, water-where-you-wanbit, will bear a dollar label like the label on distributed heat or power or the telephone. The Cost Will Appear Reasonable. The cost will appear reasonable when it has been accepted as a normal item in the economy. The hopeful projections of those VOLUME 35, NO. 5, MAY, 1958
who dream of cheap "water for the world," admirable though they are in intention, are in the writer's opinion as mistaken as they are obstructive to progress. No artificial illumination can compare in quantity and cheapness with daylight, yet most of our office buildings operate on electric light with the shades drawn and factories are often built without windows at all. No man-made ice can compare in cheapness or volume with the ice of nature; there are millions of cubic miles of fossil ice on Greenland and the antarctic continent, yet we make expensive little ice cubes in every kitchen and forget the cost. The lure of the artificial product, is convenience, ubiquity, and subservience to the whims of human need. In spite of this now obvious outcome, the early days of both fluorescent lighting and domestic refrigeration were beset by the calculators, surveyors, and argumentative persons who purported to prove that the manufactured product could not be competitive with nature. We are going through just such a period with regard to water. May we emerge from it rapidly! There is no intention to leave the impression that, efforts should be relaxed in the search for new irrigation water. If our factories are lighted with electricity, crops are still grown by sunlight. The point is that the two ends of the water problem are as widely separated as the lighting problem and pose ut.terly different: questions. A HYDROGRAPHIC REVOLUTION
I t is axiomatic that cities have started only where there is some sort of water supply. The primary need is always for potable water even though the secondary consideration may have been power or transportation. This has positioned most great cities on the banks of large rivers, generally where they pass into the ocean. We talk of ourselves as becoming short of water today, but our basic frustration, surely, is that we cannot live or operate where we will simply because we cannot conjure up non-existent water or convert foul water to usable. Conversely, the revolution in our attitude, which is taking place almost unrecognized, is that me are determined to live where we want, and we will induce the necessary water. WATER INDUCTION WILL BE A STEPWISE DEVELOPMENT
The word "induction" has previously been borrowed to describe the act of procuring water artificially. There are three important ways of inducing water: (1) by rerouting of existing usable water; ( 2 ) by caverting existringbut ununable water; (3) by creating
new liquid water, for instance by extraction from theair. Excluded from this specialized meaning of induction is the ordinarily practiced distribution of city water and the like. The three main means of induction extend in application by smaller or larger steps from the survival of the hard-pressed individual to market gardening and agric u l t u r e a n d ultimately, no doubt, to the irrigation of the arid areas of the world. Success with an earlier step is likely to facilitate a later step and may indeed be a prerequisite for so doing. For example, a device that would produce a quart of drinking water in the dry desert would enable a man to survive while he dug a well. The well (step 2) might regrettably give unusable water, hut a converting device might be installed (step 3) to make, say, 1000 gallons a day of potable water which would enable the man to establish a home and family. More wells and converters (repeat, step 3) could bring more persons and farm animals to the neighborhood, and presently the group could be important enough to warrant an irrigation canal (step 4) from a distant river. With quantities of induced water now coming in, the problem of disposition of waste in a region with no natural outlet could become troublesome and a program of polluted water processing could be initiated which would yield: (a) reusable potable water; (b) fertilizer concentrate; (c) useless, dry waste, to he dumped. Thus, in a simple, hypothetical sequence a traverse has been made in imagination across a segment of the entire field of water induction engineering. CONVERTED VERSUS NATURALLY INDUCED WATER
The example started with a quart of water extracted from the air and ended with an acre-foot per day, an increase of a million times. Had the acre-foot been extracted from the air instead of delivered by canal, the cost would have been multiplied many thousandfold. The total quantity of water falling from the sky (5) onto the five continents has been computed as 3.5 X lo'%gallons per second. The Mississippi in flood alone sends 1.8 X loLogallons a second into the ocean-many times more in one second than Greater New York City uses in a day. A modest backyard in New York State will receive an acre-foot of water in a year which will disappear without fuss or reminder; yet by August the occupant may be buying water for the lawn. The 326,000 gallons of the acre-foot were free, the purchased water will cost perhaps 25 cents per 1000 gallons. Induced water will cost more, and converted, distributed water much more than this, and there is not enough wealth in the world to process more crude water than a tiny fraction of what falls in rain. The writer is convinced that all major supplies of new, induced water must be derived from new and heroic measures of conservation, including flood control and especially the rerouting of rivers-a program which will stretch a hundred or more years into the future and involve expenditures of the proportion we currently devote to defense. I t may he a presumption to call for vast measures and powers not yet possessed by man as a factual remedy for a situation, hut only such measures appear adequate for the larger needs. Why, then, it might he asked, should so mnch atten-
tion be paid to conversion of sea and brackish waters? It is because these have a vital local significance that can never he met by conveying bulk water from somewhere else. And the argument will he developed that saline water conversion will influence, in turn, future plans for rerouting hulk water. The immediate task, then, and a great one, is to find out how to convert saline and other highly contaminated waters, economically and reliably, to fresh water. If this can be done, coastal cities can become independent of upland water and new cities spring up along the coast where there are no rivers. Easing the call on upland water means, in the case of the longer river, easing the competition between states. The direction of flow of water use becomes reversed, and the system-expanded by cyclic reuse or repurification of spent water-should liberate new large volumes for agriculture and urbanization of arid regions. Thus, the end effect of creating new dollar or fifty-cent water from the sea at the sea should be to make the five-cent water more plentiful where only five-cent water will suffice and liberate yet other five-mil water for irrigation. The millions of purchasers of expensively converted domestic water will receive a sort of "green stamp" bonus in the form of a greener agricultural economy. COSTS AND PERSPECTIVES
How much will it cost the economy to initiate this turnaround water sequence? There have existed for many years cheap and reliable devices for softening city water and these are now augmented by ion exchangers which provide completely demineralized water quite inexpensively. However, no process that we can imagine that uses chemicals will demineralize ocean or strongly brackish land-water on a large scale. If the water for Greater New York City should be taken from the ocean, the salts liberated in one day would supply the world'sneeds for chlorides for a year. There would not be enough manufactured chemicals extant to operate the exchange process. Again, some natural waters and most used waters contain organic and other non-ionic contaminants and require comprehensive purification. The only all-inelusive means appears to be distillation. Thus, while there is a legitimate and almost unlimited field for chemical, ion-exchange and electrodialysis for hard and brackish waters, their discussion may he left to experts and the present article confined to the total processing, i.e., distillation of water, either from the ocean or polluted with non-ionic contaminants, which represents a second, equally unlimited field. THE DISTILLATION PROCESS
There are three useful varieties: single effect, multiple effect, and recompression. Except for emergency use (water was distilled in the British Navy as early as 1600) or with cheap heat, as in the very promising solar still, fuel costs for single effect distillation are prohihit i v e a barrel of oil will not produce more than 15 harrels of water. Multiple effect. stills, generally triple or quadruple, will give 4&50 barrels per barrel of oil, and they have become accepted wherever fuel is unusually plentiful. The best known large installations, both a t oil refineries, are: JOURNAL OF CHEMICAL EDUCATION
Curmw Arubs.
Yield of water p w day 3200 tons 1600 tons
Epuivalent consvmptimz of oil, per day, opproz. 64 tons 32 tons
For the large-scale conversion of water, these quantities of oil are fantastic. To maintain a flow of one acre-foot of water per day, seven acre-feet of oil would be consumed per year. To become competitive and useful away from the oil field, the multiple effect still will have to throw off the shackles of conventional engineering and encompass a great many more stages (6). Thus, an Bstage still might be expected to develop some 6 theoretical effectsand deliver 90-100 barrels per barrel. With fuel a t $3 a barrel and with over-all costs, including amortization and operation, a t twice fuel, at-the-still water could be produced for 'OoO - $l.OM1.15 (9WlOO) X 55 per 1000 gallons in large installations
The recompression still parallels the mnlti-stage still, but it offers two tremendous advantages. It provides a great many more equivalent effects and it does so with a single evaporator-condenser. The corresponding drawback is that it requires mechanical power instead of low grade heat. The power is likely to be produced by a heat engine, itself not more than 33% efficient, so that in comparing costs it is necessary to divide the apparent number of effects by 3 and add the investment cost of the engine to the still. The compression still can withstand this down-grad-
ing. A 30-effect machine can be readily constructed, leading to a 10-effect utilization of the fuel to give 190 barrels of water from one barrel of 19,000-B.t.u. oil. The capital cost with Diesel power compares favorably with the cost of an equivalent thermal still, leading to at-the-still water of $1.50-$2 per 1000 gallons. THE TREND TO MINIMUM FUEL COSTS
A previous paper (4) dealt with a rough approximation of the absolute minimum expenditure of energy required to separate salt from sea water (Figure 1). The quantity is somewhere near one B.t.u. per pound of produced fresh water, supplied as mechanical energy (0.29 watt-hour), or about 3 B.t.u. in the fuel fed to the engine and still. In an idealized still, offering no thermal gradient and operated by a compressor which circumvented the losses due to adiabatic compression of the steam (both unrealizable), one barrel of 19,000 B.t.u./lb. fuel would provide 6333 barrels of water. The largest yield we can envisage ever being produced by a real applied compression cycle is 2000 barrels per barrel and this we have referred to as the "absolute millenial optimum." A good clean Diesel-operated Kleinschmidt stiU today gives 200 barrels per barrel, so that the range available for improvement is a t most tenfold. Can this limited horizon meet future needs? The answer would appear to be affirmative for a great many classes of water user. The task is to cheapen the still and cheapen in like degree all the accessories, including the power. The user of a mechanical appliance does not always have to
All therlnal dirtillstion Singie effect Triple effeot Qlladruple effeot 20 effeot 40 &eat
.4 series.
1.
', g
5 0
z 4
w
+
-
0
a
u
2. 3. 4.
5.
sehes. Eleotrvlyais 1. Single oell with overvoltape, thcoretical "due 2. Eleetromembrane 3. Eleotromembrane, but referred to a brackish water scale 3 W O p.p.m. instead of sea water. B
Comnression distillation 1. Conventionsl, tubular boiler, oompressor eleetriosliy driven 2. same. but Diere1 driven
C: Series. ", -
2
2 k u k
5
= E
:
D Sories. Centrifugal barrier, eompres. sion still 1 . With 18-ineh-diameter barriers 2. With afoot-diameter barriers 3. same, later design
E Series. Combination of compression and thermal stills, centrifugal barrier* Sise of symbola indicates range of data rather than exaot point.
LOGARITHMIC T l M E SCALE
Courtesy d Indunrid and Eneineerins Ch~mirrrv(4) Figvre 1.
VOLUME 35, NO. 5, MAY, 1958
Effi0ien.s~Trend. of vuiou.
w.te
Conv.reon
Rocnnes
think in terms of primary fuel but may employ electricity a t so much per kw.-hr. The current, in turn, may soon be derived from nuclear fuel so that we may come to equate pounds of uranium or deuterium consumed with volume of water converted, which leads to the forecast shown in the table. Yield of Product Water from &sent Compl-ession still of 1965, driven h?/
-
Oil
urn-488
2D2
He'
and Future Fueh
gallons per lb. fuel
Awe-foot per lb. fuel
Ratio, weight water to weight fwd
0.12 216,000 1,600,000
0.000367 660 4900
10W:l 1 . 8 X 10e:l 1 . 4 X 10I0:1
I000
Using the generalieed statement (CISLER,W. L., Scientific Monthlv, December, 1956, p. 295) that 1 lb. of uranium = 13M) tons of coal, and that hvdroeen when utilized as a fuel should liberate slightly less thah 8 iimes more energy than uranium, weight for weight.
Evidently future fuels can convert and reprocess unlimited quantities of water. The investment cost of water machinery becomes linked with the cost of new power plants and is, apparently, inseparable therefrom. Mechanical improvements to the still are concerned with (a) basic design, ( b ) equipment and instrumentation, and (c) mechanical and chemical reliability, freedom from scaling, corrosion, and down-time. Basic Design. The type of construction has hitherto been determined by the needs of the armed forces which are for massive, shockproof units, inheriting from high pressure steam practice. But a compression still could use the flimsiest components. The pressure differential between evaporating and condensing sides is a t most a few pounds gauge and can be as little as a few inches of water. A simple container and a primitive fan compressor should be sufficient and, in small sizes, would lead to units differing little in form and complexity from a vacuum cleaner; in fact, the kind of stills defined could be classed as "vacuum hydro cleaners." Equipment. The auxiliary parts of a compression still represent a large fraction of the cost. Unless the pumps, filters, feed-effluent heat exchangers, instruments, etc., can be cheapened in like degree, improvements to the still proper are largely wasted. Operation. The marine compression still has traditionally required cleaning every few hundred hours, either by dismantling and mechanical removal of the hard, chalky deposit or by flushing with acid. The CaCO8 Ca(HCOa)2 COz equilibrium of fresh sea water is shifted at temperatures above 160°F. t o favor calcium carbonate precipitation, especially if gaseous GO2is removed by the act of distillation. It is now established that temperatures below 150°F. are favorable to the delay or total repression of scale formation from ocean water, though there is little collected information concerning the scaling at low temperatures with hard, brackish waters. Information concerning the compression distillation of filtered sewage, domestic municipal and industrial, is also lacking.
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of a practical application. French and United States inventors took a hand at the turn of the century, also with no recorded success. The great engineering advance, inspired by a true understanding of the problem, came when Swedish engineer Olaf Soderlund with his assistants, notably T. Boberg, described various tubular stills to operate under low pressure differentials (8). A few such stills were constructed in Switzerland. Recently, the Escher Weiss Engineering Works of Zurich has put into operation a thermo compression plant (2) for concentrating beet sugar with the astounding capacity of 790,000 gallons per day. The next radical departure was made by another Swede, Nils Testrup (Q), and an Italian, Carlo Barbareschi (lo), who replaced the conventional tubular boiler-condenser with a rotating cone or drum. The crude water was picked up by or applied to the outside of the drum and maintained in relatively thick wobbling layer by slow rotation. Steam liberated spontaneously from the outside was passed through the compressor and fed into the inside of the drum where it condensed to pure water, returning its latent heat of evaporation through the drum wall and thus maintaining the evaporation process. The one essential feature for this geometry, namely, high speed rotation to spread the fluids to the thinnest economical layers on both sides, mas apparently missed by these inventors. It is not proposed to devote much space to a description of the high speed centrifugal compression still (If), which this miter has been developing under the sponsorship of such agencies as the Rochester Research Corporation, Badger Manufacturing Company, and the United States Department of the Interior. It enters the argument because it illustrates in specific form the general, non-specific goal for the would-be water con-
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THE COMPRESSION STILL: CURRENT AND FUTURE POSITIONS
The modern still is preceded by a surprisingly large prior art. The idea was patented by Harrison (7) in Englaud just one hundred years ago. There is no record
Courfesy of Industrial and Ensinewins Chcmirbv (15)
Boiler-condenser; 9. effluent heat exchanger. I.
steam oompresaor; 3.
feed-
JOURNAL OF CHEMICAL EDUCATION
verter. The goal is t o produce the least expensive barrier through which water can separate from salt m'th the least expenditure of energy and the least supervision and maintenance. This rule ran be applied t o any known separation process, and success will depend on the favorableness of the cycle and the ingenuity of the engineer. The membrane of the electrodialysis process already meets the criteria in great degree and it will inevitably continue to
stills can be built t o operate a t from 3-10 watt-hours per pound of produced water, the power being chosen to fit the circumstances. This is the realistic range; and plans can be mat,ured with confidence using these figures. (Note: The range of water costs is purposely expressed in terms of power, not dollars. The dollar costs of power, still construction, and operation-maintenance are all highly variable hut all are amenable t o reduction by human ingenuity. The basic cost of coverted water with power a t 5 mils per km.-hr. is thus 12.542 cents per 1000 gallons; the delivered cost after amortization is anybody's guess.) ADAPTING THE STILL TO USE
Courtesy oflndurlrial and En9inoorin.r Chembtry 115) Fig"..
3.
Diagram 111u.trating Principle of Centrifugal B-ier Com.re..ion Still
in~prove. A large cheap surface is also being realized in the solar still, and in certain freezing processes which ut,ilize the area of a multitude of water crystals. In the centrifugal recompression still the cheapening of the barrier is achieved by using a series of thin metal cones instead of boiler tubes and these extend both area and rat,e of transfer of heat. If a conventional compression still realizes an over-all coefficient for condensation, heat transfer and evaporation of U = 650 B.t.u./(hr.)(ft2)(OF.), then the centrifugal still routinely gives U < 2500. Figure 2 shows the conventional compression still cycle and Figure 3 the application of the centrifugal barrier principle. Photographs of early experimental rentrifugal compression stills have been reproduced in Industrial and Engineering Chemistry (15), which see. Figure 4 is a side view, panel removed, d a small household still developed by Aquastills, Inc., t o deliver 3 M 5 0 0 gallons per day of product water from sea water or brackish waters. Designated capacities, 100 or 25,000 gallons for a given unit per day, are somewhat arbitrary. As input to the still is increased, the yield increases as the square root of the power consumed. Four times the power gives twice as much water and all the water costs twice as much for power. The capital investment, however, is cut nearly in half and the total cost is the summation of pourer, amortization, and maintenance. Power costs descend toward a minimum for salt and water handling if the still boiler (barrier) is sufficiently large. Therefore, the greatest advance can come from cheapening the boiler barrier. A parallel required advance is t o cheapen the feed versus effluent heat exchanger (it)coupled with lowering the temperature of distillation. This aspect of the problem has not received the merited consideration since Dr. Kleinschmidt first drew attention t o it. The present distillation position is that compression VOLUME 35, NO. 5, MAY, 1958
Sea Water. Although this imposes the highest normally met salt load, it is the only ulliformly distributed foul water feed, and this permits st.andardization of manufact,ure and maintenance procedures. Brackish and Well E'aters. Surface waters loaded with calcium sulfate, silica, and iron; and well waters charged with Coy, H2S, or SO2, holding corresponding quantities of lime and magnesium in unstable solution, present hazards to any mechanical barrier process whet,her this be distillation, dialysis, osmosis or other, because of precipit,at.ion a t the transfer interface and in the auxiliary equipment,. This means t,hat each process must be tested with each type, and even subtype, of water and an ohjertive conservative appraisal made hy t,he supplier before the user is allowed to take possession of t,he converting machine. For certain waters it will undoubtedly be found t,hat there is as yct no easy, t,rouble-free met,hod of purification. Fortunately, the most prevalent contaminant of wells is common salt.. In many parts of the xorld-the Bahamas, the Tia Juana Valley ( I S ) ,San Diego, parts of New Jersey, and western New York, to pirk random ex-
Hogan, Designer
amples, the water table is becoming lower, and wells that once gave potable water now run brackish. A conversion process that will permit the reuse of abandoned wells will be critically important. Here, in comparing the merits of electrodialysis with compression distillation, one must remember to credit the latter with a dilution factor. Thus, if water is brought from an unusable 800 p.p.m. of solids to an acceptable 300 p.p.m. by electric treatment, then the comparable costs for distillation should be adjusted downward by (8-3)/8 because the distilled water can be reblended with the feed to make a larger volume of 300 p.p.m. product. No real difficulty is foreseen in providing satisfactory conversion means in the near future (that is to say, right now) for many well waters. A far more troublesome problem is the disposal of the resulting extract. Converter Residue Disposal. The salt concentration in the residue effluent from a converting device raries according to the degree of feedback employed. With no feedback and a 2: 1 feed :distillate ratio, the residue from an 800 p.p.m. feed will be 1600 p.p.m. If fourfifths are reblended with one-fifth new feed, the onefifth discarded will contain 8000 p.p.m. or 0.8% solids. At some concentrations, generally between 0.5% and 5.0% salt, solids will separate troublesomely and an appropriate residue must be discarded. I n sparsely settled arid districts the residue can de dumped into the ground but in urbanized regions it must be conveyed to the ocean, to a communal solar Dan, . . to a communal residue still, or to a domestic solar pan. The quantities of solids to be accommodated from the last three alternatives are large but not prohibitive. For instance, the quantity of surface water in California, said to be raised by pumping (15) is 10 million acre-feet per aunum. Much of this water is excellent quality but some wells show 500 p.p.m., some have been abandoned a t 700 p.p.m., and others a t 2000 p.p.m. If we assume that 1% of the pumped water were to be converted from 1000 p.p.m. to 200 p.p.m., the aggregate dry residue (sp. gr. 2.0) from 100,000 acre-feet would be 0.8/2 = 0.4 acre-feet per year. A moderate sized quarry would accommodate the residue for many decades. An isolated residence using 500 gallons a day might discharge 5-10 gallons per day of residue solution, for instance, to a small shallow cistern, say 8 ft. X 12 ft., covered by transparent plastic or glass but open to the wind. With an average effective receipt of 1000 B.t.u./day per square foot from sunlight, a t least 90 pounds of water should be evaporated leaving a residue inches deep per annum. I n fact we look to see, as an integral part of the water picture of the future, water residue mounds near every inland village and town, similar to the mounds of a different kind of detritus of former civilizations that are today uncovered by archeologists. Industrial Waste. The problem is more specific in industry, and one aspect is easier in that avenues for effluent rejection are already in use. The immediate task is to reduce the use and increase the effectiveness thereof. The more obvious steps are a classification of in-process waters, reuse by passing the water from one
class of service to the next, partial reclamation when pollution becomes prohibitive, and rejection of a final concentrate. The means for reclamation-distillation, chemical or electric, must necessarily be determined by consultation between the industry and process water engineers. However, the costs in power and equipment are likely to be in the range outlined and the prototype means are already available. So much more cogent material has already been presented in the various process symposia and monographs cited earlier that the matter will not be developed further a t this time. Radioactive Waste Waters. Where extremely dilute solutions are concerned, ion exchange methods appear to be serving admirably. For more concentrated liquors, the costs of housing and remote control (14) are so great that any particular economy applied to the process itself would seem misplaced. While radioactive wastes are pressing items in the field of waste recovery, they would not seem to be the immediate concern of those charged with providing cheap water or cheap reuse of water. CONCLUSION
The opinion is submitted that industry has a t its disposal, buried in the early art (185646) and visible in recent proposals, means that are already practical for converting sea water and polluted used water into fresh water, a t costs which are reasonable for a great many purposes. Steps that will convert opinion to reality are: Acceptance of a revised scale of costs which shall be considered reasonable. Acceptance of the technical means currently available. Courage to put such means to practical use. LITERATURE CITED (1) American Association for the Advancement of Science: "The Future of Arid Lands," GILBERT F. WHITE,Editor, Wsshington, D. C., 1956. "Water for Industry," J. B. editom, Washington, D.;C., G R A ~AND M M. F. BURRILL, 1956. (2) United States Department df the Interior,
