I N D UXTRIAL A N D ENGINEERING CHEIMISTRY
July, 1928
of complex substances such as fats, proteins, cellulose, etc. It is quite possible that lime accelerates the rate of the decomposition of these substances independently of its effect on neutralizing the acids, which would result in a greater accumulation of volatile acids provided the rate of decomposition of these acids did not change. Lime addition to maintain the optimum reaction of digesting fresh solids is necessary only in the first few weeks. The amounts of lime added a t this period are large and may have a decided stimulating effect on certain bacteria producing the acids and a depressing effect on the bacteria destroying these acids. The coincidence of high volatile-acid peak and large amounts of lime addition to the unseeded fresh solids in the first few weeks of digestion tends to substantiate this view. After the lime additions cease the volatile acids begin to decrease very rapidly. On the other hand, ripe sludge when used as a neutralizing or buffering agent would not have the caustic action of lime on the bacteria. The neutralizing constituents of ripe sludge would consist of the alkaline products of decomposition such as ammonia, etc., the concentration of which a t any time would not be sufficiently great to bring about a toxic action. The buffering agents of the ripe sludge, which consist of the organic matter and the inorganic salts such as the phosphates, carbonates, etc., would serve in a more ideal way than lime to regulate the reaction. Under these conditions there would not be a stimulation of certain types of decomposition
and a retardation of another type. There would not be an undue production of volatile acids or a retardation of their decomposition. They would be produced in smaller amounts and neutralized and decomposed as soon as produced. It should be emphasized again that completion of digestion as indicated by volatile-matter destruction and ash contents coincides with the disappearance of acids. (Table IV) The relationship between gas production and volatile-acid content of the seeded material is indicated in Figure 2. The volatile acids results are obtained from Table IV. This mixture consisted of fresh solids and ripe sludge in the ratio of 1.7 t o 1 on the basis of volatile matter. For the purpose of illustration the gas-production figures are taken from another experiment with a different lot of fresh solids and ripe sludge seeded in the ratio of 2 to 1. The fresh solids and ripe sludge were obtained from the same plant, but a t different dates. Although these two curves are not obtained from the same experiment, there is a striking relationship between them. lJ7hen the volatile acid content is high in the beginning we have decreasing gas production; on the other hand, with decreasing volatile acids we have rapidly increasing gas production and a t the end volqtile acids and gas production reach a low level a t about the same time. Hence volatile-acid determinations can be taken as an additional index of the completion of digestion in conjunction with gas measurements, biochemical oxygen demand, and solids and ash determinations.
Use of Exchange Silicate (Zeolite) Water Softeners in Railroad Practice’ George L. Baxter SOUTHERN PACIFICLINES, SACRAXENTO, CALIF.
Exchaiage silicate (zeolite) treatmeizt at certain points o n the Southern Pacific L i n e s has been f o u n d less expensive than treatment with lime and soda ash and has resulted in more satisfactory operatiou of statiotzary and locomotive boilers. UCH of the water in various sections of the country is not suitable for use in boilers without a preliminary treatment to remove the scale-forming materials. The lime-soda treatment has been used extensively by railroads for many years and gives general satisfaction, especially when it is carefully controlled. With this treatment facilities must be provided for the settling of water and also for the storage of the treated water. Care must also be taken that the raw materials are properly housed and in some instances mixed previous to treatment. Mechanical apparatus, such as pumps and stirrers, is needed and it is also necessary, for chemical control, that these plants be visited at least periodically by a chemist so that exact check may be had on the treatment. Of late years base-exchange silicates have come into use and in many cases they have proved a very efficient means of treating water for both stationary and locomotive boilers. Method of Use
M
Typical zeolite reactions are as follows:
++Cas04 = CaZ + NalSOl 2NaCI = CaClz + h’azZ
Treatment: NazZ Regeneration: CaZ
Received April 3, 1928. Presented before the Division of Water, Sewage, and Sanitation a t the 75th Meeting of t h e American Chemical Society, St. Louis, Mo., April 16 t o 19, 1928.
We find that 0.5 pound of salt per grain of hardness per gallon per 1000 gallons of water treated is requisite for ordinary regeneration, also that the amount of water used in rinsing is approximately 0.7 per cent per grain of hardness per gallon of all the water passing through the meter. With the zeolite system no tank for settling is necessary as the water goes directly to the storage tank when it leaves the bed. ,Common salt, which is used for regeneration of the zeolite, is the only material that has to be furnished. This material is unloaded directly from bulk shipment in cars to a large concrete tank, where it is dissolved in water and from which it is pumped to the zeolite bed when regeneration is necessary. Regeneration and washing, accomplished by the manipulation of valves, is all the work required for the maintenance of the zeolite plant. This regeneration means that the calcium and magnesium which have been eliminated from the water are in turn replaced by the sodium of the salt. The regenerating solutions and subsequent washings can generally be readily disposed of. This is quite a feature, as a t some points on our lines we have no place to dump the sludge that is formed with the lime-soda treatment and the handling of this sludge also is an operation in itself under the best of conditions. It is therefore apparent that the zeolite method is practically “fool-proof” as compared with the lime-soda treat-
INDUSTRIAL AND ENGINEERING CHEMISTRY
756
Table I-Analysis
STATION
KIND
I I
of Water before and after Treatment w i t h ZeoUtes (Figures in grains per U. S. gallon)
I
MATTER IN SOLUTION
I
INCRUSTATING
Lime
OF W A T E R
Vol. 30, No. 7
bz::;e ::;
Chloride
bz:i;e
ssk Chloride
I
NON-IXCRUSTATING
Alkali
iron, Alumina
I M~~~~~ ALL
I
NONININCRUS- CRUSTATINQ TATINQ
West Oakland
Raw Treated
6.53 0.00
0.00 0.00
0.00 0.00
3.50 0.00
0.00 0.00
0.00 0.00
1.11 1.40
0.00 10.79
3.73 3.73
3.44 3.44
18.31 19.36
7.17 17.96
11.14 1.40
San Luis Obispo
Raw Treated
4.67 Trace
0.00
None
0.00 0.00
8 . 8 6 0.00 Trace 0.00
0.52 0.00
0.41 0.93
0.00
16.68
0.29 0.29
5.48 6.18
20.23 24.08
5.77 23.16
14.46 0.93
Calexico
Raw Treated
7.70 0.29
9.33 0.00
0.00 0.00
1.05 0.47
7.70
0.00
0.00 0.00
0.58 1.05
0.00
7.70
11.43 27.70
9.04 10.61
46.83 47.82
20.47 46.01
26.36 1.81
Los Angeles Shops
Raw Treated
8.40 Trace
0.00
1.11
0.00 0.00
2.16 0.23
2.27 0.00
0.00 0.00
2.45 1.29
0.00 10.20
4.26 8.63
2.39 2.80
23.04 23.15
6.65 21.63
16.39 1.52
h' :;
0.00 0.00
0.00
1.63 0.64
5.42 0.00
0.00 0.00
2.39 2.51
0.00 12.77
3.50 9.74
19.71 19.71
46.42 47.70
25.26 44.26
21.16 3.44
Tracy
%Gated
1
0.00
ment. Furthermore, it does not require attention due to the seasonal changes in water, as the zeolite itself takes care of any variation in the chemical constituents of the water, whereas the lime-soda method may at times require considerable changing. The operator of the zeolite plant can readily determine by means of the soap test Jyhen the zeolite bed needs regenerating and also when the salt has been thoroughly washed from the bed after regenerating. In many of our plants the cost of operation of the zeolite system is at a minimum because it has been taken over by some minor supervisor or man whose regular job will permit him to leave it for a short time. When a definite amount of raw water has passed through the zeolite softener, an electrical contact is formed on the meter causing a bell to ring which is a signal to the operator that regeneration will soon be necessary, He then uses the soap test to assure himself that the regeneration should be made. Ordinarily, regeneration and washing are complete in about 30 minutes. Zeolite plants are built to dimensions, height and diameter, to take care of a definite amount of water containing a certain amount of scale-forming ingredients. The exact size of the plant is determined by the amohnt of treated water required and the amount of scale-forming materials in the raw water. This company is at present operating nineteen zeolite plants, sixteen of which are the so-called down-flow type and three up-flow type. From the results obtained it appears that the down-flow type permits considerable more than the rated capacity. These plants vary in capacity from 52,000 to 800,000 gallons per day and the treatment is just as efficient on the largecapacity plants as it is on the smaller ones. Analytical Results
The results obtained from analyses of raw and treated water where the base-exchange silicates were used for removing the hardness are shown in Table I. I n some cases there was a considerable percentage of sodium chloride and sodium sulfate present in the raw water, but so far this has not caused any great difficulty in regeneration-that is, solution of the calcium and magnesium which had previously replaced some of the sodium in the zeolite. Comparative Costs
It is costing us approximately $0.025 per thousand gallons to treat water by the zeolite system whereas the cost by the lime-soda treatment is about $0.05 per thousand gallons; both include labor. Table I1 shows the cost of one of our general shop power plants based on 1000-gallon water basis.
Table 11-Cost
Data
UNTREATED
..... ..... .....
Cost of treating Cost of upkeep Obsolescence Interest Boiler repairs Fuel
$o:i&i7
2.93664 -__-
Net cost per 1000 gallons of water Saving per 1000 gallons water, over no treatment
$3.08581
... ..
LIME-SODA
ZEOLITE
$0.03009 0.00231 0.00162 0.00243 0.08054 2.79154
$0.02150 0.00030 0.00212 0.00311 0.00515 2.71459
$2.90853
$2.74677
$0.17728
$0.33904
---
----
Assuming that the lime-soda treatment removed approximately 15.40 grains and the zeolite treatment about 20.40 grains of scale per gallon of water treated, which is very close to being correct, the net saying per pound of scale removed is, for the lime-soda treatment, $0.0806, and for the zeolite treatment, $0,11635. Use in Stationary Boilers
The first zeolite installation made by the Southern Pacific Company was for softening the water used at Los Angeles passenger station for stationary boilers and wash rooms. The second plant was installed in the laundry a t West Oakland, where it caused a large saving in the amount of soap and soda used and also in the appearance of the linen washed, as there were no calcium and magnesium salts settling in the fabric as before the zeolite treatment was commenced. During first 12 months of operation in the laundry more than double the cost of plant installation was saved by reduction in amount of the cleansing materials used and in the amount of linen replaced. Use i n Locomotive Boilers
The experience with the zeolite treatment for stationaryboiler use a t Los Angeles passenger station demonstrated that zeolite-treated water could be used to advantage. The first trial using zeolite-treated water in locomotive boilers was made on switch engines running in West Oakland yards, and it was found that engines running with zeolite-treated water soon dropped their old scale and that the tubes and sheets were cleaned off, permitting an increase in the absorption of heat by the fire box and flues. There was considerable foaming and priming, but the longer the zeolite water was used the less foaming and priming occurred, indicating that this was due to the old scale being attacked by the zeolite water and removed from the tubes and sheets. The cause of this foaming is readily appreciated when it is recalled that, if a solution of mixed alkali salts, beyond a certain concentration, contains a certain amount of inert solids and is then heated, there is an increased tendency to foaming and priming. Zeolite-treated water contains a large amount of alkaline salts in solution, and when these are concen-
INDUSTRIAL A N D ENGINEERILVG CHEMISTRY
July, 1928
trated there is a deposit of sludge which will cause foaming and priming if not removed, but frequent blow-downs have been found to reduce this tendency to a marked extent. A switch engine, equipped with a new set of flues and fire box, using zeolite-treated water gave no marked trouble due to foaming or priming. However, in some mountain districts, where it is necessary to “beat” the engine pretty hard, there is a marked tendency to foaming; this can be readily checked, however, by the addition of a castor-oil type boiler compound. It is our practice to issue a certain amount of antifoam boiler compound to engines operating with zeolitetreated water. Road engines, using the same type of water in the valley, would not show the same tendency to foam. A certain amount of the foaming and priming should not be attributed to the zeolite water but to the locomotive engineer, as it has been clearly demonstrated that engineers can successfully make a run in schedule time without the use of antifoaming boiler compound if they take every opportunity to favor the engine-viz., by not opening the throttle too quickly, not maintaining too high a water level in the boiler when on heavy grades, and blowing down a t frequent intervals to lessen concentration of the sodium salts. Sturdevant and h’oyes, of this company, have perfected a special muffler apparatus which is attached to the blow-off cock, and permits the blowing down of an engine a t any time without danger or inconvenience of any sort, as the blow-off is conducted underneath the engine and deposits the concentrated salt solution and sludge on the road bed between the tracks. With the lime-soda treatment the water always has a certain hardness due to scale-forming ingredients, which may vary from 1 to 5 or 6 grains per gallon depending upon the thoroughness of the treatment. Such a water in itself, while ordinarily considered soft, in the course of time builds up a scale which sooner or later must be removed. Water from a zeolite plant does not build up scale in boilers, even where there is a slight amount of regeneration due to high-alkali chlorides and sulfates in the raw water; such water will hardly ever contain more than 0.6 grain per gallon of scaleforming material, and the excess of the alkali salts present prevents this material from adhering to the sheets and tubes. We have had numerous instances where zeolite-treated water has removed or brought down the old scale from engines which were tied up for boiler work. As a recent example of this, two switch engines which were held up for tube work were put back into service with zeolite-treated water and are still in service after operating 13 and 18 months, respectively. This is an indication that we get considerably more aTork out of an engine between shopping. This same condition applies to road engines. Switch engines and road engines which are using zeolite-treated water do not require nearly as much boiler work as engines using the lime-soda or untreated water. These engines do not need nearly the same amount of washing; in fact, all they require is a change of water. Table I11 shows the reduction in force in six engine terminals on a district using zeolite water for locomotive and stationary boilers. Table 111-Reduction
Total - . force: .....
Before After Percentage of force reduced
in Labor D u e to Zeolite T r e a t m e n t BOILERBOILERBOILER MAKER BOILER WASHER MAKERS HELPERS WASHERS HELPERS 213 146 31.5
190 143 24.7
17
17 0
23 16 30.6
This reduction, converted to dollars and cents per year, is shown in Table IV. Not only is it fair to assume saving in labor as shown, but also that each dollar spent for labor
757
carries a certain percentage of material that each man consumes in his daily work. Our accounting department shows each dollar to consist of 31 cents material and 69 cents labor, and the figures in the table are computed on this basis to the closest dollar. This percentage of material is added to the saving as shown in labor. It is also fair to add the overhead expense, which is always added to other items, and a fair average of this is 16.3 per cent on labor for the plants concerned. R e d u c t i o n in Cost of Labor D u e t o Zeolite Treatment MEN LABOR MATERIAL TOTAL OCCUPATIONREDUCEDSAVING SAVIWC OVERHEAD SAVISC Boiler makers 67 $127,475.00 $57.275.00 S20,788.00 $205,53S.00> Boiler-maker helpers 47 57.028.00 26,623.00 9,286.00 91,947.00 Boiler-washer helpers 7 8,387.00 3,768.00 1,367.00 13,5?2.00 Table IV-Annual
Total
121
$192.890.00 $86,666.00 $31,451 00
$311 007 00
The use of zeolite-treated water has permitted our road engines to make a greater mileage between shoppings, which has proved to be a source of an invisible earning, as it is hard to estimate what a locomotive is worth per day, especially in a country such as ours where there is a heavy fruit moyement on schedule time for several months. Report of M a s t e r Mechanic
A report from one of our master mechanics on the effects of zeolite-treated water will show clearly the results obtained by the use of zeolite-treated water in engine service: As you no doubt are aware, the water a t Tracy is hard and carries approximately 20 grains of incrustating solids per gallon, which cause considerable trouble through plugging up of water spaces and flues, necessitating the renewal of flues in switch engine boilers, using Tracy water exclusively, in from 3 to 6 months’ time. Using raw water it was also necessary t o wash out switch engine boilers after every 24 hours’ service. The stationary boilers gave considerable trouble through flues, stay bolts, and crown bolts leaking, and formerly were washed out every seven days, and about once a month a few flues in scattered locations would be removed in order to clean out accumulated scale that could not be dislodged by other means. Locomotives assigned to helper service on Altamont Hill, after receiving general repairs and renewal of flues, would run about thirty days before they commenced t o give trouble; then it would be necessary t o expand and caulk from one-half t o a full set of flues every time the boilers were washed, which was after every round trip up the hill. Under this treatment naturally flues and stay bolts would have t o be renewed after a comparatively short period of service, as the heads of stay bolts would be cut down and beads on flues would become so small that it was impossible to keep them tight. A zeolite water-treating plant was installed and placed in operation on April 15, 1927, and since that time the results have been very satisfactory, although for a short time after the zeolite plant was started we experienced considerable trouble with beaded flues leaking as the treated water loosened the old scale and exposed old pits on flues. This trouble, however, disappeared after a short time. With treated water we are now running switch engines in Tracy yard from eight to ten days between washouts and very seldom find any flues or other fire box leaks, and fully expect to be able to run switch engines two years before renewal of flues is necessary, which represents a considerable saving in both labor and material. Stationary boilers are now operating sixty days between washouts, and we have not as yet found it necessary to shut them down t o caulk flues, stay bolts, or other fire-box leaks between washouts. Flues sound clear, proving that there is no accumulation of scale between flues or heavy scale forming on the flues as was formerly the trouble. Helper engines using zeolite-treated water are now washed out after four or five days’ service and, while they are inspected after every trip, we do not find it necessary to expand or caulk flues or caulk other fire-box leaks, engines remaining in service from fifteen to thirty days without developing enough leaks t o warrant boiler maker going into fire box.
758
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Before the installation of the treating plant there were a boiler maker and helper assigned to hot work, working on each eight-hour shift, and quite often they were unable to take care of all the work and it was necessary to assign another boiler maker t o hot work to help them out and get the engines ready for service. In addition, there was a boiler inspector on each eight-hour shift, whose duty it was to inspect all incoming engines and report conditions of flues, fire box, and front ends. The use of treated water has enabled us to dispense with the outside inspectors and their work is now handled by the hot worker in addition t o his performing all the hot work. Since the zeolite treating plant has been installed we have been enabled to reduce the boiler gang materially, affecting a saving of approximately $700 per month in labor alone. I am unable t o tell you a t this time just what the material saving Till be, but believe it will be many times that made in labor. The extended period for renewal of flues in switch engines alone
Vol. 20, No. 7
represents an item that, to my mind, will more than repay the cost of the zeolite plant. Another item that should not be overlooked is the fact that, with the use of treated water and the absence of leaks, it is not now necessary to blow engines down for washouts or caulking of leaks and we are enabled to double engines out when required. As t o the saving of fuel oil, I believe this will be another saving although I have no figures on this angle of the situation at the present time. I believe, however, through the elimination of scale on the flues, the saving in fuel oil should amount to a considerable figure. We also notice considerable benefit from the treated water on our road engines, as my attention has been called t o an engine now in service that has made over 60,000 miles since flues were last applied. This is considerably more mileage than we were able to get out of road engines using the raw Tracy water.
Municipal Water-Softening at St. Louis' August V. Graf WATER
DIVISION, DEPARTMEA'T
OF PUBLIC U T I L I T I E S ,
s
OFTENING of the St. Louis water supply was introduced with the use of sulfate of iron, just prior to the opening of the World's Fair at St. Louis in 1904. The Quincy process, as practiced a t Quincy, Ill, required only enough lime to hasten or insure the formation of iron hydroxide. At St. Louis a large excess of lime was employed, not with the thought of softening the water, but to aid coagulation. For most of the time no sulfate of iron was used, the coagulation and precipitation of the suspended matter being accomplished by the use of large amounts of lime with a resulting high caustic alkalinity. Later the amount of lime was reduced so that caustic water was rarely sent to the consumer. At present enough lime is added during the summer to convert all the bicarbonate alkalinity to normal carbonate before the addition of aluminum sulfate. I n winter, owing to the greater solubility of the normal carbonates in cold water, the lime is limited to an amount that will give a normal carbonate alkalinity that can be reduced to less than 30 p. p. m. by the amount of aluminum sulfate necessary to yield the desired floc for filtration. This limits the amount of softening that can be done in cold weather, and as a result the hardness of the tap water reaches its maximum during the winter. The reduction in hardness accomplished per grain of lime added does not depend alone upon the turbidity of the water, nor does it depend upon the temperature of the water. The effect of turbidity upon the consumption of chemicals has been noted by many water-works chemists and the added amount of lime necessary to accomplish the required softening of very turbid water has also been noted. Temperature might be an influencing factor in completely softening a water because of the greater solubility of the normal carbonates in cold water. I n partial softening, as practiced a t St. Louis, temperature is not an important factor. The hardness of the raw water also influences the amount of softening accomplished per grain of lime. I n partial softening the greater the hardness the greater the reduction in hardness per grain of lime. Whether this would be true of water completely softened with lime and soda ash, we do not know. The hardness of the river water varies from 126 to 257, average 177 p. p. m., and the reduction from 43 to 105, average 1 Received April 3, 1028. Presented before the Division of Water, Sewage, and Sanitation at the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 16 to 19, 1928.
ST. LOUIS, MO.
75 p. p. m. The reduction per grain of 85 per cent lime per gallon varies from 7.5 to 20.4, average 14 p. p. m. The amount of lime used varies from 1 t o 7, average 5.4 grains per gallon. When high color in the river water is accompanied by high turbidity, the water becomes extremely hard to clarify with lime and iron. At such times i t is necessary to add just enough lime to react with the sulfate of iron and to keep the water free from carbon dioxide when the aluminum sulfate is added. The amount of aluminum sulfate is increased to remove the color and also to coagulate the suspended matter passing the primary settling basins. Lime tends to fix the color and also to render colloidal the fine suspended matter and iron hydroxide so that, after 30 hours' sedimentation, the turbidity of the treated water is greater than the raw water. The milk of lime, added to the water, is prepared in the coagulant house and is made by weighing quicklime in automatic scales which dump a t set intervals into a circular slaking tank which is provided with revolving rakes. About 4 pounds of water are used for each pound of lime and a temperature of 200" F. is maintained in the slaker. The hot milk of lime overflows from the slaking tank, through boiler tubes in a heater tank, and the water used for slaking circulates around the tubes. In this may the temperature of the water is increased from 20" to 50" F., but it is still necessary to add steam t o the slaking water during a part of the winter to maintain the desired temperature in the slaker. When coagulating a very turbid water with lime and sulfate of iron, it will be found that by the time the turbidity has been reduced to a point where successful filtration is possible there will not be enough floc in suspension to furnish the gelatinous matter necessary for filtration. Aluminum sulfate is used a t St. Louis to give the required floc for filtration and also to aid in the reduction of normal carbonate alkalinity. It has been used since the filter plant was put into operation in 1915, so secondary or double coagulation is nothing new for us. During 1927 the average amount of aluminum sulfate used was 1.4 grains per gallon, and this was sufficient to furnish the necessary floc and also to reduce the normal carbonate alkalinity from 48 p. p. m. to 17 p. p. m., and the total alkalinity from 64 p. p. m. to 51 p. p. m. The bicarbonate alkalinity was increased from 16 p. p. m. to 34 p. p. m. The increase in bicarbonate alkalinity is due to the conversion of normal carbonate to bicarbonate by the carbon dioxide set free from the action of the aluminum sulfate upon the
