INDUSTRIAL AND ENGINEERING CHEMISTRY
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It must again be emphasized that this is an instantaneous coefficient. If the oil changes greatly in temperature flowing through a pipe, it is not permissible to take its average temperature and from it calculate an average coefficient. In designing a piece of apparatus in which a liquid changes enough in temperature to have a great effect on its viscosity, it is suggested that the pipe be broken up into sections in which the viscosity does not change more than, say, threefold. An alternate and more precise method would be to integrate graphically an equation obtained from a heat balance on a differential length of pipe. Conclusion
Heat-transfer coefficients for oils and water flowing in turbulent motion in horizontal pipes have been determined. The results are correlated by means of the Kusselt type of equation. hD
DV
Figure 3 shows #(cz/k) plotted against ( c z l k ) and is to be used for both heating and cooling. Figure 4 shows @(DV/z)vs. (DV/z) for heating runs.
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Figure 5 shows @(DV/z) vs. (DV/z) for cooling runs. The line drawn gives values of (b(DV/z),which are 75 per cent of those given by the heating line of Figure 4. All properties of the liquid are to be taken a t the temperature of the main body of the liquid. Nomenclature
D = diameter of pipe in inches = film coefficient of heat transfer in B. t. u. per hour per square foot per degree Fahrenheit k = thermal conductivity in B. t. u. per hour per square foot per degree Fahrenheit per foot of thickness Q/e = total heat transferred in B. t. u. per hour P = density of liquid in pounds per cubic foot u = average velocity in feet per second v = up = mass velocity in pounds per square foot per second z = viscosity in centipoises A = area of internal heat-transfer surface of pipe in square h
feet c At
= =
specific heat difference between temperature of body of liquid and that of internal surface of pipe
M = hDlk N = DUp/z = D V / z
P = czlk 4 and ii. = functions to be determined by experiment
TRADE WASTES AND OXYGEN DEMAND Symposium presented before t h e Division of Water, Sewage, a n d Sanitation a t t h e 74th Meeting of t h e American Chemical Society, Detroit, hlich., September 5 t o 10, 1927
Chemical Treatment of Trade Waste IV-Wastes from Organic Ester Synthesis Foster D. Snell and Cornelia T. Snell PRATT INSTITUTE, BROOKLYN, X. Y .
The waste to be treated consists of a calcium sulfate sludge produced in the manufacture of organic esters. This sludge is highly contaminated and strongly acid, varying in acidity with time of discharge. Neutralization with lime followed by vacuum filtration offers the best method of treatment. The use of 240 pounds of lime per thousand gallons of effluent is required. The lime is to be fed as a 20 per cent slurry at a rate to correspond to the flow and the variable acidity of the effluent, necessitating a flexible control of the feeding system.
H E plant whose waste problems are under discussion is located in the Passaic Valley in New Jersey and has in the past used the Passaic River as a natural sewer for'its trade waste. This practice is now prohibited by law. A trunk sewer has been constructed into which the plant may deliver all sanitary waste and 10 per cent by volume of its trade waste.' The remaining liquid discharges may go to the river, but only in a purified condition such as not to be injurious to fish and plant life. The part of the plant under discussion is so located as to be unable to take advantage of the 10 per cent trade-waste allotment.
T
Nature of Wastes
Two trade-waste sewers were already in use in this part of the plant, the first concrete and the second an open earthen ditch. At the time of this investigation the former carried a stream of condenser water and the discharge from one set of stills in which organic esters were synthesized. It
led to a large receiving basin which remained from a previous method of treatment that had proved impractical. The earthen drain carried the discharge from a second set of ester stills, that from a drowning tank, and wash water from the nitrating department. It led directly to the river. The sanitary waste was handled by a separate system and does not enter into this problem. The flow of condenser water in the first sewer was fairly constant, about 1.5 cubic feet of practically pure water per minute. The discharge from the stills to this sewer takes place for about 45 minutes during the day, during which a maximum flow of over 11 cubic feet per minute is reached. The stills are then washed with water. The total volume of still discharge and washings was calculated from measurements of flow to be about 4500 gallons per day. While the waste is being drawn off from the stills the sludge is very highly acid with sulfuric and acetic acids, attaining a maximum normality of approximately 2.4. The washings are also acid t o a lesser degree. This waste is highly contaminated, is a dark brown, and carries a large amount of solid calcium sulfate. Tarry discharges from ethyl acetate stills occur about once a day. The sediment fails to settle to under 30 per cent on standing overnight. Total solids determined on the effluent neutralized with lime were found to be as great as 300,000 p. p. m. during the period of still discharge, but a t other times were relatively very low. In the determination of solids the samples were neutralized with measured volumes of approximately 0.8 ?j potassium hydroxide and evaporated to dryness a t 110" C.
March, 1928
INDUSTRIAL AND ENGINEERING CHEXISTRY
A correction was applied in each case to give the corresponding amount of solid if lime were used for neutralization. The loss on ignition was roughly 10 per cent of the total solids, largely from water of hydration of the calcium sulfate, except a t the time of tar discharge. At that time a very high content of organic matter was indicated. The curves (not reproduced here) representing the variability with time of the three factors-acidity, total solids, and loss on ignition-correspond closely in form except a t the time of tar discharge. The rate of flow in the second sewer fluctuates greatly, the data showing a range from less than 2 to about 25 cubic feet per minute, and a variation from 8.5 to 18.3 cubic feet per minute within 5 minutes. About 7000 gallons were estimated as coming from the stills during 1 hour. During this time the acidity of the sludge increases from about 0.2 to 1.7 N and then diminishes. The amounts of total solids parallel closely the change in acidity during the period of stiU discharge, reaching a maximum of about 190,000 p. p. m., but decreasing continuously after the end of the discharge. The change in loss on ignition corresponds very closely to that of total solids. A wash water from the cleaning of drums is discharged a t intervals. As it is little contaminated and small in volume, it requires no treatment. A 300-gallon calcium chloride tank is emptied twice a week, giving an acid discharge which should be treated. Segregation of Discharges
The various wastes may be divided into two classes, those which require treatment and those which are not objectionable. All those in the first class are to be diverted to the concrete sewer leading to the storage basin; all those in the second, to the earthen sewer leading directly to the river. The wastes which belong in the first class include the discharges and wash water from the two sets of stills and the calcium chloride tank. I n the second class are the condenser water originally sent through the concrete sewer, and wash water from the nitrating plant which is neutralized with soda ash in that department,. Neutralization
The mixed waste for treatment amounts to about 11,500 gallons a day. This waste is first to be neutralized with lime, requiring about 2800 pounds per day. This estimate is based on the known charges t o the stills and on the known acidity of samples of the waste as determined by titrations with allowance for some excess as lime. The lime is best fed as a 20 per cent slurry introduced a t a convenient point into the open concrete sewer. Since it must be supplied within a period of about 2 hours, a storage tank having a capacity for 2000 gallons of slurry with means of keeping the lime in suspension is required. The method for feeding the lime must be very elastic to allow for rapid change in the rate of flow of' the waste and its change in acidity. Equipment for determination of the hydrogen-ion concentration of the waste which would offer a means of automatic control of neutralization has been recommended. Manual control is both clumsy and expensive. The equipment recommended consists of a tungsten electrode with suitable recorder and operation by a solenoid, as a motor-controlled valve is not suitable with lime. It is planned t o put the plant in operation with manual control and to install this automatic control later. Treatment after Neutralization
Preeigitation tests with lime and copperas on the neutralized effluent failed to diminish the color of the liquid, even with excessive amounts of the chemicals. Carbon
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used either before or after filtration shon-ed good results in removal of color from the effluent. Vacuum filtration was tried and gave a quick separation of a somewhat granular sludge cake. The best hydrogen-ion concentration for filtration is near the phenolphthalein end point, although the degree of alkalinity is not critical. Practical filtration tests were made with an Oliver filter. The cake-forming solids were 28 per cent, the forming period 20 seconds, the drying period 30 seconds, and the filter cycle 65 seconds. A 3/s-inch cake was formed and discharged with a moisture of 31 per cent. The vacuum maintained on both the form and the dry was 17 inches. As a result of these tests a 12 by 3-fOOt Oliver continuous filter, drum type, was recommended. This is not of non-corrosive construction as the effluent is alkaline before reaching it. It provides about 15 per cent excess capacity based on operation for an 8-hour day. As mentioned before, the concrete drain leads to a large tank. This tank is t o be utilized for storage of the neutralized effluent, which will be kept in suspension by air agitation from pipes in the bottom of the tank. An overflow to the river is provided in case of emergency. From the tank the waste will be pumped to the vacuum filter. The filtrate is not suitable to go directly to the river, although the worst features, the high acidity and large amount of suspended matter, have been removed. The filtrate will flow into the earthen drain, be diluted there with about two parts of condenser water, and subsequently run into the river. Tests on the diluted filtrate showed a total color reading in a Lovibond tintometer of 15 units per 50.8-mm. layer. The oxygen consumed, taken as a rough measure of tendency to putrefaction was 6000 p. p. m. Further dilution in the river will quickly reduce these values. The filter cake will discharge from the filter into an automatic conveyor which carries it to storage or to a waiting truck. The weight of moist solids to be disposed of is about 28,000 pounds per day. Cost of Treatment
The estimated cost of treatment is based on the use of 2800 pounds of lime per day. At the current market price for lime (June, 1927) this amounts t o about 929.50 per day. At a cost of about $500 equipment for automatic control of the process of neutralization can be installed to replace manual operation. This must wait for some further stages in the development of mechanical features of the feeding device. Discussion
The nature of the effluent to be emptied into the river from the filter is objectionable from the standpoint of color and contamination. Such procedure is recommended however, for the following reasons: 1-The volume of diluted discharge is relatively small, about 36,000 gallons daily. 2-The color and contamination cannot be removed by the usual coagulating agents, copperas and lime or alum and lime. 3-Purification by activated carbon or other means is so expensive as to amount to an unreasonable burden, requiring an entirely separate installation. 4-Treatment as recommended removes the most serious objections, the high acidity and large amount of suspended solids, and constitutes all that can be done a t a reasonable cost.
Acknowledgment
The results given in this paper were obtained in cooperation with Gerald TV. Knight, consulting sanitary engineer of Passaic, K. J. Publication is by permission of Maas and Waldstein, Inc.
