API - Manual on Disposal of Refinery Wastes - Volume I 1st 1930 (Contains Only Section I, Waste...

Copyright American Petroleum Institute Provided by IHS under license with API No reproduction or networking permitted without license from IHS





Manual on Dlapoaal of Refinery Waatea

METHODS AND DEVICES FOR HANDLING WASTE WATER AND REMOVING OIL The usual method of preventing the escape of oil from

refinery property is by means of a comprehensive drainage system and one or more main gravity-type oil separators of sufficient capacity to retain the oil and sediment. The main separators may be supplemented by auxiliary separators at points where slowly separating emulsions or large quantities of oil originate. Such an arrangement permits the collection of the oil at the point of origin and prevents its entry into the main drainage system, so that the main separator need be burdened only with easily separated wastes from general sources. At the same time the main separator acts as a safeguard for auxiliary separator effluent.

A comprehensive drainage system usually provides separate sewers for the fairly clean cooling water from condensers, etc., and for the waste water which contains greater quantities of oil. Each sewer is provided with a separator, although the separators on the first system may be called upon to retain very little oil. Surface drainage is passed through a separator before it leaves the refinery property. Surface drainage inlets have chambers for retaining sediment that might otherwise enter the sewers and retard or prevent flow. These sediment chambers or catch basins are cleaned as required. Sew~r systems are provided with manholes and junc

tion boxes to permit ready access for inspection and cleaning. This assures maximum capacity of the system and permits the tracing of an unusual flow of oil by observation at sewer junctions.

The functioning of gravity type separators depends upon the difference in gravity between the various kinds of oil and water. Velocity of liquid through the separator, settling time, and uniformity in direction of flow are important factors for effective operation. This type of separator is in use throughout the petroleum refining industry.

Recently attempts have been made to increase separator effectiveness by greater control of direction of flow, thereby permitting higher velocities, shorter set-

tling times, and smaller units. Direction, or flow-straightening vanes are possible aids in this connection. Greater knowledge along this line will no doubt result in further improvements in design.

Separators are provided with skimming devices and tankage for collecting and storing the oil. These tank.8 may or may not be equipped for dehydrating the oil. Pumps for collection and transfer are essential to the general process and its successful operation.

Gravity separators will not prevent the passage of emulsified oil. Emulsions must be broken before discharge to the drainage system if the escape of oil from the refinery is to be prevented. The most practical methods involve destruction of the emulsifying agent or reduction of the surface tension of the oil or water. Heating aids settling by reducing the viscosity of the oil.

As a general chemical method for oil-in-water emulsions, separation is frequently effected by adding a salt of a heavy metal, after first neutralizing the emulsions. Dilute solutions of aluminum sulfate, calcium chloride, and magnesium chloride have been used with success.

Water-in-oil emulsions, such as tank bottoms, will often break if heated. When heating is not effective, the addition of a dehydrating chemical, such as a strong sodium hydroxide solution or a strong calcium chloride solution, will sometimes help. Other means which have been used for breaking tank bottom emulsions include filtering and the application of an alternating current.

Nearly all cases of refinery emulsions involve some special chemical problem which will require study by the plant chemist. (See Appendix 3-Waste Water Emulsions.)

Waste water disposal systems are usually operated by trained men under the supervision of a capable drainage supervisor. The training and experience of these men is a great factor in the satisfactory use of the various methods and devices, especially during times of emergency operations.




8 Amerlean Petroleum Institute

APPENDIX 1

POLLUTION OF SURFACE WATERS BY OIL I. Introduction

In attempting to determine what constitutes pollution of surface water by oil, it is necessary to consider what uses are made of the water, which may include water supplies (home, factory, irrigation, and stockraising), commercial fishing, water power, transportation, and recreation (boating, bathing, fishing, and hunting). For some uses, consideration must also be given to the form in which the oil is present, whether as a surface film, as an emulsion, or in solution. The character and size of the body of water are also important. Consequently, it is apparent that it is impracticable to establish a minimum concentration of oil above which water is rendered unfit for a. specific use.

The object of this appendix is to discuss available information about the effect of oil on the uses of surface waters, with particular reference to oil film.

II. Uses for Surface Water a. Water Supply

Surface waters are rarely, if ever, used for domestic purposes without a preliminary purification designed to remove objectionable or dangerous organisms and other foreign material. It is probable that oil not in excess of 0.01 per cent will be remo,·ed by the ordinary alum coagulation.*

In certain sections of the country, surface waters are used for irrigation and stock raising. Occasions have arisen when oil was present in sufficient quantity to lower the value of the water for these purposes. Few data. are available on the maximum percentage of oil that is permissible in water to be used for irrigation and stock raising, but it is believed that O.ol per cent of oil will not seriously affect its usefulness.

Waters for industrial use may vary widely in the degree of purity. In some cases the highest degree is required, and in others no objection can be raised to a badly polluted water.

When untreated surface water is used for fire-fighting purposes, it may contain oil as long as the quantity of oil is too low to serve as fuel for the fire which is to be extinguished. Certainly 0.01 per cent oil would not interfere with the usefulness of surface water for this purpose.

b. Commercial Fishing One of the most widespread protests against oil pollu

tion has been that it destroys fish, either directly or through the destruction of the minute organisms which constitute the food supply of fish life.

There has been a wide divergence of opinion on this subject, but the results of the scattered investigations on the subject have been devoid of positive proof that water containing 0.1 per cent of oil (10 times the quantity being considered in this discussion) will destroy fish or their food supply.

One of the most recent investigations has been made by the U. S. Bureau of Fisheries.t This investigation included a study of the effect of 0.1 per cent oil in water on plankton, floating fish eggs, larval fish, and surfaceliving fish.

The principal conclusions drawn from the investigation are stated as follows:

• Waste waters diseharged from refinery properties wlll ordlnarlly not contain as much as 0.01 per cent oil. Further, this etDuent is usually dlluted with many times its volume of natural water before re-use.

t .Appendix 6 of Report to the Secretary of State by the Interdepartmental Committee on the subject: " 011 Pollution of Navigable Waters," March 13, 1926.

"1. Under conditions more nearly approaching those prevailing in nature no inhibitive effect is exerted on cod eggs by a one-tenth per cent dilution of light or heavy bunker oil.

"2. Under conditions of limited circulation or aeration a detrimental effect on cod eggs is exerted in varying degree by the same oils.

"3. A slight but not highly significant injurious effect is exerted by the same oils under the same conditions upon larval flounders.

" 4. The effects upon the larger plankton organisms are in general similar to those exerted upon the cod eggs."

While the conclusions are based upon a limited amount of study and are not proof that 0.1 per cent of oil in water will not adversely a.ffect fish life, it is indicative of the fact that the presence of such relatively large concentrations of oil would not be the cause of wholesale destruction of fish, as has often been stated.

e. Water Power Safar as known, the presence of O.ol per cent of oil in

the water used by power companies has never resulted in a reduction in the value of the water to be used by a hydro-electric power plant.

d. Transportation The only known adverse effects of floating oil on the

use of surfa.ce waters for transportation are damage to hull paint and potential fire hazard to vessels and shore structures.

For vessels in commercial transportation the damage to hull paint from O.ol per cent of oil in water may be considered to be negligible.

Similarly such a small concentration of oil may not ordinarily be considered a serious fire hazard, except when the floating oil from a large expanse of water becomes concentrated in a limited area. as the result of wind or wave action.

Experiments conducted in New York Bay indicate that oil of 175 deg. F., flash point floating on the surface of water at 54 deg. F., cannot be ignited by any ordinary means when the layer of oil does not exceed a. thickness of 0.064 in., which corresponds to approximately 1,115,000 gal. per square mile.

For pleasure vessels, where the attractive appearance of the hull paint may be important, the presence of 0.01 per cent of oil in water may be found objectionable, since this might result in a film 0.01 in. thick on a body of water averaging 8 ft. in depth.

e. Recreation The greatest objection to the presence of floating oil

is made when surface waters are used for recreational purposes.

Quantities of floating oil or oil on beaches used for bathing are obviously disagreeable to bathers and others frequenting the shores of surface waters. This oil may be injurious to bathing suits and clothing and, when carried into houses or other buildings on the clothing or persons of bathers and others, it may damage floors, floor coverings, furnishings, and clothing.

The existence of oil pollution at shore resorts tends to injure the value of property, since non-industrial shore property derives its value primarily from the recreational and resthetic advantages of a clean shore and clean water.




!lfanual on Disposal of Refinery Wastes 11

study upon the part of the technical men of our industry provides additional data.

The problem of preventing pollution by oil in waste water progresses from comparative simplicity in the case of skimming plants or complete refineries operating on unusually high grade crudes, to intricate engineering and chemical processes requiring correspondingly cpmplex equipment and processes for the pre,•ention of pollution.

Several descriptive terms used in the following pages are defined as follows:

Size: The effective volume of the entire separator, i. e., length x width x depth from water level to floor, less space occupied by partitions, etc.

Flow: The volume of liquid passing through the separator per unit of time.

Average velocity: The velocity with which the liquid passes from the inlet to the outlet of the separator. It is equal to the volume of liquid entering the separator per unit of time divided by the cross-sectional area of the separator (width multiplied by depth of liquid).

Settling time: The length of the separator divided by the average velocity.

Pocket: A compartment of the separator in which marked reduction in velocity permits the separation of the oil and water and in which the oil is retained.

Partition: A transverse suspended wall across the separator between pockets, extending downward from above the maximum water level.

Baffle: A transverse wall across the separator extending upward from the bottom.

Partition velocity: The velocity at which the liquid passes beneath a partition separating one pocket from another.

Inlet ben: The compartment at the inlet of the separator in which the proper distribution of flow to the first pocket is brought about.

Outlet box: The compartment at the outlet of the separator which functions to carry away the water at a velocity which will not affect the proper operation of the last pocket.

Effectiveness: The effectiveness of a separator cannot be based upon the percentage of oil in the inlet in relation to the percentage in the outlet, as in cases where a large quantity of oil enters the separator in the inlet mixture, a high separation effectiveness might maintain and yet so much oil pass out in the effiuent as to cause pollution. Therefore, effectiveness must be based upon actual effiuent oil content, viz., the percentage of oil actually present in the effiuent water.

A study of present-day separators has revealed a wide variety of designs as to shape, size, depth, construction details, inlet and outlet boxes, skimming de,·ices, etc. From observation of separator effluents and determinations of oil in them, it can be said that the best presentday practice in design and operation gives an effiuent containing not in excess of 0.003 per cent oil. Such an effiuent will be free of turbidity or milkiness due to the presence of oil, and will show only very slight iridescence in the surface water nearby. Any effiuent that is cloudy or at all turbid should be looked on with suspicion. The turbidity may be due only to silt or muddr water. but it may also be due to an emulsion passing through the separator and carrying sufficient oil to cause pollution upon breaking.

A review of the design of many present-da~· separators discharging water containing oil within the limit of 0.003 per cent shows that the aYerage Yelocity through the separator should not exceed 2 ft. per minute; the partition velocity should not exceed 4 ft. per minute, and the settling time should not be less than 60 minutes. Satisfactory separators exist in which these Yelocities are exceeded and which have shorter settling periods, but they represent definite exceptions and operate under more favorable conditions of temperature, type of crude,

nature of process, etc., than are normally encountered. It is possible to increase the velocity with a longer settling time, as in a long narrow separator, but the permissible variation seems to be so small that the value of any attempt to change the relationships is questionable. In general, any deviation from the limits given results in an appreciable drop in effectiveness.

It can be shown mathematically that the rise of oil to the surface of the water is seriously retarded when the velocity is high. Therefore, the velocity should be low.

The partition velocity in the separator is an important factor, and in many cases an ineffective separator results from too high partition velocities. even when velocity and settling time are normal. High partition velocities cause eddy currents which exert their influence at unexpected distances from the partition wall and cause oil to be carried along without rising to the surface.

VEIDCI'TV---......... /

120

110

100

so

80

/ I

I I I

I L ~

I

zo

10

0 0 100

/' LENG"nl/

/ A.P.I. BECQMMEH~~III!H~

/ FOR SEPARATOR DESIGfi-

I 1930 FOR LAii>ER CAMC.mES NICllfASE WIDlll av ADotnONAL uMin ~lnt OM£ fXTRAFQR GLEANING ETC.

-~ DEPTH·

I 200 300

QJ. FT. PfR MIN.

z 3 4 MIWON GALS. PER Df<V

FLOW CAPACITY

FIG. 1

4Ci0

5

500

6

The function of the settling period is to allow the globules of oil, subjected to the influence of the separator \"elocitr, but undisturbed by eddy currents from high partition velocities, to rise through the water to the surface.

Separator partitions function to retain within a given area the oil which has collected on the surface within that area, thus facilitating the skimming operation. Ther also sen·e to equalize temperature and rate of flow. Further, by dividing the separator into pockets, they will afford a final area into which yery little oil should be carried under normal operation.

Separator baffies have been used to restrict the spread of sediment, but they are not recommended owing to the possibility of creating eddy currents which tend to reduce the effectiveness of a separator.


12 American Petroleum Institute

Separators in use in various sections of the country have an almost endless variety of inlet, outlet, and mud boxes, each having claimed for it some particular feature of value. No evidence either for or against any particular form can be developed from the data at hand. There is probably considerable value in a mud box, or sediment chamber, located ahead of the separator when there is a. considerable quantity of sediment in the discharge from the sewer system. In such a chamber of sufficient size and proper design, the major portion of the sediment will be dropped as a result of the sudden and marked reduction in velocity. This will lengthen the time of operation of the separator between cleaning periods.

The principal functions of the inlet and outlet boxes are to deliver the flow to the first pocket without undue partition velocity, distribute it properly, and take the water away from the last pocket without a reduction in effectiveness. These boxes may also carry gates.

h. A Typieal Separator The first step in designing the main refinery separa

tor is to ascertain the amount of oil and water mixture

I ... .. .., N -:;-!-:ll :2 ::.2 :i 2!1 ~ i ~ J ~I ~

Duplic e of Ot r .Sepa

to be handled, due allowance being made for probable enlargement of the refinery.• Investigation should also be made to determine the amount of sediment in the mixture.

Fig. 1 will serve as a guide to the designer in determining the approximate dimensions of refinery waste water separators to be constructed in accordance with the recommendations of this manual.

The location of partition walls and the size of the openings in these walls are factors that have not been settled. There are no data on successful separators from which to determine the number of pockets to give greatest effectiveness, nor from which to determine whether the pockets should be uniform or vary in size. There are separators giving very good results in which many or few pockets are found. Four to six pockets is the usual number, however. A typical design is shown in Fig. 2.

Low partition velocity in a separator should never be sacrificed, even though the dimensions need be enlarged to permit proper planning. This element of the design is paramount in the elimination of eddy currents. It

• See appendix 3 for details of handllnJr emulsions.

a:i· I

6 Ill :p 6 ~ ~

rlj ;3 .. "tS g ; ~ (() Ql ~

fl)

~~~~ i

Plan

~~-----------rF~F .Side Elevation

.Section on A-A. Design or Typical Main Refinery Separator.

FIG. 2


1\lanual on Disposal of Reftnery Wastes 1:R

is well known that when a liquid fiows from a small opening into a larger space, the effect on the faster moving mass of liquid as it enters the larger space is largely one of impact, with a resultant loss of energy in the form of eddy currents. The infiuence of these currents is transmitted in all directions and for considerable distances, and such a condition may reduce the separating effect of an entire separator pocket by one-half.

On the other hand, the opening in the partition wall should not extend higher from the fioor of the separator than one-half the liquid depth. The reason for this feature is found in the varying temperature of the contents. By having the opening in the partition wall not more than one-half the liquid depth, a reasonably uniform temperature and fairly uniform velocity will result. This will have a further beneficial action in raising all parts of the liquid to the highest temperature possible. It has been found that separators running warm are most effective.

' Another feature of partition wall design is the rounding of the edges to minimize the formation of eddy

B~·

• s~l

Enlarged Section at A-A.

currents. It is important to have a smooth, even fiow, and the elimination of abrupt changes of direction will increase effectiveness. To this end, the openings in the partition walls should be rounded, with a radius to be no~ less than one-half the wall thickness. This feature of the design is shown in Fig. 3.

The above discussion of partition velocity and partition wall design concems the essential features only. It should be explained further that in many cases the partition walls need not be carried to the full . height of the outside wall of the separator. This will allow an economy in construction cost, since the partitiou need extend only about one foot above the maximum working water level. The one ·exception to this is the partition between the last pocket and the one preceding it. As stated before, the outside wall of the separator should be carried up to a point well above the highest anticipated water level of the body of water into which the separator discharges, or any body of water in the vicinity of the separator. Consequently, the partition wall between the last pocket and the one preceding it should

A A 4 4 ' I

Plan of Separator

Section atB::-B. Detail of Partition Wall Rounded Corners to Prevent Eddy Current from Impact.

FIG. 3


14 Amerlean Petroleum Institute

be carried to the same height. With such an arrangement, the separator pockets P.receding this partition form a ground tank in which oil that may come to it in considerable quantity can be caught and held until pumped off. Flow of this nature may originate in pipe line failure, tank rupture or other conditions on the refinery property. With the high outside wall and the one high partition wall, an emergency of this kind can be handled without causing loss of oil, even in time of serious flood water stages in the vicinity of the separator. A ba.flle following the partition wall is not desirable, as the tendency of the baflle is to reduce the effectiveness of the partition velocity by causing .eddy currents.

Another question to be considered is whether the separator should have a. water-tight bottom. H the separator is situated so that its discharge is above the high water line, it should have a. tight bottom. Where the outlet is below water at any or all times, a. bottom is not essential.

All separators should be built in two or more pa.rallel sections to provide for continuity of operations during

Plan of Inlet Box, Gate Box, .Sediment Chamber, and fnlet 5ewerTrap.

II

Section on A-A

periods of necessary cleaning and repairing. During these periods the sections in use should operate with a. reasonable effectiveness.

Separatoi'B built in multiple sections with common division walls will of necess1ty require regulating gates on the inlet. The gate box can very readily be a part of the settling chamber. This settling chamber should be of sufl.icient size to permit the use of a pump or a crane bucket in cleaning. Since, as a rule, velocities in the sewer system are comparatively high, a box that will reduce this velocity to about 10 ft. per minute will result in the dropping out of practically all the coarser sediment. Outlets from the sediment chamber will lead to the separator, one to the inlet box of each section. These outlets should enter the separator inlet box at a point above the opening which communicates between the inlet box and the first pocket.

The inlet chamber should be designed so as to prevent the sudden introduction of water into the fii'Bt pocket at a high velocity, with resultant eddy currents. A simple design is shown in Fig. 4.

• c:s . 0 Q CQ ' • 0 c c:Q

[] s:: (] 0

c 0 5 0 s:: c 0 =fl 0 :::; :::3 't) Q)

~ QJ "' Cl) U)

Detail of Separator Inlet Box, Gate Box, Sediment Chamber, and Inlet Sewer Trap.

Note.-The outlet box, gate box and outlet sewer trap are designed similarly to the inlet box, gate box and inlet sewer trap.

FIG. 4




Manual on Disposal of Refinery Wastes 17

rator for cleaning, gates or valves are necessary. The most effective equipment and the most satisfactory for this purpose is the sluice gate. Briefly, this is a sliding gate on a screw stem, which rises and falls on guides, which also serve as seats when the gate is fully closed. The sliding surfaces of these gates should be of bronze to prevent sticking as a result of corrosion. These gates are fully described in catalogues, and require no further explanation.

Wooden gates are used at times, but are not as permanent nor as satisfactory as the cast iron equipment. They are mostly of a design closely resembling the sluice gate.

Provision for measuring the flow through the separator is very desirable. This may be accomplished by especially designed velocity indicators or by means of weirs. There is insufficient information available to justify a more specific recommendation. The value of this accessory, however, is unquestioned, as the flow throu~th the separator must be known continuously in order that the proper velocities may be maintained.

VIII. Pumping Equipment a. For Normal Operation

A pump of the usual small capacity type, standard at the plant involved, is the best installation for the removal of oil at the main separator. In selecting the pump, consideration should be given to the fact that the fluid entering the suction will at times be a mixture of liquid and air, thus requiring a positive suction pump. As a rule, reciprocating pumps are installed, since they have the best lifting power, and will not easily be put out of service as a result of particles of wood, etc. that may pass the screens with the oil being collected.

Although not essential to separator operation, the pumping equipment should be installed in duplicate, in order that no interruption of separator effectiveness can occur from broken parts or other long-time repair requirements.

b. For Emergency Operation Pumps for handling emergency floods of oil should

be available for every separator. They should be of large capacity and of a type that is dependable for quick and continuous operation without loss of suction. H is, of course, expensive to install a large pump at a separator, and the expense may not seem justified in view of the fact that the pump may be used only infrequently. But there are many cases on record where such an installation has saved oil worth far above its cost; and more important yet, has avoided the excessive pollution of the nearby streams with the accompanying fire hazard.

When a large pump, normally used for other purposes, is located close to the separator and has connections to storage that can quickly be made available, advantage may be taken of the circumstance and a suction connection made to the separator. A definite ruling making this pump, with the necessary lines and storage, readily available, will then give ample protection.

No rule can be laid down as to the size of the pump, but an estimate can be made from the carrying capacity of the separator and sewer inlet, the size of tanks, etc., on the sewer system, the reserve capacity of the separator, and other factors of like nature at the particular refinery.

IX. Equipment for Reeonditioninc Oil The investigation upon which this appendix is based

revealed a great variety of procedures for reconditioning

the oil collected from the separators. The principle involved in practically all cases, however, is to heat the m"ixture to a point where the water and b. s. are separated. The temperature varies from slightly above room temperature for light oils to 180 deg. and 200 deg. F. for heavy oils.

As a rule, each separator should have at least two collection tanks. The capacity of each of these tanks should be sufficient for at least three .days' normal collection. In this way the separator is skimmed into one of the tanks and most of the water drawn off. After two or three days' collecting, the tank will be full of oil that is nearly dry. With heat on the tank the water gradually settles and can be drawn off; meantime the second tank is being filled. Normally, before the second tank is filled, the first batch of oil will contain less than 1 per cent of water and sediment, and will be transferred for disposal and the new cycle may be begun.

Another system of reconditioning is to collect continually into one tank which overflows from the side, near the top, to a second tank. Heat is constantly on the tanks, and a fairly dry oil can be pumped from the top of the second container.

Other devices are being developed as various phases of the problem present themselves at different plants. The principal factor is the extent to which the elimination of water need be carried, as in some plants a treatment with caustic soda solution is employed to obtain a yery dry product.

X. Safety Devices

A separator, being located usually at a remote and unfrequented point, presents a hazard from the standpoint of safety. It should be provided with a good railing on all sides, and the same protection should be placed around sediment basins, gate boxes, and other open basins. Spacious, smooth walkways with railings should be constructed. They will greatly add to the effectiveness of the operators. Although probably collections will not often be made at night, the separator should be well lighted, as an emergency at any hour is possible. There should be telephone communication with all parts of the plant, so that unusual influx of oil due to leaks or other difficulty at some particular point can be reported.

Although not a part of separator design, it is not too far removed from the general subject to say that a force of competent and reliable operators should be provided for operating the separator. They should be impressed with the importance of their duties, both from the standpoint of saving oil and particularly from the standpoint of preventing the pollution in any degree of waters adjacent to the refinery property.

AUXILIARY SEPARATORS

An auxiliary separator may be defined as a separator designed to catch the oil in the waste from a specific operation in the refinery, allowing only the water to go to the main separator. Another use for auxiliary separators is for trapping and holding emulsions at the point where they originate so that they may be pumped off and processed for breaking and recm·ering the oil. It is suggested that the design of auxiliary separators be based upon the recommendations given for main

separators.




20 American Petroleum Institute

e. Elimination of Emnlsifying Agent

Emulsifying agents are difficult to remove due to their colloidal nature. Filtration through stream-line filters or clay, such as diatomaceous earth, may be used to advantage where the amount of emulsion to be handled is small.

d. Elimination of Dispersion Medinm

Sodium hydroxide in solution is generally used as a neutralizing agent, and the sodium soaps formed are emulsifying agents. It is often practical to substitute dry neutralizing agents, such as alkaline minerals or chemicals in solid form, or to neutralize by adsorption with finely divided clays. Not only does the dry treatment decrease the amount of emulsifying colloids that may be present, but it also eliminates water without which the emulsion cannot be formed.

IV. Breaking Emnlaions

a. Physieal Methods

I. Heat

The use of heat promotes settling of free water by decreasing the viscosity of the oil phase. If applied to true water-in-oil emulsions, heat tends to rupture the films around the globules. If the temperature is carried high enough to cause the formation of steam within the water globule, the vapor pressure breaks the film. In practically all dehydrating operations the use of heat is advantageous because it makes emulsions less stable.

2. Distillation

Distillation methods for breaking emulsions are effective in that they involve the use of heat as described above. In addition, the water and light ends of the oil are removed as overhead products and the emulsifying agent remains with the residue.

3. Centrifuge

Comparatively stable mixtures may sometimes be separated by a centrifuge. If the difference in specific gravity of the oil and water is appreciable, centrifugal force accelerates subsidence. However, it is only slightly better than gravity for coalescence. In a few cases only is a centrifuge practicable for breaking emulsions. Free water, of course, is readily sepamted from oil or emulsions by centrifuge.

b. Eleetrieal Methods

Electricity has been used for dehydrating emulsions through an application of the principle of the Cottrell precipitator. This has met with considerable success in the treating of crude oil emulsions from the California and Gulf Coast fields.

The crude oil after pre-heating is passed between two electrodes and is subjected to a high potential alternating current causing electrification of the emulsified globules of water. Oppositely charged globules attract each other, with the result that the oil films are ruptured as the charges are neutralized and the particles unite. The principle of this method of dehydration is that of a multitude of series condensers.

Recently there has been developed a type of electrical dehydrator which utilizes a single electrode from which high-tension alternating charges are impressed on the emulsion. As this type of dehydrator is based upon the action of the space charge formed about a conductor in corona, it is desirable to use very high potentials on the electrode.

e. Chemieal Methods

Chemical methods of breaking emulsions are usually directed at the film containing the protective colloids. The classification of chemicals used for this purpose is best made with reference to their action on this film, as follows: •

1. Compounds with a strong tendency to take up water and form different substances.

2. Compounds that cause flocculation of the substance composing the protective film.

3. Compounds that may react with salts in the water or upon organic acids that may be present.

4. Compounds that tend to break the protective film by their tendency to form opposite types of emulsion.

5. Electrolytes that tend to neutralize the electrical charge on the surface of the emulsified water.

6. Solvents that tend to dissolve the material making up the protective film. . .

The selection of the proper chemicals to be used m the dehydration of an emulsion is a problem influenced by many factors. The chemist in charge of such wor~ should have little trouble in selecting the proper chemical once the types of emul~on an4 emul~ifying col~oids have been determined. Microscopic studies and microphotographs of the emulsion prove very helpful in this work. Hydrogen ion control of the effluent water . is another factor of prime importance, . and the che~1st should determine at what hydrogen IOn concentration the emulsion has the least stability.

V. Eqnipment for Demnlsifieation Three facts are to be considered in connection with

equipment for demulsification. 1. An emulsion is a potential source of pollution. 2. An emulsion is not broken by the gravity separator. 3. A relatively small amount of emulsion mixed with

other refinery waste water may chang~ the nature. of the latter so the gravity separator will not funct1on properly.

Generally two courses are open to the refiner in dealing with emulsions. He must either 4evelop met~ods of refining that will preclude the formation of emuls1ons, or else segregate the emulsions and break them. The components after breaking, may be delivered to the separator, o~, preferably, th_e oil may be retained at the plant where the emulsion IS broke'?-· .

First consideration should be given. to segregation, so. that other plant waste water Will not be affected. Tankage for the storage of emulsions ~ould be provided and in many cases the same tank will serve both for' storage and the breakin~ opera.tion. Sucl! a condition exists when the production of tpe emu~on occurs during a short period o_f the day, leavu~g sufficie~t time for breaking the emulsiOn. and s~para.tmg the _oil and water before product~on beg1ns agai!l- If pr~uction schedules do not synchronize with the time reqw!ed for the breaking process tankage should be set amde for the storage of the ~mulsion, from. which ~atches f!>r breaking may be drawn. As a rule, httle eqmpment will be found necessary.

The breaking of emulsions may well be said to present a problem for the cbemical engineer or chemist of each individual plant, because of the effect that type of crudes and processes have on the nature of the emulsion. No one procedure can be outlined as a method for use in all cases; consequently, only general processes will be described. These processes have been found effective, and will usually produce a waste water free from oil.

a. Crude Emnlsions As generally operated, the incoming wet oil is heated

in conventional pipe stills, and may then be subjected

• D. B. Dow, "Oil Field Emulsions," Bur. Mines Bull. !50.




Manual on DIIJH)IIIll of Rednery Wastes

APPENDIX4 SAMPLING AND TESTING WASTE WATER FOR OIL

I. Introduction

In order to determine the per cent of oil present in the eflluent of a. separator, it is necessary to take sa.mples and subject them to appropriate tests. S~me idea. of the effectiveness of a separator may be obtained from the general appearance of the efHuent and of the water near the point of discharge, but the oil content can only be a.pproximated from such an inspection. In cases where the clarity of the water and the absence of iridescence would lead to the belief that only small traces of oil are present, a quantity may be discharging which would cause pollution within the understanding of this manual. Conversely, a stream carrying suspended silt may appear to contain oil in emulsified form, and yet be entirely free of oily waste.

It is the purpose of this appendix to outline a general procedure for sampling separator effluents and determining their oil conte':lt. It will readily be understC?Od that, owing to the vanety of separator outlet designs and sizes, no single procedure will fit all cases.

II. Sampllnc

Separators frequently discharge through an aperture of cross-section approximating a rectangle. Under such circumstances a sampling procedure may be briefly outlined as follows:

Sampling Deviee for Separator EfBuents.

FIG. 1

Several narrow metal sampling containers, open at the top, with sharp edges, are wel~ed to rods an~ suspended from a horizontal rod at mterv.als of 6 In., ~s shown in Fig. 1. The length of the horizontal rod a IS controlled by the length of the ape.rture throu~ wh~ch the efBuent is discharged. The contamers ha.v~ dime.nsion b equal to the depth of flow of efHuent; dimenSion d equals 2 in., and dimension c is such as to give a capacity of about 1 quart. The top of the container makes an angle of about 60 deg. to the rod. This sampling device

is plunged through the efBuent stream and withdra~ a rate that will fill the containers. By means of suitable trough, the samples are transferred immedia.~ly . to bottles and the entire sample used for the detenmna.tion of oil content. To reduce the volume of the combmed sample, the volumes of the individual containers may be decreased.

Sampling devices of this type can be made to fit the cross-section of any separator outlet stream. By shortening the rods of the end boxes and lengthening those toward the center, a representative sample can be obtained from the flow throu~~:h a semi-circular trough.

When the separator outlet discharges below the surface of the body of \Vater into which it is flowing, top, middle, and bottom samples of the flow may be taken with sample bottles that may be lowered to the proper position and opened for filling.

Where the separator outlet discharges turbulently, the sample may be taken at the point of greatest turbulence.

Other methods may be used to meet special conditions. It should always be borne in mind that a representative sample is required, and that all parts of the stream should be included in making up the final sample for analysis.

III. Testing Two methods in use for determining the oil content

of separator efHuents are as follows:

a. Carbon Disulfide Method . The sample is thoroughly mixed, and approximately

100 cc. is transferred to a separating funnel and sh&:Icen successively with one portion of 50 cc. and tw_:o port1ons of 25 cc. of a mixture of equal parts of chemically_ pure carbon disulfide and ether. I~ is essential that <:heJ?Ically pure solvents be used, as thiophanes .presen~ In I!Dpure carbon disulfide may cause an emulsiOn which wdl not give a clear separation to permit the withdrawal of the solvent from the funnel. The three portion!' of the solvent are transferred through a filter to a weig~ed evaporating dish, washing the filter thoroughly mth unused solvent· the dish is placed on a steam bath, and the ether a~d carbon disulfide slowly evaporated. After the evaporation is completed, the dish is dried at 105 to 110 deg. C. in an ~>Ven for .1 hour, and then cooled and weighed. The d1ffere~ce m weight. of the evaporating dish represents the od and orgaruc matter ~resent in the 100 cc. sample, and the percentage of oil and organic matter is obtain~d by dividin~ by 100.

This percentage may 10clude orgamc matter present in the water used by the refinery, and should be corrected by running a similar determination on a. sample of water taken at the inlet to the plant and subtractmg the percentage so obtained.

b. Benzol Method The sample analyzed should not be less than 1 quart,

and a gallon sample is recommended ~or great~r accuracy. The sample or convenient successive portions of ~e

sample are transferred to a separatory funnel contammg 100 cc. of c. p. benzol.* The mixture is shaken thoroughlY:; and, after allowing to settle, the separated wat~r ~ayer IS drawn into a second separatory funnel containmg 100 cc. of c. p. benzol and again thoroughly shaken. After the entire sample has been extracted by each of the

• Standard 85 to !lO per cent benzol may. also be Ul!etl, pro· viding the residue by evaporation is determined and the necessary correction applied.


Amerie&D Petroleum Institute

portions of benzol, the sample contained is ·' swabbed with a cotton swab using two suc

.-5 r.c. portions of warm c. p. benzol. The cotton , lS pla<.<;!d on a filter paper in a funnel, and the benzol

....ed for wasuing the sample container and the benzol used in the two separatory funnels are filtered through the paper to remove suspended matter and water. The filter paper and swab are washed free from oil with successive portions of warm benzol. The filtrate is evaporated to a small volume (approximately 50 cc.) upon a steam bath and again filtered to remove solid matter a.nd water that may have separated as a result of the evaporation, and the filter paper washed free from oil with a minimum amount of warm benzol. The filtrate is caught in a small tared evaporating dish a.nd evapo-

rated to drynei!S on a steam bath. The dish is then dried in an oven at 105 deg. C. for 1 hour, cooled, and weighed.

The volume of the sample of e1lluent used is determined by measuring the water after the second extraction. From the volume of sample analyzed and the weight of oil and organic matter found, the percentage is calculated. Chemically pure benzol contains a negligible residue upon evaporation, but it is desirable to run a blank determination to guard against impurities. A sample of the water used in the refinery is tested by the same method to determine the percentage of orga.nic matter that is present.

The difference in the percentages found in the two samples is taken as the percentage of oil in the separator efHuent.

Date post:	14-Dec-2015
Category:	Documents
Upload:	kristin-white
View:	11 times
Download:	1 times

API - Manual on Disposal of Refinery Wastes - Volume I 1st 1930 (Contains Only Section I, Waste...

Documents