US EPA 2007-10-22 Guide Petroleum Guidelines 05

8/2/2019 US EPA 2007-10-22 Guide Petroleum Guidelines 05

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~; SE CT IO N VII ; C O N T R O L ~ A N D T R E A T M E N T T E g H N O L O G Y

P e t r ol e u m r e f i n e ry w a st e w a te r s v a r y i n q u a n t i t y / a n d q u a l i t y f r om refinery to refinery. H0wever, the wastes are readi ly treatable. The results of th e industry survey indicate, as would be expected, that techni ques for in-process control are general across the industry and the specificl applica tion of these techniques at individual plants determines their success. Local factors such as climate, discharge cr it er ia , avail abili ty of land, or other conside rations may dictate the use of differe nt waste water treatment processes to reach an acceptab le effluent. The survey has shown that although the end-of-pipe wa st e water treatment technologies used throughout the petroleum refi ning industry have a marked ' similari ty in operational steps, a c o n s i de r a b l e v a r i a t io n in t r e a t m e n t r e s u l t s e x i s t . T he p r o ce s s es used for treating refinery waste water, however, are similar in purpose: namely--maximizing oi l recovery and minimizing the d i s ch a r ge of o t h e r p o l l u t a n t s . Th e w a s t e w at e r t r e a t me n t technology described below is generally applic able~ across all industry suhcategories. In-Plant Control/Treatment Techniques In-p lant prac tice s are the sole -determinant of the amoun t of waste water to be treated. There are two types of in-plant practices tha tr ed uc e flow to th e treatment plant. First, reuse practices involv ing the use of wate r'fro m one process in another process. Examples of this are: ' using str ipp er bottoms for makeup to crude de sal te rs ; using h!owdown from hi gh pressure boilers as feed to low press ure " boilers; an d using tre ated effluent as makeup wa te r whereever poss ibl e, second, recycle systems that use wa te r mo re that on ce for the s a m e purpose. Examples of recycle systems ar e: the use of steam condens ate as boiler feedwater; and coo lin gt 0we rs. Th e reduction or elimin ation of aw as te stream allows thee end-of-pi pe processes to be smaller, provide better treatment, and be less exp ensive. Since no tre atm ent process can achiev e 100 percent pollutant removal from the individua l stream, reduction in flow;allows for a smaller pollutant discharge. ~ Housekeeping In addition to reuse /recyc le of water streamS and reduction in flows by other in-plant techniques, an oth er effective in-plant control is good housekeeping. Examples of good house keepi ng pract ices are: mini mizi ng waste . when sa mp li ng ~ produ ct lines; using vacuum trucks or dry cleaning method s to clean up any oil spills: using a good maintena nce pr ogr am to;keep the ref ine ry as leakproof as possible: an d individually treating waste streams with special characteri stics, su ch as spent cleaning Solutfons.


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The use of dry cleaning, with out chemicals , aids in reduc ing water discharges to the sewer. Using vacuum trucks to clean up spills and charging of this recovered mate rial to slop oil tanks, reduces the discharge of both oil and water to the waste water system. The oil can also be recov ered for reproc essing . Proces s units should be curbed to prevent the conta minat ion of clean areas with oily storm r~o ff and to prevent spills from spreading widely. Prompt cleanup of spills will also aid in red ucing discharges to the sewer systems. Additionally, sewers should be flushed regula rly to prevent the buildup of material in the sewer, eliminatin g sudden surges of poll utants during heavy rains. Collecti on vessels should also be provided whenever mainten ance is performed on liquid processing units, to prevent accidental discharge s to the sewers. Operations during turna round present special problems. Wastes generated by cleaning tanks and equipment should be collected, rather than draining directl y to the sewer. The wastes from these holding tanks should be gradually bled to the sewer, after first pretreat ing as necess ary to eliminat e deleteri ous effects on the waste water treatment system. An alternat ive method of disposal is through the use of contract carriers. While these are not all the ex amples of good h ouseke eping practices which can be cited for refinery operations, it is evident that housekee ping practices within a refine ry can have substantial impact on the loads discharge to the waste treatment facilities. The applica tion of good housek eeping practices to reduce waste loads requires judicious planning, organizatio n and operational philosophy. Process Technology Many of the newer petr oleum refini ng processes are being designed or modif ied with reduction of water use and subseque nt minimiza tion of conta minat ion as design criteria: althoug h no major innovation s in basic refining technol ogy are anticipated. Improvemen ts which can be expec ted to be implement ed in existing refineries are: primarily dedi cated to better control of refinery processes and other operations: elimi natio n of margin al processing operations, and specific substituti on of processes and/or cooling techniques to reduce discharge loads to waste treatment facilities. Examples of the possible changes which may be implemented include:

. Substi tution of improved catalysts which have higher activi ty and longer life, conseq uently requiring less regene ration and resulting in lower waste water loads.

. Replac ement of barometr ic condensers with surface condens ers or air fan coolers, reducing a major oil- water emulsion source. As an alternative, several refineries are using oily water cooling tower systems, with the barometri c condensers, equipped with oil separation/emulsion breaking auxiliary equipment.

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Substi tution of air fan coolers to relieve water cooling duties simultaneously reduces blowdown discharges. ~Installation of hydrocracking and hydr otr eat ing processes will~allow generatioh Of lower waste loadings than th eu ni ts they replace. The rapid pa ce at which such units are being in st al le d is exerting an dw il l continu e to exert a strong influence on the reduction ~of wa st e loadings, particularly sulfides and sp en t caustics.

5. Inst alla tion of automatic monitoring instrumentation, Such as TOC monitors, will allow early detec tion of process upsets which result in excessive di sc ha rg es t o sewers. 6. Increasedfinishingacids, wadisposal.

useproterof improvedcedures willwashes, and

drying,minimizefilters w e e t e n i n g ; a n dspentcaustics:andsolids requiring

Cooling Towerscooling towers elimin ate large volumes of once throu gh cooling Water by passing heated water through heat ex ch an ge equ&pment. By recycli ng the cooling water many times, the amount of water used is greatl y reduced. The number of times cooling water Can be reused is determined : by the total dissolved so li ds (T DS } conten t of the water, and the effects high dissol ved solids have on process equipment. When the TDS become s too high, scaling occurs and heat transfe r effici ency decreases. The TDS level in the circ ulati ng water is contr olled by discha rging a portion of the steam (blowdown) from the system. The high er the all owa ble TDS level, the greater number of cycles of conce ntrat ion and the less make-up water is required (87). In st al la ti on of ~: co o! in g tower s wi ll reduce the amount of water used within the refinery by at least 90 perc ent (87). Th er e are three typ es of Cooling to we rs (I06)~ wet or evap orat ive, dry, and com bin ed "wet-dry.,, EvaporativeCooling Systems -Evaporative cooling systems transport heat by tr an sf er of the latent heat of vaporization. This results in a tempe rature decrease of circula ting water and a temper ature and humid ity increase of cooling air. Spray ponds are an evapor ative cooling system using natural air currents and fo rc ed water movement. Because of their inefficiency, spray ponds are used less in indu str y than cooling towers. Cooling towers have a higher effic iency because they provide more intimat e contact between the ai~ and water~ As the water falls over the packing, it exposes a large contact surface area. As the water heats up the air, the ai r can absorb more

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water. The more water evaporated, the more heat is trans ferre d (106). Because an evap orati ve cooling tower is depe ndent on ambient tempe ratu res and humidity, its perfor mance is varia ble through out the year. There are three types of evap orat ive cooling towers: mecha nical draft towers: atmos pheri c towers, which use wind or natural air currents: and natural draft towers, which use tall stacks to move air by stack effect. Mostrefineri es use mech anica l draft towers, which have baffles,called drift eliminators, to separate entra ined water from theair stream, thus reducing the amount of water carried into theair. The evapo rative system is the least costly of all coolin gtowers.Dry Cooling S ystems There are two types of dry air cooling systems. Either system can be used with either mecha nical or natural draft cooling towers. Most refine ries use mecha nical draft towers on indirect conden sing systems. The tubes used in dry coolin g equipme nt have circu mfere ntial fins to increas e the heat transf er area. Most tube designs have an outside to inside surface area ratio of 20:1. (106) The adv anta ge of the dry air syste m is that it requires no makeup water and there is no water entrainment. Dry air cooling systems are being incr easin gly used to reduce the amount of water disc harge d to the waste water treatm ent plant. A disa dvant age of the dry cooling process is that it has low rates of heat trans fer requi ring large amounts of land and uses more power than other cooling systems. The dry cooling tower is also more expensive to install than evaporative systems. Wet-Dry Systems The wet-dry systems use an evaporative and non-evap orative cooling tower in either series or parallel, each of which can be operate d with a mech anica l or natural draft tower. The series design has the evaporative cooling process preceeding the dry

pro ces s with respect to the air flow. This lowers the tempe ratu re of the air enter ing the dry process which would mean a smaller unit could be used. The problem with this metho d is that solids are depos ited in the dry tower due to drift from the wet section. The parallel process uses a dry coolin g tower upstr eam of the wet section, each of which has its own air supply. The two air streams are mixed and discharged, reduc ing the vapor plume. Recycle/Reuse Practices Recycle/re use can be accomplished either by return of the waste wate r to its orig inal use, or by using it to sati sfy a lower quality demand. The recycle/reu se practices within the refining industr y are extre mely varied and only a few examples are described briefly below:

. Reduction of once-th rough cooling water results in tremendously decreased total effluents.

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the waste enter s the sewer. The sour wate r can be trea ted by: stripping with steam or flue gas; air oxidati on to co nvert h y d r o g e n s u l f id e t o t h i o s u l f a t e s : o r v a p o r i z a t i o n a n d incineration. Sour water strippers are designe d primaril y for the removal of sulfides and can be expected to achieve 85-99 percent removal. If acid is not requi red -to enha nce sulfi de strip ping, ammo nia will also be stripped with the perce ntage varyin g wide ly with stripping tempe ratur e and pH. If acid is added to the waste water, esse ntial ly none of the ammonia will be removed. Thus, ammonia removals in sour w ater strippers vary from 0 to 99 percent. Dependi ng upon such conditi ons as waste water pH, temperature, and conta minan t partial pressure: phenols and cyanides can also be strip ped with remo val as high is 30 percent. The bottoms from the stripper usually go to the desalter where most of the phenols are extrac ted and the waste wate r can be sent to the regular process water treating plant. COD and BOD are reduced because of the stripping out of phenol and oxidi zable sulfur compounds. The heated sour wate r is stri pped with steam or flue gas in a single stage packed or plate- type column. Two-st age units are also being installed to enhance the separate recove ry of sulfide streams and ammonia streams. Hydrogen sulfide releas ed from the waste water can be recove red as sulfuric acid or sulfur, or may be burned in a furnace. The bott oms have a low enou gh sulf ide c o n c e n t r a t i o n t o p e r m i t d i s c h a r g e i n to t h e g e n e r a l w a s t e w a t e r system for biolog ical treatment. If the waste contains ammonia, it is neut rali zed with acid before steam stripping. The waste liquid passes down the strippi ng column while the strippi ng gas passes upward. Most refiners now incin erate th sour water stripper acid gases without refluxin g the stripper. This c o n v e r t s t h e a m m o n i a t o n i t r o g e n w i t h p o s s i b l y t r a c e s o f n i t r o g e n oxides. Due to the high conc entr atio ns of sulfur dioxide produced more complex pro cessi ng will probab ly be requi red in the future. Several stripping processes are available. These include: Chevron WWT: ammonium sulfate production: a dual burner Claus sulfur plant; and the Howe- Baker ammon ex process. Deep well injecti on and oxidation to the thio sulfa te are also being used, but in the futu re pr obab ly won 't do a good eno ugh job. The Chevron WWT process (37) is basic ally two stage stripp ing with ammonia pruificati on, so that the hydrog en sulfide and ammonia are separated. The hyd rogen sulfide w ould go to a conv enti onal Claus sulfur plant and the ammonia can be used as fertilizer. Ammo nium sulfate can be produ ced by treati ng with sulfuric acid but a very dilute solution is produced and conc entr ating it for sale as fertilizer is expensive. Again the hydro gen sulfide goes to a conve ntion al Claus sulfur plant.

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A dual burner Claus sulfur process is general ly the answer in new plants, but adding the second burner to an existing sulfur plant is difficult. The second b urner is required to han dle the ammonia. A refluxed stripper is required to reduce the water vapor in the hydroge n sulf ide -amm onia mixture and the line be tw ee n the stripper and the Claus Unit must be kept at about 150OF tO prevent preci pitat ion of ammonium sulfide complexes. Howe-Bak er Enginee rs Inc. of Tyler, Texas have developed to the pilot plant stage a process they call "Amm0nex". It is a solven t

..- extracti on process that basical ly is intended to Complete withthe Chevr on WWT process. No commercial uni ts have been built.Anot'her way of treating sour water is to oxi di ze by aeration. Co mp re ss ed air i~ injected into the waste followed by suffici ent steam to raise the reaction temperature to at ~ least 190OF. Reaction pressure of 50-IC0 psig is required. Oxidat ion proceeds rapidly and converts prac tically all the sulfides to thiosul fates and about 10 percent of the th iosulfates to sulfates. Air oxidation, however, is much less effective than stripping in regard to reduct ion of the oxygen demand of sour waters, since the remaini ng thiosulf ates can later be oxidized to sulfates by aquatic microorganisms.

The stripping of sour water is normally carried out to remove sulfides and hence, the effluent may contain 50-100 ppm of ammonia, or even considerab ly high er, depending on the influ ent, ~ ammonia concentratio n. Values of ammonia have been reported as | low as I ppm, but generall y the effluent ~ ammonia conce ntrat ion is l held to approxima tely 50 ppm to provide nutrient n itrogen for th e~ refinery biological waste tr ea tm ent sy st em (2,14,33,58). Spent Caustic Treatment Caustic solutions are widely used in refining. Typical uses are to neutralize and extract:

a. Acidic materia ls that may occur natu rally in crude oil. b. Acidic re action products that may be produced by various

chemical treating processes. c. Acidic materials formed during thermal and catalytic crackin g such as hydrogen sulfide, phenolics, and organic acids. , /

J Spent caustic solutions may therefore contain sulfides, mercapti des sulfates, sulfonates, phenolates, naphthenates, and other similar organic and inorganic compounds. At least four companies process these spent caustics to market the phenolics and the sodium hyposulfide. However, the market is limited a nd mbst of the spent caustics are very dilue so the cost of shipping the water makes this operation uneconomical.

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Scme refiners neutr alize the caustic with spent sulfuric from other r efini ng process es, and charge it to the sour wate r stripper. This removes the hydrogen sulfide. The bottoms from the sour water stripper go to the desalter where the phenolics are extra cted by the crude oil. spent caustics usually originate as batch dumps, and the batches may be combi ned and equalized before being treated a nd/or discharg ed to the general refiner y waste waters. Spent caustic solutions can also be treated by neut rali zati on with flue gas. In the tre atm ent of spent caustic ~ solut ions by flue gas, hydroxides are converte d to carbonates. Sulfides, mercaptides, phenol ates, and other basic salts are conv erted by the flue gas stripping. Phenol s can be remov ed and used as a fuel or can be sold. Hydrogen sulfide and mercaptans are usually stripped and burned in a heater. Some sulfur is recover ed from stripper gases. The treated solution will contain mixtures of carbonates, sulfat es, sulfites, thiosu lfates and some phenolic compounds. Reactio n time of 16-24 hours is required for the neut raliz ation of caustic solution with flue gas. The oxidatio n phase of spent caustic treatmen t is aimed at the sulfide content of these wastes and achiev es 85-99 percent sulfid e removal. In this process, sulfides are oxid ized primari ly to thios ulfat es althoug h in some varia tions there is partial oxidation of the sulfur compounds to sulfate. Oxida tion processes are not applied to phenolic caustics, as phenols inhibit oxidation. It should be noted that those processes which oxidize the sulfide only to thiosulfate, satisfy half of the oxygen demand of the sulfur, as thios ulfat e can be oxidized biolo gical ly to sulfate. Neutr aliza tion of spent caustics is applied to both phen olic and sulfidic caustic streams: the sulfidic caustics are also steam stripped, after neutra lizati on, to remove the sulfides. When phenolic spent caustics are neutralized, crude acid oils or "crude carbolates" are sprung and thus remo ved from the waste water. The major part of the pheno ls will appear in the oil fraction, but a sig nifi can t part may remain in the waste wate r as phenola tes. Fluid bed inc ine rati on is also now being used. This proce ss was developed under an EPA demon strat ion grant (26) and at least two large units are under construction. Once the incine rator is started up, the sludge should provide the necessary heating value to keep the system operating. Oxidi zing fuels may be required when the sludge is burnt, as ash remains in the bed of the incin erator . A cons tant bed level is maint ained , so the sand bed origin ally in the incine rator is graduall y replaced by the inert sludge ash (5). The gasses pass throug h a scrubber, so the fines and par tic ula te matte r can be recovered. The ash and fines can be landfilled. This land fill is clean er than a sludge landfill, because there are no organic materials present to contami nate groun d water or run-off.

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/

In the past ocean dumping, deep well injection, evapor ative lagoons, and simple dilut ion have all been used. These meth ods will no longer be acceptable. Sewer System Segregation .. ... Waste water quanti ty is one of the major factors that affect the cost of waste treatment facilities most directly, water usage in the petrole um refining industry varies from less than 5 gallons of water per barrel of crude charge in the newer refineries to higher than 1000 gallons of wate r per barre l of crude charge in the older refi ner ies . In order to provide efficient treat ment to the wastes originatin g within a refinery, it is very importan t th at segregation of concent rated waste streams be considered. Segregation Of waste streams frequently simp lif ie swa st e treating problems as we ll as reduces treatment fac ili ty costs. Thus, treatment of highly pollued waste streams at the source can prevent gros s pollution of large volumes of relat{v ely clean waste water. Such treatment is Often a more economic al solution of arproble m than would be possible if wastes are dischar ged directly to the ref ine rys ewe rs. Treatment at the source is also helpful in recover ing by-product s from the wastes Which otherw ise could not be econ omic ally reco vere d when .the wastes are combined. In areas where wat er su pp ly is limited, reduced water requirements have. been incorporated into the de si gn and operation, thereby reducin g total Water usage. To minimize the size of the waste water treatm ent proces ses it is imp era tiv e polluted water only be tre at ed. This can be guaranteed by segrega ting the va ri ou s sewer systems. There should be a sewer carrying process and blo wd0 wn waters that are treated continuously. A polluted storm water sewer shou ld go to a storage area from which it can be grad ually dis char ged to the treatm ent facilities. A Sewer system containing cl ea n storm water can be di sc ha rg ed directly to the receivi ng water. The sanitary system should be treated separately from the process water~ because of the bacteria Present in this stream. Once through cooling water should be kept ~ep ar ate because of the large volumes of water involved and the low waste loadings encountered. A connection to the treatment plant should be provi ded in case of oil leaks int o the system. Storm Water R~off An addition al source of pollution from a petroleum .refinery area is caused by rain fall runoff. Size and age of refi nery site, housekeeping, dr ai na ge areas, and frequency and intensity of rainfall are several of the factors which compo und the assignment of allowable pollutional values.

t There are several measures that refiners can provide to minimize storm wa te r loads to their treatment system after diverting all extraneous drainage around the re fi ne ry area. The major consi derati on is a separate storm w~ter sewer and holding system.

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By providing separate collection facilities for storm water runoff, protection is afforde d the operati on of the separator and ancillary treatment systems by contr ollin g the hydraulic load to be treated. Comingling of inorganic particles with oily waste water often times produces an emulsion which is difficult to break in the oil-water separator. Design of this facility should be based on the maximum ten-year, twenty -four -hour rainfall runoff of the refinery drainage area. Diversion of the collected storm water runoff to the oil-wat er separator facilities can be provided when hydraul ic flows return to normal operations. In the event of excessi ve collect ion due to a high intensity storm, di version facilities should be provided to allow for emerge ncy bypass capab ility to divert the trailing edge of the runoff hydrog raph (the leading edge normally contain ed the mass of pollutants in urban runoff investigatio ns). An oil retention baffle and an API type overf low weir should be provided to prevent the dischar ge of free and floating oil. An alternate to the separate sewer system would be the provisi on of a storm surge pond that would receive the polluted wa ters when the flow to the oil-water separator exceeded 15 percent of the normal hydraulic flow. During normal periods, the collect ed storm wate r-ref iner y water could then be diverte d to the oil- water separator (provided process flow did not equal or exceed the units hydraulic capacity). The major cause of pollutio n by storm water runoff is the lack of house keepi ng within the refine ry confine. Proper procedures should be encourag ed to prevent the accum ulati on of materials which contribu te to pollution due to rainfall runoff. Some of the more common prev enti ve meas ures are: (I) Prov ide curb ing aroun d process unit pads; (2) Prev ent prod uct sample drain age to sewers: (3) Repai r pumps and pipes to prev ent oily losses to the surf ace areas; (4) Con tai n spi lle d oil from tur nar oun ds: (5) Dike crude and product tank areas and valve pr ecipit ation to the storm water sewer. In the event the collect ed water needs to be releas ed from the storm water detention ~n d due to overflow, samples of the water shou ld be mo nit or ed for: (1) Oil and Greas e, (2) Org an ic an aly sis such as TOC. Ballast Water Separation Ballast water norma lly is not discha rged direct ly to the refinery sewer system because the intermit tent high-v olume discharges. The potenti ally high oil concentratio ns, would upset the refiner y waste water treatm ent facilities. Ballast waters may also be treated separately, with heating, settling, and at times filtration as the major steps. The settling tank can also be provided with a steam coil for heating the tank contents to help break emulsi ons, and an air coil to prov ide agitation. The recovered oil, which may be considerable, is genera lly sent to the slop oil system.

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provided with influent and effluent flow distribu*io n and stilling devices and with oil skimming and sludge collecti on equipment. It is essential that the velocity d istribut ion of the approach flow be as uniform as possible before reac hing the inlet distribution baffle. Another type of separator finding increasing employmen t in refineries is the parallel plate separator. The separator chamb er is subdi vided by parall el plates set at a q5 angle, less than 6 inches apart. This increases the collecti on area while decr easi ng the overal l size of the unit. As the water flows through the separator the oil droplets coalesce on the underside of the plates and trav el upwards whe re the oil is collected. The parallel plate separator can be used as the primary gravity separator, or foll owin g an API separator. Further Removal of Oil and Solids If the effluent from the gravity separators is not of sufficien t quality to insure effective treatment before entering the biological or physica l-chemi cal treatmen t system, it must undergo anoth er process to remove oils and solids. Most refin erie s use either clarifiers, dissolved air flotation units or filters to reduce the oil and solids concentration. Each of these processeshas also been used to treat the efflue nt from a bio logi calsystem.Clarifiers Clarifiers use gravitat ional sediment ation to remove oil and solids from a waste water stream. Often it is nec ess ary to use chemical coagulant s such as alum or lime to aid the sedime ntation process. These clarifiers are usually equipped with a skimmer to remove any floating oil. Clarifiers used after a biological system normall y do not have skimmers as there should be no floating oils at that point. The sludge from the clarifiers is usually treated before final disposal. End-of-Pipe Control Tec~% ology End-of-pip e control technolo gy in the petroleu m refining industry relies heavily upon the use of biologi cal treatm ent methods. These are supplem ented by approp riate pretreat ment to insure that proper conditions, especi ally sufficient oil removal and pH adjustm ent, are prese nt in the feed to the bio log ica l system. When used, initial treatment most often consists of neutr aliza tion for control of pH or equal izatio n basins to minimize shock loads on the biolog ical systems. The incorp oratio n of solids removal ahead of biolog ical tre atment is not as impo rtan t as it is in treat ing mun icip al waste waters. One of the initial criter ia used to screen refi neri es for the field survey, was degree of treatme nt provid ed by their waste water treatment facilities. Therefore, the selection of plants was not based on a cro ss- sec tio n of the entire industry, but

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rather was biased in favor of those segments of the industry that had the more efficie nt waste' water treatment facilities. Table 26 indicates the types of treatment techn ology and per for man ce charac terist ics which were observed during the survey. In most of the plants analyzed, some type of biologic al treatme nt was uti liz ed to remove dissolved organic ~material. Table 27 summarizes the expected effluents from wa st e water treatment processes throug hout the petrole um refining industry. Typica l efficiencie s for these proc esses are shown in Table 28. During the Survey program, waste water tre atm ent plant performan ce histor y was obtaine d when possible. This histo rica l data were analyzed statistically and the individual plant's performance e valuat ed in compari son to the original d esi gn basis. After this evaluation, a group of plants was selected as being exempla ry and th ese plants were present ed in Table 26. The treatment data in Table 28 represe nt the annual daily average performa nce (50 percent probabi lity-of -occurr ence). There were enough plants involving only one su bca te go ry to make the inter pretat ion meaningful. In preparing the economlc da ta base, however, all the waste water treatme nt plant data were analyz ed to develo p a basis for subsequent capital and operat ing costs. The treatm ent data from the exemplar ~ plants referred to previoulsy were analyzed to formulate the basis for developing BPCTCA effluen t criteria. The effluent limitations were based on both these treatme nt data, other data included in Supplement B, and other sources as discuss ed in Section IX. These effluent limitations were de ve lo pe dfo r each subcategory individually and thus no common treatme nt eff icienc y was selected as being typical of the petroleum refin ing industry for use in the BPCTCA eff luent limitations. A brief descri ption of the various elements of end-of-pipe treatment follows. Equalization The purpose of equalizat ion is to dampe n out surges in flows and loadings. This is especia lly necess ary for a biolog ical treatment plant, as high concen trati ons of certain materials will upset or complet ely kill the bacteria in the treatment plant. By evening out the loading on a treatment plant, the equali zatio n st ep enables the treatment plant to operate more effectively and with fewer mai nten ance problems. Where equalization is not present, an accident or spill within the refiner y can greatly affec t the effl uent qu ali ty or kill the biom ass (R7, R20). The equal izati on step usually consists of a large pond that may contain mixers to provide better mixing of the wastes. In some refin eries the equ ali zat ion is done in a tank (55, R29). The equali zatio n step can be before or after the gravity separat or but is more effective befo re as it increases th e overall effi cienc y of the separator. However, care must be taken to prevent anaerob ic decompo sitio n in the equali zation facilities.

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Observed Refinery Treatment System and Effluent Loadlngs

TABLE 26

SL~BCATEGORY A B B B B B C C C D D EType of OPTreatmentRefinery R32Observed AverageEff luent LoadinssNet-ks/1000 m3 off eed s to ck(lb/lO00 bbl offeedstock)

AL-PPR18

AL-F E-DAF-ASR27

OPR26

DAF,AL,PPR7

DAY,ASR20

DAY,ASR8

DAF,AL,PPR23

E,TF.ASR24

E,ASR28

DAF,AS,PPP,25

BOD$ 8(2.8) 8:0(4.4) 5.9(2.1) lO(3.6) 3.7(1.3) 13(4.6) 2.7(0.95) 2.6(0.91) 7.4(2.6) 14(5.0) 17.5(6.2)COD .... 39(13.8) 68(24) 96(34) 71(25.0) 39(13.8) 67(23.5) . . . . . 54(19,~ 57(20) 136(48) 320(113)TSS . . . . . . . . 25(8.7) 34(12) 8.5(3.0) 4.2(1.5) 13.6(4.8) 8.5(3.0) 7(2.5) 12 (4.3) 38(13.5) 36(12.7)O&G 2.0(0 .7) 2.3(0.8) 9(3.2) 4.0(1.4) .. .. 2.8(1.0) 6.5(2.3) ..... 4(1.4) 7.2(2.55) 22(7.7)NH3-N . . . . . . . . . .. .. .. .. . 4.8(1.7) 0.14(0.05) 4.s(1.6) ..... 2(0.7) 1.2(0.44) 2.3(0.8)Phenol icCompounde 0.14(0.05) 0.003(0.001) 0.4(0.145) 0.37(0.13) 0.05(0.018) 0.0006(0.002) 0.06(0.023) 0.17(0.06) o. 017 (0. oo5)S u l f i d e 0 . 0 3 ( 0 . 0 0 9 ) 0.2(0 .07) 0(0) 0.03(0.010) 0.014(O.OOS) 0.05(o.o18) 0.20(.07)

F o o t n o t e s : AL-aerated lasoonAS-act ivated sludseDAY-disso lved a ir f lo t a t i onE - e q u a l i z a t i o n

F - f t l t r a C l o nOP-oxidacion pondPP-poltehln8 pondT-trlckln8 filter

A-Toppin8B-CrackinEC-Petrochemlcals

D-LuheE-Xncesreced

O4~

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TABLE 27 Expected Effluents from Petroleum Treatment Processes

EFFLUENT CONCENTRATION, ms/L Ps o~s s PROCESS BOD , COD TOC SS ~ ' O I LI I ~ j __m'~ :".. .1 . AF I se p ar st ~ ~ " Raw Waste 2 5 0 - 3 5 9 260-700 'NA - 56-200 2.0-100

"2 . Ci aa - l f l e r h 5 - 2 0 0 130-450 ' NA 25-60 5-353. D i s s o l v e d A i rF l o t a t i o n 45-200 130-450 ~A 25-60 5-2o~. Oraauiar Media' " F i l t e r h0-170" 'ZO0-~O0 NA 5 - 2 5 6 - 2 0~. Oxidation Pond 10-60 50-300 NA 20-100 . i.6-5o

6 . Ae r ate d Lago~ 2 , 3 , h " i 0 - 5 0 . . . . 50-200 NA "" i0-80 5-20

7 . Ac t i va te d S l udge 2 , 3 , b 5-50. 30-200 ,20-80 - 5-50 1-15

8 . T r i c k l i n g F i l t e r I .25-s0 80-350 NA 20-70 , 10-809 . C o o l i n g T o w er 2 , 3 , b , " 25-50 4%350 70-150 4 5-100 20-75

ID . ACtivated Carbon 2 , 3 , h 5-100 3 0 - ~ 0 NA 10-20 2 - 2 0

i l . o r ~ ~ ' a n z te r 5~ NA 25-6!.. 3-1712 . Actlvated~Carbon O n d ~ 3-1o 30-100 z-z7 1-.I~ 0.8-2.5

A - Data Not Available

PHENIbL'

6-100 15-15010-40 NA

lO-4O ~A 3-35 NA

o.o1-12 ,3-50

0.1-25" 4 - 2 5

0.0i-.2.0 .- . i-i00

0.5-10 25-100.1-2.0 1-30

1 I0-140

0,35-10 ' NAo-0.1 .I-i00

NA NA NA

0-20

0-0.2

0 ~ . 2

0.5-2 NA NA

NA 0-0.2

7,13,30,hi,49,59 34 ,hBa,h9 13,29,32,48a i49

18,22,23,31,42,48~,4 9 ,5 5 ,7 5 ,RI831 ,~ ,42a,h8a,49, 55,5 9 ,R7 ,R23 ,R262 3 , 2 4 , 2 7 , 3 0 , 3 4 , 3 5 ,4 2 ; 4 8 a , ~ 9 , 6 0 , 6 9 , 7 2R8 ,R20 ,R24 R25 ,R27 R28 ,R29 18,30,42,48a,49, 33,41 17,21,27,48,48a,49, 5 3 ,6 2 a17,48,54 .17,21,27,48,48a;49, 53,62&

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TABZm 28T y p i c a l Removal E f f t c i e n c t e s f o r O i l R e f i n e r ~ T r e a tm e n t P r o c e s s e s

PROCESS .- IR.I~4OVA.LEFFICIENCY,INFLUENT BOD COD TOC SS OIL PHENOL AMMONIA REFERENCESl . A l r l S e p a r a t o r Re ~ Waste 5-ho 5-30 NA 10-50 6O-99 0-50 NA NA 7,13,30,41,49,592 . C l a r i f l e r i 30-60 20-50 NA 50-80 60-95 0-50 NA NA 34,48a,495 . D i s s o l v e d A i rF l o t a t i o n 20-?0 lO-6O ~A 50-85 I0-85 I o - 75 NA - NA 13,29,32,48a,49h. F i l ~ e r i ho-7o 20-55 NA 75-95 65-90 5-20 NA NA 17,41,48a,495 . Ox ida t ion Pond I 1,0-95 30--65 6O ~0-7o 50-90 6o-99 0-15 70-i00 18,22,23,31,42,4849,55,75 ,RI86. Aerat ed Lagoon : ,3,h 75-95 6o-85 NA h0-65 7o-90 90-99 10-45 95-ioo 31,39,42,48a,49,55,59 ~R7 ,R23 ,R267 . Act iv a ted S ludge 2,3,h 80-99 50-95 ho-90 60-85 80-99 95-99 + 33-99 - 97-1oo 13,24,R7,30,34,3542,48a,49,60,69,72

R8 ,R20 R24 ,R25 ,R2R28 ,R29

8. T r i c k l i n gF i l t e r i 60-85 30-70 NA 6o-85 50-8o 70-98 15-90 7o-10o 18,30,42,48a,b99. Coo]inK Tower 2,3,4 50-90 40-90 10- 70 50-85 60-75 75-99+ 60-95 NA 33,4110 . Act iva ted

Carbon2,3,4 70-95 70-90 50-8o 60-90 75-95' 9o-10o 7-33 NA 17,21,27,48",48a,4949,53,62a

Ii. FilterOrm/u lar M ed ia 5-9 NA NA 50-65 75-95 65-95 5-20 NA NA 17,48,541 2 . A c t i v a t e dCarbon 5-9" plus ll 91-98 86-94 50-80 60-90 7o-95 9o-99

33-87 NA 17,21,27,48,~8a,49,53,62a

HA - D ata Not Avai lab le


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Dissolved Air Flotation Dissolved ai r flotation con sis ts of saturating a portion of the waste water feed, or a portion of the feed or recyc led efflue nt from ~the flotation Unit with air at a pressur e of 40 to 60 psig. The waste, water 0r ef fl ue nt 'r ec yc le is held at this pressure for IL5 minutes in- a retention tank and then released at atmospher ic pressure to the flotation cha mbe r. The sudden reduction in pressure results in the release of microscopic air bubbles which attach themselves to oii and suspended par tic les in the waste water in th e flotation chamber. This results in agglomerates which, due to the entrai ned air, h&ve greatly-incr eased vertical ri se ra te s of about 0. 5 to l.0 feet/minute. The floated materials ris e to the surface to form a froth iayer. Specially designed flight scrapers or othe r skimming devices continuo usly remove the froth. Th e retention time in the iflotation chambers is usually ab ou t 10-30 minutes. The effectiveness of dissolved air flotation depends upon th e attachment of bubbles to the suspended oi l and other par tic les whi ch are to be removed from the waste st re am . The attraction between the ai r bubble and par tic le is a result of the particle surface and bubble-s ize distribution. ~ . . . . . Chemical floc cula ting agents, such as salt s of iron and aluminum, with or without organicpolyelectrolytes, are oft en helpful in improving the effectiveness of the air flotation process and in obtaining a high degree of clarification. Dissolve d air flotation is used by a number of refineries totreat the effluent from th e oil separator. Dissolved airflotation using flocculating agentsis also used to treat oilemulsions. The froth ~ skimmed from the flotation tank can be combined with other sludges (such as - those from a gravity separator ) for disposal. The clarified effluent from a flotation unit generally receives further treatment in a biological unit, prior to discharge. In two refineries, dissolved air flotation is used for cla rifi cati on of bio logi call y t reat ed efflue nts (29). Oxidation Ponds ; The oxidation pond is practical where land is ple nti ful and cheap. An oxid atio n pond has a large surface area and a shall ow depth, usual ly not exce edin g 6 feet. These ponds have long dete ntion p eriod s fr om 11 to 110 days. Th es ha ll ow depth ~ allows the oxidation pond to be operated aerobically ~ ith out mech anic alae rato rs. The algae in the pond produce Oxygen thr oug h photosynthesis. ~ This oxygen is then used by " the bact er ia to oxidize th e wastes. Because of the low 10adings , little bio log ica !sl udg e is produced and the pond is fairly resistant to uspsets due to Shock loadings. Oxidation pon ds are usually used as the major treatment process. Some refineries use ~ onds as a -polishing process aft er other t r e a t m e n t p r 0 c e s s e s . . . .. .

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Aerated Lagoon The aerated lagoon is a smaller, deeper oxidat ion pond equipped with mechani cal aerators or diffused air units. The addition of oxygen enables the aerated lagoon to have a higher concentra tion of microb es than the ox idat ion pond. The rete ntio n time in aera ted lagoons is usual ly shorter, bet ween 3 and 10 days. Most aerated lagoons are operated without final clarification. As a result, b iota is dis char ged in the effluent, causing the efflu ent to have high BOD~ and solids conce ntrati ons. As the efflu ent standards become more strict, final clarif icatio n will be incre asing in use. Trickling Filter A trickli ng filter is an aerobic biologi cal process. It differs from other processes in that the biomas s is atta ched to the bed media, wh ich may be rock, slag, or plastic. The filter works by: 1) adso rpti on of orga nics by the biol ogica l slime 2) dif fusi on of air into the biomass; and 3) oxidat ion of the dissol ved organic s. When the bioma ss reaches a certa in thickness, part of it sloughs off. When the filter is used as the major trea tme nt process, a clarifi er is used to remove the sloughed biomass. The trickl ing filter can be used either as the complete treatm ent system or as a rough ing filter. Most app lic atio ns in the petrole um industry use it as a roughing device to reduce the loading on an acti vate d sludge system. Bio-Oxidation Tower The bio-ox idati on tower uses a cooling tower to transfer oxygen to a waste water. API (112) has called the bio -ox ida tio n towers a modified activated sludge process, as most of the biomass is suspended in the wastewater. Results from refine ries indicate it is a succ essf ul proces s to treat portion s or all of a refi nery wa st e wa te r (80, 81, 92). Activated Sludge Activa ted sludge is an aerobic biologi cal treatme nt process in which high concent rations (1500-3000 mg/L) of new ly-gro wn and recycled microorganisms are suspended uniformly throughout a holding tank to which raw waste waters are added. Oxygen is introduce d by mechani cal aerators, diffused air systems, or other means. The organ ic mate rial s in the waste are remov ed from the aqueous phase by the micro biolo gical growths and stabilize d by biochemi cal synthesis and oxidation reactions. The basic activated sludge process consists of an aeration tank follow ed by a sedimen tation tank. The flocculant microbial growths removed in the sediment ation tank are recycled to the aeration tank to maintain a high concent ration of active microorganisms. Although the microo rganis ms remove almost all of the organic matter from the waste being treated, much of the converte d organic matter remains in the system in the form of mic rob ial cells. Thes e

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cells have a relative ly high rate of oxygen demand and must be removed from the treated waste water be fo re discharge. Thus, final sedimenta tion and recircul ation of biological solids are impo rtan t elements ina n activated sludge system.

i

Sludge is wasted on a continuou s basis at a relativ ely low rate to preven~ build-u p of excess activated sludge in the aeration tank. Shock organic loads usually result in an overloaded system and POO r sludge settling characteristics. Effectiv e performan ce of activated sludge facilities requires pretrea tment to remove or sub sta nti all yr edu ce oil, sul fid es (which causes toxicity to microorgan isms), and phenol concentrations. The pretre atment units most frequently used are: gravity separato rs and air flotation units to remove oil; and sour water s trippers to remove sulfides, mercaptans, and phenol. Equaliza tion also appears necessa ry to prevent shock loadings from upsetting the aeration ba si n. Because of the high rate and degree of organic stabil izatio n possible with activated sludge, applica tion of this process to the treatment of refi nery waste waters has been incr easi ng rap idly in recent years. Ma ny Variations of the activated sludge process are currently in use. Examples include: the taper ed aeration process, which has greater air addition at the influent where the oxygen demand is the highest: step aeration, wh ic h introduces the influent waste water along th e length of the aeration tank; and contact stabilization, in which the return sludge to the aeration tank is aerated for I-5 hours. The contact stabil izatio n process is useful where the oxygen demand is in the suspended or colloidal form. The comp lete ly mixed activat ed sludge plant uses large mechanic al mixers to mix the influent with the contents of the aeration basin, decreasing the possibi lity of upsets due to shock loadings. The Pasvee r ditch is a vari atio n of the comp let ely mix ed activated sludge process that is widely used in Europe. Here brushes are used to provide aeration and mixing in a narro w oval ditch. The ad va nt ag e of this process is that the concentra tion of the biota is higher than in the conventiona l activated sludge process, an d the wasted sludge is easy to dewater. There is at least one refin ery using the Pasvee r ditch type system. The agtivated sludge process has several disadvantages. Because of the amount of mechanica l equipm ent involved, its operatin g and maintenan ce costs are higher than other biological systems. Th e small volume of the aeration basin makes the process more subject to up set sth an either oxidation ponds or aerated lagoons. As indic ated in Table 25, the acti vated sludge process is capable of achi evin g very low co nce nt rat io ns of BOD5, COD, TSS, and oil, depen dent upon the influ ent waste, loading and the part icul ar des ign basis. Reported efficienci es for BOD5 removal are in the rang e.of 80 to 99 percent. physical-chemical Treatment

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Physic al-che mical treatmen t refers to treatment processes that are non-bi ologic al in nature. There are two types of physical- chem ical processes: those that reduce the volume of wate r to be treated (vapor compress ion evaporators, reverse osmosis, etc.), and those that reduce the concentrat ion of the pollutants (activated carbon). Phy sic al-c hem ica l (P-C) proc esse s requi re less land than biologic al processes. P-C processes are not as susceptib le to upset due to shock loading as are bio logi cal processes. Anot her advan tage of P-C is that much smaller amounts of sludge are produced. Flow Reduction Systems Flow reductio n systems produce two effluents, one of relati vely pure water and one a con cen tra ted brine. The pure wate r stream can be reused within the refinery resulting in a smaller effluent flow. The brine is easier to treat as it is high ly concent rated. Both of the processes describe d herein have been demons trate d on small flows only and at prese nt the costs involv ed are extr emel y high (45, 52, 93). In the vapor compress ion evaporato r the waste water flows over heat transfer surfaces. The steam generated enters a compre ssor where the temperatu re is raised to a few degrees above the boilin g point of the waste water. The com pre sse d steam is used to evaporate more waste water while being condensed. The cond ense d steam is low in diss olve d solids. The major proces s costs are the costs of elect rical power, which is app rox ima tel y $1.0/1000 gallon s of clean water (93). The reverse osmosis pro cess uses high pressu res (400-800 psig) to force water thr ough a semi-permea ble membrane. The membrane allows the water to pass through, but contai ns the other con- stituents in the waste water. Curre ntly available membranes tend to foul and blind, requiring frequent cleaning and replacement. Until this proble m is corrected, reverse osmos is is not a practicab le process. The operating cost for a reverse osmosis unit is appr oxim atel y 20- 30/1 000 gal lons (45, 95). Granular Media Filters There are several types of granu lar media filters: sand, dual media, and multimedi a. These filters operate in basi call y the same way, the only diff eren ce being the filter media. The sand filter uses relatively uniform grade of sand resting on a coarser material. The dual media filter has a course layer of coal above a fine layer of sand. Both types of filters have the prob lem of keepin g the fine parti cles on the bottom. This prob lem is solved by using a third very heavy, very fine material , (usually garnet) beneath the coal and sand. As the water passes down throu gh a filter, the susp ende d matte r is caught in the pores. When the pressu re drop thro ugh the

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filte r becomes excessive, the flow through the filter is reversed for removal of the collecte d solids loading. The backwa sh cyc le occurs appr oxim atel y once a day, depend ing on the loading, and usuall y lasts for 5-8 minutes. Most uses of sand filters have been for removin g oil and solids prior to an activa ted carbo n unit. There is one refinery that uses a mixed media filter on the effluent from 'a biologi cal system. Granular media filters are shown to be capable of consi stent ly operated with extr emel y low TSS and oil effluent discharges, on the order of 5-10 mg/L. Activated Carbon The activated carbon (AC) process utilizes granular activated carbon to adsorb polluta nts from waste water. The adso rpti on is a function "of the molec ular size and polar ity df the adsorb ed substance. A ctiva ted carbon preferentially adsorbs large organic molecul es that are non-polar. An AC unit follows a solids removal process, usually a sand filter which prevents pluggin g of the carbon pores. From the filter the water flows to a bank of carbon columns arrang ed in series or parallel. As the water flows throu gh the columns the pollutan ts are adsorbed by the carbon, gra dua lly filling the pores. At int erva ls, portions of'the carbon are remove d to a "furnace where the ads orb ed substan ces are burnt .off. The reg ene rat ed carbon is reused in the columns, with some make up added, becaus e of handli ng and effic iency losses.

I

Activated carbon processes currently have only limited usage in the refining industry. However, there are new installations in the plann ing const ructio n stages. The incre asing use of activated carbon has occured because activated carbon can remove organic materials on an economically competitive basis with biological treatment. Activated carbo n regeneration furnaces have high energy r equirements . Sludge Handling and Dispos al Digestion Diges tion is usually used precedin g ~ the other sludge concentrati on and disposal methods. The purpose of digestion is to improve the dewat ering of the sludge. Digest ion can occur aerobically or anaerobically. During digestion, bacteria decompo se the organic mater ial in the sludge produ cing methane, car bon dio xid e and water. At the end of the dige stion process, the sludge is stable and non -de com p0s abl e. .~;~. .Vacuum Filtration The various vacuum filters, usually a revo lvin g drum, use ~ a vacuum to dewater the sludge. The revolv ing drum type has a vacuum applied against a cloth. The water passes throu gh the

"'cloth and retu rns to the influe nt of the tre atm ent plant. The sludge r emain s:on the dru m until it is scraped off with a knife.

QI

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Centrifugation Centri fugatio n uses high speed rotation to separate sludge and water. The heav ier sludge moves to the outsi de and is conve yed to one end, where it is coll ect ed for final disposal. The water flows out the opposit e end and is return ed to the treat ment plant. Sludge Disposal From any waste water t reatment plant, the sludge must be disposed of. The method s used are landfil ling, landfa rming, bargi ng to sea, and incineratio n. Landfilling A landfi ll operat ion requires a large amount of land. Before landfilling, the sludge should be digested to avoid odor problems. The sludge is disposed of in an exca vati on site. After each batch is dispo sed of, it is cover ed with a layer of earth. When the site is filled to capac ity it is covere d with a thick layer of earth. The largest problem of industrial landfills is the pollution to ground and surface waters by leaching. Leaching occurs when water percolates through the landfill. As it drains through the landfill site, the water carries with it dissol ved and suspended solids and organic matter. This water can then contam inate unde rgro und or surface streams it comes in cont act with. Incineration Incineration is gradually compl ementi ng landfills as a method of sludge disposal. The princ ipal process is fluid bed incine ration . In this process, a bed of sand is prehe ated with hot air to 482-538 oC (90(} - 1000OF). Torch oil is then used to r ai se t he b ed t e m p er a t u re t o 6 49 - 7 05 oC (1200 - 1 30 0O F) . A t this point waste water sludge and/or sludge is introdu ced and the torch oil is stopped. The solid products of comb usti on remain in the bed which is a gradually withdrawn to maintain a constant bed

heig ht. Eventually, the bed will be composed of only ash. The sludge fed to the incinera tor usually contains inorganic as well as o rgani c material. However, the sludge must conta in a minimum amount of organics to maintain the combustion process. one re finery (26) suggests a minimum of 1,930,000 cal/cu m (29,000 Btu/gal) of sludge heating value is nec essa ry to maint ain the combus tion process.

US EPA 2007-10-22 Guide Petroleum Guidelines 05

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