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Treating Process WastewaterEmploying Vacuum Distillation UsingMechanicalVapor RecompressionDerald1.McCabeBrandt, A TUBOSCOPE C O M P M , 2835 Holmes Road, Houston , Texas 77&lM.A. (Tony) VivonaWater a nd W astewater Departm ent, ICF Kaiser Engineers. Inc., 5718 Westheimer Road, Suite 1000, Houst on, Texas 77057

Process wastewater has been successfully treated using anenhan ced variable vacu um distillation system (V#Sj. Theremoval of contaminants isachieved initially by degassing theliquid under an intense vacuum which removes the volatileorganic compounds. The resulting liquid is then distilledund er a va cuu m using m echanica l vapor recompression. Ti3esystem was inven ted LyDerald McCabe.This innovative treatment system removes virtually all of thecontaminants, such as TSS, TDS, BOD, COD, heay metalsand mineral co mpo unds. Tbe resultant aqueous portion nor-mally returns to a neutralpH. Due to the un ique system opera-tion, scaling problems (often encountered in conwn tional dis-tilhtiota) have not been detected in this system.The WDS is extremely energy ejjcien t because the heat o rdistillation is generated and recycled mechanically. Usingelectricity as the en ergy source, the app roximate operating cost,based on $0 .05m, a y vary rom $0.005 o $0.01per gal-lon dependiizg on the size and capacityof the equipm ent.Bused on applications in um te s tre am performed to-date,the VVDSprocesshas yielded a distilled w ater stream a nd theconcentrated solids has been used usa byproduct or as a con-centrated non-dischargeable waste o r disposal.FLOW DESCRIPTION

Contaminated petrochemical water enters the machine bybeing pulled through a flow meter designed to measure theexisting and totalized wastew ater flow through th e system. Thewater is then routed through the electrolysis process. The elec-trolysis process cause s a three dimensional pre-treatment.

1. Metal ions which h ave an electrical charge are attract-ed to the electrodes and are b ound together and tendto mass into clusters of like materials causing them toprecipitate and become part of the reject stream.These metal assemblages can then be separated andrecycled (if desired).

2 . Nonmetallic ions which have no electrical charge act askernels around which the material coagulates, forminginsoluble clusters, which p recipitate from the solution. Afterthe metals hav e been separated, by passing thein through avertical table the remaining salts can be used for the tan-ning or pickling industries and. in som e cases, the rem ain-ing salty water can be used as a brine concentrate. Thebrine concentrate can be u sed for blow-out prevention andin certain oil well applications.

3. Electrolysis breaks chemical bonds in water and pollutantmolecules. Potentially hazardous substances are brokendow n by ox idation and reduction, into their n on-hazardou scomponents. Also, a smnall percentage of the water's mole-cules are released as oxygen, a hydroxyl radical and hydrc-gen. These pow erful oxidizing and reduction agents facili-tate materials breaking down quickly into their basic partsor degenerating into carbon diox ide gas. The oxygen left insolution will be at high enough levels to destroy both aero-bic bacteria and other biologic contaminants which may b epresent

I--FIGURE 1 Vmable Vacuum Distillation System

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The water is then drawn through a proprietary separationsystem to separate and remove any oils that have been freed bythe previous process. As it exits the separator, it is then drawninto a vertical down flow thm f h e-gassing vessel where it isexposed to a vacuum for removal of released and dissolvedgases. This process helps to adjust the pH and insure that theconipounds that have been disassociated will not reunite or mix.The discharge from the vacuum pump can be adsorbed o r usedas supplemental fuel, dependmg on the circumstance and analy-sis of the vapors.

The water then is discharged from the bottom of the de-gasser and is pumped into the distd er where it is distilled usingthe vapor compression principle. As the water in the distdler isbeing distilled, it is also constantly being recirculated from thevapor bonnet down through the bottom, and back up throughthe tubes. The p a~ cu la tehat does not settle provides the scourto prevent scale buildup. The residue settles out of the liquidand is discharged to the decant for final disposition.Since the distillate is hot when it enters the distillate tank, aportion of the steam does not condense. The non-condensedsteam. having already being stripped of n onco ndensab les, canbe reintroduced into the vapor bonnet, or discharged into theatmosphere or used for pre-heating. The distillate is thenpumped into storage or for reuse depending on the applica-tion.To prevent the distiller from becoming plugged with rejectmaterials, it is pumped in a slurry form into a decant tank

I IFIGURE 3. Case Study 1 - 20,000 GP D Discharge Elimination System(FoodProcessing W aste W ater)

W A S T E W A T E RS T R E A M

__ A_- P - 4__ - I - -

/__ - - J L

S A L E A B L EB Y P R O D U C T

n0115. FATS, A N 0IAKlICLII A1L5I IGIl lEt? T I I A N

W A l E R 1TH EVAR AB LE

VACUUMDIS LlLATlONSYSTEM (VVDS)

W A T E R

-\OU T/~ _ _

W A S T C

FIGURE2. Typical Schematic of W D Swhere the solids are settled out and the liquid is returnedthrough the distillation system for further distillation andreduction.SCALINGScaling which is common to most distillation units is virtuallyeluninated in the VVDS ,Water in the VVDS is flashed into steam without boilingwater against hot plates or membranes. Th~slash occurs on thesurface of the water in the bonnet, and not in the heat exchang-er tubes. The flow of water containing particulates through thetubes of the heat exchanger provides a scouring action. To dateno scaling tendencies have been observed in any of the VVDSmachines in operation. However, no claim is made that scalingwill never occur. However, the potential for scaling is minimizedby the systems design. The VVDS process is designed to runchemicals through the machme to clean scale if it occurs. A typi-cal simplistic schematic of the W D S is depicted in Figure 2 .

CASE STUDIESThe following are som e case studies which utilizes W D S :1. Shreveport Toxic Wastes (Conftdential Client)Industry : ndustrial non-hazardous wastewater treatment andProb2em:Wastewater was high in TDS, TSS, BOD,, COD,heavy metals, salt and some light h y d r m h n contamination.Act ion Step: Two distillers were placed in service at thislocation, one at 10,000 gpd (37.8 m3/D) capacity and theother at 20,000 gp d (75.7 m3ID). One unit is used primarilyas the main distiller with the smaller being held in reserveand used for overloads.Resu1ts:The distillers are reducing the amount of water thatwould ordmanly be hauled out for disposal at a conventionaldisposal site and method. The reject is then stabilized and dis-posed of in a properly rated landfd.The hot distdate 1 used forseveral heating applications.

disposal.

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BenefitsThere has been a sharp reduction in volume of disposal, as wellas. the related costs of conventiona l disposal me thods. The distil-late is providmg a good heat source, as well as. a superior boilerfeed stock, which needs no pretreatment with costly chemicals.The distillers also provide a broader revenue base for the com-pany, by allowing it to treat a broader range of contaminatedwater.Notes

The confidential company mentioned in the above study is awastewater disposal company which deals in wdters classifiedcurrently as non-hazardous. The sam e or improved energy effi-ciencies described in the following food industry case study canbe expected.2. Food ProcessingCase StudyIndus tp Food, specifically instant riceProb1em:Process water was high in BOD, and CO D content,with from 1.5%to 3% solids. resulting in substantial surcharge forwaste treatment.Action S t q . Installed 16,000 gpd (60.6 mj/D) variable vacuumdistillation unit to remove BOD,, COD. solids, and return dis-tde d water to boiler feed at approx inutely 18 YF (84OC),to closethe loop o n the process water.Results : Process returns 16.000 gallons per day (60.6 mj/D) ofdistilled water for reuse as boiler feed water and cooking waterfor rice products. The solid content of approximately 18,000lb/day (8192 Kg/D) is concentrated into a usable by-product.The rice company has the options of allowing aninial feed ven-dors to haul product away. eliminating disposal cost, or of pro-cessing the product into liquid animal feed for sale. or of drying

IFIGURE 4. Case Study 2 - 20,000 GP D Discharge Elimination System(Food Processing Waste Water)

the produb. The company expects a substantial return on whatwas once considered a waste product.Benefits

Elimination of disposal costs.Significant savings on chemicals for boiler feed adjustmentand efficiency.Superior water for plant operations.Costly waste produc t turned into usable by-product.

Surcharge Savings:Surcharge for 1994Surcharge for 1995Surcharge SavingsEnergy Cost

s270,000.00$ 96,000.00$174,000.00$ 27,030.00

Net Savings: S146,970.00Notes

Al l figures and statements are based on information furnishedby the rice company. Further savings and cost adjustments areexpected as more operating history is gained.3. SpentDistillercaSeStudyIndustry: Industrial fuel alcohol (ethanol)Problem: Evaporation process was not yielding desired con-centrations of grain solids for conversion to saleable by-prod-uct and was delivering higher concentrations of CO D effluentto waste treatment, resulting in higher treatment and disposalcost to the company.Purpose: Testing of JH Environmental T echnology, the holderof the patent, pilot unit on evaporator feed and evaporator con-centrate to determine the effecttveness of and cost of treating.The goal was to demonstrate the ability of this technology todeliver grain solids at any desired consistency.Test Description: Still bottoms used as feed stock for compa-ny's evaporators at 3%solids were fed to the unit throughout thefirst day. Samples were drawn throughout the first phase of hstest showing increasing concentrations of solids through the firstphase up to 23%. It is envisioned that higher concenm tions canbe achieved.

The feed stock was later changed to the evaporator concen-trate. The concentrate show ed 11% solids. The unit was run ont h ~tream with samples being drawn and tested throughout h stest run. Testing samples showed a concentrate increase up to32% solids. The h td l e d water from both of the tests was testedfor solids,using the weight and evaporation test, the water testedG% solids.COD tests were also run throughout the testing periodand exhibited CO D concentrations from 1500 mg/I to 2500ms/I. It is believed that these concentrations of COD can becontrolled by design changes in the process. The test was con-cluded and the unit was prepared for shipment.Discussion; The unit from start to finish was allowed to runvirtually unattended. However, an operator was in attendance toobserve function and collect data. Power supply was 640 vac at42 amperes. The total product w as 3,300 gallons (12.4 m3). Thetotal operating time was 33 hours, with a four hour shut down.

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FIGURE 5. Case Study 3 - 10,000 GPD Discharge Elimination System(Industrial Waste Water)

This outage was caused by the discharge valve being closed forreasons a s yet undetermined. This automatic shutdown,however, illustrates the effectiveness of the fail-safe featuresdesigned into the equipment to protect the most expensivecomponents. When the shutdown was &covered, the unit was

checked and restarted, and continued to operate trouble freethroughout the remainder of the test. The unit was rinsed priorto transporl and exhtbited no s i p of fouling.Recommendations:After observing the evaporation currentlyin place, it was accessed that the new evaporator should be con-nected to operate in series with the rest of the evaporator sys-tem, instead of parallel operation. This will allow a greater flowthrough the system and possibly help prevent fouhg of theevaporators and impmve the concentrate and condensate. If theconcentrate is not sufficiently thickened to allow for its sale as aby-product, then an adequately sized unit would be suggestedto further concentrate the effluent into a saleable by-product.After further study, a complete recycling program may besuggested to minimize water usage and greatly reduce the cur-rent waste treatment load.CONCLUSIONFunctionThe VVDS treats industrial wastewater stream or a specificportion of the wastewater stream, to produce concentrated by-product for sale, reuse or recycle or minimize waste for &posaland distilled water Q 1 W F 50F (82OFf 2.80C).AdvantagesThe W D S provides a variety of savings as a stand-alonetreatment or in conjunction with the present system: reduction orelmnation of municipal sewer &charge fee; reduction of off-site wastewater disposal fee; reduction of chemical make-upwater; reduction of heating costs for feed water; production ofheat, de-gassed distilled water Q 1WF (t 5OF) (82OC + 2.8OC)ready for immediate re-use and production of by-product forresale or re-use.

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