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3 The Water Recovery and Brine Reduction Systems Downstream from the biotreatment area at Pueblo Chemi- ACID ADDITION, FEED/DISTILLATE HEAT EXCHANGE, cal Agent Destruction Pilot Plant (PCAPP), the PCAPP water AND CO2 STRIPPING recovery system (WRS) performs the following functions:1 The effluent from the ICBs collects in the WRS-BRS feed tanks where effluent streams from three other sources, â¢ Collects and mixes immobilized cell bioreactor (ICB) namely, boiler blowdown, cooling tower blowdown, and effluent with other wastewater streams, reverse osmosis system reject water, are also introduced. â¢ Provides equalization of the collected liquid streams, This combined stream is pumped to the brine concentrate â¢ Provides up to 7 days of storage of the feed to the (BC) evaporator feed tank at a design flow-rate of 120 gal- brine reduction system (BRS), and lons per minute (gpm). The composition of the combined â¢ Transfers brine liquid from the WRS to the BRS. stream that was used for the design basis for the BRS is given in Table 3-1. To prevent calcium carbonate fouling of Consequently, the WRS at PCAPP can be considered the evaporator heat exchangers, the carbonate and bicarbon- essentially as tankage and associated piping used to collect, ate in the evaporator feed, most of which originates from mix, and condition the various liquid effluents for delivery to the biological breakdown of organic matter in the ICBs, is the main operations involved in water recovery that occur in removed by a three-stage process: (1) feed acidification, (2) the BRS. The BRS will be the focus of this chapter. feed preheating, and (3) feed deaeration. First, concentrated The BRS designed for PCAPP is a conventional Âevaporator/ sulfuric acid is metered into the BC evaporator feed tank for crystallizer system that comprises the following unit opera- acidification. The sulfuric acid converts the carbonate and tions listed in the sequence in which the liquid feed flows bicarbonate ions to CO2, which is subsequently stripped out through them: of the liquid in the feed deaerator by using excess steam vented from the evaporator. The committee notes that a pH 1. Acid addition, of ~ 2 to 4 could cause acid hydrolysis of biomass exit- 2. Feed/distillate heat exchange, ing the ICBs. This would result in some solubilization of 3. De-aeration (CO2 stripping), organic compounds (e.g., proteins, fatty acids), which may 4. Evaporation with steam compression, impact downstream processing in the BRS, such as increased 5. Caustic addition, foaming, increased organic loading to the carbon filters, and 6. Crystallization, less effective dewatering of solids. The latter could lead to 7. Belt filtration, excessive costs related to shipping water. If this becomes a 8. Condensation, and problem, a clarifier can be added to remove the biomass after 9. Activated carbon adsorption applied to both conden- the ICBs and before the WRS-BRS. sates and off-gases. Prior to entering the feed deaerator, the cold feed is heated by the hot outgoing distillate in the BC feed preheater. This Figure 3-1 is a block flow diagram of the BRS, and Fig- preheater comprises 10 shell-and-tube heat exchangers con- ure 3-2 is a photograph of the BRS installation at PCAPP. nected in series. The feed stream passes through the tubes, and the hot product distillate returning from the evaporator 1George Lecakes, Chief Scientist, PCAPP, âPCAPPâs Water Recovery and crystallizer passes through the shell surrounding the System and Brine Reduction System Briefing,â presentation to the com- tubes. The tubes are arranged in a two-pass configuration. mittee, May 1, 2012. 23
24 REVIEW OF BIOTREATMENT, WATER RECOVERY, AND BRINE REDUCTION SYSTEMS FOR PCAPP Off gas To process H2SO4 NaOH water tank to OTS Hot evaporator Deaerator Brine BRS Evaporator feed (from distillate water recovery Steam carbon Concentrated brine Distillate filters system) Distillate Crystallizer Neutralized feed Crystallizer Slurry Belt feed tank filter Steam Belt filter filtrate Filter cake FIGURE 3-1â Block diagram of the brine reduction system. NOTE: OTS, off-gas treatment system. SOURCE: Adapted from Veolia Water Solutions & Technologies, Bench Scale Evaporation of Waste Brine and Filter Testing, 2010. Used with permission. Figure 3-1 FIGURE 3-2â Brine reduction system installation at PCAPP. NOTE: The three tanks in the center-left foreground are granular activated carbon adsorbers for the product distillate. SOURCE: Provided courtesy of PCAPP staff.
THE WATER RECOVERY AND BRINE REDUCTION SYSTEMS 25 TABLE 3-1â Design Basis for Combined System Feed to Prior to the feed preheater, an antiscalant is added to the PCAPP Water Recovery and Brine Reduction Systems liquid feed stream. This antiscalant suppresses the forma- Combined System Feed, tion of solids in the feed preheater and Â eaerator, thereby d Identification lb/hr (unless otherwise noted) dramatically reducing scaling on the surfaces and the fre- Flow rate 60,700 (120 gal/min) quency of cleaning of the hardware (Veolia Water Solutions Water 59,600 & Technologies, 2012). After passing through the deaerator, Calcium 1.4 the Â eaerated liquid feed is added to the liquid in the BC d Magnesium 0.2 evaporator vessel, entering at a point above the liquid that Sodium 331 resides at the bottom of the evaporator. Potassium 0.0 Barium 0.0 Strontium 0.0 EVAPORATION WITH STEAM COMPRESSION Ammonium 2.7 Ammonia 0.0 The evaporator comprises a shell-and-tube heat exchanger Iron 6.3 located above an evaporator vessel, as shown in a simplified Bicarbonate 21.5 illustration in Figure 3-3. The shell-and-tube heat exchanger Carbonate 1.8 consists of 596 50-foot-long tubes (represented by a single Carbon dioxide 0.3 Chloride 264 tube in Figure 3-3) surrounded by a shell containing steam. Sulfate 340 As the liquid flows down inside the tubes, it partially evapo- Nitrate 0.0 rates, and steam and liquid leave the bottom of the tubes Phosphate 1.7 and enter the evaporator vessel. Fresh liquid feed from the Silica 0.3 deaerator is introduced to the evaporator vessel, where it TOC 53.7 mixes with the unevaporated liquid that leaves the tubes. Hydroxide 0.0 Hydrogen 0.0 An anti-foam additive and caustic solution to maintain the Suspended solids 60.0 pH in the range of 7.5 to 8.0 are added to the liquid in the TDS (by summation) 17,100 ppm evaporator vessel. TSS (by summation) 990 ppm This mixed liquid is then pumped from the bottom of the Temperature 102Â°F evaporator vessel to the top of the tubes where, ideally, it is Specific gravity 1.011 distributed uniformly to each tube. Evaporation is caused SOURCE: Adapted from George Lecakes, Chief Scientist, PCAPP, by heat transfer across the tube walls from the steam in the âPCAPPâs Water Recovery and Brine Reduction System Briefing,â presenta- shell to the liquid inside the tubes. The steam that is produced tion to the committee, May 1, 2012. within the tubes by evaporation leaves the tubes and enters the evaporator vessel below the heat exchanger. As shown in Figure 3-3, the steam is subsequently removed from the evaporator vessel and compressed, as described below, to increase its condensing temperature.2 The steam is then intro- Two banks of heat exchangers are provided in parallel so that duced into the shell of the heat exchanger (i.e., the encased the tubes of one bank can be cleaned while the other is online. volume external to the tubes). The steam that condenses in The feed preheater serves two purposes: (1) to recover heat the shell is taken off as distillate product. De-entrainment from the distillate product, thereby allowing the evaporator to baffles are provided in the evaporator vessel to remove liquid operate under stable conditions without using make-up steam drops from the steam before it leaves the evaporator vessel and (2) to increase the partial pressure of the dissolved CO2 to be compressed. in the feed stream, all of which allows the feed deaerator to After leaving the evaporator vessel, the steam is first operate more efficiently. Furthermore, to avoid precipitation washed in a column with water sprays to remove solids. Â of calcium sulfate in the evaporator, the calcium concentra- Then, a demister removes liquid drops before the steam tion in the feed must not exceed 3,000 ppm on a dry solids enters the compressor to ensure that no Âiquid droplets are l basis (Veolia Water Solutions & Technologies, 2012). carried over into the vapor compressor impeller. Any liquid Deaeration (also called CO2 stripping) is accomplished by droplets traveling at high Â elocities through the vapor com- v contacting the liquid feed stream with steam in a column. The pressor could damage the equipment. feed stream is introduced into the top of the column utilizing The liquid level in the evaporator vessel must be main- a spray nozzle, and steam is introduced at the bottom of the tained sufficiently high to avoid cavitation of the liquid recir- column. Contact between the feed stream and the steam is culation pump. However, an excessively high liquid level in facilitated by three baffles within the column. Should it be required, provision has been made for an entrainment separa- 2The condensing temperature of steam increases as its pressure is in- tor to be used at the top of the column to remove entrained creased. The temperature in the shell has to be higher than the temperature liquid droplets from the steam leaving the column. in the tubes to achieve heat transfer.
26 REVIEW OF BIOTREATMENT, WATER RECOVERY, AND BRINE REDUCTION SYSTEMS FOR PCAPP Liquid Compressed steam Shell and tube heat exchanger Steam Evaporator vessel Condensate Vapor Liquid washer (hot liquid Liquid feed distillate product) (from BC feed preheater and L S deaerator) Compressor L S Liquid to crystallizer BC = Brine concentrator L = Liquid S = Steam Entrainment separators FIGURE 3-3â Simplified diagram of the 596-tube brine concentrate (BC) evaporator and BC vapor washer. SOURCE: Developed by the Figure 3-3.eps committee from Bechtel Pueblo Team Drawing 24852-RD-M5-B12-B0001 Rev. P00, Process Flow Diagram, Evaporator. the evaporator vessel must be avoided to reduce carryover of pH in order to reduce the corrosiveness of the brine. This liquid droplets in the steam going to the compressor, which combined feed is transferred to the crystallizer vessel. An could result from overload of the de-entrainment devices anti-foam additive is added to the crystallizer vessel. in the evaporator vessel. This could lead to poor quality of A pump recirculates the slurry from the crystallizer the condensate distillate product and even damage the com- vessel through a shell-and-tube heat exchanger, where it is pressor. The liquid level in the evaporator is controlled by heated. Low-pressure steam is supplied to the shell of the changing the liquid flow to the crystallizer. As noted previ- heat exchanger from a boiler, and the slurry flows in two ously, an anti-foaming agent can be added to the evaporator passes through the tubes. The increased pressure of the slurry vessel, as needed. suppresses vaporization in the heat exchanger, preventing The control of pH in the evaporator is managed by feed- boiling and resultant scaling. The liquid slurry from the heat ing caustic in direct proportion to the incoming feed flow. exchanger is reintroduced into the crystallizer vessel, where Therefore, the pH must be monitored by operators during the the lower pressure causes the liquid to partly vaporize. The routine sampling program developed for the plant. unevaporated slurry falls back to the bottom of the crystal- lizer vessel. The vaporized liquid (steam), shown exiting the crystallizer vessel in Figure 3-4, flows to a condenser CRYSTALLIZER DESCRIPTION where it is condensed to distillate product. Chevron baffles A simplified block diagram of the crystallizer system is are provided in the crystallizer vessel to remove liquid drops shown in Figure 3-4. The crystallizer feed tank is a vertical from the steam before it enters the condenser. Liquid with tank operating at atmospheric pressure. The concentrated a high concentration of suspended solids forms a slurry. liquid from the evaporator is blended with the filtrate from As the water evaporates and the slurry liquor concentration the belt filter in the crystallizer feed tank (see Figure 3-1). increases beyond saturation, the supersaturated salts form Caustic is added to the crystallizer feed tank to elevate the crystals.
THE WATER RECOVERY AND BRINE REDUCTION SYSTEMS 27 Steam to condenser (distillate product) Heat exchanger Crystallizer vessel Steam (from boiler) Liquid from belt filter Condensate (to boiler) Concentrated liquid from evaporator NaOH Feed tank Slurry to belt filter FIGURE 3-4â Simplified diagram of the crystallizer. SOURCE: Developed by the committee from Bechtel Pueblo Team Drawing 24852-RD- Figure 3-4.eps M5-B12-B0002 Rev. P00, Process Flow Diagram, Crystallizer. The BRS throughput is controlled via the crystallizer heat and the crystallizer to produce a combined distillate stream, exchanger steam pressure. An increase in the flow of steam to as shown in Figure 3-5. the crystallizer heat exchanger increases the evaporation rate, The distillate product leaving the BC feed preheater is thus increasing the plant throughput. The slurry discharge cooled in the BRS distillate cooler by cooling water before rate from the crystallizer to the belt filter (see Figure 3-1) entering the BRS distillate carbon filter feed tank, which is is adjusted to maintain the desired concentration of solids part of the distillate carbon adsorption system. As the distil- in the crystallizer. As the steam flow to the crystallizer late product passes through the BRS distillate static mixers, heat exchanger is increased, the feed rate to the BRS belt the combined distillate stream is chemically treated with filter must also be increased to maintain the desired solids caustic or acid to maintain the required pH. The combined concentration. distillate stream is processed for removal of organic matter in the BRS distillate carbon filters and then returned to the plant for reuse. BELT FILTRATION The majority of the vapor entering the crystallizer con- When the slurry concentration reaches the design value, denser condenses and drains by gravity to the BC evapora- the concentration is controlled by blowing down a portion tor distillate tank. The remaining vapor combines with the of the slurry to the belt filter, which is a fully automated vented vapor from the BC feed deaerator and passes to pressure filter. Concentrated slurry is removed from the the BRS vent condenser where some condenses and drains crystallizer slurry circulation loop at a point upstream of by gravity to the BRS distillate carbon filter feed tank. As the recirculation pump. Recovered filtrate is returned to the shown in Figure 3-5, the residual vapor combines with vent crystallizer feed tank. The belt filter produces a wet cake gases from the BC evaporator feed tank, crystallizer feed that will most likely be suitable for disposal at a hazardous tank, carbon filter feed tank, and the BRS area sump. The waste landfill. combined gas flow passes through the entrainment separator of the BRS off-gas treatment system (OTS) to remove any residual water. It is then heated in the BRS OTS heater to CONDENSATION OF VAPOR FROM THE DEAERATOR, reduce the relative humidity to 50 percent or less, and the EVAPORATOR, AND CRYSTALLIZER concentration of organic material is reduced by adsorption The steam from the CO2 stripper (deaerator) is condensed in the BRS OTS carbon filters. By reducing the humidity of in a shell-and-tube heat exchanger. The condensate is then the combined gas stream, the capacity of the OTS carbon mixed with the liquid distillate products from the evaporator filters to adsorb organic compounds is increased, since there
28 REVIEW OF BIOTREATMENT, WATER RECOVERY, AND BRINE REDUCTION SYSTEMS FOR PCAPP Cold vents from BRS Hot vents from deaerator and crystallizer Vent fan BRS vent Vent Cooling water condenser Vent Offgas Treatment heater System (OTS) Condensate carbon filters Cooled distillate BRS distillate Carbon adsorption from evaporator carbon filter Recovered water system and crystallizer feed tank Combined distillate FIGURE 3-5â Block diagram of the carbon filter system. SOURCE: Adapted from Veolia Water Solutions & Technologies, Bench Scale Evaporation of Waste Brine and Filter Testing, 2010. Used with permission. Figure 3-5 is less competition with water vapor for adsorption sites on until the target compound appears in the first column effluent, the carbon. The BRS OTS fan pulls the vapors through this there would be no advantage to having two columns in series. treatment process and delivers it to the BRS OTS stack, from Operating until the target compound appears in the effluent which it is vented to the atmosphere. of the second column allows the carbon in the first column to be more fully utilized before it is replaced, and thus yields a lower carbon-usage rate to achieve the desired removal. ACTIVATED CARBON ADSORPTION Uses of Carbon ISSUES RELATED TO THE WATER FLOW STREAM Granular activated carbon removes organic contaminants The distillate carbon filters are the last line of defense from the pH-adjusted distillate before it is recycled to the controlling the quality of water to meet drinking water stan- plant for reuse in various processes, such as agent hydrolysis, dards. If contaminants are not removed to the desired extent, biological treatment, cooling towers, and the reverse osmosis or if the filters require excessive backwashing because of feed for preparing water for boiler feed. As noted above, high suspended-solids concentration in the feedwater, the granular activated carbon is also used to remove organic filters will fail. The composition of the combined distillate contaminants in the BRS OTS that treats the gaseous effluent that is expected to enter the distillate carbon filters is given from the deaerator, evaporator, and crystallizer. in Table 3-2.3 This flow is made up of cooled distillate from the evaporator and condenser and the condensate from the BRS vent condenser. It is noted from Table 3-2 that the com- Distillate Carbon Filters bined distillate contains 15 lbs/hr (230 ppm) of TOC and no Two 7-foot-diameter filters in series will be used to suspended solids. The 15 lbs/hr is made up of 9.7 lbs/hr from remove organic compounds from the combined distillate. the crystallizer and 5.3 lbs/hr from the evaporator. The origin The filters normally will be operated in lead-lag fashion; that of these numbers is not clear to the committee. It is the com- is, the system will be operated for a specified run time or until mitteeâs understanding that the design of the carbon filters the control compound(s) or parameter (e.g., TOC) appears was based on the 15 lbs/hr TOC mass flow rate, but since at a concentration higher than the treatment objective in the composition and adsorbability of the TOC is not known, the effluent of the second (lag) column in series. At that time, committee does not know how long the carbon filters can be the carbon in the first (lead) filter is replaced with new carbon operated before carbon replacement is needed. The concen- and this filter is then moved to the second (lag) position. tration of specific compounds of interest (target compounds) Operation will be resumed until the effluent concentration with respect to meeting drinking water standards and the from the lag column is again too high, and then the carbon concentration of adsorbable compounds that interfere with replacement process is repeated. The advantage of lead-lag operation comes from opera- 3George Lecakes, Chief Scientist, PCAPP, âPCAPPâs Water Recovery tion of the system until the target compound(s) appears in System and Brine Reduction System Briefing,â presentation to the com- the effluent of the second column. If it were operated only mittee, May 1, 2012.
THE WATER RECOVERY AND BRINE REDUCTION SYSTEMS 29 TABLE 3-2 Mass Flow Rates for Combined Distillates to and from Brine Reduction System Distillate Activated Carbon Filters Combined Distillate to BRS Distillate Carbon Filters, Combined Distillate from Activated Carbon Filters, Identification lb/hr (unless otherwise noted) lb/hr (unless otherwise noted) Flow rate 65,100 (131 gal/min) 65,100 (131 gal/min) Water 65,100 65,100 Calcium 0.0 0.0 Magnesium 0.0 0.0 Sodium 0.2 0.2 Potassium 0.0 0.0 Barium 0.0 0.0 Strontium 0.0 0.0 Ammonium 2.7 2.7 Ammonia 0.0 0.0 Iron 0.0 0.0 Bicarbonate 0.0 0.0 Carbonate 0.0 0.0 Carbon dioxide 0.0 0.0 Chloride 0.1 0.1 Sulfate 0.1 0.1 Nitrate 0.0 0.0 Phosphate 0.0 0.0 Silica 0.0 0.0 TOC 15.0 0.3 Hydroxide 2.6 2.6 Hydrogen 0.0 0.0 Suspended solids 0.0 0.0 TDS (by summation) 320 ppm 95 ppm TSS (by summation) 0.0 ppm 0.0 ppm Temperature 85.1Â°F 85.1Â°F Specific gravity 0.996 0.996 SOURCE: Adapted from George Lecakes, Chief Scientist, PCAPP, âPCAPPâs Water Recovery and Brine Reduction System Briefing,â presentation to the committee, May 1, 2012. (Slide 38) the adsorption of the target compounds is not known. Careful on the biodegradable organic matter in the adsorber influent. monitoring of the effluent quality from the carbon filters will The concentration of microbes in the adsorber effluent is con- be required to determine when the carbon must be replaced. trolled by the backwashing operation; the adsorber effluent Table 3-2 shows that 2 percent of the influent TOC is not will not be sterile, but the concentrations of microbes should removed by the activated carbon, thereby leaving 4.6 ppm not affect the in-plant use of the product water. Table 3-2 (0.3 lbs/hr) of TOC in the effluent. The original source of the indicates that the mass flow rate of suspended solids is zero, information in Table 3-2 is not apparent. but suspended solids could be present because of particles The concentration of suspended solids in the combined entrained in droplets, particularly from the crystallizer, and distillate and the degree of microbial growth within the these particles will likely have biodegradable organic con- adsorber will determine the rate of pressure drop increase, stituents that will serve as substrate for microbial growth in which in turn will control the frequency of backwashing the adsorber. The committee does not know the concentration required to maintain an acceptable pressure drop through of these suspended solids, so the rate of increase of the pres- the filters. Microbial growth in the form of biofilms on the sure drop will have to be determined by monitoring. granular activated carbon (GAC) particles is expected because biodegradable organic matter will likely be in the combined Finding 3-1. Much uncertainty remains whether the prod- distillate. While the organisms from the biotreatment process uct water from the distillate activated carbon filters of should have been killed at the temperatures of 100-plusÂ°C in the PCAPP BRS will meet permit requirements. There is the evaporator and crystallizer, the microbes present will be insufficient detail available on the composition of the total those that grow within the adsorber. The GAC adsorbers are organic carbon in the filter influent water to determine with not sterile and will be populated by microbes that accumulate confidence what the effluent quality will be or what the rate during shipping and installation. These microbes will grow of pressure drop increase will be.
30 REVIEW OF BIOTREATMENT, WATER RECOVERY, AND BRINE REDUCTION SYSTEMS FOR PCAPP Recommendation 3-1. PCAPP operators should monitor the TABLE 3-3â Contaminants of Potential Concern in the carbon filter effluent for compounds of concern and moni- Brine Reduction System Effluent and Applicable Drinking tor the rate of increase of the pressure drop. If the effluent Water Standards fails to meet permit requirements, it may be necessary to Drinking Water operate the carbon system for shorter periods of time before Immobilized Cell Standard maximum carbon replacement. If the rate of pressure drop increase is Bioreactor Effluent, contaminant level too large, the level of suspended solids in the influent may Contaminant Î¼g/L (MCL), Î¼g/L be reduced by modification to the crystallizer and/or more Inorganic frequent backwashing. Arsenic 25.5 10 Chromium 126 100 Lead 25 15a Drinking Water Quality Requirement Organic 1,2 Dichloroethane 10.9 5 The WRS-BRS product water will be recycled within Benzene 17.2 5 the plant to limit well water withdrawals and reduce overall 1,1-Dichloroethene 16.6 7 water use. All of the treated water will be recycled to the pro- Trichloroethylene 13.4 5 cess water feed tanks to be used in the following processes: 1,4-Dioxane 106 3.2b reverse osmosis membrane unit, the agent processing build- aFederal action level: This is a concentration that triggers a remedial ing, ICBs, and cooling towers. The recycled water will only action if exceeded; it is not an MCL. bColorado action level; it is not an MCL. be reused for non-potable water requirements in the plant. SOURCE: BPT (2005), Tables 5-34 and 5-35. In order to maintain the existing permit to recycle the water, however, the effluent must meet primary drinking water stan- dards4 (as determined by quarterly monitoring and testing). Contaminants shown in Table 3-3 could potentially exceed factor in determining the quality of the combined distillate. primary drinking water standards, based on results from The liquid in the crystallizer contains a high concentration bench-scale experiments (BPT, 2005). While such concentra- of TOC and suspended solids.5 Unless complete removal tions in the effluent from the ICBs would be reduced by the of droplets is achieved by the de-entrainment device in BRS, it has not been demonstrated that they will be reduced the crystallizer, the vent stream from the crystallizer will to acceptable levels. If the water fails to meet drinking water contain some TOC and suspended solids. The TOC in the standards, it cannot be reused and the plant would not meet design stream leaving the crystallizer is 9.7 lbs/hr. However, the permit requirements for operation. if the vapor contains as little as five-tenths of 1 percent of entrained drops by mass, then the TOC in the vapor will Finding 3-2. Drinking water standards were developed based increase from 9.7 to 19.1 lbs/hr, and the suspended solids on the need to protect public health; water that is recycled will increase to 9 lbs/hr. Therefore, the composition of the for non-potable use should not have to meet stringent drink- condensate from the crystallizer condenser is very important ing water standards. Furthermore, frequent testing for all and should be monitored carefully. It is noted that the de- regulated compounds would pose an unnecessary expense entrainment device is a chevron type, which is not as efficient at PCAPP and may prevent any water reuse, based on the as a mesh-type de-entrainment device. This is because the current permitting requirements. more efficient mesh type is more easily fouled. If the organic matter in the distillate proves to be a problem, then a more Recommendation 3-2. PCAPP should renegotiate the per- efficient device can be considered. The committee recognizes mitting requirements and consider lesser requirements that that fouling of the de-entrainment device would be increased are suitable for the intended use of the recycled water. and the washing frequency would have to increase. The Crystallizer Finding 3-3. The reported concentration of organic com- pounds and suspended solids in the PCAPP crystallizer Although the quantity of water recovered from the crystal- distillate is uncertain and may not be achieved. If the con- lizer is much smaller than the quantity recovered from the centration of organic compounds of concern is too high, the evaporator, the quality of crystallizer condensate in terms of activated carbon replacement frequency may be too high. the concentration of TOC and suspended solids is a major If the suspended solids concentration is too high, excessive backwashing of the carbon filter may be required. 4State of Colorado, Department of Public Health and Environment, Colo- rado Primary Drinking Water Regulations 5 CCR 1003-1: Primary Drinking Water Regulations, effective November 30, 2010, and Colorado Hazardous Waste Regulations 6 CCR 1007-3: Hazardous Waste, Part 261.24, Table 1â 5George Lecakes, Chief Scientist, PCAPP, âPCAPPâs Water Recovery Maximum Concentrations of Contaminants for the Toxicity Characteristic, System and Brine Reduction System Briefing,â presentation to the com- amended November 20, 2012, effective December 30, 2012. mittee, May 1, 2012.
THE WATER RECOVERY AND BRINE REDUCTION SYSTEMS 31 Recommendation 3-3. The concentrations of the organic that form, and if these crystals are too small, they will not compounds and suspended solids in the distillate from the dewater well. Furthermore, biofilm that is released from the PCAPP crystallizer should be carefully monitored. If they biotreatment system will remain in the filter cake and may prove to be unacceptably high, consideration should be given adversely affect dewaterability. A water content of the belt to upgrading the de-entrainment device in the crystallizer. filter cake of 3.6 percent has been reported,7 which the com- mittee believes to be unrealistically low. Accordingly, the water content will have to be measured after plant operations The Evaporator begin. If the water content is too high to allow shipping of Contamination of the distillate by entrained droplets the cake as a solid to a landfill, it may be necessary to ship should not be as serious for the evaporator as it is for the it as a liquid. crystallizer, because the liquid concentration of TOC and suspended solids is much lower in the evaporator, and a Finding 3-4. The impact of organic matter on the water higher-quality de-entrainment device is used to protect the content of the filter cake from the PCAPP BRS is uncertain. compressor. Recommendation 3-4. In the event that the filter cake cannot be sufficiently dewatered, PCAPP should have a contingency The Deaerator plan to ship it as a liquid to a facility licensed to accept it. Condensate from the vent condenser, which condenses steam leaving the deaerator, also contributes to the quality ISSUES RELATED TO THE ENTIRE BRS of the combined distillate. Contamination of the distillate by entrained droplets should be even less of a problem than it is The BRS for PCAPP will be a first-of-a-kind application for the evaporator, because the liquid concentration of TOC because no plant exists that has treated a similar feed. While and suspended solids is much lower in the deaerator. The Veolia Water Solutions & Technologies, the BRS technology committee understands that provision has been made to use provider, is an experienced supplier of evaporation/crystal- a high-quality de-entrainment device should it be required lization plants and has several dozen plants in operation, the in the deaerator. PCAPP WRS-BRS process will require a very high level of monitoring and operator intervention. ISSUES RELATED TO THE GAS FLOW STREAM Finding 3-5. The BRS for PCAPP will be a first-of-a-kind The Air Emissions Review (Crown Solutions, 2010) system because a similar feed has never been treated before. shows that over 99 percent of the BRS air emissions come The PCAPP WRS-BRS process will require a high level of from the BC evaporator feed deaerator. Two Environmental monitoring and operator intervention. Protection Agency computer models, Water8 and Water9, were used by Crown Solutions to estimate the air emissions Recommendation 3-5. PCAPP should enlist Veolia Water originating from the deaerator.6 There are large predicted dif- Solutions & Technologies, the BRS technology provider, ferences between the two models, and the most conservative for onsite assistance during systemization (start up), initial numbers were used in the design. The simplification used to operation, and operator training. model the deaerator as a stirred tank is a cause for concern. Some compounds will be condensed from the vapor stream Finding 3-6. Given that the biotreatment system has not into the liquid in the deaerator vent condenser. This removal been tested at full scale, the composition and concentrations of organics by condensation has been conservatively ignored of organic and inorganic compounds entering the PCAPP in the design of the OTS carbon beds. Even so, the OTS BRS are unknown. carbon filters are predicted to last about a year before carbon replacement is necessary. Recommendation 3-6. PCAPP should conduct careful monitoring of the feed stream to the BRS and the combined distillate for compounds of concern during start up and initial ISSUES RELATED TO THE SOLIDS FLOW STREAM operation of the plant. As yet unidentified compounds may A primary issue relates to dewaterability of the solids by be present in the feed to the BRS that will have a dispropor- the belt filter. Inclusion of these solids in the filter cake is the tionately high impact on the vent stream from the deaerator easiest way to dispose of them. Organic matter, which is pres- and on the operation of the vent condenser of the off-gas ent in the ICB effluent and will carry through the WRS and treatment system. BRS, is expected to affect the size of the inorganic crystals 7George Lecakes, Chief Scientist, PCAPP, âPCAPPâs Water Recovery 6Additional information is available at http://www.epa.gov/ttnchie1/ System and Brine Reduction System Briefing,â presentation to the com- software/water/water9_3/index.html. Accessed January 17, 2013. mittee, May 1, 2012.
32 REVIEW OF BIOTREATMENT, WATER RECOVERY, AND BRINE REDUCTION SYSTEMS FOR PCAPP Finding 3-7. Acid hydrolysis of biomass could occur upon State of Colorado. 2010. Colorado Primary Drinking Water Regulations 5 H2SO4 addition prior to the deaerator. This could result in CCR 1003-1: Primary Drinking Water. Effective November 30, 2010. Department of Public Health and Environment. Available at http://www. the solubilization of organic compounds such as proteins and sos.state.co.us/CCR/Welcome.do. Accessed April 24, 2013. fatty acids, leading to foaming, higher loading to the GAC, State of Colorado. 2012. Colorado Hazardous Waste Regulations 6 CCR and, eventually, less effective dewatering. 1007-3: Hazardous Waste. Amended November 20, 2012, Effective December 30, 2012. Department of Public Health and Environment. Recommendation 3-7. If biomass solubilization becomes a Available at http://www.sos.state.co.us/CCR/Welcome.do. Accessed April 24, 213. problem for downstream processing, PCAPP should consider Veolia Water Solutions & Technologies. 2010. Bench Scale Evaporation of adding a clarifier between the ICBs and the WRS-BRS. Waste Brine and Filter Testing. Plainfield, Ill. Veolia Water Solutions & Technologies. 2012. Start-up and Operating Man- ual, System Brine Reduction System (BRS) Pueblo Chemical Agent- REFERENCES Destruction Pilot Plant (PCAPP) Project. 55019650-OP. Plainfield, Ill. BPT (Bechtel Pueblo Team). 2005. Test Report for Bench-Scale Evalua- tion of HT, HD, and Energetics Hydrolysis and Biotreatment. Pueblo, Colo.: Bechtel. Crown Solutions Co., LLC. 2010. Air Emissions Review for BRS Distillate and BRS OTS Systems, Equipment Numbers MK-B12-0002 A/B/C (Distillate) and MK-B12-0001 A/B/C (OTS). 943-CS-003. Vandalia, Ohio: Crown Solutions Co., LLC.