- Email: [email protected]
MSF module
Desalination, 14 ( 1974) I-10 @I Elscvicr Scientific Publishing Company. Amsterdam - Printed in The Netherlands
CONSTRUCTION MODULE* CHARLES
AND INITIAL
OPERATION
OF THE V-l-E/MSF
GRUA
Ofice of Saline Wurer, Departmenr of the Interior. Washington, D.C. (U.S.A.) (Raeiwd
November
3, 1973)
SUMMARY
The
VTE/MSF
module being constructed
part of a supplemental
water
supply
plant
at Fountain
of advanced
Valley California,
is
technology.
The plant combines waste water reclamation and sea water desalting to provide a good quality product water that will injected into the Orange County aquifer as a barrier to sea water intrusion and for replenishment of the aquifer. The design of the desalting plant provides a highly adaptable test vehicle for the development of technolom for the VTE/MSF process. The configuration of four VTE evaporative stages and six MSF preheat stages is designed to be expandable to a 12.5 to I5 mgd plant of sixteen evaporative stages and 30 stages of feed heating. INTRODUCTION
The Ofice of Saline Water received authorization from the U.S. Congress to design, construct and test operate a module in March 1970. The appropriation approved with the authorization amounted to S4.200.000, based on conceptual design already completed. The detailed design and site selection remained to be completed. The need for the module, and perhaps its expansion to a possible full train prototype, were the results of the progression in thedevelopment oftechnology for the VTE/MSF process. The construction and operations of the pilot plant at the OSW Wrightsville !kach Facility, the 0.9 mgd plant at the OSW Freeport Facility. and the experimental large bundle configuration of the VTEX at the OSW San Diego Facility were the forerunners and gave the basis for design of module. The Freeport and Wrightsville Beach plants gave the data for coupling of the VTE/MSF process and the San Diego VTEX gave the data for large bundle configuration and design. l Presented at the Fourth September 9-14, 1973.
international
Symposium
on Fresh Water
from the Sea, Heidelberg
2
CH. GRUA
SITI: SELECTION
AND DE-SIGN
The appropriation received, although sufficient for the module construction, did not contain funding for auxiliary equipment (such as steam supply) or procurement of a site. The Orange County Water District (OCWD) of Southern California offered a suitable site that included supporting facilities and a use for the product water from the desalting plant in the module stages and the total product from the prototype desalting plant. These factors led to the decision to locate the module at the OCW D site at Fountain Valley, California (approximately 40 miles south of Los Angeles) and a cooperative agreement between the OCWD and the OSW was entered into in April 1971. Under the terms of the agreement the OSW would design, construct and operate the plant (for a period of up to five years) and the OCWD
would
provide
the site, the supporting
facilities
including
a steam
plant,
the sea water intake and outfall, utility services, and shop-warehouse and office facilities. OCWD would receive the product water from the desalting plant at no cost. The site. therefore. is mutually beneficial to both participants and is a major advance in the development of supplemental water supplies. To insure maximum influence from the U.S. desalting industry for advance technology distillation processes. proposals were solicited from distillation dcsaltins manufacturers and their selected Architect/Engineering firms for the conceptual design phase of the project. Proposals requested the conceptual design of a sea water distillation plant with a maximum scale-up goal of 200 mgd capacity, with the additional requirement that an appropriate module be separately designed. Further, this module would be utilized as part of an expanded prototype plant. From the proposals received, the Envirogenics Co.. a division of the Aerojet General Corp.. of El Monte, California, was selected to complete the detailed drawings and specifications for the construction of the VTE/MSF module in accordance with the conceptual design. The prototype expansion from the 3 mgd module would be to a 12.5 mgd plant. The selection of the VTE/MSF process offered advantages over pure VTE or MSF plants in that the benefits of both processes could be realized with resulting savings in capita! and operating costs. The advantages of the VTE process in the evaporator allows (1) minimum feed to be pretreated chemically and mechanically, (2) minimum sea water concentration at the maximum process temperature, and (3) lower pumping requirements. The MSF process utilized in the feed heater provides advantage over the VTE process in that more stages of feed heating can be used, giving a higher temperature differential, and requiring smaller heat transfer surface. By combining the processes the capita! and operating costs can be significantly reduced. The module is designed to allow process simulation of the fully expanded prototype plant. This is done by designing the four-effect VTE evaporator with the
four-effect configurations that would be utilized in the expanded plant. The MSF feed heater stages are also representative of the expanded plant. Process conditions
CONSTRUCTION
AND
INITIAL OPERATION
OF THE VTE/MSF
MODULE
3
that will exist in the expanded plant can be simulated in the module. Sea water flows. product flows, brine flows, temperatures, brine concentrations, and duties can be controlled to give data in all operating ranges from the low temperature to the high temperature stages of the plant. Thus, by constructing the module, data can be collected for the expanded plant by operations in test modes which will duplicate operations in the full plant. The module plant consists of the four-effect vertical tube evaporator, the six-stage MSF preheater (one stage is used as a trim heater for high temperature operations), the product cooler and feed preheater, the deaerator, barometric condenser and air ejector system. and chemical storage tanks. Materials of construction and design of the evaporator, feed heater. and product cooler meet the requirements of ASME code Section VIII, Division I and are constructed and tested to receive the code stamp for pressure and temperature ratings based on the maximum that can exist. The major component of the piant is the vertical tube evaporator. The evaporator is a cylindrical vessel 116 ft. long and 21 ft. ID. Four evaporative effects and the final condenser are housed in this vessel, with the steam entrance face of the etTects on alternating sides of the vessel. This configuration lessens vessel costs by reducing steam passages and improves venting and entrainment separation. Basically, the vessel is constructed of SA 5 I 5 grade carbon steel: however, corroston considerations have led to lining and cladding of all surfaces in contact with sea water and brine. Only areas in contact with pr,>duct water are exposed carbon
steel. The vertical tubes in each effect are CDA alloy 687 (aluminum-brass). the upper tube sheet is top cladded with 90-10 copper-nickel, and the water boxes are completely lined with stainless steel. The brine pumps and steam passages in each effect have been lined with a corrosion resistant cement mortar lining. which has been proven effective in other OSW plants. The configuration of each of the four effects varies and represents the configuratio,l
to bc utilized in the prototype
plant. The variance from stage to stage
is in the tube diameter, total number of tubes, and spacing. The tube bundles are 10 ft. tall, IO ft. deep, and vary in length from IO ft. to 28 ft. long. The tubes are enhanced surface of the double fluted type to give improved heat transfer coefficients. The first stage. which receives steam from the boilers, does not require entrainment evaporators; however, the entrance face of each of the 2nd effect, 3rd effect. 4th effect, and final condenser are provided with hook and vane separators and knitted wire mesh mist agglomerators for separation of salt water droplets from the vapor. The final condenser is a single pass. flooded tube heat exchanger for steam condensing service. The tubes are CDA alloy 706 (90-10 copper-nickel) 23+ft. long and an average wall thickness of 0.049 in. There are 2,672 3 in. OD tubes, with a spirally indented enhanced surface for improved heat transfer coefficients.
4
CH.
GRUA
The feed heater is a cylindrical vessel 81 ft. long and 133 ft. ID. Flashing brine and product water in the five MSF stags (the sixth stage utilizes boiler steam and functions as a trim heater for high temperature operations) provide heating as they cool to the incoming feed which passes through the heat transfer tubes which arc 1 in. OD. 0.035 in. average wall thickness. fabricated from CDA alloy 706 (90-10 copper-nickel). There are 1238 tubes. 78 ft_ Ions, with stage length varying from S ft. to 19$ ft. Materials of construction are similar to the evaporator, i.e.. basically. carbon steei with all surfaces in contact with sea water or prime coated or clod for corrosion resistance. The total heat transfer arca installed is 24,900 ft. The tubes are mechanically enhanced similar to those in the final condenser by a spirally indented surface. Where tubes pass through the interstage bulkheat teflon, inserts are used to seal each tube in the stage partitions. The water boxes are completely lined with type 316 stainless steel. The brine chambers and trays are lined with the corrosion resistant cement-mortar linings. The 316 stainless steel is utilized for the knitted wire mesh mist eliminators. Brine and product flash devices are fabricated from 316 stainless steel. The product cooler is a cylindrical vessel 32 ft. lo;lg and I If ft. OD. Tubes for feed heating are CDA alloy 706 (90-10 copper-nickel), and the water boxes are completely lined with stainless steel. The total heat transfer area of 8.245 sq. ft. is nlade up of 982 I in. OD.. 0.049 in. wall tubes. with the spirally indented enhanced surface. The sea water deaerrtor is a cylindrical vessel 13 ft. in diameter and 35 ft. tall. install&3 in the vertical position. The carbcn steel vessel is completely epoxy lined for corrosion resistance and contains 2.100 cu. ft. of packing. The vacuum system is 2 three stage, steam jet air ejector system. with barometric precondenser. two intercondensers, and a final condenser. The condensers are epoxy lined carbon steel and the ejeciors are steel with stainless steel suction chambers and noutes. Chemical storage tanks are provided for storage of process chemicals. These are cylindrical. unlined. steel vessels with capacities to operate the prototype plant for two weeks. They will store sulfuric acid, caustic, anti-foam solution. and sulfite. The barometric heat reject &denser utilized only in high temperature operating modes is epoxy lined carbon steel. The cooling and mixing tanks which are required only for module operation are cylindrical vessels fabricated from carbon steel. Ptping system designs have been designed for long life service of corrosion resistant materials. Sea water and brine piping below 150°F have been fabricated from glass reinforced plastic. Cement lined steel pipe is used for services above 150°F. Steam, condensaie and product water piping are fabricated from carbon steel. Chemical feed system lines utilize alloy 20 piping for acid service and PVC and stainless steel piping for other services. The VTE/MSF process utilizes the VTE, forward feed, multiple-effect,
CONSTRUCTlON
AND INITIhL
OPERATION
OF THE VTE//XlSF MODULE
5
falling film in the evaporator. The MSF regenerative feed heating process is counter current to the evaporator flow and a once-through multistage ilash plant. Raw sea water feed passes through the tubes of the product heater and final condenser where it is heated by the cooling product and condenses the steam from the 4th effect of the vertical tube evaporator. Prior to entry in the vacuum deaerator. this feed is treated with sulfuric acid. The deaerator removes CO* and 0, after which the fked is neutralized by the addition of caustic. and oxygen scavenged by the addition of sodium sulfite solution. It is then pumped through the tubes of the MSF preheater_ It is regeneratively heated by the flashing brine and product water. The final stage of the feed heater functions as a trim heater in high temperature operations with the use of boiler steam. Here. saturation temperature corresponding to the 1st evaporative effect is achieved. The feed is then introduced to the water box of the 1st evaporative stage. The water box is flooded and each vertical tube is provided with a distribution nozzle that imparts a swirl pattern to the brir?e as it enters each tube. Equal distribution is thus assured to each tube and the thin film requirement maintained in each tube. Steam from the boiler plant provides the ener_p input as it condenses on the outside of the tube, heating and partia!ly vaporizing the brine as it falls inside the tube. Steam condensate is returned to boiler plant from the I st effect and the trim heater. The brine/vapor mixture falls by gravity through the tube ir.to the sump of the Is effect. Vapor passages are provided to the face of the 2nd vertical tube effect. The brine concentrate flows to the feed heater through a liquid-seal flash device. From the 1st MSF stage the brine flashes to the 2nd MSF stage. which is pressure equalized with the 2nd evaporative stage. The brine flashes from stage to stage and is cooled. producing vapor which condenses on the tubes producing water and heating the incoming feed. Brine from the 2nd MSF stage is pumped to the second stage water box of the evaporator. where it is distributed to the vertical tubes. as in the first effect. The vapor produced in the 1st effect now surrounds
the second effect tubes and is condensed. giving up its latent heat to the brine inside the tubes, which is partially vaporized. The process is repeated through all effects with the vapor from the final effect condensing in the final condenser. The couple of the VTE and MSF processes involve brine transfer between units. condensate transfer from the VTE to the MSF for flashing. and the transfer of vapor between units as the combined process demands. A divided sump in the MSF stages to give minimum concentration brine, feed to the evaporative stages, is accomplished by withdrawing feed from the upstream portion of the stage and returning brine to the downstream portion of the sump. The product from the tube side of the evaporative effects is feed to the MSF stage in equilibrium with effect. This product is drained by gravity and with the product produced in the MSF stages is flashed through the stages of the MSF heater. Steam flows to or
CH. GRUA
6
from the MSF stages to the equilibrium stages in the cvaporatot as the process conditions requite. The location of the plant. five miles inland from the Pacific Ocean, leads to minimizing cold sea water requirements for cooling. The use of on-site cooling towers lessens this requirement. The first cooling tower removes heat from the brine prior to return to the ocean. The second
tower provides
fresh water cooling
in a closed loop for the condensers. vacuum system, and barometric condensers. In high temperature operating modes. the brine is precooled prior to the cooling tower by mixing with incoming sea water. ENVIRONMENTAL
PLANNING
Early in the project schedule, the importance of assessing the environmental impact of the desalting plant and the entire project. including support utilities and the waste water reclamation plant, was recognized. Thus, throughout the design stages environmental planning and recognition was an important and full member of the development team. The OSW and OCWD combined in a joint effort utilizing expertise of plant design engineers. acoustical design engineers. marine biologists. gaseous emissions experts, and environmental planning engineers. The approach to designing a facility which would contribute to the environment with the least possible negative impact was initiated. The startinS point was a complete assessment of all the existing environmental conditions at the plant site and areas affected by the water plants. such as the ocean where sea water intake is located.
the ocean at the brine outfall area. and the residential community in close proximity to the plant site. Baseline data was then available to measure the impact. Next. the impact on the environment of existing similar plants was undertaken. The areas most important were noise. appearance. odors, and outfall characteristics. The baseline conditions and existing plant measurements were used to design the plants to meet the environmental objectives established. and to prepare an environmental impact statement in conformance with Federal and State laws. Theenvironmental studies identified five potentially adverse impacts associated with the plants. These are noise generation, gaseous emissions, heavy metals in the
brine outfall, elevated temperatures of the outfall and potentially unattractive appearance. Of these, noise generation was considered most serious because of the residential area only 500 feet away from the plant location. Ambient noise levels over 24hour periods were measured and found to range from 44dBA at night to 55dBA during the day. The noise criteria selected for the plant was 45dBA at the residential area. This level will insure no adverse noise impact. To maintain these levels, noise will be continuously monitored in the plant boundaries and recorded. To meet low noise levels. the desalting plant design includes low noise steam pressure reducing valves, the addition of acousticai insulation at critical flow fines and acoustical enclosures for all pumps. In addition, intake air silencers
CONSTRUCTION
AND INITIAL OPERATION OF THE VTE/SlSF MODULF
7
on the boiler draft fans are provided as are mufflers on all safety blow off valves. Gaseous emissions from the boilers will be maintained within allowable limits by selecting natural gas as the primary fuel. During curtailment periods, fuel oil will be used, again
with emissions
within
allowable
limits.
Odors which could be emitted from the cooling towers which serve a dual function of cooling for the desalting plant. and ammonia stripping in the waste water reclamation process. will be controlled by maintaining ammonia quantities in the discharge air well below the odor limits. Since the ammonia is in a stable form, it is not oxidized to produce nitrogen oxides. Heavy metal concentrations in the waste stream will be controlled within allowable limits. During module operations these levels will be in the range 0.10 ppm to 0.16 ppm copper and 0.015 to 0.029 ppm nickel. The prototype expansion will give maximum concentration of 0.85 ppm copper and 0.07 ppm nickel. Visual appearance of the plant was also given consideration. Prior to construction activities a 125 ft. greenway was constructed along the west boundary which is adjacent to the residential neighborhood. The greenway was elevated in ail undulating fashion and planted with shrubbery and 20 ft. trees. This effectively screened the plant from visual view in the residential area. CONSTRUCTION
The initial construction activity was the site preparation. To meet seismic conditions. the top ten feet of soil was removed and recompacted to 95% Proctor. This work started in October 1971 and was completed in February 1972. Equipment foundations were started which included 73 step-taper piles poured after driving. Reinforcing steel and concrete were poured to form the pump pits and vessel foundation. This work continued into the summer of 1972. During these operations, orders were placed for long lead items including vessel steel and heat transfer tubes: and fabrication of the process components wasstarted. Thechemical storage tanks were standard equipment and by January 1972 were delivered, completely fabricated, to the site. The evaporator shell was shop fabricated and field assembled. Ten ft. sections were rolled and seam weldeo to the 23 ft. diameter. These were trucked to the site and assembled on temporary “ways” during foundation erection. Nine such sections were machine welded to form the evaporator vessel which when completed was hoisted onto the permanent concrete foundations. The final condenser section (less the final condenser) was welded in place to form the complete vessel less the heads. The effect tube bundles were shop fabricated and delivered to the site for installation in the vessel. Temporary tracks were installed the length of the vessel and the fourth effect installed first from the “hot” end of the vessel. Wheels on the supports allowed the tube bundle to be rolled into final position. The bundle was
design
CH. GRUA
8
then jacked up to the correct elevation where it was shimmed to final elevation_ The following efl’ccts were similarly placed and welded together to form a single unit. In!ernal batYes and top water box partitions were then welded into place to complete the vessel. The heads were then installed. completing the unit. The cement mortar corrosion resistant lining was installed followed by the demisters. Th+ final condenser was tubed in place. and the water box heads installed_ The MSF feed preheater was shop fabricated and assembled with the exceg tion of the heat transfer tubes and the cement mortar lining which were field installed. The structural steel to hold the deaerator and air ejector vacuum system proceeded simultaneously with major vessel installation. The components were set in the steel and piping was ready to start. Process pumps were installed as the foundations were completed. To accomplish the development program tasks, an instrumentation system and data acquisition were added to the module. This instrument package will allow rapid and practically simultaneous collection of data for analysis. Basic computations will also be within the capability of the system. Startup and initial cperations are presently scheduled to start in the summer of 19X. INITIAL
OPERATIONS
The initial operations scheduled for the summer of 1973 will be in the low temperature recycle mode. This mode provides flows identical to those in the prototype plant. To achieve high product flow, a portion of the product flow is recycled through the fed heater. Temprature is controlled by blending cooled product and hot product. To maintain concentration ratio. flow rate, and temperature of the brine, evaporator blowdown brine is blended into the feed stream after it has passed through the product cooler and final condenser. This blended feed is then fed to the deaerator and then into the tubeside of the feed heater. This recycling provides duplication of the exact conditions in the prototype plant. When low temperature recycle operations have been completed, operations to simulate other -conditions in the prototype plant will be carried out. Major emphasis of the development program will bc coniirmation of design conditions by measuring process conditions and comparison to predicted design conditions. Confimation of the test data by energy and material balance will be performed. This data will also give baseline. new plant performance for comparison with later data. Data on the VTE bundle for future bundle design wiil be collected_ Other objectives of the development program are: (I) VTE pressure drops in vapor transfer. to measure the pressure profile in effect to effect vapor transfer. (2) non-condensable test. by introducing measured amounts of noncondensables into the fourth effect to determine effectiveness of bundle design and to establish
CONSTRUCTION
AND
INITIAL
OPERATlON
OF THE VTE/MSF
MODULE
9
vent flow rates. (3) vacuum decay rates, to measure air in leakage into the plant under full vacuum conditions, (4) monitor cleanliness factor. to determine aging characteristics,
(5) final condenser tubes heat transfer coefficient, to give coeflicient
of spirally enhanced tubes, (6) foaming characteristics, to determine the necessity of anti-foam solution addition. (7) feed heater entrainment carryover, to give pressure drop and.‘efficicncy at maximum mass loading and velocities, (8) approach to equilibrium losses in feed heater. (9) process stability, (10) flashing brine behavior induced by the VTEiMSF couple, (I 1) deaerator evaluation, (12) emergency shutdown evaluations to simulate shutdown under emergency conditions, (I 3) vertical hook and vane entrainment separator studies, (14) condensate drain tests to measure the leve! protile of the condensate off the bottom VTE tube sheet. WATER
MANAGEMENT
PROGRAM
The Orange County Water District. created in 1933 by special act of the basin in the coastal State of Californi-l Legislature. manages the groundwater plain area of the lower Santa Ana River in Orar.ge County, California. This area has been on: of the most rapidly expanding area-, in the United States. This high growth rate aqd the change from an r&iculturr.l to an urban economy resulted in oberdroughts of the aquifer. To augment natural recharge. Colorado River water importation was started in !949. This supplemental supply is allowed to percolate into the aquifer in spreading lakes. To prevent sea water intrusion in the aquifer, injection wells are placed along the coast. Degradation of the quality of the Colorado River water to over 800 ppm TDS with anticipated degradation in the range of 15 to 25 ppm annually and the increasing costs of importation. havs led the management of the OCWD to look to other supplemental supplies. Feather River water from Northern California is expected in the 1976 to 1978 time frame; however, supplies will be limited and costs will be higher. Management of OCWD has taken a major step in the construction of “Water Factory 2 1,” intended to provide the technology for supplemental water for the 21st Century. Waste water received from the Sanitation district in the form of secondary effluent will be treated by a reclamation plant. The trickling filter effluent will be chemically clarified, stripped of ammonia, recarbonated. filtered, passed through activated carbon absorption beds and chlorinated. This product will be in the 1,100 to 1,300 ppm TDS ranges and. blended with the desalting plant effluent. will yield product water in the 500 to 600 ppm range. This blended product will be supplied to the coastal injection wells as a barrier to sea water intrusion and for replenishment of the underground aquifer. The construction of the VTE/MSF module will provide the advanced technology for large-scale VTE/MSF desalting plants. The coupling with a lower quality water to form an acceptable quality supplemental water supply gives new
10
CH. GRUA
potential to water managers. The advances made in these areas may well open new vistas
to water planners
for supplemental
writer supply.
REFERENCES
I. F. W. KREBS cf al.. !&XIWater Distdlation Mcdule, A lYlVrl 1.. November 1972. 2. ESVIROGENICS. Development Program VTEfMSF Module. Ofice of Saline Water. Res. Drwlop. Prgr. Rcpr. No. 3164. Novcmbcr 1972. 3. J. R. CO-R. Orange County Water District’s Water Factory 21, LVdcr &sourc~s Eng., January 1972.
CONSTRUCTION MODULE* CHARLES
AND INITIAL
OPERATION
OF THE V-l-E/MSF
GRUA
Ofice of Saline Wurer, Departmenr of the Interior. Washington, D.C. (U.S.A.) (Raeiwd
November
3, 1973)
SUMMARY
The
VTE/MSF
module being constructed
part of a supplemental
water
supply
plant
at Fountain
of advanced
Valley California,
is
technology.
The plant combines waste water reclamation and sea water desalting to provide a good quality product water that will injected into the Orange County aquifer as a barrier to sea water intrusion and for replenishment of the aquifer. The design of the desalting plant provides a highly adaptable test vehicle for the development of technolom for the VTE/MSF process. The configuration of four VTE evaporative stages and six MSF preheat stages is designed to be expandable to a 12.5 to I5 mgd plant of sixteen evaporative stages and 30 stages of feed heating. INTRODUCTION
The Ofice of Saline Water received authorization from the U.S. Congress to design, construct and test operate a module in March 1970. The appropriation approved with the authorization amounted to S4.200.000, based on conceptual design already completed. The detailed design and site selection remained to be completed. The need for the module, and perhaps its expansion to a possible full train prototype, were the results of the progression in thedevelopment oftechnology for the VTE/MSF process. The construction and operations of the pilot plant at the OSW Wrightsville !kach Facility, the 0.9 mgd plant at the OSW Freeport Facility. and the experimental large bundle configuration of the VTEX at the OSW San Diego Facility were the forerunners and gave the basis for design of module. The Freeport and Wrightsville Beach plants gave the data for coupling of the VTE/MSF process and the San Diego VTEX gave the data for large bundle configuration and design. l Presented at the Fourth September 9-14, 1973.
international
Symposium
on Fresh Water
from the Sea, Heidelberg
2
CH. GRUA
SITI: SELECTION
AND DE-SIGN
The appropriation received, although sufficient for the module construction, did not contain funding for auxiliary equipment (such as steam supply) or procurement of a site. The Orange County Water District (OCWD) of Southern California offered a suitable site that included supporting facilities and a use for the product water from the desalting plant in the module stages and the total product from the prototype desalting plant. These factors led to the decision to locate the module at the OCW D site at Fountain Valley, California (approximately 40 miles south of Los Angeles) and a cooperative agreement between the OCWD and the OSW was entered into in April 1971. Under the terms of the agreement the OSW would design, construct and operate the plant (for a period of up to five years) and the OCWD
would
provide
the site, the supporting
facilities
including
a steam
plant,
the sea water intake and outfall, utility services, and shop-warehouse and office facilities. OCWD would receive the product water from the desalting plant at no cost. The site. therefore. is mutually beneficial to both participants and is a major advance in the development of supplemental water supplies. To insure maximum influence from the U.S. desalting industry for advance technology distillation processes. proposals were solicited from distillation dcsaltins manufacturers and their selected Architect/Engineering firms for the conceptual design phase of the project. Proposals requested the conceptual design of a sea water distillation plant with a maximum scale-up goal of 200 mgd capacity, with the additional requirement that an appropriate module be separately designed. Further, this module would be utilized as part of an expanded prototype plant. From the proposals received, the Envirogenics Co.. a division of the Aerojet General Corp.. of El Monte, California, was selected to complete the detailed drawings and specifications for the construction of the VTE/MSF module in accordance with the conceptual design. The prototype expansion from the 3 mgd module would be to a 12.5 mgd plant. The selection of the VTE/MSF process offered advantages over pure VTE or MSF plants in that the benefits of both processes could be realized with resulting savings in capita! and operating costs. The advantages of the VTE process in the evaporator allows (1) minimum feed to be pretreated chemically and mechanically, (2) minimum sea water concentration at the maximum process temperature, and (3) lower pumping requirements. The MSF process utilized in the feed heater provides advantage over the VTE process in that more stages of feed heating can be used, giving a higher temperature differential, and requiring smaller heat transfer surface. By combining the processes the capita! and operating costs can be significantly reduced. The module is designed to allow process simulation of the fully expanded prototype plant. This is done by designing the four-effect VTE evaporator with the
four-effect configurations that would be utilized in the expanded plant. The MSF feed heater stages are also representative of the expanded plant. Process conditions
CONSTRUCTION
AND
INITIAL OPERATION
OF THE VTE/MSF
MODULE
3
that will exist in the expanded plant can be simulated in the module. Sea water flows. product flows, brine flows, temperatures, brine concentrations, and duties can be controlled to give data in all operating ranges from the low temperature to the high temperature stages of the plant. Thus, by constructing the module, data can be collected for the expanded plant by operations in test modes which will duplicate operations in the full plant. The module plant consists of the four-effect vertical tube evaporator, the six-stage MSF preheater (one stage is used as a trim heater for high temperature operations), the product cooler and feed preheater, the deaerator, barometric condenser and air ejector system. and chemical storage tanks. Materials of construction and design of the evaporator, feed heater. and product cooler meet the requirements of ASME code Section VIII, Division I and are constructed and tested to receive the code stamp for pressure and temperature ratings based on the maximum that can exist. The major component of the piant is the vertical tube evaporator. The evaporator is a cylindrical vessel 116 ft. long and 21 ft. ID. Four evaporative effects and the final condenser are housed in this vessel, with the steam entrance face of the etTects on alternating sides of the vessel. This configuration lessens vessel costs by reducing steam passages and improves venting and entrainment separation. Basically, the vessel is constructed of SA 5 I 5 grade carbon steel: however, corroston considerations have led to lining and cladding of all surfaces in contact with sea water and brine. Only areas in contact with pr,>duct water are exposed carbon
steel. The vertical tubes in each effect are CDA alloy 687 (aluminum-brass). the upper tube sheet is top cladded with 90-10 copper-nickel, and the water boxes are completely lined with stainless steel. The brine pumps and steam passages in each effect have been lined with a corrosion resistant cement mortar lining. which has been proven effective in other OSW plants. The configuration of each of the four effects varies and represents the configuratio,l
to bc utilized in the prototype
plant. The variance from stage to stage
is in the tube diameter, total number of tubes, and spacing. The tube bundles are 10 ft. tall, IO ft. deep, and vary in length from IO ft. to 28 ft. long. The tubes are enhanced surface of the double fluted type to give improved heat transfer coefficients. The first stage. which receives steam from the boilers, does not require entrainment evaporators; however, the entrance face of each of the 2nd effect, 3rd effect. 4th effect, and final condenser are provided with hook and vane separators and knitted wire mesh mist agglomerators for separation of salt water droplets from the vapor. The final condenser is a single pass. flooded tube heat exchanger for steam condensing service. The tubes are CDA alloy 706 (90-10 copper-nickel) 23+ft. long and an average wall thickness of 0.049 in. There are 2,672 3 in. OD tubes, with a spirally indented enhanced surface for improved heat transfer coefficients.
4
CH.
GRUA
The feed heater is a cylindrical vessel 81 ft. long and 133 ft. ID. Flashing brine and product water in the five MSF stags (the sixth stage utilizes boiler steam and functions as a trim heater for high temperature operations) provide heating as they cool to the incoming feed which passes through the heat transfer tubes which arc 1 in. OD. 0.035 in. average wall thickness. fabricated from CDA alloy 706 (90-10 copper-nickel). There are 1238 tubes. 78 ft_ Ions, with stage length varying from S ft. to 19$ ft. Materials of construction are similar to the evaporator, i.e.. basically. carbon steei with all surfaces in contact with sea water or prime coated or clod for corrosion resistance. The total heat transfer arca installed is 24,900 ft. The tubes are mechanically enhanced similar to those in the final condenser by a spirally indented surface. Where tubes pass through the interstage bulkheat teflon, inserts are used to seal each tube in the stage partitions. The water boxes are completely lined with type 316 stainless steel. The brine chambers and trays are lined with the corrosion resistant cement-mortar linings. The 316 stainless steel is utilized for the knitted wire mesh mist eliminators. Brine and product flash devices are fabricated from 316 stainless steel. The product cooler is a cylindrical vessel 32 ft. lo;lg and I If ft. OD. Tubes for feed heating are CDA alloy 706 (90-10 copper-nickel), and the water boxes are completely lined with stainless steel. The total heat transfer area of 8.245 sq. ft. is nlade up of 982 I in. OD.. 0.049 in. wall tubes. with the spirally indented enhanced surface. The sea water deaerrtor is a cylindrical vessel 13 ft. in diameter and 35 ft. tall. install&3 in the vertical position. The carbcn steel vessel is completely epoxy lined for corrosion resistance and contains 2.100 cu. ft. of packing. The vacuum system is 2 three stage, steam jet air ejector system. with barometric precondenser. two intercondensers, and a final condenser. The condensers are epoxy lined carbon steel and the ejeciors are steel with stainless steel suction chambers and noutes. Chemical storage tanks are provided for storage of process chemicals. These are cylindrical. unlined. steel vessels with capacities to operate the prototype plant for two weeks. They will store sulfuric acid, caustic, anti-foam solution. and sulfite. The barometric heat reject &denser utilized only in high temperature operating modes is epoxy lined carbon steel. The cooling and mixing tanks which are required only for module operation are cylindrical vessels fabricated from carbon steel. Ptping system designs have been designed for long life service of corrosion resistant materials. Sea water and brine piping below 150°F have been fabricated from glass reinforced plastic. Cement lined steel pipe is used for services above 150°F. Steam, condensaie and product water piping are fabricated from carbon steel. Chemical feed system lines utilize alloy 20 piping for acid service and PVC and stainless steel piping for other services. The VTE/MSF process utilizes the VTE, forward feed, multiple-effect,
CONSTRUCTlON
AND INITIhL
OPERATION
OF THE VTE//XlSF MODULE
5
falling film in the evaporator. The MSF regenerative feed heating process is counter current to the evaporator flow and a once-through multistage ilash plant. Raw sea water feed passes through the tubes of the product heater and final condenser where it is heated by the cooling product and condenses the steam from the 4th effect of the vertical tube evaporator. Prior to entry in the vacuum deaerator. this feed is treated with sulfuric acid. The deaerator removes CO* and 0, after which the fked is neutralized by the addition of caustic. and oxygen scavenged by the addition of sodium sulfite solution. It is then pumped through the tubes of the MSF preheater_ It is regeneratively heated by the flashing brine and product water. The final stage of the feed heater functions as a trim heater in high temperature operations with the use of boiler steam. Here. saturation temperature corresponding to the 1st evaporative effect is achieved. The feed is then introduced to the water box of the 1st evaporative stage. The water box is flooded and each vertical tube is provided with a distribution nozzle that imparts a swirl pattern to the brir?e as it enters each tube. Equal distribution is thus assured to each tube and the thin film requirement maintained in each tube. Steam from the boiler plant provides the ener_p input as it condenses on the outside of the tube, heating and partia!ly vaporizing the brine as it falls inside the tube. Steam condensate is returned to boiler plant from the I st effect and the trim heater. The brine/vapor mixture falls by gravity through the tube ir.to the sump of the Is effect. Vapor passages are provided to the face of the 2nd vertical tube effect. The brine concentrate flows to the feed heater through a liquid-seal flash device. From the 1st MSF stage the brine flashes to the 2nd MSF stage. which is pressure equalized with the 2nd evaporative stage. The brine flashes from stage to stage and is cooled. producing vapor which condenses on the tubes producing water and heating the incoming feed. Brine from the 2nd MSF stage is pumped to the second stage water box of the evaporator. where it is distributed to the vertical tubes. as in the first effect. The vapor produced in the 1st effect now surrounds
the second effect tubes and is condensed. giving up its latent heat to the brine inside the tubes, which is partially vaporized. The process is repeated through all effects with the vapor from the final effect condensing in the final condenser. The couple of the VTE and MSF processes involve brine transfer between units. condensate transfer from the VTE to the MSF for flashing. and the transfer of vapor between units as the combined process demands. A divided sump in the MSF stages to give minimum concentration brine, feed to the evaporative stages, is accomplished by withdrawing feed from the upstream portion of the stage and returning brine to the downstream portion of the sump. The product from the tube side of the evaporative effects is feed to the MSF stage in equilibrium with effect. This product is drained by gravity and with the product produced in the MSF stages is flashed through the stages of the MSF heater. Steam flows to or
CH. GRUA
6
from the MSF stages to the equilibrium stages in the cvaporatot as the process conditions requite. The location of the plant. five miles inland from the Pacific Ocean, leads to minimizing cold sea water requirements for cooling. The use of on-site cooling towers lessens this requirement. The first cooling tower removes heat from the brine prior to return to the ocean. The second
tower provides
fresh water cooling
in a closed loop for the condensers. vacuum system, and barometric condensers. In high temperature operating modes. the brine is precooled prior to the cooling tower by mixing with incoming sea water. ENVIRONMENTAL
PLANNING
Early in the project schedule, the importance of assessing the environmental impact of the desalting plant and the entire project. including support utilities and the waste water reclamation plant, was recognized. Thus, throughout the design stages environmental planning and recognition was an important and full member of the development team. The OSW and OCWD combined in a joint effort utilizing expertise of plant design engineers. acoustical design engineers. marine biologists. gaseous emissions experts, and environmental planning engineers. The approach to designing a facility which would contribute to the environment with the least possible negative impact was initiated. The startinS point was a complete assessment of all the existing environmental conditions at the plant site and areas affected by the water plants. such as the ocean where sea water intake is located.
the ocean at the brine outfall area. and the residential community in close proximity to the plant site. Baseline data was then available to measure the impact. Next. the impact on the environment of existing similar plants was undertaken. The areas most important were noise. appearance. odors, and outfall characteristics. The baseline conditions and existing plant measurements were used to design the plants to meet the environmental objectives established. and to prepare an environmental impact statement in conformance with Federal and State laws. Theenvironmental studies identified five potentially adverse impacts associated with the plants. These are noise generation, gaseous emissions, heavy metals in the
brine outfall, elevated temperatures of the outfall and potentially unattractive appearance. Of these, noise generation was considered most serious because of the residential area only 500 feet away from the plant location. Ambient noise levels over 24hour periods were measured and found to range from 44dBA at night to 55dBA during the day. The noise criteria selected for the plant was 45dBA at the residential area. This level will insure no adverse noise impact. To maintain these levels, noise will be continuously monitored in the plant boundaries and recorded. To meet low noise levels. the desalting plant design includes low noise steam pressure reducing valves, the addition of acousticai insulation at critical flow fines and acoustical enclosures for all pumps. In addition, intake air silencers
CONSTRUCTION
AND INITIAL OPERATION OF THE VTE/SlSF MODULF
7
on the boiler draft fans are provided as are mufflers on all safety blow off valves. Gaseous emissions from the boilers will be maintained within allowable limits by selecting natural gas as the primary fuel. During curtailment periods, fuel oil will be used, again
with emissions
within
allowable
limits.
Odors which could be emitted from the cooling towers which serve a dual function of cooling for the desalting plant. and ammonia stripping in the waste water reclamation process. will be controlled by maintaining ammonia quantities in the discharge air well below the odor limits. Since the ammonia is in a stable form, it is not oxidized to produce nitrogen oxides. Heavy metal concentrations in the waste stream will be controlled within allowable limits. During module operations these levels will be in the range 0.10 ppm to 0.16 ppm copper and 0.015 to 0.029 ppm nickel. The prototype expansion will give maximum concentration of 0.85 ppm copper and 0.07 ppm nickel. Visual appearance of the plant was also given consideration. Prior to construction activities a 125 ft. greenway was constructed along the west boundary which is adjacent to the residential neighborhood. The greenway was elevated in ail undulating fashion and planted with shrubbery and 20 ft. trees. This effectively screened the plant from visual view in the residential area. CONSTRUCTION
The initial construction activity was the site preparation. To meet seismic conditions. the top ten feet of soil was removed and recompacted to 95% Proctor. This work started in October 1971 and was completed in February 1972. Equipment foundations were started which included 73 step-taper piles poured after driving. Reinforcing steel and concrete were poured to form the pump pits and vessel foundation. This work continued into the summer of 1972. During these operations, orders were placed for long lead items including vessel steel and heat transfer tubes: and fabrication of the process components wasstarted. Thechemical storage tanks were standard equipment and by January 1972 were delivered, completely fabricated, to the site. The evaporator shell was shop fabricated and field assembled. Ten ft. sections were rolled and seam weldeo to the 23 ft. diameter. These were trucked to the site and assembled on temporary “ways” during foundation erection. Nine such sections were machine welded to form the evaporator vessel which when completed was hoisted onto the permanent concrete foundations. The final condenser section (less the final condenser) was welded in place to form the complete vessel less the heads. The effect tube bundles were shop fabricated and delivered to the site for installation in the vessel. Temporary tracks were installed the length of the vessel and the fourth effect installed first from the “hot” end of the vessel. Wheels on the supports allowed the tube bundle to be rolled into final position. The bundle was
design
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8
then jacked up to the correct elevation where it was shimmed to final elevation_ The following efl’ccts were similarly placed and welded together to form a single unit. In!ernal batYes and top water box partitions were then welded into place to complete the vessel. The heads were then installed. completing the unit. The cement mortar corrosion resistant lining was installed followed by the demisters. Th+ final condenser was tubed in place. and the water box heads installed_ The MSF feed preheater was shop fabricated and assembled with the exceg tion of the heat transfer tubes and the cement mortar lining which were field installed. The structural steel to hold the deaerator and air ejector vacuum system proceeded simultaneously with major vessel installation. The components were set in the steel and piping was ready to start. Process pumps were installed as the foundations were completed. To accomplish the development program tasks, an instrumentation system and data acquisition were added to the module. This instrument package will allow rapid and practically simultaneous collection of data for analysis. Basic computations will also be within the capability of the system. Startup and initial cperations are presently scheduled to start in the summer of 19X. INITIAL
OPERATIONS
The initial operations scheduled for the summer of 1973 will be in the low temperature recycle mode. This mode provides flows identical to those in the prototype plant. To achieve high product flow, a portion of the product flow is recycled through the fed heater. Temprature is controlled by blending cooled product and hot product. To maintain concentration ratio. flow rate, and temperature of the brine, evaporator blowdown brine is blended into the feed stream after it has passed through the product cooler and final condenser. This blended feed is then fed to the deaerator and then into the tubeside of the feed heater. This recycling provides duplication of the exact conditions in the prototype plant. When low temperature recycle operations have been completed, operations to simulate other -conditions in the prototype plant will be carried out. Major emphasis of the development program will bc coniirmation of design conditions by measuring process conditions and comparison to predicted design conditions. Confimation of the test data by energy and material balance will be performed. This data will also give baseline. new plant performance for comparison with later data. Data on the VTE bundle for future bundle design wiil be collected_ Other objectives of the development program are: (I) VTE pressure drops in vapor transfer. to measure the pressure profile in effect to effect vapor transfer. (2) non-condensable test. by introducing measured amounts of noncondensables into the fourth effect to determine effectiveness of bundle design and to establish
CONSTRUCTION
AND
INITIAL
OPERATlON
OF THE VTE/MSF
MODULE
9
vent flow rates. (3) vacuum decay rates, to measure air in leakage into the plant under full vacuum conditions, (4) monitor cleanliness factor. to determine aging characteristics,
(5) final condenser tubes heat transfer coefficient, to give coeflicient
of spirally enhanced tubes, (6) foaming characteristics, to determine the necessity of anti-foam solution addition. (7) feed heater entrainment carryover, to give pressure drop and.‘efficicncy at maximum mass loading and velocities, (8) approach to equilibrium losses in feed heater. (9) process stability, (10) flashing brine behavior induced by the VTEiMSF couple, (I 1) deaerator evaluation, (12) emergency shutdown evaluations to simulate shutdown under emergency conditions, (I 3) vertical hook and vane entrainment separator studies, (14) condensate drain tests to measure the leve! protile of the condensate off the bottom VTE tube sheet. WATER
MANAGEMENT
PROGRAM
The Orange County Water District. created in 1933 by special act of the basin in the coastal State of Californi-l Legislature. manages the groundwater plain area of the lower Santa Ana River in Orar.ge County, California. This area has been on: of the most rapidly expanding area-, in the United States. This high growth rate aqd the change from an r&iculturr.l to an urban economy resulted in oberdroughts of the aquifer. To augment natural recharge. Colorado River water importation was started in !949. This supplemental supply is allowed to percolate into the aquifer in spreading lakes. To prevent sea water intrusion in the aquifer, injection wells are placed along the coast. Degradation of the quality of the Colorado River water to over 800 ppm TDS with anticipated degradation in the range of 15 to 25 ppm annually and the increasing costs of importation. havs led the management of the OCWD to look to other supplemental supplies. Feather River water from Northern California is expected in the 1976 to 1978 time frame; however, supplies will be limited and costs will be higher. Management of OCWD has taken a major step in the construction of “Water Factory 2 1,” intended to provide the technology for supplemental water for the 21st Century. Waste water received from the Sanitation district in the form of secondary effluent will be treated by a reclamation plant. The trickling filter effluent will be chemically clarified, stripped of ammonia, recarbonated. filtered, passed through activated carbon absorption beds and chlorinated. This product will be in the 1,100 to 1,300 ppm TDS ranges and. blended with the desalting plant effluent. will yield product water in the 500 to 600 ppm range. This blended product will be supplied to the coastal injection wells as a barrier to sea water intrusion and for replenishment of the underground aquifer. The construction of the VTE/MSF module will provide the advanced technology for large-scale VTE/MSF desalting plants. The coupling with a lower quality water to form an acceptable quality supplemental water supply gives new
10
CH. GRUA
potential to water managers. The advances made in these areas may well open new vistas
to water planners
for supplemental
writer supply.
REFERENCES
I. F. W. KREBS cf al.. !&XIWater Distdlation Mcdule, A lYlVrl 1.. November 1972. 2. ESVIROGENICS. Development Program VTEfMSF Module. Ofice of Saline Water. Res. Drwlop. Prgr. Rcpr. No. 3164. Novcmbcr 1972. 3. J. R. CO-R. Orange County Water District’s Water Factory 21, LVdcr &sourc~s Eng., January 1972.