EPA-600/2-76-017
March 1976
Environmental Protection Technology Series
RENOVATION OF
INDUSTRIAL INORGANIC WASTEWATER BY
EVAPORATION WITH INTERFACE ENHANCEMENT
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-76-017
March 1976
RENOVATION OF INDUSTRIAL INORGANIC WASTEWATER
BY EVAPORATION WITH INTERFACE ENHANCEMENT
by
Hugo H. Sephton
Sea Water Conversion Laboratory
University of California
Richmond, California
Project Number R-802753
Project Officer
Richard B. Tabakin
Industrial Pollution Control Division
Industrial Environmental Research Laboratory (Cincinnati)
Edison, New Jersey 08817
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Industrial Environmental
Research Laboratory, U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the con-
tents necessarily reflect the views and policies of the U.S. En-
vironmental Protection Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation for
use.
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FOREWORD
The multi-media character of pollution resulting from
the extraction, processing, conversion, and utilization of
energy and mineral resources, and from industrial processing
and manufacturing, requires an approach which recognizes
the complex impact of these operations on our environment.
The Industrial Environmental Research Laboratory,
Cincinnati, utilizes a multidisciplinary approach in the
development and demonstration of technologies to effectively
deal with the pollution associated with these operations.
The Laboratory assesses the environmental and socio-economic
impact of industrial and energy-related activities and identifies
and evaluates control alternatives.
This report evaluates a novel method of increasing the
efficiency of an evaporative process to recycle three types of
industrial waste waters; power plant cooling tower blowdown,
industrial steam generation blowdown, and an acidic mine
drainage type of wastewater. The method, known as interface
enhancement, involves the addition of a surfactant to the
wastewater stream prior to passing the stream through a vertical
tube evaporator. For all three waste streams a considerable
increase in heat transfer performance was observed. It was
concluded that substantial capitol and operating cost savings
could be realized by modifying existing evaporation systems to
accommodate the interface enhancement technique.
This project was one of several projects undertaken by
IERL-C to demonstrate new approaches to increasing the reuse
of industrial wastewater, a source of much water pollution
throughout the country. This report will be especially interesting
to those individuals involved in the design or operation of
industrial systems which use large amounts of water for cooling
purposes, and to individuals involved in industrial waste water
research.
David G. Stephan
Director
Industrial Environmental Research Laboratory.Cincinnati
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ABSTRACT
A novel method of vertical tube evaporation (VTE) to improve heat
transfer performance was applied to the concentration of three types of in-
dustrial wastewaters. This method, interface enhancement, relies upon the
addition of a few parts per million of a selected surfactant to the waste-
water feed followed by imposed two-phase foamy liquid-vapor flow over the
heat transfer surfaces. Applied to the concentration of power plant cooling
tower blowdown and boiler blowdown, interface-enhanced VTE provided an
approximate 120 percent increase in the usual VTE heat transfer performance,
using a 5,000 gpd pilot plant having double-fluted aluminum-brass distillation
tubes, under process conditions that are realistic for large industrial plants.
Acidic mine drainage water, concentrated by double-fluted titanium evaporator
tubes provided about a 60 percent heat transfer performance enhancement.
Beneficial side effects of the surfactant additive were to inhibit the crystal-
lization of solutes, permitting concentration of the wastewaters to smaller
volumes. This work indicates feasibility and improved economics for renova-
tion-recycle of each of the three types of wastewater examined.
Industrial feasibility demonstration projects for each of the three waste-
water types examined are recommended. A method and flow diagram for the de-
salination-recycle of power plant cooling tower blowdown by interface-
enhanced VTE integrated with a typical power plant coolant cycle and utiliz-
ing waste heat from that cycle, is described and recommended.
This report was submitted in fulfillment of grant number R802753 under
partial sponsorship by the Environmental Protection Agency. Work was com-
pleted as of May 31, 1975.
*U.S. Patent No. 3,846,254, November 5, 1971*
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CONTENTS
Page
ABSTRACT jv
LIST OF FIGURES vi
ACKNOWLEDGMENTS vjf
SECTIONS
I CONCLUSIONS 1
II RECOMMENDATIONS 3
III INTERFACE-ENHANCED VERTICAL TUBE EVAPORATION 5
INTRODUCTION 5
BACKGROUND 7
PROJECT PLAN 10
UPFLOW VTE PILOT PLANT FACILITY USED FOR THIS STUDY 12
UPFLOW VTE PYREX GLASS EVAPORATOR 20
DISTILLATION TUBES USED IN THE VTE PILOT PLANT 23
EXPERIMENTAL WORK 25
1) Investigation of Cooling Tower Slowdown 25
2) Industrial Steam Generator Slowdown Concentration 36
3) Acidic Mine Drainage Concentration k6
DISCUSSION 53
REFERENCES 58
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FIGURES
Number Title Page
1 SIMPLIFIED FLOW DIAGRAM FOR UPFLOW VTE PILOT PLANT 13
2 UPFLOW VERTICAL TUBE EVAPORATION PILOT PLANT 14
3 STEAM SIDE FLOW PATTERN 16
4 TYPICAL TWO-PHASE FLOW THROUGH VTE ORIFICE PLATE 19
5 FOAMY ANNULAR FLOW FROM DISTILLATION TUBES 21
6 PYREX TUBE CRYSTALLIZING EVAPORATOR 22
7 AXIALLY AND SPIRALLY DOUBLE-FLUTED DUTILLATION TUBES 24
8 ENHANCEMENT OF HEAT TRANSFER PERFORMANCE IN VTE 27
OF MOHAVE COOLING TOWER SLOWDOWN
9 HEAT TRANSFER PERFORMANCE OF MOHAVE COOLING TOWER BLOWDOWN 28
10 CONCENTRATION OF MOHAVE POWER PLANT COOLANT BLOWDOWN 30
BY INTERFACE-ENHANCED VERTICAL TUBE EVAPORATION AT 130°F
11 RENOVATION AND RECYCLE OF POWER PLANT COOLING TOWER BLOWDOWN 31
12 UPFLOW VTE PERFORMANCE WITH BOILER BLOWDOWN 38
13 INTERFACE ENHANCEMENT RESPONSE WITH BOILER BLOWDOWN 40
]k INTERFACE-ENHANCED UPFLOW VTE PERFORMANCE WITH BOILER *»1
BLOWDOWN
15 10-FOLD CONCENTRATION OF BOILER BLOWDOWN 1*3
16 INTERFACE ENHANCEMENT RESPONSE WITH COPPER TUBES 1»9
17 INTERFACE ENHANCEMENT RESPONSE WITH ALUMINUM-BRASS AND 51
TITANIUM TUBES
VI
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ACKNOWLEDGMENTS
This work was supported by a research grant from the Environmental
Protection Agency and, in part, by the University of California. The author
gratefully acknowledges the technical assistance of Mr. Carl L. Freel, and
the helpful interest of Mr. Richard B. Tabakin of the EPA. Assistance in
providing wastewater samples for the test program was received from the
Bechtel Power Corporation and several other industrial entities. Thanks
to Margaret Knight for typing the manuscript.
VI I
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SECTION I: CONCLUSIONS
The following conclusions were drawn from or confirmed by the work
reported here:
1) The interface-enhanced mode of operating a vertical tube evaporator
(VTE) is technically feasible for the concentration-recycle of each of the
three types of industrial wastewaters examined; the main beneficial effects
to be anticipated are substantial capital and/or operating cost savings.
Evaporator heat transfer performance enhancements ranging from 60 to 150
percent were demonstrated under process conditions that are realistic for
industrial operation.
2) Side effects of the interface-enhancement agent examined provided
additional advantages; these side effects are an inhibition of the onset
of crystal formation during the gradual concentration of wastewater and the
dispersant effect of the surfactant additive.
3) In the case of the concentration-renovation of Mohave Power Plant
cooling tower blowdown, a tenfold evaporation was readily obtained after the
addition of 10 ppm of a selected surfactant, at heat transfer performance
rates about double those obtained without the additive. These results
indicate that cooling tower blowdown can be most economically desalted for
recycle by integrating a VTE loop within the temperature span available in
the coolant cycle of a large power plant, as shown in the flow diagram of
Figure 1 1.
4) Several alternative methods of cooling tower blowdown renovation-
recycle can benefit significantly from the adoption of the interface-enhanced
mode of operating an evaporator. These include concentration of blowdown
by vapor compression VTE, by multiple effect VTE with upflow or downflow of
the feed, and by low temperature VTE utilizing waste heat for evaporation.
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5) In the case of examining an industrial boiler blowdown the applica-
tion of interface-enhanced VTE provided substantial benefits; the evaporator
heat transfer performance was more than double its conventional performance,
and a concentration factor of 20 was readily obtainable without significant
precipitation of solutes occurring.
6) The renovation-recycle of industrial boiler blowdown by either the
single effect vapor compression VTE method or by a multiple effect VTE is
feasible and appears economically acceptable with the interface-enhanced
mode of operation.
7) In the case of the acidic mine drainage type of wastewater examined
it was apparent that the addition of a surfactant before its concentration
by upflow VTE provides the benefits of retaining particulates in suspension,
inhibiting the crystallization of solutes, and of increasing the evaporator
heat transfer performance substantially. Because of the highly corrosive
nature of this type of effluent, titanium tubes and stainless steel equip-
ment are indicated to be advisable; copper-based alloys were indicated as
unsuitable. The heat transfer performance of titanium distillation tubes
was increased by about 60 percent by the addition to the feed of about 10
ppm of a selected surfactant.
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SECTION II: RECOMMENDATIONS
The following recommendations are submitted, based on the work performed
under this project:
1) In order to demonstrate the advantages of this approach for industrial
wastewater renovation-recycle to the satisfaction of all interests, a mobile
pilot plant facility should be designed in cooperation with an architect-
engineering firm knowledgeable in the power plant field. Subsequent field dem-
onstration tests should be jointly sponsored by several interested utilities and
carried out in collaboration with such interests, to provide a means for the
rapid evaluation and possible adoption of these procedures by industry.
2) Regarding industrial boiler blowdown renovation, it is recommended
that a demonstration project be undertaken by a large industrial complex, for
instance a petroleum refinery. The objective of such a project would be to
design, construct and field test a vapor compression VTE plant of a size and
scope that will satisfy industry and the EPA about the application, cost and
benefits of the interface-enhanced mode of VTE operation for industrial
wastewater recycle.
3) In regard to the concentration and recycle of highly corrosive
effluents, such as acid mine drainage and plating plant effluents, it is
recommended that further definitive test data be obtained by means of a
relatively small (about 3 to 5,000 gpd) mobile vapor compression VTE, con-
structed of titanium and stainless steel, and tested on three typical waste-
waters.
k) The beneficial interface-enhanced heat transfer effects have now
been well demonstrated on several types of aqueous media. However, the effects
of surfactant additives on evaporation under crystallizing or precipitation
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VTE conditions have not been adequately defined. It is recommended that
further study be carried out in this area in the interest of wastewater
renovation-recycle.
5) The side effects of the surfactant additives that have been identified
appear to be beneficial. These are the dispersant effect, the inhibition of
solute cyrstal1ization during concentration, and the inhibition of erosion and
corrosion. These side effects should be more precisely defined, especially the
longterm benefits and disadvantages, including the useful lifetime of the sur-
factant additives during continuous recycle and the fate of their thermal
degradation products.
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SECTION I!I
INTERFACE-ENHANCED VERTICAL TUBE EVAPORATION
INTRODUCTION
The objective of this project was to obtain heat transfer performance
data on the application of a novel evaporative procedure for wastewater reno-
vation by pilot plant tests with several industrial wastewaters. These data
would provide a basis for evaluating the process feasibility, and the cost
reductions available in the possible future industrial application of this
procedure.
The novel distillation method, "Interface Enhancement Applied to the
Evaporation of Liquids," (1) relies upon the addition of a few parts per
million (ppm) of a selected surfactant to the liquid to be evaporated,
followed by imposing foamy two-phase, vapor-liquid flow over the heat transfer
surfaces. This mode of flow provides a k- to 6-fold increase in the brineside
or evaporation-side coefficient, which in turn provides an evaporator per-
formance enhancement or overall heat transfer coefficient increase of 50 to
200 percent, for multieffect vertical tube evaporation (VTE) performed under
otherwise conventional process conditions ( 1 ). The degree of enhancement
depends on the process conditions applied, such as whether the upflow or
downflow VTE mode is used, the type of distillation tube installed, and the
evaporation temperature and the temperature difference applied as well as the
type and concentration of surfactant additive used (2, 3, b, 5). In the case
of upflow VTE, the application of interface enhancement has a very significant
further effect of improving the upflow tubeside hydrodynamic stability. This
follows from the improved foamy mode of flow, whereby the liquid holdup in
the distillation tube is reduced by about a factor of 5. Stated differently,
the liquid residence time is substantially reduced; this means that the
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hydrostatic pressure drop, contributing a parasitic loss, is much reduced.
The net result is that the tubeside hydrodynamic pressure gradient is sub-
stantially lowered, usually by a factor ranging from 3 to 6. Consequently,
the upflow process stability is significantly improved; this in turn permits
stable upflow VTE operation at reduced effect-to-effect temperature differences,
in the interest of saving heat, or fuel (6, 7). It also permits relatively
high heat transfer performance at low evaporation temperatures and under
relatively low temperature differences (AT); such as used in vapor compression
VTE.
Another distinct advantage of the interface-enhanced mode of VTE operation,
especially meaningful for wastewater renovation, is that the surfactant addi-
tive tends to suppress crystallization of solutes, disperses particulates
present in the distilland to prevent their deposition on heat transfer surfaces,
and that it can provide some erosion-corrosion protection by the formation of
a surfactant layer adsorbed to the heat transfer surface and other surfaces (8).
The planned scope of work included pilot plant tests with three typical
industrial wastewaters; test data were to be obtained under typical upflow
VTE process conditions including data with the interface-enhanced mode of
operation. The wastewaters tested were power plant cooling tower blowdown,
industrial steam generator (boiler) blowdown and an acidic mine drainage type.
The pilot plant used was available from the author's earlier OSW-sponsored
projects on the development of enhanced heat transfer for VTE of seawater.
Some modifications were made for the tests reported here. In addition a small
Pyrex glass-tubed upflow VTE was constructed to determine the effect of sur-
factant additives on solute crystallization during the gradual concentration
of these wastewaters.
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BACKGROUND
The interface-enhanced mode of upflow VTE had been fairly well defined
in previous work in this laboratory, at least for seawater conversion under
typical multieffect process conditions (1, 2, 3, ^, 5). Several reports
have also appeared on work done elsewhere, confirming the effectiveness of
this enhancement procedure for downflow VTE (9) and for horizontal tube
multieffect evaporation (HTME) (10).
Approximately four years of development work by pilot plant testing in
this laboratory preceeded the present work. During this development period,
the interface enhancement effects were defined for a series of special and
commercial grade full-sized distillation tubes of both smooth-walled, and
various fluted-wall configurations. The process conditions applied included
all the most significant parameters imposed in the individual effects of a
real, industrial installation. Heat transfer performance enhancement effects
had been demonstrated to be consistently obtained with a series of about
twelve different surfactants and with both freshwater and seawater feeds
under all of the usual range of upflow VTE process conditions (3, 5, 6).
The magnitude of this enhancement effect varied in a consistent manner,
depending upon the type of distillation tube, the type and concentration of
surfactant used and the process conditions applied within the usual multi-
effect VTE range. Thus it was known that the most effective upflow VTE
performance enhancement effects were obtained when the feed entering the
distillation tubes was caused to flash or partially vaporize into a two-
phase liquid-vapor flow, for instance, by passing a preheated feed through
a suitable nozzle or orifice (3). In this manner evaporation of the liquid
is assured to occur along the entire length of the distillation tube.
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The most significant interface enhancement effects have been shown to be
the following (3, 5):
1) The imposed foamy mode of vapor-liquid flow over the heat transfer
surfaces provides for thin-film, wiped-film evaporation. This results from
the continuous renewal of the liquid film laid down onto this surface from
liquid phase carried interstitially to the vapor bubbles as a network of
foam swept over this surface by the vapor phase flow. This thin-film evapora-
tion mechanism applies to both upflow and downflow of the feed. It is im-
portant, for high interface enhancement, that the foamy layer be maintained
throughout the length of the distillation tubes. This requires initiation
of foamy flow as or before the feed enters these tubes, for instance, by
flashdown at an orifice; continuation of the foamy layer flow depends on an
adequate rate of evaporation, yet a not excessive rate of vapor flow which
tends to break the foam up. These parameters determine the diameter and
length of distillation tube of a particular metal and flute profile best
suited a given evaporation temperature and AT applied.
2) The second enhancement effect applies to the upflow VTE mode only.
It has been shown that the residence time of the liquid phase (feed) is sub-
stantially reduced as a result of the imposed foamy vapor-liquid flow through
the tubes. Stated in other words, the liquid hold-up is reduced, and this
follows from the more rapid passage of the liquid phase through the tubes as
a result of the foamy consistency. As a consequence of this reduced liquid
hold-up, the hydrostatic pressure drop axially through the distillation tubes
is substantially reduced. This in turn provides for the 3- to 10-fold hydro-
dynamic tubeside pressure drop reductions. These actual two-phase pressure
drops are constituted of a hydrostatic element, and a hydrodynamic element
which include accelerational and frictional pressure drop elements. Since the
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downflow VTE has a very low hydrodynamic pressure drop and no hydrostatic
pressure drop element, the pressure drop reduction effect of interface en-
hancement does not apply to this mode of VTE. This explains, in part, why
interface enhancement is about 50 percent less effective in downflow VTE
applications. Another reason is that stable,foamy two-phase flow is much
more readily maintained in upflow VTE than in the downflow mode, and at
much lower surfactant concentrations.
One of the main additional advantages of interface-enhanced upflow VTE
over the downflow application follows from the fact that the former operation
does not require effect-to-effect feed transfer or recirculation pumps. This
provides a significant capital cost saving and more significant operation-
maintenance (0 £• M) cost savings. A recent cost comparison study performed
by Kaiser Engineers (11) concluded that the capital cost savings provided by
interface-enhanced upflow VTE over the conventional downflow mode amount to
at least 25 percent and that 0 5- M cost savings would be about 30 percent.
The most significant single effect of interface enhancement is to improve
the upflow VTE tubeside stability; this permits stable operation even at
relatively low AT-values. As a consequence, one can increase the number of
effects permissible within the available temperature span of 120 to 250 F
usually available for a multieffect VTE plant. As a direct result of the
increased number of effects,the gain ratio, or economy ratio, is increased
by up to 50 percent In the interest of saving steam or fuel. Another result
is that design flexibility is improved, allowing improved optimization of
capital versus energy costs (k)-
Apart from process development knowledge and experience, a 5,000 gallon per
day (gpd) upflow VTE pilot plant was available in this laboratory from previous
projects sponsored by the Office of Saline Water (OSW), for use in the present study.
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PROJECT PLAN
a) An initial phase of about three months was planned during which time
the available equipment and facilities were to be reconditioned and improved,
in preparation for the main phase of the work. Some preliminary exploratory
work would also be done during this phase. Equipment and facilities made
available for this project from California State and OSW sources were inventoried
at about $75,000.
b) The main phase of this study included definitive tests, with the 5,000
gpd pilot plant, on typical wastewaters evaporated under realistic upflow VTE
multieffect process conditions, both without and with surfactant additives to
these feeds. It was anticipated that at least three typical industrial waste-
waters would be examined. These waters would be selected in collaboration with
EPA staff, or as suggested by EPA, to ensure relevance of the test data.
The main benefits to be expected from this project were:
a) A substantial reduction in the cost of renovating industrial wastewaters
by VTE, which produces a high quality distilled water for beneficial use. The
dispersing effects of surfactant additives, to prevent fouling and scaling of
heat transfer surfaces, were to be evaluated. This should permit evaporation
to increased solute concentrations, and the evaporation of wastewaters that
contain particulate and colloidal matter. Disposal of these relatively small
residual concentrates would be at reduced cost;
b) A broadened scope for applying evaporation processes in the renova-
tion of industrial wastewaters, to advance the state of the art of pollution
abatement. A reeent study by Kaiser Engineers ( 6 ) concluded that capital
cost savings of about 25 percent and annual cost savings of about 33 percent
are obtainable on a 12.5 MGD downflow VTE/MSF plant if an upflow VTE/MSF process
with interface enhancement is adopted instead of the downflow mode.
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c) Advancement of our understanding of the mechanisms responsible for
the substantial increase in heat and mass transfer rates, obtained by the
interface enhancement method of evaporation to be applied in this work.
Additional benefits anticipated included training of students while
working toward their MS or PhD degrees. Well-trained personnel should provide
a valuable service to the public, in the environmental and public utility
fields. The proposed project would also be of benefit to the University of
California, by providing opportunities and facilities for furthering the
educational process, generating innovations and advancing the state of the art
in the field of wastewater renovation.
The legal requirements for industrial compliance with water quality
standards place a high priority on the rapid development of suitable tech-
nology for purification of wastewater. The interface enhancement method for
VTE operation of this proposal appeared to provide a very promising tool for
complying with these requirements in some instances. Its development, and
introduction into this field seemed well justified.
Surfactant Additive Recovery-Recycle
A method of recovery from concentrated brine and recycle of 95~97 percent
of the surfactant, added as a heat transfer enhancement agent in the VTE, has
been developed through the pilot plant stage ' . This procedure, foam
fractionation, provides simultaneous benefits such as removing (and allowing
recovery) of metal ions of interest as well as particulates, notably ferric
hydroxide from the VTE blowdown concentrate. The foam fractionation procedure
is economically attractive.
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UPFLOW VTE PILOT PLANT FACILITY USED FOR THIS STUDY
A versatile single effect, 5,000 U.S. gpd, 18-tube VTE pilot plant was
designed and constructed primarily with OSW support under earlier research
and development projects for application of interface enhancement to seawater
desalting (k). This pilot plant was also utilized in this EPA-sponsored
work,and is represented in the simplified flow diagram of Figure 1 and shown
photographed in Figure 2. This facility, comprising a reboiler loop, an
18-tube VTE loop and a heat reject loop, could impose all the significant
process conditions, relevant to any one of the effects in a typical multi-
effect VTE plant, upon the 18-tube VTE loop. This loop was constructed from
nonferrous materials compatible with wastewater. The tubes used for these
tests were double-fluted aluminum-brass (Yorkshire Imperial Metals Ltd.) of
0.042-inch wall thickness, 2-inch OD x 10-foot heated length, in an oxidized-
annealed condition. The industrial wastewater tested was recirculated through
the VTE loop. The interface-enhanced data were obtained after the further
addition of a selected surfactant to the feed in 5 to 50 ppm concentration.
The VTE loop was washed with fresh water and charged a fresh batch of wastewater
before each test series.
In operation, the desired steam-side temperature (Ts) was preset on an
automatic controller actuating a motorized steam valve to admit boiler steam
(at^Spsig) to the tubes of the U-tube heat exchanger in the reboiler loop,
shown on the far right of Figure 1. Fresh water was evaporated on the shell-
side of this heat exchanger while in upflow, two-phase flow. This two-phase
stream was injected tangentially into the large-domed vapor release vessel
on the upper right of Figure 1. The residual liquid phase was recirculated
while the vapor produced was conveyed to the VTE loop to serve as heating
steam for the 18-tube bundle. To determine the total heat flux (Oj of the
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COOLANT
RECYCLE
COOLANT
HEAT REJECT LOOP
UPFLOW VTE EFFECT
REBOILER LOOP
SIMPLIFIED FLOW DIAGRAM FOR UPFLOW VTE PILOT PLANT
FIGURE I
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Hlk-JB
UPFLOW VERTICAL TUBE EVAPORATION PILOT PLANT
FIGURE 2
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18-tube bundle the condensates off the steam-sides of these tubes were
collected and their rates of flow measured, individually for ^ selected tubes
and, collectively for the remaining 15 tubes. These measurements showed
that variations in flux for individual tubes were within 2 percent. A
measured fraction of the total steam flow was vented from the 18-tube bundle
and condensed, to remove noncondensables and to assure positive flow across
the steam-sides of the tube bundle. All these steam-side condensates were
maintained under vacuum and returned to the reboiler loop with which it
comprised a closed cycle.
Having the steam-side temperature (Ts) controlled at a level present on
the automatic controller, the desired temperature difference (AT) across the
walls of the 18-tube bundle depended upon the total heat flux (Qj and the
duty of the heat reject loop shown on the left of Figure 1. In order to
maintain this duty at a steady rate, a large volume of relatively hot water
coolant was recirculated under moderate pressure (40 psig) through the heat
reject loop at about 1,000 gallons per minute, and cold water was constantly
injected into this coolant with the simultaneous rejection of hot water from
it. The AT for the VTE loop was in this way controlled at any desired level
(±0.1 F), after the steam-side temperature, Ts, became stabilized at its
selected, preset level (±0.1°F).
Wastewater feed was admitted into the VTE loop under vacuum, and recir-
culated at about 100 F until deaeration was completed under evacuation. The
steam-sides of the tubes were in a dark-brown, ox idized-annealed and fully
stabilized condition after intermittent operation for about 2 years without
any reconditioning. The 18-tube bundle and steam-side flow pattern are shown
in Figure 3. providing positive flow across the entire bundle and a measured
vent rate (3~10%) collected along the entire length of the tube bundle.
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STEAM SIDE FLOW PATTERN
Distillation tubes were spaced 0.5-inch on a triangular pattern, with dummy
tubes (shaded) and baffles to ensure continuous steamside flow from the
plenum to the vent tube along the entire bundle length. The vent tube had
0.125-inch holes drilled at 6-inch intervals along its entire length for
adequate vent collection.
FIGURE 3
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Under typical operating conditions, the temperature of the deaerated
feed was adjusted to correspond with the steam-side temperature (±1 F) by
passing it through a steam-heated exchanger, controlled by an automatic steam
control valve, and was then dumped into a standing leg. From this standing
leg the feed flowed through the feed distributor into the inlet ends of the
18-tube bundle, under force of gravity and in response to the inter-effect
temperature difference. Upon passing through the orifice plate, the feed
flashed down to provide a two-phase vapor-brine system for evaporative flow
up the tubes. Two-phase flow up the tubes was maintained by the vapor released
from the brine; continuous evaporation of the brine was supported by heat
passing through the tube wall from the steam condensing on the steam-sides
of the tubes. The hydrodynamic pressure drop through the tubes, measured in
a direct manner by means of sight glasses communicating with the tube inlet
ends (post-orifice) and with the vapor release vessel, provided a continuous
indication of the hydrodynamic oscillations and of the upflow stability in
the distillation tubes. The pressure drop across the orifice plate, and the
hydrostatic pressure of the feed before passing through the orifice plate,
were also measured with manometers. Outflow of brine from the tubes was usually
in the form of an annular layer on the tube inner wall, while the vapor phase
flowing up in the center of the tube was relatively free of liquid. A dis-
continuous, gushing mode of outflow was usually observed, with the annular
brine layer emerging in spurts,but with the vapor core flow appearing to be
continuous. Entrainment separation from the vapor produced was readily
accomplished with an impingement plate and a mesh demister positioned about
20 inches above the tube outlet ends, in the vapor release vessel shown in the
top center of Figure 1. Primary separation at the tube outlet ends was aided
by having the tubes extended above the upper tube sheet, and by having slots
17
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or holes in this part of the tube. The vapor produced was condensed in the
heat reject loop and returned to the brine loop.
Temperature measurements were made with platinum-resistance probes pro-
viding a direct, digital display of steam-side temperature (Ts), of feed tem-
perature below the orifice plate (Tf), of final brine temperature (Tb) immedi-
ately after passing through the vapor release vessel, and of the temperature
difference (AT = Ts - Tb). These data were checked by measuring the vapor
pressures on the steam-side (Ps) and the brine-side (Pv) with an absolute
manometer and correcting for boiling point elevation, and by mercury-filled
thermometers installed in direct contact with the flowing fluids.
Upflow VTE heat transfer data were obtained under steady-state operating
conditions, first without any addition of surfactant to wastewater feed, and
then with specific concentrations of a selected surfactant added to this feed.
Data without surfactant additives compared well with those obtained earlier in
an OSW sponsored test series with this pilot plant. The interface-enhanced
data were obtained with the same process conditions, after the addition of a
selected surfactant (Neodol-25-3A, or Neodol 25-3S, Shell Chemical Company)
to the wastewaterfeed. Surfactant addition was observed to bring about a
significant change in the mode of two-phase flow, characterized by foaming
at the inlet and outlet ends of the tubes and by a substantial reduction in
the tube pressure drop, AP. These typical modes of flow through the orifice
plate, spaced about three inches from the tube inlet ends,are shown in Figure
k. Without a foaming agent additive the feed flashed down at the orifices
into a continuous liquid layer, with the vapor and feed liquid passing through
this liquid layer into the tube inlet ends. After the addition of surfactant
the feed flow was radically changed. Flashdown at the orifice plate produced
foamy jets passing through a vapor-filled space into the tubes. This mode
18
-------
a. Without Foaming Agent Added to Feed,
b. With Foaming Agent Added, and Orifices in Line with Tube Ends.
c. With Foaming Agent, and Orifices Offset from Tube Ends.
TYPICAL TWO-PHASE FLOW THROUGH VTE ORIFICE PLATE FIGURE
19
-------
of flow is associated with a substantial reduction in the hydrodynamic pres-
sure drop (AP) through the distillation tubes, by a factor of 3 to 10 compared
to the typical AP without surfactant additives. Rotating the orifice plate
to cause impingement of some of the foamy jets against the tube sheet filled
this entire space with foam and produced a further increase in performance.
This is of significance because one can thereby ensure wetting of the tube
inlet section with foam by means of secondary orifices placed interstitially
of the regular orifices that are lined up with the tubes.
The mode of foamy two-phase flow from the tube outlet ends after the
addition of surfactant, is shown in Figure 5. The residual liquid, carried
through the tubes by the vapor phase core flow, is ejected as a foamy annulus
in contact with the tube inner wall; this liquid or foam phase flow is dis-
continuous or gushing randomly from the 18 tubes.
UPFLOW VTE PYREX GLASS EVAPORATOR
An all-glass Pyrex-tubed evaporator, shown in Figure 6, was constructed
with the objective of obtaining data and information on the solute-crystallization
behavior of wastewaters. This equipment comprised a pair of Pyrex tube upflow
VTE tubes of 1-inch x 5-foot dimensions having steam jackets, and being
tangentially connected to a 5-liter spherical cyclone vapor-liquid separator.
The top of the cyclone separator was connected via a 2-inch vapor discharge
to an efficient vacuum-operated condenser connected to a distillate reservoir
which permitted periodic removal of the distillate without interrupting the
vacuum-evaporation process. The base of the cyclone separator vessel was
connected to a 2-inch diameter standpipe for recirculation. The distil land
was recycled back to the distillation tubes via 1/8-inch orifices provided
in the form of Pyrex glass valves fused to the inlet ends of these tubes.
20
-------
tsi
FOAMY ANNULAR FLOW FROM DISTILLATION TUBES
FIGURE 5
-------
PYREX TUBE CRYSTALLIZING EVAPORATOR
FIGURE 6
22
-------
The minimal liquid holdup in this apparatus was bout 800 ml, and its
capacity was about k liters when full. Provision was made for the continuous
addition of feed during evaporation, thus providing concentration of waste-
water feed by any desired factor. This permitted close observation of the
modes of two-phase flow with and without the addition of a surfactant to the
feed, and of the concentration levels at which percipitates were formed.
Operation of this evaporator under vacuum conditions was provided by a
rotary oil vacuum pump protected by a final condenser. Typical evaporation
temperatures were in the range of 90 to 110 F depending upon the solute content
of the distil land, and the cooling water temperature. The AT applied was
such as to provide a heat flux through the walls of the distillation tubes
about equal to that of aluminum-brass tubes of the same dimensions used at
a conventional AT of about 10°F.
DISTILLATION TUBES USED IN THE VTE PILOT PLANT
The VTE heat transfer tubes used in this study were all of the double-
fluted or enhanced type, having their walls formed into axial or spiralled
grooves or flutes. This provides complementary flutes on both the inside
and outside (brineside and steamside) surfaces of the tubes. This type of
wall modification provides an approximately 5-fold increase in the steamside
coefficient at an additional cost of about 30 percent added to the cost of
the smooth tube from which the double-fluted tube is formed (9 )• Such
tube profiles are shown in Figure 7.
23
-------
r-o
2-INCH 00 DOUBLE-FLUTED
ALUMINUM-BRASS
.0^2-INCH WALL
2-INC;; SPIRALLY FLUTED
ALUMINUM-BRASS
-INCH WALL
3-INCH OD DOUBLE-FLUTED
ALUMINUM-BRASS
-INCH WALL
2-INCH OD SPIRALLY
FLUTED TITANIUM
.020-INCH WALL
AXIALLY AND SPIRALLY DOUBLE-FLUTED DISTILLATION TUBES
FIGURE 7
-------
EXPERIMENTAL WORK
I) Investigation of Cooling Tower Slowdown
Background. The adoption of evaporative cooling for steam power plants
to reduce their environmental impact by limiting undesirable effluents projects
the need for an economically acceptable method of renovating cooling tower
blowdown. Vertical tube evaporation to further concentrate the blowdown to
the concentration limits permitted by its solute content, followed by crystal-
1izing-evaporation to a slurried salt residue, relies on well-defined and
acceptable technology (12). If these evaporation procedures are performed
at relatively low temperatures, one can utilize heat rejected from the power
plant as the driving force for evaporation; low temperature evaporation in-
creases the acceptable concentration limits of calcium and magnesium salts in
the blowdown brine and reduces corrosion and fouling problems of equipment.
While heat of evaporation is essentially free at these low temperatures
(around 120 F) the evaporator performance is rather low, requiring a relatively
large heat transfer surface area and increased capital costs. Methods of in-
creasing the evaporator heat transfer performance, thereby reducing the capital
cost, provides an even more substantial overall cost reduction on this low
temperature evaporation than in the case where the cost of fuel has to be in-
cluded. Interface enhancement (1, 2, 3, *0 offers a novel and promising method
of increasing the performance of vertical tube evaporation (VTE) at quite low
added cost, while it concurrently reduces the potential for scaling, fouling
and corrosion of the evaporator.
VTE performance data. A large batch of cooling tower blowdown (1,500
gallons) was collected from the Mohave Power Plant with the assistance of the
Bechtel Power Corporation in November 1973, and trucked to the VTE pilot plant
facility for these tests. It had a pH of 8.k and contained close to 10,000
25
-------
ppm of total dissolved solids. This blowdown was slightly turbid, and was used
as such without clarification.
The heat transfer enhancement effect and the tubeside pressure drop re-
duction effect responsive to the gradual addition of a surfactant to the
blowdown brine during upflow VTE under typical steady state process conditions
are shown in Figure 8. The evaporator performance (U) at 210 F was approxi-
mately doubled by the addition of 5 ppm of Neodol-25-3A (Shell Chemical Company)
while the pressure drop (AP) was simultaneously reduced from about 30 to 7-5
inches of water. Further additions of surfactant up to 25 ppm produced a
gradual further heat transfer enhancement to 3,000 Btu per hr-ft - F. The
most effective surfactant concentration was about 10 ppm, which provided a
120 percent enhancement of the overall heat transfer coefficient. The tube-
side pressure drop was also at a minimal value of 5~inches of water with 10 ppm
of additive.
The overall heat transfer performance through the available evaporation
temperature range of 120 to 220°F under typical multi-effect upflow VTE con-
ditions, obtained without, and with 10 ppm of Neodol additive to the blowdown
brine feed are shown in Figure 9- It is apparent that, in the case without
surfactant addition, the performance was maximal at 180 F; this indicates
that some fouling or scaling occurred at the higher brine temperatures even
with the pH of the brine adjusted to 6.8. On the other hand, a substantial
increase in performance was obtained at these process conditions after the
addition of 10 ppm of a surfactant. Interface enhancement was somewhat less
effective in the 120 to 1^0°F range at this low a surfactant concentration.
This should be improved by using a somewhat higher surfactant concentration
and by using 3-inch diameter tubes (5).
26
-------
ENHANCEMENT OF HEAT TRANSFER PERFORMANCE
IN VTE OF HOHAVE COOLING TOWER SLOWDOWN
Effect of gradual addition of surfactant
to the feed on the overal1 heat transfer
coefficient, U, and the pressure drop, AP,
at an upflow VTE temperature of 210°F,
AT = 8°F, using 2.5 year-old bundle of
18 aluminum-brass tubes of the double-
fluted type. Feed pH 6.8.
3000
3
4_l
CO
O
U
I/)
i
LU
I
2000
1000
I
I
30
(M
20
_c
u
a.
<
a.
O
CC
a
cc
a.
O
cc
O
X
10
5 10 15
SURFACTANT ADDITIVE CONC., ppm
20
25
FIGURE 8
27
-------
T
3000
3
4-1
CD
2000
O
O
CD
HEAT TRANSFER PERFORMANCE OF
MOHAVE COOLING TOWER SLOWDOWN
Overall heat transfer coefficient,
U, without and with surfactant addition
at 10 ppm, through the evaporation
temperature range 120 - 220°F, AT range
16.5 - 7-5°F, during upflow vertical tube
evaporation at pH
18 aluminum-brass
fluted type.
&. 8, us i ng a
tubes of the
bundle of
double-
1000
U WITH 10 ppm ADDITIVE
U WITHOUT ADDITIVE
120
160
180
200
220
EVAPORATION TEMPERATURE,
FIGURE 9
-------
Figure 10 shows the upflow VTE performance (U) during the concentration
of cooling tower blowdown by interface-enhanced evaporation at 130 F, in
comparison with conventional evaporation (broken line). Also shown are per-
formance data calculated after deducting the AT loss due to apparent boiling
point rise as observed. The steamside temperature was held at \k2 F and the
condenser flux was held at steady state for these data. Some precipitate
formation was observed at brine concentrations of 2 percent and higher. A
slight increase in performance was observed as the brine concentration in-
creased from 1 to 1.67 percent, in spite of the increased solute content of
the brine. This is attributable to the simultaneous concentration of the
surfactant in the brine, which increases the evaporation coefficient as
indicated by Figure 8, and as also reported in earlier work (8). The decline
in performance at brine concentrations beyond the onset of crystallization
is attributable to the loss of surfactant from solution due to its adsorption
on the crystal or precipitate surfaces. This rationale requires confirmation
in further work planned.
A relatively inexpensive and effective method of stripping surfactant
additives from blowdown brines, by foam fractionation, has been developed in
this Laboratory, and demonstrated on a pilot plant scale (13). This procedure
also clarifies the brine concentrate and facilitates its further concentration
in a crystallizing evaporator to produce useful salts, such as sodium sulfate,
and a final slurried concentrate for ponding or disposal. The foamate fraction
containing the surfactant concentrate can be recycled after its clarification.
Discuss ion. The use of surfactant additives in blowdown concentration
by VTE utilizing waste heat available in a power plant cooling cycle provides
significant improvements in process flexibility and economy i 11). Figure 11 shows
a possible method of integrating this coolant renovation-recycle system into
29
-------
CONCENTRATION OF MOHAVE POWER PLANT COOLANT SLOWDOWN
BY INTERFACE-ENHANCED VERTICAL TUBE EVAPORATION AT 130°F
-------
COOLANT
MAKE-UP
BARO-
METRIC
CONDEN-
SER
COOLANT
MAKE-UP
DISTILLATE SOLIDS SLOWDOWN
RENOVATION AND RECYCLE OF POWER PLANT COOLING TOWER SLOWDOWN
FIGURE 11
-------
the flow diagram of an existing power plant. The upper half of Figure 11
represents an existing power plant coolant cycle; the lower half shows the
renovation loop added on via k valves, permitting shutdown of this loop and
reversion to the original cycle of operation, if desired. The power plant
could be reverted to the original mode of operation at any time within the
time required to close valves 1, 2, 3 and k, and opening valve 5 to resume
the usual discharge of blowdown, for instance to a reservoir for later
renovation. Since about 5 percent of the total turbine exhaust steam is
utilized in the evaporator loop (via valve 2) a small forced-draft cooling
tower is added to this loop to make up for the reduced demand on the power
plant cooling tower. The condensate of this exhaust turbine steam is returned
from the first effect (VTE-1) to the boiler via valve 1. A portion of the
hot coolant is diverted to the evaporation loop, as blowdown, via valve 3-
The vapor produced in VTE-1 serves as heating steam for the VTE-11 and the
forced circulation crystallizing evaporator (FC-VTE), and these condensates
are available (DISTILLATE) for a beneficial use such as boiler feed makeup
or potable fresh water or for return to the main coolant loop. Vapors pro-
duced in the VTE-11 and FC-VTE are returned to the main coolant loop as
condensates from the barometric condenser via valve 4; dilution of the coolant
with condensates reduces coolant makeup and pretreatment requirements. The
coolant makeup for the barometric condenser and small cooling tower need
not be softened since it is continuously diluted with this distilled water,
and becomes part of the main coolant loop. Another option is to divert the
DISTILLATE (from VTE-11 and FC-VTE) to serve as coolant makeup for the small
cooling tower, in which event this coolant will be distilled water entirely;
this provides a source of cooled distilled water (as blowdown) for the above
beneficial uses. It is apparent that the rate of producing such cooled
32
-------
distillate will depend on the rate of turbine exhaust steam flow through
valve 2, and it can be substantially increased by partial replacement of
main cycle condenser capacity with additional heat duty in the VTE's, baro-
metric condenser and small cooling tower.
In addition, the further adoption of this proposed means of evaporative
cooling, to partially replace cooling condensers in future power plants, can
provide the significant beneficial result of producing more distilled water
than that required to maintain scale-free operation of a cooling tower. This
additional, pure distilled water product could in part be diverted for another
beneficial use, for instance, for boiler feed makeup and to reduce the salinity
of a domestic or municipal water supply. In relation to the proposed Palo Verde
power plant, where secondary or tertiary treated municipal effluents are to be
used for power plant cooling, the adoption of this proposed coolant recycle
scheme could provide some pure, distilled water, for instance for the dilution
of Colorado River water to reduce its salinity. This technology will also
provide increased flexibility in coolant pretreatment; for instance, the need
for softening may be reduced, thereby reducing chemical costs as well as final
saline wastes. Since the coolant is stripped of volatile constituents by
repeated passage through the cooling towers, the subsequent evaporation of
the blowdown should produce pure distilled water of potable quality.
Conclusions. It is clear from the above data and observations that the
interface-enhanced mode of VTE operation can provide a substantial increase
in the heat transfer performance during blowdown evaporation, especially at
blowdown concentrations below the crystallization or precipitation limit.
This limiting concentration is increased by the presence of the surfactant
additive, probably by interfering with the rate of crystal growth through
adsorption of the additive on newly formed crystal surfaces.
33
-------
The benefits of increased heat transfer performance are mainly as
follows:
(a) it permits the use of an increased number of effects in the multi-
effect VIE plant while maintaining the per-effect distillate production at a
lower per-effect AT than in conventional VTE operation (k). This permits a
proportionate increase in the gain ratio, in the interest of substantial steam
or fuel savings. This aspect of interface enhancement also improves design
flexibility, permitting an improved design optimization with reference to
capital versus operating costs.
(b) Slowdown brine concentration with waste heat accentuates the sig-
nificance of interface enhancement for reducing capital costs. This applies
to both upflow and downflow VTE operation. It also permits the production
of distilled water by allowing the inclusion of a two-effect downflow VTE
within the waste heat temperature span available in a power plant cooling
cycle, as shown in Figure 11.
(c) Interface enhancement can be applied to vapor compression VTE
operation for cooling tower blowdown renovation to reduce the required heat
transfer surface in such an installation.
(d) Operation and maintenance costs of blowdown evaporators should be
reduced by the use of surfactant additives because of the particulate dis-
persant effects of surfactant; this should reduce fouling and corrosion of
heat transfer surfaces.
-------
Solute precipitation data. Observations made in earlier work, and data
obtained with the Pyrex tube evaporator indicated that the dispersant effect
of the surfactant additive delays the onset of crystallization. This side
effect is quite beneficial; it can reduce the capacity requirements of the
relatively expensive crystallizing evaporator to be used subsequently.
In a typical run, 16 liters of Mohave blowdown was evaporated at 130 F
to a residual volume of 1.8 liters (in 1.5 hours), at which concentration
a crystalline precipitate was first observed. This concentrated residue
was withdrawn and separated into a 50 ml fraction containing a muddy sedi-
ment and a clear supernatant fraction (1.75 liters) from which further
crystallization occurred over the next 48 hours. In a follow-on run with
surfactant addition at 8 ppm to the feed, 20 liters of Mohave blowdown having
0.3 ml of Neodol-25-3-S (Shell Chemical Co.) added was similarly evaporated
at 130 F to a residual volume of 1.66 liters (12-fold concentration) when
a crystalline precipitate was first observed. This residual concentrate was
separated into a 25 ml fraction containing a muddy precipitate and a clear
fraction (1.63 liters) from which further crystallization occurred over the
next two days. It was apparent from these tests that the addition of a
surfactant depresses the crystallization of solutes during evaporation of
Mohave coolant blowdown.
35
-------
2) Industrial Steam Generator Slowdown Concentration
Large industrial boilers produce a considerable volume of concentrated
blowdown, depending upon the quality of the feed water used. The blowdown
from steam generators serving a large refinery can reach 500,000 gallons per
day on the basis of using treated tapwater as boiler feed. The proportion
of blowdown to feed is determined by the scaling potential of the pre-treated
feed and the need to keep boiler heat transfer surfaces free of corrosion,
fouling and scaling in the interest of high heat transfer performance and
fuel economy. The concentration in the blowdown of the naturally occurring
salts, as well as of boiler feed additives such as antiscaling compounds and
corrosion inhibitors could render it unsuitable for discharge to, for instance,
a municipal effluent treatment plant.
It was the objective of this series of tests to determine the feasibility
of using the interface-enhanced method of VTE operation to reduce industrial
boiler blowdown to a very small volume while simultaneously pro^cing distilled
water of pure quality suitable for a beneficial use.
The use of surfactant additives as evaporator heat transfer performance
enhancement agents had been demonstrated and was anticipated to also be
effective for boiler blowdown. A second beneficial effect of these additives
previously observed is to inhibit the format ion of scale and to act as a
dispersant for particulate matter in suspension.
Three series of tests were carried out with the blowdown obtained from
a large industrial steam generation plant. These test series were;
(a) Typical upflow VTE heat transfer performance data using the 5,000
gpd pilot plant tubed with 2-inch OD x 10-foot long double-fluted aluminum-
brass tubes.
-------
(b) Test data on the upflow VTE heat transfer enhancement response
and the pressure drop reduction effect responsive to the gradual addition
of a selected surfactant to boiler blowdown feed evaporated at 210 F.
(c) Interface-enhanced upflow VTE performance data through the range
of typical effect-to-effect process conditions, comparable to the data shown
under (a).
(d) Heat transfer performance and solute precipitation behavior during
the gradual 10-fold concentration of boiler blowdown having 10 ppm of a
selected surfactant added.
(e) Solute precipitation behavior during the gradual 20-fold concentra-
tion of boiler blowdown having 10 ppm surfactant added, examined during
evaporation in the Pyrex glass upflow VTE.
(a) Typical upflow VTE data: Figure 12 shows the overall heat transfer
coefficient and tubeside pressure drop data obtained with boiler blowdown
(adjusted to pH 6 by the addition of sulfuric acid) under the usual multi-
effect evaporation temperature, temperature difference (AT) and feed flow
conditions. Data are shown for double-fluted aluminum-brass and copper tubes
of 2-inch OD x 10-foot heated length. These data are consistent with earlier
tests on freshwater and seawater obtained in this laboratory
and elsewhere ( 3 ). The heat transfer performance with 2-inch tubes is
generally low in the 120 to l60°F range where the tubeside pressure drop is
relatively high and the upflow stability low. These tubes perform satis-
factorily in the 160 to 2kO°F range; 3-inch diameter tubes would be preferable
for the lower range.
37
-------
3000
o
CM
2500
VjJ
03
^ 2000
LJ
o
o
ac
UJ
1500
1000
500
1 j ! 1 1
UPFLOW VTE PERFORMANCE WITH 301LER SLOWDOWN
Overall heat transfer coefficient U, through the evaporation
temperature range 120 to 240°F under typical multieffect process
conditions; tube bundle pressure drop.
B
A
Plot A: Heat transfer performance of Al-Br tubes
Plot 3: Heat transfer performance of Copper t'.ibe
Plot C: B'jndle tubeside pressure drop
60
50
O
l/l
Q.
O
ce
o
30
20
10
UJ
CO
10
120
140
160 180
EVAPORATION TEMP.
200
220
240
FIGURE 12
-------
(b) The upflow VTE interface enhancement response with boiler blow-
down at an evaporation temperature of 210 F responsive to the gradual addi-
tion of Neodol 25-3A (Shell Chemical Co.) is shown in Figure 13. Data were
plotted for the overall heat transfer coefficient of the 14-tube bundle of
double-fluted aluminum-brass tubes and for a double-fluted copper tube, as
well as the tube bundle pressure drop. These data were again consistent
with earlier reports (2,3,^), confirming the dramatic pressure drop reduction
effect and the substantial performance enhancement by the addition of a sur-
factant and the imposed foamy two-phase flow of the feed over the heat
transfer surfaces. For instance, the 14-tube bundle performance was increased
by 117 percent after the addition of 10 ppm of surfactant, while the pressure
drop was concurrently reduced by a factor of 11 from kO to 3.5 inches of
water. The comparable response of the copper tube was even better at 149
percent enhancement, consistent with earlier data (3). Further additions of
surfactant provided further increases in performance and a slight increase
in the tubeside pressure drop; the beneficial maximum surfactant concentration
was about 30 ppm.
(c) Figure Htshows the interface-enhanced upflow VTE heat transfer
performance through the usual multieffect evaporation temperature range of
o
120 to 2kQ F. These data, in comparison with the data discussed under (a)
above (Figure 12 ), indicate the advantage obtainable by the use of surfactant
additives in blowdown evaporation. The distillate productivity rate is about
doubled while the tubeside pressure drop is substantially reduced to ensure
stable operation of the multieffect upflow VTE.
39
-------
I I I I I
INTERFACE ENHANCEMENT RESPONSE WITH BOILER BLOWDOWN
Variations in U and AP responsive to the gradual
addition of a surfactant
o A
Plot A: Heat transfer performance, AI-Brtub«
Plot B: Heat transfer performance, Copper tub<
Plot C: Tube bundle pressure drop
30
u.
o
20
i
UJ
CC
UJ
ca
a.
LU
CO
10
10
20
30
50
SURFACTANT ADDITIVE CONC. ppm
ko
FIGURE 13
-------
3000
2500
3
*J
00
2000
£ 1500
1
§
1000
2
Ul
1 1 1 T
INTERFACE-ENHANCED UPFLOW VTE PERFORMANCE WITH BOILER SLOWDOWN
Heat transfer performance and tubeslde pressure
drop through the evaporation temperature range
120-240°F after the addition of 10 ppm of
a surfactant to the feed.
60
50
o
in
Q.
o
30
Plot A: Heat transfer performance, Al-Br tubes
Plot B: Heat transfer performance, Copper tube
Plot C: Tube bundle pressure drop
20
500
10
120
160 180 200
EVAPORATION TEMP. °F
220
FIGURE 1**
-------
(d) A large volume (800 gallons) of industrial boiler blowdown was
subjected to a gradual concentration by a factor of 10 while in recirculated
flow through the VTE pilot plant, to determine the effects of solute concen-
tration on the heat transfer performance. The pH of the blowdown was
adjusted from 12 (as received) to 5-5 by the addition of sulfuric acid (80 ml)
and 10 ppm of Neodol-25-3A (Shell Chemical Co.) was added for this test series.
Deaeration of the feed was affected by recirculating it through the VTE pilot
plant under vacuum. The steamside temperature of the VTE tube bundle was
maintained at 220 F and the initial AT applied was 10 F. The condenser flux
was held constant during the entire run, resulting in a gradual decrease in
the AT to 7 F responsive to the increase in boiling point as the solute con-
tent increased. Heat transfer performance data are plotted for the 14-tube
bundle of 2-inch OD double-fluted aluminum-brass tubes and for a similar
copper distillation tube as a function of the residual feed volume in Figure
15 . It is interesting to note that the gradual increase in solute concen-
tration did not have a negative effect on the overall heat transfer coefficient
in this case. This is the result of the simultaneous concentration of sur-
factant in the residual feed and of the fact that the solubility limit of
solutes was not reached during this 10-fold concentration of the blowdown.
In fact a gradual increase in evaporator heat transfer performance
to about 25 percent was obtained during the course of this blowdown concentra-
tion by a factor of 10. Also of interest was the fact that no excessive
foaming was experienced. The final solute content of 'this 10-fold concentrate
was about 16,500 ppm (or 1.65%) including 100 ppm of the added surfactant.
-------
3000
2500 ~
I
CO
o
- 2000
o
o
u.
in
i
1500
1000
UJ
o
500
800
700
10-FOLD CONCENTRATION OF BOILER SLOWDOWN
Heat transfer performance during the gradual concentration
of boiler blowdown after the addition of 10 ppm of a surfactant.
Plot A:
Plot B:
Heat transfer performance, Al-Br tubes
Heat transfer performance, Copper tubes
_L
_L
_L_L
600 500 400 300 200
RESIDUAL FEED VOLUME, GALLONS IN RECIRCULATION
100 80
FIGURE 15
-------
(d) In a final experiment 40 liters of boiler blowdown with 10 ppm of
surfactant added was concentrated in the Pyrex glass VTE of Figure 6.
This concentration proceeded by a factor of 20, to a residue of 2 liters,
without any significant precipitation of salts being observed. This residue
was dark colored from suspended particulates, all of which were readily
maintained in suspension by the presence of the surfactant additive.
Discussion. From the data plotted in Figure 13 it is apparent that the
addition of about 10 ppm of surfactant to boiler blowdown evaporated at 210 F
in an upflow VTE using double-fluted aluminum-brass tubes provides an
approximate 120 percent increase in the evaporator performance, and an 11-fold
reduction in the tubeside pressure drop. These data indicate that interface
enhancement should provide substantial cost reductions in the concentration
of such wastewaters. With appropriate evaporator design options, these cost
reductions can be either in terms of capital cost or operation-maintenance
costs.
It is clear, from a comparison of the data plotted in Figures 12 and
Nt, that the interface-enhanced mode of evaporation provides an approximate
doubling of the upflow VTE heat transfer performance. Stated in different
terms, one can increase the rate of concentration of boiler blowdown by
about 100 percent by the addition of about 10 ppm of surfactant to it followed
by imposing the foamy mode of two-phase flow through the upflow distillation tube
under otherwise conventional process conditions.
The 10-fold concentration of boiler blowdown at 210 F without loss in
heat transfer performance after the addition of 10 ppm of surfactant is con-
sidered very promising. These would essentially be the ideal VTE process
-------
conditions for an evaporator utilizing vapor recompression as the means
of supplying the process heat requirements. Vapor compression (VC) is
probably the least costly method of concentrating boiler blowdown. Concen-
tration by a factor of 20 to 25 should be readily achievable by VC-VTE
with an interface-enhanced performance of about 2,000 Btu per hr-ft - F.
Several alternative types of compressors, both electrically driven
mechanical, or steam-jet types, are commercially available. The main ad-
vantage provided by interface enhancement is in this instance taken in terms
of a capital cost reduction; the heat transfer surface area or number of
distillation tubes used can be reduced by half.
The alternative approach of using an interface-enhanced multiple effect
VTE provides the basis for saving heat or fuel costs. In this case the main
advantage can be taken in terms of an improved economy ratio, by increasing
the number of effects normally permissible, by about 50 percent. Economy
ratios of up to 18 pounds of distillate product per pound of heating steam
are possible (6). Intermediate choices are of course possible, thus allow-
ing flexibility for optimizing overall costs by balancing the elements of
capital and operation-maintenance costs.
The beneficial side-effects of surfactant additives were also significant
though not precisely defined in this case. The dispersant properties of the
additive had an apparent beneficial effect of retaining particulates in sus-
pension during the 10-and 20-fold concentrations of boiler blowdown. The heat
transfer surfaces remained clean during these operations.
-------
3) Acidic Mine Drainage Concentration
Drainage and seepage from active and abandoned mines and from slagpiles
associated with such mines can present effluents that are environmentally harm-
ful. These effluents are usually high in acidity due to atmospheric oxidation
of sulfur compounds producing sulfuric acid in solution. Acidity levels in the
pH-range of 2 to 4 have been reported. In addition such effluents also contain
other undesirable solutes such as salts of iron, copper and zinc. Depending upon
the length of atmospheric exposure, iron compounds can be present as ferrous
sulfate which is gradually oxidized to ferric sulfate. The drainage water ex-
amined in this study originated from a pyrites slag pile. Two types of this
effluent were examined: the first was collected directly from the slagpile
before significant exposure to air oxidation and was high in ferrous content;
the second type was high in ferric content, substantially fully oxidized by
prolonged exposure to air and partial solar evaporation-concentration. The
highly corrosive nature of these effluents presented a major operating problem.
The VTE pilot was in part constructed of copper-based alloys and stainless
steel, and subject to corrosive attack, especially at higher temperatures.
The experimental procedures applied can be summarized as follows:
(a) The solute behavior of these drainage waters was examined by gradual
concentration in the pyrex glass VTE, to the point of precipitation of ferrous
or ferric sulfate, both without and with a surfactant additive.
(b) Heat transfer performance data were obtained in the VTE pilot plant
within the evaporation temperature range of 120 to 200°F. Data were obtained
with copper, aluminum-brass and titanium tubes of the fluted type.
(c) The highly corrosive nature of this wastewater dictated limited use of
the VTE pilot plant for its examination. Solid precipitation studies were there-
fore conducted with the pyrex tube exaporator. This wastewater is comparable to
electroplating rinsewater, at least in terms of its metal ion content and cor-
rosiveness. Therefore, pilot plant tests with electroplating rinsewater were
also avoided.
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(a.l.) The fresh ferrous-containing drainage water had a TDS of about
5^,000 and a pH of 3.3. Other constituents were about 100 ppm of copper
sulfate and about 150 ppm of zinc sulfate. Six liters of this were evaporated
in the glass-tubed evaporator of Figure 6, at 40 C (104 F). to a residual
volume of 2.0 liters, at which point a whitish crystalline precipitate started
to form, at 3-fold concentration.
Eight liters of this drainage water containing 5 ppm of added Neodol-25~3A
(Shell Chemical Co.) were evaporated in the glass-tubed evaporator at 90-105 F,
to the onset of crystallization which occurred at a residual volume of 2.2
liters. Further crystallization occurred upon standing in this 3-6-fold
concentrate.
Comment: It was apparent that the addition of a surfactant to this
water (a) facilitated its evaporation by upflow VTE, and also inhibited or
retarded the onset of crystallization, but did not necessarily influence
the final solute concentration level in the presence of crystalline precipitates.
(a. 2.) The oxidized, ferric containing drainage water had a TDS of
about 66,000 and a pH of about 2.0. Other constituents were about 120 ppm
•>f copper and 180 ppm of zinc sulfates.
Eight liters of this water were evaporated at about 100 F in the glass-
tubed evaporator to the appearance of crystalline material in the concentrate.
From this k.4-fold concentrate (1.80 liters), further crystallization occurred
upon standing.
Eight liters of this water containing 5 ppm of surfactant additive
(Neodol-25-3A) were concentrated at about 90 F in the glass-tubed evaporator
to initial crystal formation, and then drained. This 6-fold concentrate
(1.35 liters) was set aside to deposit additional crystalline material.
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Comment: It was apparent that the addition of 5 ppm of a surfactant
retarded crystallization and also improved upflow VTE stability and efficiency.
On a basis of these results it was decided that definitive heat transfer
performance tests with the pilot plant were justifiable.
(b.l.) Heat transfer performance data obtained were limited by the
corrosive nature of this acidic water. Two pilot plant runs were conducted
with the 5,000 gpd VTE shown in Figure 1, using separate 80 gallon samples
of the fresh, ferrous-sulfate high drainage water only.
First run: The pilot plant was tubed with 18 spiral-corrugated copper
tubes of 2-inch OD x 10-foot length x 0.30-inch wall thickness (Yorkshire
Imperial Metals, Ltd.) for this test.
Eighty gallons of drainage water were deaerated in the pilot plant by
recirculation under vacuum (29.5-inch Hg). VTE heat transfer performance
data were then taken as described earlier at evaporation temperatures of
140°, 160° and 180°F using typical multi-effect process conditions with feed
flows of one gallon per minute per tube. Neodol 25-3A was then added to the
feed at 10 ppm concentration, and heat transfer performance data were again
taken at evaporation temperatures of 180, 160, 140 and 118 F. These data
are shown in Figure 16 attached.
Comment: It was clear from the data in Figure 16 that interface enhance-
ment provided an approximate 71 percent heat transfer performance enhancement
at 180 F with 10 ppm of Neodol-25-3A additive. The two-phase pressure drop
(AP) through the tubes was simultaneously reduced from about 39 to 8 inches
of water, to improve the upflow stability and increase distillate production
proportionately.
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INTERFACE ENHANCEMENT RESPONSE WITH COPPER TUBES
o
CM
•fci
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There was an apparent reduction in the enhancement effect of Neodol
with time of the test, but this was not conclusive and it was decided to
defer to a second test.
Second run: For the second run, four of the 18 distillation tubes in
the bundle were replaced with a double-fluted aluminum-brass tube (Yorkshire),
a spiral-corrugated titanium tube (ORNL), and two double-fluted titanium
tubes (Timet-Grobb).
Eighty gallons of fresh slagpile effluent were deaerated in the pilot
plant at 29.5 inch Hg, after which its pH was 3-1. Heat transfer performance
data were then taken at evaporation temperatures of 125, 150, 180 and 200 F
as before. At 200°F Neodol-25-3A was added to the feed to the 10 ppm level,
and the performance data were repeated. The process conditions were then
held at steady state, at 200 F evaporation temperature, for 2 hours, re-
peating data-taking at 30 minute intervals without observing any significant
reduction in the performance, thus showing that the surfactant additive is
not significantly degraded by these process conditions.
Heat transfer performance data are shown in Figure 17. The aluminum-
brass tubes responded best to Neodol addition; the overall heat transfer
coefficient (U) increased by 100 percent, from 1302 to 2718 Btu per hr-ft -°F.
at 200 F. The titanium tubes showed an interface enhancement response of 63
percent. The tube bundle pressure drop was reduced from 40 to 9.5 inches of
water by the addition of the surfactant, comparable with the first run, and
the spiral-corrugated copper tubes also responded similarly to the first run
in heat transfer performance, as shown in Figure 16.
Comment: The heat transfer performance enhancement effect by Neodol
addition ranges from about 60 to about 100 percent at an evaporation tempera-
ture of 200 F, depending upon the type of distillation tubes used. Aluminum-
50
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o
CM
1 1 r
INTERFACE ENHANCEMENT RESPONSE WITH ALUMINUM-BRASS AND TITANIUM TUBES
Overall heat transfer coefficients (U) responsive to 10 ppm Neodol
addition to acidic wastewater feed at 200°F, with double-fluted
aluminum-brass and titanium tubes in the 18-tube upflow VTE pilot plant.
-C
I.
o.
2000
wi
o
O
1000
<
QC
Plot A
Plot B
Plot C
U vs Evap. Temp., Double-fluted Aluminum-brass tube
U vs Evap. Temp., Double-fluted Titanium tube
U vs Evap. Temp., Spiral-corrugated Titanium tube
I I
120
140
160
EVAPORATION TEMPERATURE,
180
200
FIGURE 17
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brass (double-fluted) performed best, but titanium tubeswi 1 1 be the better
choice because of corrosion-fouling problems. The double-fluted titanium
tubes showed a performance enhancement of 63 percent with 10 ppm Neodol.
The 4-fold pressure drop reduction by surfactant addition permitted stable
upflow VTE operation at AT levels of 6-7 F, within the range of vapor com-
pression operation. Neodol has sufficient thermal stability at these process
conditions for use as an interface enhancing agent. Considerable deposition
of what appeared to be porous copper was observed at the distillation tube
outlet ends. Metal surfaces were generally fouled by brownish deposits
requiring repeated washing with dilute acid feed at pH. to remove.
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DISCUSSION
Several methods of wastewater concentration are available, for the
purpose of providing recycle water having a relatively low solute content
and a concentrated wastewater residue for disposal. The selection of what
method to use is of course dominated by their comparative economics and by the
technical feasibility as it depends on the chemical properties of the waste-
water. Combinations of the available concentration procedures should also
be considered ,in the interest of overall cost reductions. The most significant
solute concentration methods are by evaporation, of which several alternative
procedures are applicable: by reverse osmosis (RO), by electo dialysis (ED),
by ion exchange (IE) and by precipitation techniques. Included in evaporation
technologies are vertical tube evaporation (VTE) either with upflow or downflow
of the feed, multistage flash evaporation (MSF) and crystallizing evaporation (CE).
The determination of the comparative economics of these concentration
methods are quite complex and beyond the scope of the present study. However,
recent studies conducted at the Bechtel Corporation provide a comparative
cost evaluation at least for the case of cooling tower concentration-recycle;
their conclusions provide a cost basis for ranking VTE with respect to other
feasible alternative methods. The present study provides a basis for com-
paring the cost of interface-enhanced VTE with that of the conventional VTE
used in the Bechtel studies. Recent design comparison studies performed by
Kaiser Engineers provide a capital cost comparison of interface-enhanced VTE
with conventional VTE and MSF plants of large size for sea water desalination.
The above studies by Awerbuch and Rogers (12) on the desalination of
cooling tower blowdown for a large (2,200 MWE) power plant using cold lime
soda softened river water for cooling, were reported in the recent EPA-AIChE
sponsored Watereuse conference. A 20-fold concentrated blowdown
53
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was considered for further concentration to a solid residue, utilizing a
total of fourteen alternative procedures, and the comparative costs (capital,
operating and total) were determined. Their process combinations considered,
and the costs computed can be summarized as follows:
Costs In $M
Concentration Method Cap!tal Operating Total
1. Crystallizing evaporation 15.7 25-7 41.4
2. MSF preconcentration at 230°F maximum 9.1 20.3 29.4
feed temp.; Crystallizing evaporation
3. MSF preconcentration as in 2; Vapor 15.8 21.2 37.0
compression evaporation with
crystal slurry recycle feed
4. MSF preconcentration' at 19°F maximum 7.2 17.8 25.1
feed temp;
Crystallizing evaporation
5- MSF preconcentration as in 4; 10.9 19.4 30.3
Vapor compression evaporation with
crystal slurry recycle feed
6. Ion exchange; 8.8 17.8 26.6
Reverse osmos is;
Crystallizing evaporation
7. Ion exchange; 21.8 23.4 45.1
Reverse osmosis;
Vapor compression evaporation with
crystal slurry recycle feed
8. Ion exchange; 5.2 12.1 17.2
Reverse osmosis;
MSF with 230 F max. temp.;
Crystallizing evaporation
9. As in case 8 except using a 7.4 12.6 20.0
vapor compression evaporator with
crystal slurry recycle feed
10. Ion exchange; Reverse osmosis; 6.0 13.9 '9-9
MSF with 190°F max. temp.;
Crystallizing evaporator
11. As in case 10 except using a Vapor 8.3 14.7 23.0
compression evaporator with crystal
slurry recycle feed
54
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Costs In $M
Concentration Method continued
12. Hot-coolant heated upflow VTE
for preconcentration; Crystallizing
evaporator heated by hot coolant
13. Turbine exhaust heated upflow VTE
for preconcentration; Crystallizing
evaporator similarly heated
14. Downflow VTE preconcentrator and
crystallizing evaporators replacing
one power plant condenser, both
heated with turbine exhaust steam
Capital Operating Total
8.3 11.6 19.9
7.7
6.1
9.9
3.6
17.6
9.7
The least expensive method of blowdown concentration-recycle thus requires
replacement of one of three typical power plant condensers with a VTE for pre-
concentration followed by a VTE for crystal 1izing-evaporation, both heated by
turbine exhaust steam. This method, however, wi 1 1 probably require demonstration
before it wi11 be considered acceptable by the power industry since it requires
a change in the established coolant cycle. Alternative method 13 appears the
most acceptable from the power plant operators point of view since it requires
only an addition to conventional coolant cycles. The last three and most
promising of the fourteen alternative methods can be further improved, and
their cost figures can be reduced by applying interface enhanced evaporation
in the blowdown concentration by VTE. The emphasis in the above Bechtel
study was to obtain comparative cost figures; the absolute costs may need
adjustment.
Another alternative method of blowdown concentration recycle was recently
proposed by the author (ll) based on data from this study, using turbine
^Private communication with the authors.
55
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exhaust steam for preconcentration by interface-enhanced VTE, followed by
conventional crystallizing evaporation. The main advantage of this method
is that it permits the use of two evaporation effects within the temperature
span available within a conventional power plant coolant cycle. This pro-
vides a basis for either producing distilled water for a beneficial purpose,
such as for boiler feed or potable use, or to dilute the coolant in the main
power plant coolant cycle. Since the heat transfer performance is in this
case about double that of case 13 above, those cost figures would apply
fairly closely here and the distillate produced would be the gain, approxi-
mately. Alternatively one could use the single-effect approach of case 13
and reduce the VTE heat transfer surface by a factor close to 50 percent.
The capital cost advantage of the reduction in distillation tube requirements
and the ability to use upflow VTE instead of downflow VTE provide a capital
cost saving of about 25 percent for a large seawater desalting plant, accord-
ing to a study by Kaiser Engineers ( 6 ). In a recent design comparison
study of the interface-enhanced upflow VTE with conventional MSF for sea-
water desalination by Kaiser Engineers ( 5 ) it was shown that the heat
transfer surface requirement of this VTE is only about half that of MSF and
the evaporator vessel size is reduced by about 40 percent.
In order to arrive at realistic capital and operating cost figures for
the use of interface-enhanced VTE in the concentration of cooling tower blow-
down by waste heat, one would have to perform a detailed design study which
was outside the scope of this work. However it is apparent that a flow dia-
gram such as in Figure 11 should be both acceptable to power plant operation
and more economical than the other alternatives considered. In the case of
the most economical of the fourteen above proposed methods the use of interface
enhancement will undoubtedly reduce this cost further by a significant amount.
56
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The recommended procedure for cooling tower blowdown concentration,
based on this study, is the one based on the flow diagram of Figure 11.
This approach was presented at the Second National Conference on Complete
Watereuse by the author in a paper titled "Recycle of Power Plant Cooling
Tower Blowdown by Vertical Tube Evaporation with Interface Enhancement,
Utilizing Waste Heat."
This procedure combines the advantages of minimal interference with the
normal power plant operation and good economy, and it provides distilled
water for boiler feed makeup or another beneficial use. This recommended
procedure can be added on to a pre-existing power plant or can be designed
into a new plant. Normal operation of a pre-existing power plant can be
resorted to at any time, within the approximately 30 seconds required to
close k valves through which the added-on loop interfaces with the power
plant coolant cycle. The only difference between the normal, pre-existing
operation and the added-on, combined operation is that the demand on the
original cooling tower is reduced by about 5 percent; this is a beneficial
effect, especially during hot weather conditions.
57
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REFERENCES
1) "Interface Enhancement Applied to Evaporation of Liquids," Hugo H. Sephton,
U.S. Patent No. 3,846,254, November 1974.
2) "Vertical Tube Evaporation Utilizing Vortex Flow and Interface Enhancement,"
Hugo H. Sephton, U.S. Department of the Interior, Office of Saline Water,
Research and Development Report No. 574, May 1970.
3) "Interface Enhancement for Vertical Tube Evaporators: A Novel Way of
Substantially Augmenting Heat and Mass Transfer," Hugo H. Sephton,
Presented at the American Society of Mechanical Engineers Heat Transfer
Conference, Tulsa, Oklahoma, August 1971, ASME Publication 71-HT-38.
4) "Upflow Vertical Tube Evaporation of Seawater with Interface Enhancement:
Process Development by Pilot Plant Testing," Hugo H. Sephton, Desali nation.
Vol. 16, No. 1, pp. 1-13, February 1975.
5) "Desalination by Upflow Vertical Tube Evaporation with Interface Enhancement,"
Hugo H. Sephton, Proceedings, International Desalting and Environmental
Association Conference, Ponce, Puerto Rico, April 1975-
6) "Interface Enhancement for Vertical Tube Evaporation of Seawater," Hugo
H. Sephton, Proceedings of the 4th International Symposium on Fresh Water
from the Sea," Vol. 1, pp. 471-480, September 1973.
7) "Upflow Vertical Tube Evaporation with Interface Enhancement: Pressure
Drop Reduction and Heat Transfer Enhancement by the Addition of a Surfactant,"
Howard L. Fong, C. Judson King and Hugo H. Sephton, Desalination, Vol. 16,
No. 1, pp 15-38, February 1975.
8) "Effects of Alkyl Amine Surfactants on Mass Transfer Controlled Corrosion
Reactions," G. Kar, I. Cornet and D. W. Fuerstenau, J. Electrochem. Soc.
119, 33-39 (1972).
9) "Performance Characteristics of Advanced Tubes for Long Tube Vertical
Evaporators," L. A. Alexander and H. W. Hoffman, Office of Saline Water,
Research Development Progress Report No. 644, January 1971, p. 68.
10) "Some Factors Affecting Heat Transfer Coefficients in the Horizontal
Tube Multiple Effect (HTME) Distillation Process," R. B. Cox, Proceedings
of Third International Symposium on Fresh Water from the Sea, 1 (1970) 247-263.
11) "Recycle of Power Plant Cooling Tower Slowdown by Vertical Tube Evaporation
with Interface Enhancement," Hugo H. Sephton, Presented at EPA-AIChE Second
National Conference on Complete WateReuse, Chicago, Illinois, May 4-8, 1975.
12) Desalination of Cooling Tower Slowdown," L. Awerbuch and A. N. Rogers,
Presented at EPA-AIChE Second National Conference on Complete WateReuse,
Chicago, Illinois, May 4-8, 1975.
53
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-6QO/2-76-017
2.
3. RECIPIENT'S ACCESSION-NO'.
4. TITLE AND SUBTITLE
Renovation of Industrial Inorganic Wastewater by
Evaporation with Interface Enhancement
5. REPORT DATE
March 19T& (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Hugo H.
Sephton
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Sea Water Conversion Laboratory
University of California
1301 South U6 Street
Richmond, California 9U80U
10. PROGRAM ELEMENT NO.
1BBQ36;ROAP 21 AZQjTask 019
11. CS»KM«SCT/GRANT NO.
R-802753
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 1+5268
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT • , ,.
A novel method of vertical tube evaporation (VTE) to improve heat transfer
performance was applied to the concentration of three types of industrial waste-
waters. This method, interface enhancement, relies upon the addition of a few
parts per million of a selected surfactant to the wastewater feed followed by
imposed two-phase foamy liquid-vapor flow over the heat transfer surfaces. Applied
to the concentration of power plant cooling tower blowdown and boiler blovdown,
interface-enhanced VTE provided an approximate 120 percent increase in the usual
VTE heat transfer performance, using a 5,000 gpd pilot plant having double-fluted
aluminum-brass distillation tubes, under process coaditions that are realistic for
large industrial plants. Acidic mine drainage water, concentrated by double-fluted
titanium evaporator tubes provided about a 60 percent heat transfer performance
enhancement. Beneficial side effects of the surfactant additive were to inhibit
the crystallization of solutes, permitting concentration of the wastewaters to
smaller volumes. This work indicates feasibility and improved economics for renova-
tion-recycle of each of the three types of wastewater examined.
Industrial feasibility demonstration projects for each of the three wastewater
types examined are recommended. A method and flow diagram for the desalination-
recycle of power plant cooling tower blowdown by interface-enhanced VTE integrated
with typical power plant coolant cycle and utilizing waste heat from that cycle, is
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Heat exchangers
Evaporation*
Heat transfer*
Waste water
Evaporation enhancement
Surfactant enhancement
Inorganic brine concen-
tration
Foam fractionation
Waste water treatment
13B
20M
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO.-O.F PAGES
67
20. SECURITY CLASS (Thiipage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
. U. S. GOVHNMENT PUNTING OFFICE: 1976-657-635/538? Reg I on No. 5- II
59
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