Title of Invention

METHOD AND APPARATUS FOR HIGH EFFICIENCY PRE-TREATMENT OF FEED WATER

Abstract A process for treatment of an aqueous stream to produce a low solute containing distillate stream and a high solute/solids containing blowdown stream utilizing a method to increase the efficiency of an evaporator while providing an essentially scale free environment for the heat transfer surface. Multi-valent ions and non-hydroxide alkalinity are removed from aqueous feed streams to very low levels and then the pH is increased preferably to about 9 or higher to increase the ionization of low ionizable constituents in the aqueous solution. In this manner, species such as silica and boron become highly ionized, and their solubility in the concentrated solution that is present in the evaporation equipment is significantly increased. The result of this is high allowable concentration factors and a corresponding increase in the recovery of high quality reusable water with essentially no scaling.
Full Text METHOD AND APPARATUS FOR HIGH EFFICIENCY
PRE-TREATMENT OF FEED WATER
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on and claims priority from provisional patent
Application Number 60/419,552 filed on October 18,2002 and provisional patent
Application Number 60/419,549 filed on October 18,2002.
TECHNICAL FIELD
This process relates generally to a method and to a water evaporation system
for the treatment of waters that contain dissolved organic materials and inorganic
salts and in particular to a method that results in a non-scaling heat transfer
surface. In various embodiments, this process relates to methods for feed -water
pretreatment that results in higher design concentration factors (higher recovery),
an increase of the on-stream availability of the evaporation system, and an
essentially scale free environment at the heat transfer surface.
BACKGROUND
In today's world of increased awareness of the environment along with the
high costs and regulations that prohibit and/or limit wastewater disposal to publicly
owned treatment services or the environment, there is a demand for water treatment
equipment that minimizes wastewater, promotes water reuse in the process, and
lowers the quantity of fresh water that has to be imported from wells or public
water supplies.
The restraints put on many industries, such as steam-electric power plants,
nuclear power plants, and oil production companies, have led to adoption of a Zero
Liquid Discharge (ZLD) policy in many instances. A facility can achieve ZLD by
collecting and recovering most or all of the water from the wastewater. The
resulting highly concentrated wastewater, or dry solids, are then held in ponds on
site or the dry solids can be transported to a landfill.
[00005] A variety of technologies have been developed to recover water from
wastewater or to reduce the volume of the wastewater. These technologies have
limitations of complexity and susceptibility to interruption of service or failure of
components due to corrosion, fouling, or scaling by the wastewater constituents,
especially when feed waters vary from foreseen conditions.
[00006] A continuing demand exists for a simple and efficient process which can
reliably provide water of a desired quality, in equipment that requires a minimum
of maintenance. In particular, it would be desirable to improve efficiency of feed
water usage, and lower both operating costs and capital costs for high quality water
systems as is required for the various industries.
[00007] In most water treatment systems for the aforementioned industries, the plant
design and operational parameters generally are tied to final concentrations (usually
expressed as total dissolved solids, or "TDS"), which are tolerable in selected
equipment with respect to the solubility limits of the sparingly soluble species
present. In particular, silica, calcium sulfate, barium sulfate, calcium fluoride, and
phosphate salts often limit final concentrations achievable or require operation of
the system using the so-called seeded slurry design. To avoid scale formation and
resulting decreases in heat throughput, the design and operation of an evaporation
based water treatment plant must recognize the possibility of silica and other types
of scale formation, and must limit water recovery rates and operational practices
accordingly. In fact, typical evaporation plant experience has been that a reduction
in distillate flow rates requires chemical cleaning of the evaporator at regular
intervals. Such cleaning has been typically required because of scaling, participate
fouling, biofouling, or some combination thereof. Because of the cost,
inconvenience, and production losses resulting from such cleaning cycles, it would
be advantageous to lengthen the time between required chemical cleaning events as
long as possible.
[00008] It would be desirable to reduce the scaling, fouling, and corrosion tendencies
of the feed water to the point where concentration factors could be increased in the
design, and where flux rates could be increased, compared to limits of conventional
scale control methods used in water evaporation systems. Raising the allowable
concentration factors and flux rates, along with lowering the corrosion potential, is
always important to the end user as these design points result in a lowering of
capital costs.
[00009] Present state of the art embodies several different strategies to alleviate the
problems associated with scaling and fouling in higher concentration systems.
These include the use of chelating agents, dispersants, solubility promoters, filters,
silica precipitators, operating at low concentration factors, and the use of
preferential deposition in a seeded slurry of calcium sulfate (CaSO4) crystals. In
the preferential deposition method, the low solubility precipitating crystals tend to
deposit on the seeds that are suspended in the circulating solution rather than on the
heat transfer surface.
[00010] Membrane separation processes have also been used to obtain reusable water
from wastewaters but they are typically limited to low recovery operations due to
fouling/scaling limits, frequent cleanings, and replacement intervals of three years
or less due, in part, to the frequent cleanings which can cause them to lose their
rejection capability as well as productivity. A newly patented RO technology,
HERO1"1, utilizes softening and high pH operation to obtain recoveries up to 90
percent but has yet to show an extended membrane life comparable to the 20 years
expected of an evaporator. This process is also limited in allowable concentration
factor attainable due to osmotic pressure limitations, which currently is around
about ten percent total dissolved solids.
[00011] The prior art methods have the following shortcomings: (a) they rely on anti-
scaling additives to prevent scale formation, or (b) they rely on seeding techniques
for preferential deposition to minimize scaling of the heat transfer and other
surfaces. Preferential deposition, while It works well in some applications, is not
the final answer as it cannot be expected to pick up every individual crystal that is
precipitating and some invariably end up on the heat transfer surface, or sump
walls, where they themselves then act as a seed site for scale buildup. In addition,
certain feed waters do not have enough calcium sulfate (CaSO4) in solution to serve
as a self-renewing seed slurry. These feed waters then require the use of additional
chemical treatment systems to supply the needed calcium (Ca) or sulfate (SO4), or
both, needed for this type of scale control method. Further complications inherent
to the preferential deposition method are, (1) the need to carefully control the
amount and size of seed that is circulating at any given time as too small a seed will
cause fouling to occur in the laminar flow portion of the stream and too much seed
will result in plugging of areas like water distribution trays, and (2) there is a limit
to the concentration factor obtainable when the presence of double salts, such as
glauberite (NaCa(SO4)2) will form scale as the concentration factor is increased.
[00012] Thus, for the most part, the prior art methods have one or more of the
following shortcomings: (a) they rely on anti-scaling or dispersant additives to
prevent scale formation, (b) are subject to scaling, fouling, and a short useful life,
(c) they rely on seeding techniques to minimize scale deposition, or (d) are not able
to concentrate beyond 7 or 8 percent TDS. Thus, the advantages of our treatment
process, which exploits (a) multi-valent cation removal to non-precipitating
residual levels, and (b) efficient dealkalization, to allow extended trouble free
evaporator operation at high pH levels, are important and self-evident.
[00013] As water is becoming increasingly expensive, or in short supply, or both, it
would be desirable to increase the ratio of treated product water to raw water feed
in evaporator systems. Therefore, it can be appreciated that it would be desirable to
achieve reduced costs of water treatment by enabling water treatment at higher
overall concentration factors than is commonly achieved today. Finally, it Would be
clearly desirable to meet such increasingly difficult water treatment objectives with
better system availability and longer run times than is commonly achieved today.
Glassman, Patent 4323430 discloses an ammonia recovery process for coal conversion facilities
utilizing two stage distillation techniques. In the process they use Ca(OH)2 to convert NH4 to NH1
which comes off in the vapor during the stripping process. By conversion of the ammonia salts to
ammonia, the pH is lowered and strippping off the acidic gases such as CO2, HCN, and H2S occurs
The pH is lowered to about 8, where removal of the gases is expected. Those that donot convert
to gas are subjected to the lime treatment to precipitate CaCO3, CaS, and Ca(CN)2 as sludge in the
2nd stage distiller to recover a high purity ammonia vapor. The concentrated stream from the
distillation steps has to be sent through a clarifier prior to discharge into a receiving body of water.
The ammonia and acid gases present in the above invention does not address bound CO2 present in
the carbonate ions. The present invention removes all of the dissolved carbon di-oxide to make the
evaporator operate in a non-scaling environment.
Riggs, Patent 4746438 discloses post-treatment of distillate from an evaporator to make it suitable
for boiler makeup. By definition, the distillate is already a high quality water that is contaminated
with carry over in the vapor along with non-condensable gases. It uses a SAC or WAC for
demineralization, a pH out of the demineralization zone of 3.5-4 based on the resin action, a
preferred air driven degassifier
and pH adjustment to 9-10 with an ammonium compound.
Applebaum, Patent 2807582 deals with the removal of alkalinity, degassification, and silica to
allow boiler operation to a pre-determined concentration factor based on how much silica is left
after treatment.
Weigert, Patent 4235715 deals with the removal, of alkalinity and hardness from boiler feed waters
through the use of deionization and degassing. It does not address silica at all.
The above mentioned other three patents , though disclose common use of deionization and
degassing, specifically state that they are for 'boiler feed waters' that need hardness, alkalinity, or
silica removal, while the present invention can operate with high silica levels.
[00014] In so far as we are aware, no one heretofore has thought it feasible to operate
an evaporator based water treatment system in a scale free environment and at an
elevated pH, in continuous, sustainable, long-term operations to produce a high
quality water product. The conventional engineering approach has been to design
around or battle scale formation, by use of moderate pH, by limiting final
concentration factors, by use of chemical additives, or by use of preferential
deposition.
[00015] In contrast to prior art methods for water treatment, the method described
herein uses the essential design philosophy of virtually eliminating any possible
occurrence of scaling phenomenon during evaporator operation at the maximum
feasible pH, while maintaining the desired concentration factor, and taking the
benefit of water recovery that results.
SUMMARY
[00016] We have now invented a novel water treatment method that emphasizes
feeding an evaporator with an essentially multi-valent cation free water that allows
high pH evaporation in a scale free environment, to produce a high quality distillate
at greater cycles of concentration.
[00017] In a unique feed water treatment process, raw feed waters of suitable
chemical composition are preferentially treated with a weak acid cation ion
exchange resin, operated in the hydrogen form, to simultaneously remove multi-
valent cations and alkalinity. The weak acid cation ion exchange resins can be
operated at incoming raw feed water hardness and alkalinity levels well above
those that would cause conventional ion exchange systems to fail due to hardness
breakthrough.
[00018] The preferred treatment train design used in our wastewater treatment plant
overcomes a number of important and serious problems. First, the low levels of
multi-valent cations, combined with virtual elimination of non-hydroxide alkalinity,
substantially eliminates the precipitation of scale forming compounds associated
with sulfate, carbonate, or silicate anions. Thus, cleaning requirements are
minimized. This is important commercially because it enables a water treatment
plant to avoid lost water production, which would otherwise undesirably require
increased treatment plant size to accommodate for the lost production during
cleaning cycles. Second, the preferred high pH operational conditions enable a high
degree of ionization to be achieved in various species which are sparingly ionized
at neutral or near neutral pH in aqueous solution, to enable such species to be
concentrated to higher levels before precipitation. Third, the method does not have
the osmotic pressure limitation of membrane based systems and allows operation
and much higher TDS concentrations with resultant higher recovery or water and
reduction in final waste quantity. Finally, operation at high pH and heat provides
protection against biological contamination, thus preventing undesirable
contamination of the distillate stream. At the preferred high operational pH,
bacteria and endotoxins are effectively destroyed. In essence, water treatment
systems operated according to the process herein normally operate at conditions,
which might ordinarily be considered cleaning conditions for conventional
evaporation systems.
[00019] We have now developed a novel process design for use in the treatment of
water. In one embodiment, the process involves treatment of a feed water stream,
which is characterized by the presence of (i) multi-valent cations, (ii) alkalinity, and
(iii) molecular species which are sparingly ionized when in neutral or near neutral
pH aqueous solutions, to produce a low solute containing distillate stream and a
high solids containing blowdown stream. The process involves effectively
eliminating the tendency of the raw feed water to form scale when the raw feed
water is concentrated to the desired concentration factor at a selected pH by
removing multi-valent cations from the raw feed water stream and by effecting, in
any order, one or more of the following:, (i) removing alkalinity from the raw feed
water stream, (ii) removing dissolved gases whether initially present or created
during the multi-valent cation or alkalinity removal steps, or (iii) raising the pH.
The pH of the feed water is raised to a selected pH in a range between 9 and 10, or
otherwise in excess of 10, and more preferably to about 11 to 12 or somewhat
more, until the benefits gained by high ionization of silica and other species is
outweighed by the additional cost. The pH increase is accomplished by adding a
selected base to the softened and degassed feed stream, preferably by direct
injection into the feed stream or alternately into the sump of the evaporator. The pH
increase urges the molecular species, which are sparingly ionized when in neutral
or near neutral pH toward increased ionization. The pH adjusted feed water is then
sent through heat transfer evaporation equipment to produce a concentrated
blowdown stream and a low solute containing distillate stream. The evaporation
equipment is typically of the falling film type wherein the heat transfer surface is
comprised of a number of tubes with evaporation on either the interior or exterior
surface, a plurality of plate style with evaporation on the outer surface, or a forced
circulation process. It is important that in our process, the evaporation equipment
operates in an essentially scale free environment to produce a distillate stream,
which is substantially free of the normally undesirable species while operating at an
increased efficiency due to increased solubility limits of sparingly soluble salts at
an elevated pH.
OBJECTS, ADVANTAGES, AND FEATURES
[00020] From the foregoing, it will be apparent that one important and primary
object of the present invention resides in the provision of a novel method for
treatment of water to reliably and continuously produce, over long operational
cycles, a water distillate stream of high quality, suitable for reuse, at a reduced
capital and operating cost.
[00021] More specifically, an important object of our invention is to provide an
evaporation based water treatment method which is capable of avoiding common
scaling and fouling problems, so as to reliably provide a method of high quality
water generation when operating at increased efficiency on a variety of
wastewaters.
[00022] Other important but more specific objects of the invention reside in the
provision of a method for water treatment as described in the preceding paragraphs
which:
[00023] allows for the removal of multi-valent cations and alkalinity from a
selected feed water to be done in a simple, direct manner;
[00024] has high efficiency rates, that is, provide high product water outputs
relative to the quantity of feed water input to the water treatment plant;
[00025] allows operation at pH above 9, which reduces the concentration of
hydrogen ion present in the aqueous solution;
[00026] allows operation at higher specific heat transfer rates, which reduces
the amount of heat transfer surface required;
[00027] allows removal of dissolved oxygen from the aqueous solution;
[00028] in conjunction with the preceding objects, the reduction of hydrogen
ion and oxygen concentration reduces the corrosiveness of the aqueous
solution allowing the use of lower cost materials for most feed waters;
[00029] provide lower unit costs to the water treatment plant operator and
thus to the water user, than is presently the case;
[00030] in conjunction with the just mentioned object, results in less chemical
usage than in most water treatment facilities, by virtually eliminating use of
some types of heretofore commonly used chemical additives, particularly
scale inhibitors or chemicals needed to maintain a seeded slurry, and
eliminates expensive physical/chemical scale removal techniques and
downtime;
[00031] in conjunction with the scale free environment object previously
mentioned, results in a lower corrosion potential and allows for lower grade
materials of construction in lieu of high alloy materials.
[00032] A feature of one embodiment of the present invention is the use of a unique
combination of weak acid cation ion exchange with substantially complete hardness
and alkalinity removal, and subsequent high pH evaporation operation, thereby
enabling the water treatment plant to minimize the percentage of blowdown water.
This results in high overall cycle efficiencies.
[00033] Another feature of the present invention is the use of a high pH operation to
highly ionize weakly ionizable species such as silica or boron, thus enabling
operation with silica or boron concentration limits considerably exceeding the
limits of conventional evaporation treatment systems when treating feed waters of
comparable chemistry.
[00034] Another feature of the present invention is the capability to remove
ammonia from the feed stream as a part of the process instead of another separate
process. The ammonium ion (NH4) is very soluble in water with a dissociation
constant (pKa) value of 9.24. At a pH of 11.2 in the feed stream, a typical process
operating point of the present invention, it is over ninety nine percent (99%)
dissociated into the ammonia (NH3) ion and can be removed in the degassifier.
[00035] Yet, another feature of the present invention is the capability to retrofit
existing evaporation plants to operate according to the present process design, to
increase capacity without increasing the installed heat transfer surface.
[00036] Other important objects, features, and additional advantages of the invention
will become apparent to those skilled in the art from the foregoing, and from the
detailed description which follows, and from the appended claims, in conjunction
with the accompanying drawings.
BRIEF DSECRIPTION OF THE DRAWINGS
[00037] AH the exemplary embodiments shown herein incorporate the Zero Liquid
Discharge (ZLD) concept option as a part of the illustration. Those skilled in the
art will recognize that merely minimizing the blowdown stream without the use of
a dewatering device may, on certain occasions, also qualify the system as ZLD.
The high efficiency evaporation method is highly site specific wherein individual
process steps are customized to fit the specific feed water, and needs of the
customer, at the specific site. For that reason, all possible embodiments of this
novel method of water treatment are not illustrated and, as those skilled in the art
can appreciate, other illustrative embodiments would merely reflect variations and
arrangement of some components without affecting the spirit or concept of this
invention.
[00038] The same identifier will reference identical features depicted in each of the
drawings.
[00039] Figure 1 is a graph illustrating the ionization of silica as a function of pH;
[00040] Figure 2 is a flow diagram illustrating one embodiment of the novel water
treatment method disclosed herein to obtain high efficiency evaporation utilizing a
weak acid cation exchange system to remove divalent cations and alkalinity
associated with hardness in one step;
[00041] Figure 3 is a flow diagram illustrating another embodiment of the novel
water treatment method disclosed herein to obtain high efficiency evaporation and
high purity distillate simultaneously;
[00042] Figure 4 is a flow diagram illustrating another embodiment of the novel
water treatment method disclosed herein to obtain high efficiency evaporation,
minimized blowdown, and low solute containing distillate for use as cooling tower
or scrubber makeup;
[00043] Figure 5 is a flow diagram illustrating another embodiment of the novel
water treatment method disclosed herein showing the arrangement of equipment
wherein sodium zeolite softening is sufficient for high efficiency evaporation. The
use of an optional lime or lime/soda softener for hardness removal is also depicted;
and
[00044] Figure 6 is a flow diagram illustrating another embodiment of the novel
water treatment method disclosed herein wherein acid addition adequately removes
any alkalinity present in the feed stream and where hardness removal, if present,
can be optionally accomplished with lime or lime/soda softening.
DETAILED DESCRIPTION
[00045] Since many industrial applications of various types generate large quantities
of wastewater that is becoming increasingly expensive and regulated, it has become
desirable to process it for internal reuse and limit or eliminate discharge into public
utilities. Present day state of the art is limited on how much water can be recovered
by scale causing ions, such as hardness and silica, which are inherent in these waste
streams. The addition of expensive scale inhibiting agents or scale control methods
are beneficial but still have their limits of usefulness. We have designed a novel
process to overcome these limitations and recover more of the wastewater for reuse
than was previously possible by providing a scale free environment in the
evaporator. As used herein the term "scale" is intended to encompass not only a
thin coating, layer or incrustation (usually rich in sulfate or calcium) that is
deposited on a surface, but also particulate fouling, biological fouling, or some
combination thereof.
[00046] Attributes that characterize the high efficiency evaporator (HEVAP) process
design and operation are:
[00047] (1) Very high solubility of weak acid anions such as silica.
[00048] (2) Very high achievable concentration factors (recovery—ninety
percent (99%) or higher recovery can be achieved).
[00049] (3) Biological fouling is essentially eliminated.
[00050] (4) Particulate fouling is substantially reduced.
[00051] (5) Cleaning frequency is substantially reduced.
[00052] (6) Addition of scale inhibitors is virtually eliminated.
[00053] (7) Corrosion potential is reduced.
[00054] (8) Higher heat flux is achievable.
[00055] (9) Reduced overall capital cost, compared to conventional
evaporation systems.
[00056] (10) Reduced overall operating cost, compared to conventional
evaporation systems.
[00057] The HEVAP evaporation system is highly site-specific. Individual process
steps are customized to fit the specific feed water at a specific site. Regardless of
the difference in the pretreatment process for different sites, one process parameter
is common for all applications, namely that the evaporator system is operated at the
highest feasible blowdown pH and that the circulating solution provides a scale free
environment at the heat transfer surface.
[00058] In order to operate an evaporative system with a pH of at least about 9.0,
preferably at least about 10.5, and most preferably between 11 and 12, or above,
several process conditions must be met in order to effectively eliminate the
potential for scale formation on the heat transfer surface. Some of those process
conditions are also necessary for operating an evaporative system at very high
concentration factors. Such process conditions are as follows:
[00059] (1) The calcium, magnesium, strontium, and barium concentration
in the evaporator feed must be substantially absent, preferably to near zero,
and most preferably, to essentially zero.
[00060] (2) Aluminum, iron, manganese, and other multi-valent cation
content including organically bound species, as well as the presence of
colloidal particles containing such materials, should be substantially absent,
and preferably to near zero.
[00061] (3) Buffering anions (specifically bicarbonate, or carbonate,
and/or phosphate species) should be reduced to as low of a level as can be
practically achieved.
[00062] (4) Dissolved and suspended gasses such as oxygen, ammonia,
and others should be minimized.
[00063] The selection of specific operations and control points, to fulfill the above
process condition requirements, is influenced by the characteristics of each specific
feed water. The concentration factor needed (or desired for a specific application)
also affects the operations and control point criteria as well. FIG. 2 represents a
highly effective evaporator unit process sequence.
[00064] The first step is to adjust the hardness-to-alkalinity ratio of the feed water, if
needed. Optimizing this ratio, which is typically done by alkali addition, makes
complete hardness removal feasible in a weak acid cation ion exchange process
operated in the hydrogen form as described in the next process step.
[00065] The second step in the evaporator process train involves the utilization of a
weak acid cation (WAC) resin (e.g. DOWEXRTM. MAC-3, or Lewatit CNP-80,
Amberlite.RTM. IRC-86). Operated in either the hydrogen or sodium form, the
WAC resins remove multi-valent cations and, in the hydrogen form removes any
alkalinity associated with hardness.
[00066] The third step involves pH adjustment by adding acid to the WAC effluent.
Acid is added to destroy any alkalinity remaining, after multi-valent cation
removal, if any such alkalinity is present.
[00067] In a fourth step, the acidified effluent, containing virtually zero alkalinity, is
then treated for carbon dioxide removal. This removal can be accomplished in any
of various type degasifiers. The degasified feed water stream with multi-valent
cation levels below the limits required for scale free operation and essentially zero
alkalinity, is then injected with a soluble alkali, preferably for adjusting pH to 9.0
or higher, more preferably 10.5 or higher, and most preferably 11.0 or above.
[00068] In other embodiments where ammonia is a concern, a variation of the steps
is required. Alkali is added to the feed stream to decrease ammonia solubility at
elevated pH prior to removing it as a gas in a degassifier. In applications where
both alkalinity and ammonia are present, two degassifiers are required, one for
removing any gases such as carbon dioxide at low pH and one for ammonia
removal at high pH. In cases where there is no alkalinity due to a very low pH in
the feed stream, the ammonia can be removed by injecting alkali prior to a single
degassifier after reducing the multi-valent cations to a non-scaling level in the feed
stream.
[00069] Feed waters utilized for production of reusable water, especially those
encountered in wastewater treatment, include the presence of silicon dioxide (also
known as silica or SiO2) in one form or another, depending upon pH and the other
species present in the water. For evaporator systems, scaling of the heat transfer
surface with silica is to be religiously avoided. This is because (a) silica forms a
relatively hard scale that reduces productivity of the evaporator, (b) is usually
rather difficult to remove, (c) the scale removal process produces undesirable
quantities of spent cleaning chemicals, and (d) cleaning cycles result in undesirable
and unproductive off-line periods for the equipment. Therefore, regardless of the
level of silica in the incoming raw feed water, operation of conventional
evaporation processes, without a preferential deposition seeded slurry process,
generally involves concentration of SiO2 in the high solids stream to a level not
appreciably in excess of 150 ppm of SiO2 (as SiO2). This requires that evaporator
systems be operated at lowered concentration factors (recovery rates) to prevent
silica concentration in the blowdown stream from exceeding solubility limits.
Seeded slurry systems can be taken to concentration factors that surpass the
solubility of silica but rely on seed management procedures and are still prone to
scaling of the evaporator.
[00070] Scaling due to various scale forming compounds, such as calcium sulfate,
calcium carbonate, and the like, can be predicted by those of ordinary skill in the
art and to whom this specification is directed, by use of the Langelier Saturation
Index (LSI) or the Stiff-Davis Index (S&DI), or other available solubility data.
Operating parameters, including temperature, pH, distillate and blowdown flow
rates, must be properly accounted for, as well as the various species of ions in the
raw feed water, and those species added during pretreatment. The Nalco Water
Handbook, copyright 1979, by McGraw-Hill details the procedure for use of the
indexes.
[00071] With reference to Figure 2, wastewater stream 20 of this invention will
typically contain, soluble and insoluble, organic and inorganic components. The
inorganic components can be salts such as sodium chloride, sodium sulfate,
calcium chloride, calcium carbonate, calcium phosphate, barium chloride, barium
sulfate, and other like compounds. Metals such as copper, nickel, lead, zinc,
arsenic, iron, cobalt, cadmium, strontium, magnesium, boron, chromium, and the
like may also be included. When treating a wastewater stream from an oil refinery,
organic components will be present and are typically dissolved and emulsified
hydrocarbons such as benzene, toluene, phenol, and the like.
[00072] It is commonly understood that the solubility of silica increases with
increasing pH, and that silica is quite soluble in high pH aqueous solution. Along
with solubility, the degree of ionization of silica also increases with increasing pH.
While the increase in silica solubility is not directly proportional to the degree of
ionization, the rate of increase in silica solubility is basically proportional to the
rate of change in ionization as increased ionization results in the soluble silicate ion
being the dominant species. This discrepancy between solubility and ionization is
explained by the fact that even undissociated silica exhibits some solubility in
aqueous solutions, typically up to about one hundred twenty (120) ppm to one
hundred sixty (160) ppm, depending upon temperature and other factors. In
comparison, it has been demonstrated that silica solubility at pH 10.5 is in excess of
one thousand five hundred (1,500) ppm at ambient temperature; silica is
increasingly soluble as temperature and/or pH increases.
[00073] Silica is very weakly ionized when in neutral or near neutral aqueous
solutions and is generally considered to exist as undissociated (meta/ortho-) silicic
acid (H4 SiO4) in most naturally occurring waters with a pH of up to about 8. The
dissociation constant (pKa) value for the first stage of dissociation of silica has
been reported at approximately 9.7, which indicates that silica is approximately
fifty percent (50%) ionized at a pH of 9.7; the other fifty percent (50%) remains as
undissociated (ortho) silicic acid at that pH. A graphical representation of the
relationship between pH and the percent silica ionization is shown in FIG. 1.
Clearly, it would be advantageous, where silica ionization is desired, to operate at a
pH in excess of 10, and more preferably, in excess of 11, and yet more preferably,
in excess of 12 where all of the silica molecule is present as a soluble silicate ion.
[00074] Therefore, increasing the pH of the evaporator operation thus provides the
major benefit of increased silica solubility. To gain maximum benefit from silica
ionization at high pH, the evaporator system should be operated at a pH as high as
possible, Preferably, the evaporator system is operated at a pH of about 10.5 or
above, and more preferably, at a pH of 11 or higher. This contrasts with typical
evaporator operation practice, where operating pH has been maintained at less than
9 in order to avoid scale formation, particularly silica and carbonate scales.
[00075] Referring to FIG. 2, one embodiment of this process for evaporation
equipment operation is shown. In this method, raw water 20 is first treated in a
weak acid cation (WAC) ion exchange unit 22, where hardness and bicarbonate
alkalinity are simultaneously removed. For those cases where raw water 20
hardness is greater than alkalinity, operation of the weak acid cation ion exchange
unit 22 must be facilitated by addition of a source of alkalinity 21, such as by
addition of an aqueous solution of sodium carbonate (Na2 CO3). Preferably, the
WAC unit 22 is operated in the hydrogen form for ease of operation and
regeneration. However, it would also work in the sodium form, followed by acid
addition. In any case, in the just mentioned case and otherwise optionally where
appropriate, acid 23 is added to the effluent 27 from the WAC unit(s) 22 to enhance
bicarbonate destruction. Sufficient acid is added to lower the pH where bound
carbonates are converted to a free gas carbon dioxide. Then, the carbon dioxide 32
that has been created in the WAC (and/or by acid addition) is removed, along with
other non-condensable gasses such as oxygen and nitrogen, preferably in an
atmospheric pressure or vacuum/flash degasifier 30. Finally, an alkali 31 (base) is
added, preferably by pumped injection of liquid solution, to increase the pH of the
feed water 34 to a selected level. Any of a variety of conveniently available and
cost effective base products may be used, provided that no appreciable scaling
tendency is introduced. Besides use of common sodium hydroxide, other chemicals
such as sodium carbonate, potassium hydroxide, or potassium carbonate might be
selected. In fact, in certain cases, an organic base, such as a pyridine type
compound, may be used effectively to carry out this process.
[00076] The pH of the feed water is raised to a selected pH of at least about 9.0, or
up to about 10, or preferably to a range between 10 and 11, or otherwise in excess
of 11, and more preferably to 12 or more, and most preferably, to 13 or more.
[00077] The weak acid cation ("WAC") ion-exchange resins used in the first step of
the preferred embodiment of the method defined herein, as illustrated in FIG. 2, are
quite efficient in the removal of hardness associated with alkalinity. Such a reaction
proceeds as follows:
[00078] Ca+++2RCOOH-(RCOO)2 Ca+2H+
[00079] Then, the hydrogen combines with the bicarbonate to form carbonic acid,
which when depressurized, forms water and carbon dioxide, as follows:
[00080] H+ +HCO3-H2 CO3-H2 O+CO2
[00081] Regeneration of the resin is accomplished by use of conveniently available
and cost effective acid. It is well known by those in the art that regeneration of
WAC ion-exchange resins may proceed quite efficiently, at near stoichiometric
levels (generally, not more than about one hundred and twenty percent (120%) of
ideal levels). Preferably, hydrochloric acid may be used, since in such cases highly
soluble calcium chloride would be produced, and the regeneration process would
not pose the potential danger of formation of insoluble sulfate precipitates, such as
calcium sulfate, even with high strength acids. However, by use of a staged
regeneration procedure, i.e., by using a low concentration acid followed by a higher
concentration acid, it is possible to reliably utilize other acids, including sulruric
acid (H2 SO4), while still avoiding undesirable precipitates on the resin. In this
manner, hardness ions are solubilized to form soluble salts, which are eluted from
the resin bed and are typically sewered.
[00082] Other polyvalent cations, most commonly iron (Fe++/Fe+++), magnesium
(Mg++), barium (Ba++), strontium (Sr++), aluminum (AI++), and manganese (Mn++
/Mn++++), are also removed by the WAC resin. Since the presence of even very
small quantities of hardness or other species of decreasing solubility at increasing
pH will result in precipitation of sparingly soluble salts under the process
conditions present in our process, care must be taken to prevent precipitation on the
heat transfer surface of the substances such as calcium carbonate, calcium
hydroxide, magnesium hydroxide, and magnesium silicate. One precaution that
should be observed is that both hardness and non-hydroxide forms of alkalinity
should be aggressively reduced in the feed water, prior to upward pH adjustment to
selected evaporator operating conditions. Once the multi-valent cations and non-
hydroxide forms of alkalinity have been removed, then the desired pH increase may
be accomplished with any convenient alkali source, such as sodium or potassium
alkali. Once this pretreatment has been thoroughly accomplished, then an
evaporator system can be safely operated at very high pH levels, in order to take
advantage of the aforementioned silica solubility.
[00083] The treated and conditioned feed water 34 is directed into the evaporator 40
where it mixes with and dilutes the concentrated high solids stream 43. This stream
is recirculated with pump 42 and a small portion is removed as evaporator
blowdown 47 on each pass through the evaporator 40. In the evaporator 40 the
solutes in the feed water 34 are concentrated by removing water from the diluted
recirculating solution 43 as it passes over the heat transfer surface. As depicted in
Figure 2, the evaporator utilizes falling thin film evaporation wherein the
recirculated stream 43 is thinly spread across the inner surface of a plurality of heat
transfer tubes. A small portion of water is removed from the thin recirculating
stream in the form of steam 45 driven by heated, compressed steam 48 which is
condensing on the outside of the heat transfer tubes. The water that has been
removed, in the form of steam 45, is compressed through the compressor 46, and
the compressed steam 48 is condensed on the outer surface of the heat transfer
tubes to generate more steam 45, and keep the evaporation process going. The
condensing steam 48 is known as distillate or condensate, as is known to those
skilled in the art of evaporation, and contains a low level of non-volatile solutes,
typically, in some embodiments, less than 10 parts per million (ppm). It should be
noted that the use of a tubular falling film evaporator 40 design is provided only for
purposes of enabling the reader to understand the evaporation process and is not
intended to limit the process to the use of the same. Those familiar with the art will
recognize that other designs, such as, for example, a rising film evaporator, or a
forced circulation evaporator, or a plate style evaporator may be alternately utilized
with the accompanying benefits and/or drawbacks that may be inherent in the
alternative designs.
[00084] The condensing steam 48 descends by gravity to the bottom of the tubular
heat transfer surface and is collected as distillate stream 44. A small portion of the
distillate 44 may be sent to the earlier discussed degasser 30 via line 100 for use in
mass transfer, i.e., adding heat to the feed water stream 27 to remove non-
condensable gasses such as carbon dioxide 32. However, the bulk of the distillate
44 is directed to the terminal point of the evaporator where it is available for use in
any process that requires high quality water as a makeup stream. Typical, but not
limiting, uses include those shown in the Figure 4 embodiment of the high
efficiency evaporation process in which the distillate can be used as makeup to a
cooling tower or scrubber. Other uses would include low-pressure boilers and, in
the hydrocarbon recovery field (produced water), as feed water to a once through
steam generator (OTSG) that generates steam for injection into oil-bearing
formations.
[00085] Although the low solute containing distillate 44 produced by the evaporator
is relatively pure water, there are instances where a higher purity is required.
Figure 3 depicts an embodiment wherein several different options are shown for
obtaining different levels of high purity. In most cases the residual solutes in the
distillate stream 44 involve salts other than hardness. In one embodiment, the
distillate 44 is passed through a cation ion exchange system 70, followed by an
anion ion exchange system 72, and then polished in a mixed bed ion exchange
system 76 to produce a very high purity water. The inclusion of all three ion
exchange systems is for illustration only and those of ordinary skill in the ion
exchange arts and to which this disclosure is directed will recognize that only those
ion exchange systems required to meet the requirements for purity will be used. In
any event, the ion exchange systems will require regenerant chemicals and that will
result in a regeneration waste stream 73 which can be directed to the inlet of the
degasifier 30 for further treatment in the evaporator 40. In an alternate
embodiment, the removal of residual solutes in the distillate stream 44 can be
accomplished by passing the stream through an electrodeionization (EDI) unit 80.
The EDI reject is also capable of being recycled to the evaporator by directing it to
the inlet of the degasifier 30.
[00086] The impact of very low levels of silica, etc., in the relatively pure distillate
44 obtainable by evaporation on the behavior/operation of a post-evaporator ion
exchange system is extremely significant. Since the vast majority of post-
evaporator ion exchange is regenerated on the basis of either silica or boron
breakthrough, a factor often reduction in the influent silica/boron content will
provide much longer run times between regenerations. Absence of carbon dioxide,
as well as bicarbonate in the distillate 44 (due to a high pH, typically at least 10),
will also increase on-line time before silica/boron leakage exceeds normal threshold
values. Reduction of strongly ionized species concentration in the distillate 44 is of
relatively less significance, since most post-evaporator ion exchange is ultimately
silica or boron limited.
[00087] The just described combination of treatment steps when combined with the
novel process described hereinabove produces a water of sufficient quality, and
economic quantity, to be used in high pressure and packaged boilers. Typical users
would be the power generation industry and hydrocarbon recovery operations
wherein 100% quality steam is utilized for steam flooding applications.
[00088] The evaporator blowdown 47 containing the concentrated solutes originally
present in the feed water 34 along with any chemicals used to raise the pH and/or
regenerate post ion exchange systems can be disposed of by the standard approach
used at individual sites. This includes holding on-site in waste evaporation ponds,
trucking to a waste site, or injection into deep wells.
[00089] Alternatively, the blowdown stream 47 can be directed to a crystallizer 55
that further processes the concentrated stream to recover low solute distillate 53 and
a high-suspended solids stream 60. The distillate stream 53 is then combined with
the falling film evaporator distillate stream 44 to effect increased recovery of the
evaporator feed stream 34. The high-suspended solids containing stream 60 can
then be directed to a dewatering device 50., typically a belt filter but alternatively a
filter press or even a spray drier. The final product is a dried solid that is suitable
for landfill or possibly even reused within the originating process. The two
different filter methods generate a high solute/low suspended solids stream 52 that
is directed back to the crystallizer 55 for further processing.
[00090] In other embodiments, and as suited to meet the particularized needs of a
selected raw feed water chemistry, various forms of hardness removal may be
utilized, including sodium form strong acid cation exchange 65, followed by
acidification (see FIG. 5) or even the use of a lime 82 (or similar lime/soda)
softener as an additional pretreatment step to either sodium form strong acid cation
exchange 65 or weak acid cation exchange 22 (see FIGS. 2 and 5). The direct
injection of lime and sodium carbonate into the feed stream can also be utilized and
the resulting precipitate filtered out in a membrane separation process, such as
ultrafiltration, as a substitute for the lime/lime soda 82 softener.
[00091] For particularly soft waters, the lime or lime/soda softener 82 may be totally
inappropriate, and this method may proceed with no softening of the raw water, and
only a simple acid 24 feed before degasifying, as can be seen in FIG. 6. On the
other hand, where softening is appropriate, some raw feed waters can be
appropriately treated for reductions in hardness and alkalinity to a desired extent by
softener 82.
[00092] In still other embodiments and for a selected feed water, the use of softening
membranes for partial removal of hardness may be incorporated into the process as
a replacement for sodium zeolite 65 or weak acid cation 22 softening.
[00093] In cases where raw water composition is such that sodium zeolite softening
is advantageous, as is depicted in FIG. 5, elimination of calcium hardness proceeds
as follows:
[00094] Ca+2+Na2X-CaX+2Na+
[00095] Then, bicarbonate alkalinity is converted to carbon dioxide, with a selected
acid, in a manner similar to the following:
[00096] NaHCO3 +HCl.-NaCl+H2 O+CO2
[00097] For those waters where lime softening may be an acceptable or preferred
method for initial hardness and alkalinity reduction, the addition of lime to the
water reduces calcium and magnesium hardness, and associated bicarbonate
alkalinity, as follows:
[00098] Ca(HCO3)2 +Ca(OH)2 -2 CaCO34+2H2O
[00099] Mg(HCO3)2 +2Ca(OH)2-Mg(OH)2+2 CaCO3+2H2O
[000100] Regardless of the equipment configuration selected for treatment of a
particular raw water chemistry, the key process parameters are (a) to remove those
cations which, in combination with other species present at high pH, would tend to
precipitate sparingly soluble salts on the heat transfer surfaces, and (b) eliminate
non-hydroxide alkalinity to the maximum extent feasible, to further protect against
precipitation of scales on the heat transfer surfaces when operating at an elevated
pH.
[000101] FIG. 10 illustrates the use of our novel method of evaporator system
operation for cooling tower makeup water or for scrubber makeup water. The
evaporator unit 40 and various pretreatment equipment are operated according to
the methods set forth hereinabove, to produce a high quality distillate 44. Although
the cooling tower 95 and scrubber 90 could be fed with distillate 44, more typically,
the cooling tower 95 and scrubber 90, for example in a steam-electric power plant,
would be supplied by usual raw water 20 supplies, such as municipal or well water.
Therefore, cooling tower blowdown 96 and scrubber blowdown 91 are typically
high in both hardness and alkalinity. Likewise, this system may be used to treat
water having intimate contact with ash, such as ash pond water or ash-sluicing
water from coal fired steam-electric power plants. In our evaporation process, a
significant amount of reusable water can usually be obtained by our method of
evaporation pretreatment and operation, unlike the case with conventional
evaporative systems.
[000102] Another advantage, since an evaporator system when operated as described
herein will not be subject to scaling or fouling conditions, wastewaters from
refineries, hydrocarbon recovery operations, pulping and papermaking operations,
membrane concentration systems, and municipal sewage treatment plants, are
candidates as suppliers of raw water 20. Typical industrial uses where water of
sufficient quality may be attained when treating wastewaters include cooling
towers, boiler makeup, scrubber makeup, and the like.
[000103] Benefits of HEVAP Evaporation Process Design and Operation
[000104] Many exemplary and desirable process benefits provided by the HEVAP
evaporation system process design and operation were listed above. Detailed
explanation of such benefits include:
[000105] (A) High solubility of silica
[000106] It has been documented by others that silica solubility in water at 25°C.
approaches 6000 milligram per liter (mg/l)at a pH of 11 and at a pH of 12, the
solubility approaches 60,000 mg/1 when in equilibrium with amorphous silica. It
has also been documented that the solubility of silica in water goes up with an
increase in temperature leading to the conclusion that evaporator operation at
temperatures in excess of 100°C. at an elevated pH and silica levels up to 6000
mg/l is feasible. However, this is only possible if precipitating species such as
calcium and magnesium and the like have been removed from the feed stream so
that they cannot encourage the polymerization of silica and subsequent scaling on
the heat transfer surface. The novel process disclosed herein wherein an aggressive
approach to multi-valent cation and alkalinity removal is practiced, allows
operation at much higher levels of silica concentration than were previously
possible in normal evaporators. Since the high pH utilized by this novel process
assures increased silica solubility, a concentration factor (i.e., ratio of feed rate 34
to blowdown rate 47) for the evaporator 40 can be selected so that silica solubility
is not exceeded.
[000107] (B) High Recovery Rates
[000108] Since multi-valent ions such as calcium, magnesium, barium, strontium,
aluminum, iron, manganese, etc., have been removed prior to concentration in the
evaporator, undesirable precipitation of species such as calcium carbonate, calcium
fluoride, calcium sulfate, barium sulfate, magnesium hydroxide,
aluminum/magnesium silicate, etc., does not occur in the high efficiency evaporator
process, and thus that type of precipitation no longer limits the recovery achievable
by an evaporator system. Importantly, silica solubility is increased dramatically at
the normal high efficiency brand evaporator operating pH (preferably at
approximately 11 or above). Since silica usually represents the ultimate limiting
criterion, in terms of maximum allowable concentration in an evaporator system,
increased silica solubility along with essentially total absence of species such as
calcium, barium, etc., in the evaporator feed, will allow evaporator operation at
very high recovery rates (98 to greater than 99 percent) with the vast majority of
feed waters.
[000109] (C) Biological Fouling Eliminated
[000110] Most commonly occurring microbial species are completely lysed
(physically destroyed by wall rupture) at the high operating pH. In fact, even virus,
spores, and endotoxins are either destroyed or rendered incapable of
reproduction/proliferation at very high pH levels. Saponification of lipids (fat) is
expected to play a role in the process as well since fatty acids and their
corresponding glycerides will form soluble 'soaps' at the high operating pH. This
characteristic of the new process can be of significant benefit for sites with known
biofouling problems or for the treatment of bio-contaminated/bio-active
wastewater.
[000111] (D) Cleaning Frequency Reduced
[000112] The HEVAP process, which utilizes aggressive removal of multi-valent
cations and alkalinity along with a high pH in the evaporator, lengthens the time
between shutdowns to clean the equipment, Typically, two weeks per year are used
to clean heat transfer surfaces and sumps by opening them up to allow access for
expensive high pressure hydro-blasting procedures to remove the bulk scaling
material. This is then followed by time-consuming washes with costly proprietary
chemicals to remove any scale not removed by hydro blasting.
[000113] In contrast, the HEVAP process, by removing essentially all minimal
solubility ions and alkalinity, incurs only minimal scaling due to small leakage
from the softeners used. The result of this is that cleaning intervals can be extended
and that they can be simply and effectively accomplished by commodity cleaning
chemicals, such as hydrochloric acid solutions, tetra-sodium EDTA, and sodium
hydroxide. Expensive proprietary chemical cleaning agents are not required. The
scales that could occur would be predominantly calcium carbonate, magnesium
hydroxide, magnesium silicate, and the like, all of which can be removed with a
simple acid wash.
[000114] The increased system availability, with minimal scaling and virtually non-
existent bio-fouling, is clearly another important benefit of this novel operational
method.
[000115] (E) Scale Inhibitors
[000116] The use of antiscalants, scale dispersants, scale inhibitors, or scale control
methods, while not harmful or incompatible with the new process, can be
minimized, if not completely eliminated, due to the aggressive removal of multi-
valent cations along with virtually all non-hydroxide alkalinity as practiced by the
HEVAP pretreatment process.
[000117] (F) Higher Flux
[000118] Present day state of the art evaporators are heat flux (flow) limited due to the
presence of low solubility scale causing ions such as calcium carbonate, calcium
sulfate, silica and the like. A higher flux can be incorporated into the evaporator
design when these ions are absent in the feed stream and that is what is
accomplished with the process described herein.
[000119] (G) Reduced Capital Cost
[000120] The lowered corrosion potential that results from operating the evaporator
with a high pH in the concentrated circulating solution allows the use of lower cost
materials for heat transfer tubes or plates and other wetted surfaces that are
contacted by the concentrated solution, such as sump walls. This is an important
advantage since the costs of these materials have a substantial impact on the capital
cost of an evaporator. In most cases the use of high cost duplex and AL6XN (6
percent minimum molybdenum) type stainless steels, which are normally used in
high chloride salt solutions, can be eliminated in favor of a lower grade stainless
such as 316.
[000121] (H) Reduced Operating Cost
[000122] Water plant operating costs can be reduced due to minimizing, or
eliminating, costly proprietary antiscalants and/or dispersants. Additional savings
can be found by eliminating the need for seeded slurry operation at installations
where the multi-valent ions are at a low level in the feed stream but are
accompanied by high silica levels. Along with the cost of seeding the evaporator
with calcium sulfate crystals, there is also incurred costs associated with calcium
chloride and/or sodium sulfate injected chemicals to provide enough precipitating
ions to maintain the seed bed at many installations. Further savings can be realized
by the reduction in frequency of cleaning operations, less expensive cleaning
chemicals, less downtime for cleaning, and no requirement for costly physical
cleaning operations. Still further, if the ZLD option is incorporated, the cost of
sending the blowdown to a public utility company is eliminated.
[000123] It will thus be seen that the objects set forth above, including those made
apparent from the preceding description, are efficiently attained, and, since certain
changes may be made in carrying out the above method and in construction of a
suitable apparatus in which to practice the method and in which to produce the
desired product as set forth herein, it is to be understood that the invention may be
embodied in other specific forms without departing from the spirit or essential
characteristics thereof. For example, while we have set forth an exemplary design
for simultaneous hardness and alkalinity removal, other embodiments are also
feasible to attain the result of the principles of the method disclosed herein.
Therefore, it will be understood that the foregoing description of representative
embodiments of the invention have been presented only for purposes of illustration
and for providing an understanding of the invention, and it is not intended to be
exhaustive or restrictive, or to limit the invention to the precise forms disclosed. On
the contrary, the intention is to cover all modifications, equivalents, and alternatives
falling within the spirit and scope of the invention as expressed in the appended
claims. As such, the claims are intended to cover the methods and structures
described therein, and not only the equivalents or structural equivalents thereof, but
also equivalent structures or methods. Thus, the scope of the invention, as indicated
by the appended claims, is intended to include variations from the embodiments
provided which are nevertheless described by the broad meaning and range
properly afforded to the language of the claims, or to the equivalents thereof.
We claim:
1.A process for treatment of an aqueous feed stream in heat transfer equipment, said
heat transfer equipment comprising at least one evaporator with at least one heat transfer
surface, to produce a low solute containing distillate stream and a high solute/solids
containing blowdown stream, in which said feed stream has minimal tendency to scale said
heat transfer surface, said process comprising:
(a)providing a feed water stream containing soluble and insoluble inorganic and
organic species therein, said species comprising:
(II)multi-valent metal cations,
(III)alkalinity,
(IV)at least one molecular species which is at low ionization levels
when in solution at around neutral pH;
(b)removing a portion or substantially all multi-valent cations metal from said
feed stream, and
(c)reducing the tendency of said feed water to form scale on said heat transfer
surfaces, when said feed water is concentrated to a selected concentration factor at a
selected pH, by effecting, in any order, one or more of the following;
(I)removing substantially all alkalinity from said feed water stream;
(II)removing dissolved gas from said feed water stream;
(III)raising the pH of said feed water stream to at least 9 or higher;
(d)passing the product from step (c) into said heat transfer equipment, wherein
said heat transfer equipment:
(I)contains a plurality of heat transfer surfaces,
(II)contains a circulating high solids solution, and
(III)wherein the pH of said circulating solution is maintained to at least
9, or higher,
(e) so as to concentrate said feed water to said selected concentration
factor, to produce:
(I)a high solute/solids containing blowdown stream, and
(II)a low solute containing distillate stream.
2. A process as claimed in claim 1, wherein the step of removing said multi-valent
cations includes removing substantially all said alkalinity associated with hardness, and is
accomplished in a single unit operation.
3.A process as claimed in claim 2, wherein said single unit operation comprises a weak
acid cation ion exchange system operated in a hydrogen form.
4. A process as claimed in claim 1, wherein the said step of said multi-valent cation
removal is accomplished in a weak acid cation ion exchange system that is operated in a
sodium form.
5.A process as claimed in claim 1, comprising the step of adding acid before the step
of removing said dissolved gas, to effect conversion of alkalinity to carbon dioxide.
6.A process as claimed in claim 3, wherein said feed water stream contains more
multi-valent cations than alkalinity, and further comprising, before feeding said feed water to
said weak acid cation exchange system, the step of adjusting the ratio of multi-valent cations
to alkalinity by adding a base to said feed water, so as to raise the alkalinity of said feed water.
7.A process as claimed in claim 3, wherein said feed water stream contains more
alkalinity than multi-valent cations, and further comprising, before feeding said feed water to
said weak acid cation exchange system, the step of addition of acid to said feed water, so as to
remove the excess alkalinity in said feed water.
8. A process as claimed in claim 1, wherein the step of multi-valent cation removal is
accomplished by passing said feed water through a sodium form strong acid cation ion
exchange system.
9. A process as claimed in claim 1, wherein said sparingly ionized species when in
neutral or near neutral pH aqueous solution comprises a weak acid with a pKa, of 7.5 or
higher.
10.A process as claimed in claim 1, wherein said low ionized species when in neutral
or near neutral pH aqueous feed stream comprises silica (SiO2).
11. A process as claimed in claim 1, wherein said low ionized species when in neutral
or near neutral pH aqueous feed stream comprises meta/ortho silicic acid (H4 SiO4).
12.A process as claimed in claim 1, wherein said low ionized species when in neutral
or near neutral pH aqueous feed stream comprises an ionizable organic carbon species.
13. A process as claimed in claim 1, wherein said low ionized species when in neutral
or near neutral pH aqueous feed stream comprises boron, or derivatives thereof.
14. A process as claimed in claim 1, wherein the step of removal of multi-valent
cations is accomplished by addition of an alkali to simultaneously raise pH while precipitating
hardness from said feed water stream.
15.A process as claimed in claim 1, comprising the step of adding caustic before the
step of removing dissolved gas, to effect removal of gases such as ammonia.
16.A process as claimed in claim 1, wherein said at least one molecular species which is
at low ionization levels when in solution at around neutral pH comprises silica, and wherein said
blowdown stream contains silica up to 100,000 ppm.
17.A process as claimed in claim 1, wherein said feed water stream comprises silica,
and wherein said heat transfer equipment is operated without limitation of the concentration of
silica present in said blowdown stream.
18. A process as claimed in claim 1, wherein the ratio of the quantity of said distillate
stream produced to the quantity of said feed water stream provided is greater than 50%.
19.A process as claimed in claim 1, wherein said heat transfer equipment comprises
falling thin film evaporation equipment, operating as a single unit, or operating in series, or
operating in parallel to generate said distillate stream and said blowdown stream.
20 .A process as claimed in claim 1, wherein said heat transfer equipment comprises
forced circulation evaporation equipment operating as a single unit or operating in parallel to
generate said distillate stream and a high solids blowdown stream.
21 .A process as claimed in claim 1, wherein said heat transfer equipment comprises
natural circulation evaporation equipment operating as a single unit or operating in parallel to
generate said distillate stream and a high solids blowdown stream.
22.A process as claimed in claim 19 or claim 20 or claim 21, wherein said heat transfer
surfaces are tubular.
23.A process as claimed in claim 19 or claim 20 or claim 21, wherein said heat transfer
surfaces are plates.
24.A process as claimed in claim 22 or claim 23, wherein said heat transfer surfaces are
operated in a vertical position.
25.A process as claimed in claim 22, wherein said heat transfer surfaces are operated in
a horizontal position.
26.A process as claimed in claim 22, wherein said heat transfer surfaces are designed for
enhanced heat transfer.
27.A process as claimed in claim 22, wherein said circulating solution is heated on the
interior of the tubes.
28.A process as claimed in claim 22 or claim 23, wherein said circulating solution is
heated on the exterior of the tubes or plates.
29.A process as claimed in claim 23, wherein said plates are die pressed plates.
30.A process as claimed in claim 23, wherein said plates are made from flat sheets
welded together and then formed into final shape by internal pressure.
31 .A process as claimed in claim 23, wherein said plates are fabricated as welded
assemblies.
32.A process as claimed in claim 23, wherein said plates are gasketed.
33.A process as claimed in claim 19 or claim 20 or claim 21, wherein said heat transfer
equipment is operated in a steam driven multiple effect mode.
34.A process as claimed in claim 19 or claim 20 or claim 21, wherein said heat transfer
equipment is operated in a mechanical vapor recompression mode.
35.A process as claimed in claim 19 or claim 20 or claim 21, wherein said heat transfer
equipment is operated in a thermal compression mode.
36.A process as claimed in claim 19 or claim 20 or claim 21, wherein said heat transfer
equipment is operated as a multiple stage flash evaporator.
37.A process as claimed in claim 19 or claim 20 or claim 21, further comprising the step
of treating said high solute concentrate stream in a crystallizer operating as a single unit or
operating in parallel to generate said distillate stream and said high solids blowdown stream.
38.A process as claimed in claim 20 or claim 37, comprising the step of further treating
said high solids blowdown stream after reaching said selected concentration factor in a solids
dewatering device operating as a single unit or operating in parallel.
39.A process as claimed in claim 38, comprising the step of generation of a high solute
low suspended solids filtrate water stream, and still further comprising the step of directing said
low filtrate water stream to the inlet of said heat transfer equipment for further processing.
40.A process as claimed in claim 39, comprising the step of generation of a dry solids
product for disposal.
41 .A process as claimed in claim 1, wherein the step of removing said dissolved gases,
is further comprised of lowering the pH of said feed stream to remove any remaining alkalinity
and release carbon dioxide.
42.A process as claimed in claim 41, comprised of heating said acidified feed water
stream to enhance gas removal in a degasifier prior to entering said heat transfer equipment.
43.A process as claimed in claim 1, wherein step (d) comprises distributing said
circulating solution across one side of said plurality of heat transfer surfaces to generate a steam
vapor.
44.A process as claimed in claim 43, comprising collecting said steam vapor and
slightly compressing it to form a compressed steam vapor.
45.A process as claimed in claim 44, comprising directing said compressed steam
vapor to a second side of said plurality of heat transfer surfaces to condense said compressed
steam vapor into said distillate stream.
46.A process as claimed in claim 1, wherein the step of raising the pH is accomplished
by addition of a base in aqueous solution, said base selected from the group consisting of (a)
sodium hydroxide, (b) sodium carbonate, (c) potassium hydroxide, and (d) potassium carbonate.
47. A process as claimed in claim 1, wherein the step of raising the pH is accomplished
by addition of an aqueous organic base.
48. A process as claimed in claim 1, wherein the ratio of the quantity of said distillate
stream produced to the quantity of said feed water stream provided is between 90 and 98
percent.
49.A process as claimed in claim 1, wherein said feed water stream further comprises
cooling tower blowdown.
50.A process as claimed in claim 1, wherein said feed water further comprises scrubber
blowdown.
51 .A process as claimed in claim 1, wherein said feed water further comprises water
utilized in ash transport in a coal fired steam-electric power plant.
52.A process as claimed in claim 1, wherein said feed water stream comprises ash pond
water.
53.A process as claimed in claim 1, wherein said feed water stream comprises ash-
sluicing water.
54.A process as claimed in claim 1, wherein said feed water stream comprises effluent
from sewage treatment.
55.A process as claimed in claim 1, wherein said feed water stream comprises effluent
from a food processing treatment.
56.A process as claimed in claim 1, wherein said feed water stream comprises boiler
blowdown.
57.A process as claimed in claim 1, wherein said feed water stream comprises a
concentrated stream from membrane separation equipment.
58.A process as claimed in claim 1, wherein said feed water stream comprises effluent
from oil refining operations.
59.A process as claimed in claim 19 or claim 20 or claim 21 , comprising the step of
further treating said high solids blowdown stream after reaching said selected concentration
factor in a spray dryer to dry solids.
60.A process as claimed in claim 1, wherein the step of multi-valent cation removal is
partially accomplished by passing said feed water stream through membrane softening
equipment.
61 .A process as claimed in claim 1, wherein the step of multi-valent cation removal is
accomplished by increasing the pH to at least 10 in said feed water stream and passing the pH
adjusted stream through membrane separation equipment to filter out hardness precipitate.
62.A process for the concentration of an aqueous feed stream in an evaporator to
produce a low solute containing distillate stream, and retaining at least a portion of said aqueous
feed stream in said evaporator to increase the concentration of a solute to a selected
concentration factor at a selected pH in said retained portion of said aqueous feed stream,
comprises feeding said evaporator with an aqueous feed stream characterized by at the time of
initial entry into said evaporator ,there is :
(I)substantially no multi-valent cations,
(II)substantially no alkalinity,
(III)substantially no dissolved or suspended gases, and
(IV)a pH of at least 9 or above.
63 .A process as claimed in claim 62 wherein greater than 80% of the multi-valent
cations are removed from said feed stream.
64.A process as claimed in claim 62 wherein greater than 80% of the alkalinity is
removed from said feed stream.
65. A process as claimed in claim 62, wherein greater than 80% of the gases are removed
from said feed stream.
66.A process as claimed in claim 62, wherein said bases are selected from the group
consisting of carbon dioxide, ammonia, oxygen, nitrogen and mixtures thereof.
67.A process as claimed in claim 62, wherein said aqueous feed stream is further
characterized by minimizing or eliminating scale inhibitor solution or scale dispersant solution
in said aqueous feed stream.
68.A method for treating a feed water stream, in at least one evaporator system and for
simultaneously (a) reducing the scaling potential and (b) allowing an increased heat transfer rate
and (c) allowing higher recovery and (d) minimizing or eliminating scale control methods in an
existing heat transfer system, to produce a low solute containing distillate stream and a high
solute/solids containing blowdown stream, said method comprising:
(a)providing a feed water stream containing soluble and insoluble species
therein, said species comprising two or more of the following:
(I) multi-valent metal cations,
(II)alkalinity, and
(III)at least one molecular species which is at low ionization levels when
in solution at around neutral pH;
(b)removing a portion or substantially all multi-valent cations from said feed
stream, and
(c)reducing the tendency of said feed water to form scale when said feed water is
concentrated to a selected concentration factor at a selected pH, by effecting, in any
order, one or more of the following;
(I)removing substantially all alkalinity from said feed water stream;
(II)removing dissolved or suspended gases from said feed water stream,
whether initially present or created during said multi-valent cation or said
alkalinity removal step or said pH adjustment step;
(III)raising the pH of said feed water stream to at least 9 or higher;
(d) passing the product from step (c) into heat transfer equipment, wherein
said heat transfer equipment:
(I)contains a plurality of heat transfer surfaces,
(II)contains a circulating high solutes/solids solution, and
(III)the pH of said circulating solution is maintained to at least 9, or
higher,
(e) so as to concentrate said feed water to said selected concentration factor,
to produce:
(I)a high solute/solids containing blowdown stream, and
(II) a low solute containing distillate stream.
69. A process for the purification of an aqueous feed stream comprising solutes and
solvent by using evaporation equipment to increase the concentration of said aqueous stream to
a selected concentration factor by generating a low solute containing distillate stream and
retaining at least a portion of said aqueous feed stream in said evaporation equipment to increase
the concentration of a selected solute to a selected concentration factor in said retained portion
of said aqueous feed stream, the improvement which comprises controlling solutes, multi-valent
metal cations, alkalinity, and carbon dioxide in said aqueous feed stream to a level where the
tendency to form scale is effectively eliminated at said selected concentration factor, by
(a) prior to feeding of said aqueous feed stream to said evaporation
equipment, in any order,
(I)minimizing multi-valent cations in said aqueous feed stream,
(II) minimizing alkalinity of said aqueous feed stream,
(III)minimizing gases dissolved or suspended in said aqueous feed
stream;
(b)then, after step (a), increasing the pH of said aqueous feed stream in said
evaporation equipment to at least 9, or higher.
70.A process as claimed in claim 1, or claim 62, or claim 68, or claim 69, comprising,
during the step of removing alkalinity, the additional step of removing substantially all non-
hydroxide alkalinity not associated with hardness.
71 .A process as claimed in claim 1, wherein said feed water stream comprises effluents
from hydrocarbon recovery operations as produced water.
72. A process as claimed in claim 14, wherein a high solids containing waste stream is
generated and, further comprising, de-watering of said high solids containing waste stream.
73. A process as claimed in claim 72, wherein a low suspended solids stream is
generated and, further comprising directing said low suspended solids stream back to the inlet of
said softener.
74. A process as claimed in claim 1, wherein the steps of (b) removing multi-valent
cations, and (c) removing alkalinity, removing dissolved gases, and increasing pH are
accomplished prior to a membrane process to pre-concentrate the feed stream upstream of said
heat transfer equipment described under step (d).
75. A process as claimed in claim 1, wherein the removal of multi-valent cations and
partially raising the pH are accomplished prior to pre-concentrating said feed stream in a
membrane process prior to step (c).
76. Apparatus for treatment of a feed water stream by the method as claimed in any of the
preceding claims, wherein two or more of the following are present in said feed water stream:
(I)multi-valent metal cations,
(II)alkalinity,
(III)at least one molecular species which is at low ionization levels when in
solution at around neutral pH,
to produce a low solute containing distillate stream and a high solute/solids containing
blowdown stream, said apparatus comprising:
a)pretreatment equipment for effectively eliminating the tendency of said
feed water to form scale on heat transfer surfaces when said feed water is
concentrated to a desired concentration factor at a selected pH, comprising, in
any order:
(I)at least one softener for removing a portion or substantially all
multi-valent cations from said feed stream,
and one or more of the following:
(II)at least one de-alkalizer for removing essentially all alkalinity
from said feed water stream,
(III)a degasifter for removing dissolved gases,
(IV)chemical addition apparatus for raising the pH of said
circulating solution in said heat transfer equipment to a selected pH of at
least 9 by adding a selected base thereto, to urge said at least one
molecular species with low ionization levels when in solution at about
neutral pH toward increased ionization;
(b)one or more evaporator units, said one or more evaporator units, treating said
feed water to produce a high solute/solids containing blowdown stream and a low solute
containing distillate stream, and to concentrate said feed water to said selected
concentration factor.
77.An apparatus as claimed in claim 76, comprising, downstream of one or more said
evaporator units, to further process said low solute containing distillate stream therefrom, a
cation exchange unit.
78.An apparatus as claimed in claim 76, comprising, downstream of one or more said
evaporator units, to further process said low solute containing distillate stream therefrom, an
anion exchange unit.
79.An apparatus as claimed in claim 76, comprising, downstream of one or more said
evaporator units, to further process said low solute containing distillate stream therefrom, at
least one mixed bed ion exchange unit.
8O.An apparatus as claimed in claim 77 or claim 78 or claim 79, comprising an ion
exchange resin regenerator that generates an ion exchange regenerant stream, and further
comprising means for directing said ion exchange regenerant stream to the inlet of said
degasifier unit in order to treat said ion exchange regenerant stream in said evaporator.
81 .An apparatus as claimed in claim 76, comprising downstream of one or more said
evaporator units, to further process the said low solute containing distillate stream therefrom, a
continuous electrodeionization unit to produce (a) a substantially solute free water stream and
(b) a solute containing waste stream.
82.An apparatus as claimed in claim 81, having means for directing said solute
containing waste stream to the inlet of said degasifier for further processing.
83.An apparatus as claimed in claim 78. comprising de-oiling apparatus upstream of
said multi-valent cation removal softener.
84.An apparatus as claimed in claim 76. comprising filtration equipment downstream o
said softener.
85.An apparatus as claimed in claim 76, having means for directing backwash water to
the inlet of said softener for further processing.
A process for treatment of an aqueous stream to produce a low solute containing
distillate stream and a high solute/solids containing blowdown stream utilizing a method to
increase the efficiency of an evaporator while providing an essentially scale free environment
for the heat transfer surface. Multi-valent ions and non-hydroxide alkalinity are removed from
aqueous feed streams to very low levels and then the pH is increased preferably to about 9 or
higher to increase the ionization of low ionizable constituents in the aqueous solution. In this
manner, species such as silica and boron become highly ionized, and their solubility in the
concentrated solution that is present in the evaporation equipment is significantly increased.
The result of this is high allowable concentration factors and a corresponding increase in the
recovery of high quality reusable water with essentially no scaling.

Documents:

828-kolnp-2005-granted-abstract.pdf

828-kolnp-2005-granted-assignment.pdf

828-kolnp-2005-granted-claims.pdf

828-kolnp-2005-granted-correspondence.pdf

828-kolnp-2005-granted-description (complete).pdf

828-kolnp-2005-granted-drawings.pdf

828-kolnp-2005-granted-examination report.pdf

828-kolnp-2005-granted-form 1.pdf

828-kolnp-2005-granted-form 13.pdf

828-kolnp-2005-granted-form 18.pdf

828-kolnp-2005-granted-form 3.pdf

828-kolnp-2005-granted-form 5.pdf

828-kolnp-2005-granted-gpa.pdf

828-kolnp-2005-granted-reply to examination report.pdf

828-kolnp-2005-granted-specification.pdf

828-KOLNP-2005-OTHER PATENT DOCUMENT.pdf


Patent Number 226791
Indian Patent Application Number 828/KOLNP/2005
PG Journal Number 52/2008
Publication Date 26-Dec-2008
Grant Date 24-Dec-2008
Date of Filing 06-May-2005
Name of Patentee AQUATECH INTERNATIONAL CORPORATION
Applicant Address ONE-FOUR COINS DRIVE, CANONSBURG PA 15317
Inventors:
# Inventor's Name Inventor's Address
1 MINNICH, KEITH, R W291 N3821 ROUND HILL CIRCLE, PENWAUKEE, WI 53072
2 KARLAPUDI, RAMKUMAR 1981 FOXCROFT LANE, WAUKESHA WI 53189
3 SCHOEN, RICHARD, M N67W29767 HARTLING ROAD, HARTLAND WI 53029
PCT International Classification Number C02F 1/02, 1/04
PCT International Application Number PCT/US2003/033066
PCT International Filing date 2003-10-17
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/419,549 2002-10-18 U.S.A.
2 60/419,552 2002-10-18 U.S.A.