Note: Descriptions are shown in the official language in which they were submitted.
21 qO299
COMBINED MULTI STAGE FLASH- MULTI EFFECT
DISTILLATION SYSTEM WITH BRINE REHEAT
SPECIFICATIONS
Field Of The Invention
This invention relates generally to saline water des~lin~tion systems and more
particularly to Multi Stage Flash (MSF) and Multi Effect (ME) ~listill~tion systems.
Description Of The Previous Systems
Des~lin~tion of saline water by ~istill~tion is a very effective process, because most of
the chemical materials found in saline water are non-volatile at the temperaturenormally employed and hence remain in the un-evaporated brine. The two most proven
distillation technologies are: the Multi Stage Flash (MSF) and Multi Effect(ME)
systems. The differences between the two types of technologies are derived from the
difference in the method of heat transfer. The saline water is sensibly heated in the
tubes in MSF system and boiled in a thin film on the tubes in ME system. Comparisons
between MSF and ME systems indicated, in general, the superiority of each systemover the other in one aspect or the other.
MSF system has proven to be the most simple, and reliable technology for producing
potable water on large scale. Due to its advantages and the acc-lmul~ted operational
experience gained, MSF of the recirculated flow dominates the market. MSF has the
advantage that the incoming brine is heated without evaporation and fl~hing
evaporation occurs without heat transfer, thus reducing the tendency for scale to form
on the heat transfer surface. The significant drawback of the MSF system, as compared
to other cost effective systems, are the high energy consumption (steam, pumping and
other operating costs). The system production and performance can be increased (and
production cost can, therefore, be reduced) by increasing the Top Brine Temperature
(TBT). The TBT is limited, however, due to the high temperature hard scale deposits
in the brine heater and the up-to-date antiscalent limitations.
On the other hand, ME systems are widely used in the chemical industry forthe
concentration of solutions. In seawater des~lin~tion, ME has not achieved similar
importance, in terms of the total installed capacities, as MSF. The ME distillation
system is significantly more efficient and has a thermodynamic superiority over MSF.
The striking feature of ME system is the significant low specific power consumption as
compared to MSF system.
Patent ( 8128196 ) 2 Dr. Hassan E. S. Fath
~1 qO2~q
The Invention Idea
The objective of the invented system (named hereas: CombinedMSF-MESystem
W th Brine Rehea~) is to increase saline water distillation unit capacity, improve its
performance and, therefore, reduce the fresh water production cost over the existing
MSF systems. The invented combined MSF-ME system wifh brine reheat introduces
the concept of increasing the MSF fl~hing range through brine reheat, and utilizes the
superior advantages of both MSF and ME systems simultaneously.
The invented system uses a combination of: i) the up-to-date (proven design) MSFevaporation system as a base system with dirrele.lt methods to improvetheflash
chamber effectiveness (non-equilibrium factor) and fl~hin~ evaporation rate; ii)increases the fl~hing range through brine reheat, i.e. supply (all or part ofl the brine
with additional (external) heat in brine reheaters (located after the brine heater and/or
within the flash chambers), and; iii) superimposes the ME evaporation concept and
system on the MSF base system. Themodificationsoftheinventedsystemoverthe
existing MSF system are:
a- Since additional (external) heat, for higher fl~.~hingrange and morewater
production, can't be supplied before or at the brine heater in existing MSF
system (due to TBT limitations), increasing the fl~hin~ range is carried out,
in the present invented system, through brine reheat; i.e. the additional
(external) heat is supplied to (all or part ofl the brine after the brine heaterand/or within flash chambers.
b- In addition to increasing brine superheat from (a), other methods are
considered for improving MSF flash chamber effectiveness (the non-
equilibrium factor) and fl~shing evaporation rate, for additional vapor
production and better system performance. This includes; increasing fl~hin~
surface area, improving brine turbulence ( brine temperature gradient), and
introducing more active nucleation sites for bubbles formation.
c- The vapor generated due to: i) brine reheat (from a) ii) the improvement in
flash chamber effectiveness (from b), and iii) possibly part of the main vapor
generated inside the flash chambers, is then used as a source of heat to
generate more vapor in the next successive stages (effects) in a way similar to
the conventional ME system; i.e.theinventedsystemsuperimposestheME
evaporation concept and system on the existing MSF system designs.
The invented system increases saline water distillation unit capacity, improves its
performance and reduces the fresh water production cost. In addition, the invented
system operates within the existing (proven design) MSF and ME system's constraints
and limitations, and allows for the possibility of utilizing waste heat as the external heat
source for brine reheat. The invented system presents, therefore, a break-through for
the future generation of saline water desalination systems.
Patent ( 8128196 ) 3 Dr Hassan E. S. Fath
- 2l9029q.
Description Of The Invention
a- MSF Base System Conf guration
Figure 1 shows (for demonstration) a small unit of a typical Multi Stage Flash (MSF)
distillation system of the recirculation type. The unit consists of four stages of heat
recovery section and two stages of heat rejection section as shown. Seawater enters
the condense tubes of the heat rejection section at the lowest temperature, Tl", and is
heated up to temperature Tc5~ by condensation of the vapor generated bybrine
fl~ching in the heat rejection section. At this point, much ofthe cooling seawater, mrej,
is discharged from the plant for heat rejection and thebalance make-up, mr~ p, is
rnixed with part of the brine flowing out of the last stage of the heat rejection section.
This mixture (at Trcc) forms the recirculated brine, mrec, and ispumped throughthe
condenser tubes of the heat recovery section where it is heated up to Tcl From there,
the heated recirculated brine is passed through the brine heater, where it is heated to
its Top Brine Temperature (TBT). Brine at TBT exiting the brine heater, enters the
flash chamber of the first stage heat recovery section, atbrinetemperature of Tbl =
TBT. Then, the brine cascades downward through the several stages oftheunit,
flashing off some product vapor in each stage and leaving the last stage atbrinetemperature Tb7 . Part of the last stage brine is blown-down, mbd, and the rest is mixed
with the make-up where the cycle is repeated.
b- Invented SYs~em Modifications
There are three major modifications in the invented system which are superimposed on
the MSF base system configuration described above. These modifications are
illustrated in Figures 2 to 5 and are sumrnarized as follows (more detailed description
of Figures 2 to 5 are given lafer in the drawing section):-
1- Improve the Flash Chamber Effectiveness
Flashing brine, coming out of the flash chamber of the existing MSF systems,
always retains some residual non-equilibrium superheat that considerably aggravates
the technical and economical characteristics of the MSF system. Approaching
thermodynamic equilibrium is achieved, in the present invented system, through
enhancing flashing rate within the flash chamber by:
i) increasing the brine flashing surface area and brineturbulence (improvebrine
temperature gradient); for example two flashing trays with dripping (falling or
sprayed) brine, from the upper to the lower tray(s), as shown in Figures 2 & 3.
ii) increasing brine superheat and the numberofactivenucleationsitesforvapor
bubbles formation and vapor generation, using additional (external) heat,
through a heating surface, placed between fl~hing trays, as will be presented
below (brine reheat).
The number of brine flashing trays may increase more than two, for more
evaporation surface in future larger capacity units. In this case, the additional
heating surface may also be divided between these trays.
Patent ( 8128/96 ) 4 Dr. Hassan E. S. Fath
- ~ 1 902~
2- Brine Reheat
- For higher production rate of MSF system, additional vapor generation canbe
attained by increasing brine flashing range. Additional (external) heat can not be
supplied to the brine before or at the brine heater (due to TBT limitations). In the
present invented system, additional (external) heat is supplied to the brine, after the
brine heater (known here as brine reheaf)
The additional (external) heat (for brine reheat) could be supplied to (all or part of)
the brine: i) within the flash chamber(s) (named here as: internal brine reheaters),
ii) through outside heat exchanger(s) (named here as: ex~ernal brine rehea~ers); or
iii) combination of both (i) and (ii).
Adding heat to the brine, within the flash chamber, will be supplied through a tube
bank under the dripping (falling or sprayed) brinefromtheuppertray, Figure 3.
Sup.plying the system with additional heat through tube bank has the following
advantages:
(i) generating more vapor due to the additional heat (higher fl~ching range),
(ii) enhancing brine fl~hing rate due to higher brine superheat,
(iii) improving the brine turbulence and the temperature gradient, due to the
brine falling over heating surface tube bank,
(iv) creation of additional active nucleation sites for more bubbling and more
vapor production (better flash chamber effectiveness)
Based on the optimum arrangement (design, operational, scale and corrosion
control, cost,...etc.), the brine reheat could be attained at single brine reheater (top
drawing of Figure 4) or being divided between two brine reheaters (middle and
bottom drawings of Figure 4), or through more than two reheaters.
3- SuperimposingME System
In the present invented system, each stage supplied with external (additional) heat
(brine reheat, through internal or external brine reheaters) is considered as the first
effect of ME system superimposed on the MSF base system. The vapor generated
due to: i) improving flash chamber effectiveness, from 1 above, ii) the additional
external heat (from 2 above), and iii) possibly partofthemainvaporgenerated
inside the earlier flash chamber(s), is used as the source of heat to generate more
vapor in the next successive stages (effects) as in ME concept, i.e. ME system is
superimposed on MSF base system, as shown in Figures 2 to 4.
The additional vapor generated in each effect is condensed insidethe additional
heating surface(s) of the following effect(s) as additional distillate, Figure 2 & 3.
The latent heat of condensation is used as a source of heat for that (next) effect,
similar to the conventional ME system.
The main (and the additional) distillate formed in each stage (effect) is discharged
through orifices to the next stage (effect) where it forms more vapor by fl~shing and
Patent ( 8128196 ) 5 Dr. Hassan E. S. Fath
2 1 90299
augments the heating in that stage (effect), in a similar way to the conventional MSF
(ME) systems.
The heat transfer surface (tube bank) in each effect is a placed under the dripping
(falling or sprayed) brine from an upper tray(s), Figure 3. This arrangement has the
following additional features:
(i) there will be a partial brine flashing from the upper tray(s) and fromthe
dripping (falling or sprayed) brine before cont~cting the heating surface. This
causes larger temperature difference between the heating surface and the
boiling brine (in addition to the higherheattransfercoefficientofthefalling
brine) which enhances boiling heat transfer and reduces the required heating
surface area.
(ii) dripping (falling or sprayed) falling brine, decreases the residence time required
. for scale formation on the additional heating surface, as in conventional ME
system.
The additional heating surface(s) inside the flash chamber of each effect may, however,
be elimin~ted. Direct contact heating of the brine could beused instead of surface
heating. The heating vapor will, therefore, be injected from the previous effect into the
flash chamber and under the falling brine. In such case:
(a) The injected heating vapor will be de-pressurized and superheated through the
throttling process from the previous effect pressure.
(b) Mass & heat will directly be exchanged between the superheated heating vaporand the saturated (or superheated) fallingbrine. Theheatingvapor superheat
energy will be used to generate the additional vapor in this effect.
(c) The heating vapor will be condensed on the flash chamber condensertubes,
while the additional vapor will be injected into the next effect where the process
is repeated.
(d) Flimin~tion of the heating surface will reduce the total plant costs and will
eliminate the problems of heating surface(s) corrosion and scale deposits.
(e) The present (or modified) methods and techniques for enhancing the heat and
mass transfer between the heating vapor and falling brine may be used. Part of
the heating vapor may also be injected into the brine layer(s) in orderto
improve the evaporation rates (due to increase the brine superheat, turbulence
and the number of active nucleation sites for bubbles formation).
With large number of stages, more ME effects could be superimposed on the MSF
base system to improve the system performance and increase theproduction. The
invented system may then be divided into two or more segments of ME systems.
In the invented system, each stage supplied with external heat (brine reheat through
either internal or external brine reheaters) is considered the first effect of ME system
superimposed on the MSF base system. The first effect of each ME segment need not
to be the first stage of the MSF segment. It may be the first, second, or other stages
based on the optimum design and operational arrangement. The second effect need not
Patent ( 8128/96 ) 6 Dr. Hassan E. S. Fath
21 90299
to be the following stage, but it may be one of other following stages, depending on
the temperature difference required for optimum heating surface area. Similarly for the
third and following ME effects. Typical examples of the invented system combinations
are illustrated in Figure 4.
Additional Considerations for The Invention
Due to the increase in the reheated brinetemperature,thevacuumofthefollowing
stages can partially be relaxed and redistributed along the rest of reheated stages. The
saturation temperature can, therefore, be increased to enhance the heat transfer across
the condenser heat transfer surface. Higher heat transfer rate across leads to areduction in the heat transfer surface required and/or increase in the recirculating brine
temperature that reduces the brine heater heating steam requirements. These factors
have the economical value of reducing both capital (heating surface) and operating
(heating steam) costs.
The additional heat could be live heating steam (extracted from the turbine, part of the
steam exits from a back pressure turbine, or from auxiliary steam source) or other hot
fluid. Alternatively, a waste heat recovery system could be installed to utilize the plant
waste heat (For example: boiler blow-down, flue gas energy,...etc.) instead of all (or
part of) the additional heat source.
Since fl~chin.~ brine is at or above saturation temperature, the supplied additional
(external) heat as well as heat generated in each effect are fully used for the
evaporation of the additional vapor production (in the following effects). No heat is
required to preheat the brine (from the cold seawater temperature to theboiling
temperature).
With minim~lm pressure drop of the fl~hing brine flow, the brine may have sufficient
interstage pressure di~rel enlial to raise the brine from the lower tray of one stage to the
upper tray of the next stage. In case the pressure dirrel elllial is not sufficient, either i)
a reduction in the total number of flash stages may be necessary, or ii) the required
pressure di~e. enlial could be attained through an additional head per stage; potential
head (stepped down stages) and/or pressure head (circ~ ting pumps), as described in
the drawing section and shown in Figures 5 (a, b and c).
Brine temperatures, inside the condenser tubes of the MSF base system, is m~int~ined
within optimum design range by the adjustments of the recirculation, reject blow-down
and make-up flow rates. In case of increasing the recirculated brine flow, part of the
additional generated vapor could be condensed on the condenser tubes of each stage to
m~int~in the system parameters near optimum values. In this case, the required
additional heating surface area (for brine reheat) is reduced. Similarly, TopBrine
Temperature (TBT) is also m~int~ined withinthe specified (up-to-date) upperlimit(for maximum fl~ching range and brine heater hard scale control).
Part of the main vapor generated inside the flash chambers may be used as a source of
heat (for brine reheat). In this case, the heat transfer surface area required for the main
Patent ( 8128196 ) 7 Dr. Haccan E. S. Fath
21 ~029~
condensers as well as the brine recirculation rate (and, therefore, recirculation pump
size and power) will be reduced, and the brine temperature difference across the brine
heater will be increased (for better heat transfer). Optimum design parameters should
be obtained.
A small part of the vapor generated inside the flash chambers in earlier stages (effects),
could also be used for bubbling & heating the brine in later stages (in direct contact).
This higher pressure vapor will first be throttled to the lowerpressure stages. The
bubbling superheated vapor will increase the brine superheat (in the later stages) and
will act as an additional source for active nucleation sites to enhance brine bubbling
and fl~ching rate; i.e. improve the flash chamber effectiveness (non-equilibrium factor)
and production rate. Optimum design parameters ( such as vapor rate, stages number
and bubbling arrangement,... etc.) should be obtained.
Optimum design parameters, (such as number of stages, number of segments, numberof effects, brine reheaters's size, type and number, stage size, heattransfer surface
area(s), the recirculation, reject blow-down and make-up flow rates... etc.) will be
selected, based on full or partial utilization of the given invented system combinations.
The other design limitations should also be preserved when considering the flashchamber re-sizing, for example: i) brine velocity insidethe condensertube, ii) tube
length and tube diameter, iii) stage maximum specific brine flow, and, iv) stagemaximum vapor release velocity.
With the supply of a percentage of the brine heater heat load (for brine reheat), the
invented system increases the specific unit capacity and production rate, and improves
the unit performance (i.e. Gained Output Ratio-GOR), and reduces, therefore, thefresh water production cost, as compared to the present MSF system. GOR is further
increased and production cost is further reduced when waste heat is used as (part or all
of) the additional (external) heat source for brine reheat.
The additional heat transfer surface temperature will be m~int~ined less than the brine
heater tubes surface temperature. On the other hand, brine concentration in the flash
chambers is controlled within acceptable range by the adjustments of the recirculation,
reject blow-down and make-up flow rates. Since brine contains enough antiscalent (for
brine heater hard scale control), and is partially flashed and cooled down in the flash
chambers of earlier stages, and with its small residence time on the additional heating
surfaces (brine reheater and ME boiling surfaces), problems of high temperature hard
scale deposits on these additional heating surfaces will be under control.
The additional vapor generated in the last stage is condensed on the condenser tubes of
the heat rejection section as conventional MSF and ME systems. Another alternative to
be considered, is to compress the vapor generated in the last stage through a vapor
compression system (VC) and utilize the compressed hot vapor as the source of heat
for brine reheat (instead of additional live steam). Optimum MSF + ME + VC system
combination should be obtained.
Patent ( 8128196 ) 8 Dr. H~ss~n E. S. F;lth
21 90299
DRAWINGS
Brief Descripfion of the Drawings
T,??e schema~ic process diagrams shown in Figures I ~o 5 and brief ly described below,
do not show all the auxiliary sys~ems and componen~s required to opera~e ~he plan~,
and should be regarded as limi~ed ~o ~heir s~a~ed purpose of illustra~ing ~he invented
sysfem (combined MSF-ME system wi~h brine rehea~) process concept
Figure I
Figure 1 shows (for demonstration) a small unit of a typical Multi Stage Flash (MSF)
distillation system of the recirculation type. The unit consists of four stages of heat
recovery section and two stages of heat rejection section as shown. Seawater enters
the condenser tubes of the heat rejection section at the lowest temperature, T", and is
heated up to temperature TC5a by condensation of the vapor generated, by brine
fl~ching, in the heat rejection section. At this point, much ofthe cooling seawater, mrej,
is discharged from the plant for heat rejection and thebalance make-up, m~r,",,p, is
mixed with part of the brine flowing out of the last stage of the heat rejection section.
The mixture, at TreC~ forms the recirculated brine, mr~c, and is pumped through the
condenser tubes of the heat recovery section where it is heated up to TCI- From there,
the heated recirculated brine is passed through the brine heater, where it is heated to
its Top Brine Temperature (TBT). Brine at TBT exiting the brine heater, enters the
flash chamber of the first stage of the heat recovery section, at brine temperature of Tbl
= TBT. Then, the brine cascades downward throughtheseveralstagesoftheunit,
fl~ching off some product vapor in each stage and leaving the last stageatbrine
temperature Tb7 . Part of the last stage brine is blown-down, mbd, and the rest is mixed
with the make-up where the cycle is repeated.
Figure 2
Introduction
Figure 2 shows the conceptual process diagram of the invented combined MSF-ME
system with brine reheat. Figure 2 is the process design configuration MSF small unit
presented in Figure 1 with following modifications: i) improved flash chamber
internals for higher effectiveness, ii) brine reheat for higher fl~chinp range (the addition
of external heat supplied to the brine), and iii) superimposing the ME system on the
MSF system. More details of these modifications are:
Descrip~ion
i) Each flash chamber contains two (or more) trays with dripping (falling or sprayed)
brine from the upper tray to the lower tray(s). The brine enters the flash chamber
into the upper tray, partially flash and then falls down, throughthe additional
heating surface (if any), with more flashing, to the lower tray(s) for more fl~ching
and, then, exits to the next stage. Higher flash chamber effectiveness (better non-
equilibrium factor) is, therefore, attained due to higher fl~ching surface area, brine
turbulence, additional brine superheat and extra active nucleation sites. The heat
Patent ( 8128/96 ) ~ / Dr. Hassan E. S. Fath
21 9()299
transfer surface is a tube bank under the dripping (or sprayed) brine fromthe
upper to the lower tray.
ii) Additional external heat (heating steam or waste heat) is supplied to the brine (for
brine reheat) in the flash chamber of the third stage of the MSF system (one
internal brine reheater). Flashing range is increased and additional vapor is
generated, and the plant production is, therefore, increased.
iii) The third MSF stage with brine reheat is considered as the first effect in the ME
system superimposed on the MSF system. External heating is supplied to this (first
ME effect) stage and may also be supplemented by some vaporgenerated in
earlier (first & second) stages. Additional vapor is generated in this third MSFstage (first ME effect) due to improving the flash chamber effectiveness from (i)
and due to the brine reheat from (ii). The additional vapor generated will pass to
the fourth MSF stage as the additional heating source. The fourth stage is
considered the second effect of the ME system superimposed on the MSF system.
This vapor is condensed as additional ~i~till~te and the latent heat of condensation
is used to generate more vapor in the next effect (fifth MSF stage). The fifth stage
is considered as the third effect of the ME system, where the process is repeated.
Addifional Considerations
A small part of the vapor generated inside the flash chambers in earlier stages (effects),
could also be used for bubbling & heating the brine in later stages (in direct contact).
This higher pressure vapor will first be throttled to the lowerpressure stages. The
bubbling superheated vapor will increase the brine superheat (in the later stages) and
will act as an additional source for active nucleation sites to enhance brine bubbling
and flashing rate, i.e. improve the flash chamber effectiveness (non-equilibrium factor)
and production rate. Optimum design parameters, (such as vapor rate, stages number
and bubbling arrangement,... etc.) should be obtained.
The main and additional distill~te formed in each stage (effect) is discharged through
orifices to the next stage (effect) where it forms vapor by fl~hing and augments the
heating in that stage (effect), in a similar way to the conventional MSF (ME) systems.
The vapor generated in the last (sixth) stage will be condensed through the heatrejection section as conventional MSF and ME systems. Anotheralternative, isto
compress this vapor through a vapor compression system (VC) and utilize the
compressed hot steam as the source of heat for brine reheat, instead of (all or part of)
the additional (external) heating steam.
The rest of the MSF-ME system flow diagram is similar to that described in Figure 1
above and the conventional MSF and ME systems.
/~
Patent ( 8128196 ) ~ Dr. Hassarl E. S. Fath
21 90299
Figure 3
Introduction
Figure 3 shows an enlargement of one intermediate combined MSF-ME flash chamber
of the invented system configuration presented in Figure 2. The flash chamber contains
two (or more) trays with dripping (or sprayed) brine from the upper tray to the lower
tray. External heat or internally generated heating vapor is supplied to the brine
through a tube bank under the dripping (sprayed) brine from the upper tray (falling
film). The vapor generated due to this additional heating source and due to improving
fl~ching chamber effectiveness is used as the heating source (to generate more
additional vapor) in the next and successive stages (effects).
Description
Similar to the existing (up-to-date) MSF provendesign,thetopsectionoftheflash
chamber contains the condenser tubes where the recirculated brine of flow rate mc~;)
enters .at temperature TC(i+l) and exits at temperature Tc,;). The flashed vapor condenses
as the main distillate and exits the flash chamber at flow rate mp; and temperature Ts;
The bottom section of the flash chamber contains the two trays of dripping brine and
the additional heating surface. Superheated brine enters the uppertrayoftheflashchamber at flow rate of mbi and temperature Tb;. The brine is partially flashed in the
upper tray while the rest of the brine falls down to the lowertray(s) through the
additional heating surface. The falling brine will further be flashed/boiled (due to the
extra superheat, large fl~hing surface area, turbulence and the active nucleation sites)
and generate additional vapor. More flashing takes place at the lower tray after which
the brine exits to the next stage (effect) at flow rate mb(j+l) and temperature Tb(j+l). The
vapor rises (through the conventional demisters), partially to the condenser tubes and
partially as a heating vapor to the next effect.
Heating vapor from the previous effect [stage (i-l)] enters the additionalheating
surface, condense as additional distillate, and its latent heat of condensation is used as
the heating source to heat and boil the falling brine. The additional vapor generated
(due to the additional heat and due to improving fl~hing chamber effectiveness) will
exit the flash chamber as the heating vapor to the next effect [stage (i+1)], similar to
ME system.
Figure 4
Introduction
The additional external heat (for brine reheat) could be supplied: (i) within the flash
chamber (named here: internal brine reheater), (ii) through an outside heat exchanger
(named here, external brine reheater); or (iii) combination of both (i) and (ii). In
addition, for MSF units of large number of stages, more ME effects are utilized to
increase the unit production and performance. ThecombinedMSF-MEsystemwith
brine reheat may, therefore, be divided into two or more segments and each MSF-ME
segment starts with brine reheater. Each stage supplied with external heat (for brine
reheat) is considered as the first ME effect superimposed on MSF base system.
Patent ( 8/28/96 ) ,~ // Dr. Hassan E. S. Fath
2 1 90299
The first effect of ME system need not to be the first stage of the MSF system. It may
be the first, second, or other stages based on the optimum design arrangement ( cost,
operational, scale and corrosion control,...etc.). The second effect of each ME segment
need not be the next stage, but may be one of the other following stages, depending on
the temperature difference required for the heating surface. Similarly for the third and
following effects.
Descripfion
Figure 4 shows three arrangements (as examples) of the invented combined MSF-ME
sys~em with brine rehea~ of a larger number of stages. 12 MSF stages are shown for
demonstration, where the stage number is shown on the top of the Figure. The same
conceptual arrangement is applied to other larger units.
In the top drawing arrangement . the external additional heat (forbrine reheat) is
supplied to a single MSF stage (MSF stage number 3) and considered as the first effect
of the ME system. This additional heat is supplied to the brine through one internal
brine reheater. The ME second effect is superimposed on MSF-stage 5, the third effect
is on MSF-stage 7 and the fourth and fifth effects on MSF stages 9 and 11
respectively. The first effect (MSF stage 3) is suppliedwithexternal heatwhilethe
subsequent effects (from 2 to 5) obtain their heat source from the vapor generated in
the previous effect, i.e. this drawing illustrates 1*5 effects of ME system, with single
internal brine reheater, superimposed on the 12 stages of MSF system.
In the middle drawing arrangement, the invented system is divided into two segments.
Each segment consists of 6 MSF stages, 5 ME effects and one internal brine reheater.
In the first segment, the external additional heat (for brine reheat) is supplied at the
second MSF stage (and considered as the first effect of the first ME segment). For the
second ME segment, the external additional heat (for brine reheat) is supplied at the
eighth MSF stage (the first effect of the second ME segment). The first ME effect in
each segment is supplied with external heat through intemal brine reheater, and the
subsequent effects in each segment (from 2 to 5) obtaintheirheat source fromthe
vapor generated in the previous effect, i.e. this drawing illustrates 2 * 5 effects of ME
system, with two internal brine reheaters, superimposed on the 12stagesofMSF
system.
In the bottom drawin~ arrangement. the invented system is also divided into two
di~lelll segments. The firsf segment consists of 7 MSF stages, one internal brine
reheater and 4 ME effects. In this segment, the first three stages are pure MSF with
enhanced fl~shing The external additional heat (forbrinereheat)issuppliedatthe
fourth MSF stage (first ME effect of the this segment). The subsequent effects (the
second, third, and fourth effects) obtain their additional heat from the vapor generated
in the previous effect. The second segment consists of the following 5 MSF stages,
one external brine reheater and 5 ME effects. The external additional heat (for brine
reheat) is supplied at the eighth MSF stage (first ME effect of the second segment).
The subsequent effects (from second to fifth effects) obtain their additional heat from
the vapor generated in the previous effect, i.e. this drawing illustrates 1 * 4 + 1*5
effects of ME system, one internal + one external brine reheaters, superimposed on the
12 stages of MSF system.
/~
Patent ( 8128196 ) ~, Dr. Hassan E. S. Fath
2 1 qO299
For larger number of stages of MSF units similar MSF-ME-brine reheaterscombination with dirrel e.-l break-downs could be applied.
r~gure S
In~roduction
With minim~lm pressure drop of the flashing brine, the brine may havesufficient
interstage pressure di~erential to raise the brine from the lower tray of one stage to the
upper tray of the next stage. In case thepressuredirrelenlialisnotsufficient: (i)a
reduction in the total number of MSF stages will be necessary, or (ii) the required
pressure dirrere,.~ial could be attained through an additional external potential or/and
pressure head per stage.
Descripfion
Figure 5 presents three basic concepts to obtain higher inter-stage pressure
di~eren~ials. The invented system consists of 2*4 effects of ME system, twobrinereheaters superimposed on 12 stages of MSF system. Similar conceptual arrangement
will be applied to other larger or di~erent arrangement units.
Fi~ure Sa is a full stepped-down configuration. Additional interstage pressure
dirreren~ial is obtained from the hydro-static (potential) head difference. Thisarrangement may need, however, a stronger supporting structure (due to thehigh
elevation) in the first stages.
Figure 5b is a combination of stepped-down configuration and the utilization of
circ.ll~ting pumps. In each segment (or group of stages) the additional interstage
pressure dirrere"lial is obtained from the hydro-static (potential) head difference. The
circul~ting pumps provide the pressure head required between each two segments and
to overcome the brine reheater pressure drop. This arrangement reduces the need for
stronger supporting structure. However, this should be balanced with the capital and
running costs of the pumps.
Figure Sc is similar to the arrangement in Figure 5b except that the arrangement of
stages in each segment is made vertical rather than the stepped-down configuration of
Figure 5b. In each segment (or group of stages) the additional interstage pressure
differential is obtained from the hydro-static (potential) head difference. The circlllating
pumps provide the pressure head required between each two segments and to
overcome the brine reheater pressure drop.
Patent ( 8128196 ) ~G /3 Dr. Hassan E. S. Fath
