CA2177740A1 - Combined multi stage flash-multi effect distillation system with brine reheat - Google Patents
Combined multi stage flash-multi effect distillation system with brine reheatInfo
- Publication number
- CA2177740A1 CA2177740A1 CA002177740A CA2177740A CA2177740A1 CA 2177740 A1 CA2177740 A1 CA 2177740A1 CA 002177740 A CA002177740 A CA 002177740A CA 2177740 A CA2177740 A CA 2177740A CA 2177740 A1 CA2177740 A1 CA 2177740A1
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- Prior art keywords
- brine
- msf
- reheat
- heat
- additional
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/06—Flash distillation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D1/00—Evaporating
- B01D1/26—Multiple-effect evaporating
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D1/00—Evaporating
- B01D1/28—Evaporating with vapour compression
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/06—Flash distillation
- B01D3/065—Multiple-effect flash distillation (more than two traps)
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/041—Treatment of water, waste water, or sewage by heating by distillation or evaporation by means of vapour compression
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/048—Purification of waste water by evaporation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/06—Flash evaporation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/16—Treatment of water, waste water, or sewage by heating by distillation or evaporation using waste heat from other processes
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/08—Seawater, e.g. for desalination
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/124—Water desalination
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- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
- Heat Treatment Of Water, Waste Water Or Sewage (AREA)
Abstract
A new Multi Stage Flash (MSF) distillation system of enhanced flashing, brine reheat and superimposed Multi Effect (ME) distillation system (named herein as: Combined MSF-ME System With Brine Reheat) is disclosed. The invented system has special features designed to increase the distillation unit capacity and production rate, and improve its performance. The invented system uses a combination of: i) the up-to-date (proven design) MSF system as a base system with different methods to improve the flash chamber effectiveness (non-equilibrium factor) and flashing evaporation rate; ii) increases the MSF system flashing range through brine reheat, i.e. supply (all or part of) 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 distillation concept and system on the MSF base system. The invented system utilizes the mainfeatures and advantages of both MSF and ME systems simultaneously, and operates within the existing (proven design) system's constraints and limitations. The invented system allows, also, for the possibility of utilizing waste heat as the externalheat-source for brine reheat. The invented system, therefore, presents a break-through for the future generation of saline water desalination systems of higher capacity, better performance and lower water production costs.
Number of claims = 19 Number of pages = 25 [18 (Text) + 7 (Figures)]
Number of Figures = 5 (Figure No.5 = 5a, 5b, 5c)
Number of claims = 19 Number of pages = 25 [18 (Text) + 7 (Figures)]
Number of Figures = 5 (Figure No.5 = 5a, 5b, 5c)
Description
2 1 777~0 COMBINED MULTI STAGE FLASH- MULTI EFFECT
DISTILLATION SYSTEM WITH BRINE REHEAT
SPECIFICATIONS
Field Of The Invention This invention relates generally to saline water (' " systems and more pa~ ,uLly to Multi Stage Flash (MSF) and Multi Effect (ME) distillation systems.
Description Of The Previous Systems Desalination of saline water by distillation is a very effective process, because most of the chemical materials found in saline water are non-volatile at the; ~ - d~ulr normally employed and hence remain in the lln Cv~l/ulaLcli brine. The two most proven distillation terhn~lOglrC are: the Multi Stage Flash (MSF) and Multi Effect (ME)systems. The differences between the two types of ~r~ g ~ 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 MSP 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. Duetoitsadvantagesandthe~ "l~-'rdoperational experience gained, MSF of the Ir~ ' ~ ' flow dominates the market. MSF has the advantage that the incoming brine is heated without c~Va~ulaliclll and flasbing c v /.,uol aLiull 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 ~,ull~u~ Lioll (steam, pumping and other operating costs). The system production and ~ ~u~ a~lce 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 ~CIII~ à~UI r hard scale deposits in the brine heater and the up-to-date antiscaient limitations.
On the other hand, ME systems are widely used in the chemical industry forthe cul~crll~la~iull of solutions. In seawater d~ , ME has not achievedsimilar importance, in terms of the total installed capacities, as MSF. TheME distillation system is sig.tiG~,~..lly more efficient and has a thermodynamic superiority over MSF.
The striking feature of ME system is the significant low specific power c. ,.~ l".~ as compared to MSF system.
Patel~t ( 5119196 ) 2, Dr i iar~n= r,. s. Fath ~ 21 77740 The Invention Idea The objective ofthe invented system (namedhereas: CornbinedMS~-MZSystemW-th Brine Rei~eat) is to increase saline water distillation unit capacity, improve its p."ru~ ud and, therefore, reduce the fresh water production cost over the existing MSF systems. The invented combined MSF-ME system with brine reheat introduces the concept of increasing the MSF flashing range through brine reheat, and utilizes the superior advantages of both MSF and ME systems ~ Iy The invented system uses a r."~ of: i)theup-to-date(provendesign)MSF
CVC~Uld~iUI~ system as a base system with different methods to improvetheflash chamber e~ulh,.,..~, (non-equilibrium factor) and flashing e~ulaLioll rate; ii) increases the flashing range through brine reheat, i.e. supply (all or part of) the brine with additional (external) heat in brine reheaters (located after the brine heater and/or within the flash chambers), and; iii) ~u~ o~ theMEevaporationconceptand system on the MSF base system. The mnrlifir~tinnc ofthe invented system over theexisting MSF system are:
a- Since additional (external) heat, for higher flashing range and more water production, can't be supplied before or at the brine heater in existing MSF
system (due to TrsT limitations), increasing the flashing range is carried out, in the present invented system, through brine reheat; i.e. the additional (external) heat is supplied to (all or part of) 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 ~ , (the non-equilibrium factor) and flashing Cv~)uldliol~ rate, for additional vapor production and better system p~.ru~ ,ci. This includes; increasing flashing surface area, improving brine turbulence ( brine t~ alul~; gradient), and introducing more active nucleation sites for bubbles formation.
c- The vapor generated due to: i) brine reheat (from a) ii) the illl~JlUV~,.II.,II~ in flash chamber effectiveness (flrom b), and iu) 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 .,UIl~ iU...ll ME system; i.e.theinventedsystem~u~ s~3theME
eva~ul aliull concept and system on the existing MSF system designs.
The invented system increases saline water distillation unit capacity, improves its p.,.rull.l~t~l~,d and reduces the fresh water production cost. In addition, the invented system operates within the existing (proven design) MSF and ME sy$em'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 ,' ' systems.
Pate~lî ( 5/19/96 ) 3 Dr. H~ut E. S. P~UI
~ ~ 7774~
D~ D Of The lovenlion a~ Fl~ase Svstem Curlr~ul u~iu~l Figure 1 shows (for d.;...o..,i- d~ion) a small unit of a typical Multi Stage Flash (MSF) distillation system of the ~ Uld~iUII type. The unit consists offourstages of heat recovery section and two stages of heat rejection section as shown. Seawater enters the condense tubes ofthe heat rejection section at the lowest i . _.dlule, T"" and is heated up to temperature Tc5 by, ' of the vapor generated bybrine flashing in the heat rejection section. At this point, much of the cooling seawater, m,ei, is discharged from the plant for heat rejection and the balance make-up, m~ "p, is mixed with part of the brine flowing out of the last stage of the heat rejection section.
This mixture (at Tr~c) forms the ~ .ula~d brine, mrec, and is pumped through thecondenser tubes of the heat recovery section where it is heated up to TCl~ From there, the heated ~e~ ,ul~Ltd brine is passed through the brine heater, where it is heated to its Top Brine Temperature (TBT). Brine at TBT exitingthebrine heater, entersthe flash chamber of the first stage heat recoverysection,atbrine~e...l!.,.d~u.~ofTbl=
TBT. Then, the brine cascades downward through the several stages oftheunit, flashing off some product vapor in each stage and leaving the last stage at brine JC;I d~UI e Tb~ . 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- Inven~ted Svstem ~odificatio71s There are three major, ~ in the invented system which are ~u~ s~d on the MSF base system .~ullrl~uld~iull described above. These mr-~lifi~tir~ne are iilustrated in Figures 2 to 5 and are ~ull~la~i~.,J as follows (more detailed descriptio of Figllres Z to 5 are give71 later in the drawi~lg section) :-I- Improve the Flash Chamber Effective71ess Flashing brine, coming out of the flash chamber of the existing MSF systems, always retains some residual non-equilibrium superheat that ~,ul~6i~c.dbly aggravates the technical and economical ul~ .,t~ iiu~ 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 J.,. d~UI e 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.
u) increasing brine superheat and the number of active nucleation sites for vapor bubbles formation and vapor generation, using additional (external) heat, through a heating surface, placed between flashing trays, as will be presented below (brine reheat).
The number of brine flashing trays may increase more than two, for moreevd~u.dliol~ surface in future larger capacity units.Inthiscase,theadditional heating surface may also be divided between these trays.
Patn~î ~ 5/19 96 ) 4 Dr. Hassan r s. Falh ~ 2~7774~
2- Bri~1e Reheat For higher production rate of MSF system, additional vapor generation canbe attained by increasing brine flashing range. Additional (external) heat can notbe 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 reheat).
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: inten~al brlne reheaters), ii) through outside heat exchanger(s) (named here as: extennal bri~le reheaters); or iii) ~.~,,,.1.;,,,.1,1.,. 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) brinefrom the uppertray, Figure 3.
Supplying the sy$em with additional heat through tube bank has the following a~v~l--l~v6.
(i) generating more vapor due to the additional heat (higher flashing range), (ii) enhancing brine flashing rate due to higher brine superheat, (iii) improving the brine turbulence and the ~ ,.d~ulr; 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 all ~ (deslgn, 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.
DISTILLATION SYSTEM WITH BRINE REHEAT
SPECIFICATIONS
Field Of The Invention This invention relates generally to saline water (' " systems and more pa~ ,uLly to Multi Stage Flash (MSF) and Multi Effect (ME) distillation systems.
Description Of The Previous Systems Desalination of saline water by distillation is a very effective process, because most of the chemical materials found in saline water are non-volatile at the; ~ - d~ulr normally employed and hence remain in the lln Cv~l/ulaLcli brine. The two most proven distillation terhn~lOglrC are: the Multi Stage Flash (MSF) and Multi Effect (ME)systems. The differences between the two types of ~r~ g ~ 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 MSP 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. Duetoitsadvantagesandthe~ "l~-'rdoperational experience gained, MSF of the Ir~ ' ~ ' flow dominates the market. MSF has the advantage that the incoming brine is heated without c~Va~ulaliclll and flasbing c v /.,uol aLiull 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 ~,ull~u~ Lioll (steam, pumping and other operating costs). The system production and ~ ~u~ a~lce 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 ~CIII~ à~UI r hard scale deposits in the brine heater and the up-to-date antiscaient limitations.
On the other hand, ME systems are widely used in the chemical industry forthe cul~crll~la~iull of solutions. In seawater d~ , ME has not achievedsimilar importance, in terms of the total installed capacities, as MSF. TheME distillation system is sig.tiG~,~..lly more efficient and has a thermodynamic superiority over MSF.
The striking feature of ME system is the significant low specific power c. ,.~ l".~ as compared to MSF system.
Patel~t ( 5119196 ) 2, Dr i iar~n= r,. s. Fath ~ 21 77740 The Invention Idea The objective ofthe invented system (namedhereas: CornbinedMS~-MZSystemW-th Brine Rei~eat) is to increase saline water distillation unit capacity, improve its p."ru~ ud and, therefore, reduce the fresh water production cost over the existing MSF systems. The invented combined MSF-ME system with brine reheat introduces the concept of increasing the MSF flashing range through brine reheat, and utilizes the superior advantages of both MSF and ME systems ~ Iy The invented system uses a r."~ of: i)theup-to-date(provendesign)MSF
CVC~Uld~iUI~ system as a base system with different methods to improvetheflash chamber e~ulh,.,..~, (non-equilibrium factor) and flashing e~ulaLioll rate; ii) increases the flashing range through brine reheat, i.e. supply (all or part of) the brine with additional (external) heat in brine reheaters (located after the brine heater and/or within the flash chambers), and; iii) ~u~ o~ theMEevaporationconceptand system on the MSF base system. The mnrlifir~tinnc ofthe invented system over theexisting MSF system are:
a- Since additional (external) heat, for higher flashing range and more water production, can't be supplied before or at the brine heater in existing MSF
system (due to TrsT limitations), increasing the flashing range is carried out, in the present invented system, through brine reheat; i.e. the additional (external) heat is supplied to (all or part of) 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 ~ , (the non-equilibrium factor) and flashing Cv~)uldliol~ rate, for additional vapor production and better system p~.ru~ ,ci. This includes; increasing flashing surface area, improving brine turbulence ( brine t~ alul~; gradient), and introducing more active nucleation sites for bubbles formation.
c- The vapor generated due to: i) brine reheat (from a) ii) the illl~JlUV~,.II.,II~ in flash chamber effectiveness (flrom b), and iu) 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 .,UIl~ iU...ll ME system; i.e.theinventedsystem~u~ s~3theME
eva~ul aliull concept and system on the existing MSF system designs.
The invented system increases saline water distillation unit capacity, improves its p.,.rull.l~t~l~,d and reduces the fresh water production cost. In addition, the invented system operates within the existing (proven design) MSF and ME sy$em'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 ,' ' systems.
Pate~lî ( 5/19/96 ) 3 Dr. H~ut E. S. P~UI
~ ~ 7774~
D~ D Of The lovenlion a~ Fl~ase Svstem Curlr~ul u~iu~l Figure 1 shows (for d.;...o..,i- d~ion) a small unit of a typical Multi Stage Flash (MSF) distillation system of the ~ Uld~iUII type. The unit consists offourstages of heat recovery section and two stages of heat rejection section as shown. Seawater enters the condense tubes ofthe heat rejection section at the lowest i . _.dlule, T"" and is heated up to temperature Tc5 by, ' of the vapor generated bybrine flashing in the heat rejection section. At this point, much of the cooling seawater, m,ei, is discharged from the plant for heat rejection and the balance make-up, m~ "p, is mixed with part of the brine flowing out of the last stage of the heat rejection section.
This mixture (at Tr~c) forms the ~ .ula~d brine, mrec, and is pumped through thecondenser tubes of the heat recovery section where it is heated up to TCl~ From there, the heated ~e~ ,ul~Ltd brine is passed through the brine heater, where it is heated to its Top Brine Temperature (TBT). Brine at TBT exitingthebrine heater, entersthe flash chamber of the first stage heat recoverysection,atbrine~e...l!.,.d~u.~ofTbl=
TBT. Then, the brine cascades downward through the several stages oftheunit, flashing off some product vapor in each stage and leaving the last stage at brine JC;I d~UI e Tb~ . 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- Inven~ted Svstem ~odificatio71s There are three major, ~ in the invented system which are ~u~ s~d on the MSF base system .~ullrl~uld~iull described above. These mr-~lifi~tir~ne are iilustrated in Figures 2 to 5 and are ~ull~la~i~.,J as follows (more detailed descriptio of Figllres Z to 5 are give71 later in the drawi~lg section) :-I- Improve the Flash Chamber Effective71ess Flashing brine, coming out of the flash chamber of the existing MSF systems, always retains some residual non-equilibrium superheat that ~,ul~6i~c.dbly aggravates the technical and economical ul~ .,t~ iiu~ 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 J.,. d~UI e 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.
u) increasing brine superheat and the number of active nucleation sites for vapor bubbles formation and vapor generation, using additional (external) heat, through a heating surface, placed between flashing trays, as will be presented below (brine reheat).
The number of brine flashing trays may increase more than two, for moreevd~u.dliol~ surface in future larger capacity units.Inthiscase,theadditional heating surface may also be divided between these trays.
Patn~î ~ 5/19 96 ) 4 Dr. Hassan r s. Falh ~ 2~7774~
2- Bri~1e Reheat For higher production rate of MSF system, additional vapor generation canbe attained by increasing brine flashing range. Additional (external) heat can notbe 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 reheat).
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: inten~al brlne reheaters), ii) through outside heat exchanger(s) (named here as: extennal bri~le reheaters); or iii) ~.~,,,.1.;,,,.1,1.,. 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) brinefrom the uppertray, Figure 3.
Supplying the sy$em with additional heat through tube bank has the following a~v~l--l~v6.
(i) generating more vapor due to the additional heat (higher flashing range), (ii) enhancing brine flashing rate due to higher brine superheat, (iii) improving the brine turbulence and the ~ ,.d~ulr; 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 all ~ (deslgn, 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~ o~ S ME 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 f rst effect of ME system au~ Jva~d on the MSF base system. The vapor generated due to: i) improving flash chamber ~ ,Li~ ,Da, from I 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 inME concept, i.e. ME system isau~ Juac;d on MSF base system, as shown in Figures 2 to 4.
The additional vapor generated in each effect is condensed inside the additionalheating surface(s) of the following effect(s) as additional distillate, Figure 2 & 3.
The latent heat of ~ is used as a source of heat for that (next) effect, similar to the ~:Ullv~ iUIl~:ll 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 flashing and P~eene ( 5/19 96 ) 5 Dr. H/lssan r~ s. rreh ' ~ ~l 777~0 augments the heating in that stage (effect), in a similar way to the co~ iolldl MSP
(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 I ~ has the following additional features:
(i) there will be a partial brine flashing from the upper tray(s) and from the dripping (falling or sprayed) brine before contacting the heating surface. This causes larger ~u...~J~,Ialul~ 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 ~,ol.v~"lLi.,llal ME
system.
With large number of stages, more M.~effectscould be~u,~c.i.ll,~o~edontheMSF
base system to improve the system p~ r.ulllldl~Cc; and increase the production. The invented system may then be divided into two or more segments of ME systems.
In the invented system, each stage supplied with externa'. heat (brine reheat through either internal or external brine reheaters) is considered the first effect of M.~ system ~U,~J~,I illl"~ d on the MSF base sy$em. The first effect of each M.~ 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 dllal~gqlll~ . The second effect need not to be the following stage, but it may be one of other following stages, depending on the ICIII,~J~,ldlUiC~ difference required for optimum heating surface area. Similarly for the third and following ME effects. Typical exaT.ples of the invented system . .1., l .l ,l, ,,, l ;.:,, ,~
are i..ustrated in Figure 4.
Additional Cc~ lions for The Invention Due to the increase in the reheated brine~ll"~qld~ul~,thevacuumofthefollowing stages can partially be relaxed and . q,l~ along the rest of reheated stages. The saturation ~qlll,~.,, a~ul ~ 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 1 ~l,;l ~.UIaLillg brine t~lll,'J~.d~Ulq that reduces the brine heater heating steam l~uu;lqlll.,.l~. These factors have the economical va'.ue 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. A'.ternatively, a waste heat recovery system could be installed to utilize the plant waste heat (For example: boi'.er blow-down, flue gas energy,...etc.) instead of all (or part of) the additional heat source.
P~te~t ( 5119/96 ) 6 rJr. Hassari E. S. Ftit~i 2~ 77740 Since flashing brine is at or above saturation L~ pcild~ulr;, the suppliedadditional (external) heat as well as heat generated in each effect are fully used for the C~ r~iOI~ of the additional vapor production (in the following effects). No heat is required to preheat the brine (from the cold seawater l~ aLulG to theboiling ;I rl~U~ r;) With minimum pressure drop of the flashing brine flow, the brine may have sufficient interstage pressure differential to raise the brine from the lower tray of one stage to the upper tray of the next stage. In case the pressure differential is not sufficient, either i) a reduction in the total number of flash stages may be necessary, or ii) the required pressure differential could be attained through an additional head per stage; potential head (stepped down stages) and/or pressure head (circulating pumps), as described in the drawing section and shown in Figures 5 (a, b and c).
Brine ~ d~UIU.~, inside the condenser tubes of the MSF base system, is maintained within optimum design range by the a lj ,~l." ,1~ ofthe recirculation, reject blow-down and make-up flow rates. In case of increasing the ~ ;luulaL~d brine flow, part of the additional generated vapor could be condensed on the condenser tubes of each stage to maintain 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 maintained withinthespecifed (up-to-date)upperlimit (for maximum flashing 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 condensers as well as the brinelt~,;..,ula~iù.~rate(and,therefore,lr;.,;..,ula~;o.~pump size and power) will be reduced, and the brine ~.,..,.~lul ~: 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 bubbllng & heafing the brine in later stages (in direct contact).
This higher pressure vapor will first be throttled to the lowerpressure stages. The bubbling bU~ ,a~d 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 all- ~g. .,1, . 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, heat transfer surface area(s), the Ic~,i uuLl~iu~., reject blow-down and make-up flow rates... etc.) will be selected, based on full or partial utilization of the given invented system . . ., "1.;" ~
The other design limitations should also be preserved when ~ the flash chamber re-sizing, for example: i) brine velocity insidethe condensertube, ii) tube length and tube diameter, iii) stage maximum specifc brine flow, and, iv)stage maximum vapor release velocity.
P~tclt ( 5/19196 ) 7 Dr. H~ss~rt E. 5. F~th ' 2 ~ 777~0 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 p~ e Gained Output Ratio-GOR), and reduces, therefore, the fresh 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 ofl the additional (eAYternal) heat source for brine reheat.
The additional heat transfer surface t~ Ult; Will be maintained less than the brine heater tubes surface It7~ Ult;. On the other hand, brine Ç~ ntrAtiA~n in the flash chambers iscontrolledwithinacceptablerangebythe '; ofthe,ti~,;l.,ulALiu.., 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 andMEboilingsurfaces),problemsofbigh ~ Ulr; 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 Cu..~ ~ItiOlldl MSF and ME systems. Another alternative to be considered, is to compress the vapor generated in the last stage tbrough a vapor uulll~lu~;on system (VC) and utilize the ~,u-"l"~,.".,d hot vapor as the source of heat for brine reheat (instead of additional live steam). Optimum MSF + ME + VC system should be obtained.
PateAt ( 5/19 96 ) 8 Dr. Hr~n E S. Fath DRAWINGS
BAef Description of the Drawings The schemafic process dtagrams shown in Figl~res I to 5 and brieJ~y described belov,~, do not show an the au~ciliary systems and .~ . . required to operate the plant, and should be regarded as limited to their stated purpose of illustrafing the invented sysfem (combined MSF-ME~ system with brine reheat) process concept.
Figure 1 Figure I shows (for ~ .) a small unit of a typical Multi Stage Flash ~ISF) distillation system of the l~,ucula~iOII type. The unitconsistsoffourstagesofheat recovery section and two stages of heat rejection section as shown. Seawater enters the condenser tubes of the heat rejection section at the lowest It~ UI C, T"" and is heated up to ~ )Cld~UII; T~s~ by ' of the vapor generated,bybrine flashing, in the heat rejection section. At this point, much of the cooling seawater, m"j, is discharged from the plant for heat rejection and thebalance make-up, m""O,p, is mixed with part of the brine flowing out of the last stage of the heat rejection section.
The mixture, at T,~, forms the lc~,;luula~cd brine, m"",andispumpedthroughthe condenser tubes of the heat recovery section where it is heated up to Tc~. From there, the heated .c~,;l, ' ' brine is passed through the brine heater, where it is heated to its Top Brine Temperature (TBT). Brine at TBT exitingthebrineheater, entersthe flash chamber of the first stage of the heat recovery section, at brine ttlll~u.~l d~UI t; of Tbl = TBT. Then, the brine cascades downward through the several stages of the unit flashing off some product vapor in each stage and leaving the last $age at brinetemperature 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 I,.", ~,~
Figure 2 shows the conceptual processdiagramoftheinventedcombinedMSF-ME
system with brine reheat. Figure 2 is the process design l.. l~;.. ,.l;~.,. MSF small unit presented in Figure I with following ~ i) improved flash chamber internals for higher ~rt~ , ii) brine reheat for higher flashing range (the addition of external heat supplied to the brine), and iii) bU~ O~ lg the ME system on theMSF system. More details of these mr~," ' are:
Description 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, through the additionalheating surface (if any), with more flashing, to the lower tray(s) for more flashing and, then, exits to the next stage. Higher flash chamber efi'ectiveness (better non-equilibrium factor) is, therefore, attained due to higher flashing surface area, brine turbulence, additional brine superheat and extra active nucleation sites. The heat P~bnt ( 5/19 96 ) 13 r~r. H~ n r s. Falll 21 777i~a transfer surface is a tube bani~ 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 interna'i brine reheater). Flashing range is increased and additional vapor is generated, and the plant production is, therefore, increased.
uu) The third MSF stage with brine reheat is considered as the first effect in the ME
system b' '1''-' i '1 '' '~;i on the MSF system. External heating is supplied to this (first ME effect) stage and may also be ~,,1,l,l~..,..- - .1 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 t~ iV~ oo from (i) and due to the brine reheat firom (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 ~UjJ~ V~sC ;l on the MSF system.
This vapor is condensed as additional distii~iate and the latent heat of ~onrli~n~qti~n 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.
Addttional ~onsideratiojns A small part of the vapor generated inside the flash chambers in earlier stages (effects), could also be used for b~bbling & heatillg the brine in later stages (in direct contact).
This higher pressure vapor will first be throttled to thelower pressure stages. The bubbling ~u~ L~d vapor will increase the brine superheat (in the later stages) and wiini act as an additional source for active nucleation sites to enhance brine bubbling and flashing rate, i.e. improve the flash chamber ~ oa (non-equilibrium factor) and production rate. Optimum design parameters, (such as vapor rate, stages number and bubbling ~Ul~ ,... etc.) should be obtained.
The main and additional distillate formed in each stage (effect) is discharged through orifices to the next stage (effect) where it forms vapor by flashing and augments the heating in that stage (effect), in a similar way to the ~,u,.~. ' MSF (ME) systems.
The vapor generated in the last (sixth) stage will be condensed through the heatrejection section as .,u"~-~,..Liu,.~il MSF and ME systems. Anotheralternative,isto compress this vapor through a vapor, . ~oa;UII system (VC) and utilize the l,Ui-ljJI ~ hot steam as the source of heat for brine reheatj instead of (all or part of) the additional (external) heating steam The rest of the MSF-ME âystem flow diagram is similar to that described in Figure 1 above and the ~,u..~.,..liu..~ MSF and ME systems.
Piitent ( 5/19 96 ) 14 r~. Iii~sari E S. Fi~t~i 2 1 777~Q
Figure 3 JntroG7uctiQn Figure 3 shows an ~llial~ ' of one ;"~ combined MSF-ME flash chamber of the invented system ~,UI fl~ iull 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 intemally generated heating vapor is supplied to the brine through a tube bank under the dripping (sprayed)brinefromtheuppertray(falling film). The vapor generated due to this additional heating source and due to improving flashing chamber crrt~,liVcll~,D~ is used as the heating sûurce (tû generate more additional vapor) in the next and successive stages (effects).
Descrip~ion Similar to the existing (up-to-date) MSF proven design, the top seçtiQr~ ofthe flash chamber contains the condenser tubes where the ~~ - ul ~td brine of flow rate mc(i) enters at lt~ ul c TC~i+l) and exits at i . . d~UI ~ Tc~,). The flashed vapor condenses as the main distillate and exits the flash chamber at flow rate mpi and i , __d~UI c T~i.
The bottom sectiûn 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 mb; and ~tlll~UCld~UI~ Tbj. 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 brinewillfur~+herbe l /1 (duetothe extra superheat, large flashing 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+~) and Lt ~ .d~ul~ 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: 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 flashing chamber ~c~ a) will exit the flash chamber as the heating vapor to the next effect [stage (i+l)], similar to ME system.
Figure 4 Intro~ction The additional external heat (for brine reheaf) could be supplied: (i) within the flash chamber (named here: inter71al brine reheater), (ii) through an outside heat exchanger (named here, e~ter7lal bri7e reheater); or (iii) ~,.",~,;" 1,1." 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 p~,.ru~ an~. ThecombinedMSF-MEsystemwith brine reheat may, therefore, be divided into two or more segments and each MSP-ME
segment starts with brine reheater. Each stage supplied with external heat (for brine reheat) is considered as the first ME effect DUp.~l i".~os~ ;i on MSF base system.
P~î(5119n6) 1~ Dr.Hassanr s.r ,~ ~ 777~9 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 àllall~lllc;llL ( 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 i , _ d~U-I; difference required for the heating surface. Similarly for the third and following effects.
Descripfion Figure 4 shows three ~ (as examples) of the invented combined MSF-ME
sysfern wifh brine reheaf of a larger number of stages. 12 MSF stages are shown for f~ t,, ~ ;f~ ~, where the stage number is shown on the top of the Figure. The same conceptual al I ,~ lIL is applied to other larger units.
In the top drawin~ allall~ . the extemal additional heat (forbrinereheat)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 intemal brine reheater. The ME second effect is ~ " ~l 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 supplied with extemal heat while the 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 IvtE system, with single internal brine reheater, ~u~ uSe;i on the 12 stages of MSF system.
In the ~ drawing al l allg.,~ . 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 extemal 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 extemal 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)obtaintheirheatsourcefiromthe vapor generated in the previous effect, i.e. this drawing illustrates 2 ~ 5 effects of ME
system, with two internal brine reheaters, ~u~J.,.illlpo~e(l on the 12stagesofMSF
system.
In the bottom drawing all~1~1~,...1...~ the invented system is also dividedintotwo different segments. The f rsf 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 flashing. 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 extemal brine reheater and 5 ME effects. The extemal additional heat (for brine reheat) is supplied at the eighth MSF $age (first ME effect of the second segment).
The subsequent effects (from second to fifth effects) obtain their additional heat from the vapor generated in the previous effect, i.e. this drawing illustrates I ~ 4 + 1~5 effects of ME system, one intemal + one external brine reheaters, bU~ . ' on the12 stages of MSF sy$em.
P~tf nt ~ 5119196 ) 16 cr. ~la~sarl E. S. Fath ~ 2~ 7774~
~or larger number of stdges of MSF units similar MSF-ME-brine reheaters with different break-downs could be applied.
F'igure S
Introduction With minimum pressure drop of the flashing brine, the brine may have sufficient interstdge pressure differential to raise the brine from the lower tray of one stdge to the upper tray of the next stdge. In case the pressure differential is not sufficient: (i) a reduction in the total number of MSF stages will be necessary, or(ii) the required pressure differential could be attained through an additional external potential or/and pressure head per stage.
Descrip~ion Figure 5 presents three basic concepts to obtain hiBher inter-stage pressure d;~.~ ' The invented system consists of 2*4 effects of ME system, two brine reheaters ~u~ u~.,d on12stagesofMSFsystem.Similarconceptualallailgcll.~...
will be applied to other larger or different al . n~, units.
Fi~ure 5a is a full stepped-down ~ ;,.,. Additional interstage pressuredifferential is obtdined from the hydro-static (potential) head difference. Thismay need, however, a stronger supporting structure (due to the high elevation) in the first stages.
~i~re Sb is a ~ ' of stepped-down ~.,.,,1~,..,.1;,1.~ and the utilization of circulating pumps. In each segment (or group of stages) the additional interstdge pressure differential is obtained from the hydro-static (potential) head difference. The circulating pumps provide the pressure hedd required between each two segments and to overcome the brine reheater pressure drop. This dll ~ 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 all ~ in Figure 5b except that the a.l....~,_....,.l~ of stages in each segment is made vertical rather than the stepped-down, 9, aliull of Figure 5b. In each segment (or group of stdges) theadditional interstagepressuredifferential is obtained from the hydro-static (potential) head difference. The circulating pumps provide the pressure head required between each two segments and to overcome the brine reheater pressure drop.
Patent ~ $/19 96 ) 17 r~. Ha~sa~ r s. F~th ~ 2 1 77740 NOI~ENCLATURE
m = Mass Flow Rate ME = Multi (Multiple) E~ect MSF = Multi Stage Flash T = Temperature TBT = Top Brtne Temperature VC = Vapor Subsclipts b = brine bd = blow-down c = condenser - stage number (i) mkup = make-up p = product rec = ~ ,ul~ d rej = reject sat = saturation sea .= seawater st = Steam 1, 2, = stage (e~ect) number P~tent ( 5/19196 ) 18 Dr. H ~lian E S. Fath
The additional vapor generated in each effect is condensed inside the additionalheating surface(s) of the following effect(s) as additional distillate, Figure 2 & 3.
The latent heat of ~ is used as a source of heat for that (next) effect, similar to the ~:Ullv~ iUIl~:ll 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 flashing and P~eene ( 5/19 96 ) 5 Dr. H/lssan r~ s. rreh ' ~ ~l 777~0 augments the heating in that stage (effect), in a similar way to the co~ iolldl MSP
(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 I ~ has the following additional features:
(i) there will be a partial brine flashing from the upper tray(s) and from the dripping (falling or sprayed) brine before contacting the heating surface. This causes larger ~u...~J~,Ialul~ 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 ~,ol.v~"lLi.,llal ME
system.
With large number of stages, more M.~effectscould be~u,~c.i.ll,~o~edontheMSF
base system to improve the system p~ r.ulllldl~Cc; and increase the production. The invented system may then be divided into two or more segments of ME systems.
In the invented system, each stage supplied with externa'. heat (brine reheat through either internal or external brine reheaters) is considered the first effect of M.~ system ~U,~J~,I illl"~ d on the MSF base sy$em. The first effect of each M.~ 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 dllal~gqlll~ . The second effect need not to be the following stage, but it may be one of other following stages, depending on the ICIII,~J~,ldlUiC~ difference required for optimum heating surface area. Similarly for the third and following ME effects. Typical exaT.ples of the invented system . .1., l .l ,l, ,,, l ;.:,, ,~
are i..ustrated in Figure 4.
Additional Cc~ lions for The Invention Due to the increase in the reheated brine~ll"~qld~ul~,thevacuumofthefollowing stages can partially be relaxed and . q,l~ along the rest of reheated stages. The saturation ~qlll,~.,, a~ul ~ 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 1 ~l,;l ~.UIaLillg brine t~lll,'J~.d~Ulq that reduces the brine heater heating steam l~uu;lqlll.,.l~. These factors have the economical va'.ue 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. A'.ternatively, a waste heat recovery system could be installed to utilize the plant waste heat (For example: boi'.er blow-down, flue gas energy,...etc.) instead of all (or part of) the additional heat source.
P~te~t ( 5119/96 ) 6 rJr. Hassari E. S. Ftit~i 2~ 77740 Since flashing brine is at or above saturation L~ pcild~ulr;, the suppliedadditional (external) heat as well as heat generated in each effect are fully used for the C~ r~iOI~ of the additional vapor production (in the following effects). No heat is required to preheat the brine (from the cold seawater l~ aLulG to theboiling ;I rl~U~ r;) With minimum pressure drop of the flashing brine flow, the brine may have sufficient interstage pressure differential to raise the brine from the lower tray of one stage to the upper tray of the next stage. In case the pressure differential is not sufficient, either i) a reduction in the total number of flash stages may be necessary, or ii) the required pressure differential could be attained through an additional head per stage; potential head (stepped down stages) and/or pressure head (circulating pumps), as described in the drawing section and shown in Figures 5 (a, b and c).
Brine ~ d~UIU.~, inside the condenser tubes of the MSF base system, is maintained within optimum design range by the a lj ,~l." ,1~ ofthe recirculation, reject blow-down and make-up flow rates. In case of increasing the ~ ;luulaL~d brine flow, part of the additional generated vapor could be condensed on the condenser tubes of each stage to maintain 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 maintained withinthespecifed (up-to-date)upperlimit (for maximum flashing 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 condensers as well as the brinelt~,;..,ula~iù.~rate(and,therefore,lr;.,;..,ula~;o.~pump size and power) will be reduced, and the brine ~.,..,.~lul ~: 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 bubbllng & heafing the brine in later stages (in direct contact).
This higher pressure vapor will first be throttled to the lowerpressure stages. The bubbling bU~ ,a~d 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 all- ~g. .,1, . 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, heat transfer surface area(s), the Ic~,i uuLl~iu~., reject blow-down and make-up flow rates... etc.) will be selected, based on full or partial utilization of the given invented system . . ., "1.;" ~
The other design limitations should also be preserved when ~ the flash chamber re-sizing, for example: i) brine velocity insidethe condensertube, ii) tube length and tube diameter, iii) stage maximum specifc brine flow, and, iv)stage maximum vapor release velocity.
P~tclt ( 5/19196 ) 7 Dr. H~ss~rt E. 5. F~th ' 2 ~ 777~0 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 p~ e Gained Output Ratio-GOR), and reduces, therefore, the fresh 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 ofl the additional (eAYternal) heat source for brine reheat.
The additional heat transfer surface t~ Ult; Will be maintained less than the brine heater tubes surface It7~ Ult;. On the other hand, brine Ç~ ntrAtiA~n in the flash chambers iscontrolledwithinacceptablerangebythe '; ofthe,ti~,;l.,ulALiu.., 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 andMEboilingsurfaces),problemsofbigh ~ Ulr; 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 Cu..~ ~ItiOlldl MSF and ME systems. Another alternative to be considered, is to compress the vapor generated in the last stage tbrough a vapor uulll~lu~;on system (VC) and utilize the ~,u-"l"~,.".,d hot vapor as the source of heat for brine reheat (instead of additional live steam). Optimum MSF + ME + VC system should be obtained.
PateAt ( 5/19 96 ) 8 Dr. Hr~n E S. Fath DRAWINGS
BAef Description of the Drawings The schemafic process dtagrams shown in Figl~res I to 5 and brieJ~y described belov,~, do not show an the au~ciliary systems and .~ . . required to operate the plant, and should be regarded as limited to their stated purpose of illustrafing the invented sysfem (combined MSF-ME~ system with brine reheat) process concept.
Figure 1 Figure I shows (for ~ .) a small unit of a typical Multi Stage Flash ~ISF) distillation system of the l~,ucula~iOII type. The unitconsistsoffourstagesofheat recovery section and two stages of heat rejection section as shown. Seawater enters the condenser tubes of the heat rejection section at the lowest It~ UI C, T"" and is heated up to ~ )Cld~UII; T~s~ by ' of the vapor generated,bybrine flashing, in the heat rejection section. At this point, much of the cooling seawater, m"j, is discharged from the plant for heat rejection and thebalance make-up, m""O,p, is mixed with part of the brine flowing out of the last stage of the heat rejection section.
The mixture, at T,~, forms the lc~,;luula~cd brine, m"",andispumpedthroughthe condenser tubes of the heat recovery section where it is heated up to Tc~. From there, the heated .c~,;l, ' ' brine is passed through the brine heater, where it is heated to its Top Brine Temperature (TBT). Brine at TBT exitingthebrineheater, entersthe flash chamber of the first stage of the heat recovery section, at brine ttlll~u.~l d~UI t; of Tbl = TBT. Then, the brine cascades downward through the several stages of the unit flashing off some product vapor in each stage and leaving the last $age at brinetemperature 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 I,.", ~,~
Figure 2 shows the conceptual processdiagramoftheinventedcombinedMSF-ME
system with brine reheat. Figure 2 is the process design l.. l~;.. ,.l;~.,. MSF small unit presented in Figure I with following ~ i) improved flash chamber internals for higher ~rt~ , ii) brine reheat for higher flashing range (the addition of external heat supplied to the brine), and iii) bU~ O~ lg the ME system on theMSF system. More details of these mr~," ' are:
Description 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, through the additionalheating surface (if any), with more flashing, to the lower tray(s) for more flashing and, then, exits to the next stage. Higher flash chamber efi'ectiveness (better non-equilibrium factor) is, therefore, attained due to higher flashing surface area, brine turbulence, additional brine superheat and extra active nucleation sites. The heat P~bnt ( 5/19 96 ) 13 r~r. H~ n r s. Falll 21 777i~a transfer surface is a tube bani~ 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 interna'i brine reheater). Flashing range is increased and additional vapor is generated, and the plant production is, therefore, increased.
uu) The third MSF stage with brine reheat is considered as the first effect in the ME
system b' '1''-' i '1 '' '~;i on the MSF system. External heating is supplied to this (first ME effect) stage and may also be ~,,1,l,l~..,..- - .1 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 t~ iV~ oo from (i) and due to the brine reheat firom (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 ~UjJ~ V~sC ;l on the MSF system.
This vapor is condensed as additional distii~iate and the latent heat of ~onrli~n~qti~n 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.
Addttional ~onsideratiojns A small part of the vapor generated inside the flash chambers in earlier stages (effects), could also be used for b~bbling & heatillg the brine in later stages (in direct contact).
This higher pressure vapor will first be throttled to thelower pressure stages. The bubbling ~u~ L~d vapor will increase the brine superheat (in the later stages) and wiini act as an additional source for active nucleation sites to enhance brine bubbling and flashing rate, i.e. improve the flash chamber ~ oa (non-equilibrium factor) and production rate. Optimum design parameters, (such as vapor rate, stages number and bubbling ~Ul~ ,... etc.) should be obtained.
The main and additional distillate formed in each stage (effect) is discharged through orifices to the next stage (effect) where it forms vapor by flashing and augments the heating in that stage (effect), in a similar way to the ~,u,.~. ' MSF (ME) systems.
The vapor generated in the last (sixth) stage will be condensed through the heatrejection section as .,u"~-~,..Liu,.~il MSF and ME systems. Anotheralternative,isto compress this vapor through a vapor, . ~oa;UII system (VC) and utilize the l,Ui-ljJI ~ hot steam as the source of heat for brine reheatj instead of (all or part of) the additional (external) heating steam The rest of the MSF-ME âystem flow diagram is similar to that described in Figure 1 above and the ~,u..~.,..liu..~ MSF and ME systems.
Piitent ( 5/19 96 ) 14 r~. Iii~sari E S. Fi~t~i 2 1 777~Q
Figure 3 JntroG7uctiQn Figure 3 shows an ~llial~ ' of one ;"~ combined MSF-ME flash chamber of the invented system ~,UI fl~ iull 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 intemally generated heating vapor is supplied to the brine through a tube bank under the dripping (sprayed)brinefromtheuppertray(falling film). The vapor generated due to this additional heating source and due to improving flashing chamber crrt~,liVcll~,D~ is used as the heating sûurce (tû generate more additional vapor) in the next and successive stages (effects).
Descrip~ion Similar to the existing (up-to-date) MSF proven design, the top seçtiQr~ ofthe flash chamber contains the condenser tubes where the ~~ - ul ~td brine of flow rate mc(i) enters at lt~ ul c TC~i+l) and exits at i . . d~UI ~ Tc~,). The flashed vapor condenses as the main distillate and exits the flash chamber at flow rate mpi and i , __d~UI c T~i.
The bottom sectiûn 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 mb; and ~tlll~UCld~UI~ Tbj. 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 brinewillfur~+herbe l /1 (duetothe extra superheat, large flashing 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+~) and Lt ~ .d~ul~ 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: 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 flashing chamber ~c~ a) will exit the flash chamber as the heating vapor to the next effect [stage (i+l)], similar to ME system.
Figure 4 Intro~ction The additional external heat (for brine reheaf) could be supplied: (i) within the flash chamber (named here: inter71al brine reheater), (ii) through an outside heat exchanger (named here, e~ter7lal bri7e reheater); or (iii) ~,.",~,;" 1,1." 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 p~,.ru~ an~. ThecombinedMSF-MEsystemwith brine reheat may, therefore, be divided into two or more segments and each MSP-ME
segment starts with brine reheater. Each stage supplied with external heat (for brine reheat) is considered as the first ME effect DUp.~l i".~os~ ;i on MSF base system.
P~î(5119n6) 1~ Dr.Hassanr s.r ,~ ~ 777~9 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 àllall~lllc;llL ( 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 i , _ d~U-I; difference required for the heating surface. Similarly for the third and following effects.
Descripfion Figure 4 shows three ~ (as examples) of the invented combined MSF-ME
sysfern wifh brine reheaf of a larger number of stages. 12 MSF stages are shown for f~ t,, ~ ;f~ ~, where the stage number is shown on the top of the Figure. The same conceptual al I ,~ lIL is applied to other larger units.
In the top drawin~ allall~ . the extemal additional heat (forbrinereheat)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 intemal brine reheater. The ME second effect is ~ " ~l 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 supplied with extemal heat while the 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 IvtE system, with single internal brine reheater, ~u~ uSe;i on the 12 stages of MSF system.
In the ~ drawing al l allg.,~ . 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 extemal 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 extemal 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)obtaintheirheatsourcefiromthe vapor generated in the previous effect, i.e. this drawing illustrates 2 ~ 5 effects of ME
system, with two internal brine reheaters, ~u~J.,.illlpo~e(l on the 12stagesofMSF
system.
In the bottom drawing all~1~1~,...1...~ the invented system is also dividedintotwo different segments. The f rsf 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 flashing. 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 extemal brine reheater and 5 ME effects. The extemal additional heat (for brine reheat) is supplied at the eighth MSF $age (first ME effect of the second segment).
The subsequent effects (from second to fifth effects) obtain their additional heat from the vapor generated in the previous effect, i.e. this drawing illustrates I ~ 4 + 1~5 effects of ME system, one intemal + one external brine reheaters, bU~ . ' on the12 stages of MSF sy$em.
P~tf nt ~ 5119196 ) 16 cr. ~la~sarl E. S. Fath ~ 2~ 7774~
~or larger number of stdges of MSF units similar MSF-ME-brine reheaters with different break-downs could be applied.
F'igure S
Introduction With minimum pressure drop of the flashing brine, the brine may have sufficient interstdge pressure differential to raise the brine from the lower tray of one stdge to the upper tray of the next stdge. In case the pressure differential is not sufficient: (i) a reduction in the total number of MSF stages will be necessary, or(ii) the required pressure differential could be attained through an additional external potential or/and pressure head per stage.
Descrip~ion Figure 5 presents three basic concepts to obtain hiBher inter-stage pressure d;~.~ ' The invented system consists of 2*4 effects of ME system, two brine reheaters ~u~ u~.,d on12stagesofMSFsystem.Similarconceptualallailgcll.~...
will be applied to other larger or different al . n~, units.
Fi~ure 5a is a full stepped-down ~ ;,.,. Additional interstage pressuredifferential is obtdined from the hydro-static (potential) head difference. Thismay need, however, a stronger supporting structure (due to the high elevation) in the first stages.
~i~re Sb is a ~ ' of stepped-down ~.,.,,1~,..,.1;,1.~ and the utilization of circulating pumps. In each segment (or group of stages) the additional interstdge pressure differential is obtained from the hydro-static (potential) head difference. The circulating pumps provide the pressure hedd required between each two segments and to overcome the brine reheater pressure drop. This dll ~ 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 all ~ in Figure 5b except that the a.l....~,_....,.l~ of stages in each segment is made vertical rather than the stepped-down, 9, aliull of Figure 5b. In each segment (or group of stdges) theadditional interstagepressuredifferential is obtained from the hydro-static (potential) head difference. The circulating pumps provide the pressure head required between each two segments and to overcome the brine reheater pressure drop.
Patent ~ $/19 96 ) 17 r~. Ha~sa~ r s. F~th ~ 2 1 77740 NOI~ENCLATURE
m = Mass Flow Rate ME = Multi (Multiple) E~ect MSF = Multi Stage Flash T = Temperature TBT = Top Brtne Temperature VC = Vapor Subsclipts b = brine bd = blow-down c = condenser - stage number (i) mkup = make-up p = product rec = ~ ,ul~ d rej = reject sat = saturation sea .= seawater st = Steam 1, 2, = stage (e~ect) number P~tent ( 5/19196 ) 18 Dr. H ~lian E S. Fath
Claims (19)
1- A new Multi Stage Flash (MSF) distillation system of enhanced flashing, brinereheat and superimposed Multi Effect (ME) distillation system, called herein:
combined MSF-ME system with brine reheat, as described in the specifications above (and described & illustrated later in the drawings Figures 2 to 5), has special features designed to increase the distillation unit capacity and production rate, and improve its performance and, therefore, reduce the fresh water production cost.
combined MSF-ME system with brine reheat, as described in the specifications above (and described & illustrated later in the drawings Figures 2 to 5), has special features designed to increase the distillation unit capacity and production rate, and improve its performance and, therefore, reduce the fresh water production cost.
2- A combined MSF-ME system with brine reheat as claimed in claim 1, uses a combination of: i) the up-to-date (proven design) MSF evaporation system as a base system with different methods to improve the flash chamber effectiveness (non-equilibrium factor) and flashing evaporation rate, ii) increases the MSF system flashing range through brine reheat, i.e. supply (all or part of) the brine withadditional (external) heat in brine reheaters (located after the brine heater and/or within the flash chambers), and iii) superimposes the ME evaporation concept andsystem onto the MSF base system.
3- A combined MSF-ME system with brine reheat as claimed in claims 1 & 2, uses the up-to-date (proven design) MSF system as a base with different methods to improve the flash chamber effectiveness (non-equilibrium factor) and flashing rate, for more vapor production and better overall system performance. These methods include: i) increasing brine flashing surface area and brine turbulence (improve brine temperature gradient). For example, two (or more) trays with dripping (falling or sprayed) brine, from the upper tray to the lower tray(s), are used, as shown in Figures 2 & 3, ii) increasing the brine superheat and the number of active nucleation sites (for example; brine reheat through additional heating surface located between the trays, and steam bubbling within brine). The number of brine flashing trays may be increased more than two for more evaporation surface in larger capacity unitsand the additional heating surface may also be divided between these trays.
4- A combined MSF-ME system with brine reheat as claimed in claims 1 to 3, increases the MSF system flashing range through brine reheat, i.e. supplying thebrine with additional (external) heat after the brine heater and/or within the flash chambers. Since additional heat, for higher flashing range and more vapor production, can not be supplied to the brine before or at the brine heater (due to Top Brine Temperature (TBT) limitations), the additional heat is supplied to thebrine, in the invented system, after the brine heater (named here: brine reheat). The additional heat (brine reheat) could be supplied to the brine; (i) within the flash chamber(s), named here, internal brine reheaters, (ii) through outside heat exchanger(s), named here, external brine reheaters; or (iii) combination of both (i) and (ii). 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.
5- A combined MSF-ME system with brine reheat as claimed in claims 1 to 4, the additional heat could be live heating steam (for example: 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) additional heat source.
6- A combined MSF-ME system with brine reheat as claimed in claims 1 to 5, superimposes the ME distillation concept and system on the up-to-date (proven design) MSF base system. Each stage supplied with external (additional) 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 vapor generated due to: i) the improvements in flash chamber effectiveness (from claim 3), ii) due to brine reheat (from claims 4 and 5), and iii) possibly part of the main vapor generated inside the earlier flash chamber(s), 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, Figures 2 to 4.
7- A combined MSF-ME system with brine reheat as claimed in claims 1 to 6, the additional vapor generated from each stage is condensed inside the additional heating surface of the next effect, and used as additional distillate, Figures 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 flashing and augments the heating in that stage (effect), in a similar way to the conventional MSF (ME) systems.
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 flashing and augments the heating in that stage (effect), in a similar way to the conventional MSF (ME) systems.
8- A combined MSF-ME system with brine reheat as claimed in claim 1 to 7, since flashing 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. No heat is required to preheat the brine (from the cold seawater temperature to the boiling temperature) as in conventional ME system.
9- A combined MSF-ME system with brine reheat as claimed in claim 1 to 8, with large number of stages, more ME effects could be superimposed on the MSF base system to improve the combined systems performance and increase the production. The invented system may then be divided into two or more segments of ME system superimposed on the MSF base system segments. Each stage supplied with external heat (brine reheat; through either internal or external brine reheaters) is considered the first effect of the ME 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 also not to be the next stage, but it may be one of other following stages, depending on the temperature differences requiredfor the optimum heating surface area. Similarly for the third and following effects as well. Typical examples of the invented system combinations are illustrated inFigure 4.
10- A combined MSF-ME system with brine reheat as claimed in claim 1 to 9, withminimum pressure drop of the flashing brine flow, the brine may have sufficient interstage pressure differential to raise the brine from the lower tray of one stage to the upper tray of the next stage. In case the pressure differential is not sufficient, either: i) a reduction in the total number of flash stages may be necessary, or ii) the required pressure differential could be attained through an additional head per stage; either potential head (stepped down stages) and/or pressure head (circulating pumps) as described in sections 4 and drawing sectionand shown in Figures 5 (a, b and c).
11- A combined MSF-ME system with brine reheat as claimed in claim 1 to 10, brine temperature, inside the condenser tubes of the MSF system, is maintained 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 eachstage to maintain the system parameters near optimum values. In this case, the required additional heating surface area (for brine reheat) is reduced. Similarly, Top Brine Temperature (TBT) is also maintained within the specified (up-to-date)upper limit (for maximum flashing range and brine heater hard scale control).
12- A combined MSF-ME system with brine reheat as claimed in claims 1 to 11, using part of the main vapor generated inside the flash chambers as a source of heat (for brine reheat) will reduce the heat transfer surface area required for the main condensers as well as the brine recirculation rate (and, therefore, recirculation pump size and power), and increases the brine temperature difference across the brine heater for better heat transfer. Optimum design parameters should be obtained.
13- A combined MSF-ME system with brine reheat as claimed in claims 1 to 12, 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 lower pressure stages. The bubbling superheated vapor will increase the brine superheat (in thelater stages) and will act as an additional source of active nucleation sites toenhance 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.
14- A combined MSF-ME system with brine reheat as claimed in claim 1 to 13, theadditional heat transfer surface temperature will be maintained less than the brine heater tubes surface temperature. On the other hand, brine concentration in theflash chambers is controlled within acceptable range by the adjustments of the recirculation, reject blow-down and make-up flow rates. Since the brine containsenough 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 surface ( brine reheaters and ME boiling surfaces), problems of high temperature hard scale deposits on these additional heating surfaces will be under control.
15- A combined MSF-ME system with brine reheat as claimed in claim 1 to 14, Due to the increase in the reheated brine temperature, the vacuum of the following stages can partially be relaxed and redistributed along the rest of reheated stages. The saturation temperature can, therefore, be increased and redistributed along the rest of reheated stages, to enhance the heat transfer across the condenser heat transfer surface. Higher heat transfer rates across the stages condensers leads to a reduction in the heat transfer surface required and/or increase in the recirculating brinetemperature that reduces the brine heater heating load requirements. These factors have the economical value of reducing plant cost; both capital cost (condensers heating surfaces) and operating cost (brine heater heating steam).
16- A combined MSF-ME system with brine reheat as claimed in claim 1 to 15, the additional vapor generated in the last stage is condensed on the condenser tubes of the heat rejection section as in 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 the additional live steam).
Optimum MSF + ME + VC system combination should be obtained.
Optimum MSF + ME + VC system combination should be obtained.
17- A combined MSF-ME system with brine reheat as claimed in claims 1 to 16, with the supply of a percentage of the brine heater heat load (for brine reheat), theinvented system increases the specific unit capacity and production rate, and improves the unit performance (i.e. Gained Output Ratio-GOR), and reduces, therefore, the fresh water production cost, as compared to the present MSF
system. GOR is further increased and production costs are further reduced when waste heat is used as (part or all of) the additional (external) heat source for brine reheat.
system. GOR is further increased and production costs are further reduced when waste heat is used as (part or all of) the additional (external) heat source for brine reheat.
18- A combined MSF-ME system with brine reheat as claimed in claim 1 to 17, optimum design parameters, (such as: number of stages, number of segments, number of effects, brine reheaters's size, type and number, stage size, heat transfer 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 flash chamber re-sizing, for example: i) brine velocity inside the condenser tube, ii) tube length and tube diameter, iii) stage maximum specific brine flow, and, iv) stage maximum vapor release velocity.
19- A combined MSF-ME system with brine reheat as claimed in claims 1 to 18, utilizes the main features and advantages of both MSF and ME systems simultaneously, and operates within the up-to-date existing (proven design) system's constraints and limitations. The invented system allows, also, for the possibility of utilizing waste heat as (all or part of) the external heat source. The invented system presents, therefore, a break-through for the future generation of saline water desalination systems of high unit capacity, high production rate, better performance, and, therefore, lower fresh water production cost.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002177740A CA2177740A1 (en) | 1996-05-30 | 1996-05-30 | Combined multi stage flash-multi effect distillation system with brine reheat |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002177740A CA2177740A1 (en) | 1996-05-30 | 1996-05-30 | Combined multi stage flash-multi effect distillation system with brine reheat |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2177740A1 true CA2177740A1 (en) | 1997-12-01 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002177740A Abandoned CA2177740A1 (en) | 1996-05-30 | 1996-05-30 | Combined multi stage flash-multi effect distillation system with brine reheat |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2012032355A1 (en) * | 2010-09-09 | 2012-03-15 | Pdx Technologies Ag | Thermal desalination using breaking jet flash vaporisation |
-
1996
- 1996-05-30 CA CA002177740A patent/CA2177740A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2012032355A1 (en) * | 2010-09-09 | 2012-03-15 | Pdx Technologies Ag | Thermal desalination using breaking jet flash vaporisation |
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| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |