HomeMy WebLinkAbout1994-10-26; Municipal Water District; 1026.01; Pilot Cogeneration Desalination Facilities\B # 1026.3 TITLE: PRESENTATION ON PROPOSAL FOR "PILOT
IIITG.
IEPT. CMWD-
10/26/94 COGENERATION DESALINATION FACILITIES"
BY SUPERSYSTEMS, INC.
?ECOMMENDED ACTION:
DEPT. HD.
CITY MGR. -,
CITY 'ATTY
Staff is requesting the Commission discuss the potential for District involvement in a pilot cogeneration desalination facilities subsequent to a presentation by Mr. Sam Tadros,
President of Supersystems, Inc.
ITEM EXPLANA TION:
Staff has had recent occasion to be present at a meeting with Mr. Sam Tadros of Supersystems, Inc. and Mr. Rick Graff, General
Manager of Encina Wastewater Authority.
Mr. Tadros wants to construct a pilot cogeneration desalination
facilities in a cooperative effort with the U.S. Bureau of
Reclamation. Mr. Tadros will be at the meeting to give
presentation on this project in hopes that the District will
express an interest in participating in the pilot project.
Some information on this topic is attached.
SUPERSYSTEMS, INC,
~
17581 TEACHERSAW. FAX (714) 733-3430
=LEX 710 11 1 5328
' SUPER SYSTEMS
IRVINE. CA 92714
(714) 786-71 17
ENGINEERS DEVELOPERS
June 15,1994
Mr. Bill Plummer
District Engineer
City of Carlsbad
2075 Las Palmas Drive
Carlsbad, CA 92009
CC: Mr. Bob Greany: Water District Manager
Subject: DesaIInation-Cogeneration Plant RoJect
Dear Mr. Plummr,
is currently conducting a feasibility study under
contract to the U.S. Department of Interior, Bureau of Reclamation for the location of
a coastal desalinationcogeneration plant in Southern California. Following compktion
of the study by this June, we will be prepared to initiate Phase II of the program which
consists of the design and installation of a pilot plant to verify performance and cost
effectiveness of the plant system at the selected site.
Supersystems Inc. (SSI)
SSI jointly with the Bureau of Reclamation will finance, design, and install the
pilot desalinationcogeneration plant at no capital cost to the city. The city would
purchase the high quality product water at a negotiated price competitive with your
current rates. The praduct water will be a high quality water which can be blended
with other high salinity sources'of water to improve the city's overall water quality.
The purpose of this fetter is to determine your potential interest in locating this
pilot plant within your area of jurisdiction. SSI would li to schedule a meeting with
you to discuss the findings from the feasibility study ahd the details of the second phase of the project. SI has adequate information from our feasibility study to present: site
requirements, plant size, fuel needs, and product water quality.
SSI and its principle have 25 years of experience in the design and construction
of desalination-cogeneration plants with facilities in the Middle Wt, the Virgin
Tstands, and other countries around the world. We look forward to meeting with you
to discuss our experience and the potential benefits of thig project for your community.
Sincerely,
FILE: 194/MS/ClTY
STICC
COGENERATION SMALL POWER DESALXNATION HEATXNC & COOLING 9 ENVIRONMENTAt STUDIES DESIGN CONSTRUCTION SUPERVISION FINANCE 4 TURNKEY PROJECr -
O€P€€€LPIL'oN 131 3NI SW31SAS2l3dnS
SUPERSYSTEMS, INC.
17581 TEEICHERS AVE. PAX (714) 733-3430 SUPER SYSTEMS
IRWNE, CA 927 I4 TELEX 710 11 1 5328 e----- ENGINEERS * DEVELOPERS (7141 786-71 17 (M882461
Sept. 19, 1994
Mr. Richard Graff, P.E. ................................................................ Via Fax
General Manager
Encina Wastewater Authority (EWA)
6200 Avenida Encinas
Carlsbad, CA 92009-0171
CC: Mr. Bob Gmney, P.E. .................................................. Vi Fax
General Manager
City of Carlsbad
Subject : 1- U.S. Bum Cogeneration Desalination plant Feasibility Study
2- Design and Construction of Pllot Cogen/Dessl Facility
Dear Mr. Graff :
We greatly appreciated the opportunity to meet with you and Mr. Greaney to
discuss the subject study.
This letter, with the enclosed information, is sent to you pursuant to our
discussion in your office on September 8, 1994 with yourself and Bob Greaney,
Carlsbad Municipal Water District, regarding the subject project being conducted by
Supersystems, Inc. (SS?) for the U.S. Bureau of Reclamation (BUREC). We greatly
appreciated the opportunity to meet with you and Bob Greaney to discuss the subject
study. As stated in our meeting, the results of the study confirm the potential merits of
the novel power generation and sea water desalination technology. The next phase in
the program will be to design, construct, and operate the first demonstration plant of
this type in the United States on the Southern California Coastline. Demonstration plant
performance data and operational economic options, according to this production of
electricity and quality of processed water, could be used for implementation in larger
facility designs at ocher potential sites in Southern or Northern California.
Funding for design and construction of the demonstration plant would be
provided jointly by SSI and the U.S. BUREC. It would be necessary for the site host
owner to cover some expenses required during the design,' construction, and operation
of the plants. Potential areas of need would involve site preparation, lay down area,
equipment installation, interfacing of plant instrumentation and controls, environmental
monitoring, operation and maintenance, fuel supply, process water distribution, and
reject water-brine outfall to the ocean.
' COGENERATION SMALL POWER DESA1.INATION HEATING & COOLING ENVIRONMENTAL
STUDIES DESIGN CON.mUCTION SUPERVISION FINANCE TURNKEY PROjECr
In the event that during the next few months you decide to "recook" at your
existing cogeneration plant upgrading options, we would be happy to submit a propod
to provide a cogeneration-desalination plant at your facility that wouId outperform
existing cogeneration units, reduce your electricity costs, and provide p~ocessed water.
Utilizing gas turbine with digestor gas is normally easier to permit from the AQMD
when they apply their BACT..
PRELIMINARY ASSESSMENT:
The following represent our preliminary estimates regarding the economics of the two
potential alternatives shown below, assuming the facility in each case will be installed
inside the Encina Waste Water plant and that the Bureau of Reclamation will contribute
20 96 of plant capital cost:
0 ALTERNATIVE I: Cogeddesalination facility firing digestor gas at
no wst.
1100 KW/150,000 Grrllons per day distilledldrinking water quality
0 ALTERNATIVE 2: Cogenldesalination firing natural gas at
$2.6 /MMBTU
1100 KW/lSO,OO Galloas per day distilled/dhkhg water quality
Please note that the product water from the desal plant can be increased by
approximately 80% of the above, if we include a supplementary firing system with the
cogen plant. Also the size of both power and water can be reduced to approximatety
50 96 of the above by utilizing a smaller system size. In general, The cogen facility
will be designed to tire digestor gas, natural gas, or a combination of both at any ratio.
-
3NI SW31SASd3dfiS
OTHER ADVANTAGES FOR THE DESAL PLANT:
1- As stated in our meeting, the desalination facility will pduce water at 3-15
ppm, TDS. By blending this pure water with other sourea of brackish water in the
area, an improvement in the total quality of water will be achieved.
2- This pure water can also be added to the relatively high waste water salinity
presently discharged to the ocean which will lower this stream TDS to an acceptable
level and therefore enable the facility to meet state and federal regulations.
3- The combined simultaneous production of electricity and water will enable us
to sell the Encino facility and/or the City electricity at a reduced rate compared to
SDG&E's current or future rates (we will guarantee this saving during the contract
term).
4- The high punty distilled water can be pumped and sold to the adjacent
SDG&E Encino power plant to be used as a boiler make up water (cunently this high
purity distilled water is costing SDG&E approximately $ 18/1OOO gallon to produce).
5- If you allow us to utilize a gas turbine bad cogen, this distilled water would
also be used to reduce NOx emission from 145 ppm to approximately 25-30 ppm which
could be approved by the air quality as representing the BACT (no additional pollution
control equipment would be required).
6- The existence of the ocean oiitfdl and its current length will have positive
effects on reducing the cost of produced water and on desalination plant permitting. In
generat, the Encino site is very favorable for the installation of desalination plant.
7- Combining the cogen with desalination will ensure that the facility will
operate as a Qualified Cogen Facility since the desal plant will act as a heat sink. This
concept will entitte the facility to all the advantages of cogeneration regulations
including having the utility power on stand by. All the existing electrical and heating
systems will remain intact and ready to serve the facility at any time. The cogen can
also provide Encino with the heating requirement for the sludge operations and
therefore minidze the current OkM cost.
8- Mr. Greaney indicated the need for water specially if it is of high punty, we
will provide provisions in plant design for the addition of more ded units, or the
addition of one or more combined cogen desal units, if so desired in the future.
9- The results from this pilot demonstration facility could be applied toward a
full scale power desalination of much larger capacity, that for example, could make
the city of Carlsbad and the surrounding areas self sufficient in drinking water supplies
and electricity, as it is the case in all of the Virgin Islands.
3 N I s w 3 1 s A s a 3 d n s
PLANT FINANCING ARRANGEMENT:
We ate confident that ptant finance an be arranged if the sale of electricity and
water are secured through a long term agreement. In addition to the Bureau's fmancial
contribution, a plant financing arrangement has been discussed and approved by my
company, and by our partner which is a large size company, in case a much larger size
is required. We do not expect any difficulty to finance the facility.
If these outlines are acceptable to you, I would reeommead that we start a
detailed technical and economical feasibility study ASAP so that you can also
benefit from the participation of the Bureau of Reclamation In this project.
COCEN PLANT ENCINEERINC & PERMlTIWG SERVICES:
SSI would also be pleased to provide engineering/design servia, permitting
services, construction supervision, and start up services for the planned cogen system
of the gas engine type. We have bum engineering and permitting such facilities since
1983. I would be pleased to arrange a tour for some of our operating gas fued cogen
facilities in Southern California. In the Santa Monica area, we have several operating
cogen systems that could prove to be more cost effective for the Encina plant.
PRESENTATION ON DESAUCOGEN:
If you are interested in a general stide and overhead presentation on cogen and
desalination, their design features, and the economics of various technologies, 1 would
be glad to arrange for such a presentation at your convenience.
I am looking forward to a long term and mutually beneficial relationship
between our organization.
If you have any questions or desire additional information, please calf Frank
Ducey or Sam Tadros at (714) 786-7117.
Very Truly Yours,
SSI
(Sam Tadros, P.E., MSME)
CC: Mr. Roben Greaney, P.B.
Mr. Frank Ducey, P.E.
Fils: 941develop92094
ST/PP
Electric Power and Desalinated Seawater, Sam Tadros, RE.
In view of mpidly risingjbl
costs, cogenemtion plants
have acquired a new
significance. Recent studies
and applications have shoun
results relevant to the design
and economy of cogenemtion
plants for the production of
electric power and
desalinated seawaim Part 1
is included hew to be
fibwed in the l~ext issue sf
Cogeneration World ttrith the
conclusion.
The mater ddindon cycle
rekatd for detaikd compariscm m this
dudy is the well-knawn mubage flash
evaporator (MSF). which uses brine
rreLrulation and acid or polyphosphete for rak proledion.
Interesi in a dual-purpose pht4r
cogeneration d eledric pcwr and steam-
SIC~ Gom its inherent thermodynamic
efliciency. Fossil-fuel-find central SLStions
COIIWI( one-third of enew input to
ekdlicity but dows the remaining two-thirds
to escape in the form ofthvmal discharges.
By using the rejeded heat cogeneretion-or
dualpurpose phs-can rhim a thermal
e&ciency as high as 80%.
This is the reason for rcant
widespread use of cogenemtion dual-purposc
plants and is $so emibuted to the fad that the energy share of the produd water cost is
high. In the United States in 1954. heal
COSI in the d production co~l of sehd
stcam consuming industties nas 4.14% for
the beer sugar indw, 2.95% Cor paper
pulp mills and 5.62% for the chlorine
industn. In 1972. the enew share of
pduci Mer cog was up to 35%. and in
1984 the energ? ShaR of produci Mater cost
was higher than 50%.
Extraction TurbinelMSF Scheme
Rcnbilit! and Daw F~rues
In this cogeneration scheme the
steam isd from the bine a a s~tabk point and passcs to the brine healer
d the desahahn plant aher being desuperhcsrd. .s shun in Fw 1. The remainder is completely
arpanded in a kw pnssure turbine and
ahausted to a ltsndard condenser. slcam is
nWmany curaued a about 30 psig for an
rid dcsalinetion plan^ with a
maximum brine heater tempermum of 250° E and at a ~IF!SSWV of5 psig for a poljphosph treatment Won plant
with 195O F maximum brine heater
temperature
sulphate scak especially in the brine heater
tubes it is prdid halthe stcam
temperatm m the brine heer em
(afier being cksuperheated), not amd
262O F for dd dnsing and 212O F for
PollPhosp~e dosing, during Ph operation.
Charaderizcd by Ksy good flaibility. Nal
Howc~z in order to mid calcium
The exmaion turbinedeme is
only can the water to pcwr ratio (gallkwh
or rngdhW) be varied hm wry low dues
to values ready as &h as hose for the
back prrssure qvk but this scheme aL0
permits the operetion to produce water only
or puwer only. In caw of Wine breakdom
the scheme pmvides for a bypass circui~
hugh which high prwu~ steam hm the
boikr is supplied dirrclly to the desalination
plant via, a pnssurc Rducing station and a
desuperheater. Powr quid for ph
opekon could be pmkkd from a -up
diesel genemr ~e(.
by appropdc modifii d the *am h. A control \9hr W on the turbine
is arranged to msi& the Oon- of rlc~m
through the h pressure tidon SO thm he
attraction *am ma be msintained through the bw pmsurc stages. eKn a maximum
actrabion rmes to pmnt overheating of he
turbine bladea This minimum tlou.
cormponds IO about 10 to 15% ofhe
med capacity ofhe lm prrssurc &on. At
this minimum lbw condition. he atradon
scheme will haw its maximum water
produdon capecity. This maximum water
production could be obtained continuously
and independently of the power load. U we amumed a turbine hde
condition of 900° F and 850 psig. this
scheme could have a mter ID pmwr do about 11.6 galkU'h or I mgd for every
3.7MU. The cogeneration index, apressed
in kUh gemmed per million Btu absorbed
by chc brine heater. would be about
104 kUhllO* Btu for an add dosing plant
m a performance ratio "R" equal io
10 pounds of distillate per 1.OOO Btu.
Howwc the water to powr ratio
varies with the performance do a the
same cogenemtion index. For R in the range of 7 to 15 lbfl.OO0 Btu. the wter to per
ratio for his scheme would vary from
8.1 gal.kWh to 27.3 gaLkW'h.
900" FB50 psig thmak conditiom
lOMw/mgd power to w do and 10 R
@eriormMcc do) for an mid dosing
desalination plant, the madmum au~n flow
m the low prec~lrt turbine (ii, when the plant is in the power+ mode) will bc about 1.5 tines the c*eamfbw 1 full bad
conditions of the dual pup= Iryrtem. AI a
powr IO waer ratio of 3.7MWmyd, this
steam flow ratio in the law pressurr redion
oftheturbinewouMbetqpr&d) ' 12.
To dow for this condition in plarl deciign would nwlt m a considenbie increase in
boh capital and opuaring ape~ch
Every dolt should be mede not to mrsizc the cogenemtion pbnt. A careful
malysis should be made d& hepr and
ekmical loads to ensm th maximum ulie is made of diKrsity fedonr The nad for
this eRort is shictly economic The kr the
equipment aiae is to the adusl demands, the
hq$er the capecity f&or will be 'lk
capital cost of the planc is a funmon d the
size or capacity of the plant, but the mnue earned by the pht is a fwrrion ofthe size
Continued on pg. 27
A change in pomr demand is met
For cogeneration syseenr~ oparting a~
-
20 Cogeneration World, SepemberKktober 1984
.. .'
Desalinated Seawater
Continued {rum pg. 20
of the load. Load cycling on the elecuical
side or the w%er side can o+- be achieved
PI he apcnv of bwer lhermodynamic
a1cienq.
Scheme Econom?
For the same stem and feedwater
conditions as for regeneratiw cycle this
xkmc win he a variable heat rate and
dincy depending on the proportion of
steam extracted for the consumption of he desalination plant. When the extraction
steam to desalination ,plant is zem the
turbine heat me will be essentially the same
as for the regenerative cycle (neglecting the
small pmsw drop acm the extraction
control de). When the madmum steam is
extracted. i.e. at a maximum water IO power
ratio of abou~ 0.27 mgd per MIL
&superheated and supplied to an acid
dosing desalination plant. ?stem thermal
ctTicienq jumps to appruximately 76%. as
shown on F~re 2 whew 1 kQ.h was taken
equivalent to one unit. Bd on one unit of
eiectririp output. 5.04 units are heat input
in the form of fuel and 2.82 units in the
form of steam would be supplied IO the
brine heater.
The economic features am bawd on
the fhct that he heat in the steam supplied
IO the dcsalinaion plant can be included as
a positiw \slue in the system's dliriency
equation. ALsa the tempratwe of boiler
kcduatcr uas assumed qual to the brine
heater condensate kmperattulc Hownrr. for
both condensing and berkprrssurr wheme~.
low Mw-cr temperaturv rmghc caw a
thermal shock IO the boiler urd set up
undcsirabk 9resse~. The re~uming
condensate might also be contaminated b?
dissolved eases through the makeup water or
through brine leakage in the brine heater.
For these reasons the inclusion of the
feedwater heaters and deaemor and
polishing sgrms will be required.
plant when using the condensing scheme
will be a system heat rate of about
4.600 BtukNI. Approximately 69% of the
he* &mise waed in this scheme is
rrca~red in he form of steam supplied IO the desalination plant. This heat recovery muhs in a ratio of recavered heat IO
ekdricity of appruximately 2.8 to 1.0. using
In tern of primary mcr~ resources,
each don kWh produced by chis scheme
as compared IO separate ph producing
the same mount of power and water and
using the same fuel can saw appmximately
29.000 gallons of oil (or 157 tons of coal of
a heat value of 12.000 Btuhb).
The combined power/desalination
the condensing scheme
To asses the annual dollar saving.
the follming ssumptjons M made:
1. lOOMU' mgenedon *ern the condensingatradon scheme
2. Water to power &o of 0.27 +NW.
3. Pomr-onl) pP.1 thermal e&cjency of
plant performance ntio d 4. Ikdumon .. 36%.
10.
5. Operation d90% apacity bor for 11
months every year. At 83' per gallon dhrl dGs type d
cagenerdon wwld MVC $17.8 d6on each
y~r in the lbnn offuel oil QIllLumption or
a sawing equivalenr IO 0.5 dion hmb d
oil mdy. ff0 be contimd)
SAM TADROS
.. . . , , . . . . , .- ~
.. .
5401 Business puk South - Suite 210 - Bakersfield, California 93309
2833 N. 3rd Street
phoenix, Arizona 85004 6021265-2791 602/265-1259 Telex 165017 - 8051322-2234
Cogeneration World, SeptemberlOctober 1984 27
.*
' - _. .. Continwd from pqr 25 power and water and using the same
fuel, can have a net annual saving of
approximately 40,000 gallons of oil.
In terms of net annual dollar
savings, if a cogeneration system of
this type having a capacity of 100
MU' and a water to power ratio of
0.15 mgd/MW is compared to a
separate gas turbine unit of thermal
efficiency 27% and a separate
seawater desalination plant of 10
performance ratio (assuming that this
cogeneration system will be operating
at 90% capacity factor for 11 months
every year), at 83 cents per gallon of
oil. this cogeneration scheme would
save approximately $26 million each
year in the form of fuel oil.
Dieeel Enpm ' elMSF Sch erne
Design Feature19
The concept of diesel engine
scheme is shown in Figure 2. The
diesel eee drives an electric
generator. Process steam for the
desalting plants is made in the heat
recovery boiler that uses the engine
exhaust and jacket cooling as heat
sources. The back-pressure exhaust will
res& in a shght decrease in the
electric power generation from this set.
Diesels currently are using
under way far a dual-fuel system that
can ust both liquid and &aseous fuels
such as propane and methane. Research hasalso started on the use of
ly expand the cogeneration schemes
petr0km-W fuels. Restarch is
bk. These significant-
through died applications.
Diesels are currently available up
to 25 MW. Basic thermal efficiencies
range hm 30 to 35%.
ratio for the diesel engine is much
lower than that for gas turbines.
Therefore, the diesel engine has the lowest steam to power ratio and conse-
quently the hest water to power ratio.
Diesel engine cogeneration cycle
is recommended for smd viIlages
located on the sea, and where the
water demand is not relatively high or
where the demand on electrid power
is signi6candy high.
The excess air or the airhel
Table 2 Thermal Efficiency and Performance Values for Died EnainemSF Scheme
Watedpower ratio (gal/kWh)*
Heat recovered (waste heat)
2.2 to 4.6
System thermal efiiciency 57%
Cogeneration index (kWhllO6Btu) 390
38 %
Scheme Economy If we assume, as previously
mentioned, that the exhaust steam from
the heat recovery boiler win be
supplied to the brine heater where it
would be condensed at inlet brine
heater saturation pressure and returned
as boiler feedwater at that tempemture,
the system efficiency jumps from 35 to
57% approximately, as shown in Table 2.
If we assume 1 kwh power
output from the generator or one unit
output, then the fuel requid for this combined cycle will be equivalent to
2.97 units. procesS heat supplied to
desalination plant is 0.75 unit with
system heat rate of 5800 Btukwh.
Refer to Figure 2.
The cogeneration index for this
cogcieration system woukl reach $15
million per year when compared to the
diesel generator set and desalination
working separately, wing he me fuel
and having the same capady.
GmchMiom
(1) The extraction turbinelMsF scheme
heat rate and the4 efficiency are
highly sensitive to the spread been
throttle and exhaust conditions, in both
ideal and mal cycles. This scheme is
the most flexible regarding load cycling,
but has the disadvantage of datively
high cost.
(2) The backpressure turbine/MSF
scheme has the highest water to power
ratio, highes~ thermal efficiency and
lowest cogemtion index. This scheme
has a limited response to load CY&K --
To Ataoepkre Boikr Fw.2 Diesel
GeneratorlhISF II~EJC~ 1 I~YI Scheme
FaL*
because the MSF needs sdcknt time scheme is around 390 kwhMBtu heat
to the proass for an acid dosing
dednation plant. The diesel engine
cogeneration system provides the
highest elechicity to water ratio, or ksst
water production per kWh. In the
above figure, the waterEpomr ratio is
approximately 3.1 gallonskwh or 13.3 MW per mgd water production. In this scheme, approximately
38% of the heat othenvise wasted is
recovered in the form of steam
supplied to the desalination plant.
AssumingalOOMWl8mgd
combined cycle, with a dcsahtion
capacity factor of 90% and availability
of 92%. the net annual saving of fuel
consumption of this (otherwise wasted)
plant performance ratio of 10, plant
Table 1 Thermal Efficiency and Performance Values for Gas Turbinewaste Heat
Boiler/MSF Scheme
Water/power ratio (gal/kWh)*
System thermal efficiency 69%
Cogeneration index (kWhllOLBtu) 196
4.3 to 9.2
Heat recovered (waste heat) 57%
Cogeneration R'orld NovemberIDecember 1984
to respond to change in its autput.
(3) The gas aubine/MSF scheme has
the bwest instalkd costs and the highest rate of return. Only when gas
or distilkd fuel is unavailabk can other
schemes be justi6ed on an economic besis.
(4) The diesel engine./MSF &me has
hitationonunitsizeandsmaller
amount ofncoverable heat has
cogeneration 6eld.
(5) In light of rapidly rising fuel costs,
the optimum performance ratio is
expected to inuease for any cogenem-
tion scheme. The design of muhistage
flesh evaporators should be mimed m
view of the requirements of more
stages, more heat der ana and
higher pumping costs. New de
protection additives which are eflective
at higher maximum brine temperatures
are needed to enhanct the economical
the highest power to water ratio. Its
restricted a applications in the
aspecrsofthisprocess..
27
.,. tends to reserve the simpk gas 1 0 filectric rower ana €3 e salinate d 1 1. 1
Seawater -
by Sam Tadms, RE.
A new significance has been
acquired by cogeneration plants
in the production of electric
power and desalinated
seawater. Included is the
conclusion of a two part series
on the design and economy of
cogeneration plants on
desalinated seawater.
Gar Tarbine/MSF Scheme
Flexibility and Design Features
In today’s gas turbine application, the
exhaust heat of gas turbine combus-
tion of the type frequently used for
utilities possesses features that can be
used effectively in cogeneration (dud
purpose installation) for the produc-
tion of power and desalinated water,
by adding a heat recovery boiler for
generating the steam required for
desalting plant operation. Conventional boilers arranged
for the latter are essentially to accept
the exhaust gases. However, the net
heat rate improved with an increase in
the amount of refiring. The discussion
and figures presented in this paper will be limited to u&ed heat
recovery boilers.
heat recovery would vary with gas tur-
bine ekctrical output, additional
source of steam is needed to enable
the desalination plant output to be maintained at times of low electrical
load or when the gas turbine is shut
down in case this system was design-
ed to operate at its maximum water to
power ratio.
The gas turbine desalination
plant scheme has a water to power
ratio of around 6.2 galkwh or ap
proximarely 1.50 mgd per 10 MW at R- 10. As .R varies between 7 and
15, the power to water ratio varies between 4.3 and 9.2 gaVkWh. This
ratio is influenced by the exhaust gas
from the heat recovery boiler. This, in
Since the steam available from
turn, h controlled by the sulphur con-
tent of the fuel, as coohg below the
dew point must not take place to
avoid corrosion. Currently, the ma-
hum size available for a gas turbine
is 130 MW.
Although the reliabiity of the
gas turbine is mot as high as that of
steam turbines, one main advantage is
the capability for quick start and
quick delivery of power and process
heat.
components of a combined gas
turbineldesalination plant. This
arrangement enables the gas turbine
to operate while the desalination plant
is shut down. The supplemental fuel
to the waste heat boiler, if added, will
enable the gas turbine and the
desalination plant to operate separate- ly while one is shut down and also to
operate at various water to power
ratios.
However, at low values of the
water to power ratio, supplemental fir-
ing for the heat recovery boiler may
not be required for the full-load pro-
duction of water, provided the water
plant heat demand is within the limit
of the cogeneration index.
Scheme Economy
plants operate at thermal efficiencies
well below 30%. The heat rate is
12,000 to 14,000 BtulkWh. A short
time is needed for it to reach full load
conditions. This combination of factors
Figure 1 demonstrates the main
Current gas turbine power
turbine cycle for gas pe&g and
standby use. Future development of
the gas turbine will reduce the heat
rate, probably to 10,OOO BtulkWh or even lower. Also, research is under
way to enable the gas turbine to use
other types of fuels.
In a dual purpose cogeneration
system, advantage is taken of the hot
exhaust gas to provide stcam for the
desalination plant. In Fv 1 for
each 3.6 he1 units’ heat input in the
gas turbine combustion system, 1.5
units are saved from the exhaust gas
stream and are absorbed by the brine
recycle stream in the brine heater.
Approximately 57% of the heat other-
wise wasted through the exhaust
system is recovered in the form of
steam supplied to the brine heater.
The recoverable heat rate of the
scheme shown in Figure 4 k approx-
imately 4950 BtukWh.
efficiency is now approximately 69%
or a system heat rate of 5000
BtukWh when operating at design full
load conditions, for an acid dosing
desalination plant with SOo F
maximum brine temperature. The cogeneration index for this
scheme under the above conditions
would be 1% kWhllWBtu as shown
in Table 1. In general, the ideal, most
economic situation for any cogenera-
tion system is to have steady
year-round demands for both electrici-
ty and water so that both demands
can be met from a correctly sized dual purpose system operating at the
highest @le system thermal
efficiency. In terms of primq energy
resources, each don kwh produced
by this scheme, as compared to
separate gas turbine and desalination
plant producing the same amount of
The combined overall system
Gndnuedon~27
Cogeneration World NovemberlDecember 1984 25