a hybrid power generation and refrigeration cycle with ammonia-water mixture

7/27/2019 A Hybrid Power Generation and Refrigeration Cycle With Ammonia-water Mixture

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NOMENCLATURES Y M B O L :

G mass flow rate [kg/s]h specific enthalpy [kJ/kg K]P pressure [MPa] abs.Q heating rate [kW]T tempera ture [C]W output power [kW]z amm onia mass fraction [kg/kg]

Subscript:E: EvaporatorD: DesorberR: Reflux or RectificationS: Heat source

SYS: System

SYSTEM CHARACTERISTICSThe hybrid power generating and refrigerating system is

composed of two cycles, that is, an AWM turbine cycle and anammonia absorption refrigeration cycle. These two cycles areheated by common low-temperature waste heat source such aslow pressure process steam, exhaust gas, hot water and soon(see fig. 1). These two cycles can be driven independently.However, the hybrid system is able to produce more pow er withsharing the working fluid, AWM.

Turbine Cycle ] ][ H ea t S ou rc e ~ [ ~ _ _ _ _ _ ~ - ' - A W M [

~ . . _ l R e f r i g e r a t i n C yc le r ~

[ HybridSystem ]

Fig. 1 H ybrid system

Am m onia Absorp t ion Refr igerator: AARThe ammonia absorption refrigeration cycle is single-stage

absorption type as shown in fig.2. The evaporator saturationtemperature at the outlet is assum ed to be TE [C] with saturatedvapor leaving. The mass flow rate of solution through solutionpump is Gs [kg/s]. The m ass flow rate of the bleed saturatedvapor and saturated liquid from bleed heat exchanger are Gb"[kg/s] and Gb' [kg/s]. The rectifying column produces a vaporwith a mass fraction of 0.998. The mass flow rate of leansolution at the outlet(point 1) of the desor ber is Ga [kg/s]. T hemass flow rate feed to rectifying colunm is Gr [kg/s] and refluxlow rate from condenser to rectifying column is GR [kg/s].G r;[kg/s] is the mass flo w rate of rectified liquid.

The COP(Coefficient of Performance) is defined by theequation (1).

C O P = Q E Z (1 )D

Rectifying .column i (

Gr

Solution heatexchanger (

7

GK+G R

Fig.2

9

"x. 1.'.

Flo w sheet of single-effect am m oniaabso rption refrigeration cycle.

Table 1 The specifications of AAR.Item

Evaporating temperatureCooling capacity

Heat sourceCooling watea" emperatureAmmonia mass fraction of

rectifie d v aporEfficiency o f rectification

Specifications-10 C

100 USRTSteam sat.(0.59 MPa.gagC,

Inlet: 32 C0.998 kg/kg

0.8

The energy balance equations at the desorber and rectifyingcolumn are as follows:

Q D = ( G K + G R)h9+ G ~ l h - G R h l 3 - a r h 8= GR(h9 - h i 3 ) + GKh9 +G a h l - G , . h s=QR + Gx(hg - h , )+ Gr(h, - h s ) (2 )

Where, QR is the heat of rectification.The equations (1) and (2) show that the reduction of heat of

rectification means high COP because o f the reduction ofQD.Itfollows that the mass flow rate of the heat source tends to besmall. As a result, the more heat source could be provided to theturbine cycle.

There are several means to decreaseQo:(1) D ecrease hg.

(2) Decrease QR.(3) D ecrease G r.

2 Copyright (C) 2000 by ASME


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(4) Decrease the specific enthalpy difference(h rhs ) . Thismeans the decrease of heat-exchange loss at solution

heat exchanger.Figure 3 shows that the specific enthalpy of vapor at the

state point of 9 versus saturated vapor pressure. Thespecifications of the AA R is listed on the table 1. The fig. 3shows that there is a maximum point at P=l.23[MPa], so youshould avoid the pressure point. However the correspondingpressure is determined by the condensing pressure, and thecondensing pressure is derived from evaporating pressure atevaporator. Therefore, the specific pressureh9 is fixed by theevaporating pressure. The mechanism is illustrated by theD iihling plot in fig. 4.

The heat o f rectif ication is deeply depend on the amm oniamass fraction of the solution: zs. Figure 5 show s the theoreticalheat o f rectif ication Q ~,~ versus am monia m ass fraction zs.From the energy and mass balance equations at the desorber andrectifying column, the following equation (3) is derived.

G , = z 9 - z , G K ( 3 )

Z 8 -- Z 1

The equation also shows that the high-ammonia massfraction at the state 8 contributes the decrease of the Gr. Theenthalpy difference between the state of point 1 and 8 (hrhs)tends to be small when thedi ffe renceof the ammonia massfractions i.e., z8 - zn decrease. Figure 5 is the enthalpy-massfraction diagram. Th is diagram shows that the increasing of themass fraction of the state point 8 d ecrease the theoretical heat ofrectification.

The challenge is now to make the am monia rich solution atthe state point of 8 to feed rectifying column. One of the answeris to supply amm onia rich solution to the point from other cycle,i.e., the AWM turbine cycle.

==

"Eo

o')

1550

1540

1530

1520

1510

15001490

0 1 2 3 4Pressure P MPa

Fig.3 Specific enthalpy versus saturationv a p o r pressure

10, - . . . . . . . . . . - ' ----- ' -----!---- ~ . . . . . . . . !---- ' . ---A--b-. ' . . . . . . . . ,ZL 1. ' / . '. J , . ~, , t%~.. /(~, I

7 r ........by the formulation o f ~ ind Klein-~l

:

3 i . .. .. .. .. .. i - - . - - i - - - - ! - - - - i - - , e m p e r a t u r ~ / , 7 / ~

2 FI--- C o~d e 'n s i ' ngi ~,~? Z7 ~" ~

,, o ii6 :iteTperature~S~J-.i:/,-::~:/F;-Y-'K:[~::~i:i:~/~i~:::~:~"14 , ~ ...,...:..~s : ' , . ; g

1 . ~ . o . . 5 . _ 0 . . , 4 . ' 0 . . , . 3 ] _ . 0 _ : ~ o . 1o::

o , , / / : , / i A) i ' r i l lZ , g , k g i ,, , i li i- 2 0 -1 0 0 1 0 2 0 3 0 5 0 7 0 1 0 0 1 5 0 2 0 0

T C

F i g . 4 D ~ h l i i n g p l o t o f c y c l e s o l u t i o n i n A A R ,

3 . 0 X 1 0 3

2,5

2 .0

1 . 5"E

Z(D

1.0

0.5

0.00.0 0. 2 0.4 0.6 0.8

Ammonia mass raction z kg/kg

F i g . 5 E n t h a l p y -m a s s f ra c t io n d i a g r a m .

1.0



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S t e a m

AW M Tu r b i n e S y s t e mAWM Turbine

A m m o n i a A b s o r p t i o n R e f r i g e r a t o r

Reflux

Pre-heater- l l Sub-cooler

Condenser [$;5 ; ~, I Condensel

v. . ;/ C o o f i . g ~ C o o l i n gHigh-pressure ll~trer Low-pressure g:~tte~'

Pump Pump

Fig. 10 F low sheet of the h ybrid co nfiguration of the AWMTS and AAR.

H vbr id Conf iaura tionFigure l0 shows the hybrid configuration of the two cycles:

AW MTS and AAR. To maintain the mass balance, dashed threelines are conne cted to each other to sharing the working fluid.In this configuration, simulation model was constructed. Thethermodynam ic propert ies of the AWM are calculated with the

PROPATH ver 11.1 which is based on the literature(Ibrahimand Klein, 1993).The assumptions for the calculation are following:

[common]Cooling water:Heat source:

inlet:32 [C] / outlet:37 [C]dry sat. steam/0 .69[MPa.abs] /2200[kg/h]

[AAR]D esorb er outlet: 130[C]Absorb er outlet : 42[C]E vapo rating temperature : - 10[C]Mass fraction of bleed: 0.960[kg/kg]E fficiency of rectif ication: 0.8

Cooling capacity: 100 U SRT

[AWMTS]Turbine/pump efficiency: 1.OPintch point temperature

differen ce at heat exchang ers: IO[C]

The characterist ics of the hyb rid configuration and separateconfiguration. The separate configuration of the two cycles doesnot share AWM and share the same heat source to keep coolingcapacity is 100 U SRT. First, applicable range of the ammoniamass fraction at the outlet of the evaporator in AWMTS(zIN) isinvestigated. The result is from 0.4 to 0.6 [kg/kg]. Next, thesystem output power versus AWM temperature at the inlet ofthe separator-2 in AWMTS(Tsp.2) is investigated. The results

are shown in the f ig. 11. The figure shows that the system outputpow er is max imum at z ~ -- 0A5 [kg/k g] an d TsP.2=53~62[C]. I tis about 13.3% higher than that o f the separate configuration.Figurel2 shows the relat ionship between the output power andturbine inlet pressure Pn~ in the case o f ziN = 0 .45[kg/kg].When the P~ is about 2.8[MPa.abs], the system output power is

12 0

~ 110

o~ 100

~ 90

O380

40

L - t =.. separate

- Ammoni a mass fraction ZIN = 0.4 5 [kg/kg]

. . . . . . . . I . .. . I . .. . I . .. . I . .. .4 5 5 0 5 5 6 0 6 5 7 0

Temp erature Tsp.2 C

o ~Q .

E

cO

Fig. 12 System ou tpu t ve rsus t emp eratu re a tthe inlet of th e separator-2 (Z,N = 0. 45 [k g/kg])

12 0

115

110 ----

105

100

9 5

9 00 .5

L: - - s e p a r a t e - -

"1 i i i l i i i

1.0

/ \ : . - ' 7 " " . . . . . "~ '"" / " "

" = ' ' " IAmmonia mass fraction ZIN---0.45 ' [kg/kg]~. . . . t . . . . i . . . . i . . . . i . . . . -7

1.5 2.0 2.5 3.0 3.5 4.0Pressure P=N MPa

Fig. 12 System o utp ut versus turb ine inletp ressure ( ZIN = 0 .4 5[k g/kg] )



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maximum value. In the case, the heat of rectification isdecreas ed that is shown in fig.13. T he CO P o f the AA R isrepresented in fig.14. In tho se case, other parameters such asturbine inlet pressure and so on are selected to producemaximum output power to the parameter of the bottom axis ofthe figures 11 to 14.

12 0

11 0

10 0O

-t"

9 0

8 O

7 0

6 O1. 0

' ' ' ' 1 ' ' ' ' 1 ' ' ' ' I ' ' ' ' 1 ' ' ' ' 1 ' ' ' '

Ammon ia mass frac t ion ZlN = 0 .45 [kg/kg]_t I ~ t i

. . . . . . . . . ~ . . . . . . . . ~ . . . . . . . . ~ . . . . . . . . . I . . . . . . . . ~ -separate i ~ i

, , , , I , , , , , , , , I , , , , I , , , , I , , , ,1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 , 0

Pressure PIN MPa

Fig. 13 H eat of rec t i f ica t io n versustu rb ine inl e t p re s su re ( z~x = 0 .4 5 [k g /kg] ) .

0 . 6 2

0 . 6 0

0 . 5 8

0 0 . 5 6

0 . 5 4

0 . 5 2

0 . 5 00 .5

. . . . . . . . i . . . . ! . . . . ! . . . . ! . . . . i . . . .

, ' Ammonia mass f r ac t ion Z tN = 0 .45 [kg /kg ]

. . . . . . . . i . . . . . . . . . . . . . . ~ - . . . . . . . . . . . . . [ . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . [ - . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . .

m m ir

. . . . . . . . . . . . i ............. ...... . . . . . . . . . . . . . . .

r ................. r ................. [ ..........1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 0

Pressure PiN MPa

Fig . 14 COP o f th e AAR ve r sus tu rb ineinle t p re s su re ( z~ . = 0 .4 5 [k g /kg] ) .

C O N C L U S I O NThe simulation results show that the hybrid configuration

produces 13.3 % higher ou tput power and COP than those o fthe separate configuration because o f the decrease o f heat ofrectification in AAR w ith sharing the working fluid. In thehybrid configuration, only the operating condition o f thesolution cycles in AAR and AWMTS are altered from theseparate configuration.

R E F E R E N C E S

1) Amano, Y., Tanzawa, Y., and et. al., "M OD E LIN G A N DEXPERIMENTAL INVESTIGATION OF DYNAMICSO F A D I R E C T LY C O M B I N E D B I N A RY T U R B I N ESYSTE M U SING A MIXTU RE (R134a/R123)" Proc.Renewable and A dvanced Energy Systems for the 21 stCe ntu ry/ AS M E RAES99-7647 No.25 (1999) pp. 1-6 .Amano,Y., et. al., "Effectiveness of an ammonia-watermixture turbine system to hot water heat source" Proc.1999 IJPGC-ICOPE ASME/JSME PWR-Vol.34 vol.2(1999), pp.67-73.Enick, R obert M., et. al., "The Modeling of LE B S-Kalina Power Cycles," Proc. 1997 IJPGC PWR-

Vol.32(2), ASME (1997), pp.55-67.Ibrahim, O.M., and Klein, S.A., "ThermodynamicProperties of Ammonia-Water Mixtures," A SH RA ETrans. 99, (1993), pp.1495-1502.Kalina, A. and Tribus, M., "Advances in Kalina CycleTechnology (1980-1991): Part II IterativeImprovements," Proc. O f the Florence World EnergyRes. Symp., Firenze, Italy, (1992), pp. 111-125.Mathias, P.M., "A Versatile Phase Equilibrium Equationof State," Ind. Chem. P rocess D es. Dev., Vol.22, (1983),pp.385-391.Oman, H and Shaw, R., "Routes to 50 Percent Efficiencyin Heat Engines," ACS publication 869097 (1986),pp.326-330.Tanzawa, Y., et al., "Modeling and ExperimentalInvestigation of D ynamics of A D irectly CombinedB inary Turbine System Using Steam and R123," Proc.IMECE'98 AES-vol.38, (1998), p35-40.Tillner-Roth, Reiner and Friend, Daniel G., "AHehnhotz Free E nergy Formulation of theThermodynamic Propertie s of the Mixture {Water +Ammonia}," J. Phys. Chem. Ref. Data 27, 63 (1998),pp63 -97.

10) Stambler, I., "Kalina Cycle Provides 25% More Powerand 3 % Better Net Efficiency," Gas Turbine World(July-August 1995), pp.38-41.

11) Schwartzentruber, J. and Reno n, H., "E xtension ofU NI FAC to Higher Pressures and Temperatures by U seof a Cubic Equ ation of State," Ind. Eng. Chem. R es.,Vol.28 (1989), pp.1049-1055.

12) Z iegler, B , and Trepp, C., " Euation o f State forAmmonia-Water Mixtures," int.J.Refrig. 7(2), (1984),pp.101-106.

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a hybrid power generation and refrigeration cycle with ammonia-water mixture

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