Component 9: Feedwater Tank

In This Topic

Component 9: Feed Water Container / Deaerator

Specifications

Line connections
1	Main condensate inlet
2	Feed water outlet
3	Heating steam inlet
4	Auxiliary condensate inlet (without throttle)
5	Vapour mass flow loss (vent)
6	Averaged liquid volume fraction (liquid level) during time step

General User Input Values Physics Used Displays Example

General

This component can be used to model a deaerator. A more detailed option for a deaerator is also available in component 63.

If you have assigned vapour losses (vent), then these must be taken as water losses that need to be reintroduced into the system as makeup water in the right quantity and at the right place (otherwise no steady state is present). This can be handled very easily with a signal translator that registers the mass of vapour and translates it into the additional water connection.

With the new set value DP32F a fixed (i.e. load-independent) fraction of the pressure loss can be defined. This serves to take the filling level into consideration: As the steam is introduced below the water surface, there is a pressure difference between the pressure of the steam in the container and the pressure of the incoming steam, which does not depend on the mass flow but only on the filling level.

The pressure drop can also be adjusted via a kernel expression.

Transient modeling

Component 9 also allows to model the feed water tank with deaerator in the transient case. The flag FINST can be used for this purpose. A thermodynamic equilibrium between the liquid and the gaseous phase is assumed.

The transient calculation requires the specification of the geometric details of the component.　The fluid volume, wall storage mass, and exchange surface area between wall and fluid are calculated from the geometric details. The properties of the wall material like density, thermal conductivity, and heat capacity can either be specified from the stored library (flag FMAT) or by the user.

The heat exchange between the fluid and the tank wall and the temperature development in the tank wall over time respectively are also considered. For this purpose, identical algorithms as in　Component 119　are used. There are 2 algorithms in component 9 for the computation of the wall temperature. Like in comp. 119 for FALGINST=1 the equation (2.3) is solved numerically using Crank-Nicolson-Algorithm . For FALGINST=4 the combined analytic and numeric method is used instead.

For the calculation of the inner heat transfer coefficient (ALPHI), the user can choose between the formulae for free convection available in the VDI Heat Atlas and own specifications, also e.g. in the form of a user function (EALPHI).

The transient mass balance considers a change of the filling level of the tank during the time step. For the mass balance, the user can decide between the specification of the filling level or of the mass flow M1 by means of the flag FSPIN. The calculated filling level is output as the volume fraction of the liquid phase in the total volume of the tank to Pin 6 as mass flow M6.

Notes:

Vapour losses:

The vapour losses can now optionally be specified via specification value M5 (as before) or set on the line externally. Switching over between the two modes of calculation is effected by means of the flag FM5.

External Specification of the Pressure of the Auxiliary Condensate:

Previously, the pressure of the auxiliary condensate was always set by the feed water tank as the auxiliary condensate is at the same pressure level as the feed water at the outlet. When modeling, it was therefore necessary to place a control valve or a condensate valve on the auxiliary condensate line in order to decrease the pressure to the condenser level.

Mode: P4 given externally:

To simplify the modeling, there is now a mode “P4 given externally“ that can be set by means of the flag FP4. This mode allows to connect a line with a higher pressure on Pin 4. Within the feed water tank, the auxiliary condensate is then reduced to the condenser pressure. The result is the same as with an external control valve.

The new mode is now the default setting for newly inserted components. For existing models, FP4 is set to “P4=P2“.

User Input Values

FINST	Transient mode: Like in Parent Profile (Sub Profile option only) Expression 0: Transient solution (time series or single calculation) 1: Always steady state solution
Steady state calculation
DP32N	Pressure drop of heating steam (by flow), (nominal)
DP32F	Heating steam pressure drop (by fill level)
FP4	Throttling of secondary condensate Like in Parent Profile (Sub Profile option only) Expression =0: No throttling (P4=P2) =1: Throttling at pin 4 (P4 given externally)
FM5	Method for specification of exhaust vapour M5 Like in Parent Profile (Sub Profile option only) Expression = 0: Use specification value M5 =-1: M5 given externally
M5	Vapour mass flow losses Mass flow of evaporation In case the value entered is greater than 5% of the water feed, the vapour mass flow is restricted to 5%. If FSPEC=1 (see below) is set, a higher value can also be set.
FEDP	Usage of EDP (off-design only) Like in Parent Profile (Sub Profile option only) Expression =0: Not used =1: Correction: DP32=DP32F+DP32N(M3/M3N)^2EDP =2: Replacement: DP32=DP32F+DP32N*EDP
EDP	Pressure loss function
FMODE	Flag for calculation mode =0: GLOBAL =1: local off-design = -1: local design
FSPEC	Handling of a possible available steam portion in the feed water Like in Parent Profile (Sub Profile option only) Expression = 0: Output of an error message (normal case), vapour loss remains as specified in M5 = 1: Steam portion is separated as vapour steam via line 5. For this specification, at least the vapour stem specified in M5 is extracted, and also more, if required. =-11: Consider mass and energy balances only =11 : Consider mass and energy balances and H4=H' only
M3N	Mass flow heating steam (nominal)
Transient calculation
FINIT	Flag: Initializing state =0: Global, which is controlled via global variable "Transient mode" under Model Options "Extras" ->"Model Options" -> "Simulation" -> "Transient" -> Combo Box "Transient mode" (See -> Used Physics / equations -> Global Initialization of Transient Components ) =1: First run -> Initializing while calculating steady state values =2: Continuation run -> Values from previous time step are input for the present ones
FALGINST	Flag: Determination of transient calculation algorithms = 1: Crank-Nicolson-Algorithm = 4: Combined numerical and analytical solution
Physical dimensions
FGEOM	Geometry configuration details =0: Storage tank only =1: Storage tank with deaerator shell
DIAMT	Inner diameter storage tank
LENGT	Length storage tank
THWALLT	Wall thickness storage tank
DIAMD	Inner diameter deaerator shell
LENGD	Length deaerator shell
THWALLD	Wall thickness deaerator shell
THISO	Thickness of insulation
MRINPART	Ratio of internal parts to wall mass
Material properties
FMAT	Wall material =0: ST35_8 =1: ST45_8 =2: 15MO3 =3: 13CRMO44 =4: 10CRMO910 =5: X20CRMOV121 =6: X10NICRALTI3220 =7: 8_SiTi_4 =8: 10_CrSiMoV_7 =9: 11_NiMnCrMo_5_5 =10: 14_MoV_6_3 =11: 15_MnNi_6_3 =12: 15_NiCuMoNb_5 =13: 16_Mo_5 =14: 17_CrMoV_10 =15: 17_Mn_4 =16: 17_MnMoV_6_4 =17: 19_Mn_5 =18: 19_Mn_6 =19: 20_CrMoV_13_5 =20: 20_MnMoNi_4_5 =21: 25_CrMo_4 =22: 28_CrMoNiV_4_9 =23: 30_CrNiMo_8 =24: 34_CrMo_4 =25: 34_CrMo_4 =26: 36_Mn_4 =27: 36_Mn_6 =28: 40_Mn_4 =29: 42_CrMo_4 =30: 46_Mn_5 =31: H_I =32: H_II =33: M_2 =34: StE_285 =35: StE_315 =36: StE_355 =37: StE_380 =38: StE_415_7_TM =39: StE_420 =40: TStE_460 =41: 12_CrMo_19_5 =42: X_1_CrMo_26_1 =43: X_10_Cr_13 =44: X_10_CrAl_7 =45: X_10_CrAl_13 =46: X_10_CrAl_18 =47: X_10_CrAl_24 =48: X_10_CrAl_24 =49: X_12_CrMo_7 =50: X_12_CrMo_9_1 =51: X_20_Cr_13 =52: X_40_CrMoV_5_1 =53: X_2_CrNi_18_9 =54: X_2_CrNiMo_18_12 =55: X_2_CrNiMo_25_22_2 =56: X_5_CrNi_18_9 =57: X_5_NiCrMoCuTi_20_18 =58: X_6_CrNi_18_11 =59: X_8_CrNiMoNb_16_16 =60: X_8_CrNiMoVNb_16_13 =61: X_8_CrNiNb_1_6_13 =62: X_12_NiCrSi_36_16 =63: X_15_CrNiSi_20_12 =64: X_15_CrNiSi_25_20 =65: DMV 304 HCu (SUPER304H) =66: DMV 310 N =67: TiAl6V4 =68: X10CrMoVNb91 =-1 : Properties calculated by Kernel Expression ERHO, ELAM, ECP
ERHO	Function for material density
ELAM	Function for material heat conductivity
ECP	Function for material heat capacity
LAMISO	Thermal conductivity insulation
FTTI	Temperature used for material table lookups =0: Actual temperature at the end of time step =1: Average temperature for time step interval =2: Linear interpolation at each time step
Control parameters for transients
FTSTEPS	Flag: Specification of (sub-) time steps Like in Parent Profile (Sub Profile option only) Expression =1: By specification value TISPEP =2: 0.2 of the stable theoretical time increment =3: 0.5 of the stable theoretical time increment =4: 1.0 of the stable theoretical time increment =5: 2.0 of the stable theoretical time increment =6: 5.0 of the stable theoretical time increment
ISUBMAX	Maximum number of time sub steps for initialization
IERRMAX	Maximum allowed error for initializing step
TISTEP	Internal time (sub-)step
FFREQ	Frequency of transient calculations =1: At each iteration step =2: At each 2nd iteration step =3: At each 4th iteration step =4: At each 8th iteration step
NRAD	Number of points in wall normal direction (max. 30)
FSPIN	Transient balance calculation mode 0: Liquid level given, mass flows computed 1: M1 given, liquid level computed
WF	Averaged liquid volume fraction (liquid level) during the time step
WFMIN	Minimal liquid level
WFMAX	Maximal liquid level
Heat transfer coefficients
FALPHI	Determination of alpha inside 0: Internal formulas VDI Wärmeatlas Edition 11 F3 (free convection) 1: from constant value APLHI 2: from function EALPHI
ALPHI	Inner heat transfer coefficient (to fluid)
EALPHI	Function for alpha inside
FALPHO	Determination of alpha outside 0: from specification value ALPHO 1: from function EALPHO
ALPHO	Outer heat transfer coefficient (to ambient)
EALPHO	Function for alpha outside
Limits and ambient conditions
TMIN	Lower limit for storage temperature
TMAX	Upper limit for storage temperature
FSTAMB	Definition of ambient temperature 0: by specification value TAMB 1: defined by reference temperature (comp. 46)
TAMB	Ambient temperature
Initial conditions
FISTART	Specification of start temperature
TIMETOT0	Total time at start of calculation

The quantities marked in blue represent reference quantities for off-design.

Generally, all inputs that are visible are required. But, often default values are provided.

For more information on colour of the input fields and their descriptions see Edit Component\Specification values

For more information on design vs. off-design and nominal values see General\Accept Nominal values

Specification matrix MXTSTO and result matrix RXTSTO

The matrix MXTSTO is linked to the output field RXTSTO in the same way as the characteristic curves and result curves mentioned above.

The distribution of the values in the storage and the fluids is stored in both matrices (default matrix MXTSTO for time step t-1 and result matrix RXTSTO for time step t).

For the structure of the matrices, see matrices of component 9.

Physics Used

Equations

Steady state solution. All cases

For the 1^st iteration: M3 = M3N

F = (M3/M3N) ** 2

If GLOBAL = design, then F=1.0

DP32 = DP32N * F

P2 = P3 - DP32

T2 = f'(P2)

H2 = f (P2,T2)

M2 = M1 + M3 + M4 - M5

Q2 = M2 * H2

P5 = P2

P1 = P2

P2 = P4

T5 = T2

H5 = f"(T5)

Q5 = M5 * H5

M3 = ((M2*H2 - M1*H1 - M4*H4 + M5*H5))/H3

Component Displays

Display Option 1

Display Options 2

Example

Click here >> Component 9 Demo << to load an example.

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