EBSILON®Professional Online Documentation
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Line connections |
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1 |
Feed water inlet |
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2 |
Saturated steam outlet |
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3 |
Extraction of circulating condensate |
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4 |
Heating steam inlet |
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5 |
Extraction of the condensate mass flow (drain) |
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6 |
Averaged liquid volume fraction (liquid level) during time step |
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General User Input Values Physics Used Displays Example
The component steam drum needs an estimated value for the steam flow produced. This value must be specified as initial value with a component 33 (general input value/ start value) at the feed water inlet.
The desired pressure for the drum has to be set at the connection of the circulating condensate with a component 33 (general input value/start value component). The same applies for the circulating water mass flow that is introduced into the evaporator. The selected circulating water mass flow has to be about four to five times larger than the expected steam production. Make sure that the steam content (X-value) of the steam produced in the evaporator is around 0.2-0.25. If necessary, adapt the circulating water mass flow.
Connection 4 (heating steam) is normally the entry for the steam produced in the evaporator upstream.
It is possible to define a drain quantity at connection 5 with the help of component 33. However, note that this mass flow is extracted from the circulation as water loss. Thus, the same quantity must be added at another suitable point in the cycle.
The main input for this icon is the variable FSPEC, which either
- calculates wet steam flow M1 (=M2) and accepts incoming heating steam enthalpy H4
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- accepts heating steam wet steam production (M1, M2) and calculates steam enthalpy H4.
Specification of the Drain Mass Flow:
Previously, the drain mass flow M5 had to be specified externally on the line. Now there is a flag FM5 that allows to also have this mass flow set by the drum, optionally in absolute or relative terms.
There are the following variants:
If the inlet temperatures and the outlet temperature of the evaporator are fixed, the saturated steam flow defines the pinch point or the terminal temperature difference.
If the amount of saturated steam to be produced is given for example if the heating steam requirement of a connected deaerator is specified, then the energy balance of the drum defines the necessary heating steam enthalpy entering the drum and the thus heating steam outlet temperature of the evaporator. The pinch point or the terminal temperature difference is calculated by the program under these circumstances.
The connection of the circulation condensate must not be connected with the connection for the sub-condensate, because otherwise no results can be achieved.
A warning was issued for the steam drum when a steam mass fraction of X>10-5 existed at the inlet. This warning threshold can be set via the specification value TOLX.
The approach temperature (i.e. the temperature difference by which the inflowing feed water is super cooled compared to the drum temperature) is shown as result value TAPP.
Brine:
The drum can now be operated with brine too. Here it must be pointed out that no salt is contained in the steam. As in steady state the same amount of salt has to be discharged as is supplied and only the drain is available for the discharge, the drain mass flow must be great enough for the salt to remain dissolved.
It is assumed that the salinity in the drum and also in the recirculation corresponds to that of the drain. In the evaporator, care has to be taken that the steam mass fraction remains small enough so that the salt can still be dissolved in the liquid phase.
Component 20 also allows to model the steam drum 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 drum wall and the temperature development in the drum wall over time respectively are also considered. For this purpose, identical algorithms as in Component 119 are used. There are 2 algorithms in component 20 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 drum 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 or M2 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 drum to Pin 6 as mass flow M6.
| 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 |
| FSPEC |
Specifications Like in Parent Profile (Sub Profile option only) Expression =0: Input: pinch point, calculate: mass flow (saturated steam) =1: Input: mass flow (saturated), calculate: pinch point =2: For design as FSPEC=1, for off-design as FSPEC=0 |
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FM5 |
Specification of M5 Like in Parent Profile (Sub Profile option only) Expression =0: Input: pinch point, calculate: mass flow (saturated steam) =1: Input: mass flow (saturated), calculate: pinch point = 2: M2 calculated in the design as in FSPEC = 1, H4 in the off-design as in FSPEC = 0 |
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M5S |
M5-Specification value |
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FSTART |
Source of start value Like in Parent Profile (Sub Profile option only) Expression =0: Internal start value through START =1: External start value by component 33 |
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START |
Start value of the mass flow M2 |
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TOLX |
Warning level for steam at condensate inlet (default value 2,5%) |
| FINIT |
Flag: Initializing state =0: Global, which is controlled via global variable "Transient mode" under Model Options =1: First run -> Initializing while calculating steady state values |
| FALGINST | Flag: Determination of transient calculation algorithms = 1: 2D grid with Crank-Nicolson algorithm = 4: Combined numerical and analytical solution |
| DIAM | drum inner diameter |
| LENG | drum length |
| THWALL | wall thickness |
| THISO | thickness of insulation |
| MRINPART | Ratio of internal parts to wall mass |
| 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 |
| FTSTEPS |
Flag: Specification of (sub-) time steps Like in Parent Profile (Sub Profile option only) =1: By specification value TISPEP |
| 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 |
| 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 2: M2 given, liquid level computed |
| WF | Averaged liquid volume fraction (liquid level) during the time step |
| WFMIN | Minimal liquid level |
| WFMAX | Maximal liquid level |
| 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 |
| TMIN | Lower limit for storage temperature |
| TMAX | Upper limit for storage temperature |
| FSTAMB | Definition of ambient temperature |
| TAMB | Ambient temperature |
| FISTART | Specification of start temperature |
| TIMETOT0 | Total time at start of calculation |
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 20.
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Steady state solution. All cases |
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X1 = f(P1, H1) T1 = f(P1, H1) Sub-condensateP5 = P1 T5 = f'(P5) H5 = f'(P5) Q5 = M5 * H5 Circulating condensateP3 = P1 P4 = P1 T3 = f'(P3) H3 = f'(P3) M3 = M4 Q3 = M3 * H3 Primary outlet (saturated steam) P2 = P1 T2 = f'(P2) H2 = f"(P2) { M2 = M1 - M5 M1 = (M2*H2-M4*H4+M3*H3+M5*H5)/H1 } M1 = (M3*H3–M4*H4-M5*(H2-H5) ) / (H1-H2) M2 = M1 - M5 Q2 = M2 * H2 X2 = 1.0 Expected heating steam mass flowQK = Q2 + Q3 + Q5 - Q1 QK must be positive, else the economizer has to be reduced D = |Q4 - QK| / Q4 |Q4 - Q5| V = --------------- (Q4-QK) if D > 0.001 and V > 0, then the heating is too low: the evaporator must be increased if D > 0.001 and V < 0, then the heating is too high: the evaporator must be reduced |
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Display Option 1 |
Click here >> Component 20 Demo << to load an example.