Component 70: Evaporator with Steam Drum

In This Topic

Component 70: Evaporator with steam drum

Specifications

Line connections
1	Condensate inlet
2	Saturated steam outlet
3	Flue gas inlet
4	Flue gas outlet
5	Drain / Blow Down

Drain / Blow Down

6	Logic input for pump output (optional connection)

Auxiliary lines for calculation:

H6	Water outlet pipe out of drum (saturated to mildly sub cooled)
H7	Water outlet pipe out of pump ( Forced circulation)
H8	Inlet into drum (two-phase mixture)

General User Input Values Characteristic Lines Physics Used Displays Example

General

Saturated M2 is determined via M2=(Q87-M5*(H5-H1) ) / (H2-H1-CN*DH) (for derivation see section on Physics used), which results from the setting of the pinch point respectively k*A. This is an important statement because some modeling errors result from an over-determination of mass flow, when the user tries to enforce M2 via component 1 or 33.

Or in other words, the setting of the pinch point respectively k*A gives the saturated steam mass flow M2.

However, for M2 a user-entry of a starting value M2N is necessary in the design case. This should lie in the range of the expected steam production. This starting value should not be 0. After the design calculation, the start value entered for M2N is replaced by the calculated nominal value.

In the case of this component, the design via an ”effectiveness” factor is possible. It refers to the theoretically possible maximum heat exchange (for an infinitely large heat exchanger surface area). Thus an effectiveness of 0.8 means that 80 percent of the theoretically possible heat is exchanged.

Pressure drop limitations in off-design (Extras --> Model Options--> Calculation -->Relative pressure-drop maximum) :
As the pressure drop rises quadratically with the mass flow, pressure drops that are significantly too high can quickly arise in the event of a transgression of the nominal mass flow. These will then cause phase transitions and convergence problems. For this reason, pressure drop limitations have been installed.

Pin for Pump Power:

There is now an optional Pin 6 where the pump power is output. Depending on the desired level of detail of the modeling, a mechanical shaft, an electric line or a logic line can be connected.

When connecting a shaft, the isentropic efficiency of the circulating pump can be entered in specification value ETAIN and the motor can be modelled separately. Otherwise, the efficiency of the motor should also be considered in ETAIN.

The component only writes the power on Pin 6. When connecting a shaft and electric line respectively, default values are then used for frequency, voltage, current type, and phase (unless the setting of default values on shafts and electric lines has been disabled by the respective model option). If required, however, the desired values can be set by means of a start value (Component 33).

View:

Also for this component there has been a modification in design:

In the case of shape 1, optional connection 6 is not required.

In the case of shape 2, the flue gas inlet and outlet have been swapped to be able to model waste heat boilers top-down without the steam drum having to be upside down.
In the case of shapes 3 and 4, the pump is omitted in the design.
In the case of shape 5, the steam drum is situated above the flue gas path.

Flag FTAPPN allows the user to specify whether the feed water temperature is specified outside the component or whether the approach temperature is entered.

A kernel expression can be used as an alternative to the adaptation polynomial. The control is effected via the Flag FADAPT.

Specification of the surface area for designing heat exchangers

Usually, heat exchangers are designed in Ebsilon by specifying the terminal temperature differences or temperatures to be achieved. In an iterative process, the transferred amount of heat and the product of heat transfer coefficient and surface area (k*A) characteristic for the heat exchanger are calculated from this. Its nominal value KAN then serves to calculate the temperatures in off-design calculations. It is not necessary to know the individual values k and A here.

In the case of the components ECO/Evaporator/Superheater (exponents, Component 61), Duplex heat exchanger (Component 62), and Evaporator with steam drum (Component 70), however, the off-design behaviour is defined by exponents of heat transfer coefficients AL12 and AL34. As k can be calculated from it, the heat exchanger surface area A is available as well.

This has been used to implement a design calculation via the specification of the surface area. It is, however, essential to correctly specify the nominal values for the heat transfer coefficients AL12N and AL34N, which had only an effect on the partial load behaviour before to implementation of AN (area).

For the Evaporator with steam drum (Component 70), AL12N (used only for area calculation) has been newly implemented as a specification value, as it was not required before (because Al12N>>AL34N for the evaporator).

The specified surface area AN is only used for the design calculation to determine KAN from it. In the off-design calculation KAN is then used for the calculation.

Pinch point violations in the case of heat exchangers see Heat Exchanger General Notes:

Up to release 10.0, a pinchpoint violation was only determined subsequently in partial load, i.e. KA was calculated for the respective load case and from this the transferred heat quantity and then it was checked whether this heat quantity can be transferred at all at the correct temperature level. Since in the case of evaporation or condensation the temperature remains constant despite heat input or heat removal, there are cases where heat transfer is not physically possible despite the overall balance being correct. In this case, an error message was issued in Ebsilon.

The calculation has now been changed in such a way that the transferred heat quantity is reduced as far as it is still physically possible, with the minimum pinch point
can be set in a default value PINPMIN. This results in a correspondingly reduced KA.
The user is informed of this by a warning message ("KA reduced to avoid pinchpoint violation") and can then adjust the part-load characteristic curve or the part-load exponent for KA accordingly so that the warning no longer occurs. The advantage, however, is that one gets a physically possible result in any case.

Furthermore, at the end of the calculation there is a check if there is a pinch point violation due to curved course of Q(T) (caused by significant changes of cp depending on the temperature). This can be verified by dividing the heat exchanger into individual sections.
This case can occur, for example, when on the hot side the cp at the inlet is significantly smaller than at the outlet (for example, steam that has a cp of about 2 kJ/kgK at high superheat, but more than 5 just above the boiling line). This means that this steam provides more heat at a lower temperature level than at a high one. At appropriately low degrees, this can be a limitation on the amount of heat transfer that is possible.
The QT diagrams take into account the non-linearity (curvature of the curves) in areas without phase change.

The flag FSPEC (deprecated) has been divided into two flags:

FSPECD indicates in which way the component is to be designed
FIDENT serves to activate a component identification mode, i.e. the respective condition of the component is determined on the basis of temperature specifications

Note:

When loading a model that was created with Release 11 (or older), the corresponding values for FSPECD, and FIDENT are determined from the value of the flag FSPEC, and
FSPEC is set to “void” (-999). The model then calculates the same result values. If required, however, the flag FSPEC can still be used as well.

To remove ambiguity, the terms “primary side” and “secondary side” respectively have been replaced by “cold side” and “warm side” in the input screens. The cold side (previously “primary”) is the flow from Pin 1 to Pin 2 that is heated. The warm side (previously “secondary”) is the flow from Pin 3 to Pin 4 that gives off the heat.

Effectiveness Method

The effectiveness method for the design is available for the Evaporator with Steam Drum (Component 70) . In analogy to other heat exchangers, this option is selected via the flag FSPECD=0.
In the case of Components 25, 26, 27, 51, 55, 61, 70, 124, and 126 a calculation of the effectiveness in the context of the heat exchanger calculation is effected for other design methods as well (however, not in identification mode).
REFF is the ratio of the actual heat transferred to the theoretical maximum in case of infinite size of the heat exchanger surface.

A result value REFF has been implemented for this. In the design case, the calculated effectiveness is also stored in specification value EFF when the reference values are taken over.

Note on Component 70 :

Compared to other heat exchangers, this component yields different results for the effectiveness, even if all line values at inlets and outlets are identical. The reason for this is a different calculation of the maximum possible exchanged heat at an infinitely large heat exchanger. For Component 70 this heat quantity is determined under the boundary condition of constant enthalpies on the water side, i.e. the generated steam quantity is varied. For the other components this heat quantity is implemented under the boundary condition of constant mass flows, i.e. the outlet enthalpy of the cold flow is varied. Therefore for Component 70 the maximum possible heat transfer is different from that of the other heat exchangers, and thus also the effectiveness.
In case of supercritical pressure p1, the steam mass flow is set to 0 and in addition an error message (p1> critical pressure, no evaporation possible) is output.

Design in the Case of Concurrent Flow see Heat Exchanger General Notes:

The heat exchanger (Components 70) it is possible to carry out a design via the upper and lower terminal temperature difference also in the case of concurrent flow.

Flag FDQLR

In Release 13, you can use the FDQLR flag to define how DQLR (factor for modeling heat losses) should be interpreted.

Note on mixtures as working fluid:

In addition to the boiling temperature TSAT, this component also displays the dew point temperature TTAU as result value. In the case of mixtures as working fluid, the two temperatures may be different.

Note about the result values:

Performance factor RPFHX

The quotient from the current value for the heat transfer capability k*A (result value KA) and the k*A expected in the respective load point due to the component physics and characteristic lines respectively (result value KACL) serves to assess the condition of a heat exchanger.

The quotient KA / KACL is displayed as result value RPFHX.

User Input Values

FSPECD	Calculation method in design-case Like in Parent Profile (Sub Profile option only) Expression =0: Effectiveness given as EFF =2: Specification of pinch point PINPN Specification of the upper terminal temperature difference Temperature difference between the two streams: Outlet side of heat-flow and outlet side of the heated stream =8: Specification of steam production M2 (externally), specification of the outlet enthalpy of the cold flow as enthalpy H“ (saturated steam) =9: specification of the heat exchanger surface
FIDENT	Component identification (only in off-design) Like in Parent Profile (Sub Profile option only) Expression =0: No identification mode, in off-design the steam generation and flue gas outlet temperature are calculated =2: M2 given externally in all load cases, KA calculated =4: Outlet temperature of hot stream (T4) given externally in off-design, KA calculated Note: An identification via the specification of T2 (steam outlet temperature) does not make sense in the case of this component as the outlet condition in this component is always saturated steam, and the outlet temperature is thus defined by the pressure.
FCIRC	Circulation method Like in Parent Profile (Sub Profile option only) Expression =0: Natural circulation =1: Forced circulation
EFF	Effectiveness
AN	Heat transfer area (nominal)
FTAPPN	Flag for specification of approach temperature in design Like in Parent Profile (Sub Profile option only) Expression =0: By specification value TAPPN =1: T1 given externally
TAPPN	Approach temperature difference (nominal) TAPPN = Tsat(P-drum) - T(Economizer-exit) for H(ECOexit) in the design case applies { if TAPPN > 0.01 then { H(Economizerexit) = H(Tsat(Pdrum) -TAPPN) } if TAPPN <=0.01 then { H(Economizerexit) = from Economizer-heat balance } } for H(Economizerexit) in the off-design case applies { H(Economizer-exit) = from Economizer-heat balance }
FDP12RN	Water side pressure drop method Like in Parent Profile (Sub Profile option only) Expression =1: absolute : calculated by DP12N=DP12RN =2: relative : calculated by DP12N=P1N*DP12RN
DP12RN	Pressure drop of internal circulation (nominal) [absolute or relative to P1] DP12N is the pressure loss, which must be compensated by a circulation pump For a natural circulation boiler, DP12N is set to 0.
FDP34RN	Gas side pressure drop method Like in Parent Profile (Sub Profile option only) Expression =1: absolute : calculated by DP34N=DP34RN =2: relative : calculated by DP34N=P3NDP34RN = -1: P4 given* from outside
DP34RN	Pressure drop line 34 (nominal) [absolute or relative to P3]
FDQLR	Heat loss handling Like in Parent Profile (Sub Profile option only) Expression =0: Constant (DQLRQN in all load cases) DQLR refers to the design value QN (which equals the heat quantity given off by the hot flow in the design case) in all load cases, i.e. it has a constant value in all load cases. If, however, this value exceeds 10 percent of the heat quantity given off by the hot flow, the heat loss will be limited to this value, and a warning will be output. =1: Relative to actual heat input (DQLRQ34) DQLR refers to the heat quantity given off by the hot flow. If the corresponding warning is ignored, losses of more than 10 percent can be modelled here too.
DQLR	Heat loss (relative to the heat transferred)
FDRAIN	Handling of blow down Like in Parent Profile (Sub Profile option only) Expression =0: Blow down flow rate given by specification value M5 =1: Blow down fraction given by specification value M5M2 =2: Blow down given externally =3: Blow down mass flow given by function EDRAIN
M5	Blow down mass flow (absolute)
M5M2	Blow down mass flow (relative to M2) (related to the saturated steam mass flow) M5=M5M2*M2
EDRAIN	Function for blow down mass flow
ETAIN	Isentropic efficiency of the circulation pump (no characteristic line used: ETAI=ETAIN)
CN	Circulation number of the drum CN= M6/M2 M6=Water mass flow from the drum to the evaporator inlet
FVOL	Cartload pressure drop Like in Parent Profile (Sub Profile option only) Expression =0: Only depending on mass flow DP/DPN = (M/MN)*2 =1: Depending on mass and volume flow DP/DPN = V/VN(M/MN)**2 =2: constant pressure drop (equal nominal value) DP = DPN
FMODE	Calculation mode Like in Parent Profile (Sub Profile option only) Expression =0: Global =1: local off-design (i.e. always off-design mode, even when a design calculation has been done globally) =2: special local off-design (Special case for compatibility with the earlier Ebsilon-versions, should not be used in new models, because the results of the real off-design calculations are not always consistent) = -1: local design
FFLOW	Direction of flow, see Heat Exchanger General Notes: Like in Parent Profile (Sub Profile option only) Expression =0: Counter Current flow =1: Concurrent flow =2: Cross flow
NROW	Number of rows (for cross flow)
NPASS	Number of passes (for cross flow)
FARR	Arrangement of passes (input for cross flow) Like in Parent Profile (Sub Profile option only) Expression =0: Counter Current flow =1: Concurrent flow
AL12N	Cold side heat transfer coefficient (used only for area calculation)
AL34N	Hot side heat transfer coefficient line 3 to 4 (nominal)
EX34	Mass flow exponent of AL34 AL34= AL34N(M3/M3NEX34) (1 - (TM34N-TM34)*5E-4/°K)
FADAPT	Flag for using the adaptation polynomial ADAPT/ adaptation function EADAPT Like in Parent Profile (Sub Profile option only) Expression =0: Not used and not evaluated =1: Correction for kA [KA = KAN K/KN* polynomial] =2: Calculation of kA [KA = KAN polynomial] =1000: Not used, but ADAPT evaluated as RADAPT (Reduction of the computing time) = -1: Correction for kA [KA = KAN K/KN * adaptation function] = -2: Calculation of kA [KA = KAN adaptation function] = -1000: Not used, but EADAPT evaluated as RADAPT (Reduction of the computing time)
EADAPT	Adaptation function for KA
FFU	On-/Off switch Like in Parent Profile (Sub Profile option only) Expression =0: Heat-exchanger off (no heat transfer, but pressure losses) =1: Heat-exchanger active
PINPMIN	Minimum value for the pinch point (KA is reduced automatically if the pinch point would fall below this value)
PINPN	Pinch point (nominal): T4-Tsat(P7) with P7=P1+DP12N Please note that only FFLOW = counter current flow is allowed only for the calculation mode FMODE=GLOBAL where PINPN is used
FSPEC (deprecated)	Specification combi switch (deprecated) Like in Parent Profile (Sub Profile option only) Expression = -999: unused (FSPECD and FIDENT used instead) old values: =0: Forced circulation, user specifies EFF in design =1: Natural circulation, user specifies EFF in design =10: Forced circulation, user specifies the pinch point-temperature PINPN in design =11: Natural circulation, user specifies the pinch point-temperature PINPN in design =20: Forced circulation, M2 is specified (e.g. by component 33) in design =21: Natural circulation, User specifies M2N, which determines M2, in off-design =30: Forced circulation, heat transfer area (nominal) AN given in design =31: Natural circulation, heat transfer area (nominal) AN given in design
KAN	Heat transfer coefficient * area (nominal) , Design Heat Transfer Capability
QN	Generated heat flow
M2N	saturated steam mass flow in the design case: starting value for the internal iteration for calculating M2 in off-design: saturated steam mass flow rate (nominal)
M3N	Hot side mass flow (nominal)
TM34N	Medium temperature of flue gas (nominal) TM34N=(T3N+T4N)/2
V1N	Specific volume at point 1 (nominal)
V3N	Specific volume at point 3 (nominal)
P1N	Pressure at point 1 (nominal)
P3N	Pressure at point 3 (nominal)

The identification value that is marked in blue is a reference quantity for off-design mode. The actual off-design values refer to these quantities in the equations used.

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

The saturated steam production is determined by an iteration procedure. M2N is taken as start value, which should have the same order of magnitude as M2 and M2N. Both quantities should not differ by a factor of more than 3-5.

Heat Transfer

TM34 = 0.5*(T3+T4)

FK2=(1-.0005*(TM34N-T34N))*(M3/M3N)**EX34

1 / KN = 1/ AL34N

1 / K = 1/(AL34N*FK2)

KA / KAN = K / KN

Physics Used

Equations

All cases

if FDP12RN=relative, then {DP12N=P1*DP12RN} else {DP12N=DP12RN}

if FDP34RN=relative, then {DP34N=P3*DP34RN} else {DP34N=DP34RN}

Design case (Simulation flag: GLOBAL = design case AND FMODE = design case)

Condition: FFLOW = counter current

PH8=PH6=P5=P2=P1

T2=T5=TH6=TH8=fsat(P1)

T1= T2-TAPPN

H1=f(P1,T1)

H2=fsat(P2,T2,X=1)

H5=fsat(P5,T5,X=0)

SH6 = f(PH6,TH6)

PH7=PH6+DP12N

SH7 = f(PH7,SH6)

DHS = H7S H6

DH = DHS/ETAIN

HH7 = H6 + DH

T7 = f(P7,H7)

P4 = P3 - DP34N

T4=T7+PINPN

H4=f(P4,T4)

M4=M3

Q3=M3*H3

Q4=M4*H4

QN= Q3-Q4

Q87=(Q3-Q4) *(1-DQLR)

Determination of M2 and QPUM

{

M2*H2-M1*H1+M5*H5-QPUM=Q87

M1=M2+M5

QPUM= DH*MH6

MH6 = M2*CN

}

M2=(Q87-M5*(H5-H1) ) / (H2-H1-CN*DH)

MH8=MH7=MH6

QPUM= DH*MH6

QH7=M7*H7

}

DTLO = T4 TH7 (for FFLOW = counter current)

DTUP = T3 TH8 (for FFLOW = counter current)

LMTD = (DTUP - DTLO)/(ln(DTUP) - ln(DTLO))

KAN = DQ/LMTD

KAN*LMTD = MH8*H8 MH7*H7

KAN*LMTD = (M3*H3 - M4*H4)*(1 - DQLR)

Off-design case (Simulation flag: GLOBAL = off-design case or FMODE = off-design case)

TOL = 0.00001

if FVOL= without, then {

F1 = (M1/M1N) ** 2

if FMODE=1, then F1=1.0

F3 = (M3/M3N) ** 2

if FMODE=1, then F3=1.0

}

if FVOL= with, then {

F1 = V1/V1N*(M1/M1N) ** 2

if FMODE=1 then F1=1.0

F3 = V3/V3N*(M3/M3N) ** 2

if FMODE=1, then F3=1.0

}

PH8=PH6=P5=P2=P1

T2=T5=TH6=TH8=fsat(P1)

T1=f(P1,H1)

H2=fsat(P2,T2,X=1)

H5=fsat(P5,T5,X=0)

SH6 = f(PH6,TH6)

PH7=PH6+DP12N*F1

SH7 = f(PH7,SH6)

DHS = SH7 HH6

DH = DHS/ETAI

HH7 = HH6 + DH

TH7 = f(PH7,HH7)

P4 = P3 - DP34N*F2

M4=M3

if FMODE = off-design, use KAN and characteristic line, then {

Marking1

TM34 = 0.5*(T3+T4)

FK2=(1-.0005*(TM34N-T34N))*(M3/M3N)**EX34

KN = 1/ AL34N

K = 1/(AL34N*FK2)

}

if FMODE = off-design: use KAN, no characteristic line, then { K = KN}

KA=KAN*K/KN

Iteration1{

H4 = (Q3 Q87/(1-DQLR) )/M4

T4 = f(P4,H4)

DTLO = T4 TH7 (for FFLOW = counter current)

DTUP = T3 TH8 (for FFLOW = counter current)

DTLO = T4 TH8 (for FFLOW = concurrent flow)

DTUP = T3 TH7 (for FFLOW = concurrent flow)

LMTD = (DTUP - DTLO)/(ln(DTUP) - ln(DTLO))

QQ = KA * LMTD

DQQ_1 = DQQ

DQQ = Q87 - QQ

regula - falsi method {

Size = (Q87 Q87_1)/(DQQ - DQQ_1)

for iteration step 1: Size of the last global iteration step

Q87X = Q87 - DQQ * Size

Q87_1 = Q87

Q87 = Q87X

}

DQ = |DQQ /((Q87+QQ)*.5)|

if DQ < TOL, then end iteration 1

else continue the iteration

}

KA*LMTD = MH8*HH8 MH7*HH7

KA*LMTD = (M3*H3 - M4*H4)*(1 DQLR)

For FMODE = off-design, use KAN and characteristic line go to Mark 1, till convergence occurs

Determination ofM2 and QPUM

{

M2*H2-M1*H1+M5*H5-QPUM=Q87

M1=M2+M5

QPUM= DH*MH6

MH6 = M2*CN

}

M2=(Q87-M5*(H5-H1) ) / (H2-H1-CN*DH)

M1=M2+M5

MH6 = M2*CN

QPUM= DH*MH6

M7=M6

QH7=MH7*HH7

Results

Performance	Short Name	Dimension
Heat given to cold stream (incl. heat from pump and to drain)	Q21	kW
Transferred heat	QT	kW
Heat delivered from hot side flow	Q34	kW
Performance factor heat transfer	RPFHX	-
Heat Transfer
Heat transfer coefficient *area	KA	kW/K
Heat transfer coefficient	K	W/m2K
Heat transfer area	A	m2
Mean log temperature difference	DTM	K
Lower terminal temperature difference	DTLO	K
Upper terminal temperature difference	DTUP	K
Alpha number 34 (operation)	AL34	W/m2K
KA according to component specific off design behaviour	KACL	kW/K
Calculated effectiveness (-actual heat transfer / theoretical maximum in case of infinite size)	REFF	-
Part Load
Relative steam mass flow (Ratio of current steam production to steam production in the design case)	M2M2N	-
Relative hot side mass flow (Ratio of the current exhaust gas mass flow to the exhaust gas mass flow in the design case)	M3M3N	-
Peripheral Results		-
Circulation pump power	QPUMP	kW
Volume flow at cold side inlet	VM1	m3/s
Volume flow at hot side inlet	VM3	m3/s
Steam quality (X) at cold side outlet	X2	-
Heat transfer to flow 12 up to intermediate point	Q12IP	kW
Temperature at flow 12 at intermediate point	T12IP	°C
Temperature difference between flow 34 and flow 12 at intermediate point	DTIP	K
Result of ADAPT / EADAPT	RADAPT	-
Saturated liquid enthalpy or max (HSAT,H1)	HLS	kJ/kg
Boiling temperature	TSAT	°C
Dew point temperature	TDEW	°C
Boiling pressure	PSAT	bar
Saturated liquid enthalpy or max (SSAT, S1)	SLS	kJ/kgK

Component Displays

Use option 1 or 2 in case of forced circulation, options 3 to 5 in case of natural circulation.

	Display Option 1		Display Option 2
	Display Option 3		Display Option 4
	Display Option 5 1

Example

Click here >> Component 70 Demo << to load an example.

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