Component 84: Coal Dehumidifier

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Component 84: Coal Dehumidifier

Specifications

Line connections
1	Coal inlet (wet)
2	Coal inlet (dry)
3	Steam outlet
4	Heating steam inlet
5	Heating steam (water) outlet
6	Circulating steam inlet
7	Control inlet for nominal coal outlet humidity

General User Input Values Characteristic Lines Physics Used Displays Example

General

Component 84 models a fluidized-bed coal dehumidifier.

The wet coal is fed in the component via line 1. The moisture bound in the coal (XH2OB) and the water specified as XH2O is extracted from the coal and fed to the re-circulation steam flow (from line 6 to line 3). The heat needed for this is extracted from the hot steam (line 4), which is condensed and comes out of line 5. The dried coal leaves the component in line 2.

The component has numerous setting options for the various calculation variants.

The properties of the wet coal at the inlet (mass flow, temperature, calorific value, chemical composition) are to be specified on the coal line.

The flag FSPECT defines different calculation methods for the fluidized-bed temperature T2 and the moisture content of the coal at the outlet:

= 0: P2 from P3_sat und characteristic line CDT23, PHI2 from characteristic line CXH2OB, T2 from characteristic line CT2 (Design:T2=T2N, because M1/M1N=1)

= 1: P2 or P6 given, PHI2 from characteristic line CXH2OB, T2 from absorptions isotherms CSORPTx

= 2: P2 or P6 given, T2 from characteristic line CT2 (Design:T2=T2N, because M1/M1N=1), PHI2 from absorptions isotherms CSORPTx

The absorption isotherms comprise of a set of characteristic lines, whereby a specific pressure is assigned to each characteristic line as parameter. Each characteristic line describes the residual moisture as a function of the temperature at the respective pressure. These characteristic lines contain absolute values (not referring to nominal values) and are used in design as well as off-design cases.
The following are the options for usage:
- No use (old mode)
- Specification of P and residual moisture, calculation of T
- Specification of P and T, calculation of residual moisture

Even the characteristic lines for binding enthalpies are to be specified absolute and are used in design as well as off-design cases. These characteristic lines describe the binding enthalpy depending upon the temperature at the respective pressure. The binding enthalpy is needed, in order to break up the capillaries, in which the water is present. Here, mechanical work (deformation work) is done, which is lost irreversibly (i.e. does not lead to an increase in the calorific value). The binding enthalpy thus leads to a real loss in the energy balance. This is indicated in the result value DQBIND.

In case the residual moisture is very high, the fluidized-bed can no longer be stabilized. To take account of this, one can specify a limiting value for the moisture in the specification value XLIM, which, when exceeded, generates an error message.

Handling of mass flow:

The coal mass flow must always be specified.

The circulation and the hot steam mass flows can be specified as follows:

Calculation of both the mass flows from the mass and energy balances in case of a closed circulation (FSPEC=3. In this case the mass flow of the condensed hot water M5 matches with the mass loss of the coal through moisture separation.
Specification of the hot steam mass flow M4, the circulation mass flow M6 results from the energy balance (FSPEC=0)
Specification of the circulation mass flow M6, the hot steam mass flow M4 results from the energy balance (FSPEC=2)
Hot steam mass flow M4 and circulation mass flow M6 are specified (FSPEC=1). In this case, the energy balance can be violated.
This is indicated as the result value DQVIOL. See under Note.

Pressure losses for the circulation and the hot steam are considered separately. The pressure loss of the hot steam is calculated according to

DP45 = DP45N * (M4/M4N) * (M4/M4N) * (V4/V4N),

whereby M4 is the hot steam mass flow and V4 is the specific volume of the hot steam at the inlet. "N" refers to the respective design value.

The pressure loss for the circulation steam is the fluidized-bed pressure loss, which is calculated from 2 fractions (for FSPEC=1):

the pressure loss of the distributor plate: DPNF = DPNFN * (M3/M3N)*(M3/M3N)*V3/V3N
the pressure loss of the fluidized bed (constant): DPFB

Alternatively, it is also possible to specify the inlet pressure of the circulation steam from outside (FSPECP=0).

Note - Characteristic Lines Related to Nominal Temperature

For the component 84 there is a characteristic line CT2, which refers to a nominal value of temperature. This is the characteristic line CT2 for the outlet temperature (dehumidified coal) of the coal dehumidifier, which provides the ratio T2 / T2N.

Unfortunately, such temperature ratios depend on the selected system of units. In contrast to other units where the conversion is effected only via a certain factor and therefore has no effects on the quotient, in the temperature conversion there is an additive offset whereby the value of the quotient changes.

There is the possibility to specify this characteristic line in other units (°F, K).

Users who prefer other unit systems for the temperature (eg ° F, K) must set the selected temperature unit in the new flag FTNI, because Ebsilon calculates internally with the temperature unit ° C.

Note:

Formation of the energy balance

For this component, the energy balance is now displayed differently.
As coal and water/steam in Ebsilon have different reference points for the enthalpy, you cannot compare the contributions to the energy

balance directly.
In Release 10, all contributions were transformed to the reference system of the coal (FDBR polynomials). The disadvantage of this

transformation was a small inaccurateness as in FDBR, steam is handled as an ideal gas.
In Release 11 this transformation is not used any more. Instead, each portion is referred to its reference system at the inlet.
Therefore, we can simply sum up all contributions at the inlets:
QSUPP = Q1 + Q4 + Q6 + M1*NCV1
It is important to consider the latent heat (M1*NCV1) as well, as the heating value of the coal is changed during the dehumidification,

and this is an essential contribution to the energy balance.
At the outlet, each portion is calculated according to the reference system that this portion had at the inlet. Therefore, the steam at

outlet 3 must be split into two parts:
• the part coming from the water in the coal (this is a mass flow of M2-M1) which must be calculated according to FDBR
• the part that came into the dehumidifier already as steam (this is M6) which must be calculated according to the water/steam table
With that, the total delivered heat is
QDEL = Q2 + M2*NCV2 + Q5 + (M1-M2)*H_FDBR_H2O(P3,H3) + M6*H3
where H_FDBR_H2O is the enthalpy of a coal pipe with 100% water.
Due to the change of the reference value, the result value QSUPP and QDEL are quite different in Release 11.

For all other parts of the calculation, the change is quite small.

Logic Pin for Residual Moisture

The residual moisture of the coal can be calculated from the specification value XH2OBN and the characteristic. However, it is also possible to control the residual moisture from the outside using logic connection 7. For this, a flag FXH2OB has been implemented; it has the following settings:

FXH2OBN=0: use of specification value XH2OBN (as before, default setting)
FXH2OBN=1: use of the enthalpy of the logic line on Pin 7 as XH2OBN instead of specification value XH2OBN

User Input Values

FSPEC	Case differentiation for mass flow handling Like in Parent Profile (Sub Profile option only) Expression The coal mass flow must always be specified. =0: Heating steam mass flow M4 given, circulation mass flow M6 calculated from energy balance =1: Heating steam mass flow M4 and circulation mass flow M6 given, energy balance violation possible. This is shown as result value DQVIOL. See under Note. =2: Circulation mass flow M6 given, heating steam mass flow M4 calculated from energy balance =3: Closed circulation, mass flows M4 and M6 result from mass and energy balances In this case, the mass flow of the heating water M5 with the mass loss of coal by the moisture deposition match.
FSPECT	Case differentiation for temperature and moisture handling Like in Parent Profile (Sub Profile option only) Expression =0: T2 calculated from T2N and coal mass flow characteristic line CT2 (in design T2=T2N, because M1/M1N=1), P2 from steam pressure, moisture from default value XH2OBN and characteristic line CXH2OB (old mode). Absorption isotherms are not used. =1: P2 specified from outside, moisture (coal outlet) from default value XH2OBN and characteristic line CXH2OB, T2 (fluidized-bed temperature) calculated from P2, residual moisture and absorptions isotherms =2: T2 calculated from T2N and coal mass flow characteristic line CT2 (in design T2=T2N, because M1/M1N=1), P2 specified from outside, moisture calculated from absorptions isotherms
FSPECP	Handling of pressure drop Like in Parent Profile (Sub Profile option only) Expression =0: P6 given externally (old mode) =1: Pressure drop calculated from DPFB and DPNFN
FXH2OBN	Method for specification of nominal coal outlet humidity Like in Parent Profile (Sub Profile option only) Expression =0: Given by specification XH2OBN =1: Given by enthalpy on control inlet 7
XH2OBN	Moisture content of coal at outlet 2 (nominal)
XLIM	Limiting value for moisture (threshold for error message)
FTNI	Unit used for calculation of T2/T2N in CT2 Like in Parent Profile (Sub Profile option only) Expression =0: Celsius =1: Fahrenheit =2: Kelvin
T2N	Temperature of coal at outlet 2 (nominal)
DT23N	Temperature difference between coal outlet and circulation steam outlet (nominal)
DT5S5N	sub cooling (T5saturated-T5) (nominal)
DP45N	Pressure loss heating steam (nominal)
DPFB	Pressure loss fluidized bed (constant quantity)
DPNFN	Pressure loss of distributor plate (nominal)
FMODE	Calculation mode design /off-design Like in Parent Profile (Sub Profile option only) Expression =0: GLOBAL =1: Local off-design i.e. always off-design mode, even when the model is calculated in the design mode.
M1N	Mass flow of coal (nominal)
M3N	Mass flow steam outlet (nominal)
M4N	Mass flow heating steam (nominal)
V3N	Specific volume steam outlet (nominal)
V4N	Specific volume heating steam inlet (nominal)

The specification values marked in blue are reference quantities for the off-design calculations, which are calculated by EBSILON^®Professional in the design case.

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

Characteristic Lines

Characteristic line 1, CXH2OB: Moisture-characteristic line: XH2OBO/XH2OBN = f (M1/M1N)

     X-axis          1         M1/M1N                         1^st point
                        2          M1/M1N                        2^nd point
                        .
                      N         M1/M1N                         last point

     Y-axis        1          XH2OB/XH2OBN           1^st point
                        2          XH2OB/XH2OBN           2^nd point
                        .
                        N         XH2OB/XH2OBN           last point

Characteristic line 2, CT2: T2-characteristic line: T2/T2N = f (M1/M1N)

     X-axis          1         M1/M1N           1^st point
                        2          M1/M1N          2^nd point
                        .
                      N         M1/M1N          last point

     Y-axis          1          T2/T2N           1^st point
                        2          T2/T2N             2^nd point
                        .
                        N         T2/T2N             last point

Characteristic line 3, CDT23: DT23-characteristic line: DT23/DT23N = f (M1/M1N)

     X-axis          1         M1/M1N                      1^st point
                        2          M1/M1N                     2^nd point
                        .
                      N         M1/M1N                     last point

     Y-axis          1          DT23/DT23N               1^st point
                        2          DT23/DT23N               2^nd point
                        .
                        N         DT23/DT23N               last point

Characteristic line 4, CDT5S5: DT5S5-characteristic line: DT5S5/DT5S5N = f (M1/M1N)

     X-axis          1         M1/M1N                             1^st point
                        2          M1/M1N                            2^nd point
                        .
                      N         M1/M1N                            last point

     Y-axis          1          DT5S5/DT5S5N                 1^st point
                        2          DT5S5/DT5S5N                  2^nd point
                        .
                        N         DT5S5/DT5S5N                  last point

CSORPT1 to CSORPT4 - Absorption isotherms

This characteristic represents the fluidized-bed temperature (=T2) depending upon the residual moisture of the coal. Thereby, it is possible to specify different absorption isotherms for the various pressure levels.

x-value: Residual moisture (absolute value XH2OB in the coal coming out)

y-value: Fluidized-bed temperature (absolute value of the coal outlet temperature T2)

Parameter: Pressure level (absolute value of the pressure P2 at the coal outlet)

CBIND1 to CBIND4 - Binding enthalpy

This characteristic displays the binding enthalpy (see above) depending upon the residual moisture of the coal. Thereby, it is possible to specify different absorption isotherms for the various pressure levels.

x-value: Residual moisture (absolute value XH2OB in the coal coming out)

y-value: Binding enthalpy (absolute value)

Parameter: Pressure level (absolute value of the pressure P2 at the coal outlet)

Physics Used

Equations

Design case

(Simulation flag:

GLOBAL = Design case

and

FMODE = GLOBAL)

XH2OBO = XH2OBN *f (M1/M1N) from characteristic line 1

T2= T2N * f (M1/M1N) from characteristic line 2

DT23 = DT23N * f (M1/M1N) from characteristic line 3

DT5S5= DT5S5N * f (M1/M1N) from characteristic line 4

F1 = (M4/M4N ** 2) * (V4N/V4)

Composition and mass flow line 2:

Balance through dehumidification of moisture state 1 to

reference moisture FE2 state 2 (dehumidification mass flow MFE)

M2 = M1-MFE

M3 = M6+MFE

If FSPEC = 2 then {

M4 = (M2*H2-M1*H1+MFE*H3-D6*(H6-H3))/(H4-H5)

}

M5 = M4

If FSPEC = 0 then {

M6 = (M2*H2-M1*H1-M4*(H4-H5)+MFE*H3)/ *(H6-H3)

}

P3 = P3SATT(T2-DT23)

P1 = P3

P2 = P3

DP45 = DP45N* F1

P5 = P4 DP45

H2 = H2(T2,P2, composition)

H3 = H3(T3,P3)

H5 = H5(T5,P5)

Component Displays

Display Option 1

Option 2

Example

Click here >> Component 84 Demo << to load an example.