Component 128: hard-coal mill

In This Topic

Component 128: hard-coal mill / Pulverizer

Specifications

Line connections
1	Hot drying gas inlet 1
2	Main outlet (fine coal and carrier medium)
3	Cooling drying gas inlet 2
4	Fuel inlet
5	Sealing air inlet
6	Electric power inlet
7	Drying gas mixing
8	Classifier temperature
9	Raw fuel water content

General User Input Values Results Characteristic lines Physics used Displays Example

General

Component 128 is intended for the thermodynamic balancing of a hard coal mill (pulverizer) with coal grinding and drying process considered. It can be used for the modeling of a bowl mill.

The raw coal (specified at PIN 4) is grinded within the mill. The electric power (specified at PIN 6) is used to move the milling plant. The coal dust contacts the mixture of the hot (PIN 1) and the cool (PIN 3) drying gas (normally air) and is, therefore, dried (a certain fraction of water in coal evaporates). Finally, the mixture of dried and grinded coal, water steam and drying gas exits the component at PIN 2. In real mills / pulverizers the dust particles are classified by a classifier. The coarse particles are returned to further grinding building an internal circulation within the mill. This circulation is, however, neglected in the stationary computations of component 128. The exactly closed mass balance is presumed. I.e. the sum of all incoming mass flows is equal the mass flow at the outlet (PIN 2).

The mixing temperature of the drying gas 1 and 2 as well as the mass flow of that can be specified at the logical PIN 7.

The PIN 5 is used for the specification of the sealing air fraction penetrating into the component.

The computed raw coal water content is available at the logical PIN 9. The user can use that within the simulation e.g. for a controller or a value transmitter component.

The component assumes that the raw coal water content corresponds to the value of XH2OB at PIN 4. It is therefore expected that the user specifies only solid material fractions at PIN 4 (no gas or liquid substances make sense). The specified residual water content (RXH2OB) is interpreted also as XH2OB fraction regarding to the solid phase composition at PIN 2 (not regarding to the overall composition at PIN 2!). Thereby the complete solid phase at PIN 2 is taken as a basis for the residual water content without distinguishing between the fine coal and e.g. the ash or unburnt carbon fractions coming with the drying gas into the mill.

Important. There is a deviation from the thermodynamic equilibrium state between the fine coal residual water content and the gas phase at the outlet of the real coal mill. The water in grains remains in the liquid phase although the temperature of gas is higher than the water saturation temperature. The classifier temperature TCLASS is therefore specified at the logical PIN 9. The gas phase at the outlet is assumed to be at T=TCLASS. The temperature of the mixture (gas and solid phase) at PIN 2 may therefore deviate (be less than) from TCLASS depending on the residual water content of the fine coal. The computed temperature T2 is only a theoretical temperature corresponding to the thermodynamic equilibrium state which can not be measured in the real coal mill. The temperature T2 should not be compared to any measured value (e.g. classifier temperature). TCLASS=T9 must be used instead. The classifier temperature computed from the energy balance is available as result value RTCLASS. The outlet temperature T2 corresponding to the desired classifier temperature is available as result value T2FTCL.

In some cases when the classifier temperature is too low and / or the raw fuel water content is too high the specified residual water content of the fine fuel can lead to condensed water fraction XH2OL at mill outlet. To avoid it the residual water content of the fine fuel is increased in the calculation and the corresponding warning is generated.

Note - Characteristic Lines Related to Nominal Temperature

For the component 128 there is a characteristic line CL_12, which refers to a nominal value of temperature. This is the characteristic line CL_12 for the residual water content of fine coal , which provides the ratio TCLASS / TCLASSN.

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.

Relative heat loss (DQLR) / Load-independent heat loss (QLA)

In the case of the component 128, a relative heat loss can be specified via the specification value DQLR.
In practice, however, the temperature conditions for the mill change only slightly with the load, so that a load-independent heat loss occurs. This can be specified via the specification value QLA. The flag FLOSS serves to define whether the relative or the absolute loss is to be used.

User Input Values

FFU	Mill ON/OFF =0: OFF (If FFU=0, all inlet mass flows and enthalpies are expected to be specified, consequently, the values of FTMIX, FMMIX, FCM and FCMEB are of no relevance) =1: ON
FMODE	Flag for calculation mode Design / Off-design = 0: global = 1: local off-design (i.e. always off-design, even if global design mode was selected) =-1:local design
FDP12	Pressure drop calculation (cold side) =0: using DP12N and characteristic field 1 (characteristic lines CL_1...CL10) =1: P2 given from outside
DP12N	pressure drop (nominal)
FTMIX	Mixing temperature TMIX13 specification =0: computed internally =1: externally at PIN 7
FMMIX	Mixed drying gas mass flow specification MMIX13 =0: computed internally =1: externally at PIN 7
FCM	Gas mixing calculation =0: M1 OR M3 computed from TMIX13 =1: M1 AND M3 given =2: MINGAS=M1+M3 given, M1 AND M3 computed =3: MINGAS=M1+M3 AND M1 OR M3 given
FCMEB	Mass and energy balance treatment =0: Compute the raw coal water content =1: TCLASS given, compute TMIX13 =2: All inlet conditions given, T2 (TCLASS) computed =3: The fine coal residual water content calculated from the energy balance
FQEL	Electric power specification =0: calculated from Q6N and characteristic line Q6/Q6N=f(M4/M4N) =1: externally (PIN 6)
MQEL	Fraction of el. power converted to heat
FLOSS	Specification of heat losses =0: Specification by DQLR =1: Specification by QLA
DQLR	Heat loss (relative), (relative to the total heat supplied except chemically bound energy)
QLA	Heat loss (absolute)
RXH2OBN	Residual water content of fine coal nominal
TOLMF	Tolerance for mass fraction deviations (a warning is provided if the deviation between the computed and the specified water content of the raw coal exceeds the specified tolerance value)
FTNI	Unit used for calculation of TCLASS/TCLASSN in CL_12 =0: Celsius =1: Fahrenheit =2: Kelvin
MINGASN	Inlet drying gas mass flow (M1+M3) (nominal)
TCLASSN	Classifier temperature (nominal)
M4N	Raw coal mass flow (nominal)
Q6N	Electric power (nominal)
DGRN	Raw coal to drying gas ratio (M4/MINGAS) (nominal)

The parameters marked in blue are reference parameters for off-design, which are calculated by Ebsilon in the design mode. The actual off-design values refer to these parameters in the equations used.

Allowed combinations of flags

	FCM	0	1	2	3
FCMEB
0		yes (FTMIX=1)	yes (FTMIX=0)	yes (FTMIX=1)	yes (FTMIX=0)
1		yes (FTMIX=0)	no	yes (FTMIX=0)	no
2		yes (FTMIX=1)	yes (FTMIX=0)	yes (FTMIX=1)	yes (FTMIX=0)

Results

CWC4	Computed raw coal water content
CWC4DIFF	Difference between CWC4 and the spec. raw coal water content at PIN 4
CWCB4	Computed minimal raw coal XH2OB value expected due to RXH2OB specification
CWCB4DIFF	Difference of CWCB4 to the spec. raw coal XH2OB value at PIN 4
QDIFF	Energy balance violation
DP12	Pressure drop
DP12R	Reference pressure drop
Q6CL	Electric power from characteristic line
RXH2OB	Residual water content of the fine coal (based on the mass flow at connection 2, but without carrier medium components (gases))
MINGASCL	Inlet drying gas mass flow from characteristic line
QLOSS	Heat loss
DGR	Raw coal to drying gas ratio
QT	Heat transferred from drying gas to coal
MIMIN	Relative drying gas mass flow
M4M4N	Relative fuel mass flow
TCTCN	Relative classifier temperature
DGRDGRN	Relative raw coal to drying gas ratio
RTCLASS	Computed classifier temperature
T2FTCL	Thermodynamic equilibrium outlet temperature T2 for desired classifier temperature

Characteristic lines

Char. lines 1 to 10: Pressure drop DP12/DP12N = f (MINGAS/MINGASN) for different DGR/DGRN

X-axis 1 MINGAS/MINGASN 1. point

2 MINGAS/MINGASN 2. point
.

N MINGAS/MINGASN last point

Y-Axis 1 DP12/DP12N 1. point

2 DP12/DP12N 2. point

N DP12/DP12N last point

Char. line 11: Electric power Q6/Q6N = f(M4/M4N)

X-axis 1 M4/M4N 1. point

2 M4/M4N 2. point

                     N        M4/M4N                           last point

     Y-axis       1        Q6/Q6N                           1. point
                       2        Q6/Q6N                            2. point
                       .
                     N        Q6/Q6N                         last point

Char. line 12: Water content of fine coal RXH2OB/RXH2OBN = f(TCLASS/TCLASSN)

X-axis 1 TCLASS/TCLASSN 1. point

2 TCLASS/TCLASSN 2. point
.

N TCLASS/TCLASSN last point

Y-axis 1 RXH2OB/RXH2OBN 1. point

2 RXH2OB/RXH2OBN 2. point

N RXH2OB/RXH2OBN last point

Char. line 13: Drying gas inlet mass flow MINGAS/MINGASN = f(M4/M4N)

X-axis 1 M4/M4N 1. point

2 M4/M4N 2. point
.

N M4/M4N last point

Y-axis 1 MINGAS/MINGASN 1. point

                    2        MINGAS/MINGASN             2. point
                    .
                    N        MINGAS/MINGASN             last point

Physics used

Equations

FFU=1

MF2 - mass flow fine coal at outlet
MH2O2 - mass flow of water steam at outlet
QFM2 = Q((M1+M3+M5), TCLASS) – heat of gas at outlet
HH2ODAMPF(TCLASS) - enthalpy water steam for T=TCLASS
HF2 = HCoal(P2,TVIRT, RXH2OB) – enthalpy fine coal with residual water content RXH2OB at TVIRT, P2
TVIRT - temperature at which the water in coal remains to be in the liquid phase at P2
COMP2 - composition at outlet 2

FMODE=0:
{
   If FDP12=0
        DP12 = DP12N
    If FDP12=-1
        DP12 = P1 – P2

    Q6CL = Q6N
    RXH2OB = RXH2OBN
    MINGASCL = MINGASN
}

FMODE=1:
{
    If FDP12 = 0
         DP12 = f(Char. lines 1-10)*DP12N
    If FDP12=-1
         DP12 = P1 – P2

    Q6CL = f(Char. line 11) * Q6N
    RXH2OB = f(Char. line 12) * RXH2OBN
    MINGASCL = f(Char. line 13) * MINGASN
}

P1 - P2 = DP12 (1)

If FMMIX=0
MMIX13 = MINGASCL
If FMMIX=1
MMIX13 = M7

If FTMIX = 1
TMIX13 = T7
HMIX13 = f(TMIX13) - mixing enthalpy of drying gas

All FMODE

    M2 = M1 + M3 + M4 + M5                                                      (2)
    M7 = M1 + M3                                                                        (3)
    If FQEL=0
       QEL = Q6CL                                                                          (4)
    If FQEL=1
        QEL = Q6
    QGRIND = QEL*MQEL
    QLOSS = DQLOSS*(Q1+Q3+Q4+Q5+QGRIND)

If FCM = 0
    M1 or M3 computed from
    M1*(H1-HMIX13)+M3*(H3-HMIX13)=0                                      (5)
If FCM = 1
    HMIX13 = f(M1, M3)
If FCM = 2
    M1 or M3 computed from
    M1 + M3 = MMIX13                                                               (6)
If FCM = 3
     M1 or M3 computed from (5) and (6)

If FCMEB = 0
    Heat transferred from drying gas to coal:
    QT = Q1 + Q3 + Q5 + QGRIND –QFM2
    Water content raw coal:
    M9 = CWC4 = ((QT + Q4 - QLOSS)*(1- RXH2OB)/M4 – HF2 +
    HH2ODAMPF(TCLASS)* RXH2OB) / (HH2ODAMPF(TCLASS) - HF2) (7)
    CWC4DIFF = CWC4 - XH2OB4 – XH2O4
    Energy balance violation due to CWC4DIFF
    M2*H2EB = Q1+Q3+Q4+M4*HU4+Q5+QGRIND-QLOSS
    QDIFF = M2*H2EB - M2*(H2+HU2)
If FCMEB = 1
    QT = HF2*MF2 + MH2O2 * HH2ODAMPF(TCLASS)-Q4
    QMIX13 = QT – QGRIND –Q5 + QFM2 + QLOSS
    H7 = HMIX13 = QMIX13 / MINGASCL                                       (8)
If FCEMEB = 0 OR FCMEB = 1
    TCLASS = H8
    H2 = f(P2, TCLASS, TVIRT, COMP2)                                            (9)
    T2 = f(P2,H2,COMP2)
If FCMEB = 2
    H2 = (Q1+Q3+Q4+Q5+QGRIND-QLOSS) / M2                          (10)
    Composition at outlet without residual water content of fine coal:
    COMPVIRT = COMP2 – f(RXH2OB)
    corresponding enthalpy:
    H2VIRT = (Q1+Q3+Q4-QF2+Q5+QGRIND-QLOSS) / (M2-MF2)
    TCLASS = f(H2VIRT, P2, COMPVIRT)
    H8 = TCLASS                                                                           (11)

Component Displays

Display option 1

Example

Click here >> Component 128 Demo << to load an example.

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