Component 50: Coal Gasifier

In This Topic

Component 50: Coal Gasifier

Specifications

Line connections
1	Oxidizing inlet
2	Crude gas outlet
3	Water-/Steam inlet
4	Coal inlet
5	Ash extraction

General User Input Values Characteristic Lines Physics Used Displays Example

General

The component for coal gasification simulates the chemical conversion in the reactor of a coal-to-gas plant under design and off-design conditions.

At the nominal load point, the model returns the adiabatic outlet temperature and the gasification products under consideration of the boundary conditions

Properties of coal (components, calorific value)
O/C-ratio (coal and oxidant flow can be entered alternatively)
Ratio of steam to coal (a steam mass flow can be entered alternatively)

For off-design mode, the calculation is carried out in the same way as for the design mode, but with the difference that the load-dependent characteristic lines are used.

For simulating the complete system of "gasifier", a high temperature heat exchanger must be used for describing the reactor wall cooling.

The reactor model permits the simulation of

Flue dust gasifiers, or
Fluidized bed gasifiers

Solid bed gasifiers can only be described approximately. Because of the low temperature, the shift-balance is not reached and a number of higher hydrocarbons will develop that are not contained in the crude gas library.

Model

The model of the coal gasifier comprises of two sub models:

the reactor for calculating the crude gas analysis and the outlet temperature, and
the high temperature heat exchanger for simulating the reactor wall cooling.

The description given below restricts itself to the reactor; the high temperature heat exchanger (component 51) is handled analog to the known heat-exchanger components (component 26).

However, an additional radiation characteristic line allows a more realistic consideration of radiant heat transmission.

The reactor model is essentially based on the assumption that the water-gas shift balance

KP(T) = CO H2O/(CO2 H2)

is valid. This is a good approximation for gasifier systems with operating temperatures between 1472 and 1652 °C, so that flue-dust and fluidized bed gasifiers become accessible for a simulation. There are three methods for calculating the shift constants.

The adiabatic outlet temperature is used for KP-calculation.
A reaction temperature used for calculating the KP can be defined by specification values. (shift temperature: limiting temperature, below which no reaction takes place)
KP can be entered directly as specification value. It determines measured concentrations

Regardless of these simplifications, the calculation of the reactor process requires five more limiting values, which are based on experience or measurements.

These are:

Efficiency of carbon gasification
CH4-concentration
Sulfur conversion ratio to H2S or COS
Ash splitting (ratio of flue-dust to total ash)
Carbon concentration in the ash

The supplied and the extracted mass flows can be defined in two ways:

Input of the O/C-ratio between the oxidant and the coal and also the steam/coal ratio. The ash mass flow results from the ash splitting, which must be entered. The crude gas mass flow is calculated from the total balance. An absolute mass flow is the only necessary input, when a closed solution method is used.
Input of the three mass flows for coal, oxidant and steam; calculation of the ash mass flow from the ash splitting and the crude gas mass flow from the balance for each mass flow.

In the off-design mode, the same model is used with the difference that

the conversion degree of carbon gasification
the CH4-formation, and
the shift constants

are defined as load-dependent characteristic lines.

The following new result values are output for the gasifier components: RFA, RFAST, EQRAT

User Input Values

DP12N	Absolute pressure loss (nominal)
ROCN	Oxygen/Carbon ratio
RWM4N	Water-Steam/Coal ratio
RFLAS	Fly ash ratio
RCFA	ratio C (fly ash) /C (fly ash and ash)
RGASN	Efficiency of carbon gasification (nominal)
RCCH4N	C in CH4/C total ratio (nominal)
RSH2SN	S in H2S/S total ratio (nominal)
CWGS	Water-gas shift constants
TFRE	Freezing temperature of the shift reaction
TASHE	Ash temperature
FMODE	Calculation mode Like in Parent Profile (Sub Profile option only) Expression =0: GLOBAL =1: local off-design
FSFT	Calculation of the shift reaction Like in Parent Profile (Sub Profile option only) Expression =1: calculate shift reaction at temperature T2 =2: calculate shift reaction at TFRE =3: calculate shift reaction at input CWGS
FMAS	Switch for calculation type of the mass balance Like in Parent Profile (Sub Profile option only) Expression =1: Input of 1 mass flow from M1/M2/M3/M4 =2: Input of 3 mass flows from M1/M2/M3/M4
M1N	Mass flow of oxidizing fluid (nominal)

The parameters marked in blue are reference quantities for the 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

Result values

ROC	Oxygen to carbon ratio
RWM4	Steam to coal ratio
RCWGS	Calculated water gas shift constant
RGAS	Carbon gasification
RCCH4	CH4-production (C in CH4 / C total)
RSH2S	H2S-production (S in H2S / S total)
NCVCG	Net calorific value of natural gas at 0°C
NCVCOAL	Net calorific value of coal at 0°C
RQCGC	Energy ratio of natural gas to coal
RFA	Ratio fuel mass flow to air mass flow
RFAST	stoichiometric ratio of fuel mass flow to air mass flow (i.e. the ratio required for complete combustion)
EQRAT	equivalence ratio = RFA / RFAST (according to https://www.sciencedirect.com/topics/engineering/equivalence-ratio). An equivalence ratio EQRAT greater than 1 always indicates a fuel excess in the fuel-oxidant mixture, i.e. more fuel than required for a complete combustion (stoichiometric reaction), irrespective of which fuel and which oxidant are used, whereas ratios smaller than 1 indicate a lack of fuel or an equivalent oxidant excess in the mixture. Please note that the equivalence ratio relates to the air number λ as follows: λ = 1 / EQRAT.

Characteristic Lines

Characteristic line 1, CCSL: C-degree of the gasification characteristic line RGAS/RGASN = 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          RGAS/RGASN            1^st point
                        2          RGAS/RGASN             2^nd point
                        .
                        N         RGAS/RGASN             last point

Characteristic line 2, CCH4: CH4-conversion-characteristic line RCCH4/RCCH4N = 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          RCCH4/RCCH4N        1^st point
                        2          RCCH4/RCCH4N         2^nd point
                        .
                        N         RCCH4/RCCH4N        last point

Characteristic line 3, CH2S: H2S-conversion-characteristic line RSH2S/RSH2SN = 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          RSH2S/RSH2SN         1^st point
                        2          RSH2S/RSH2SN          2^nd point
                        .
                        N         RSH2S/RSH2SN           last point

Physics Used

Equations

All cases

Elementary components

---------------------------------------

Calculation of the elementary mass portions EL4

C, H, O, N, S, CL, AR, ash, KLKof coal

Calculation of the elementary mass portions EL1

C, H, O, N, S, CL, AR, ash, KLKof the oxidant

Different load cases

------------------------------

if FMAS = 1 (Calculation of the mass flows through ROCN and RWM4N), then {

M3M4= RWM4N

M1M4 = f(ROCN) }

if FMAS = 2 (Input of the mass flows through M1, M3, M4), then {

M3M4 = M3/M4

M1M4 = M1/M4 }

if FSFT=1 (shift constant at T2), then { SH = A*EXP(-B/(T2+273.15)) }

if FSFT =2 (shift constant at TFRE), then {

SH = A*EXP(-B/(TFRE+273.15)) }

if FSFT =3 (shift constant for CWGS), then {

SH = CWGS }

Calculation of the components in crude gas and ash

-------------------------------------------------------------------------------------------------

Ash formation

ZA= EL4_ASH*RFLAS

SA = EL4_ASH*(1-RFLAS)

C-gasification

CV = EL4_C * RGASN

carbon remaining in crude gas and ash

ZC = EL4_C*RCFA* (1-RGASN)

SC = EL4_C*(1-RCFA)*(1-RGASN)

CH4-portion in crude gas

ZCH4= EL4_C*RCCH4N*MCH4/MC

H2S-portion in crude gas

ZH2S = EL4_S * RSH2SN *MH2S/MS

ZCOS = EL4_S * (1-RSH2SN)*MH2S/MS

HCL-portion in crude gas

ZHCL = EL4_CL* MHCL/MCL

N2-portion in crude gas

ZN2= EL4_N+EL1_N*M1M4

AR-portion in crude gas

ZAR= EL4_AR+EL1_AR*M1M4

O2-portion in crude gas

ZO2= 0

Solution of the reactions equation

------------------------------------------------------

The 4 components in the crude gas

ZCO2

ZCO

ZH2

ZH2O

are calculated from

the shift balanceSH = CO2*H2/(CO*H2O),

the C-balance,

the H-balance,

the O-balance

Calculation of the crude gas components

------------------------------------------------------

ZSUM = ZN2+ZO2+ZAR+ZH2O+ZCO2+ZCO+ZCOS+ZH2+ZH2S+ZCH4+ZHCL+ZC+ZA

d2tod4 =ZSUM

XN2 = ZN2/ZSUM

XO2 = ZO2/ZSUM

etc.

Calculation of the ash components

-----------------------------------------------------

ASUM = SA+SC

M5/M4 =ASUM

A = SA/ASUM

C = SC/ASUM

Equations for pressure

==============================

F = 1.0

F = (M1/M1N) ** 2 for GLOBAL = off-design

DP12 = DP12N * F

P2 = P1 - DP12

P4 = P1

P3 = P1

P4 = P5

Calculations for enthalpy

===========================

T5 = TASHE

H5 = f(P5,T5)

M2 = M1 + M3 + M4 - M5

H2 = (M1 * H1 + M3 * H3 + M4 *(H4+NCV4) - M5 * H5)/M2 - NCV2

Calculations for mass flow

============================

M1 = M1M4 * M4

M2 = M2M4 * M4

M3 = M3M4 * M4

M5 = M5M4 * M4

Component Displays

Display Option 1

Example

Click here >> Component 50 Demo << to load an example.

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Combustion Chambers and Reactors

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