Component 86: SCR-DeNOx-Plant (NOx-Removal)

In This Topic

Component 86: SCR-DeNOX-Plant (NOX-removal)

Specifications

Line connections
1	Flue gas inlet
2	Flue gas outlet
3	NH3-inlet

General User Input Values Characteristic lines Physics Used Displays Example

General

Component 86 simulates a denitrogenization plant (SCR). Here, the fraction of nitrogen oxide (NO, NO2) is reduced in the flue gas by using ammonia (NH3) or a mixture containing ammonia. The scope of this reduction is determined by three characteristic lines.

The first characteristic line CRNO1 describes, how the fraction of the remaining nitrogen oxide (NOX2/NOX1) changes depending on the flue gas mass flow. This characteristic line refers to the nominal mass flow determined in the design calculation.

The second characteristic line CRNO2 describes, how the fraction of the remaining nitrogen oxide changes when the supply of ammonia is increased. The reference point of this characteristic line is the stoichiometric minimum of the ammonia quantity M3MIN, which is needed for the desired conversion (i.e. not the nominal mass flow!). This characteristic line needs to be defined only for values > 1. Caution: In case of this characteristic line the y-values must cover the entire possible range, because the program here searches the x-value for a given y. Especially, it should go asymptotically to infinity for small values of M3/M3MIN.

The third characteristic line CRNO3 describes the effect of the temperature on the fraction of the remaining nitrogen oxide. This characteristic line is not normalized, i.e. the temperatures must be entered directly.

In the design case the outlet concentrations of NOx and NH3 must be specified by NOXN und NH3N. The necessary quantity of ammonia is then calculated.

In off-design mode there are two calculation possibilities set through the flag FSPEC:

The desired NOx-concentration in the flue gas outlet is defined as the specification value NOXT. EBSILON^®Professional then calculates the necessary quantity of ammonia M3.
The quantity of ammonia M3 is set on line 3 . EBSILON^®Professional then calculates the NOx-concentration, which can be achieved at the outlet.

In both the cases, the input values of the flue gas (mass flow, pressure, temperature as well as the material composition) on line 1 must be specified. On line 3, NH3 must be entered in the composition; moreover, pressure and temperature must also be specified. The program calculates the properties of the flue gas coming out (line 2).

Pressure drop limitations:
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.
(See: Model Settings -> Simulation -> Calculation)

The component considers the following reactions, which take place in the catalyst at 300 - 400 °C in the presence of oxygen:

4 NO + O2 + 4 NH3 --> 4 N2 + 6 H2O

2 NO2 + O2 + 4 NH3 ---> 3 N2 + 6 H2O

User Input Values

FCON	Flag for interpreting the given concentrations (NOXN, NOXT, NH3N, NH3MAX) Like in Parent Profile (Sub Profile option only) Expression = 1: Mole fraction at reference O2 concentration = 2: Normalized mass fraction at reference O2 concentration The difference between FCON=1 and FCON=2 is the fact that for FCON=2 you have to specify some kind of "density" for the pollutant fraction, i.e. mass of pollutant per volume of flue gas (therefore the dimension mg/Nm³). If you divide this density by the density of the pure pollutant, you get the corresponding volume fraction. In the implementation, the case FCON=2 is traced back to FCON=1, using a constant density of 0.759629 kg/m³ for NH3 and 2.05204 kg/m³ for NOx (independent of NOSPL).
NOXN	Outlet-NOX-concentration (nominal) This value is used only for the design calculation
FSPEC	Flag for operation type Like in Parent Profile (Sub Profile option only) Expression = 1: NOXT given, M3 calculated = 2: M3 given from outside, NOX calculated at the outlet
NOXT	NOX-reference-concentration (in off-design) This value is used only for the off-design calculation
NH3N	NH3-concentration at the outlet (nominal) This value is used only for the design calculation
NH3MAX	Maximum NH3-concentration at the outlet A warning message is given if this concentration is exceeded
TMIN	Minimum temperature for NOX-separation
TMAX	Maximum temperature for NOX-separation
DP12N	Pressure drop within flue gas (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.
RNON	NOX-reduction NOX2/NOX1 (nominal)
RNO1N	Nominal reduction for characteristic line 1
RNO2N	Nominal reduction for characteristic line 2
RNO3N	Nominal reduction for characteristic line 3
NH3V	Relative NH3-mass flow M3N/M3min (nominal)
M1N	Inlet flue gas mass flow (nominal)
M3N	Ammonia mass flow (nominal)
V1N	Specific volume at the inlet (nominal)

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

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

RNO	Calculated reduction coefficient
RNOXO2	NOX concentration at the outlet translated to reference O2 concentration, depending on FCON as molar or normalized mass fraction
RNH3O2	NH3 concentration at the outlet translated to reference O2 concentration, depending on FCON as molar or normalized mass fraction
M3MIN	stoichiometric minimum value for the ammonia supply (quantity required for the reaction if the entire ammonia reacted and no residual ammonia remained in the exhaust gas)
M3M3MIN	ratio M3 to M3MIN
LNH3	absolute NH3 slip (NH3 mass flow at the exhaust gas outlet): LNH3 = $._2.M*$._2.XHN3
LRNH3	relative NH3 slip (NH3 mass flow at the exhaust gas outlet in relation to the NH3 supply): LRNH3 = $._2.M$._2.XHN3 / ($._1.M$._1.XHN3 + $._3.M*$._3.XHN3) Also when using 2-phase fluid or binary mixture at connection point 3.
RCRNO1	value calculated from characteristic line CRNO1
RCRNO2	value calculated from characteristic line CRNO2
RCRNO3	value calculated from characteristic line CRNO3

Characteristic Lines

Characteristic line 1, CRNO1: Effect of the flue gas mass flow on the NOx-reduction

NOX-Removal (NOX2/NOX1in mol%) = 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         NOX2/NOX1              1^st point
                        2         NOX2/NOX1              2^nd point
                        .
                        N        NOX2/NOX1               last point

Characteristic line 2, CRNO2: Effect of the ammonia mass flow on the NOx-reduction

NOX-Removal (NOX2/NOX1 in mol%) = f(M3/M3MIN)

     X-X-axis      1          M3/M3MIN                1^st point
                        2          M3/M3MIN                2^nd point
                        .
                      N         M3/M3MIN                last point

     Y-axis          1         NOX2/NOX1              1^st point
                        2         NOX2/NOX1              2^nd point
                        .
                        N        NOX2/NOX1               last point

Characteristic line 3, CRNO3 : Effect of the flue gas temperature on the NOx-reduction

NOX-Removal (NOX2/NOX1 in mol%)= f(T1)

     X-axis         1         T1                               1^st point
                        2          T1                               2^nd point
                        .
                      N         T1                               last point

     Y-axis         1         NOX2/NOX1              1^st point
                        2          NOX2/NOX1               2^nd point
                        .
                        N         NOX2/NOX1               last point

Physics Used

Equations

All cases

P2 = P1 DP12

M2= M1 + M3

H2 = ((H1+DH_REAK)*M1+(H3-DH_VERD)*M3)/M2

DH_REAK: Reaction heat of reactions 1), 2)

DH_VERD: Heat of evaporation of NH3

Design case

(Simulation flag:

GLOBAL = Design case

and

FMODE = GLOBAL)

Pressure drop

P2 = P1 DP12N

Energy balance

H2 = ((H1+DH_REAK)*M1+(H3-DH_VERD)*M3)/M2

DH_REAK: Reaction heat of reactions1), 2)

DH_VERD: Heat of evaporation of NH3

Mass balance

M2= M1 + M3

Calculation of the reduction

Input: Concentrations of flow 1

Default Nox-reference = NOXN

Default NH3-reference = NH3N

Calculation:

Concentrations of flow 2 and

mass flow 3 as per

1) 4 NO + O2 + 4 NH3 = 4 N2 + 6 H2O

2) 2 NO2 + O2 + 4 NH3 = 3 N2 + 6 H2O

3) NH3 = NH3N

4) NOX=NOXN

5) Split NO/NO2 remains intact

Mass flow 3 (minimum) as per

1) 4 NO + O2 + 4 NH3 = 4 N2 + 6 H2O

2) 2 NO2 + O2 + 4 NH3 = 3 N2 + 6 H2O

3) NH3 = 0

4) NOX=NOXN

5) Split NO/NO2 remains intact

Ratio VNH3=M3/M3MIN

RNO = NOX(Flow 2)/NOX(Flow 1) (in mol%)

RNO1N from characteristic line 1 with M1/M1M = 1

RNO2N from characteristic line 2 with VNH3

RNO3N from characteristic line 3 with T1=T1N in limits TMIN/TMAX

Off-design

(Simulation flag:

GLOBAL = Off-design

FMODE = Local Off-design)

Pressure drop

V1: Specific volume of flow 1

DP12 = DP12N*(M1/M1N)**2*(V1/V1N)

P2 = P1 DP12

Energy balance

H2 = ((H1+DH_REAK)*M1+(H3-DH_VERD)*M3)/M2

DH_REAK: Reaction heat of reactions 1), 2)

DH_VERD: Heat of evaporation of NH3

Mass balance

M2= M1 + M3

Calculation of reduction

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

IF FSPEC = 1 THEN

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

Input: Concentrations of flow 1

Default Nox-reference = NOXT

Default NH3-reference = NH3MAX

Calculation:

Concentrations of flow 2 and

mass flow 3 according to

1) 4 NO + O2 + 4 NH3 = 4 N2 + 6 H2O

2) 2 NO2 + O2 + 4 NH3 = 3 N2 + 6 H2O

3) NH3 = NH3MAX

4) NOX = NOXT

5) Split NO/NO2 remains intact

Mass flow 3 (minimum) according to

1) 4 NO + O2 + 4 NH3 = 4 N2 + 6 H2O

2) 2 NO2 + O2 + 4 NH3 = 3 N2 + 6 H2O

3) NH3 = 0

4) NOX = NOXT

5) Split NO/NO2 remains intact

Maximum ratio VNH3MAX=M3/M3MIN

RNO = NOX(flow 2)/NOX(flow 1) (in mol%)

RNO1 from characteristic line 1 with M1/M1M

RNO3 from characteristic line 3 with T1 in limits TMIN/TMAX

RNO2 = RNO2N*(RNO/RNON)/((RNO1/RNO1N)*(RNO3/RNO3N))

VNH3 from characteristic line 2 with RNO2

ITERATION 1 START

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

Input: Concentrations of flow 1

Default NOX-reference = NOXT

Default VNH3

Calculation: Concentrations of flow 2 and

mass flow 3 according to

1) 4 NO + O2 + 4 NH3 = 4 N2 + 6 H2O

2) 2 NO2 + O2 + 4 NH3 = 3 N2 + 6 H2O

3) NH3 = fromVNH3

4) NOX = NOXT

5) Split NO/NO2 remains intact

RNO = NOX(flow 2)/NOX(flow 1) (in mol%)

RNO1 from characteristic line 1 with M1/M1M

RNO3 from characteristic line 3 with T1 in limits TMIN/TMAX

RNO2 = RNO2N*(RNO/RNON)/((RNO1/RNO1N)*(RNO3/RNO3N))

VNH3 from characteristic line 2 with RNO2

IF RNO2 constant THEN

ITERATION 1 END

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

IF FSPEC = 2 THEN

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

NOX = NOXT

ITERATION 2 START

Same algorithm as for FSPEC = 1 but with

1) NOX variable

2) M3actual as function of NOX

3) Iteration according to REGULA-FALSI by varying NOX

M3actual = M3

ITERATION 2 END

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

FSPEC END

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

V1: Specific volume flow 1

DP12 = DP12N*(M1/M1N)**2*(V1/V1N)

Component Displays

Display Option 1

Example

Click here >> Component 86 Demo << to load an example.