Burner L2 Dynamic fuelDrying

Created Montag 24 Juni 2019


A 0d-burner volume model with dynamic mass and energy balance considering heat exchange with neighbouring furnace models and boiler casing walls. In addition to the other burner models this one dries unburnt fuel leaving the burner volume.

1. Purpose of Model



This model is well suited to model the burner areas of a boiler. In combination with Hopper_L2, FlameRoom L2 Dynamic and FlameRoomWithTubeBundle L2 Dynamic models a 1-dimensional boiler model can be developed which is discretised in flow direction. Radiative and/or convective heat transfer between linked furnace models or boiler casing walls can be calculated using replaceable models.

2. Level of Detail, Physical Effects Considered and Physical Insight


2.1 Level of Detail

Referring to Brunnemann et al. [1], this model refers to the level of detail L2.

2.2 Physical Effects Considered


2.3 Level of Insight


Heat Transfer


The following listed heat transfer models are the recommended ones. Other heat transfer models (e.g. generic ones: Generic HT) can be chosen to simplify the model.

top (radiation to neighbored furnace volumes)

wall (radiation or convection to boiler casing walls) :


Pressure Loss

No pressure losses are considered.

Combustion

The following replaceable models are used to model the combustion of fuel inside the different furnace volume models. The model for the chemical conversion of fuel can be chosen with the replaceable model ChemicalReactions. The models BurningTime and ParticleMigration are used to calculate the amount of fuel burned inside the current furnace volume. If the preset burning time is lower than the time span for the fuel particles needed to travel though the current furnace volume, the complete amount of fuel is burned inside this component. If the burning timer is higher than the particle migration time, unburnt fuel is entering the following downstream furnace model.

Chemical Reaction

Burning Time

Particle Migration

3. Limits of Validity

4. Interfaces


4.1 Physical Connectors


Basics:Interfaces:FuelSlagFlueGas inlet inlet
Basics:Interfaces:FuelSlagFlueGas outlet outlet
Basics:Interfaces:FuelFlueGas inlet fuelFlueGas_inlet

Basics:Interfaces:HeatPort a heat_top
Basics:Interfaces:HeatPort a heat_bottom
Basics:Interfaces:HeatPort a heat_wall

4.2 Medium Models

5. Nomenclature


6. Governing Equations


6.1 System Description and General model approach

This model is used to build up furnace models with 1-dimensional discretisation and is used together with other models of the furnace package.

The following sketch shows the modelling principle of the component. The flows of fuel and flue gas are mixed separately before being processed inside the bulk zone with nonstationary energy and mass balance (only thermal expansion considered). The amount of burned fuel takes the particle migration time and the burning time from the replaceable model BurningTime into account. The lower heating value of the fuel can either be set in the parameter dialog or is calculated from the fuel's elementary analysis according to the "Verbandsformel" from [?]. Based on the elemental composition of the used fuel and a generalised ideal fuel combustion, the formation enthalpy is calculated to be considered in the energy balance.
All chemical reactions are calculated inside the replaceable model CoalReactionZone which determines the resulting flue gas mixture according to a combustion calculation and fixed parameters for the produced amount of CO and NOx, as well as the fraction of ash turned into slag. The slag moves through the furnace models in reverse direction (downwards). The slag outlet temperature is given by a parameter.


The component exchanges heat flows with up- and downstream models (via the heat ports heat_top and heat_bottom) as well as the surrounding walls (heat_wall) which are calculated with replaceable models for heat transfer correlations. If radiative heat transfer correlations are used inside a 1-dimensional discretised (sequential model arrangement) furnace, radiative heat flows are exchanged between the directly connected models (via heat ports top and bottom) and the surrounding walls (heat port wall). The calculation is performed with view factors which are calculated inside the heat transfer correlations. The following sketch shows the modelling principle for radiative heat transfer between the sequential arranged volumes and the calculation formula for the view factor. The amount of emitted radiation is calculated for a three dimensional volume, but the radiative heat flow between the models is assumed to be exchanged between two flat surfaces with the size of the furnace cross sectional area.


6.2 General Model Equations


In the following equations, ξ describes a vector filled with mass fractions of fuel or gas compositions. The indexed brackets are used to account for a single composition species. Please have a look at the picture in the system description for an overview of the mass flow handling and mixture before entering the combustion zone.

The overall gas mass inside the volume is calculated with the mean value of the the inflowing gas mixture and the bulk density as follows:

The solid particles of fuel (here mainly coal) are neglected.

An auxiliary, static energy balance for the inflowing gas mixture is modelled to calculate the inlet mixture enthalpy:

The mixture composition is calculated as follows:

The fuel composition which enters the volume is calculated in the same manner:

The non-stationary mass balance for the flue gas is calculated as follows. Except the ash fraction, the amount of burned fuel is added to the flue gas:

with

The mass balances of slag and fuel are modelled stationary and are not effected by the thermal expansion of the flue gas:


The molar low rates of the educts are calculated as follows:

The amount of excess air is calculated for the whole control volume (λtot) and for the air/fuel mixture entering by the side inlet (λprim). Therefore the stoichiometric amount of air required to burn the side inlet (burner) fuel mass flow completely is calculated:

For the calculation of the total stoichiometric amount of air, the fuel diffusivity is taken into account too:

The fuel diffusity is calculated with the dwell time of the flue gas and the burning time of the (coal) particles to estimate the amount of fuel burned inside the control volume.

The dwell time of the fuel particles is calculated with the migration speed (calculated inside MeanMigrationSpeed for example) :

The amount of air required is calculated with the mass fraction of oxygen inside the flue gas:


The excess air for the side or burner inlet (primary) and the overall volume (not supposed to use as control parameter), including unburnt fuel from lower combustion chambers, is calculated as follows:


The lower heating value of the burnt fuel (and the unburnt fuel leaving the volume) is calculated as a mixture of the unburnt fuel from upstream sections and the fuel entering the volume through the burner inlet.

The lower heating value is used to calculate the formation enthalpy of the used fuel. Therefore the flue gas products of an idealised combustion of 1 kg of fuel per second with the given composition are needed which are calculated inside the replaceable model CoalReactionZone. The produced flue gas flow per combustion of 1 kg of fuel per second is calculated as follows:

With the composition:

The formation enthalpy is calculated as follows:

In addition the formation enthalpy for the dried fuel leaving the volume is calculated in the same way with the fuel composition after evaporation of water.

The flue gas enthalpy inside the control volume, which is used to calculate the outlet temperature, is calculated with the following energy balance. In comparison to the energy balance of the Burner L2 Dynamic, here the outlet formation enthalpy of the coal as well as evaporated water inside the fuel are considered.

The resulting flue gas composition after combustion is calculated with the burned fuel mass and evaporated water:

The pressures are calculated with the flue gas pressure losses:

The resulting control volume temperature Tfg(hfg)as well as the composition ξfg are set to the corresponding stream connector variables of the component.

Summary

A summary record is available which bundles important component values.


7. Remarks for Usage


8. Validation

The adiabatic outlet temperature of this model has been validated with Ebsilon calculations at identical boundary conditions.

The image below shows the flue gas temperatures over the furnace height. As can be seen there is a good compliance with the design values.

9. References

[1] Johannes Brunnemann and Friedrich Gottelt, Kai Wellner, Ala Renz, André Thüring, Volker Röder, Christoph Hasenbein, Christian Schulze, Gerhard Schmitz, Jörg Eiden: "Status of ClaRaCCS: Modelling and Simulation of Coal-Fired Power Plants with CO2 capture", 9th Modelica Conference, Munich, Germany, 2012

10. Authorship and Copyright Statement for original (initial) Contribution

Author:
DYNCAP/DYNSTART development team, Copyright 2011 - 2022.
Remarks:
This component was developed during DYNCAP/DYNSTART projects.
Acknowledgements:
ClaRa originated from the collaborative research projects DYNCAP and DYNSTART. Both research projects were supported by the German Federal Ministry for Economic Affairs and Energy (FKZ 03ET2009 and FKZ 03ET7060).
CLA:
The author(s) have agreed to ClaRa CLA, version 1.0. See https://claralib.com/pdf/CLA.pdf
By agreeing to ClaRa CLA, version 1.0 the author has granted the ClaRa development team a permanent right to use and modify his initial contribution as well as to publish it or its modified versions under the 3-clause BSD License.

11. Version History


Backlinks: ClaRa:SubSystems:Furnace:BurnerSlice L4