RegenerativeAirPreheaterPrimaryAndSecondaryAir L4

Created Thursday 20 March 2014

A simplified model for simulation of regenerative air preheaters with different sections for primary and secondary air.

1. Purpose of Model


This model is used to simulate regenerative air preheaters with different sections for primary and secondary air in a simplified way due to neglection of a moving storage mass. This simplification is compensated by a special heat transfer correlation. The heat transfer correlation used can be found in Effenberger [2].

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 L4.

2.2 Physical Effects Considered


2.3 Level of Insight


Heat Transfer

Pressure Loss



3. Limits of Validity


4. Interfaces


4.1 Physical Connectors


Basics:Interfaces:GasPortIn primaryAirInlet
Basics:Interfaces:GasPortOut primaryAirOutlet
Basics:Interfaces:GasPortIn secondaryAirInlet
Basics:Interfaces:GasPortOut secondaryAirOutlet
Basics:Interfaces:GasPortIn flueGasInlet
Basics:Interfaces:GasPortOut flueGasOutlet

5. Nomenclature


6. Governing Equations


6.1 System Description and General model approach


This model of an regenerative air preheater is build up from submodels of four VolumeGas L4 components, two ThinWall L2 models and different junction elements FlueGasJunction L2 and ThreeWayValveGas L1 simple. Compared to the simple air preheater model RegenerativeAirPreheater L4, this one is modelled with two different air paths for primary and secondary air. Because the rotation of the storage mas is not modelled (the recommended heat transfer correlation compensates this), internally the flue gas is also split up into two paths by a factor calculated with the cross sectional areas hit by primary and secondary air.
Gas cell arrays are used to discretise the hot and the cold side of this heat exchanger. Mass leakages are considered from hot primary air to hot secondary air path and from from cold secondary air to cold flue gas path and are calculated with a constant factor inside controllable splitters. The storage mass can be calculated out of the given parameters or set with a parameter m_fixed.



Summary

A summary record is available which bundles important component values.

7. Remarks for Usage


8. Validation


The outlet temperatures of this air preheater model were compared within two simulated scenarios. In the first scenario the results of a stationary simulation point are compared with the design values of an air preheater. In the second scenario the results of a dynamic simulation with a step of the secondary air inlet temperature are compared with calculation results of an established power plant simulator software for training purposes.

Scenario 1: Stationary operation


Model name:
ClaRa.Components.HeatExchangers.Check.Airpreheater_SP_validation_stat

Model parameters:
The simulation of the stationary operation is carried out with the following inlet conditions:

The regenerative air preheater is parametrised with the following reference values. Concerning the geometry, only the height and diameter of the air preheater were known. Thus, the parameter N_sp (number of storage plates) was adapted such that the known reference storage mass is met. With the density of the known storage material, a realistic void ratio could be achieved. The percentages of the overall cross sectional area hit by primary/secondary air (and primary/secondary flue gas) are calculated according to the ratio of the reference values of the outlet air mass flows (primary: 80.26 kg/s; secondary: 372.45 kg/s) after losses are regarded. The hub cross section is subtracted from the flue gas area.

Simulation Setup:
The model is simulated until stationary conditions are reached.

Result:
The following temperature characteristics along the flue gas and air paths are attained from the stationary simulation:

The red circles mark the reference results of the power plant simulator software. The air temperatures are about 15 °C lower compared to the reference outlet temperature of approx. 360 °C (both secondary and primary air). The outlet temperature of the flue gas is about 12 °C higher than the reference value of 120 °C. Nevertheless this result can be regarded as good result for this simplified model neglecting the rotation of the storage mass.

Scenario 2: Dynamic simulation with a step of the secondary air inlet temperature


In this simulation scenario the same air preheater is simulated with measurement input data for the inlet values (mass flow and temperature) of the flue gas, primary and secondary air mass flows, which are fed in after the stationary point is reached. A step of approx. 50 °C is applied in the secondary air inlet temperature.

Model name:
ClaRa.Components.HeatExchangers.Check.Airpreheater_SP_validation_dyn_loadchange

Simulation Setup:
The simulation time should amount 20000 seconds.

Result:
The following diagram shows the simulation results of the different temperatures after the step in the secondary air inlet temperature is applied (the time span needed for the air preheater to become stationary is not shown in this diagram).

There are differences between the outlet temperatures of the Documentation:ClaRa results and the reference simulation values that vary between 3 - 20 °C. Nevertheless this result can be regarded as good result for this simplified model neglecting the rotation of the storage mass.

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
[2] Helmut Effenberger: "Dampferzeugung", Springer-Verlag Berlin Heidelberg New York, 2000, ISBN:3-450-64175-0

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

Date - Version - Description of changes - author/revisor
25.06.2013 - v0.1 - initial implementation of the model - Lasse Nielsen, TLK-Thermo GmbH


Backlinks: ClaRa:Components:HeatExchangers:RegenerativeAirPreheater L4