FeedWaterTank L2

Created Monday 10 June 2013

A feedwater tank model with ideal phase separation depending on the filling level. Appropriate when reduced precision during transients is sufficient. No venting or auxiliary condensate ports supported.

1. Purpose of Model

In most cases the degasification of the feedwater is integrated in the feedwater storage tank. There are two main concepts for degasification. For small and medium capacities trickling deaerators are common, see left illustration below. In this type the condensate trickles through a structured or unstructured package or through a set of trickle plates thus increasing the condensate's surface allowing the gas to be dispensed from the liquid. For large capacities this enhancement of the liquid surface is achieved by spraying the condensate into the vessel.
Both types can be modelled with this component model. This model assumes an ideal heat and mass transfer between the liquid and vapour phase resulting in feedwater supply at the vessels boiling enthalpy. Note that the storage capacity of the package for trickling deaerators is not considered. Furthermore no ports for venting the exhaust vapour and the supply of fresh water are provided.

The model suits well if high transients with temporary subcooling or two-phase states in the liquid and vapour phase can be ruled out. If the precise transients in the tank are of interest the more complex model FeedWatertank L3 is recommended. This might be the case when short term changes of tapping mass flows are considered, e.g. applying condensate stop for primary control.

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 because the system is modeled with the use of balance equations, which are spatially averaged over the component.

2.2 Physical Effects Considered

dynamic mass conservation in the tank volume
dynamic energy conservation in the tank volume, neglecting changes in kinetic energy
pressure differences due to friction and geostatic pressure
ideal, level-dependent phase separation
ideal mixing of tapping mass flow and condensate mass flow

2.3 Level of Insight

Heat Transfer

no heat transfer to the surrounding

Pressure Loss

PhaseSeparation

Basics:ControlVolumes:Fundamentals:SpatialDistributionAspects:IdeallySeparated :
Ideal phase separation, state at ports are either on the dew line or at the boiling line. The states depend on the filling level.

3. Limits of Validity

Subcooling of the condensate is not supported due to the fact that only a lumped balancing of liquid and steam is considered at the condensing side. This implies that the outlet state equals the dew state which conflicts with subcooling.

4. Interfaces

5. Nomenclature

— no model-specific nomenclature —

6. Governing Equations

6.1 System Description and General model approach

The model applies balances for mass and energy for the tank volume. There is no separate balancing of steam and liquid phase. The model instantiates a Basics:ControlVolumes:FluidVolumes:VolumeVLE L2

Summary

A summary is available including the following:

an outline record:

and three records of type FlangeVLE named heating steam, condensate and feedwater
please note that there is further summary data available from the instantiated class VolumeVLE 2

7. Remarks for Usage

It is strongly recommended to initialise this model with a fixed level. Doing so it can be ensured that the pump that is usually located upstream the feedwater pump gets liquid water.

8. Validation

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 Simulationof 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

2012 -v 0.1 - initial implementation - Friedrich Gottelt, XRG Simulation

Backlinks: ClaRa:Components:MechanicalSeparation:FeedWaterTank L3