Barometric Condenser

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General Description

This is a direct contact cooler. The unit has separate water and steam inlets; and mixture and vapour outlets.

There are two operational modes:

As a stand-alone unit
As part of a Flash Train

The operational mode is decided by the overall configuration of the flowsheet in which the unit is located. If the Barometric Condenser is correctly connected to other units such as a Heat Exchanger or Flash Tank 2, the model may become part of the entire Flash Train. The user does not have to specify whether the unit is part of a Flash Train, SysCAD will do this automatically. Refer to Flash Train for the rules governing this behaviour.

The Barometric Condenser will combine all of the incoming streams to form a homogeneous mixture, rejects heat lost to atmosphere (EHX) and performs any reactions (RB), before flashing the incoming streams. If a vapour vent is connected any non-condensable vapours and excess steam exit via the vapour outlet at flash pressure. The remaining mixture reports to the hotwell and the pressure is changed to the required hotwell pressure before exiting. The unit calculates the temperature, composition and flow rate of the exit streams. All of the liquid is pumped from the mixture outlet at the hotwell pressure.

The optional Environmental Heat Loss (EHX) may be included in the unit to allow the user to specify a heat loss, or gain, between the unit and the environment.

Notes:

The Barometric condenser will perform the VLE calculations on the species specified by the user in the VLE block. This is normally H2O, but it may be any species with VLE information in the Species Database, e.g. NH3. The Help documentation will refer to 'Steam' as the vapour stream, but this may also be the vapour phase of the flashing species if it is NOT H2O.
The Evaporation Project, which is distributed with SysCAD in the Examples folder, demonstrates the use of this model in a SysCAD project.

Diagram

The diagram shows the default drawing of the Barometric Condenser, with the required connecting streams. The vapour connection allows for the removal of non-condensable as well as any excess steam. The user does not have to connect a stream to the vapour outlet.

The physical location of the connections is not important; the user may connect the streams to any position on the drawing. When the user inserts a Barometric Condenser into a flowsheet, they may choose a different drawing from a pull down menu.

Inputs and Outputs

Label	Required Optional	Input Output	Number of Connections		Description
Label	Required Optional	Input Output	Min	Max	Description
Steam	Required	In	1	1	The steam feed to the Barometric Condenser
Water	1 Required	In	1	10	The liquid or slurry feed.
Mixture	Required	Out	1	1	The hot liquid stream, containing the heated water and condensed steam.
Vapour	Optional	Out	0	1	Vent for non-condensable gases and excess steam.

Behaviour when Model is OFF

If the user disables the unit, by un-ticking the On tick box, then the following actions occur:

All streams connected to the inlets will be mixed, but NO condensation will occur in the unit;
If a vapour stream is connected then the steam will flow out of this pipe;
If no vapour stream is connected then the steam will flow out of the mixture pipe with the liquids;
No reactions will occur.

Model Theory

The unit is configured to achieve Vapour:Liquid equilibrium (VLE) at a required pressure using VLE calculations for the user defined species (normally H2O). If non-condensable gases are present these are taken into account through the use of partial pressures. The temperature and amount of material which changes phase is calculated using an adiabatic flash routine¹.

The unit will attempt to condense the steam at the user defined flash pressure or at the steam inlet pressure when used in a flash train. The equilibrium point of the unit will be that of saturated steam plus any Boiling Point Elevation equations that may be associated with the liquor.

Note: In this document when we use the word Steam this refers to the Flash Component vapour, which is normally H2O, but the user may define other flash species.

Steam Requirement Calculations

The user may select either the Approach Temperature or the Delta Temperature to determine the Steam requirement, either if the unit is part of a Flash Train, or in Stand-alone mode:

Approach Temperature = Steam Saturated Temperature - (Heated Liquid Temperature - Heated Liquid BPE).
- The Approach Temperature is normally used in the Alumina industry. In this case, the approach temperature is in terms of Steam partial pressure, which will be the same as total pressure if there are no other gas species present.
Delta Temperature = Steam Temperature - Heated Liquid Temperature.
- The Delta Temperature is normally used in the Potash industry, where the cooling liquor is often brine.

Approach Temperature

Under perfect conditions the unit would be at equilibrium and the heater liquor temperature would be at the saturation pressure of the liquor. This is not normally possible on an operating plant and hence we have an Approach Temperature, which is a measure of the efficiency of the Barometric Condenser. This is also referred to as the Terminal Temperature Difference.

The Approach Temperature is the difference between the Saturation temperature of the Steam at the operating Pressure of the condenser and the outlet temperature of the mixture from the hotwell less the Boiling Point Elevation (BPE) of the heated liquor.

The Approach Temperature may be calculated at the Total Pressure of the unit, or at the Partial Pressure (PP) of the Steam. Any non-condensable gases in either Steam line or the feed liquid line will be used to determine the Partial Pressure values.

Notes:

It is important to use the saturation temperature of Steam, rather than simply the temperature of the incoming Steam, which may be superheated - for example where the Steam is flashing from a liquid with a boiling point elevation.
The Partial Pressure calculations take into account non-condensable gases present in either the Feed liquid or Steam streams.
Typical approach temperatures would 2°C to 10°C.

Reference

Coker, A.K., Equilibrium flash calculations quickly computed on PC, Oil & Gas Journal, Jan 14, 1991.

Flowchart

The following shows the sequence of events if sub model options are switched on. See next heading for more information.

Data Sections

The default sections and variable names are described in detail in the following tables. The default Barometric Condenser access window may consist of a number of sections, which may change, based on user configuration.

BaroCond tab - This first tab contains general information relating to the unit.
RB - Optional tab, only visible if the Reactions are enabled.
EHX - Optional tab, only visible if the EnvironHX is enabled.
QFeed - Optional tab, only visible if ShowQFeed is enabled. This page shows the properties of the mixed stream as the feed to the unit.
- This is before any sub-models models or condensing.
QProd - This page shows the properties of the unit contents as a single stream before the exit stream flows are calculated.
Info tab - contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
Links tab - contains a summary table for all the input and output streams.
Audit tab - contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.