Boiler

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General Description

The Boiler model requires a feed water inlet and produces steam, either saturated or superheated and a blow-down water stream. The model calculates the energy required to produce the steam.

The user can set the following parameters:

  • The Temperature and Pressure of the produced Steam;
  • The required drum pressure; and
  • The blowdown fraction; and
  • The Efficiency of the Boiler.

If the user sets a Demand value in the Steam pipe, then the Boiler unit will calculate the required amount of feed water to satisfy the steam demand plus the blowdown stream. This required value will be passed to the feed water inlet pipe. For an example on how to set up the boiler in steam out demand mode, please see Hints and comments below. Alternatively, in Build 137 or later, there is an option in the model itself to set the required steam flow using the new SteamOutDemand function.

This simple Boiler model does not include a Heater section. Therefore, there is no requirement for the user to specify the fuel type or the method of heating the water and steam. However, the unit does calculate the energy required by the boiler and therefore this information can be used elsewhere to set the amount of fuel required by the boiler.

Note: The Boiler & Combustion Project, which is distributed with SysCAD in the Examples folder, demonstrates the use of this model.

New in SysCAD 9.3:

  1. The user may attach a Hot stream (usually containing hot gases) to the Heat Exchange connections on the Boiler model and the model will remove the required amount of energy from the Hot stream to accomplish the boiler steam conditions.
  2. The user may select between saturated or superheated steam for the final steam conditions.

Diagram

Models-Boiler.png

The diagram shows the default drawing of the Boiler, with the connecting streams. The physical location of the connections is not important; the user may connect the streams to any position on the drawing.

Inputs and Outputs

Label Required
Optional
Input
Output
Number of Connections Description
Min Max.
Feed 1 Required In 1 20 The Boiler Feed Water.
Steam 1 Required Out 1 1 The superheated Steam Outlet.
Blowdown Optional Out 0 1 The boiler blow down.
Heat Exchange Optional In 0 10 The hot input stream that provides heat for the boiler, SysCAD 9.3 Only
Heat Exchange Optional Out 0 1 The exhausted heating stream, SysCAD 9.3 Only. NOTE: if Heat Exchange In is connected, then this stream must also be connected.

Behaviour when Model is OFF

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

  • No energy will be added to the incoming feed water stream, and hence no evaporation or heating will occur.
  • If a stream is connected to the 'Blowdown' connection, then all the feed flowing into the unit will flow out of the 'Blowdown' pipe (at the incoming temperature and pressure).
  • If there is no stream connected to the 'Blowdown' connection, then all of the feed will flow out of the Steam connection (at the incoming temperature and pressure).

In SysCAD 9.3:

  • If Heat Exchange streams are connected, Heat exchange In will exit Heat Exchange Out with no heat exchange.

Model Theory

The Boiler is designed to

  1. Heat a stream of high pressure Boiler Feed Water to Saturated conditions at the specified Drum pressure.
  2. A specified fraction of the saturated liquid is split off to blow down. A typical blow down is 2 to 8%.
  3. The remaining liquor is heated to vapour at the specified outlet temperature and pressure (superheated steam).

The energy required to do the above divided by the boiler efficiency is reported as fuel energy required.

Assumptions and Limitations

  1. The Feed (Boiler Feed Water) stream will contain water and is at a pressure higher than the Boiler Drum pressure.
  2. The drum pressure should be higher than the outlet steam pressure.
  3. All feed water will be evaporated to steam. Thus the outlet steam conditions specified must be at saturated or superheated conditions.
  4. Heat Exchanger Out temperature must be higher than the Drum Temperature, to avoid temperature cross over error. SysCAD 9.3 Only.

Data Sections

The default sections and variable names are described in detail in the following tables. The default Boiler access window may consist of a number of sections. This number may increase, based on user configuration.

  1. Boiler tab - The first tab contains general information relating to the unit as well as a tick box for ShowQFeed.
  2. QFeed - Optional tab, only visible if ShowQFeed is enabled. This page shows the properties of the combined feed to the unit.
  3. Info tab - contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  4. Links tab - contains a summary table for all the input and output streams.
  5. Audit tab - contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

Boiler Page

Unit Type: Boiler - The first tab page in the access window will have this name. NOTE: Variables in this table has been updated to SysCAD 9.3 conventions.

Tag (Long/Short)

Input / Calc

Description/Calculated Variables / Options

Common Data on First Tab Page

Requirements

On Tick Box If this option is deselected, the boiler will not be operational and thus all material will report to the blow down stream, if it is connected.
SteamSpecification / SteamSpec
(Only available in SysCAD 9.3)
T and P Both TemperatureReqd and PressureReqd can be user specified.
SuperHeat T,P / SuperHeat Both TemperatureReqd and PressureReqd can be user specified, TemperatureReqd must be greater than or equal to the Saturated Temperature at the specified pressure.
SuperHeat dT,P Only available in Build 137 or later. Both SuperHeatReqd and PressureReqd can be user specified, SuperHeatReqd must be greater than or equal to zero, so that TemperatureReqd will be greater than or equal to the Saturated Temperature at the specified pressure.
Saturated T TemperatureReqd can be user specified, PressureReqd is Saturated pressure at the specified temperature.
Saturated P PressureReqd can be user specified, TemperatureReqd is Saturated temperature at the specified pressure.
TemperatureReqd / T_Reqd Input / Display The temperature required for the outlet steam. Note: this must be >= Saturation Temperature @ outlet pressure.
PressureReqd / P_Reqd Input The pressure required for the outlet steam. Note: This must be lower than or equal to the drum pressure.
SuperHeatReqd Input Only visible if SuperHeat dT,P is chosen for the SteamSpecification. The degrees of superheat required for the outlet steam. Note: this must be >= 0.
DrumP_Reqd Input The drum pressure. Note: Feed Water P > Drum P >= outlet P.
Blowdown Input The amount of boiler blow down. Note this will be ignored (assumed 0) if the physical blowdown connection is not present.
Efficiency Input This is the efficiency of the boiler. This value is used when calculating the energy required by the boiler.
SteamOutDemand
(Only available in Build 137 or later)
None The amount of steam produced will be a function of the feed flow and unit configuration.
Fixed Flow The user can specified the desired mass flow of steam to be produced. This requirement will be fed back to the feed stream/s using the General Demand functionality.
Flow From Tag The user can specify a tag that contains the desired mass flow of steam to be produced. This requirement will be fed back to the feed stream/s using the General Demand functionality.
MassFlowReqd / QmReqd Input This field is only visible if Fixed Flow is chosen for SteamOutDemand. The required mass flow of steam to be produced.
QmReqdTag Input This field is only visible if Flow From Tag is chosen for SteamOutDemand. The required SysCAD Tag for desired mass flow of steam to be produced, e.g. P_001.Qm (t/h).
QmReqd.Meas Calc This field is only visible if Flow From Tag is chosen for SteamOutDemand. The current value of the SysCAD Tag for the desired steam flow.
QmReqdFactor Input This field is only visible if Flow From Tag is chosen for SteamOutDemand. The mass flow factor. Desired mass flow = QmReqd.Meas * QmReqdFactor. The Factor must be ≥ 0.

Options

ShowQFeed Tick Box QFeed and associated tab pages (eg Sp) will become visible, showing the properties of the combined feed stream. See Material Flow Section.

Feed

Feed.MassFlow / Feed.Qm Calc The total mass flow of the combined Feed stream.
Feed.Temperature / Feed.T Calc The temperature of the combined Feed stream.
Feed.Pressure / Feed.P Calc Only available in Build 137 or later. The pressure of the combined Feed stream. If different feed streams have different pressures, then the lowest pressure is used.

Drum

DrumTemperature / DrumT Calc Drum Temperature. This is the saturation temperature at the Drum Pressure.

Energy

HeatReqd1 Calc The energy required for heating boiler feed water to Saturation Temperature at the Drum Pressure.
HeatReqd2 Calc The energy required to evaporate all the preheated water (less boiler blow down) to the required outlet temperature and pressure.
TotalHeatReqd / TtlHeatReqd Calc The Total Heat (energy) required = HeatRqd1 + HeatRqd2
FuelEnergyReqd Calc This is the amount of fuel required to run the boiler = Total Heat Required / Boiler Efficiency.
HeatFlow Calc This is the amount of energy lost due to inefficiency. HeatFlow = Total Heat Required - Fuel Energy Required. Since this is a loss of energy, it will be displayed as negative heat flow.

Blowdown

BlowDown.MassFlow / BlowDown.Qm Calc This is the mass flow of the boiler blow down.
BlowDown.Temperature / BlowDown.T Calc Drum Temperature.
BlowDown.Pressure / BlowDown.P Calc Drum Pressure.

Steam

SteamOut.MassFlow / SteamOut.Qm Calc This is the mass flow of the boiler steam outlet.
SteamOut.Temperature / SteamOut.T Calc The boiler steam outlet temperature.
SteamOut.Pressure / SteamOut.P Calc The boiler steam outlet pressure.
SteamOut.SatT Calc The boiler steam outlet Saturation Temperature.
SteamOut.SuperHeat Calc This is the degree of superheat the steam outlet contains. Thus, the temperature above its saturation temperature.

General Demand

(Only visible if Steam outlet pipe (or downstream pipe) has demand specified or using SteamOutDemand functionality)

SteamOut.DemandQm Calc Displays the Steam outlet flowrate required (as specified in the outlet pipe Qm_Demand.Rqd or via the SteamOutDemand settings within the Boiler model).
SteamOut.MassFlow / SteamOut.Qm Calc Displays the Steam outlet actual flowrate
SteamOut.MassFlowErr / SteamOut.QmErr Calc Only available in Build 137 or later. Displays the difference between the Steam outlet flowrate required and Steam outlet actual flowrate (SteamOut.DemandQm - SteamOut.Qm).
Feed.DemandQm Calc Displays the makeup stream flowrate into the Boiler. (This flow is from the feeder with Demand.On selected.)
Feed.FixedQm Calc Displays the remaining feed rates into the Boiler (less the make up stream).

Heat Exchange

(Available in SysCAD 9.3 and only visible if Heat Exchange In and Out are connected)

HX.MassFlow / HX.Qm Calc The Mass flow of the combined Heat Exchange In streams.
HX.TemperatureIn / HX.Ti Calc The Temperature of the combined Heat Exchange In streams.
HX.TemperatureOut / HX.To Calc The Temperature of the Heat Exchange Out stream.
HX.Pressure / HX.P Calc The Pressure of the combined Heat Exchange In streams.
HX.Duty Calc The Heat Exchange Duty.


Hints and Comments

A) Example Project: Boiler and Combustion Example

B) Setting the Boiler Water Makeup on demand mode:

For SysCAD 9.3 Build 137 or later:
  1. Set up one feeder with Demand.On, any remaining feeders must have feed rates defined or cross-page connected.
  2. Set the boiler "SteamOutDemand" field to FixedFlow, then enter a flowrate in the "QmReqd" field.
  3. SysCAD will then calculate how much makeup water is required.

Boiler03.png

For SysCAD 9.3 Build 136 or earlier:
  1. Set up one feeder with Demand.On, any remaining feeders must have feed rates defined or cross-page connected.
  2. Set up the Steam outlet pipe with a demand flowrate in the Qm_Demand.Reqd field. (This can be on a downstream pipe if preferred, the demand will pass back to this pipe.)
  3. SysCAD will then calculate how much makeup water is required.

Boiler02.png

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 

DLL: (Build 136 or earlier)

HeatXch1.dll

Units/Links

Heat Transfer: Boiler

 

DLL: (Build 137 or later)

HeatExchange.dll

Units/Links

Heat Transfer: Boiler

or

Group:

Energy Transfer

Units/Links

Heat Transfer: Boiler

See Project Configuration for more information on adding models to the configuration file.


Insert into Project

 

Insert Unit

Heat Transfer

Boiler

See Insert Unit for general information on inserting units.