General Model Thermal (GMT)

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General Description

NOTE: In SysCAD 9.3, Tab page GMT has been renamed SplitT.

This sub-model allows the user to specify different temperatures for the outlet streams from a unit. Units that may have a GMT or SplitT enabled are currently the Tank or Tie. The user may either:

  1. Specify the temperatures for all outlet streams and allow SysCAD to Add/Remove heat to satisfy the requirements OR
  2. Specify n-1 streams to allow the last stream be the balance of the total energy to ensure a conservation of energy across the unit operation.

Note:
The SplitFlows option MUST be selected before the SplitThermal, option is available to the user.

Adding Split Thermal (SplitT) to a Unit

The SplitT is enabled in a unit when the user enables the tickbox for SplitThermal under Options as shown below:

GMT.png


A new Tab page becomes visible, SplitT, that the user can then configure to adjust the outgoing stream temperatures from the unit.

Options

The user may specify a number of different methods for setting the temperature in the exiting streams. Some Examples are shown on the bottom of the page.

  1. Required
    • The user sets the actual required temperature in the outgoing stream.
  2. Change
    • The Change value is the difference between the exiting stream temperature and the Feed temperature to the GMT block, i.e. the actual temperature within the unit.
    • The temperature difference may be limited if ChangeT.Limit is enabled.
  3. FreeDiff
    • The User may set a temperature difference for the selected outlet stream to the streams that are set at Free.
    • The temperature difference may be limited if ChangeT.Limit is enabled.
  4. Free
    • This is the default option. It does not allow the user to set the value of the exiting stream. Therefore, if all streams remain in the default mode, they will leave the unit at the same temperature as the unit temperature.
  5. AllowHX
    • If AllowHX is enabled, then the user may set the values for ALL of the exiting streams, as SysCAD will either add or remove energy from the unit to maintain an energy balance. The values for each stream may be any value.
    • If AllowHX is NOT enabled, then the user may set the values for N - 1 exiting streams, where N is the total number of exiting streams. SysCAD will then adjust the temperature of the Nth stream to maintain an energy balance. The values for each stream may be any value.
  6. User may set the value for only a single stream, if required, and the other streams will then all be at the same (different) temperature.

Data Sections

A description of the variables on the GMT tab page is given here.

Tag/Symbol Input/Calc Description
Mixture temperature before thermal split
Feed.Temp Feedback The temperature of the mixture before splitting of streams - this is the temperature in the unit.
Condition Feedback OK if no errors, otherwise displays error message.
AllowHX Tickbox Selecting this option allows the user to specify temperatures for all outgoing streams. SysCAD will add or remove energy to conserve the energy across the unit operation. Any energy added/removed will be shown on the PowerInput field.
PowerInput FeedBack This is visible when the AllowHX option has been enabled. This shows the amount of energy added or removed in order to achieve temperatures specified by the user.
TIOs.[stream name](IO)...
Order FeedBack This can be changed using the Priority field (if available).
Priority List This is used to change the order of the output streams if the Required or Change modes are selected.
Mode (See
Options and Examples for more info)
Required The user may specify the required temperature of the outlet stream. This temperature may be limited by the temperature change limits specified.
Change The user may specify the required temperature change for the outlet stream. This temperature may be limited by the temperature change limits specified.
FreeDiff The user can set a temperature difference for the selected outlet stream to the streams that are set at Free. For example, if the unit operation has two outlet streams, stream 1 is set at FreeDiff = 10, stream 2 is set at Free, then Stream 1 will be 10 degrees hotter than stream 2 when solved. This temperature may be limited by the temperature change limits specified.
Free The user may not specify any outlet temperature requirements, SysCAD will determine the outlet temperature. If Free is used for all streams then all streams will have the same outlet temperature (same behaviour as when GMT model is not used at all).
TempReqd Input This is visible with mode set to Required, use this to specify the stream outlet temperature.
TempChange Input This is visible with mode set to Change, use this to specify the stream outlet temperature change.
TempDiff Input This is visible with mode set to FreeDiff, use this to specify the stream outlet temperature difference for the current stream and the streams that are set at Free.
TempOut FeedBack This is the outlet temperature for the stream.
Result FeedBack This shows whether the user specified temperature conditions have been achieved.
Temperature change limits
FinalT.Min Input The minimum temperature of the mixture leaving the unit operation. If the balance stream temperature falls below this minimum when the AllowHX option is ticked, heat will be added to make it up to the minimum temperature. If AllowHX option is not selected, all outlet stream temperatures will be adjusted to keep a balance of heat.
FinalT.Max Input The maximum temperature of the mixture leaving the unit operation. If the balance stream temperature is above this maximum when the AllowHX option is ticked, heat will be removed to limit it to the maximum temperature. If AllowHX option is not selected, all outlet stream temperatures will be adjusted to keep a balance of heat.
ChangeT.Limit Tickbox Selecting this option allows the user to specify temperature limits for all outgoing streams. If AllowHX option is selected, SysCAD will add or remove heat to conserve the energy across the unit operation. Any energy added/removed will be shown on the PowerInput field.
ChangeT.MaxDrop Input Only visible if ChangeT.Limit is enabled. This is the maximum amount that any stream be below the Feed temperature of the GMT block.
ChangeT.MaxRise Input Only visible if ChangeT.Limit is enabled. This is the maximum amount that any stream be above the Feed temperature of the GMT block.

Examples

Input Specification SplitT Configuration Results
Required Mode on (1) Stream
  • Feed Temperature = 150°C
  • Two outlet streams P411 and P404
  • P411 = Required Temperature of 130°C
  • AllowHX not enabled.
  • The temperature of P404 cannot be set.
GMT01.png
  • P411 will have a temperature of 130°C (as required)
  • P404 T is higher as the energy removed from P411 is added to P404.
Required Mode on both Streams
  • Feed Temperature = 150°C
  • Two outlet streams P411 and P404
  • P411 = Required Temperature of 130°C
  • AllowHX enabled.
  • With "AllowHX = ON" P404 = Required T of 140°C.
GMT02.png
  • P411 will have a temperature of 130°C (as required)
  • P404 will have a temperature of 140°C (as required)
  • The energy change is shown in PowerInput.
    (The excess energy is removed)
Change Mode on (1) Stream
  • Feed Temperature = 150°C
  • Two outlet streams P411 and P404
  • P411 = Change value of -3°C,
  • AllowHX not enabled.
  • The temperature of P404 cannot be set.
  • The dT may be limited if ChangeT.Limit is enabled.
GMT03.png
  • P411 will have a temperature of (150-3=147)°C (as required)
  • P404 T is higher as the energy removed from P411 is added to P404.
FreeDiff Mode on (1) Stream
  • Feed Temperature = 150°C
  • Two outlet streams P411 and P404
  • P411 = FreeDiff of 3°C,
  • P404 will be 3°C lower than P411.
  • AllowHX not enabled.
  • The dT may be limited if ChangeT.Limit is enabled.
GMT04.png
  • P411 is 3°C higher than P404 as required.

Notes:

  1. If AllowHX is enabled, then the user may set the values for ALL of the exiting streams,
    as SysCAD will either add or remove energy from the unit to maintain an energy balance.
    The values for each stream may be any value.
  2. If AllowHX is NOT enabled, then the user may set the values for N - 1 exiting streams, where N is the total number of exiting streams.
    SysCAD will then adjust the temperature of the Nth stream to maintain an energy balance.
    The values for each stream may be any value.
  3. The user may set the value for only a single stream, if required, and the other streams will then all be at the same (different) temperature.