Evaporation Project

From SysCAD Documentation
Jump to navigation Jump to search

Navigation: User Guide ➔ Example Projects ➔ 10 Alumina: Evaporation


Example 1: Evaporation Project - using Flash Tanks and Heat Exchanges

Evaporation with Cooling Tower.png

Project Location

This is a Steady State project and is stored at:
..\SysCADXXX\Examples\10 Alumina\Evaporation with Cooling Tower Example.spf

Features Demonstrated

  1. Shows the use of Bayer3 properties model.
  2. Shows how to set up a multistage Flash Trains.
  3. Shows how to set up Barometric Condenser
  4. Shows how to set up a Cooling Tower.
  5. Shows how to set up a simple PGM file.
  6. Shows how to set up PID controls.
  7. Shows how to set up Annotation Blocks.

Brief Project Description

  • Weak Spent liquor is concentrated via evaporation of water through 9 stages of flashing.
  • A majority of the circuit is under vacuum.
  • Live steam heater is added to heat up the liquor feeding to the first flash tank.
  • A barometric condenser is used to condense the flash vapour from the last stage.
  • A cooling tower is set up to cool the hotwell mixture.
  • PID controllers are used to adjust the steam and cooling water additions.
  • Cooling tower water make up is calculated using the PGM file.

Project Configuration

  • Spent Liquor Feed to the project is defined using the DefineLiquor option.
  • Spend Liquor feed location is to the last stage.
  • The steam addition to the circuit is set as a cascade control, to meet a target concentration on the output stream. (Alternatively controls can be modified to control the evaporation rate)
  • The set up of the flash stages are as per the Digestion Projects.
  • The Barometric water addition is used to control the cold end temperature.
  • The Cooling water make up is to counter for losses in the cooling tower (evaporation and blow down loss)
  • The cooling tower is set up:
    1. Using the Merkel method
    2. User defined outlet Air Wet buld Temperature
    3. User defined Liquid to Gas Ratio
    4. User defined tower characteristic factor
    5. Cooling tower will estimate the require air flow and energy
  • Steam economy and cooling water make up side calculations are done in the PGM file.

Included Excel Reports One demonstration excel reports are included in the project.

  1. Evaporation.XLS - this excel report show some basic report formats for the project, these include Input Criteria and simple overall balance and Stream data report

Example 2: Falling Film Evaporation Project

This project was distributed with SysCAD 9.3 Build 136.19154 or earlier. It has since been replaced by a new project using the FFE4 unit. The new FFE4 unit can be included in a flash train and requires much less user PID control setup. Please see Falling Film Evaporation (FFE4) Project for more information.

Falling Film Evaporation.png

Project Location

This is a Steady State project and is stored at:
..\SysCADXXX\Examples\10 Alumina\Falling Film Evaporation Example.spf

Features Demonstrated

  1. Shows the use of Bayer3 properties model.
  2. Shows how to set up a multistage Falling Film Evaporator(2) trains.
  3. Shows how to set up PID controls to balance the pressure in the circuit.
  4. Shows how to use the SetTag Controller to change configuration data for multiple units.
  5. Shows how to set up simple PGM files.
  6. Shows how to set up Annotation Blocks.

Brief Project Description

  • The first Evaporator uses live steam, this unit is using the Live Steam OpMode.
  • The remaining evaporators are using the condensing OpMode.
  • Heat transfer coefficient and area are specified for all the evaporators.
  • Recirculation flows are set up for the evaporators.
  • The Falling Film Evaporator (FFE) unit is not included in the suite of flashing train models, therefore, SysCAD will NOT auto balance the pressures in this circuit. To balance the pressures, the project used a series of PID controllers to fine tune the pressure requirements in the various FFE units.
  • The Flash Tank pressures are set using the PGM file.

Project Configuration

The configuration of this falling film evaporator has a number of key components:

  1. Live Steam Addition and Configuration of the first FFE Unit
    • FFE01 is set with Live Steam OpMode with DemandMode option selected. This means the unit will estimate the amount of steam required under the Calculated Vapour Flow Demand section (found under the ... tab page).
    • NOTE: In earlier versions of SysCAD, this amount cannot be auto set to the Live_Steam feeder, user needs to transfer this either using a PGM file (as demonstrated in the project) or a SetTag Controller. In the latest version of SysCAD, user may use the Demand.On option in the Feeder, and set the DemandConnection to GeneralDemand in the FFE01 unit to auto set this value.
    • The amount of live steam required is set by the FFE heater size, HTC as well as the pressure control within the unit.
    • The PShell (steam condensing side pressure) will set the condensate temperature, and hence the amount of energy available to heat up and vaporise the liquor.
    • The POut (Evaporator Pressure) will set flashing conditions for the evaporator, this value needs to be balanced with down stream equipment, that is, the flashed vapour has to be handled by the next stage, it cannot not provide too much. This pressure control is done in the FFE_P_CTRL.
  2. Pressure balance and Reflash
    • Pressure balance is important in the circuit, each FFE stage needs to have a Pressure control (all done in FFE_P_CTRL) to ensure the flashed vapour + Reflash Vapour can be handled by downstream equipment.
    • If the combined vapour is too high, user may need to increase the FFE Heat Transfer Area to accommodate the excess vapour
    • It is also important to check the reflash feed points to make sure the reflash vapour is feeding the correct stage.
    • The balance of pressure for the reflash stages are done in the FFE_LOGIC PGM.
  3. Feed Temperature and Feed Location
    • The feed location is important, if the feed is too hot, pre-flash (as shown in the project) may be used, alternatively, feed location may be changed to accommodate the higher temperature.
  4. Factors affecting heat balance
    • Number of FFE stages used
    • Extra flashing stages (pre and post)
    • Condensate re-flash vapour usage
    • Hot and Cold end Temperature
    • FFE configuration, HT Area, HTC, Recirculation, Pressure balance

Included Excel Reports One demonstration excel reports are included in the project.

  1. FFEvaporation.XLS - this excel report show some basic report formats for the project, these include Input Criteria and simple overall balance and Stream data report