Multi-Effect Evaporation: Heating Tab (MVR)

ContEvaporationMVRHeating.jpg

This tab appears on the interface dialog of the Continuous Multi-Effect Evaporation operation if the Vapor Recompression Option is set to “Mechanical Vapor Recompression” in the Oper. Conds Tab (see Multi-Effect Evaporation: Oper. Conds Tab).

Variable Definitions, Ranges and Default Values

The following table shows a brief description of the variables appearing in this tab; for a detailed description of these variables, see Multi-Effect Evaporation: Description of Terms The table also displays their default values and their generally acceptable range. Note that due to how the variables are used in the modeling equations, the range of acceptable values may be further reduced; for more details, see Multi-Effect Evaporation: Modeling Assumptions & Constraints.

Variable

Default Value

Range

 

○ Heating Agent Name
Indicates the heating agent used in the evaporator. Click on the list box to bring up a list of available heating agents in order to select one.

Steam

Any Heating Agent

● Supply Temp. of Heating Agent (oC)
The temperature of the heating agent before the heat transfer.

152.0

Positive

● Return Temp. of Heating Agent (oC)
The temperature of the heating agent after the heat transfer.

152.0

Positive

● Mass-to-Energy Factor of Heating Agent (kcal/kg)
The specific heat source of the heating agent between supply and return.

503.683

Positive

● Duty of Heating Agent (kcal/h)
The heat transfer rate of the heating agent.

0.0

Positive

● Flow of Heating Agent (kg/h)
The mass flow rate of the heating agent.

0.0

Positive

○ Same Properties As Vapor?
The heating fluid in the first effect may be a mixture of heating agent, desuperheating agent and recompressed vapor. Check this box to indicate that the unknown thermodynamic properties of this fluid (outlet enthalpy, pressure) will be calculated based on the properties of recompressed vapor only.

<Yes>

Yes/No

● Flow of Heating Fluid in First Effect (kg/h)
The mass flow rate of the heating fluid in the first effect.

0.0

Positive

● Specific Inlet Enthalpy of Heating Fluid in First Effect (kcal/kg)
The specific enthalpy of the heating fluid at the steam chest inlet of the first effect.

0.0

Positive

● Outlet Temp. of Heating Fluid in First Effect (oC)
The temperature of the heating fluid at the steam chest outlet of the first effect.

152.0

Positive

◙ Condensing Temp. of Heating Fluid in First Effect (oC)
The temperature at which the heating fluid will condense in the steam chest of the first effect (corresponding to the pressure that the heating fluid exhibits in the steam chest of that effect).

152.0

[Supply Temp., Return Temp.]

◙ Specific Outlet Enthalpy of Heating Fluid in First Effect (kcal/kg)
The specific enthalpy of the heating fluid at the steam chest outlet of the first effect.

0.0

Positive

◙ Pressure of Heating Fluid in First Effect (bar)
The pressure of the heating fluid in the steam chest of the first effect.

1.013

Positive

● Specific Heat Duty of Heating Fluid in First Effect (kcal/kg)
The specific heat source of the heating fluid used in the steam chest of the first effect.

0.0

Positive

○ Recompressed % Set By User?
Check this box in order to set the recompressed % of vapor from the last effect.

<No>

Yes/No

◙ Recompressed % (% of Vapor from Last Effect)
The percentage of vapor produced in the last effect that is drawn from the vapor outlet of that effect, recompressed by mechanical compression, and sent back to the steam chest of the first effect.

0.0

[0,100)

● Flow of Vapor in Compressor (kg/h)
The mass flow rate of recompressed vapor.

0.0

Positive

● Inlet Pressure of Vapor in Compressor (bar)
The pressure of vapor at the inlet of the compressor (same as the pressure of vapor in the last effect).

1.013

Positive

● Inlet Density of Vapor in Compressor (g/L)
The density of vapor at the inlet of the compressor.

0.0

Positive

● Outlet Pressure of Vapor in Compressor (bar)
The pressure of vapor at the outlet of the compressor.

1.013

Positive

○ Specific Heat Ratio of Vapor in Compressor Set By User?
Check this box in order to set the specific heat ratio of vapor in the compressor.

No

Yes/No

◙ Specific Heat Ratio of Vapor in Compressor
The ratio Cp/Cv for the vapor in the compressor, where Cp is the specific heat capacity of vapor at constant pressure and Cv is the specific heat capacity at constant volume.

0.0

Positive

○ Isentropic Efficiency of Compression (%)
The efficiency of isentropic mechanical compression.

100.0

(0,100]

● Compression Work (kcal/kg)
The specific enthalpy change of vapor by mechanical compression.

0.0

Positive

○ Use Desuperheating Agent?
Check this box in order to use a desuperheating agent after mechanical vapor recompression.

No

Yes/No

○ Desuperheating Agent Name
Indicates the desuperheating agent used in the evaporator. Click on the list box to bring up a list of available cooling agents in order to select one as desuperheating agent.

Cooling Water

Any Cooling Agent

● Supply Temp. of Desuperheating Agent (oC)
The temperature of the desuperheating agent before the heat transfer.

25.0

Positive

● Return Temp. of Desuperheating Agent (oC)
The temperature of the desuperheating agent after the heat transfer.

30.0

Positive

● Mass-to-Energy Factor of Desuperheating Agent (kcal/kg)
The specific enthalpy change (heat sink) of the desuperheating agent between supply and return.

4.997

Positive

● Duty of Desuperheating Agent (kcal/h)
The heat transfer rate of the desuperheating agent.

0.0

Positive

● Flow of Desuperheating Agent (kg/h)
The mass flow rate of the desuperheating agent.

0.0

Positive

Symbol Key: ○ User-specified value (always input); ● Calculated value (always output); ◙ Sometimes input, sometimes output

Specification Choices / Comments

The following list describes the available specification choices in this tab; for more details on how these are implemented, see Multi-Effect Evaporation: Modeling Calculations.

•If the option “Same Properties As Vapor” is checked...

You must specify the Specific Outlet Enthalpy and Pressure of the heating fluid in the first effect. If the option to “Use” a desuperheating agent is also checked, then you must also specify the Specific Heat Duty of that fluid.

•If the option “Same Properties As Vapor” is not checked...

The Specific Outlet Enthalpy and Pressure of the heating fluid in the first effect will be calculated by the program based on the assumption that the thermodynamic properties of the heating fluid in the first effect (which may consist of heating agent, desuperheating agent and recompressed vapor) are the same as those of recompressed vapor. If the option to “Use” a desuperheating agent is also checked, then the same thing will be done for the Specific Heat Duty of that fluid.

•If you check the option to ‘Use’ a desuperheating agent...

A desuperheating agent will be added to the mixture of recompressed vapor and heating agent before it enters the first effect in order to improve heat transfer in the first effect. If the flow of the heating agent is not zero, the outlet temperature of the desuperheating agent must be the same as that of the heating agent (since both agents exit from the same outlet).

•If you do not check the option to ‘Use’ a desuperheating agent...

No desuperheating agent will be used.