The Vapor Compression Evaporator model is used to simulate a typical mechanical vapor recompression evaporator. The generated secondary vapor of a single step falling film evaporator is compressed and and mixed with primary steam. An optional post heater is available inside the evaporator. An optional secondary condensate inlet is available to the shell space. If the heat requirements exceed the heat gained by compression then make up steam is required. Otherwise the excess of the compressed vapor is delivered through the Compressed Vapor Extraction Outlet. A fraction of both the uncompressed and compressed vapor can be optionally extracted. If the make up steam parameters are not specified, the default low pressure steam (40 psig and 308 F) will be used.

The Liquor_In, Liquor_Out, Make_Up_Steam_In, Excess_Steam2_Out and Condensate_Out streams are required. Post_Heater_In and Post_Heater_Out streams are optional, but needed for a post-heater. The Condensate_In, Work_In and Excess_Steam1_Out streams are optional. Please specify the Dome Pressure and either the Heat Transfer Coefficient or the heat transfer Area of the evaporator space.

The heat transfer Area is calculated, if the Heat Transfer Coefficient is given. The Heat Transfer Coefficient is calculated, if the heat transfer Area is given. The Energy Efficiency is required. The Liquor_Out is extracted at the Dome Pressure.

Please specify the heat transfer Area and the post-heater Delta T change, if a post-heater is included . The default Post_Heater_In pressure will be used, if the post-heater Pressure is not specified.

What do you want to see?

Data Description

Data		Unit		Description
Set	Item	Type	Native	Description
Equipment Properties	Dome Pressure	Pressure	psia	Pressure at the top of the evaporation space. Also the pressure of Liquor_Out stream.
	Heat Transfer Coefficient	Heat Trans Coef	BTU/hr/F/ft2	Heat Transfer Coefficient of the evaporator zone. If given, the heat transfer Area is calculated.
	Area	Area	ft2	Heat transfer Area of the evaporator zone. If given, the Heat Transfer Coefficient is calculated.
	Energy Efficiency	Fraction or Percent	Fraction	Fraction or percent of the available energy transferred to the evaporating liquor.
	CompressionType			The type of the compression process regarding the heat exchange with the environment. Adiabatic Compression accounts no heat exchange with the environment. Polytropic Compression takes into account the losses due to thermodynamic cycle efficiency.
	Option			Specify how to calculate the the compressor's discharge pressure. Discharge Pressure input the specified value. Pressure Ratio input the discharge to suction pressures ratio. Compression ratio input the discharge to suction volumes ratio.
	DischargePressure	Pressure	psia	Discharge Pressure input the specified value for the compressor.
	PressureRatio	Pressure	psia	Pressure Ratio input the discharge to suction pressures ratio for the compressor.
	CompressionRatio			Compression ratio input the discharge to suction volumes ratio of the compressor.
	Efficiency>	Fraction or Percent	Fraction	The polytropic Efficiency is defined as the ratio of polytropic work to actual work. The adiabatic (isentropic) Efficiency is defined as the ratio of adiabatic (isentropic) work to actual work.
	Generated Vapor Fraction	Fraction or Percent	Fraction	Generated Vapor Fraction is the fraction or percent of the evaporated vapor mass flow extracted according to the user request.
	Compressed Vapor Fraction	Fraction or Percent	Fraction	Compressed Vapor Fraction is the fraction or percent of the compressed vapor mass flow extracted according to the user request.
	VCEOption	Fraction or Percent	Fraction	Specify if the equipment will be controlled to achieve an input Compressor Actual Power or an input Outlet Dissolved & Solids Fraction or percent.
	DissSolidFractionOut	Fraction or Percent	Fraction	Specify the input Outlet Dissolved & Solids Fraction or percent. The Compressor actual Motor Power is calculated.>
	MotorPower	Work	BTU/hr	Specify the input Compressor actual Motor Power. The Outlet Dissolved & Solids Fraction or percent is calculated
Post Heater Properties	Heat Transfer Coefficient	Heat Trans Coef	BTU/hr/F/ft2	Heat Transfer Coefficient of the post-heater zone. If given, the heat transfer Area of the post-heater zone is calculated.
	Area	Area	ft2	Heat transfer Area of the post-heater zone. If given, the Heat Transfer Coefficient of the post-heater zone is calculated.
	Delta T	Temperature Change	Delta F	The temperature change from Post_Heater_In to Post_Heater_Out streams.
	Pressure	Pressure	psia	Outlet and inside Pressure of the post-heater. The Post_Heater_In stream pressure is used by default.
Calculated Properties	Dome Pressure	Pressure	psia	Pressure at the top of the evaporation space. Also the pressure of Liquor_Out stream.
	Heat Available for Transfer	Energy Flow	BTU/hr	The heat input to the equipment.
	Evap Heat Transfer Coef	Heat Trans Coef	BTU/hr/F/ft2	The heat transfer coefficient calculated for the saturated liquor in the evaporation zone, assuming the logarithmic average temperature difference between the inlet and outlet flows. Evaporator heat transfer area is input.
	Evap Delta T	Temperature Change	Delta F	Temperature difference between the evaporator inlet saturated vapor and the Liquor_Out temperature at saturation.
	Evap Heat Transferred	Energy Flow	BTU/hr	The heat transfer coefficient calculated for the saturated liquor in the evaporation zone, assuming the logarithmic average temperature difference between the inlet and outlet flows. Evaporator heat transfer area is input.
	BPR	Temperature Change	Delta F	The boiling point rise of the outlet liquor.
	Post Heater Area	Area	ft2	The heat transfer area calculated for the saturated liquor in the post-heater zone, assuming the logarithmic average temperature difference between the inlet and outlet flows. The post-heater heat transfer coefficient is input.
	Post Heater Heat Trans Coef	Heat Trans Coef	BTU/hr/F/ft2	The heat transfer coefficient calculated for the saturated liquor in the post-heater zone, assuming the logarithmic average temperature difference between the inlet and outlet flows. The post-heater heat transfer area is input.
	PH LM Delta T	Temperature Change	Delta F	The post-heater mean logarithmic temperature difference.
	TheoreticalPower	Work	BTU/hr	The theoretical compression work.
	ActualPower	Work	BTU/hr	The actual compression work, taking into account the compressor efficiency.
	Gamma			Adiabatic (Isentropic) or Polytropic compression exponent.
	CondensingTemperature	Temperature	F	The condensing temperature of the compressor's discharge stream.
	DissSolidFractionOut	Fraction or Percent	Fraction	The final calculated Outlet Dissolved & Solids Fraction or percent.
	Delta T Cond Compressor	Temperature Change	Delta F	The temperature difference between the saturated discharge stream and the suction stream of the compressor.
	EvapCapacity	Mass Flow	lbs/hr	The mass flow rate of the evaporated vapor at the evaporator outlet.
	VCEEconomy			The steam economy of the vapor compression evaporator, calculated by dividing the evaporated vapor mass flow rate with the apparent inlet steam. The apparent inlet steam is the make up steam added to an amount of make up steam energy-equivalent of the compressor actual work.
	FeedPerSteamRatio			The mass flows ratio of the Liquor_In and vapor at the evaporator section inlet.
	CapacityPerSteamRatio			The mass flows ratio of the generated vapor and the vapor at the evaporator section inlet.

Top of Page

Equipment Properties

Top of Page

Example of using equipment

Top of Page

Method&Equations

The model calculates the unknown variables based on the following thermal balance on the falling film evaporator as follows:

(Q_steamInEvaporator + Q_condensateIn - Q_condensateOut) * Evaporator Energy Efficiency = q_trans =

= (Q_steamOutEvaporator + Q_liquorOut - Q_liquorIn) + q_trans_PH

The heat transfer for the evaporator section is calculated as follows:

q_trans � q_trans_PH = U_EVAP * A_EVAP * LMTD_Evap

The heat transfer for the post heater section is calculated as follows:

q_trans_PH = U_PH * A_PH * LMTD_PH

Both for the evaporator and the post heater sections the log mean temperature difference (LMTD) is calculated as follows:

LMTD = (deltaT_A - deltaT_B) / ln(deltaT_A / deltaT_B)

where A and B are the inlet and the outlet of the heat exchange zone.

The compressor can simulate two compression types which raise the temperature at the discharge end: adiabatic (when no heat is transfered to the environment) or polytropic (characterizing the real compressors when part of the accumulated heat due to the compression is released).

To see the Method&Equations used for the compressor section, please follow the next link:

Compressor - Method&Equations

VCE Steam Economy = Evaporator Capacity / Apparent_Steam_Inlet

Apparent_Steam_Inlet = Make_Up_Steam + Actual Compressor Power / Make_Up_Steam_Latent_Heat

where:

Q_steamInEvaporator is the heat input with the primary vapor

Q_condensateIn is the heat input with the secondary condensate (Condensate_In stream)

Q_condensateOut is the heat output with the primary condensate (Condesate_Out stream)

Q_steamOutEvaporator is the heat output from the evaporator with the secondary vapor

Q_liquorIn is the heat input with the feed Liquor_In stream

Q_liquorOut is the output heat with the Liquor_Out stream

q_trans is the heat total heat transferred in the evaporator