Power Generation in a Gas Expander-Generator: Expansion Data Tab

This tab appears on the interface data dialogs of the following operations:

● Power Generation in a Steam Turbine-Generator (for a Straight Flow Steam Turbine-Generator)

● Power Generation in a Gas Expander-Generator

Variable Definitions, Ranges and Default Values

The following table shows a brief description of the variables appearing in this tab. 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 Power Generation in a Steam Turbine-Generator: Modeling Assumptions & Constraints.

Variable	Default Value	Range

● Exhaust Pressure (atm) The pressure of the outlet stream. If a condensing turbine is used, it is equal to the operating pressure of the condenser.	1.0	Positive
◙ Specific Heat Ratio The average specific heat ratio of steam during expansion.	1.3	Positive
◙ Isentropic Efficiency (%) The isentropic expansion efficiency of the turbine.	60.0	0-100
◙ a Parameter of condensate-free isentropic efficiency model.	-5.872	Any Number
◙ b Parameter of condensate-free isentropic efficiency model.	0.6464	Any Number
◙ c Parameter of condensate-free isentropic efficiency model.	-0.0184	Any Number
● Condensate-Free Isentropic Eff. (%) The condensate-free value of isentropic efficiency.	60.0	0-100
● Specific Inlet Enthalpy (W) The specific enthalpy of gas at the turbine inlet.	0.0	Positive
○ Mech. Losses (%) Mechanical losses between rotor and shaft.	0.0	0-100
● Shaft Power (Per Unit) The power that is delivered to the shaft of each turbine unit.	0.0	Positive
● Exhaust Pressure (atm) The exhaust pressure of the turbine.	1.0	Positive
● Exhaust Temp. (^oC) The exhaust temperature of the turbine.	100.0	Positive
● Exhaust Specific Enthalpy (W) The specific enthalpy of the gas at the turbine exhaust.	0.0	Positive
● Exhaust Vapor (%) The quality of exhaust steam.	0.0	Positive
○ Power Type Indicates the power type that is used by the operation. Click on the list box to bring up a list of available power types in order to select one.	<Std Power>	Any Power Type
○ Power Generator Efficiency (%) The power generator’s efficiency of conversion of shaft power to electric power.	90.0	0-100
● Electrical Power (W) The electric power that is produced by the operation.	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 Power Generation in a Steam Turbine-Generator: Modeling Calculations.

•Specific Heat Ratio Options...

These options are available only if the Analytical Isentropic Expansion Model is selected through the Oper. Conds Tab. In that case, you can either set the specific heat ratio for each expansion, or let the program calculate its value by assuming ideal gas behavior.

•Isentropic Efficiency Options...

You can either set the isentropic efficiency directly or calculate it based on the condensate-free isentropic efficiency.

•Condensate-Free Isentropic Efficiency Options...

If the isentropic efficiency is calculated based on condensate-free isentropic efficiency, you can either use the built-in quadratic curve or specify custom parameters for that curve in order to calculate the condensate-free isentropic efficiency. The built-in curve is valid for steam and for power output in the range of 100 W - 1.5 MW. If you choose the custom curve, the model checks that the following additional constraints are satisfied with respect to the values of curve parameters a, b, and c:

a) a must be <=0.

b) If c=0, then b must be <>1.

c) If c<>0, then the discriminant of the quadratic curve must be >0.