Gasification: Oper. Conds Tab

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 Gasification: Modeling Assumptions & Constraints.

Variable	Default Value	Range

○ Set Shift from Chemical Equilibrium? Check this box to specify the % shift from chemical equilibrium of the equilibrium constants of the gasification reactions considered (water-gas shift reaction and methane reaction). Note that this option is available only if the chemical equilibrium calculation option is set to “Equilibrium Constants”.	No	Yes/No
○ Water-Gas Shift Reaction Shift (%) The positive or negative shift of the water-gas shift reaction from equilibrium.	0.0	Any
○ Methane Reaction Shift (%) The positive or negative shift of the methane reaction from equilibrium.	0.0	Any
● Oxidant Stream (Air or O2) Name Indicates the name of the stream that is connected to the designated input port for the oxidant stream. If an input stream is already present at this port, then the button next to the stream’s name will be active. Click on this button to bring up the attached stream’s simulation data dialog in order to provide its composition (typically, air or oxygen) and flow (if the “Available in Stream” option is selected for this stream’s flow).	<None>	Any
◙ Equivalence Ratio (%) The ratio of the actual amount of oxygen supplied to the stoichiometric amount of oxygen required for complete combustion of the supplied fuel, expressed as percentage.	20.0	0-100
○ Include Moderator Stream? Check this box to use a moderator stream.	No	Yes/No
● Moderator Stream (Steam) Name Indicates the name of the stream that is connected to the designated input port for the moderator stream. If an input stream is already present at this port, then the button next to the stream’s name will be active. Click on this button to bring up the attached stream’s simulation data dialog in order to provide its composition (typically, steam) and flow (if the “Available in Stream” option is selected for this stream’s flow).	<None>	Any
◙ Steam/Carbon Ratio (mol/mol) The ratio of the moles of inlet steam (supplied through the moderator stream) to the moles of carbon in the supplied fuel.	0.0	Positive
◙ Final Temperature (^oC) The gasification temperature.	25.0	Positive
◙ Heating Duty (kcal/h) The heat required in order to achieve the desired final temperature.	0.0	Positive
○ Heating Agent Indicates the heating agent used by the operation. Click on the list box to bring up a list of available heating agents in order to select one.	<None>	Any Heating Agent
● Inlet Temp. (^oC) The inlet temperature of the selected heating agent.	0.0	Positive
● Outlet Temp. (^oC) The outlet temperature of the selected heating agent.	0.0	Positive
● Rate (kg/h) The mass flow rate of the selected heating agent.	0.0	Positive
○ Heat Transfer Efficiency (%) The ratio of the required heating duty to the actual heat that must be supplied by the heat transfer agent in order to account for heat losses during the transfer of heat from the heating agent to the gasifier.	100.0	(0,100)
○ Operating Pressure (bar) The pressure in the gasifier.	1.01325	Positive
○ Carbon Conversion (%) The fraction of carbon contained in the inlet fuel that is converted into gasification reaction products, expressed as percentage.	100.0	Positive
○ Heat Losses (%) The fraction of the HHV of Dry Fuel (see Energy Balance tab) that is lost to the surroundings.	0.0	0-100
● Volumetric Dry Gas Production Rate (STP) (m³/h) The total standard volumetric flow rate of the dry producer gas produced by all equipment units. This is calculated based on the specified standard temperature and pressure values for the flowsheet considered (0^oC and 1 bar, by default).	0.0	Positive
● Cold Gas Eff. on HHV Basis (%) The value of cold gas efficiency on HHV basis.	0.0	0-100
● Cold Gas Eff. on LHV Basis (%) The value of cold gas efficiency on LHV basis.	0.0	0-100
● Hot Gas Eff. on HHV Basis (%) The value of hot gas efficiency on HHV basis.	0.0	0-100
● Hot Gas Eff. on LHV Basis (%) The value of hot gas efficiency on LHV basis.	0.0	0-100

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 Gasification: Modeling Calculations.

•Chemical Equilibrium Options...

You may either choose to calculate the chemical equilibrium based on equilibrium constants or based on the minimization of Gibbs energy.

If the equilibrium constants option is selected, the program will try to solve the M&E balances and estimate the composition of the producer gas by assuming that a set of known stoichiometric reactions (water-gas shift reaction and methane reaction) takes place. These reactions may be either in equilibrium or shifted from equilibrium by a specified percentage (if the option to set a shift from chemical equilibrium is checked).

If the Gibbs energy minimization option is selected, the program will try to solve the M&E balances and estimate the composition of the producer gas in equilibrium by applying the Gibbs energy minimization method. This method does not require any assumptions regarding the type and number of reactions that occur during gasification.

•Set Shift from Chemical Equilibrium Option...

This option is only available if the chemical equilibrium is based on equilibrium constants.

If you check this option, then you can specify a positive or negative shift from chemical equilibrium for each stoichiometric reaction considered (water-gas shift reaction and methane reaction). The program will try to solve the M&E balances and estimate the composition of the producer gas by assuming that the above reactions are shifted from equilibrium by the specified amounts.

If you do not check this option, then the program will try to solve M&E balances and estimate the composition of the producer gas by assuming that the above reactions are in equilibrium.

•Oxidant Stream Flow Specification Options...

Two options are available for specifying the flow of the oxidant stream: “Available in Stream” or “Calculated Based on Equivalence Ratio”.

If the “Available in Stream” option is selected, then you must specify the flow of the oxidant stream directly, that is, by visiting the oxidant stream’s data dialog. You may access this dialog by clicking on the View/Edit the Stream’s Composition () button next to the name of that stream. The equivalence ratio will be calculated by the program based on the specified flow of oxidant stream.

If the “Calculated Based On Equivalence Ratio” option is selected, then you must specify the

equivalance ratio, and the program will calculate (and auto-adjust) the flow of the oxidant stream based on that.

•“Include Moderator Stream?” option...

If you check this option, then a moderator stream (i.e., a stream connected to the designated input port for the moderator stream) must exist. The program will account for that stream in the M&E balance calculations.

If you do not check this option, then the program will do the M&E balance calculations as if there is no moderator (even if a moderator stream exists).

•Moderator (Steam) Stream Flow Specification Options...

Two options are available for specifying the flow of the moderator stream: “Available in Stream” or “Calculated Based on Steam/Carbon Ratio”. Note that these options are available only if the “Include Moderator Stream?” option is checked.

If the “Available in Stream” option is selected, then you must specify the flow of the moderator stream directly, that is, by visiting the moderator stream’s data dialog. You may access this dialog by clicking on the View/Edit the Stream’s Composition () button next to the name of that stream. The steam/carbon ratio will be calculated by the program based on the specified flow of moderator stream.

If the “Calculated Based On Steam/Carbon Ratio” option is selected, then you must specify the steam/carbon ratio, and the program will calculate (and auto-adjust) the flow of the moderator stream based on that.

•Thermal Mode Options...

Three thermal modes of operation are available: “Set Final Temperature”, “Adiabatic”, or “Set Heating Duty”. If you choose the option to set the final temperature or the heating duty, then you must also select a heating agent. In the case that the final temperature is set, the program will calculate the required heating duty. In the other two cases, the program will calculate the final temperature.

You may use the adiabatic option to simulate an adiabatic gasifier, and the other two options to simulate an externally heated gasifier.