Species Table in 9.1

From SysCAD Documentation

Navigation: User Guide -> Data Libraries -> Species Table

NOTE: This page is valid for SysCAD 9.1, see Species Table in 9.2 for SysCAD 9.2.

Introduction

Species data can be added or edited in the database. The user can alter the data either directly from MS Access or via the Species Database / Default Database commands in SysCAD.

It is the responsibility of the user to review and check all the specie properties for the species used in your project.

The fields in the species table will be explained in the following sub-headings, but first, some important points to keep in mind:

The properties of Steam/Water are built in. See Water and Steam Properties. Note: Any user values inserted into the species table will be ignored.

HINT: If the user requires solid H2O (ice, or water trapped in a solid crystalline structure), then the Compound can be called 'H2O', the phase 'solid', but the Definition must NOT be H2O1, rather use O1H2.

Each record in the Database must be unique. The uniqueness of the record is determined by fields [Compound] + [Phase] + [Ts] + [Te]. These four fields may be set up as the primary key of the table.

For Example:

Compound	Phase	Ts	Te	Status
CaOH	g	298.15	400	OK
CaOH	g	400	3100	OK
CaOH	g	3100	6000	OK
CaOH	g	273	6000	Temperature overlap error
CaOH	g	298.12	400	Not allowed or ignored

Related topics: Models help Standard Species Model | Steam / Water Properties .

Additional information can be entered on the Solution Table. This includes density correction functions and solubility functions.

Name

This is an optional field.

This string describes the compound. If the display tags option in the Access window is enabled, this will be used to display the compound name.

Compound

This field must be filled in.

It is used as a label to uniquely identify the compound.

The format for compound names is:

xxx.xx[xxx]x

Where x is any alphanumeric character

[ ] / are optional delimiters. Note "(" and ")" brackets are NOT permitted

Examples:

H2O

NaAl[OH]4

3CaO.Al2O3.1/2SiO2.5H2O

This field should be part of the primary key in the Access Database Table Design.

Definition

This field must be filled in.

This defines the elemental make up of the compound. SysCAD has a built in Periodic Table and will recognise the elements. Using the Periodic Table and the definition, SysCAD calculates the molecular weight of the compound. An elemental definition is required if the compound is a reactant or product of a chemical reaction. The format is:

AmBnCo

Where

A, B, C formula for element eg H for hydrogen, Au for gold, Pb for lead etc. This IS case sensitive, so Cl is NOT the same as CL; and Co is not the same as CO.

m, n, o are the number of moles of elements A, B and C in the compound, respectively. These can be expressed as integers, fractions or decimals.

Example:

For compound 3CaO.Al2O3.1/2SiO2.5H2O

The definition is Ca3O12Al2Si1/2H10 or Ca3O12Al2Si0.5H10

Notes:

Each element must only be defined once. Therefore a definition of Ca3O1Al2O3Si1/2O1H10O5 where O is repeated is incorrect!
If there is only one mole of an element the 1 must be specified. For example CO2 is incorrect, it should be C1O2.
Element names are case sensitive.

If the elemental breakdown of a compound is unknown and not required, the user can insert a false element with it's own molecular weight.

Example:

Nn(123) (Nn will have a molecular weight of 123)

Ore(50) (Ore will have a molecular weight of 50)

Stuff1(37.3) (Stuff1 will have a molecular weight of 37.3)

Phase Name

This field must be filled in.

This is the individual phase in which the species occurs and may be made up by any combination of alphabetical letters. This description does not have any bearing on the phase to which SysCAD will assign the species, but is used for appearance only. See Occurrence below.

Examples:

a) If the species is NaCl in the aqueous form, then the phase name could be aq, a or l. (recommended use is aq)

b) If the species is RNi, representing the organic nickel phase in a solvent extraction plant, then the phase name could be o, or og.

Note that aq and a are special cases and are recognised as aqueous species.

This field should be part of the primary key in the Access Database Table Design.

Occurrence

This field must be filled in.

It is the actual phase in which the species occurs. The user may choose only one of the following:

s (solid), l (liquid), or g (gas).

This defines how the species is manipulated within SysCAD.

Density (Rho)

This field is optional, but it should be filled in to ensure that the density calculations for any stream containing this compound are correct.

This is the density of the species in the defined phase. Generally a constant is expected. The unit for density is kg/m³.

If it is left blank SysCAD will assume a constant value of 2000 kg/m³ for solids and 1000 kg/m³ for liquids.

The density provided here will also be used in volume calculations. The equation used is Volume = mass / density.

Refer to Stream Density for an example of how these individual densities are used to determine the density of a stream.

Special Cases

The equations for water and steam density are built into SysCAD and the user cannot change any values used in this case. For further information on these equations, please see Water and Steam Properties.
For gases, if the user leaves this field blank SysCAD will use the Ideal Gas density calculation to determine the density of the gas. Alternatively, the user may use one of the following two input formats (the formulation for Ideal Gas is also shown here):
- Constant
- LinearGasDensity(value) - the density value provided in brackets is expected to be at 0°C and Std. Pressure. Density @ T, P will be corrected based on:
- IdealGasDensity() - The density value will be calculated based on the Ideal gas law. Equations used are:
  
  Rearranging the above equations will give:
  
  Where:
  m = mass of compound
  V = Volume of compound
  P = Partial Pressure of the Gas
  R = Universal Gas Constant = 8.314 472J/mol.K (Reference: National Institute of Standards and Technology)
  T = Temperature in Kelvin
  n = number of moles of compound
  M = molecular weight of compound
For Aqueous Solutions or ionic species where it's density changes according to the solution concentration, separate density correction functions can be used. This is described in a separate section, see Density Correction Function for more information.
If the user has defined a specie that will normally exist in the aqueous form, but the user does not have a density correction function, then it is recommended that the density of the specie be set to the water density using the special density function LiqH2ORho(). This will ensure that the specie has the same density as water and hence the specie will not change the density of the solution. For further info on this equation see Water and Steam Properties.

Heat of Formation (dHf)

This field is optional (but is usually defined). If it is left blank, SysCAD will assume a value of +100 J/mol.

This is the Heat of Formation at 25°C.

All elements have zero heat of formation. The unit is expressed in J/mol.

This value is used to calculate heats of reaction for chemical reactions specified in SysCAD. If the compound is used in chemical reactions, this number will determine the accuracy of the heat balance. If this field is left blank due to lack of data, then the user should define the Heat of Reaction (HOR) manually in the reaction file. See Reaction Block (RB) for further information on reactions.

Refer to Stream Heat of Formation values (Hf) for an example of how these individual heats of formation are used to determine the heat of formation of a stream.

Entropy (S298)

This field is optional.

This is the entropy value for the species. The unit for Entropy is J/mol.K. This parameter is optional as it is typically not used in SysCAD calculations. S°298 may be used in free energy minimisation calculations.

Heat Capacity (Cp)

This field is optional, but if it is left blank SysCAD will assume a constant value of 2.0. This assumption will be shown as a warning in the message window when loading a project

The unit for Heat Capacity is J/mol.K. Valid Cp equations must be supplied for all components used in the project to obtain a correct Energy balance in SysCAD. The Cp equations are integrated over a temperature range to obtain the change of enthalpy around a unit operation.

$\Delta H = \int\limits_{T_1}^{T_2}Cp dT\,$

Where T1 is Initial temperature and T2 Final temperature

Please note that the temperature range is bound by Ts and Te specified for the component. If T1 < Ts then T1 = Ts; if T2 > Te then T2 = Te.

The enthalpy calculation for the part/s outside the defined temperature range is calculated using the Cp at the limit of the defined temperature range.

If T1 < Ts then:

$\Delta H _{T1 \to Ts}= Cp_{Ts}*\left ( T_s - T_1 \right)\,$

Similarly, if T2 > Te then:

$\Delta H _{Te \to T2}= Cp_{Te}*\left ( T_2 - T_e \right)\,$

Related topics: Start Temperature (Ts) and End Temperature (Te).

The valid Cp equation formats are as follows:

CRC Equation

CRC_Cp(a,b,c,d)

$C_p = a + b.10^{-3} T + \frac{c.10^5}{T^2} + d.10^{-6} T^2\,$

where T - Temperature in K

CRC Equation (alternative format 1)

CRC1_Cp(a,b,c,d)

$C_p = a + b.10^{-3} T + c.10^{-6} T^2 + \frac{d.10^5}{T^2}\,$

where T - Temperature in K

CRC Equation (alternative format 2)

CRC2_Cp(a,b,c)

$C_p = MolecularWeight * \Bigg( a + b.T - \frac{c}{T^2} \Bigg)\,$

where T - Temperature in K

HTE Equation Format

HTE_Cp(a,b,c,d)

$C_p = 4.186 * \Bigg(b + 2*c.10^{-3} T - \frac{d.10^5}{T^2}\Bigg)\,$

where T - Temperature in K

Note: the first parameter a is required but is not used in the HTE equation and is ignored by SysCAD.

HSC Equation format

HSC_Cp(a,b,c,d)

$C_p = a + b.10^{-3} T + \frac{c.10^5}{T^2} + d.10^{-6} T^2\,$

where T - Temperature in K

Note: This equation is the same as the CRC format 1 equation.

Polynomial Equation format

Poly_Cp(a,b,c,d)

$C_p = a + bT + cT^2 + dT^3\,$

where T - Temperature in K

General Polynomial Equation format

GenPoly_Cp(c1,p1,c2,p2,c3,p3,c4,p4)

$C_p = c_1 T^{p_1} + c_2 T^{p_2} + c_3 T^{p_3} + c_4 T^{p_4}\,$

where T - Temperature in K

Shomate Equation (Gas Phase Heat Capacity)

Shomate_Cp(a,b,c,d,e)

$C_p = a + b.10^{-3} T + c.10^{-6} T^2 + d.10^{-9} T^3 + \frac{e.10^6}{T^2}\,$

where T - Temperature in K

NOTE: All temperatures in the above formulae are in degrees Kelvin.

Refer to Stream Specific Heat values (Cp) for an example of how these individual heat capacities are used to determine the heat capacity of a stream.

NOTES:

If the user does not have the data constants for any of the above equations to calculate Cp as a function of temperature, but they have a single constant value for Cp, then use the following format: CRC_Cp(value,0,0,0).
If the user does not specify any value at all for Cp, SysCAD will assume a constant value of 2.0. This assumption will be shown as a warning in the message window when loading a project.
Heat capacity MUST increase with temperature with the exception of AQUEOUS compounds. Therefore, if as a result of the values in the species database for the specified temperature range, a negative increase for Cp with temperature is calculated, SysCAD will not initialise and the user will see the following error message: Bad Enthalpy: msH decreases with T for species (where species is the actual species with the negative Cp). The database Cp parameters will need to be corrected before you will be able to continue with a project. For an aqueous compound, the Cp data can effectively be used as a correction factor for that compound in solution. The Cp equation for an aqueous species may not be intended to be valid for the compound in it's pure state. To be recognised as an aqueous compound, the phase name must be "aq" or "a".
The Shomate Equation is used to fit data from the NIST web site for gas components with higher temperature ranges. eg Oxygen
The Cp values for water and steam are calculated using equations within SysCAD. Therefore the Cp values for these two species cannot be changed by the user. Please see Water and Steam Properties.

Start Temperature (Ts)

This field must be filled in.

It is the lowest temperature at which the species occurs in the defined phase, expressed in Kelvin. This temperature is used as a lower limit for Enthalpy and Specific Heat calculations.

End Temperature (Te)

This field must be filled in.

It is the highest temperature at which the species occurs in the defined phase, expressed in Kelvin. This temperature is used as a higher limit for Enthalpy and Specific Heat calculations.

Vapour Pressure (Vp)

This field is optional.

If a component is to be used in flash calculations Vapour Liquid Equilibrium (VLE), the Vapour Pressure must be provided for the vapour phase of the component. The Critical Temperature must also be defined. The other critical constants and the acentricity values are also normally defined.

The user does NOT have to provide this information for steam, as SysCAD will use in-built equations to calculate the vapour pressure of water. Please see Water and Steam Properties.

Where the VLE flash calculations will be used, the user should also check that both the liquid and vapour phase of the component are defined and selected for the project.

Note that in all cases, temperature T used in the equation is limited by the specified Critical Temperature (Tc). In other words if T>Tc, then Tc is used in the calculation.

General format

1) One representation of the Vapour Pressure equation is:

This vapour pressure function can be used in one of these formats:

Vp(a,b,c,d)

Where T is in Kelvin and Vp is in mmHg. SysCAD then converts the Vapour Pressure into kPa by multiplying 101.325/760 or 0.133322.

VpAtm(a,b,c,d)

Where T is in Kelvin and Vp is in Atmospheres. SysCAD then converts the Vapour Pressure into kPa by multiplying 101.325.

VpKPa(a,b,c,d)

Where T is in Kelvin and Vp is in KPa.

Antoine format

2) The Antoine Vapour Pressure equation is:

$\mathbf {\mathrm {\ln V_p = A - \frac B{T+C}}}$

The format is:

VpAnt(A,B,C)

where T is in Kelvin and Vp is in mmHg. SysCAD then converts the Vapour Pressure into kPa by multiplying 101.325/760 or 0.133322.

The equation may also be supplied with two additional parameters:

VpAnt(A,B,C, tmin, tmax)

where tmin and tmax are limits on the range of applicability of the equation. If the temperature is outside this range, then the Lee-Kesler equation is used, which calculates the vapor pressure from the critical constants and accentric factor.

The Lee-Kesler equation takes the form $V_p = p_c e^{L_0 + \omega_{ac} L_1}$ where

$L_0 = 5.92714-\frac{6.09648}{T_r}-1.28862\ln(T_r)+.169347 \,T_r^6$

$L_1 = 15.2518-\frac{15.6875}{T_r}-13.4721\ln(T_r)+.43577 \,T_r^6$

and $T r$ is the reduced temperature.

Finally, if the equation is specified with *no* parameters:

VpAnt()

and the critical constants are available, then the Lee-Kesler equation is used by default. SysCAD will report an error at load time if critical constants are not available.

Discussion

The Antoine equation is generally intended for low pressures, up to approximately 2-3 bar (absolute). It is based on experimental data obtained at these relatively low pressures and is useful (and very accurate) in this range. It should not be used above the range indicated as it does not extrapolate well.

The Antoine equation has a lower limit as well, but for temperatures below this limit the material is typically solid; there is no downside to using the equation below the minimum value.

The Lee-Kesler equation is very accurate for high pressures, and is exact for the critical temperature, since the terms in the equation sum to unity at that temperature. It is also exact for $T_r = 0.7 T_c\,$ by the definition of the acentric factor:

$w_{ac} = -\log \left(P_r^{sat}\right)_{T_r = 0.7} - 1\,$

It is less accurate for lower temperatures, especially for polar molecules. For example, for water it predicts a vapor pressure of 90kPa at 100°C compared to the true value of 1atm (101.3 kPa).

One concern is the transition between the two ranges. Discontinuities can lead to problems with the SysCAD solver, so we use interpolation in the range just above the Antoine maximum limit.

To find the overlap range, consider the possibilities: the discontinuity may be positive or negative, and the slopes may not match.

We calculate $dT_a = \delta/f_{ant}'(t_{max})\,$ and $dT_a = \delta/f_{mil}'(T_{max})\,$ , and (conservatively) set the overlap range limit to be

$T_o = T_{max} + dT_a + dT_m\,$

Within this range we linearly interpolate between the two equations, so that if $\alpha = (T-T_{max})/(T_o-T_{max})\,$ we have

$V_p = (1-\alpha)f_{ANT}(T) + \alpha f_{LK}(T)\,$

Polynomial format

3) You can also use the polynomial equation for vapour pressure if required.

The format is:

Poly(a,b,c,x)

Where a, b, c etc are coefficients of the polynomial.

$V_p = a + bT + cT^2 + dT^3 + ...\,$

Critical Pressure (Pc)

This field is optional.

The critical pressure is the saturated pressure of the species at the critical temperature. Required in MPa.

This is required for components involved in VLE flash calculations and in some forms of the vapour pressure equation (eg VPAnt).

Critical Temperature (Tc)

This field is optional.

The critical temperature is defined as the temperature above which the species will not condense, no matter what the pressure. This temperature is required in Kelvin.

This is required for components involved in VLE flash calculations and in some forms of the vapour pressure equation (eg VPAnt).

Critical Volume (Vc)

This field is optional.

The critical volume is the specific volume of the species at its critical temperature and pressure. Required in l/mol.

This is required for components involved in VLE flash calculations and in some forms of the vapour pressure equation (eg VPAnt).

Acentricity (Ac)

This field is optional.

The Acentric Factor for the species.

This is required for components involved in VLE flash calculations and in some forms of the vapour pressure equation (eg VPAnt).

(Acid / Base) Dissociation

This field is optional.

If the user requires a component to be included as an acid or base in the acidity, or pH, calculations, then this field must have the required acid or base dissociation constant. A number of 'standard' acids and bases are included in the default database with their associated dissociation constants. See Acidity Calculations for a full list of the included acids and bases.

The acid/base dissociation constant is the equilibrium constant for the dissociation reaction of the particular acid or base in water:

For the equation $AB \rightleftharpoons A^+ + B^-$ , the dissociation constant, K (Ka for acid, Kb for bases), is calculated as:

$K = \frac{[A ] [ B]}{[AB]}$

where [AB] = concentration of the acid/base in mol/L in water

The form of the variable is:

Acids: Ka(Ka1, Ka2, Ka3)

where

Ka1 - required

Ka2 - optional (only relevant for diprotic and triprotic acids)

Ka3 - optional (only relevant for triprotic acids)

NOTE: For Ka ≥ 10, SysCAD assumes total dissociation.

Bases: Kb(Kb1)

where

Kb1 - required

NOTE: For Kb ≥ 1, SysCAD assumes total dissociation.

Examples: (with corresponding dissociation reactions)

Hydrofluoric Acid (HF) - Ka(6.8e-4) (a monoprotic acid) $(HF \rightleftharpoons H^+ + F^- )$

Phosphoric Acid (H3PO4) - Ka(7.2e-3, 6.3e-7, 4.2e-13) (a triprotic acid) $(H_3PO_4 \rightleftharpoons H^+ + H2PO4^-\rightleftharpoons H^+ + HPO4^{2-}\rightleftharpoons H^+ + PO4^{3-})$

NaOH - Kb(1) $(NaOH \rightleftharpoons Na^+ + OH^- )$

Checked

This field is Optional.

SysCAD uses the physical and thermodynamic qualities in this database to determine all of the stream properties in a project. Therefore, it is very important that the user verifies these values. This column allows the user to confirm that the values for the species have been checked and are correct. If the values are verified, then the user may type their initials, or any other reference, into this column. This allows other users to check the source of the data values.

When a project is loaded the following message will appear in the Message Window:

X Species not Checked, where X is the number of species without anything in the Checked column.

Reference

This field is optional.

It allows the reference of the data be entered. It is good practice to reference where the different data (eg Cp, Vp, density, etc) has been obtained from.

Species Table in 9.1

From SysCAD Documentation

Contents

Introduction

Name

Compound

Definition

Phase Name

Occurrence

Density (Rho)

Special Cases

Heat of Formation (dHf)

Entropy (S298)

Heat Capacity (Cp)

Start Temperature (Ts)

End Temperature (Te)

Vapour Pressure (Vp)

General format

Antoine format

Polynomial format

Critical Pressure (Pc)

Critical Temperature (Tc)

Critical Volume (Vc)

Acentricity (Ac)

(Acid / Base) Dissociation

Checked

Reference

Views

Personal tools

Document Sections

General

Search

Toolbox

Species Table in 9.1

From SysCAD Documentation

Contents

Introduction

Name

Compound

Definition

Phase Name

Occurrence

Density (Rho)

Special Cases

Heat of Formation (dHf)

Entropy (S­­298)

Heat Capacity (Cp)

Start Temperature (Ts)

End Temperature (Te)

Vapour Pressure (Vp)

General format

Antoine format

Polynomial format

Critical Pressure (Pc)

Critical Temperature (Tc)

Critical Volume (Vc)

Acentricity (Ac)

(Acid / Base) Dissociation

Checked

Reference

Views

Personal tools

Document Sections

General

Search

Toolbox

Entropy (S298)