1 | #*------------------------------------------------------------------- |
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2 | * Model of a tray |
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3 | *-------------------------------------------------------------------- |
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4 | * - Streams |
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5 | * * a liquid outlet stream |
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6 | * * a liquid inlet stream |
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7 | * * a vapour outlet stream |
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8 | * * a vapour inlet stream |
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9 | * * a feed stream |
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10 | * |
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11 | * - Assumptions |
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12 | * * both phases (liquid and vapour) exists all the time |
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13 | * * thermodymanic equilibrium (Murphree plate efficiency=1) |
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14 | * * no entrainment of liquid or vapour phase |
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15 | * * no weeping |
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16 | * * the dymanics in the downcomer are neglected |
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17 | * |
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18 | * - Tray hydraulics: Roffel B.,Betlem B.H.L.,Ruijter J.A.F. (2000) |
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19 | * Computers and Chemical Engineering and |
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20 | * The gPROMS Model Library |
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21 | * |
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22 | * Specify: |
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23 | * * the Feed stream |
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24 | * * the Liquid inlet stream |
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25 | * * the Vapour inlet stream excluding its flow |
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26 | * * the Vapour outlet flow (Outlet.F) |
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27 | * |
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28 | * Initial: |
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29 | * * the plate temperature (OutletL.T) |
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30 | * * the liquid height (hl) |
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31 | * * (NoComps - 1) OutletL (or OutletV) compositions |
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32 | * |
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33 | *---------------------------------------------------------------------- |
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34 | * Author: Paula B. Staudt |
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35 | * $Id: tray.mso 37 2006-10-23 16:47:17Z paula $ |
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36 | *--------------------------------------------------------------------*# |
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37 | |
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38 | using "streams"; |
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39 | |
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40 | Model trayBasic |
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41 | |
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42 | PARAMETERS |
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43 | ext PP as CalcObject; |
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44 | ext NComp as Integer; |
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45 | V as volume(Brief="Total Volume of the tray"); |
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46 | Q as heat_rate (Brief="Rate of heat supply"); |
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47 | Ap as area (Brief="Plate area = Atray - Adowncomer"); |
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48 | |
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49 | VARIABLES |
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50 | in Inlet as stream; |
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51 | in InletL as stream; |
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52 | in InletV as stream; |
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53 | out OutletL as stream_therm; |
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54 | out OutletV as stream_therm; |
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55 | |
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56 | M(NComp) as mol (Brief="Molar Holdup in the tray"); |
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57 | ML as mol (Brief="Molar liquid holdup"); |
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58 | MV as mol (Brief="Molar vapour holdup"); |
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59 | E as energy (Brief="Total Energy Holdup on tray"); |
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60 | vL as volume_mol (Brief="Liquid Molar Volume"); |
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61 | vV as volume_mol (Brief="Vapour Molar volume"); |
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62 | Level as length (Brief="Height of clear liquid on plate"); |
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63 | yideal(NComp) as fraction; |
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64 | Emv as Real (Brief = "Murphree efficiency"); |
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65 | |
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66 | EQUATIONS |
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67 | "Component Molar Balance" |
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68 | diff(M)=Inlet.F*Inlet.z + InletL.F*InletL.z + InletV.F*InletV.z |
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69 | - OutletL.F*OutletL.z - OutletV.F*OutletV.z; |
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70 | |
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71 | "Energy Balance" |
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72 | diff(E) = ( Inlet.F*Inlet.h + InletL.F*InletL.h + InletV.F*InletV.h |
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73 | - OutletL.F*OutletL.h - OutletV.F*OutletV.h + Q ); |
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74 | |
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75 | "Molar Holdup" |
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76 | M = ML*OutletL.z + MV*OutletV.z; |
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77 | |
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78 | "Energy Holdup" |
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79 | E = ML*OutletL.h + MV*OutletV.h - OutletL.P*V; |
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80 | |
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81 | "Mol fraction normalisation" |
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82 | sum(OutletL.z)= 1.0; |
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83 | sum(OutletL.z)= sum(OutletV.z); |
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84 | |
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85 | "Liquid Volume" |
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86 | vL = PP.LiquidVolume(OutletL.T, OutletL.P, OutletL.z); |
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87 | "Vapour Volume" |
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88 | vV = PP.VapourVolume(OutletV.T, OutletV.P, OutletV.z); |
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89 | |
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90 | "Chemical Equilibrium" |
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91 | PP.LiquidFugacityCoefficient(OutletL.T, OutletL.P, OutletL.z)*OutletL.z = |
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92 | PP.VapourFugacityCoefficient(OutletV.T, OutletV.P, OutletV.z)*yideal; |
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93 | |
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94 | "Murphree Efficiency" |
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95 | OutletV.z = Emv * (yideal - InletV.z) + InletV.z; |
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96 | |
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97 | "Thermal Equilibrium" |
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98 | OutletV.T = OutletL.T; |
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99 | |
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100 | "Mechanical Equilibrium" |
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101 | OutletV.P = OutletL.P; |
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102 | |
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103 | "Geometry Constraint" |
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104 | V = ML* vL + MV*vV; |
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105 | |
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106 | "vaporization fraction " |
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107 | OutletV.v = 1.0; |
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108 | OutletL.v = 0.0; |
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109 | |
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110 | "Level of clear liquid over the weir" |
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111 | Level = ML*vL/Ap; |
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112 | end |
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113 | |
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114 | Model tray as trayBasic |
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115 | |
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116 | PARAMETERS |
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117 | Ah as area (Brief="Total holes area"); |
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118 | lw as length (Brief="Weir length"); |
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119 | g as acceleration (Default=9.81); |
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120 | hw as length (Brief="Weir height"); |
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121 | beta as fraction (Brief="Aeration fraction"); |
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122 | alfa as fraction (Brief="Dry pressure drop coefficient"); |
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123 | |
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124 | VARIABLES |
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125 | rhoL as dens_mass; |
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126 | rhoV as dens_mass; |
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127 | |
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128 | EQUATIONS |
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129 | "Liquid Density" |
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130 | rhoL = PP.LiquidDensity(OutletL.T, OutletL.P, OutletL.z); |
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131 | "Vapour Density" |
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132 | rhoV = PP.VapourDensity(InletV.T, InletV.P, InletV.z); |
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133 | |
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134 | if (Level > (beta * hw)) then |
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135 | "Francis Equation" |
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136 | OutletL.F = 1.84*"m^0.5/s"*lw*((Level-(beta*hw))/(beta))^1.5/vL; |
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137 | else |
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138 | "Low level" |
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139 | OutletL.F = 0 * "mol/h"; |
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140 | end |
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141 | |
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142 | end |
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143 | |
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