Page 148 - Gas Purification 5E

Alkanolaniines for Hvdrogen .%&de and Carbon Dioxide Removal 137

Table 2-20
Nomenclature for Simplified Design Procedure Equations

C, = Heat capacity, Btu/(lb)("F) T = Temperature,"F
h = Latent heat of water vapor, Btdlb W =Mass flow, total, Ibh
L = Solution loading, mole acid gad W' = Mass flow, dry basis, lbhr
mole amine
M = Gas flow rate, total, mol& Subscripts:
M' = Gas flow rate, dry basis, mole/hr A = Acid gas stream at reflux drum outlet
MW = Molecular weight, lb AG = Acid gas
P = Pressure or partial pressure, psia B = Solution at regenerator bottom
PO = Equilibrium vapor pressure over a C = Stripper overhead condensate
solution, psia F = Feed gas entering absorber
QRx = Total heat of reaction, Btu/hr L = Lean solution entering absorber
QRc = Regenerator condenser duty. Btu/hr LX = Lean solution exiting leadrich heat
Qm = Ledrich heat exchanger duty, exchanger
Btu/hr P = Product gas leaving absorber
QRE = Reboiler duty, Btu/hr R = Rich solution leaving absorber
R = Acid gas ratio in feed gas, mole REF = Reference value
C02/mole H,S SO = Acid gas stream at stripper overhead

c. Use VLE chart data and the following equation (GPSA? 1987; Lee et al., 1973C) to
determine the C02 and H2S partial pressures at the estimated rich amine solution tem-
perature, TR. based on published data at TI and T2:

(2 - 26)

Equation 2-26 is based on the fact that the vapor pressure of acid gas 2bove the rich
amine solution is inversely proportional to the logarithm of the absolute temperature.
Use of this equation is usually necessary as the VLE chart data cover a limited number
of temperatures.
d. Adjust the estimated rich solution loadings appropriately until the calculated vapor
pressure of one of the two acid gases is equal to its partial pressure in the feed gas. One
of the two acid gases, usually H2S, will be controlling. When the vapor pressure of one
of the acid gases above the rich solution corresponds to the partial pressure of the same
acid gas in the feed gas, the equilibrium solution loading at the estimated rich amine
temperature has been determined.
8. Next, estimate the split of the heat of reaction, &. between the sweet gas product and the
rich amine solution. The split of the heat of reaction is controlled by the ratio of A, the
product of the mass flow and the specific heat of the product gas, and B, the product of the
mass flow and the specific heat of the lean amine solution. If A/B is less than one, all the
heat of reaction leaves the amine contactor with the rich amine solution. If the ratio is
greater than 1, some of the heat of reaction leaves with the product gas: