Carbon dioxide removal in indirect gasification - SGC

SGC Rapport 2013:277
For the building of an accurate gas separation model, a number of fundamental
physical and chemical data is required.
For the physical properties of the system - such as density, viscosity, surface
tension, diffusivity of the amines in water solution, diffusivity of gases in the amine
solution, gas solubility in the amine solution and heat capacity - data was taken
from the literature [41, 55-69]. However, only one journal publication on the heat of
reaction for the investigated system was found with very limited data [70]. The only
other reference found was an interim report from North Carolina State University
[71]. For this reason an investigation on the heat of reaction for the system was
conducted for the MDEA/PZ-system [72]. The data acquired from this investigation
was used in the simulation model.
In order to perform the calculations on the absorber and the stripper, integral
balances for each unit have to be solved prior to the differential balances. For the
calculation on the absorber the principle for the simulation model is as follows. The
integral balances for the absorption tower give the flow rates of the incoming and
outgoing gas and liquid streams, as well as the incoming and outgoing temperatures
of the gas and liquid, according to Figure 20. The incoming gas flow is given
by the previous steps. From the integral balances the diameter required for the
absorption column can be determined, as well as the pressure drop over the column.
Figure 20. System boundary, gas flows, liquid flows and temperature used for the
integral balances.
For the differential calculations the principle of the model is illustrated in Figure 21.
Data from the literature has been used for the differential calculations for the absorber
[53, 73-76]. The calculations start at the top of the absorption tower, i.e. for
the outgoing gas and incoming liquid flow. The calculations are performed within a
given column volume, given by the height, dh. This height is then added to the total
height of the column for each calculation step (h = h + dh), as the calculations
proceed. The size of the step should be small enough to ensure that the temperature
for the previous step does not differ significantly from that of the current step.
Mass and energy balances are solved for each step, giving the concentration and
42 Svenskt Gastekniskt Center AB, Malmö – www.sgc.se