Calculating Absorber Tray Size and Design
This procedure is similar to those described in other sections of this handbook.
Emphasis is made here, however, to the foaming tendencies of MEA and DEA.
Most of these units contain facilities to inject antifoaming chemicals. Under normal
operation, these chemicals subdue foaming to a large extent, particularly in the
contactors. The addition of a filter in the rich amine line also helps combat severe
foaming.
It is believed that foaming is enhanced by the absorption of large quantities of
hydrocarbons into the amine stream. This can occur quite easily if the temperature
or pressure change forces the hydrocarbon gas into a condition below its dew point.
The presence of large quantities of impurities such as COS (carbonyl sulfide) or the
tarry derivative of COS may also induce foaming. The addition of the filter and
reclaimer usually solves this problem to a large extent.
Loading of amine towers nevertheless is critical due to the foaming nature.
Consequently the towers are designed with more latitude than most other towers.
In evaluating its performance also the acceptable level of flooding is lower by
20–30 % than that for normal towers.
The calculation to evaluate the tower flooding follows the same steps as those
described in the chapter on “▶ Distillation of the “Light Ends” from Crude Oil in
Petroleum Processing” in this handbook. In this case, however, the calculated value
for V L is multiplied by a system factor between 20 % and 30 %. If the unit is being
used in service where a high concentration of impurities is present, a figure of 30 %
should be used.
Calculating the Heat Transfer Area for the Lean/Rich Amine
Exchanger
The amine in the contactor picks up the heat of reaction which occurs with the
absorption of H 2 S. On leaving the amine contactor or absorber, the rich amine is
heat exchanged against hot lean amine leaving the bottom of the stripper. The
performance of this exchanger is critical to the process as a whole. Usually the rich
amine receives no other heat before it enters the stripper. As in light ends towers,
the feed condition is vital to the proper operation of the tower. The purpose of this
section is to provide a calculation procedure to evaluate the heat transfer coefficient
of this exchanger. The following steps give the procedure:
Step 1. Using lab data for operational units or the design specification for those units
to be designed, determine the quantity of H 2 S absorbed in the contactor.
Step 2. From the data given in Table 1, calculate the total heat of reaction in Btu/h.
Step 3. Set the temperature of the lean gas leaving the absorber to be the same as the
amine entering.
Refinery Gas Treating Processes
511
This procedure is similar to those described in other sections of this handbook.
Emphasis is made here, however, to the foaming tendencies of MEA and DEA.
Most of these units contain facilities to inject antifoaming chemicals. Under normal
operation, these chemicals subdue foaming to a large extent, particularly in the
contactors. The addition of a filter in the rich amine line also helps combat severe
foaming.
It is believed that foaming is enhanced by the absorption of large quantities of
hydrocarbons into the amine stream. This can occur quite easily if the temperature
or pressure change forces the hydrocarbon gas into a condition below its dew point.
The presence of large quantities of impurities such as COS (carbonyl sulfide) or the
tarry derivative of COS may also induce foaming. The addition of the filter and
reclaimer usually solves this problem to a large extent.
Loading of amine towers nevertheless is critical due to the foaming nature.
Consequently the towers are designed with more latitude than most other towers.
In evaluating its performance also the acceptable level of flooding is lower by
20–30 % than that for normal towers.
The calculation to evaluate the tower flooding follows the same steps as those
described in the chapter on “▶ Distillation of the “Light Ends” from Crude Oil in
Petroleum Processing” in this handbook. In this case, however, the calculated value
for V L is multiplied by a system factor between 20 % and 30 %. If the unit is being
used in service where a high concentration of impurities is present, a figure of 30 %
should be used.
Calculating the Heat Transfer Area for the Lean/Rich Amine
Exchanger
The amine in the contactor picks up the heat of reaction which occurs with the
absorption of H 2 S. On leaving the amine contactor or absorber, the rich amine is
heat exchanged against hot lean amine leaving the bottom of the stripper. The
performance of this exchanger is critical to the process as a whole. Usually the rich
amine receives no other heat before it enters the stripper. As in light ends towers,
the feed condition is vital to the proper operation of the tower. The purpose of this
section is to provide a calculation procedure to evaluate the heat transfer coefficient
of this exchanger. The following steps give the procedure:
Step 1. Using lab data for operational units or the design specification for those units
to be designed, determine the quantity of H 2 S absorbed in the contactor.
Step 2. From the data given in Table 1, calculate the total heat of reaction in Btu/h.
Step 3. Set the temperature of the lean gas leaving the absorber to be the same as the
amine entering.
Refinery Gas Treating Processes
511