الفهرس 
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Abstract
Carbon dioxide (CO2) removal from natural gas by using amine-based solvents can be enhanced by the addition of accelerators such as piperazine (PZ) to the diglycol amine (DGA) solution. In this work, the effect of the addition of piperazine on the amount of CO2 removal was studied and simulated using Hysys software. In addition, the effect of process variables variation on the amount of CO2 removal were also studied. Process flow diagram (PFD) of an actual natural gas plant was used to study the sweetening process using new solvent mixture based on an actual feed gas stream from Egyptian natural gas treatment plant.
The gas stream contains 10% CO2 and it was treated to decrease the CO2 content to less than 1% by mole. Efficiency of the CO2 removal was studied by using various strengths of DGA; 45%, 50% and 55% in addition to different piperazine ratios (3, 5, 7, 9 and 11%) at constant DGA strength (55%). In addition, variable operating parameters of the process were tested, such as absorption temperature (ranging from 38 oC to 58 oC), column pressure (ranging from 45 kg/cm2 to 77 kg/cm2), amine strength and the amine recirculation rate.
It was found that adding piperazine enhanced the efficiency of absorption, but to a specified limit, when the reaction is mass transfer limited. Decreasing the operating temperature enhanced the absorption efficiency but to certain limit to prevent hydrocarbon condensation. Also, decreasing column pressure, decreased the CO2 partial pressure in the gas and as a result the rate of reaction with amine was reduced. Moreover, increasing the recirculation rate was found to enhance the efficiency of absorption until equilibrium is reached.
The study indicates that the minimum amine rate of circulation required to decrease content of CO2 less than 1% was 3750 kgmole/h when using DGA of 55% concentration while it was 3250 kgmole/h when using PZ and DGA mixture of 55% and 9% respectively which means that adding PZ to DGA reduces the circulation rate required to decrease CO2 content to less than 1% by mole. Circulation rate is the main factor in amine solvents economics; It affects the sizing of pumps, piping, stripper and coolers. The energy needed for regenerated solvent is affected by the rate of circulation because the heat duty of reboiler is affected directly by the circulation rate, so, this will greatly affect the total cost of the gas sweetening plant. In this study using 55% DGA+9% PZ decreased the circulation rate required to achieve CO2 content to less than 1% (mole) by 500 kgmole/hr. caused decrease in the regeneration cost lead to decrease the capital and operating cost by nearly 13 %, 10 % respectively.