{"id":1367,"date":"2012-06-01T12:04:24","date_gmt":"2012-06-01T17:04:24","guid":{"rendered":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/?p=1367"},"modified":"2012-10-23T08:15:25","modified_gmt":"2012-10-23T13:15:25","slug":"solubility-of-acid-gases-in-teg-solution","status":"publish","type":"post","link":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/2012\/06\/solubility-of-acid-gases-in-teg-solution\/","title":{"rendered":"Solubility of Acid Gases in TEG Solution"},"content":{"rendered":"

In gas dehydration service, triethylene glycol (TEG) will absorb limited quantities of BTEX (benzene, toluene, ethylbenzene, and xylene) and acid gases such as carbon dioxide (CO2<\/sub>) and hydrogen sulfide (H2<\/sub>S) from the gas. Predicted absorption levels for acid gases can be as high as about 10 SCF\/gallon (75 SCM\/m3<\/sup>) of TEG solution and depends on temperature, pressure, acid gas concentration in the vapor phase and TEG concentration. Figure 18.16 in reference [1] shows the solubility of H2<\/sub>S in TEG at various H2<\/sub>S partial pressures. This is true absorption that takes place in the absorber and corresponds to typical actual plant data. Figure 18.17 also in reference [1] shows solubility of CO2<\/sub> in a 96.5 weight percent TEG solution. The absorption of acid gases increases with TEG purity. The solution of acid gases in TEG solution lowers its pH and enhances corrosion. In addition, one of the main issues is dealing with the H2<\/sub>S that comes off the still regenerator. This is a problem if vented (bad smell & poisonous) and can be a significant source of emissions (SO2<\/sub>) if burned.<\/p>\n

In the June 2011 tip of the month (TOTM), we presented diagrams for quick estimation of absorption of BTEX in the glycol dehydration systems using the experimental vapor-liquid equilibrium data. The objective of this TOTM is to reproduce similar diagrams covering wide ranges of operating conditions. First we demonstrate the accuracy of a recent model proposed by Mamrosh et al.<\/em> [2] against Gas Processors Association experimental data and then reproduce some of their recommended diagrams for approximate and quick estimation of acid gas absorption in TEG solution.<\/p>\n

Mamrosh-<\/strong>Fisher-Matthews Solubility Model:<\/strong><\/p>\n

Recently, Mamrosh et al.<\/em> [2] presented the following correlation based on the experimental data to estimate solubility of CO2<\/sub> and H2<\/sub>S in TEG solution.<\/p>\n

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The values of the A, B, C,<\/em> D, and E<\/em> parameters are given in Table 1. For details of the calculation procedure and a sample calculation refer to reference [2].<\/p>\n

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Accuracy of Mamrosh-<\/strong>Fisher-Matthews Solubility Model:<\/strong><\/p>\n

The accuracy of the Mamrosh et al.<\/em> [2] model was evaluated against the experimental data of Gas Processor Association Research Reports RR 183 [3] and RR 189 [4] for CO2<\/sub> and H2<\/sub>S solubility in TEG solution, respectively. The summary of our evaluation results is shown in Table 2.<\/p>\n

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It should be noted that for three cases of experimental data of H2<\/sub>S in TEG\/H2<\/sub>O system, the absolute percent deviations were abnormally high (128, 260, and 319 %); therefore, they were eliminated from our analysis. Considering the error analysis shown in Table 2, the proposed model by Mamrosh et al.<\/em> [2] has good accuracy for estimating solubility of acid gases in TEG\/H2<\/sub>O solution. All experimental data reported in GPA RR 183 and RR 189 were collected at equilibrium. No consideration in the proposed model is given to the rate at which processes reach equilibrium.<\/p>\n

Figures 1 and 2 present a graphical comparison of the calculated CO2<\/sub> and H2<\/sub>S solubility (mole fraction of acid gas in the liquid phase) with the experimental data of GPA RR 183 and GPA RR 189 for CO2<\/sub> and H2<\/sub>S, respectively. Overall, good accuracy is observed for both systems in these two figures. The ranges of data are the same as those shown in Table 2.<\/p>\n

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Figure 1. Accuracy of the proposed model by Mamrosh et al.<\/em> [2] for estimating CO2<\/sub> solubility in TEG solution against GPA RR 183 experimental data [3]<\/p>\n

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Figure 2. Accuracy of the proposed model by Mamrosh et al.<\/em> [2] for estimating H2<\/sub>S solubility in TEG solution against GPA RR 189 experimental data [4]<\/p>\n

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In Figures 3 through and 8 we have reproduced the CO2<\/sub> and H2<\/sub>S solubility (on volumetric basis of SCF\/gallon of TEG solution or SCM\/m3<\/sup> of TEG solution) for pressures of 1000 and 500 (6897 and 3448 kPa) representing contactor pressure, and 50 psia (345 kPa) representing the flash separator in a typical TEG dehydration unit. In each of these diagrams the solubility is presented as a function of temperature, acid gas mole % in the gas phase, and H2<\/sub>O weight % in TEG solution based on the model proposed by Mamrosh et al. <\/em>[2]. These figures are reproduced in the field or Engineering<\/em> (FPS) and SI<\/em> (International) systems of units. They can be quickly used to estimate acid gas absorption by TEG solution. In addition, Figures A1 through A6 in Appendix A present solubility of acid gases in terms mole fraction instead of volume basis.<\/p>\n

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Conclusions:<\/strong><\/p>\n

We have performed an independent evaluation of a recently developed model by Mamrosh et al.<\/em> [2] for estimation of acid gas absorption by TEG solution while dehydrating natural gas.\u00a0 Our evaluation was based on the experimentally measured data reported in the GPA RR 183 [3] and GPA RR 189 [4]. All experimental data reported in GPA RR 183 and RR 189 were collected at equilibrium. No consideration in the proposed model is given to the rate at which processes reach equilibrium.<\/p>\n

The analysis of Figures 1 and 2 and Table 2 indicates, that even though the Mamrosh et al.<\/em> [2] model is simple and easy to use, it is relatively accurate for estimation purposes. It also covers a wide range of operating conditions. Based on this model we have reproduced Figures 3 through 8 in the field<\/em> and SI<\/em> systems of units that can be used to estimate the absorption of CO2<\/sub> and H2<\/sub>S in TEG solution during gas dehydration. The analysis of Figures 3 through 8 also indicates that at the same conditions, the solubility of H2<\/sub>S is almost 5 times greater than that of CO2<\/sub>. In addition, it can be concluded that the absorption of acid gases increase as:<\/p>\n