**Table 7.**

*Hydrate formation conditions.*


#### **Table 8.**

*Thermodynamic range of hydrate formation.*

The analysis of the conditions of hydrate formation of dry gas at a pressure of 3462 kPa and a temperature of 23°С conditions is given in **Table 7**.

At a pressure of 3462 kPa and a temperature of 23°C, dry gas can be transported without the formation of hydrates.

The formation of hydrates in process plants and pipelines can occur within a few minutes; therefore, it is necessary to know the range of hydrates formation.

**Table 7** shows the range of temperatures and pressures at which hydrates are formed (**Table 8**).

The following figure allows better visualization of hydrate formation as a function of temperature and pressure (**Figure 4**).

The diagram shows the critical properties of the dry gas flow; critical temperature Tcr = 63.12°C, critical pressure Pcr = 6170 kPa.

The figure shows the temperatures and pressures indicated in **Table 2** at which the hydrate is formed.

Thus, in order to ensure the transportation of gas without the formation of hydrates, it is necessary that the transportation be carried out outside these values of temperature and pressure.

#### *2.2.4 Effects of the stripping gas on TEG regeneration*

Stripping gas is an optional element that is used to achieve very high glycol concentrations that cannot be obtained with normal regeneration. This will ensure maximum dew point reduction and greater dehydration. It is also used to ensure

*Analysis of Efficiency of Natural Gas Absorption Process from Water Impurities DOI: http://dx.doi.org/10.5772/intechopen.100417*

**Figure 4.** *Diagram of the formation of hydrates.*

#### **Figure 5.**

*TEG concentration versus stripping gas velocity.*

intimate contact between hot gas and lean glycol after most of the water has been removed by distillation.

The concentration of the regeneration glycol depends on the rate of circulation of the stripping gas. We will analyze the effect of the boil-off gas flow rate adopted for dry gas on the glycol purity. The speed varies from 50 to 300 kg/hr (**Figures 5** and **6**).

#### **Figure 6.** *TEG losses versus stripping gas velocity.*

By analyzing the effect of the stripping gas flow rate, it can be seen that at a reboiler pressure of 100 kPa, the more the stripping gas flow rate increases, the more the glycol concentration increases, but on the other hand, there is little glycol loss. The amount of stripping gas produces a cleaner glycol but causes an increase in glycol loss.

To optimize the operation and from an economic point of view, it is recommended to work on a plant where the reboiler pressure is set at 100 kPa with a boil-off gas flow rate of 200 kg/h, which will allow us to recover glycol up to 99.62% with a loss of 7.5 g/1000 m<sup>3</sup> .

#### *2.2.5 Regeneration of glycol with an azeotropic agent*

The agent is used to form a ternary azeotrope with the mixture.

The DRIZO process provides glycol enrichment by using its own internal stripping medium, a mixture of paraffinic and aromatic hydrocarbons with a boiling range of C5 +.

The patent works with an isooctane solvent, but the typical composition of the stripping medium is aromatic hydrocarbons, naphthene, and paraffin.

In our study case, hexane is used to separate binary water and triethylene glycol. Based on the DRIZO process principle, a 100% hexane hetero-azeotrope is used as our gas does not contain C5+ hydrocarbons (**Figure 7**).

Azeotropic distillation was carried out at various reboiler pressure and the results allowed us to see the concentration of regenerated glycol and the loss of glycol according to the parameters (**Table 9**).

*Analysis of Efficiency of Natural Gas Absorption Process from Water Impurities DOI: http://dx.doi.org/10.5772/intechopen.100417*

#### **Figure 7.**

*The process of regeneration using an azeotropic agent.*


#### **Table 9.**

*Results of the regeneration process.*

Analyzing the results, we see that at atmospheric pressure and a reboiler temperature of 200°C, we can achieve a glycol concentration of 99.981% with a loss of 2.432 kg/h.

Lowering the temperature of the reboiler does not significantly reduce the TEG concentration; therefore, to reduce the heat consumption, the temperature of the reboiler can be set to 140°C.
