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US-12616933-B2 - Hot circulation enhancement in amine units

US12616933B2US 12616933 B2US12616933 B2US 12616933B2US-12616933-B2

Abstract

A method for preparing a gas sweetening system for less shutdown time is provided. The method includes stopping a sour gas feed to a gas sweetening system, and raising the set point for a temperature of a lean amine cooler to about 150° F. The H 2 S concentration in a lean amine is monitored. The preparation of the gas sweetening system for maintenance is completed when the H 2 S concentration reaches a target value.

Inventors

  • Yousef Nassir Alfnais

Assignees

  • SAUDI ARABIAN OIL COMPANY

Dates

Publication Date
20260505
Application Date
20230830

Claims (9)

  1. 1 . A method for preparing a gas sweetening system for maintenance, comprising: stopping a sour gas feed to a gas sweetening system; raising the set point for a temperature of a lean amine cooler to about 150° F.; monitoring an H 2 S concentration in a lean amine; and completing the preparation of the gas sweetening system for maintenance when the H 2 S concentration reaches a target value.
  2. 2 . The method of claim 1 , wherein monitoring the H 2 S concentration comprises taking samples of a lean amine for laboratory analysis.
  3. 3 . The method of claim 1 , wherein monitoring the H 2 S concentration comprises tracking a concentration with an analyzer disposed on a lean amine line downstream of a regenerator.
  4. 4 . The method of claim 1 , wherein the target value is between 0 ppm H 2 S and 50 ppm H 2 S.
  5. 5 . The method of claim 1 , wherein the target value is about 30 ppm H 2 S.
  6. 6 . The method of claim 1 , wherein completing the preparation of the system comprises draining the lean amine from the gas sweetening system to a storage tank.
  7. 7 . The method of claim 1 , comprising placing the gas sweetening system back in service after maintenance comprising adding amine to the gas sweetening system from a storage tank.
  8. 8 . The method of claim 7 , comprising, after adding the amine to the gas sweetening system, lowering the set point for the temperature of the lean amine cooler to 130° F.
  9. 9 . The method of claim 7 , comprising restarting the sour gas feed to the gas sweetening system.

Description

TECHNICAL FIELD This disclosure relates to methods of shutdown in amine sweetening systems for service. BACKGROUND Gas sweetening is a process used for removing acid gases from gaseous hydrocarbon streams, such as natural gas, termed a sour gas feed. The sour gas feed is contacted with a lean amine which absorbs hydrogen sulfide and carbon dioxide from the natural gas, sweetening the natural gas and forming a rich, or acid gas saturated, amine. The rich amine is passed through a regenerator for reprocessing, which removes the acid gases and regenerates the lean amine. Diglycolamine (DGA) and methyldiethanolamine (MDEA) are the most the common amine chemicals utilized for acid gases removal. During a shutdown of the unit for Turnaround and Inspection (T&I), a hot circulation process is performed to remove acid gases that remain in the system after stopping the sour gas feed. During the hot circulation process, the amine is circulated inside the amine loop until the concentration of H2S reaches below low concentration levels in order to ensure safe maintenance work execution. To achieve targeted criteria for H2S concentration, The duration of the hot circulation process often takes up to 43 hrs. Commonly, the amine loop temperature is maintained and the steam flow inside the regenerator boilers is increased for faster stripping of acid gases. SUMMARY An embodiment described herein provides a method for preparing a gas sweetening system for maintenance. The method includes stopping a sour gas feed to a gas sweetening system, and raising the set point for a temperature of a lean amine cooler to about 150° F. The H2S concentration in a lean amine is monitored. The preparation of the gas sweetening system for maintenance is completed when the H2S concentration reaches a target value. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a simplified process flow diagram of a gas sweetening system. FIG. 2 is a plot of the H2S concentration in the sweet gas as a function of the temperature of the lean amine. FIG. 3 is a plot of the CO2 concentration in the sweet gas is a function of the temperature of the lean amine. FIG. 4 is a plot comparing historical data for reaching low H2S concentration with the current techniques. FIG. 5 is a process flow diagram of a method for clearing a gas sweetening system for maintenance. DETAILED DESCRIPTION Embodiments described herein provide a method for decreasing the shutdown time for a gas sweetening system in order to complete maintenance or inspections. The common practice for clearing gas sweetening systems is to maintain the amine temperature at about 130° F. using the lean/rich amine exchangers and amine fin fans coolers at set point. The steam flow inside regenerator reboilers is then increased for faster stripping of acid gases. However, this resulted in clearance times of up to 43 hrs to achieve targeted criteria based on operation instruction manual for H2S concentration. The technique is based on raising the temperature of the lean amine by adjusting the set point of an amine fin fan cooler from about 130° F. to about 150° F. to increase desorption of the acid gases. This results in reaching the targeted H2S concentration in less time and steam, for example, providing a lower H2S concentration in about 75% less time and decreasing steam consumption by about 23%, as less steam flow will be needed. Thus, the reduction in steam consumption reduces fuel gas consumption by 8 MMSCF, which provides 0.53 kTons of reduction in CO2 emissions. FIG. 1 is a simplified process flow diagram of a gas sweetening system 100. In the gas sweetening process, H2S and CO2 are absorbed from sour gas 102 in a contactor column 104. The acid gases interact with lean amine 106, such as DGA or MDEA, with differential temperature of higher than about 15° F. for optimum absorption. The sweet gas 108 exits the contactor 104 from the top with less than about 4 ppm H2S concentration and less than about 50 ppm CO2 concentration, depending on the product specifications. Variations in the temperature of the lean amine 106 entering the contactor may change the concentration of the H2S and CO2, as the solubility of these acid gases in the amine changes depending on the temperature and type of amine. The temperature of the lean amine 106 can be controlled by adjusting the set point of an amine fin fan cooler 108. After absorbing the acid gases in the contactor 104, the resulting rich amine 110 is processed in a regenerator 112 which strips the acid gases from the rich amine 110, reforming the lean amine 106. The stripping rate in the regenerator 112 is controlled by steam flow through a reboiler 114. This is discussed further with respect to FIGS. 3 and 4. FIG. 2 is a plot of the H2S concentration in the sweet gas as a function of the temperature of the lean amine. FIG. 3 is a plot of the CO2 concentration in the sweet gas is a function of the temperature of the lean amine. As a result of the effect of the temperature of