TGTU feed gas: H S 6.8%v, CO 3.5%v
TGTU feed gas: H S 6.8%v, CO 3.5%v
90 80 100
200
16
200
H S spec
Reboiler steam (t/h) Amine circulation rate (%)
14
175
175
Max H S spec
150
12
150
0 30 20 10 40 50 60 70
125
10
125
100
8
100
6
75
75
50
50
4
H S spec Reboiler steam (t/h)
25
25
2
0
0
0
Conversion
Optimisation
Conversion within 26 hours
Figure 4 Case study 2 optimisation
Figure 3 Case study 2 OASE yellow conversion results
By switching from MDEA to OASE yellow, the refinery’s annual average sulphur capacity increased, which allowed it to run additional sour crude. In addition, it was no longer necessary to rent chillers to cool the lean amine, leading to considerable operating cost savings. Figure 2 illustrates the actual performance test results collected from the unit during the 72-hour swap process. With the stepwise addition of the OASE yellow enhancer system, a noticeable decrease of the H 2 S at the outlet of the unit absorber (red dots) was observed. The solvent circula- tion rate was able to be reduced at the same time, resulting in operational cost savings for the unit. In this case study, a refinery located in South Korea oper - ated a TGTU with acidified MDEA. The feed gas to this unit includes a higher H 2 S content compared to the previous case, with 6.8 mol% H 2 S and a lower CO 2 content of 3.5 mol%. This study aimed to reduce steam consumption while maintaining the environmental permit limit for SO 2 emissions from the thermal oxidiser. Similar to the previous unit, the changeover from acidified MDEA to OASE yellow had a constraint to be done during the unit operation with- out shutting down the process. Case study 2: Switching from acidified MDEA to OASE yellow BASF completed a study considering the unit’s mechani - cal details and concluded that it was possible to reduce the H 2 S content from 150 ppmv to 25 ppmv, maintaining the current steam consumption to the unit. In turn, the steam consumption could be reduced by 35% while still meeting the unit’s environmental limits. Figure 3 illustrates the first step of the conversion with the actual performance test results collected from the unit during the 26-hour swap process. As the OASE yellow enhancer system was added to the system, the treated gas H 2 S content decreased even as the circulation rate was reduced by 25%. In the second step (see Figure 4 ), steam consumption was reduced by 35%, allowing H 2 S concentration to increase to the acceptable limit of 150 ppmv. This steam rate reduction
resulted in an annual Opex savings of approximately $1 million for the unit. Conclusion The selective removal of H 2 S has become an important topic over the last 20 years. With dwindling sweet gas reserves, H 2 S selective gas treatment at low pressure (acid gas enrichment, tail gas treatment, or a combination of the two) has become necessary to produce a high-quality Claus gas, enabling sulphur removal and monetisation of these gas fields. Savings in energy and circulation rate (Opex), as well as a reduction in equipment sizing (Capex), are the obvious benefits of enhanced H2 S selective treatment. Even more, many of the newest projects require a high degree of oper- ational flexibility combined with a robust operation in warm locations enabled by these technologies. Capacity, operational flexibility, reliability, and the ability to achieve specifications are all considered during BASF’s technology selection process, utilising the in-house simula- tion tool, OASE connect. OASE yellow technology utilising the most common selective base amine, MDEA, allowed for smooth swaps from generic solution to meet the stricter emission limits and optimise the unit operational costs. The technology can also be utilised in grassroots designs to achieve further savings on the capital investment of these projects, making them economically more attractive and feasible.
OASE is a trademark of BASF, and FLEXSORB SE PLUS is a trade- mark of ExxonMobil.
Ashraf Abufaris is Senior Technical Market Manager Middle East and gas treatment expert at BASF Middle East Chemicals LLC in Abu Dhabi, UAE. He presented on the effectiveness of BASF’s H2 S selec- tive removal technologies in hot climates at the 28th International Conference and Expo ‘Oil and Gas of Turkmenistan’ held in Ashgabat.
Blake Morell is Technical Market Manager at BASF Corporation in Houston, Texas, USA.
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