7/29/2019 Sour Gas Processing

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Special Supplement to

HYDROCARB

PROCESSING

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Challenges andopportunitiesor the global reining industry

Natural gas is widely seen as a key element in the energy mix that willmeet the worlds growing demand over the coming decades becauseo its abundance, its accessibility, and its contribution (as the lowest-carbon ossil uel) to solving the global emissions challenge.

Over the decades, gas development projects have evolved a long way,rom the relatively simple exploitation o sweet gas reserves that weredirectly routed into domestic and industrial supply networks, to theexploitation o contaminated and remote gas deposits throughliqueaction, marine transport and regasication.

In recent years, production o gas resources has increasingly requiredthe removal o sulphur species as well as H

2S, CO

2and H

2O, making

the gas treating process much more complex and more expensive:today, the capital expenditure o the treating section can sometimesamount to more than 50% o the total capex in developing a sour gaseld. Complexity has also been increased by recent tightening oproduct specications or both sales gas and Liqueed Natural Gas(LNG), as well as stricter environmental standards.

However, challenging times tend to be good or stimulating innovation.Experience o three recent projects is presented here, whichdemonstrates the benets o an integrated approach to the acid gasremoval and sulphur recovery sections o sour gas processing.

Finding the most suitable solutionShell has extensive experience with gases containing a wide range ocontaminant levels, up to around 50 mol% H

2S and above 20 mol%

CO2. Treatment can involve a wide variety o dierent process

technologies. The three projects described here used:

n the Shell Sulnol process, which removes H2S, CO2, carbonylsulphide, mercaptans and organic sulphur components rom natural

and synthesis gas rom coal or oil gasiers and steam reormers; and

n Shell-Paques/THIOPAQ, a biological desulphurisat ion process, whichdirectly removes H

2S rom gas streams and recovers it in the orm o

elemental sulphur, with up to 100 tons a day o sulphur produced per unit.

The choice o the optimal treating line-up can be quite a complexendeavour, depending on the level o contamination and presence otrace components such as mercaptans. A rule o thumb or the selectionis that it can be considered as a unction o the H 2S to CO2 ratio and theamount o sulphur produced per day.

Solutions and partners where deep removal o H2S, CO2 and tracesulphur components was required.

In one example, with eed gas containing around 2.5 mol% H2S

and 2.4 mol% CO2, as well as mercaptans, deep removal o all t

contaminants was perormed in the AGRU with Sulnol-X technolThis is a second generation version o Shells Sulnol process, in the removal o mercaptans in the AGRU results in a smaller molesieve unit. A separate regeneration gas-treating unit is not needeas the regeneration gas stream contains only a minor amount omercaptans and can be recycled back to the main absorber o thAGRU. The result is a much simpler process arrangement, with seadvantages: higher CO

2and COS removal rates due to enhance

reaction kinetics; lower steam requirement, leading to reduced

energy consumption; no oxazolidone ormation; tighter spe cicaachievable; and lower chemicals consumption leading to lowerwaste disposal.

In this particular instance, liquid petroleum gas (LPG) extractionollowed the treatment o the gas. By perorming deep removal o athe contaminants in the AGRU with Sulnol-X technology, it was poto avoid the need or an additional downstream treating acility omercaptans removal rom the LPG raction and as a result gainadditional capex benets rom the integrated line-up.

Project 1: Enhanced enrichment line-up with Sulnol-MAcid gas enrichment can be required beore sulphurrecovery, in situations where the H

2S to CO

2ratio is

signicantly lower than 1. An eective way to achievethis involves a highly selective process line-up, employingSulnol-M technology in the acid gas removal unit(AGRU), together with an integrated enrichmentabsorber and a hot fash to increase the H

2S content o

the acid gas.

One o the projects where we have applied this approachis a large gas plant in the Middle East. The plant has adesign capacity o 2.7 billion standard cubic eet per day;the eed gas contains about 7.7 mol% CO

2and about

4.3 mol% H2S, with some heavy hydrocarbons such as

benzene, toluene and xylene as well. The specication othe treated gas is 4 parts per million (ppm) o H

2S and

1000 ppm o CO2.

Loaded acid gas rom the acid gas absorber is sent to anenrichment fash vessel, where fashing at elevatedtemperature occurs. Flashed CO

2is sent to the selective

enrichment absorber to remove remaining H2S, and the

loaded solvent is then combined with the loaded solventrom the hot fash and sent t o the regenerator. Thedownstream sulphur recovery unit (SRU) employs JacobssEuroClaus technology.

The results o this integrated line-up with Sulnol-M includea H

2S content o around 60 mol% in the acid gas

signicantly better than the 36 mol% that would beachievable using a generic methyl diethanolamine(MDEA) line-up without the integrated enrichmentabsorber and hot fash. This increase in H

2S content led

to a signicant decrease in the size o the SRU, yieldingcapex savings that ar outweigh the slightly higher capexrequired or the integrated Sulnol-M AGRU. Estimatedoverall capex savings or this gas plant were aroundUS$200 million.

Project 2: Biological desulphurisation o associated gasShell Global Solutions, with our technology partner

Paques, recently secured the application o our biologicaldesulphurisation technology, THIOPAQ, or the rstassociated gas reuse project in the Caspian region.

This desulphurisation process was selected or itssimplicity and low operational complexity whenintegrated into the overall process scheme. Theintegrated process allows direct sulphur removal romsour gas, without having to rst capture H

2S and then

recover sulphur.

The design capacity o the desulphurisation plant is 2million standard cubic eet per day o sour associatedgas with around 4 mol% H

2S; this translates into about

18.5 tons o sulphur produced per day. Because ouncertainty over the presence o mercaptans andaromatics, it was important to adopt a fexible approachto the acilitys design, with the possibility o sending

vent gas to an incinerator. As the eld is located in avery remote area, careul management o the causticsupply is also required. Currently, an advancedrecycling technology or caustic, which is underdevelopment, is being considered as an option ordeployment at the Caspian project site to minimisechemicals consumption.

Project 3: All-in-one removal with Sulnol-XSeveral projects have been conducted by Shell Global

sour gasproCessingreCent projeCt experienCeS demonStrate the effeCtiveneSS of inteGrated SolutionS

L

C

Feedgas

Treatedflashgas to

incinerator

Regenerator

Mainabsorber

Treatedgas

1

4

2

Treatedflashgas to fuel gas

3

Enrichmentabsorber

Condensates

Enrichmentflash vesselFlash vessel

An integrated gas treating line-up

[H2S] / [CO

2] Ratio

SulphurProduction

(t/day)

Acid GasEnrichment Required

Amine + Claus+ Tail Gas Treating

Biological Desulphurization

100

Schematic showing the choice of treating solutions as a function of

the H2S to CO

2ratio and the amount of sulphur per day

Special Supplement to

HYDROCARB

PROCESSING