7/25/2019 Gastech2015_WSA Case Study

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DAY TWO Gastech Conference Newspaper16 Wednesday, 28 October 2015

The Senoro Upstream Gas Project is located in Cen-

tral Sulawesi Province, Indonesia. It produces feed gas

for LNG production from the Donggi-Senoro project.

The Senoro facility has a total production capacity of 310

MMscfd of gas and 8.5 Mbpd of condensate. It is jointlyowned by MedcoEnergi, Pertamina and Tomori EP.

Haldor Topsoe's WSA technology has been chosen to

treat acid gases originating from the gas sweetening pro-

cess at the production facility. The H2S in the gases, com-

ing from both the acid gas removal unit (AGRU) and the

low-pressure fuel gas treatment unit, are converted into

commercial-grade sulfuric acid.

Challenges.Hurdles for the application of the WSAtechnology include:

Stringent local emission regulations

Low H2S concentration of only

1.78 vol%2.33 vol%, and a gas

flow of 2,200 lbmole/h

High reliability and availability are needed for this

kind of project.

Evaluation.Job Tomori created a technology evaluationmodel based on several criteria, namely:

It must be a proven, available, reliable technology

with many references

A technical feasible solution is required for very lean

H2S gases without concentrating

The simplicity of the process will bring down the

cost of maintenance and overall OPEX

Investment costs must be considered, since

concentration of the acid gas would be too expensive

Energy recovery must be sufficient to justify a steam

turbine

The market potential for sulfuric acid is morediverse compared to sulfur.

Application.Based on these criteria, Job Tomori'sinternal evaluation and a third-party evaluation performed

by an international engineering company, Haldor Topsoe's

WSA technology emerged as the optimal solution for

the gas sweetening project. The WSA solution included

several components:

A WSA plant (FIG. 1) that produces 45 tpd of

sulfuric acid

Production of 780 tpd of steam (433C, 28.5 barg),

allowing power production of 5.5 MW

Guaranteed minimum SO2conversion of 97%.

The WSA plant will, in this single catalytic bed layout

(FIG. 2), convert a minimum of 97% of the sulfur and

produce 45 tpd of commercial-grade sulfuric acid, whichis sold on the local market. In addition, about 780 tpd of

superheated steam will be produced, and the steam will be

routed to a turbine to produce power.

To maximize the steam production in the WSA plant,

energy from the condensation of sulfuric acid is recov-

ered in the form of hot air, most of which is supplied to

the combustor. The rest of the hot air is used for preheat-

ing the incoming boiler feedwater. This design makes

the plant extremely energy efficient due to the fact that

most of the heat is recovered back into

the process.

Advantages. The WSA processconverts H2S into sulfuric acid, while a

traditional Claus process produces ele-

mental sulfur. Inherent advantages in theWSA concept emerge when compared

with other technologies:

1. Higher energy efficiency.

Going from H2S to H2SO4

instead of stopping at elemental

sulfur is much more favorable

because of thermodynamics.

Due to the number of exothermic

reactions occurring in the WSA

process, approximately four

times the amount of steam

(of higher quality) is produced

when compared to the

conventional Claus process.

2. Feed flexibility.The WSA process design

allows for very low H2S concentrations in the

feed gas. Furthermore, it is able to accommodate

significant changes in feed gas flow and

composition. This is mainly due to the factthat, in the WSA process, there is a complete

combustion of the feed gases in the initial step,

while the Claus process may have a somewhat

more complex combustion that controls the H2S-

to-SO2ratio. It should be noted that, if significant

amounts of nitrogen-containing compounds

are present in the feed gas, a selective catalytic

reduction (SCR) reactor must be installed to

reduce NOxformed in combustion.

3. Catalysts.In a WSA plant, the combustion of

the feed gas takes place with a large surplus of

oxygen. Therefore, there is no risk of carbon

formation on the catalyst in the WSA process, as

can be the case for the Claus process, especially

when treating lean feeds or feeds containing

benzene, toluene and xylene (BTX). In a Clausplant, carbon deposition can lead to unwanted

stoppage of the plant or insufficient sulfur yield.

4. Product. Sulfuric acid can, in many ways, be

a beneficial product compared to elemental

sulfur; however, this should be evaluated on

a case-by-case basis, taking local conditions

into consideration. Approximately 90% of all

elemental sulfur produced worldwide will be

further processed into sulfuric acid. Therefore,

it can be argued that going from H2S to sulfuric

acid in one stepcompared to a multistep

approach where elemental sulfur is produced as

an intermediateis more efficient

in many aspects. Moreover, sulfuric acid has

a broader market segment with users, such as

the fertilizer industry, steel industry, watertreatment sector, polymer industry, oil refining

sector, chemical industry, etc. In addition,

sulfur can liberate H2S, which can make

product handling troublesome.

5. Cost.A WSA plant typically wil l have lower

investment cost when compared with a

conventional plant equipped with a downstream

tail gas treatment unit (TGTU). This is due to the

simple WSA design, which includes relatively

few pieces of equipment. When considering

operating costs, the WSA technology also has

some important benefits. The large amount

of high-pressure steam produced in the WSA

process will have a positive impact on the

operating income. Finally, the relatively simple

design and operation of a WSA plant result

in lower operations and maintenance costs

compared to a more complex plant.

Recommendations.The WSA process is a simple andefficient sulfur recovery process that meets the demands

of the industry for environmental compliance, low energy

usage and low overall operating costs. Sulfur in any form

is recovered as concentrated sulfuric acid of commercial

quality, and the energy released in the process is efficiently

recovered as high-pressure superheated steam.

The WSA technology can be applied in a variety of

industries, ranging from natural gas treatment and sulfur

recovery in oil refining to the fixation of SO2gases in the

metallurgical industry.

Over the years, Haldor Topsoe has gained considerable

experience in the design and operation of WSA plants for

many different applications. Today, more than 130 WSAplants have been licensed worldwide.

For more information about the latest technologies offered

by Haldor Topsoe, visit the exhibition #A354.

How to treat lean H2S gas from

gas sweetening plantsAMRUL ATIQI and ANNE METTE SRENSEN,Haldor Topsoe

FIG. 1. The WSA plant produces 45 tpd of sulfuric acid.

SO2converter

Combustor

Product sulfuric acid

WHB

SSH

CW

Combustion air

Superheated steam to turbineHot air

Blower

Blower

Acid cooler

Air

Stack gas

Acid gas

Raw LP fuel

BFW

BFWpreheat

WSAcondenser

Steamdrum

Gascooler

FIG. 2. Single catalytic bed layout for the WSA plant.