- Article :
Natural Gas Desulfurization with High Pressure Redox Process SULFINT HP

- Diaporama :
THE CATALYTIC NOX AND DIOXINE REMOVAL UNIT OF THE SEWAGE TREATMENT PLANT OF COLOMBES (France) (DENOX)

Natural Gas Desulfurization

with High Pressure Redox Process SULFINT HP

 

 

S.  Guillon, P.Y. Le Strat                     Gaz de France, France

J.P. Ballaguet, C. Streicher                Institut français du Pétrole, France

J.P. Cousin                                          Le Gaz Intégral, France

 

Summary

  

Introduction

Redox processes allow the removal of H2S from gases along with its direct conversion into elemental sulfur, in a single unit. Due to their high sulfur removal efficiencies and their simplicity, redox processes are economically attractive, compared to other desulfurization processes (Claus chains,...), in the field of moderate sulfur production (from some tens of kg up to a few tons per day). Unfortunately current redox technologies are not applicable for treating gases at high pressures.

IFP and LGI in association with GDF have developed a new redox process, SULFINT HP, which is applicable for the direct treatment of high pressure gases, like natural gas.

This new process has been successfully demonstrated under industrial conditions on a pilot plant treating high pressure (80 bara - 1150 psia) natural gas from an underground storage at Soings en Sologne (France) operated by GDF.

Redox processes

Redox processes are desulfurization processes of gases where H2S containing gases are washed by a solution containing a catalyst, usually an aqueous solution of chelated iron ions. H2S is absorbed by the solution and converted into elemental sulfur. The catalytic solution is then regenerated by contact with air and recycled. Redox processes allow a direct oxidation of H2S into elemental sulfur, at ambient temperature, with nearly 100% selectivity, leading to residual H2S levels in the treated gas lower than 1 ppm.

When high pressure gases are to be desulfurized with a redox process, the aqueous solution leaving the absorber at high pressure contains elemental sulfur in the form of a suspension of very fine particles and a significant amount of dissolved gases. Experience showed that the depressurization of this mixture before the atmospheric air oxidation step can yield severe foaming and plugging problems. Despite some attempts, the direct treatment of gases at pressures above 35 bar remains challenging and the most common way for high pressure gas desulfurization remains H2S extraction with an amine unit, followed by a low pressure redox unit treating the acid gas from the amine.

 

 

Figure 1- Redox processes principles

Sulfint HP processes

The new redox process Sulfint HP developed by IFP and LGI, in association with GDF, allows direct H2S removal from high pressure gas.

The Sulfint HP process differs from the other redox processes by its flowsheet configuration that is shown in figure 2. Its technical innovation lies in a continuous separate high pressure filtration used to remove the elemental sulfur particles from the redox solution before the depressurization, and a subsequent low pressure oxidation of the catalyst. The high pressure sulfur separation is performed by a filter designed for continuous high pressure operation. Filtration cartridges, constituted of flexible filtration clothes, are alternatively loaded and discharged by reverse flow. The settled sulfur cake is periodically removed through a depressurization chamber.

The continuous filtration of the solution before its depressurization and subsequent oxidation offers many advantages compared to more conventional flow schemes where the sulfur is removed only after the oxidation step. In particular, foaming and plugging problems are avoided. Moreover, only the stoechiometric quantity, needed for H2S removal, of clear redox solution is depressurized.

 

 

 

Figure 2- Sulfint HP flowsheet (A : absorber, F :filter, O : oxydizer)

Pilot plant tests and results

A Sulfint HP pilot plant, treating up to 2000 m³(n)/h - 1.7 MMSCFD of high pressure (80 bara - 1150 psia) natural gas from an underground storage at Soings-en-Sologne (France) operated by GDF, has been operated successfully for more than 3000 hours between 1999 and 2000.

The operation of the process has always been very stable and reliable, without any foaming or plugging problem, even at high sulfur loading. During the year 2000 campaign, the tests were conducted with H2S levels between 15 and 5000 ppm vol., obtained by injection of additional H2S in the feed gas.

The H2S conversion is above 99.5%. At design conditions, the H2S outlet concentration is lower than 0.1 ppm vol. This outlet H2S level remained constant for more than 1000 hours, under fixed operating conditions. No troublesome sulfur deposits could be observed.

 

 

 

Figure 3- Performance of the pilot scale unit Sulfint HP at different operating conditions (year 2000 campaign)

Economic advantages

For high pressure natural gas desulfurization and in the field of moderate sulfur production (from 100 kg up to 20 tons per day), studies have concluded that up to 50% investment savings could be gained using redox processes instead of the conventional Amine+low pressure redox system currently used.

In addition, Sulfint HP allows the reduction of operation costs. In particular, plugging and foaming risks are reduced, which allows the reduction of catalytic solution loss. Pumping costs are also minimized since only the minimal amount of redox solution which is stoechiometrically required has to be depressurized and oxidized.

 

Conclusion

The new redox Sulfint HP process has proved to operate satisfactorily for the direct desulfurization of natural gases containing H2S with a concentration from 15 to 5000 ppm vol. Two test campaigns (in 1999 and 2000) confirmed that the filtration of the sulfur loaded redox solution at high pressure allows to operate without any foaming or plugging problems. At the pilot unit design conditions, the desulfurization efficiency is greater than 99.5%.

A third test campaign is foreseen during winter 2000-2001 in order to get data for the operation of the process under various gas compositions representative of field natural gases.

Note : A video presenting the pilot tests can be showed (7 mn).

Contact :        Filippo ROSSATI

                        LE GAZ INTEGRAL

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