DESULPHURIZATION

Introduction

 

Industrial gases, for example natural gas, gas obtained from crude oil processing and associated gas from oil fields, biogas and landfill gas often contain hydrogen sulfide (H2S). Removal of this component is crucial, since H2S can cause corrosion in upstream and downstream operations and is highly toxic.

Several desulphurization processes are readily available, which are only economically viable for specific gas compositions and gas flow rates. Moreover, deep removal of H2S cannot always be obtained, and existing processes are often not selective towards H2S (e.g. co-absorption of CO2).

Procede has developed a novel and innovative desulphurization process called Vitrisol® which is

• 100% selective towards H2S,

• Without co-absorption of CH4 and/or CO2,

• Can obtain deep removal of H2S in one step,

• Is cost effective,

• Patented

The Vitrisol® regeneration process is operated with regeneration of the absorption liquid to minimize operational costs. Vitrisol® can be applied to a wide range of gas streams to be treated, for example from small biogas streams with low concentrations of H2S up to large refinery/natural gas streams with high concentrations of H2S.

The absorption section of the Vitrisol® process was successfully demonstrated and validated in 2011 and 2012 at two biogas sites. The regeneration section was developed from 2011 till 2015 for small scale and large scale gas purification operations. Currently a high-tech, state-of-the-art integrated biogas purification process operated continuously is being designed and constructed. The process does not require the use of activated carbon, and removes H2S, CO2 and H2O more efficient and cost-effectively compared to competing technologies. Moreover, no chemical waste is produced, the sulphur is obtained as a pure crystalline substance and the removed CO2 has food-grade quality.

 

Absorption

 

The Vitrisol® process, a recently developed desulphurization process, is based on the removal of H2S in an absorber by precipitation with copper sulphate (CuSO4) in an aqueous, acidic solution. Copper sulphide (CuS) and sulphuric acid are formed in the process.

The reaction between Cu2+ and H2S proceeds instantaneously and is irreversible, as the reaction product (CuS) is a solid. Therefore the process is completely limited by mass transfer in the gas phase.

Moreover, the Vitrisol® solvent is 100% selective towards H2S, therefore deep removal to concentrations below 1 ppm can be achieved. Due to this selectivity Vitrisol® can be used in systems where other components are utilized downstream of the unit, like CO2 capture systems (as is most often the case in biogas systems). Therefore no need exists anymore to use a process that removes simultaneously CO2 and H2S, which requires an additional separation step of H2S and CO2 downstream.

The absorption can take place under both low and high pressures respectively as well as under moderate and elevated temperatures, making the process suitable for all sorts of gas streams that contain H2S.

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Regeneration

 

In-situ regeneration of the absorption liquid is required to retain a cost effective process.

The Vitrisol® liquid leaving the absorber is treated downstream in an oxidizer, in which the solid CuS is oxidized to Cu2+ and elemental sulphur under the influence of oxygen at moderate temperatures. The sulphuric acid produced in the absorption step is consumed in the oxidation step, resulting in no net increase or decrease of sulphuric acid concentration. The overall oxidation reaction is according to

Subsequently, in an extraction step elemental sulphur is removed from the Vitrisol® by dissolving in a nonpolar solvent at moderate temperatures. Afterwards, crystalline sulphur is produced in a crystallization step, and the lean nonpolar solvent is returned to the extraction step. By doing so, a Vitrisol® absorption liquid closed cycle is obtained with no losses of Vitrisol® absorption liquid. Furthermore, crystalline sulphur as end product is produced.

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Outlook

 

Procede is currently in the process of designing and building a high-tech, state-of-the-art integrated biogas purification process operated continuously. The process does not require the use of activated carbon, and removes H2S, CO2 and H2O more efficient and cost-effectively compared to competing technologies. Moreover, no chemical waste is produced, the sulphur is obtained as a pure crystalline substance and the removed CO2 has food-grade quality.

Besides small case applications like biogas purification, the Vitrisol® technology is ready to be applied to larger scale gas purification applications like e.g. shale  gas.

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                                                Process flow diagram Vitrisol®