ELSOR Process to Extract Hydrogen Sulfide from Natural Gas

Published in the Collection of Theses and Reports at: Scientific and Practical Conference “Ecological Technologies in Oil Refining and Petrochemistry”, Ufa, October 7-10, 2003

V.M.Bakhir, Yu.G.Zadorozhnii

OAO NPO “EKRAN”, Moscow

The main principle of ELSOR process is the absorption of hydrogen sulfide from gas by alkali produced in the electrochemical reactor from a sodium sulfate aqueous solution and subsequent regeneration of the hydrogen sulfide-saturated absorbent with acid produced by the same electrochemical reactor.

The figure on the right shows the schematic diagram of ELSOR process. The initial 10% sodium sulfate aqueous solution is electrochemically treated in the cathode chamber of RFE electrochemical reactor and, while being transformed into sodium hydroxide, accumulates in tank T1. At the same time a sulfuric acid solution is being formed in tank Т2. The whole process that takes place in the electrochemical reactor can be presented as follows: Na2SO4 + 4H2O ® 2NaOH + H2SO4 +2H2 + O2.

With the help of high pressure pump P1, sodium hydroxide solution is fed into absorber A where the acid components of natural gas interact with the absorbent as follows: 2NaOH + H2S ® Na2S + 2H2O; 2NaOH + CO2 ® Na2CO3 + H2O; Na2CO3 + H2S ® Na2S + H2CO3.

By way of throttle valve TV, a saturated solution of the absorbent is supplied from absorber A into mixer M where absorbent regeneration processes occur: Na2S + H2SO4 ® Na2SO4 + H2S; Na2CO3 + H2SO4 ® Na2SO4 + H2O +CO2.

Acid gases are removed from desorber D, and when the regeneration process is over, sodium sulfate solution again fills the electrode chambers of the RFE electrochemical reactor.

The quantity of sodium hydroxide needed to purify 1 m3 of natural gas from hydrogen sulfide, no matter what the content ratio of [ CO2] : [ H2S] is, can be determined from the following dependence:

c1 = k × c2,

in which c1 is the quantity of sodium hydroxide necessary for cleaning 1 m3 of natural gas, g;

c2 – hydrogen sulfide content in 1 m3 of natural gas, g;

k – proportionality ratio equal to 2.5 if [ CO2] : [ H2S] < 1 and 2.8 if [ CO2] : [ H2S] > 1;

[ CO2] , [ H2S] - carbon dioxide and hydrogen sulfide concentrations in natural gas, g/m3.

Power consumption for sulfuric purification is calculated from the dependence:

W = (k · c2 · F · Q · U) : 144,

where W is power consumption, kWh; U – voltage on reactor electrodes, V; Q – crude gas discharge, m3/h.

Thus, the current strength being technologically conditioned, power consumption for sulfuric purification mainly depends on the design of an electrochemical reactor. The lower voltage on its electrodes, i.e. the lower the total electrical resistance, which is the sum of diaphragm, electrodes and electrolyte resistances, the lower the consumption of power required for producing the sodium hydroxide in catholyte solution and the sulfuric acid in anolyte solution. The voltage on the RFE reactor electrodes made up of FEM-7 elements, developed and serially manufactured by NPO “EKRAN”, is 3.5 V, which provides for the best technical and economic parameters of absorbent synthesis and regeneration process.

Compactness of the technological device, high safety of the technological equipment, ability to monitor the process selectivity and the degree of hydrogen sulfide and mercaptan extraction allow efficient cleaning of oil field associated gases, purifying fuel gases coming to heat-and-power engineering facilities and technological gas release (salvo and regular) at chemical and petrochemical plants as well as in the manufacture of special equipment and arms.

Quantity of NaOH needed to purify 1000 nm3 of gas from hydrogen sulfide at any CO2:H2S ratio

Hydrogen sulfide content in gas, %

Hydrogen sulfide content in 1000 nm3 of gas, kg

Quantity of NaOH necessary to purify1000 nm3 of gas, kg

Power consumption for NaOH synthesis, kWh

0.1

1.5

5.0

14

0.2

3.0

10.0

28

0.3

4.5

15.0

42

0.4

6.0

20.0

56

0.5

7.5

25.0

70

1.0

15.0

50.0

140

5.0

75.0

250.0

700

10.0

150.0

500.0

1,400

Working parameters of 10 kg NaOH/h-capacity device for electrochemical synthesis of sodium hydroxide and sulfuric acid from sodium sulfate solution

Name

Value

Power consumption for electrochemical synthesis of NaOH and H2SO4, kWh

28

Power consumption for auxiliary purposes (preparation and purification of additional feeding solution, supply of cooling water, making solution to clean electrochemical reactors), kWh

2

Quantity of sodium sulfate used at the moment of setting the device in motion, kg

120

Quantity of sodium sulfate used for preparing additional feeding solution, kg/day

5

Discharge of water (any quality) for cooling electrochemical reactors, L/h

200

Published in the Collection of Theses and Reports at: Scientific and Practical Conference “Ecological Technologies in Oil Refining and Petrochemistry”, Ufa, October 7-10, 2003.

ELSOR Process to Extract Hydrogen Sulfide from Natural Gas

V.M.Bahir, Yu.G.Zadorozhnii

NPO "EKRAN", Moscow