5-10 TPD Sulferox Unit (10 TPD nameplate capacity)( 5tpd for a low pressure gas stream & 10tpd for a high-pressure gas stream)
Product: 25% Soda
Capacity: 10 m3
Sulferox is a redox-based process that converts H2S in sour gas to elemental sulfur through reaction with aqueous ferric iron, Fe(lll). Organic Ligands or chelating agents (denoted L) are used to increase the solubility of iron in the operating solution. The reaction of H2S to elemental sulfur is carried out in the absorber and can be summarized as follows:
2 Fe+3 L + H2S ---------> 2 Fe+2 L + S° + 2 H+
Because the chelating agents have a high affinity for iron, corrosion-resistant stainless steel must be used for process vessels and piping. Carbon steel and some other metals (e.g. aluminum, brass, copper) are aggressively attacked and readily dissolved by the chelates, even though the solution is not corrosive to the skin. Any spills or leaks of the solution onto non-stainless metal components of the plant should be thoroughly washed as soon as possible to avoid excessive corrosion problems.
Because Sulferox is a continuous process, the above reaction cannot be carried out indefinitely without depleting the Fe(lll) in the solution. The spent iron chelate from the absorber must therefore be regenerated via reaction of Fe(ll) back to Fe(lll). This is accomplished by reacting the solution with oxygen from an air source in the regenerator vessel. The reaction is shown below:
2 Fe+2 L + 1/2 O2 + 2 H+ --------> 2 Fe+3 L + H2O
Because water is formed in the process, the unit must be monitored to ensure that excess water does not accumulate and dilute the solution. The overall process reaction is therefore:
H2S + 1/2 O2 --------> H2O + S°
The Sulferox process forms solid sulfur that is chemically regulated to form large easily-filtered particles which sink under normal process conditions. These particles are first concentrated and then sent to a filtration system for removal. The resulting filtrate is returned to the process for maximum process solution recovery.
Under the conditions of the process, the chelating agent is susceptible to both chemical and thermal degradation, which results in the formation of species which may or may not be effective ligands. The solution composition is maintained to minimize the rate of chelate degradation to minimize chemical makeup and operating costs.
The temperature of the solution must be controlled within desired operating ranges, ( because thermal degradation of the chelate can occur if the solution is subjected to excessive heat. Normal operating temperatures are 110 to 140 °F.
Degradation products formed in the process are carried out as a loss of solution with the moist sulfur cake. This natural "bleed", if properly controlled, will eliminate the need for a deliberate process purge to reduce the degradation product concentrations in the solution. If degradation products are not allowed to go out on the filter cake, a separate purge stream would be required.
The operating discipline of the process is to reduce the amount of degradation, rather than attempt to eliminate degradation. Solution process temperatures are carefully monitored and controlled to reduce thermal degradation. Degradation inhibitors are added to the process to reduce the rate of chemical degradation.
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