Liquid-phase Claus Process Medium-scale Hydrogen Sulphide Removal Technology Figure 3: CrystaSulf Plant in Europe
• pH 3.8 (non-corrosive); • total petroleum hydrocarbons, 515ppm; • benzene, 0.041ppm; • toluene, 0.054ppm; • ethylbenzene, 0.3ppm; and • total xylenes, 0.29ppm.
Toxicity testing: •
fathead minnow screen – zero dead at 750mg/l.
Even though the CrystaSulf sulphur has lower hydrocarbon levels than is the case with other aqueous processes and can be used for agriculture, acid production or blended with Claus sulphur, it is darker and not as cosmetically appealing as typical Claus sulphur.
CrystaSulf Commercial Operation
The Norsea gas terminal is located near the city of Emden in north-west Germany along the North Sea coast. Gassco operates this facility and the network of gas pipelines which transport the associated gas from the North Sea oil platforms to onshore processing plants. A portion of this gas flows to the Norsea gas terminal where the gas, which contains
filters. However, if, during severe upsets, some liquids reach the CrystaSulf absorber, they will not cause operating problems.
Tests where liquid hydrocarbons were purposely added to the
CrystaSulf system at up to 25 volume per cent did not affect H2S removal or operability. Obviously, if enough heavy hydrocarbons are allowed to contaminate the system, solution reclamation or replacement will eventually be required.
Product Sulphur Quality Table 1 compares the CrystaSulf demonstration unit sulphur composition with the composition of sulphur from one of the aqueous liquid redox pilot units that was tested by the Gas Research Institute. As shown, the CrystaSulf demonstration unit produced sulphur of 96% purity on a wet basis and 98% purity on a dry basis. The purity for the aqueous-produced sulphur, on the other hand, ranged from 81% on a wet basis to 93% on a dry basis. The sulphur from the CrystaSulf unit, even though produced in a hydrocarbon system, had less carbon than sulphur from the aqueous-iron system. Further, the vertical press-type filter used on the aqueous-iron sulphur cake in the testing is a very costly system designed especially to produce a low-moisture product.
Because the sulphur is crystallised in solution, the sulphur product from the CrystaSulf demonstration unit was also larger in size than that produced in an aqueous liquid redox plant. Compared with the large particles shown in Figure 2 (which are typically tens to hundreds of microns in size), aqueous processes produce sulphur in the 1–10 micron range and must use surfactants and additives to allow the sulphur agglomerate to be removed.
Analytical results and other testing have shown that CrystaSulf sulphur is acceptable for use in agricultural applications:
•
non-detected – metals, cyanides, gasoline-range organics and reactive sulphide;
48
H2S, is conditioned prior to distribution in Europe. During 2005, CrystaSulf was installed at the facility so that the sales gas could meet a new total sulphur specification of 3.3ppmv, while reducing the amount of scavenger injected for control of H2S on an offshore
Elemental sulphur has traditionally been a problem in aqueous systems because sulphur is extremely insoluble in water and thus nucleates, rapidly forming small particles.
platform in the network. The CrystaSulf unit, shown in Figure 3, was brought into service treating gas in 2006.2–4
The characteristics of CrystaSulf made it an ideal fit for the high-pressure gas stream at the
Norsea gas terminal, so it was chosen for H2S removal after an extensive evaluation of all available technologies. The factors favouring the selection of CrystaSulf are summarised below:
• lowest-cost option; • •
low circulation rate of solution to the high-pressure absorber; low pumping cost and electrical requirement;
• not affected by CO2; •
• sulphur is dissolved in the non-aqueous solvent;
• handles fluctuating H2S load and gas flow; •
can be turned down to 10% of design; non-toxic byproduct sulphur stream; and
• SO2 needed by CrystaSulf is available from a nearby producer, who also takes the sulphur produced.
The CrystaSulf process offered the inherent capital cost benefits of a one-step approach while avoiding both the operating and
HYDROCARBON WORLD – VOLUME 6 ISSUE 1
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