SS2100 - H2S Catalytic Reformer H2 Recycle Analyzer Solution

Application Note

Catalytic Reforming Unit

The Catalytic Reformer Unit of a modern refinery is an important process unit for converting lower octane naphtha streams into higher octane aromatic compounds.

These chemical conversions are done in catalytic reactors that transform straight-chain C6-C8 compounds found in the naphtha into light aromatics such as Benzene, Toluene and Xylenes (BTX). This high octane reformate can then be used in gasoline blending or sold to chemical plants.

As shown in Figure 1, depentanized naphtha feed is mixed with recycled Hydrogen gas, preheated and passed through a series of reactors where the conversion to aromatics takes place.

After the last reactor, a Hydrogen Separator strips out the hydrogen and other light gases from the stream. After the removal of the Hydrogen, the stream enters a Stabilizer Tower (also called a Debutanizer) which removes the Butanes and lighter gases with the Reformate leaving the Bottoms for gasoline blending or sent to a chemical plant.

The catalyst in the reactors is very expensive and sensitive to poisoning if exposed to certain compounds; most notably H2S. Traces of sulfur compounds are converted to H2S in the reformer and accumulate in the H2 recycle, where the H2S is readily measured. Recommended H2S levels to prevent poisoning in the feed are 0.25 – 1.0 ppm.

Lead Acetate paper tape analyzers have been used but they require frequent replacement of the paper tape and many regard the paper tape itself as a handling and disposal problem due to its lead content. Gas Chromatographs have often been used but the desired measurements require Flame Photometric and other trace sulfur detectors that can be maintenance intensive.

SpectraSensors SS2100 is the ideal solution for this challenging application. It is extremely fast (<1 sec. updates if desired) and very sensitive (0.5 ppm repeatability). No cylinder gases are required, and the only consumable part, the H2S scrubber, is sized to last a minimum of 18 months between changes. The use of Tunable Diode Laser technology means measurement interferences from other infrared absorbing compounds are avoided.

Refineries normally operate around 5 – 50 ppm moisture level in the hydrogen recycle stream, and attempt to keep the H2S at a minimum. The SS2100 Analyzer can be configured with two cells to measure both moisture and H2S.

SpectraSensors analyzers require no calibration in the field and the calibration is stable for the life of the analyzer, however, validation of the measurement is very desirable. Validation is done with a certified blend of H2S in N2 background available for a number of reputable specialty gas blenders.

The background stream composition must be specified for proper calibration and measurement performance. Specify the Normal composition, along with the minimum and maximum expected values for each component, especially water, the measured component. Other stream compositions may be allowable with approval from SpectraSensors. 

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Data Sheet

Performance
Target Components	H2S in Hydrogen Recycle Gas
Typical Measurement Ranges	0 – 50 through 0 – 300 ppm*
Typical Precision	±2% of full scale*
Measurement Response Time	1 to ~60 sec
Principle of Measurement	Differential Tunable Diode Laser Absorption Spectroscopy (H2O Scrubber Included)
Environmental Temperature Range	-20º to 50ºC (-4º to 122ºF) -10º to 60ºC (14º to 140ºF) optional
Sample Inlet Pressure	70 kPag (10 psig) typical 210 kPag (30 psig) maximum
Cell Temperature	Maintain at 50ºC +/- 0.2ºC
Maximum Cell Pressure	70 kPag (10 PSIg)
Sample Flow Rate	3-4 L/min (6.4 to 8.5 scfh)*
Validation	Certified blend of H2S in Nitrogen balance
Electrical
Power	100-240 VAC, 50-60 Hz standard
Max Current	Controller: 1 A @ 120 VAC
Controller to Cell Cable Length	1m standard (3m, 5m & 10m available optionally)
Communication	Current Loop Output 4-20 mA Isolated, 1200 ohms @ 24 VDC max load Serial: ASCII Text RS232C standard Modbus RS232C
Digital Outputs	4 ea. 12 VDC for valve operations Scrubber (if required), Process/Val, Val 1, Val 2 5 SPDT (Form C) Dry Contact Alarms Common Fault, Val 1 Active, Val 2 Active, Val Fail, one user-assignable to any alarm
LCD Display	Concentration, Cell Pressure and Temperature, Diagnostic Data
Physical
Controller Enclosure	NEMA 4X - Stainless Steel standard
Controller Dimensions	343mm H x 305mm W x 165mm H (13.5" H x 12" W x 6-7/16" D)*
Weight Approximately	13.1 Kg (28.6 lbs)*
Sample Cell Dimensions	28m cell 559 mm H × 127 mm W (22” H × 5” W)
Sample Cell Construction	316L Series Polished Stainless Steel standard
Number of Sample Cells	1 (single channel SS2100) or 2 (dual channel SS2100)
Area Classification	CSA Certified for Class I, Division 2, Groups B,C,D Temp Code T3C  ll 2G Ex d llB+H2 T5; Tamb : -20 ÷ +60 °C
Dimensions with Sample System	1678 mm H x 613 mm W x 427 mm D (66” H x 24-1/8” W x 16-13/16” D)
Weight with Sample System (approx.)	68 kg (150 lbs.)
Note: The Analyzer scope of supply is the controller and enclosure, the cell and the interconnecting cables. SSI or qualified systems integrator can supply sample conditioning systems appropriate to the applications. * Application specific; consult factory

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Drawings

Typical Accessories

Photos

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