SS2100 - CO2 GTL/SynGas (Sasol Process)

Application Note

Catalytic Reforming Unit
The Synthol process starts with synthesis gas from coal or natural gas to make hydrocarbon liquids and waxes in a Fischer-Tropsch reactor. The liquids are separated and refined to make transportation fuels and chemicals.

Critical Control of Carbon Dioxide
Carbon Dioxide must be removed prior to downstream cryogenic recovery and separation of the C2’s and C3 hydrocarbons present. Benfield Hot Potassium Carbonate systems (Fig. 1) are used for CO2 removal. Monitoring of the CO2 at the outlet is essential to the operation of the plant, and high CO2 concentrations present a shut-down situation for the plant.

Traditional Measurement Solutions
On-line gas chromatographs have been the traditional method for monitoring the levels of CO2 in cracked gas streams. Unfortunately, even with the latest in chromatography techniques, the analysis can take 3-6 minutes between measurement updates. Due to rapid changes in the acid gas concentration, this delay may not be acceptable. Also, gas chromatographs consume carrier and flame fuel cylinder gases, as well as requiring hydrocarbon-free air for flame ionization detectors, so the consumable costs of GC’s are high. Spectroscopic methods using broadband light sources and narrow band pass filters are prone to interferences from changing background concentrations. The concentrations of CO2 present are too low for Raman spectroscopy.

SpectraSensors’ Solution
The SpectraSensors SS2100 offers a new solution to this control measurement. The use of Tunable Diode Laser technology means that analysis results can be updated every second if desired. Furthermore, the high resolution that is inherent to TDL technology eliminates errors due to interferences that have hampered other spectrometric approaches. There are no consumables required for CO2 analysis at normal concentrations, so cost of ownership is low.

Validation
Validation is done with a certified blend of Carbon Dioxide in a background of Nitrogen, typically at a concentration in the middle of the measured range.

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Data Sheet

Performance
Target Components	CO2 in GTL/SynGas (Sasol Process)
Typical Measurement Ranges	0 – 100 ppm* through 0 – 1000 ppm (specify range)
Typical Precision	±2% of Full Scale
Measurement Response Time	1 to ~60 sec*
Principle of Measurement	Tunable Diode Laser Absorption Spectroscopy Non-differential
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 CO2 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 - 304 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	8m Herriot 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 ABCD 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.)
* Application specific; consult factory

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