SS2100 - Acetylene (Back End) Converter - Midbed Analyzer Solution

Ethylene is one of the most important feedstocks for the petrochemical industry. Since it is used in the manufacture of a wide range of compounds, Ethylene has very stringent purity specifications. One of the more important steps in purifying the ethylene is removing the acetylene. There are 4 common methods of Acetylene removal in Ethylene process that have evolved over the years:

Solvent Extraction using Dimethyl Formamide (DMF)
Cracked Gas Train or Raw Gas Catalytic Hydrogenation
Back End Catalytic Hydrogenation
Front End Catalytic Hydrogenation

Product Code: 54611

Application Note

Drawings

Application Note

Acetylene Converter Unit
The Acetylene Converter Unit consists of a series of reactors (Fig. 1) or a single vessel with multiple beds of catalyst (Fig. 2) which reacts the acetylene with hydrogen to form ethylene. The first reactor or bed will reduce the amount of acetylene from the percent levels down to the high ppm ranges. The second reactor or bed will then reduce the acetylene level even further to the low ppm and even ppb levels. Acetylene converters can be located at different points in the process. “Front End” Converters are upstream of the separation section, while “Back End” Converters may be located downstream of the De-Propanizer or De-Ethanizer. Measurements may also be made at the inlet of the Acetylene Converter Unit for feed-forward control strategies. Each stream type presents different analytical challenges for measuring Acetylene.

Critical Control of Acetylene
It is critical that the acetylene be brought down to the proper levels as it exits the final reactor; otherwise, any acetylene present will follow the ethylene all the way to the final product stream. But if the unit operates too aggressively, it could hydrogenate some of the ethylene back into ethane. So the proper operation of the unit requires the fast and precise monitoring of acetylene in between the two reactors (mid bed) and as it exits the final reactor.

Traditional Measurement Solutions
On-line gas chromatographs have been the traditional method for monitoring the levels of acetylene in the process streams. Unfortunately, even with the latest in chromatography techniques, the analysis can take 3-6 minutes between measurement updates. Due to the very short residence times in the reactors, this delay in measurements can easily lead to excursions in concentrations before it is detected.

SpectraSensors’ Solution
The SpectraSensors SS2100 is the ideal solution for this challenging application. The use of Tunable Diode Laser technology means analysis results can be updated every second. Furthermore, the high resolution is inherent to the laser eliminates errors due to interferences that have hampered other spectrometric approaches. Also, the non-contact nature of the measurement with no moving parts in the analyzer means the analyzer is simple to operate and has no routine maintenance needed.

In addition to acetylene, Hydrogen Sulfide, another important purity measurement, can be made using TDL analysis.

Typical Stream Composition

Component	Unit	Typical Concentration	Min. for Application	Max. for Application
Acetylene (C₂H₂)	ppmv	1500 - 5000	0	5000
Ethylene (C₂H₄)	Mole%	65	60	90
Ethane (C₂H₆)	Mole%	33	0	40
Hydrogen (H₂)	ppmv	0	0	1000
Carbon Monoxide (CO)	ppmv	0.5	0	1000
Carbon Dioxide (CO₂)	ppmv	< 1.0	0	1000
Methane (CH₄)	ppmv	50 - 100	0	1000
Propylene (C₂H₆)	ppmv	3000	0	5000
Total	Mole%	100

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	Acetylene in Back End Acetylene Converter Midbed
Typical Measurement Ranges	0 – 3000 ppm
Typical Precision	±100ppm*
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	1 - 2 L/min (2.1 to 4.2 scfh)*
Recommended Validation	Certified blend of C2H2 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	0.8m cell for ranges >100 ppm 438 mm H × 108 mm W (17-1/4” H × 4-1/4” W)* 28m cell for ranges <100 ppm 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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Drawings

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Typical Accessories

	SS2100 ARM9 Electronics
80000-02199	Temperature Control Board
23000-00030	4-20 mA Current Loop Board
80000-02203	Power Supply Assembly, 120/240 VAC 50/60 Hz
80000-02300	Power Supply Assembly, 24 VDC
01902-17106	External Serial Output Cable
01902-30011	Keypad Assembly
24601-00002	Display Assembly
02203-13100	Daughter Board
45000-02002	Relay, DC12V SPDT 3 A/120 VAC
	Herriott Cell (8m & 28m)
02101-17102	Pressure Transducer Assembly
02101-17103	Thermistor Assembly
02199-00006	Spares Kit (o-rings, fuses), AC, Viton
02199-00007	Cleaning Kit (domestic only)
	Cell (0.8m)
01902-17102	Pressure Transducer Assembly
02199-00001	Spares/Cleaning Kit (o-rings, fuses), AC, Viton (domestic only)
02199-00005	Spares Kit (o-rings, fuses), AC, Viton