SS2100 - Propane/Propylene (C3) Product

Application Note

Propane/Propylene Mix
There are three major sources of pure Propylene for polypropylene feed: Refinery Fluidized Catalytic Cracking (FCC) byproduct, Ethylene Cracking Furnaces as a byproduct of Ethylene production and Propane dehydration; of these three, Refinery FCC byproduct is by far the largest source.

Sulfur compounds in the feed to the FCC unit are converted to H2S and follow the Propane/Propylene product.

Depending on the processing, there are three different products: an essential pure Propane, a 65/35 mix of Propane/Propylene and a 35/65 Propane/Propylene mix (see stream composition table). These products are further refined for their eventual use.

Critical Control of H2S
The primary method of H2S control is removal in the stripper section of the vapor recovery unit.

Traditional Measurement Solutions
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’ Solution
The SpectraSensors SS2100 offers a new solution to this challenging measurement. There are no cylinder gases or Lead Acetate tapes to replace on a routine basis, so the analyzer is very low maintenance and has a low cost of ownership over the life of the analyzer. The high resolution that is inherent to TDL technology eliminates errors due to interferences that have hampered other spectrometric approaches.

Only SpectraSensors employs Differential Spectroscopy to cope with the changes in background spectrum of the sample caused by changing operating conditions and feedstocks. The sample gas is passed through a copper nanoparticle scrubber to remove H2S, and the spectrum of the H2S-free sample is measured. The scrubber is then bypassed to measure the raw sample with H2S, and the H2S is measured by spectral subtraction. As the H2S-free background spectrum can be applied repeatedly to the sample, the scrubber is only used as needed, controlled by logic in the electronic controller.

The scrubber lifetime in normal service is a minimum of 18 months, so consumable costs and maintenance are low. Tunable Diode Laser technology means that analysis is fast; results can be updated every second if desired.

Typical Stream Composition

Stream Composition	Background 1 - Propane
Component	Minimum (Mole %)	Normal (Mole %)	Maximum (Mole %)
Ethane	0	1	2
Propane	65	78	100
Propylene	0	20	35
C4+	0	1	2.5

 

Stream Composition	Background 2 - 35/65
Component	Minimum (Mole %)	Normal (Mole %)	Maximum (Mole %)
Ethane	0	1	2
Propane	0	20	35
Propylene	65	78	100
C4+	0	1	2

 

Stream Composition	Background 3 - 65/35
Component	Minimum (Mole %)	Normal (Mole %)	Maximum (Mole %)
Ethane	0	1	2
Propane	65	78	100
Propylene	0	20	35
C4+	0	1	2.5

 

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 H2S, the measured component.  Other stream compositions may be allowable with approval from SpectraSensors.

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Data Sheet

Performance
Target Components	H2S in Propane/Propylene (C3) Product
Typical Measurement Ranges	0 – 10 ppm*
Typical Precision	±0.5 ppm
Measurement Response Time	1 to ~60 sec
Principle of Measurement	Differential Tunable Diode Laser Absorption Spectroscopy (H2S 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	A certified blend of H2S in N2 is diluted with dried sample in the sample conditioning system under flow control
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 Herriot Cell 559 mm H × 127 mm W (22” H × 5” W)
Sample Cell Construction	316L Series Polished Stainless Steel standard  SilcoNert® coated
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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