SS2100 - Desiccant Dryer Outlet Analyzer Solution

Application Note

Desiccant Dryers
Molecular Sieves, Activated Alumina and Silica Gel desiccants are the most common drying techniques for Natural Gas Processing plants. Typically, two desiccant vessels are operated in series, using a piping system that allows either bed to be the first bed in the line, and allows either to be removed from the process for regeneration. As the first bed in the line is exhausted, it is put into the regeneration circuit where hot, dry gas drives the absorbed moisture out. The freshly regenerated bed becomes the second bed in the series.

Critical Control of Moisture
Normally, when the inlet gas moisture concentration is constant or can be measured, the desiccant dryers have a predictable operational period between regenerations. But as the desiccant ages, or from overheating, or from contamination in the process or regeneration circuit, the desiccant can lose capacity. Desiccant beds can also channel, allowing small concentrations of wet gas to flow through the bed without being dried. In any case, as the gas will subsequently be cooled for cryogenic separations downstream, the gas must be dry.

Traditional Measurements Solution
Electrochemical and vibrating quartz crystal moisture analyzers have been the traditional method for monitoring the levels of H2O in Desiccant Dryer Outlets Unfortunately, trace¬ hydrocarbons and other contaminants present in the stream contaminate the electrochemical probes, resulting in high maintenance costs due to the need to be constantly replaced. It’s not uncommon for moisture probes to be replaced multiple times a year. Quartz crystal moisture meters have slow wet-up and dry-down times that allow water downstream and prolong regeneration times.

SpectraSensors' Solution
SpectraSensors SS2100 is the ideal solution for this challenging application. Its non-contact laser and detector is impervious to damage from contaminants. Tunable Diode Laser technology means that measurement interferences from other infrared absorbing compounds are avoided. There are no wet-up or dry-down delays, resulting in fast updates even when the concentration changes dramatically. Only SpectraSensors employs Differential Spectroscopy, which incorporates a dryer using metal getter technology to subtract the spectrum of the dry gas from the wet spectrum. This allows the SS2100 to measure streams whose background gas compositions changes.

Validation
Validation of low level (<10 ppm) water measurements is essential, but also extremely difficult, as certified blends at such low levels are not readily available. Some have attempted to put permeation devises, but these require regular maintenance to prevent drying out, and there is no independent way to verify the accuracy of the permeation device. SpectraSensors employs a dilution system that dilutes a relatively high concentration certified standard of H₂O in Methane using dried sample gas. Thus the validation is accurate and traceable.

Typical Background Stream Composition

Component	Minimum (Mole%)	Normal (Mole%)	Maximum (Mole%)
Water	0.05 ppm	<1 ppm	10 ppm
Nitrogen	0	1 – 3	3
Oxygen	0	<1	1
Methane	75	75 - 95	100
Carbon Dioxide	0	0 - 2	3
Ethane	0	0 - 10	10
Propane	0	0 - 5	5
Butanes	0	0 - 2	2
C5+	0	0 – 0.5	0.5

Data Sheet

Performance
Target Components	H2O in Desiccant Dryer Outlet
Typical Measurement Ranges	0 – 10ppm* (other ranges available by request)
Typical Precision	±0.05 ppm or 2% of Full Scale* (whichever is greater)
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	A certified blend of H2O in Methane balance 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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