Product Code: 44201
Application Note
Desiccant Dryers
Molecular Sieves desiccants are the most common drying techniques for Liquefied Natural Gas (LNG) plants. Typically, two desiccant vessels are operated in series, using a piping system which 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 can lose capacity as it ages, or from over heating, or from contamination. 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 liquefaction downstream, the gas must be dry.
Traditional Measurement Solutions
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 which 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 which 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 which dilutes a relatively high concentration certified standard of H2O in Methane using dried sample gas. Thus the validation is accurate and traceable.
Molecular Sieves desiccants are the most common drying techniques for Liquefied Natural Gas (LNG) plants. Typically, two desiccant vessels are operated in series, using a piping system which 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 can lose capacity as it ages, or from over heating, or from contamination. 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 liquefaction downstream, the gas must be dry.
Traditional Measurement Solutions
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 which 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 which 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 which 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 for LNG Feed Gas Streams
(Downstream of Acid Gas Removal and Drying)
(Downstream of Acid Gas Removal and Drying)
|
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 |
<0.001 |
|
Ethane |
0 |
0 - 10 |
10 |
|
Propane |
0 |
0 - 5 |
5 |
|
Butanes |
0 |
0 - 2 |
2 |
|
C5+ |
0 |
0 – 0.5 |
0.5 |
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 water, the measured component. Other stream compositions may be allowable with approval from SpectraSensors.
Data Sheet
Performance |
|
|
Target Components |
H2O in LNG Product (export/import) |
|
Typical Measurement Ranges |
0 – 10ppm* (other ranges available by request) |
|
Typical Precision |
±0.05 ppm or 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 |
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 - 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 |
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
|
| 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
|
|
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)
|