The world’s safest tail gas analyzer. TLG-837 continuously measures the concentrations of H2S, SO2, COS, and CS2 in the Claus process tail gas stream. Using the patented in situ DEMISTER sampling probe and a full-spectrum UV-Vis spectrophotometer, this system provides extremely fast, accurate response for tight process control.
H2S is toxic at 10 ppm, entirely lethal at 800 ppm, highly corrosive to equipment, flammable when in excess of 4.3% by volume in air, and unpleasantly odorous at a threshold of less than 1 ppb.
Unfortunately, H2S occurs abundantly in the world’s fossil fuel reserves. The sulfur recovery unit (SRU) of a refinery is dedicated to processing the H2S stripped from the hydrocarbon fuel through a series of operations that convert it into water and harmless elemental sulfur, which can be sold and repurposed in fertilizer, gunpowder, and more.
The Claus process is the industry standard for treating the H2S-rich “sour” gas. In a furnace, H2S is combusted:
3H2S + 3⁄2O2 SO2 + H2O + 2H2S
A catalytic converter reacts the products of the combustion to create elemental sulfur in various crystalline forms:
2H2S + SO2 2H2O + 3⁄XSX
As can be deduced from the second reaction above, the typical Claus reaction runs most efficiently when the stoichiometric ratio of H2S to SO2 is controlled at 2:1. The 1st reaction above demonstrates that this ratio is controlled by adjusting the amount of available oxygen.
As demonstrated above, the efficiency of sulfur recovery hinges on the ability to maintain a set H2S/SO2 ratio in the Claus reaction. This adjustment requires knowing the exact H2S/SO2 ratio in the tail gas at all times.
A tail gas analyzer measures H2S and SO2 in the stream and continuously outputs the “Air Demand” control signal, calculated by multiplying the expression (2[SO2] – H2S) by a scaling factor. Additionally, operators sometimes require online measurement of COS and CS2 due to side reactions in the reactor.
The DEMISTER sampling probe was designed to be lightweight and compact, so it can easily be installed by a single technician. The probe is mounted on the process pipe via flange.
The actual interaction between the sample gas and the light signal occurs in the flow cell disk within the probe head, where fiber optic connections on opposite ends transmit light across the path length of the disk.
Tail gas contains elemental sulfur which is quick to condense and plug mechanical cavities or obstruct optical signals. The DEMISTER Probe removes sulfur from the rising sample as an internalized function within the probe body. Recycling the steam generated by the Claus process, the probe controls the temperature along its body at a level where all sulfur vapor in the rising sample condenses and drips back down to the process pipe.
Inside the probe, an internal ‘demister’ chamber (concentric to the probe body) is fed with low pressure steam. Since the LP steam is much cooler than the tail gas, this chamber has a cooling effect on the rising sample. Elemental sulfur has the lowest condensation point of all of the components in the tail gas. Due to the internal probe temperature maintained by the LP steam, all of the elemental sulfur in the rising sample is selectively removed by condensation while a high-integrity sample continues upward for analysis in the probe head.
The point of interaction between the light signal and the sample gas occurs in the flow cell disk inside the probe head. The flow cell disk has a built-in HP steam channel to heat the cell and ensure that any present sulfur remains gaseous—eliminating the possibility of condensation on the optical windows.
An aspirator creates a Venturi effect which pulls the sample up the probe body intake path, through the flow cell for analysis, and down the return line. The used sample is released back into the process pipe.
Note: All performance specifications are subject to the assumption that the utility control panel and unit installation are approved by Applied Analytics. For any other arrangement, please inquire directly with Sales.
|Measurement Principle||Dispersive ultraviolet-visible (UV-Vis) absorbance spectrophotometry|
|Detector||nova II™ UV-Vis diode array spectrophotometer|
|Spectral Range||200-800 nm|
|Light Source||Pulsed xenon lamp (average 5 year lifespan)|
|Signal Transmission||600 μm core 1.8 meter fiber optic cables
Other lengths available
|Sample Introduction||In situ DEMISTER Probe|
|Analyzer Calibration||Calibrated with certified calibration fluids; no re-calibration required after initial calibration; measurement normalized by Auto Zero|
|Reading Verification||Simple verification with samples|
|Human Machine Interface||Industrial controller with touch-screen LCD display running ECLIPSE™ Software|
|Data Storage||Solid State Drive|
|Analyzer Environment||Indoor/Outdoor (no shelter required)|
|Ambient Temperature||Standard: 0 to 35 °C (32 to 95 °F)
With optional temperature control: -20 to 55 °C (-4 to 131 °F)
To avoid radiational heating, use of a sunshade is recommended for systems installed in direct sunlight.
|Standard Outputs||1x galvanically isolated 4-20mA analog output per measured analyte
5x digital relay outputs for indication and control
1x K type ungrounded thermocouple input
|Optional Outputs||Modbus TCP/IP; RS-232; RS-485; Fieldbus; HART|
|Wetted Materials||Stainless Steel 316/316L, Kalrez
Other materials available
|Analyzer Enclosure||wall-mounted NEMA 4X stainless steel type 304 Enclosure
Other enclosures available
|Probe Material||Stainless Steel 316/316L
Other materials available
|System Dimensions||Analyzer: 24” H x 20” W x 8” D (610mm H x 508mm W x 203mm D)
Probe (Average): 36” length x 12“ widest diameter (914mm x 305mm)
|System Weight||Analyzer: 32 lbs. (15 kg)
Probe (Average): 29 lbs. (13 kg)