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TDL Analyzers for Olefins Production
Accurate and Reliable Measurement of C2H2, NH3, H2O, H2S, and CO2
Front-End Acetylene Hydrogenation
Scrubber
Cracking Furnace
Cooling
Deethanizer
C2 HydrogenationAcetylene Converter
Demethanizer
DepropanizerC3+
Ethane/Ethylene Splitter
Ethylene
Ethane
H /CH2 4
AX
AX
AX
Measurement Point Range
Inlet 0-2.5%
Mid-Bed 0-3,000 ppm
Outlet 0-5 ppm
Production of high-purity olefins (ethylene and propylene)
involves a number of unit operations to remove or convert
contaminants. Accurate measurement of C2H2, H2S, and CO2 is
required to monitor and optimize acetylene conversion and
caustic gas scrubbing. Measurements of NH3, H2O, and H2S
ensure olefin products are meeting stringent purity
specifications.
Tunable diode laser absorption spectroscopy (TDLAS) analyzers from SpectraSensors are
specifically designed to perform on-line, real-time measurement of C2H2, NH3, H2O, H2S, and CO2 in
process gas streams. Measurements from SpectraSensors TDL analyzers help olefin plants improve
process efficiency, reduce operating costs, and deliver high purity ethylene and propylene
required for downstream catalytic polymerization processes.
Laser-Based Process Analyzers for Olefins Production
AX
Back-End Acetylene Hydrogenation
Scrubber
Cracking FurnaceCooling
Deethanizer
C2 HydrogenationAcetylene Converter
C3 Hydrogenation
Demethanizer
Depropanizer
C4+
C2
C3 Ethylene
Propylene
AX
AX
Measurement Point Range
Inlet 0-2.5%
Mid-Bed 0-3,000 ppm
Outlet 0-5 ppm
CH CO, H4, 2
Management of acetylene in ethylene directly affects the operational efficiency and profitability of olefin
plants. Separating acetylene (C2H2) from ethylene (C2H4) is difficult due to the similar volatility of these gases.
A catalytic hydrogenation step is typically employed to convert acetylene into ethylene. An acetylene
converter unit consists of a series of reactors, or a single vessel with multiple catalyst beds. The first reactor or
bed reduces acetylene concentration from several thousand ppm down to several hundred ppm. The second
reactor or bed reduces acetylene down to low ppm or ppb levels. TDL analyzers are installed to monitor
acetylene levels in the inlet line, at a mid-bed sampling point, and the outlet line of the converter vessel.
Real-time measurement of acetylene using TDL analyzers facilitates tighter control and optimization of the
hydrogenation process. The fast response of TDL analyzers detects changes in acetylene concentration in
seconds versus the delayed response of gas chromatographs with analysis times of several minutes. Under
certain operating conditions the concentration of acetylene can change suddenly. A GC may fail to detect
such excursions, or respond in time to allow normal reaction conditions to be restored and avoid taking the
process off line or routing gas to flare.
Acetylene in Ethylene - a Critical Measurement
Pipeline and Polymer Grade Olefins
Caustic Gas Scrubbing
The acid gas produced by steam
cracking of hydrocarbon feed
stocks must be scrubbed to
remove CO2 which can freeze and
damage heat exchange and
fractionation equipment, and H2S
which is corrosive and a catalyst
poison. TDL analyzers are installed
in the inlet line to caustic wash
tower units to monitor the
concentration of CO2 and H2S in
the cracked gas stream.
Olefin Purity Measurement
The purity specifications for ethylene and propylene are dictated by the downstream use of these olefin
feed stocks. Catalysts used in HDPE, LDPE, LLDPE, and PP polymerization processes exhibit different
sensitivity to contaminants that poison and reduce catalyst activity. Out-of-spec ethylene may be rejected
by polyethylene producers, or sent to flare incurring high costs.
Ethylene can pick up traces of
water and other impurities during
transportation in pipelines or
ships, and storage in salts caverns.
When ethylene from multiple
sources is mixed, purity may be
compromised and must be
measured to ensure contaminant
levels are within required
specifications. SpectraSensors TDL
analyzers are utilized to monitor
the purity of ethylene at olefin
plants, in pipelines, and at the inlet
of polymer plants. The
concentration of C2H2, NH3, H2O,
H2S, and CO2 impurities can be
measured down to sub-ppm
levels.
Cracker
Quench Tower
Separator
Compressors
CausticTower
Molecular Sieve Dryers
Caustic Gas Scrubbing Process
AX
Analyte Range
CO2 0-500 ppm
H2S 0-500 ppm
Silos
High PressureSeparator
LowPressureSeparator
AutoclaveReactor
PrimaryCompressor
SecondaryCompressor
Extruder
RecycleGas System
Ethylene Gas
PolyethylenePellets
Additives
Low Density Polyethylene (LDPE) Production Process
AX
Analyte Range
NH3 0-5 ppm
H2O 0-10 ppm
TDL Gas Analyzers from SpectraSensorsIn operation process gas from a sampling probe is introduced into
the sample cell of the analyzer. A tunable diode laser emits a
wavelength of light specific for the target analyte into the sample
cell where it passes through the gas and is reflected back by a
mirror at the opposite end of the cell to a solid state detector.
Analyte molecules present in the gas sample absorb and reduce
the intensity of laser light energy in direct proportion to their
concentration according to the Beer-Lambert law. The difference
in light intensity is measured by the solid state detector and this
signal is processed using advanced algorithms to calculate analyte
concentration in the process gas.
The pathlength of the sample cell can be increased to create a
multi-pass Herriott cell in which laser light traverses the cell
multiple times to increase analyzer sensitivity for trace (sub-ppm)
level measurements.
SpectraSensors AdvantageThe design and performance characteristics of SpectraSensors TDL analyzers provide significant advantages over
other technologies for monitoring critical impurities during the production of high-purity olefins.
Fast Response and
Analysis TimeProvides real-time data for process control and optimization
Non-contact Measurement
TechniqueAvoids fouling and corrosion from contaminants for reliable long-term operation
High-resolution Tunable
Diode LaserHelps eliminate interferences and improves trace-level analyte measurement
Low Service and
Maintenance RequirementsMinimizes technician manpower devoted to analyzer support versus other techniques
No Consumable Analyzer
ComponentsEnsures long-term uninterrupted operation and low cost of ownership
Factory-calibrated Using
Process GasEnsures accurate analyte measurement and stable, long-term field calibration
SpectraSensors, Inc.
4333 W. Sam Houston Pkwy N., Suite 100Houston, TX 77043Tel: +1 713 300 2700 +1 800 619 2861
Fax: +1 713 856 6623
[email protected] | [email protected]
www.spectrasensors.com
© 2014 SpectraSensors, Inc. Products or references stated may be trademarks or registered trademarks of their respective owners. All rights reserved.
BR OLEFIN EN 01 (12/14)
LNG Natural Gas
Refinery
Gas Processing
Petrochemical Specialty GasesAtmospheric
SpectraSensors is an Endress+Hauser company. We design and manufacture laser-based instrumentation
for on-line monitoring of process gas streams. Our instruments are used in the natural gas, gas processing,
petrochemical, refinery, and atmospheric testing industries. The company’s technology center is located in
Rancho Cucamonga, California and our headquarters office is in Houston, Texas.
The leading global provider of laser-based process instrumentation