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

sales@spectrasensors.com | service@spectrasensors.com

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