Analysis Options for Ethylene Production

Objectives

• Ethylene and its derivatives are in high demand and low natural gas costs in the US are driving expansion and grass roots facilities

• There are a variety of options and factors to consider when developing a plan for control and efficient operation – Most effective combustion control scheme - TDL or zirconia ?

Combination of both ? – Fuel gas BTU and composition are important – Location of the combustion analyzer is very important – Radiant and convection section measurements are possible – Remote extractive installation is an option to consider – Environmental concerns such as flare combustion efficiency / steam

assist require fast speed of response and speciation – Total Cost of Ownership needs to be evaluated for each installation – Servomex has a variety of technologies and solutions to meet the

customers requirements – We provide analyzers for control and efficiency

PIONEERS IN RESEARCH AND INNOVATION

Servomex is a leader in the science of

gas analysis, an innovator in sensing

techniques and inventor of

Paramagnetic oxygen sensing

technology.

We are the only business to supply the

complete range of available sensor

technologies. Whatever the

requirement, Servomex diagnoses

and supplies the

best solution for application.

Experts in Gas Analysis

Paramagnetic Technology

Oxygen is unique.

It is strongly attracted

into a magnetic field.

It is described as being

“ paramagnetic ”

O2

O2

O2

O2

O2

O2

O2

O2

O2

O2

O2

O2 O2

O2

O2

O2

CO

CO

CO2 CO2

SO2 HCl HCl

N2

NO NO

N2

O2

O2

CO CO

CO2 CO2

SO2 SO2

HCl N2

NO2 NO2 NO2

O2

O2

O2

CO CO

CO2 CO2

SO2 SO2

HCl N2

Current is fed to the feedback

coil to establish a force that

exactly opposes the rotation.

This force returns the dumbbell

suspension to the zero position.

The current used is proportional

to the amount of oxygen in the

sample.

Servomex Paramagnetic Cell

Oxygen in the sample deflects

the spheres out of the magnetic

field.

This rotation is detected by the

optical feedback system.

During calibration using nitrogen,

the final rest position of the

dumbbell suspension establishes

the zero point.

O2 O2

O2

O2

O2 O2

Performance

• Fast response

• Exceptional linearity and repeatability

• High stability & accuracy

Economics

• Long operational life

• Extractive sample system required

• Simple validation / calibration

Paramagnetic Technology Provides:

Zirconia Oxide Technology

At high temperatures, zirconia

conducts electricity through the

movement of oxygen ions.

Heated Chamber

Zirconium oxide (zirconia) based techniques

Zirconia disk

Electrodes

Combustion Control: O2 Measurement

Detecting air rich conditions

0 100

Reference Sample

7000C

When the oxygen concentration

on each side is different,

an emf related to oxygen

concentration is generated.

Nernst Equation

Cell output, E = K x Ln ( Pr/ Ps) mV

assuming a constant cell temperature

Zirconium oxide (zirconia) based techniques

Combustion Control: O2 Measurement

Detecting air rich conditions

Performance

• Fast response

• Unaffected by background gases

• Sample at hot / wet conditions

Economics

• Very acceptable operational life

• Low maintenance requirements

• Simple validation / calibration

Zirconium Oxide Technology Provides:

TDL Technology

Measurement based on Beer Lambert Law Thus: Beer Lambert law: Ix = Io exp[- cL] = extinction coefficient (absorption

strength) is wavelength dependent

IO

Absorbent concentration c

Ix

Path length L

Laser Spectroscopy - How it works

Gas to be measured , typical absorption line-width 0.05 nm

Absorption lines from other (background) gases

Laser scan range, typically 0.2 - 0.3 nm, note Laser spectral line width is ca. 0.0001 nm

UV / IR absorption spectroscopy linewidth > 2 nm

Laser selectivity – super narrow bandwidth

Benefit of WMS of FM Signal Recovery Technique

Demodulation at f is analogous to the AM radio. Its is also called Direct Absorption Spectroscopy (DAS). • Easy to implement (first generation technology) • Yields a relatively noisy signal • Broad and extended lineshape

The high frequency “carrier” signal – frequency f can either be demodulated at its fundamental frequency f or at its second harmonic 2f

Demodulation at 2f (second Harmonic) is analogous to the FM radio. Its is also called Wavelength Modulated Spectroscopy (WMS). • Second generation technology • Much sharper narrower lines • High Signal to noise ratio

Utilized in the ServoTough Laser analyzer

Performance

• Fast response

• In-situ measurement at process conditions

• Temperature and moisture measurement possible

Economics

• Long operational life

• Low maintenance requirements

• Inferred validation

TDL (Tuneable Diode Laser) Provides:

Combustion Efficiency:

Detecting breakthrough

in a fuel rich condition

A special catalyst that is

selective to CO is then

printed over two quadrants

Combustion Efficiency: Combustibles via Thick Film Sensor

CO

CO

CO

CO CO

CO

CO

CO CO

CO CO

CO CO The change in temperature is detected by the platinum tracks

underneath, changing their resistance, which can be detected.

Combustion Efficiency: Combustibles via Thick Film Sensor

Performance

• Fast response

• Reliable detection of breakthrough condition

• Provides measurement in low oxygen scenario

Economics

• Reasonable operational life

• Simple validation / calibration

Combustibles via Thick Film Technology Provides:

Tuneable Filter Spectroscopy

Challenges of Hydrocarbon Spectroscopic Analysis

21

1600 1650 1700 1750 1800

0

2

4

6

8

10

12

14

16

18

x 10-7

Wavelength (nm)

Methane

Ethane

Propane

n-Butane

iso-Butane

Ab

so

rptio

n M

agn

itu

de

• Hydrocarbon IR spectra are broad, heavily overlapped.

• Servomex SpectraScan achieves precise separation into constituent

components achieved through breakthrough Chemometric algorithm.

TFS™ Sensor Wavelength Scanning Technology

λ

Wavelength

scanning

2500 3000 3500 4000 4500 5000

0

0.5

1

1.5

2

2.5

x 10-4

3 separate regions

H2O

THC

CO2

CO

Spectral Scan achieved by custom designed tunable band-pass filter

Unique design enables simultaneous scanning of selected wavelength band

Performance

• Fast response

• C1-C5 speciation

Economics

• Long operational life

• No utilities needed – no carrier gases

Tuneable Filter Spectroscopy Technology Provides:

Review of Technologies

Paramagnetic – Extractive for air rich conditions and

CEMS

Zirconia – close coupled extractive for air rich conditions

Thick Film – for fuel rich conditions

Tuneable Diode Laser – for both air and fuel rich

conditions

Tuneable Filter ( TFS ) – fast speciation of C1-C5 with

BTU/Wobbe

Combinations of these technologies often employed

for the most cost effective solutions!

Ethylene cracker plant and combustion control

Save fuel and increase combustion efficiency

Prevent cracking tube failures, increase lifetime

Increase the time between decoke cycles

Improve operational safety

Lower (NOx) emissions

Improve process revenues

Lower maintenance cost of analyzers and

complete furnace !

Combustion control goals Ethylene cracker plant and combustion control

Ethylene cracker plant and combustion control sing right techniques for combustion control

CO laser analyser

Walkway 1

O2 Zirconia

COe thick film

catalytic sensor

Stack/CEM’s

O2

paramagnetic

CO Infra red

NOx Infra red

Extractive

Front view Side view

O2 laser analyser

Xmitter Receiver

Flare

BTU

Steam assist

Installation Considerations

• Best point for measurement – Zones - Use multiple units or path measurement

– Convection or radiant – Combined options

– Measurement requirement – Quality, speed of response, validation, utilities required

• Maintenance – Easy to access – All technologies require maintenance

– Calibration and validation – confidence in measurement

Location

• In general, the O2 measurement should be made at the exit of each combustion chamber ( just above the radiant section ). This location should ensure a representative sample. Care should taken to minimize errors due to air leakage ( tramp air )

• CO / Combustibles samples can be taken in phase with O2 and / or above the convection section to indicate tube leaks

Speed of Response

• Determined by furnace / flare control parameters – Natural draft with manual dampers

– Forced draft with automatic controls

– Minimum safe operating limits of O2

– Sample point location

• These and other factors important in evaluation of technologies – what do you really need ?

Point versus Path

• Multiple points can provide important diagnostic information – burner balance – Need to consider adequate coverage

– Location to ensure representative sample

• Path measurement can provide “system” measurement – fast, average of process – Unable to determine “were the

problem is”

– Measurement errors dues to installation

Measurement Requirement

• Confidence in measurement

– O2 / CO used for efficiency, safety and reliability

– Used along with temperature, fuel pressure, BTU value, flame detectors and others to make critical process decisions

• Validation and Calibration

– How effective is it and what does it prove

Sources of Errors for Zirconia / Catalytic Measurement

• Plugged or partially plugged probes in extractive design – Reading not representative – undetected failure

• Speed of response – Insitu requires diffusion – unpredictable

• Net O2

– Reducing atmospheres ( high combustibles ) consume O2

• Combustibles measurement – Requires auxiliary air to ensure a measurement in reducing

atmospheres

Sources of Error for In-Situ Laser Measurement

Laser Transmitter

Laser Receiver

Window

Window Purge Inlet

Purge Outlet

Process Stream

Sample pressure / temperature variations

Purge gas flow variations Purge gas dilution

Pathlength variations (temperature cycles)

Stack vibration

Purge gas measurement contribution (O2 in Air)

Beam Obscuration by Particulates

Issues with BTU for Flare BTU / Steam assist

• GC too slow to respond • 6-8 minute cycle time of longer

• Residual O2 / Thermopile

• Does not speciate – cannot adjust for carbon ratio

• Rarely room to add to the existing shelter

• Large size, utilities of GC, residual O2 require new shelter

Solutions for Ethylene Furnaces

SERVOTOUGH Fluegas

Sensor Head and Remote Controller

Aux

Air

Rest.

Aspirator Air

200ml/min

Aspirator &

Sample Outlet

Heated

Enclosure

Flame

Trap

Internal

Filter

O2 Cell

Comb Cell

Aspirator

Flame

Trap

Temperature

Interlocked

Solenoid Valve

Probe 100 ml/min

1.5ltr/min typical

1.7ltr/min typical 300 ml/min

Model C version dual sensor shown

Cal Gas Inlet 600ml/min

During calibration the

sensor head is ‘flooded’

with calibration gas to

prevent process sample

from interfering

During calibration the flow

of sample gas through the

analyser & transducer

remains unchanged

Flow

alarm

Confidence in measurement

Auxiliary air

to ensure

Comb

reading

Heated to prevent

Condensation / corrosion

Flame arrestors for safety

SERVOTOUGH Flue Gas

Zirconia

Sensor

Thick Film

Sensor

Insulated

cover keeps wetted

components above

210°C

Keep it hot =

Increase performance.

Stop condensation.

Stop blockage.

Stop corrosion.

Increase life.

Internal

Sample

Filter (5 micron)

Flame

Arrestor (tested by

external agency)

Flame Traps and Filter

Flame traps prevent risk of sensors igniting unburnt fuel at start up and causing an explosion

°F

Stainless Steel 316 Probe

can be used up to 1292F

at any probe length

Alloy Probe used for temperatures <

1832F Max temp will be dependent

upon probe length

High Temperature Probe for

temperatures < 3182F

°C

0

500

1000

1500

32

932

1832

2732

3182 1750

1292 700

Cera

mic

s

All

oys

Sta

inle

ss

Probes

Features and Benefits:

Performance

• Fast response

• Unaffected by background gases

• Sample at hot / wet conditions

• Combines oxygen and combustible analysis

Economics

• Very acceptable operational life

• Reasonable maintenance requirements

• Low Total Cost of Ownership

• Simple validation / calibration

SERVOTOUGH Flue Gas

SERVOTOUGH Laser

SERVOTOUGH Laser

Lens Lens Transmitter Unit (TU) Receiver Unit (RU)

TU

RU window

Power cable

Concentration as 4-20 mA output

RS 232

LAN

Family of Lasers

• High temperature, long path CO/CH4

• Short path flare and vent lines

• Tight locations – limited access

Mini Laser – Oxy available

now !

Oxygen 0-1 / 0-25%

(0.01%LDL)

Div 2 / Zone 2 Hazardous

Area (ATEX, IEC, US)

SIL 2 Certified

Features and Benefits:

Performance

• Fast response

• In-situ measurement at process conditions

• Temperature and moisture measurement possible

• Ideal for corrosive, high particulate process conditions

Economics

• Long operational life

• Low maintenance requirements

• High initial installed cost – structure, access

•

SERVOTOUGH Laser

Solutions for Difficult Installations - Zirconia

• Hard to access sample taps

– High ambient temperature, tight space, only one sample port available

– Remote extractive - Easy to access, measurement is not compromised

Hard to Access Sample Port

Port behind

process piping

High ambient

temperature results in

analyzer failure and

unsafe maintenance

Ideal

measurement

location

Remote Extractive System

Controller

Sensor

Sample panel

- All electrical

- All utilities

Solutions for Difficult Installations - Lasers

• Laser installation on long path furnace – Moving furnace walls : No problem for CO/O2 measurements due to

laser beam divergence. Experience with (12 meter ) to (22 meter ) ethylene crackers

– N2 Savings : Huge savings on N2 supply because Servomex uses cold and hot line O2 line laser technique allowing client to use air purge instead of N2 purge, without compromising reliability and accuracy for O2 measurements

– Hot ambient : Lasers are specially designed for hot ambient : 65C. This is proved during hot summer months in Middle East (+50 - +55 C).

– Hot flange and furnace wall: Thermal spacer is designed and installed for hot flanges helping to keep the laser cool and prevent heat radiation through flange.

Location of Laser is crucialuccess: 1. Location

Beam divergence is needed to maintain transmissionsuccess: 2. Alignment + Movement of the

stack Ø

Transmitter

Ø offset

Transmitter Offset

Beams do move due to wall movement

Laser detector (4 cm)

Laser beam (20 cm)

Beam divergence is needed to maintain

transmissionsuccess to success: 2. Alignment +

Movement of the stack

SERVOTOUGH

Laser

Transmitter Receiver

Process

Diverging Laser Beam

- This is possible because of 2nd Harmonic laser signal !

- Receiver only needs < 1% transmission

High ambient temperature must be addressede to

success: 4. Hot ambient and thermal spacer

Solutions for Difficult Installations - BTU • Fast BTU analysis of Flare Gas for Steam Assist control

– It is becoming increasingly important to save energy while reducing harmful emissions when using a pollution control device such as a flare stack. Maximizing flare combustion efficiency (>98%) is an important way to minimizing flare emissions.

– US EPA code 40 CFR 60.18 states the following: Steam or air assisted flares shall be controlled at or above net heating value of the gas being combusted of 300 Btu/scf at 15 minute intervals or for non-assisted flare a net heating value of the gas being combusted of 200 Btu/scf or greater at every 15 minutes.

– Gas chromatographs is not a continuous analyzer (batch –type) thus has a slower response time (7-8 minutes per cycle); therefore, it is not ideal for advance controls.

– For advance controls, a continuous analyzer is needed for a faster response resulting in many data points utilized for control.

SpectraScan for fast BTU

Key Benefits

₋ Robust, Reliable, Low Maintenance

₋ Requires no carrier gas

₋ Fast Speed of Response

₋ Hi Accuracy, low cross sensitivity

₋ instantaneous analysis of light hydrocarbons C1-C5+

₋ Lower cost to install, use existing sample system possible

SpectraScan for fast BTUSpectraScan: replacing both a

Chromatograph & Wobbe meter

57

SpectraScan packs three instruments into

one in less than 25% of the volume of

traditional solutions with (1) real-time

speciated hydrocarbon measurements, (2)

BTU/CV heating value and (3) Wobbe Index.

Note that the SpectraScan requires no

carrier gas, requires no instrument gas, and

is calibrated for the life of the instrument.

The image shows the SpectraScan Analyzer (shown on the left) relative to the

incumbent Residual-Oxygen type Wobbe Index analyzer installed at a refining facility.

Conclusions

• Both zirconia and TDL offer great advantages when considered as complementary techniques for combustion control

• Zirconia offers specific point measurement with a higher level of inherent accuracy coupled with true calibration / validation

• TDL offers a faster, overall measurement with less associated maintenance

• TFS offers fast speciation for BTU / Wobbe index for flare combustion efficiency

HARNESS THE POWER OF

expertise

SERVOTOUGH Combustion Solutions