Servomex Analysis Options for Ethylene Production (Reference / Paper)
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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 Experts in Gas Analysis 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. Paramagnetic Technology Oxygen is unique. O2 O2O O2 2 O2 O2 O2O2 O2 O2 O2 O 2 NO NO O2 O2 O2 O2 O2 O2 NO2 NO2 NO2 O2 SO2 HClSO CO O2 CO SO O2 SO2 CO2 SO2 CO 2 2 2 CO HCl 2 2 CO CO CO CO 2 2 HCl CON2 N HCl CO 2 N2 CO N2 It is strongly attracted into a magnetic field. It is described as being “ paramagnetic ” Servomex Paramagnetic Cell O2 O2 O2 O2 During calibration using nitrogen, the final rest position of the dumbbell suspension establishes the zero point. O2 O2 Oxygen in the sample deflects the spheres out of the magnetic field. Current is fed to the feedback coil to establish a force that exactly opposes the rotation. This rotation is detected by the optical feedback system. This force returns the dumbbell suspension to the zero position. The current used is proportional to the amount of oxygen in the sample. Paramagnetic Technology Provides: Performance • Fast response • Exceptional linearity and repeatability • High stability & accuracy Economics • Long operational life • Extractive sample system required • Simple validation / calibration Zirconia Oxide Technology Combustion Control: O2 Measurement Detecting air rich conditions Zirconium oxide (zirconia) based techniques Heated Chamber Zirconia disk At high temperatures, zirconia conducts electricity through the movement of oxygen ions. Electrodes Combustion Control: O2 Measurement Detecting air rich conditions Zirconium oxide (zirconia) based techniques Sample Reference When the oxygen concentration on each side is different, an emf related to oxygen concentration is generated. Nernst Equation 7000C Cell output, E = K x Ln ( Pr/ Ps) mV assuming a constant cell temperature 0 100 Zirconium Oxide Technology Provides: Performance • Fast response • Unaffected by background gases • Sample at hot / wet conditions Economics • Very acceptable operational life • Low maintenance requirements • Simple validation / calibration TDL Technology Laser Spectroscopy - How it works Absorbent concentration c IO Ix Path length L Laser selectivity – super narrow bandwidth Measurement based on Beer Lambert Law Thus: Beer Lambert law: Ix = Io exp[- cL]  = extinction coefficient (absorption strength)  is wavelength dependent 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 Benefit of WMS of FM Signal Recovery Technique The high frequency “carrier” signal – frequency f can either be demodulated at its fundamental frequency f or at its second harmonic 2f 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 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  TDL (Tuneable Diode Laser) Provides: Performance • Fast response • In-situ measurement at process conditions • Temperature and moisture measurement possible Economics • Long operational life • Low maintenance requirements • Inferred validation Combustion Efficiency: Detecting breakthrough in a fuel rich condition Combustion Efficiency: Combustibles via Thick Film Sensor 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 The change in temperature is detected by the platinum tracks CO underneath, changing their resistance, which can be detected. Combustibles via Thick Film Technology Provides: Performance • Fast response • Reliable detection of breakthrough condition • Provides measurement in low oxygen scenario Economics • Reasonable operational life • Simple validation / calibration Tuneable Filter Spectroscopy Challenges of Hydrocarbon Spectroscopic Analysis • Hydrocarbon IR spectra are broad, heavily overlapped. • Servomex SpectraScan achieves precise separation into constituent components achieved through breakthrough Chemometric algorithm. -7 Absorption Magnitude x 10 18 Methane 16 Ethane 14 Propane n-Butane 12 iso-Butane 10 8 6 4 2 0 1600 21 1650 1700 1750 Wavelength (nm) 1800 TFS™ Sensor Wavelength Scanning Technology  Spectral Scan achieved by custom designed tunable band-pass filter  Unique design enables simultaneous scanning of selected wavelength band x 10 -4 2.5 THC 2 CO2 H 2O Wavelength scanning 1.5 CO 1 λ 0.5 0 2500 3000 3500 4000 4500 5000 Tuneable Filter Spectroscopy Technology Provides: Performance • Fast response • C1-C5 speciation Economics • Long operational life • No utilities needed – no carrier gases 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 Ethylenecracker crackerplant plantand andcombustion combustioncontrol control Combustion control goals  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 ! Ethylene cracker plant and combustion control sing right techniques for combustion control Front view O2 laser analyser CO laser analyser Stack/CEM’s O2 paramagnetic CO Infra red NOx Infra red Extractive Side view Steam assist O2 Zirconia COe thick film catalytic sensor Xmitter Walkway 1 Receiver Flare BTU 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 Purge gas measurement contribution (O2 in Air) Laser Transmitter Sample pressure / temperature variations Stack vibration Window Purge Inlet Laser Receiver Process Stream Window Purge Outlet Purge gas dilution Pathlength variations (temperature cycles) Beam Obscuration by Particulates Purge gas flow variations 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 During calibration the flow of sample gas through the analyser & transducer remains unchanged Temperature Interlocked Solenoid Valve Aspirator Air 1.5ltr/min typical Heated to prevent Condensation / corrosion Heated Enclosure Aspirator Aspirator & Sample Outlet 1.7ltr/min typical Comb Cell 300 ml/min Flame arrestors for safety Probe Aux Air Rest. Flame Trap Internal 200ml/min Filter Auxiliary air to ensure Comb reading 100 ml/min O2 Cell Flame Trap During calibration the sensor head is ‘flooded’ with calibration gas to prevent process sample from interfering Model C version dual sensor shown Cal Gas Inlet 600ml/min Flow alarm Confidence in measurement SERVOTOUGH Flue Gas Insulated cover keeps wetted components above 210°C Keep it hot = Increase performance. Stop condensation. Stop blockage. Stop corrosion. Increase life. Thick Film Sensor Zirconia Sensor Flame Traps and Filter Internal Sample Filter (5 micron) Flame Arrestor (tested by external agency) Flame traps prevent risk of sensors igniting unburnt fuel at start up and causing an explosion Probes 3182 2732 1500 Alloy Probe used for temperatures < 1832F Max temp will be dependent 1832 upon probe length 1000 Stainless 1292 Alloys Ceramics High Temperature Probe for temperatures < 3182F 1750 Stainless Steel 316 Probe can be used up to 1292F 932 at any probe length ° F 32 700 500 ° C 0 SERVOTOUGH Flue Gas 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 Laser SERVOTOUGH Laser Transmitter Unit (TU) Lens Lens TU RU window RS 232 LAN Power cable Concentration as 4-20 mA output Receiver Unit (RU) 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 SERVOTOUGH Laser 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 • 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 Ideal measurement location High ambient temperature results in analyzer failure and unsafe maintenance 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 Ø stack Ø offset Transmitter Laser beam (20 cm) Laser detector (4 cm) Transmitter Offset Beams do move due to wall movement Beam divergence is needed to maintain transmissionsuccess to success: 2. Alignment + Diverging Laser Beam Transmitter of the stack Receiver Movement SERVOTOUGH Laser Process - 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 nonassisted 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 C1C5+ ₋ Lower cost to install, use existing sample system possible SpectraScan for fast BTUSpectraScan: replacing both a Chromatograph & Wobbe meter 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. 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. 57 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