Fundamentals Of Process Chromatography February 2010 Fundamentals of Chromatography Key Messages Pre-launch meetings are designed to provide a learning base 700XA advantages over competition and legacy products – Total Cost of Ownership – Increased Analytical Capabilities • # of valves • Temperature • Column Types – Extended Application Capabilities Ease of use Communication options Software features Fundamentals of Chromatography Overview of Chromatography Sample Handling Systems Chromatograph Oven GC Controllers What is a Process Gas Chromatography? On-line continuous sampling Cyclic – cycle times vary and can be critical Multiple components Wide range of gas / hydrocarbon liquid measurements – %, ppm, ppb by detector selection Used in many industrial applications – Refinery, Gas Plant, Chemical, Petrochemical, Landfill, Ammonia, Fertilizer, Steel mill. – Turbine efficiency – Ambient air monitor, gas custody transfer. Fundamentals of Chromatography Basic Chromatograph System Fundamentals of Chromatography Overview of Chromatography Sample Handling Systems Chromatograph Oven GC Controllers Fundamentals of Chromatography Sample Handling Repeatability achieved by controlled Temperature, Flow, Inject Volume Fundamentals of Chromatography Sample Handling Sample handling is critical for the reliable and accurate operation of the analyzer Sample handling system must perform the following: – – – – – – Take a representative sample Maintain the composition of the sample Remove solid particles to at least 5 micron Remove any free liquid (water or liquid hydrocarbons) Reduce/control the pressure of the sample Maintain the temperature of the sample over its dew point (application dependent) 80% of gas chromatograph “problems/failures/alarms” are a result of a failure in the sample conditioning system Fundamentals of Chromatography Sample Handling – Sample Probe A sample probe should ALWAYS be used Sample probe should be inserted in the center third of the pipeline, or 10 inches, whichever is the smallest 1/3 Sample probe should be located away from disturbances, in 1/3 straight run section Can be heated or unheated Sample probes with particle filters, 1/3 moisture filters and regulators are HIGHLY recommended – Exception: If sample point is not easily accessible Fundamentals of Chromatography Sample Handling – Sample Probe Genie Probe Regulator Liquids and solids are removed from the sample before it enters the sample Membrane handling system. Coalesced Liquid Foot Valve Gas Flow Fundamentals of Chromatography Sample Transport Tubing Sample transport tubing moves the sample gas from the extractive probe to the sample conditioning system. Sample transport tubing must: – Maintain the composition of the sample • • • • Heated to maintain sample above the dew point Constructed of materials which do not react with the sample Stainless steel components should be used for natural gas Silica coated tubing should be used when measuring trace sulfur – Transport the sample to the analyzer in a timely manner • Tubing bore should be as small as possible to reduce the volume in the sample lines, but not restrict sample flow Typical heat traced tubing Increasing Pressure Fundamentals of Gas Chromatography Phases Explained Liquid Increasing Temperature Gas - Liquid Gas Fundamentals of Chromatography Minimal Sample Conditioning System Particulates should be removed to at least 5 microns Filters should not be coalescing type to avoid large volumes in the sample system Liquids should be removed using Membrane technology Sample probes which provide liquid and solids filtration inside the line are highly recommended Typical sample system on a simple application. This is the “last line of defense” Fundamentals of Chromatography Process Sample Conditioning Systems Custom-engineered per measurement requirements to provide the best protection for sensitive chromatograph components – Conditions sample to proper pressure and temperature – Filters particulates – Eliminates contaminants even in high-flow, high-moisture samples – Provides programmed stream selection Liquid with vaporizing regulators and double-block-and-bleed solenoids 4 x gas stream with vacuum pump for lowpressure sample Fundamentals of Chromatography Effects of liquids • If liquids (such as compressor oil or glycol) enter the chromatograph oven, the valves and columns will become contaminated, resulting in a failure of the analyzer • If liquids are to be analyzed, then they will be vaporized into a gas. – Achieved with a vaporizing regulator (in SCS) or liquid sample injection valve (LSIV) in GC More on injection valves later Fundamentals of Chromatography Sample Conditioning Systems - Review Take a representative sample Transport the sample to the analytical oven Condition the sample for optimum analysis – Filter – Maintain a single phase – Control Temperature, Pressure and Flow Provide sample stream switching and calibration Accommodate sample return or venting systems Accomplish above without excessive maintenance and service attention Fundamentals of Chromatography Overview of Chromatography Sample Handling Systems Chromatograph Oven GC Controllers Fundamentals of Chromatography Analytical Oven Functional Blocks Within the Analytical Oven Inject a sample onto the separation columns Separate the sample into individual compounds Detect concentration of individual compounds Amplifier/s Measure Reference Vent Diaphragm Valves Vent Fundamentals of Chromatography Functions of The Analytical Oven Houses valves and columns Inject a sample onto the separation columns Separate the sample into individual compounds Detect concentration of individual compounds Air-less Heat Sink Ovens Air bath Oven Analysis Kiosk “Kiosk” block provides heat to analysis hardware Airless heating Software-driven temperature set point Valves mounted on kiosk Columns mounted inside kiosk Thermistor-based TCD or µFID Dual TCD/TCD or TCD/FID External FPD Module Kiosk Top View FID Detector Valves (6 or 10 port) Columns TCD Detector Fundamentals of Chromatography Oven Temperature The analytical oven is heated to maintain a constant temperature of the columns and the detector Changes in the oven temperature will cause: – Changes in the separation of the components through the columns – Change the detector output and response to the components The oven is maintained above ambient temperature to remove ambient temperature changes as an influence on the performance of the gas chromatograph Types of Sample Injection Valves Rotary valve Diaphragm valve Liquid sample injection valve Rotary Valve Diaphragm Valves LSIV Rotary Valve Sample Loop Sample Loop Sample In Carrier In Sample Out To Columns Valve Off Sample In Carrier In Sample Out To Columns Valve On Diaphragm Valve Port 1 Port 2 Valve Off Port 3 Port 1 Port 2 Port 3 Air On Air Off Air Off Air On Valve On Liquid Sample Injection Valve Air On Sample Out Carrier In Valve Off To Columns Air Off Heated Flash Chamber Sample In Oven Wall Air Off Sample Out Carrier In Valve On Air On To Columns Heated Flash Chamber Sample In Fundamentals of Chromatography Carrier Gas The sample is pushed through the columns (or carried) by the carrier gas Helium is a very common carrier gas because: – It is inert – It is not usually a component of interest – It has a very large difference in thermal conductivity to the components typically measured Ultra high purity carrier gas must always be used – Any contaminants may be the same components that are being analyzed Different Types of Columns Separation by boiling point differences Separation by polarity differences Separation by molecular size Column Types Packed – 1/8” O.D. Micropacked - 1/16” O.D. MXT – Glass-lined, Stainless Steel Housing (Capillary) - 1/32” O.D. Column Housing Fundamentals of Chromatography Column Theory To understand how the columns separate the components, the (famous) elephants, deer, and foxes analogy may help. Fundamentals of Chromatography Column Theory Imagine there is a group of animals peacefully grazing in a clearing to the left. They are surrounded by cliffs, and a dense forest to the right. Fundamentals of Chromatography Column Theory Suddenly a large grass fire is whipped up by winds blowing from the left to the right! The only way out for them is to run into the forest… Mixture Fundamentals of Chromatography Column Theory The small and agile foxes have no trouble running through the forest. The slightly larger deer have some trouble penetrating the forest and take a little bit longer. The large and heavy elephants encounter considerable difficulty in penetrating and passing through the forest. Fundamentals of Chromatography Column Theory As all three are kept under pressure by the fire to keep moving to the right, the foxes move through the restricted area fastest, the deer next, and finally the elephants bring up the rear. The animals have now been separated into the three distinct groups from the original mixture Elephants Deer Foxes Fundamentals of Chromatography Column Separation • Essentially the same effect is achieved using Chromatograph columns, where instead the animals are components of the gas mixture, the fire is the carrier gas, and the forest is the column. CARRIER GAS A C BA C B A CB A TO DETECTOR COLUMN A C BA C B ACB AAAA CCC BBB AAAA CCC GAS MIXTURE INJECT PARTIAL SEPARATION FULL SEPARATION BBB Column Switching Techniques (How to speed up the analysis) Where does the injected sample end up? Backflush to Vent – Flushes unwanted components, minimize cycle time. • Example only want C1, C2 in C1, C2, C3, C4 stream Backflush to Detector – Gives total stream with the final component as a sum • Example C1, C2, C3, C4, C5+ Trap Bypass – Enables columns to be bypassed and avoid column contamination by other components, e.g. gas metering N2 / C1/ C2/ C02 Column “3" Heart Cut – Used to “cut” ppm components from high purity balance gas • Example 5ppm CO2 in ethylene Column Switching — Backflush To Vent Carrier Column # 1 SIV Carrier Column # 2 Detector Column Switching — Heartcut Ethylene Tail 100% Product Ethylene (1,000,000 ppm) 1 ppm Acetylene 1 ppm Acetylene DETECTOR INJECT Column # 1 Column # 2 Bulk of Ethylene peak Typical GC Column Arrangement Fundamentals of Chromatography Types of Detectors Available Flame Photometric Detector (FPD) Flame Ionization Detector (FID) Thermal Conductivity Detector (TCD) 1 PPM 10 PPM 100 PPM 1000 PPM Range 1 Mole % 100 Mole % Thermistor-Based Thermal Conductivity Detector Amplifier/s Measure Reference Vent Vent Universal Detection Typically Sensitive Down To below 100 ppm – Minimum detectability of H2S is 3ppm Flame Ionization Detector Vent Igniter Collector Amplifier Flame Polarizing voltage Hydrogen Carrier Air Note: • Flame produces water ensure proper vent drain orientation Hydrocarbon detection only Sensitive down To <1 ppm Flame Photometric Detector Vent Igniter Amplifier Flame Optical Filter Photo-Multiplier Tube Hydrogen Carrier Air Sulfur & phosphorus detection only Sensitive down to <100 ppb Note: • Flame produces water ensure proper vent drain orientation Fundamentals of Chromatography Dual Detector System Sample In Sample Valve 1 Column Train 1 Detector 1 Carrier 1 Detector Vent Sample Valve 2 Carrier 2 Sample Out Column Train 2 Detector 2 Detector Vent Fundamentals of Chromatography Overview of Chromatography Sample Handling Systems Chromatograph Oven GC Controllers Fundamentals of Chromatography Controller Fundamentals of Chromatography Controllers Control system operation Convert peak area to mole % Perform system diagnostics Provide user interface Transmit results and operational status 2350A Controllers – for Model 500 Series Gas Chromatographs Model 700 Electronics Compartment Fundamentals of Chromatography Controller output The controller will output the results of the analysis and calculations using: – Analog Outputs - 4 – 20 mA. As there are many components and calculations, this is not usually practical. – Serial (RS-232/485/422). Using MODBUS communications. This is the most common solution. – Ethernet. Using Modbus TCP/IP. Now becoming more widespread. – Printer. Once the only method, now becoming rare. – Foundation Fieldbus - New Gas Chromatograph Digital Communications Network
