混合气体反应监测 - MKS FTIR

Technology for Productivity Page 2For further information， call your local MKS Sales Engineer or contact the MKS Applications Engineering Group at 800-227-8766.MKS Global HeadquartersApp. Note 03_10-6/10C 2010 MKS Instruments， Inc.All rights reserved.Technology for Productivity Application NoteMKS FTIR Analysis for Syngas Reactions PROBLEM The rising cost of fossil fuels and the worldwide need forreduction in green house gases have sparked renewed interestin alternative fuel sources that require less energy to produce.Gasification of biomass， coke and other residuals frompetroleum， coal， municipal and industrial wastes can producesynthetic gas or "syngas". Syngas can be used directly as fuel；as well， it can be used to produce hydrocarbon fuels， hydrogenfor fuel cells， and chemical feedstocks such as methanol. Theanalytical methods employed for quality assurance in syngasproduction must provide simultaneous and accurate dataon mixtures of contaminants in the presence of high COand CO， content. The contaminant levels in syngas range inconcentration from high ppm to % levels， depending upon thefinal product required. BACKGROUND Gasification breaks hydrocarbons and other carbon-containingmaterials down into a mixture of hydrogen and carbonmonoxide (CO) in which the relative ratio of hydrogen tocarbon monoxide depends on the H/C ratio in the startingmaterial. This product is then purified and the final CO andH， gas mixture is separated or further converted to otherproducts. The process uses a gasifier that converts carbon-containingsolid feedstocks into ash and syngas at high temperature(650°C up to 1400℃) and pressures using the exothermicwater-gas shift reaction： After the coke bed cools， the exothermic reaction no longeroccurs and oxygen or air is added to remove CO，. Thisproduces two further reactions that complete the productioncycle of syngas to CO and H： The final fuel matrix contains % level concentrations of CO(up to 40%) in H . When this mixture is analyzed at elevatedtemperatures， accurate analysis of low level hydrocarbon andsulfur impurities is very difficult. Depending on the final product requirements， the H，/COratio in syngas needs to be adjusted and monitored. Since thegasification of hydrocarbon sources produces crude hydrogenas a mixture with multiple byproducts and contaminantsat varying concentrations， accurate chemical analysis of thesyngas processes represents a unique challenge. This analysis of the gas mixture must simultaneously determine concentrationsfor multiple components having contaminant levels thatrange from low ppm to 40%. Table 1 lists the typical speciesconcentration ranges found in Syngas product gas streams. Component Typical Product Hydrogen (H，) 50%-90% Carbon Monoxide (CO) 0-50% Carbon Dioxide (CO，) 0-30% Water(H，O) 25-45% Methane (CH) 0-15% Non-methane Hydrocarbons 0-5% Ammonia (NH) 0-4000 ppm Hydrogen Sulfide (H，S) 0-800 ppm Table 1-Typical Crude SynGas Concentration Profile SOLUTION The MKS MultiGasTM 2030 provides an effective solution forthe simultaneous and accurate analysis of multicomponentmixtures such as those found in the syngas process. Figure 1shows the FTIR spectrum of a syngas calibration gas standardas determined using the MultiGasTM 2030. Color codedinfrared bands due to 13% carbon monoxide， 8% carbondioxide， 1.5% methane and ppm levels of water are apparentin the spectrum. Figure 1 - Syngas Standard 1.5% CH (Yellow)， 13% CO (Blue)，8% CO， (Green)， balance H， The dashed sample spectrum shown in white in Figure 2 wasobtained using an electropolished nickel-free stainless steelgas cell with a 5 meter path length. The cell was heated to150℃ but can be heated to 191°℃ if higher vapor pressurecomponents are present to prevent them from condensing inthe sample line. The system sampling lines were also heated toensure that any moisture in the sample remained in the vaporphase. This allows analysis of all production products to beperformed without the removal of moisture. Figure 2-Syngas product spectrum CH，(Yellow)， CO (Blue)， CO，(Green)， Ethane (Pink)， Ethylene (Red)， Propane (Dark Blue)，Moisture (Purple) in a balance H， MultiGasTM is a trademark of MKS Instruments， Inc.，Andover， MA. A 16u broad band， LN， cooled detector， capable of accuratedeterminations at concentrations ranging from high ppb to %，provided a linearized response over the entire concentrationrange. If quantification of low levels (ppb to low ppm) ofimpurities is not required then the MultiGas 2030 can beconfigured with a 2 cm stainless steel gas cell. This provides aminimum detection limit from 250 to 500 ppm (dependingupon the component) up to 100% for all components aswell as provides very rapid response times due to the 10 cm’internal volume of the gas cell. For the analysis of syngas theMultiGas 2030 FTIRs are configured with a heated， highlypolished nickel-free stainless steel gas cell (either 2 cm or5.11 m) to avoid any chance of producing toxic Ni(CO)4through exposure of nickel plating to high CO levels at 150℃or 191°C. The high resolution (0.5 cm") of the spectra obtained usingthe MultiGasTM 2030 permits excellent speciation of likemolecules， with the instrument capable of separate analyses forsuch similar species as butane， propane， ethane and methane.It also allows for low level analysis even in the presence of highlevels of moisture (in particular， for SO， and NOx). ( 2 Tech Drive， Suite 201 Andover， MA 01810 978.645.5500 800.227.8766 ( within USA) www.mksinst.com )