Abstract After GC was introduced by James and Martin in 1952, GC was well established within the petrochemical industry already in 1956 (Ref 1). Since then part of the GC has evolved from the laboratory into the process environment. Analytical techniques and in particular GCs are used in process plants to determine product quality & yield and GC is used as a guarding technique to protect essential process operations. Such as the protection of catalyst in a reactor against contaminants.
Speed
Industrial processes are operated by process control systems which is based on the measurement of physical properties and composition of the product. The composition of the product is mainly determined in the laboratory. Laboratory analyses are done within hours and, since such measurement takes a relatively long time it can have a negative impact on the process plant’s throughput and product quality (an upset condition at the front may results in an off-spec condition at the output when not quickly corrected). Therefore fast analyses are required. Some of these analyses are performed on-line in the plant at different critical points in the process. This will speed up the measurement and the operation of the plant, resulting in a better control of product specification. Installing on-line analytical instruments will also minimize the errors that are introduced when taking manual samples.
Eventually on-line process analyses will result in the increase in the plant’s product yield and in the return on investment of the analytical system. It is not a matter of how much an on-line analytical system cost but how much money the implementation of an on-line process analyses can make, by the product quality and yield improvement!
How is GC up to now used in process companies?
Tim Lenior: “GC- analyses are well established into the process industry worldwide, routine control analyses are performed in the process laboratories inside the industrial companies, or at the commercial laboratories for the smaller sized companies. With new developments over the last decades in the area of capillary columns more complex applications became available for the process. For the moderate applications the analyses are partly integrated into the process control by means of online and inline analyses. The sample handling including calibration is automated and a 24/7 operation is established in those factories using online process analyzers and in particular process gas chromatographs (PGCs). How are µGC’s used?
The first micro-Gas chromatograph (µGCs) was developed for the international space program. Currently, after some adaptations, the integration of the µGCs into a micro process gas chromatograph analyser (µPGC) is available. The combination of more analytical channels (one channel consists of an injector, column and detector fvg) into one Eex certified instrument makes the analyses very fast and flexible in comparison with the conventional Process GC techniques.
The combination of narrow and medium-bore capillary columns and MEMS resulted in further integration and fast and accurate analyses for the µGC. Due to this combination, quantification limits gain and a dynamic range of over 5 decades can be reached using a thermal conductivity detector (1ppmv to 100vol%).
We see now that µGC applications are rapidly growing in the area of petrochemical applications Shell uses the technique for their Gas To Liquid process, first in R&D environment and then in one of their factories in Bintulu. Because of its small size and high separation power we use µGCs for fast analysis and integration at several sample points in a process plant.
Why are µGC’s becoming popular?
The first advantage of micro process gas chromatography over the conventional methods is speed: µGCs are fast due to the use of narrow and medium-bore columns. Size and separation power of µGCs allows it to be used for fast analysis and integration at more sample points in a process plant. Moreover, for a number of practical reasons it is an advantage to miniaturize the equipment for process analyses. Those advantages are:
• close mounting to the sample take-off point
• lower amounts of sample gas needed (lower environmental waste)
• lower transfer times of the samples
• shorter delay times for analyser results
• low energy and utility consumptions
• easier explosion proof (ATEX, GOST, CSA) integration
• increased reliability (24/7) operation
• increased precision and accuracy
• Low maintenance (modular design)
In general, conventional PGCs are complex and costly in terms of total cost of equipment and consumables. They can be replaced by µPGCs, in fact often a combination of several continuous measuring devices can be replaced by one single µPGC instrument. The rapid determination of multiple sample points is another advantage of the µPGC technique.
Will µGC’s be replacing regular GC’s?
The method is now ATEX certified and fully automated versions are available. However, it is a new technique and users are careful to make changes in their process since the stakes are so high. It takes time to build confidence. Nevertheless a group of technologists stuck out their neck to use this new technique and they are successful. The applications are often a result of the R&D phase of new process developments e.g. the Gas To Liquid process. Another incentive is the reduction of total cost of the equipment and analytical installation. Engineers within Exxon and Dow invented a platform on which sample handling equipment and instrumentation is integrated (NeSSI for New Sampling/Sensor Initiative). This platform combines micro scale analytical equipment and sensors onto a miniaturized sample-handling platform and has a standardized foot print.
Who is using it currently?
Shell uses the technique for their Gas To Liquid process, they produce high quality fuels from paraffin’s that are produced in the Fischer Tropsch Process from natural gas. The µPGC is used in the syngas production and conversion step for compositional analyses and catalyst protection. Speed is of utmost importance to guard the expensive catalyst. In the area of Chemical companies Clariant (D) used the analyzer for quality control in the production of Ethyleen Oxide (EO). The EO quality determination requires fast response for this rapid process. Other areas of use are: Repsol (ES) reforming process for H2 production (fuel cells). Total (UK), Statoil (NO) and the Dutch Gasunie uses it for natural gas analyses for on- and offshore production platforms for the determination of Hydrocarbons (to C12) and the impurities in natural gas; H2S, COS, MeOH, H2O (pipeline detection). In the latter case the pipeline interference should be fast to maintain product specification in case of a contaminant breakthrough. Further use is in Biogas tie-in points, a number of environmental analyses including CO2 for greenhouses and Yara’s Fertilization process for the production of ammonia nitrates. A growing area is the natural gas transportation and trade where custody transfer is gathered based on fast analyses. The µPGC plays an important role in this application due to its accuracy, speed and cost of installation at often-remote locations. Energy and dew point calculations are incorporated in this application.
© 2012 Chromedia
