A look at the past, present and future of the most flexible measuring system for analysing discrete hydrocarbons, the on-line process gas chromatograph.
The most prolific and flexible online analytical measurement device for analysing discrete hydrocarbons in the hydrocarbon processing industry (HPI) is the process gas chromatograph (GC). It is estimated that there are more than 30,000 process gas chromatographs installed worldwide.
This article takes a look at the past, present and a glimpse of the future of the online process gas chromatograph.
Process gas chromatography
A process gas chromatograph is an analyser that has been designed for installation and operation on line taking the sample directly, from a chemical process. The primary purpose of locating the analyser on line or adjacent to the chemical process is to obtain the analytical results with a speed of response that is comparable to process changes.
In general, such an analyser is designed with the separation columns, valves and detectors to perform a particular analysis on a single stream or at most a few liquid or gas streams of similar composition. The typical process chromatograph is designed to measure only key components necessary for process control in the stream.
The early years
In the 1950s a privately-owned company by the name of Watts Manufacturing located in Ronceverte West Virginia, United States, had the ability to produce complex temperature control equipment. This led to contracts from Union Carbide to produce Carbide-designed analysers for measuring concentrations of gas mixtures. Union Carbide licensed this analytical measurement technique ‘gas chromatography’, to Watts. Watts redesigned the gas chromatograph to better suit their manufacturing scheme and offered it for sale to the chemical and petrochemical industries.
In 1956 Beckman Instruments purchased Watts Manufacturing. Beckman’s main interest was to obtain the license to manufacture the gas chromatograph. After about one year of operation in the Ronceverte plant, Beckman announced they were moving the operation to California. Key individuals of the Ronceverte plant decided to start their own company building gas chromatographs under the name Greenbrier Instruments. Fifty years later what was once Greenbrier Instruments is now owned by ABB Inc and Beckman Instruments is now owned by Emerson Process Management.
Early process GCs were primarily used to measure light hydrocarbon gases up through C6 and inerts in the percent range with a Thermal Conductivity (T/C) Detector. Analytical columns, which provided the separation, were quite challenging to make in the beginning and were not always stable in there performance. Column packing solid support materials with large surface area were not commercially available until 1960. This led to some very interesting solid support materials ranging from crushed fire bricks to soap powder. In addition, early liquid coatings were not very pure which added to the lack of stability and performance.
By 1965, with more commercially-available solid support material and pure liquid phases, two additional and very major components were added to the Process GC that expanded its measurement capability to include C7s up to C14s in percent or ppm range. A liquid sample valve introduced by Micro Tech in Louisiana and ionisation detectors such as flame ionisation, photo ionisation, and electron capture were introduced to the market. This allowed process streams to be vapourised, separated and measured. The ionisation detectors enabled low range ppm measurements.
The swinging ‘70s
The 1970s brought about three more major advancements in process chromatography. The flame photometric detector for measuring sulfur species, on-line temperature programmed GC for measuring hydrocarbon streams with a wide range of boiling points, and the first microprocessor controller.
The clean air act 40 CFR updated in the early 1970s included a requirement to measure ambient levels of SO2. The Bendix Environmental and Process Instruments Division, formally Greenbrier Instruments, developed a Flame Photometric Detection method for meeting this requirement. In 1974, the detector used in this method was incorporated into the online gas chromatograph to measure trace sulfur species, the first in the industry.
Prior to the development of the temperature-programmed GC, hydrocarbon streams with a wide range of boiling points would require at least 2 GCs. The first online temperature programmed GC incorporated analogue temperature control of two ovens connected together, one isothermal and one temperature programmed, with some control electronics from lab chromatographs. Current versions, discussed later, incorporate a temperature controlled oven inside an isothermal oven with digital temperature control, provided by a microprocessor controller.
The development of the microprocessor played a significant role in advancing peak integration, signal linearisation and timing control of the online process GC. It also enhanced troubleshooting, data logging and expanded the process GC communications capabilities.
In the 1970s the online process GC was becoming a more hardened and reliable analytical measurement tool with a much greater acceptance in the HPI market.
Temperature control in the ‘80s
The 1980s gave us two more major components, digital temperature control and capillary columns. With these two additions you could now measure hydrocarbons with a wide range of boiling points up to C26.
Early commercial capillary columns were made with metal or glass. They were difficult to make and very expensive compared to industry standards and expectations.
Since these early materials were not that flexible and amenable to large temperature swings they had limited use in temperature programmed applications. During this time period, the Fiber Optics Industry introduced fused silica material. This material was very inert, flexible, and amenable to large temperature swings making it an excellent material for capillary columns and temperature programmed applications.
A major application in the 1980s was the Refinery Distillation Analysis using gas chromatography with digital temperature program control, first produced by Combustion Engineering, formerly, Greenbrier Instruments.
Digital temperature programming of ovens, columns, and traps have resulted in many specialty applications in the HPI industry such as Paraffins, Naphthenes, and Aromatics (PNA), Normal and iso Paraffins, Naphthenes and Aromatics(PINA) and Olefins.
Data access and the 1990s
One of the biggest contributors to the 1990s in process GCs was in the area of analyser networking. Providing data access and remote control of the process GC to any subscriber with a pass key allowed managers, supervisors, operators and technical support personnel to analyse the data statistically, make adjustments remotely, and maintain the health of the complete process GC network in the plant.
This was all made possible by designing into the analyser operating system the ability to communicate with the commercially available PC with Microsoft Operating system. This has led to a more open, commercially-based network architecture using ethernet and OPC to connect to third party devices as well as many DCS protocols.
Once again in the 1990s environmental regulations, specifically for clean fuels, EPA (40CFR Parts 80,85, and 86) concerning sulfur in gasoline and diesel, led to the development of an online chromatographic method. This method incorporates a furnace within the GC oven to oxidise all the components in the fuel sample to SO2, H2O and CO2, and a column to separate the H2O and CO2 from the SO2. A FPD detector is then used to measure SO2 as total sulfur in the 0-15 ppm range. This chromatographic method was developed by ABB Inc, formally Greenbrier Instruments. It is the first online method of any kind to become an ASTM method (D7041-04).
Current trends, smaller & faster
Many HPI plants today have a limited amount of space, limited air supplies and utilities. This, of course, is creating a requirement for a smaller process GC that can be installed on the process line itself without a shelter and using minimal air, carrier gas and detector fuel gases.
The natural gas industry, where process GCs are used to determine the heating value of the natural gas, has always required the process GC to be located in sites with limited space, minimal utilities and in many cases, no air supply. Rosemount Analytical, now Emerson Management Group, was the first to introduce such a small field mounted process GC to address these issues.
Now, this process GC approach is starting to be applied to the HPI industries. Some of these field mounted process GCs incorporate more than one analytical train and detector enabling them to measure C1 thru C9+, inerts and H2S in various HPI streams. The field mounted process GC is an excellent choice for most gas processing industry applications because these analysers provide simple, reliable, easy to service, low cost measurements.
Another HPI trend is the use of engineering procurement companies (EPCs) to lower capital cost of building new plant or expanding unit capacity. EPCs provide a lump sum, turn key, fixed capital project to meet the user’s specification. This requires all suppliers bidding on the individual portions of the project to provide the most competitive price possible.
These requirements have resulted in process GC suppliers reducing space and consumables by placing multiple applications on a single platform to reduce cost. Over 30 per cent of today’s process GC installations average two or more detectors, five to six analytical valves, and eight to 10 analytical columns in one oven. The result is more complexity, more maintenance, more long term cost and less reliability.
Finally, speed of analysis is always required for better process control, faster safety response, and improved process unit through put just to name a few. There are two approaches today to give a faster analysis time on the process GC, one is to provide a detector for each analytical train rather than using a selector valve to select between trains to an isolated detector.
The other method is to use precise digital temperature control to apply direct heat to the column. This second method has just been introduced for the first time as an online process GC method for gasoline distillation analysis in the refinery. The average of 15 minutes for existing process GC distillation analysis is reduced to just 90 seconds with the new method. Again, ABB Inc, formally Greenbrier Instruments, was first to introduce this method.
What’s next for online GCs
With downsizing plant personnel and the mergers in the 1990s reducing engineering staff, the online process GC of the future needs to be intelligent so as to inform the user of any pending problems before they occur, that is more prognostics as opposed to diagnostics. The process GC of the future will have neural intelligence designed into the product to make this possible.
The process GC of the future will incorporate a graphical user interface that will inform the user of everything from analyser status to graphical 3D removal and replacement procedures for all major components. Multiple smaller ovens will be used to simplify complex analysis, minimise analytical hardware, provide multiple isothermal temperature zones, and increase the speed of analysis.
The ovens will be designed to operate in a shelterless environment. Simply put, the future online process GC will inform the user of a pending problem, order the required part, schedule the maintenance and bill the user, all from the GC itself. Welcome to the next fifty years!
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