DECENTRALIZING PROCESS GAS CHROMATOGRAPHS WOULD THERE BE ANY BENEFITS?

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1 DECENTRALIZING PROCESS GAS CHROMATOGRAPHS WOULD THERE BE ANY BENEFITS? Ulrich Gokeler, Bob Farmer Friedhelm Mueller Siemens Applied Automation Siemens AG 500 West Highway 60 A&D PA25 Bartlesville, OK 74003, USA Karlsruhe, Germany KEYWORDS Process Gas Chromatographs, On Line, Decentralization ABSTRACT Due to their complexity, performance requirements and maintenance, on line Process Analyzers are typically installed in controlled environments. In order to reduce the number of analyzer shelters as well as the costs associated with them, centrally located analyzer shelters throughout plants are used to accommodate a number of analyzers each analyzing multiple sample streams in sequence. This centralized analyzer densification demands that the samples to be analyzed are transported from the individual sampling points to the analyzers and back without changing sample integrity which frequently requires pumps and heat tracing. Consequently, the costs of analyzer shelters as well as the associated costs such as sample lines are frequently exceeding the costs of the analyzers installed. The thought of decentralization of on line Process GC s refers to the utilization of small, individual analyzers at or next to the sampling points. Initially one may be intrigued by the benefits of such decentralized analyzers such as the lack of analyzer shelters required, much lower installation costs, simple sample preparation and faster result update. On the other hand, there would be certain dramatic design changes required that makes this type of analyzer very different compared to today, such as very compact and modular design for interchangeability, process suitability at the sampling points environment and significantly cheaper costs per sampling point. This presentation attempts to summarize the thought of decentralization, the hardware requirements needed for such a design as well as a cost comparison. 1

2 INTRODUCTION Process Gas Chromatographs are one of the most important analytical instruments used to analyze specific constituents on line and automatic in vapor and liquid sample streams. The precision, performance and on line time makes this technique a necessity for process and quality control. An entire Process Gas Chromatography system consists not only of the actual analyzer but also of the sample extraction, sample preparation and stream selection, analyzer shelter with infrastructure as well as the sample transport tubing and signal conduit to the control and observation center. Typical on-line Process Gas Chromatographs have to have extensive analytical flexibility in order to be used in a wide variety of different applications and installations. Consequently, despite most of the applications do not utilize these flexibility and capabilities, it is reflected in the analyzer costs, installation requirements and some even in the required maintenance. Consequently an entire Process Gas Chromatographic system not only represents a significant capital investment but also significant life cycle costs. Therefore it is desired to reduce life cycle costs and still conserving flexibility, precision and performance. So far one way to reduce costs is the common practice to centralize analyzers at common locations to utilize common infrastructure, such as shelters and gas supplies. In addition if process control and sample composition permits it, Process Gas Chromatographs are typically analyzing several sample streams sequentially. Another way of thinking to reduce costs and simplify analytical systems is the demand to have simple, cheap, transmitter type analyzers that can be mounted directly at individual sampling points without the need of sample transport tubing or analyzer shelters. Recent progress and reports of techniques and applications that may permit some simplification of on-line Process Gas Chromatographs as well as the availability of some compact analyzers renewed this issue. This demand actually affects all type of analyzers in a process plant. However in order to simplify the issue, only aspects of on-line Process Gas Chromatographs are considered. This paper discusses the factors that lead to the present centralization of analyzers and attempts to determine if there is a need of decentralized analytical systems and if so, what the requirements for such an analyzer may be. CENTRALIZED ANALYZER INSTALLATION Presently it is common practice that on-line analytical instruments are in some kind of enclosure. Some can be large accommodating a number of different analyzers, some smaller one for a few analyzers and some non-walk-in enclosures. Depending on the requirement, they are just vented, heated or air conditioned, satisfy electrical classification from general purpose to electrical hazardous and can consequently be turn key from a few thousand to a few hundred thousand dollar. Typically several Process Gas Chromatographs and even other analytical instruments are permanently installed, plumbed and wired with sample preparation and stream selection systems mounted outside. Why are several analyzers typically mounted in a common shelter at a centralized location and not individually at the sampling points? The answer is simple: To increase analyzer reliability and reduce costs. Because the flexibility of the analyzers makes 2

them more sensitive to ambient changes, the environment can have an adverse influence on analyzer lifetime, reliability and stability. FIG.

Because it is too expensive to mount each analyzer with a shelter next to the sampling point, it is common practice to mount several analyzers together into a common shelter and bring the samples to

Of course one trade off is a slower sample update frequency.

3 them more sensitive to ambient changes, the environment can have an adverse influence on analyzer lifetime, reliability and stability. FIG. 1: TYPICAL ANALYZER SHELTERS OF VARIOUS SIZES TO ACCOMMODATE ON-LINE PROCESS ANALYZERS Consequently Process Gas Chromatographs should be installed in a climate-controlled environment. Because it is too expensive to mount each analyzer with a shelter next to the sampling point, it is common practice to mount several analyzers together into a common shelter and bring the samples to the analyzers. In order to save even more, similar sample streams are analyzed with the same analyzer sequentially and consequently the number of analyzers can be reduced. Of course one trade off is a slower sample update frequency. Analyzer shelters reduce maintenance and service because analyzers perform more reliable, more precise and longer in a climate controlled environment. Analyzer shelters also provide a suitable and comfortable environment for the analyzer technicians to maintain and service analyzers in a timely and efficient manner. Additionally, all utilities, from power supply to auxiliary gases, calibration standards, communication hubs and vapor or condensate vents are all on one location. Lets not forget, it is also cheaper and more efficient to build these analyzer shelters turn key and just drop them on an analyzer pad for utility hook up instead installing, wiring and plumbing them individually on site. However, each sample has to be piped from the sampling points to the shelters, either just in a tube or heat-traced. Typically a fast loop is used to keep sample lag times low. Some sample 3

4 returns can be combined with others for a common return to the process. Others have to be returned individually. Sample lines with individual Returns Sample Lines, some heat traced, with common Sample Return Standards GC Power Signal / Data Supply Gases Sample Lines to two Analyzers Analyzer Shelter SSS Condensate Drain Air Conditioner *FIG. 2: TYPICAL ANALYZER SHELTER CONFIGURATION CONTAINING * 4 PROCESS GAS CHROMATOGRAPHS *Many & sometimes long Sample/Return Lines DECENTRALIZED ANALYZER INSTALLATION Decentralizing analyzers is the concept of having individual analyzers directly at the sampling points. Is it possible and does it make sense to move the analyzers to the sampling points? Can the analyzer shelters be eliminated? Probably there are cases were it makes sense, others where it doesn t. The issue right away then is when does it make sense to have analyzers at sampling points? What are the issues and what are the analytical hardware requirements? Furthermore, there are going to be different infrastructures and service requirements. And the most important question is what is the cost situation? Because the location of the sampling points, it must be expected that most of the time a specific analyzer at a certain sampling point can only take care of one sampling point. That would then multiply the number of analyzers right away. In the real world example shown in Figure 3, 7 single stream and 2 dual stream, all together 9 PGC s would be required to analyze the same 11 sample streams that are analyzed by 4 PGC s in Figure 2. The advantage is the much higher sample update frequency from each analyzer. Also because the proximity of the analyzer and sampling point, there is no fast loop required and sample flow and lag time is very short. Nevertheless, there is the issue of sample disposal from each sampling point. Because the 4

5 decentralized sample locations, power supply and communication wiring is needed throughout the plant as well as auxiliary gas supply and the local availability of calibration standards. Because the higher number of analyzers required, it is cost and typically also space prohibitive to have a shelter for each analyzer. This has a direct influence on the analyzer design because present analyzer designs typically do not permit to mount them without a shelter. Calibr. Calibr. Supply Gases Supply Gases Calibr. Supply Gases Sample Prep. Analyzer Power Signal / Data *FIG. 3: DECENTRALIZED ANALYZERS FOR SAME EXAMPLE AS IN FIGURE 2, REQUIRING 9 PROCESS GAS CHROMATOGRAPHS FOR 11 SAMPLING POINTS Multiplying and transferring analyzers to the individual sampling points may or may not be the solution depending on available instrumentation, design and capabilities. In order to determine if decentralizing is the solution, it is necessary to look at, define and evaluate the issues related to it, which are: Cost Reduction of initial costs and cost of ownership. SPS Sample preparation systems complexity, functionality and maintainability. Analyzer Size, maintainability, environmental compatibility. Maintenance Parts, accessibility, simplicity. Speed Increase of result frequency ARGUMENT COST SAVINGS Very often decentralization is considered because the expected general reduction of cost. This has to be looked at for every particular project and configuration. The following two simple 5

6 examples demonstrate that point assuming that a typical PGC cost about $ 30,000 and represents about 1/3 of the total system costs, hence the $ 90,000. The other 2/3 can be contributed to the system integration and the onsite requirements such as sample tubing, conduits, power and gas supply. Configuration 1 1 Traditional PGC 6 x8 Shelter with Air Con 1 Stream $ 90 K 1 Decentralized GC No Shelter 1 Stream $ 30 K Configuration 2 3 Traditional PGC s 8 x8 Shelter with Air Con 10 Streams total cycle times of 19, 8.5 and 16 min./analyzer 9 Decentralized GC Rain/Sun roof 9 Streams total cycle time of 8 and 4 min./analyzer $ 250 K $ 290 K System configuration 1, utilizing a single analyzer shows great cost advantage because savings on the analyzer shelter and the on-site installation cost. However, the second configuration does not show any cost advantage for the decentralized configuration. In opposite, it is about 15% more expensive. The real benefit of configuration 2 is in the increased frequency of results. The second example uses actual costs for an existing installation utilizing traditional Process Gas Chromatographs and estimated costs for a decentralized configuration. Now here it is assumed, that a compact decentralized analyzer GC provides a hardware cost advantage and does not need any analyzer shelter. For multiple sampling points it can be said that despite the higher hardware costs of traditional analyzer and their analyzer shelter requirements, they are cheaper per sampling points compared to individual analyzers at the sampling points which in turn have a cost advantage for single sampling points. ARGUMENT SAMPLE PREPARATION SYSTEM One of the most important aspects of an analytical system is the sample preparation and stream selection system. We also know that a substantial number of system failures to perform properly are due to sample system problems. Single point sample preparation systems can be of a more simple design, with fewer parts and consequently improved functionality and performance. The entire sample preparation system can not only be much smaller, but it might be possible to utilize standardization and modularization. Because the proximity of the analyzer to the sampling points, very low sample vapor flows in the cc/min result in very short sample lag time resulting in less memory and higher confidence in sample integrity. The low sample flow might also make sample disposal into the environment easier. Otherwise it may be necessary to pump these small flows back into the process or have vapor or condensate vents throughout the plant. Consequently, sample preparation systems at the individual sampling points provide a simpler and more reliable configuration that needs less maintenance. The process control benefit is clearly the short sample lag time. 6

7 ARGUMENT ANALYZERS Because of the location of the sampling points and the space constraints, existing analyzers can not easily be accommodated, especially not if shelters would be required. If there are no shelters to be used, existing analyzer designs may not be suitable. A more compact design might not have the analytical flexibility of existing state of the art analyzers and consequently compact analyzers may not be usable for all type of applications. Without having the option of a climate-controlled shelter, the analyzer must be environmentally independent over a wide range of temperature and not be influenced by rain, snow or dust. This has an immediate an impact on the required instrument design, maintainability and serviceability as described in the next paragraphs. Consequently analyzers to be mounted directly at sampling points need to be compact, environmentally independent and either without maintenance or with very simple and quick exchange procedures. ARGUMENT MAINTENANCE Because the flexible design of existing sample preparation systems and analyzers, a large variety of parts are used. Consequently it must be the desire to have fewer parts, especially fewer maintainable parts in usage. The discussed Modular Sample Preparation System (1-3) is focussing in that direction. A compact, standardized sample preparation system with the ability to adjust, read and monitor all sample parameters through the analytical system would greatly enhance performance and on line time if not for all than at least for a wide variety of sample conditions. From an analyzer standpoint, it seems likely, that miniaturizing existing techniques will not achieve the desired benefits. Miniaturizing existing analytical techniques, such as injection and column switching valves, multi column configurations or analyzer purge requirements only leads to multiplying maintainable items in more analyzers. The at-the pipe locations of these analyzers, the lack of analyzer shelter and the environmental situation makes it obvious that on site maintenance is an unlikely option because the motivation, ability and efficiency of service technicians is directly proportional to the environmental conditions. Very simple modular exchange or the availability of exchange GC s would be required. This necessitates great simplification of the analytical and electronic design. Consequently it also seems to imply that the universal analytical flexibility and capabilities may have to be reduced. ARGUMENT SPEED Because the proximity of the analyzer to the sampling point will reduce sample lag time significantly and because the dedication of this analyzer to this specific sampling point, faster result update can be achieved. The higher result frequency can achieve better process control, increased quality and higher product yield. This is especially true under unstable process conditions such as process upsets or process start. On the other hand it should also be noted that 7

8 utilizing traditional analyzers with multi application capabilities, column trains or multiple traditional analyzers could also achieve the same benefits (5-6). It also has to be accepted that if that individual analyzer is off line, there may be no option to divert the stream and analyze it with another analyzer. Hence again, very simple exchange or repair. Consequently, speed seems to be the greatest beneficiary in having decentralized analyzers at the sampling points. WHAT ARE THE ANALYTICAL REQUIREMENTS? Consequently, in order to make the concept of decentralization successful and beneficial for selected applications and installations, there are some substantial requirements to be fulfilled: - Environmental independency of analyzer and sample preparation system from 15 to 120 F ambient temperature, independent of rain, ice, sun, dust - Smaller hardware because lack of space close to sampling points - Modular, so that sections or the entire analyzer could be exchanged quickly; consider standardized application modules. - Elimination or at least minimizing analytical maintenance by utilizing state of the art techniques for presently maintainable items such as column switching or injection devices. - Auxiliary gas consumption (carrier, combustion, air and oven/analyzer purge gas) has to be minimized or eliminated because limited availability in the vicinity of the analyzers. Otherwise tubing from central gas supply locations has to be installed which is cost detrimental. - Costs of sample preparation system and analyzer should be reduced or there is limited cost advantage. - Connectivity of every sample preparation part with the analyzers is desired to adjust and monitor set and actual parameters, variations and trended to predict possible failure in advance. Connectivity of all analyzers is desired for continuous data exchange, especially if more than one analyzer is required to analyze all required constituents at a specific sampling point. Together these are some pretty high requirements that indicate some fundamental changes of system design. CONCLUSION Decentralized Process Gas Chromatographs can be beneficial. But when, how and where is project and situation dependent and the benefits and trade off have to be evaluated case by case. Benefits could be cost reduction and, or increase of result frequency. To achieve benefits decentralized Process Gas Chromatographs could provide they have to have certain hardware characteristics. Some of the benefits decentralized Process Gas Chromatographs could provide are also available by proper application of traditional Process Gas Chromatographs techniques. Cost reduction and information gains are the possible benefits. If all the requirements indicated earlier could be met, there is the possibility of reductions in 8

9 investment costs and cost of ownership for specific analytical applications, systems and locations. With the aforementioned design requirements, it does not look like there will be a loss of maintenance capabilities or decrease of on-line availability. The maintenance philosophy and way of performing maintenance certainly has to be adapted. There would be a very significant increase in measurement frequency that permits a better process control, especially under upset conditions. Update Time, Information Information Update Time Service & Maintenance S & M Utilities, Sample Lines, Power, Data Communication Central, Air Conditioned x Streams & stream switching valves x Streams analyzed in sequence On Site Installation Shelter SPS Traditional PGC S & M On Site Installation SPS Single Analyzer PGC Less Service & Maintenance Utilities, Power, Data Communication Rain/Sun Roof x Single Stream Sample Preparation Systems x Streams analyzed simultaneously Centralized Decentralized FIG. 4: SYSTEM COST REDUCTION AND INFORMATION GAIN REFERENCES 1. Doe, S. Surface Mount Technology for Sample Conditioning Systems, Proceedings of the 46 th Annual ISA Analysis Division Symposium, Vol. 34, Houston,TX, Hughes, R., An Introduction to the Advanced Modular Sample System and a Concept for Cost reduction, Proceedings of the 46 th Annual ISA Analysis Division Symposium, Vol. 34, Houston,TX, Simco, D., Advantages of Miniature modular Sample Systems, Proceedings of the 46 th Annual ISA Analysis Division Symposium, Vol. 34, Houston,TX, Bade, Robert et al, Applications in Parallel Chromatography, IFPAC

10 5 Gokeler, Ulrich et al, Process Multi Dimensional Gas Chromatography, Chapter 5 or Cortes, H.J.; Multi Dimensional Chromatography, Techniques & Applications, Vol.50, Marcel Dekker, Mahler, Harald et al, Multi Column System in Gas Chromatography, Chapter 9 of Adlard, E.R.; Chromatography in the Petroleum Industry, Elsevier,

A MINIATURIZED PROCESS GAS CHROMATOGRAPH - A SINGLE ANALYZER MODULE

A MINIATURIZED PROCESS GAS CHROMATOGRAPH - A SINGLE ANALYZER MODULE Ulrich Gokeler Friedhelm Mueller, Udo Gellert Siemens Applied Automation Siemens AG 7101 Hollister Road A&D PI Houston, TX 77040, USA