Product - Gas burners of various designs and performance classes are frequently tested and certified with regard to their efficiency and emission levels. These procedures use test gases whose composition and calorific value must be precisely determined.

For this purpose, the Dutch company KIWA Gastec uses a mobile test stand, the central unit of which is the compact MicroSAM gas chromatograph. This solution has proven to be both very flexible and economical. Gas burners are devices with which the chemically bonded energy of a fuel gas - described by its inferior or superior calorific value - is released by means of oxidation.
The essential functions of a burner consist of the delivery and mixture of the reactants (gas and air), the ignition and stabilization of the combustion. The development of modern gas burners is influenced by the demands on design and material, but especially by demands for optimum efficiency with minimal emission of pollutants. To verify their properties, the gas burners are tested on test stands under realistic operating conditions and the test results are generally documented by means of a certificate.

Testing and Certification of Gas Burners

KIWA Gastec is the market leader in Europe in the field of testing and certifying gas-operated devices, including gas burners. The testing is performed on test stands in which the burners are tested in continuous operation using a variety of fuel gases.

KIWA Gastec uses 14 different gas mixtures and two additional calibration gases. The 14 gas mixtures are fed via individual pipes to a total of eight test stands. The two calibration gases are available on a separate gas bottle trolley located next to the mobile test stand. An important factor in assessing the combustion behavior is the precise and reliable analysis of the composition of the fuel gas and thus its superior calorific value.

Special gas chromatographs are used for this purpose that determine the composition of the gas and derive the superior calorific value, standard density, Wobbe index and compressibility value as the quality parameters of the fuel gas using defined calculation procedures.

Mobile Gas Measurement Station

In view of the economical and legal significance of a burner certification, the composition and superior calorific value of the gas types used for the test must be measured with great reliability directly at the test stand and the measurement values must be documented, guaranteeing their assignment to the burner under test. An expensive solution for this would be the permanent installation of suitable test equipment on each test stand. A considerably more economical solution however is offered by a mobile measurement station that can be freely moved around the test hall and connected quickly and easily as required to the respective test stand. Above all, a solution of this kind must meet four requirements:

• The measurement station must be compact and easy to operate in terms of its size and weight.
• The measurement station must be capable of autonomous operation when switching between two test stands, which means it must manage without permanent connections for the power supply or data communication.
• The analytical part of the measurement station (gas chromatograph) must be at least the equivalent of stationary measurement apparatus in terms of separating capability, detection sensitivity and suitability for automatic calculation of calorific value.
• The mobile solution must use appropriate methods so that the possibility of any mistake in assigning the test results to the burner actually tested is reliably ruled out.

The mobile measurement station shown in fig. 1 was developed by Siemens in close collaboration with Kiwa Gastec and meets all the above requirements. For its analytical section it uses the MicroSAM gas chromatograph that is based on micromechanical technology and in this case contains special software for determining superior calorific value.
The mobile measurement station consists of a baseplate on rollers on which a rack frame is mounted with equipment installed on both sides:

• On the front of the frame there are two heated enclosures in which the MicroSAM gas chromatograph and the associated gas processing unit are installed.
• Mounted on the rear of the frame are the operating elements (monitor and keyboard) and the terminal box as well as the battery for non-mains operation while the measurement stand is being moved between two test stands.
• The computer for recording and processing the measurement data is mounted on the baseplate.
• The measurement station also comprises two mobile test gas bottles (not shown in picture).

The MicroSAM gas chromatograph is equipped with capillary columns, valveless metering and column switching and micro WLD detector. In addition, three "measurement methods" are stored in the MicroSAM which are permanently assigned to the measurement tasks at the eight test stands. Each method contains all specifications and values such as time sequences or pressure values for the column switching that the MicroSAM requires for the correct execution of the associated measurements. Thanks to this arrangement, the test engineer only needs to select the measurement method number which indicates which measurement station the test station is currently connected to.This guarantees the required assignment of measurement result to test stand. Similar conditions apply to the two calibration methods.

MicroSAM

Process gas chromatographs are used in countless processes in many industrial sectors, traditionally constructed devices often being mounted in large enclosures and these in turn located in large analyzer shelters. As part of the continuous optimization, however, the user demand for saving space in plants and thus for more compact devices can no longer be ignored. The micro-process gas chromatograph MicroSAM (fig. 2), based on micro system technology - in addition to many other attractive features - offers the advantage of an extremely compact design, roughly the size of a soccer ball, and of low weight.

If the MicroSAM is set up together with conventional PGCs, significantly smaller analyzer shelters are required, resulting in considerable savings. In combination with its user-friendly remote operating concept, MicroSAM can also be mounted and operated directly at the sampling point. Even in the case of remote locations with limited infrastructure and restricted maintenance options, the MicroSAM proves to be a good solution. One particularly attractive example of the advantages of such a compact design combined with a high analytical performance is the development of the mobile measurement stations described here.

Analytical performance

A decisive factor for the accuracy and reliability of the measurement values (superior calorific values) achieved is the ability of the chromatograph to completely separate the gas components in question and to demonstrate a high mechanical stability over a long period of time. By means of details of its construction, especially the use of capillary columns in conjunction with valveless column switching technology, the device delivers excellent values.