Sensitive gas analyses help plant safety regimes

Paul Boughton

Gas analysis, says Eugene McCarthy, has a key role to play in plant optimisation and this includes plant safety.

Syngas (synthesis gas) is manufactured from feedstocks containing carbon, such as coal, heavy oil, natural gas or biomass, to produce a mixture of hydrogen and carbon monoxide.

The production process involves a number of phases that start with gasification of the feedstock and efficiency and safety are greatly improved when hydrogen levels are monitored using a new sensor technology that is able to measure without interference from other gases. Syngas is used in the production of synthetic petroleum, lubricants, fuels for internal combustion engines and as an intermediate in the production of other chemicals.

The gasification phase requires very high temperatures, depending on feedstock and process, which are obtained from an external heat source or by partial oxidation of part of the feedstock to release heat. A purification process then removes impurities such as carbon dioxide, water vapour, methane, sulphur compounds, tar and ash. After which, the proportion of hydrogen and carbon monoxide is adjusted depending on the intended use of the syngas.

Continuous hydrogen measurement provides an opportunity for real-time control of the production process by enabling the operator to make adjustments to ensure maximum efficiency and safety. For example, water may be added to increase levels of hydrogen, or water might be removed to increase the carbon monoxide level. As a result, the operator is able to produce a final product with the correct ratio and to then check that this has been achieved. In the absence of hydrogen measurement, the end product ratio can only be an estimate.[Page Break]

Quantitech supplies its H2scan hydrogen-specific analysers to the UK market. These employ a solid-state hydrogen specific technology based on palladium/nickel alloy that requires no sample gas, reference cell or routine calibration.

The sensing material is inherently specific to hydrogen and has the capability to operate in a variety of multi-component and varying-component gas compositions, including tolerance to percentage levels of hydrogen sulphide and carbon monoxide. Custom conditioning and calibration in contaminant gas streams along with a very precise on-board temperature control loop provides high accuracy and long-term stability. The analysers are also adaptable to conventional or NeSSI type sample systems.

"The H2scan technology removes guesswork from the syngas production process and adds new levels of efficiency to an established process, ensuring that the process is able to respond quickly to variables. This is a further example of the many applications in which hydrogen-specific gas measurement has delivered tremendous benefits," says Quantitech md Keith Golding.[Page Break]

Quality and purity

Servomex has been selected by Linde Gases to design and supply gas analysis systems that will maintain quality and purity for medical gases distributed across Brazil. Installed in a network of stations responsible for filling Linde's medical gas cylinders, Servomex's expertise in systems engineering ensures the continuous traceability and reliability for all required gas measurements.

Designed to meet the highest pharmacopeia standards, a Servomex-designed sample system integrates the company's advanced gas sensing technologies with third-party measurements for humidity, nitric oxide and nitric dioxide.

Utilising the SERVOPRO 4100 multigas analyser, designed for the process control and product qualification requirements of industrial gas production, exceptional gas purity is maintained using Servomex's advanced paramagnetic technology to measure oxygen and GFX infrared technologies to measure trace carbon monoxide and trace carbon dioxide.

In addition to the ability to deliver a world-class gas analysis solution, Linde selected Servomex on the quality of support offered by Servomex's South Americas business centre. Offering expert sales, technical and engineering assistance and fast, local response from operations based in Sao Paulo, Servomex was able to demonstrate complete commitment to meeting Linde's requirements.

The result is a high-quality customised solution for the transportation of Linde medical gases in Brazil, ensuring high gas quality is consistently maintained throughout the supply chain while ensuring a low cost of ownership.[Page Break]

With Metrohm's MARGA monitor, gas and aerosol composition of ambient air can be measured simultaneously and continuously. The analytical part of the instrument consists of two Metrohm ion chromatograph systems for anion and cation measurements respectively.

Through a size selective inlet (for example to only measure particles smaller than 10µm) air is drawn into the MARGA system. It enters a wet rotating denuder (WRD) in which the gases from the air are absorbed into a thin layer of water. From the WRD the air flow continues into a steam jet aerosol collector (SJAC) in which aerosols present are collected in water. The whole MARGA system runs autonomously, generating aerosol and gas concentrations every hour and only requiring user intervention once per week to supply new solutions. The system can operated in the field in remote places.

The sensitivity of the ion chromatographs is sufficient to reach detection limits below 0.1µg/m3 at a 1m3/h air sampling flow. The detection system is continuously calibrated by the use of an internal standard of LiBr, containing anions and cations normally not present in ambient air.[Page Break]

FTIR solutions

In Fourier Transform Infrared (FTIR) spectroscopy, a gas analyser detects gaseous compounds by their absorbance of infrared radiation.

Gasmet's FTIR gas analyser collects a complete infrared spectrum 10 times/second. Multiple spectra are co-added together according to selected measurement time (improving signal-to-noise ratio). The actual concentrations of gases are calculated from the resulting sample spectrum using patented modified classical least squares analysis algorithm.

The analyser includes: signal processing electronics with digital signal processor technology for high speed data collection; a GICCORTM interferometer. During the manufacturing process, each interferometer must pass extensive shock and temperature stability tests (+/-20°C) without any decreases in modulation.

In business news, with the acquisition of the US company SpectraSensors, Endress+Hauser is tapping into the market for gas analysis. This further reinforces the position of the Swiss group in the area of analytical measurements.

With headquarters in Houston, Texas, and production facilities in Rancho Cucamonga, California, SpectraSensors develops, manufactures and distributes laser-based gas analytical instrumentation (Fig. 1). The devices are used in natural gas pipelines and plants, petrochemical refineries and chemical plants as well as for atmospheric monitoring. The company employs about 90 people and generates annual sales of approximately $US30m (EUR23m).[Page Break]

Speed and accuracy for oxygen analyses

Michell Instruments has released details of the XTP601, the latest addition to its range of oxygen analysers. Based on the highly stable thermo-paramagnetic sensor, the XTP601 provides fast, accurate measurements of oxygen levels in various background gases.

Capable of measuring oxygen from 0-1 per cent up to 0-25 per cent and suppressed zero ranges, such as 90-100 per cent, the analyser provides solutions for applications ranging from biogas plants to monitoring blanketing gases in oil tankers.

The XTP601 is configurable to suit specific applications and budgets with three options: blind transmitter version (settings, controls and readings accessible via application software); transmitter with status LEDs (settings, controls and readings accessible via application software); and full display analyser (settings and readings are accessible with on-screen controls or via application software).

All of these options may be rated for either safe or hazardous area use. Hazardous area classifications are available for ATEX, IEC Ex with CCSAUS pending approval.

The full display version of the XTP601 has a touch screen interface to enable easy operation without needing to remove the lid. This means that users can calibrate, change settings and interrogate the instrument in the hazardous area without the need for a hot permit. Menus allow easy access to information such as: oxygen concentration; analyser status; a graph showing oxygen trends over a user-defined time period; alarm history; minimum and maximum concentrations and other parameters to aid diagnosis of plant conditions.

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