Lean air

from Wikipedia, the free encyclopedia

Lean air is air with an oxygen content that is lower than the oxygen content of normal breathing air . The generic term for this is synthetic air and can refer to gas mixtures with a lower but also higher oxygen content. Synthetic air is z. B. used in gas analysis as zero or operating gas for the detection of nitrogen oxides . In chemical processes, the mixture is used in significantly larger quantities and has an influence on the product quality. The requirements for quantity, quality, security and availability are individually graded and correspond to company-specific needs.

Definition of terms

Lean air is artificially produced "air" with a lower proportion of oxygen. The oxygen content of 20.95% by volume in air should therefore be reduced (emaciated) to a lower content (e.g. 4–10% by volume of oxygen in the gas mixture ). For this purpose, gases are mixed: either technical air ( compressed air ) or oxygen with nitrogen , so that lean air with the desired oxygen concentration is generated.

Lean air can be obtained from manufacturers of technical gases filled in gas cylinders or gas cylinder bundles. If higher quantities are required, companies usually operate their own systems for generating lean air. Systems for generating such gas mixtures are called gas mixers , more specifically lean air systems or air conditioning systems.

use

Lean air is often required in processes for supplying solvent boilers and reactors, e.g. B. in the production of synthetic resins (also called resins ). During these processes, heat is supplied and flammable gases escape from the product . Thus, in the case of production under normal breathing air, the three necessary factors of the combustion triangle ( combustible material , oxygen, ignition energy ) would coincide spatially and temporally, which can lead to an explosion or deflagration , with serious accidents as a result. Overlaying the product with pure nitrogen during manufacture prevents explosion or deflagration. However, product components require oxygen for the desired chemical reaction . For this purpose, lean air is used with an oxygen content that remains safely below a defined limit concentration, so that the lower explosion limit is not exceeded and accidents are avoided.

Regular use in potentially explosive areas means that compliance with the oxygen content specified for the lean air is essential for both the quality of the production process (desired chemical reaction) and for safety-related issues (combustion triangle).

Requirements for lean air generation

The use described shows that the factors quality, safety and availability are important for the process plant operator. With regard to lean air systems, this means:

  1. Exact compliance with the defined oxygen concentration in the lean air gas mixture for the production of a constant product quality ( quality )
  2. Safe shutdown if a specified oxygen concentration is exceeded so that there is no risk of explosion ( safety )
  3. Through backup solutions or a bypass with pure nitrogen, ensuring the availability of the production plant ( availability )

The choice of system technology itself has an influence on the gas mixture quality and thus on the product quality.

quality

As an additional measure to monitor the correct gas mixture quality , a gas analyzer can be provided which continuously monitors the oxygen concentration. The measured oxygen value can be displayed and transferred to a higher-level process control system via an online link . If the limit value is exceeded, a change in the gas mixture quality (with automatic, dynamic lean air systems) can be initiated, shutdown or switchover to a possibly existing bypass can be initiated.

safety

The safe maintenance of a defined oxygen concentration in the lean air influences the safety of the supplied process system. The functional safety can be increased even further by means of a Safety Integrety Level (SIL) consideration. A safety requirement level according to the standardization IEC 61508 / IEC 61511 is referred to as SIL or safety level. The monitoring system used for this (usually consisting of a gas analyzer, output shutdown, blow-out line and solenoid valve) is jointly assessed with regard to its reliability through this SIL analysis. This further reduces the risk of malfunction.

Availability

To ensure the availability of a properly designed lean air system, at least the following measures are usual:

  • Gas filter on the inlet side, to avoid the impairment of the functionality of the fittings by particle entry,
  • Pressure control of compressed air and nitrogen to the same mixed pressure so that Avogadro's law of the ideal gas applies, i.e. the density of the gases is proportional to the molar mass at the same pressure and temperature,
  • Interconnection of the constant pressure regulators in the input lines so that the inadmissible enrichment of admixture gas is excluded at any time Additional locking via the gas analysis so that a redundant safety lock is created
  • Measurement of the volume flow (temperature and pressure compensated),
  • Use of non-return gas valves in each individual gas line to prevent transferring,
  • Enabling continuous or discontinuous gas mixture acceptance through constructive measures,
  • Ensuring self-sufficient plant operation, even in the event of a malfunction in a higher-level process control system or communication with it.

Web links

  1. ↑ basi Gas GmbH: basi synthetic air, HC-free - product data sheet. basi Gas GmbH, accessed on February 17, 2020 .
  2. ↑ zero gases. Retrieved February 13, 2020 .
  3. ↑ chemiluminescence. Retrieved February 13, 2020 .
  4. ↑ Linde Gas AG: Linde opened Europe's first fully automated gas filling plant in the Marl industrial park. In: https://www.linde-gas.de . Retrieved on February 13, 2020 (German).
  5. ↑ Syntetic Air. (PDF) Messr Group GmbH, accessed on February 17, 2020 (English).
  6. ↑ LT gas technology. Retrieved February 17, 2020 .
  7. ↑ Synthopol Chemie Deutschland focuses on expansion. May 16, 2014, accessed February 17, 2020 .
  8. ↑ Patent EP2365036 : Radiation curable aqueous coating compositions. Registered on March 12, 2010 , published on September 14, 2011 , applicant: Cytec Surface Special Ties, SA, inventor: Philippe De Micheli, Edmund Urbano. ‌
  9. ↑ Alexander C. Hanf: The oxygen content in the lean air must remain safely below a defined limit concentration. In: https://www.chemanager-online.com . ChemManager Wiley-VCH Verlag GmbH & Co. KGaA, August 7, 2018, accessed on February 13, 2020 .
  10. ↑ Alexander C. Hanf: Lean air systems. January 15, 2017, accessed February 13, 2020 .