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Varying gas properties
The undeniably positive effects of the liberalization of the gas market have been accompanied by problems as well. This applies specifically to industry sectors for which the production and quality of their products requires stable and defined firing processes with high temperatures, specified air ratios, and even defined flame shapes. We are talking here about the thermal processes characteristically found in the glass, ceramics, and metallurgy industries. Nowadays these industry sectors are confronted with the fact that the composition and energy-related characteristic values of the combustion gas delivered via the gas network are subject to fluctuation. The era of largely constant L- and H-gases from a few supply sources has been replaced by a growing number of suppliers and infeeds from predominantly renewable sources with variable gas composition that necessitates stabilization through controlled additions for thermal processes.
Gas measuring technology provides assurance
An effective remedy is the integration of suitable gas analysis measuring technology such as the INCA multicomponent gas analyzer in the open- and closed-loop control systems of the gas feed. This allows timely detection of changes in the combustion gas composition so that measures for assuring processes based on closed-loop control of gas additions can be taken. Combustion gases are defined by their chemical composition as well as state variables, such as density, pressure, and temperature. Key indices such as combustion value, heating value, methane number, and air requirement are derived from this. Terms for gas properties in Europe are the Wobbe index, which is the ratio of the combustion value to the square root of the relative density of the gas, and the air ratio lambda, which is an important process-related control value for many thermal processes. For example, this is influenced significantly by the content of higher hydrocarbons (C2H6, C3H8 etc.) in the combustion gas because these gases require more air for
combustion compared to the usual CO.
Two-stage closed-loop control model from the technology specialists
A new closed-loop control model for taking into account varying combustion gas properties developed by the technology-oriented engineering company STG Combustion Control GmbH & Co. KG (focus: glass manufacturing) is based on two levels, which can be used independently of one another and at melting furnaces as well as feeding channels:
Successful use of INCA in a container glass factory
The combination of the new STG closed-loop control approach with the INCA gas analyzer of UNION Instruments GmbH provides an innovative solution that has already proven itself in a container glass factory. Noteworthy here is that the utilized INCA device is the INCA 1050 "Natural Gas Analyzer" that has been in proven use for many years and measures only the concentration values of CH4 and the C2+ fraction. From these two measurements, the analyzer calculates the heating value and density of the gas by using table values and correlation approaches and finally the Wobbe number. From the Wobbe number and the measured pressure difference value p of the assigned volume flow measurement (according to the differential
pressure principle, not the vortex principle!), the control system determines the necessary control variables. The success of this closed-loop control approach "Stabilization of the Wobbe index using closed-loop air addition" is demonstrated in the constancy of the drop temperature in the feeder of the glassworks at 0.1%. Due to the limited investment costs for the INCA gas analyzer compared to other analysis methods this successful solution could significantly affect future closed-loop control concepts and instrumentation in the glass industry.