When we think about modern gas mixing systems for the energy transition today, we are working on a foundation that was laid back in the early 19th century: Avogadro’s law. As early as 1811, Amedeo Avogadro recognized that equal volumes of different gases – at identical temperature and pressure – always contain the same number of particles. This simple but fundamental observation later led directly to the ideal gas law (law of ideal gases, thermal equation of state of ideal gases). This made it possible for the first time to describe the relationship between volume, pressure, temperature and amount of substance with mathematical precision (p x V = n x R x T, i.e. the product of pressure and volume is equal to the product of the amount of substance in moles, the molar gas constant and the thermodynamic temperature).
Why is this so important for gas mixing technology? Quite simply, the production of gas mixtures – whether in static or dynamic systems – is essentially about supplying certain quantities of different gases in the correct ratio to one another. Avogadro’s law provides precisely the physical basis for reliably mixing volume flows, mass flows and material quantities. Provided the pressure and temperature of the gases are known.
In both static and dynamic gas mixing systems from LT GASETECHNIK, a controlled, reproducible equal pressure is therefore first established between the inlet gases.
Static gas mixers
In so-called static or manual gas mixers, variable area flow meters and manual control valves are typically used. The volume flow for each gas is set manually using control valves. If the temperature and pressure are constant, the measured volume is directly proportional to the number of particles and therefore to the amount of substance.
In practice, this means, for example, for the production of a gas with 18% hydrogen in natural gas: if you open the valve for hydrogen (H2) so that 18 Nm³/h flows through the variable area flow meter and the valve for natural gas so that 72 Nm³/h flows, then the mixture contains 18% H2 and 72% natural gas – exactly as expected according to Avogadro’s law. Complex sensor technology is not necessary as long as the boundary conditions remain constant.
This technology is robust, economical and proven. It is used in particular where simple but precise gas mixtures with stable pressure and temperature conditions are required. However, it reaches its limits when operating conditions change or maximum precision is required. For this reason, high-quality static gas mixers are offered with guarantees of up to +/- 0.5 vol% accuracy under the same operating conditions.
Fluctuations in pressure can be eliminated by using high-quality dome pressure regulators. Different temperature influences on the individual gases distort the proportionality between volume flow and substance quantity – and shift the mixing ratio.
Dynamic gas mixing systems
Dynamic gas mixing systems that are equipped with mass flow controllers (MFCs) or a combination of mass flow measurement and automated control valves work differently. These systems measure the amount of substance or the mass flow of the gas directly and in a temperature-compensated manner. As the mass is directly linked to the amount of substance via the molar mass, Avogadro’s law remains the underlying principle here too: the ratio of particle number and volume can be taken into account precisely in real time via pressure and temperature measurement.
In such systems, gases are mixed with high precision regardless of external fluctuations. This is particularly important in processes where even the smallest deviations can have a major impact. These gas mixing systems are offered with guarantees of up to +/-0.1% accuracy by volume under the same operating conditions.
Another advantage of dynamic systems is their flexibility. Mixing ratios can be adjusted automatically, recipes can be stored and retrieved digitally, and the systems react to changes in the target values in fractions of a second. Here, classic gas laws are combined with modern automation technology to create a powerful tool.
Basis for the energy transition?
It’s a long way from a 200-year-old law to decarbonization, but Avogadrosche provides the foundation. Because with the energy transition, gas blending technology is becoming even more important. The gradual integration of hydrogen into existing infrastructures or the use of green propane (rLPG) mixed with air require precise gas mixtures. Avogadro’s law provides the theoretical basis for reproducible and safe processes.
This combination of 200-year-old scientific findings and state-of-the-art industrial technology shows how closely the classical laws of nature and modern engineering technology are linked. No gas law without Avogadro, no precise gas mixing systems without it.