Space velocity

The space velocity is the volume flow of a fluid in relation to a reference volume . ${\displaystyle {\dot {V}}_{Gas}}$ ${\displaystyle V_{Kat}}$

The space velocity is a term that in industrial chemistry and in the process technology is important. By forming a quotient, it sets a volume flow - usually of a gas , but also for liquids - with a spatial volume V - z. B. a catalyst or adsorber bed - according to the formula ${\displaystyle {\dot {V}}_{Gas}}$

${\displaystyle v_{Raum}={\frac {{\dot {V}}_{Gas}}{V_{Kat}}}={\frac {1}{\tau }}}$

in relationship. The space velocity is the reciprocal of the more commonly used residence time . ${\displaystyle \tau }$

If the volume flow is related to the hour, the unit is:

${\displaystyle {\frac {m^{3}}{h\ m^{3}}}={\frac {1}{h}}}$

In the case of catalysts, the volume refers to the macroscopic volume of the catalyst, so the volume flow is independent of the shape or internal structure of the catalyst. ${\displaystyle V}$

Depending on the application, space velocities in exhaust gas treatment can range between values ​​of less than 5000 h ⁻¹ (for substances that are difficult to break down) and greater than 100,000 h ⁻¹ (engine exhaust gases). The information is based on the standard condition . Depending on the application, the space velocity has a significant influence on the degree of conversion .

Applications

• In heterogeneous catalysis , the required catalyst volume for the conversion of a known volume flow can be calculated in this way. In order to determine the active catalyst surface, however, it is necessary to know another parameter, the surface velocity.
• In ad- or absorption , the required amount of ad- / absorber volume for treating a given volume flow can thus be determined.

literature

• Jens Hagen: Chemical reactors. Design and simulation. Wiley-VCH, Weinheim 2004, ISBN 3-527-30827-X , p. 16 ( limited preview in Google book search).

Individual evidence

1. ↑ ^{a b} VDI 3476 sheet 2: 2010-01 exhaust gas cleaning; Process of catalytic exhaust gas purification; Oxidative processes (Waste gas cleaning; Catalytic waste gas cleaning methods; Oxidative processes). Beuth Verlag, Berlin, pp. 42–43.
2. ↑ ^{a b} VDI 3927 sheet 1: 2015-11 exhaust gas cleaning; Reduction of sulfur oxides, nitrogen oxides and halides from exhaust gases from combustion processes (flue gases) (Waste gas cleaning; Reduction of sulfur oxides, nitrogen oxides and halides from combustion flue gases). Beuth Verlag, Berlin, p. 83.
3. ^ Günter Baumbach: Air pollution control . Springer-Verlag Berlin, Heidelberg, New York, 2nd edition 1992, ISBN 3-540-55078-X , p. 352.
4. ↑ VDI 3476 sheet 2: 2010-01 exhaust gas cleaning; Process of catalytic exhaust gas purification; Oxidative processes (Waste gas cleaning; Catalytic waste gas cleaning methods; Oxidative processes). Beuth Verlag, Berlin, p. 5.
5. ↑ VDI 3476 sheet 3: 2012-01 exhaust gas cleaning; Process of catalytic exhaust gas purification; Selective catalytic reduction (Waste gas cleaning; Methods of catalytic waste gas cleaning; Selective catalytic reduction). Beuth Verlag, Berlin, p. 45.