Oxygen balance

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The oxygen balance , short ( Engl. Oxygen balance) of any material mixture gives the relative oxygen amount of which is in excess or missing (with a negative sign ) to a balance between oxidants and combustible reach components. A mixture of substances with a balanced oxygen balance can be converted into completely oxidized products by heating in a closed container without external oxygen supply, i.e. completely burned without oxidizing agents remaining or additionally necessary.

definition

Let be the number of atoms of the chemical element in a chemical compound with the sum formula and be the molar mass of the compound. The mixture of substances with the total mass consists of various chemical compounds (components) with the masses and the mass fractions . The number of moles of the element in the mixture results in:

Let it be the most stable valence of the chemical element under combustion conditions .

The lack of or excess for a complete Valenzausgleich valence in Mol results from a sum of all the chemical elements: .

The oxygen balance is calculated from:

or

Here is g / mol and .

List of the most stable valencies of all chemical elements under "combustion conditions" :

, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Calculation from the oxygen balance of the components

The oxygen balance of a mixture of substances results from the oxygen balance of the individual components (pure substances) and their mass proportions according to:

Examples

Digester gas-air mixture

Digester gas is a flammable mixture of around 40% by weight CH 4 (methane) and 60% by weight CO 2 (carbon dioxide), which is formed during the bacterial decomposition of organic substances (e.g. in the human intestine). Air is a mixture of 75.5 wt% N 2 (nitrogen), 23.1 wt% O 2 (oxygen), 1.3 wt% Ar (argon) and 0.1 wt% CO 2 (carbon dioxide) in addition to negligible trace levels of other noble gases , hydrocarbons , hydrogen , nitrogen oxides , carbon monoxide , ozone and dust .

What is the oxygen balance of a mixture of 1 kg digester gas and kg air, if it is considered as a variable?

The following applies:

 ;  ;  ;  ;
; ; ; ;
; ; ; ; ;

For the number of moles of the elements it contains:

; ; ; ;

The oxygen balance as a function of results in:

For is . With the standard densities (15 ° C) and it follows:

6.2 m³ of air are required to completely burn 1 m 3 of digester gas.

Combustion air ratio for fuel-air mixtures

In heating systems and internal combustion engines, combustibles or fuels are burned with atmospheric oxygen and the energy released in the process is used for heating or for performing mechanical work. A suitable quantity ratio of combustion air and fuel is decisive for the best possible utilization of the chemical energy stored in the fuel. The minimum amount of air that is required per unit of mass of fuel for complete combustion is called the minimum air requirement . The ratio of the actually supplied to the theoretically required minimum amount of air for complete combustion is called the air ratio and is usually referred to as. With an ideal combustion with a stoichiometric air ratio is . Fuel-air mixtures contain an excess of fuel and as a rich mixture , while those denoted with an excess air contained and lean mixture may be cited.

See also: