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# Combustion Engineering Calculation Formulas

When doing calculations on cement kilns it is usual to work with specific quantities referred to 1 kg of clinker. Therefore the fuel consumption is expressed as q in MJ/kg cli and the kiln gas volume as VKiln gas in Nm3/kg cli.

The cement kiln exhaust gas results from the following sources:

## Gas from stoichiometric combustion of the fuels ## Gas from water content in raw meal ## Excess air ## Kiln Exhaust Gas Volume (Dry Kilns)

Using the above data the stoichiometric kiln exhaust gas volume V Stoichiometric kiln gas can be calculated for kilns with dry kiln feed: The relation between wet and dry gas volume is as follows, W% is
the gas humidity in Vol %: Therefore the kiln exhaust gas volume V Kiln gas, wet with excess air at the actual measured O2 concentration is for kilns with dry kiln feed:  The formula above for VKiln gas wet also is used to calculate the amount of false air in the kiln exhaust gas system by measuring oxygen concentrations at different locations in the exhaust gas system.

## Gas Volume at Kiln Inlet

To calculate the gas volume at the kiln inlet (V Kiln inlet gas, wet ) the true calcination degree (%decarb) of the hot meal has to be considered, because the CO2 already released in the preheater and precalciner does not pass the kiln inlet section.

When determining the calcination degree by analyzing a hot meal sample the measured (apparent) calcination degree is higher than the degree of pure “fresh” hot meal, because the hot meal sample always contains a certain amount of clinker dust which was already in the kiln calcining zone (dust cycles).

Further to calculate V the heat input from secondary or calciner firing (%PC) has to be subtracted, as the offgas released from this fuel portion does not pass the kiln inlet:  ## Secondary Air and Air to Kiln

The total air volume V Air to kiln  added to the kiln (primary, secondary, transport and false air) is calculated from the minimum air for combustion  A min  (0.26 Nm3/MJ) and the O2 concentration in the kiln inlet (measured inside the kiln, without false air from kiln inlet seal). For the calculation of the secondary air volume, the primary, transport and false air need to be subtracted from the total air volume added to the kiln (see above). # Tertiary Air

The tertiary air volume can approximately be calculated as the stoichiometric combustion air for the combustion in the precalciner according to the following formula: Note: The quantity of false air to the precalciner can not be measured and must be estimated. Especially with AFR feeding the false air can increase significantly. Assuming the primary air, transport air and false air to the calciner as zero, the above formula leads to: Holcim