BASIC PRINCIPLES OF CALCULATING RESULTS
Sensonic 4000
Mass concentration calculated by
Sensonic 4000
is comparable with the results obtained by other methods
(or different types of analysers) only when b o t h c a l c u l a t i o n s h a v e b e e n c a r r i e d o u t
b a s e d o n t h e s a m e s t a n d a r d c o n d i t i o n s .
7.5.2
Mass concentrations relative to the concentration of oxygen in combustion gases
As well as absolute mass concentration, the mass concentration relative to oxygen concentration in the
combustion gases is calculated. The concentration of a given component in relation to oxygen concentration
is expressed by the following formula (as an example for CO value):
COrel
20.95% - O2ref
20.95% - O2meas
CO
mg
m
mg
m
3
3
where:
COrel
- CO concentration in relation to oxygen expressed in [mg/m3]
O2ref
- reference oxygen, conventional parameter (chosen by selecting fuel or entered
independently from keyboard) expressed in [% vol]
O2meas
- the measured concentration of O2 in combustion gases expressed in [% vol]
20.95%
- oxygen concentration in pure air
CO
- the measured concentration of CO in combustion gases expressed in [mg/m3]
(absolute mass concentration)
Using similar formulae, the concentrations in relation to oxygen concentration of sulphur dioxide SO2,
nitrogen oxides NOx and other gases are calculated. The concentration related to oxygen concentration was
introduced to make the evaluated concentration independent of the way the combustion process is carried
out. The absolute value (expressed in [ppm]) can be lowered artificially in the combustion process with an
increase in excess air (large amount of O2 in combustion gases). It does not have to be a decrease of the
total emission. The formula which calculates concentration related to oxygen takes into account the oxygen
concentration of the combustion gases, making the results independent of the excess air factor.
The parameter O2ref - reference oxygen is a standard value. Standards recommend different values of this
parameter for various types of fuel. In the system SENSONIC 4000 the value of reference oxygen can be
accepted automatically in the process of fuel selection (the so-called a u t o m a t i c reference oxygen
choice) or entered by the operator from the keyboard (the so-called m a n u a l selection of reference
oxygen). Relative mass concentration calculated from two different measurements are comparable only if
t h e s a m e r e f e r e n c e o x y g e n a n d t h e s a m e s t a n d a r d c o n d i t i o n s have been used.
Note:
If O
2meas
< O
2ref
then relative concentration CO
rel
calculated from formula
is
less than absolute concentration. I n s u c h a c a s e , t h e a n a l y s e r
r e p l a c e s t h e v a l u e o f r e l a t i v e c o n c e n t r a t i o n w i t h t h e
v a l u e o f a b s o l u t e m a s s c o n c e n t r a t i o n .
7.6
Calculating combustion parameters
Beside calculating gas component concentrations the analyser calculates some parameters describing the
combustion process. The formulas for calculating combustion parameters are empirical formulas.
Sensonic
4000
analyser calculates the parameters of the combustion process according to the principles predicted by
DIN standards.
The most important parameter is the amount of heat convected by combustion gases to the environment - the
so-called chimney loss (stack loss) SL. Chimney loss in calculated on the basic of empirical formula known
as Siegert's formula:
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