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UEi Test Instruments SMART BELL PLUS KIT User Manual

Page 10

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N

ear

i

deal

c

omBuStioN

This is When we burn pure hydro-

gen

in the air. Our atmosphere is 20.9% oxygen

with

the remaining 79.1% nitrogen.

This is nearly as desirable as the example for

ideal

combustion with the only added loss being

the

heat that is carried away from your target

with

the nitrogen. Because nitrogen isn’t part of

the

combustion process, it enters the combustion

chamber at the inlet temperature and leaves

with some of the heat created by the combus-

tion.

If this isn’t recovered at the heat exchanger it is

lost

up the flue.

The main problem with this example is again

the

availability and cost of pure hydrogen.

B

eSt

o

f

t

he

r

eal

w

orld

Natural gas is

a

readily available fuel, and our atmosphere

contains sufficient oxygen. When this is

used as a fuel we get the reaction; shown

in figure 3.

Now the other added outputs are CO2

and hot nitrogen compared to the Ideal

World situation. In addition to this we

have added the output Excess Air.

Excess Air is exactly what the name

implies, air that is in excess of what is

needed to burn all of the fuel. The

reason for this is more related to the

ability to mix all of the fuel and O2 for

complete combustion. Without some

amount of excess air not all of the fuel

would burn completely, and this leads to

the formation of CO instead of CO2.

Other fuels all contain the basic ingre-

dients for combustion, but also may

include other components such as

sulfur, fuel bound nitrogen, soot and

ash and water. These either react with

the oxygen to form other pollutants or

contribute to

additional losses.

Wet Loss

Dry Loss

figure 3

Carbon Monoxide

is formed from incomplete combustion (partial oxidation of carbon in

the fuel). Typical causes are incomplete mixing of fuel and air, low combustion temperatures,

or not enough excess air.

8

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