Installation guide

Measurement of
Carbon Dioxide or Oxygen
Historically, to deterroJne the weight of the
combustion gases per gallon of fuel oil burned,
carbon dioxide has been measured with equip-
ment like that shown in Figures 47 and 50. This is
a rugged, inexpensive, and easy-to-operate
device. However, if you recall from Chapter 1,
the percent oxygen also can be used to detenmne
the weight of the combustion gases. There are
devices that measure oxygen rather than carbon
dioxide percent for the determination of steady
state efficiency, but let's turn our attention to the
most common device first---CO 2 analyzers.
Bacharach Instrument Company manufactures a
carbon dioxide analyzer called "Fyrite", which is
the most well-known instpament on the market.
The Fyrite (shown in Figures 47 and 50) and
other similar instruments work on the following
principles:
_' Chemical absorption of a gas sample by a
liquid chemical absorbent.
V Chemical absorbing fluid is also used as
indicating fluid.
I
The Fyrite analyzer contains potassium hydrox-
ide, a liquid with a capacity to absorb large
amounts of carbon dioxide. The Fyrite consists of
two main parts---sampling pump and analyzer.
The sampling pump consists of:
_' A metal sampling tube which is inserted into
the flue gases
• ' A yarn filter and water trap which stops soot
and water droplets from entering the analyzer
I' A sample pump--a rubber bulb with a suction
valve and a discharge valve. These valves are
rubber flapper check valves which allow flow
in only one direction
Y A rubber connector which seals the sampling
pump system to the analyzer
The analyzer is molded of clear plastic containing
top and bottom reservoirs and a center tube
connecting the two reservoirs. The bottom of the
lower reservoir is sealed off by a flexible rubber
diaphragm which rests on a perforated metal
plate. The upper reservoir is covered by a molded
plastic cap which contains a double-seated
plunger valve. A spring holds this valve
against a finished seat in the top cap providing
a seal which makes the instrument spill-proof
in any position. When the valve is fully
depressed, it vents the top reservoir to the
atmosphere and seals the center tube beneath
it. When the valve is partially depressed, the
entire instrument is open to the atmosphere.
The bottom reservoir is filled with the absorb-
ing fluid which extends about 1/4 inch into the
bore of the center tube when the instrument is
held upright. The scale, which is mounted to
one side of the center tube, is movable so that
before each test the scale may be conveniently
adjusted to locate the zero scale division
exactly opposite the top of the fluid column in
the center tube.
To measure the amount of CO 2 in a gas
stream, you must measure a known volume of
gas, bring the gas into contact with the
absorbing solution, and measure the loss in
volume after the CO 2 is absorbed. To accom-
plish this, you must first prepare the instrument
for sampling by purging the solution and
adjusting the scale so that the zero mark is
level with the liquid level. Be sure of the
following:
36 FIGURE 50 Construction ofCO2 analyzer