1172

THE COLLIERY GUARDIAN.

December 4, 1914.

the real difficulty. The author has, while testing a
sample 10 ton truckload* of coal on a 100 sq. ft. grate,
found the amount of CO2 to drop from 14 per cent, to 8
per cent., and the evaporation from 30,000 lb. to
18,000 lb. per hour, and he expects that others have had
a similar experience.

With a stoker and furnace specially designed for coal
with a very high proportion of duff, with which only 8
per cent, of CO2 could be got with great effort, a run of
good coal has softened the arch and made the walls
“ run in ” in less than an hour. It is comparatively
easy to produce an amount of CO2 ranging from 12 per
cent, to 14 per cent, on a chain grate with a long arch
when the duff is not above 30 to 40 per cent.; but when
this rises above 60 per cent, it has an extraordinary
blanketing action on the fire, and it is difficult to keep
the amount of CO2 up to 8 or 9 per cent., even under

250 300 350 400 450 5OO 550 600 650 7OO 750
Flue temperature in degrees Fa.hr

NOTES:

Fan power omitted \
Northumberlard steam \

Calorific value HTh I?

(higher)

-Carbon.....66-<j%--------

Hydrogen.....4-4%

Moisture......35%

Ash ........15.7%

Boiler radiation

and unburnt fuel -5%

B oiler efficiency
in terms of % C0t (by“Orsat’> and
flue temperature

Fig. 2.

test conditions. To sum up, an average of 10 per cent-
would be exceedingly good working. This refers to the
gases at the boiler exit. The amount of CO2 at the
economiser exit is often 2 per cent, lower, and this
difference is one that will repay close attention.

If anything can be done, it is well to separate as far
as possible the known bad coals, and to burn them on
a specially arranged furnace adapted for such types of
fuel. A scheme something like this has been adopted
at Birmingham for the riddling.

The size of the economiser has a large effect on the
final temperature. The temperatures on full load
should be taken, say, 24 hours after sweeping, and
should be used as a standard. If at any subsequent
time the boiler exit temperature is found to be 150 degs.
Fahr, higher, or the economiser outlet to be 100 degs.
Fahr, higher, the boiler needs cleaning. Values of
600 degs. Fahr, for the former and 350 degs. Fahr, for
the latter may be considered satisfactory. A result
therefore of, say, 10 per cent. CO2 and 300 degs. Fahr,
final temperature, both measured at the economiser
outlet, may be considered a good test result.

Efficiency — per cent

Fig. 3.

0-75

85

6o

8o

65

55

,350"

Boiler efficiency
tns of % C0£ (by’Ora
flue temperature

14 13 12 II IO 9	7 o *

Percentage <f C0t m flue gases by’Orsat
apparatus

^Flue temperature (’’Fahr)

25O1

From the operation point of view of testing, this
completes the case for efficiency, but from the point of
view of the contractor’s test and commercial coal
testing it is advisable that one boiler of a type should
be set aside for testing work, and fitte t up with
measuring instruments. A sample truck or trucks of
coal can then be run through the grates, and the actual
evaporation measured. The author does not wish here
to go into the question of hand and automatic sampling,
except to mention in passing that with accepted
methods of hand sampling discrepancies of as much as
7 per cent, have been obtained in his own experience,
and also in that of co-workers in the United States, who,
as is usual, have gone into the question on an extensive
scale. For ordinary commercial working the special
boiler is by far and away the most effective calorimeter.

Pig. 5 shows an arrangement of tanks and a weigh-
bridge which has been found convenient for power-
station work. By reversing the order of use and
omitting the pump, it becomes of equal service for
turbine testing. A slight inaccuracy is introduced by
the suction pipe of the pump, but it can of course be
allowed for.

* A suggested standard amount of coal for a trial.

Turbines and Generators.

As regards the steam end of the plant, measurements
of the temperature of the steam have been greatly
improved, both by the use of the Whipple indicator and
by tne specially adapted form of thermometer described
last year in Engineering*

The measurement of temperature at the exhaust end
of the turbine has little connection with the turbine
itself, and mainly concerns the condenser. The vacuum
should be measured at the exhaust flange of the turbine
—a difficult but most important measurement.

The tank and the electrical meter measurements
should be absolutely correlated by hell, light, and
telephone signals, without the intervention of the time
element at all. It should be purely a measurement of
matter against energy.

It is necessary t > omit many questions which could
here be raised, such as correct phasing in, the use of
instrument fuses on the high-tension side, earthing a
common point of the pressure and current secondary
windings, adjustment for power factor, and the regula-
tion of voltage and load.

Condensers and Air Pumps.

It is almost impossible to arrive at any just apprecia-
tion of a condenser performance without knowing at
the same time the air leakage with which the air pump
is dealing and the rating of the pump. In this direction
the Scanes gauge will be a great educating force.

The ability of a steam jet to handle large volumes of
gases is unequalled, and the author thinks that the
ultimate type of air pump will be a steam augment or
jet in series with a pump of the kinetic or Leblanc
type, which is capable not only of maintaining by itself
an excellent vacuum, but also of acting as a jet condenser
to the steam from the augmentor. The steam jet may

<D
a?

$

Econo m i ze r ouCleC~
____	Sarnplinfl p/be J

Ksbck of boiler c	i•

Sampling Cuoe

Omnibus suction pipe

Fig. 4.—Apparatus for Sampling Flue Gases.

only be required when an air leak develops, but it is a
good thing to be able to double or treble the effective
size of the air pump by a turn of the hand.

The amount of air to be dealt with in practice varies
greatly. To include provision for occasional leaks, the
author would suggest that provision should be made for
at least 1’3 lb. of air per 1,000 lb. of steam for plants of
moderate size, and for 1 lb. per 1,000 lb. with large
plants. Under these circumstances the vacuum main-
tained by the air pump when dealing with this amount
of air, but disconnected from the condenser, should be
within 0 3in. (mercury) of the vapour pressure of the
water that it is using.

The performance of the condenser depends almost
entirely on the steam distribution. The author’s feeling
is that the buyer should specify the surface that he
requires, especially if he is at all troubled with di ty
condensing water. In this case it is well to arrange for
1 square foot of surface for every 5 lb. of steam to be
condensed per hour, and he will then have a condenser
that will run a considerable time without cleaning or
much loss of vacuum. The author suggests, as a
standard for testing, that a condenser having 1 square
foot of surface for 71b. of steam, and a water velocity
of 6 ft. per second through the tubes, together with the
air pump already described, should be expected to have,
three days after brushing the tubes, a value of “ K ” not
les< than 450. By “ K ” is meant the number of
B.Th.U.’s transmitted per square foot <»f surface per
hour per degree (Fahr.) mean difference between the
temperature inside and outside the tubes the tempera-
ture outside being assumed to be uniform and measured
at the inlet, and the water temperature to be the mean
of the inlet and outlet temperatures. Tlu-se temperature
meisuremen s are to be combined with an accurately
calculated figure for the heat per lb. of steam condensed,
which with modern plants is often found to be between
970 and 980 B.Th.U.’s per lb. of original steam.

Cooling Towers.

As regards the testing of cooling towers, very great
care is necessary in taking the wet and dry bulb
temperatures. Delicate open-scale thermometers are
used, and must be shielded from radiation and yet have
a free stream of air passing over them. The only fair

* Engineering, vol. 96, p. 437, 1913.

way to take the temperature of the water before and
after cooling is on the condenser inlet and outlet pipes.
The amount of heat taken in or lost by these pipes is
negligible, whereas it is possible to get all sorts of
temperatures by floating a thermometer on the surface
at the base of the tower. If a 12 in. pocket be put in
the inlet to the condenser, and another m the outlet as
far away from the condenser as may be convenient
while still in the engine room, and if a special thermo-
meter be used with a big bulb and open scale, the
temperatures can be taken m an effective manner.

The author thinks that it is the duty of the maker of
the cooling tower to produce such distribution in his
tower as to obtain the guaranteed temperature at the
inlet of the circulating pump or condenser,* and outside
this he should be allowed a free hand.

It is difficult to measure such large quantities of
water as are cooled in towers, say, up to 250,000 gallons
per hour. It can, of couse, be done by a Venturi meter,
or weir. Alternatively, it is much better done by the
thermal method, in which the amount of water is
calculated from the measured condensate, its known
loss of heat per lb. in the condenser, and the rise of
temperature of the circulating water. The principle is
the well-known one of adding a known quantity to the
unknown quantity to produce a mixture of which the
properties are measurable.

General Remarks.

The organisation of the personnel for accurate testing
is a matter for concern. In the author s opinion, in no
case is it advisable to undertake any permanent testing
work unless there are at least three engineers, or two
engineers and a chemist, in constant collaboration with
each other. In arranging a test it is advisable to have
full instructions typed out and handed to eveiy person
engaged in a trial; and even then it is necessary to
make certain that these instructions are read.

There are rare cases where a plant has to be tested
by measuring the water pumped into the boilers, and
this calls for a special test on the boilers alone,
generally known as a “ still ” test, in order to measure

A. Supply or buffer tank

B Weigh tank

,C we<gh bridge

D FioCwell

E .Motor & Centrifugal pump
a .Water supply or Turbine
discharge

bite fland-operated
ttuieh-disdharge values

d .Overflow pipe.

e Pump suction

S Dram g. Steps toplatform
h Discharge from tqnJt B to
k Feed-pump suction

D

Fig. 5.—Diagrammatic Sketch

Showing arrangement for measuring water pumped
to boilers or discharged from turbines.

any leakage. It is a difficult test to carry out, as even
with everything shut down the circulation rate of the
water contained varies if the pressure rises or falls, and
since a small fire has to be kept going to make up for
radiation losses it is very difficult to avoid one or the
other. By testing on a rising pressure it is easy to
make the amount of water in the boilers appear to
increase, but the author is satisfied that a batch of five
boileis can be isolated and made absolutely tight, so
that given a sufficient length of test the figures are
above suspicion.

The author always recommends at least an hour’s
interval between the tests at half, three-quarter, and
full load, the load being increased to the higher rating
immediately after the finish of the previous run.
Corrections should be avoided ii possible, and by
judicious working of boilers, and by testing at such
time of the year that the vacuum producible is superior
to that on which the turbine guarantees are based, it is
nearly always possible to adjust the conditions so that
the corrections do not amount to more than 1 per cent.

It is very important that the condenser should be
tested for tightness on the water side. The method
favoured by the author is that when the brushing of
the condenser tubes is finished the inside of the
condenser should be filled up with fresh water on the
steam side to as high a level as possible. This serves
the double purpose of actually indicating the leaking
glands or perforated tubes, and at the same time
revealing any small air leaks that there might be in
the casing.

The author thinks it would be fair to say that the
turbine must run six months on commercial load before
being tested; and the contractor should be then allowed
48 hours to open out and examine the machine in
preparation for the test. Alternatively, the specification
may state that the machine must be tested as soon as it
is on commercial load, and again at the end of its year
of maintenance, not showing more than, say, 3 per cent,
decrease in efficiency at the end of that period.

* 774 ft. head == 1 deg. Fahr.

President Wilson has appointed a commission of three,
headed by Mr. Seth Lois, to endeavour to settle the
Colorado miners’ strike, which has existed for a year,
resulting in numerous conflicts and the destruction of
property, and has finally necessitated the use of Federal
troops to maintain order.