gas, and further serves to break up the tarry particles as before
described. The water condenser is regarded by many eminent
authorities upon gas manufacture as being much superior to the
air condenser, inasmuch as it admits of easy regulation, while the
cooling agent (water) is much more powerful than air, since water
has a far greater power of absorbing heat than air has. As a type
of the water condenser, the Livesey maybe mentioned. In the
Livesey condenser the gas passes through a series of pipes placed
in a tank of water divided into separate channels, with the water
flowing in an opposite direction from the gas, the cool water
entering the apparatus at the gas outlet end, and getting gradually
warmer as it approaches the gas inlet. According to the amount
of water admitted, so will the temperature of the gas be raised or
lowered.
On leaving the condensers, the gas is put through the
exhauster (Fig. 11, p. 29), which is a kind of rotary fan or
pump employed in order to overcome the resistance offered to
the passage of the gas on its way from the retorts to the gas-
holder. The whole of the apparatus through which the gas has
to pass offers a certain amount of resistance ; the seal of the dip
pipes, the friction of the condensers, the seal of the washer, the
filling material of the scrubber, the rotating bundles of the
washer-scrubber, the materials in the purifier, the measuring
wheel of the meter, and finally the weight of the gas-holder, all
32 PRACTICAL GAS-FITTING.
exercise an amount of back pressure as it is termed, and the
combined resistance of the whole apparatus is sometimes very
great, so that if means were not taken to overcome this, the whole
of the gas would not find its way to the gas-holder, but a great
portion of it would pass through the porous walls of the retort
and be burnt in the furnace. The exhauster overcomes or
neutralises the resistance of the seal of the hydraulic main, and
causes a partial vacuum in all the pipes in the retort-house and
condenser. On the outlet of the exhauster, however, a pressure
is given sometimes equal to 42 in. head of water, or a little under
2 Ib. per square inch ; this is required to force the gas through
the remaining purifying apparatus, and to fill up the holders.
Another reason for employing the exhauster is that its use lessens
the deposition of carbon on the walls of the retort. When gas
passes over hot surfaces under such a pressure as results when
an exhauster is not employed, it is partially decomposed, and the
carbon thus set free settles on the retort in the familiar form of
carbon or scurf, which takes up retort space and entails a waste
of fuel, in addition to impoverishing the quality of the gas. The
exhauster is usually turned either directly from the axle of a
steam engine, or, in some small works, by a gas engine, the tarry
matters remaining in the gas serving as lubricants to the fans. 1 )
The next step is to arrest the remaining tarry vapours and
some of the ammoniacal liquor. This is done by means of tar-
extractors or washers ; in these the gas is made to pass through
inverted troughs with serrated edges just below the level of weak
ammoniacal liquor, which causes the latter to bubble up and
expose a large surface to the gas. The reason of the use of weak
ammoniacal liquor, instead of clean water, is the affinity it has
for carbon dioxide, sulphuretted hydrogen, and other sulphur
compounds, and the fact that the liquor is brought up to the
requisite commercial strength.
Scrubbers are of many kinds, but in all the patterns the gas
is made to pass in finely divided streams between wetted surfaces.
This is done by the scrubber shown at Fig. 12, p. 29, which is a
cylindrical vessel on end, in which layers of thin boards are
placed on edge with small spaces between, and are set to cross
one another. Water is distributed from the top over the boards,
and trickles down their sides ; while the gas, entering at the
bottom, is broken up into finely divided streams, and thus a
large surface is exposed to the wetted faces of the boards. An
COAL GAH FROM HE TORT TO GA8-HOLI)ER. 33
overflow, suitably trapped) is provided at the bottom to carry off
the ammoniacal liquor to wells generally built underground.
The most common form of scrubber is that known as the
tower, so called because it is frequently of a considerable height.
/Y pair of such scrubbers is shown in Fig. 13. They are cylindrical
in shape, and are constructed of cast-iron plates, with faced or
Baulked flanges, the plates varying from 6 ft. to 20 ft. in diameter ;
they are put together in sections, attaining a height of from 20 ft.
to 80ft. The plates are from gin. to 1 in. in thickness, with
mouldings as shown. Strong cast-iron brackets are fixed at the
Fig. 13. Pair of Tower Scrubbers.
top for the purpose of supporting a circular gallery, which con-
nects the scrubbers together, two or more being usually so con-
nected. Each scrubber is provided with a penthouse, which
contains the water-distributing machinery, to which ready access
is obtained by a spiral staircase. In the interior of the scrubber
is a series of iron grids, on which are placed various materials,
usually coke, but sometimes thin boards set on edge. The gas
enters the scrubber at the bottom, and leaves it at the top
through a pipe which occupies the centre of the apparatus. The
action of the apparatus is as follows : The gas enters at the
bottom, as previously stated, and a fine stream of water or
ammoniacal liquor descends from the top, and in its course,
having to descend through the material in the vessel, thoroughly
34 PRACTICAL GAS-FITTING.
wets it, with the result that the ascending gas is deprived of its
ammonia. The resulting ammoniacal liquor collects at the
bottom and passes away through a seal pipe sealed in a seal pot
to the liquor well. The usual practice is to work two scrubbers
in series, the first one being supplied with weak liquor from the
hydraulic main and condensers, and the liquor resulting from the
other scrubber, which is supplied with clean water. By making
scrubbers in this way the liquor is concentrated and the absorp-
tive power of virgin ammoniacal liquor for the impurities
SH 2 + CO 2 is fully utilised, while the gas, coming in contact
finally with clean water, is rendered quite free from ammonia.
Another type of scrubber is shown in section by Fig. 14, and
is called (after the inventor, Mr. George Anderson) Anderson's
brush scrubber. The apparatus consists of a rectangular cast-
iron vessel, -4ft. by 10ft. inside, and about 24ft. high, standing
upon end, divided into a series of shallow pans or tanks contain-
ing ammoniacal liquor. These tanks are arranged one above the
other, each one being provided with a drum, which revolves
within the tank, the circumference of the drum being fitted with
a brush of whalebone or other suitable material. The brush
drums are made to exactly fit their respective chambers, while
their lower side dips into the liquor contained in the tanks.
Motion is given to the drums from the outside by means of a
vertical shaft and gearing actuated by a line-shaft and worm-
wheel, and each drum revolves in the contrary direction to that in
which the gas is passing. Hand-holes are provided in the side of
the vessel for the examination or replacement of the brushes as
they wear out. The apparatus is usually combined with one of
Anderson's washers, and stands on the last-named apparatus. The
direction taken by the gas is shown by the arrows on first enter-
ing the washer at A (Fig. 14), it comes in contact with the serrated
edges on the underside of the first horizontal plate ; it rises at the
end and returns among similar serrations in the plate depending
from the cover, and thence passes up into the first compartment
containing the brushes. The washer is charged with weak
ammoniacal liquor, and the passage of the gas through the liquor
causes an increase of pressure at the inlet as compared with the
outlet end, so that, according to the pressure at which it is
desired to work, the teeth at the inlet end are made proportion-
ately longer, in order that they may be parallel to the inclined
plane which the passage of the gas causes the water to assume.
GOAL GA8 FROM RETORT TO GAS-HOLDER. 35
Means are provided for raising or lowering the water line, in
Drcler to raise or lower the pressure according to requirements.
The gas on entering the scrubber proper passes about two-
thirds round the lower brush
md thence out at the opposite
3nd to that at which it entered,
ind similarly with each of the
brushes, until finally it escapes
it the outlet B (Fig. 14). The flat
pipe communicating with the
several brush compartments ex-
bends nearly the whole length
of the brush, and is cast on a
portion of the outer case, with
the object of ensuring an equal
distribution of gas. Each com-
partment contains liquid to the
height of the pipe that brings
the gas from the compartment
below. Pure water is run into
the upper compartment, ulti-
mately finding its way down
the pipes up which the gas
passes, until it arrives in the
washer at the bottom. The
shafts of the several brushes
are provided with driving-gear,
so that the brushes move
in opposite directions, and
always in the reverse direction
to that in which the gas is
passing in any particular com-
partment. The efficiency of
the machine depends to a
great extent on the speed A
at which the brushes re-
volve, but in practical
working from three to five
revolutions per minute will
ensure the removal of all the Fig . 14 . -Anderson's Scrubber and
from the quantity of Washer,
3fi
PRACTICAL GAS-FITTING.
gas for which the macliine is designed. The brushes by revolving
with their lower side dipping in liquid lift a quantity of
the latter in their fibres, through which the gas has to pass,
leaving a portion of its impurities, which is washed off by
the continuous revolution of the brush. The liquid in the several
compartments is therefore of different strengths, that at the
bottom being the strongest, whilst pure water is found at the top.
When purifying gas made by carbonising Newcastle coal, from
10 to 12 gallons of pure water are run in at the top of the appa-
ratus for every ton of coal carbonised, and the weak arnmoniacal
liquor from the hydraulic main is poured into the sealed pipe in
the top of the washer. The merits that the inventor claims for-
this over other types of scrubber are, that for the same quantity
Water Wet bipe
of gas to be purified the vessel can be made much smaller, that
the distance through which the gas has to travel is about double
for the same height, and that there is no risk of the gas failing
to come into intimate contact with the scrubbing liquid, the
result being the complete removal of the whole of the ammonia.
Another form of scrubber that has been very largely adopted
is called a " washer- scrubber" (Fig. 15). This is also a cylindrical
cast-iron vessel ; it is fixed horizontally, and divided into sections,
in which a series of discs or chambers containing wooden balls,
or other filling, is made to revolve slowly on a central shaft. The
liquid is at a different height in each chamber, but averages about
one-third up the discs, which are wetted as they rise from it,
whilst the gas passes between them and gives up its ammonia and
a portion of its other deleterious compounds. The clean water
entering at one end meets the gas that enters at the other,
COAL GAS FROM RETORT TO GAS-HOLDER. 37
through a space in the middle of the discs, and increases in
strength as it flows from one chamber to another, until it reaches
the desired amount, generally known as 10 oz. or 12 oz. ammo-
niacal liquor; the gas passes on, and, meeting the cleaner water,
gives up in each compartment a portion of the ammonia, until
the latter is all eliminated.
The bulk of the carbon dioxide, sul-
phuretted hydrogen, and bisulphide of
carbon, however, still remains in the gas,
and must be removed. This is most
effectually done by what are called
purifiers (Fig. 16). These are usually
rectangular boxes containing several
layers of wooden grids, on which the
purifying material is laid, and through
which the gas has to pass from the inlet
at the bottom to the outlet at the top.
In London, where the law requires that
the gas shall be in a high degree of
purity, no sulphuretted hydrogen what-
ever is allowed to be in the gas. Of
other sulphur compounds not more than
17 grains in 100 cubic feet of gas is
allowed in summer, and not more than
22 grains in 100 cubic feet of gas in
winter, while the maximum amount of
ammonia (NH 3 ) must not exceed 4 grains
per 100 cubic feet. It is therefore
necessary to carry the puri-
fication much further than
is considered sufficient in
other parts of the country.
Whether this great refine-
ment is necessary need per-
haps hardly be discussed
here ; suffice it to say that
the cost of removing the
impurities to such an extent
is considerably more to the consumer than would be the case
if only the same portion had to be taken away that Ls suffi-
cient in the country. In some country works only lime is
38
PR A G TIC A L GAS FITTING.
used for purification, and in others oxide of iron only is used.
Each of these can be made to remove what for all practical
purposes it is necessary to eliminate ; but where more than this
has to be done, it is usual to employ a combination of the two,
arranged in what may at first sight appear to be a rather peculiar
manner. To work this system successfully, eight purifiers are
required. In the first two, hydrated lime is used, and the gas in
passing through them gives up all the OCX that it contains ;
it then passes on to the next two vessels, which are filled with
hydrated oxide of iron, this material having a great affinity
for sulphuretted hydrogen, which it effectually removes. The
gas then passes through two more vessels containing lime, and
it is here that the peculiarity just mentioned occurs.
Hydrated oxide of calcium (lime), which has great affinity for
CO-2 (carbon dioxide), is useless for removing the sulphur com-
pounds, principally in the form of bisulphide of carbon; but
hydrated oxide of calcium, which has been siilphided by means
of sulphuretted hydrogen, has this power, and therefore, in
preparing a set of purifiers for use, the gas is passed first through
the two purifiers containing the lime (CaO) for the removal of
the COo, and then through the two others, which also contain
lime. These latter take up and assimilate with themselves the
H L .8, forming a sulphide of lime, which is then used in its proper
turn to remove the CSo ; but in doing so a certain quantity of
sulphuretted hydrogen is given off from the sulphided lime, and
to prevent this passing along with the gas two check purifiers are
used, filled with oxide of iron, or in some cases Weldon mud a
substance containing a large proportion of oxide of manganese.
Below is a diagram explaining this. Gas contains CO 2 HJ3, CS 2 .
Purifier
Purifier
Purifier
Purifier
containing
containing
containing
containing
lime re-
iron oxide
sulphided
iron oxide
moves CO-2
removes
lime re-
or Weldon
and some
remainder
moves
mud re-
H 2 8.
of H,S.
CS,.
moves H 2 S.
Gas contains Gas contains Gas contains Gas clean.
H 2 S, CS., CS... small quantity
ELS from lime.
GOAL GAS FROM RETORT TO GAS-HOLDER. 39
All that now remains to be clone is for the gas to be measured,
which is done in an apparatus which is in all respects similar to
the wet meter found in many houses, but, of course, on a very
much larger scale, as shown at Fig. 17, p. 37. An ordinary wet
meter is a drum of a known size, with partitions so arranged that
while the gas is entering one compartment it is being passed out
from that portion previously filled, a direct communication
between inlet and outlet never being possible. The revolution
of the drum causes certain wheels to turn, and pointers affixed
on it to indicate the number of revolutions made, thus showing
the quantity of gas passed through.
The station meter is employed to measure the gas made on a
gasworks, so as to enable the engineer to see that he is getting
the proper amount of gas from his coal ; it also serves to tell the
amount of leakage or unaccounted-for gas. The station governor
is employed for the purpose of controlling the pressure under
which gas is supplied at the works to the amount necessary for
the proper supply of the district and no more. The station meter
is shown in section in Fig. 18, p. 40, and consists of a round or
rectangular cast-iron outer case containing a cylindrical vessel of
tinned iron known as the drum, which revolves on a horizontal
shaft resting on suitable bearings. The dram is immersed to a
certain height in water contained in the outer case. The drum
varies in size according to the capacity of the meter, and is
divided by partitions into four longitudinal compartments
arranged somewhat after the fashion of the four blades of an
Archimedean screw. The inlet-end or unmeasured gas is isolated
from the outlet or measured gas, by the contrivance known as
the "spout and bottom cover," shown at v. Owing to the
manner in which the partitions that form the compartments or
chambers are arranged, there is not a clear way through the
drum, since the opening at one end of a measuring chamber is
above the water line at the same time that the corresponding
opening at the other end is below it, so that two of the com-
partments are constantly above the water-line, the one filling
with gas and the other discharging. The openings at the ends
of the chambers through which the gas passes are known as
hoods. The action of the apparatus is briefly as follows : The
gas enters at w through the spout above the level of the water,
and enters one of the measuring chambers, causing it to revolve.
As soon as the chamber is filled with gas, its inlet has passed
4'J
PRACTICAL GAS-FITTING.
beneath the water level by the revolution of the drum, with the
result that the gas is sealed up, while the inlet of the next
chamber rises at the same time above the water level, and thus
allows gas to enter. As soon as the inlet to each chamber is
sealed, a corresponding outlet slit that opens into the space
between the drum and the outer case is unsealed, and water
entering by the inlet forces the gas through the slit to the meter
outlet. Each chamber in rotation as it fills with gas turns the
drum round a quarter of a revolution, and expels the gas from
the chamber that has preceded it. The cubical space in each
Fig. 18. Section of Station Meter.
chamber when out of the water and full of gas is known. Four
times this space represents the total capacity of the drum, or the
contents for one revolution. The shaft of the drum is connected
to a train of wheels provided with pointers traversing the meter
dials, by which the number of revolutions made by the drum is
recorded and the amount of gas passed is registered. In order to
maintain the water in the meter at the proper level, a small
continuous supply of water is constantly admitted, a syphon
overflow pipe being provided to take off any excess.
The gas, not being required in all cases immediately it is
made, is stored in what are commonly known as gasometers, but
which are more correctly termed gas-holders (Fig. 19). These are
vessels made of thin sheet-iron, free to travel up or down in a
vertical direction as they are filled or emptied. They are worked
GOAL GAS FROM RETORT TO GAS-HOLDER. 41
in circular tanks, which, in small works, are the same depth as
the gas-holder is high ; but in large works the gas-holder is made
in two or more lengths, each smaller than the other, so that when
down they may telescope into one another. To prevent the gas
escaping, what are known as a "cup" and "grip" are made, the
one at the bottom of each " lift," as each length is called, and the
other at the top of the next outer lift. The cup is formed so
that the lower end of the lift is bent outwards and up a certain
height all round, thus making it a concentric vessel, which, as it
rises from the water in the tank, takes up with it sufficient of the
Fiq;. 19. Gas-holder.
latter to fill the cup. At the same time it engages with or
catches the grip of the next outer lift, which is made so that the
upper end is bent outward and downwards about the same depth
as the cup, thus, owing to the sealing of the grip in the water in
the cup, preventing the passage of the gas from the gas-holder to
the outer atmosphere.
Most gas-holder tanks of any size are made with what is
known as a dumpling in the middle ; this is shown at F (Fig. 19).
It is merely a certain quantity of the ground left in when the
remainder was being excavated, so as to save work and to lessen
the quantity of water required. Some also are made with con-
centric tanks, space for the lifts to fit in only being allowed
42 PRACTICAL GAS-FITTING.
Others, again, have cast-iron tanks when the ground is much
saturated, and these are generally placed above ground.
Fig. 20 gives a sectional elevation of an un trussed gas-holder
and puddle tank. The holder is telescopic and in three lifts ; the
tank is 230 ft. in diameter by 50 ft. 6 in. deep from bearing stones
to top of coping, and is built of brick set in Portland cement
mortar in the proportion of one part of cement to two of sand.
The sides and bottom of the tank are both puddled to the thick-
ness of the puddle behind, the side walls being 24 in., and on the
bottom 15 in. The holder when not inflated rests on a timber
framing, as shown in the illustration, the size of the timbers being
12 in. by 12 in. for the uprights and diagonals, and 13 in. by Tin.
for the curved portion of the framing. The outer lift is 226 ft. in
diameter and 50 ft. deep ; middle lift, 223 ft. diameter and
50 ft. 3 in. deep ; inner lift, 220 ft. diameter and 50 ft. 6 in. deep.
The crown has a rise of 15ft., and is untrussed. The curb is
formed of f-in. plates, bent to a radius of 2ft. 3 in., and is
strengthened by a plate-girder and gusset stays. The standards
are of the lattice-girder type, and are braced together by three
rows of girders, as shown, and by diagonal flat bars. The
thickness of the roof sheets is as follows : Outer row r , forming
part of curb, in. thick, of mild steel plates, 3 ft. wide ; next row,
No. 7 B.W.G., then follows another row of No. 9 B.W.G., the
remainder being all of No. 10 B.W.G., the latter being riveted
with Y\-in. rivets of 1-in. pitch. The No. 7 B.W.G. sheets are
riveted to the f-in. curb, plated by ^-in. rivets 2A-in. pitch. The
side sheets are of No. 11 B.W.G., secured to each other with -fVin.
rivets, 1-in. pitch, lap of sheets Hin. ; the bottom and the top row
of the sheets in the outer lift are i in. and ^ in. thick respectively,
in the middle lift T \in., .and in the top lift t\in. and iin.
respectively, being riveted to the other sheeting with |-in. rivets,
li-in. pitch, i-in. lap. Inlet and outlet pipes, 36 in. diameter.
A gas-holder throws a pressure varying acccording to its
weight and the area covered by it, but the pressure is nearly
always more than is required to be sent out on the district, and,
if delivered, would cause escapes at many of the fittings in the
consumers' houses otherwise sufficiently sound. A governor is
therefore used ; it is in reality a small gas-holder, which rises and
falls according to the pressure of gas on the district, opening or
closing a valve, as may be desired, by means of a cone.
The station governor in its simplest form consists of a small
COAL GAS FROM RETORT TO GAS-HOLDER, 43
cast-iron tank, which is filled to a certain height with water, and
through the bottom of which the gas from the gas-holder enters by
a pipe provided at the top with a flanged seating. Surrounding
this inlet pipe is the outlet pipe, whose open end projects some
distance above the level of the water in the tank, the gas passing
to the street mains by way of the annular space between the two
pipes. The governor usually employed is shown in Fig. 21, p. 44,
and consists of a small cast-iron tank x, which is filled to a certain
44 PRACTICAL GAS-FITTING.
height with water. Firmly floating in the tank is a tinned iron
gas-holder Y, having suspended from its crown a parabolic plug z.
The gas inlet pipe is in the centre of the tank, and is provided at