fors
Year: 1898

page_text: I, ERNEST DIGBY HOPCROFT, of Farfield, Kidderminster, in the County of
Worcester, Boiler Inspector, do hereby declare the nature of this invention to be-
as follows:-
My invention has for its object a new or improved process for removing scale.
from boilers by which the scale can be readily removed from the whole of the
interior of the boiler including the angles without recourse to the expensive
processes now in force and without the necessity of removing the boiler from its
bed. At the same time the use of anti scale solutions is thereby obviated. During.
the formation of the scale in boilers the boiler is naturally in expansion and in
carrying my invention into effect after emptying the boiler I apply a suitable
refrigerating apparatus to the interior thereby reducing the temperature to or
below freezing point by which means I obtain a contraction of the boiler and as
the scale is not effected by the lowering of the temperature to the same extent as
the metal the scale is cracked and separated from the metal and can then be readily
removed from the boiler.
Dated this 30th day of September 1898
LEWIS WM. GOOLD,
Agent for Applicant, 5, Corporation Street, Birmingham.
COMPLETE SPECIFICATION.
A New or Improved Process for Removing Scale from Boilers.
I, ERNEST DIGBY HOPCROFT, of Farfield, Kidderminster, in the County of
Worcester, Boiler Inspector, do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
_
My invention has for its object a new or improved process for removing scale
from boilers which is equally applicable to all kinds of boilers, whether tubular or
otherwise as well as to steam condensers, economisers, and other similar apparatus
by which the scale is readily removed from those parts of the interior surface of
the boiler upon which it has accumulated, including the surface of the tubes, and
other parts hitherto unaccessable, and this is effected without recourse to the
expensive process now in use and without removing the boiler from its bed or
position while at the same time the use of anti-scale solutions is thereby obviated.
In order that my invention may be clearly understood and more easily carried
into practise I have appended hereunto a sheet of drawings upon which I have
illustrated the application of my process to an ordinary vertical boiler and from
which its application to other forms of boiler and other apparatus will readily
be understood.

page_text: Figure 1 is a vertical section through a boiler and through the apparatus for
removing the scale therefrom.
Figure 2 is a plan of a similar boiler but shewing a modification in the apparatus
suitable for use when dealing with certain classes of scale.
In carrying my invention into effect I first empty the boiler of all superflous
moisture and afterwards lower the temperature of the interior to below freezing.
I generally however find it necessary to lower the temperature below 25 F. the
variations of the requirement being rendered necessary by the different character
and thickness of the various scales as well as by the quantity of surface to be
dealt with while at the same time it is important that as far as possible an even
temperature shall be maintained over the whole area of the boiler required to be
treated.
I believe the action of removing the scale which takes place to be as follows:-
During the formation of the scale the whole of the metal in the boiler is in a
state of expansion with the result that upon cooling down to a natural tempera-
ture the metal is contracted while the scale remains in its original condition, but.
upon lowering the temperature within the boiler to say 15° or 25° F. the metal of
the boiler is further contracted and as the scale is not affected by the lowering of
the temperature in the same way or to the same extent as the metal the scale is
broken up and separated from the metal.
During the process of contraction of the metal I believe that the natural
moisture contained in most classes of scale is expanded by the lower temperature
which I provide and that therefore the extra contraction of the metal in com-
bination with the expansion of the scale which combination is effected by my
improved process is responsible for the easy removal of the scale from the surface
of the metal. In most cases and especially where the scale is hard and not
absorbent I find it advantageous to freeze it two, three, or several times according
to the thickness hardness and tenacity of the scale allowing it between each
reduction of temperature to attain its normal condition of warmth by which
means a process of sweating takes place after each freezing the moisture of which
sinks into the scale and is afterwards expanded by the next process of freezing and
so on until the moisture has reached the metal under the scale the latter being
then loosened by the expansion of the moisture under the frost. To assist the
sweating and save time I may bring up the temperature of the scale to a normal
state by passing warm air over the scale but the temperature of such warm air
must never be sufficiently high to dry up the moisture produced by the sweating.
I will now proceed with reference to Fig. 1 to describe one method of obtaining
and evenly distributing the temperature required in the ordinary vertical boiler
illustrated by A in connection with which the compressor B condenser C and
air cooling chamber D form part.
The compressor B may be of any well known form such as here illustrated
having plunger 63 and cylinder 6 with inlet valve 6 and outlet valve the latter
of which is connected with the condenser coil C at C¹. This coil C is in turn
connected with the pipe e in cooling chamber D and from thence a series of
circulating coils E pass to the pipe e which is connected with the inlet valve b' of
the compressor. The condenser tank is supplied with water at F which passes
off again at F and a centrifugal pump H is provided in the air cooling chamber D.
for raising a solution of chloride of calcium into troughs h¹ which are placed over
each circulating coil E and perforated for the chloride of calcium to drip on to
the members of the coil and thereby prevent the accumulation of frost on the
pipes. The air cooling chamber is provided with the air propeller K the
outlet k¹ of which is connected to the boiler through hand doors a¹ and a² by the
pipes and the compressor B is provided with stop valves P and R and is
driven by any suitable means such as the driving band bas also the centrifugal
pump H and air propeller K which are respectively driven by the bands and k
The action of the apparatus for the lowering of the temperature in the boiler A
is as follows.

page_text: The compressor condenser and cooling chamber coils being charged with
ammonia gas or other suitable gases, the circulation as indicated by the arrows
is set up by the action of the compressor with the consequent cooling of the air
in the chamber D. The cold air is then drawn from the chamber D and propelied
into the boiler A at any convenient point or points such as the mud holes a¹ and u
but so as to get the distribution of the temperature over that portion of the boiler
covered with scale as even as possible the air then being allowed to escape at or
near the top from any convenient point such as the manhole or in
where the temperature is lower than the exterior atmosphere it may be conveyed
back to the cooling chamber D by any suitable flexible pipe S.
cases
In cases where the scale is hard and particularly free from moisture and where
copper does not form part of the boiler or apparatus I may expand the ammonia
direct into the boiler A in which case I omit the cooling chamber D) and connect
the one end of the condensing coil C direct with the boiler A as shewn at C Fig. 2
in which case the boiler is connected near the top with the compressor B by
pipes by which the ammonia or other gases may be expanded into the boiler
in which case I first create a vacuum in the boiler of say from 30" to 33".
To effect this I open valves P¹ and draw spindle of valve T for discharge of air,
all the other valves being closed thus by means of the compressor creating a
vacuum in the boiler after which I close discharge valve T and open valves R¹
and regulate quantity of gas entering the boiler by the regulating valve Y. The
valve W and cylinder X containing gas is for charging machine.
In cases where it is desirable to first test the boiler by air pressure the valves R¹
and are closed valve V is opened for the admission of the air and valves T and U
are opened by which the air is conveyed to boiler by pipe p³.
When working under direct expansion such as described I find by feeding in the
gas at or near the top of the boiler A I obtain the best and most even results as
the gas being particularly heavy and dense falls to the bottom, while to further
facilitate even distribution I find it advantageous to feed in through perforated
pipes such as Z which are so varied in arrangement as to suit the various forms
of boilers and apparatus to be met with.
I may obtain the required reduction in the temperature in several ways as for
instance by liquefied air which in the case of boilers or apparatus either large or
small may be effected by the introduction of such liquefied air into the boiler at
various points or by perforated pipes through the hand holes or valve connections
in a similar manner to that described for the direct expansion of the ammonia the
boiler being closed and under pressure of the atmosphere formed by the expansion
of the liquefied air and with a valve for the escape of such expanded air when
warm.
In some cases where motive power is difficult and expensive to obtain for the
working of the refrigerating apparatus I may effect the required reduction of
temperature by the use of chlorides or freezing mixtures applied in a similar
manner to that described with reference to liquified air.
In classes of scale having 15 % or more of salt I find it necessary to coat the
scale with a solution of sal ammoniac.
The form or shape of my refrigerating apparatus and the particular mode of
application is immaterial to the effect and may be adapted to the local circum-
stances and situations so long as it is capable of producing and evenly distributing
the required change of temperature as hereinbefore set forth.
For purposes of ready transport I pefer to build up my compressor condenser
and cooling chamber with a motor complete upon a suitable carriage by which it
may be readily conveyed to the various boilers requiring to be scaled.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is:-
1st. The process for removing scale from boilers and other such annaratus he

page_text: reducing the temperature of the same down to or below freezing point substantially
as herein set forth.
2nd. The process for removing scale from boilers and other such apparatus by
reducing the temperature to or below freezing point then allowing the temperature
to rise preferably to the temperature of the atmosphere and repeating the process
once, or more than once, according to the nature of the scale and the boiler or
other apparatus to be cleansed substantially as herein set forth.
Dated this 28th July 1899.
LEWIS WM. GOOLD,
Agent for Applicant, 5, Corporation Street, Birmingham.