Process for Preventing Boller-incrustation.
Year: 1894

page_text: Date of Application, 21st Nov., 1894-Accepted, 9th Feb., 1895
proved Process for Preventing Boller-incrustation.
A communication from ALWIN NIESKE, of Chemnitzerstrasse 9, and Wielandstrasse,
Dresden, Saxony, Empire of Germany.
I, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
Chartered Patent Agent, 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. :-
In spite of the innumerable attempts that have been made to find ways and
means for the complete prevention of boiler-incrustation, no one has yet been in a
position to point with confidence to any one of the numerous processes, that have
been recommended to protect from or prevent boiler incrustation, as being perfect
and complete, and applicable to all cases. Thus, in the case of the most generally
used process, viz. the addition, to the feed-water, of potassium carbonate, with a
view to precipitate the calcium-bicarbonate and calcium sulphate as calcium
carbonate, that object is only completely attained when the deposited calcium-
monocarbonate enters into combination with the undecomposed gypsum to form
fresh incrustation.
The process suggested about 20 years ago by E. de Haën (Hanover), according
to which the calcium-bi-carbonate is to be precipitated by milk of lime and the
gypsum by barium-chloride, before the feed-water is run into the boiler, certainly,
if strictly and properly carried out, effectually prevents boiler-incrustation; but the
proper carrying out of that process is so minute and difficult that it can only be
done by a trained chemist; to be reliable moreover, the process requires an
enormous area of clarifying tanks. The greatest difficulty, however, consists in the
fact, that, in precipitating the gypsum with barium-chloride, a corresponding
quantity of calcium chloride is taken up by the solution, and as the latter, under
continuous steam pressure gives up muriatic (or hydrochloric) acid, which attacks
the metallic shell of the boiler, an effect which may have very dangerous results,
this process has quite ceased to be employed.
Similarly, in the employment of the many other means that have been and are
recommended for this purpose, various other mistakes or misconceptions bring
themselves under notice, or, as in many cases, there is no beneficial result
whatever.
Contrary to the above mentioned unsuitable and inefficient methods of retnoving
boiler-incrustations when formed or preventing their formation, I have found that,
by the addition of chromate salts to the feed-water, the formation or deposit of all
incrustations is thoroughly prevented. The calcium contained in the feed-water, in
the form either of bicarbonate or sulphate, is thrown down in the form of a light
sediment at the bottom of the boiler, but the inside surface of the metallic shell
remains perfectly clear, without being attacked or corroded in the smallest
degree.
The chemical reactions which are set up by the introduction of the chromate-
salt e.g., sodium bichromate, upon calcium-bicarbonate or calcium sulphate, or

page_text: a mixture of those two salts, may be set forth in the form of equations, as
follows:-
1) CaCO, CO, + Na,Cr,O, = CaСro₁ + Na₂CгO, +2 CO,
2) CaSO + Na2Cr₂O, = CaCrO4 + Na₂SO + CгO,
3) (CaCO, CO₂+ CaSO4) + Na,Cr₂O, = 2 CaCrO4 + Na₂SO, + 2 CO₂.
Now, while at ordinary atmospheric pressures calcium-chromate in solution
is precipitated in the form of calcium-carbonate or sulphate by a solution of soda or
of Glauber's-salts, on the other hand calcium-carbonate and sulphate, at higher
temperatures, are thrown down as calcium-chromate by chromic acid salts. An
excess of chromic acid salt or of free chromic acid has no prejudicial influence upon
either the metallic parts or the materials employed as packing; these therefore are
severally unaffected.
In experiments which I have made, extending over continuous working periods of
about two months, no chrome salts being added to the feed-water, a thick coating
of incrustation amounting to from 10 to 12 millimetres in depth of extremely hard
fur, very difficult of removal, and composed of gypsum and calcium-mono-carbonate
was formed on the boiler-shell.
Contrariwise, after using chrome salts (it being found best to use the bichromate,
in slight excess) for a period of from 4 to 5 months, no incrustation whatever was
perceptible in the boiler, and nothing but a thin sedimentary mud at the bottom,
which was completely got rid of by blowing out the boiler. The boiler-surface was
perfectly clean and not in the least degree attacked.
The employment of chrome-salts for this purpose, and the process for the
complete prevention of boiler-incrustation is quite new."
Having now particularly described and ascertained the nature of the said inven-
tion as communicated to me by my foreign correspondent and in what manner
the same is to be performed, I declare that what I claim is :-
A process for prevention of and protection from boiler-incrustation by the
addition of chromates or di-chromates to the boiler-feed water.
Dated this 21st day of November 1894.
BOULT & WADE,
Agents for the Applicant.