An improvement in the Manufacture of Cement.
Year: 1886

page_text: An improvement in the Manufacture of Cement.
I, HENRY HARRIS 'LAKE, of the firm of Haseltine, Lake, & Co. Patent Agents
Southampton Buildings, in the County of Middlesex, 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:-
This invention relates to the manufacture of cement.
Hydraulic or Portland cement is usually manufactured by mixing together 'clay
and carbonate of lime in such proportions that after calcination the resulting
compound will contain about 62 parts of lime, 28 parts of silicic acid and 10 parts
of alumina by weight. During the process of calcination the carbonic acid
contained in the carbonate of lime is expelled and the silicic acid combines with
the bases and forms therewith silicates of lime and alumina which are afterward
reduced to powder and known as hydraulic or Portland cement. The carbonic
acid which is expelled during the process of calcination has no commercial value
and is allowed to escape into the air..
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The object.of this invention is to reduce the cost of the cement by the manu
facture of sulphuric acid as a bye product, and the invention consists to that end
in manufacturing cement from clay or silicic acid and sulphate of lime, as hereinafter
set forth.
'
In practising my invention I mix together gypsum or sulphate of lime and clay
in the proportion of about 1266 pounds of gypsum to 400 pounds of clay. I prefer
to pulverize the gypsum, and dry the clay and pulverize the same, then intimately
mix the pulverized gypsum and clay and add a small quantity of water, and
mould the mixture into blocks substantially in the manner practised in making
Portland cement from carbonate of lime and clay by the well known dry process.
I then subject this mixture to calcination in a suitable kiln. At the high degree
of heat which is maintained during the process of calcination the silicic acid
contained in the clay expels the sulphuric acid contained in the sulphate of lime,
and combines with the lime and alumina and produces therewith silicates of lime
and alumina which, upon being reduced to powder, are in every particular a
hydraulic or Portland cement,

page_text: The sulphuric acid is expelled during this process of calcination either in the
form of vapour, or it is decomposed and forms sulphurous acid and oxygen; or
the escaping gas is a mixture of vaporized sulphuric acid, sulphurous acid and
oxygen, according to the degree of heat which is maintained during the process of
calcination, and which may vary somewhat at different times owing to differences
in the quantity or quality of fuel employed, strength of draught etc. The gases
escaping during the process of calcination are cooled in suitable chambers or
passages lined with lead in which the sulphuric acid is condensed and collected,
The sulphurous acid, if any, is converted into sulphuric acid in the ordinary
manner by means of steam and nitric acid. The sulphuric acid so obtained is then
concentrated or further treated in any usual manner practised in the manufacture
of sulphuric acid.
The mixture of gypsum and clay above specified produces about 711 pounds of
hydraulic or Portland cement and 580 pounds of sulphuric acid from every
1666 pounds of the mixture, the balance being moisture which is expelled. The
cost of the sulphate of lime is about the same as that of carbonate of lime, and the
cost of manufacturing hydraulic or Portland cement by this improved method is.
about the same as that of the old method in which carbonate of lime is employed,
but the sulphuric acid which is obtained as a bye-product in my improved method,
is valuable, and the value which it represents materially reduces the cost of the
cement.
In practising this invention any suitable kiln in which the process of calcination
can be carried out may be employed, and any ordinary apparatus may be used for
recovering the sulphuric acid...
The condensing and converting chambers are connected with the top of the kiln
by a suitable flue, and the waste gases are. discharged from the condensing or
converting chambers by a stack or chimney or a suitable fan which maintains a
proper draught through the kiln and chambers.
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The proportions herein specified are found to be well calculated to produce
the desired results, but they may be varied in accordance with the nature of
the gypsum-rock and clay employed, within certain limits, without changing the
general results.. If the proportion of clay used be too great the cement will be of
an inferior quality, but the sulphuric acid contained in the sulphate of lime will be
driven off and recovered. If an excess of gypsum be used, the lime contained,
therein is in excess of the true combining, proportions with, the silicic acid, and the
sulphuric acid will not all be driven off, and the resulting cement will be inferior
in quality by reason of the presence of sulphate of lime, although a small per-
centage of the latter may be present without exerting any specially deleterious.
influence.
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Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed as communicated to
me by my foreign Correspondent, I declare that what I claim is:
The berein described method of manufacturing hydraulic or Portland cement
which consists in calcining a mixture of clay and sulphate of lime, substantially in
the proportion specified, as set forth.
.:,
1000.