IMPROVEMENTS IN CALCINING LIMESTONE AND ROASTING ORES AND IN KILNS THEREFOR
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Stephen Collier at the Office of
the commissioners of Patents on the 27th January 1882.
STEPHEN COLLIER Junior of Bridgend in the County of Glamorgan, Lime
Manufacturer and Merchant "IMPROVEMENTS IN CALCINING LIMESTONE AND
ROASTING ORES AND IN KILNS THEREFOR,"
The method hitherto almost invariably adopted is to mix certain proportions of
lime stone and fuel in a kiln of circular or oval shape and to burn till calcination
is complete.
This is a very uncertain, wasteful and rude method; in fact with the exception of
the "Hoffman" kiln there has been little or no improvement in the process at all-
it is all done in open kilns by rule of thumb. There is no command over combustion,
either to increase or diminish it, consequently the result is irregular; sometimes the
limo is over burnt, at other times insufficiently burnt, either of which is a source of
great loss to the producer.
The object of this Invention is to burn lime and roast ores by a new process and
kiln so as to effect a great saving of fuel and a uniform quality of product.
I also propose to adopt my plan to existing kilns when they are of conical
shape.
At some distance from the top of kiln it is completely arched over the entire area
with specially shaped bricks of fire-clay in each of which is a thorough perforation,
say two inches diameter, to admit of passage of air and piping. Over this arch and
separated from the lower one by a layer of fireclay or sand, another arch of ordinary
firebrick will be built and the top levelled with fire brick. The two inch holes pass
through from bottom to top. This is the floor of the kiln and in the centre of it
will be a hole say fifteen inches diameter and say four other holes say of twelve
inches diameter. These are the draw holes. Fuel and stone will be prevented from
falling through by means of fire bars underneath. Under the arch and about five
feet below it is the floor on which the men stand to take the lime from the draw
holes and the lime may be wheeled out through a door way in the side of this
chamber. The door to be closed during burning. Immediately under the brick
arch and suspended thereto are annular rings of gas piping connected with a supply
pipe from outside. In these annular rings connections are made at frequent intervals
so as to attach vertical pipes which are inserted into the small holes in the arch of
kiln. These will convey the igniting agent either gas or oil or any other cheap
inflammable gas, such as the "Dowson Economic Gas," or a mixture of petroleum and
naphtha or the gaseous fuel from a regenerative furnace. The gas jets will quickly
set fire to the coal which is in contact with the flames and which is thinly distributed
over the floor of kiln and intermixed with the lime stone.

page_text: The strong draught (which is an indispesible part of my Invention) will carry
the flames up amongst the fuel and stone, disengage the carbonic acid gas in the
limestone, turn it into carbonic oxide an inflammable gas, and these gases, from fuel
and stone, fed with all the oxygen which will by the strong current of air be conveyed
upwards, develope in a short time a very strong fire.
The modus operandi is this. The gas or oil jets being all in their places and
ignited with the smallest possible flame, a thin layer of bituminous coal is distri-
buted over the floor of kiln, then a layer of lime stone with the usual sprinkling of
coal. The kiln is loaded with its full charge and supplied with fuel necessary to
maintain rapid and continued combustion so as to keep the stones in a red heat in
which state the carbonic acid gas escapes from the limestone.
When all this is ready, the gas is fully turned on, the aperture through which the
draught enters from below is enlarged gradually so as to heat the stones slowly.
Later on the full blast is put on and afterwards the whole mass will be an intense
body of fire.
The fire may be regulated with the greatest nicety, if too strong in one part of
the kiln the gas may be lowered there and the supply of oxygen cut off by the
insertion of stoppers in the air holes contiguous to the strong fire, and vice versa if
the fire is seen to get weak.
When calcination is complete, that is when all the carbonic acid gas (which
amounts to two fifths of the weight) is driven out of the stone, the gas is turned off,
if not already done, the air is hermetically sealed from the fire and combustion
ceases. Then the air holes and draw holes are fully opened and cooling proceeds
till the lime is fit to be removed.
During the charging of the kiln a steam jet is turned on under the arch and
continued-more-or-less-during-calcination. Its-effect is that the quantity of coal
required is much less when the stones are moistened.
My kiln is covered over. A floor (of iron) left above the kiln is utilized to dry
bricks preparatory to burning. Above this is a roof with stack to assist draught
and carry away waste products.
My high kiln answers the purpose of a chimney, but where this may not be
suitable or applicable, a stack must be built, or what is equally efficacious a small
fan, such as is used in foundries to smelt iron, will create sufficient draught to
ensure rapid combustion.
The advantages of my improved method are as follows, viz:-Absolute certainty
in the process and much less consumption of coal than in the present practice.
Every charge is a complete and separate operation and can be regulated. with
precision. Lime may be produced only when required. At present a kiln must be
kept going so that the fire should not go out or be extinguished, and there is great
waste of fuel, the line slakes in the kiln, resulting in loss. In every district the
demand for lime is more or less irregular, it varies often from ten to two hundred
tons per week, and the lime burner is obliged to keep a kiln of the latter capacity
going for weeks to supply the smaller quantity.
With my improved kiln and method all this is altered, no more need be produced
than the requirement of the moment demands.
The quality of the lime will be much improved as the operation of calcination
will be under complete control. It will come from the kiln in large lumps with
a small percentage of sinall or dust lime. The loss with the present method is
enormous, not only in fuel but in consequence of inability to tell in what state the
fire is in.