AN IMPROVED METHOD OF PURIFYING Coal Gas
Year: 1876

page_text: LETTERS PATENT to William Marriott, of Huddersfield, in the County of York,
Manufacturing Chemist, for the Invention of "AN IMPROVED METHOD OF
PURIFYING Coal Gas."
PROVISIONAL SPECIFICATION left by the said William Marriott at the
Office of the Commissioners of Patents on the 4th January 1876.
WILLIAM MARRIOTT, of Huddersfield, in the County of York, Manufacturing
Chemist. "AN IMPROVED METHOD OF PURIFYING COAL GAS."
This Invention relates to improvements in the purification of coal gas by means
of a solution of ammoniacal liquor, or of sulphite of soda or other salts as herein-
after specified.
The impurities in gas obtained from the destructive distillation of coal are
principally carbonic acid, sulphuretted hydrogen, ammonia, and certain other
sulphur compounds, the composition of which is not at present well understood.
Some of these impurities are partly removed by scrubbing the gas with ammoniacal
liquor (gas liquor), or water, and then passing the gas through hydrate of lime or
peroxide of iron to separate carbonic acid and sulphuretted hydrogen.
My Invention consists in so treating ammoniacal liquor (gas liquor), or sulphite
of soda, of potash, of lime, or of magnesia, as to convert the same into a solution
which will remove the whole or nearly the whole of the above-named impurities
present in the crude gas.
I pass into the gas liquor sulphurous acid; this acid decomposes with the
sulphite of ammonia therein, sulphur being precipitated, I continue this treatment
until all the sulphites are decomposed, and then I use the ammoniacal liquor so
prepared for separating the impurities from crude gas by passing the gas through
scrubbers down which this liquor is percolating.
I may use scrubbers in the form of tubes filled with coke or fitted with boards or
any other suitable scrubbers. The liquid from these scrubbers may be subjected
to treatment with a further quantity of sulphurous acid, and used for the
purification of a fresh quantity of gas.
One advantage arising from the use of my said Invention is the recovery of the
sulphur in a pure condition.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said William Marriott in the Great Seal Patent Office on the 7th June
1876.
WILLIAM MARRIOTT, of Huddersfield, in the County of York, Manufacturing
Chemist. "AN IMPROVED METHOD OF PURIFYING COAL GAS."
This Invention relates to the purification of coal gas by means of a solution of
ammoniacal liquor, or of sulphite of soda or other salts as herein-after specified.
The impurities in gas obtained from the destructive distillation of coal are
principally carbonic acid, sulphuretted hydrogen, ammonia, and certain other
sulphur compounds, the composition of which is not at present well understood.
Some of these impurities are partly removed by scrubbing the gas with ammoniacal
liquor (gas liquor), or water, and thence passing the gas through hydrate of lime or
hydrated peroxide of iron to separate carbonic acid and sulphuretted hydrogen.
According to my said Invention I so treat ammoniacal liquor (gas liquor), soda,
or potash, or lime in solution, as to convert the same into sulphite or bisulphite
which will remove the whole or nearly the whole of the above-named impurities
present in the crude gas.
Before proceeding to describe my Invention I will first explain the action of
sulphurous acid on ammoniacal liquor (called herein-after gas liquor). This gas
liquor is chiefly a weak solution of carbonate and sulphide of ammonia, varying in
the proportions thereof with the strength of the liquor, but containing more
carbonate than sulphide of ammonia.
When sulphurous acid gas is passed through gas liquor the sulphide of ammonia
is decomposed, sulphur being precipitated. When all the sulphide of ammonia in
the gas liquor is decomposed the liquor no longer discolours lead solution, which is
therefore used as a test in this operation. If the passing of sulphurous acid gas
into the gas liquor is still further continued the carbonic acid is next expelled, and
all the ammonia is converted into sulphite of ammonia. If moré sulphurous acid is
now added the sulphite of ammonia is converted into bisulphite.
The accompanying Drawing which represents apparatus for the conversion of
gas liquor into sulphite or bisulphite of ammonia will assist in explaining this
operation.
A is a tower charged with coke or other suitable material, down which tower
the gas liquor is allowed to percolate; B is a burner for burning sulphur, the
sulphurous acid from which passes up the said tower. A slight draught or current
up the tower is produced by a steam jet or by a chimney.
By regulating the flow of gas liquor down the tower according to the quantity of
sulphurous acid passing up the said tower the gas liquor may be all converted into
sulphite or bisulphite of ammonia as required. This operation will be completely
under the control of the attendant and there need be no loss of sulphurous
acid.
I wish it understood that this apparatus although convenient for my purposé
forms no part of my Invention.
I will now proceed to explain how I use the sulphite or bisulphite of ammonia,
called herein-after prepared gas liquor, to separate the sulphuretted hydrogen and
ammonia from crude gas.
The crude gas is passed up apparatus called scrubbers, which apparatus is in
general use in gas works, while the prepared gas liquor percolates downward
through the same. Immediately these two substances, namely, the prepared gas
liquor and the crude gas meet each other, the sulphuretted hydrogen of the crude
gas is decomposed and sulphur is precipitated. The prepared gas liquor is pumped
repeatedly through the scrubber until it no longer decomposes sulphuretted
hydrogen when it is replaced by a fresh quantity of prepared gas liquor.
The exhausted prepared gas liquor which contains a quantity of sulphur in
suspension must be allowed to settle when the solution can be drawn off from the

page_text: precipitated sulphur, and again passed down the tower A to be resaturated with
sulphurous acid. Any scrubber which exposes a large surface to the gas and offers
little obstruction to its passage will answer my purpose.
As the use and construction of scrubbers is well understood by gas engineers
their working in connection with my Invention need not be particularly described.
The size and number of the scrubbers must be in proportion to the quantity of gas
to be passed through them in a given time; but this is a matter which must be
left to the discretion of the engineer.
Three scrubbers are required to afford the proper capacity for purifying the gas
generated. Down the second or middle scrubber the prepared gas liquor is passed
by means of a pump as it comes from the tower A. This liquor as it leaves the
second scrubber is again passed down the first scrubber and then down the third
scrubber, so that the prepared gas liquor passes down all three of the scrubbers.
It is then pumped through the tower A to be resaturated with sulphurous acid, and
again through the scrubbers, the process being continuous with the same quantity of
prepared gas liquor.
The points which require the principal attention of the gas engineer are that the
proportion of crude gas to the prepared gas liquor is such that all the duty or
effect shall be obtained from the prepared gas liquor before it is again passed down
the tower A. And that the prepared gas liquor runs from the third scrubber in a
neutral state; attention to these points will insure that no sulphurous acid
brought by the gas current from the first or second scrubber passes the third
scrubber.
'
The gas is finally passed through a lime purifier to separate the carbonic acid.
As this process decomposes the sulphuretted hydrogen no nuisance arises on
emptying the lime purifiers. As the bisulphite of ammonia decomposes with the
sulphuretted hydrogen part of the sulphur forms fresh sulphur compounds, principally
hyposulphite and pentathionate of ammonia, but these compounds do not prevent
the solution from again absorbing sulphurous acid, or the renewal of its property of
decomposing sulphuretted hydrogen.
I do not confine myself to the above order of working or any special form of
apparatus for using the sulphites in gas purification.
When the gas contains ammonia this substance is absorbed in the scrubbers, and
will accumulate in the prepared gas liquor, so that after a time there will be more
liquor than is required. When it is desired to work up this excess of ammonia or
renew the solution of prepared gas liquor, the whole of the sulphur contained
therein may be recovered by adding to the liquor the quantity of sulphuric acid
required to saturate the ammonia; this liberates sulphurous acid, and the same may
be utilized by passing the liquor down the first scrubber, where the sulphurous acid
decomposes with a further precipitation of sulphur. The solution after depositing
the sulphur may be evaporated and crystallized into sulphate of ammonia.
In the course of my experiments with the sulphites to separate sulphuretted
hydrogen from coal gas, I have found that sulphur compounds other than
sulphuretted hydrogen are removed at the same time, but as this result is
uncertain I make no claim under this head.
I call the liquor exhausted or spent liquor when it no longer decomposes
sulphuretted hydrogen.
The precipitated sulphur from the exhausted liquor is recovered in a marketable
form by a process which consists in introducing the precipitated sulphur into a
boiler, and heating the same by steam up to 230 degrees Fahrenheit at which
temperature sulphur is liquid, and the sulphur being much heavier than the solution
in which it is precipitated accumulates at the bottom of the boiler, and is thence
discharged into shallow vessels to cool.
As all the sulphur existing in sulphuretted hydrogen in the gas is recoverable,
there is a much larger quantity produced at any works than will be required for
generating the sulphurous acid necessary to convert a given quantity of gas liquor
into sulphite of ammonia.

page_text: Soda, or potash, or lime may be converted into sulphite or bisulphite in the
manner above described for converting the ammonia of gas liquor into sulphite or
bisulphite, and the sulphite or bisulphite of soda or potash, or lime may be used for
separating the sulphuretted hydrogen from the crude gas.
Having thus fully described my said Invention, and the manner of performing
the same, I wish it understood that I claim,―
First. The method or process of purifying gas by the employment of sulphite or
bisulphite of ammonia, or of soda, or of potash, or of lime or sulphurous acid, free or
combined with ammonia, potash, or lime, as above described.
Second. In the aforesaid process of purifying gas the precipitation of sulphur, as
above described in a free and marketable state from crude gas by the use of
sulphites or bisulphites of ammonia or of soda, or of potash, or of lime.
In witness whereof, I, the said William Marriott, have hereunto set my hand
and seal, this Sixteenth day of May, in the year of our Lord One thousand
eight hundred and seventy-six.
Witness,
JAB. EDWARDS,
8, Southampton Buildings,
London,
W. MARRIOTT. (L.S.)