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Page 31
Many forms of generator have been used in the United States for the
production of water gas, which, after or during manufacture, is mixed
with the vapors and permanent gases obtained by cracking various
grades of paraffin oil, and "fixing" them by subjecting them to a high
temperature; and in considering the subject of enrichment of coal gas
by carbureted water gas, I shall be forced, by the limited time at my
disposal, to confine myself to the most successful of these processes,
or those which are already undergoing trial in this country.
In considering these methods, we find they can be divided into two
classes:
1. Continuous processes, in which the heat necessary to bring about
the interaction of the carbon and steam is obtained by performing the
operation in retorts externally heated in a furnace; and
2. Intermittent processes, in which carbon is first heated to
incandescence by an air blast, and then, the air blast being cut off,
superheated steam is blown in until the temperature is reduced to a
point at which the carbon begins to fail in its action, when the air
is again admitted to bring the fuel up to the required temperature,
the process consisting of alternate formation of producer gas with
rise of temperature, and of water gas with lowering of the
temperature.
Of the first class of generator, none, as far as I know, have as yet
been practically successful, the nearest approach to this system being
the "Meeze," in which fire clay retorts in an ordinary setting are
employed. In the center of each retort is a pipe leading nearly to the
rear end of the retort, and containing baffle plates. Through this a
jet of superheated steam and hydrocarbon vapor is injected, and the
mixture passes the length of the inner tube, and then back through the
retort itself--which is also fitted with baffle plates--to the front
of the retort, whence the fixed gases escape by the stand pipe to the
hydraulic main, and the rich gas thus formed is used either to enrich
coal gas or is mixed with water gas made in a separate generator. In
some forms the water gas is passed with the oil through the retort. In
such a process, the complete breaking down of some of the heavy
hydrocarbons takes place, and the superheated steam, acting on the
carbon so liberated, forms water gas which bears the lower
hydrocarbons formed with it; but inasmuch as oil is not an economical
source of carbon for the production of water gas, this would probably
make the cost of production higher than necessary. This system has
been extensively tried, and indeed used to a certain extent, but the
results have not been altogether satisfactory, one of the troubles
which have had to be contended with being choking of the retorts.
Of the intermittent processes, the one most in use in America is the
"Lowe," in which the coke or anthracite is heated to incandescence in
a generator lined with firebrick, by an air blast, the heated products
of combustion as they leave the generator and enter the superheaters
being supplied with more air, which causes the combustion of the
carbon monoxide present in the producer gas, and heats up the
firebrick "baffles" with which the superheater is filled. When the
necessary temperature of fuel and superheater has been reached, the
air blasts are cut off, and steam is blown through the generator,
forming water gas, which meets the enriching oil at the top of the
first superheater, called the 'carbureter,' and carries the vapors
with it through the main superheater, where the "fixing" of the
hydrocarbons takes place.
The chief advantage of this apparatus is that the enormous
superheating space enables a lower temperature to be used for the
"fixing." This does away, to a certain extent, with the too great
breaking down of the hydrocarbons, and consequent deposition of
carbon. This form of apparatus has just found its way to this country,
and I describe it as being the one most used in the States, and the
type upon which, practically, all water gas plant with superheaters
has been founded.
The Springer apparatus, which is under trial by one of the large gas
companies, differs from the Lowe merely in construction. In this
apparatus the superheater is directly above the generator; and there
is only one superheating chamber instead of two. The air blast is
admitted at the bottom, and the producer gases heat the superheater in
the usual way, and when the required temperature is reached, the steam
is blown in at the top of the generator, and is made to pass through
the incandescent fuel, the water gas being led from the bottom of the
apparatus to the top, where it enters at the summit of the
superheater, meets the oil, and passes down with it through the
chamber, the finished gas escaping at the middle of the apparatus.
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