_Difference in the quantity of Gas evolved during different periods of
the distillatory process, and economical considerations resulting
therefrom in the manufacture of Coal Gas._
In conducting the decomposition of coal, the evolution of the gas is far
from being, with regard to quantity, uniform during different periods of
the distillatory process. The formation of the gas is more rapid in the
beginning of the process, and gradually slackens as the operation
proceeds. The gas also differs in its chemical constitution, at
different periods of the process; although in the case of large
supplies, this difference is of little consequence after the gas is
purified in the usual manner. The former consideration, however, has
given rise to various modes of operating, of which it will be proper to
take some notice.
It must be obvious, that in proportion as the mass of coal in the retort
becomes carbonized or converted into coke, the exterior surface becomes
a gradually increasing obstacle to the action of the heat upon the
interior or central part of the coal remaining to be decomposed. The
heat required on that account must be more intense, and kept up to no
purpose, and the extrication of gas becomes slower and slower, as the
operation proceeds.
The loss occasioned by this rapid diminution of the means employed, is
serious in every point of view, in regard as well to the quantity of
fuel used and time wasted, but it is unavoidable in the operation of
decomposing coal in masses or layers from 5 to 10 inches in thickness,
and must be a great drawback on the value of the gas-light discovery.
The loss of fuel, it is obvious, must be just in proportion to the
quantity of carbonised matter, or coke, which is kept hot to no purpose,
awaiting the decomposition of that portion of coal, which it is the
very means of protecting from becoming decomposed.
A striking exemplification of this statement will be seen in the
following table, exhibiting the result of the progressive produce of
coal gas, obtainable, in a given time, by means of cylindrical and
parallelopipedal retorts.
_Experiment with one cylindrical Retort, containing two bushels of
coal._
Hours of the Quantity of Gas
distillatory process produced.
First hour 115 cubic feet
Second ditto 81 ditto
Third ditto 78 ditto
Fourth ditto 70 ditto
Fifth ditto 66 ditto
Sixth ditto 55 ditto
Seventh ditto 49 ditto
Eighth ditto 42 ditto
---
555 cubic feet.
The quantity of gas is at the rate of ten thousand cubic feet to the
chaldron (27 cwt.) of coal.
_Experiment[14] with eighteen cylindrical Retorts, containing one
chaldron of coal._
Hours of the Quantity of gas
distillatory process produced.
First hour 2000 cubic feet
Second hour 1488
Third hour 1400
Fourth hour 1301
Fifth hour 1208
Sixth hour 1000
Seventh hour 897
Eighth hour 691
----
9985
This experiment was made with retorts set on the flue plan.
The coal employed was (Bewick and Craister’s Wall’s End), Newcastle
coal.
[14] Communicated by Mr. T. S. Peckston, of the Westminster Gas Works.
_Experiment with thirty-six parallelopipedal retorts, each containing
two bushels of coal._[15]
Hours of the Quantity of Gas
Distillatory Process produced.
In the first hour 4,058
Second hour 3,028
Third hour 2,871
Fourth hour 2,526
Fifth hour 2,380
Sixth hour 1,971
Seventh hour 1,754
Eighth hour 1,450
------
20,038
[15] Own Experiments.
The same heat as we have seen from the preceding table, p. 79, which is
necessary during the first hour of the operation, for the evolution of
one hundred and fifteen cubic feet of gas, is required in the eighth
hour for the production of no more than forty-two cubic feet, being a
decrease in effect of nearly two-thirds.
When larger retorts are employed for decomposing coal in masses, from
five to ten inches in thickness, the loss of heat is in a much greater
ratio.
In the hope of remedying in some measure the evils thus distinctly
ascertained to arise from the undue thickness of the masses of coal
subjected to the distillatory process, there have not been wanting
manufacturers who have had recourse to experiments on a large scale, to
ascertain with certainty whether they might not be gainers by suffering
the distillatory process, when the retorts are charged with two bushels
of coal, to proceed only for the space of six hours, instead of eight.
But the result of these experiments, as will be presently explained, has
shown satisfactorily that it is more profitable to keep up the
distillatory process for a period of eight hours, with the retorts fully
charged, than to abridge the operation by terminating it at the end of
six hours.
Others again, have imagined, that it would be more economical to
decompose a less quantity of coal at once, or to decrease the thickness
of the stratum of coal in the cylindrical, or in any of the before named
retorts; but then again, serious difficulties occur in the practice.
The more frequent charging of the retorts and luting on the covers,[16]
which such a mode of operating require, occasions a prodigious waste of
fuel, time and labour. A greater number of retorts and more workmen must
likewise be employed, in order to produce the requisite quantity of gas
daily, which the manufacturer is called upon to supply; more space of
ground is required, and more dead capital must be sunk in the
establishment. The more frequent and sudden alterations of temperature
which the retorts necessarily suffer, by the more frequent introduction
of cold coal, renders them extremely liable to become injured; and it is
almost impossible to maintain a number of retorts thus worked, at an
uniform temperature.
[16] When the cover is ground on, air-tight, the cost of the retort is
much increased.
From various statements, which I have been favoured with, in
confirmation of my own observations on the best method of working
cylindrical retorts, it may suffice to lay before the reader the result
of a series of operations instituted by one of the largest and best
conducted establishments in this country; the public-spirited and
indefatigable directors of which have done more in the way of extensive,
costly, varied and long continued experiments, to improve the new art of
lighting with gas, than any other similar body in the kingdom; and
without whose exertions the gas light illumination would never have
reached the state of perfection it has attained.
_Report on a course of Experiments made to ascertain the comparative
Economy[17] of manufacturing every week, 857,667 cubic feet of gas, by
means of Cylindrical Retorts variously worked._
[17] The cost of materials and price of labour in this estimate, as
well as in all subsequent statements, is given such as they actually
were, at the time, when the experiments to which they refer were made.
_Gas Light and Coke Company’s Works,
Westminster Station._
_February 8th, 1819._
_SIR_,
_Enclosed are the result of a series of experiments made under my
direction with a view of ascertaining the relative value of the
different modes of working cast-iron cylindrical retorts, from which
you will perceive that it is more economical to work eight hours
charges, as the workmen call it, that is to say, to suffer the
distillatory process to go on for eight hours, when nearly two bushels
of coal are contained in each retort, than to discontinue the operation
at the end of six hours._
_I am with respect,
Sir, Yours, &c.
T. S. PECKSTON._
_To Mr. F. Accum,
Compton Street, Soho._
_Process A._
=========+=======+================+================+========+=========
Number of|Number | | |Quantity|Quantity
Days the | of |Quantity of Coal| Quantity of | of | of Gas
Retorts |Retorts| decomposed for | Coal used | Gas |from one
were | in | obtaining Gas. | for Fuel. | pro- |Chaldron
worked. |action.| | | duced. |of Coal.
---------+-------+----------------+----------------+--------+---------
| |_Chal- _Bushel._|_Chal- _Bushel._| _Cubic | _Cubic
| |dron._ |dron._ | Feet._| Feet._
Monday | 87 | 10 30 | 4 24 | 94,987| 8,768
Tuesday | 88 | 14 24 | 6 8 | 128,597| 8,784
Wednesday| 88 | 14 24 | 6 8 | 122,188| 8,331
Thursday | 94 | 15 24 | 6 26 | 131,176| 8,373
Friday | 96 | 16 0 | 6 32 | 127,696| 7,981
Saturday | 96 | 16 0 | 6 20 | 127,536| 7,971
Sunday | 96 | 15 18 | 6 4 | 125,487| 8,092
| +----------------+----------------+--------+---------
| | 103 12 | 43 14 | 857,667|8,300[18]
=========+=======+================+================+========+=========
[18] Average proportion of gas from a chaldron of coal.
_Expenditure of Process A._
Coals, decomposed, 103 chaldron 12 bushel, at £ 2. 11_s._
6_d._ the chaldron, (27 Cwt.) £ 266 2 0
Small Coal, 43 chaldron, 14 bushels, used for fuel, at £ 2.
2_s._ the chaldron 91 2 4
Wages of two additional workmen (not required had the
retorts been worked at eight hours charges,) at £ 1. 16_s._
each man, the week 3 12 0
-----------
Total expenditure, £. 360 17 0
_Products of Process A._
Coke, 103 chaldron, 12 bushel, at £ 1. 7_s._ the chaldron £ 139 10 0
Breeze, or small coke, 6 chaldron, 9 bushels, at 18_s._ the
chaldron 5 12 6
Tar, 7³⁄₄ tons, at £ 6. the ton 46 10 0
Ammoniacal liquor, 1864 gallons, at 1¹⁄₂_d._ the gallon 11 13 0
Gas, 857,667 cubic feet, at 15_s._ the thousand cubic feet 643 5 0
----------
Total for products, £ 846 10 6
Hence the amount of expenditure for procuring 857,667 cubic feet of gas,
is £ 360. 17_s._
The value of the saleable products £ 846. 10_s._ 6_d._
And the average proportion of gas obtained from one chaldron of
Newcastle coal, 8,300 cubic feet.
_Process B._
=========+=======+================+================+========+=========
Number of| Number| | |Quantity| Propor-
Days the | of |Quantity of Coal| Quantity of | of | tion of
Retorts |Retorts| decomposed for | Coal used | Gas | Gas to a
were | in | obtaining Gas. | for Fuel. | pro- | Chaldron
worked. |action.| | | duced. |of Coals.
---------+-------+----------------+----------------+--------+---------
| |_Chal- _Bushel._|_Chal- _Bushel._| _Cubic| _Cubic
| |dron._ |dron._ | Feet._| Feet._
Monday | 57 | 9 18 | 2 13 | 94,987| 10,000
Tuesday | 77 | 12 31 | 3 8 | 128,597| 10,000
Wednesday| 73 | 12 8 | 3 2 | 122,188| 10,000
Thursday | 79 | 13 4 | 3 10 | 131,176| 10,000
Friday | 76 | 12 27 | 3 7 | 127,696| 10,000
Saturday | 77 | 12 27 | 3 6 | 127,536| 10,000
Sunday | 76 | 12 20 | 3 6 | 125,487| 10,000
| +----------------+----------------+--------+---------
| | 103 12 | 21 16 | 857,667| 10,000
| | | | | [19]
=========+=======+================+================+========+=========
[19] Average proportion of gas from a chaldron of coal.
_Expenditure of Process B._
Coal, decomposed, 85 chaldron, 27 bushels, at £ 2.
11_s._ 6_d._ the chaldron £ 220 16 10¹⁄₂
Small Coal, 21 chaldron, 16 bushels, used for fuel, at
£ 2. 2_s._ the chaldron 45 0 8
---------------
Total expenditure, £. 265 17 6¹⁄₂
_Products of Process B._
Coke, 100 chaldron, at £ 1. 7_s._ the chaldron £ 135 0 0
Breeze, or small coke, 3 chaldron, at 18_s._ the chaldron 2 14 0
Coal tar, 6 Tons, 8 Cwt. at £ 6. the ton 38 8 0
Ammoniacal liquor, 1536 gallons, at 1¹⁄₂_d._ the gallon 9 12 0
Gas, 857,667 cubic feet of, at 15_s._ the thousand cubic
feet 643 5 0
------------
Total for products, £. 828 19 0
From the result of this process it appears, that at the expence of
265_l._ 17_s._ 6¹⁄₂; the value of the products obtained is £ 828. 19_s._
By comparing the two preceding processes, A and B, it will be observed
that the same quantity of gas was generated each day, notwithstanding
there were fewer retorts in use, and less coal decomposed by process B,
than by Report A, and that the expence of fuel, when the distillatory
process was continued for a term of eight hours, was considerably less.
Also, that the proportion of gas obtained from a chaldron of coals, was
greater than when the process was continued for only six hours.
Hence, if from the products of
process A, £. 846 10 6
we take the products of process B, £. 828 19 0
-----------
The difference is, £. 17 11 6
which, being subtracted from the difference between the expenditure, as
specified in the process alluded to, namely
Process A, £. 360 17 0
Process B, 265 17 6¹⁄₂
---------------
The difference is £. 94 19 5¹⁄₂
Less 17 11 6
---------------
And leaves a balance of £. 77 17 11¹⁄₂
in favour of _working eight hours charges_, for one week, and producing
a like quantity of gas, as had been obtained by working _six hours
charges_.
Thus, having compared the quantity of coals actually used when working
six hours charges, with what was used to produce a like quantity of gas
from eight hours charges, I shall next point out, in process C, the
quantity of gas obtained when working the same number of retorts for a
period of eight hours which had been worked at the process of six
hours.
_Process C._
=========+=======+================+================+=========+========
Number of| Number| | | Quantity|Propor-
Days the | of Re-|Quantity of Coal| Quantity of | of Gas |tion of
Retorts | torts | decomposed for | Coal used | pro- |Gas to
were | [20] | obtaining Gas. | Fuel. | duced. |a Chal-
worked. | in | | | |dron of
|action.| | | |Coals.
---------+-------+----------------+----------------+---------+--------
| |_Chal- _Bushel._|_Chal- _Bushel._| _Cubic |_Cubic
| |dron._ |dron._ | Feet._ |Feet._
Monday | 87 | 16 18 | 3 22 | 165,000| 10,000
Tuesday | 88 | 14 24 | 3 24 | 146,667| 10,000
Wednesday| 88 | 14 24 | 3 24 | 146,667| 10,000
Thursday | 94 | 15 24 | 3 33 | 156,666| 10,000
Friday | 96 | 16 0 | 4 0 | 160,000| 10,000
Saturday | 96 | 16 0 | 4 0 | 160,000| 10,000
Sunday | 96 | 15 18 | 3 32 | 155,000| 10,000
| +----------------+----------------+---------+--------
| | 107 0 | 26 27 |1,070,000| 10,000
| | | | | [21]
=========+=======+================+================+=========+========
[20] Worked at six hours charges in process A, page 85, but here
worked at eight hours charges.
[21] Average proportion of gas from a chaldron of coal.
_Expenditure of process C._
Coal decomposed, 107 chaldron, at £ 2 11_s._ 6_d._ the
chaldron £ 275 10 6
Small coal, 26 chaldron, 27 bushels, used for fuel, at £ 2
2_s._ the chaldron 56 3 6
----------
Total expenditure £ 331 14 0
_Products of process C._
Coke, 124 chaldrons, at £ 1 7_s._ the chaldron £ 167 8 0
Breeze, or small coke, 4 chaldrons, at 18_s._ the
chaldron 3 12 0
Tar, 8 tons, at £. 6 the ton 48 0 0
Ammoniacal liquor, 1945 gallons, at 1¹⁄₂_d._ the gallon 12 3 1¹⁄₂
Gas, 1,070,000 cubic feet, at 15_s._ for a thousand cubic
feet 802 10 0
-------------
Total for products £ 1033 13 1¹⁄₂
RECAPITULATION.
Products by process C. £ 1033 13 1¹⁄₂
Products by process A. 846 10 6
-------------
Difference £ 187 2 7¹⁄₂
Expenditure by process A. £ 360 17 0
Expenditure by process C. 331 14 0
----------
Difference £. 29 3 0
From the above recapitulation it will appear, that by working equal
numbers of retorts, at six and at eight hours charges, the balance is
considerably in favour of the latter method; for, from the foregoing
statement, there appears to be on the practice of the latter method an
increase of saleable products amounting to
£ 187 2 7¹⁄₂
obtained at 29 3 0 less expence;
consequently there is a -------------
balance of £ 216 5 7¹⁄₂ in favour of
working the retorts, as stated in process C, over that method shewn in
process A; and in such proportion, _let the number of retorts worked be
what it may, an advantage will always be gained in this mode of
manufacturing coal gas, by working the retorts at eight hours charges,
as the workmen call it, in preference to adopting the shorter process_.
From a series of operations made[22] with twenty parallelopipedal and
with twenty cylindrical retorts, worked for one month, it has been
ascertained that the decomposition of coal is most economically
conducted when each retort is charged with 100 pounds of coal, and the
distillatory process be continued for eight hours. Two men, one by day
and one by night, can attend nine or ten retorts.
[22] By H. Morrison, Esq. and Self; the coal used, was Newcastle
(Bewick and Craister’s Walls End) coal.