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tar,is to prevent their conversion into that closed. The water gas, therefore, descended body.
the ascension pipes on this side, passed through . In a lecture I gave before the Incorporated i the retort, and up the ascension pipes on the Institution of Gas Engineers in 1900, I sug., other side along with the coal gas. gested that instead of using water gas merely! The quaiitity of water gas which could be as a diluent, it should be made a factor in the passed through each cock, when partly and distillation itself. I then proposed that a stream when full.open, was ascertained before the of water gas should be passed through the test by measurement through a meter. This crown of the retort during the process of car- enabled an approximate measurement of the bonisation, so as not only to hurry the newly ., quantity of water gas put into each retort to born hydrocarbon gases out of contact with i be made ; but the actual quantity used in each the hot walls of the retort, but also by diluting, experiment was checked by noting the quantity them to prevent the secondary reactions which taken out of the holder. The heat of the were so important a factor in the production of retorts was. maintained as nearly uniform as tar from taking place, and by so doing to save possible throughout the tests, and at as high many of the important lighting and heating a temperature as is used in ordinary working. constituents from destruction.
Many experiments were made in this way, Through the kindness of Sir George Livesey | all of which showed that important economies and Mr. S. Y. Shoubridge experiments were could be attained by the process. The shortly afterwards made at the Crystal Palace following experiment will give an idea of the . District Gas Works, giving results which result obtained by using the 40 per cent. of pointed to this method of utilising water gas blue water gas in this way as compared with as of the greatest possible importance to the 40 per cent. simply mixed with the coal the future of coal gas.
gas: In these experiments a Derbyshire coal was
Coal carbonised ........ 82 tons. employed, and the yield of gas and candle Make of mixed gas per power given by the coal was tested on a large
ton ................ 13,730 cubic ft. scale before, during, and after the water gas Water gas added per ton 4,005 experiments. It was found that under ordi Proportion water gas adnary conditions of carbonisation the coal yielded
41°1 per cent. 10,468 cubic feet per ton of 15.88 candle power
Proportion water gas in
mixture ............ 291 , Candle power, ,........
14.87 candles. The plant used in the earlier experiment consisted of six beds of seven retorts each, and later of twelve beds of seven retorts. The section of all retorts was 22 inches by 16 inches
=32,416 , and 20 feet long, they were heated by regenera Gain in candle feet on tive furnaces and charged by power-stoking
... 25 per cent. machinery. The gas from them was passed through one complete section of the works
ANALYSIS OF GAS. separately, and was therefore condensed,
I. II. scrubbed, purified and measured in the usual Hydrogen .............. 50:37 50:62 way-the ordinary gas manufacture being
Saturated hydrocarbons .. 29.24 carried on at the time in other sections of the
Unsaturated hydrocarbons 2.98 - 2.48 works.
Carbon dioxide.......... 0:49 0:49 The water gas was made in the ordinary
Carbon monoxide........ 14:92 14.92
Nil “Economical” water gas plant, and conveyed
Nil Nitrogen ........
2.CO 2.00 from the relief holder to the retort house by a special pipe. This pipe was continued over
100.00 100.00 the retort bench, just above the arch pipes on
CALORIFIC VALUE. one side, and a connection was made from it
Calories...... 149 8 gross. 132.9 nett. to the top of each ascension pipe on that side
B.T.U. ...... 599-2 , 531:6 , of the bench. Each connection was fitted with a cock having a lever handle, with rod attached These experiments were renewed in 1901 to it, so that the cock could be regulated from with inclined retorts instead of horizontal, and the charging floor. The dip pipes on this side a bench of 70 inclined retorts which had been were blocked and the hydraulic main valves newly erected, was utilised for the purpose.
Candle ft 13.730 X 14.87
-=40,833 Standard 10.468 x 15.88
The water gas was made, as in the previous days with the coal alone, the tests being made experiments, in the generator of the “Econo every hour, day and night, so as to obtain a mical " plant usually employed for the manu- standard for comparison. The principal results facture of carburetted water gas. The gas obtained werewas passed into a holder of 469,800 cubic feet
Total coal carbonised
603 tons.'... capacity, and thence was carried to the in
Total gas made (coniected). 5,973,682 c. st.;. clined retorts, into which it entered at atmo- | Make per ton............... 9,907 » spheric temperature. The gas was not purified Average illuminating power before being admitted to the retorts, but was (table photometer) .... 16:55 candles. tested for carbon dioxide, of which it contained Total tar (hydraulic)...... 5,060 gallons. from 5 to 6 per cent. The carbon dioxide, Tar per ton
8.3 after estimation, was deducted by calculation Calorific power gross...... 152:6 calories per c. ft. from the volume of water gas used, because
„ nett ...... 138.8 '10 "), the volume of mixed gas produced was measured in station meters after the whole
These figures give the value of 32.792 candle
feet per ton for the coal, and this figure is taken of the carbon dioxide had been removed by
as the standard in the following experiments. purification in the usual manner. To ascertain whether the carbon dioxide in the
In arranging the apparatus for the experie
ments, the upper mouthpiece of each retort water gas was converted into carbon monoxide
was fitted with a pipe and stopcock for the by passage through the retorts, the inixed gas
admission of the water gas. was examined at the inlet to the washers, and found to contain 3 per cent. of carbon dioxide.
These experiments were continued from
June 19th to August 23rd, 1901. Passage It may therefore be assumed that the carbon
of water gas in varying proportions through dioxide, as it passed through the retorts, was
the retorts was tried, and also the influence of not converted to any appreciable extent into
the period of carbonisation at which the flow of carbon monoxide.
diluting gas was started. It was found that No station meter could be placed at my dis
although the results obtained were far better posal for the measurement of the water gas.
than in the experimeuts made with the horiThe holder of known capacity (469,800 cubic
zontal retorts, they were of the same kind, and feet) was therefore filled before the commence
that the gain in candle feet per ton gradually ment of each experiment, no gas being ad
rose with increase in the volume of water gas mitted to the holder during any trial. The
used, reaching a maximum with about 40 volume of the gas was obtained by recording
volumes of water gas per 100 of coal gas, the height of the holder at the commencement and completion of the experiment, and making
and decreasing when this point was passed. all the necessary corrections for temperature and pressure. The quantity of water gas used Water Gas added Candle Feet Percentage Gain per
Ton of Coal in during 24 hours varied in the different experi
Ton of Coal. Candle Feet. ments from 200,000 to 370,000 cubic feet. The
37 582 gas leaving the retorts was purified in the
25-5 usual manner, and then passed through station
16 6 meters, from which readings were made every
40,936 · During every hour the gas was slowly by
42.0 passed into a small holder, from which gas
310 was drawn at the completion of each hour, for
234 the determination of the illuminating power by means of the Referees' Table Photometer, | The most important data with regard to and from this once every day gas was drawn these experiments were given in a Table at for analysis and for the determination of | the end of a paper read before the Interits calorific power by means of a Junker's | national Engineering Congress at Glasgow, calorimeter.
last year, but the results are so extraordinary, The coal used in the experiments was the and so full of interest, that it is as well to give same kind of Derbyshire coal as had been used the full data for two experiments, in which 40 in the previous tests, but of slightly inferior and 42 per cent. of water gas respectively quality. Before commencing the experiments were added, as it gives a better idea of the with water gas, a trial run was made for seven | scale of the experiment.
per cent. of
27.8 37.6 40-1
Coal used .........
88 order to maintain a temperature of not less Total make (cor
than, say, 500° F. (277° C.) 18 inches above the rected).
1,274,656 c. ft. 113 - 1,294,946 Make per ton...... 14,925
mouthpiece, a very large proportion of water
gas may be used during the first two hours of power (table
distillation, and then should either be reduced photometer...... 14'4 candles
or cut off, the latter being the course most Total tar (hydraulic) ......... 695 galls.
likely to be adopted in practice. During Tar per ton.........
74 carbonisation the large volume of gas which is Water gas added
420 per cent.
evolved during the earlier periods of the charge Water gas in mixture 29-5
is that which contains the highest proportion
» Water gas per
of rich hydrocarbons, and these are the com. ton of coal
pounds, not only of highest illuminating value, carbonised ...... 4,415 c. ft.
4,215 Candle feet per
but those most liable to be broken down ton ......... 14,925 X 14'4 = 42,984 14.715 X 14:85 = 43,703 into less valuable illuminating bodies by undue
heating, whilst the gases evolved in the later Standard for coal
stages of carbonisation are of low illuminating 32,792
power and will withstand a higher temperIncrease in candle feet..... 31'07 per cent.
This falling off in the quality of the gas Calorific Value.
during carbonisation is partly due to decrease Gross. Nett. Gross. Nett. Calories
127*2 116'8 125.8 1187 in the quantity of gas evolved leaving the gas BTU ............ 5068 4672 5032 4746 exposed too long to the action of the heated Carbon monoxide
walls of the retort, and still more to the fact present in purified gas ...
14 0 per cent. 15'2 per cent. that as the heat in the retort acts upon the Gain in calorific
charge of coal it is the large outer surface 25°5 '224
which is first affected, the bottom of the charge So that a gain of 31 to 33 per cent. in candle | by direct contact with the retort, and the upper feet and 22 to 25 per cent. in total calorific portions by radiation from the walls. Messrs. value is attained.
Folkard and Heisch showed that with six hour point which should be clearly borne in charges only one-sixth of the coal remained mind when using water gas to clear the hydro- uncarbonised at the end of the third hour. carbon compounds out of the retort, is that This remained as a core in the charge surcold water gas will have a cooling effect upon rounded by a crust of three inches of coke, and the crown of the retort and upon the gases | as the coke would be at a temperature not very evolved by the coal.
far below that of the retort the heavy hydroEvery gas manager knows to his cost that carbons evolved during the last period of the unless the temperature in the ascension carbonisation would have been so degraded by pipes rises above 470° F., he runs great risk filtering through the heated crust that the of choked ascension pipes, and although the water gas would have but little chance of showadmixture of water gas reduces, and, indeed, ing any profitable influence. does away with stoppages, owing to alteration That this is so is indicated by the fact that in the character of the tar and to dilution, yet in experiments made with cold water gas inthe cooling of the gas if carried to extremes is troduced an hour after carbonisation had quite capable of bringing about the very trouble started, and carried on for three hours, i.e., that the process when properly applied would until four hours of carbonisation had elapsed, entirely prevent. This is one reason why a gain of only 16 per cent, in candle feet was hot water gas should be employed in preference obtained, whilst when the water gas was to cold. If, however, the conditions are such admitted directly after the charge and was that the use of hot water gas is an impossi. | continued for three hours, a gain of 33 per cent. bility, then the passage of the diluting gas in candle feet showed itself. should not be carried on for too long. Mr. In order to show the greatest gain from the Foulis has shown that the temperature of the process, the water gas would have to be brought gases in the ascension pipe at a distance of in a pipe through the retort itself, so as to be 18 inches from the mouthpiece average 890° F. | heated to the same temperature as the retort, (476°C.) shortly after the charge is introduced, and should then be discharged in the body of and fall to 518° F. (287° C.) towards the end of the coal, so as not only to hurry the gas out of the charge. It is evident from this that in the retort, but also out of the coke. To do
this in a practical way so as not to interfere which I have made to him from time to time, with the charging and drawing of the retort is, has perfected an apparatus which should be of I admit, an engineering difficulty. But I think the greatest possible value where the gas if the value of the process was realised, it supply is only of moderate dimensions. would soon be found possible with horizontal | At the present time the recovery of benzol retorts to have the water gas tube, perforated from the coke ovens on the Continent has so at intervals, fixed on the bottom of the retort, | increased the output of that material that tar, and to slide in the charge of coal in a sheet | which used to be the only practical source iron tray loosely fitting the retort, and with a from which it could be obtained, has fallen in perforated and recessed ridge in its lower price until many works would be glad to disportion, which would slide over the water gas pose of all they produce at id. per gallon. supply pipe, whilst the coke would be with Indeed in many cases it is being used as a drawn in the tray when carbonisation was com fuel in the works, and the only way in which pleted, and a fresh tray slid in to take its the price of small quantities of tar can be kept place. In this way the water gas would be | up for special purposes is by reducing as far heated in the pipe, and would pass through as possible the amount for sale. the charge, washing out the escaping gas, The lines on which Mr. Tully has been and giving a further gain. I fear, however, that working have been to take my idea of decomthe water gas itself would, under these condi- posing hydrocarbons, such as heavy oils, in the tions, attack an iron tube, and that a porcelain fierce heat of the fuel of the water gas geneor fire-clay tube will have to be used.
rator itself instead of in cracking chambers, as The process has been tried at Remscheid in is usually done in making carburetted water Germany, and has given results of the same l gas, a process which demands a not too heavy character as those recorded here, whilst stopped grade of oil, and adapt it to the decomposition ascension pipes, which were a constant trouble of tar, so regulating the temperature and the with the class of coal used there, have been 'l volume of tar that the latter is completely reduced to one-third the previous number. I decomposed to carbon, methane, and hydrogen,
There is one point which must be clearly together with small traces of more valuable borne in mind by the gas manager in con illuminating hydrocarbons, and then to filter sidering the economic use of water gas in the off the finely divided carbon produced by dilution of coal gas and the distillation of coal, passage through the coke which is afterwards and that is that the output of the works must to feed the generator. be large enough to keep the water gas The apparatus which he has designed for generator continuously working, as it is only this purpose consists of an iron shell lined under these conditions that the expenses can with fire brick, and provided at the bottom be reduced to a minimum. While it is with clinkering doors. The fuel used in it is perfectly possible to make water gas by the under ordinary circumstances coke, although Dellwik process at a little over 3d. a thousand | of course anthracite or even a certain proporwhen the plant is being worked to its full tion of bituminous coal mixed with coke may capacity, the price will naturally increase occasionally be employed. The fuel after where the size of the works only demands its ignition is raised to incandescence by air being used for a few hours a day.
blasts from jets arranged close to the bottom In large works blue water gas will, in the of the generator. These air injectors carry in future, be an absolute necessity, but in the their interior the 'steam pipes so that when the hundreds of small works that supply our necessary degree of incandescence has been country towns the benefits to be derived from reached, steam can be directed on the hottest its use are minimised to an almost vanishing part of the fuel. In the generator lining about point by the extra cost of production of a midway is a flue provided with openings into comparatively small quantity of gas. I have, the generator : the flue passes entirely round during the last ten years, given a large amount the generator and has its exit into a stack pipe of time to the question of how best to supply closed at the top by a snift valve. The small works with an ally which shall prove of top of the generator has another exit as much value to them as the Dellwik plant will leading into the upper part of the stack to their larger brethren.
pipe. In this way during the blow the Mr. Tully, of Sligo, some two or three years products of combustion are led away through ago, had a long conversation with me on the the openings into the flue, ensuring a bed of subject, and acting upon the suggestions incandescent fuel of constant height, and at the same time, when steam is turned on, the using up the surplus tar and coke in a small resulting gases can be drawn off through either works would be a valuable adjunct. of the exits. Between the flue and the floor - From this, rapid review of the processes of the generator is a constriction, in the space which are available for increasing the volume below which are arranged the injectors, by of gas obtainable from coal, so as most ecomeans of which the tar is driven in by steam nomically to obtain a large volume of a good pressure.
quality heating gas, and, at the same time, to In actual working the fuel is first raised to l utilise to the full the illuminating value of such incandescence by the air blasts in the lower hydrocarbons as can be obtained from coal, it part of the generator, and the products, con is clear that considerable economies can be sisting of little else but carbon dioxide and effected. In a large works where the blue nitrogen, escape into the air through the flue, water gas could be made at 4 d. or sd. a thouthe snift valve being left open. When the sand cubic feet, it would be possible to put a desired temperature has been attained the 14 candle gas with a calorific value of 500 snift valve is closed, and tar or other heavy B.T.U.'s, or a little over, into the holder, at a hydrocarbons are injected by steam into the cost of not much more than 9d. per thousand, annular space below the constriction. · Rising | as against is. per thousand, which we may through the incandescent fuel both the hydro- take it now costs in large works to make a carbon and the steam are decomposed, the 16 candle power gas in the holder, so that an .former into soot and gaseous products, whilst economy of about 24d. per thousand would be the latter yields water gas. During this time arrived at in this way. But whilst strongly some steam is injected through the pipes in urging the importance of reducing the sale the interior of the air jets, by which means the price of the gas to the consumer to the clinker is broken up and more water gas lowest possible point, it cannot be too formed.
strongly insisted upon that the main The mixed gases then pass upwards with cost of the gas is not to be found in the the finely divided carbon from the decomposi retort house, and that therefore the economy tion, and this latter is removed by passing to be effected can only be limited. The through the fuel in the upper part of the chief items which swell the cost of the generator, and, being brought down as the red coal gas to the consumer are charges on hot fuel sinks, it reaches the zone of action the enormous amount of capital sunk in mains where it at once is utilised for decomposing and plant and the distributing charges, which the steam before the larger masses of fuel are cannot be avoided. acted on, on account of its : finely divided | In considering the question of the illuminatcondition.
ing value of the gas and its calorific value it The gases, consisting of a mixture of must be apparent to every one who has studied hydrogen, methane, and carbon monoxide, pass the question that no definite relation can exist away through the stack pipe by a cross pipe, between them. You may take a dozen samples which is fitted with a valve, by which it is of illuminating gas of the same candle power, closed during the blow.
each of which will differ from the others in its The results obtained are that for a consump composition, and as the calorific value is entirely tion of 28 lbs. of tar and 20 lbs. of coke, 1,000 dependent on the composition, you will often cubic feet of a 10 to 12 candle gas can be find two 16 candle gases varying in calorific obtained, having the composition :
value to a greater extent than between a 16
and a 15 candle power gas more nearly equal Hydrogen................ 04:4
in composition. (See Table, p. 125.) Methane ................ 12.0
One of the most important points that has Unsaturated hydro-carbons. 3.0 Carbon monoxide ..........
to be definitely settled, is the method which
150 Nitrogen and carbon dioxide 5.6
shall be adopted in testing the illuminating
value of low grade gas, i.e., gas having an Calorific value............ 400 B.T.U.'s.
illuminating value of from 15 to 10 candles.
The Gas Referees have provided a well nigb The small coke consumption due to the bulk of perfect photometric method for testing gas of the water gas being made from the carbon of an illuminating value of 16 candles, and one the tar, reduces the price of the gas, and Mr. which gives satisfaction alike to the gas comTully estimates that it costs 6d. per 1,000 cubic panies and the authorities whose duty it is to feet. It is quite clear that such an apparatus see that the gas companies fulfil their Parlia