1845.1 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



173 



PURIFICATION OF COAL GAS, AND ITS ADAPTATION 

 TO AGRICULTURE. 



" On the Pitrijication of Cual O'as, ami Ik application of the products, 

 thereby ohlaimd, to Agricultural and otkr purposes." \iy AncmiiAi.i) 

 Angus Choli., Assoc. Inst. C.E.— Paper read at the Inntiiutc of Civil 

 Engineers. 



The proihiction of coal gas is now become of such importance, from 

 the amount of capital employeil in it, and tlie high degree of public 

 utility resulting from the introduction of gas light, that the author 

 conceives it to be his iluty to lay before the Institution, an accoinit of 

 his improvements in the process of purifying and preparing gas for 

 combustion. In London alone, the annual rental paid to the diU'erent 

 Gas Companies, for the supply of coal gas, amounts to about £6011,000, 

 and iSO.OOO tons of coal are annually consumed in its manufacture. 

 As nearly every town of two or three thousand iidiabitants, is now 

 lighted with gas, vast as is the consumption of London, it forms but a 

 small portion of the quantity of coal gas produced in the United 

 Kingdom. The use of gas seems, however, to be capable of much 

 greater extension than it has yet attained, for though almost univer- 

 sally adopted in the lighting of streets, workshops, warehouses, and 

 places of business, it has been only partially introduced into domestic 

 use. The causes of this limitation in the use of gas, are sulficiently 

 obvious; they consist mainly in thi; unpleasant odours and unhealthy 

 eilluvia, supposed to be exhaled in its combustion; nor have the ob- 

 jections maile, on that account, been without foundation; for it is well 

 known to chemists, that notwithstanding all that modern science and 

 invention have hitlierto dune, to purify gas, a considerable portion of 

 ammonia, and its compounds, the origin of the otl'ensive and injurious 

 vapour complained of, still exist in combination with the gas, and 

 compounds of a deleterious character are given olf'during combustion. 



The author's attention has long been directed towards the manufac- 

 ture and purifying of gas, and in the progress of numerous experi- 

 ments, which were continued through several years, he has been for- 

 tunate in the discovery of a very simple process, of entirely freeing 

 coal gas from ammonia, and its various combinations. The gas used 

 for illumination, is carburelted hydrogen, and the object of all gas 

 manufacturers, is to obtain that gas, in the greatest possible state of 

 purity, and at the least comparative expense. The mi-thod of making 

 coal gas is this : coal being placed in retorts, and subjected to a high 

 degree of heat, the carburetteil liydrogen gas is generated, from, 

 whence it passes, by well-known contrivances, into the condensing 

 apparatus; but the carbuietted hydrogen thus generated, contains 

 several gaseous impurities, the most prominent of which are, — 1st, 

 sulphuretted hydrogen; 2d,hydro-sulphuret of ammonia; 3d, cyanuret 

 of ammonia; 4tli, carbonic acid, &c.; all these impurities have, to a 

 great extent, been got rid of in all weU-conducted gasworks. The 

 sulphuretted hydrogen and the carbonic acid, are most eflectively re- 

 moved, by means of dry lime; but to its use (until the application of 

 tills process), insuperable objections existed, and it has therefore been 

 usually abstracted from carburetted hydrogen, by wet lime purifiers. 

 A large portion of the hydro-sulphuret of ammonia, the cyanuret of 

 ammonia, and the carbonic acid, have been thus expelled, with much 

 trouble and inconvenience. Still a very great quantity of ammonia 

 remains unaffected by all the processes used fur purification and 

 passes, as before observi'd, into consumption with the gas itself. The 

 carburetted hydrogen, thus generated, passes, with all the impurities 

 mentioned, into the condensers, where the hydro-sulphuret of am- 

 monia is to some extent removed, by a reduction of the temperature 

 of the gas, and in this way the ordinary ammoniacal liquor of the gas 

 woiks is obtained. That liquor is generally sold to manufacturing 

 chemists, and from it, after saturation with either sulphuric or muria- 

 tic acid, the ordinary ammoniacal salts are produced. From each gal- 

 lon of this liquor about 11 ounces of sulphate of ammonia are pro- 

 duced. 



The author's new process of purification is generally employed, 

 immediately after the gas passes out of the condensers; or it may be 

 applied, when the gas has undergone the usual wet or dry lime puri- 

 fication. The gas is conducted into a circular vessel (Figs. 1 and 2), 

 constructed like those in use for the purpose of washing gas, and lined 

 with lead, that metal not being acted upon by sulphuric acid ; it is 

 divided at the bottom into a number (d' sections (lig. 2,) S inches or 

 10 inches in height, which support a lead plate, covering the whole 

 surface of the vessel, except about 5 inches round the eilge. The 

 vessel is charged, up to the height of the plate, with water, to which 

 oil of vitrol, at the rate of about 2i lb., or thereabouts, of acid, to lnO 

 gallons of water, has been added ; the gas is then passed under the 

 leaden plate, where the divisions, by which it is supported, completely 

 separate the gas, and bring each portion of it into coutact with the 



aci<l solution. The ammonia contained in the gas, combineg chemi- 

 cally with the sulphuric acid, and forms sulphate of ammonia. But 



Fig. 2.-H 



the acid being thus constantly in process of neutralization, the solution 

 would soon lose its power of separating the ammonia from the gas, 

 but for a small reservoir of sulphuric acid, which being carried into 

 the vessel by means ofa]iipe furnished with a stop cock, insures a 

 regular supply of acid. The gas thus freed from ammonia, is carried 

 to the dry lime purifiers, which with this process can always be used. 

 In large works, two vessels of this kind are preferable for passing the 

 gas twice over the weak solution of sulphuric acid, which secures a 

 more absolute certainty of the extraction of all the ammonia, should 

 there have been any accidental or temporary deficiency of acid in one 

 of the vessels. 



Two vessels of 10 feet diameter and 3 feet deep will purify 500,000 

 feet of g IS every 21 hours, and making that quantity, will require to 

 be charged with the acid solution about every two days. In order to 

 [irevent too great a strength of free acid in the vessel, which would 

 precipitate the carbon of the gas, and diminish its illuminating power, 

 the liquor may be tested with the common ammoniacal liquor of the 

 gas-works. When the solution in the vessel has become of the speci- 

 fic gravity of 1170, or thereabouts, as ascertained by the hydrometer, 

 the supply of acid is to be shut off, and the gas is passed through the 

 vessel, until that solution will restore the colour to reddened litmus 

 paper. The liquor thus obtained is evaporated, and produces sulphate 

 of ammonia of remarkable purity, and of such strength, that one gallon 

 produces SO ounces of sulphate of ammonia, instead of the 11 ounces 

 only, which are produced from the ordinary ammoniacal liquor of the 

 gas-works. And this last-mentioned liquor, must first undergo the 

 process of saturation with sulphuric acid before evporation. The 

 same degree of purification of gas from ammonia, may be obtained, by 

 nieans of chloride and sulphate of manganese, or chloride and sulphate 

 of zinc, which salts are afterwards reproduced, to be used again and 

 again in the same process. 



In the ordinary mode of purification, the gas was conveyed directly 

 from the condensers, to t!ie wet lime purifiers; a considerable pres- 

 sure on the retorts, was requisite to force the gas through the fluid 

 lime, and thus a loss of gas ensued, with a larger incrustation of car- 



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