1820.] Accitm on Coal Gas. 293 



Adaanlages of the Method of manufacturing Coal Gas by Means of Horizontal Rotary 



Retorts. 



The advantages of the mode of manufacturing coal gns by means of horizontal 

 rotary retorts, consist in a saving of fuel, time, labour, and macliinery, a gain in the 

 quantity of gas, and increase in the quantity of coke. 



Saving of Fuel. — Tlie ma-s of coal sulyecled to decomposition being reduced front 

 the dimensions require.! in the old plan (by mcanj of cylindrical retorts) to the nar- 

 rowest available limits, there being no oiclward crust of coke to be kept red-hot 

 •for hours to no purpose, while the decompo>ition of the interior mass of coal is 

 going on ; the coke itself being as soon as formeJ removed from the source of heat, 

 and applied, while cooling, to uarm op a fresh supply of coal next in order of 

 becoming decomposed, instead of being discharged in a red-liot stale, into the open 

 air, as requires to be done in the practice before detailed — the whole fuel in short 

 being nece-sarily and beneficially expended — die saving of coal employed as fuel iit 

 this respect, is exactly the gaining of all that is lost on the plan of employing 

 cylindrical or any of the retorts before dc^cribed. Hence one chaldron of coal is 

 decomposed at the gas establishments where horizontal rotary retorts are in action 

 by means of 20 per cent, of fuel, and at some establishments an expert stoker will 

 work the retorts with 15 per cent, of fuel. 



Saving of Time. — The saving of time docs not merely amount to what is conse- 

 quent on the speedier decomposition of the coal, and the saving of that heatwhicli 

 formerly required to he kept up a length of time to no adequate purpose ; it also 

 includes all that is gained inconsequence of the revolving motion to which (he coal 

 is submitted, superseding, as has been already mentioned, the necessity of discharg- 

 ing the coke in an ignited state from the retort. 



When the coke is removed red-hot from the cylindrical, parallelopipedal, semi- 

 cylindrical, or ellipsoidal retorts, the charging of the distillatory vessel with fresli 

 coal pioduces such a sudden reduction of temperature that from three to four hours 

 Inevitably elapse before tlie reloi t is agiin in a full ivorking slate, and to this cir- 

 cumstance the workmen (perhaps very justly) attribute the frequent sudden injury 

 which the distillatory cast-iron vessel sustains. 



Another striking advantage of the new mode of decomposing coal is, that besides 

 saving the time which is wasted in keeping up an intense temperature unnecessarily 

 the revolving apparatus prevents entirely the lo^s occasioned by these three or four 

 hours of unneces.-ary cooling of the distillatory vessel. For each series of trays, 

 or coal-boxes, containing the ignited coke, of the horizontal rotary retort, beinj 

 sufl'ered to cool within tiie reloit before the coke is discharged', and beliig placei 

 in contact with a fresh sujjply of coal, the temperature of the retort is kept up uui- 

 formly the same from beginning to end. 



Saving of Lnbour. — In consequence of the superior facility with which the 

 mode of decomposing coal in thin layers and remuving the coke as fa^t as it Is 

 formed is effected, the saving in point of labour is very great. The charging and 

 discharging of the retort is performed in two minutes. Hence one chalrfron of coal 

 may be decomposed by means of three horizontal rotary retorts, each 12 feet C in- 

 ches in diameter, and with the attendance of two men, in eight hours, and produces 

 from 13,000 to 18,000 cubic feet of gas ; while 10,000 cubic feet of gas can only 

 be obtained from the same quantity of coal in eight hours by means of 20 cylindrical 

 retorts, attended by thesame number of workmen. 



Saving of Machinery. — When we compare the original cost and wear and tear of 

 the horizontal rotary retorts, with the cost anil deterioration of a set of cylindrical, 

 panillelopipedal, ellipsoidal, or semi-cylindrical retorts of an equal power (that is 

 to say, t;> produce a like quantity of gas in a given timej, a difference not less strike 

 ing presents itself in favour of the horizontal retort. 



\Ve have stated already that cylindrical, ellipsoidal, parallelopipedal, or semi-^ 

 cylindrical retorts, when constantly kept in action, and worked to the greatest 

 advantage, cannot be made to last longer than six months. 



Only one-third part of the top and bottom plates of the rotary retort being ex- 

 poseil to the action of heat are alone liable to deterioration. It is only nece ,fary, 

 therefore, that these (larts of the vessel be renewed, while the other parts r.emain 

 uninjured for years. Tlie new top and bottom plates being rivetledlo the old and 

 undecayed part, without deranging the rest, the retort is rendered as goi:,<l r.s new. 

 Guinia the Quanlitijiif Gas.—X large increase; in the quantity of gas ubtained is a 

 natural consequence of the mode in which the dt'COaipobitiun of coal is effected by 

 tBcans of the horizontal rotary retort. 



