470 CHAPTER XXIII 



100 sq. ft. of heating surface, or per i lb. of bagasse per hour on the basis 

 outliTied above : including the space beneath the boiler as combustion 

 volume, this ratio is roughly halved. The writer believes that the ex- 

 aggerated combustion volumes sometimes found are inefficient, as exposing 

 a large area for radiation and affording opportunity for leakage of cold air. 



Drying of Bagasse. — The earliest proposals to use waste heat for drying 

 bagasse preliminarj^ to its combustion are those of Merrick (U.S. patent 

 3994, 1845) and Crosley (U.K. patent 11158, 1846). These patents claimed 

 the use of endless horizontal metallic belts arranged in a brick chamber, 

 through which the waste flue gases were exhausted to a chimney. This 

 device has become a part of routine practice in Mauritius, where their 

 introduction is due to Eynaud. The general arrangement followed is in- 

 dicated in Fig. 284. In a factory working up 50 tons of cane per hour the 

 secherie was 40 feet long, 7 ft. wide and 30 ft. high. The carriers ran at 7 ft. 

 per minute, the period of exposure being 18 minutes. The bagasse entered 

 with 50 per cent, of water and left with 35 per cent., corresponding to the 

 removal of one half of the water. These secheries are operated in combination 

 with induced drafts ; other arrangements use a vertical shaft, down which 

 the bagasse falls in counter-current relation to the ascending hot gases. 

 This scheme appears in Gros-Desormeaux's patent (1532 of 1882), and again 

 has been experimented with by Kerr and Nadler,^^ ^^g place in the shaft 

 a series of inclined trays. For a mill working up 1,000 tons cane per day, 

 they estimate the total cost erected of the plant to be $15,000- $16,000. 

 A third scheme is the Huillard dryer,^^ based on the beet pulp dryer, and in 

 operation in Egypt. This arrangement consists of a vertical brickwork 

 chamber, down which the bagasse travels in a spiral. A fourth scheme 

 emplo\^s a rotating drum slightly inclined from the horizontal and similar 

 in principle to the sugar dryer described in Chapter XXT. In a series of 

 boiler trials made by Kerr and Nadler with bagasse containing 53-5 per cent, 

 of water, and the same bagasse dried to 45 -4 per cent., the evaporation from 

 and at 212° F. was 1-63, and 2-35 lbs. water per lb. of fuel, or 3-51 and 4-65 

 lbs. per lb. of dry fuel. This result is probably to be correlated with the 

 incomplete combustion that occurs when the water in a bagasse exceeds a 

 certain limit. 



Although computation will show that a very sensible benefit obtains 

 from drying bagasse, the scheme is little used, and the benefits are counter- 

 balanced in other ways. There has to be supplied fan draft, together with 

 the power required to operate the dryer machinery ; some mechanical 

 loss occurs on handling ; and difficulty is experienced in firing the very 

 light material, which has a tendency to be swept through the flues unburnt. 

 Furthermore, in operating a secherie in Mauritius, the writer observed that 

 a little inattention would result in the contents of the secherie igniting, 

 with the loss of fifteen minutes' supply of fuel. 



Value of Bagasse as compared with other Fuels. — The relative value of 

 bagasse, wood and coal is often required, as fuel statistics are generally based 

 on the coal value of the fuel burnt. There is no constant fuel value for either 

 bagasse or coal, and any factor adopted depends on the local conditions ; 

 coal, depending on its quality and the skill used in firing, may give from 7 

 to 12 lbs. of steam per lb. consumed. On an average from 4 to 5 tons of 

 bagasse are equal to a ton of average coal. Woods, weight for weight and 



