468 CHAPTER XXIII 



modern practice seeming to be equally divided between the horizontal fire- 

 tube boiler and some form of the water-tube. In some houses two distinct 

 batteries have been installed ; the latter to supply steam at higher pressure 

 to the engines, and the former to give steam at a lower pressure to the 

 heating and evaporating stations. 



It was for long considered a fundamental idea in sugar-house design 

 that a type of boiler of large water capacity should be installed, so as to allow 

 for unequal consumption of steam in the boiling house. This argument 

 has been used to support the fire-tube as opposed to the water-tube boiler. 

 In badly designed or badly operated houses these unequal loads may occur, 

 but rational operation is capable of eliminating them. In addition, water- 

 tube boilers with specially constructed large water spaces are made, and in 

 any case the difference is not large. 



The first cost of the fire-tube boiler is less, but the water-tube being con- 

 structed in larger units decreases the cost of operation, though large units 

 are objectionable when it comes to cutting out a unit for cleaning or washing 

 out. In the writer's opinion economy in steam is not so much a question 

 of the boiler as it is of the furnace, of the firing of the bagasse, and of the 

 intelligence with which the whole factory is operated as a co-ordinated whole. 



The " Boiler Horse Power " required in a Cane Sugar Factory. — Given the 

 number of tons of cane to be ground per hour, the designer of a factory has 

 to determine the " Boiler Horse Power " or square feet of heating surface 

 to be installed in the steam-producing plant. To give a rational answer 

 to this question the designer should be supplied with complete data showing 

 how much steam is intended to be used in the factory in heating, in evapora- 

 tion, and in pipe and cylinder condensation, etc. This will depend on the 

 quantity of mixed juice to be obtained per ton of cane and on the system of 

 heating and evaporation adopted. 



In the beet sugar industry this is a comparatively simple matter, since 

 the rate of operation can be regulated to a uniform daily output, and all the 

 fuel consumed is independent of any supplied as a waste material. 



In the cane sugar industry in many localities it has come to be considered 

 that the bagasse should afford all the fuel necessary, and the operations 

 in the factory are often controlled by the quantity of bagasse, or in other 

 words by the fibre in the cane. This quantity varies between the limits 

 of 10 and 15 per cent., so that between different factories there may be a 

 50 per cent, variation in the quantity of fuel available from the cane. Hence, 

 a ratio of Boiler Horse Power to cane correct for one factory may be quite 

 inadequate for another, if it is only desired to burn a certain quantity of 

 bagasse at its maximum efficiency. It is fortunate, however, that steam- 

 producing plants permit of very considerable elasticity, whilst remaining 

 within reasonable economic limits. For example, in the data of boiler 

 trials collected in this chapter there is very wide variation in the quantity 

 of dry bagasse burnt per sq. ft. of heating surface, and very much less varia- 

 tion in the efficiency. Evidently the greater the heating surface the greater 

 is the opportunity to abstract heat from the hot gases ; but, after the tem- 

 perature of the gases has been reduced to a certain temperature, very large 

 heating surfaces are required to effect any further reduction, and conversely 

 the capacity for producing steam by burning increased quantities of fuel per 

 sq. ft. of heating surface is but little affected. This point has been discussed 

 at length in a previous section. 



