December 2 0 , 1934
I N D U S T R I A L
A N D
E N G I N E E R I N G
C H E M I S T R Y
453
European Chemical Industries Adopt New Type Steam Generators C. H. S. TUPHOLME, 6, Hamilton Gardens, London, N, W. 8, England A GREAT D E A L of interest has been aroused b y the efforts of certain European steam-boiler designers to improve the over-all efficiency of the steam-generating process, and the principles of such boilers as the Loeffler and the Benson are already familiar. The demand of t h e chemical and allied plants is, of course, for steam-generating equipment of high efficiency which will, at the minimum cost, supply adequate power and also heat for processing without recourse t o the older methods of low-pressure generation in separate boilers. T w o answers have been forthcoming in the form of the supercharged boiler and the single-tube generator, both of which are being installed in chemical plants, particularly in Germany, Switzerland, and France.
of space, is easily erected, and can be set to work in a very short time. In addition, load variations are so rapidly dealt with by the automatic governing system, that variations from half t o full load and vice versa require only 20 seconds. E v e n when full load is cut out suddenly, no blowing off occurs. The other steam generator is characterized by t h e fact that it consists entirely of a single tube throughout. T h i s tube is led in many coils through the flue gas stream and also lines t h e walls of a combustion chamber. Feedwater is forced in a t one end at a speed sufficiently high to prevent any steam bubbles from a d hering to the surface of the tube walls. In the superheating zone of t h e tube, by increasing the speed t o some 150 f t . per second, the coefficient of heat transmission is considerably increased, so that there is n o danger of the tube being damaged, even when the radiation is intense. Intermediate injection of fresh water at the point of the tube where superheating begins makes it possible t o secure reliable control of the steam temperature at t h e outlet. Feedwater delivery, and also, if required, the intensity of firing, are controlled by hydraulically operated regulation, which is under t h e influence of a thermostat placed at the outlet end of the tube. By these means it is found that, on a boiler of this type, for generating 7.5 tons of steam per hour at 1470 lb. and 400° C. superheat, when suddenly changing the rate of steamraising b y about 50 per cent of the maximum, the fluctuation in temperature at the boiler outlet amounted to 24° C., when reducing t h e rate of steam-raising, and 17° C. when increasing it.
FIGURE 1. STEAM GENERATOR OF THE SUPERCHARGED TYPE
Figure 1 shows a steam generator of the supercharged type, the diagram below representing the temperatures and pressures prevailing in the various sections of the plant. Combustion of the fuel takes place in the combustion chamber, 2, where air and fuel enter through the burner, 1. The air is under a pressure of about 35 lb. per sq. in. absolute, and the fuel at about 300 lb. gage. The gases give up part of their heat content by radiation through the external walls of the evaporator tubes, 3, which line the walls of the combustion chamber. More heat is transmitted b y convection, while the gases pass upward through the internal tubes, 3A, of the evaporators to the flue-gas collecting chamber. The initial temperature of combustion is thus reduced to about 1500° F., while t h e pressure drops to about 33 lb. abs. With this temperature and under this pressure the gases enter the superheater, 5, t o leave it cooled down to 900° F. a t a pressure of about 31 lb. The gas turbine, which is then entered, causes the flue gas temperature to drop to about 700° F . , while the pressure drops t o about 16.5 lb. Finally, the gases escape through the feedwater heater, 7, which forms part of the stack. From thence they continue, through t h e stack, 8, itself, t o t h e atmosphere, where they leave a t 200° F . The water and steam circuit is as follows: The make-up water is fed by t h e feed pump, 12, through the preheater, 7, to the separator, 4, where i t mixes with the evaporating water. This water is kept in continuous circulation by t h e circulating pump, 11, which pumps i t through the combustion chamber, 2, and evaporating tubes, 3, back t o the separator, 4, at the rate of about ten times t h e full load evaporation. The water enters the separator through t h e nozzle, 9, tangentially t o its wall. This nozzle has the smallest sectional area of any tube in the circuit, so that a sufficiently high pressure builds up in the tube before the water enters the nozzle. This pressure is converted into velocity, and the resultant mixture of water and steam spins round on the inside of the cylinder. The water then falls through a small gap in the lower partition of the separator, while the steam is pressed out from t h e center and enters the superheater, 5, where it is superheated up t o the amount required in the turbine. The advantages of this unit are that it requires the minimum
FlGUBE 2 A1, A3, preheater for low-pressure feedwater; B1, inlet of highpressure feedwater; B2, B3, preheating zone; C1, inlet to combustion chamber; C2, outlet from the boiler; D1, D2, oil burners; E, primary air inlet for oil burners and secondary air for coalfiring ; F, coal passage in under-feed stoker;. left and right, of the grate, clinker removers.
The first commercial installation of this type of boiler w a s made in the dyeing and bleaching plant of Charles Weber a t Winterthur (see Figure 2). This generator has a heating surface of 2100 s q . ft., of which 796 sq. ft. are in t h e combustion space. The tube is 4290 ft. long. Steam is raised at 1470 lb. gage and 400° C. and drives a de Laval turbine of 500 kw. T h e boiler also supplies the plant with heating steam for processing, for which purpose the steam is condensed to about 140 lb. in a highpressure condenser and then led back to the s t e a m generator. The heat of condensation is used to evaporate the so-called "cooling water," which is at a pressure of 112 lb., and is preheated in a flue of t h e steam generator.
B R I T I S H G A S FEDERATION F O R M E D T H E GOVERNING BODIES of the Institution of G a s Engineers
(1863), t h e National Gas Council of Great Britain and Ireland (1916), t h e British Commercial Gas Association (1911), and t h e Society o f British Gas Industries (1905), have formed, without alteration of their respective constitutions and work, the British Gas Federation, with the object of furthering the interests and welfare of the gas industry. Lord Macmillan h a s been elected president-
