The Flow of Gases in Natural Draught Furnaces
JSGT 1941 V25 T021 T085
In the first part of the paper a method of measuring the values of aerodynamic resistances and buoyancies in a glass-tank-furnace system is described, and the results obtained on two such furnaces are discussed. Static pressure measurements were 1nade at various points throughout the system. Temperature determinations were made at various points in the regenerators and uptakes using a suction pyrometer and a rare metal thermocouple. Differential pressure measurements were also obtained vertically across the regenerators. The results are expressed in diagrams showing the pressure variation through the furnace system. From the temperature measurements the stack effects in the regenerators are calculated, and the results compared with the measured pressure differentials. It is shown that the resistance to flow through the regenerators is negligible. In a similar manner the buoyancy effects through the ports are calculated, and by subtraction from the measured pressure values the port resistances were obtained in pressure units. These buoyancies and resistances are indicated on the diagrams mentioned above. In general terms the flow in the furnace system can be described as follows. A current of air and gas is driven by the buoyancy force in the incoming regenerator and the stack, minus that in the outgoing regenerator, against the resistances of the valves and ports. In the case of the gas the flow is also assisted by the positive pressure in the main from the producer. The second part of the paper deals with methods of measuring the distribution of flow within the regenerator and the subdivision of gaseous flow through the four ports leading from the regenerator to the furnace. Before the furnace was heated up various measurements were made, using cold air-flow through suitable openings in the gas and air mains, suction being obtained by a fan. Velocity measurements were made at the ports, within the furnace and at the inlet holes in the mains using Boyle-Alner velometers. In addition, static and differential pressure readings were obtained in the regenerators, uptakes and furnace. These measurements indicated that the air entered the base of the regenerator and most of it continued to flow more than half-way along the base before passing upwards. At the top it tended to flow back in the opposite direction. The relative quantities of air flowing through the four ports were due to a balance between the pressure system in the regenerator produced by the flow described, and the relatively high resistance of the ports causing a large pressure drop through them. Through the regenerator packing, therefore, the flow was a maximum up the end farthest from the inlet. For the hot furnace there were superimposed on the momentum and resistance forces operating in the cold-flow tests the buoyancy forces due to temperature. Three methods were employed to investigate the subdivision of the flow in regenerators and ports for the hot furnace:
(a) Differential pressure measurements in the regenerators.
(b) Temperature measurements in the regenerators and uptakes.
(c) Differential pressure measurements in the gas-ports, using the constrictions in the ports as if they were orifices. Two general principles are derived to enable temperature measurements to be utilised to indicate hot gas-flow in the regenerators, so that methods (a) and (b) were complementary.
From these measurements it is shown that the buoyancy effect has a predominating influence in the regenerators, the momentum being subsidiary and the regenerator resistance negligible. Deductions are made with regard to flow in the gas and air regenerators and uptakes, and for waste gases, and the results are shown diagrammatically. Throughout the paper emphasis is placed on methods, and the results obtained are used mainly to indicate the application of the methods to particular furnaces.
E. J. Gooding, B.SC., Ph.D., and M. W. Thring, B.A.
