GB688297A - Improvements in tubular heaters - Google Patents

Abstract

<PICT:0688297/III/1> <PICT:0688297/III/2> <PICT:0688297/III/3> In a heater for carrying out thermal decompositions such as cracking hydrocarbons, comprising a set of vertical tubes or vertical bank of horizontal tubes, heated by a burner, a current of gas which is semi-opaque to heat-rays and which is at a temperature below that of the products of combustion of the burner-flame, is caused to flow in a vertical direction between the burner-flame and the tubes so as to form a continuous gaseous shield therebetween, and the flow of radiant heat to the tubes is regulated by changing the composition, temperature and/or velocity of current of gas at different points in the same horizontal plane, in order to obviate local overheating among the tubes. The shielding gas may consist of the combustion gases formed by auxiliary burners, recirculated flue gas, or steam, with or without the addition of air. The heater shown, Figs. 1 and 2, has vertical tubes 6 arranged in a circle, a main burner 7, and a ring of auxiliary burners 8. Burner 7 is provided with an adjustable fuel-cock 12; and is supplied with primary air through adjustable register 13, while secondary air is aspirated through adjustable register 14. The hydrocarbon to be cracked is introduced into the upper ends of tubes 6, and flows through them in a plurality of parallel streams. The upper part of the heater is in the form of an annular convection section 16, from which the flue gases escape through holes into hood 3 Each auxiliary burner 8, Fig. 3, is provided with an adjustable fuel-cock 10; and primary air is supplied to it through adjustable register 11. Air from inlet 29, or recirculated flue gas from duct 30, or a mixture of air and flue gas, is supplied under pressure by blower 27 into wind-box 9; it is then distributed to the auxiliary burners. The auxiliary burners are adjusted so that a cylinder wall of semi-opaque gas, cooler than the combustion gases from burner 7, is ejected upwards to spread the effect of the radiation from burner 7 and at the same time throw a protective shield between the flame from burner 7 and the tubes 6. The effective height of the shield is controlled by changing the speed of operation of blower 27 or by adjusting damper 28. By the individual adjustment of the several cocks 10, the temperature and composition of the shielding gas is controlled at different circumferential points of the heater in the same horizontal plane. The temperatures of the individual tubes can be determined by thermocouples inserted in wells 32; and the local overheating of certain tubes is prevented by lowering the rate of fuel admission to the corresponding auxiliary burners. The opacity of the shield may be increased by turning down all the burners 8, or by spraying water into the wind-box. When recirculated flue gas of a sufficiently high temperature is used, the operation of burners 8 may be unnecessary. It is possible to supply steam through cocks 10 and thus utilize burners 8 as nozzles instead of burners: the use of wind-box 9 is optional in this case, for sufficient air can be drawn in by injector action of the steam jets. A heater having two vertical banks of horizontal tubes mounted on opposite (plane) walls is also described. This is heated by a row of burners, having straight slits on either side for the introduction of shielding gas. The dehydrogenation of hydrocarbons and of alcohols, and the conversion of ethylene dichloride to vinyl chloride, are also referred to.