GB718011A - Improvements in or relating to furnaces and methods of operating the same - Google Patents

Abstract

In the manufacture of nitrogen oxides by passing a mixture of nitrogen and oxygen, e.g. air, through a regenerative pebble bed furnace wherein the gaseous mixture is passed through a first preheating pebble bed, a reaction zone heated to nitrogen fixing temperatures and a second pebble bed to chill and stabilize the nitric oxide formed and in which the direction of flow is periodically reversed, the pebbles are passed periodically or p continuously into and out of the beds during the operation of the furnace. In the preferred apparatus, Fig. 2, the regenerative furnace is a unitary roof structure extending over both beds and the reaction zone. The reaction zone 110 is formed between a roof 114 composed of refractory bricks supported on a tubular water-cooled structure 115 and a base 112 formed of refractory material such as rammed magnesium oxide. On either side of the reaction chamber are pebble-filled spaces 121 and 122. The walls of the pebble chambers are formed by superposed layers 123 of refractory bricks that slant towards the centre of the furnace at the angle of repose of the pebbles and rest on base plates 125 and 126; successive strata of refractory material 123 are separated by metallic baffle plates 152 which terminate flush <PICT:0718011/III/1> <PICT:0718011/III/2> with the inner surface of the chamber 121. The baffle plates may be made of differing material depending on the temperature to be encountered in the zone 121; thus the lower plates 153 may be of stainless steel, the middle ones of a metal alloy and the upper ones are made of an iron free material such as nickel. Pebbles are fed to the two chambers 121, 122 from pebble reservoirs 141, 142 to flow between the edge of the roof 114 and the uppermost refractory stratum of the chamber wall, the pebbles assuming their natural angle of repose as they enter the beds. Pebbles may be withdrawn from the bottom of the chambers by rocking arms 131 and 132. In operation air is supplied alternately through pipes 161 and 162; for example is passes up through the hot chamber 121 and through the reaction zone 110, heated by the injection of fuel from nozzles 160; the nitric oxide formed is stabilized by passing through the bed of pebbles 122 which is cold. When bed 122 becomes hot and 121 becomes cold the direction of the passage of air is reversed. An alternative means of withdrawing pebbles from the bed is shown in Fig. 5 where a sheet 215a is oscillated about a crank 217 whereby quantities of pebbles from bed 211 are brought to the left by the oscillating plate and during the movement to the right of the plate the pebbles withdrawn are forced over the left edge of plate 215a by further pebbles which have by then dropped from chamber 211.