Patent GB-984563-A (GB)
Title: Improvements in or relating to the supply of heat to materials at high temperatures
Inventor: MACCORMAC MICHAEL
IPC: F22B1/04
Filed: 1960-05-09
Abstract: <PICT:0984563/C4-C5/1> <PICT:0984563/C4-C5/2> <PICT:0984563/C4-C5/3> Heat is supplied to materials at elevated temperatures by preparing a homogeneous mixture of a combustible gas or vapour and such excess of air that it cannot propagate flame, and burning the mixture to supply heat directly to the material.  The invention is applied particularly to gasification processes comprising a make period in which air and steam is passed over a catalyst or contact material, followed by the burning off of carbon from the catalyst &c. in an air stream during a heating period, or to analogous processes in which the catalyst &c. is continuously circulated, additional heat being supplied to the catalyst &c. during the heating period, for example where the use of light oils in the feed stock results in the carbon deposited in the catalyst &c. being insufficient on burning off to maintain it at reaction temperature, by the burning of a weak mixture as above.  The gas or vapour used may be petroleum gas or light distillate, methane in the form of fire-damp or sewage gas, or blast furnace or producer gas of low hydrogen content, or mixtures of such materials.  The air used may be admixed with flue gases, in which case the calorific value of the mixture used which for safety would not otherwise be raised above about 30 B.T.U. per cu. ft. may be increased by enrichments to up to 45 B.T.U. per cu. ft. subject to the oxygen content of the "air" not exceeding 13%. Apparatus for carrying out the process comprises, Fig. 1, a fan 1 delivering air to a main 2 which is connected to a catalyst chamber 3 and has a branch 12 leading to other parts of the plant. The main 2 has a cyclicallyoperated valve 4 linked to a steam valve 6 such that scavenging steam is admitted to the main when valve 4 is closed during the make period. The valve 4 is positioned in Venturi 7, 8, furnished with tubes 9, 10 for measuring gas flow.  The main contains a butterfly valve 11 and an explosion vent 20 closed by metal foil. Fuel, such as primary flash distillate is supplied in advance of the valve 4 through a batswing jet 13 the supply pipe 14 to which contains a main cock 15, a valve 17 openable only when valve 4 is opened and the measuring tubes 9, 10 indicate at least a specified minimum flow, a preheater 16, and a solenoid-controlled by-pass valve 19.  At the delivery end of the main 2 are mounted a pair of Venturi mixing tubes 21 supplied with fuel from piping 32 containing a valve 36 controlled to open and close with the valve 17.  The tubes 21 each have a jet 30 supply of fuel to which from piping 32 passes through a fixed orifice 37 or a solenoid valve-controlled by-pass 38.  The front ends of the tubes 21 are so shaped as to create a vortex in the issuing gas and maintain a stable flame thereat.  The flames are maintained by sparkplugs 34 and the correct functioning of these is monitored by photo-electric cells 43 having relays which close the fuel valves 17, 36 if either spark fails while valve 4 is open.  The presence of flames in the tubes 21 is detected by photo-electric cells 44 relays connected to which operate to close the solenoid-controlled valves 38 in the fuel supply lines to the jets 30. The control devices on the apparatus are so adjusted and interconnected as to provide for enriching the gas flow through the two Venturi tubes 21 to slightly different extents and allowing an increase in the main fuel supply through valve 17 until one of the tubes 21 flames and the other does not; in addition, any excessive increase in the main fuel supply (or decrease in air supply), liable to cause explosion in the main stream, produces flaming of both tubes 21 and, through operation of the cells 44, the cutting down of the main fuel supply or putting the plant on stand-by. Apparatus for indicating the calorific value of the gas in the main 2 comprises sampling tubes 41, 47 connected in advance of the valve 4 and close to the tubes 21 respectively, the tubes leading to identical burners 51, 52 in flues 49, 50, which contain the elements 55, 56 of a thermocouple connected to a voltmeter 60 with a central zero. A positive reading of the voltmeter during the blow period indicates the extend of enrichment of the supplied gas; a negative reading during make indicates leakage of fuel through the valve 17 requiring putting the apparatus on stand-by.  In a modification, usable with flash distillate only, preheated or other fuel is sprayed downwardly on to a steam-heated trough which volatilizes any liquid which does not immediately vaporize the spray nozzle and trough being placed in advance of the main air supply valve and of a constriction having impulse tubes so connected as to allow opening of the fuel valve only when the air flow is above a minimum.  This arrangement is stated to be sufficient safeguard provided the fuel valve is leakproof and is set to provide a blast of no more than 20 B.T.U. per cu. ft. at minimum air supply. In a further modification, Fig. IV, a fan 66 draws flue gases from a stack 63 having an oxygen analyser 62 and air from a duct 75, and delivers the mixed gases, with added fuel, to a catalyst vessel 103 past a main control valve 104 and adjacent detecting and control devices.  The flue gas duct 65 and duct 75 contain interconnected dampers moved by a motor 81 operated by the oxygen analyser 62 to maintain the oxygen content of the blast constant. Fuel is supplied from a tank 70 to jets 113, 1131 in constrictions in the ducts 65, 75, and to one or more auxiliary jets 11311 by a line 114, the main fuel line being controlled by a valve 118 linked to the main gas valve 104 and by a valve 76 held open by a solenoid and shut, by de-energizing the solenoid, by a thermocouple 262 if the temperature at the outlet to the fan exceeds 270 DEG  C. The line 114 is controlled by a hand-adjusted valve 92, a solenoid-operated valve 89 similar to, and for the same purpose as, the valve 76, a main valve 117 interlocked with the main gas valve to open only when the latter is open (with a lag to allow the gas mixture to be stabilized), and a fine control valve 119 controlled by the detector devices. These devices comprise a pair of Venturi tubes 122 mounted side-by-side on a baffle plate 301 and supplied with fuel through lines 131 from a common line having a main valve opened only with the main gas valve. The fuel lines 131 are set to supply slightly different quantities of fuel and have by-pass lines held open by solenoid valves.  Gas passing through the tubes 122 is ignitable by burners 303 and the flames so produced are detected by photo-electric cells 144.  The arrangement is such that any increase in fuel content of the gas stream or any reduction in gas supply, which causes one or both tubes 122 to ignite results, through the detection of flame by the cells 144, in reducing or closing the main fuel supply.  In addition, a photo-electric cell 93 in the main duct 102 and a smoke detector in the stack 63 are arranged to close the valves 76, 89, if flame or smoke respectively are detected in those parts.  Fig. VII shows plant for making town's gas from steam and oil delivered through a duct 93 to a catalyst bed 94 and checker brick packing 95.  If the fuel used is a light distillate too little carbon is deposited on the catalyst during the make to maintain the temperature during the blow phase; apparatus 13 according to the invention may then be used to produce, for blowing, a non-flaming gas-fuel mixture which ignites when its temperature is raised in the packing 95 and burns completely in the catalyst bed 94. A like mixture may be used in place of the air blast in moving bed catalyst gas-forming apparatus in which such a blast is used to circulate the catalyst.