Patent GB-780273-A (GB)
Title: Method for the operation of a boiler and apparatus therefor
IPC: F22B1/26
Filed: 1955-02-04
Abstract: 780,273. Boiler furnaces. OXY-CATALYST, Inc. Feb. 4, 1955 [Feb. 10, 1954], No. 3382/55. Class 51 (1). Auxiliary fuel, liquid, gaseous or pulverized, added to the hot gas stream of a boiler at a point within the heat-exchange system thereof, is catalytically oxidized at a location downstream from the point. The boiler shown, comprising gas passes I, II, III, and boiler tubes T, is fired by a line of burners B to which primary air is inspirated through an inlet 11 and secondary air is supplied through openings 13. Auxiliary fuel is supplied at the end of pass I through a distributing network having a conduit 16 feeding perforated conduits 17. A bed of oxidation catalyst C is disposed at the beginning of pass II. This bed comprises a plurality of units 19, Fig. 6, which are laid upon the boiler tubes. Each unit comprises porcelain end-plates 21 supporting between them porcelain rods 22. These units are described in Specification 697,551, [Group III]. The rods 22 are coated with a thin film of catalytic alumina. Suitable catalysts are described in Specification 690,825, [Group III]. The assembly of the catalytic bed C is described in U.S.A. Specification 2,718,460. Liquid, gaseous or solid fuel may be utilized in the boiler. When solid fuel is fired, provision must be made to protect the catalyst from any fly-ash. The fuel must be burnt in an excess of air such that the gas stream at the auxiliary fuel introduction point contains combustion products and free oxygen. The amount of free oxygen must, however, be such that it is impossible to form a flammable mixture with the auxiliary fuel added irrespective of the proportion of the added fuel. Preferably the amount of added fuel is such that the fuel concentration is below the lower limit of flammability of that particular fuel in air. If desired, additional oxygen-in amount limited to avoid an inflammable mixture-may be added to the boiler gas stream. Such oxygen may be admitted by adding air or an air and combustion gas mixture to the auxiliary fuel. This additional oxygen may be necessary in boilers where the proceedure of catalytically oxidizing added fuel is repeated a number of times. Precautions should be taken to ensure the supply of auxiliary fuel only when the boiler is operating normally. The auxiliary fuel must be shut off when the burners fail or when the gas stream temperature drops below the minimum activation temperature of the catalyst. Fig. 7 shows a system for automatically effecting this shut-off. The fuel supply to burners B is through a pipe 10 and is controlled by a valve 28 biased by a solenoid 29 in a normally closed position. The branch line 15 supplies fuel to the auxiliary distributing network through manually-operated valve 32, motor-operated valve 33, solenoid 36 biased in closed position valve 34 and motor-operated valve 35. Solenoids 29, 36 controlling respective valves 28, 34, are connected in parallel in the main boiler control system circuit 30, 31, and operate so that all fuel is cut off simultaneously. Switches 39 and 42 are placed in the circuit of solenoid 36, the switch 39 remaining open as long as the temperature of the gas stream in the vicinity of the auxiliary distributing network is below the minimum catalyst activation temperature. Thermocouples placed at the end of pass I and connected to the switch 39 by line 40 actuate the switch. Switch 42 remains open as long as a continuous combustible gas analyzer located downstream from the catalytic bed shows the concentration of combustibles in the gas exceeding a predetermined maximum. Known means including a line 43 is used to actuate switch 42. The valve 35 is a flow controller for controlling the flow of auxiliary fuel in accordance with the gas temperature at the end of pass II. Thermocouples disposed at the end of this pass and connected to the valve controlled by line 41 measure the gas temperature at this point and actuate the valve accordingly.