Patent GB-727060-A (GB)
Title: Improvements in or relating to safety systems for carbon black plants
IPC: C09C1/50
Filed: 1953-08-14
Abstract: <PICT:0727060/III/1> In a carbon black plant in which fuel gas is burned with air in a reactor and the effluent gas and reaction products are passed through a header to a precipitator unit having a damper in its outlet, a safety system comprising pneumatic control and co-operating pressure responsive elements is provided, adapted to maintain a predetermined relationship between the gas supply pressure and the air supply pressure to the reactor when the air supply pressure is within a marginal operating range; to stop the gas supply to the reactor when the air supply pressure falls below the operating range; to close off air supply to the reactor at a point immediately upstream of the reactor when the air supply pressure falls below the operating range; and to operate the damper in the precipitator outlet in response to a drop in pressure below a predetermined value in the header conveying the reaction products from the reactor to the precipitator unit.  In addition the pneumatic control may be adapted to admit purge gas to the precipitator unit when the air pressure falls and to cut off air supply downstream of an electrically-operated air supply blower in the event of power failure.  In the drawings a carbon black furnace 10 (see Specification 711,816) is fed with fuel gas from line 12, air from line 11, and a vaporized hydrocarbon such as heavy gas oil from tank 13 through preheater 9.  The effluent gases pass through line 18 to a precipitator 19 having a damper 21 at its outlet.  Air is supplied by pump 42 driven by motor 43 and controlled by switch 45.  When the air supply pressure drops below a critical value a pneumatic motor operated valve 54 is closed, thus shutting off the air supply.  The valve 54 is connected by line 55 to an independent instrument air source 47 by way of a pressure regulator 56 and a three-way bleed valve 59 controlled by pressure controller 60 in turn actuated by air pressure in line 61 from air source pipe 11, so that on air supply pressure dropping, air is bled from valve 59 which opens under the action of pressure controller 60, and valve 54 closes.  Line 61 also transmits input air pressure to a pressure controller 63, the latter controlling fuel gas input line 12.  A pressure responsive bleed valve 67 is incorporated in line 65, leading from pressure controller 60 to a shut-off valve 64 in fuel line 12, so that when pressure in line 65 drops under the action of pressure controller 63 through a decrease in input air pressure in 11, the valve 67 opens thereby closing valve 64 in the fuel line 12 rapidly.  Pressure controller 63 also supplies air to pressure controller 68, which through valve 70 maintains constant a desired pressure ratio between input air and input fuel gas and thus simultaneously through line 71 controls the fuel supply to preheaters such as 9.  A pneumatically-operated vent 73 is also provided in line 12, which vents fuel gas in response to pressure drop in line 55 in turn controlled by pressure controller 60 by input air pressure in 11. A line 26 leaves header 18 from the furnace to pressure controller 25, whereby the pressure in header 18 through pneumatic motor 28 and the illustrated linkage controls the damper 21 by cables 36. Controller 25 serves, by varying the position of the damper 21, to maintain a constant superatmospheric pressure in the reactor.  A line 38 supplying purge gas to the precipitator 19 is also responsive to input air pressure through pressure controller 40, whereby on input air pressure drop, purge gas is fed to the precipitator by valve 39 to maintain superatmospheric pressure therein.  If the current to motor 43 driving blower 42 fails, valve 46 in air supply line 11 is immediately closed by fall in pressure normally maintained thereto through line 49 from instrument air source 47, by operating bleed valve 50 in turn controlled by solenoid 51 connected to the motor terminals or alternatively to the power supply, the valve 46 in the latter case closing only on power failure.  Valves 46, 54 and 64 must all be manually reset after shut-down.