GB649735A - Improvements in method and apparatus for preventing combustion and/or corrosion in storage compartments - Google Patents

Abstract

649,735. Carrying bulk cargoes. CARGOCAIRE ENGINEERING CORPORATION. April 6, 1948, No. 9611. [Classes 113 (i) and 113 (ii)] [Also in Group XXI] A method for preventing corrosion within a, storage tank which is initially, at least partially filled with gas such as air and which is sealed against the inlet of air, said method comprising, subjecting gas such as air from the atmosphere or a combustion inhibiting gas, including water vapour, to dehumidification and substituting the dehumidified gas for the air previously in the tank, the dehumidification being to a sufficient degree to reduce the aqueous dewpoint of the gas directed into the tank to a point less than the temperature of the contents of the tank and the tank, the dewpoint being reduced to a value such that within a preselected change in temperature in and of the tank and the relative humidity of the atmosphere therein will not exceed about 50 per cent. In the apparatus for carrying out the method shown in Fig. 2, flue gas from the boiler uptakes 50 is delivered through a conduit 51 to a gascleaning device 52 supplied with sea water coolant from a conduit 53, thence to a separator 56, past an automatic safety valve 58, through an eliminator 62, into a pre-cooler 63 supplied with sea water by conduit 63a, and through a conduit 55 into a desiccant bed type dehumidifier 64. An air inlet 61 is provided for cases where it is desired to use atmospheric air instead of flue gas. The air or gas is admitted through a four-way valve 67 to either of the beds 65 or 66 of the dehumidifier 64, which valve also directs wet exhaust from the bed undergoing reactivation to the atmosphere. While one bed is undergoing an absorption cycle the other is subject to a reactivation cycle, air for which is supplied from a fan 70a, a heater 70b heated by steam from conduit 70c, and four-way valve 68. The valve 68 also directs the dehumidified gas into an after-cooler 69 and conduit 68a from which it is delivered by a blower 72 powered by a motor 72a to a conduit 55a, past a butterfly valve 75, into a conduit 55b and storage tank 73. Air under pressure is communicated by a conduit 33 to control units 78 and 84, which units are responsive to the pressure in the tank 73 for governing the operation of the system. The unit 78 controls an operator 76 for actuating the valve 75 which is normally spring urged to its closed position. After the blower 72 has started the pressure in conduit 55a will rise to a desired minimum and, entering a conduit 79, actuate the control 78 to overcome action of the spring in the operator 76 and open the valve 75 to allow dehumidified gas to flow into the conduit 55b and tank 73. When the pressure in the tank reaches a predetermined maximum, the pressure in a conduit 80 actuates the control 78 to release the spring in operator 76 to close the valve 75, while pressure in a conduit 89 actuates control unit 84 which shuts off air to valve operators 83 and 86 and to a pressure switch 90, thereby cutting off the reactivation steam supply from conduit 70c and the coolant from conduits 53 and 63a, and de-energizing the interconnected blower motor 72a and fan 70a. So long as the pressure in the tank remains between the selected maximum and minimum values the operation of the systems will be suspended. Increased pressure is released through a relief valve 73c. When the pressure in the conduit 55b falls below the lower limit, the switch 90 is closed and the valves 82 and 85 are opened, allowing reactivation steam to flow to the dehumidifier and the coolant to flow to the gas cleaning device 52, the precooler 63, and the after-cooler 69. Also the control circuit of the motor 72a is energized, and after a predetermined time controlled by a delay relay 91, the blower starts. The delay in starting permits a flow of reactivation steam and coolant to the system in advance of the movement of the flue gas therethrough. The system may be controlled in response to temperature changes by connecting a thermostatic control 108 to the relief valve 73c. The thermostatic control may act in combination with a timing device 110 which maintains the valve in an open condition for a predetermined time. Specification 501,269, [Group XXI], is referred to.