GB680322A - Improvements in or relating to a method of and apparatus for pickling of iron and steel materials - Google Patents

Abstract

<PICT:0680322/III/1> <PICT:0680322/III/2> In a continuous process of pickling iron and steel and regenerating the spent liquor by precipitating ferrous sulphate, the liquor, both during pickling and regenerating, is maintained at a temperature between 180 DEG and 220 DEG F, the ferrous sulphate being thus precipitated as the monohydrate. Steel strip passes through pickling tanks 10...13, concurrently with pickling acid, the latter being withdrawn from the tank 13 by a pump 16 whence it passes to regenerating tanks comprising a mixing tank 21 where fresh acid is added (at 22), an evaporating tank 23 to which heat is supplied, a settling tank 25 and a dilution tank 30 to which fresh water is supplied at 37. The sulphate slurry <PICT:0680322/III/3> from the tank 25 and any crystals settling in the tanks 21, 23, pass to a filter 32 to which cold water is supplied at 33, the filtered liquor being pumped at 35 to the tank 30. The liquid level is controlled by a float 40 in the tank 30 which also has an overflow 41. A hot air inlet 38 is also provided in the filter 32. In the form shown in Fig. 2, the strip is heated at 57 to 240-250 DEG F before immersion in the first of the pickling tanks 50...53, is sprayed with warm water at 60, as it passes from the first to the second tank, and at 61 and immersed in warm water in a tank 64 after leaving the last pickling tank 53. The spent liquor from the tank 53 passes through the pipe 56 to a surge tank 71, pipes 70 being provided for flushing when necessary, and thence is pumped at 72 to the filter 73 and mixing tank 75 where acid is added from the tank 76 via the pump 77. From the tank 75, the liquor is pumped at 80 to a spray 82 in a stream of hot gas supplied from the furnace 83, an air byepass 87 being provided to regulate the temperature. 85 is a blower supplying the furnace and byepass. The liquor and gases pass to a centrifugal evaporator 90 from which the gases are withdrawn through the pipe 92 and to which additional water may be supplied through the sprays 91. The rinse water from the tanks 62, 64, passes through the pipe 63 and is introduced into the pipe 92 through the spray 93, whence together with the cooled gases and condensate, it passes to the separator 94, gas then passing to a precipitator 96 from which any precipitated acid may be passed to the tank 75 through the pipe 97. The concentrated liquid from the separator 90 passes to a settling tank 101 from which moisture laden air passes through the pipe 103 to the pipe 92 and to which hot gases are supplied from the furnace 83 through the pipe 104; steam coils 107 are also provided in the tank 101. Recirculation of liquor through the spray 82 and tank 101 may be ensured by provision of a pipe 105 and pump 106 discharging into the pipe 81. Supernatant liquid from the tank 101 passes to a dilution tank 111 to which water is supplied from the separator 94 through the pipe 112, the diluted liquor passing through the pipe 54 to the first pickling tank 50. The sulphate precipitated in the tank 101 discharges to a filter 114 where it is washed with cold water and removed to a drier 117. The liquid from the filter 114 passes to a receiver 121 whence it may be pumped at 122 to the dilution tank 111. Vapour from the receiver 121 passes to a condenser 125 and moisture trap 126, condensate from both passing to the pump 122.