Patent GB-710731-A (GB)
Title: A process and installation for the boiling or disintegration of straw or similar fibrous material
IPC: D21C7/08
Filed: 1952-01-21
Abstract: In a continuous process for the disintegration or digestion of straw and similar fibrous material by boiling or heating at substantially atmospheric pressure in a liquid containing lime, sodium carbonate or other alkali, a higher velocity is imparted to the digesting liquid in the direction towards the discharge of the boiler than to the fibrous mass.  The boiler may be either horizontal or vertical and may be fitted with mechanical stirring means, or the contents may be stirred by injection of hot air, gas or steam.  The concentration of fibrous material in the boiler may be below 5 per cent.  In order to improve the relative velocity of the liquid to the fibrous mass, part of the boiling liquid may be removed at the discharge end and reintroduced near the supply end, the recirculated liquid being heated directly or indirectly if desired.  Any precipitate produced during the digestion may be withdrawn with the circulating lye and be allowed to settle out by sedimentation before the lye is returned to the boiler.  Fresh p  disintegrating agent may be added if desired to the circulating lye, or it may be mixed with the straw and introduced directly into the boiler.  Lime may be introduced as milk of lime or in the slaked form; if it is to be used as slaked lime the slaking may be carried out in the boiler or in a preheater to conserve the heat evolved.  Using other alkalis the heat of solution may be similarly utilized.  The fibrous mass withdrawn from the boiler may be washed with water sprays, the heated water so obtained being introduced into the boiler.  A mammoth pump is preferred for removing the contents of the <PICT:0710731/IV (a)/1> boiler, but if a helix is used for stirring it may also be used to remove the fibrous mass and lye.  As shown, a vertical boiler 1 provided with a flue 2 for air, gases and steam is provided with one or more inlets 3 above the level of the liquid in the boiler through which inlets chaff, straw and disintegrating agent may be introduced together or separately.  These inlets may be tangential, so that as the raw materials are blown in a cyclone action is set up.  The contents of the boiler are heated to 95 DEG  to 100 DEG C. and stirred by compressed air or steam introduced from pipe 5 through nozzles 6.  Part of the air or steam is introduced through a line 7 into a vertical pipe 8, which thus acts as a mammoth pump.  The boiled mass and lye are discharged from the upper end of the pipe above the level of the liquid in the boiler and pass over a filter 9, the lye returning to the boiler through pipe 11.  This lye may be heated by passage through a pipe 12 surrounded by a jacket 13, heated by steam or other means. Compressed air may also be introduced into the pipe 12 by means of pipe 16 connected to the pressure supply pipe 5, to improve the circulation through the re-heating device.  If desired, a settling basin may be connected to the return pipe 11.  The mass on the filter 9 may be sprayed with water by the device 17, thus recovering the heat in the discharge mass, washing it and also helping to maintain the level of liquid in the boiler.