Patent Publication Number: US-4731937-A

Title: Process and apparatus for the dry sluicing of grit, slag or sediments from pressurized systems

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a process and apparatus for the dry sluicing or removal of grit, slag or sediments from pressurized systems. 
     2. Description of the Prior Art 
     Sluicing systems are known in which sediments derived from a gasification process are cooled in a water bath and then removed by means of pressurized sluicing. This and similar processes have the fundamental disadvantage that there are problems to be resolved involving water and sediment management. 
     Further, sluicing systems are known in which fine flue ash is cooled in a convection cooler and then sluiced from the system. 
     This invention provides a dry process for sluicing coarse grit or sediments from gasification processes (for example partial and complete gasification of coal) thereby by-passing the need to resolve the problems associated with known processes. 
     SUMMARY OF THE INVENTION 
     In the process according to the invention sediments which appear in a gasification or other process are cooled indirectly, i.e. through radiation cooling to below their release or fusing point, whereupon, after the main gas stream has been led away, the stream of sediment, now being conveyed by the force of gravity, is deflected at least once and preferably several times from the vertical falling direction to a direction determined by deflection, which increases the residence time, in another cool zone where it is then likewise cooled indirectly, that is, from the outside, but is also simultaneously cooled directly to temperatures below 300° C. by a cold countercurrent gas, whereafter the sediment is sluiced from the system. 
     Cooling of the sediment from a temperature below the release temperature to a temperature allowing for removal of the sediments, i.e. temperatures less than 300° C., therefore results from combined exterior and interior cooling. This is done by increasing the length of the sediment removal route thereby enabling intensive cooling. As a result of the deflection of the sediment off the cooled surfaces, any sediment lumps are simultaneously reduced in size. 
     Direct cooling of the sediments in the initially diagonally and then vertically directed sediment conduit results from blowing a cool countercurrent gas into the lower end of the vertical sediment shaft. The cool gas can be used to cool the outside of the lower part of the sediment shaft by directing the gas such that it first flows around the outside of the lower part of the sediment shaft before it enters the interior of the sediment shaft from below and then leaves the pressure tank with the main gas stream. 
     Sluicing results in a known manner from alternate pressurization and depressurization by means of a sluicing gas. However, the sluicing is advantageously undertaken by retaining fine ash particles at the sediment outlet as well as at the sluicing gas outlet. Retention is advantageously achieved by means of sintered metal filters. 
     The apparatus according to the invention comprises a pressure resistant container with a conically tapering lower region to which is connected an outlet branch; at least the conically tapering lower region is cooled, preferably by means of cooling pipes welded to the part of the outer circumference which is to be cooled, the inside of the outlet branch having a sediment conduit which is cooled on the outside and comprises an upper section, into which the sediments are directed diagonally, and a second vertical sediment shaft to which a first sluicing valve, followed by a sluice as well as an additional sluicing valve, are connected. 
     The upper section of the sediment conduit is so arranged that it is not possible for the sediments to directly enter the vertically directed second section or sediment shaft. This section is only reached by way of opposed conical cooling surfaces. 
     The lower section of the vertical sediment shaft is cooled, in a preferred embodiment, by contact with a cool counter-current gas before the gas enters the sediment shaft from below. To this end, the section of the sediment shaft which is not provided with outer cooling pipes is surrounded by a jacket through which the cool countercurrent gas is passed. 
     Advantageously, all inner surfaces which come into contact with sediment are of a corrosion resistant material and are smoothly finished. 
     Although the sediments are already cooled to temperatures below their release temperature before reaching the conical lower region of the pressure tank, the lower region can also be cooled from the outside to prevent any sediment which is still soft from baking onto the conical lower surface. Cooling pipes are advantageously welded to the outside of the sediment conveyance structures inside the outlet branches of the pressure tank and to at least part of the sediment shaft. 
     A cooling jacket is provided on the lower section of the sediment shaft for additional cooling and cool counter-current gas is fed into it to flow over the outer surface of the sediment shaft before the gas enters the shaft from below. 
     The sluicing equipment which is the final stage in sediment removal, may be equipped with a sintered metal filter, preferably in the form of a ring, on the sediment outlet side as well as the sluice gas outlet side, to prevent the escape of fine sediment particles with the coarse sediments or the sluicing gas. 
     Sluicing is carried out in a known manner by cyclic pressurization and depressurization of the sluice via corresponding valves and conduits. Cool recirculated gas may be used as the principal pressurization gas. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The process and apparatus of the invention are further described with reference to the accompanying process diagram. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Before reaching the conical base A, sediment from a process is cooled to below its release or fusing temperature (less than 900° C.) in a first cooler zone, which is not shown, by indirect heat exchange, preferably by means of radiation coolers. 
     At least part of the outer surface of the lower end of the cone A is cooled and this, in conjunction with the use of a smooth corrosion resistant material, prevents any of the sediments which are still soft from baking onto the inner surface of the conical base. Cooling of cone A is preferably achieved by welding cooling pipes to the outer surface thereof. 
     From the conical base A the sediment stream enters another cooled zone comprising a sediment conduit connected to the outlet branch of the pressure tank connected to the conical base A. The main gas stream is conveyed through the opening B. The sediment conduit comprises an upper section, including two opposed half cones E and F, and a lower vertical sediment shaft G. In falling from the conical base A the heavy sediment particles strike the surface of the cone E. From here they fall onto the diagonal surface F and then slide into the vertical shaft G. Here too, all inner surfaces coming in contact with sediments are smoothly lined. Sediment in the sediment shaft G is cooled, at the base of the shaft, by a cool countercurrent gas which is fed through a conduit H. By routing the countercurrent gas around the outer surface of the base of the shaft G, the gas also cools the inner wall in the lower region of the sediment shaft as well as a first sluicing valve J. Along the route from the conical base A to the lower end of the shaft G, the sediment is cooled to a temperature below 300° C. 
     The geometry of the actual removal apparatus, comprising two superimposed semi-conical conveying shafts E,F and a perpendicular shaft G, ensures that direct entry of sediment into the vertical shaft G is not possible. The diagonally opposed cooling surfaces not only produce an increase in the residence time in the sediment conduit, but the impact of the sediment on the lower cone surfaces results in an automatic reduction in size. 
     The sluicing valve J is connected to a sluice K. A sintered metal ring L is provided at the base in the sediment outlet region of the sluice K. The ring L prevents sediment particles from being carried along when the sluice is depressurized through a valve M. Upon opening a sluice valve N, the sediment falls down, thereby cleaning the sintered metal ring mechanically. The sluice K is pressurized by means of a valve O, so that the pressurizing process automatically cleans the sintered metal ring L. 
     Cold gas from the countercurrent gas supply can be supplied to the sluice K by means of a valve P when, for example, sufficient cooling is not achieved in the sediment shaft G as a result of excessive sedimentation. To this end, a sintered metal ring R is placed at the gas outlet end of the sluice through which cooling gas from the counter-current gas supply can be vented to the main gas stream via a valve S. 
     While the diameter of the sediment conduit reduces from the conical base A to the sediment shaft G, there is no further reduction until the point of extraction to avoid a build-up of sediment as a result of bridging. 
     The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawing, but also encompasses any modifications within the scope of the appended claims.