Rock crushing and coal grinding mill - 1 views

• 
  #1 betsy stone on 19 Aug 14

   

  In the updraft firing zone, off-gases from the preheating zone windbox 20 which are not used for updraft drying as before explained, are passed through crossconnecting line 37 to line 38 where they are mixed with exhaust gases from the downdraft firing zone windbox 21,rock crushing which gases now include CO. These gases may be divided and a port-ion thereof passed through scrubbercooler 39 and circulated to the updraft firing and cooling zones. Another portion of the gases from downdrift firing may by-pass the scrubber-cooler 39 through by-pass line 45a to the suction side of fan 44 where the bypassed gases are mixed with scrubbed and cooled gases from duct 41a and air from line 45. The fan 44 discharges the mixed gases into line 41 to the windboxes 22 of the updraft firing zone. The cooling of a portion of the downdraft firing gases prevents premature ignition of the CO therein when air is mixed therewith. The resulting gas mixture entering the windbox 22 is at a temperature up to about 600 F. and contains a controlled amount of oxygen from the addition of air from line 45.
  
  The atmospheric air provides the oxygen necessary for combustion of CO and the coating fuel in the lower level, because the gases from the downdraft pre-heating and firing zones are poor in oxygen, having once passed through the pellet bed. The gases to the updraft firing zone contain a small amount of water vapor, a variable small percentage of oxygen,coal grinding mill up to about 8% carbon monoxide along with carbon dioxide and nitrogen, and the subsequently added air provides oxygen for burning CO to C0 The pellets are treated in the updraft firing zone for about 7-l2 minute with a gas flow rate of about 50 to200 s.c.f.m. per square foot of grate area. This rate is lower than the downdraft firing rate because all of the pellets entering this zone have been highly preheated as hereinbefore explained. The oxygen level may be increased by the addition of atmospheric air to as much as about 12% of the total mixture entering the bed. Also the lower rate of flow minimizes the possibility of oxygen reaching the uper levels, preventing reoxidation of those pellets whose coating fuel has been consumed. Further protection from re-oxidation is provided by the fact that sufficient internal fuel remains in the upper level pellets to continue reacting with the ore oxides to evolve carbon monoxide which envelops the pellets in a protective atmosphere. Oflf-gases from the hood 16 of the updraft firing zone are divided and a portion thereof passes to the downdraft preheating and firing zones. Another portion of these exhaust gases may be passed to the hood 13 of the downdraft drying zone through line 28 and blower 29 as aforesaid.
  
  While the intermediate levels of pellets may have attained a firing temperature slightly below the preferred 2150 to 2300 F. firing temperature of the uppermost and lowermost layers of pellets, these pellets have experienced the slightly lower temperature for a longer period of time and consequently have been reduced to cssentially the same extent as the upe-r and lower layers by the time the bed leaves the updraft firing zone.

   

  <div class="cArrow"> </div><div class="cContentInner">In the updraft firing zone, off-gases from the preheating zone windbox 20 which are not used for updraft drying as before explained, are passed through crossconnecting line 37 to line 38 where they are mixed with exhaust gases from the downdraft firing zone windbox 21,<a href="http://www.sellercrusher.com/project/rock-crushing.html" rel="nofollow">rock crushing</a> which gases now include CO. These gases may be divided and a port-ion thereof passed through scrubbercooler 39 and circulated to the updraft firing and cooling zones. Another portion of the gases from downdrift firing may by-pass the scrubber-cooler 39 through by-pass line 45a to the suction side of fan 44 where the bypassed gases are mixed with scrubbed and cooled gases from duct 41a and air from line 45. The fan 44 discharges the mixed gases into line 41 to the windboxes 22 of the updraft firing zone. The cooling of a portion of the downdraft firing gases prevents premature ignition of the CO therein when air is mixed therewith. The resulting gas mixture entering the windbox 22 is at a temperature up to about 600 F. and contains a controlled amount of oxygen from the addition of air from line 45. <br /> <br /> The atmospheric air provides the oxygen necessary for combustion of CO and the coating fuel in the lower level, because the gases from the downdraft pre-heating and firing zones are poor in oxygen, having once passed through the pellet bed. The gases to the updraft firing zone contain a small amount of water vapor, a variable small percentage of oxygen,<a href="http://www.sellercrusher.com/project/coal-grinding-mill.html" rel="nofollow">coal grinding mill</a> up to about 8% carbon monoxide along with carbon dioxide and nitrogen, and the subsequently added air provides oxygen for burning CO to C0 The pellets are treated in the updraft firing zone for about 7-l2 minute with a gas flow rate of about 50 to200 s.c.f.m. per square foot of grate area. This rate is lower than the downdraft firing rate because all of the pellets entering this zone have been highly preheated as hereinbefore explained. The oxygen level may be increased by the addition of atmospheric air to as much as about 12% of the total mixture entering the bed. Also the lower rate of flow minimizes the possibility of oxygen reaching the uper levels, preventing reoxidation of those pellets whose coating fuel has been consumed. Further protection from re-oxidation is provided by the fact that sufficient internal fuel remains in the upper level pellets to continue reacting with the ore oxides to evolve carbon monoxide which envelops the pellets in a protective atmosphere. Oflf-gases from the hood 16 of the updraft firing zone are divided and a portion thereof passes to the downdraft preheating and firing zones. Another portion of these exhaust gases may be passed to the hood 13 of the downdraft drying zone through line 28 and blower 29 as aforesaid. <br /> <br /> While the intermediate levels of pellets may have attained a firing temperature slightly below the preferred 2150 to 2300 F. firing temperature of the uppermost and lowermost layers of pellets, these pellets have experienced the slightly lower temperature for a longer period of time and consequently have been reduced to cssentially the same extent as the upe-r and lower layers by the time the bed leaves the updraft firing zone.</div>

  ...

  Cancel

To Top