Page 301 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition
P. 301

Mechanical Separations                                     273

                          r,orn  Dust                               c. Chemical  composition  of  vapor  and  of  dust,
                          Sources                                     including any abrasive, hydroscopic or other char-
                                                                      acteristics.

                                                                  2. Define dust recovery, as percentage below a certain
                                                                    particle size.
                                                                  3. Indicate,  if  known,  preferred  bag  material  that
                                                                     will withstand  environment,  e.g., fibers of  glass,
                                                                     polyester, Teflon@, Nomex@, polypropylene, poly-
                                                                     ethylene, cotton, wool, nylon,  Qrlon@, Dacron@,
                                                                     and Dynel@. The type of weave of fiber should be
                                                                     recommended by  the manufacturer.  The fabrics
                                                                     may  be  felted  or  woven  [4$,48]  in  weaves  of
                                                                     plain,  satin, or twill, and should  be  resistant  to
                                                to  Fan
                                                to   Fan
                                  k                                  any  corrosive  material  in  the  solid  particles  or
                           Cleaning Air  from                        the gas stream.
                             ~  ~  ~  a  s  ~  h  ~  g  ~
                                 th  continuous  reverse  air  cleaning.   4. Manufacturer should recommend
                                                                    a. Bag size, (diameter, length).
                                                                    b. Bag  holding  hardware:  anti-collapse  spreader
                                                                      rings, snap rings, etc.
                                                    Manjrold
                                                                    c. Number  of  baghouse  compartments, number  of
                                                                      bags per compartment.
                                                                    d. Air/gas flow cycle to compartments.
                                                    Secondary
                                                    nozzle          e. Complete  description with  mechanical  details of
                                                                      bag cleaning system (shaking, air-jet, etc.)
                                                    Venturi
                                                                    f. Dust removal arrangement.
                                                    Dust          The  cleaning  system  set  up  for  a  particular  bag
                                                    precipitation
                                                    to hopper   house will determine whether the filtering system oper-
                                                                ates  continuously  or  batch/intermittently.  Some  sys-
                                                                tems operate as a continuous batch, with sections of the
                                                                entering  chambers  being  isolated  by  vahing  to  auto-
          FIL  TERING
          POSITION  L/ POSITION                                 matically switch from one section of  one bag house  to
                                                                another. Thereby, one or more bag groups/sections  fil-
                       ulse-jet cleaning (above) uses a         ter while another one or more are not operating, but
                      controlled blast of compressed air from
                      the primary into the secondary nozzle,    are in the dust removal  cycle. The permeability  of  the
                      which IS magnified by induced air being   fabric  is  generally  stated  as  the  clean  airflow  in  (cu
                      arawn into the bag  The sudden release of
                      air causes the bag to expand fully        ft/min) /square  foot of fabric at a pressure differential
                      throwing the dust from the outer surface   of  0.5 inches water  as  determined  by  the ASTM  stan-
                      Dislodged dust falls into the collection
                      hopper  Pit right, types of  duty cycles   dard D-737 (Frazier Test) [47]. Whereas this test is use-
                                                                ful, several fabrics may have the same permeability yet
                       I            Continuous automafic
                                                                have different  fiber surfaces, and thereby do not per-
                                                                form the same for a specific application.
                                                                  The  felted  fabrics are  generally used  for  maximum
                                                                recovery of product and are used at high face velocity for
                                                                airflow-to-cloth-area ratio. The felt promotes the greatest
                                                                dust collection surface.
                         Time
                              cleaning of  fabric  bags.  By  permission,   Monofilament  fibers  require  special  attention  to
                              cGraw-Hill Go.,  Inc., New York, p. 41.   ensure a uniform open space between the filaments.
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