Thermal calculation of the radiation chamber of a hydrocarbon pyrolysis furnace with a non-symmetric arrangement wall-mounted burners

Abstract

RELEVANCE. The possibility of predicting the operating conditions of individual elements of high-temperature  technological  units  of  petrochemical  industries  even  at  the  design  or  modernization stage  is  relevant  for  many  reasons.  THE  PURPOSE.  Carrying  out  numerical  studies  of  thermal parameters and features of the turbulent movement of flue gases in the radiative part of the hydrocarbon pyrolysis furnace with a central arrangement of coils with an asymmetric arrangement of burners of low thermal  power  on  the  side  lined  walls  and  on the  vault of  the  chamber. Such  furnaces  are  used  to produce  lower  olefins,  which  are  the  primary  products  for  the  production of  synthetic  resins, rubbers,  plastics  and  fibers.  METHODS.  In  the  radiant  chamber  of  the  furnace,  interrelated processes  of  combustion  of  gaseous  fuel,  turbulent  flow  of  combustion  products,  radiant-convective heat exchange and cracking reactions of hydrocarbons in tubular coils occur with the  formation  of  a  mixture  of  light  hydrocarbons rich  in  olefins. The  formation  of  pyrolysis products of hydrocarbons becomes essential when the temperature of the vapor-gas mixture in tubular reactors is within 800-855  oC in the presence of dilution steam.. The heat required for this  will  be  obtained mainly  due  to  the  thermal  radiation  of  the  combustion  products  and  the hot  lined  surfaces  of  the  radiation  chamber.  The  physical  processes  taking  place  in  the combustion  chamber  are  modeled  by  two-dimensional  equations  of  the  model  gorenje hydrocarbons in the air, energy transfer by radiation and equations of motion. The package of applied programs is used, which is based on the numerical solution of the mentioned system of transfer equations. As a result of numerical studies, the velocity and temperature fields of flue gases  formed  during  the  combustion  of  a  fuel  gas  mixture  in  the  furnace  chamber  of  a  tube furnace  were  constructed.  In his  work,  it  is  assumed  that  on  one  side  wall  of  the  radiation chamber, wall burners in the amount of 64 pieces are placed in eight horizontal rows, and on the  other  wall  of  the  chamber,  the  same  burners  are  installed  in  seven  tiers  and  one  row  of burners  on  the  vault of  the  chamber.  The  combustion products  emanating  from  these burners form  complex  velocity  and  temperature  fields  in  the  volume  in  both  halves  of  the  radiation chamber. RESULTS.  As  a  result  of  numerical  calculations,  the  fields  of  temperature  and  flue gas velocities in both parts of the radiation chamber are constructed. The temperatures of the inner  surfaces  of  the  lining  walls  are  calculated.  The  distributions  of  the  surface  densities  of radiant  heat  fluxes  to  the  reaction  pipes  along  the  height  of  the  pyrolysis  furnace  of  the propane-butane  fraction  are  determined.  Comparisons  of  some  of  the  results  obtained  were carried out for cases when all burners are installed only on the side walls of the chamber and with  the  above  arrangement  of  burners. CONCLUSION.  Calculations  show  that  the  use  of  a large  number  of  low-power  wall  burners  leads  to  the  emergence  of  complex  velocity  and temperature fields in the radiation chambers of tubular furnaces. At the same time, the spread of temperature values in the volume of the furnace chamber is much smaller than for the case when  all  burners  of  higher  power  are  installed  only  on the  vault  and  on  the  hearth  of  the furnace. By changing the location of the tiers of burners, it is possible to achieve a relatively uniform supply of heat to the heated product along the length of the pyro coil.