Pneumatic transport of granular materials with a stagnated dense bed in pipelines of complex configuration

Abstract

In pneumat ic transport by a s t agna ted dense bed (SDB), the specific air f low rate is decreased, the solut ion to the p rob lem of removing dust f rom used air is s ignif icant ly s implif ied, and the granulometr ic compos i t ion o f the solid phase changes very little due to breakdown of the granules [1]. These advantages caused by the use o f low gas and t ransported material f low rates are responsible for its promise. We prev ious ly [ 1] revealed the industr ial possibi l i t ies o f using vertical SDB pneumatic transport. However , in the condi t ions of operating plants, the layouts of pneumatic t ransport lines are frequently a complex combina t ion of vert ical , horizontal , and curved sec t ions . Judging by the charac ter i s t ics descr ibed in the literature, the phys ica l condit ions of vert ical and horizontal pneumat ic transport d i f f e r significantly. For ver t ical SDB pneumatic t ranspor t , the condit ions [ 1] for stable, s teady-s ta te transport are de te rmined and the dependences are obtained for def in ing the basic pa rame te r s of the process; such data do not exist for SDB pneumatic t ransport in pipelines of c o m p l e x configurat ion. We de termined the design and process parameters of SDB pneumatic t ransport of granular mater ia ls in compl ica ted layouts. The studies were conducted on the spec ia l ly designed exper imenta l setup whose d iagram is shown in Fig. 1. Compres sed air from two mode l O-38B compressors enters receiver 12 and goes through cyl inder 13 for drying to feeder 2. At low pressure, the compressed gas is f i l tered through the bed of granular material in the feeder and pass ing into its pores a long the transmission p ipe l ine , is removed from the installation without mo v in g the material . The gas f low rate in the p ipe l ine increases with an increase in the pressure of the ~,,as 9 in the feeder, and at the end of the pipeline, removable thro t t l ing orifices having di f ferent internal d iameters are used as the regula t ing instrument . In upper hopper 9, the two-phase s t ream is separa ted into the individual components : gas is removed into the atmosphere through ro tameters 11, passing through a cloth filter; the granular material is sent through dis t r ibutor 6 to intermediate hopper 5. In s tudying vertical SDB pneuma t i c transport, it was found that al tering the level of the material in the feeder within certain limits does not a f fec t the transport pa rame te r s , so that no addit ional measures were inst i tuted to ensure a constant level of granular mater ia l in the feeder. In opera t ion of this instal lat ion, the level of the mater ia l in the feeder gradual ly decreases and accord ing to [1], at some t ime becomes lower than the critical value. For this reason, the pressure loss of the entire sec t ion decreases sharply, the steady state o f the process is per turbed, mater ia l is abrupt ly discharged from the p ipe l ine , and the gas f low rate increases s t rongly. A series of measures was inst i tuted to prevent these condi t ions. The intermediate hopper was equipped with a leve l -gauge glass with control marks . A certain amoun t of granular mater ia l is loaded into it before the unit is turned on, entering the feeder when cock 4 is opened. Since the t ransport system is closed, the rise in the level of granular material in the in te rmedia te hopper is con t ro l led during operat ion of the unit. The level of the material in this hopper approaching the control mark is the signal to totally empty the