Impact of a draft tube on industrial‐scale Fluid Coker™ Spray Jets in fluidized beds

Abstract

In fluidized bed reactors such as Fluid Cokers TM , liquid injections are used. Good contact between liquid and bed solids is required to maximize product yields and quality, and gas-atomized nozzles are, therefore, used in all these processes. The spray nozzle technology is known to affect the liquid distribution. Therefore, the objective of this study is to assess the effect on liquid distribution of a draft tube located downstream of the spray nozzle, inside the fluidized bed. Experiments were conducted at a relevant scale, using a commercial-scale nozzle with a liquid flow rate of about 100 L/min in a large-scale pilot fluid bed containing about 7 tonnes of silica sand. Liquid injected into a fluidized bed either forms liquid-solid agglomerates or free moisture, consisting of individual particles coated with a thin layer of liquid. Several electrodes were used to map the free moisture distribution throughout the bed. A draft tube greatly improves the contact efficiency throughout the bed. It also increases the penetration of the gas-liquid jet formed by spray inside the fluidized bed.

Review of Research Related to Fluid Cokers

“…Enhancing radial mixing can therefore promote interactions between droplets and particles . This can be achieved by confining the jet with a draft tube located downstream of the spray nozzle tip. ,− The distance from the nozzle tip should be such as to allow for sufficient particle entrainment into the jet cavity. ,, The entrainment of particles into the jet can also be improved by modifying the draft tube geometry . Although a draft tube will reduce particle entrainment into the jet, therefore increasing the average liquid content of the wet solids formed at the tip of the jet, its beneficial impact results from the reduction of variations in liquid content within the wet solids; CFD modeling confirmed that a draft tube reduces the amount of the wettest agglomerates, which are the most resistant to breakup in the fluidized bed. , Draft tubes have also been shown to improve the liquid distribution with vertical spray jets…”

Experimental study of liquid vaporization in a fluidized bed

“…[27][28][29][30][31][32][33][34] Agglomeration also occurs, even with spray nozzles that generate tiny droplets, when the bed solids on which the droplets impact are not renewed fast enough; agglomerate formation can be reduced by increasing the fluidization velocity, redirecting gas bubbles to the spray jet cavity, [35] or changing the particle mixing in the spray region. [36][37][38][39][40] Laboratory experiments suggest that the benefits of a better nozzle design and better local bed hydrodynamics complement each other. [41] Finally, agglomeration is more likely to occur when the sprayed liquid wets particles more effectively, that is, when wettability is increased.…”