Shahid Rabbani, Imen Ben Salem, Humair Nadeem, Mohamed Sassi

Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates

Trapping and suspension of Fine particles inside the Trickle Bed Reactors greatly increase the pressure gradient of the Trickle Bed Reactors. These fine particles may arise from the reaction either in the form of coke, corrosion products or it can be brought as clay and minerals into the reactors. The size of these particles is in the range of 0.7-20 um which is much smaller than the size of the catalysts. These fine particles deposit onto the surface of the catalyst thereby obstructing the flow of the feed by narrowing the space between the catalysts which subsequently results in excessive pressure drop. This excessive pressure drop not only leads to process shutdown but also incurs the cost of catalyst replacement.

In order to study the effect of fine particles on pressure gradient of the TBR, the experiments were performed with different configurations of packed bed with Lite Gas Oil (LGO)-nitrogen system. The experiments were performed in Pilot Plant Reactor with different flow rates in trickle and pulse flow regime. Each set of experiment was performed in different system pressure configurations. The effect of system pressure and flow rates of liquid and gas phase on pressure drop were investigated.

The present study consists of two major parts:

1. Experimental Setup

The Pilot Plant was used to determine the pressure drop across the Trickle Bed Reactor with fine particles brought in by the liquid feed. The pilot plant consisted tubular reactor with length 0.79 m and dia. 0.0183. Due to its similarity to the fines found commercial TBRs, kaolin particle of size 0.7 um were used as fine particles. In order to prevent cake formation, kaolin particles were treated ultrasonically and were stirred continuously in different concentrations with LGO in the feed tank. The desired flow of LGO through the feed tank was pumped to the inlet of the reactor where it mixes with the desired flow of incoming gas and enters the Trickle Bed Reactor.  

In order to record pressure drop across the reactor, two pressure transducers were installed, each at the inlet and the outlet of the reactor. After passing through the reactor, the LGO-nitrogen mixture enters the separator where gas is separated and liquid goes into the collector tank. The amount of liquid that leaves the feed tank and enters the collector tank is measured by placing the tanks at the weighing scale. The pressure of the transducers can be monitored and recorded by the electronic unit associated with the pressure transducers. The system was single pass and LGO obtained at collector end was not recycled to the feed tank to maintain concentration of fine particles in the feed.

2. Comparison of Pressure Drop and Formulation of Correlations

The experiments were performed with and without fine particles in the trickle bed reactors different flow parameters. Velocity of nitrogen and LGO varied from 0.2 m/s to 0.9 m/s and 0.001 m/s to 0.015 m/s respectively. The experiments were performed with two bed configurations: one with glass beads of size 1 mm and other with glass beads of size 2.5 mm. All these parameters were performed at pressure 1 bar, 5 bar and 10 bar. First LGO was fed into the system without any fine particles and with all above flow parameters. Then fine kaolin particles were introduced in LGO feed and pressure drop for each configuration was recorded. Finally flow parameter dependent correlations were formulated to give correlation between these parameters and pressure drop with and without fine particles.