Measurement of Liquid and Gas Flow Distribution in A Fixed Bed Reactor Using a Gamma-ray Tomographic System

A Koudil, C Boyer and Y Bentolila

Institut Français du Pétrole. BP 3. 69390 Vernaison. France, abdelhakim.koudil@ifp.fr

ABSTRACT

Fixed bed reactors are extensively used in industrial processes. In the refining industry, the hydrotreating in general and hydrodesulfurization in particular involve two-phase gas-liquid flow through a fixed catalyst bed. Fixed bed reactors can be operated in different flow regimes depending on the process. The trickle flow and the bubbly flow regime are the two main flow regimes that are adopted. An improved design of the internal reactor equipment is therefore part of the solution to enhance reactor performances in term of both conversion and selectivity. For instance, the gas-liquid distributor in the catalytic bed inlet must provide a homogeneous gas-liquid distribution. Improving the contact between the three phases (gas, liquid and catalyst) enhances both the reaction kinetics and the transport phenomena.

In this study, two phase gas-liquid flows through fixed bed columns are investigated inside cold flow mock-ups (400 to 600mm ID) representative of the industrial units at a smaller scale (1/10 - 1/6).

A γ-ray tomographic system has been developed to scan the column at different heights. A back- projection algorithm is used to reconstruct a 2D map of the phase distribution across a reactor section. When a high-density gradient exists a new algebraic algorithm, called ARTUR, is tested.

The γ-ray tomographic system is validated by reconstructing images of phantoms of known attenuation that are introduced into a stainless steel column. The accuracy of the determination of the gas hold-up or liquid retention is found to be satisfactory for the different flow regimes. Finally, different kinds of mal-distribution for the bubbly flow or the trickle flow regimes are investigated.

Keywords Process tomography; reconstruction algorithm; fixed bed; two-phase flow.