1. Introduction - Firenze University Press

preparatory to further applications, such as biogas upgrading and CO 2 replacement in methane
hydrates.
2. Experimental apparatus
The experimental apparatus consists of a high-pressure cylindrical AISI 304 stainless steel vessel
with internal diameter of 200 mm, an internal length of 800 mm and a total internal volume of 25 l.
It has been designed for pressure values up to 120 bar and provided with a safety valve (Fig. 2).
Fig. 2. Schematic diagram of the experimental apparatus.
To remove reaction heat and to ensure a rather constant internal temperature, the reactor was
provided with copper cooling coils wrapped around the outside of its vessel wall and with an
internal heat exchanger constituted by a finned tube.
The external cooling coils were coated with a thermally insulating paste and a metallic sheet to
minimize thermal dispersion from coils to external environment. The cooling medium is ethylene
glycol – water solution supplied by an air-cooled chiller (GC-LT Eurochiller).
Two side flanges and a bottom- smaller - flange are used to seal the reactor. One side flange has
appropriate ports for access to the interior. The five ports are used for inserting 2 temperature
sensors, for gas inlet and outlet and for pressurized aqueous solution recirculation. The temperature
sensors are mineral insulated type T thermocouples (accuracy class 1) and measure the temperature
inside the vessel in the lower part and in the upper part, near spray nozzles (see Fig. 1). The gas
inlet line is equipped with a pressure sensor, that is a digital piezo-resistive manometer (Kobold -
accuracy class 0.5) and a mass flow meter (Bronkhorst Hi-Tech) to measure flow rate of gas
injected in the reactor. Gas is supplied directly by gas bottles through a pressure-reducing valve,
that provides adjustment of the pressure to the gas injection line. Gas is injected through a manifold
on which five check valves are mounted.
The bottom flange has two ports, the former is used for the initial aqueous solution uploading and
the latter is connected to a pump for recirculation. The pump flows the aqueous solution, previously
uploaded inside the reactor, to the atomizing manifold. Water is atomized by six hydraulic nozzles
mounted on the internal part of the manifold itself. Such devices for water spraying allow control of
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