Everything You Need to Know About Marine Fuels - Martin's Marine ...

10. Hydrotreating
A hydrotreating process is, as the name indicates,
a process, which uses hydrogen to remove impurities
from product streams, and replaces them with
hydrogen. Hydrotreating is generally used to
remove sulphur (re very low sulphur limits in the
specifications of gasoline and gasoil) and is then
called hydro-desulphurization. It is a catalytic
process. The process is generally used on kerosene
and gasoil fractions. Residual hydro-desulphurization
is an existing process, and is in theory feasible, but
the economics are not favorable.
11. Merox
A merox unit is used on naphtha and kerosene
streams. It is a catalytic process which is not
intended to remove the sulphur from the stream,
but to convert mercaptan sulphur type molecules
(corrosive, and with a very obnoxious smell) into
disulphide type molecules.
12. Sulphur recovery
As a result of the removal of sulphur from the
refinery streams by hydrotreating, the generation of
hydrogen sulphide during cracking and coking,
refinery gases contain a very high concentration of
hydrogen sulphide. The simple solution to eliminate
the hydrogen sulphide (extremely toxic) is to burn it,
but this then generates SO2, which contributes to
acidification problems. In order to safeguard the
environment, the hydrogen sulphide is converted in
refineries to elemental sulphur. This is typically
accomplished by extracting the hydrogen sulphide
from the refinery gas by a chemical solvent, e.g. an
aqueous amine solution. The rich solution is then
preheated and stripped by steam. The Claus process
consists of the partial combustion of the hydrogen
sulphide rich gas stream (sufficient air is introduced
to combust 1/ 3 of the H2S to SO2). This SO2 then reacts
(under influence of a catalyst) with H2S in the order
of 1 SO2 for 2 H2S, and thus provides elemental
sulphur. The tail gas of the Claus unit is still rich in
SO2, and environmental legislation can require the
further clean-up of this tail gas.
22 Everything you need to know about marine fuels
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