| dc.description.abstract | This research work has been carried out to enhance the performance of the membrane
unit of an Autothermal Reforming (ATR) plant. The plant in question refers to the ATR
plant of one of the leading petrochemical industries in South Africa.
The membrane is used to separate hydrogen from a feed of hydrogen-carbon monoxide
mixture (reformed gas) containing gases such as carbon dioxide and small amounts of
methane, nitrogen, oxygen, argon, water, ammonia and hydrogen cyanide. The exit
streams from the membrane are permeate (hydrogen gas) and non-permeate (synthesis
gas, a mixture of hydrogen and carbon monoxide) with trace quantities of the other
aforementioned gases.
This dissertation investigated into the causes of decreasing membrane hydrogen
(permeate) purity and insufficient membrane capacity to achieve the required synthesis
gas (non-permeate) ratio.
High differential pressure across the membranes as well the presence of ammonia and
water in the feed gas to the membrane fibres were some of the causes of the
membranes' low performance. Others include high speed of the membrane feed gas, the
presence of strongly adsorbed gas - methane and insufficient heating of the feed gas by
the preheaters. These led to broken and twisted membrane fibres. As a result, carbon
monoxide and other constituents of the feed slipped into the permeate stream.
From the research work, ways of enhancing the performance of the membrane unit were
proffered. They include integrating a Pressure Swing Adsorption unit (upstream) with the
membrane unit, recycling the permeate back to the feed stream, increasing the
temperature of the feed gas and lowering the differential pressure across the
membranes.
Furthermore, the condensate should be prevented from getting to the membrane fibres
by installing a drying unit, a demister unit or drains in the membrane feed gas header. In
addition, periodic maintenance and backwashing should be carried out on the
membranes.
However, recommendations were made on further study regarding the cost impacts of
implementing the ways of optimizing the membrane unit and simulation of the membrane
unit's operation. The latter was suggested in order to obtain the process variables and
parameters for improving the performance of the unit in question. | |
