(459g) Design Development of a Novel Sour Water Stripper

justify;line-height:normal">With an increasing focus on energy
performance improvements and strict environmental laws, there is a need to
recycle water resources and reuse them in the industry. Refineries consumes
huge amounts of water which offer an opportunity to reprocess it in an
efficient manner. This study focusses on the design and simulation of sour
water stripping (SWS) unit in the refinery setup for the reuse of sour water.
The stripper removes the H₂S and NH₃ content from the
sour water making it recyclable for various processes. In this study, process
simulation has been performed to analyze the energy saving and cost reducing
prospects in the sour water stripping unit. First, a base case design has been
simulated using a reference sour water stripping unit data. The developed model
is validated against the plant data in order to ensure
the model validity. Various alternative designs have been developed to seek
process improvements either by improving the energy efficiency or by reducing
the sour water stripping unit cost. All the process designs were compared in
terms of energy requirement and economics while maintaining the stripped water
purity of 10 ppm H₂S and 100 ppm NH₃ content.

text-align:justify;line-height:normal"> font-family:" times new roman>A
novel design has been proposed in this study that can significantly reduce the
energy requirement compared to the conventional designs. The proposed design
employs mechanical work using a compressor instead of hot and cold utilities.
In this design, the stripped water stream leaving at the bottom of the column
is flashed to a reduced pressure, whereby, some amount
of vapors are generated. The produced vapors leave at the top of the flash drum
and are fed to the two-stage compression train. A compression ratio of three is
assumed in each compressor stage with an inter-cooler. The compressed vapor
stream at 2.1 bar and 240.7 °C then heats up the incoming feed stream and is
fed to the bottom of the column at 121.7 °C.

line-height:107%;font-family:" times new roman>The results of this study provide a meaningful analysis in
terms of energy and economic considerations to improve the performance of the
sour water units in the refineries. The
results show that the proposed vapor recompression design can reduce the hot
and cold utilities requirement by 90 % and 22 % respectively compared to the
base case design. Despite the fact that vapor
compression design requires higher initial capital investment because of
expensive compressors, the economic analysis shows that over the 25 years plant
life, the operating energy savings are substantial which makes vapor
compression design more economical. The results reveal that the vapor
compression design requires 53 % less operational energy compared to the base
case design which translates into the annual operating cost savings of more
than 60 %. This results in total annual cost of M$ 3.09 for the vapor
compression design compared to the M$ 6.49 for the base case design.

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Figure 1: Process flow scheme for the proposed
vapor compression design