Page 16 - Industrial Plants 2014

Process water overall treatment by aeration in specific tanks; after the secondary
In the gasification section (figure 2), syngas is treatment, water is partially recycled to process and
processed in different units before arriving to the partially discharged in the environment.
CCU, in order to remove unwanted compounds or
matters which are recoverable for further purposes.
In these conditioning units large amount of utilities Wastewater pre-treatment unit
are used. Waste water treatments are necessary to The unit consists mainly in a stripping column
process the water utilities before discharge in order (figure 3) where the water is separated from
to comply with local environmental regulations. ammonia by means of thermal separation. In order
Waste water main source hence are represented by to perform an effective separation, the wastewater
soot water coming from gasification unit. inlet stream is added with soda (NaOH) [1] whose
Soot water from gasification unit first is sent to quantity is regulated by a devoted pump. The
carbon recovery unit were the ashes and carbon stripper thermal balance is guaranteed by a pump
content is abated; after this treatment, a crucial step around where the water exchanges heat with steam
is represented by the heavy metal recovery unit were in a specific reboiler; steam coming from low
all the pollutants are removed and stored as metal pressure network is controlled and adjusted in ratio
cake for disposal. Residual waste water purified with the actual wastewater column inlet. The column
from metals and solids is then sent to the wastewater top stream, rich in ammonia, is successively sent to
pretreatment unit which represents the scope of this other process units, while the bottom stream
application. represents the pre-treated water which is sent to
In this unit water, coming from different processes, sour water treatment unit.
is treated with chemicals and stripped with steam. One of the major challenges in this process is
At the end, treated water is then sent to the related to the effective control of the stripping
secondary water treatment unit external to IGCC column, whose objective is to maintain the value of
Fig. 2 - Gasification plant. the pH and residual ammonia content of the outlet
flow diagram Secondary process is based on biological treatment water within pre-determined ranges. Maintaining at

IndustrIal Plants - May 2014
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