Sour Water Stripper
Some contaminated water in the refinery cannot be mixed with other wastewater
such as sour water from distillation reflux drums containing dissolved hydrogen
sulphide, organic sulphur compounds and ammonia, since they are not treatable by
conventional methods. For such cases, the sour water stripper is often required in the
pre-treatment section before discharging sour water to the wastewater plant for
removal of hydrogen sulphide, ammonia, etc. (Speight 2014).
All the preliminary devices should be operated and maintained with care.
Primary Treatment
The main aim of the primary treatment is removal of the suspended solids, organic
matter, oily sludge from wastewater by physical means, usually by gravity separation. This treatment of wastewater uses oil-water separator or screener or skimmer
where oil, water and suspended solids are segregated from each other. Neither
dissolved solids are separated nor oil-water emulsion is broken in this stage. For
separation of colloidal materials, some chemicals are used in primary treatment.
However, the oil in effluent is recovered at this step itself and is recycled
(Patwardhan 2008; Shahryar 2017; Alireza 2014).
In this treatment method, the flow rate of wastewater is reduced sufficiently to
allow suspended solids to settle down and light materials to float at the surface of
water. There are many devices which are used in primary wastewater treatment such
as settling tanks, clarifiers, skimmers, screeners, filters, etc. (International Petroleum
Industry Environmental Conservation Association 2010).
The primary treatment of a petroleum refinery consists mainly of two stages for
the isolation of oil, water and solids (International Petroleum Industry Environmental Conservation Association 2010; Shahryar 2017).
First Stage
Oil-water separation is achieved using American petroleum institute separators,
corrugated plate interceptors or parallel plate interceptors separators or tilted plate
interceptor separators or hydrocyclone separators or buffer or equalization tanks.
Wastewater is allowed to pass very slowly over the separator, so that demulsified oil
floats on the surface and suspended solids settle down at bottom of the separator due
to gravity. The free oil is skimmed off, while the settled solids are removed using
scrapers or flights to a sludge-collecting hopper. The wastewater flows down the
separator towards the outlet through a diffusion barrier. To prevent the oil from
flowing to the outlet, baffle plates are employed. However, the American petroleum
institute separator has certain limitations. It cannot separate the dissolved or emulsified oil. It can stabilize emulsions at high pH. So, spent caustic must be added to
reduce pH of the American petroleum institute separator. In wastewater treatment for
252
M. Samanta and D. Mitra
Some contaminated water in the refinery cannot be mixed with other wastewater
such as sour water from distillation reflux drums containing dissolved hydrogen
sulphide, organic sulphur compounds and ammonia, since they are not treatable by
conventional methods. For such cases, the sour water stripper is often required in the
pre-treatment section before discharging sour water to the wastewater plant for
removal of hydrogen sulphide, ammonia, etc. (Speight 2014).
All the preliminary devices should be operated and maintained with care.
Primary Treatment
The main aim of the primary treatment is removal of the suspended solids, organic
matter, oily sludge from wastewater by physical means, usually by gravity separation. This treatment of wastewater uses oil-water separator or screener or skimmer
where oil, water and suspended solids are segregated from each other. Neither
dissolved solids are separated nor oil-water emulsion is broken in this stage. For
separation of colloidal materials, some chemicals are used in primary treatment.
However, the oil in effluent is recovered at this step itself and is recycled
(Patwardhan 2008; Shahryar 2017; Alireza 2014).
In this treatment method, the flow rate of wastewater is reduced sufficiently to
allow suspended solids to settle down and light materials to float at the surface of
water. There are many devices which are used in primary wastewater treatment such
as settling tanks, clarifiers, skimmers, screeners, filters, etc. (International Petroleum
Industry Environmental Conservation Association 2010).
The primary treatment of a petroleum refinery consists mainly of two stages for
the isolation of oil, water and solids (International Petroleum Industry Environmental Conservation Association 2010; Shahryar 2017).
First Stage
Oil-water separation is achieved using American petroleum institute separators,
corrugated plate interceptors or parallel plate interceptors separators or tilted plate
interceptor separators or hydrocyclone separators or buffer or equalization tanks.
Wastewater is allowed to pass very slowly over the separator, so that demulsified oil
floats on the surface and suspended solids settle down at bottom of the separator due
to gravity. The free oil is skimmed off, while the settled solids are removed using
scrapers or flights to a sludge-collecting hopper. The wastewater flows down the
separator towards the outlet through a diffusion barrier. To prevent the oil from
flowing to the outlet, baffle plates are employed. However, the American petroleum
institute separator has certain limitations. It cannot separate the dissolved or emulsified oil. It can stabilize emulsions at high pH. So, spent caustic must be added to
reduce pH of the American petroleum institute separator. In wastewater treatment for
252
M. Samanta and D. Mitra