ammonia. So, the wastewater (condensed steam) from atmospheric distillation unit is
mostly oily sour water (Central Pollution Control Board, India 2018).
Vacuum Distillation
The heavier fractions cannot be refined in atmospheric distillation at high temperature and hence are sent to the vacuum distillation unit where distillation is carried out
at a low pressure. From vacuum distillation, the main wastewater is oily sour water
similar to atmospheric effluents. Sometimes, vacuum pump and surface condenser
are used in vacuum distillation unit in place of barometric condenser to do away with
the generation of oily wastewater (Central Pollution Control Board, India 2018).
Cracking (Thermal and Catalytic)
In cracking unit, heavy and long-chain hydrocarbons are cracked into smaller-size
and lighter molecules as per market demand in presence of catalyst (catalytic
cracking), or by applying high pressure and temperature (thermal cracking). The
quantity of wastewater produced during coking is 25 litres per unit feedstock
(approximately). The typical wastewater generated from this type of unit contains
pollutants like phenol, cyanides, sludge containing heavy hydrocarbons, sulphur
compounds and fine coke particles and heavy metals etc. So, this wastewater has
high chemical oxygen demand, biochemical oxygen demand, total suspended solid,
pH and temperature. This water is directly dispatched to the refinery water treatment
plant (Central Pollution Control Board, India 2018).
Catalytic Reforming
Catalytic reforming is a process to upgrade the octane number of gasoline and
naphtha. From this unit, the main constituents of wastewater are organometallic
compounds, high levels of oil, suspended solids, mercaptans, hydrocarbons related
to spillage along with other inorganic compounds like chloride, ammonia, hydrogen
sulphide as well as sour water (Central Pollution Control Board, India 2018).
Solvent Extraction
Solvent extraction, dewaxing and propane deasphalting are required for removal of
aromatics, wax and asphalts from lube base oil for improving viscosity index,
oxidation stability, colour and pour point. The common solvents used are furfural,
phenol, toluene, methyl-ethyl-ketone and propane. So, these used solvents when
disposed contaminate the water (Central Pollution Control Board, India 2018).
8 Treatment of Petroleum Hydrocarbon Pollutants in Water
235
mostly oily sour water (Central Pollution Control Board, India 2018).
Vacuum Distillation
The heavier fractions cannot be refined in atmospheric distillation at high temperature and hence are sent to the vacuum distillation unit where distillation is carried out
at a low pressure. From vacuum distillation, the main wastewater is oily sour water
similar to atmospheric effluents. Sometimes, vacuum pump and surface condenser
are used in vacuum distillation unit in place of barometric condenser to do away with
the generation of oily wastewater (Central Pollution Control Board, India 2018).
Cracking (Thermal and Catalytic)
In cracking unit, heavy and long-chain hydrocarbons are cracked into smaller-size
and lighter molecules as per market demand in presence of catalyst (catalytic
cracking), or by applying high pressure and temperature (thermal cracking). The
quantity of wastewater produced during coking is 25 litres per unit feedstock
(approximately). The typical wastewater generated from this type of unit contains
pollutants like phenol, cyanides, sludge containing heavy hydrocarbons, sulphur
compounds and fine coke particles and heavy metals etc. So, this wastewater has
high chemical oxygen demand, biochemical oxygen demand, total suspended solid,
pH and temperature. This water is directly dispatched to the refinery water treatment
plant (Central Pollution Control Board, India 2018).
Catalytic Reforming
Catalytic reforming is a process to upgrade the octane number of gasoline and
naphtha. From this unit, the main constituents of wastewater are organometallic
compounds, high levels of oil, suspended solids, mercaptans, hydrocarbons related
to spillage along with other inorganic compounds like chloride, ammonia, hydrogen
sulphide as well as sour water (Central Pollution Control Board, India 2018).
Solvent Extraction
Solvent extraction, dewaxing and propane deasphalting are required for removal of
aromatics, wax and asphalts from lube base oil for improving viscosity index,
oxidation stability, colour and pour point. The common solvents used are furfural,
phenol, toluene, methyl-ethyl-ketone and propane. So, these used solvents when
disposed contaminate the water (Central Pollution Control Board, India 2018).
8 Treatment of Petroleum Hydrocarbon Pollutants in Water
235