Introduction
Arvand Petrochemical Co. is situated in southern of Iran. It
has been constructed at site 3 of Bandar Imam Petrochemical Special Economic
Zone, on the northern coast of the Persian Gulf. Sprawling on a
108-hectare, it seeks to help the country move towards
self-sufficiency, industrial development and to provide the related local and
downstream sector with the required raw material. Arvand was initially planned
to implement olefins, MEG and EOG plants. But, the olefins plant was later transferred
to Gachsaran petrochemical Co.
In 2002, the petrochemical industries Development Management
Co.,a subsidiary to the National Petrochemical Co. (NPC) of Iran and a
consortium of Uhbe of Germany and Sazeh of Iran entered into a
contract for the construction of Chlor-alkali(CA), ethylene
dichloride (EDC), vinyl chloride monomer (VCM) and polyvinyl chloride (PVC)
units. Arvand Petrochemical Co. was tasked with implementing these projects.
The APC complex consists of EDC/VCM and PVC plants as well as an air separation
unit (ASU),a CF unit, cooling towers, an air plant, a salt washing unit and
brine transfer pipeline.lts output includes valuable products such as NaOH 50%,
chlorine gas, Sodium hypochlorite, EDC, E-PVC and S-PVC. After the bidding, an
EP contract was awarded to the Uhde- Sazeh consortium in 2003.
CA plant
The plant is slated to produce 660,000 ton/year of caustic
soda 100% or its equivalent 1,320,000 ton/year of caustic soda 50%. the
plantconsists of two lines each producing half of the overall output.
Its major feedstock is brine with a density of 300-310
gr/lit. Thisrequired feed is obtained by processing 1,196,000 t/y of washed
Salt from the Sarbandar salt pond.
The plant can be classified into four major sections:
1-Brine filtration and precipitation
2-Cell room (electrolysis of sodium chloride)
3-Purification unit
4-Wastewater treatment
At the first section Na2 Co3
Sodium carbonate (Na2CO3)and sodium hydroxide (NaOH) are
added to the input brine. Then, suspended solid impurities are settled and the
brine is fed to the filtration unit where three different kinds of filters namely anthracite, candle and ion-exchange
filters are used
respectively to remove the suspended solid content, the
dissolved solid content and the calcium
and magnesium impurities to a level of 20 ppb. (Due to the sensitivity of the
membranes, the brine should have a high purity.)
The second section
Includes 24 BM 2.7 Electrolyzer. Each
electrolyzerconsists of 168electrolyzing
cells 5 of which remain stays in stand- by mode.
In electrolyzing cells, the saturated brine will be
decomposed electrically into CL- and Na+ with a current density of 5.46 KA/m2
and a current of 14.86 KA. Some amount of hydrogen is produced in the cathode
compartment of each cell.The CL- ions are oxidized and
produce chlorine gas.And the Na+ ions, after passing through the membranes,
combine with OH- ions and form NaOH or caustic soda.
The third section
Includes cooling, drying and concentration of chlor in which
the chlorine gas produced by the electrolyzers will be pumped to the drying
unit.
The out coming the chlorine gas will be sent to users.
At the concentration Unit, the 32% NaOH coming from the
cells is concentrated ot 50%. This is then sent storage tank for sales.
In the acidification unit, portions of the freed hydrogen
during hydrogen purification and the out coming chlor from the compressors are
combined and burnt in a furnace. As a result, the obtained chloridric acid will
convert to HCL in a column after absorbing water.
This will be used for the plants consumption. The
combination of chlor and NaOH will produce sodium Hypochlorite.
In the water Treatment Unit, the waste water coming from
various units will be neutralized and diluted. It is pumped to the nearby Fajr
UT complex after its PH is regulated and its free chlorine is eliminated.
EDC/VCM
Plant
The plant is designed to produce ethylene di- chloride (EDC)
and vinyl chloride monomer (VCM) as feed for the production of polyvinyl
chloride (PVC).
The process of PVC production consists of two phases:
Phase one
Phase one includes production and purification of EDC which
is carried out at the Direct Chlorination, Oxy Chlorination and EDC
Purification Units.
The Second phase
The second phase includes EDC Cracking, VCM Purification, Gas
and Liquid Waste Incinerators and Storage Tanks Units. The chlorine gas
produced at the Chlor-alkali Unit with react with the incoming ethylene within
the reactor at the Direct Chlorination Unit yielding EDC. At the
OxyChlorination reactor, HCL reacts with oxygen and ethylene producing with the
EDC produced at the Direct Chlorination Unit will be sent to Unit 130 for
purification. The purified EDC will be pumped to the intermediary
storage tanks in Unit 170 or the export storage tanks in
Unit 180. Some portion of the purified EDC will be dispatched to the Cracking
Unit and will yild VCM and HCL within the furnaces there. The HCL yielded at
this unit will be sent back to the Oxy Chlorination Plant. The VCM produced
from cracking reactions within the Cracking Unit (Unit140) will be transferred
to Treatment and purification Unit (Unit150) where it will be purified and
stored at the cicular storage tanks for use at the PVC Unit.
In this unit, medium peressure steam is also be produced
using the heat yielded from burning waste gases.
PVC Plant
Producing PVC is one of the major goals behind setting up
Arvand Petrochemical Complex. It is desingned to produce
300,000 tons per annum of S-PVC and 40,000 tons per annum of E-PVC for local
consumption.
The excess produce will be exported to international
markets.
The plant produces eight different grades of S-PVC powder
and five different grades of E-PVC powder. The S-PVC and E-PVC Units consist of
the following sections:
VCM &Dematerializad Water Supply
Dissolving & Catalysts-Production
Polymerization
Degassing
Drying & Bagging
The VCM produced at the EDC/VCM Plant is the major feedstock
of the PVC Plant. The modern Vinnolittechnology is employed for the production
of PVC which has improved the quality and the efficiency of the plant output.
At the S-PVC plant, the VCM feedstock from the EDC/VCM Unit
is dehydrated and sent to polymerization section which consists of six batch
reactors.They use Intercooler technology that helps minimize production cost
and improve the efficiency of this section.
In the polymerization unit of the S-PVC Plant, PVC is
producedsuspension method within the polymerization reactors. Meanwhile,in
addition to the VCM feed, a number of chemicals such as catalysts,dispersants
are injected in to reactors along with VCM.
The out coming suspension from reactors, enters dehydrators
after passing through degassing columns. It is dehydrated by centrifuges and is
conveyed to dryers.
The suspension produced in the reactors is dehydrated
withincentrifuges. The product is dried by hot air from dryers.
The final PVC powder product is conveyed to bagging section.
The bagged product is stored at the plant’s warehouses.
In the E-PVC Plant,much of the production process resembles
that of the S-PVC Plant. The polymerization process takes place ina continuous
form.
The polymerization section of the E-PVC Plant comprises
three reactors that operate continuously and yield PVC by an emulsion process.
In these reactors, VCM is converted to PVC. The produced
latex iscontinuously injected into degassing and then to dryers sections.
The 50% concentrated latex is then turned into PVC by dryers
using hot air.
The obtained PVC granules are put through a sieve to control
the size of the granules. The sieved granules are then conveyed to silos and
eventually end up in storehouses after they are bagged.
In addition to the feedstock that is used for the production
of E-PVC and S-PVC , a number of substances are also used as additives.
They include dispersant agents, catalysts, stoppers,
emulsifiers,
stabilizers, inhibitors, cross-linkings, de-foamers to name
some of the most important ones. In a broad comparison, at the S-PVC Plant the
PVC cake is dehydrated by centrifuges and at the E-PVC Plant latex is
concentrated by employing the Memberane technology. At both
plants, hot and dried air is used to
obtain PVC power.
The dried powder obtained at both plants is later sieved and
eventually bagged and stored in warehouses.
Sulphuric
Acid Concentration (SAC) Unit
The Unit is designed to recover the sulphuric acid required
to be used by the CA Plant. The 78% sulphuric acid current from the CA Plant is
purified and concentrated within the stripper column yielding 96% acid which is
returned to the CA Plant after going through certain processes. The SAC Unit
has a capacity of 32 ton per day.
ASU Plant
The plant, built by Hangzhou Fortune Group of China, is
designed to supply the Oxy Chlorination with the oxygen it requires for its
operation. It comprises of two identical units each with a capacity of 7,500
normal cubic meters per hour of oxygen and 7,500 normal cubic meters per hour
of nitrogen. The two unit will be built on a piece of land covering an area of
1 hectare.
The Oxy Chlorination will require 59,400 tons of oxygen per
year.
Plant Air
Arvand Complex consumes 15343 normal cubic meters per hour
of industrial air. The Plat Air Unit was built to supply this requirement. The
excess volume is supplied to the neighbouring complexes. To this end, three
centrifugal compressors, each with a capacity of 8000 normal cubic meters per
hour, built by Kobelco of japan, were bought and put in operation.
Salt
Washing Plant
Salt saturation pits are 22 km from the boundary of Arvand
complex.
It supplies the concentrated brine that the complex requires
for processing at its Chlor-alkali (CA) Plant. The process is designed so as to
either produce brine with a concentration of 300-310 g/lit from sea water or
out of the diluted brine which is returned from the CA Plant.
The Chlor-alkali plant comprises three brine concentration
saturates each with a capacity of 480 cubic meters.
The concentrated brine is pumped from a distance of 22
kilometers and is stored in a tank built at Unit 020 in the CA plant.
Before it is sent to the next unit, the brine is passed
through exchangers and is warmed by the diluted brine returning from the unit.
The diluted brine is then stored in another tank
and is sent to concentration pond where it is concentrated.