This document provides information about vocational training at Durgapur Chemicals Limited (DCL) in West Bengal, India. It discusses DCL's bleaching powder production process. DCL produces bleaching powder with 34-36% available chlorine using a reaction between hydrated lime and chlorine in a jacketed reactor. The multi-step production process involves lime feeding, chlorination, drying, cooling, and packing. Bleaching powder has various uses including water purification, bleaching carpets and paper, and disinfecting.

1. A PRESENTATION ON VOCATIONAL TRAINING IN
DURGAPUR CHEMICALS LIMITED
15thJune to 14th July
BY- SATYAGHOSH MAURYA
09/CHE/04

2. Durgapur chemicals ltd. (DCL) was incorporated on 31 July
1963 as a public sector company wholly owned by the
Government of West Bengal.
It presently has mainly the following plants:
1. Caustic Soda plant
2. Monochloro Benzene plant
3. Stable Bleaching Powder plant
4. Sodium Pentacholorophenate plant
5. Hydrochloric acid plant

3. DCL produces bleaching powder having specification of Grade-1,
strength of 34-36% available chlorine with capacity of 15ton/day.
The plant has some of the modern technologies such as:
1. Special designed jacketed chlorination reactor;
2. Screw conveyer;
3. Bucket elevator;
4. Rotary air lock;
5. Dust return screw conveyer;
6. Cyclone separator and dust collector.

4. RAW MATERIALS:
2. Liquid chlorine –purity of 99.5%
1. Hydrated lime- from Jodhpur Rajasthan. (size
250-300 mesh having 80±1% purity.)

5. CHEMICAL RXN. INVOLVED:
Ca(OH ) 2 Cl2 Ca(OCl )Cl H 2O
2Ca(OH ) 2 2Cl2 Ca(ClO) 2 CaCl2 2H 2O
Reaction occurs under vacuum in the reactor.
The reactor has scrapper having 40 arms
rotating with the help of spur gear and pinion
arrangement connected to a motor having
capacity of 100 hp.
Reaction is carried out at 55-60ºC.

6. PROCESS DESCRIPTION
STEPS:
1. The lime feeding and transporting process.
2. The chlorination , drying and cooling process
3. Packing of the product
4. Water regeneration system

8. THE LIME FEEDING AND TRANSPORTING PROCESS.
godown
storage hopper(D-411) consisting of a rotary air lock(RAL)
with help of one inclined screw conveyer (CY-462)
bucket elevator(CY-465) & one horizontal conveyer (CY-463) (moisture
content of slaked lime 1-1.5%)
From one storage hopper and one screw
bucket elevator(CY-465) conveyer (CY-412),
bucket elevator(CY-418)
Through a screw conveyer (CY-459)
Approximately 30-45 min. are needed to charge 4.5-4.8 MT
Charge hopper (D-419) The charge hopper is provided with electromagnetic impact
vibrator

9. CHLORINATION, DRYING AND COOLING PROCESS:
This process consists of one specially designed,
horizontally mounted, cylindrical, insulated, jacketed
chlorination reactor. Reaction is batch type, reactor has
scrapper assemblies (40 arms in four rows), attached
motor has a capacity of 100hp with 900 rpm, which is
reduced to 9 rpm for the reactor vessel, with the help of a
reduction gear, a spur gear and pinion system.

10. Before chlorination starts the reactor should be under complete
vacuum .Slaked lime is fed by opening the slide gate consisting of a
electromagnetic vibrator. Chlorine is fed from the longer sides of the
reactor consisting of four inlets & is controlled by flow monitoring
integrator (FIQ-421). The vessel is provided with one temperature & one
inlet pressure indicator. Generally a vacuum of 660-680 mm Hg is
maintained. Chlorine should be fed to the reactor until the fall in
vacuum is not more than 20 mm Hg.
Chlorine is fed roughly as follows:
15min @ 3MT/hr until 700kg of chlorine at 670-680mm Hg.
15min @ 2MT/hr until 1200kg of chlorine at 670-680mm Hg.
30min @ 0.8-1MT/hr until 1600kg of chlorine at 670-680mm Hg.
30min @ 0.8MT/hr until 2400kg of chlorine at 670-680mm Hg.

11. The chlorination reaction requires about 2.5-3hrs for
completion.
The inside chlorine pressure is checked by pressure indicators
and any loss
of chlorine is identified by change of color of the absorbing 10-
12% caustic solution circulating through the vacuum
condenser from green to dark red.
DRYING PROCESS
Once the reaction is completed, steam at 1-1.5kg/m² is
circulated from top to bottom
through four steam inlet pipes for drying of the final product after
stripping off all the water in the
jacket. This process needs 2-2.5hrs for completion at 78 to 80ºC.
Condensed steam is removed from the jacket through common
header for cooling water inlet.

12. COOLING PROCESS
After drying the product is cooled by circulating cooling
water through the jacket for 1.5-2hrs to reduce the inlet
temperature to 35-40ºC. Altogether there are four steam
inlet and four cooling water inlet pipes are connected
respectively at the top and bottom of the jacket.

13. OTHER EQUIPMENTS:
A vapor hood with a slide door and a seal is provided in the center of
the reactor for charging slaked lime to the reactor.
Next to vapor hood a horizontally mounted Dust Return Screw
Conveyer(DRSC) is provided for returning the major portion of dust
carried by the vapors to the reactor and is connected with steam
jacket to avoid condensation and jamming.
After DRSC, the particulate solids and gases are sent through a vacuum
pipe to a barometric condenser which has one tail pipe and one
overflow pipe.

14. PACKING OF THE PRODUCT
The finished product is discharged through bottle seal opening of the
reactor into the chain conveyer to flow freely by gravity. The SBP is
transferred to a SBP hopper(D-430) by chain conveyer (CY-427).
It is next sent to a pulveriser unit and then to a cyclone separator to
separate desired sized product particles. Below the pulveriser is one
motor of capacity 50hp connected for easy separation and
transportation of particulate solids.
The bleaching powder is packed into double inner lined HDPE bags
having capacity of 25 kg each.
Also there is a facility to collect the dust in a dust collector from which
the dust is collected and sent back to the packing unit.

15. WATER REGENERATION SYSTEM
The vapors along with the unabsorbed chlorine from the reactor are
condensed in the barometric condenser (BC-423). Firstly the gases
pass through vacuum pipe through pipe by water ring vacuum
pump(VP-424A or VP-424B) and is absorbed in 10-12% caustic
solution. It is disposed or treated to purify the chlorinated water.

16. USES AND CONSUMPTION OF BLEACHING POWDER
Stable Bleaching powder is used in a number of areas
affecting public health as well as some industrial processes
for treatment and washing processes.
Some of the uses are:
1. For water purification.
2. In carpet industry for bleaching and finishing.
3. In paper and pulp industry as bleaching agent.
4. In leather industry as disinfectant material & also for making
cotton used for medical purpose.
5. For sewage disposal, mosquito and epidemics control and
general hygiene.