Durgapur chemicals limited

vocational training

1. 15 th June to 14 th J uly

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

3. STABLE BLEACHING POWDER 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: Special designed jacketed chlorination reactor; Screw conveyer; Bucket elevator; Rotary air lock; Dust return screw conveyer; Cyclone separator and dust collector.

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

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

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

8. 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.

9. 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.

10. The chlorination reaction requires about 2.5-3hrs for completion. The inside chlorine pressure is checked by pressure indicators and any loss o f chlorine is identified by change of color of the absorbing 10-12% caustic solution circulating through the vacuum condenser from green to dark red. Once the reaction is completed, steam at 1-1.5kg/m² is circulated from top to bottom t hrough 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. DRYING PROCESS

11. 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.

12. 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.

13. 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.

14. 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: For water purification. In carpet industry for bleaching and finishing. In paper and pulp industry as bleaching agent. In leather industry as disinfectant material & also for making cotton used for medical purpose. For sewage disposal, mosquito and epidemics control and general hygiene.

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