General Features & Process Description

Heavy Water Plant at Hazira (also known as Hazira Ammonia Extension Plant - HAEP), employs the ammonia-hydrogen exchange mono-thermal process. The plant is located at a distance of about 16 km from Surat city. Work on HWP (Hazira) commenced in August 1986 and the plant was commissioned in January 1991.

Process Description
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This plant comprises of two streams consisting of two separate isotopic exchange units, final enrichment units, final production units & cracker units, but a common ammonia synthesis unit. Feed synthesis gas (a mixture of one part of nitrogen and three parts of hydrogen containing deuterium from the Ammonia plant) is routed through the plant at a flow rate of about 96 T/Hr. at a pressure of about 181-220 kg/cm². The pressure of the gas is first raised by 40 kg/cm² by a booster, to take care of pressure drop in the plant. It is then cooled in a heat exchanger by the outgoing cold gas returned from the plant. The gas is thereafter passed through a purification unit. In this unit the oxygenated impurities contained in the gas are removed and the gas is saturated with ammonia. The purified synthesis gas saturated with ammonia is then passed through the first isotopic exchange tower working at minus 25 °C where deuterium in the gas is transferred to a counter current stream of liquid ammonia containing potassium amide catalyst fed from the top of the tower. The deuterium enriched ammonia from the bottom of the exchange tower is then fed to the second isotopic exchange tower where it gets further enriched by coming in contact with the enriched synthesis gases obtained by cracking of enriched ammonia. A part of the enriched gas and liquid from the second isotopic exchange tower is then taken to the final enrichment section where the concentration of deuterium in the ammonia can be further increased as desired upto 99.89%. Finally, the enriched ammonia so obtained is made free of the catalyst and is cracked. A portion of this enriched synthesis gas is burnt with dry air to produce heavy water or off grade liquid ammonia is exchanged with de mineralised water reject of Distillation unit to produce off grade heavy water. However, for reasons of better recovery efficiency the concentration of deuterium in ammonia in the feed to final enrichment section is kept low so as to produce heavy water of about 35-40% which is then vacuum distilled to produce heavy water of nuclear grade in final enrichment unit.

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The cold synthesis gas depleted in deuterium from the first exchange tower, before its return to Ammonia Plant, is heated by the incoming feed gas and is passed through an ammonia synthesis unit. In this unit, a portion of the synthesis gas equivalent to the amount of the ammonia cracked in the crackers is converted into liquid ammonia and fed to the top of first exchange tower. The rest of the depleted synthesis gas equivalent to the feed gas supplied is returned to the ammonia plant. The power to the plant is supplied by Gujarat State Electricity Board from their 66 KV grid. The fuel used for heating of the crackers of the plant is natural gas which is supplied by GAIL.

Some of the special features of the plant are:
  • HWP (Hazira) is the second heavy water plant in the country based on the ammonia-hydrogen exchange process which has been set up without foreign collaboration. The basic design of isotopic exchange unit was developed in-house.
  • The plant adopts the latest technology using micro-processor based distributed digital control system for instrumentation and process control instead of the conventional pneumatic analogue system. The system provides control, supervisory and monitoring functions for field control stations. It displays and records data acquired from the plant system and has facilities for data logging and printing alarm messages.
  • This plant comprises of two streams with some common units like synthesis unit, sub-station, inert gas unit, instrument air unit, catalyst preparation unit, cooling towers etc.
  • Completion of the project has been successfully achieved without any time overrun.

Last updated on: 07-Feb-2019