Heavy Water Plant
Heavy Water Plant at Thoothukudi employs the ammonia hydrogen exchange process (monothermal). The plant is located at distance of about 14km from Thoothukudi Railway Station. Work on HWP Thoothukudi was commenced in September 1971 and the plant was commissioned in July 1978.
Process description:
Synthesis gas (containing a mixture of three parts of hydrogen and one part of nitrogen) is routed through the plant at a flow rate of about 48 T/hr. at a pressure of about 191-216 kgs. / cm2. The pressure of the gas is first raised by 40 kg. / cm2 to take care of pressure drop in the HWP. It is then cooled in a heat exchanger by the outgoing cold gas to Ammonia Plant. The gas is thereafter passed through a purification unit. In this unit the impurities contained in the gas such as water, carbon monoxide, carbon dioxide and oxygen are removed and the gas is saturated with ammonia. The cooled and purified synthesis gas saturated with ammonia is then passed through the first isotopic exchange tower working at minus 25 degree Celsius where deuterium in the gas is transferred to a counter current stream of liquid ammonia fed from the top of the tower in the presence of potassium amide catalyst dissolved in liquid ammonia. 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 cracked gases obtained by cracking of enriched ammonia. A part from 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, up to 99.8%. However, for reasons of better recovery efficiency, the concentration of deuterium in ammonia from the final enrichment section is kept at around 60%. The enriched ammonia so obtained is cracked and a portion of this enriched synthesis gas is burnt with dry air to produce off grade heavy water is further distilled in an upgrading plant to produce nuclear grade heavy water.
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 from the same plant 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 to ammonia and fed back to top of the first exchange tower. The rest of the depleted synthesis gas equivalent to the feed gas supplied is returned to Ammonia Plant.
The power supply to the Plant is provided by Tamil Nadu Electricity Board from their 110 KV grid. Naphtha for the cracker of the plant is supplied by the IOCL-Thoothukudi Depot. Make-up water for the cooling tower of the plant is supplied by Tamil Nadu Water Supply & Drainage Board from their 20 mgd water supply line. The plant has its own inert gas (nitrogen) generation unit.
Salient Features of Heavy Water Plant, Thoothukudi
Process Used NH3 - H2 Exchange (Monothermal)
Date of Commissioning July 1978
Capital Cost of the Plant Rs. 3741 Lakhs
Plant Area 8.40 Hectares
Number of Employees (Man Power) 476 (As on 1.4.1991)
Operating Pressure 250 Kg/Cm2
Synthesis Gas Flow Rate 48 Te/Hr
Total Weight of Structure 2840 Te
Total Weight of Equipment 1700 Te
Weight of Heaviest Equipment 365 Te
Maximum Diameter of Equipment 2.8 M approx.
Maximum Height of Towers 40 M approx.
Total Length of Piping 27.25 Km
Total Length of Electrical Cables 90 Km
Substation Capacity 11 MVA
Connected Load 13.76 MW
Power Consumption 210 MWH / Day
Water Consumption 1200 M 3 / Day
Naphtha Consumption 48 Te.Day
D.M Water Consumption 100 M3 / Day