Search

Byline: Sangita Pal, S. Prabhakar, K.L. Thalor, P.K. Tewari Research and technological developments are being pursued vigorously all over the world to reduce the cost of desalinated water. Thermal and membrane-based desalination processes are very well known and plants are being operated to augment the demand of fresh water essential for drinking in water-scarce countries and to sustain the industrial processes. Any further improvement in energy reduction can only be marginal considering the complexity of the desalination system. The alternative approach is to add value by recovering edible salt, rare and valuable metals, such as caesium, titanium, uranium and vanadium, from the reject brine streams. In this regard, a novel polymeric chelating resin was designed and developed in Desalination Division, BARC laboratory with significant potential for this achievement. In this paper, the characteristics and potential of the resin have been described for the recovery of valuable elements based on experimental findings.

Byline: A.K. Adak, V.K. Srivastava, P.K. Tewari When a nuclear reactor is used to supply steam for a desalination plant, the method of coupling has a significant technical and economic impact. The exact method of coupling depends on the type of reactor and the type of desalination plant. As a part of Nuclear Desalination Demonstration Project (NDDP), BARC has successfully commissioned a 4500 m[sup.3]/day multi-stage flash desalination plant coupled to Madras Atomic Power Station at Kalpakkam. A desalination plant coupled to nuclear reactor of pressurised heavy water reactor type is a good example of dual-purpose nuclear desalination plant. This paper presents the thermal coupling system analysis of this plant along with technical and safety aspects.

Byline: V. Murugan, R. Nagaraj, A.Y. Dangore, S. Prabhakar, P.K. Tewari A 1800 m[sup.3]/day Seawater Reverse Osmosis (SWRO) plant was commissioned in October 2002 at Kalpakkam, India, as part of the Nuclear Desalination Demonstration Project (NDDP). The conventional pretreatment scheme was adopted consisting of a lamella clarifier, pressurised sand filter, activated carbon filter and cartridge filter. The dosing of pretreatment chemicals, ferrous sulphate and polyelectrolytes was done at optimum levels to keep the Silt Density Index (SDI) value between 3 and 4. Experimental trials indicated that the dosing of chemicals may not be necessary below a particular turbidity level. Similarly, the dosing of proprietary antiscalant chemicals instead of sodium hexametaphosphate to control the sulphate scaling did not affect the process performance. Rather it helped the operation, as the antiscalant is in liquid form and the addition of hydrochloric acid could be eliminated. The overall cost per unit water production was also reduced.

Byline: A. Raha, I.S. Rao, V.K. Srivastava, P.K. Tewari By 2020, desalination and water purification technologies are expected to contribute significantly to ensure a safe, sustainable, affordable and adequate water supply in India. The cost of producing water from the current-generation desalination technologies has declined over time at a rate of only approximately 4% per year. Hence the need to accelerate our Research and Development (R&D) activities with a near and long-term objectives for evolution of current generation desalination technology along with the creation of revolutionary next-generation advanced desalination and water purification technologies that will offer a promise of 'step reduction' in the cost of producing water. There are five broad technological areas (thermal technologies, membrane technologies, alternative technologies, concentrate management technologies, reuse and recycle technologies) that encompass the spectrum of desalination technology. In this paper, high-priority research areas in all the above technological areas are discussed to help make decisions about the research direction that will address our nation's future water supply challenges.

Byline: J. Justin Robert Paden, P.K. Tewari, D. Venkatram, D. Barnabas A new spray-type flash evaporator is suggested for the application of saline water desalination. The flash evaporator is 1000 mm in height and 1200 mm in diameter, with a water injection arrangement inside. The evaporator design is based on experiments conducted at vacuum pressures between 10 and 18 mm of Hg, and at saline feed water temperatures between 26[degrees]C and 32[degrees]C. The saline water is injected into a vapouriser through a pair of high-flow swirl injectors with a nominal flow rate of 1.5 litre/sec. per jet and the distance between the injectors is taken as 200 mm for design. The influence of the different thermal, hydrodynamic and geometric parameters on the evaporator performances was investigated. The results obtained are presented, which prove the validity of the proposed system.

Byline: A.K. Adak, G. Kishore, V.K. Srivastava, P.K. Tewari Desalination plants based on Mechanical Vapour Compression (MVC) technology are inherently the most thermodynamically efficient. The thermodynamic efficiency of the MVC process is derived from the application of the heat pump principle. A single unit of a two-effect MVC desalination pilot plant of 50 m[sup.3]/day capacity has recently been commissioned at Trombay, Mumbai. The desalination unit is very compact and unique in the seawater desalination technologies and is being operated by using electricity only. Horizontal tube thin-film spray desalination evaporators are used for efficient heat transfer. It is suitable for a site where feed water is highly saline and condenser cooling water is absent, and where a thermal heat source is not available. The unit produces high-quality water, nearly demineralised (DM) quality directly from seawater. There is no need for a polishing unit and product water can be used directly as make-up of boiler feed and for other high-quality process water requirements in industry. This paper includes the design and highlights the technical features of this unit.

Byline: A. Raha, A. Srivastava, I.S. Rao, M. Majumdar, V.K. Srivastava, P.K. Tewari Utilisation of waste heat is one of the ecofriendly ways to produce low-cost desalted water. Keeping this in mind, Low-Temperature Evaporation (LTE) desalination technology utilising low-quality waste heat in the form of hot water (as low as 50[degrees]C) or low-pressure steam (0.13 bar) has been developed to produce high-purity water (conductivity

Byline: P.K. Tewari The demand for water in India is increasing rapidly owing to progressive increase in the use of water for irrigation, rapid industrialisation, population growth and improving life standards. A holistic approach is therefore required to cope with the freshwater needs of the country. It includes: seawater desalination in coastal areas; brackish water desalination; water purification; water reuse; rainwater harvesting; water supply schemes. The contribution of seawater and brackish water desalination would play an important role in augmenting the freshwater needs of the country.

Byline: A.K. Adak, I.S. Rao, V.K. Srivastava, P.K. Tewari The use of thorium for nuclear power generation is an important element of the Indian atomic energy programme. The design and development of the Advanced Heavy Water Reactor (AHWR) is a step in this direction. Intensive design activity is underway to set up a 300-MWe AHWR. The design of the AHWR incorporates several features to simplify the design and to eliminate certain systems and components, making it economically competitive with other available options for power generation. Utilisation of low-grade or waste heat is an additional feature incorporated in the overall design of the reactor system. A proposal to utilise waste heat from the Main Heat Transport (MHT) purification circuit to produce high-quality desalinated water by the low-temperature evaporation process has been envisaged. This paper presents the proposed nuclear desalination system utilising MHT purification circuit waste heat of AHWR along with its coupling arrangement and technical details.

Byline: Saly T. Panicker, P.K. Tewari Desalination systems are mostly based on membrane (RO) and thermal (MSF and MED) processes. High-pressure operation and high level of corrosion are the major aspects of concern in a Seawater Reverse Osmosis (SWRO) Plant. Selection of the appropriate material for construction and the following of the proper design, fabrication and testing codes, and safe operational procedures ensure the safety of the plant. Proper selection of feed seawater source, provision of standby equipment, proper instrumentation and controls, and periodical maintenance improve the reliability. When the desalination plant is integrated into a nuclear power plant, safety measures have to be more stringent, in order to achieve smooth operation and public acceptance. In this paper, the safety and reliability aspects of SWRO desalination plants are discussed in detail, including the case study of an SWRO plant integrated with a nuclear desalination system.

Byline: Saly T. Panicker, S. Prabhakar, P.K. Tewari The trouble-free operation of a Reverse Osmosis (RO) plant relies on the quality of the treated feed water, which highlights the need for optimisation of the pre-treatment steps. The quality of raw seawater varies with time in terms of suspended and colloidal load, along with the dissolved salt content. In a conventional pre-treatment scheme, consisting of clarification and particulate and micron filtrations, along with chemical conditioning, the chemical dose rates are required to be pre-determined and monitored according to the changing raw water quality. In the RO section, operating pressure and membrane area should be variables as the need arises, depending on the variation in dissolved salts, for maximum production of better quality water. In this paper, the theoretical evaluation of RO performance with respect to seasonal variation in feed salinity is presented, which tells of the need to incorporate sufficient flexibility in operation when designing a plant.

Byline: A.Y. Dangore, S. Prabhakar, P.K. Tewari A hybrid desalination system of 6300 m[thorn]/day capacity has been envisaged, comprising 4500 m[thorn]/day Multi-Stage Flash (MSF) and 1800 m[thorn]/day Seawater Reverse Osmosis (SWRO) plants, and sharing basic utilities with Madras Atomic Power Station. The SWRO plant has been commissioned and has been operating for more than two years. The MSF plant is under construction. The construction of the MSF plant has thrown up a number of challenges, particularly as it is being retrofitted to the existing power plant. The steam supply system and the intake system for seawater required a unique approach both in design and erection. With notable variation in raw water quality, the operation of the SWRO plant has provided valuable insight into the performance of the pre-treatment system and of the membrane.

Byline: G. Kishore, A. Raha, A.K. Adak, V.K. Srivastava, P.K. Tewari A model is presented to study the steady and transient state responses of the system during startup and sudden load changes/disturbances of the Multi-effect Mechanical Vapour Compression (ME-MVC) desalination system. Some of the main dependent parameters like the compressor work, and the mass flow rate of distilled water against the independent parameters like the evaporation side pressure and the water inlet temperature have been studied. Also, the Performance Ratio (PR) and the heat transfer area dependency on the number of effects and Top Brine Temperature (TBT) have been studied. The material and energy balance equations for the feed, product and brine flow for each effect have been written and then solved simultaneously to obtain the time-dependent parameters under various transients. The effects of a step change in feed flow and temperature with respect to brine salinity and product flow rate, etc. have also been studied.

Byline: S.A. Tiwari, D. Goswami, S. Prabhakar, P.K. Tewari The seawater reverse osmosis system requires extensive pre-treatment in order to ensure reliable performance. The conventional pre-treatment system involves dosing of chemicals, which requires frequent monitoring of raw water quality, and also involves adjusting the dosage. Besides being cumbersome, there is a lot of time lag involved in carrying out these measures. This calls for pre-treatment systems based on physicochemical mechanisms. During the last few years, Ultrafiltration (UF) has emerged as a leading unit operation in order to render raw seawater compatible with reverse osmosis operations. In this context, the Desalination Division of BARC has already installed an operational UF pre-treatment system. In this paper, we examine the role of UF in the overall operations of the seawater reverse osmosis system.

Byline: M. Chandrasekhar, M. Majumdar, V.K. Srivastava, P.K. Tewari To improve heat transfer efficiency, Horizontal Tube Thin Film (HTTF) evaporators are being used in multieffect desalination plants. These plants require less pumping energy than thermal-based desalination plants. To generate the design data, experimental studies were carried out in a single-tube HTTF experimental setup, and heat transfer correlations were developed at BARC. The experimental findings and results are presented and discussed in this paper.

Byline: A.K. Adak, P.K. Tewari Thermal desalination technologies are very energy intensive. The utilisation of nuclear energy for seawater desalination provides a safe, feasible and economic solution for the production of very good quality water. The Multi-Stage Flash (MSF) desalination plant of the Nuclear Desalination Demonstration Project (NDDP) of the Department of Atomic Energy (DAE), Government of India, is coupled with a nuclear power plant on the south east coast of India to share the common facilities and steam. The MSF desalination plant is under construction. This paper describes a case study of the coupling aspects of the MSF desalination plant with the existing nuclear power plant and gives an estimate of the loss of electrical power generation due to extraction of steam. Loss of electrical power is also compared with the Desalination Economic Evaluation Program (DEEP) of the IAEA.