Masthead Reprint & Permissions All rights reserved. Without the written permission of the publisher, reproduction / republishing / reprinting of this magazine, in whole or in part, are strictly prohibited. To acquire permission write to info@watertoday.org The Publishers and the Editors do not necessarily, individually or collectively, identify themselves with the views expressed in this magazine. The views expressed are those of the authors only. The Magazine also does not claim any responsibility for information contained in the advertisements. The magazine assumes no liability or accountability of any kind in connection with the information thereof. Editor Naina Shah editor@watertoday.org Resident Editor Hemlatha Govindaraj editor@watertoday.org Senior Designer N. Sirajudeen siraj@watertoday.org Circulation subscribe@watertoday.org Advertisement & Sales info@watertoday.org Corporate offices and academic institutions looking to order for bulk subscriptions, please contact us on +91 44 4291 6900 or write to us at subscribe@watertoday.org Printed & Published by S. Shanmugam on behalf of WATER TODAY PVT. LTD. Printed at Dawood Graphics, No. 63, Muthu Street, Royapettah, Chennai 600014, Tamil Nadu, India. Published at 3D, III rd Floor Bhagheeratha Residency, 124, Marshall s Road, Egmore, Chennai - 600 008 Tamil Nadu, India Regional Offices: No.504, Windflower, Mantripark, Goregaon East, Mumbai 400 065, India Maharashtra, India Submissions We inspire and encourage perspective authors to write articles, case studies, technical papers and application stories on water and wastewater industry and follow Water Today s Author s guidelines before submitting manuscripts. Write to us at editor@watertoday.org Head Offices: to obtain Author s Guideline. WATER TODAY Pvt. Ltd. 3d, III Floor Bhagheeratha Residency, 124, Marshall s Road, Egmore, Chennai - 600 008, TN, India Tel : +91-44 - 42916900 Email : info@watertoday.org Web: www.watertoday.org UNITING THE VIBRANT WORLD OF WATER - TO PROVIDE A PROACTIVE PLATFORM FOR THE WATER INDUSTRY TO CONVERGE AND WORK TOGETHER IN ACHIEVING SOLUTIONS TO GLOBAL WATER PROBLEMS. 8 Water Today - The Magazine l June 2017
CONTENTS Latest R&D Trends in Desalination by Membrane Technologies...26 This article gives an overview of the most important innovations that are being developed and implemented in desalination of seawater or brackish water by membrane technologies. By Alfonso José García Laguna Forward Osmosis A Brief Introduction...32 This paper outlines some of the aspects of the Forward Osmosis process and its derivatives, with regard to key issues, concepts and some applications. By Peter G. Nicoll Solar Energy for Water Desalination...52 This article discusses the different solutions to the most commonly used desalination process (RO, MSF, MED), and solar energy production technology compatible with desalination. By Pascale Compain Simultaneous Evaporation & Condensation in Connected Vessels...60 The article discusses a new water desalination technology which is less expensive in both capital and operating cost, simpler to implement and more operationally flexible than conventional thermal desalination technologies like low temperature thermal desalination & mechanical vapour recompression. By Amit Katyal Antiscalants & Dispersants: Potential Additives in Desalination...82 The article discuses the use of antiscalants and dispersants as the potential additives in Desalination process. By Dr. Piyush Kumar Verma Latest Advances & Opportunities in Desalination Technologies...74 Desalination refers to the process by which pure water is recovered from saline water by application of energy. By Parimal Pajankar Advanced Method to Optimize Reverse Osmosis Performance...80 RO Membrane Management System is a predictive solution that gives you the opportunity to improve membrane efficiency and the predictability of failures. By Soumitra Banerjee Water Today - The Magazine l June 2017 9
CONTENTS Geothermal Desalination Potential for Clean & Affordable New Water Solutions...88 By Leon Awerbuch Hydroflow Electronic Water Conditioners Desalination Application...100 By Dr. Denzil Rodrigues Desalination...96 By Dr. M. Lakshmi Prabha & B. Darshan A Project Case Study: They like it fast? Do it Fast-track!...104 By Amir Nassiri R E G U L A R S Masthead...8 Editorial Calendar...99 Water Wire...14 Subscription Form...108 Launch Pad...18 Classifieds...109 Event Zone...20 Ad. Index...111 Product Zone...24 Editor s Note...112 10 Water Today - The Magazine l June 2017
Simultaneous Evaporation & Condensation in Connected Vessels The article discusses a new water desalination technology which is less expensive in both capital and operating cost, simpler to implement and more operationally flexible than conventional thermal desalination technologies like low temperature thermal desalination (LTTD) and mechanical vapour recompression (MVR). By Amit Katyal Water treatment generally involves separation of solids from water. These solids can be suspended solids or dissolved solids. Many simple and low-cost methods exist to reduce suspended solids from water. These include decantation of water in large vessels and filtering of water using filters. However many processes like producing fresh water from sea water or from highly saline brines coming out of various chemical processes as by-product require reduction of dissolved solids. The process of producing fresh water from sea water or from highly saline brines coming out of various chemical processes as by-product is known as desalination. Sea water primarily contains NaCl as the dissolved salt whereas other kind of brines comprise of other salts like CaCl2, KCl, MgCl2, KBr, LiCl, CsCl etc. and mixtures of various salts dissolved in water. The reduction of dissolved solids from water is an expansive process and most of the existing technologies for desalination are highly energy intensive. The existing technologies for reduction of dissolved solids from water can be categorised into membrane based technologies and thermal technologies. Membrane based technologies are based on principle of reverse osmosis and require a semi-permeable membrane separating desalinated water and saline water which allows pure water to move from saline water side to desalinated water side when saline water side is pressurized to overcome osmotic pressure. Membrane based technologies require high pressure to desalinate water and cannot desalinate water after a certain salinity is reached on the saline water side. Thermal technologies are not bound by these limitations and can desalinate saline water of any salinity till salt crystallization. Thermal technologies require either vaporizing or freezing water, separating water vapours or ice and condensing water vapours or melting ice to form desalinated water. As latent heat of fusion of water is much lower than latent heat of vaporization of water so thermal technologies based on freezing require lesser energy than thermal technologies based on vaporization. However depression in freezing point temperature is much more than elevation in boiling point temperature for same concentration of salts dissolved in water and achieving low sub-zero Celsius temperatures require costly apparatus. Few gas hydrate based freezing technologies have shown promise as they elevate the temperatures required for operations but gas hydrate based freezing technologies are not yet commercialized. At present thermal technologies based on vaporization of water are the most tried and tested ones primarily when environmental concerns desire maximum desalinated water to be extracted from saline water. However these distillation based technologies are highly energy intensive as they require water temperature to be raised to above the boiling point temperature of water. Few technologies like low temperature thermal desalination (LTTD) carry out distillation of saline water at negative pressures thus lowering the boiling point of water and reducing the energy required to raise the temperature of saline water to its boiling point temperature. But the general configuration of apparatus to carry out low temperature thermal desalination does not allow the process to be carried out efficiently 12 Water Today - The Magazine l June 2017
requiring high difference between vaporization temperature and condensation temperature and cannot vaporize water till crystallization of salt. Also low temperature thermal desalination (LTTD) technology require a hot or cold source or utility. This hot or cold source or utility can be originating as a byproduct from some other process or has to be created specifically for the process. In absence of a hot or cold source or utility, other thermal technologies like mechanical vapour recompression can be used to desalinate water. Mechanical vapour recompression (MVR) technology involves vaporization of saline water followed by compression and condensation of water vapours at a higher pressure. However MVR technology require a compression ratio of more than two if it is to be used for desalination of near eutectic NaCl brine to crystallize salt from it. Costly and more energy intensive multi-stage compressors are required to give a compression ratio greater than two. This problem becomes more pronounced when stronger brines containing salts and salt mixtures with boiling point elevation higher than NaCl brine are to be desalinated using mechanical vapour recompression technology. Also general structure of apparatus used for MVR is only designed to concentrate saline water without crystallization of salt. So a separate stage and apparatus has to be designed for crystallization of salt using mechanical vapour recompression technology. Also apparatus has to be designed to transfer concentrated brine to this stage. A new thermal desalination technology for desalinating saline water of any salinity is developed. The technology relates to more efficient and more operationally flexible form of distillation. The technology is based on a new concept given by the inventor. As per the concept which relates to simultaneous evaporation and condensation in connected vessels under negative pressure, the molar rate of evaporation in evaporation vessel, molar rate of transfer of vapours from evaporation vessel to condensation vessel through a connected pipe and molar rate of condensation in condensation vessel at a given instance of time will always be same. Any change in temperature or pressure of evaporation or condensation vessel will result in automatic change in the temperature and pressure of the other vessel so as to maintain equal rate of evaporation, transfer and condensation but at a different value from the rate before the change. The concept can be extended to a distillation system wherein molar rate of transfer of vapours from evaporation to condensation vessel is increased by compression or other means. The concept is further explained below with the help of three figures. Figure 1 illustrates a distillation system in accordance with the invention. The system comprises of two vessels i.e. an evaporation vessel and a condensation vessel connected to each other through their vapor spaces by a connecting pipe. The evaporation vessel has provision of heating whereas the condensation vessel has provision of cooling through internal or external heat transfer coils. The system further includes a water inlet pump 108 for pumping in saline water and a water outlet pump for pumping out pure water. Figure 1 Water Today - The Magazine l June 2017 13
The system is further provided with hot heat transfer fluid inlet and outlet; hot heat transfer fluid flow control valve; cold heat transfer fluid inlet and outlet and cold heat transfer fluid flow control valve for allowing the hot heat transfer fluid and cold heat transfer fluid to enter in and exit out of the system. The system is further provided with a low pressure steam inlet for supplying low pressure steam to the evaporation vessel to replace air in the condensation vessel and evaporation vessel. The system further includes a vapour transfer valve for varying the area of opening the connecting pipe to control the transfer of vapours and an air removal valve for removing air from the system. Optionally, a demister could be placed in the evaporation vessel to prevent entrainment of saline water along with water vapours to the condensation vessel. A regular supply of hot heat transfer fluid and cold heat transfer fluid preferably at constant temperatures is ensured to heat the evaporation vessel and cool the condensation vessel respectively. Water, glycol, low pressure steam or any other suitable heat transfer fluid can be used in the system. Other conductive, convective or radiative methods of heating like electric heaters, gas fired heaters or solar heaters and of cooling like fans or water wetting/ ice covering of outer surface could also be used. The molar rate of evaporation and condensation of water could be adjusted by changing any of the following: Flowrate or temperature of hot heat transfer fluid; Flowrate or temperature of cold heat transfer fluid; Area of opening of vapour transfer valve configured in the connecting pipe or any combination of these. The complete distillation system including the evaporation vessel, the condensation vessel, and the connecting pipe is insulated to prevent any heat exchange with the atmosphere. Also, the evaporation vessel, the condensation vessel and the connecting pipe are made air-tight not allowing any air to enter the distillation system while in operation. The rate of transfer of water vapours transferred from evaporation vessel to condensation vessel depends on the pressure differential between evaporation vessel and condensation vessel and area of opening of connecting pipe connecting evaporation vessel and condensation vessel. Pressure of evaporation vessel and condensation vessel depends on the temperature of evaporation vessel and condensation vessel and is equal to vapour liquid equilibrium pressure of saline water in evaporation vessel and desalinated water in condensation vessel corresponding to the maintained temperature. The amount of water evaporated from evaporation vessel and condensed in condensation vessel depends on heat transfer area of coils placed externally or internally in the evaporation vessel and condensation vessel and the flow rate and temperature of hot and cold heat transfer fluid flowing in the coils. For a small increment in time, salinity of water remaining in the evaporation vessel can be considered constant. For this small time increment, as the flow rate of hot heat transfer fluid in the evaporation vessel is lowered for a fixed flow rate of cold heat transfer fluid in condensation vessel, the rate of evaporation in evaporation vessel decreases. This results in decrease in pressure of evaporation vessel due to decrease in number of moles in vapour space of evaporation vessel. As the pressure of evaporation vessel decreases, the temperature of evaporation vessel which is equal to the vapour liquid equilibrium temperature of saline water also decreases. Also the decrease in pressure of evaporation vessel results in lower pressure differential between evaporation vessel and condensation vessel and a lower rate of transfer of water vapours from evaporation vessel to condensation vessel. As less water vapours at lower temperature are transferred to the condensation vessel from evaporation vessel for same flow rate of cold heat transfer fluid in condensation vessel so the pressure of condensation vessel and temperature of condensation vessel (which is equal to vapour liquid equilibrium temperature of pure water corresponding to pressure of condensation vessel) decreases. However, this decrease in pressure of condensation vessel is less than the decrease in pressure of evaporation vessel as the flow rate of cold heat transfer fluid in condensation vessel is unchanged whereas the flow rate of hot heat transfer fluid in evaporation vessel has decreased. This results in an overall decrease in pressure difference between evaporation vessel and condensation vessel and an overall reduced rate of transfer of water vapours from evaporation vessel to condensation vessel. The decrease in temperature of condensation vessel results in lower outlet temperature of cold heat transfer fluid from condensation 14 Water Today - The Magazine l June 2017
vessel coil and a lower temperature difference between cold heat transfer fluid inlet temperature and outlet temperature at same cold heat transfer fluid flow rate. As the flow rate of cold heat transfer fluid in condensation vessel is unchanged, lower rate of condensation of water vapours in condensation vessel results as per equation 1 given below. Rate of heat transfer (Q) = Mass flow rate of hot heat transfer fluid (m) * Specific heat of hot heat transfer fluid (C) * difference in inlet and outlet temperature of hot heat transfer fluid ( T) ---------- (1) A reverse effect results when the flow rate of hot heat transfer fluid is increased in the evaporation vessel. Similarly when the flow rate of cold heat transfer fluid is decreased in the condensation vessel and the flow rate of hot heat transfer fluid in evaporation vessel is kept constant, an increase in temperature of condensation vessel and a relatively lower increase in temperature of evaporation vessel results. This results in lower rate of generation of water vapours, lower rates of transfer of water vapours and lower rates of condensation of water vapours. A reverse effect results with an increase in flow rate of cold heat transfer fluid in condensation vessel. For a fixed area of opening of the connecting pipe and fixed temperature and flow rates of heat transfer fluids in heat transfer coils of evaporation vessel and condensation vessel for a small time increment in which salinity of water remaining in evaporation vessel can be considered constant, an equilibrium state is automatically achieved. In such a case, the pressure and temperature of evaporation vessel and condensation vessel get adjusted such that same amount of water vapours are produced in the evaporation vessel, same amount of water vapours are transferred through the connecting pipe from evaporation vessel to condensation vessel and same amount of water vapours are condensed in the condensation vessel so as to maintain constant pressure and temperature in the evaporation vessel and condensation vessel. As per ideal gas law for compressible vapours. P*V=n*Z*R*T ---------- (2) In order to maintain the pressure and temperature in evaporation vessel and condensation vessel for a small time increment in which salinity of water remaining in evaporation vessel can be considered constant, considering small change in vapour space volume and compressibility factor during this small time increment, number of moles in evaporation vessel and condensation vessel vapour space will remain the same. This implies that same number of moles of water vapours are produced in the evaporation vessel, same number of moles of water vapours are transferred through the connecting pipe from evaporation vessel to condensation vessel and same number of moles of water vapours are condensed in the condensation vessel for this small time increment. However variation in pressure and temperature of evaporation vessel and condensation vessel with time outside this small time increment will be observed for the process due to variation of salinity of the saline water remaining in the evaporation vessel with time. As the equilibrium pressure of saline water for a given temperature decreases with increasing salinity and as the salinity of left over brine in the evaporation vessel keeps on increasing as the desalination process continues so the pressure of evaporation vessel decreases as the desalination process continues. This implies presence of lesser moles of water vapours in the vapour space of evaporation vessel or lower rate of evaporation of water. The decrease in rate of evaporation of water with increasing salinity results in a higher outlet temperature of hot heat transfer fluid or higher temperature of evaporation vessel as per equation 1. The decrease in pressure of evaporation vessel with increased salinity results in lower rate of transfer of water vapours from evaporation vessel to condensation vessel. Though the temperature of water vapours being transferred from evaporation vessel to condensation vessel increases with increasing salinity, as the heat required to cool these water vapours to condensation temperature is very less so this decreased rate of transfer of water vapours from evaporation vessel to condensation vessel results in an overall decrease in pressure and temperature of condensation vessel. However the decrease in pressure of evaporation vessel is more than the decrease in pressure of the condensation vessel with increasing salinity resulting in lower pressure difference between evaporation vessel and condensation vessel and a lower rate of transfer of water vapours from evaporation vessel to condensation vessel. Water Today - The Magazine l June 2017 15
The final result of increased salinity is an increase in temperature of evaporation vessel resulting in a lower rate of evaporation of saline water, a decrease in temperature of condensation vessel resulting in a lower rate of condensation of water vapours and a lower pressure difference between evaporation vessel and condensation vessel resulting in lower rate of transfer of water vapours from evaporation vessel to condensation vessel. So with increased salinity, the temperature of evaporation vessel keeps on increasing and the temperature of condensation vessel keep on decreasing such that an equilibrium state is maintained for a small time increment in which salinity of water remaining in the evaporation vessel can be considered constant wherein water vapours are produced, transferred and condensed at same molar rate for this small time increment. However, this equilibrium state molar rate of water vapours produced, transferred and condensed decreases as the desalination process continues. In figure 2, a compressor or fan can be placed in the connecting pipe to increase the molar rate of transfer of water vapours from evaporation vessel to condensation vessel, decrease the pressure of the evaporation vessel and increase the pressure of the condensation vessel. A bypass pipe to the compressor is provided to depressurize and pressurize the complete system during start and end of the desalination process. A demister could be placed in the evaporation vessel to prevent entrainment of saline water with water vapours in the compressor to avoid damage to compressor. The operation of compressor is to increase the rate of transfer of water vapours from evaporation vessel condensation vessel results in decreased pressure in the evaporation vessel and increased pressure in the condensation vessel. This will result in decrease in temperature of evaporation vessel and increase in temperature of condensation vessel such that the temperature and pressure of condensation vessel exceeds the temperature and pressure of evaporation vessel. This will result in a higher rate of evaporation of water vapours in evaporation vessel due to increased difference in inlet and outlet temperature of hot heat transfer liquid for unchanged flow rate of heat transfer liquid and a higher rate of condensation of water vapours in condensation vessel due to increased difference between inlet and outlet temperature of cold heat transfer liquid for unchanged flow rate of cold heat transfer liquid as per equation 1. As the mass flow rate of a compressor is inversely proportional to its pressure ratio (discharge pressure/ suction pressure) so operation of a compressor in the connecting pipe between evaporation vessel and condensation vessel results in an increased rate of transfer of water vapours from evaporation vessel to condensation vessel and an automatic adjustment in the pressure and temperature of evaporation vessel and condensation vessel such that water vapours are produced, transferred and condensed at the same rate. Optionally, the system can be made more operationally flexible by configuring a vapour transfer valve in the bypass pipe. In Figure 2 16 Water Today - The Magazine l June 2017
Figure 3 such a case, the system could also be operated for low evaporation and condensation rate requiring lesser energy by isolating the compressor or fan configured in the connecting pipe and using the bypass pipe and vapour transfer valve to transfer vapours from evaporation vessel to condensation vessel. This vapour transfer valve could be closed completely when compressor is used to transfer the vapours from evaporation vessel to condensation vessel. Referring to Figure 3, as the compressor is configured in the connecting pipe, the pressure in of condensation vessel is more than the pressure of evaporation vessel. For a required rate of production, transfer and condensation of water vapours and for a suitably high capacity of compressor configured in the connecting pipe, the temperature and pressure of condensation vessel exceeds that of evaporation vessel and the same circulating heat transfer fluid can initially cool the condensation vessel and gets heated in the process and then heats the evaporation vessel and gets cooled in the process to give the required rates of production, transfer and condensation of water vapours. The heat transfer fluid used can be stored at ambient temperature in a single tank at the start of the process. As the desalination process continues in the above described system, the salinity of water remaining in evaporation vessel keeps on increasing. This results in increase in temperature of evaporation vessel and condensation vessel and decreased rate of production, transfer and condensation of water vapours. After the desalination process is completed, a low capacity refrigeration system comprising a refrigeration compressor, a water cooled or air cooled condenser and an expansion valve can be used to decrease the temperature of heat transfer fluid stored in the heat transfer fluid storage tank to a desired value. Water at ambient temperature could be used as the heat transfer fluid. In case the temperature rise of the heat transfer fluid tank storing heat transfer fluid at ambient temperature after the desalination process is small then the heat transfer fluid tank could be left un-insulated and the use of low capacity refrigeration system for cooling the heat transfer fluid tank could be avoided. The technology is similar to but better than both low temperature thermal desalination (LTTD) technology when operated without a compressor and mechanical vapour compression (MVR) technology when operated with a compressor. Low temperature thermal desalination (LTTD) technology claims to desalinate sea water without crystallizing salt when the difference in temperature of evaporation vessel and condensation vessel is around 8 C whereas the present technology can desalinate sea water till complete salt crystallization when this temperature difference is just around the elevation in boiling point due to salt of around 4 C. Unlike mechanical vapour recompression (MVR) technology, the present technology can crystallize salt out of near eutectic brine at any low value of compression ratio by circulating same Water Today - The Magazine l June 2017 17
heat transfer fluid at a suitable high rate successively through evaporation and condensation vessel without requiring additional stages or apparatus. Apart from water desalination, the technology has got application in separation of miscible liquids and suspended solids from water and separation of miscible liquids, suspended solids and dissolved solids from liquids other than water. The technology has been deeply analysed and various embodiments of the technology have been extensively simulated using MS Excel and VBA. Post filing of three provisional applications with Indian Patent Office, a PCT application for the technology has been filed which has been published by WIPO and the technology is at present international patent pending. Companies interested in licensing the technology can contact the inventor of the technology, Amit Katyal, at amit@eq-comp.com. About The Author The above described Simultaneous Evaporation and Condensation in Connected Vessels technology has been invented by Amit Katyal who is an independent researcher/ inventor based in New Delhi, India. Amit, Bachelor in Chemical Engineering from IIT, Delhi, has over 23 years experience in hydrocarbon and water treatment sector in diverse segments like research, operations and technical services. Amit has also developed some very useful softwares for hydrocarbon sector like EQ-COMP, HYD-PREDIC, LIQ-PROP, BUBBLE- SIM and MIX-CP. Additionally, Amit has also invented two other technologies, one of which gives usage of gas hydrate concept to desalinate high salinity brines whereas the other provides a horizontal solution to vertical tray columns used in refineries and other chemical plants. A US patent for the Gas Hydrate Based Water Desalination technology has recently been granted by the USPTO with US patent number 9643860 and an Indian patent is pending for this technology. US, UK and Indian patents are pending for Horizontal Distillation Column technology. He can be reached at amitkatyal.asim@gmail.com. 18 Water Today - The Magazine l June 2017