Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/459793
TECHNOLOGY | 24 | Desalination & Water Reuse | February-March 2015 temperature differentials between the heat source and the re-cooling source. For a plant overall a typical differential would be 10-20 K but for each stage a 2 K temperature differential is adequate. Much of the process' performance potential was established during 2012-13 at a 500 m³/d pilot plant at El Gouna, Egypt. Halabi says the TPTec LTDis can operate at "very, very high brine concentrations" of nearly five times the 70,000 mg/l maximum achievable using established technologies. He goes on to say the absence of evaporation bundles in MED eliminates scaling and corrosion and the need for chemicals to address those issues. He estimates that LTDis requires "less than one 10th of the chemicals" used in conventional thermal desalination and in some cases there are no chemicals used at all other than in disinfection. The capacity to drive LTDis using only low-grade heat gives the technology huge economic and environmental advantages compared to thermal and membrane desalination processes says Halabi. He says for every 1 kWh used in LTDis reverse osmosis requires 3-3.5 kWh while MED consumes 12 kWh and multiple stage flash desalination requires 14 kWh. SCaLabiLiTY aNd pOTENTiaL Halabi says the "most feasible size" for an LTDis unit to operate from waste heat is about 500-1,500 m³/d but he highlights the technology's scalability: "At the moment we could produce modules at 2,000 m³/d. We haven't ventured there yet but we will look at larger sizes if and when they come along. MED units were always thought of as 500 m³/d, maybe 1,000 m³/d and now they go up to 50,000 or even 75,000 m³/d. It will take time but things can develop," he says. Mansfeldt emphasizes further the capacity to ramp up the size of a TPTec LTDis facility: "Scaling up would not be a challenge for the technology itself. At this stage we are looking at projects all the way up to 10,000 m³/d so it is a broad range. Following that there would probably be a phase where we look at even larger projects, he says. He summarizes its potential: "At the end of the day the strength of the system is that we can use heat very efficiently. We can pick up low-value or no-value waste heat sources and perhaps others that are not currently being used. And in some instances we are seeing that processes have to cool water before it's expelled so that is something we could use quite easily." Metito has far-reaching ambitions for the technology (see table 1). It claims LTDis promises to "quickly become the leading thermal solution, in time, swapping places with the current reverse osmosis and thermal desalination technologies." According to Halabi: "LTDis has the potential to redefine the practice of thermal desalination, as it not only offers advanced benefits over existing thermal and membrane technologies, but it also provides significant energy and cost savings compared with other technologies." Does the company have a timetable in mind for LTDis' rise to the top? Halabi is circumspect, choosing to focus on immediate prospects: "We are now at the stage where we are commercializing the process we are going out to the various industries," Halabi says. "We expect to see market penetration in the first half of 2015 and we are basically about to install our first plant in the first quarter of 2015." MarkETS aNd appLiCaTiONS Metito's arrangement with TPTec gives it the licence for the African and Asian markets. With that geographic focus Metito's sector targets are on industries where waste heat is a feature and the oil and gas sectors Halabi explains. 'We are already in discussions with several entities that are looking for solutions to water desalination problems in wastewater. Basically in oil and gas, petrochemicals and other process industries and power there is a wide scope for this application. So these are prime targets," he says. Halabi highlights also uses for LTDis to improve the efficiency of thermal desalination plants and in membrane plants where there is a waste heat source. At the same time TPTec is looking to deploy an extension of the LTDis concept that can be applied to high-salinity waste – such as waste from existing desalination plants – to produce zero liquid discharge. Mansfeldt reinforces industrial reuse as the early chief target: "The focus for us is on industry where there is a need for clean water so there are a number of industrial situations where we can create value for the customer. Sometimes it's in combination with high-cost or problematic-to-dispose- of polluted water and we can assist in that. In one or two projects it's zero liquid discharge that we are involved in and in others even salt production because the client uses salt for other purposes in its industry." He goes on to list other opportunities for LTDis deployment including the power sector "from diesel generators right up to modern power plants" along with geothermal and solar heat as well as district cooling. LTDis has great potential as a means to up the recovery of an existing desalination plant says Mansfeldt. "If you take places like the Gulf, where land along the coast is scarce or expensive, and there may be environmental limitations on additional permissions, LTDis technology can be used to extend the capacity of an existing plant in a very cost effective way. That can be very interesting in places where land and space is limited," he says. He says this potential is particularly strong in inland desalination where the feedwater is pumped from deep down and often at a significant distance from the plant itself. In such instances some 3-4 kWh of electricity is used just to deliver the feedwater so extracting more from it becomes an attractive proposition. This is made still more attractive in instances where the water comes out from very deep wells at a temperature of 65-70°C. Not only can it be a heat source for LTDis but also LTDis could cool the water before membrane desalination is used. For a modest investment Mansfeldt says LTDis could improve the recovery from an inland desalination plant by some 20%. Halabi adds another detail. An TECHNOLOGY