A tough task

| 07/08/2012 | 0 Comments

President of Leading Edge Technologies (LET) and past president of International Desalination Association (IDA), Leon Awerbuch is currently a director of IDA, and co-chairs IDA’s technical programmes committee. In April this year, he was named chairman of IDA’s energy task force steering committee whose goal is to achieve a 20% reduction in energy consumption in all major seawater desalination processes by 2015. He spoke to Anoop K Menon on the challenges of pushing the efficiency envelope, how hybridisation can contribute to energy efficient desalination, and the future of existing stock of multi-stage flash (MSF) desalination plants in the region.

How did the energy efficiency task force come into being?

The emphasis on energy efficiency is part of the global climate change debate, and particularly in desalination industry, one of our major challenges is to reduce energy consumption. International Desalination Association (IDA) had been discussing the nexus of water and energy and their inter-relationship for past two to three years, notable highlights being a two-day conference on energy efficiency in seawater desalination in Huntington Beach, California in 2010, and the Water-Energy Nexus Challenge sessions I chaired at the Singapore International Water Week (SIWW) 2011 Water Leaders Summit. This year we decided to really focus on this area by creating an energy task force.

We made a big splash in Marseille during the World Water Forum by committing to develop the guidelines to reduce energy consumption in all major seawater desalination processes by 20% by 2015. The energy task force, which will comprise of experts from around the world, will be leading this effort. We will be looking at thermal, membrane and hybrid desalination as well as power interlinks to achieve that. With the energy consumption of most desalination processes being quite efficient, even in relative terms, squeezing 20% efficiency will not be an easy task.

Taking up your comment on the relatively high energy efficiency of existing desalination technologies, where do you think additional gains can be tapped?

The biggest impact will come from technology solutions, whether it is pushing the energy recovery envelope in membrane processes or improving membranes to use smaller differential pressure or reducing losses from intake to outfall. In the case of thermal desalination, Multiple-Effect Distillation (MED) has achieved significant improvement in electrical power consumption. If we exclude pumping, we can build MED to deliver at 1kWh/m3, but that needs steam. So we would look at reducing the pressure of steam in order to extract more power from the turbine.

Leon Awerbuch

MED is unique because today, the technology operates at 65°C Top Brine Temperature (TBT) and we are still using a steam of 2.7 bars. Here the challenge would be how to use a much lower pressure of steam so that we can extract more power and run MED fully. MSF too has achieved improvements with the ‘double pass’ method. In the case of hybrids, I have always believed in taking advantage of the best properties of membrane and distillation processes to achieve reduction in costs and energy. In the case of Reverse Osmosis (RO), while isobaric energy recovery devices have done a very good job, demonstrating up to 95% energy recovery, the next step will be to increase the recovery of water, which will reduce the consumption of energy. Even with energy recovery devices, you have to look at bigger dimensions for the huge capacities found in this part of the world, and higher reliability too. To achieve the 20% reduction in energy consumption, we are going to look at closer integration between machinery, processes and systems.

What would be the key steps towards achieving this goal?

The starting point would be to establish a benchmark for each technology as each is different from the other. Given the different waters, salinities and temperatures, we have to find a technique to bring them to bases and decide the benchmark. We will also looking for ideas from manufacturers or suppliers of desalination equipment and utilities. If the manufacturers are open to sharing their ideas, we will try to demonstrate those ideas in the utilities Our job is to get everybody to think and work together on the same topic. The energy task force is not going to invent the process but try to focus people to think and find solutions that we can put up as basic guidelines. We will ask chemical manufacturers to allow higher temperatures TBT in the thermal process, the membrane manufacturers to improve performance so that there can be more water recovery. There are also aspects like Zero Discharge, for example, and whether that is helping the process or not? By the same token, how do you see different desalination technologies coming together to achieve energy efficiency?

In Kuwait, for example, they used the outlet of MSF and power plants as a source of feed to the RO plant. You save on intake and outfall, and when you have warm water, you can increase efficiency or flux of the membrane. For Fujairah expansion too, they have proposed the same idea. This is an example of process improvement from a hybridisation side resulting in significant energy and capital cost savings.

Are there ‘low hanging fruits’ when it comes to improving energy efficiency?

Historically, the top performance ratio for MED was eight i.e. eight tonnes of water per tonne of steam. Today, we are doing it at 10, 11, and there is also the example of a project in China where they achieved 15. Why can’t we try and implement that in this region? The way I see it, we have to gather all the knowledge and make them available to the utilities so that they can specify. Even the existing MSF stock in this region can be refurbished and upgraded with the latest technology. There are new chemicals with properties that improve efficiency and output. You cannot scrap the old MSF plants entirely.

Some time ago, I did a study for DEWA for a 32 year plant. We realised that we could improve the efficiency and output of the plant by 30%. Corrado (Corrado Sommariva, President,IDA – editor) implemented an energy efficiency solution for DUBAL which saved the company 3MW of specific power consumption in desalination process by the simple expedient of changing the impellers of the pump. The bottom line is to save the energy.

In private projects, energy is a significant component of the costs. Apart from cutting capital costs, if we can cut energy costs through technical solutions, we can achieve substantial reduction in water costs. Of course, if the material costs skyrocket as it happened with copper and nickel not long ago, some of the progress achieved could get negated.

 Do you see a role for the new IDA Desalination Academy play in these efforts?

The new IDA Desalination Academy will definitely be looking at energy efficiency issues. In fact, the Academy has an important role linked to the energy taskforce to propagate the information we will collect. The academy will hold its first courses in conjunction with the 2012 Singapore International Water Week (SIWW).

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