By 2035, the world’s energy consumption will increase by 35 per cent, which in turn will increase water use by 15 per cent, according to the International Energy Agency.
Taking just one continental example, presently in the US thermoelectric power plants account for nearly 50 per cent of all freshwater withdrawals.
As if that wasn’t alarming enough, compared to today, five times as much of the world’s landmass is likely to be under “extreme drought” by 2050. Myron Van Ert, industrial sales director, engineered systems—water and process technologies for GE Power & Water took Power Engineering International through some of the ways it is helping utilities to meet their obligations to preserving water supplies.
“Clearly when it comes to resource management and sustainability water is paramount. There is a lot of demand on water resources but there are a lot of opportunities for us to improve overall water efficiency and that’s what we strive to do with clients.”
From using municipally treated discharge or reducing the loss of water in power plant cooling towers, there continues to be progress in the efficient use of water by power plants the world over.
Van Ert says often the first port of call in water management for GE is the boiler house.
“With a high pressure boiler – one of the areas adapted for efficient make-up is reverse osmosis (RO), which reduces regeneration needed on demineralisers. That regenerated waste needs to go somewhere and be treated in the wastewater treatment plant. Overall that increases the efficiency in the boiler house.”
“Related to that is higher efficiency reverse osmosis in the boiler house, higher efficiency RO plus electro-deionisation (EDI), which creates the high quality water you need but doesn’t generate any ion exchange regenerated waste.”
Another massive user of water in a power plant is the cooling towers. Side stream filtration of the cooling towers can help increase the loop efficiency and basically minimise the amount of blowdowns.
“Also depending on the dynamics, we look at using the cooling tower blowdown for re-use. A little harder than side stream filtration, harder meaning more costly, but it’s certainly possible and can recover some of that water and tighten up efficiency.”
In terms of cooling tower efficiency, there are several options.
“One (GE client) example uses a pond for make-up water. They bring well water, storm water runoff and all of their re-circulated blowdown into that pond. They basically diluted that cooling tower blow down a bit and drew that water off the pond to be used for their utility needs in the power plant.”
“It’s a more efficient means of driving their power plant because they’re not purely making up on fresh water – they’re using a balance of fresh water as well as re-circulated, cooling tower blowdown and being more efficient in utilising that water overall.”
Another frequently deployed method utilised by GE, which is gaining a lot of attention by power plant stakeholders, is to use municipally treated wastewater, re-using that water as makeup water for the plants.
One particular GE client took to this solution, not simply out of the requirement for water preservation, but as an economic decision, the cost of water in the jurisdiction being a significant motivator.
“They were in close enough proximity to a municipal treatment plant, that they were able to buy municipally treated wastewater for a fraction of the cost and were able then to put in the necessary treatment at their plant which was in this case a UF and RO system to treat that water and use it for their cooling tower needs.”
“It’s a much better solution in terms of impact, sustainability, and total return on environment perspective –we are in the second phase of that project now where we are going to use a little more water and further treat that for the boiler house makeup water.”
For some regions sheer water scarcity is of course much more of a factor than any economic consideration, California being a prime case, from a North American perspective.
“It’s a region which is a bit more water-stressed and water-conscious. So it’s about finding a viable option around source reliability. The power plant (GE client) was able to access municipally treated wastewater and they do further treatment in their plant which included UF and RO.
It’s become a drought-proof solution and did not impact on waste water consumption.”
Also coming under the banner of municipal water re-use is another example, in the country’s central region. This times the drivers are regulatory.
“What they’re using here is municipally-treated secondary effluent. The nature of that water means it needs further treatment so it undergoes a membrane bioreactor process. That water would be used for cooling water makeup and they further use it in the boiler house to demineralise it appropriately.
In terms of GE’s client-base, possibly the purest example of efficient use of water in a power plant is a project undertaken in Florida, although the company frequently provides similar solutions on a global basis.
“The facility is located in Florida and based on regulations and dynamics there, they need to go full zero liquid discharge so it’s an all-encompassing solution. They are permitted to discharge nothing or just a very small stream.”
“So they take all of the water streams – the boiler blowdown, the cooling tower blowdown and ion exchange regenerated waste, which all goes to central waste treatment. All of that is processed to thermal equipment. In this instance they are running about 1700 gallons a minute of evaporators where they are evaporating that water out and that distillate is re-used for other operations in the plant. They actually have crystallisers there where they are truly running to zero.”
Despite it being a growingly acute global problem, it remains to be seen if that most extreme example of power plant water use, as seen in Florida, is to become the norm. However there is no doubt that power plants the world over will need to remain conscious of its duties in the area of preserving water.
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