Thirst for power: improving water efficiency in coal-fired power plants
From China to India and South Africa, coal-fired power plants are being linked to water shortages and collectively consume enough water to meet the needs of one billion people worldwide. What can be done to improve water efficiency in the ever-thirsty global energy sector?
On 16 May, Adani Power, the largest private thermal power producer in India, announced that it was shutting down four 660MW units at the Tiroda plant in Maharashtra, India due to an acute water shortage.
The news would likely have been dismissed as a minor, isolated incident had it not taken place in the wake of a damning new report published by Greenpeace to mark World Water Day on 22 March.
The first plant-by-plant study of the coal industry's current and future water demand revealed that the world's 8,359 coal-fired units already consume enough water to meet the needs of a billion people - and that vital freshwater resources are under threat if plans for hundreds of new coal plants go ahead.
Assessing the water used both in producing electricity and mining coal, the report found that 44% of current coal-fired units and 45% of planned plants were situated in areas in a state of water stress.
Roughly a quarter of the proposed new coal plants are earmarked for what Greenpeace calls 'red-list areas', regions where freshwater is in deficit and being used faster than it is naturally replenishing.
The top countries with proposed additional coal plant capacity in red-list areas are China (237GW), India (52GW) and Turkey (7GW); almost half of the proposed Chinese coal fleet is in red-list areas.
In Australia, Greenpeace's data shows that the coal industry uses up over 537 million cubic metres (Mm3) of water every year - more than could fit in Sydney Harbour (500Mm3).
"Coal is contributing less and less to Australia's economy, but is still taking up enormous resources and inflicting lasting damage to our environment," says Greenpeace campaigner Dr Nikola Casule. "The cost of propping up this industry is simply too high for Australia and can no longer be justified."
"[Coal] deprives us of our most precious resource - water," he adds. "If all the proposed coal plants around the world were built, the water they consume globally would almost double."
Satisfying the industry: why water is essential to global electricity generation
Like most other steam-producing electricity plants, coal units typically withdraw and consume water from nearby water bodies such as lakes, rivers or oceans, to create steam for turning their turbines.
The Union of Concerned Scientists (UCS) reports that a typical coal-fired power plant employing a once-through cooling system withdraws 70−180 billion gallons of water every year and consumes 0.36-1.1 billion gallons of it. A coal plant with a wet-recirculating cooling system extracts only a fraction of that figure, but still consumes 1.7−4.0 billion gallons a year, while a dry-cooled system uses much less.
Around 53% of US coal plants use once-through cooling and 40% wet-recirculating systems. The US Environmental Protection Agency (EPA) estimates that dry-cooling facilities produce around 7% less power than wet-recirculating plants; hence, under 1% of units use this technology.
Water also plays a pivotal role in coal mining and transportation. In addition to burying streams, contaminating water sources and increasing the risk of flooding - all of which are side effects of strip and mountaintop mining used to exploit seams close to ground level − coal may need to be treated with water and chemicals to remove sulphur and impurities before it can be burned in a power plant.
According to the US Geological Survey (USGS), an estimated 5.3 billion gallons of water were withdrawn for mining every day in 2010, while a 2015 Scientific American report reveals that oil and natural gas fracking, on average, uses more than 28 times the water it did in 2000, at up to 9.6 million gallons per well.
Finally, and again using the US as an example, coal is often transported using the slurry pipeline method, which withdraws hundreds of gallons of water for every MW/h of electricity produced.
Liquid assets: IGCC technology and eutectic freeze crystallisation
Coal provides 40% of the world's electricity and could account for 50% of the growth in global water consumption for power generation over the next 20 years. New technologies that promote efficient fresh and wastewater management in new and existing coal-fired units are therefore at a premium.
Integrated gasification combined cycle (IGCC) technology uses a coal gasification system to convert coal into a synthesis gas (syngas) and produce steam. The hot syngas fuels a combustion turbine generator, which produces electricity. Along with reducing air pollutants, the IGCC process has the potential to decrease water consumption by 35%-60% compared with conventional coal plants.
China's first IGCC power plant is currently under construction in the city of Tianjin in the north-east of the country. Upon completion, the 250MW plant will generate up to 1,470GW/h of electricity annually.
South Africa's Eskom has invested in a pilot eutectic freeze crystallisation plant to test whether the solution could eliminate effluent liquid discharge from power plants, materially reduce raw water consumption and even enable the utility to begin treating acid mine drainage for use in its plants.
Eutectic freeze crystallisation is based on the principle that, when water freezes, salts and impurities are excluded from the water matrix, which can then be removed. Eskom currently utilises 1.39L of water for every kW/h of electricity production and is aiming to reduce that figure to 1.34L by 2020.
Building a stable supply: the future of coal-fired power plants
The location of future coal-powered power plants is also key, not only to relieve pressure on water reserves, but also ensure there is sufficient water to ensure a stable electricity supply to the grid.
A July 2015 report by the National Renewable Energy Laboratory (NREL), part of the US Department of Energy, offers details on the first US national electricity capacity expansion model to incorporate water resource availability and costs as a constraint for the future development of the electricity sector.
"At current prices of water and energy technologies, it can be economically advantageous to build water-intensive power plants in certain locations where there is water rather than build power plants with lower water intensities in locations with water scarcity," the report states.
This chimes with Greenpeace's call for an immediate moratorium on coal expansion in regions with high water stress, chief among them China, where in the first nine months of last year, state-owned firms received initial or full approval to build 155 new coal plants with a total capacity of 123GW.
Despite new capacity from natural gas and renewables, coal continues to supply nearly 30% of global energy consumption. In South East Asia where energy demand is projected to spike by 80%, coal will likely be the single largest energy source, owing to its abundance and relative affordability.
In light of this, and with nearly one billion people worldwide living without access to clean, safe drinking water, the onus is on the coal industry to come up with technological and operational solutions that will ensure the continued supply of energy − while also protecting one of mankind's most elemental resources.