Friday, April 22, 2011

Drought, renewable energy, Texas, London and Florida

The Governor of Texas has asked the denizens of the state to pray for rain. The state has not had serious rain for months, and the drought conditions have turned severe.

The current drought conditions in Texas.

Conditions are not anticipated to get any better in the next few months. The recent predictions are that the conditions will persist in the area through July.

Predictions of the weather changes through July (NOAA )

Droughts around the world are one of the unfortunate consequences of changing weather, in much the same way as we have seen high snowfalls in other parts of the country this past winter. There will likely be cries about the underlying causes (with folks forgetting that droughts have occurred throughout history), but this post was started because of a potential event-changing occurrence.

This week Thames Water, which supplies 687 million gallons of water a day to the inhabitants of London and the immediate vicinity, was running its first water desalination plant. The region has faced droughts in the recent past as have other regions of the United Kingdom. Earlier solutions included building large water reservoirs, that at Kielder is the largest man-made reservoir in Europe. There is, however, only a certain limited amount of land that can be made available for this use, and so desalination proves an alternate way of supplying the increasing global demand for water.

In the United States droughts have threatened the viability of nuclear power stations, since the shortage of cooling water (as we recently learned again in Japan) is essential to safe plant operation. And therein lies one of the rubs to the situation. As the spokesman for Thames Water noted, the intent is not just to run the plant when there is a drought, since that is going to be too late. Rather at times of lower rainfall the plant (which can produce up to 150 million gallons a day) will pump clean water into the reservoirs, maintaining their integrity, and building up a reserve that will reduce the drought impact if it occurs. The plant was apparently completed last June at which time it was expected that it would just be used in times of drought. Within the last year that thinking has changed, and the plant is now running intermittently, partly to train operational staff, partly potentially also to help meet demand.
According to the Environment Agency, average water use is 148L per person per day in the UK and in the south-east of England it’s as high as 170L (far higher than the government target of 130L). Despite the popular perception of London as an overcast, rain-soaked city, its rainfall rate is, in fact, on a par with Rome, Dallas and Istanbul.

Schematic of the flow path through the desalination plant.

One question that I had relates to the amount of power that will be needed at Beckton. A calculation assuming that it takes 4 kWh to produce a cubic meter of fresh water, suggests that it will need a 21 MW plant. In 2009 the company CEO noted
The (20 MW) plant will be the first in the world to generate all its energy on-site, from renewable sources, including recycled cooking oil.
However the plant has been controversial, not least because although planning to use rapeseed oil, it could also burn palm oil, which is apparently cheaper. That is much more controversial. Planning permission for a second plant nearby at Southall, was refused in June 2010.

Biofuel powered stations in the UK, which includes that in the Tees Valley, where a plant burning 300,000 tons of recycled wood and specially grown wood from plantations, have had a somewhat mixed reception.

But to get back to the original idea of desalination, the largest plant in the United States is in Tampa with a maximum projected size of 35 million gallons/day, though it currently only produces some 25 million, sufficient for 10% of the region’s water needs. It went on line in 2008.
The plant uses about 44 million gallons per day (mgd) of seawater from a nearby power plant’s cooling system, which is pretreated with sand filters and a diatomaceous earth filtration system to remove particles. Reverse osmosis filters then separate 25 mgd of freshwater from the seawater. The unused concentrated seawater is diluted with up to 1.4 billion gallons of cooling water before it is discharged to the bay and that dilution is why environmental studies show no measurable salinity change in Tampa Bay related to plant production.
Which brings us back to Texas. In the latest report on desalination in the state, two possible developments are cited. There is a plan to install a 2.5 million gallon a day plant at Brownsville and a 1 million gallon a day facility on South Padre Island. Unfortunately the South Padre Island initiative failed in a bond election last year, and its future is considered doubtful. Meanwhile the Brownsville Public Utilities Board is considering combining a renewable energy source (shades of the UK) into the plant, in order to leverage funding, and possibly qualify for DOE funds.

But in the meantime, as the discussion continues, the drought gets worse. The discussions started with an initiative in 2002. As those in Texas may find out the hard way, waiting until the crisis is upon them makes it too late to construct the solution that might have helped. It appears that those in the UK and Florida were just a little more prescient. It might be noted that the initial planning for the Florida plant started in 1996.


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