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Chapter 3, Page 7: Converting Natural Gas Power Plants To Thorium Instead Of Carbon Capture         <  6  Page  8  >
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   Recycling Natural Gas Power Plants Into Thorium Power Plants

Almost all smaller old coal power plants will be getting combined-cycle gas conversions for both economy and emissions reasons.
Adding a further upgrade to thorium rather than carbon capture is obvious.
One EBASCO size molten salt reactor - 1 gW (e) - could power a half-dozen turbines and small steam generating units simultaneously.

A 1,300°F thorium-fueled MSR powered turbine is minimally efficient but maximally clean.
(It is unlikely the turbines would be as powerful after being converted to Stirling turbines.)

Repowering an old coal burning power plant previously repowered with cleaner burning natural gas.
 - Common these days.

(Below)  Repowering a power plant and long steam pipe lines are commonplace.  A few miles to the North of Big Bend, also on Tampa Bay, is Tampa Electric Company's (TECO) "Bayside" power plant.  Bayside was originally a coal burner - you can see the old, original stacks for two large coal boilers, the boiler house, and turbine gallery on the left.  Notice two of the old boilers attached to the right end of the turbine gallery are larger than the other four.  To become both cleaner and more powerful, Bayside was converted from coal to combined cycle natural gas turbines (natural gas turbine - think of a 747 size jet engine driving an electric generator).  In addition to making electricity, the hot exhaust blast of the jet engine is used to heat a heat recovery steam generator which, in turn, drives an old, existing steam turbine which also makes electricity. 

It's not unusual for over a billion dollars to be spent upgrading an old power plant to be cleaner and more powerful.  Worldwide, there are perhaps 15,000 power plants the size of Bayside or larger.  http://www.platts.com/Products.aspx?xmlFile=worldelectricpowerplantsdatabase.xml has their addresses.

Gas turbines are much smaller in power than most large steam turbines so several have to be hitched up like teams of horses to repower a large steam turbine.  In the case of Bayside, 3 gas turbines, in addition to making their electricity, provide steam for one large, old, steam turbine with the other four gas turbines heating small boilers (just above the turbine stacks) for a second, larger old steam turbine.

Notice how long the steam lines are? - bottom of picture, many expansion "U" - from the gas turbines to the old coal steam turbine gallery.  Steam pipe lines a half mile long or longer are common worldwide.  So while they may look long in the marked up Big Bend photo above, in practice they would be considered of only medium length. 

This also points out that converting power plants from one fuel to another has become commonplace. 

(Left) Bayside natural gas turbine heat recovery steam generator stack row.  Natural gas makes 2/3 as much CO2 as coal.  Bayside Power Plant Tour .pdf

These steam plants are conventional sub-critical superheated steam technology.  According to the IEA, supercritical status for hard coal plants is defined as achieving outlet steam temperatures of 540-566 °C (1,000-1,050 °F) and a pressure of 250 bar (3,600 psi). Ultra-supercritical units are defined as those with outlet steam temperatures above 590 °C (1,100°F) and pressures above 250 bar (3,600 psi). Supercritical and ultrasupercritical plants can achieve efficiencies of up to 45%; conventional sub-critical plants rarely achieve thermal efficiencies of 40%.