Over 80% of the flue gas desulfurisation (FGD) systems installed around the world utilize limestone as a reagent and spray towers to recirculate the limestone slurry and capture the sulphur dioxide.
The McIlvaine Company predicts that after forty years of use, this approach will give way to newer technologies. These technologies will achieve higher efficiencies, consume less energy, capture multiple pollutants and generate more valuable byproducts. Forecasts by system type are included in the McIlvaine report FGD World Markets.
Power plants will spend $4 billion for new FGD systems this year. They will spend $18 billion to operate and maintain over 1.6 million MW of installed systems. Many of these systems are either obsolete or unable to meet the latest environmental requirements. In some cases, corrosion has been extreme and major replacements of segments are necessary.
The first scrubbers applied at commercial scale in the 1968-72 period were tray and mobile bed scrubbers. These were very efficient but required careful chemistry control to avoid scaling. At the time there was not enough known about chemistry control, so power plants looked for a solution in a simple spray tower with no internals other than nozzles. This solution became a standard and most scrubbers sold now are of the spray tower design.
Limestone is much less expensive than lime or sodium compounds. It is less reactive. However, if you design the spray tower with enough height and recirculating slurry, it is possible to achieve efficiencies in excess of 95%. The problem is that the size and flow to achieve 98% is more than double that to achieve 90%. Many systems were installed to achieve efficiencies as low as 80%. The average efficiency requirement has been 90%. The latest environmental regulations are requiring higher efficiencies. In some cases, the efficiency requirement is 99%.
There are now a variety of options based on: mode of operation (wet or dry); need to remove multiple pollutants (HCl and mercury); need for very high efficiency (98% or better); demand for by-products; water scarcity; better control chemistry; and new designs with better economics.
