Zurich, Switzerland, December 19, 2005 - ABB, the leading power and automation M. Rübner-Petersen & F. Pollastro October 2005 – page 3 of 9
3.2 Process flexibility
A major advantage of the CT-121 process is its inherent operating flexibility. The process
is designed for wide operating ranges of flue gas flow rates and SO2-loads. SO2 removals
of 99% on SO2-contents of 7,000 ppm have been demonstrated. Moreover, the flexibility of
the CT-121 not only allows the process to fit a wide range of owner requirements, it also
handles changing operating and regulatory requirements.
When designing an FGD plant the central consideration is how to remove the desired
amount of sulphur at the minimum cost. The operating costs are mainly limestone and
energy. Whereas there may be an advantage of a few percent in limestone consumption for
the CT-121 compared to a conventional open spray tower FGD process, due to the lower
possible operating pH, the advantage in power consumption can be significant.
The JBR relies on the liquid submergence of the sparger pipes (i.e. the absorber level) to
generate the gas-liquid contact. The cost of this is pressure drop that has to be overcome
by the flue gas fan. As the flue gas fan can be continuously controlled it is possible to
optimise the JBR operation for any conceivable operating case within the design range.
A conventional open spray tower relies on large recirculation pumps to generate the
gas/liquid contact required for SO2 removal. The energy spent is the power consumption of
the pumps and the fan power needed to overcome the pressure drop generated in the tower.
As the pumps have to be operated on/off this means that the open spray tower is operated
in steps and is only running at optimum conditions for the exact load cases for which the
pumps are designed.
3.3 Reactor design and materials
The CT-121 can be supplied in any of the normally applied materials of construction, e.g.
carbon steel with resin/rubber lining, carbon steel with high alloy cladding, solid high
alloy, concrete with Stebbins tile, or FRP. The final choice will depend on the client’s
preferences, technical specifications and an overall economical assessment.
Furthermore the reactor shape can be either circular or rectangular. The general experience
is that the rectangular absorber allows a simpler and more compact layout with a lower
capital cost, and the large majority of the units that have been commissioned over the last
10 years have been of the rectangular type. In both designs the inlets and outlets can be
rotated freely.
3.4 Superior gas flow distribution
A major uncertainty in operating large FGD absorbers at high SO2 removal efficiencies is
gas flow distribution. As the size of a gas processing unit increases, the potential for
maldistribution of gas flow and thereby the risk of compromising the performance also
increases. In any FGD system, good gas flow distribution at any gas flow rate is critical to
achieve the desired SO2 removal.
The JBR is a natural gas distribution device due to the differential pressure mainly
resulting from the submerge of the sparger pipes. Since the spargers are evenly spaced in the JBR inlet plenum, the pressure drop guarantees, that the gas flow is evenly distributed.