Advanced Nuclear Power Jan2002

Advanced Nuclear Power - The Magazine of Framatome ANP

The moisture separator reheater (MSR) plays a key role in the steam cycle of PWR and BWR plants. The MSR, usually located between the high-pressure (HP) and low-pressure (LP) sections of the steam turbine, dries the HP steam (with its initial water content of approximately 13%) and reheats it prior to admission to the LP section. However, due to changes in process conditions or operating modes occurring during a plant's service life, the steam that is fed to the MSR no longer conforms to the original design specifications. As a result, more heated steam is needed to evaporate the residual moisture or wet steam is admitted to the LP turbine. Both cases lead to a reduction in plant output and erosion/corrosion problems.

An Additional Pre-separator - POWERSEP
This situation can be reversed by installing an additional pre-separator in the steam cycle to improve plant output and extend component service life. Framatome ANP now offers a highly efficient and reliable high-velocity centrifugal separator called POWERSEP, manufactured by Balcke-Dürr. The pre-separator is of a simple, robust and compact design. The pressure drop occurring across the component is compensated for by the fact that single-phase flow conditions now prevail in the downstream piping.

The POWERSEP is installed in the crossunder piping (cold reheat line) upstream of the MSR in a horizontal, vertical or inclined position. It is therefore easy to retrofit into any operating plant.

It also can be installed in turbine extraction steam lines, e.g. upstream of HP feedwater heaters, to provide piping and heat exchangers with additional protection against erosion.

POWERSEP: Design and Operating Principle
A swirler consisting of stationary vanes in the inlet of the POWERSEP imparts a spin to the steam-water mixture. The resulting centrifugal action causes the water droplets to spin outwards against the inner cylinder wall, separating them from the steam. The water is discharged via external collecting chambers. Separation efficiency can be improved even further by internally routing part of the steam back into the hub of the inlet swirler.

Examples for Plant Output Gain:

Nuclear Power Plant		MWe Gain with POWERSEP	Payback Period*
Stade	(672-MWe PWR)	2.5 - 3.0 MWe	1.75 years
Brokdorf	(1,395-MWe PWR)	5.5 MWe	1.25 years

Benefits

Simple, compact and service-proven design
Robust construction
Long-term references
Highly efficient moisture separation
Erosion/corrosion in downstream piping and other components eliminated
No additional motive steam (e.g. turbine extraction steam) required
Economical solution (payback period less than 2 years)
Plant output increased (e.g. 1% less moisture results in MWe gain of around 0.5%)

Very Short Payback Period
Plant design features, such as accessibility, primarily govern the cost of installing a POWERSEP. The payback period depends, to a large degree, on the residual moisture content of the steam. In the case of moisture contents greater than 1.2%, cost savings are particularly large and the payback period is less than two years. This saving is further supplemented by reduced maintenance costs.

First Set of References
The centrifugal separation principle employed in the POWERSEP is already in use in MSRs installed at the Argentinean Atucha nuclear power plant as well as at Doodeward and Borssele in the Netherlands where they have seen many years of trouble-free operation with separation efficiencies of 90 to 95%.

Two new POWERSEPs have been in operation at the German Stade nuclear power plant since February 2000 where they are performing very well. Residual moisture was reduced from approximately 1.3% to around 0.3% and plant output increased by about 3 MWe. Heating steam flow was reduced and reheater outlet temperature raised without any increase in pressure drop.

Another four POWERSEPs also were retrofitted at Germany's Brokdorf plant in mid-2000.