Knocking the SOx Off Emissions
AFT Arrow™ Technical Paper
Authors: Adam Klepacki, Energoprojekt Katowice SA; Trey Walters, P.E., Applied Flow Technology, June 2012
ABSTRACT
Curbing SOx emissions from thermal power plants remains a challenge for operators but a project involving the refurbishment of the flue gas desulphurisation installation at a Polish power plant offers a way forward.
Power plants built in Poland from the 1960s to the 1980s were not equipped with flue gas after-treatment systems (except for dedusting installations) as the contemporary environmental regulations did not require them. Over the years, however, the situation has changed and power plants were obliged to carry out environmental projects that reduce emissions such as SOx and NOx.
The hydraulic calculations for this problem can always be done using hand calculations because a careful engineer must first have a feel for these issues and, second, know the theoretical foundations of hydraulic calculations to accurately interpret the results.
However, in the era of computers, one can use a specially designated software less complex than three-dimensional programmes. Commercially available programmes for conducting this type of calculation in a more straightforward way include AFT Arrow, developed by American company Applied Flow Technology. The main goal of this paper is to present results of numerical simulations of flue gas system in the GDF Suez Połaniec power plant carried out in AFT Arrow and to compare them with measurements collected during actual plant operation.
CONCLUSION
It is therefore confirmed that the flue gas, which by default is treated as a compressible fluid in this type of calculation, and even large flue gas ducts, can be treated as incompressible. Therefore, the use of computational tools simpler than full three-dimensional flow analysis is justified. Creating such a model and hydraulic analysis enables:
- Design of a system ” determination of duct diameter, the way connections are done (tees);
- Prediction of the pressure distribution in the system ” determining the location of overpressure and vacuum;
- Checking of the reserve on the fans, which can influence the decision to build new systems (replacement of existing system) or other remedial action;
- Ability to simulate various situations which allows the engineer to analyze the operation of the system in all expected configurations.
The project, which ended in complete success, allowed the desulphurization of flue gas of each power unit of the Poà…‚aniec power plant and met all emission standards.
GDF Suez Energy Poland achieved the target production model and finalized the construction of a new power unit, which will be completely fired with biomass ” the so-called Green Unit ” will replace unit 8, which was turned off in November 2011. The new unit will meet very stringent emission standards (<150 mg/Nm3 for both SO2 & NOx and <20 mg/Nm3 for dust) and therefore emissions from this unit will not require further desulphurization or denitrification.
In addition, existing power units 2″7 were modernized to improve efficiency and meet NOx emission standards that come into force. The future of unit 1 was determined pending full compliance with existing legislation (Industrial Emissions Directive and national law).
Below is an excerpt. Use the links above to view the full paper.
Flue Gas System
In the case of NOx, the situation was not complicated, since the implementation of air staging systems and low-emission burners were sufficient to meet the required standards. It was more difficult in the case of SOx because it was necessary to build flue gas desulphurization (FGD) which was substantially more expensive. Moreover, the spatial layout of the power plant often prevented the convenient location of the FGD plant so in many cases the complexity of the flue gas system increased.
Flue gas systems are one of the basic elements of a typical coal-fired power plant. The system primarily consists of ID fans ” forcing the flue gas flow; flue gas ducts with the necessary equipment such as shutoff dampers, expansion joints, measurement systems, and others ” directing the flue gas; and the stack ” releasing flue gas to the atmosphere.
In recent years, flue gas ducts have become significantly more complicated, with many additional components such as bends, dampers, and expansion joints. This change has created a need to define how the flue gas system will operate under the new conditions. What will be the pressure drop of the flue gas flow? What will be the pressure in each key part of the system? Will new flue gas fans be necessary? What are the reserves on the existing fans? These questions can only be answered by a multivariate analysis of the complete flue gas system.
The flue gas system discussed here is in Poland in the Poà…‚aniec power plant, belonging to GDF Suez, on the banks of the Vistula River in the southeast of the country.
The power plant has eight power units, each rated at 225 MW. In 1998 the FGD plant was commissioned, and connected to power units 5″8. Additional booster fans were installed to overcome flow resistance from the FGD plant. The first stage was already associated with the construction of new flue gas ducts with a set of accompanying equipment. But the project’s subsequent second stage was more complex ” connecting power units 1″4 to the FGD installation. Hydraulic analyses were performed to see if the system would operate properly and what modifications might be required.
The general objective of the second stage was to enable the operation of all power units through the FGD. The FGD plant was designed only for four power units, but a few capacity tests confirmed that it could accommodate flue gas from almost six power units, which gave the green light for the project.
Although the yearly average load of the power plant was equal to six power units in operation, it was necessary to build a relief duct in the installation to dump the flue gas stream directly to the new stack in case of an excessive pressure rise in the ducts. This duct acts as a pressure stabiliser if more than six power units are in operation. This was also foreseen in the calculation model.