Flue Gas Testing

Identifying Potential Problems and Finding Solutions
Prior to commissioning the SCR is often advantageous to quantify some specific flue gas constituents which are most critical and can potentially deactivate the catalyst within a very short period or time.

Arsenic Testing and Limestone Injection
Testing for gaseous arsenic (As2O3) and/or the development of a SO3 gas and aerosol balance and/or the determination of the total level of Hg as well as the speciation between Hg0, Hgpart and Hg++ should be conducted.  Our test program includes coupon testing for arsenic in parallel with testing of gaseous arsenic (As2O3) with and without limestone (CaCO3) injection, and the mitigation effect on the concentration of As2O3 in the flue gas. Our test will verify the effects of limestone addition and establish a unit specific correlation between the actual gaseous arsenic levels and the test data.

Boiler Fouling
Evonik Steag also provides boiler fouling behavior tests to determine any potential influence of limestone injection. It is a well known fact that a large amount of free calcium oxide in the fly ash can lead to accelerated boiler fouling. However, based on Evonik Steag’s operating experience, such fouling should not be observed at the small quantities of limestone required to effectively mitigate gaseous arsenic in the flue gas.

SO3 and Aerosols
During our test program, a unit specific SO3-gas and aerosols balance can be developed during normal boiler operations, as well as during soot blowing to predict:

• The expected impact on air heater pluggage and required washing frequencies.
• The expected SO2/SO3 conversion rates of the boiler for various fuels.
• The expected SO3 concentrations of various fuels after installation of the SCR.

In order to limit the impact of additional SO3 in the system, Evonik Steag will make recommendations for maintaining a tolerable overall SO3 concentration after the SCR system to ensure reasonable air heater washing intervals, e.g. once per year. This recommendation may include fuel blending, specific soot blowing intervals, or other  measures to optimize operations.

Mercury Testing
Evonik Steag can also determine the overall concentration and speciation of mercury in the flue gas at various locations in the plant.  As elemental mercury can be oxidized across the SCR reactor and subsequently absorbed in a wet FGD scrubber, the overall fate of mercury can be determined during such a program and we can provide the expertise to mitigate the problem.