Pollutant abatement control – technologies & solutions
Coal combustion is a dirty process, releasing a range of pollutants including sulfur dioxide, nitrogen oxides, carbon dioxide, volatile organic compounds, fly ash and a range of heavy metals. Neutralization/absorption of acidic pollutants, namely the NOx and SOx gases, prior to the fly ash filtration and treatment is essential to avoid damage to the filter media and excess of emissions. This operation is realized by the DeNOx (NOx reduction) and the FGD (SOx reduction) systems and is carried out by several techniques, including injecting a quantity of lime, limestone slurry, activated carbon or sodium bicarbonate, proportional to the pollutant concentrations.
To calculate and precisely adjust this pollutant reduction, on-line monitoring of HCl, NOx or SO2 (precursor of SO3 and sulfuric acid derivates) must be set on the process upstream of the abatement plant. The advantage of flue gas Process monitoring with ENVEA’s MIR 9000 analyzer ensures that the pollutant abatement function is optimized, whilst reducing the overuse of valuable materials in the abatement process, in turn providing cost savings to the plant operator and minimizing pollutant releases. Measuring additionally the water content would additionally allow the detection of a possible leak in the boiler.
The dust (fly ash) is captured and removed from the flue gas by electrostatic precipitators (ESP) or fabric bag filters (or sometimes both) located at the outlet of the furnace and before the final release point. To ensure that the dust filtration plant is operating at its maximum efficiency and ensuring optimum pollutant control, we can consider ENVEA’s range of filter performance monitoring systems. For bag filters, we install our Electrodynamic sensors in the outlet of each filter compartment, to confirm where leaking filter bags are present, which greatly decreases maintenance time and costs by highlighting the bags that need to be changed. For plants with ESP fitted, we can use the advantages of ENVEA’s unique, real-time data collection, via our “Pulse Log”, where precise variations in the emission profile during rapping (cleaning) of the ESP units is monitored. Such precise data provides the plant teams with the benefit of being able to adjust the voltages applied to the ESP plates, providing cost saving and emission optimization outcomes. The fly ash is periodically removed from the collection hoppers below the precipitators or bag filters.
To comply with NOx emission limits the application of ammonia or derivatives of ammonia (e. g. urea) as a reduction agent has proved successful. The nitrogen oxides in the flue-gas basically consist of NO and NO2 and are reduced to N2 and water vapor by the reduction agent. Two processes are important for the removal of nitrogen from flue-gases: selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR). In both these systems, the flow rate and control of NH3 must be continuously adjusted and controlled to prevent excess NH3 emissions (slip), to avoid ducts corrosion increase catalyst lifetime and reduce environmental impact and cost of reagents. To optimize this process, it is essential to use a gas analysis system for simultaneous and continuous monitoring of NH3 and/or NOx.
ENVEA’s involvement with the Power generation industry over many years and all over the world, has led to the development of a unique range of process and pollution monitoring solutions, as well as approved (TÜV and MCERTS) technologies for in-stack measurement of gas, particulate, and flow rate. They allow to control in real time the efficiency of the FGD, DeNOx and ESP systems and to optimize the whole-plant’s efficiency through measurement & control, to reduce air pollution and facilitate legislative compliance. Furthermore, they help saving operational costs by reducing plant’s maintenance requirements and process downtime.