Flue Gas Cleaning during Sewage Sludge Incineration

Raw Water Treatment After Flue Gas Cleaning

The sludge that mainly consists of feces-consuming microorganisms remains in modern biological wastewater treatment plants. The sludge contains toxic admixtures such as heavy metals, halogenated hydrocarbons, and pathogens that argue against composting or agricultural use as fertilizer. With the reorganized sewage sludge utilization, phosphorus recovery became mandatory in Germany. Phosphorus can be recovered from the ashes of incinerated sewage sludge.

The energy gained during combustion can generate electricity for centrifuges, pumps, etc. The waste heat can be used to dry sludge. But corrosive gases that must not end up in the environment are released during the sludge combustion. After NOx removal, the wet flue gas cleaning process separates the remaining pollutants. The flue gas is guided against sprayed water from below in counterflow, and gaseous pollutants are bonded to the aqueous phase. The resulting raw water has a pH of approx. 2.

In a second cleaning step, sodium hydroxide solution is added to bind the gases (mostly sulfur compounds), which are particularly smell-intensive. In that process, the pH value should not fall below 7. Because several scrubbers are typically deployed in proximity, using multi-channel devices for pH monitoring has many economic and practical benefits.

More effective maintenance options with Memosens sensors

To determine the concentration of the sodium hydroxide solution, conductivity is measured using the?SE656?toroidal sensor. The sensor with high resistance to chemicals was designed especially for heavily polluted and strongly oxidizing media. For pH measurement of the alkalization in scrubbers, which have permanent pH values of 12, we recommend using the Memosens pH glass electrode?SE555, which has a service life of approx. Six months.

Protos: Reliable process monitoring and high flexibility

Since several measuring points can be implemented with only one?Protos-series transmitter, the analyzers have proven outstanding in flue gas cleaning applications.

In simple cases, sodium hydroxide solution dosing can be controlled via Protos relay contacts. In the basic version, the modular transmitter has four relay outputs that meet the minimum requirement for 2-channel measurement.