Flue gas cleaning & external cooling in waste incineration

Because of the variety of combustion products produced, waste incinerators have an extensive process chain for the cleaning of the flue gas. This is important in order to protect the environment and keep emissions within the regulations and permitted limits. Both dry and wet flue gas cleaning technologies have been developed and applied. Fly ash is removed from the flue gas using an electrostatic precipitator (ESP). The flue gas is then quenched and the main content of HCl is removed from the gas stream. After further removal of particles by another ESP or baghouse filter, further HCl is scrubbed out of the flue gas. A second scrubber stage removes sulphur and heavy metals from the flue gas. Special care has to be taken with the piping and construction materials used in the flue gas treatment sections, because of the aggressive nature of the resulting aqueous scrubber solutions. The cleaned flue gas leaves the plant via the stack, where the total flue gas flow is measured, and analysers are used to monitor the composition of the discharged gas.

Measurement and control of fly ash levels in the ash handling processes or in bulk in a silo is not a trivial task; uneven surfaces, different moisture and di-electricity levels and high levels of dust in the gases reflect only some of the challenges. KROHNE pioneered radar level measurement technology for process applications and today offers a broad range of sophisticated FMCW and TDR technologies for both liquids and all kinds of solids, with products to suit almost every application. The patented drop antenna of the OPTIWAVE 6500 securely avoids dust buildup (compared to that with metallic horns), which significantly improves the availability of the instrument. This makes the OPTIWAVE 6500 system suitable for level measurement in a fly ash silo. The OPTIBAR DP 7060 C dP transmitter offers low range measuring cells for the monitoring of the differential pressure in ESP’s or baghouse filters. Level measurement of the absorber fluids is performed by OPTIBAR DP 7060 C with special chemically sealed diaphragms. The absorber and scrubber fluids are highly aggressive. To monitor and control the flow of these liquids, non-contact OPTISONIC 6300 W/F ultrasonic meters, or the OPTIFLUX 5000 electromagnetic flowmeter with a ceramic measuring tube, as these can both cope with these harsh conditions.