MechChem Africa March-April 2021

Optimising DeNOx plants in the cement industry This article describes how SICK Automation’s GM32 in-situ gas analyser is being used in the cement industry to minimise emissions in a denitrification (DeNOx) plant that is using selective catalytic reduction (SCR).

N ew environmental legislation and companies’ self-imposed sustainability obligations have contributed to a marked increase inenvironmental awareness. This is especially the case when it comes to the emission of hazardous substances andenvironmental pol- lution. Many industries, therefore, are taking steps to reduce or prevent these dangerous emissions. SICK Automation’s innovative in- situ gas analyser GM32 helps to reduce emis- sions in denitrification (DeNOx) plants using selective or non-selective catalytic reduction (SCR or SNCR). SICK Automation’s GM32 in-situ gas analysermeasures nitric oxide (NO), nitrogen dioxide (NO 2 ), ammonia (NH 3 ) and sulphur dioxide (SO 2 ), as well as pressure and tem- perature directly inside the plant’s process gas stream. The analyser unit is equipped with a gas permeable probe (GPP), which is positioned inside the duct. The direct measurement enabled from this location facilitates a short response time, leading to fast measuring results. The analyser is ideal for use with selec- tive catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), two of the accepted secondarymeasures used to reduce NOX emissions. Primary measures include flame cooling, installation of low NOX burn - ers, staged combustion and general process optimisations.

Cement industry case study To comply with local emission regulations of 200 mg/Nm 3 for NOX and 30 mg/Nm 3 for NH 2 , HeidelbergCement Group in South WesternGermany invested inanSCRplant to supplement its existing SNCR solution. The main difference between the two technologies is theuseof acatalyst. TheSNCR is installed in the riser duct or calciner of the rotary kiln at temperature ranges of 900 to 1000 °C. TheSCR, on theother hand, consists of a specific number of catalyst layers that operate at approximate temperatures of 300 to350 °C. They canbeplaced in thehighdurst rawgas streamor before themain stack in the low dust gas stream. The gas analyser would be placed at the SCR inlet between the ammonia water injec- tion nozzles and the catalyst. The advantages of having the measuring location at the inlet is that simultaneous measurements of NH 3 andNOentering the SCR, and in this instance NO from the combustion process, can be collected. To achieve sufficient SCR control, the analyser had to meet two requirements: it needed to have fast response times for effi - cient control of the ammoniawater injection; and extended maintenance-free intervals becauseof thechallengingconditions inwhich it operates. HeidelbergCementGroupcontactedSICK for a solutionand theGM32, designed tocope with high dust, high temperatures and vibra- tions, was selectedas the ideal solution. Itwas agreed that the analyser would be installed for a 12-month test period fromMarch 2019 to March 2020. The installedSICKgas analyser andfilter requires checking, cleaning andmainte- nance only every nine to 12 months. Stack movements are possible due to higher temperatures and tem- perature fluctuations at the measuring sta- tion, and are

compensated for with the analyser’s auto alignment correction. This continuouslyaligns the light beam during operation to ensure stable and reliable measurement. Compared to other measuring systems that require frequent calibration using test gases, integrated filters for zero and span automatically compensate for drift and en- sure a correct and accurate measurement. Thismeans less frequent test-gas calibrations and lower operational expenditure. Using the SICK Meeting Point Router remote service, onsite tests were conducted and a large amount of additional process data was col- lected and evaluated. The test period proved that the analy- ser has a stable reaction time of less than 20 seconds without the need for cleaning or maintenance. The results show that with a delay of two to 17minutes, depending on the measuring component, a continuous emission monitoring system alone is not sufficient for DeNOX process control. The 12-month test was successful and, subsequently, another HeidelbergCement plant inGermanyequipped itsDeNOXsystem with two GM32 analysers for SCR control. The two devices were commissioned in June 2020. How the GM32 works Using the wavelength-specific light absorp - tion by the gas mixture on the activemeasur- ing path, the sender/receiver unit determines the concentration of the gas components present. UV light sent from the sender/re- ceiver unit passes the active measuring path of the GPP probe and is reflected by a triple reflector at the end of the probe. Thepermeablefilter element – theheart of the GPP – keeps all dust outside of the mea- suring path, while the gas permeates quickly through the pores ensuring the required fast response time. The GM32 uses differential optical absorption spectroscopy (DOAS), where the absorption lines of specific gases in a particular wavelength range are evaluated. With its GM32 in-situ gas analyser, SICK Automationhas proved that companies in the cement industry can maintain and restore a clean environment, effectively supporting climate protection. www.sickautomation.co.za

The SICK in-situ gas analyser GM32 – measure aggressive gases directly and quickly, even in ATEX zones

34 ¦ MechChem Africa • March-April 2021