Measuring Multiple Emissions

The latest developments in optical and electronic component technology enables the simultaneous measurement of several process emissions in the cement plant by one analyzer, resulting in significant savings in capital expenditure and operational costs.

by Ravi Narayan, Cemtrex Inc, USA


The measurement of emissions by kilns, coolers and mills through the use of online analyzers helps cement plants to collect the information required to run the plant within a narrow band of process parameters. This type of process control aims to reduce off-spec product and maintain a high product quality. In addition, the data is used for environmental control and compliance with current legislation.


Overcoming conventional challengesprobe2

One of the main challenges in both process and emissions monitoring is maintaining sample conditioning systems with high capital and operating expenditures. While absorption infrared spectroscopy has been applied in a wide range of analytical instrumentation applications, challenges remained in terms of moving laboratory instruments to field applications.


However the latest developments in micro-optics and micro-electronics have made it possible to redesign conventional in-situ analyzers. The new folded beam and paired collimated optics-based design has overcome the fixed optical profiles of conventional optics-based analyzers, which are inserted into the process or industrial stacks and provide online real-time measurements with 'fixed' optical path lengths.


By adapting a 'straight path' design using paired collimated optics, the infrared beam can be extended to longer distances with minimum loss of energy to detect low levels of gas phase concentrations. It also allows the flexibility to alter the insertion lengths of the optical probe. The insertion lengths are critical for a representative in-situ sampling to simultaneously measure a range of emissions. Therefore, the same hardware can be used without any design modifications, delivering significant savings in capital and operating expenditure.


One analyzer, multiple gases

CO2 emissions

A key threat to global climate control initiatives, greenhouse gas (GHG) emissions - particularly CO2 emissions associated with fuel combustion, power generation and the decarbonation of limestone - require monitoring with suitable analyzers. The new analyzer includes measurement data exclusively for CO2 emissions at several plant process locations, which can be linked together for data compilation and comprehensive GHG reporting and control. This interconnectivity also enables plant operators to make intelligent decisions relating to market-based programmes such as carbon trading and exchange rate control. The new analyzer design incorporates interface features that enable data exchange between the probe and other standard protocols for line access in a data highway.


NOx emissions

The new analyzer is also able to simultaneously measure both NO and NO2 in the same probe and add up both measurements to obtain total NOx emissions. Due to their technological limits, conventional techniques convert NO2 to NO and the measure only the NO in the process. The current need for estimating NO and NO2 ratio is avoided with the new analyzer as wavelength selection with narrow-band 'triple' spectral line techniques selectively measures NO and NO2.


NOx/CO2 ratio

High-temperature combustion in the kiln leads to higher NOx emissions. While lower NOx emissions can be achieved by a low secondary air flow, low-NOx burners and water cooling of the kiln flame, this may result in higher CO2 emissions, which impacts the thermal efficiency of the flame. Online NOx and CO2 emissions monitoring of the kiln exhaust gases helps to achieve a balance in water cooling, leading to an optimum NOx/CO2 ratio.


The newly-designed analyzer monitors both types of emissions and controls the water cooling process to achieve this optimum ratio as well as providing emissions data for reporting.


SO2 emissions

SO2 emissions can vary over a wide range, depending on the quality of raw materials in terms of sulphur content. To remove SO2, cement plants use flue gas desulphurisation (FGD) systems that inject calcium carbonate (CaCO3), which is an expensive catalyst. The control of such CACO3 injection plays a key role in reducing emissions control costs at the cement plant and the online real-time monitoring of SO2 emissions avoids unnecessary injections both at the inlet and outlet of the FGD systems. In addition, the data collected can be used for reporting.


Volatile organic compounds

Due to their strong alkaline atmosphere and high flame temperatures, kilns are able to burn high calorific value waste fuels such as used solvents, waste oil, used tires, waste plastics and organic chemical waste (including polychlorinated biphenyls [PCBs], obsolete organochlorine pesticides, and other chlorinated materials).


However, the use of these waste fuels can lead to emissions of volatile organic compounds (VOCs), polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs), hydrogen fluoride (HF), hydrogen chloride (HCl), and toxic metals and their compounds if not properly controlled and operated.


To help effectively control such emissions, the Insitu probe applies specific measurement wavelengths for HCL and HF in the online continuous monitoring. The flexible insertion length design provides low-level monitoring HCl and HF at the outlets of the control equipment.


Additional benefits

The new design also incorporates a heated stainless steel or Hastelloy filter sleeve that protects the probe optics and can be automatically cleaned for any dust accumulation, particularly in cement process applications. The filtration media can be selected for their porosity and material construction based special requirements.


The optical head houses the electronics and optics in a protective enclosure that is certified for hazardous area installations. The 'head' purge design enables the probe to operate at extreme ambient temperatures, relative humidity and corrosive environments.


The 'smart' data processing electronics inside the head is capable of exchanging data over the cloud or with standard 'legacy' signal interfaces. Unattended automatic calibration enables easy verification of the probe for the plant operators and environmental authorities.


The new folded beam and paired collimated optics-based analyzer combines a range of key benefits to deliver an improved cost-effective process and environmental monitoring application.

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