Any facility that depends on a combustion process passing a low threshold must deal with one or more regulatory agencies to measure air pollutant emissions from said combustion. This can be anything from a common natural-gas-fired boiler to a cement kiln burning petcoke, waste solvents, and old tires. The common element of all these is that the relevant regulatory agencies will require continuous monitoring, calling for a continuous emissions monitoring system (CEMS).
Of the two cases just mentioned, the requirements will be drastically different and there will be countless possibilities in between those two extremes. The process of evaluating your processes and selecting suitable analyzer technologies is the topic of my article in Control Engineering, Understanding EPA Requirements for CEMS Design.
The common element is that applications must be monitored continuously whenever operating, and a continuous emissions monitoring system (CEMS) must quantify whatever individual pollutants and emission rates the regulatory agency specifies. Each agency generates a list of pollutants connected with these fuels, which may include:
- Nitrogen oxides (NOX)
- Sulfur dioxide (SO2)
- Hydrogen sulfide (H2S)
- Carbon monoxide (CO)
- Carbon dioxide (CO2)
- Hydrogen chloride (HCl)
- Mercury and other heavy metals
- Dioxins and furans
- Unburned hydrocarbons
- Other acid gases
- Ammonia (NH3)
So how does a facility select an analyzer, or more likely, a combination of analyzers, to detect and quantify the relevant pollutants associated with each combustion application? For starters, the regulatory agency will indicate which pollutant measurements it requires for each application. The next step is figuring out which analyzer technology is required to measure each pollutant.
Once the list of specific pollutants to be measured is finalized, it is possible to select which technologies may be necessary to cover the required measurements. Most situations are unique, but there is a large degree of commonality within various industries. Traditional analyzer selections and the analytes they can measure include:
- Non-dispersive infrared spectroscopy (CO, CO2, CH4, SO2, NO, NH3)
- Non-dispersive ultraviolet spectroscopy (NO2, SO2)
- Ultraviolet and fluorescence technology (SO2)
- Gas chromatography (total hydrocarbons, H2S, sulfur species)
- Paramagnetic technology (oxygen)
- Chemiluminescent technology (NOX).
Some applications might require several technologies if following the traditional methods just mentioned. Fortunately, Emerson offers newer and more versatile methods using laser technologies.
Quantum cascade laser (QCL) and tunable diode laser (TDL) analyzers have grown in popularity thanks to their ease of operation and ability to measure a wide variety of analytes. Generally, QCL covers the mid-infrared spectra, while TDL covers near-infrared spectra. These two technologies, working together in a single unit, can replace all the technologies just mentioned in many applications, and provide measurements of all the pollutants common to CEMS applications.
The specific product able to deliver this advantage is Emerson’s Rosemount CT5100 Continuous Gas Analyzer. It can be configured with up to six laser modules, some of which can measure two analytes, with each laser type covering its respective pollutants. This can cover up to 10 gas components in real time, greatly reducing cost of ownership compared to using multiple analyzers and technologies. For less complex applications, Emerson’s Rosemount CT4400 Continuous Gas Analyzer is usually sufficient where the primary concern is NOX from natural gas-fired combustion.
The article goes into more detail on other analyzer technologies, analyzer placement, sampling systems, and data acquisition and handling systems, so give it a full read. Talk to your local Emerson representative, and we can help configure the system for your application, simple or complex.
For more information, visit Emerson’s CEMS pages at Emerson.com.
