Laser Gas On-site Online Analyzer Technology and Product Application

In-situ analysis and measurement of industrial process gas composition is becoming increasingly important in the world's industrial field.

In-situ gas analysis and measurement is also one of the most important areas for complex industrial processes and emissions. In particular, users' needs for low-content and high-precision gas analysis and measurement also require gas analyzer manufacturers to adopt newer and more advanced technologies.

Meeting this need is the main purpose of the Norwegian company Nasik to develop laser gas in-situ analyzers. Nasik can provide a series of laser gas in-situ analyzers based on unique technology and superior performance than traditional gas analysis products.

Laser gas in-situ analyzers have opened up a new field of industrial process and emission gas measurement. Through unique technologies such as advanced solid-state diode laser technology, optical solutions, spectroscopy and rugged industrial design, laser gas in-situ analyzers can work without cross-interference from other gases. Process pressures can reach 5 bar and temperatures exceed 1600°C.

- Measurement principle

Laser gas in-situ analyzers are optical instruments that emit laser light from a temperature-stabilized, single-mode diode laser to a receiver diametrically opposite the transmitter. The diode laser operates near room temperature.

Conventional on-line analyzers such as infrared (IR) on-line analyzers are often affected by cross-interference from other gas components (including dust, moisture background components, etc.), which becomes increasingly serious when the detection content is very low. In contrast to conventional IR infrared on-line analyzers that use broadband spectral filtering, laser gas on-site on-line analyzers use single-line spectroscopy technology in the near-infrared spectral range.

Single-line spectroscopy measurement technology is based on the selection of a single absorption line of the gas to be measured in the near-infrared region. By analyzing the spectrum of the selected absorption line, there is no absorption line of other gases within the wavelength of the selected absorption line (no cross-absorption interference). Then, by adjusting the diode laser temperature and drive current, the diode laser frequency is adjusted to correspond to the single absorption line of the gas. The laser spectrum width is correspondingly adjusted to be narrower than the spectrum width of the single absorption line of the gas to be measured. By changing the current of the diode laser, the laser wavelength containing the single absorption line is scanned and emitted.

During the laser scanning emission, as a characteristic of the wavelength, the light intensity detected by the receiving unit will change, and this change is only due to the absorption of light by the gas molecules to be measured in the optical channel between the laser and the receiver. The shape and size of the detected single absorption line are used to calculate the gas content between the transmitter and the receiver. The absorption lines of other gases do not appear in the selected wavelength range and therefore do not interfere with the single absorption line and thus affect the gas content measurement.

The laser gas on-line analyzer is not affected by absorption such as water, dust or contaminants on the window in the process gas. This is because the calculation of the gas content is based on the size and shape of the unique single absorption line, thus achieving more reliable measurements and reducing the need for maintenance.

- Installation

The laser gas on-line analyzer is easy to install due to its small and rugged mechanical unit. It consists of three basic units: the

transmitter unit with purge, adjustment mechanism, DN50 installation
receiving unit with purge, adjustment and calibration mechanism, DN50 installation
electronic unit with display The

transmitter and receiver units are directly assembled to the DN50/PN10 or PN16 flanges welded on the pipe or flue through their own flanges. Flange valves (recommended ball valves) can also be inserted between them. During installation, a PC is connected to the analyzer electronic unit and the service software is run. The

optical window, stainless steel flange and purge mechanism establish the interface between the process gas and the analyzer. To prevent dust and other contaminants from accumulating on the windows, they should be purged continuously with dry and oil-free compressed air, gas (usually nitrogen) or a fan.

Adjustment of the analyzer is performed by adjusting the flanges of the transmitter and receiver. Valves (ball valves are recommended) to prevent process gas leakage during installation and maintenance can be installed between the process gas and the flanges. These valves also protect the windows.

- Maintenance

The rugged industrial design and continuous purging make the laser gas on-line analyzer very easy to maintain and the maintenance workload is quite low (almost maintenance-free). Since there are no moving parts in the instrument, preventive maintenance is limited to visual inspection and cleaning of the optical windows. Experience has shown that maintenance intervals are usually more than three months and are as simple as cleaning the optical windows. Since key parameters are internally detected, the instrument will give a reminder if maintenance is required outside the recommended maintenance interval.

- Calibration

The laser gas on-line analyzer is calibrated when it leaves the factory. No calibration is required for the first use. Recalibration is only required after at least six months or several years. Calibration is very easy due to the advanced technology used in the analyzer. Calibration is performed by blowing calibration gas into the built-in "fluid flow cell" of the receiving unit. Therefore, on-site calibration is possible without removing the transmitting and receiving units. Calibration is performed via a PC and the calibration process is very easy - the service software running on the PC completes all calculation tasks. Off-line calibration with a calibration tube is also optional.

- Input and output signals

The laser gas on-line analyzer provides three main gas content output signals as standard signals:

4-20 mA analog output measurement value, 500 Ω Max., isolated.
Display on the electronic unit (LCD): gas content, light intensity, warning and error messages
RS 232 port on the electronic unit
Optional: fiber optic signal output measurement value (synchronous ASCII format)

- Service software

The laser gas on-line analyzer consists of a transmitter, a receiver and an electronic unit. It communicates with the PC via RS 232 during installation, maintenance and calibration, and can also communicate with the PC remotely via a MODEM. The analyzer service software is specially designed to complete all necessary operations, such as setting the output range, gas temperature and pressure, optical channel length, etc.

- Summary

The laser gas on-line analyzer has a rugged design and uses the world's most advanced technology. It is therefore suitable for high-precision emission measurement and process control applications. It includes the following features:

Continuous, on-site online measurement
High sensitivity and high accuracy
Response time is generally less than 2 seconds
Optional measurement range
Optional output unit
Working at 0.1 to 5 bar pressure, gas temperature exceeds 1600°C
Easy to install
Minimal and simple maintenance required
Built-in purge and calibration mechanism
No gas sampling pretreatment required
No cross interference from other gases (not affected by dust, moisture, background components, etc.)
Dust and dirt on the window have no effect on the measurement