The nitrogen oxides contained in the flue gas emissions of coal-fired boilers are important precursors to air pollution, and controlling the total amount of NOx emissions from coal-fired flue gas is a key focus of environmental regulations in various countries. Selective catalytic reduction (SCR) and selective non catalytic reduction (SNCR) technologies are currently the mainstream technologies for flue gas denitrification. By injecting ammonia or urea into the flue gas, its main component NH3 reacts chemically with nitrogen oxides to generate environmentally friendly N2 and H2O. To achieve optimal ammonia injection efficiency and reduce NH3 emissions and consumption, real-time monitoring of residual NH3 concentration in flue gas is necessary. In general, the monitoring instrument for ammonia escape is installed at the end of the reduction reaction after ammonia injection (as indicated in the figure below).

Typical SCR denitration process diagram for coal-fired power plants

The problems of traditional online analysis methods for ammonia escape
The flue adopts a direct installation of the injection type, and the precision requirements for the opening of the injection flange are high. Under harsh installation conditions, such as vibration, expansion, and contraction of the flue, the optical accuracy of the instrument is difficult to meet the requirements for use, which directly affects the stability and accuracy of the system.
The in-situ online analysis system cannot introduce standard gas for inspection and calibration
The available absorption spectrum for NH3 near-infrared analysis is narrow, with small absorption peaks, and is susceptible to interference from other gas components
NH3 near-infrared analyzer has a lower measurement limit of 1ppm and low resolution

Introduction to Tunable Semiconductor Laser Absorption Spectroscopy (TDLAS) Technology

At present, the effective and cost-effective high-temperature denitrification ammonia escape detection method is the TDLAS detection method. TDLAS is more favored by users due to its fewer vulnerable parts and no need for sample gas dilution. The basic principle is to tune the wavelength of a specific semiconductor laser to scan the absorption spectrum of the measured gas. The transmitted light absorbed by the gas is received by a photodetector, and the harmonic components of the transmission spectrum are extracted by a lock-in amplification module to invert the concentration information of the measured gas.

Shanghai Jilian QCL-TDLAS technology advantages
Shanghai Jilian adopts QCL-TDLAS technology, and the target spectral line is the strongest absorption peak of ammonia molecules in the mid infrared band. Molecular spectroscopy studies have shown that the infrared absorption lines in ammonia molecules are tens of times stronger than the near-infrared absorption lines. Under the same measurement conditions, the detection accuracy can reach the ppb level, which is tens of times higher than near-infrared TDLAS. Jilian Company has revolutionized the use of internationally leading semiconductor QCL as the laser source, combined with stable and reliable optical path design and exclusive signal processing technology, to achieve unprecedented accuracy and stability in TDLAS optical sensing technology, solving the problem of poor stability and low accuracy of near-infrared ammonia meters and fully meeting market demand.

Comparison of absorption line intensity between near-infrared (blue box) and mid infrared (red box) of ammonia molecules

Product advantages

Resolve the distortion of large cross-section and micro concentration flue gas detection in in-situ laser analysis systems; Inaccurate alignment of light caused by factors such as flue vibration, environmental temperature changes, and changes in flue stress; The high dust and high moisture content affect the laser transmittance in laser detection; Smoke, dust, and corrosive gases adsorb on the surface of the lens, causing lens coking and scaling, which affects laser detection; Unable to perform online calibration and other application issues.
The laser extraction measurement method adopts the extraction sampling method, which extracts the flue gas from the flue and enters the gas analysis room after dust removal and purification, and uses TDLAS technology for detection. The entire sampling process is accompanied by heat, and the concentration data of the gas to be measured is true and reliable. This device can be calibrated and zeroed using standard gas detection. Effectively avoiding the influence of factors such as flue vibration and thermal expansion on laser detection. Suitable for monitoring smoke pollution sources in harsh environments and complex working conditions.
The system structure facilitates later maintenance, calibration, cleaning, and functional expansion

Comparison between Shanghai Jilian QCL-TDLAS and general NH3 detection technology

Technical parameters

Measurement Principle: Second Generation Ultra High Precision Quantum Cascade Laser Absorption Spectroscopy Technology (QCL-TDLAS)

technical indicators

Range 0~10ppm, 0~100ppm (more range options available)
Response time ≤ 10s
Linear error ≤  1% F.S
Repeatability ≤ 1% F.S
Range drift ≤  1% F.S./Half year
Detection limit 0.01ppm
Calibration/maintenance cycle ≤ 2 times/year
Preheating time ≤ 30 minutes
Data anomaly rate ≤ once/half a year
Vibration resistance ≤ 7mm/s (able to withstand general vibrations)
Built in data storage capacity of 8GB, capable of continuously storing data for 2 years under normal working conditions

working conditions
Power supply 200-240 VAC 50Hz
Compressed air for blowback gas purification instruments
Environmental temperature -10 ℃~50 ℃ (non condensing)
Flue gas temperature 100-600 ℃
Power consumption<1.5KW

preprocessing

Product dimensions 1700 × 600 × 600mm (height × width × depth)
Processing method: direct extraction (hot wet method)
Sampling flow has no special requirements
Sample gas temperature ≥ 180 ℃ (no cold spots throughout the entire process)
Moisture content does not require condensation for water removal
Dust filtration accuracy<0.5 μ m
Humanized human-machine interaction (HMI) interface
Protection level IP54

Interface signal

Analog output 2 channels 4-20mA output (isolated maximum load 750 Ω)
Digital output standard RS485 Modbus, optional Ethernet
Relay output with 3 channels of output

install

Installation method: Ground installation
Sampling probe docking flange DN65 PN16 (GB HG20592-97)

Industry applications

Denitrification process section of thermal power plant

Denitrification process of cement rotary kiln
Garbage incineration treatment plant