Solution for continuous monitoring system of flue gas emission

The continuous monitoring system for flue gas emission from fixed pollution sources of our company consists of sampling probe, dust meter, temperature pressure flow integrated monitor, analysis cabinet, standard sample gas, pipeline, etc. The sampling probe, dust meter and temperature pressure flow probe are installed at the monitoring point (flue or chimney), and the analysis cabinet is installed indoors. The sample gas enters the analyzer cabinet through the sampling probe and heat tracing pipeline, and enters the flue gas analyzer through the pretreatment system in the analyzer cabinet to measure SO _two 、NO _X , oxygen content and other parameters; The dust meter is used to measure the dust concentration, and the temperature, pressure and flow integrated monitor is used to measure the temperature, pressure and flow rate. The measurement signal is transmitted to the data acquisition and processing system in the analyzer cabinet through cables; The industrial control system inside the analyzer cabinet can realize the functions of real-time data display, data transmission, data storage, historical data query, graphic data analysis, report statistics, etc. The standard gas is used to calibrate the analytical instrument.

1、 Sampling probe

The sampling probe includes sampling probe rod, sampling chamber, heating device, temperature control device, probe filter element, main body casing, etc. to avoid condensation and ensure that the sample gas enters the pretreatment system normally.
Features of sampling probe:
1. The heating automatic regulating unit is adopted, and the heating temperature is maintained to about 150 ℃ to avoid condensation.
2. The probe filter element is made of nickel titanium alloy with 2um pores to effectively remove smoke and dust in the sample gas.
3. The probe has a blowback function, which can realize automatic blowback through the control system, to greatly overcome the blocking problem and reduce the amount of maintenance.
4. The parts in contact with flue gas and flanges are made of 316L stainless steel to avoid material corrosion, measurement error and other problems after long-term use.
5. The shell of the probe body is treated with baking varnish.

2、 Flue gas heat tracing pipe

The flue gas heat tracing pipe is connected with the sampling probe and the pretreatment system. It is composed of two sets of corrosion-resistant high performance tetrafluoroethylene pipes supplemented by high-temperature constant power ribbon heaters and compensation cables, plus imported raw material insulation layer, and later coated with polyethylene (PE) protective jacket. The temperature in the sampling tube is controlled at about 120 ℃, so that the water content in the flue gas exists in the form of vapor, preventing water condensation and SO _two Produce acid.

3、 Pretreatment system

The pretreatment system includes gas condenser, fine filtration combination, drain filter, peristaltic pump, regulating valve, etc., to complete the dust removal and water removal of sample gas, ensure that clean and stable flow sample gas enters the gas analyzer, and ensure the accuracy and reliability of the analyzer.
Pretreatment system process:
When the sample gas enters the cabinet, it passes through a stop valve, which is usually open. When purging, the stop valve is closed to prevent the purge gas from entering the cabinet and protect the pretreatment system; Then it enters the cooler to remove moisture, and the condensate is gathered under the cooler and discharged through the liquid discharge peristaltic pump; Then the gas passes through a protective filter for dust removal; Then, after passing through a two position one way solenoid valve, the clean air for automatic zero calibration passes through this valve and is sampled by the sampling pump to calibrate the zero point of the analyzer; Then the gas enters the secondary cooler for further dehumidification. The dehumidified gas passes through the sampling pump, and then through a manual three-way valve, it is injected with standard gas to calibrate the instrument range, and then through the water blocking filter, the sample gas is further dehydrated, and then enters the analyzer.
Characteristics of pretreatment system:
1. The pretreatment system is placed inside the analyzer cabinet, with reasonable and beautiful layout, large reserved space and easy maintenance.
2. Two stage cooler can enhance the cooling effect and effectively remove the moisture in the sample gas.
3. The combination of two-stage fine filtration enhances the purification effect of sample gas.
4. Two peristaltic pumps ensure drainage effect in case of heavy sample gas moisture.
5. Add drainage filter to enhance the protection of the analyzer.

4、 SO _two NOx measurement unit

The working principle of gas analyzer is based on Lambert Beer law, and its analysis method belongs to ultraviolet absorption spectrometry. The measuring unit of the analyzer is composed of light source, gas chamber, optical fiber, spectrometer (including diaphragm, holographic grating, linear array detector) and other components.
 
Schematic diagram of photoelectric principle of analyzer
The ultraviolet light emitted by the light source enters the gas chamber through the optical window, and is absorbed by the measured sample gas flowing through the gas chamber. The light carrying the absorption information of the measured sample gas is converged through the lens, coupled into the optical fiber, and transmitted through the optical fiber to the spectrometer for light splitting, and the absorption spectrum of the gas can be obtained.
The concentration of relevant components in the gas can be obtained by differential analysis of the spectrum and combining with the chemometric algorithm.
1. Technical characteristics
● UV spectral analysis technology is adopted to eliminate cross interference and measure the concentration of various gases at the same time;
● Differential absorption spectrum algorithm is adopted to eliminate the influence factors such as smoke, moisture, light source change, and ensure the accuracy and stability of measurement;
● The absorption intensity of gas in different wave bands is different, which can realize range switching and large dynamic range;
● Optical fiber connection is adopted between light source, measuring room and spectrometer, without moving parts, with good reliability and convenient installation and maintenance;
● The pulsed xenon lamp light source is adopted, with a service life of more than five years, no preheating time is required, and the stability is good;
● Automatic instrument calibration every day enhances the reliability of data;
● Automatic alarm and recording function in case of fault, power failure, detection data exceeding standard and other abnormalities;  
● Touch screen display, simple and convenient operation, friendly interface.

5、 Oxygen content measurement unit

Measurement method: electrochemical method
Large range: (0~25)%
Output signal resolution:<0.2% of output signal range
Repeatability: ≤ 0.05% O _two
Deviation: in case of automatic calibration, it can be ignored; In the absence of automatic calibration, the typical value of exposure to air for 1 year is 1% O _two /Year

6、 Dust measurement unit

The principle of laser backscattering is adopted, with high resolution, which can be applied to the monitoring requirements of low concentration emissions as well as high concentration emissions; The structure is installed at a single end, without the need for optical alignment, and is not afraid of the beam swing caused by the mechanical vibration of the flue and the uneven refractive index caused by the uneven flue gas temperature; The instrument design process greatly reduces the complexity of on-site installation, installation and maintenance are extremely simple, and many problems caused by on-site installation and commissioning are greatly reduced; Standard 4-20mA industrial standard current output is adopted for convenient connection; The overall power consumption of the instrument is very small, about 5W; The calibrator shall be placed locally to avoid confusion and loss; Non point measurement, with large sampling area, can be used for chimneys of various diameters.
The dust meter includes laser light source and power control unit, photoelectric sensor and small signal pre-processing unit, scattered light receiving unit, display and input unit, output drive unit and main control unit. The 650 nm beam emitted by the laser shoots into the emission source at a small angle. The laser beam interacts with the soot particles to generate scattered light. The back scattered light enters the sensor through the receiving system and is converted into electrical signals for processing. The circuit part realizes photoelectric conversion, laser beam modulation, signal amplification, demodulation, light source power control, V/I conversion functions. The whole system consists of the host and calibration system, purging system, connecting accessories and rain box.

System schematic diagram
1. Technical characteristics
● The principle of laser backscattering is adopted, and it is not afraid of the beam swing caused by the mechanical vibration of the flue and the uneven refractive index caused by the uneven flue gas temperature.
● Single end installation without optical alignment.
● After the laser beam is modulated, the anti-interference ability of the system can be greatly improved.
● Instrument design implements the idea of "no tools" on-site installation, which greatly reduces the complexity of on-site installation.
● Standard (4-20) mA industrial standard current output is adopted for convenient connection.
● The overall power consumption of the instrument is very small, about 5w.

7、 Temperature, pressure and flow measurement unit

1. Flow rate

Measuring principle: Pitot tube
Measurement range: 0~40m/s.              
Measurement accuracy: ≤± 2% F.S
Input voltage: 220VDC
Output current: two-wire system 4 ～ 20mA

2. Temperature

Measuring principle: temperature sensor

Measurement range: 0~150 ℃. (Standard range: 0-400 ℃)
Measurement accuracy: ± 0.5%
Input voltage: 220VDC
Output current: two-wire system 4 ～ 20mA

3 Pressure

Measuring principle: pressure sensor
Measurement range: - 1~1Kpa. (Standard range - 10kPa -+10kPa)
Measurement accuracy: ± 0.5%
Input voltage: 220VDC
Output current: two-wire system 4 ～ 20mA

8、 Data acquisition and processing system

The data acquisition and processing system is used to acquire and process the data transmitted from each analyzer, and carry out real-time and effective control and processing, with high reliability and stability. The system includes programmable logic controller (PLC) and data processing and control subsystem.
PLC is the data acquisition and control unit of CEMS system. Different from the conventional control mode, PLC provides richer functions and higher reliability and expansion capability. In the CEMS system, PLC provides input and output signals of various analog and digital quantities, and carries out in-depth processing through software. PLC provides a 24-hour recording interface system, which can transmit processed data to DAS, and its control commands are activated through DAS.
The data processing and control subsystem can realize data acquisition, data processing, data storage, data real-time display, historical data query, graphic data analysis, report statistics, data transmission, control calibration, blowback and other functions.

 
1. Real time display interface
 
2. Parameter setting interface
 
 
3. Real time curve interface
 
4. Historical data interface
   
5. Report Menu Interface
 
6. Operation record interface
   
7. Calculation Formula Interface
 
8. Communication protocol interface
    
Chapter III System Installation

1、 System installation requirements

1. Monitoring point selection requirements
The monitoring point shall be located at a distance not less than 4 times the diameter from the elbow, valve and reducer downstream, and not less than 2 times the diameter from the upstream of the above components. For rectangular flue, its equivalent diameter D=2AB/(A+B), where A and B are side lengths. If such conditions cannot be met, the sampling pipe shall be installed at a ratio of 2/3 to the inlet and 1/3 to the outlet, with the installation hole as the boundary. It can also be installed on the vertical chimney of total flue gas emission, which is generally installed at one third of the total height of the chimney from the ground (brick chimney), but mainly at the place where the flue gas emission airflow is stable.
The specific requirements shall meet the requirements of Article 6 of HJ/T75-2017 Technical Specification for Continuous Monitoring of Flue Gas Emissions from Stationary Pollution Sources and Article 6 of HJ/T76-2017 Technical Requirements and Monitoring Methods for Continuous Monitoring of Flue Gas Emissions from Stationary Pollution Sources. The overview is as follows:
1) Located downstream of the fixed pollution source emission control equipment.
2) It is easy for people to reach and has enough space. When the platform height is>5m, Z ladder/spiral ladder/elevator shall be provided.
3) Vertical pipe section and negative pressure area of flue shall be preferred.
4) The monitoring points shall be kept away from the flue bend and the parts with sharp changes in cross section.
5) Each fixed pollution source emission equipment shall be installed with a set of flue gas CEMS.
6) If the exhaust of a fixed pollution source first passes through multiple flues and then enters the main discharge outlet of the fixed pollution source, the flue gas CEMS shall be installed on the main discharge outlet as far as possible.
7) The monitoring point measuring CEMS at the point shall be more than 30% of the flue diameter from the flue wall, no less than 1 m, and located at or close to the rectangular center of the flue cross-sectional area.
2. Preparation of installation platform
1) Maintenance platform is generally 400kg/m ^two For the design of equivalent uniform load, if it is greater than this value, it shall be designed according to the actual requirements or the adjacent floor load coefficient.
2) Other components of the steel platform shall be designed in accordance with the Code for Design of Steel Structures.
3) The platform is made of steel with mechanical properties higher than A3F.
4) All open edges of the platform shall be provided with safety guard rails. The design of protective railings shall meet the requirements of GB 4053.3-83 Fixed Industrial Protective Railings.
5) Platform planking shall be made of anti-skid steel plate with a thickness of more than 4mm or Φ 16 round steel to make rungs. In rainy days, the platform shall not accumulate water.
6) The platform shall be installed on a firm and reliable supporting structure and rigidly connected with it; The landing shall not be suspended on the flight.
7) All platforms shall be welded, and the welding requirements shall comply with the Specification for Welding of Steel Structures.
8) The steel beam of the platform shall be flat and straight, and the planking shall be flat and free of skew, warp and other defects.
9) The finished platform shall be coated with antirust paint and finish paint.
10) The distance from the outer edge of the platform to the outer wall of the chimney shall not be less than 1200mm.

1) The height of protective railings shall not be less than 1200mm.
2) All components of the railing shall be made of steel with performance no less than Q235-A · F.
3) The structure of the railing should be welded, and the welding requirements should comply with the technical provisions of GBJ 205.
4) The handrail should be made of steel pipes with an outer diameter of Φ 33.5~50mm, and the column should be made of angle steel of 50 × 50 × 4 or steel pipes with a diameter of Φ 33.5~50mm. The column gap should be 1200mm (outer diameter).
5) The cross bar shall be 25 × 4 flat steel or Φ 16 round steel. The clear distance between the cross bar and the upper and lower components is less than or equal to 380mm.
6) The baffle should be made of 100 × 2 flat steel or more. If the platform is equipped with other structural edges that meet the baffle function and strength requirements, it is allowed not to set additional baffle.
7) The clearance between outdoor railing, baffle and platform is 10-20mm, and no clearance is left indoors.
8) All structural surfaces shall be smooth and free of burrs, and there shall be no deflection, distortion, deformation and other defects after installation.
9) The railing surface must be carefully derusted and coated with anti-corrosion paint.
10) The design of the handrail must ensure that the load that the handrail can bear vertically in the horizontal direction is greater than or equal to
500N/m。
3. Preparation of monitoring room
3.1 Requirements for monitoring room
1) The size of the monitoring room shall not be less than 3000mm (length) × 3000mm (width) × 3000mm (height), and the size of the door shall not be less than 1000mm (width) × 2200mm (height).
2) The monitoring room is equipped with a window whose size is not less than 1500mm (width) × 1000mm (height).
3) The instrument room is equipped with a distribution box, equipped with 220V/8KW AC power supply, one general air switch (40A), two 20A air switches, and one 10A air switch. The air switch must be independently grounded.
4) The monitoring room must be equipped with a lighting system and a cold and warm air conditioner to ensure that the indoor temperature is 20 ℃~30 ℃, the humidity is kept below 90%, and there is no vibration.
5) The monitoring room must be equipped with a water and oil removal air source with a pressure of 0.4~0.8Mp.
6) At 2500mm above the ground in the monitoring room, a cable tray with a size of 100mm (width) × 50mm (height) shall be laid for the opening of flue gas heat tracing pipe and cable pipeline. A Ф 30mm hole shall be opened on the back wall of the cabinet near the ground to discharge waste gas and water.
7) The monitoring room shall do a good job of leakage prevention and lightning protection, the ground shall do a good job of moisture-proof and dust-proof, provide a good and reliable grounding point, and the grounding resistance shall be less than 4 Ω.
8) The ground of the monitoring room must be 10cm higher than the outdoor ground to prevent rain from flowing back. At the same time, a ramp with a smaller angle should be used to facilitate the handling of the cabinet.