I. Preface

CEMS system is a very important part of the desulfurization system, whether it can work properly is related to the safe and stable operation of the desulfurization facilities. Whether it is semi-dry desulfurization or wet desulfurization, when the flue gas is desulfurized, the SO2 content in the flue gas is low, and the flue gas temperature is low and contains a lot of water, so it is easy to condense in the flue gas sampling line and cause the measurement value to be inaccurate. Especially, the flue gas contains large amount of soot, which is easy to block the sampling line when it meets water.

Our plant I desulfurization CEMS system is using SMC-9021 system, the principle is direct extraction sampling method. The purpose is to maintain the flue gas temperature in the process of extracting flue gas from the chimney to the flue gas pre-processor, to prevent the flue gas composition from changing due to condensation, and to make the data of analysis and measurement deviate. The flue gas sampling pipe is heated continuously to keep the sampling pipe at a temperature above 140°C. The heating stops when the temperature is above 140°C and starts when the temperature is below 140°C.

Second, the working principle

Corrosion-resistant sampling composite tube is a group of corrosion-resistant high-performance resin tube and self-limiting heating tape composed of the inner core, plus insulation layer, aluminum belt, and finally lay a flame retardant polyolefin protection jacket composite. Self-limiting heating line is characterized by working temperature of 140 ℃ (national standard), power 40 ~ 60W/m, through the form of thermal conduction will sample tube heating, so as to ensure that in the sample gas transmission process does not condensation, self-limiting heating line for: piece of point-like parallel heating material composition, reach 140 ℃ constant temperature no longer heated, when lower than 140 ℃ began to heat. That is, the temperature of the entire pipeline temperature, reliability.

Self-controlled temperature electric tropical "temperature control" principle of work is: self-control temperature electric tropical electric heating element, is in two parallel metal bus bar between the uniformly extruded layer of PTC material made of core tape. One end of the cable when the two busbars and the power supply is connected, the current from one busbar lateral flow through the PTC material layer to reach another busbar, PTC layer is a continuous parallel connection between the busbar resistance heating body, the electrical energy into heat energy, the operating system for heat insulation. The core band resistance increases with the temperature, and when it reaches the high resistance area, the resistance is so large that it almost blocks the current, and the core band temperature reaches the high limit and no longer rises but limits the temperature automatically. The output power of the cable is mainly controlled by the heat transfer process to the temperature of the heated system.

PTC effect is the positive temperature coefficient of resistance effect (Postive Tempcrature coefficient), specifically refers to the material resistance increases with temperature, and in a certain temperature region a sharp increase in the characteristics. With PTC effect of the material is called PTC material.

Electric tropical corresponding to be heated system with automatic adjustment of output power, so will not burn because of their own heat, can be due to the actual need for heat compensation, so for a new generation of energy-saving constant temperature heater. Low temperature state, fast start, uniform temperature, easy installation, high level of automation, low operation and maintenance costs, safe and reliable, long life.

Three, installation precautions

The installation requirements of the corrosion-resistant heat sampling composite tube are strict, and the failure is easy to occur when using carelessly, which affects the service life of the corrosion-resistant heat sampling composite tube.

(1) composite tube in storage and transportation, installation, try to avoid dragging in the ground or immersed in water, oil, so as not to damage the sheath and insulation layer.

(2) the self-limiting temperature associated with heat tape, sampling pressure guide tube for testing (after testing to be closed with heat-shrinkable casing). Review the corrosion-resistant heat-tracing sampling composite tube before construction, no damage.

(3) composite tube installation should prevent heavy objects from falling and smashing, touch damage.

(4) where crossing the line connection box and easy to wear parts of the band body must have special protection measures to prevent vibration abrasion, should generally be placed in the bridge or special pipe rack. Should avoid laying with the power cable together.

(5) to corrosion-resistant sampling composite tube in the self-limiting temperature tapes test insulation resistance and safety inspection. Composite tube in the installation before and after, should be self-limiting temperature with tropical electric performance test, wire core insulation resistance> 20MΩ is appropriate. In the case of the weather humidity can be relaxed to > 2MΩ, in < 2 MΩ is to find out the reason, the party allowed to power commissioning, up and down the process requires a detailed handover records

(6) Gas tightness check of sampling tube (with dry instrument air).

7) whether the design of the distribution capacity to meet the requirements of self-limiting temperature with tropical, self-limiting temperature with tropical with PTC characteristics, decided a power supply start when there is "inrush current" phenomenon, usually by the designer, user negligence. Because of the distribution capacity switch is too small, leading to wire heating, tripping, can not be put into operation. Composite tube length> 20 meters of the pipeline need to be equipped with HY01-B-220/35-100 automatic current limiter produced by Zhejiang Huayuan Electric Heating Co.

(8) compound tube in the self-limiting temperature with tropical power supply voltage must be relatively stable. If the power supply voltage fluctuation is too big, easy to make the compound tube in the with tropical damage, must take corresponding measures, such as adding voltage stabilization device.

(9) power line should be used three core cable, one of the core as grounding and with the tropical shielding layer at the same time connected to the grounding terminal, inside and outside the grounding bolts must be solid and reliable.

(10) should be very careful when stripping out the core line with the heat, to avoid multi-strand core broken strands, so that the core cross-section becomes small, causing overload and burned, the wire in the twisted knot with heat-shrinkable casing seal.

(11) compound tube in the self-limiting temperature with the two cores of the heat tape, in the end of the band is strictly prohibited to touch the short connection, in general, with heat-shrinkable casing seal, and closed with the terminal. In the explosion-proof, humidity areas must use special explosion-proof terminal. After wiring the nut should be tightened firmly and reliably, so that it is not pulled off by external forces.

Four, daily maintenance

Corrosion-resistant sampling composite pipe is an important part of CEMS system, if it does not work properly, the sampling pipeline is easy to condensation, resulting in inaccurate measurement values. Especially when the content of soot in the flue gas is relatively large, it is easy to block the sampling pipeline after meeting water. At the same time, the corrosion-resistant sampling composite tube inspection, maintenance is not timely, not in place, easy to occur corrosion-resistant sampling composite tube fire combustion, resulting in fire accidents, I plant has occurred two corrosion-resistant sampling composite tube fire combustion accidents, because found in time, did not cause significant losses. So in the daily inspection and maintenance, we must pay attention to whether the corrosion-resistant heat sampling composite tube works normally.

In CEMS inspection, we should check carefully whether the leakage protection switch is tripped, whether the automatic current limiter is working normally, and whether the corrosion-resistant heat sampling composite tube is heating normally. If you find that the leakage protection switch is tripped, you should stop the system work to avoid a large amount of water in the pipeline to damage the equipment. First, check whether the probe heater is working normally. If the probe heater switch trips, check the probe heater first to make it work normally. If the probe heater is working normally and the cartridge is wet, notify the operator to adjust the operation mode. Secondly, check whether the pipeline of the corrosion-resistant heat sampling composite pipe is smooth, experiment with the pipeline with compressed air of the instrument, and if the pipeline is blocked unblock the pipeline. Do not blindly close the gate, should identify the reason for tripping and then close the gate. If you close the gate blindly, the pipeline will easily overflow and cause fire.