First, the main problem

1. Influence of flue gas humidity on the test

The high humidity smoke brings two problems to the monitoring work. In terms of dust collection, under certain conditions, wet smoke will cause the glass fiber filter cylinder to be wet, thus increasing the resistance of the sampling system. If the resistance increases to a certain extent, a series of problems may occur, such as dust cannot be collected at the same speed, the sampling process is interrupted when the loading of the collection instrument is too high, the filter cylinder cannot bear the pressure rupture, and the sampling filter cylinder cannot be taken out normally when it is wet and rotten. On the other hand, SO2 is easily soluble in water. In the process of SO2 testing, the flue gas is extracted from the relatively high temperature of the flue, and the water vapor condenses into water at room temperature or low temperature. SO2 is dissolved in water to form non-volatile sulfuric acid separated from the flue gas, so the test data is generally low.

2. Influence of high negative pressure on the test

The flow of boiler flue gas in the pipeline is a system consisting of boiler furnace, dust collector, blast ventilation and pipeline, and it flows under a certain external power. The hydromechanical parameters are formed by a number of factors, so the high negative pressure is not only caused by the excessively fast flow rate of flue gas in the test point area.

High negative pressure has no direct effect on the smoke test, but has a direct effect on the smoke test. For example, the concentration of SO2, NOx and other components in the constant potential electrolysis test flue gas will be affected by the size of the gas flow through the sensor, and the size of the negative pressure will directly affect the size of the gas flow rate inhalation sensor, thus affecting the size of the concentration measurement.

3. Influence of charged dust particles on the test

Electrostatic precipitator is one of the widely used equipment for removing dust from industrial pollution sources. The principle of electrostatic dust removal is to make the internal particles with high voltage static electricity, through the law of positive and negative electrodes to remove dust. However, the particles that have not been removed may carry static electricity, which is transmitted to the host through the signal cable used to measure the smoke temperature and discharge electronic components, resulting in abnormal operation or even damage to the instrument.

Second, the main countermeasures

1. Treatment of high humidity flue gas

The sampling gun is the core technology in the monitoring of boiler and kiln. The influence of high humidity gas on the accuracy of solid and gaseous pollutants monitoring was overcome by improving the internal structure and working mode of the sampling gun.

In order to solve the problem of collecting dust under low temperature and high humidity, corundum filter cylinder is first used instead of glass fiber filter cylinder. Practice has proved that corundum filter cylinder can well solve many problems caused by wet filter cylinder. However, it is difficult to deal with the residue of corundum filter cylinder in the early stage, and it will be scrapped due to the blockage of filter cylinder in the recycling process. These limit the use of corundum filters.

The sampling tube with constant temperature heating at the position of the filter barrel is used to keep the temperature of the filter barrel at more than 120 ℃ to ensure the relative drying of the filter barrel. This kind of sampling tube has a good effect in the field test, but the disadvantage is that the weight and volume of the sampling tube should be increased correspondingly.

Measurement of water-soluble gaseous pollutants under the condition of high humidity flue gas, generally adopt refrigeration dehydration or high temperature heating of the two ways to pretreat the flue gas, refrigeration dehydration method due to the traditional semiconductor refrigeration efficiency is not high, resulting in water and gas separation speed slow and incomplete dehydration, water and gas separation process and residual water vapor will take away a part of the gaseous pollutants, Therefore, the flue gas measurement process will bring great deviation to the measurement of such pollutants, resulting in inaccurate measurement results. High temperature heating method is used for high temperature treatment of flue gas before measurement, but this method requires the airway to have good thermal insulation effect, which will inevitably increase the volume and weight of the airway. For the environmental protection industry that often carries out high altitude testing, such requirements are impossible to achieve. Therefore, the traditional refrigeration device with air as the medium has been improved, with antifreeze as the medium for refrigeration, based on the excellent thermal stability of antifreeze, when the high temperature flue gas into the flue gas pipeline in antifreeze, antifreeze temperature changes little, which greatly improves the refrigeration efficiency, gas condensation dehydration is complete, and the freezing point of antifreeze below -40 ℃, Therefore, when the cooling temperature of the semiconductor refrigeration device is set at about 0 ℃, the icing phenomenon will not occur.

2. Reduction of positive pressure and negative pressure

In order to reduce the influence of the high negative pressure flue on the test, a scheme is to use the large pump of the smoke sampling system to overcome the negative pressure resistance of the flue. A multi-path device is designed in the gas channel. The dust collection pump can be connected to the smoke sampling gun, and then the small pump of smoke sampling is connected to the multi-path device to collect the gas entering the device.

3. Elimination of static electricity of gas particles

General instruments adopt sampling tube grounding, anti-electrostatic lightning protection devices and other measures, but can not solve the problem of electrostatic interference to the instrument. In this regard, on the basis of the original EMC design process and comprehensive application of photoelectric isolation, transient interference suppression, EMI filtering, shielding grounding and other comprehensive technologies, the way of electrostatic discharge has been changed. The traditional method of electrostatic discharge is to introduce static electricity into the power supply, and the accumulation of static electricity affects the normal operation of the power supply. The circuit board or even the CPU of the instrument is damaged so that the instrument can not work normally. After the test, the static electricity into the instrument shell, through the metal shell of the large volume pump in the instrument and the instrument shell grounding way to discharge the static electricity, for this program has done a lot of tests, and achieved preliminary success; In addition, the industrial ZigBee wireless communication mode between the sampling tube and the host is adopted. The application of this technology reduces the connection between the host and the sampling tube, and further fundamentally eliminates the influence of flue static electricity on the sampling instrument.

Third. Conclusion

With the improvement of waste gas treatment and the progress of treatment technology, the state of waste gas emission has been complicated. In the process of waste gas treatment, high positive (negative) pressure, high humidity and low pollutant concentration often occur in the sewage system, which leads to inaccurate monitoring results and even contrary to objective values. Therefore, it is recommended that enterprises consider factors such as gas pressure, humidity and pollution concentration comprehensively and select on-line monitoring equipment that meets environmental monitoring requirements.

In addition, the selection of instruments to meet the needs of monitoring work, in addition to their own accuracy, stable performance, fully consider a wide range of applicability, especially to the special environment. POTS (kilns) furnaces and discharge devices are often installed in continuous production links, not an independent unit, and often in flammable and explosive, strong corrosion environment, so monitoring instruments should have explosion-proof, corrosion resistance and other characteristics; Different factors contained in the same emission source should be synchronously monitored and quantified in the monitoring process, and there should not be a large time span, so as to meet the requirements of monitoring data identity.

In the actual test work, it is found that the monitoring points of sewage facilities in newly built enterprises do not meet the national requirements on the standardization of sewage outlet, especially in large enterprises; Old enterprises and reconstruction and expansion units due to the limited area of the factory, the transformation of old equipment is limited by the original pattern of bondage, can not find the relatively straight pipeline phenomenon more and more, smoke in the pipeline surge, scattering and other irregular movement and smoke in the pipeline in the irregular distribution of the test phenomenon is common. This will cause a huge error in the test, even if the method of encrypting measuring points and encrypting canisters, the accuracy of the test results will become difficult to grasp. It is suggested that when designing and installing waste gas treatment equipment for boilers, kilns and discharge devices in newly built enterprises, the needs of environmental management during the operation period must be fully considered. When installing and arranging discharge pipelines, the technical requirements of environmental monitoring should be met, and the content of environmental protection acceptance should be included. The standardization of pollutant discharge facilities should be included in the technological transformation of old enterprises.