What is "Dust Monitor"?
(Type, Principle, Characteristic)

Need to measure dust concentration

In exchange for industrial development, various substances emitted become a burden on the environment, and the attention is increasing year by year. There are various environmental issues, but one that we have focused on, having been in the powder industry for many years, is air pollution caused by dust.
For example, dust in the atmosphere can be taken into the human body through breathing and can affect health. Additionally there is a need for improved labor productivity and comfortable workplaces and environmental measures are becoming increasingly important.

Therefore many plants install dust collectors to prevent dust from being emitted into the atmosphere. But there is a risk that dust may be accidentally emitted due to deterioration of the dust collector or maintenance errors.

It is not enough to just install a dust collector and necessary to take any measures for future development. Therefore, it is essential to measure the dust concentration in order to monitor the effectiveness of dust collection.

 

What is Powder measuring instrument?

The powder measuring instrument is the sensor that measures the concentration of fine particles in the air that are normally invisible and is also called a dust concentration meter.
The powder measuring instrument are classified into several types depending on the usage.
For example, particle counters to measure clean rooms. The digital dust meter measures the concentration of dirt, rocks, minerals, metals or carbon dust in the air in indoor workplaces. The device that monitors the emissions from the dust collector is called Dust Monitor. They are indicated as dust concentration (mg/m3) or cleanliness, and vary depending on the equipment, such as single measurement or continuous measurement.

Here we will explain "Dust Monitor" monitoring the dust from dust collectors.


JIS standard of Dust Monitor

Due to the need for continuous measurement of Powder Measuring Instrument for dust collectors in response to recent severe public opinion, in January 2018, a method for evaluating the performance of automatic dust concentration measuring instruments was established as JIS standard. (JIS B 7996 established on January 22, 2018)

As a result, performance evaluation methods have been established for three types of automatic measuring instruments: light scattering method, light transmission method, and triboelectric detection method.
Nowadays, it is widely used for continuous monitoring through automatic measurement for
the purpose of environmental conservation measures and monitoring.

Establishment of JIS on performance evaluation method of automatic measuring device for dust concentration in exhaust gas



1. Purpose and Background of the Establishment of JIS
In terms of atmospheric environment conservation measures and monitoring, continuous monitoring by automatic measurement is required at thermal power plants and incinerators of incineration plants, so automatic dust concentration measuring instruments are used. 

However, JIS Z8852 (method for continuous measurement of dust concentration in exhaust gas) only specifies the measurement method, and until now there has been no official standard for evaluating the performance of automatic dust concentration measuring instruments.

In addition, since the data obtained by automatic dust concentration measuring instruments is expected to be used as evidence of the status of compliance with environmental laws and regulations, automatic dust concentration measuring instruments will also be included in the official law of the Air Pollution Control Act.  There was a need for standards for performance evaluation methods.

2. Main points of JIS establishment
By specifying the performance evaluation method for 3 types of automatic measuring instruments: light scattering method, light transmission method, and Trivoelectric detection method(see Note), most of the equipment used in Japan will be covered.


(Note) The light scattering method is a method of measuring dust concentration that utilizes the fact that when exhaust gas is irradiated with measurement light, the intensity of the light scattered by dust has a correlation with the dust concentration.  The light transmission method is a method for measuring dust concentration that utilizes the fact that when exhaust gas is irradiated with measurement light, the amount of attenuation of the measurement light blocked by dust is correlated with the dust concentration.  The triboelectric detection method is based on the fact that when a probe(electrode) is inserted into exhaust gas, the movement and induction of electric charges that occur when dust collides with or passes near the probe  is correlated with the dust concentration.

Source: Ministry of Economy, Trade and Industry, Industrial Science and Technology Environment Bureau, International Standards Division website
"Document 2" JIS on performance evaluation method of automatic measuring equipment for dust concentration in exhaust gas established
https://www.meti.go.jp/policy/economy /hyojun-kijun/katsuyo/shinshijo/pdf/20181220seitei2.pdf



Types of "Dust Monitor" for dust collector

There are three methods for "Dust Monitor" for dust collectors:
light scattering method, light transmission method, and triboelectric detection method.

 

Method Light scattering method Light transmission method Triboelectric method
 Image
 Principle

When the measurement light is irradiated on the dust in the exhaust gas  in the duct, the measurement light is absorbed by the dust and scattered. This is a measuring device based on that the intensity of scattered light has a correlation with the dust concentration.

When the measurement light is irradiated to the dust in the exhaust gas in the duct, the measurement light is blocked by the dust and the original light intensity is attenuated. This is a measuring device based on that the amount of suspended measurement light has a correalation with the dust concentration.

 When two solid particles come into contact, a transfer of electric charge occurs between the particles.  This transfer of charge is known as tribostatic or contact charging.  Similarly, when a probe sensor is inserted into the exhaust gas and the particles in the air collide with or pass near the probe, charge transfer and the induction phenomena occur between particles and sensor.  This is a measuring device based on that the amount of charge movement has a correlation with dust concentration.

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