Exhaust gas processing method and exhaust gas processing system

Abstract

An exhaust gas processing method and an exhaust gas processing system for controlling the spatial density distribution of particulate matter in exhaust gas by utilizing corona discharge in exhaust gas containing floating particulate matter such as diesel engine exhaust gas to form a relatively particulate matter-rich area and a relatively particulate matter-lean area, and diving exhaust gas particulates to the former and the latter. An exhaust gas processing system (10) provided with a high-voltage electrode (12) and a low-voltage electrode (11), wherein exhaust gas G is allowed to flow between the facing high-voltage electrode (12) and low-voltage electrode (11), and a high voltage is applied to between the counter electrodes to generate corona discharge in the exhaust gas G, whereby floating particulate matter (20) in the exhaust gas G is charged, the spatial density distribution of the floating particulate matter in the exhaust gas is controlled by an electrostatic force between the counter electrodes, and the exhaust gas G is divided into a high-concentration exhaust gas Gb in the vicinity of the low-voltage electrode where a particulate matter concentration is relatively high and a low-concentration exhaust gas Ga in the vicinity of the high-voltage electrode where a particulate matter concentration is relatively low.

Description

FIELD OF THE INVENTION [0001] The present invention relates to an exhaust gas processing method and system for collecting floating particulate matter in exhaust gas using corona discharge. DESCRIPTION OF RELATED ART [0002] To remove floating particulate matter (particulate matter: hereafter referred to as PM) included in the exhaust gas emitted by diesel engines, a technique that collects the particulate matter with a filter, referred to as a diesel particulate filter (hereafter referred to as DPF), so as to decrease the quantity of PM to be externally discharged is being developed. [0003] On the other hand, in the case of the PM which causes air contamination, ultra-fine particles with diameters of 2.5 μm or smaller (particularly, with diameters of tens of nanometers) referred to as PM2.5 have recently become a problem on antipollution measures. It is considered that ultra-fine particles are also discharged from the direct-injection gasoline engine that is frequently used as an aut...

AI Technical Summary

Benefits of technology

[0015] According to this exhaust gas processing method, even a particulate matter with comparatively small electric resistance that abnormal re-entrainment in the case of electric dust collection, like the PM in the exhaust gas emitted by diesel engines, can be easily condensed.

[0032] Furthermore, large floating particulate matter is removed from low-concentration exhaust gas, and the PM quantity is extremely decreased. Therefore, it is possible to collect ultra-fine particles by using a fine-mesh filter when purifying the exhaust gas by the filter in order to raise the degree of purification. Furthermore, it is possible to remove the PM at a low pressure-loss for a long period of time because clogging hardly occurs even when using a fine-mesh filter. Furthermore, it is possible to decrease the capacity of the filter because the quantity of the low-concentration exhaust gas is smaller than the quantity of the original exhaust gas.

Problems solved by technology

On the other hand, in the case of the PM which causes air contamination, ultra-fine particles with diameters of 2.5 μm or smaller (particularly, with diameters of tens of nanometers) referred to as PM2.5 have recently become a problem on antipollution measures.

However, when collecting the ultra-fine particles using only a DPF method, a filter with extremely fine meshes is necessary.

Therefore, it is very difficult to collect the ultra-fine particles without a large pressure loss.

However, though the electric dust collector captures electrified particulate matter by using electrostatic force and using a vessel wall surface with a low voltage potential (generally, ground potential) as a dust-collecting electrode, there is a problem that a purifying performance is deteriorated in a comparatively short time (for example, in several minutes).

Therefore, the quantity of particulate matter that can be collected becomes small, and the purifying performance is deteriorated in a comparatively short time due to deposition of particulate matter on the dust-collecting electrode.

Moreover, in the case of collecting the PM in the exhaust gas emitted by an internal combustion engine such as a diesel engine, there is a problem that a re-entrainment easily occurs because the PM has a comparatively low resistivity.

However, to keep the collection performance of the filter and prevent the pressure loss from increasing, it is necessary to decrease the flow rate of exhaust gas flowing into the filter to a certain extent (for example, 3 m / s or less), and the opening area of the filter is inevitably increased.

Therefore, a problem occurs that the dust collector cannot be downsized.

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