WO2009119845A1

WO2009119845A1 - Exhaust gas purification apparatus

Info

Publication number: WO2009119845A1
Application number: PCT/JP2009/056383
Authority: WO
Inventors: 寿仁加藤; 雄一磯崎; 内田　直喜; 兼久今井; 彰一茨木; 克憲松岡
Original assignee: 三井造船株式会社
Priority date: 2008-03-28
Filing date: 2009-03-27
Publication date: 2009-10-01
Also published as: JPWO2009119845A1

Abstract

Disclosed is an exhaust gas purification apparatus that separately controls the oxidizing action of plasma on an electrode surface and the number of microparticles that attach onto electrodes, with respect to the increase and decrease of microparticle concentration within the exhaust gas. The exhaust gas purification apparatus is provided with at least one pair of electrodes (2a, 2b) that are disposed within the exhaust gas (g), and a power supply (3) that periodically applies high voltage in order to generate thermal nonequilibrium plasma between the electrodes (2a, 2b). The power supply can output a voltage waveform with a short high-voltage holding time and a voltage waveform with a long high-voltage holding time, and generates, at a constant frequency, voltage waveforms with both short and long high-voltage holding times between the two electrodes at any cycle rate.

Description

Exhaust gas purification device

The present invention relates to an exhaust gas purification apparatus that reduces fine particles mainly composed of soot contained in engine exhaust gas or boiler exhaust gas.

Examples of the exhaust gas purification device include the following inventions. That is,
(A) Japanese Patent Application Laid-Open No. 2007-245094 (Patent Document 1) discloses that a high-voltage AC voltage is applied to an electrode of a dust collecting unit in a two-stage electric dust collector having a charging unit and a dust collecting unit. Therefore, it is described that the charged particles collected by the dust collection unit are separated and re-scattered.
(B) Japanese Patent Application Laid-Open No. 2002-213228 (Patent Document 2) describes a charging unit that generates plasma to charge fine particles, and a dust collection that is fixed to a ground potential to collect the charged fine particles. An exhaust gas purification device comprising a part is described.
(C) Japanese Patent Laid-Open No. 2006-261040 (Patent Document 3) describes that two or more plasma generating electrodes are provided in the flow direction of exhaust gas, and plasma is generated by independent power sources. .
(D) Japanese Patent Application Laid-Open No. 2007-23861 (Patent Document 4) discloses that discharge is intermittently performed by setting a discharge period and a discharge pause period, and when the concentration of fine particles in exhaust gas increases, It is described that when the voltage and frequency are increased and the exhaust gas flow rate is increased, the discharge pause period is shortened.

However, as in Patent Document 1, when the function is separated into the charging unit for charging the fine particles and the dust collecting unit for collecting the charged fine particles, two sets of electrodes and a power source are required, which reduces the size and cost of the entire apparatus. There is a drawback that becomes larger. In addition, it is necessary to periodically clean the electrode that collects the fine particles.

As in Patent Document 2, when a power source is not used for the dust collecting portion, it is not necessary to prepare a plurality of power sources, but the structure is complicated because the electrode is divided into a charging portion and a dust collecting portion. In addition, the ability to oxidize and remove the fine particles collected in the dust collection part depends on the amount of active material generated by the upstream charging part plasma, but the charging part plasma is strongly strengthened to increase the amount of active substance. As a result, the amount of fine particles collected in the dust collection portion also increases, and there is a risk that fine particles accumulate in the dust collection portion when the concentration of fine particles in the exhaust gas is high.

In Patent Document 3, there is no expression of a charging unit or a dust collecting unit, but there is a drawback that the size and cost of the entire apparatus are increased because a plurality of electrodes and a power source are used. As in Patent Document 4, if the discharge voltage is increased when the fine particle concentration is increased, the exhaust gas purification efficiency can be increased. However, the amount of fine particles adsorbed on the electrode also increases, so the exhaust gas fine particle concentration is high. In some cases, there is a risk that fine particles accumulate on the electrode. In addition, when the discharge voltage is increased, the voltage applied to the electrodes and the like is increased, so that there is a disadvantage that the size and cost of the entire apparatus are increased.

Also, when changing the discharge frequency, it is necessary to change the discharge voltage and the burst period in order to make the power constant, so that the control becomes complicated. Further, since the discharge frequency is limited to a range that does not disturb the consistency of the oscillation system between the power supply circuit including the high-frequency transformer and the electrode, the frequency range that can be selected by one set of power supply and electrode is not always sufficient.

By the way, when non-thermal equilibrium plasma is generated by applying an alternating voltage having a voltage waveform close to a sine wave or a sine wave to at least a pair of electrodes through which exhaust gas containing fine particles mainly containing soot is passed, the fine particles are generated by the plasma. It is charged and attracted to the electrode surface, and a part is adsorbed on the electrode. The fine particles adsorbed on the electrode surface are oxidized into gas such as CO ₂ or H ₂ O by ozone or NO ₂ generated by plasma, and are discharged as a part of exhaust gas.

When the concentration of fine particles in the exhaust gas is high, a large amount of fine particles exceeding the oxidizing ability of the electrode surface by plasma are adsorbed on the electrode surface, and eventually the electrode surface is covered with the fine particles. Then, it becomes difficult to generate a normal non-thermal equilibrium plasma. Increasing the plasma power to increase the electrode surface's ability to oxidize the plasma also increases the amount of fine particles that are electrically adsorbed to the electrode. Is difficult to change.
Japanese Unexamined Patent Publication No. 2007-245094 Japanese Unexamined Patent Publication No. 2002-213228 Japanese Unexamined Patent Publication No. 2006-261040 Japanese Unexamined Patent Publication No. 2007-23861

The present invention has been made in order to solve the above-described problems, and its object is to reduce the size and cost of the entire apparatus while reducing the concentration of fine particles in the exhaust gas. It is an object of the present invention to provide an exhaust gas purifying apparatus capable of individually controlling the oxidation action of the electrode surface due to and the amount of fine particles adhering to the electrode.

The exhaust gas purification apparatus of the present invention comprises at least a pair of electrodes installed in the exhaust gas, and a power source that periodically applies a high voltage for generating non-thermal equilibrium plasma between the electrodes, the power source being a high voltage A voltage waveform with a short holding time and a voltage waveform with a long high voltage holding time can be output, and a voltage waveform with a short high voltage holding time and a voltage waveform with a long high voltage holding time between the electrodes can be output at a constant frequency. Are generated at an arbitrary cycle ratio.

The exhaust gas purifying apparatus of the present invention is characterized in that a power source is formed by an H bridge circuit constituted by four switching elements A _P, A _N , B _P , and B _N and a high frequency transformer.

According to the present invention, since the combustion mode plasma generates a high voltage in a pulsed manner, the time for sucking charged fine particles to the electrode is short, and the adsorption ability of the fine particles is small. Since plasma is generated when the voltage of the electrode changes, there is no problem in generating active species even if the high voltage application time is short. Therefore, even if the plasma power is increased, the oxidation capacity of the electrode surface can be increased without increasing the adsorption amount of the fine particles.

On the other hand, the plasma in the adsorption mode consumes a part of energy for accelerating the ions generated by the plasma by the electric field because the high voltage is applied for a long time. The oxidation capacity of the electrode surface is slightly lower than that of plasma. However, since the adsorption capacity of the fine particles is high, the adsorption amount of the fine particles can be greatly increased by increasing the plasma power.

By using a power source that can select the combustion mode plasma and adsorption mode plasma for each output cycle, the ratio of the number of output cycles of the combustion mode plasma and the adsorption mode plasma and the total power are set individually, so that With respect to the increase / decrease of the fine particle concentration, it is possible to individually control the oxidation action of the electrode surface by the plasma and the amount of fine particles adhering to the electrode.

As a result, even when exhaust gas having a high concentration of fine particles is treated, the electrode surface is not covered with fine particles, and can be continuously adsorbed and oxidized. In addition, power consumption can be kept low.

FIG. 1 is a schematic configuration diagram of an exhaust gas purifying apparatus according to the present invention. FIG. 2 is a diagram showing definitions of voltage waveforms in the combustion mode and the adsorption mode. FIG. 3 is a diagram showing the movement of charged particles between electrodes in the combustion mode. FIG. 4 is a diagram showing the movement of charged particles between the electrodes in the adsorption mode. FIG. 5 is a schematic configuration diagram of an exhaust gas purifying apparatus according to the present invention including an H bridge. FIG. 6 is a diagram showing the relationship between the voltage / current waveform in the combustion mode and the switching element operation. FIG. 7 is a diagram (example 1) showing the relationship between the voltage / current waveform in the adsorption mode and the switching element operation. FIG. 8 is a diagram (example 2) illustrating the relationship between the voltage / current waveform in the adsorption mode and the switching element operation. FIG. 9 is a diagram illustrating the operation of the H bridge in period 1. FIG. 10 is a diagram illustrating the operation of the H bridge in period 2. FIG. 11 is a diagram illustrating the operation of the H-bridge in period 3. FIG. 12 is a diagram illustrating the operation of the H bridge in period 4. FIG. 13 is a diagram illustrating the operation of the H bridge in period 5. FIG. 14 is a diagram illustrating the operation of the H-bridge in period 6. FIG. 15 is a diagram illustrating the operation of the H bridge in period 7. FIG. 16 is a diagram (No. 1) showing a method for controlling the oxidation action on the electrode surface and the amount of fine particles adsorbed on the electrode. FIG. 17 is a diagram (part 2) illustrating a method for controlling the oxidation action on the electrode surface and the amount of fine particles adsorbed on the electrode. FIG. 18 is a view showing a stack structure of plasma electrodes. FIG. 19 is a diagram showing an experimental apparatus of the example. FIG. 20 is a diagram showing experimental results in the example. FIG. 21 is a diagram showing a voltage waveform in the adsorption mode (in the case of 0.75 kW and 3 kHz in the electrode of the example). FIG. 22 is a diagram showing a voltage waveform in the combustion mode (in the case of 0.75 kW and 3 kHz at the electrode of the example). FIG. 23 is a diagram illustrating an example in which combustion mode plasma and adsorption mode plasma are alternately output in three cycles.

Explanation of symbols

g Exhaust gas 2a, 2b Electrode 3 Power supply

Embodiments according to the present invention will be described below with reference to the drawings. As shown in FIG. 1, the exhaust gas purification apparatus 1 of the present invention is excellent in at least a pair of electrodes 2a and 2b and non-thermal equilibrium plasma, that is, generation of active species or charging of fine particles between the electrodes 2a and 2b. A plasma having an effect (for convenience, referred to as a combustion mode plasma) and a plasma having an effect excellent in the electrical adsorption of charged fine particles (for convenience, referred to as an adsorption mode plasma) have a constant frequency. And a power supply device 3 that is generated at an arbitrary cycle ratio.

The electrode 2a is connected to the power supply device 3, and the electrode 2b is connected to the earth 4. Further, the electrode (electrode plate) is preferably one in which a metal plate made of SUS304 is sandwiched between two alumina ceramic plates, but is not limited thereto.

The combustion mode plasma is a plasma having a voltage waveform in which the voltage decreases rapidly after a high voltage is applied to the electrode in order to generate plasma. “The voltage generated at the electrode is 50% or more of the maximum value. And a voltage waveform in which the total of the period that is 50% or less of the minimum value is 30% or less in one cycle is defined (see FIG. 2).

When this plasma is generated, a streamer discharge is formed between the electrodes due to a high electric field generated between the electrodes, and active materials such as radicals of various atoms and O ₃ are generated by high energy electrons generated by the discharge. Further, in exhaust gas containing NO _X , NO is oxidized to NO ₂ or NO _X is reduced to N ₂ .

As shown in FIG. 3, the fine particles m present in the exhaust gas g are combined with electrons or ions generated in the plasma to be charged either positively or negatively and either positively or negatively by receiving a high electric field between the electrodes 2a and 2b. The electrode is electrically attracted. However, since the high voltage application time is short, acceleration by the electric field ends before reaching the electrode surface. And it is moved away from the electrode which it approached earlier by the electric attractive force to the electrode on the opposite side by the plasma of the next reverse electric field. Thereafter, in order to repeat such an amplitude operation, most of the charged fine particles m pass through the electrodes without being adsorbed by the electrodes 2a and 2b.

The adsorption mode plasma is a plasma having a voltage waveform that maintains a high voltage for a long time after a high voltage is applied to the electrode in order to generate plasma. “The voltage generated at the electrode is 50% of the maximum value. It is defined as “a voltage waveform in which the sum of the above period and the period that is 50% or less of the minimum value is 70% or more in one cycle” (see FIG. 2).

When this plasma is generated, as shown in FIG. 4, since the charged fine particles m are electrically attracted to the electrodes 2a and 2b for a sufficiently long time and finally adsorbed to the electrode surfaces, the charged fine particles m Can be adsorbed to the electrodes 2a and 2b.

As shown in FIG. 5, the power supply device 3 includes at least a pair of H bridge circuit 5 configured by four switching elements A _P , A _N , B _P , and B _N and a high frequency transformer 6. A power supply circuit capable of generating a periodic high voltage between the electrodes 2a and 2b is provided.

By appropriately setting on / off timing of the switching elements A _P , A _N , B _P , and B _N by a computer (control device), at least the pair of electrodes 2a and 2b, that is, the plasma electrode unit 2A The generated high voltage waveform and the cycle ratio at a constant frequency can be easily changed.

FIG. 6 to FIG. 8 show the relationship between the timing when the switching elements A _P , A _N , B _P and B _N are turned on / off and the voltage V _P and current I _P generated in the plasma electrode section. In addition, the current I _H inside the H bridge circuit is indicated by a dotted line in FIGS. 9 to 15 for each period indicated by a number in parentheses in FIGS. 9 to 15, the circuit is simply described by replacing the transformer 6 and the plasma electrode unit 2A, which are parts other than the H-bridge circuit shown in FIG. 5, with coils and capacitors, respectively.

By the way, the period 11 (the period of the numeral 11 with parentheses) to the period 17 (the period of the numeral 17 with parentheses) in FIGS. 6 to 8 are respectively the period 1 (the period of the numeral 1 with parentheses) to the period 7 (the circle). This corresponds to the reverse phase of the period 7 in parentheses. That is, the legend of _{A P} in FIGS. 9 to 15 in _{B P,} the _{B P} to _{A P,} the _{A N} on _{B N,} the _{B N} to _{A N,} the replaced it respectively, the current flowing through the coil and a capacitor It is a figure explaining the switching operation in which the direction of IH is reversed.

(A) Operation of H Buritchi circuit period 1 (period parentheses subscript 1), A _P and B _N are On next, as shown in FIG. 9, the capacitor is charged voltage of the capacitor by the power supply voltage To rise.

(B) Operation of H Buritchi circuit period 2 (period parentheses subscript 2), _{A P} and _{B N} are On next, as shown in FIG. 10, at the same time Shorting _{B N} side, the _{A P} side Apply power supply voltage to quickly reverse capacitor voltage.

(C) Operation of H Buritchi circuit period 3 (period parentheses subscript 3), only the B _N is On next, as shown in FIG. 11, the inductance of the coil even if the power supply is cut off voltage, for a while The loop power in the figure flows. The capacitor voltage rises until the current is zero.

(D) In the operation of the H-blitch circuit in period 4 (period 4 with parentheses), all the transistors (switching elements) are turned off, and the high voltage of the capacitor is maintained as shown in FIG. (The secondary side of the transformer is an LC loop structure isolated from the primary side, so that the voltage of the capacitor slowly decreases according to the time constant.)

(E) In the operation of the H-blitch circuit in period 5 (period 5 with parentheses), only _BP is turned on, and, as shown in FIG. Discharge the capacitor by half the wave) and store energy in the coil.

(F) The operation of the H-blitch circuit in period 6 (the period of the number 6 with parentheses) is that all transistors (switching elements) are turned off, and the energy stored in the coil is stored in the capacitor of the power supply circuit as shown in FIG. regenerated to C _0. Since C ₀ has a large capacity, the voltage rise of C ₀ is small.

(G) In the operation of the H-blitch circuit in period 7 (period 7 with parentheses), all the transistors (switching elements) are turned off, and as shown in FIG. May remain.)

As described above, using the power supply device 3 that can select the combustion mode plasma and the adsorption mode plasma for each output cycle, the ratio of the number of output cycles of the combustion mode plasma and the adsorption mode plasma and the total power are individually set. By setting to, the oxidizing action of the electrode surface by the plasma and the amount of fine particles adhering to the electrode can be individually controlled with respect to the increase / decrease of the fine particle concentration in the exhaust gas. As a result, even when exhaust gas having a high fine particle concentration is treated, the electrode surface is not covered with fine particles, and the fine particles can be continuously adsorbed and oxidized. In addition, power consumption can be kept low.

Further, an example of processing exhaust gas particles having a high particle concentration will be described with reference to FIG. When it is desired to process a hatched portion that is about 30% of the total particle amount shown in the bar graph, the power P1 that is slightly larger than the power at which the particulate oxidation amount in both modes becomes 30% is selected. When both modes are output together, the oxidation capacity of the electrode surface and the amount of fine particles adsorbed on the electrode are intermediate values between the two modes. For example, the combustion mode is combined with 5 cycles and the adsorption mode is combined with 2 cycles. (For convenience, it is referred to as a cycle ratio of 5: 2.) When plasma is output, the oxidation ability of the electrode surface can be made larger than the amount of fine particles adsorbed on the electrode.

If a power supply device that can output only plasma in combustion mode or plasma having a waveform similar to that in combustion mode is used, the desired amount of fine particle processing cannot be obtained with power P1, so a larger power P2 is input. There must be.

In addition, when a power supply device that can output only adsorption mode plasma or plasma having a waveform similar to that of the adsorption mode is used, the amount of fine particles adsorbed on the electrode is too much at the power P1 due to the plasma due to the plasma. Therefore, the electrode is eventually covered with fine particles. If the power is reduced to P3 so that the amount of fine particles adsorbed on the electrode is about 30% of the total fine particles, the electrode surface is also covered with the fine particles because the oxidation ability is also reduced on the electrode surface.

Suppose that the operating state of the engine has changed and the particulate concentration of the exhaust gas has decreased from the state of FIG. 16 to the state of FIG. When the amount of fine particles to be oxidized and removed by the electrode is kept constant, the oxidation power on the electrode surface can be made the same as in FIG. 16 by selecting the same power P1 as in FIG.

However, if the cycle ratio remains at 5: 2, the amount of fine particles adsorbed on the electrode decreases. For example, by setting the cycle ratio to 1: 3 and increasing the ratio of the adsorption mode plasma, The amount of fine particles adsorbed on the electrode can be kept constant without increasing the electric power.

When using a power supply device that can output only a plasma with a cycle ratio of 5: 2 or a plasma whose oxidation capacity on the electrode surface and the amount of fine particles adsorbed to the electrode are equivalent to a plasma with a cycle ratio of 5: 2. In order to keep the amount of fine particles to be oxidized and removed by the electrode constant, it is necessary to input a larger electric power P4.

In the above description, the case where the amount of fine particles to be oxidized and removed by the present apparatus is kept constant, but control for keeping the amount of fine particles in the exhaust gas (white portion of the bar graph) after leaving the present apparatus constant. The same way of thinking can be applied to the above.

A metal plate 11 made of SUS304 having a thickness of 0.05 mm sandwiched between two alumina ceramic plates 10 having a thickness of 1 mm is used as one electrode plate 12, and each of the 17 electrode plates is 1.5 mm. The electrode stack 22 having a 16-layer gap (electrode space) was formed (see FIG. 18). One of the electrode plates 12 a and 12 b facing each other was connected to the high voltage generation source 13 and the other was connected to the ground 14. The discharge area of one electrode plate is 110 mm × 95 mm.

The above-described electrode stack 22 was installed in the box 20 (see FIG. 19), and the experiment was conducted by ventilating the exhaust gas g of the diesel engine. In the experiment, a diesel engine MAC-30 (model F3L912, displacement 2.827L, output 26.5 kW, rotation speed 1500 rpm, fuel oil used is low sulfur A heavy oil) manufactured by DEUTZ (Mitsui Engineering & Machinery Service). The engine was operated at an engine output of 4 kW and a part of the exhaust gas g was diverted to flow into the box 20.

As the fine particle concentration, in this embodiment, the exhaust gas is sucked from the exhaust gas flow path on the downstream side of the electrode stack 22 by using a smoke meter, model 415S, manufactured by AVL, and the soot is converted from the darkness of the filter paper using the conversion formula recommended by the company. The concentration (mg / Nm ³ ) was calculated. Further, the soot reduction rate was determined by the following equation, assuming that the soot concentration when plasma was generated was A (mg / Nm ³ ), and the soot concentration when plasma was not generated was B (mg / Nm ³ ). The value of B was approximately 5 (mg / Nm ³ ) in each experiment.
Soot reduction rate (%) = ((BA) ÷ B) × 100

The experimental results are shown in [Table 1] and FIG.

When compared with the same plasma power, the soot reduction rate was larger in the mixed mode in which the combustion mode and the adsorption mode were output at a ratio of 3: 3 than in the combustion mode. Examples of voltage waveforms measured at the electrode portions are shown in FIGS.

Claims

And at least a pair of electrodes installed in the exhaust gas, and a power source that periodically applies a high voltage for generating non-thermal equilibrium plasma between the electrodes. A voltage waveform having a long voltage holding time can be output, and a voltage waveform having a short high voltage holding time and a voltage waveform having a long high voltage holding time can be generated between the electrodes at an arbitrary cycle ratio at a constant frequency. An exhaust gas purification apparatus characterized by that.
The exhaust gas purifying apparatus according to claim 1, wherein the power source is formed by an H bridge circuit constituted by four switching elements A P, A N , B P , and B N and a high frequency transformer.