# US 8,464,517 B2 · Method of controlling NOx purification system, and NOx purification system

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- Number: US 8,464,517 B2
- Document ID: US8464517B2
- Status: Granted
- Kind: B2
- Application number: 12/736,090
- Filed: 2008-11-27
- Published: 2011-02-24
- Granted: 2013-06-18
- Earliest claimed: 2008-03-11
- Assignees: Isuzu Motors Limited
- Applicants: Tetsuya Fujita
- Inventors: Tetsuya Fujita
- Web page: https://patentgrep.com/patent/US8464517B2

## CPC

- B01D 53/9431: {Processes characterised by a specific device}
- B01D 53/9495: {Controlling the catalytic process}
- F01N 3/103: {Oxidation catalysts for HC and CO only}
- F01N 3/106: {Auxiliary oxidation catalysts}
- F01N 3/2053: {By-passing catalytic reactors, e.g. to prevent overheating}
- F01N 3/2066: {Selective catalytic reduction [SCR]}
- F01N 3/208: {Control of selective catalytic reduction [SCR], e.g. by adjusting the dosing of reducing agent}
- F01N 13/009: {having two or more separate purifying devices arranged in series}
- B01D 2251/2062: Ammonia
- B01D 2257/404: Nitrogen oxides other than dinitrogen oxide
- F01N 3/0814: {combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts}
- F01N 2410/00: By-passing, at least partially, exhaust from inlet to outlet of apparatus, to atmosphere or to other device
- F01N 2410/12: in case of absorption, adsorption or desorption of exhaust gas constituents
- F01N 2560/026: for measuring or detecting NOx
- F01N 2610/02: the substance being ammonia or urea
- Y02A 50/20: Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
- Y02T 10/12: Improving ICE efficiencies
- B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28)
- F01N: GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES (arrangements in connection with gas exhaust of propulsion units in vehicles B60K13/00; combustion-air intake silencers specially adapted for, or arranged on, internal-combustion engines F02M35/00; protecting against, or damping, noise in general G10K11/16)
- Y02A: TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION

## Abstract

Method to reduce NOx contained in an exhaust gas by including an oxidation catalyst device and a selective reduction type NOx catalyst device, which are arranged in this order from an upstream side, and a NOx purification system. Whether a volume of NO2 adsorbed in the oxidation catalyst device increases or decreases is estimated, and a flow rate of exhaust gas which bypasses the oxidation catalyst device on a basis of the increase or decrease in the estimated volume of adsorbed NO2 is controlled. This avoids incorrect supply of ammonia.

## Claims

### Claim 1

A NOx purification system configured to reduce NOx contained in an exhaust gas, the system including:
an oxidation catalyst device, a first valve, and a selective reduction type NOx catalyst device which are arranged in order from an upstream side of an exhaust gas passage, the first valve to supply an ammonia-based solution to the exhaust gas passage;
a bypass passage branching from the exhaust gas passage at an upstream side of the oxidation catalyst device and joining together with the exhaust gas passage at an upstream side of the first valve;
at least one second valve to control a flow rate of the exhaust gas which flows through the bypass passage, and
a controller configured to calculate volumes of NOx respectively in stages before and after the oxidation catalyst device,
estimate whether a volume of NO2 adsorbed in the oxidation catalyst device increases or decreases on a basis of the calculated volumes of NOx,
control a flow rate of the exhaust gas which passes the oxidation catalyst device and a flow rate of the exhaust which passes the bypass passage on a basis of the increase or decrease in the estimated volume of adsorbed NO2, and
control an amount of the ammonia-based solution to be supplied by the first valve.

### Claim 2 (depends on 1)

The NOx purification system according to claim 1, wherein:
the controller is further configured to:
perform control such that the flow rate of the exhaust gas which passes the bypass passage is set to zero, when the estimated volume of adsorbed NO2 increases;
perform control such that part of the exhaust gas is caused to pass the bypass passage and the remaining part of the exhaust gas is caused to pass the oxidation catalyst device, when the estimated volume of adsorbed NO2 decreases;
estimate a proportion (molar ratio) of NO2in NOx contained in the exhaust gas which flows out of the oxidation catalyst device, when the estimated volume of adsorbed NO.sub.2 neither increases nor decreases;
perform control such that all of the exhaust gas is caused to pass the oxidation catalyst device, when the estimated proportion of NO2 therein is not larger than 50%; and
perform control such that part of the exhaust gas is caused to pass the bypass passage and the remaining part of the exhaust gas is caused to pass the oxidation catalyst device, when the estimated proportion of NO2 therein is larger than 50%.

### Claim 3 (depends on 2)

The NOx purification system according to claim 2, wherein:
the controller is configured to estimate a proportion of NO2 in the exhaust gas which flows into the selective reduction type NOx catalyst device, and when the estimated volume of adsorbed NO2 decreases, the controller is configured to estimate the proportion of NO2 in the exhaust gas which flows out of the oxidation catalyst device based on a condition of an equilibrium composition between NO and NO2 which is determined by a temperature of the oxidation catalyst device and an oxygen concentration in the exhaust gas.

### Claim 4 (depends on 2)

The NOx purification system according to claim 2, wherein:
when the controller causes the part of the exhaust gas to pass the bypass passage, and the remaining part of the exhaust gas to pass the oxidation catalyst device, the controller is configured to control an amount of the exhaust gas to be allowed to pass the bypass passage in order that the proportion of NO2 which flows into the selective reduction type NOx catalyst device becomes equal to 50%.

### Claim 5 (depends on 4)

The NOx purification system according to claim 4, wherein:
the controller is configured to estimate a proportion of NO2 in the exhaust gas which flows into the selective reduction type NOx catalyst device, and when the estimated volume of adsorbed NO2 decreases, the controller is configured to estimate the proportion of NO2 in the exhaust gas which flows out of the oxidation catalyst device based on a condition of an equilibrium composition between NO and NO2 which is determined by a temperature of the oxidation catalyst device and an oxygen concentration in the exhaust gas.

### Claim 6

A method of controlling a NOx purification system configured to reduce NOx contained in an exhaust gas, the system including:
an oxidation catalyst device, a first valve, and a selective reduction type NOx catalyst device which are arranged in order from an upstream side of an exhaust gas passage, the first valve to supply an ammonia-based solution to the exhaust gas passage;
a bypass passage branching from the exhaust gas passage at an upstream side of the oxidation catalyst device and joining together with the exhaust gas passage at an upstream side of the first valve;
at least one second valve to control a flow rate of the exhaust gas which flows through the bypass passage, and
a controller,
the method comprising utilizing the controller to perform the following steps:
calculating volumes of NOx respectively in stages before and after the oxidation catalyst device,
estimating whether a volume of NO2adsorbed in the oxidation catalyst device increases or decreases on a basis of the calculated volumes of NOx,
controlling a flow rate of the exhaust gas which passes the oxidation catalyst device and a flow rate of the exhaust which passes the bypass passage on a basis of the increase or decrease in the estimated volume of adsorbed NO2, and
controlling an amount of the ammonia-based solution to be supplied by the first valve.

### Claim 7 (depends on 1)

The method of controlling a NOx purification system according to claim 1, wherein:
when the estimated volume of adsorbed NO2 increases, the flow rate of the exhaust gas which passes the bypass passage is set to zero;
when the estimated volume of adsorbed NO2 decreases, part of the exhaust gas is caused to pass the bypass passage, and the remaining part of the exhaust gas is caused to pass the oxidation catalyst device;
when the estimated volume of adsorbed NO2 neither increases nor decreases, a proportion (molar ratio) of NO2 in NOx contained in the exhaust gas which flows out of the oxidation catalyst device is estimated;
when the estimated proportion of NO2 therein is not larger than 50%, all of the exhaust gas is caused to pass the oxidation catalyst device; and
when the estimated proportion of NO2 therein is larger than 50%, part of the exhaust gas is caused to pass the bypass passage, and the remaining part of the exhaust gas is caused to pass the oxidation catalyst device.

### Claim 8 (depends on 7)

The method of controlling a NOx purification system according to claim 7, wherein:
a proportion of NO2 in the exhaust gas which flows into the selective reduction type NOx catalyst device is estimated, and when the estimated volume of adsorbed NO2 decreases, the estimation of the proportion of NO2 in the exhaust gas which flows out of the oxidation catalyst device is based on a condition of an equilibrium composition between NO and NO2 which is determined by a temperature of the oxidation catalyst device and an oxygen concentration in the exhaust gas.

### Claim 9 (depends on 7)

The method of controlling a NOx purification system according to claim 7, wherein:,
when the part of the exhaust gas is caused to pass the bypass passage and the remaining part of the exhaust gas is caused to pass the oxidation catalyst device, an amount of the exhaust gas to be allowed to pass the bypass passage is controlled in order that the proportion of NO2 which flows into the selective reduction type NOx catalyst device becomes equal to 50%.

### Claim 10 (depends on 9)

The method of controlling a NOx purification system according to claim 9, wherein:
a proportion of NO2 in the exhaust gas which flows into the selective reduction type NOx catalyst device is estimated, and when the estimated volume of adsorbed NO2 decreases, the estimation of the proportion of NO2 in the exhaust gas which flows out of the oxidation catalyst device is based on a condition of an equilibrium composition between NO and NO2 which is determined by a temperature of the oxidation catalyst device and an oxygen concentration in the exhaust gas.