Integrated engine exhaust emission control system

Claim 2

In a method for controlling engine exhaust emissions in which the initial exhaust gas stream emitted by the engine contains noxious impurities including nitrogen oxides, hydrocarbons and carbon monoxide, said initial exhaust gas stream is passed through a reducing catalyst bed for the catalytic reduction of nitrogen oxides to nitrogen, the intermediate exhaust gas stream discharged from said reducing catalyst bed is passed through an oxidizing catalyst bed for the catalytic oxidation of at least a portion of said hydrocarbons and carbon monoxide to innocuous oxidation products, secondary air being added to said exhaust gas stream prior to passing the exhaust gas stream through said oxidizing catalyst bed, and a resulting catalytically treated exhaust gas stream is discharged from said oxidizing catalyst bed, the improvement during successive time periods of operation of said engine after startup which comprises a. operating said engine during a first time period, said first time period commencing with engine startup and extending for a duration of up to about 10 minutes, said initial exhaust gas stream being emitted at a temperature below 250* C and containing an abnormally high concentration of hydrocarbon vapor during said first time period, b. injecting a first stream of secondary air into said initial exhaust gas stream during said first time period, said first stream of secondary air being injected prior to passing said initial exhaust gas stream through said reducing catalyst bed, c. contacting said resulting catalytically treated exhaust gas stream with a solid absorbent bed during said first time period, whereby residual hydrocarbon vapor in said resulting exhaust gas stream is absorbed by said solid absorbent bed and a final exhaust gas stream substantially free of hydrocarbon vapor is discharged from said solid absorbent bed, d. operating said engine under normal operating conditions during a second time period after the termination of said first time period, said initial exhaust gas stream being emitted from said engine at a temperature in the range of 250* to 700* C during said second time period, e. reducing the flow rate of said first stream of secondary air during said second time period, whereby the free oxygen content of said initial exhaust gas stream at entry into said reducing catalyst bed is less than about 30 percent in excess of the stoichiometric requirement to oxidize carbon monoxide contained in said initial exhaust gas stream, f. injecting a second stream of secondary air into said intermediate exhaust gas stream during saId second time period, said second stream of secondary air being injected prior to passing said intermediate exhaust gas stream through said oxidizing catalyst bed, whereby substantially all of the hydrocarbon vapor and carbon monoxide in said exhaust gas stream are catalytically oxidized in said oxidizing catalyst bed during said second time period, g. dividing the resulting catalytically treated exhaust gas stream discharged from said oxidizing catalyst bed during said second time period into a major portion and a minor portion, h. discharging said major portion of said resulting catalytically treated exhaust gas stream to atmosphere during said second time period, discharged from said absorbent bed i. passing said minor portion of said resulting catalytically treated exhaust gas stream through said absorbent bed during said second time period, whereby hydrocarbon previously absorbed during said first time period is desorbed and a mixed gaseous stream containing desorbed hydrocarbon vapor and exhaust gas is dischargedfrom saidasorbent bPd during said second time period, and j. passing said mixed gaseous stream formed by step (i) into said engine during said second time period, whereby at least a portion of the desorbed hydrocarbon vapor in said mixed gaseous stream is burned in said engine.

Claim 3

The method of claim 1, in which said engine is an internal combustion engine.

Claim 4

The method of claim 2, in which said internal combustion engine is an automobile engine.

Claim 5

The method of claim 1, in which said reducing catalyst bed and said oxidizing catalyst bed contain an active catalytic agent selected from the group consisting of nickel, cobalt, copper and manganese, and mixtures thereof, deposited on a carrier.

Claim 6

The method of claim 1, in which said solid absorbent bed contains an active hydrocarbon adsorbent selected from the group consisting of activated carbon, zeolite, activated alumina, fuller''s earth, kaolin, and organic resin, and mixtures thereof.

Claim 7

The method of claim 1, in which said secondary air stream is injected into said initial exhaust gas stream according to step (b) by injecting said secondary air stream into the exhaust manifold of said engine.

Claim 8

The method of claim 1, in which the duration of said firt time period is in the range of about 2 to 6 minutes.

Claim 9

In a method for controlling engine exhaust emissions in which the initial exhaust gas stream emitted by the engine contains noxious impurities including nitrogen oxides, hydrocarbons and carbon monoxide, said initial exhaust gas stream is passed through a reducing catalyst bed for the catalytic reduction of nitrogen oxides to nitrogen, the intermediate exhaust gas stream discharged from said reducing catalyst bed is passed through an oxidizing catalyst bed for the catalytic oxidation of at least a portion of said hydrocarbons and carbon monoxide to innocuous oxidation products, secondary air being added to said exhaust gas stream prior to passing the exhaust gas stream through said oxidizing catalyst bed, and a resulting catalytically treated exhaust gas stream is discharged from said oxidizing catalyst bed, the improvement during successive time periods of operation of said engine including operation at an abnormally high temperature which comprises a. operating said engine under normal operating conditions, whereby said initial exhaust gas stream is emitted from said engine at a normal operating temperature in the range of 250* to 700* C, b. injecting a first stream of secondary air into said initial exhaust gas stream under normal operating conditions, said first stream of secondary air being injected prior to passing said initial exhaust gas stream through said reducing catalyst bed, whereby the free oxygen content of said initial exhaust gas stream at entry into said reducing catalyst bed is less than about 30 percent in excess of the stoichiometric requirement to oxidize carbon monoxide contained in said initIal exhaust gas stream, c. injecting a second stream of secondary air into said intermediate exhaust gas stream under normal operating conditions, said second stream of secondary air being injected prior to passing said intermediate exhaust gas stream through said oxidizing catalyst bed, whereby substantially all of the hydrocarbon vapor and carbon monoxide in said exhaust gas stream are catalytically oxidized in said oxidizing catalyst bed under normal operating conditions, d. operating said engine under abnormal operating conditions during a first time period after normal operation of said engine, whereby said initial exhaust gas stream is emitted from said engine at a temperature in the range of 700* to 1,000* C during said first time period, e. cooling said initial exhaust gas stream by indirect heat exchange with the surrounding atmosphere during said first time period, by passing said initial exhaust gas stream through means adapted to receive and cool exhaust gas during said first time period, f. maintaining steps (b) and (c) during said first time period, g. operating said engine under abnormal operating conditions during a second time period after the termination of said first time period, whereby said initial exhaust gas stream is emitted from said engine at a temperature above 1,000* C during said second time period, and h. terminating the flow of said first and second streams of secondary air during said second time period.

Claim 10

In a method for controlling engine exhaust emissions in which the initial exhaust gas stream emitted by the engine contains noxious impurities including nitrogen oxides, hydrocarbons and carbon monoxide, said initial exhaust gas stream is passed through a reducing catalyst bed for the catalytic reduction of nitrogen oxides to nitrogen, the intermediate exhaust gas stream discharged from said reducing catalyst bed is passed through an oxidizing catalyst bed for the catalytic oxidation of at least a portion of said hydrocarbons and carbon monoxide to innocuous oxidation products, secondary air being added to said exhaust gas stream prior to passing the exhaust gas stream through said oxidizing catalyst bed, and a resulting catalytically treated exhaust gas stream is discharged from said oxidizing catalyst bed, the improvement during successive time periods of operation of said engine including operation at an abnormally high temperature which comprises a. operating said engine under normal operating conditions, whereby said initial exhaust gas stream is emitted from said engine at a normal operating temperature in the range of 250* to 700* C, b. injecting a first stream of secondary air into said initial exhaust gas stream under normal operating conditions, said first stream of secondary air being injected prior to passing said initial exhaust gas stream through said reducing catalyst bed, whereby the free oxygen content of said initial exhaust gas stream at entry into said reducing catalyst bed is less than about 30 percent in excess of the stoichiometric requirement to oxidize carbon monoxide contained in said initIal exhaust gas stream, c. injecting a second stream of secondary air into said intermediate exhaust gas stream under normal operating conditions, said second stream of secondary air being injected prior to passing said intermediate exhaust gas stream through said oxidizing catalyst bed, whereby substantially all of the hydrocarbon vapor and carbon monoxide in said exhaust gas stream are catalytically oxidized in said oxidizing catalyst bed under normal operating conditions, d. operating said engine under abnormal operating conditions during a first time period after normal operation of said engine, whereby said initial exhaust gas stream is emitted from said engine at a temperature in the range of 700* to 1,000* C during said first time period, e. cooling said initial exhaust gas stream by indirect heat exchange with the surrounding atmosphere during said first time period, by passing said initial exhaust gas stream through means adapted to receive and cool exhaust gas during said first time period, f. maintaining steps (b) and (c) during said first time period, g. operating said engine under abnormal operating conditions during a second time period after the termination of said first time period, whereby said initial exhaust gas stream is emitted from said engine at a temperature above 1,000* C during said second time period, and h. terminating the flow of said first and second streams of secondary air during said second time period.

Claim 11

The method of claim 8, in which said engine is an internal combustion engine.

Claim 12

The method of claim 9, in which said internal combustion engine is an automobile engine.

Claim 13

The method of claim 8, in which said reducing catalyst bed and said oxidizing catalyst bed contain an active catalytic agent selected from the group consisting of nickel, cobalt, copper and manganese, and mixtures thereof, deposited on a carrier.

Claim 14

The method of claim 8, in which said first stream of secondary air is injected into said initial exhaust gas stream according to step (b) by injecting said secondary air stream into the exhaust manifold of said engine.

Claim 15

In a method for controlling engine exhaust emissions in which the initial exhaust gas stream emitted by the engine contains noxious impurities including nitrogen oxides, hydrocarbons and carbon monoxide, said initial exhaust gas stream is passed through a reducing catalyst bed for the catalytic reduction of nitrogen oxides to nitrogen, the intermediate exhaust gas stream discharged from said reducing catalyst bed is passed through an oxidizing catalyst bed for the catalytic oxidation of at least a portion of said hydrocarbons and carbon monoxide to innocuous oxidation products, secondary air being added to said exhaust gas stream prior to passing the exhaust gas stream through said oxidizing catalyst bed, and a resulting catalytically treated exhaust gas stream is discharged from said oxidizing catalyst bed, the improvement during successive time periods of operation of said engine after startup which comprises a. operating said engine during a first time period, said first time period commencing with engine startup and extending for a duration of up to about 10 minutes, said initial exhaust gas stream being emitted at a temperature below 250* C and containing an abnormally high concentration of hydrocarbon vapor during said first time period, b. injecting a first stream of secondary air into said initial exhaust gas stream during said first time period, said first stream of secondary air being injected prior to passing said initial exhaust gas stream through said reducing catalyst bed, c. contacting said resulting catalytically treated exhaust gas stream with a solid absorbent bed during said first time period, whereby residual hydrocarbon vapor in said resulting exhaust gas stream is absorbed by said solid absorbent bed and final exhaust gas stream substantially free of hydrocarbon vapor is discHarged from said solid absorbent bed, d. operating said engine under normal operating conditions during a second time period after the termination of said first time period, said initial exhaust gas stream being emitted from said engine at a temperature in the range of 250* to 700* C during said second time period, e. reducing the flow rate of said first stream of secondary air during said second time period, whereby the free oxygen content of said initial exhaust gas stream at entry into said reducing catalyst bed is less than about 30 percent in excess of the stoichiometric requirement to oxidize carbon monoxide contained in said initial exhaust gas stream, f. injecting a second stream of secondary air into said intermediate gas stream during said second time period, said second stream of secondary air being injected prior to passing said intermediate exhaust gas stream through said oxidizing catalyst bed, whereby substantially all of the hydrocarbon vapor and carbon monoxide in said exhaust gas stream are catalytically oxidized in said oxidizing catalyst bed during said second time period, g. dividing the resulting catalytically treated exhaust gas stream discharged from said oxidizing catalyst bed during said second time period into a major portion and a minor portion, h. discharging said major portion of said resulting catalytically treated exhaust gas stream to atmosphere during said second time period, i. passing said minor portion of said resulting catalytically treated exhaust gas stream through said absorbent bed during said second time period, whereby hydrocarbon previously absorbed during said first time period is desorbed and a mixed gaseous stream containing desorbed hydrocarbon vapor and exhaust gas is discharged from said absorbent bed during said second time period, j. passing said mixed gaseous stream formed by step (i) into said engine during said second time period, whereby at least a portion of the desorbed hydrocarbon vapor in said mixed gaseous stream is burned in said engine, k. operating said engine under abnormal operating conditions during a third time period after the termination of said second time period, whereby said initial exhaust gas stream is emitted from said engine at a temperature in the range of 700* to 1, 000* C during said third time period, l. cooling said initial exhaust gas stream by indirect heat exchange with the surrounding atmosphere during said third time period, by passing said initial exhaust gas stream through means adapted to receive and cool exhaust gas during said third time period, m. maintaining steps (e), (f), (g), (h), (i) and (j) during said third time period, n. operating said engine under abnormal operating conditions during a fourth time period after the termination of said third time period, whereby said initial exhaust gas stream is emitted from said engine at a temperature above 1,000* C during said fourth time period, o. terminating the flow of said first and second streams of secondary air during said fourth time period, and p. terminating the flow of said minor portion of said resulting catalytically treated exhaust gas stream through said absorbent bed during said fourth time period, and thereby terminating the flow of said mixed gaseous stream into said engine during said fourth time period.

Claim 16

In a method for controlling engine exhaust emissions in which the initial exhaust gas stream emitted by the engine contains noxious impurities including nitrogen oxides, hydrocarbons and carbon monoxide, said initial exhaust gas stream is passed through a reducing catalyst bed for the catalytic reduction of nitrogen oxides to nitrogen, the intermediate exhaust gas stream discharged from said reducing catalyst bed is passed through an oxidizing catalyst bed for the catalytic oxidation of at least a portion of said hydrocarbons and carbon monoxide to innocuous oxidation products, secondary air being added to said exhaust gas stream prior to passing the exhaust gas stream through said oxidizing catalyst bed, and a resulting catalytically treated exhaust gas stream is discharged from said oxidizing catalyst bed, the improvement during successive time periods of operation of said engine after startup which comprises a. operating said engine during a first time period, said first time period commencing with engine startup and extending for a duration of up to about 10 minutes, said initial exhaust gas stream being emitted at a temperature below 250* C and containing an abnormally high concentration of hydrocarbon vapor during said first time period, b. injecting a first stream of secondary air into said initial exhaust gas stream during said first time period, said first stream of secondary air being injected prior to passing said initial exhaust gas stream through said reducing catalyst bed, c. contacting said resulting catalytically treated exhaust gas stream with a solid absorbent bed during said first time period, whereby residual hydrocarbon vapor in said resulting exhaust gas stream is absorbed by said solid absorbent bed and final exhaust gas stream substantially free of hydrocarbon vapor is discHarged from said solid absorbent bed, d. operating said engine under normal operating conditions during a second time period after the termination of said first time period, said initial exhaust gas stream being emitted from said engine at a temperature in the range of 250* to 700* C during said second time period, e. reducing the flow rate of said first stream of secondary air during said second time period, whereby the free oxygen content of said initial exhaust gas stream at entry into said reducing catalyst bed is less than about 30 percent in excess of the stoichiometric requirement to oxidize carbon monoxide contained in said initial exhaust gas stream, f. injecting a second stream of secondary air into said intermediate gas stream during said second time period, said second stream of secondary air being injected prior to passing said intermediate exhaust gas stream through said oxidizing catalyst bed, whereby substantially all of the hydrocarbon vapor and carbon monoxide in said exhaust gas stream are catalytically oxidized in said oxidizing catalyst bed during said second time period, g. dividing the resulting catalytically treated exhaust gas stream discharged from said oxidizing catalyst bed during said second time period into a major portion and a minor portion, h. discharging said major portion of said resulting catalytically treated exhaust gas stream to atmosphere during said second time period, i. passing said minor portion of said resulting catalytically treated exhaust gas stream through said absorbent bed during said second time period, whereby hydrocarbon previously absorbed during said first time period is desorbed and a mixed gaseous stream containing desorbed hydrocarbon vapor and exhaust gas is discharged from said absorbent bed during said second time period, j. passing said mixed gaseous stream formed by step (i) into said engine during said second time period, whereby at least a portion of the desorbed hydrocarbon vapor in said mixed gaseous stream is burned in said engine, k. operating said engine under abnormal operating conditions during a third time period after the termination of said second time period, whereby said initial exhaust gas stream is emitted from said engine at a temperature in the range of 700* to 1, 000* C during said third time period, l. cooling said initial exhaust gas stream by indirect heat exchange with the surrounding atmosphere during said third time period, by passing said initial exhaust gas stream through means adapted to receive and cool exhaust gas during said third time period, m. maintaining steps (e), (f), (g), (h), (i) and (j) during said third time period, n. operating said engine under abnormal operating conditions during a fourth time period after the termination of said third time period, whereby said initial exhaust gas stream is emitted from said engine at a temperature above 1,000* C during said fourth time period, o. terminating the flow of said first and second streams of secondary air during said fourth time period, and p. terminating the flow of said minor portion of said resulting catalytically treated exhaust gas stream through said absorbent bed during said fourth time period, and thereby terminating the flow of said mixed gaseous stream into said engine during said fourth time period.

Claim 17

The method of claim 13, in which said engine is an internal combustion engine.

Claim 18

The method of claim 14, in which said internal combustion engine is an automobile engine.

Claim 19

The method of claim 13, in which said reducing catalyst bed and said oxidizing catalyst bed contain an active catalytic agent selected from the group consisting of nickel, cobalt, copper and manganese, and mixtures thereof, deposited on a carrier.

Claim 20

The method of claim 13, in which said solid absorbent bed contains an active hydrocarbon absorbent selected from the group consisting of activated carbon, zeoLite, activated alumina, fuller''s earth, kaolin, and organic resin, and mixtures thereof.

Claim 21

The method of claim 13, in which said first stream of secondary air is injected into said initial exhaust gas stream according to step (b) by injecting said secondary air stream into the exhaust manifold of said engine.

Claim 22

The method of claim 13, in which the duration of said first time period is in the range of about 2 to 6 minutes.

Claim 23

The method of claim 13, in which the flow of said first stream of secondary air is terminated during said second time period.