Segmented Particulate Filter For An Engine Exhaust Stream

Abstract

A particulate filter is fluidly connected to and disposed downstream from a diesel engine exhaust stream outlet. The filter has a plurality of filter segments that have differing physical properties or structural characteristics such that the engine exhaust stream to fuel stream ratio is maintained substantially consistent among segments during their regeneration. A method for regenerating a segmented filter comprises maintaining the engine exhaust stream to fuel stream ratio substantially consistent among segments during their regeneration.

1 . An engine exhaust stream particulate filter comprising at least two filter segments wherein said segments are structured so that if they were each supplied with a gas stream under identical conditions, the gas stream mass flow through each of said segments would be different. 
   
   
       2 . The engine exhaust stream particulate filter of  claim 1  wherein said segments differ from each other in at least one structural characteristic selected from the group consisting of cross-sectional area, longitudinal filter length, filter porosity and filter cell density. 
   
   
       3 . The engine exhaust stream particulate filter of  claim 1  wherein said at least two filter segments are unequal in their in cross-sectional area. 
   
   
       4 . The engine exhaust stream particulate filter of  claim 1  having a longitudinal axis, wherein said at least two filter segments are unequal in length in the longitudinal direction. 
   
   
       5 . The engine exhaust stream particulate filter of  claim 1  wherein said segments differ from each other in at least one structural characteristic such that the engine exhaust stream mass flow rate through each segment during their sequential regeneration is approximately equal. 
   
   
       6 . The engine exhaust stream particulate filter of  claim 1  wherein said at least two filter segments are housed in a common enclosure. 
   
   
       7 . A method for operating a particulate filter comprising a plurality of filter segments, the method comprising:
 (a) directing an exhaust stream from a combustion engine through said plurality of filter segments;   (b) selectively introducing a hydrogen-containing gas stream at least periodically into each of said filter segments to regenerate said segment;   (c) maintaining the engine exhaust stream to hydrogen-containing gas stream heat value ratio used for regeneration of each segment substantially consistent among said plurality of segments.   
   
   
       8 . The method of  claim 7  wherein said hydrogen-containing gas stream is introduced into said plurality of segments sequentially in a regeneration sequence. 
   
   
       9 . The method of  claim 8  wherein the engine exhaust stream mass flow rate through each segment is different so that said heat value ratio is maintained substantially consistent among segments during their regeneration. 
   
   
       10 . The method of  claim 9  wherein said segments are structured so that if they were supplied with a gas stream under identical conditions, the gas stream mass flow through each one of said plurality segments would be different. 
   
   
       11 . The method of  claim 7  wherein said heat value ratio is maintained substantially consistent among segments during their regeneration by varying the mass flow rate of said hydrogen-containing gas stream that is introduced to regenerate each segment. 
   
   
       12 . The method of  claim 11  wherein said hydrogen-containing gas stream is introduced into said plurality of segments sequentially in a regeneration sequence. 
   
   
       13 . The method of  claim 12  wherein the mass flow rate of said hydrogen-containing gas stream that is introduced to regenerate each segment depends upon its position in the regeneration sequence. 
   
   
       14 . The method of  claim 7  wherein the duration of regeneration of each segment is substantially the same. 
   
   
       15 . The method of  claim 7  where said hydrogen-containing gas stream is being introduced into at least one filter segment at a given time so that at least one filter segment is undergoing regeneration during operation of said particulate filter. 
   
   
       16 . The method of  claim 8  further comprising
 (d) monitoring at least one of a pressure P 1  of said engine exhaust stream upstream of said particulate filter, a temperature T 1  of said engine exhaust stream, and a time interval t 1  related to operation of said particulate filter, and initiating said regeneration sequence by selectively introducing a hydrogen-containing gas stream into a first segment in said sequence when at least one of P 1 , T 1  or t 1  is greater than a predetermined threshold value.   
   
   
       17 . The method of  claim 8  further comprising:
 (d) monitoring at least one of pressure differential ΔP across said particulate filter, a temperature T 1  of said engine exhaust stream, and a time interval t 1  related to operation of said particulate filter and initiating said regeneration sequence by selectively introducing a hydrogen-containing gas stream into a first segment in said sequence when at least one of ΔP, T 1  or t 1  is greater than a predetermined threshold value.   
   
   
       18 . The method of  claim 17  further comprising:
 (e) ceasing regeneration of said first filter segment and each subsequent segment in said regeneration sequence when ΔP falls below a predetermined threshold value.   
   
   
       19 . The method of  claim 17  further comprising:
 (e) ceasing regeneration of said first filter segment and each subsequent segment in said regeneration sequence when the rate-of-decrease in ΔP falls below a predetermined threshold value.   
   
   
       20 . The method of  claim 8  wherein the flow of said hydrogen-containing gas stream to each segment in said regeneration sequence is ceased after a predetermined segment regeneration time. 
   
   
       21 . The method of  claim 8  further comprising
 (d) monitoring a temperature T 2  of said exhaust stream downstream of said particulate filter and the flow of said hydrogen-containing gas stream to a particular segment is ceased when said temperature T 2  exceeds a predetermined third threshold value.   
   
   
       22 . The method of  claim 7  wherein said hydrogen-containing gas stream is selectively introduced into each of said plurality of segments depending on a monitored operating parameter of each said segment. 
   
   
       23 . The method of  claim 22  wherein said operating parameter is a temperature of said engine exhaust stream passing through each segment. 
   
   
       24 . An engine and exhaust after-treatment system comprising:
 (a) a combustion engine;   (b) a particulate filter connected to receive an exhaust gas stream from said engine via an exhaust stream conduit, said particulate filter comprising a plurality of filter segments with different structural characteristics from one another, wherein during operation of said particulate filter said exhaust gas stream is directed through said segments in parallel;   (c) a syngas generator for producing a syngas stream;   (d) a controller configured to selectively direct said syngas stream to each of said segments in sequence to regenerate said segment.   
   
   
       25 . The engine and exhaust after-treatment system of  claim 24  wherein said filter segments are structured so that if they were each supplied with a gas stream under identical conditions, the gas stream mass flow through each of said segments would be different.