Gas separation: processes – Filtering – With cleaning of filter
Reexamination Certificate
2001-06-26
2003-06-03
Smith, Duane (Department: 1724)
Gas separation: processes
Filtering
With cleaning of filter
C095S285000, C095S286000, C095S115000, C095S129000, C095S148000, C096S115000, C096S130000, C096S143000, C096S154000, C055S282200, C055S282300, C055S283000, C055S286000, C055S287000, C055S288000, C055S523000, C055S524000, C055SDIG003, C060S299000, C060S300000, C060S303000, C060S311000
Reexamination Certificate
active
06572682
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to an electrically regenerable filter cartridge system. More specifically, the present invention relates to the regenerable self-cleaning filter cartridge system for removing carbon, lube oil and unburned fuel particulates from the exhaust of internal combustion engines. In addition, the present invention relates to a regenerable filter cartridge system for removing particulates from Diesel engine exhaust gases. Further, the present invention also relates to a trap or filter for nitrogen oxide (NOx) to convert such gases to more desirable gases and to purge the exhaust of sulfur.
In the automotive industry, there has been a tremendous concern over the introduction of harmful pollutants into the air which have been generated by vehicle exhaust. Due to the negative health effects of such emissions, the Environmental Protection Agency of the United States has expressed a desire to reduce particle emissions from internal combustion engines. In the United States, the majority of particulate emissions come from Diesel engines on trucks and buses, which have not been regulated as closely as vehicles with gasoline engines.
Various attempts have been made to decrease the particulate emissions from Diesel engines. Unlike with gasoline engine vehicles, existing catalytic converters do not work well with Diesel engines since particulates typically clog these devices since the temperatures within them are too low to effectively burn carbon, lube oil and unburned fuel particles. Other efforts have been made to specifically address the Diesel particulate emissions problem. For example, fired burner systems have been employed to heat a combustion chamber, which receives Diesel exhaust for the purpose of burning the particulates within the chamber at very high temperatures. Such combustion chambers suffer from the drawbacks of high initial cost, high complexity, large size, high-energy consumption and high maintenance cost.
Another prior art attempt is the employment of passive particle filters and configurations to trap the particulates associated with Diesel emissions. These passive particle filters are commonly made from ceramic and metal, for example. These passive particulate filters are inadequate because when the filter fills up with carbon particles, the back pressure within the exhaust increases to such a level which necessitates that the filter be either regenerated in some fashion or replaced entirely. Since replacing the filter is not practical, many types of regeneration have been attempted, including the raising of the temperature of the filter above the combustion point of the carbon particulates in similar fashion to a self-cleaning oven. These prior art methods of filter regeneration include using a fired burner assembly using some type of fuel; raising the exhaust gas temperature by turbo charging the engine or other means; reducing the ignition temperature of carbon particles by adding a suitable catalyst to the fuel or filter material; and electrical heating. The foregoing methods of filter regeneration are not typically used in vehicles today due to their associated cost and practicality.
Further, there have been prior art attempts to employ electrically regenerable filter media instead of the passive filters that need to be replaced and fired burner systems which burn off the collected particulate matter. While the prior electrically regenerable filter media is suitable for burning off collected particulate matter, there is no known complete filter media cartridge system that can accommodate selective regeneration of multiple cartridges in a single system to achieve continuous operation. Further the prior art systems are not compact and, as a result, not suitable for many vehicle applications. Moreover, existing filter media systems cannot be precisely controlled to provide customized continuous filtration. The energy consumption is very high in these prior systems.
Specifically, there are a number of products that address the problem of reducing diesel engine emissions through the use of Diesel Oxidation Catalysts (DOC). DOCs are usually constructed of a ceramic or metal substrate coated with a catalytic material. Although a DOC can reduce the Soluble Organic Fraction of the Particulate Matter, it has no effect on the carbon particles. Most systems based on catalytic oxidation achieve only in the order of 20-25% reduction in PM, the level presently approved by the EPA and which will soon be inadequate as new tougher standards are applied. Furthermore, as soot covers the surface of the catalytic converter, the catalyst quickly becomes ineffective which shortens the service life and degrades the performance of the system. Most of the systems rely on high exhaust temperature to initiate and maintain the regeneration, a factor that limits the useful range of these systems.
In the world market, many producers have emerged as key players, especially in Europe, taking advantage of the significant support from governments and diesel engine manufacturers. Currently, the European market is dominated by a few technologies, mainly variations of the ceramic substrates. The most prevalent mode of regeneration, unlike the USA market, is fuel additives. It is important to mention that the effect of such additives has not been thoroughly studied, but there are indications that perceived harmful side effects will impede their introduction to the USA market and might lead to limiting their wide spread use in Europe.
Diesel particulate filters available in today's market are typically built on a ceramic substrate that traps soot by forcing the exhaust to flow through porous walls in a monolith. A catalyst is coated on the inside surface of the monolith. This lowers the soot combustion temperature, allowing the filter to regenerate at lower temperature than the ignition temperature of soot. An inherent limitation of such systems is that they rely on high exhaust temperatures and are practically inoperable at lower temperatures. For optimal performance, these systems require that the hot duty cycle of the engine be at least 20% of its operation, some system producers specify a hot duty cycle as high as 40-50% of the engine's operation. In some driving conditions, it is difficult to maintain the necessary exhaust temperature required to regenerate this type of filter. Such a situation can cause excessive accumulation of particulate matter (soot overloading) and clogging of the filter and may later lead to uncontrolled combustion resulting in the destruction of the filter. To overcome this problem, some filters have installed electric heaters to maintain the necessary temperature for regeneration. Two regeneration strategies have developed in the market:
a. Regeneration while the engine is running, usually requiring large electric currents.
b. Regeneration while the engine is off. This is usually done after 8 engine hours, and requires plugging into an external power source, and is not convenient for normal driving conditions.
Another inherent limitation of the catalyzed ceramic filters is the fact that sulfur compounds in the Diesel fuel poison the catalysts needed to reduce the particulate matter emitted by Diesel engines.
In the prior art, it is also desirable to employ a nitrogen oxide (NOx) trap in addition to a particulate filter to improve the overall operation of the engine. Lean NO.sub.x traps operate cyclically. During the lean portion of the cycle (fill duration), NO.sub.x is adsorbed. After running lean for a period of time, the trapping efficiency becomes low and the trap must be regenerated. This is done by operating rich of stoichiometric. The hydrocarbons and CO emitted during rich operation causes the NO.sub.x to reduce to N.sub.2 and O.sub.2. The lean part of the cycle may typically last for one minute followed by the regeneration or purge part of the cycle for one second.
It is desirable that the transition between the fill and purge portions of the cycle be imperceptible to the driver. Accordingly
Ibrahim Osama M.
Peter Klaus J.
Barlow Josephs & Holmes, Ltd.
Greene Jason M.
Rypos, Inc.
Smith Duane
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