Gas separation – Means within gas stream for conducting concentrate to collector
Patent
1989-01-30
1990-05-15
Hart, Charles
Gas separation
Means within gas stream for conducting concentrate to collector
515273, 515283, 515284, 515523, 515DIG30, 60303, 60311, B01D 4604
Patent
active
049254634
DESCRIPTION:
BRIEF SUMMARY
The invention refers to an exhaust gas cleaning system for Diesel engines.
Filtration of the Diesel exhaust gases is necessary because engine measures to reduce soot are not sufficient on their own. A wide variety of devices fitted with filters has already been suggested for this after-treatment of the exhaust gases, using ceramic or electrostatic filters, for example. These filters are used to filter out the soot particles from the exhaust gas, which are deposited on the filter. This results in the necessity for removal of the deposited soot from time to time, so as to preserve the functional capacity of the filter. This process is generally known as filter regeneration.
Thus, SAE Paper No. 850015 describes a device with monolithic ceramic filters and the regeneration of these filters by specific selection of motor setting parameters in conjunction with a filter position close to the engine. However, in this device filter regeneration is subject to substantial random influences, with one of the risks involved being that the filter block will become thermally overloaded.
Regeneration can be improved by the metered addition of metallic additives which are mixed with the fuel, as is described by way of example in SAE Publication No. 860137. However, this causes the further problem of the emission of metallic compounds.
A fundamentally different approach to the filter regeneration problem aims at burning off the soot using an additional burner which is switched on when required and burns away the soot via the burner gases (compare, for example, DE-OS No. 3219948). However, this involves the particular problem of adapting the burner function to the relevant operating status, i.e. exhaust gas volume, exhaust gas temperature and exhaust gas pressure of the engine gases. Even small deviations from the setting required may result in thermal damage to or destruction of the filter.
In order to avoid these difficulties, change-over devices with two identical filters have been suggested, with one filter being located in the exhaust gas flow at any one time and the other being independently regenerated using a burner (DE-OS No. 3204176). The disadvantages of such a device are the large construction volume, the construction expense and the required change-over units which are exposed to the hot, corrosive combustion gases.
For this reason, a proposal has also been made for regenerating the filter sector by sector with an appropriately constructed combustion chamber being passed sector by sector over the filter block (compare, for example U.S. Pat. No. 4,481,767). A major disadvantage here is the fact that because of the variations in heat development and the lever action of the fixing device, the burner cover is distorted which, in turn, means that the cover cannot seal cleanly against those filter sections which are not being regenerated at any particular time.
In order to avoid this disadvantage, the invention proceeds, from kinematic reversal of this known proposal, in which the filter is rotated sector by sector into the vicinity of the burner in the known fashion (U.S. Pat. No. 4,573,317). Apart from its considerable construction expense, this generic device has major disadvantages. These include, in particular, the cooling problem. Since the burner gases and the soot constitute an additional source of heat, a heat sink with direct action should be available to protect the components from thermal overload. Admittedly, a heat sink is present in all the known devices, but this is inadequate so that heat buildup occurs which can very quickly result in the destruction of the filter.
It is in this respect that the invention should provide a remedy, as the proposed system for the cleaning of exhaust gases no longer has the disadvantages mentioned above and also produces additional and substantial advantages.
The filter elements are advantageously designed in the form of tubes, through the sides of which the exhaust gases flow radially, so that a large filter area is available. The exhaust gas can be fed to either the fir
REFERENCES:
patent: 4276066 (1981-06-01), Bly et al.
patent: 4481767 (1984-11-01), Stark
patent: 4519820 (1985-05-01), Oyobe et al.
patent: 4573317 (1986-03-01), Ludecke
patent: 4641496 (1987-02-01), Wade
Greigg Edwin E.
Hart Charles
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