Patent Publication Number: US-2006011112-A1

Title: Method and device for pollution reduction from exhausts emissions

Description:
FIELD OF THE INVENTION  
      The disclosed invention relates to a method, an apparatus designed accordingly, to reduce and/or eliminate polluting exhaust components from combustion thermal-generator emissions.  
      The method and apparatus are intended to be used to reduce and/or eliminate polluting exhaust components from combustion thermal-generator emissions comprising at least a combustion chamber and at least an fixed exhaust duct, the duct be used to direct exhaust from inside volume to outside volume of said combustion chamber.  
     BACKGROUND OF THE INVENTION  
      One of the major problems nowadays in highly populated towns and cities is air pollution.  
      Air pollution is both to substances mixed with air and to substances that modify air natural components. All these substances are commonly named pollutants. Thus we have to pollutants families: direct pollutants and indirect pollutants.  
      Direct pollutants are typically divided in gaseous pollutant and solid pollutants. As example some direct pollutants are those substances able to modify air oxygen turning it from its bi-atomic molecular state to a modified tri-atomic state (named ozone). This behaviour was originated by exhaust emissions.  
      In order to reduce pollution and its related damages, the inventors identified pollution sources and thus proper technological intervention for each of the sources was addressed. All of the pollution sources are those that emits gaseous and solid particles in air, they are vehicles, buildings and industrial plants.  
      The solutions used to reduce the pollutants released in air, their effects on health are different according to type of pollution source, type of pollutant and historical period.  
      At the beginning the attention was towards the reduction of some pollutants from industrial plants, see as example patent U.S. Pat. No. 5,879,645 that discloses a catalyst and related method to reduce nitrogen oxides from industrial emissions. With emissions they refer principally to combustion exhausts.  
      Consequently similar solution was applied to a different field such as vehicles, specifically cars, trucks etc.  
      Effectively, in patent U.S. Pat. No. 5,879,645 a catalyst and related method are applied according to the same scheme to vehicles exhaust. The introduction of catalyzed mufflers allowed reducing drastically pollutants from vehicles.  
      Nevertheless, is was observed that all these solutions able to reduce pollutants and emissions from industrial plants and internal combustion vehicles are not enough to reduce pollution especially in big cities.  
      As we anticipated at the beginning it is necessary to reduce pollutants from buildings, too. Residential density contributes substantially to polluting emissions in air mainly due to heating systems and to hot water production systems installed in residential buildings and offices.  
      Emission reduction is thus mainly related to the reduction of pollutants directly at the source through the introduction of dedicated devices. In order to have a clear advantage it is necessary to install such pollution reducing system on the most of vehicles and residential buildings.  
      Nowadays most developed countries have regulations that forces automobile producers to sell cars with emission reduction devices to meet specific reduction targets. The mean automobile age made it possible to had the most of circulation cars, which did not adopt such devices, substituted by new existing low emission ones. Unfortunately the residential building situation is different; mean residential building age is so long compared to automobile one that it is not possible to imagine, even in case of regulation similar to automotive field, a fast substitution of the existing device with new ones with low emission profiles. In such case the solutions devoted to residential buildings should be: easy to install on existing plants, have a low cost profile in order not to have a great economical impact on building owners, last for a period comparable to the mean maintenance period and timing of buildings. The mean forecasted lasting time for obsolete components is an important parameter; this time is considerably great in civil field compared to automotive field, indeed are more interesting low impact and revamping solution compared to complete new ones that requires reconstructions.  
      Each Country issues safety and health regulations related to plant safety especially in case of fire or explosion. In an industrial plant, a catalytic device demands for an high temperature thermal regime. The high temperature is reached by burning gas, gasoline, diesel fuel or others. In a civil building the required modifications for such a device are often incompatible with typology of existing rooms or requires modifications of the environment to satisfy fire and safety regulations especially of explosion-proof regulation in case of gas.  
      Devices to improve air quality are known for closed environments, such devices suck air from outside changing chemically and mechanically their properties, and pumping inside buildings or in vehicles.  
      Devices for reducing the pollutants in exhaust gases, of the type described in the following patents are likewise known.  
      Document DE 19824204 discloses a method and a device for reducing pollutants in exhaust gases produced by combustion in a heater for a house or a dwelling. More particularly the device comprises a combustion chamber, a fixed exhaust duct, means for regulating the pressure of exhaust gases passing through the duct, an air pressure jet system linked to a compressor and a ventilator, and means for separating gaseous pollutants (a noble metal three-way catalyst). The catalyst is, if needed, set to a temperature sufficient for decomposition by a heating element that heats the exhaust gas. The catalyst causes, due to its flow resistance, a pressure loss which is compensated for by the ventilator.  
      Document DE 19627028 discloses a method and a device for reducing pollutants in exhaust gases produced by combustion in a heater for a house or dwelling. The device comprises a combustion chamber (not shown), a fixed exhaust duct, a ventilator for regulating the pressure of exhaust gases passing through the duct, a ceramic filter for separating particulate pollutants, and an oxidation catalyst for removing gaseous pollutants, which, due to its flow resistance, is able to generate a pressure increase in the duct when the exhaust gas is passing through the catalyst. The catalyst is heated by the exhaust gases to a temperature which is sufficient to decompose the gaseous pollutants. All three units can be positioned at any point in the duct.  
      Both the apparatus for reducing pollutants described in the two abovementioned German patents have the drawback, which is common to many solutions of the known type, that they are directly arranged on the duct for discharging the exhaust gases. This results in the drawback that it is required to decommission the heat generator in the case where maintenance of the apparatus is required.  
      These known apparatus, moreover, do not treat adequately the particles in particular of uncombusted products which are released by the heat generator during the repeated lighting operations.  
      Consequently the catalysts of the apparatus of the known type are not sufficiently protected against the particles which may be deposited and burn on them in particular during the start-up transients of the combustion heat generator.  
     DISCLOSURE OF THE INVENTION  
      Therefore the problem underlying the present invention is that of providing a method and an apparatus for reducing and/or eliminating the pollutants present in the exhaust gases produced by combustion heat generators, which may be easily installed in pre-existing plants, which does not have a high cost so as not to discourage installation thereof and which can be easily configured and/or personalized. Another object of the present invention is that of providing a method and an apparatus, the maintenance of which does not involve decommissioning of the heat generator to which it is connected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The technical features of the invention, in accordance with the abovementioned objects, may be clearly determined from the content of the claims below and the advantages thereof will emerge more clearly from the following detailed description, provided with reference to the accompanying drawings, which show a purely exemplary and non-limiting embodiment in which:  
       FIG. 1  shows a system for heating a dwelling using an apparatus according to the invention;  
       FIG. 2  shows a first example of an apparatus according to the invention in particular for gas oil or gas, associated with a heat generator having an exhaust duct;  
       FIG. 3  shows a cross-sectional view of the apparatus according to  FIG. 2 ;  
       FIG. 4  shows a different example of an apparatus according to the invention resting on the ground;  
       FIG. 5  shows a cross-sectional view of the apparatus according to  FIG. 4 ;  
       FIG. 6  shows a detail of the apparatus, relating to a protection grille of the catalyst. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EXAMPLE OF EMBODIMENT  
       FIG. 1  shows an example of a system for heating a dwelling according to the invention, comprising a combustion heat generator  1  of the known type, which is typically positioned inside the dwelling itself and connected to an apparatus  6  for supplying a fuel  7  and to an exhaust duct  2  (or flue) able to convey the exhaust gases of the heat generator  1  outside the dwelling by means of the apparatus  12  according to the present invention.  
      The heat generator  1  comprises a combustion chamber  5  able to burn the fuel  7  so as to produce heat. The fuel  7  is fed into the combustion chamber  5  by the apparatus  6  of a type known per se.  
      Typically the exhaust duct  2  terminates in a chimney  3  which may optionally be equipped with a device  4  for facilitating the introduction and dispersion of the exhaust gases into the atmosphere.  
      The apparatus  12  has a support structure  20  provided with legs  21  for resting on the ground, as in the case of the example in  FIG. 4  which is designed in particular for feeding the heat generator with fuel oil, wood or chippings, or simply with a cylindrical sleeve  22 , as in the example of  FIG. 2  for gas oil or gas.  
      As is known, the term “chippings” refers to fragmented wood or wood chips which are obtained by means of special machines. In order to produce chips, inferior quality wood is used, such as that left over from pruning performed in woodland, agricultural or urban areas, Toppings or also the by-products of sawmills. The wood converted into chips may in fact advantageously be used for fuelling purposes, since, being easy to handle, it can be automatically fed into boilers. It should be remembered, however, that in this latter case the size of the chips must be homogeneous and small (3-5 cm).  
      The abovementioned structure  20  of the apparatus  1  supports a vertically extending pipe  23  having the function of a by-pass for a section of the exhaust duct  2 . This by-pass pipe  23  is connected at the top to the exhaust duct  2  and at the bottom to a connecting part  30  (shown in  FIGS. 2 and 3 ) which is in turn connected on opposite sides to the exhaust gas discharge outlet  81  of the heat generator  1  and to the exhaust duct  2 . Therefore, the pipe  23  is connected to the exhaust duct  2  by means of two sections, i.e. a first safety section  24  for conveying the exhaust gases from the combustion chamber  5  and a second exhaust gas expulsion section  25  for evacuating them into the atmosphere.  
      A filter  26 , in particular of the mechanical type, is arranged on the by-pass pipe  23 , immediately downstream of the connecting part  30 . This filter  26 , in the case of fuels likely to produce a considerable amount of residual combustion product, as for example in the case fuel oil or chippings, is advantageously of the cyclone (or vortex) type since it allows a significant reduction in the solid particles suspended in the exhaust gases by means of a separating action due to the centrifugal force.  
      By way of an indication, this filter allows a reduction in the particles present in the fuel oil and in the chippings from an amount, respectively, of about 50 mg Nm 3  and 100 mg Nm 3  down to an amount of about 5 mg Nm 3  (miligrammes per normal cubic metre).  
      As can be seen in  FIG. 5 , the exhaust gases leaving the combustion chamber  5  via the connecting part  30  (not shown) rise up through the central tube  27  and then descend inside the individual conically shaped cyclones  28 , being forced to perform a rotating movement. This movement, owing to the action of the centrifuging force, produces a separation of the solid particles which consequently fall into the underlying container means  29  (consisting, for example, of an extractable drawer for emptying the accumulated material), leaving the exhaust gas purified and free to rise up again along the central channel until it emerges from the upper outlets  31 .  
      In order to optimize the efficiency of the filter, depending on the power of the heat generator  1 , only a corresponding number of the outlets  31  are advantageously open. With reference to the example shown in the accompanying figures it may be considered that each cyclone  28  processes on average 90 cubic metres per hour of exhaust gases and that the 12 cyclones envisaged will all be open in order to meet the requirements of a 350 kW heat generator.  
      Moreover, preferably in order to reduce the production costs, the cyclones  28 , except for the outlets  31 , are incorporated in a single cylindrical body which is formed as one piece by means of casting.  
      In the case where the heat generator  1  is intended to be fed with gas oil or with gas, or with products producing a small residual amount of suspended particles after combustion, it is possible to provide a simpler and less costly mechanical filter  26 , for example consisting of a simple meshwork.  
      The by-pass pipe  23  also has, arranged inside it in succession, an electric heating resistance  40 , an exhaust gas intercepting grille  41 , a catalyst  42  and suction means  43  preferably consisting of a centrifugal ventilator.  
      From an operational point of view, when the ventilator  43  is switched off or not operating, the exhaust gases do not pass through the by-pass pipe  23  where the filter  26 , the catalyst  42  and the grille  41  are located, since these act like a bung causing a slight loss of pressure, but instead pass through the connecting part so as to reach directly the exhaust duct  2  via the first section  24 .  
      On the other hand, when the ventilator is operated, the exhaust gases are instead forced to circulate inside the pipe  23  so as to subject the flow to treatment by the filter  26 , the catalyst  42  and the grille  41 .  
      The electric resistance  40  is preferably activated only during the very initial stages of operation of the apparatus  12  or whenever the combustion heat generator is started up or restarted. It performs the dual function of burning the particles deposited on the grille  41  during the previous operating cycle of the heat generator and pre-heating the catalyst  42  prior to arrival of the exhaust gases.  
      More specifically, upon ignition of the flame of the heat generator, which can be directly detected by the start signal or by means of a pressure sensor  50 , for example, arranged downstream of the combustion chamber and sensitive to the arrival of the shockwave caused by ignition of the flame, the electric resistance  40  heats up and in a few seconds by means of irradiation heats the surface of the grille  41  to a temperature of between 400 and 700° C. so that it burns all the carbon-containing particles which are deposited on it during the previous operating cycle of the heat generator.  
      At the same time, the resistance  40  heats up the catalyst  42  so as to allow it to be already fully operative already before arrival of the exhaust gases. The same catalyst  42  is able to treat the emissions produced by the particles which burn on the grille  41 .  
      For example, it is possible to envisage that with a 300 kW heat generator it is sufficient to provide a resistance with a power of 6 kW intended to remain switched on during the initial stage of operation of the apparatus or whenever the heat generator is restarted, for a period of 10 to 120 seconds. The consumption of the resistance  40 , which is advantageously intended only to produce heat by means of irradiation, is therefore practically negligible.  
      Moreover, owing precisely to the presence of the resistance  40 , it is possible to consider that the grille  41  is practically advantageously of the self-cleaning type.  
      Once the catalyst  42  has been heated up and before the exhaust gases reach the apparatus  12  (the exhaust gases travel relatively slowly so as to release heat inside the exchanger of the heat generator  1 ), the ventilator  43  is switched on, regulating its flowrate so that it conveys the entire exhaust gas flow leaving the heat generator through the by-pass pipe. Basically, the power required of the ventilator is minimal and equal to the loss of pressure inside the by-pass pipe due to the presence of the filter  26 , the grille  41  and the catalyst  42 . In this way, the apparatus does not modify the operating conditions of the heat generator  1 , which is not affected at all by operation of the apparatus  12 .  
      Advantageously, the speed of the motor of the ventilator  43  is regulated by means of an inverter which is controlled depending on the flowrate of the exhaust gases leaving the heat generator  1 , which is, for example, detected by a special flow meter.  
      In accordance with the embodiment shown in  FIG. 6 , the grille  41  is composed of several superimposed sheets  41 ′ of metal meshes  44  which have dimensions increasing in the direction of the resistance  4 .  
      The present invention also relates to a method for reducing or eliminating the pollutants present in the exhaust gases produced by combustion heat generators. For the sake of simplicity of the description, the same terms already adopted with reference to the apparatus  12  will be used.  
      The method therefore envisages a step involving treatment of the exhaust gases which are circulated by the ventilator  43  inside the vertically extending by-pass pipe  23 .  
      Treatment of the exhaust gases envisages filtering, in particular by means of a centrifugal action, in order to purify them of the polluting solid particles, as well as conveying them through the catalyst in order to eliminate the polluting gases.  
      In accordance with the idea underlying the present invention, the method envisages that, during start-up of the apparatus  12  following lighting of the heat generator  1 , with the suction means  43  initially switched off, heating of the grille mounted inside the by-pass pipe  23  is performed by means of the electric heating resistance  40 , so as to burn particles deposited on the grille  41  and preheat the catalyst  42 .  
      The heating step is transitory and terminates when the suction means are switched on, namely soon afterwards, so as to allow the grille to burn also the particles of uncombusted products present in the first fumes produced by lighting of the heat generator.  
      The invention thus conceived therefore achieves the predefined objects.  
      Obviously, it may also assume, in its practical embodiment, forms and configurations different from that illustrated above without thereby departing from the present scope of protection.  
      Moreover, all the details may be replaced by technically equivalent elements and the dimensions, forms and materials used may be any depending on the requirements.