WO2009049647A1

WO2009049647A1 - Post-combustion device, for filtering and reducing emission of particulate as well as optimizing thermal performance

Info

Publication number: WO2009049647A1
Application number: PCT/EP2007/008986
Authority: WO
Inventors: Robert Dal Pra'
Original assignee: Dal Pra Robert
Priority date: 2007-10-17
Filing date: 2007-10-17
Publication date: 2009-04-23
Also published as: EP2198200B1; EP2198200A1; CA2704157A1

Abstract

Post-combustion device used for filtering and reducing emission of harmful particulate and optimising thermal performance, to be used on biomass, wood, pellet, woodchips, oil seeds and other similar products fuelled burners especially for domestic use equipment such as stoves and fireplaces. Said device comprises a plurality of elements (3, 8, 9, 10, 12), used to create depression along the entire gases route as well as releasing said gases.

Description

TITLE: POST-COMBUSTION DEVICE, FOR FILTERING AND REDUCING EMISSION OF PARTICULATE AS WELL AS OPTIMIZING THERMAL PERFORMANCE

Description

The present finding concerns a post-combustion device, for filtering and reducing emission of particulate as well as optimizing thermal performance, to be used on biomass fuelled burners.

As it is well known, the main problem regarding the use of combustion heating appliances based on boilers equipped with biomass fuelled burners (wood, pellets, wood chips, oil seeds and other similar material), especially when used for domestic purposes - stoves, boilers and fireplaces - concerns optimising thermal performance (recovery of combustion heat) alongside ensuring least pollution possible (lowest emission of combustion products into the atmosphere).

According to the current state of the art, there are several stove and fireplace performance enhancement methods. Some of these methods include creating airflows in the fire chamber thus enhancing combustion and consequently reducing emissions (for example as described in the VI93A000161 Italian patent). Alternatively, the heating appliance can be equipped with a chamber with a secondary airflow or a water coil which, upon contact with the combustion exhaust gases, transfers some of the heat from the gases mentioned beforehand to the transfer fluid, thus increasing the appliance's thermal performance (for example as described respectively in the 253.010 and

VI2004A000049 Italian patents). This patent aims at manufacturing a combustion heating appliance capable of guaranteeing both enhanced thermal performance and low pollution compared to corresponding parameters of similar products already known.

This can be achieved by means of a device to be applied downstream a burner - to be found in wood, pellet, wood chips, oil seeds and generally biomass fuelled stoves/boilers - comprising at least one mechanical pre-filter (a cyclone filter), at least one smoke ionization chamber, at least one electrostatic collection filter (made of a cellular monolithic catalyst with an impregnated metal substrate), at least one oxygen addition intake to control post-combustion, at least one post-filtration electrostatic chamber, at least one heat exchanger, at least one suction device used to create depression along the entire gases route (burner - cyclone pre-filter - ioniser - collector/catalyst - electrostatic post- filter - heat exchanger).

Constructively, a cyclone separator may be used for mechanical pre-filtration operations. Such cyclone separator is used to remove heavy visible particles (ash for instance which could end up settling on the catalyst substrate and thus clogging it) from the smoke generated following normal combustion. Such particles end up in a removable collection tray under the appliance. Then, once the coarse particles are removed through the cyclone separator, smoke is channelled into the primary ionizing section, where there is an exhaust gases ionization chamber, made of a metal sheet mesh with a 10 kV electrostatically charged catalyzing substrate, to cause particulate polarisation. Next, the electrically charged gases are channelled into an electrostatic filtering collector, made of a catalyst with a previously treated and earthed metal substrate, operating as a post-burner through combustion of the CO (carbon monoxide) previously mixed with oxygen and of the particulate electrostatically collected and applied on the surface of the abovementioned substrate.

More precisely, the catalyst serves as a collector in the electrostatic scrubbing process, collecting fine dusts while converting harmful substances - both to health and environment - usually produced by biomass combustion into harmless substances. This occurs through surface chemical reactions taking place onto the heated metal substrate previously coated with noble metals (such as platinum, palladium and rhodium) which cause oxidation of carbon monoxide and other unburned hydrocarbons, converting them into carbon dioxide and water alongside the reduction of nitrogen oxides and fine dusts, commonly referred to as PM 10, (environmentally friendly outcome).

In addition, when the gases generated by combustion pass through the catalyst mentioned beforehand, not only do they undergo a chemical conversion, but they also trigger a post-combustion process of the of the gases still unburned after the first stage, thus increasing the temperature of the gases (reaching 800°C) exiting from the catalyst mentioned beforehand considerably (heat recovery).

Advantageously, according to the finding, a secondary electrostatic filter, comprising a two-stage electrostatic chamber made of metal sheet with a treated substrate, made up of an ionising section and a collection section, can be arranged downstream the catalyst.

The electrostatic two-stage chamber mentioned beforehand collects the fine dusts (diameter below 1 μm) produced during the initial igniting stage of the burner. These fine dusts remain unburned after going through the previous post-combustion group, as this is still inefficient within that ignition period of time due to low temperatures at that stage. Once the post-burner reaches the temperature required for regular operation, the secondary electrostatic filter is disabled and its collection surface is cleaned up under the effect of the high temperature of the gases exiting from the post-burner.

Then, the gases mentioned beforehand, purified and considerably hot exiting from the catalyst, pass through a heat exchanger thus recovering the greater part of the heat held in the post-burner gases. This heat exchanger is used to produce hot water or heated air for the environment.

Exploiting the maximum thermally conductive surface, the ideal performance of a bundle heat exchanger can be obtained only by positioning said exchanger after the particulate filtration system, thus allowing the scrubbing of fine dusts. Indeed, were said dusts still present during the thermal exchange stage, they disadvantageous^ would settle onto the internal walls of the exchanger, thus reducing its performance i.e. external thermal conduction.

Lastly, a suction device is fixed at the end of the exhaust gas pipe where gases have already considerably cooled down. Such suction device is used to create depression along the canal outlining the entire exhaust gas route, thus starting the suction operation directly from the combustion chamber of the heating appliance.

The entire system shall be fixed downstream the combustion chamber of the heating appliance. Basically, this is due to the fact that the system should collect burnt gases while they are still flames and at temperatures not below 300-350°C, the maximum value required to neutralise polluting gas substances through the catalyst. Practically, laboratory tests have proved that upon final exit, not only are the exhaust gases free of polluting dusts (environmental benefit) but they also transfer most of their heat compared to the traditional systems (energy saving).

This finding shall be explained in details through a description of a possible embodiment, as illustrative but not limiting examples, with the help the annexed drawings, wherein:

- fig.l illustrates a front elevation view of the device according to the finding;

- fig.2 illustrates a side view of the abovementioned device, partially cross- sectioned by line H-II of fig.1 ;

- fig.3 illustrates an overall view of the filtering group;

- fig.4 illustrates an exploded view of the group according to fig 3;

- fig.5 illustrates a cross-section, according to line V-V of fig 4, under the filtering group;

- fig. 6 illustrates a cross-section, according to line VI-VI of fig 3, under the filtering group;

- fig.7 illustrates a block diagram of how the device operates according to the finding;

From the operational point of view, the device 1 provided for by this finding operates in five stages: in the first stage, mechanical pre-filtration of coarse particulate occurs, as illustrated in the drawing at Fl; (fig. 1); in the second stage, oxygen regulated ionization and mixing occurs as illustrated in the drawing at F2; in the third stage, collection of fine dusts alongside conversion and post-combustion of gases occurs with electrostatic precipitation as illustrated in the drawing at F3; in the fourth stage, electrostatic post-filtration of fine particulate occurs as illustrated in the drawing at F4 and in the fifth stage, heat exchange with the external environment occurs as illustrated in the drawing at F5.

As illustrated by the drawings, in the first operational stage, the exhaust gases find their way from the combustion chamber "C" into the mechanical separation filter through the pipe 2. Said filter is made of a cyclone 3, which separates coarse particles, which in turn settle in a manually removable tray 4 beneath.

Subsequently, the combustion gas exits from the upper collector 5 of the cyclone 2 then it undergoes mechanical pre-filtration and addition of oxygen coming from an external source through an intake canal 6 equipped with an automatic gate valve 6.1.

Next, in the second stage, by means of a pipe 7, the gas is channelled through an ionization chamber 8 supplied with a 10 Kv positive electric charge, through which it is treated, charging the fine particles still present after the first mechanical filtration stage electrostatically.

After that, particulate collection is performed in the third stage through the action of the metal substrate of a cellular catalyst 9 earthed with negative charge.

Through surface post-combustion of the substrate at high temperatures, the substrate mentioned beforehand - treated using noble metals such as platinum, palladium and rhodium - serves to eliminate the unburned substances, cause oxidation of carbon monoxide and unburned hydrocarbons converting them into carbon monoxide and water, alongside reducing nitrogen oxide and PMio (environmentally friendly purpose).

There is a two-stage electrostatic chamber 10, directly coupled with the catalyst 9. This chamber, completing the fourth stage, is used to collect fine dusts (diameter below 1 μm) produced during the initial igniting stage of the burner and not neutralised during the previous phase in that the catalyst 9 has not yet reached the required temperature.

Such two-stage electrostatic chamber 10, made of the same material as the previous cellular catalyst 9, consists of a first stage 10.1 which allows ionization of particles at 7,5 and 10 kV (positive pole) not collected by the catalyst mentioned beforehand, due to low temperature or due to temperature excursions under normal operation conditions (change of temperature/speed, on/off, lack of combustion). The two-stage electrostatic chamber 10 also consists of a second stage 10.2 used to collect previously ionised particles, settling the rejected particles of the charged substrate at a 1/3 of the ionization voltage, on the earthed surface.

In the fifth stage, through a pipe 11, the gases are channelled into a high exchange surface tube bundle heat exchanger 12, where heat exchange occurs with environment air/air or air/water and where gas intake occurs from the top towards the bottom while the tube bundle encloses the entire post-combustion group (8,9,10) thus allowing to recover even the heat produced by the previously mentioned post combustion group surface coating, through the circulation of air to perform the heat exchange.

A suction motor 13, is fixed onto the heat exchanger 12 on the "S" openings. Such suction motor sucks cooled gases keeping the depression along the entire appliance at a constant level and releases said gases. The descriptions above show the benefits achieved through the use of the device provided for by this finding. In particular, this device performs heat exchange and combustion exhaust gas purification operations occupying little space and with maximum performance.

Obviously, the device herein described may be made according to different embodiments, depending on the dimensions and type of components used, provided that such methods comply with the following claims.

Claims

1. POST-COMBUSTION DEVICE USED FOR FILTERING AND REDUCING EMISSION OF HARMFUL PARTICULATE ALONGSIDE OPTIMIZING THERMAL PERFORMANCE, to be used on biomass, wood, pellet, wood chips, oil seeds and other similar products fuelled burners, especially for domestic use appliance such as stoves and fireplaces, said device (1) being characterised in that it comprises at least one mechanical cyclone filter (3), at least one primary ionization chamber (8), at least one catalytic post-combustion precipitator or a grounded catalyst (9), at least one two-stage electrostatic filter (10), at least one heat exchanger (12) and at least one suction device (13) aimed at creating a depression along the gases route (cyclone filter - oxygen suction pipe - ionization chamber - post-burner - two-stage electrostatic filter - heat exchanger) alongside releasing said gases.

2. DEVICE, according to claim 1 characterised in that it serves as a post-burner and in that it is positioned downstream the combustion chamber "C" of the biomass fuelled heating appliance.

3. DEVICE, according to claim 2 characterised in that it serves as a filtration system for particulate generated by the combustion of biomass.

4. DEVICE, in according to claim 2 characterised in that the catalyst (9) is of the metal monolithic kind, with a cellular substrate impregnated with noble metals such as platinum, palladium or rhodium, which cause oxidation of carbon monoxide and unburned hydrocarbons converting them into carbon dioxide and water.

5. DEVICE, according to claim 3, characterised in that that the ionization chamber (8) has a 10 kV electric charge and it is positioned before the catalyst

(9).

6. DEVICE, according to claim 3 characterised in that the post-combustion inside the catalyst is optimised through addition of oxygen directly from an external source through a pipe (6) equipped with a self-regulated valve (6.1).

7. DEVICE, according to claim 1, characterised in that the catalyst (1), being earthed, serves as an element collector for fine dusts.

8. DEVICE, according to claim 4 characterised in that the primary ionization causes settling of particulate in the catalyst substrate, even when the latter has not reached required post-combustion operation temperatures.

9. DEVICE, one or more of the previous claims characterised in that the filter or the two-stage electrostatic chamber (10), positioned after the catalytic post- burner (9) is of the two-stage type with double voltage (10 kV - 7.5 kV) and it consists of an ionising section (10.1) and a collection section (10.2), which prevents leakage of particles from the catalyst (9).

10. DEVICE, according to claim 8 characterised in that the two-stage electrostatic filter (10) positioned after the catalyst (9), is made of the same material as the abovementioned catalyst, thus avoiding ongoing manual cleaning of the precipitator positioned after the ionising section (10.1) through surface combustion of the particulate deposited on the substrate, triggered by the high temperature of the gas produced by the previous post-combustion.

11. DEVICE, according to one or more of the previous claims characterised in that the electrostatic filter (10) performs filtration operations withholding any dusts and gases produced due to poor post-combustion, irregular operation of the heating appliance or malfunctions during burner on/off operations.

12. DEVICE, according to one or more of the previous claims characterised in that that the heat exchanger (12) is a tube bundle exchanger with gas intake from the top towards the bottom thus allowing heat to spread over the entire surface of the same exchanger.

13 DEVICE, according to one or more of the previous claims characterised in that the exchange bundle (12) encloses the post-burner group (8,9,10) thus allowing to recover even the heat produced by the surface coating of the same post-burner through air circulation within the same post-burner.

14. DEVICE, according to one or more of the previous claims characterised in that the device (1) provided for by this finding operates in five stages: a first stage (Fl), where mechanical pre- filtration of coarse particles occurs; a second stage (F2) where oxygen regulated ionization and mixing occurs; a third stage (F3), where collection of fine dusts occurs alongside conversion and post- combustion of gases with electrostatic precipitation; a fourth stage (F4), where electrostatic post-filtration of fine particulate occurs; a fifth stage (F5) where heat exchange with the external environment occurs.

15. HEATING APPLIANCE, such as a wood, pellet, wood chip, oil seeds and generally biomass fuelled stove/burner characterised in that it is equipped with the energy saving/environmentally friendly device (1) made according to one or more of the previous claims.