DE102007043854A1 - Catalyst unit with automatic bypass flap for combustion plants operated with solid fuels - Google Patents

Abstract

It is known that the combustion quality of solid fuel combustion plants can be improved by using oxidation catalysts. The present invention relates to a catalyst unit with automatic bypass flap, which causes flue gas is passed through the catalyst only at a suitable temperature. The problem is that, when the catalyst is operated at too low a temperature, hydrocarbons condense on its surface and coat it as if with paint, thereby losing its effectiveness. The air ducts are no longer burning freely, they are growing. A non-drawing chimney and a destroyed catalyst are the consequences. The installation of a catalyst was previously not necessary, since the required emission limit values could be achieved without aftertreatment of the flue gas. Today, however, where heating with wood is again up-to-date and the potential for improvement in the combustion chamber geometry has been exhausted, the use of catalysts could be a possible way forward.

Description

State of the art

That the combustion quality of with Solid fuels operated combustion plants z. B. stoves, pellet stoves, solid fuel stoves, pellet & wood chips, Gasification boilers, fireplace inserts ... (hereinafter referred to as oven or ovens for the sake of simplicity) through the use of precious metals (palladium, platinum, rhodium) coated oxidation catalysts are significantly improved can, is known.

• • Image und Kosten: eine moderne Heizung war in der Vergangenheit stets eine Öl- oder Gasheizung. Bei diesen ist aber aufgrund des standardisierten Brennstoffes eine beinahe rückstandsfreie Verbrennung auch ohne Katalysator möglich. Festbrennstofföfen waren seit den 50er Jahren des letzten Jh. erstens die Heizung der unteren Einkommensbezieher und zweitens ohnehin eine aussterbende Spezies. Es wäre daher politisch sicherlich nicht opportun gewesen, gerade derartige Geräte zu verteuern. Inzwischen hat sich die Situation aufgrund des anhaltend hohen Ölpreises jedoch grundlegend verändert: mit Holz zu heizen ist in! In Österreich wurden 2005 mehr als doppelt so viele Holzpelletheizungen installiert wie Ölheizungen; und bei Kaminöfen und Festbrennstoffherden sprechen heute (2006) alle Hersteller von einem Boom, mit dem noch vor wenigen Jahren niemand gerechnet hätte.
• • Keine praktikable technische Lösung: Katalysatoren werden schon seit einiger Zeit, vor allem in den USA, erfolgreich in Kaminöfen eingesetzt – allerdings in Kombination mit einem Gebläse. In den USA wird die Leistungsregelung mittels Zwangsbelüftung erreicht. Gebläseunterstützte Öfen hatten aber in Europa bisher keinen Erfolg – womit auch der Katalysator den Sprung über den großen Teich nicht geschafft hat.
• • Zu niedrige Umweltstandards: und hier beißt sich die Katze in den Schwanz: keine praktikable technische Möglichkeit den Schadstoffausstoß zu reduzieren bewirkt den politischen Unwillen, Grenzwerte zu fordern, die von der Industrie mit herkömmlichen Mitteln nicht erreichbar sind. Würde der Gesetzgeber strengere Standards fordern, dann müßte sich die Industrie etwas einfallen lassen, tut er dies nicht, so wird sich eine Technik, die Öfen zuerst einmal verteuert, nicht, oder nur schwer durchsetzen.

Nevertheless, catalysts have not yet gained acceptance in this area. The reasons could be:

• • Image and costs: in the past, modern heating has always been an oil or gas heating system. In these, however, a nearly residue-free combustion is possible without a catalyst due to the standardized fuel. Solid fuel stoves were the heating of the lower income earners since the 1950s and, secondly, a dying species anyway. It would therefore certainly not been politically opportune to increase the price of such devices. In the meantime, however, the situation has changed fundamentally due to the persistently high oil price: to heat with wood is in! In Austria, more than twice as many wood pellet heating systems were installed in 2005 as oil heating systems; and in the case of wood-burning stoves and solid fuel stoves today (2006), all manufacturers speak of a boom that only a few years ago nobody would have expected.
• • No practical technical solution: Catalysts have been used successfully in wood-burning stoves for some time, especially in the USA - but in combination with a blower. In the US, the power control is achieved by forced ventilation. Fan-assisted ovens have so far been unsuccessful in Europe - which means that the catalyst has not made the leap across the pond.
• • Too low environmental standards: and here the cat bites its tail: no viable technical possibility to reduce pollutant emissions causes the political reluctance to demand limits that are not achievable by the industry by conventional means. If the legislature demanded stricter standards, then the industry would have to come up with something, if it does not do so, then a technique that first increases the price of ovens will not, or only with difficulty, prevail.

Now is rarely targeted to the solution working on a problem, a viable technical solution to a problem wanted, if this problem does not arise. Meanwhile have but the conditions, as already described, changed: fixed Fuels, In particular wood, Pellets (wood, straw), Wood chips, Crops are no longer considered as either outmoded or half-baked, but instead especially with regard to the greenhouse effect as the energy policy Future par excellence - and This will make it necessary to think about their emissions as well.

Of the Use of a catalyst, as in road traffic for a long time prescribed, offers itself. While it is at Gasoline is a purified, standardized fuel, which is always available in standardized, consistent quality and quality, this is, in particular in manually fed systems such as stoves and solid fuel stoves not the case. However, impurities are related to the combustion not only paint residues, but z. B. also so natural like water! (Water leads to a lower combustion temperature as an essential part the energy released during combustion for the vaporization thereof must be spent.)

These Impurities, condensing hydrocarbon compounds (creosote) and mineral constituents (ash) may cause the laying of the channels lead in the catalyst.

Especially during the warm-up phase problems can occur:
the stove is still cold, the flue gases flowing into the chimney are cold, a chimney draft has not yet built up. In a furnace without a catalyst it normally builds up after a short time. However, the honeycomb structure of the catalyst requires a not to be underestimated air resistance. This can lead to train problems even when the catalyst is completely clean during the start-up phase. But if this is first laid with dust, soot, tar, then the convection can not get going at all; the fatal consequence would be a possible leakage of smoke into the living space.

This Although now relatively easy means of a so-called. Anheizklappe (or Bypass flap) can be prevented whereby the flue gases past the catalyst be routed into the fireplace. And indeed are manual heating flaps in the US in combination with state of the art and state-of-the-art catalysts therefore common - but have this the serious disadvantage that you either at all can forget to press her or just served at the wrong time.

The consequences of such faulty or non-operation may be that with the flap closed during the heating phase, smoke is emitted, or itself If the valve opens too early, it will form creosote deposits on the catalyst surface and render the catalyst ineffective.

aim The present invention is now a unit of catalyst and automatic bypass door of the type to ensure that that will Flue gas only at a correspondingly high temperature through the catalyst is directed. Furthermore the unit should be compact, if possible without addition to mounting parts get along so they can easily go into an oven installed, or u. U. can even be retrofitted.

The Task is solved by that the Bypass flap automatically, d. H. temperature controlled opened or is closed, thereby ensuring is that flue gas, only from a certain temperature (T> about 350 ° C) passed through the catalyst becomes. In this case, the control and operation in a variety of ways carried out: electronically with servomotor, thermohydraulic by volume change a fluid in a piston or expansion vessel or thermo-mechanically, z. B. by bimetal.

Claims (6)

Catalyst unit consisting of catalyst ( 1 ) and automatic bypass flap ( 2 ) for combustion plants operated with solid fuels, characterized in that at least one catalyst and a temperature-controlled bypass flap are connected to form a component in such a way that it is ensured that flue gas, which does not fall below a certain temperature (T <about 350 ° C) , or is passed through the catalyst only in small amounts. Temperature-controlled bypass flap according to claim 1, characterized in that it is either thermomechanical, for instance by means of bimetal ( 3 ), thermo-hydraulically by volume change of a fluid or electrically by means of temperature sensor and actuator works. Temperature-controlled bypass flap according to claim 2, characterized in that this not just as a flap in the true sense of the word, but as a general one Control valve, as well as lid, slide or knob can be trained. Catalyst unit according to claim 1, characterized in that the holder for the catalyst and the bypass flap usefully as a removable frame ( 4 ) is designed to not only exchange the catalyst easier, but also to be able to clean easier if necessary. Catalyst unit according to claim 1, characterized in that that the Flap of a housing and / or Insulation material may be surrounded, whereby the mechanism with a certain delay reacts on the one hand sufficient to operate the stove Chimney can build and on the other hand, the catalyst to operating temperature is brought before it is traversed by the flue gas. Catalyst unit according to claim 1, characterized in that that these with enough space in the trains an existing furnace can also be retrofitted.