DE102008010329A1 - Process for the treatment of waste gas streams in the processing of biogenic gas streams - Google Patents

Abstract

The invention relates to a process for the production of biogas from raw biogas, wherein an exhaust gas stream obtained during the treatment of raw biogas is treated with a catalyst. The invention further relates to the use of a catalyst for the treatment of an exhaust gas stream resulting from the production of biogas.

Description

The The invention relates to a process for the production of biogas Raw biogas, whereby one in the treatment of raw biogas accruing Exhaust gas stream is treated with a catalyst. The invention further relates the use of a catalyst for the treatment of a in the production of biogas accumulating exhaust stream.

biogas is a mixture of the main components methane and carbon dioxide and arises in the anaerobic fermentation of organic Material. In contrast to aerobic composting, the process takes place under exclusion of air. The fermentation process takes place in the Nature z. B. in the rumen of cattle, in bog or marshes or on rice fields instead.

Table 1 shows a typical composition of biogas. Table 1: Typical composition of biogas methane 45-70% carbon dioxide 25-55% Steam 0-10% nitrogen 0.01-5% oxygen 0.01-2% hydrogen 0-1% ammonia 0.01-2.5 mg / m ³ hydrogen sulfide 10-30,000 mg / m ³

The industrial production of biogas is realized in special biogas plants. Typical starting materials for this purpose are, for. As farm manure (eg manure) and energy crops (renewable resource). The technical fundamentals for the production and use of biogas are described several times in the literature and state of the art. Good summaries are for. In the book "Biogas Practice" by Heinz Schulz (Publisher: Ökobuch Verlag, ISBN 10: 3922964591 ISBN 13: 978-3922964599) to find.

in principle exist various energetic and chemical uses and Utilization of biogas. The oldest and simplest Usage path is direct combustion for heat generation.

The Current main technical use is the motor conversion in electricity and heat. This is an internal combustion engine with Biogas fed and with the generated kinetic energy a generator operated for power generation. The in the combustion process On the one hand, waste heat is returned to the fermentation process as necessary process heat for fermentation supplied and / or combined combined heat and power systems used.

current The main purpose of a biogas plant is the generation of electricity and its Feed into the public network. Biogas flow can be different as electricity from wind and solar plants permanently in a power grid be fed and thus base loads in the power supply cover.

Further Opportunities for biogas use are z. B. the energetic Power generation in fuel cells (eg MCFC systems, "cfc-solutions") as well as the production of synthesis gas with subsequent synthetic steps such as As a methanol synthesis or a Fischer-Tropsch synthesis.

A recently discussed usage path is biogas upgrading to natural gas. The "biomethane"("bio natural gas") generated in the process can be connected or fed into the natural gas grid in a decentralized manner and used. According to the Association Biogas e. In future, in Germany alone, up to 20% of natural gas consumption could be covered by biomethane. So that the gas can be fed into a natural gas network without any problems, other accompanying substances must be permanently separated in addition to CO ₂ . The quality requirements for the production of natural gas substitutes are specified in DVGW G260, 261 and 262.

• – Druckwasserwäsche
• – Aminwäsche (drucklos sowie druckbetrieben)
• – Membranverfahren
• – kombiniertes Membran-Waschverfahren
• – CO₂-Verflüssigung
• – Adsorptionsverfahren
• – Druckwechseladsorption über Aktivkohle und/oder Kohlenstoffmolekularsieb

All uses of biogas require different levels of treatment (gas purification) of the raw biogas for subsequent use. The gas purification can for example by the separation the unwanted components take place. Several methods can be combined with each other. Often, at least one gas separation separation process is required. This can basically be realized by the following methods [ DGMK Conference Report 2002-2; ISBN 3-931850-91-9, P. 37-44, Schulte-Schulze Berndt ]:

• - Pressure water wash
• - amine scrubbing (pressureless and pressure operated)
• - Membrane method
• - combined membrane washing process
• - CO ₂ liquefaction
• - Adsorption process
• - Pressure swing adsorption on activated carbon and / or carbon molecular sieve

A detailed description of processes for processing raw biogas into biomethane and the possible use of waste gas streams is available in EP 1 634 946 A1 ("Environmentally friendly process for the production of biomethane").

Each separation process has several advantages and disadvantages. However, all separation processes are inherent in that after separation of the main gas stream containing biogas, which contains a high proportion of methane gas (ie higher than in the riobiogas) (depending on the selectivity of the separation process), a remaining gas stream is obtained, the so-called offgas stream or partial gas stream, which methane in lesser Contains concentration and other hydrocarbons, CO, H ₂ , NH ₃ , NO _x and O ₂ may contain.

A typical procedure for the production of biogas from raw biogas is the scheme in 1 can be seen, wherein also the emergence of an exhaust gas flow (partial gas flow) is illustrated.

Often these partial gas flows (see 1 ) as exhaust gas into the atmosphere. Since components of this gas stream are harmful to health and the environment (eg methane is one of the greenhouse gases and is more harmful than CO ₂ by a factor of 21), untreated emissions to the environment should be avoided.

moreover the exhaust gas flow through the components contained a calorific value which are not used for direct release into the environment would.

In EP 1 634 946 A1 For example, it is described how the methane content in this exhaust gas stream can be varied by modifying the separation process. The aim is to adjust the composition of the exhaust gas stream in such a way that a combustible composition is produced which can be burned thermally (eg by burning). B. for the production of raw biogas (eg., For heating a fermenter) can be used. As a result, less polluting methane is released from the exhaust gas stream as exhaust gas to the environment. However, a disadvantage of this method is that the combustion of the exhaust gas stream produces sulfur oxides and nitrogen oxides, which are further emitted to the environment.

The Object of the present invention is thus in the provision a process in which the exhaust gas flow from harmful Components is released and also contained in the exhaust stream Energy can be used.

• a) Bereitstellens von Rohbiogas,
• b) Aufbereitens des Rohbiogases durch Abtrennen eines Biogas enthaltenden Hauptgasstroms mittels eines Trennverfahrens, und
• c) Abtrennen eines bei der Aufbereitung des Rohbiogases resultierenden Abgasstroms

und das dadurch gekennzeichnet ist, dass der Abgasstrom mit einem Katalysator behandelt wird.The object is achieved by a method for the production of biogas from raw biogas, comprising the steps of

• a) provision of raw biogas,
• b) preparing the raw biogas by separating a main gas stream containing biogas by means of a separation process, and
• c) separating an exhaust gas stream resulting from the treatment of the raw biogas

and characterized in that the exhaust gas stream is treated with a catalyst.

The Provision of the raw biogas can be made according to the state of the art known methods, such as anaerobic digestion in an industrial biogas plant.

As well may be any of the separation techniques known in the art be used for the treatment of raw biogas.

These include pressurized water washing, amine scrubbing (pressureless and pressurized), the membrane process, a combined membrane scrubbing process, CO ₂ liquefaction, the adsorption process, or pressure swing adsorption via activated carbon and / or a carbon molecular sieve. Through these methods, the biogas can be effectively separated from the raw biogas. Back remains a partial gas stream, commonly referred to as exhaust gas, which in addition to residual methane other components such. B. contains other hydrocarbons, CO, H ₂ , NH ₃ , NO _x and O ₂ .

According to the invention the exhaust stream treated with a catalyst. This means that the exhaust stream is passed over the catalyst, thereby a heat of reaction is produced which is reused can.

Preferably the catalyst used is an oxidation catalyst. The catalyst may consist of one or more layers that are the same or different could be. Preferably, the oxidation catalyst is a monolithic catalyst, for example with metal and ceramic honeycombs. Further preferably, the catalyst is a foam or a bulk catalyst, For example, a shell catalyst, a solid material or a Extrudate, with a variety of geometric shapes and dimensions possible are. The catalysts can with a or more layers of washcoat and one or more Precious metals and / or metal oxides and / or mixtures thereof as active Components included.

Usually the catalyst is constructed so that a catalytically active compound is present as a coating on a suitable carrier. The catalytically active layers are preferably based on aluminum, cerium, Tungsten, titanium, iron, silicon and zirconium oxide, or combinations the mentioned, which additionally catalytically active precious metals and / or kata lytically active metal oxides of Fe, Cu, Mn, or combinations thereof can contain. Suitable noble metals are preferred selected from the group comprising platinum, palladium, Rhodium, copper, silver and ruthenium.

The Catalytically active layer is preferably in the form of a washcoat by soaking, spraying or sucking (Incipient Wetness method) applied, the catalytically active substances, especially the metals. The metals (precious metals) are usually in the form of their nitrates, chlorides, sulfates, Sulfites, acetates, etc. or complex compounds of these metals applied. Of course, the corresponding oxides in the form of Slurries usable.

To the application of the washcoat is typically carried out by a drying or calcination step, whereupon in addition a metal or noble metal doping of the washcoat surface with further catalytically active metals or their compounds, such as nitrates, chlorides, sulfates, sulfites, acetates or complex compounds, can be done.

As well For example, the oxidation catalyst may be zeolite or zeolite-like Be material or a carrier material can be with the zeolite or zeolite-like material. Also preferred For the purposes of this invention is a combination of a zeolite or zeolite-like material with an oxidation catalyst, as described above.

Of the Zeolite is preferably selected from a group of zeolites with the topologies AEL, BEA, CHA, EUO, FAO, FER, KFI, LTA, LTL, MAZ, MOR, MEL, MTW, LEV, OFF, TONE and MFI.

The term "zeolite" is used in the context of the present invention as defined by the International Mineralical Association ( DS Coombs et al., Canadian Mineralogist, 35, 1979, 1571 ) a crystalline substance from the group of aluminum silicates having a spatial network structure of the general formula M ^{n +} [(AlO ₂ ) _x (SiO ₂ ) _y ] x H ₂ O understood that consist of SiO ₄ / AlO ₄ tetrahedra, which are linked by common oxygen atoms to a regular three-dimensional network.

The ratio of Si / Al = y / x is always> 1 according to the so-called "Löwenstein rule", which prohibits the adjacent occurrence of two adjacent negatively charged AlO ₄ tetrahedra, although there are more at a low Si / Al ratio Exchange places for metal are available, however, the zeolite becomes increasingly thermally unstable.

The zeolite structure contains voids, channels that are characteristic of each zeolite. The Zeo Lithe are divided into different structures according to their topology. The zeolite framework contains open cavities in the form of channels and cages that are normally occupied by water molecules and additional framework cations that can be exchanged. An aluminum atom has an excess negative charge which is compensated by these cations. The interior of the pore system represents the catalytically active surface. The more aluminum and the less silicon a zeolite contains, the denser the negative charge in its lattice and the more polar its internal surface. The pore size and structure is determined by the Si / Al ratio, which is the major part of the catalytic character of a zeolite, besides the parameters of manufacture, ie, use, or type of template, pH, pressure, temperature, presence of seed crystals accounts.

The presence of divalent or trivalent cations as a tetrahedral center in the zeolite framework gives the zeolite a negative charge in the form of so-called anion sites, in the vicinity of which the corresponding cation positions are located. The negative charge is compensated by the incorporation of cations in the pores of the zeolite material. The zeolites are mainly distinguished by the geometry of the cavities formed by the rigid network of SiO ₄ / AlO ₄ tetrahedra. The entrances to the cavities are formed by 8, 10 or 12 rings, the expert speaks here of narrow, medium and large pore zeolites. Certain zeolites show a uniform structure structure, e.g. For example, the ZSM-5 or the MFI topology, with linear or zigzag-shaped channels, in others close behind the pore openings larger cavities, z. As in the Y or A zeolites, with the topologies FAO and LTA.

Prefers the zeolite is a metal-exchanged zeolite, more preferred a Fe zeolite. The zeolite or zeolite-like material may also be coated or doped with a noble metal. Suitable noble metals are also preferably selected here from the group comprising platinum, palladium, rhodium, copper, silver and ruthenium. The production process for metal exchanged Zeolites, for example via solid or liquid phase exchange, are known in the art. Likewise, methods for coating or doping of zeolites with precious metals known to those skilled in the art.

The The present invention thus describes a combined method for the production of biogas from raw biogas, which consists of a separation process and a downstream method, wherein the downstream Procedure harmful and dangerous to the environment Components of the exhaust gas stream from the separation process by catalytic Oxidation be removed and the released during the oxidation Heat is available for further use.

A schematic overview of the method according to the invention is in 2 to see.

Surprisingly could be found that it is in the inventive Method is not necessary, a certain methane concentration to achieve in the exhaust stream, since for this process no combustible Composition of the exhaust stream is required. this leads to to ensure that the methane yield in the main gas stream is maximum.

• • Das Abgas enthält weniger schädliche Komponenten;
• • Die entstehende Wärme kann genutzt werden;
• • Im Vergleich zur thermischen Verbrennung entstehen keine Stickoxide und/oder Schwefeloxide;
• • Im Vergleich zur thermischen Verbrennung ist keine Stützgasfeuerung notwendig („Flammloser Schwachgasbrenner");
• • Es ist kein aufwändiger Regelungsbedarf in Abhängigkeit der Abgasstromzusammensetzung oder dessen Volumenstroms, der durch die zyklische Betriebsweise des Trennverfahrens bedingt ist, notwendig;
• • Der Katalysator dient als Wärmespeicher zum Ausgleich dieser zyklischen Schwankungen (minimaler Regelungsbedarf).

Further advantages of the method according to the invention are:

• • The exhaust gas contains less harmful components;
• • The resulting heat can be used;
• • Compared to thermal combustion, there are no nitrogen oxides and / or sulfur oxides;
• • Compared to thermal combustion, no supporting gas firing is necessary ("Flammeless low-gas burner");
• • There is no complex control requirement depending on the exhaust gas flow composition or its volume flow, which is due to the cyclic operation of the separation process, necessary;
• • The catalyst serves as a heat storage to compensate for these cyclical fluctuations (minimum regulation requirement).

additionally For example, the catalysts defined above may also be used to be generated when using the biogas produced Exhaust gas streams (for example, in the combustion in a Gas engine) to clean and so also harmful to health and environmentally hazardous components.

additionally For example, the catalysts defined above may also be used be to the resulting in the production of raw biogas waste gas streams To clean (for example, heating the fermentation) and so also harmful and environmentally hazardous Remove components.

additionally For example, the catalysts defined above may also be used to be used in the generation, purification or use of a biogenic gas resulting exhaust gas streams (for example by gasification of organic (bio) mass) and so on also harmful and dangerous for the environment Remove components.

As well The scope of the invention includes a biogas plant, which for carrying out the inventive Method is suitable and at least one catalyst, as he described above. Preferably, the catalyst in the exhaust gas of the resulting in the treatment of the raw biogas waste gas arranged.

According to one Another preferred embodiment is another catalyst in an exhaust line of a resulting in the fermentation in the bioreactor Exhaust gas (eg in the generation of heat for the fermentation occurring waste gas or incurred in the fermentation biogenic exhaust) arranged.

According to one is also further preferred embodiment of the invention an additional catalyst in an exhaust line of a when using the generated biogas (incineration) incurred Arranged exhaust gas. For example, the methane content depends on or biogas-powered stationary engines (eg in combined heat and power plants) typically below 3000 ppm (equivalent to about 0.3% by volume). Of the Oxygen content is about 8-12 vol .-%. That stands definitely enough oxygen for the catalytic or thermal total oxidation available. Prefers a catalyst is used which consists of a ceramic and / or metallic Carrier consists of a washcoat based on of alumina and platinum as the active component. The Platinum concentration is preferably in the range of 1.0 to 1.5 g / l honeycomb volume. This allows CO reductions in the exhaust gas of 70% to over 90%.

The Catalysts for the respective exhaust gas lines can be the same or different. Preferred are the Catalysts, however, adapted to the respective use. For example is the catalyst which is located in an exhaust line of the Use of the generated biogas (combustion) accumulating exhaust gas is located preferably high temperature stable, since the combustion of Biogas produced heat an exhaust gas with a temperature of can produce more than 400 ° C.

By The combination of multiple catalysts ensures that always enough thermal energy for biogas production is available. Excess thermal Energy generated by the use of one or more catalysts is received, for example, collected in hot water tanks or used for other purposes (eg for power generation) become.

The Invention will now be described with reference to some embodiments, which in no way as limiting on the scope of To understand invention, explained in more detail.

EXAMPLES

Example 1:

Catalyst composition for the purification of the partial gas flow occurring in the production of biogas (exhaust gas flow):
A catalyst was used with a ceramic support coated with an alumina-based washcoat layer containing platinum and palladium as active components.

The Total noble metal concentration was 3 g / l, 4 g / l and 5 g / l honeycomb volume.

Example 2:

Catalyst composition for the purification of the partial gas flow occurring in the production of biogas (exhaust gas flow):
A metallic support catalyst coated with a washcoat layer based on alumina with platinum and palladium as the active component was used.

The Total noble metal concentration was 3 g / l, 4 g / l and 5 g / l honeycomb volume.

Example 3:

Catalyst composition for the purification of an exhaust gas stream obtained during the combustion of biogas in a stationary engine:
A catalyst having a ceramic support comprising a washcoat layer based on alumina and platinum as the active component was used. The platinum concentration was in the range of 1.0 and 1.5 g / l honeycomb volume.

Example 4:

Catalyst composition for the purification of an exhaust gas stream obtained during the combustion of biogas in a stationary engine:
A metallic support catalyst comprising a washcoat layer based on alumina and platinum as the active component was used. The platinum concentration was in the range of 1.0 and 1.5 g / l honeycomb volume.

In order to CO reductions in exhaust gas of 90% could be achieved.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 1634946 A1 [0011, 0016]

Cited non-patent literature

• - "Biogas Practice" by Heinz Schulz (Publisher: Ökobuch Verlag, ISBN 10: 3922964591 ISBN 13: 978-3922964599) [0004]
• - DGMK Conference Report 2002-2; ISBN 3-931850-91-9, p. 37-44, Schulte-Schulze Berndt [0010]
• DS Coombs et al., Canadian Mineralogist, 35, 1979, 1571 [0029]

Claims (15)

Process for the production of biogas from raw biogas, comprising the steps of a) providing raw biogas, b) preparing the raw biogas by separating a main gas stream containing biogas by means of a separation process, and c) separating an exhaust gas stream resulting from the treatment of the raw biogas, characterized in that the exhaust gas stream is treated with a catalyst. Method according to claim 1, characterized in that the catalyst is an oxidation catalyst. Method according to claim 1 or 2, characterized that the catalyst in the form of a monolithic catalyst or is present as a bulk catalyst. Method according to one of claims 1 to 3, characterized in that the catalyst with a washcoat is coated. Method according to one of the preceding claims, characterized in that the catalyst is a precious metal and / or a metal oxide and / or a mixed oxide. Method according to one of the preceding claims, characterized in that the exhaust gas stream after the treatment with the catalyst substantially free of harmful Components is. Method according to one of the preceding claims, characterized in that in the treatment of the exhaust stream used with a catalyst thermal energy is used. Method according to claim 7, characterized in that that the thermal energy is used to produce raw biogas becomes. Use of a catalyst for treating a in the production of biogas accumulating exhaust stream. Use according to claim 8, characterized the catalyst is an oxidation catalyst. Use according to claim 8 or 9, characterized that the catalyst in the form of a monolithic catalyst or is present as a bulk catalyst. Use according to one of claims 8 to 10, characterized in that the catalyst with a washcoat is coated. Use according to one of claims 8 to 11, characterized in that the catalyst is a noble metal and / or a metal oxide and / or a mixed oxide. Use according to one of claims 8 to 12, characterized in that the treatment of the in the production from biogas accumulating exhaust stream reducing harmful Substances in the exhaust stream comprises. Use according to one of claims 8 to 13, characterized in that the catalyst for treatment the exhaust stream is part of a biogas plant.