DE202008016134U1 - Device for enriching the fuel gas components in lean gases - Google Patents

Abstract

Device for the limited enrichment of fuel gas components, in particular methane, in input gases by CO ₂ separation by means of gas permeation,
characterized in that
- A reactor for generating input gases (A), preferably for microbial lean production, at least one membrane separation plant (1) is connected downstream, wherein at least one gas permeation module of the membrane separation plant (1) with the supplied input gas (A) for partial separation of CO ₂ from the input gas ( A) using the CO ₂ partial pressure gradient between the input gas (A) and the ambient air is acted upon and compared to the supplied input gas (A) enriched with methane product gas (B) with less than 20 vol .-% CO ₂ and an im Comparison with the supplied input gas (A) with CO ₂ enriched separating gas (C) with at least 4 vol .-% methane is obtained
- The membrane separation plant (1) permeatseitig via a line with a suitable means, preferably a combustion chamber (4), for afterburning of the separation gas (C) is connected and
- The membrane separation plant (1) retentate side via a line with a gas supply system (5) or ...

Description

The invention relates to a device for the limited enrichment of fuel gas fractions, such as methane, in lean gases (eg biogas, landfill gas), by CO ₂ separation with membranes.

at conventional biogas plants is usually at one Methane enrichment omitted; average methane content of 50 to 70% are for the utilization of biogas in combined heat and power plants perfectly adequate. Is, however, a higher methane content necessary, such as for biogas grid feed-in, such as pressure swing adsorption (PSA), pressurized water washing, gas scrubbing, low pressure membrane adsorption, cryogenic gas separation or gas permeation through membranes for methane enrichment to disposal. The latter method can also be used when the methane concentration of a lean gas for motor utilization is no longer sufficient, for example at a landfill gas in the aftercare phase.

In the mentioned separation process of gas permeation by means of membranes, the different permeability of the gas components is used, so CO ₂ molecules can migrate through the membrane faster than methane molecules. To accelerate the separation process, it is possible to work with increased pressure. Methane accumulates on the high-pressure side of the membrane, while CO ₂ molecules and even small amounts of methane permeate through the membrane.

A disadvantage of separation processes by means of gas permeation are the methane losses due to the methane molecules passing through the membrane. This effect is conventionally avoided by a series connection of several membranes and the return of the methane-rich partial streams. Thus, the membrane separation according to the 1 take place in two stages, that is, the enriched with CO ₂ permeate a first membrane module is fed as feed 2 a second membrane module. In this case, the retentate 2 of the second membrane module is admixed with the feed of the first module. Retentate 1 is a methane-enriched lean gas. Such a series connection of several membranes leads on the one hand to an increase in the yield, but at the same time also leads to an increase in investment and operating costs.

Another way of increasing efficiency in the utilization of lean gases describes the DE 100 47 264 A1 , Here, method for the use of methane-containing biogas, in particular of landfill gas and biogas from fermentation plants or digestion processes on sewage treatment plants, proposed, the biogas is supplied to the purpose of power generation a gas engine of a gas engine / generator set and the biogas in a gas engine upstream membrane separation plant into two gas streams is separated, wherein the first gas stream has a higher compared to the biogas composition methane content and is used as fuel gas for the operation of the gas engine and wherein the second enriched with CO ₂ gas stream is returned to the landfill body or digester a sewage treatment plant. However, such feedback is only possible or useful in a few specific applications.

The Object of the present invention is a cost-effective and economical device for enriching the fuel gas fractions to provide in lean gases.

• – einem Reaktor zur Erzeugung von Eingangsgasen, vorzugsweise zur mikrobiellen Schwachgaserzeugung, mindestens eine Membrantrennanlage nachgeschaltet ist, wobei mindestens ein Gaspermeationsmodul der Membrantrennanlage mit dem zugeführtem Eingangsgas zur Teilabscheidung von CO₂ aus dem Eingangsgas unter Ausnutzung des CO₂-Partialdruckgefälles zwischen dem Eingangsgas und der Umgebungsluft beaufschlagt wird sowie ein im Vergleich zum zugeführten Eingangsgas mit Methan angereichertes Produktgas mit weniger als 20 Vol.-% CO₂ und ein im Vergleich zum zugeführten Eingangsgas mit CO₂ angereichertes Trenngas mit mindestens 4 Vol.-% Methan erhalten wird,
• – die Membrantrennanlage permeatseitig über eine Leitung mit einem geeigneten Mittel, vorzugsweise einer Brennkammer, zur Nachverbrennung des Trenngases verbunden ist und
• – die Membrantrennanlage retentatseitig über eine Leitung mit einer Gasnetzeinspeiseanlage oder einer Gasaufbereitungsanlage verbunden ist.

The object is achieved by a device for enriching fuel gas limited proportions, in particular methane, in input gases by CO ₂ separation by means of gas permeation, wherein

• - A reactor for generating input gases, preferably for microbial lean production, at least one membrane separation plant is connected, wherein at least one gas permeation module of the membrane separation plant with the supplied input gas for partial separation of CO ₂ from the input gas by utilizing the CO ₂ -Partialdruckgefälles between the input gas and the ambient air as well as a product gas enriched with methane compared to the supplied input gas with less than 20 vol.% CO ₂ and a separating gas enriched with CO ₂ in comparison with the supplied input gas having at least 4 vol.% methane,
• - The membrane separation plant permeatseitig via a conduit with a suitable means, preferably a combustion chamber, is connected to the afterburning of the separation gas and
• - The membrane separation plant retentate side is connected via a line with a gas grid feed system or a gas treatment plant.

• – Beaufschlagen mindestens eines Gaspermeationsmoduls einer Membrantrennanlage mit zugeführtem, vorzugsweise in einem Bioreaktor mikrobiell erzeugtem, Eingangsgas zur Teilabscheidung von CO₂ aus dem Eingangsgas unter Ausnutzung des CO₂-Partialdruckgefälles zwischen dem Eingangsgas und der Umgebungsluft, wobei ein im Vergleich zum zugeführten Eingangsgas mit Methan angereichertes Produktgas mit weniger als 20 Vol.-% CO₂, vorzugsweise mit weniger als 18 Vol.-% CO_{2 ,} ganz besonders bevorzugt mit weniger als 15 Vol.-% CO₂, und ein im Vergleich zum zugeführten Eingangsgas mit CO₂ angereichertes Trenngas mit mindestens 4 Vol.-% Methan, vorzugsweise mit mindestens 8 Vol.-% Methan, erhalten wird,
• – energetische, insbesondere thermische, Nutzung des Trenngases durch dessen Nachverbrennung und
• – Weiterleitung des mit Brenngasanteilen angereicherten Produktgases zu einer Gasnetzeinspeiseanlage mit direkt angeschlossenen Verbrauchern oder zu einer Gasaufbereitungsanlage zur Erzeugung einer angestrebten hohen Konzentration von Brenngasen bei gleichzeitig starker Reduktion des CO₂-Anteiles.

The device according to the invention is particularly suitable for carrying out a method for enriching fuel gas fractions, in particular methane, in input gases by CO ₂ separation by means of gas permeation, the method comprising at least the following steps:

• - Applying at least one gas permeation module of a membrane separation plant with supplied, preferably microbially produced in a bioreactor, input gas for partial separation of CO ₂ from the input gas under Aus utilization of the CO ₂ partial pressure gradient between the input gas and the ambient air, wherein a product gas enriched with methane compared to the input gas fed in is less than 20% by volume CO ₂ , preferably less than 18% by volume CO _{2 , with} very particular preference with less than 15% by volume of CO ₂ , and a separating gas enriched in CO ₂ with at least 4% by volume of methane, preferably with at least 8% by volume of methane, compared to the input gas fed in,
• - Energetic, especially thermal, use of the separation gas by the afterburning and
• - Forwarding of enriched with fuel gas product gas to a gas grid feed system with directly connected consumers or to a gas treatment plant to produce a desired high concentration of fuel gases with a strong reduction of the CO ₂ content.

In the context of this invention, an input gas is understood to mean a lean gas, preferably a biogas, a sewage gas, a mine gas or a landfill gas, with a gas composition of at least 18% by volume of CO ₂ . The remainder consists mainly of methane, water vapor and nitrogen.

The membrane material used is not determined by the method; Any suitable materials may be used here, such as cellulose acetate, polysulfones, silicones or polycarbonates, etc. According to a preferred embodiment of the method, when the gas permeation module is supplied with input gas, the product gas enriched with methane in comparison with the input gas fed in is used as a retentate and that in comparison obtained to the supplied input gas with CO ₂ enriched separation gas as permeate. CO ₂ molecules permeate faster through the membrane than methane molecules. With a suitable embodiment of the membrane, an enrichment of CO ₂ in the retentate and of methane in the permeate of a membrane separation unit is alternatively possible.

The advantages achieved by the invention are that only a membrane for the partial separation of CO _{2 is} required. Another decisive advantage of the method according to the invention lies in the complete energetic utilization of the input gas or lean gas. Thus, both the retentate, either directly or after further work-up, as well as the permeate can be used. The CO ₂ -rich permeate has so far only been disposed of or returned.

To optimize the energy consumption and the expenditure on equipment, the aim is not high gas quality of the treated product gas, but only an enrichment to the desired quality requirements of the respective applications. For this purpose, during the CO ₂ enrichment, the partial pressure gradient between CO ₂ in the input gas or lean gas and the ambient air is used to separate off CO ₂ . To reduce the energy consumption, a negative pressure is generated on the permeate side of the membrane and / or purge gas, for example air, supplied. If necessary, the partial pressure gradient of CO ₂ across the membrane can be increased by compressing the lean gas on the feed side (feed side of the inlet gas into the gas permeation module). The implementation of the method according to the invention can be carried out both by single-stage as well as by multi-stage separation steps or membrane modules.

As the permeate CO ₂ should preferably be separated, with small amounts of other gas components, such as methane, are separated. The resulting separation gas as permeate with combustible fractions has a low calorific value. The heat utilization of the separation gas of the membrane separation plant can be done by post-combustion in a special combustion chamber, an engine, a gas turbine or a fuel cell with or without admixture of another fuel or by mixing in another combustion process with another fuel. The resulting in the separation gas use of the permeate heat Q is the usable heat that accumulates in the immediate vicinity of the membrane module and the biogas plant and should be used there, preferably for Fermenterbeheizung a biogas plant. For such use of the separation gas, a minimum content of 4% by volume of methane, preferably 8% by volume of methane, is required.

The described gas separation with membrane and the use of heat from the afterburning of the separation gas or permeate gas of the membrane separation plant should preferably be used to achieve an improvement of the product gas quality using the existing partial pressure difference of the CO ₂ between input gas and ambient air with a simple apparatus and low energy consumption. The removal of carbon dioxide from input gases should be done by a membrane. This is associated with the limited enrichment of the combustible gas components such as methane in product gases, wherein in the CO ₂ separation, the feed gas is compressed and on the permeate side a negative pressure is generated or air or exhaust gases are used as purge gas on the permeate side.

According to an advantageous embodiment The method utilizes gas separation with membrane and heat utilization from afterburning of the separation gas to produce a product gas for a gas network that can be burned in commercial heating burners and hobs without retrofitting. The requirements for such heating burners and hobs, ie domestic appliances, are generally higher than for gas engines of a power plant, in particular the former tolerate less CO ₂ . Therefore, a maximum proportion of carbon dioxide is below. Thus, the present method can be used for CO ₂ enrichment and treatment of the input gas to provide a product gas with a gas quality that easily allows the combustion in commercial heating burners and hobs. For this purpose, the carbon dioxide content must be sufficiently reduced. The methane-enriched product gas should contain less than 20% by volume of CO ₂ , preferably less than 18% by volume of CO ₂ and very particularly preferably less than 15% by volume of CO ₂ . The product gas processed in this way can be used directly in a gas network with connected consumers. This results in the significant advantage that only an already usable product gas needs to be transported to the end user. It can thus be achieved an efficiency gain over the use of lean gases in a combined heat and power plant with subsequent transfer of heat (with associated losses).

According to an advantageous embodiment of the method, the gas separation by means of membrane and the heat from the afterburning of the separation gas is used to increase the pre-separation of CO _2, the throughput capacity for product gas in gas treatment plants, where high quality requirements of CO ₂ -Abscheidegraden and CO ₂ rest such as B. must be met in the natural gas feed. Thus, the method can be used to increase the performance of existing gas treatment plants with carbon dioxide removal by pre-circuit.

According to a further advantageous embodiment of the method is facilitated by the CO ₂ pre-separation of distributed biogas plants or weak gas sources, the line transport to a central gas treatment plant to higher gas quality and at the same time an efficient heat source for Fermenterbeheizung the biogas plant through the use of heat from the afterburning of the separation gas of the membrane separation plant Cogeneration is possible. Thus, in particular a volume reduction of lean gas from decentralized biogas plants or other weak gas sources is achieved by the pre-purification and the further transport of the product gases into gas lines to a central gas treatment is simplified.

According to a preferred further development of the method, the range of the admixable liquefied gas quantity in a product gas network with liquid gas admixing and direct use for combustion in commercial heating burners is increased by a variable CO ₂ separation from the lean gas without the permissible limits of the gas qualities, such as calorific value and Wobbe index , To exceed.

The variation possibilities in the CO ₂ separation rate can be used to produce a constant gas quality of fuel gases with fluctuating quantities of mixed LPG (ie LPG Liquefied Petroleum Gas) - ie propane, butane and their mixtures - liquefied natural gas (LNG) or liquid biomethane ,

at a preferred embodiment of the invention Device is the membrane separation unit for compression of the input gas a compressor upstream and permeatseitig for support the separation process downstream of a vacuum pump. The at the afterburning the heat recovered from the separation gas can be used in particular for fermenter heating is used. The combustion chamber may optionally be adjacent to the separation gas Additional fuel to be supplied. In the afterburning The separation gas can additionally also electrical energy be gained and derived. The gas grid feed system is preferably over Lines of a biogas network directly connected to consumers, wherein the gas grid feed system optionally a liquefied gas can be added. The membrane separation plant retentate side Downstream gas treatment plant can be a product gas with natural gas quality provide.

Further For example, the devices for limited enrichment of Fuel gas components in input gases of a variety of decentralized biogas plants retentate side with a central gas supply system or a be connected to central biogas upgrading plant.

The Device is preferred for pre-cleaning and volume reduction of lean gas from decentralized biogas plants or other weak gas sources before the subsequent transfer of the product gas a central gas treatment or to a gas supply system used.

Further Advantages and details of the invention Method and apparatus emerge from the claims and from the reference to the drawings described below and the invention non-limiting embodiments. Show

2 a depletion of CO ₂ in the biogas through a membrane module to a usable quality for commercial gas burners quality,

3 a pre-depletion of CO ₂ from biogas through a membrane module to increase the capacity of a downstream biogas upgrading to natural gas quality,

4 a depletion of CO ₂ in biogas as a decentralized preliminary stage in distributed biogas plants in front of a central biogas upgrading and

5 a flexible depletion of CO ₂ in the biogas through the membrane to adapt the gas quality in the biogas network as a function of the load and liquefied gas admixture.

2 shows a depletion of CO ₂ in biogas A through a membrane module 1 to a usable quality for commercial gas burners quality. In a biogas network E with methane-enriched product gas, here with the biogas B, while a gas quality is to be achieved, can be operated by the commercial heating appliances of consumers 1 to N. For this, the CO ₂ content in the biogas network E must be reduced to a value suitable for these heaters. The required CO ₂ separation rates are achieved by membrane separation in a membrane module 1 reached. If necessary, the partial pressure gradient of CO ₂ across the membrane can be achieved by compression of biogas A on the feed side by means of a compressor 2 be enlarged. On the permeate side of the membrane of the membrane module 1 Air G is supplied as purge gas. The CO ₂ -rich separation gas C becomes the separation gas utilization 4 fed. With the help of a vacuum pump 3 can the separation process in the membrane module 1 get supported.

At the in 2 illustrated embodiment, in the case of biogas, the gas separation with a membrane in the vicinity of a biogas plant in which the biogas A was generated, placed so that a use of the heat Q from the separation gas 4 , For example, a post-combustion, the separation gas C of the membrane separation plant 1 for the fermenter heating is possible. For separation gas use 4 Optionally, an additional fuel F can be used. The at the separation gas use 4 resulting CO ₂ -rich exhaust gas is discharged via the line D. Alternatively or additionally, in addition to the heat Q and other energy P, such as electricity, produced and derived.

One advantage is the energetically much more efficient energy transport and the much cheaper lines for the product gas B to the consumer as in a district heat transport when using the product gas in a combined heat and power plant. The cost of an optional subsequent treatment for higher gas quality is reduced. The enriched with methane biogas B is favorable according to this embodiment of the gas grid feed system 5 supplied from where then the distribution of biogas via a biogas network E to the consumers 1 to N takes place.

According to 3 Pre-depletion of CO ₂ from biogas A takes place through a membrane module 1 to increase the capacity of a downstream biogas upgrading 5 ' on natural gas quality E '. In the biogas treatment 5 ' produces a _CO2 - rich exhaust H. By pre-separation of CO ₂ from the lean gas is used for the final purification of the product gas, such as biogas B, be separated on high quality fuel gas CO ₂ amount reduced. This can be done in a subsequent gas treatment 5 ' After the pre-separation of CO ₂ with membrane a larger volume of product gas to be processed than without pre-separation of CO ₂ . At the same time, the energy expenditure of the last stage of the gas treatment is reduced due to the small amount of CO _{2 to be} separated off. Since the CO ₂ separation with membrane is designed neither for high separation rates nor for high product purities, the right system design offers the potential for energy savings in gas processing up to the desired gas quality.

Depletion of CO ₂ in biogas A1, A2, An as a decentralized preliminary stage in distributed biogas plants (biogas plants K1, K2 to Kn) before central biogas upgrading 5 '' according to an embodiment variant is in 4 , shown. The plant components of the biogas plants K1, K2 to Kn are with the additions 1, 2 or n analogous to the 1 to 3 designated. By pre-separation of CO ₂ from lean gas with the described method with membrane and heat from the afterburning of the separation gas of the membrane separation plant, the first stage of the gas treatment of lean gas from distributed biogas plants or weak gas sources should be performed. The product gas B1, B2 and Bn from this first treatment step of several, distributed biogas plants or weak gas sources can then in a gas line with a smaller cross-section to a large, central gas treatment plant 5 '' and be processed there to the desired high gas quality with low CO ₂ content. The heat utilization Q1, Q2 and Qn from the afterburning of the permeate side separation gas of the membrane separation plant is used in the case of biogas directly at the biogas plant K1, K2 to Kn to Fermenterbeheizung (each symbolized by the arrow from Q1, Q2 or Qn to the biogas plant K1, K2 or Kn) and thus contributes to the efficient use of biogas.

According to 5 there is a flexible depletion of CO ₂ in the biogas A through a membrane for Adjustment of the gas quality in the biogas network E as a function of the load and liquid gas admixture. In a gas network, where the lean gas is used inter alia for heat generation, different load requirements arise. Since a biogas plant or other weak gas sources can only react to a limited extent to the change in load, liquid gas J is added to the product gas. With increasing admixture, the calorific value of the gas mixture would rise and other gas qualities such as density would change. To avoid this and to achieve a constant gas quality in the biogas network E, by reducing the CO ₂ separation in the opposite effect on the generation of the gas mixture can be achieved. Due to the variable adaptation of CO ₂ separation in the membrane module 1 As large a range of load cases in the weak gas network can be made possible.

A, A1, A2, An

Input gas, biogas

B, B1, B2, Bn

Methane-enriched Product gas, biogas

C

gas separation

D

Line for CO ₂ -rich exhaust gas

e

biogas power

e '

product gas with natural gas quality

F

additional fuel

G

air

H

CO ₂ -rich exhaust gas

J

LPG

K1, K2, Kn

biogas plants

Q, Q1, Q2, Qn

warmth

P

Further energy

1

Membrane separation unit, membrane module

2

compressor

3

vacuum pump

4

Separating gas use, combustion chamber

5

Gasnetzeinspeiseanlage

5 '

downstream biogas processing

5 ''

biogas processing

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 10047264 A1 [0005]

Claims (9)

Device for the limited accumulation of fuel gas components, in particular methane, in input gases by CO ₂ separation by means of gas permeation, characterized in that - a reactor for producing input gases (A), preferably for microbial low-gas production, at least one membrane separation plant ( 1 ), wherein at least one gas permeation module of the membrane separation plant ( 1 ) is supplied with the supplied input gas (A) for partial separation of CO ₂ from the input gas (A) by utilizing the CO ₂ -Partialdruckgefälles between the input gas (A) and the ambient air and enriched compared to the supplied input gas (A) with methane Product gas (B) with less than 20 vol .-% CO ₂ and a comparison with the supplied input gas (A) enriched with CO ₂ separation gas (C) with at least 4 vol .-% methane is obtained - the membrane separation plant ( 1 ) permeate side via a conduit with a suitable means, preferably a combustion chamber ( 4 ), for post-combustion of the separation gas (C) is connected and - the membrane separation plant ( 1 Retentate side via a line with a gas supply system ( 5 ) or a gas treatment plant ( 5 ' . 5 '' ) connected is. Apparatus according to claim 1, characterized in that the membrane separation plant ( 1 ) for compressing the input gas (A) a compressor ( 2 ) upstream and permeate side to support the separation process, a vacuum pump ( 3 ) is connected downstream. Device according to claim 1, characterized in that that in the afterburning of the separation gas (C) recovered heat (Q) is used for fermenter heating. Device according to claim 3, characterized in that the combustion chamber ( 4 ) in addition to the separating gas (C) an additional fuel (F) is supplied. Device according to claim 3, characterized in that that in the afterburning of the separation gas (C) and electric Energy (P) is extracted and derived. Apparatus according to claim 1, characterized in that the gas supply system ( 5 ) is connected via lines of a biogas network (E) directly to consumers. Apparatus according to claim 1, characterized in that the membrane separation plant ( 1 Retentate side downstream gas treatment plant ( 5 ' . 5 ' ) provides a product gas (E ') of natural gas quality. Apparatus according to claim 1, characterized in that devices for limited enrichment of fuel gas fractions in input gases (A1, A2, An) decentralized biogas plants (K1, K2, Kn) retentate side with a central gas grid feed system or a central biogas upgrading plant ( 5 '' ) are connected. Apparatus according to claim 6, characterized in that the gas supply system ( 5 ) a liquefied gas (J) is added.