KR101138899B1 - A method for increasing a productivity of methane and digester heating using a synthesis gas - Google Patents

Abstract

The present invention relates to a method for enhancing methane production by using a synthesis gas obtained by thermochemically gasifying various combustible wastes such as biomass and wastes. Inducing the production of acetic acid as a substrate.

In the method according to the present invention, energy efficiency can be increased by using the synthesis gas for heating the anaerobic digester. The heating of the anaerobic digester according to the invention is achieved by direct contact of the synthesis gas with the anaerobic digestion liquid.

Syngas, Methane, Warming, Digester, Acetic Acid, Waste

Description

A method for increasing a productivity of methane and digester heating using a synthesis gas}

The present invention relates to a method of increasing methane production by using synthesis gas obtained from various combustible wastes such as biomass and waste, and increasing energy efficiency by using the synthesis gas as a heat supply energy source for heating an anaerobic digester. .

Syngas is obtained by supplying a limited amount of air to various combustible wastes such as coal, biomass and domestic waste. Gasification is a classic method for obtaining synthesis gas from the above solid fuels. The main components of the synthesis gas produced by gasification are carbon monoxide and hydrogen. Korean Patent Application No. 2000-0049655 discloses a method for obtaining synthesis gas from food waste. See also A study on manufacturing of synthesis gas from biomass, Seung-Kye Lee et al., Theories and Applications of Chem. Eng., 2002, Vol. 8, No. [2] describes a method for producing syngas from organic waste. Various other synthesis gas production methods are known. See, eg, Korean Patent Application Nos. 2005-0001812, 2004-0088136, 2004-0027440, 0027456, 0027457, these documents and all references cited herein by reference. The entirety of which is incorporated herein].

Syngas is used as a fuel to heat and / or power an engine or to produce synthetic fuel through a chemical process. In some countries where there is a sufficient amount of biomass available, the development of syngas provides gaseous fuels for community heating or cooking. However, there have been no studies to increase methane production using syngas for anaerobic digestion.

On the other hand, anaerobic digestion treatment is also called 'methane fermentation', the main purpose is to recover the energy of methane at the same time as waste water or waste treatment. Anaerobic digestion is the process of decomposing degradable organic matter in the absence of oxygen and converting it into methane. Within the biological treatment category, normally anaerobic anaerobes act at the point where hydrolysis and acid fermentation occur, and at the point where oxygen is depleted. Formed anaerobic bacteria, methane, produce methane. Methane fermentation is an active means of petroleum alternative energy as an active means of petroleum alternative energy as a means of recovering energy from many organic wastes, such as municipal waste, as well as municipal waste, from the advantage of low power consumption compared to activated sludge method that requires a large amount of air. Research is ongoing.

The amount of methane produced during anaerobic digestion varies somewhat depending on the type of organic matter, but it is 400 to 600 l per Kg of organic matter, and 100-120 m3 of gas is generated per ton of organic waste. Account for 50 to 60%. Considering the increasing use of methane gas as an alternative energy means, it is necessary to further increase the content of methane gas.

In addition, anaerobic digesters for methane fermentation basically require warming operations. The warming is heated to 35 ° C. for medium temperature digestion and 55 ° C. for high temperature digestion. In order to maintain the overall temperature without affecting the microorganisms in the heating operation, there is a method of installing a jacket around the reaction tank and sending hot water or steam to the jacket. Alternatively, there is a method of taking out the extinguishing liquid to the outside and re-injecting it after heating, and a gas circulation method for injecting and heating the biogas in the upper part of the digester. Both of these methods require a heating process through an external heat source, such as a hot water boiler or a steam boiler, so that energy efficiency is limited.

Accordingly, an object of the present invention is to pioneer new fields of utilization of syngas generated from various combustible wastes such as biomass and wastes and to increase methane production.

Further, it is an object of the invention to increase energy efficiency by warming without methane for the production of methane.

The present invention relates to a method for enhancing methane production by using a synthesis gas obtained by thermochemically gasifying various combustible wastes such as biomass and waste, and the method produces acetic acid by fermenting the synthesis gas with acetic acid producing bacteria. Inducing a step.

In the present invention, the step of producing the acetic acid by fermenting the syngas by anaerobic microorganism is carried out before the methane fermentation so that the methane producing bacteria can use the acetic acid.

In the method according to the invention, the production of methane can be enhanced by directly contacting the synthesis gas with the digestive fluid to improve the degree of decomposition of organic matter in the digestive fluid.

In the method according to the present invention, energy efficiency can be increased by using the synthesis gas for heating the anaerobic digester. The heating of the anaerobic digester according to the invention is achieved by direct contact of the synthesis gas with the anaerobic digestion liquid.

The present invention can not only increase the amount of methane produced using the synthesis gas, but also has the advantage of increasing energy efficiency by heating the digester at low cost by using the high temperature of the synthesis gas.

Furthermore, the thermochemical process for producing syngas from biomass and combustible wastes with relatively low water content can be combined with biological anaerobic digestion to operate as an integrated system for waste treatment and energy recovery.

Synthesis gas used in the present invention refers to a gaseous substance obtained by gasification of various combustible wastes such as biomass and waste, and the main components of the synthesis gas are hydrogen and carbon monoxide. The temperature of the synthesis gas discharged from the gasifier is about 300 to 800 ° C. In addition, the temperature of the synthesis gas may be at least 800 ° C.

In one embodiment of the present invention, the increase in the amount of methane produced is a gasification apparatus for producing a synthesis gas, a temperature control unit for controlling the temperature of the high temperature synthesis gas, a syngas fermentation tank for producing acetic acid by syngas fermentation, the production of methane Being made through a series of processes consisting of anaerobic digester, which will be described in detail below.

In the present invention, the gasifier is a device for gasifying various combustible wastes such as biomass and waste to obtain a synthesis gas. Conventionally known syngas devices can be used in the present invention. Since the synthesis gas contains carbon monoxide and hydrogen, the production of acetic acid can be induced by injecting a digestion liquid containing an anaerobic microorganism that oxidizes carbon monoxide and hydrogen to produce acetic acid. The digestive fluid is preferably a part of the digestive fluid in the anaerobic digester, but may be a culture medium in which acetic acid producing bacteria are separately cultured.

The process of injecting syngas into the digestive fluid to produce acetic acid is referred to herein as 'synthetic gas fermentation'. The fermentation broth containing acetic acid produced by the syngas fermentation process is reinjected into the anaerobic digester and the methane producing bacteria contained in the anaerobic digester use this acetic acid to produce additional methane.

Synthesis gas according to the present invention may be harmful to microorganisms such as tar or organic acids, so it is preferable to purify through a purification process before using in the present invention. In the present invention, the anaerobic bacteria producing acetic acid as a product of anaerobic respiration include acetogen, and specific examples thereof include Clostridium ljungdahlii and Clostridium autoethanogenum . Acetogen metabolism uses carbon dioxide as its main carbon source and requires hydrogen as its energy source. Its substrate includes a mixture of carbon dioxide and hydrogen, a mixture of carbon monoxide, methanol and carbon dioxide. Acetogen has the following reaction in consuming hydrogen and carbon dioxide.

Scheme 1

4H ₂ + 2CO ₂ → CH ₃ COOH + 2H ₂ O

This pathway is called the acetyl-CoA pathway, which is the acetyl residue of acetyl-Coenzyme A (CoA) where carbon dioxide is consumed to retain energy and build up cellular biomass. Several microorganisms have been observed to depend on hydrogen, CO or CO ₂ via the acetyl-CoA pathway as a carbon and energy source. CO-dependent acetogen has the following scheme.

Scheme 2

4CO + 2H ₂ O → CH ₃ COOH + 2CO ₂

The process of producing acetic acid using hydrogen and carbon monoxide as a raw material is shown in the following reaction scheme.

Scheme 3

2H ₂ + 1.03 CO → 0.43CH ₃ COOH + 0.13 Cell

Where cell represents the carbon equivalent of the cell mass produced.

Thus, acetic acid is produced here from syngas using the acetic acid producing microorganism as reported above.

Then, when the culture medium or digestive liquid containing the produced acetic acid is added to the anaerobic digester, methane producing bacteria contained in the anaerobic digester utilize methane to produce methane. More than 70% of methane is known to be produced from acetic acid in anaerobic digestion (Yang and Lee, 2004). Thus, it is expected that further methane will be produced if additional acetic acid is provided by CO fermentation by acetogen bacteria.

Additionally, the heat obtained by cooling the syngas can be used to heat the digester when the digester and gasification system are combined.

Therefore, in the present application, since the digester is directly heated by using the heat of the synthesis gas produced through the gasification system, a separate heat source such as a hot water boiler or a steam boiler is not required.

In the present invention, the method of heating the digester using the synthesis gas may be directly injecting the synthesis gas directly into the digester, but the synthesis gas is at a high temperature of about 300 to about 600 ° C., and an appropriate temperature in the digester is about 35 ° C. to Considering that it is about 55 ℃ can be additionally installed a temperature control unit. As an example of the temperature control unit, the synthesis gas is cooled to be adjusted to a temperature of 400 ° C. or lower, preferably 300 ° C. or lower, or a part of the digestion liquid is extracted from the digester and brought into contact with the synthesis gas to thereby obtain a high temperature energy of the synthesis gas. There is a way to control the temperature by passing on. Preferably, the temperature is controlled by extracting some of the digestive fluid and providing it with synthesis gas. Direct contact of the high temperature synthesis gas with the digestion fluid in the temperature control unit kills the microorganisms and destroys the cells.

The synthesis gas having the proper temperature through the temperature control section is then subjected to the synthesis gas fermentation process for acetic acid production. In the synthesis gas fermentation process, some bacteria in the digestive liquid produce acetic acid using hydrogen and carbon monoxide in the synthesis gas as substrates. Carbon monoxide and hydrogen are used as substrates by microorganisms with the Wood-Ljungdahl pathway, which are known to produce mainly acetic acid and produce trace amounts of ethanol.

Since the digestion liquid used in the synthesis gas fermentation process also includes methane producing bacteria, a small amount of methane may be produced using acetic acid produced by the synthesis gas fermentation as a substrate.

The synthesis gas fermentation process increases the concentration of acetic acid in the fermentation broth, and the fermentation broth is reinjected into the anaerobic digester and used as a substrate for methane-producing bacteria in the anaerobic digester.

The high temperature synthesis gas may be supplied into the anaerobic digester via a temperature control unit, a syngas fermenter, or may be mixed with biogas of the anaerobic digester directly via a temperature control unit. The supply of syngas to the anaerobic digester or syngas fermenter may be provided with a disperser at the bottom of the anaerobic digester or syngas fermenter so that the syngas is supplied from the bottom into the digester or fermenter to be uniformly distributed throughout the digester. have.

Part of the digested liquid extracted from the anaerobic digester is re-introduced into the anaerobic digester via the temperature control unit, syngas fermentation tank, or reintroduced into the anaerobic digester via the synthesis gas fermentation tank.

In the present invention, by using the heat of the synthesis gas, it is possible to heat the digester without a separate boiler device for heating the digester.

Specific embodiments are described below to aid the understanding of the present invention, but the present invention is not limited to the embodiments specifically set forth below.

1. Experimental Method

CO fermentation experiments were performed using liquid digests obtained from digesters operated by a biogas research center at Hankyong National University. Digestive system on a daily influx of pig manure contains approximately 5m ³ 150m ³ of the digestive juices. A tubular bioreactor system corresponding to an anaerobic digester was prepared for the experiment (see FIG. 1). The reactor was 9.9 cm in diameter and 39.3 cm in height. Each reactor has a separate gas reservoir at a volume of 3225 cm ^{3 at} the top of the reactor. The reservoir cap is sealed with water and can be easily moved up or down depending on gas production or consumption (see FIG. 3). Peristaltic pumps were installed to circulate the gas. The temperature of the reactor was placed in a commercial BOD incubator to maintain below the control temperature (see FIG. 2).

Nitrogen gas was charged into the gas reservoir of the control reactor. The prepared synthesis gas was fed to another reactor. 29.9 (v / v)% of the synthesis gas was hydrogen, 50.2 (v / v)% was carbon monoxide and the rest was nitrogen. Half of the prepared synthesis gas was used for this experiment, and the rest was used for the next experiment. Gas was continuously fed to the reactor through a ceramic disperser located at the bottom of the reactor. Changes in the gas reservoir were measured and gas compositions were analyzed for methane, carbon monoxide and carbon dioxide. Gas composition was analyzed using a gas detection tube (Gastec, Japan) and a monitoring sensor. Detection tube models 1HH and 2H were used for carbon monoxide and carbon dioxide detection, respectively. Methane concentrations were measured using a gas analyzer, Delta 1600-S (MRU, Germany).

Each experiment lasted until the gas reservoir volume had settled for a while or until the storage cap reached the bottom. Pumps for gas circulation were run continuously throughout the entire process of each experiment. The change in the height of the storage cap was measured every 30 minutes. The gas composition was analyzed after turning off the circulation pump at the end of the experiment.

2. Results

1) Change in gas storage volume

The gas volume increased as soon as gas circulation began in the N ₂ -feed control experiment. Bacteria respiration produces carbon dioxide, which appears to increase the volume of the gas reservoir. Gas production was observed in both reactors, but gas consumption prevailed under syngas feed. The reduction in gas storage volume indicates that carbon monoxide and hydrogen gas consumption is shielding the production of carbon dioxide microbial respiration. The control reactor also showed a slight decrease in gas volume over time.

4 is an example of a change in a gas reservoir. The height of the reservoir cap represents the storage volume of gas in the graph. Each experiment showed a different rate of change. Experimental results showed a similar change in storage volume. As shown in FIG. 4, the storage volume of the synthesis gas was reduced by about 15% within 2 hours. However, the N ₂ -feed reactor increased gas production than the initial. The gas volume began to decrease after reaching the peak of the volume. The decrease in the amount of gas storage in the N ₂ -feed reactor appears to show that carbon dioxide was consumed in the reactor.

Other experiments showed very different changes in gas volume. Gas production, estimated to be carbon dioxide, is much higher than in previous experiments. The fermentation process was performed immediately after sampling the liquid digestion liquid without any intervening storage. Net gas yield was dominant in both reactors. Contrary to the results obtained in FIG. 4, the gas storage volume increased in both nitrogen and syngas as in FIG. 5. When CO is digested, CO ₂ is produced by Scheme 2. On the other hand, CO ₂ is consumed by Scheme 1 when hydrogen is supplied.

2) gas composition

Analysis of the gas composition confirmed that methane was produced and carbon monoxide was reduced. As shown in FIG. 6, the methane concentration was 1-10% in the syngas feed reactor, while 0.05-0.98% in the N ₂ -feed reactor. The CO ₂ concentration increased from 12 to 41% in the synthesis gas reactor and to about 20% in the control reactor. Initially, there was no carbon dioxide in the storage tank. Final CO concentrations ranged from 12 to 45%. That is, 55 to 88% of the CO was consumed by bacteria inside the reactor. Based on the gas composition, it was confirmed that CO ₂ production by cell respiration was present. For controls using only nitrogen, methane was produced, although the yield was quite low.

3. Mass Conversion

CH ₄ and CO ₂ produced during fermentation were calculated by reading the storage cap height and using the concentration of each gas. As shown in Table 1, the methane production rate was 3-15.6 ml / hr, CO ₂ was 18-90 ml / hr, and the CO consumption rate was 77-190 ml / hr.

The experimental results show that synthesis gas can be provided to the anaerobic reactor to increase methane productivity.

3. Syngas Reactor and Anaerobic Digester

A series of methane generation processes consisting of a syngas generator 1, a gas purifier 2, a temperature control unit 3, a syngas fermenter 4 and an anaerobic digester 5 according to an embodiment of the present invention In-house manufacturing was conducted to induce methane production.

This is illustrated in FIG. 7. The syngas generator 1 used a self-made gasification apparatus, and used the biomass from the biogas research center of Hankyong National University as a gasification raw material in the gasifier.

The temperature controller 3 contacts a part of the digestion liquid in the anaerobic digester 5 with the high temperature syngas obtained from the syngas generator 1 so that the high temperature energy of the syngas is transferred to the extinguishing liquid. In the temperature control unit 3, a temperature sensor was installed, and when the temperature reached 300 ° C. or lower, the gas moved to the syngas fermenter. The syngas was moved to the syngas fermenter by connecting the temperature control unit 3 to the top of the syngas fermenter 4. In addition, by connecting the lower end of the temperature control unit 3 and the lower end of the syngas fermentation tank (4), the heated digestion liquid flows into the anaerobic digestion tank (5) through the syngas fermentation tank (4). In the syngas fermenter 4, the extinguishing liquid and the syngas were retained for 12 hours sufficiently to cause syngas fermentation. It was confirmed that acetic acid was produced by the synthesis gas fermentation because it contained some of the digestion liquid in the anaerobic digester 5. The upper end of the synthesis gas fermentation tank (4) is connected with the upper end of the anaerobic digestion tank (5) so that the synthesis gas is introduced into the anaerobic digestion tank (5) to warm the anaerobic digestion tank.

In addition, the lower end of the synthesis gas fermentation tank (4) was connected to the anaerobic digestion tank (5) to allow the digestion liquid containing acetic acid to be mixed into the anaerobic digestion tank. The temperature of the anaerobic digester was maintained at about 55 ° C. by warming through syngas contact.

By the above experiment, it was confirmed that the synthesis gas can be used to increase the methane production in the anaerobic digester, and the synthesis gas can be used to warm the anaerobic digester without an external heat source.

1 is a schematic diagram of a tubular bioreactor system (anaerobic digester).

2 is a photograph showing a bioreactor coupled to a gas storage tank installed in an incubator.

3 is a photograph showing a gas storage tank of FIG. 2.

4 is a graph showing the change in gas storage cap height over time in the N ₂ control group and the synthesis gas administration group.

Figure 5 is a graph showing the change in height of the gas storage cap over time in the N ₂ control group and CO administration group.

6 is a graph comparing methane concentration after circulating with N ₂ control and syngas.

FIG. 7 illustrates a methane production process consisting of a syngas generator, a temperature controller, a syngas fermenter, and an anaerobic digester according to an aspect of the present invention.

Claims (5)

Thermochemically gasifying the biomass to produce syngas; Fermenting the generated chemical gas with acetic acid producing bacteria to produce acetic acid; And Fermenting methane producing bacteria using the produced acetic acid as a substrate in an anaerobic digestion tank, to produce methane, The syngas is used to warm the anaerobic digester, the method of increasing methane production. delete The method according to claim 1, wherein the acetic acid producing bacterium is Clostridium ljungdahlii or Clostridium autoethanogenum . delete The method according to claim 1, wherein the heating of the anaerobic digester is made by direct contact with the digestive fluid partially discharged from the anaerobic digester, and through the process of returning the digestive liquid in contact with the synthesis gas back to the anaerobic digester, methane How to increase production.

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