DD228535A1 - METHOD FOR REMOVING AND INERTIZING BIOGAS PLANTS - Google Patents

Abstract

The aim of the invention is to perform the process explosion-proof and effective, without additional use of inert gas. The task is to carry out the shutdown of biogas plants, in which wastewater and bark is worked up, while inerting, whereby the formation of explosive gas mixtures avoided and the activity of the digested sludge for a quick restart of the biogas plant is obtained. According to the invention, this is achieved by blowing air directly into the digested sludge, dispersing it and distributing it over a large area. The air injection takes place in such a way that the oxygen content of the gas mixture formed does not exceed a maximum concentration of 6%. It is advantageous, prior to the injection of air into the digested sludge, to supply this substrate, which is still obligately aerobic and / or optionally arrob microorganisms, and which is expediently cold. Due to the sensitivity of the methane-producing bacteria to oxygen, the methane content of the biogas, whose production is gradually coming to a standstill, decreases. At a methane content of less than 2% by volume, the inerting process is ended and the biogas reactor can be opened safely.

Description

Title of the invention

Method for driving off and inerting biogas plants

field of use

The invention relates to a method for driving off biogas plants while inerting, especially larger biogas plants in which wastewater and manure from facilities of agriculture, water and communal services are processed and biogas is produced.

Characteristics of the known technical solutions The shutdown of biogas plants in practice causes problems, because the production of biogas must be interrupted. In addition, the activity of digested sludge in the biogas reactor should be largely retained in order to enable a restart of the plant quickly.

If the methane-containing biogas mixed with air due to the opening of the biogas reactor, an explosive gas mixture is formed.

Danger of explosion exists with a methane content of 4.9 to 15.4 % and an oxygen content of more than 12 %.

To counteract this risk, it is already known to perform an inerting before the shutdown of the plant and the opening of the biogas reactor. This is done by blowing in so-called inert gas such as. Nitrogen and engine exhaust into the gas space of the biogas reactor. However, considerable disadvantages must be taken into account.

To greatly reduce biogas production and thus avoid the formation of explosive gas mixtures, large quantities of inert gas, i. 20 times the amount of biogas needed. In addition, inerting with inert gas requires a high time expenditure of about 10-14 days without substrate feed.

In addition, inert gas is not always available and its provision requires additional costs. The supply of inert gas is also only a dilution of the biogas. A safe shutdown of the biogas plant is not possible.

Other, technically satisfactory, solutions for the safe departure of biogas plants with simultaneous inertization are not known.

Object of the invention

The aim of the invention is to perform the shutdown of biogas plants with simultaneous inerting explosion-proof and effective without the additional use of inert gas.

Explanation of the essence of the invention

- task

The invention has for its object to develop a method for shutdown and simultaneous inerting of biogas plants, in which prevents the formation of explosive gas mixtures, the digested sludge is not poisoned and its activity is largely retained for a quick restart of the biogas plant.

- Characteristics

The object is achieved in that air is blown directly into the anaerobically treated Paul mud, dispersed therein and distributed over a large area, so that thus a long residence time of the air bubbles is ensured in the digested sludge. Due to the sensitivity of the methane bacteria to the oxygen contained in the air, the production of methane is reduced or prevented. At the same time, the sludge contained in the sludge

aerobic microorganisms, a part of oxygen respired (consumed). The required for the oxygen solubility partial pressure gradient in the digested sludge is thus maintained. The carbon dioxide formed, together with the remaining nitrogen, enters the gas space of the biogas reactor. The oxygen partial pressure in the gas mixture thus formed thereby increases.

The air injection into the digested sludge takes place in such a way that the maximum concentration of oxygen in the gas mixture formed from air and biogas does not exceed 6 % . This provides a sufficient safety distance to the explosion area.

The air is injected via the pressure or suction port of a circulating pump connected to the biogas reactor.

The gas-liquid mixture produced thereby is preferably introduced at high speed near the bottom of the biogas reactor, whereby the dispersion of the gas bubbles and the large-scale mixing of the reactor contents is made possible.

However, it is also possible to introduce the air into the pressure line of the recirculation gas line of a blower connected to the biogas reactor, if homogenization of the reactor contents takes place by circulating biogas. In this case, however, a delay in the inerting process occurs due to a reduced dispersion of the gas-air mixture in the digested sludge. The Umwälzfahrweise the biogas between the biogas reactor and its downstream piping and equipment allows these downstream facilities are also inerted with.

Advantageously, the process for traversing and inerting can be accelerated if, prior to blowing in the air, the anaerobically treated digested sludge is inoculated with fresh substrate containing aerobic microorganisms.

The substrate may contain obligate aerobic microorganisms, which is the case with liquid manure. The substrate can

but also optionally aerobic microorganisms, or even a combination of both.

The aerobic microorganisms accelerate the oxygen depletion already described above. It is particularly expedient to carry out this addition with cold substrate, such that the digested sludge undergoes a Teraperaturabsenkung of at least 2 K. This temperature shock causes an immediate decline in biogas production.

However, if not enough cold substrate for dosing available can also be dispensed with. The following positive effects can be obtained with the inventive method: D _u rch the entry of air is first a mixing of the air with the methane-containing biogas, whereby the partial pressure of oxygen rises in the gas mixture. In the digested sludge, oxygen is dissolved simultaneously according to the partial pressure. Due to the sensitivity of the raethanproduzierenden bacteria to oxygen, the biogas formation process gradually comes to a halt, so that the methane content in the gas mixture slowly decreases. At a methane content of less than 2% by volume, the inerting process is completed. The biogas reactor can be opened without danger. This is achieved by aerobic or facultative aerobic microorganisms, the oxygen is extracted from the air bubbles to a part and carbon dioxide is produced as a reaction product. This makes it possible to perform the Abfahrprozeß outside the explosion area.

As a surprising effect is to be considered that in the biogas plant, which contains combustible biogas in addition to the digested sludge, additional air is injected and thus still an explosion-proof, inertized driving is possible.

The particular advantage of the invention is also that the digested sludge due to its oxygen treatment

did not lose his activity. Biogas production is only temporarily interrupted. After renewed creation of an anaerobic environment, biogas production starts again.

embodiment

The invention will be explained in more detail below with reference to an embodiment.

In a biogas reactor there are 480 digested sludge from pig manure of pigsty facilities. The digested sludge has a dry matter content of 6 to 7 %.

If the treatment of liquid manure is stopped and the biogas reactor is opened, at least 70 m cold, untreated liquid manure, which in each case contains sufficient aerobic microorganisms, is added. As a result, a temperature reduction of at least 2 K is achieved, which results in a reduction in biogas production of about 20 to 25 % .

Subsequently, 30 m / h of air is blown into the suction or pressure line of a circulating pump connected to the reactor. The line ends with a nozzle at the bottom of the reactor in which an exit velocity of about 10 m / s is achieved. The amount of air is increased after 4 to 6 hours to about m / h. The amount of air is injected so that the oxygen concentration in the resulting biogas-air mixture remains less than 6 vol .-%. This ensures a sufficient safety distance to the explosion range, which is at least 12 % for methane-nitrogen mixtures. This type of air supply ensures that the bubbles are dispersed and distributed over a large area in the digested sludge. Thus, a long residence time of the air bubbles is achieved when ascending in the digested sludge and there is a substantial solution of oxygen in the digested sludge. The depletion of the oxygen by the aerobic microorganisms maintains the required for the oxygen solubility partial pressure gradient in the digested sludge upright. The

Increasing the amount of air leads to an increase in the oxygen partial pressure and an inactivation of the oxygen-sensitive methanogenic bacteria, so that the methane content continues to decrease.

This involves a constant control of the methane and oxygen content. The required air flow control takes place according to the oxygen concentration in the biogas-air mixture by hand

 At a methane content of the gas of less than 2% by volume, the inerting process is stopped. This happens after about 10 to 15 hours.

Now the reactor can be opened safely. However, there is further ventilation to prevent the accumulation of explosive mixtures due to renewed methane formation.

The advantage of this solution is that the shutdown of the biogas plants with simultaneous inertization without the provision of inert gas, thereby worked explosion proof and only a small amount of equipment is needed.

This treatment "does not poison the digested sludge and its activity remains largely intact.

Claims (3)

claim 1. A method for driving off and inerting of biogas plants in which manure »and sewage sludge are processed anaerobically and by supplying gases, the formation of explosive gas mixtures is avoided, characterized in that air is blown directly, such as in the aerobic microorganisms containing digested sludge, that the formed Gas mixture has a maximum oxygen concentration of <6 % and the injected air is dispersed in the digested sludge and distributed over a large area 2. The method according to claim 1, characterized in that before the injection of air, fresh, obligatory and / or facultative aerobic microorganism-containing substrate is supplied to the digested sludge. 3. The method according to claim 2, characterized in that cold substrate is fed to the digested sludge, up to a temperature drop of at least 2 K.