DE10116144A1 - Process for fermenting biomass - Google Patents

Abstract

The invention relates to a method for fermenting biomass in fermenters during which, in a first step, the biomass is homogenized, is introduced into a fermenter, and is aerobically hydrolyzed or desiccated to a solids content of approximately 20 %, and is subsequently rendered inert by increasing the pH value. At the same time, the required volume and population of anaerobic bacteria are separately cultured in a second anaerobic fermenter in order to immediately start the anaerobic fermentation of the biomass that is rendered inert.

Description

The present invention relates to a method for fermenting biomass to form biogas. In a first phase, the optionally crushed material is initially aerobically from ubiquitous or cultured bacteria by splitting the organic substance into short-chain molecules such as. B. alcohol and acids etc. broken down, after which the anaerobic fermentation by acetic acid and Me thanobacter sets in, which ultimately leads to the formation of acetic acid to CO ₂ and methane (Schlegel, Fischer "Allgemeine Mikrobiologie", Springerverlag).

However, the amount of biomass is often intermittent due to the season, so very much Large amounts are to be dealt with, which is the capacity of the available far exceeds the fermenter. On the other hand, there is anaerobic fermentation much more slowly in front of you, so that the quantities are not coped equally that can. If you temporarily store the product of aerobic fermentation, it works ses spontaneously into anaerobic fermentation and the material becomes unusable seen from the associated odor nuisance.

The object of the present invention is therefore to provide a method with which even intermittent biomass can be processed without problems leaves and an odor nuisance by spontaneous aerobic fermentation as far as possible is avoided.

This task is accomplished by means of a process for fermenting biomass in Fer ment, in which according to the invention in a first step the biomass homogenized, placed in a fermenter and aerobically hydrolyzed or up to a solids content of about 10-20% dewatered and then by pH Increase in value inertized, with parallel in a second anaerobic ferment the amount and population of anaerobic bacteria needed to make the inerted  To put biomass directly into anaerobic fermentation, cultivated separately and add it batch-wise.

This method therefore has two essential features. One day it will aerobically fermented biomass inerted in batches, d. H. against attack by me thanobacter and vinegar bacteria protected so that these can be conveniently between stored and can also be treated batchwise anaerobically.

This inerting is done by raising the pH, or by partial Ent watering, since Methanobacter bacilli and vinegar bacteria in residual water kept below about 10% cannot be active. The pH-Er also performs increase to values above about 7.2 to be harmful to Methanobacter Milieu.

As mentioned above, anaerobic fermentation takes significantly more time than that aerobic. It also starts more slowly.

The second measure essential to the invention is therefore that in a separate fermenter bacterial population from acetic acid bacteria and Manufactures and stores Methanobacter in nutrient solution. Now activate one suitable portion of the inertized intermediate by pH-Anhe exercise and / or water addition, mixing with the separately generated leads Bacterial population nutrient solution immediately at the start of the fermentation, whereby due to the precisely adjustable amount of bacteria, this is also significantly faster runs.

The water can of course be added by the nutrient solution itself.

Treatment with Aceto and Methanobacter can basically be done in the same Digestion tower in which the aerobic fermentation takes place. A third reactor is preferred so that the digestion tower becomes free for a new one Partial approach to biomass.  

In particular, it is proposed to use methano specified on the substrate to breed bacter species in the second fermenter.

It is of course advantageous to reduce the water content of the inerted biomass to Keep the addition of the Aceto and Methanobacter solution constant.

In the second fermenter, the cultivation fermenter, naturally occurring ones and / or genetically engineered Methanobacter species. This happens in oxygen-free nutrient solution, which is added to the biomass.

The Methanobacter can be extracted from shredded in a particularly simple manner Win rumen.

In the manner described above, intermittent biomass can be obtained Process autumn leaves, fruit or grape pomace, etc., taking large amounts pre-fermented and then rendered inert to this mass in batches work up, these masses of course with continuously accumulating Substances can be mixed.

In order to even out the gas delivery, it is also proposed that inertized biomass in several reactors (digesters) one after the other to process, the number and / or size of the digestion towers on the amount of Output from the first fermenter is matched. It is also possible to drive these digestion towers cascaded one after the other, with the first part of the Cascade by adding the nutrient solution the biomass becomes pumpable.

The present process diagram explains the present invention on the basis of an embodiment closer.  

A larger, shredded biomass quantity is kept in a pulp collecting basin 1 . Here it is already undergoing aerobic fermentation due to ubiquitous bacteria. From this pulp collecting basin, this mass reaches a first fermenter 2 equipped with a stirrer 4 and is aerobically hydrolyzed here with the aid of bacteria added from a storage container 3 . This produces gases (O ₂ ; CO ₂ ; H ₂ ) and alcohols as well as acids and aldehydes. This takes about four days.

After completion of this fermentation, the product is rendered inert either by dehydration (evaporation) or by increasing the pH (lyes), ie rendered insensitive to the attack of Aceto or Methanobacter. The residual water quantity is about 20%, the pH <7.2. This inertized biomass is brought to an intermediate storage facility ( 11 ) and from there processed in batches in one or more digestion towers ( 5 ). For this purpose, the mass is mixed again with water or the pH is adjusted to 6.8-7.2.

A nutrient solution for Methanobacter and Acetobacter is kept in a second fermenter ( 6 ). Crushed (cattle) rumen containing these bacteria is preferably used. Bacteria specialized in the substrate are also kept here and with particular effectiveness, which are obtained by breeding or by genetic engineering. The bacterial solution is precisely matched to the amount and the type of material presented in the digestion tower, so that the dwell time in the digestion tower is kept short by the reaction starting quickly. It is z. B. just over 15 days and is roughly four times as long as aerobic fermentation, but compared to the prior art by up to 30% shorter.

Raw gas is withdrawn from the digester tower ( 5 ) via line ( 8 ) and passed through a filter ( 9 ), where CO ₂ and N _{2 are} separated.

Fine gas with a purity of over 98% reaches the natural gas network via the line ( 10 ) and a meter ( 11 ) or a gas engine with heat utilization ( 7 ) with a connected generator (with meter) and from here into the power network.

LIST OF REFERENCE NUMBERS

1

Marc reservoir

2

first fermenter

3

reservoir

4

agitator

5

digester

6

second fermenter

7

Gas engine with heat use

8th

management

9

filter

10

management

11

interim storage

Claims (7)

1. Process for fermenting biomass in fermenters, characterized in that the biomass is homogenized in a first step, placed in a fermenter and aerobically hydrolyzed or dehydrated to a solid content of about 20% or rendered inert by increasing the pH, in parallel in a second anaerobic fermenter, the required amount and population of anaerobic bacteria in order to put the inertized biomass directly into anaerobic fermentation, grown separately and adding this batchwise to the inertized biomass. 2. The method according to claim 1, characterized in that one in two ten fermenter breeds substrate-specific Methanobacter species. 3. The method according to claim 1 or 2, characterized in that one before adding the Methanobacter the pH of the inerted bio mass reduced to about 7.2 to 6.8. 4. The method according to claim 1-3, characterized in that the Water content of the inertized biomass before adding the methano bacter is kept constant. 5. The method according to claim 1-4, characterized in that in Cultivation fermenters are naturally occurring and / or genetically engineered provided Methanobacter species increased in oxygen-free nutrient liquid and this to the biomass presented in a digester according to needs inflicts.   6. The method according to claim 5, characterized in that one to breeding the Methanobacter homogenized rumen used. 7. The method according to claim 1-6, characterized in that the anaerobic fermentation for the purpose of continuous gas production carried out in several reactors, which are added in succession by adding Aceto and Methanobacter solution are started.