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DIGESTERS FOR PRODUCTION OF DIGESTER GAS / BIOGAS
How can digester gas be technically produced?
The organic substances which are the basis for the biogas
production are basically brought in as a hydrous sludge. The
sludge from the waste water treatment or liquid manure of pigs and
cows from animal farms are liquid sludge. Thus it is possible to
build simple plants for the generation of digester- and biogas.
The digester gas is generated in the digester. This part of the
plant is build as an anaerobic re-actor because the gas producing
bacteria are operating merely free from oxygen. Therefore the
digester has to be gas tight. This tank is available in very large
dimensions.
The continually produced sludge is pumped into this digester which
is approximately designed to gain the sludge arising from 10 up to
30 days. This specified time it averagely needs for digestion is
defined as retention time. In the digester it contains very large
amounts of methane bacteria. The constantly brought in sludge
serves as food for the bacteria respectively the containing
organic substances. The digester gas is the metabolite/
intermediate catabolic product of the methane bacteria.
Continuous mode of operation
The operational mode is referred as continuous. This is the
standard at modern digestion tanks. That means that the discharged
amount of sludge is equal to the initiated. The quantity of sludge
inside the digester does not change. This ensures constant
operating conditions with high process stability and a calculable
gas production.
Temperature
With increasing temperatures the activity of the methane bacteria
and consequently the gas production is rising. Therefore the
digesters are heated. Under normal conditions they are running
with temperatures between 30 and 38°C. This range is called
mesophile. There are also bacteria working between 50 and 55 °C.
Then the digestion runs faster and the digester tanks can become
smaller. But this thermophile mode of operation is rarely used
because the effort of process energy which is necessary to reach
these operating temperatures is too great. Also the stability of
the process decreases.
Design of the digesters
The digesters are manufactured as welded or screwed steel tanks.
Also concrete or reinforced concrete tanks are used. The digesters
are built as upright vertical cylinders, often.with conical
bottoms. On municipal sewage plants many egg formed digesters have
been built. This design had proved advantageously, although it
needs more expenditure in technical manufacturing.
Steel is a suitable material; corrosion cannot proceed in the
absence of air-oxygen.
The heat exchanger is thermal insulated against heat radiation
loss
Mixing plants for digester sludge
For a equal mixture of the sludge agitators are integrated.
There are many reasons for mixing:
• The fresh sludge is the food source for the methane bacteria.
It has to be homogeneously distributed.
• A good mixture also leads to a smooth distribution of
temperature in the digester.
By that no cold areas could occur.
• Sedimenting and floating layers can be arisen in the tank.
Layers of sand and other heavy components can reduce the usable
digester room.
Floating layers of hairs and other felt-like materials can become
very thick. They disturb the sludge input and output as well as
the draw off of gas. These circumstances can lead to serious
interruptions.
The agitators can be different depending on the design of the
tanks and depends on the stirring task. There are the following
methods of application: mechanical agitators, hydraulic stirring
by pumping over the digester sludge and the pressing in of
digester gas.
DELIVERY SCHEDULE
Digesters for
• Sludge of municipal wastewater treatment plants
• High contaminated wastewater of industrial processes:
• Production of beverages
• Distilleries
• Sugar-factories
• Starch-factories
• Dairies
• Slaughter-houses
• Flaying-houses
• Liquid manure of live-stock-farming
• Bio waste
TYPES
Design of digesters in standing cylindrical design with conical or
flat bottom
Material: reinforced steel, welded steel, enamelled steel,
screwed, each one with thermal insulation or weather protection
pod
Mixing device with inside agitators, gas injection or turnover
with outside mounted pumps
Complete equipped with gas hood, floating sludge removal, sludge
liquor removal, heating system and stair tower
Digester for high contaminated industrial wastewater as fixed bed
reactors or as sludge bed reactors in all sizes
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GAS
GENERATION
