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Content archived on 2022-12-27

CENTRALIZED PLANT FOR THE TREATMENT OF ANIMAL MANURE WITH PRODUCTION OF BIOGAS

Objective

To treat, in an industrial process, 100 000 tons yearly (as a demonstration for 1 000 000 tons yearly units) manure centralised from intensive pig-breeding farms by biomethanation to produce biogas and thereby electricity and low-Joule heat in a completely automatic way. The expected yearly energy production is 6.7 GWh electricity and 11 MWh low Joule heat. The expected payback time is 8 years.
The project can be considered as a partial technical success. It has not been possible to process the 100.000 T/y manure but only a quarter of it for the following reasons :
Because of the presence of a mixture of nitrate + organics which is very inlfammable the drying temperature had to be decreased to about 130 deg. C. As a result of this the maximum capacity of the dryer was halved. Making the dryer work under these conditions and adapting it to manure drying have for a period of time caused stops in the plant. Some problems with foam formation and settlebility of the active sludges also took their time to solve.
This, together with the fall in energy prices in 1986, explains greatly why the digestion process does not pay back as a result of energy production.
The functioning of the digesters can be characterized as follows :
residence time 18 days, gas yield 16 m3 biogas/m3 manure with methane content 70%, total solids content manure 10,5%., organic gas 67% of TS, COD 94 g/l.The hydrogen sulfide content in the gas of the first phase is 1,4%, in the second phase 0,7%.
The biogas production from mid-1989 until mid-1990 has been 331.00 m3/y which corresponds to 215 TOE/y.
Two main problems have been encountered in the manure digestion which are not completely solved :
- a clear separation of the hydrolysis and methanation phases is not achieved. The gas produced in the first step already contains some CH4 while the gas produced in the second step still contains a non negligible percentage of H2S. As a consequence, all the gas produced must be washed;
- the scum formation in the hydrolysis step is important and difficult to control. The addition of anti-scum chemicals is expensive.
Following a modification in the concept of the digested manure drying, the biogas produced is now burned in addition of natural gas in the boiler to produce steam which is used in the downstream dryer.
Globally, the project has proven to be technically a feasible alternative for the treatment of excess manure which becomes more and more an acute problem in the regions of intensive stock-rearing.
The innovative centralised manure treatment and biogas plant will be constructed in Helmond, which is located from 0 to 20 km of a series of municipalities producing yearly 2.7 Mtons of pig manure.
Three methane digesters will be built. Two of these will have a capacity of 1100 m3 and the third one is a completely mixed digester of 2000 m3 capacity.
For the two 1100 m3 digesters, a central inner cylinder will serve for the 1st step of the process. An outer cylinder will serve for the 2nd step of the process.
Both cylinders are linked by their bottom parts, not by their top part. This design originates from the Messerschmitt-Bolkow-Blohm system. There is normally no additional mixing. But mixing can in case of need be generated by gas recirculation.
275 m3 manure will be treated daily half of which will be digested in the two phase digesters. The residence time will be 1 day in the first step and 12-14 days in the second step.
Upstream of the innovative plant, the manure will be collected and transported in closed 33 tons lorries to a storage tank. The manure will be screened for particles larger than 5 mm and stored in the storage tank of 1500 tons capacity.
After preheating to 35 deg. C, the manure is sent to the methane digester.
Downstream of the innovative plant, 2000 m3 gas daily produced of the 1st step containing CO2 and H2S is collected separately.
The H2S is neutralised and the remaining gas discharged to the atmosphere. The biogas from step 2 containing 80% CH4 and little if any H2S no longer longer needs to be purified, and will be used in 4 cogenerators each using 250 m3 biogas per hour. A 900 kW boiler will be put in as stand-by.
The digested effluent with 12% dry matter will be dehydrated to 30% dry matter by flotation. The digested effluent is separated by a centrifugal decanter into a liquid and a solid fraction. The liquid fraction is aerobically depurated by active sludges. The effluent from this aerobic treatment is concentrated by evaporation.
The evaporator gives a distillate which may be discharged into the surface water and a concentrate which is mixed with the solid fraction menntioned before. The mixture is then fed into a indirect rotating dryer which rises the dry matter content up to 95%. The digested manure powder produced may finally be transformed into manure-pellets or granulates.
The liquid portion after flotation will be partly recycled upstream, partly returned to the flotation unit and partly discharged after a post-treatment involving biodisc and decanting units to contain 1000 mg COD and 500 mg total Kjeldahl nitrogen per liter. The discharged water will contain a substantial part of the phosphorous originally present in the manure.
The solid portion after flotation will be dried in a cylone, using the low-Joule heat, to 90% dry matter, and, pathogen-free, will become the basis for the preparation of a compost-like fertilizer.
The whole system will work in a closed atmosphere to minimise odourproblems.

Call for proposal

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Coordinator

MESTVERWERKING HELMOND BV
EU contribution
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Address
Kastanjeweg 68
5401 JP Uden
Netherlands

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Total cost
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