CC BY
11UDC 620.95
BIOGAS PRODUCTION BASIC PRINCIPLES
Marus O., Golub G., Goh V.
National University of Life and Environmental Sciences of Ukraine 03041, Ukraine, Kiyv, Geroiv Oborony st., 12, +38(044)527-81-29, E-mail: [email protected]
Ключевые слова: биогаз, метантенк, базовые принципы.
Keywords: biogas, methanetank, basic principles.
Аннотация: Одним из путей утилизации жидкого навоза в сельскохозяйственном производстве есть его ферментация в анаэробных условиях с получением биометана, который обеспечивает дезинфекцию и дезодорацию жидкого навоза. Производство и использование биометана требует значительных капитальных затрат, но в тоже время обеспечивает защиту окружающей среды, что требует сосредоточения на разработку методов и средств обеспечения рентабельности производства и использования биогазовых установок.
Abstract: One of the ways of liquid manure utilization in agricultural production is its fermentation in anaerobic conditions to obtain biomethane, which provides partial disinfection of manure and its deodorization. Production and use of biomethane requires significant capital expenditures, but it is impotent to preserve natural environment, which requires focusing on the development of methods and means to provide cost-effective production and use of biogas installations.
The experience of using biogas plants was completely analyzed by the Agency for renewable resources in Germany [1]. The authors of the analysis indicate that in the absence of biomass mixing in the reactor, after a while there is a separation of biomass with layer forming due to the difference in density of certain mineral and organic components, as well as to flotation of particles while gas yielding. Thus, the biggest part of the anaerobic bacteria biomass is situated at the bottom of the reactor, and the organic part of the biomass substrate accumulates at the top of the reactor. As a result, the contact zone of anaerobic bacteria with biomass substrate is limited by a boundary layer of mentioned parts of the reactor. Floating crust of solid organic substances also blocks biogas yield. Facilitation anaerobic bacteria contact with substrate biomass is provided by mixing the substrate, but
intensive mixing should be avoided, because it can cause stopping of anaerobic fermentation at the expense of disturbance of symbiosis of acetogenic and methanogenic bacteria. In practice, a compromise is achieved by slow rotation of agitators or by their work within a short period of time. Part of the solid mineral inclusions contained in substrates based on manure is released in the process of biological decomposition inside the reactor. Mineral sediment reduces the useful volume of the reactor.
Experience of using biogas reactors showed that there are reactors already half-filled with mineral sediment, which can be removed only with an excavator after total stopping of fermentation process. Floating layers, especially based on fibrous substrates, often form a crust and if it is not mixed, the reactor must also be stopped to remove it.
Thus, the improvement of biogas reactor work to ensure the mixing of biomass substrate layers requires new technical solutions, one of which is mixing by rotation of the suspended reactor submerged into water.
We have developed and patented several designs of modular anaerobic digesters of rotational type [2], the design of one of which is shown in fig. 1.
Our calculations showed that the microbiological decomposition while anaerobic fermentation of 1 kg of organic matter is accompanied by about 0.4 kg of methane yield and by 0.7 kg of carbon dioxide yield.
Adopting the assumption that the volume of produced biogas is determined by the intensity of organic matter decomposing during organic biomass fermentation, biogas yield while fermentation in terms of normal conditions can be defined as follows [3]:
( W \ m
j W em * - d m 1
vee Pem
100
k kp '"ef (1)
komk om h , (1)
Pee
where VEr - is a specific biogas yield from the reactor under normal conditions, M3Rr /m\m per day; pm — biomass density,
lEr/JnEM ^ rEM
f W 1 — W EM I 100 J
KZEM /m\m ; WeM — biomass dampness, %;
— dry
matter content in relation to the total biomass, K2CM / KZ EM ; kOM -organic matter content in relation to the volume of the total dry weight in fermenting biomass, KZOM / KZCM ; — the number of
decomposed organic matter per day in relation to the total organic mass, kz pom / kz om per day; mEr - biogas yield per unit of decomposed organic matter, K2Br / KS poM ; — biogas density under normal conditions, KZEr /m\f .
1 - horizontal outer casing, 2 - cylindrical reactor 3 - longitudinal bulkhead, 4, 5 - fermentation chambers, 6, 7 - tubes for cart and removal of organic matter, 8 - pipe for biogas runoff, 9 - unloading camera, 10 - joints 11 - mixing fingers, 12 - pipe for organic matter
removing
Figure 1 - Construction of anaerobic digester immersed into thermostatic liquid
At the same time, specific biomethane yield will be:
VcH4 = Vr *CH4, (2)
where VCHa — is specific biomethane yield from the reactor
under normal conditions, M(\H /m^
per day; kCH^ — volume
biomethane content in biogas, M 3/m.
Table 1 - Calculation of the specific release of biogas and biomethane
[3]
Indicator Measurement Values
Manure density kgsu/^EM 1062
Humidity % 90
Water content kgs/kgsM 0,9
Dry weight % 10
kgcM/kgsM 0,1
Organic matter content % 80
kgoM/kgcM 0,8
The intensity of organic matter decomposing % per day 3,0
kgpoM/kgoM per day 0,03
kgpoM/M3EM per day 2,55
Biogas yield from decomposed organic matter under normal conditions kgsr/kgroM 1,1
m3er/kgpoM 0,92
Biogas yield from the reactor under normal conditions M3Er/M3EM per day 2,34
Biomethane yield under normal conditions m3CH4/m3EM per day 1,666
The maximum level of organic biomass decomposing % 38
ktpom/m3EM 32,5
Fermentation time days 12,74
With the parameters introduced in table 1, the relationships between the intensity of organic matter decomposing and specific biomethane and biogas yields, and fermentation time, will take the form shown in fig. 2.
Biogas and biomethane yields increase proportionally with increasing of level of organic biomass decomposing in the reactor, and the fermentation time decreases exponentially till it achieves 38% fermentation level.
The main direction in manure fermentation process intensification is increase of organic matter decomposition at the cost of creation of appropriate conditions for the development of anaerobic microflora.
The level of decomposition of organic matter in
the reactor, % per day ♦ methane ■ biogas ^^fermention time
Figure 2 - The effect of organic matter decomposing intensity on the specific yield of biomethane, biogas and fermentation time
This can be achieved by creating stable fermentation temperature conditions and, what is more important, by providing quality biomass mixing, which, on the one hand, must not to disturb the symbiosis of acetogenic and methanogenic bacteria, and, on the other hand, to prevent the exfoliation of biomass in the reactor to mineral sediment and floating organic layer.
References
1. Руководство по биогазу. От получения до использования / Специальное агентство возобновляемых ресурсов (FNR). 5-е издание. - Гюльцов: Германия, 2012. - 213 с.
2. Голуб Г. А., Рубан Б.О., Дубровша О.В. Метантенк: Патент на винахад 97995. Украша. МПК C02F11/04, C02F3/28, C02F3/06, C12P5/00. - Заявка № а201002089; Заявлено 25.02.2010; Опублковано 10.04.2012, Бюл. № 7. - 5 с.
3. Голуб Г.А., Дубровша О.В., Войтенко В.О., Гох В.В. Аналiз метаноутворення в бюгазових установках. - Сучасш проблеми збалансованого природокористування: Збiрник наукових праць / Под№ський державний аграрно-техшчний ушверситет (ПДАТУ); Науковий редактор: Бахмат М.1. - Кам'янець-Подшьський, 2012. - Спещальний випуск до VII науково-практично! конференцii. - 334 с. - С. 141-145.
УДК 631.147:632.937.3
