RESUMO
The focus of this work is the development of a model for the estimation of methane emissions for storage tanks of biogas plants. Those can be estimated depending on (i) hydraulic retention time in the digester, (ii) an arbitrary removal rate of the digestate from the storage tank and (iii) arbitrary temperature conditions in the storage tank. Furthermore, the model is capable of considering an arbitrary mixture of manure and crops in the input material. The model was validated by data from 21 full scale biogas plants in Germany digesting cow manure and crops. A realistic scenario for the removal rate and temperature conditions in the storage tank was then investigated and special emphasis was given to the effect of hydraulic retention time and proportion of crops in the mixture on the input VS methane yield from the digester and the storage tank.
Assuntos
Biocombustíveis/análise , Esterco/análise , Metano/análise , Modelos Teóricos , Eliminação de Resíduos/métodos , Animais , Reatores Biológicos , Produtos Agrícolas , Alemanha , TemperaturaRESUMO
Data from 24 full scale biogas plants in Germany digesting cow manure and crops were evaluated. Special emphasis was given to the effect of hydraulic retention time HRT and proportion of crops in the mixture (VS basis) p(VS,Crops)(Inp) on the methane yield from the digester [Formula: see text] and the storage tank [Formula: see text] at 37 and 22°C. The evaluation has shown model parameters for maximal methane yield of manure and crops [Formula: see text] at 270 and 420 Lkg(-1), respectively. For example, at HRT of 60days, maximum methane yield result to 249 and 388 Lkg(-1) for a crop proportion in the input of 0.0 and 1.0, respectively. The calculation of [Formula: see text] considers first order reaction rates and a temperature term f(T). Hence, at any arbitrary temperature in the range of 12°CAssuntos
Biocombustíveis
, Reatores Biológicos
, Produtos Agrícolas/metabolismo
, Esterco
, Metano/metabolismo
, Modelos Biológicos
, Animais
, Bovinos
, Temperatura
, Fatores de Tempo
RESUMO
In this article a mathematical model is introduced, which estimates the distribution of the four anaerobic digestion phases (hydrolysis, acidogenesis, acetogenesis and methanogenesis) that occur among the leach bed reactor and the anaerobic filter of a biogas plant. It is shown that only the hydrolysis takes place in the first stage (leach bed reactor), while all other anaerobic digestion phases take place in both reactor stages. It turns out that, besides the usually measured raw materials of the acetogenesis and the methanogenesis phases (organic acids), it is also necessary to analyze the process liquid for raw materials of the acidogenesis phase, i.e., sugars, fatty acids, amino acids, etc. The introduced model can be used to monitor the inhibition of the anaerobic digestion phases in reactor stages and can, thus, help to improve the control system of biogas plants.
Assuntos
Biocombustíveis , Reatores Biológicos , Metano/biossíntese , Modelos Teóricos , Poaceae/metabolismo , Anaerobiose , Biomassa , HidróliseRESUMO
Acetoclastic methanogenesis in the second stage of a two-phase biogas reactor is investigated. A mathematical model coupling chemical reactions with transport of process liquid and with the variation of population of the microorganisms living on the plastic tower packing of the reactor is proposed. The evolution of the liquid is described by an advection-diffusion-reaction equation, while a monod-type kinetic is used for the reactions. Moreover, a new inhibition factor MO(max) is introduced, which hinders the growth of microorganisms when the plastic tower packing is overpopulated. After estimating the reaction parameters, the acetate outflow measured experimentally is in good agreement with that predicted by simulations. For coupling liquid transport with reaction processes, a spatial discretization of the reactor is performed. This yields essential information about the distribution of acetate and the production of methane in the reactor. This information allows for defining a measure of the effectiveness of the reactor.