Biomethane Quality Research Articles

A short-cut model for predicting biomethane availability after biogas upgrading

Biomethane increasingly grows in importance in the bioenergy sector, as it is a renewable energy source that promotes waste recovery and GHG (greenhouse gases) reduction. In Brazil, the legal framework for biogas and biomethane is being developed, especially in the State of São Paulo. However, many of the final uses to biomethane require an upgrading and cleaning process, to remove contaminants such as H2S and CO2. Facing the great number of technological options to promote biogas upgrading and cleaning so far, policymakers and energy planners might lack the tools to accurately and readily estimate biomethane potentials to comply with a given biomethane quality standard. Our main objective thus is to propose a short-cut, mass balance-based model to predict biomethane availability after promoting a biogas cleaning and upgrading process, regardless of the source of organic feedstock. The model development results in the ratio of biogas to biomethane production and other relevant parameters regarding biomethane use, such as its LHV. The correlation with data from the literature shows that the model has a satisfactory prediction, even when using upgrading technologies that have high methane losses. The model was applied to a case study of upgrading biogas from vinasse from ethanol production in the state of São Paulo; it aided in choosing the upgrading technology for biogas focusing on biomethane injection in the natural gas pipeline and in replacing diesel oil in trucks and heavy-duty machinery in the ethanol plant. Using the proposed model, it was estimated that 1.975x109 Nm3/y of biomethane could be produced, supplying 16.6% of the NG consumption in the State of São Paulo and making it possible to displace the entire diesel oil consumption in ethanol mills. The use of biomethane in the ethanol plants of São Paulo would avoid 3.965x106 tCO2eq of GHG emissions, which represents 5.48% of the GHG emissions of the state in 2016.

Influence of alkalinity and temperature on photosynthetic biogas upgrading efficiency in high rate algal ponds

Algal-bacterial photobioreactors have emerged as a cost-effective platform for biogas upgrading. The influence on biomethane quality of the inorganic carbon concentration (1500, 500 and 100 mg L−1) and temperature (12 and 35 °C) of the cultivation broth was evaluated in a 180 L high rate algal pond (HRAP) interconnected to a 2.5 L absorption column via settled broth recirculation. The highest CO2 and H2S removal efficiencies (REs) from biogas were recorded at the highest alkalinity (CO2-REs of 99.3 ± 0.1 and 97.8 ± 0.8% and H2S-REs of 96.4 ± 2.9 and 100 ± 0% at 12 and 35 °C, respectively), which resulted in CH4 concentrations of 98.9 ± 0.2 and 98.2 ± 1.0% at 12 and 35 °C, respectively, in the upgraded biogas. At the lowest alkalinity, the best upgrading performance was observed at 12 °C (CO2 and H2S-REs of 41.5 ± 2.0 and 80.3 ± 3.9%, respectively). The low recycling liquid to biogas ratio applied (0.5) resulted in a negligible O2 stripping regardless of the alkalinity and temperature, which entailed a biomethane O2 content ranging from 0 to 0.2 ± 0.3%.

Single-step purification of raw biogas to biomethane quality by hollow fiber membranes without any pretreatment – An innovation in biogas upgrading

Abstract Herein, a radical innovation in biogas production is presented using a single-step membrane purification technology without any necessary pretreatment steps for contaminant removal and with the usage of low feed pressure. Asymmetric hollow fiber membranes with a thin, selective, non-porous layer made from polyester carbonate on the bore side were successfully used in a single-step raw biogas upgrading process at biogas plant Choťovice in the Czech Republic. A double-stage arrangement operated at 17 °C exhibited the best CO2/CH4 separation factor (β ∼ 23) with 96 vol% CH4 purity. This single-step biogas upgrading technology with highly H2S and water-resistant membrane modules allows reductions in capital expenditures of ∼20% and in operational expenditures of ∼50% compared to high-pressure water scrubbing (HPWS) and ∼70% compared to pressure swing adsorption (PSA). Due to the small energy consumption required merely for biogas compression, our units consumed around only ∼2 MJ/Nm3 CH4. Thus, our approach with significantly improved performance and robustness of the membrane separation process can be seen as a major breakthrough of membrane gas separation for inexpensive biogas production.

Influence of the seasonal variation of environmental conditions on biogas upgrading in an outdoors pilot scale high rate algal pond

The influence of the daily and seasonal variations of environmental conditions on the quality of the upgraded biogas was evaluated in an outdoors pilot scale high rate algal pond (HRAP) interconnected to an external absorption column (AC) via a conical settler. The high alkalinity in the cultivation broth resulted in a constant biomethane composition during the day regardless of the monitored month, while the high algal-bacterial activity during spring and summer boosted a superior biomethane quality. CO2 concentrations in the upgraded biogas ranged from 0.1% in May to 11.6% in December, while a complete H2S removal was always achieved regardless of the month. A limited N2 and O2 stripping from the scrubbing cultivation broth was recorded in the upgraded biogas at a recycling liquid/biogas ratio in the AC of 1. Finally, CH4 concentration in the upgraded biogas ranged from 85.6% in December to 99.6% in August.

INCREASE OF QUALITY OF BIOMETHANE USED FOR HYDROGEN SYNTHESIS

The paper studies the features of biomass energy use and presents the main directions of biogas application. It is shown the connection between the main indicators of biogas quality and the possibility of its use in various technological processes. The relevance of improving the quality of biomethane used for synthesis of high purity hydrogen is substantiated. The classification of the methods for separation and purification of methane-containing gas mixtures is given, their advantages and disadvantages are analyzed. Comparative characteristics of the presented methods for cleaning quality, specific energy costs, and design features are given. A method of short cycle free adsorption for bio-gas purification is proposed as the most economically feasible for small capacity plants. The main types of industrial adsorbents are considered. The dependence of sorption properties on the effective pore diameters of sorbent materials is shown. The distinctive features of adsorption in microporous structures are noted. The most significant of these features is the high value of the adsorption energy in comparison with adsorption materials having larger pores in the structure. Among microporous adsorbents, zeolites are identified as the most promising. The adsorption properties of synthetic and natural zeolites are analyzed. The theoretical bases of the adsorption purification processes are considered, the adsorption competition of the main macrocomponents of the gas mixture being cleaned is evaluated. The scheme of the experimental installation and the process of separation and purification of biogas using natural zeolite as an adsorbent are described. The results of application of a natural zeolite for the production of high purity biomethane due to purification from water vapor, hydrogen sulphide and adsorption of carbon dioxide are presented. The conversion of biomethane to hydrogen was noted as the most promising direction of biomass energy use, the advantages of using natural zeolites for obtaining high purity biomethane are shown.

Influence of the gas-liquid flow configuration in the absorption column on photosynthetic biogas upgrading in algal-bacterial photobioreactors

The potential of an algal-bacterial system consisting of a high rate algal pond (HRAP) interconnected to an absorption column (AC) via recirculation of the cultivation broth for the upgrading of biogas and digestate was investigated. The influence of the gas-liquid flow configuration in the AC on the photosynthetic biogas upgrading process was assessed. AC operation in a co-current configuration enabled to maintain a biomass productivity of 15gm−2d−1, while during counter-current operation biomass productivity decreased to 8.7±0.5gm−2d−1 as a result of trace metal limitation. A bio-methane composition complying with most international regulatory limits for injection into natural gas grids was obtained regardless of the gas-liquid flow configuration. Furthermore, the influence of the recycling liquid to biogas flowrate (L/G) ratio on bio-methane quality was assessed under both operational configurations obtaining the best composition at an L/G ratio of 0.5 and co-current flow operation.

Analysis of process related factors to increase volumetric productivity and quality of biomethane with Methanothermobacter marburgensis

The biological conversion of H2 and CO2 into CH4, using methanogenic archaea is an interesting technology for CO2 conversion, energy storage and biogas upgrading. For an industrial application of this process however, the optimization of the volumetric productivity and the product quality is an important issue. Since the reactants in this fermentation process are, unlike in most microbial fermentations, solely gasses, the gas liquid mass transfer is supposed to play an important role on the way to a higher volumetric productivity.This work aimed at investigating the effects of the gassing rate, the reactor pressure, as well as reactor design issues on the performance of Methanothermobactermarburgensis by using continuous cultures. Our results show that biological methanogenesis with M. marburgensis is gas limited. Maximum physiological capacity is not reached yet. The gassing rate influenced mainly the volumetric methane production rate (MER), the reactor pressure influenced mainly the offgas quality. Based on this information, we demonstrated how a combination of increased gas flow rate and increased reactor pressure can be used to reach high volumetric productivity at high offgas quality. Maximum MER was 950mmolL−1h−1 at a CH4 concentration of 60Vol.-%, maximum CH4 concentration reached was 85Vol.-% at a MER of 255mmolL−1h−1.The reactor design currently limits further increase in gas flow rate and reactor pressure. Therefore Interdisciplinary bridges from bioprocessing to chemical reactor design must be followed in the future to boot this promising bioprocess to gain biomethane via CO2 fixation.