Technology For Biogas Upgrading Research Articles

Production of ammonium bicarbonate from the condensate of the upgrading biogas-pipelines

Developing a suite of biofuels for different applications relies heavily on upgrading technologies to remove nitrogen compounds and carbon dioxide. Particularly in the upgrading of biogas to biomethane, simple water scrubbing is the most widely used technology for biogas upgrading. This technology can be synergistically implemented without the need for additional equipment for processing steps, although this design has not been conceived yet. Samples of biogas-pipeline condensates were collected from 3 different anaerobic digestion plants processing 3 different feedstocks (i.e., food waste, agrowaste, and manure) at 3 different locations in each plant (i.e., biodigester and postdigester condensate pits, digestate pasteurizer, and biogas booster and chiller). The methodology for the analysis of the 5-mL biogas-pipeline condensates was acid-base titration with 0.06 M hydrochloric acid and 0.13 M sodium hydroxide solutions as titrants, and induction of crystallization by cooling at 3 °C, adding up to 40 mL of acetone as antisolvent, and settling for 12 h. The results showed that the concentration of ammonium bicarbonate in the condensates ranged from 0.75 to 50 g/L. The most suitable location to enhance the upgradation of biogas, formation of condensate, and precipitation of ammonium bicarbonate was the pit after the anaerobic digester and before the biogas storage. The most concentrated condensate was retrieved from the biogas-pipeline coming out of the pasteurization tank, but the operation at 70.5 °C also led to volatilization of organic compounds that negatively affected the biogas quality. Future work aims to investigate coating and granulation of ammonium bicarbonate crystals to improve their stability and commercialization.

An analytical hierarchy process based decision support system for the selection of biogas up-gradation technologies.

Recent developments in biogas upgradation have opened new horizons for its utilisation because upgradation technologies are fully developed and commercially available. However, the implementation of biogas upgrading technologies is not at the scale required to harness the full potential of biogas. Therefore, it is requisite to adopt a multicriteria decision-making methodology (MCDM) to select the most appropriate biogas up-gradation technology as each technology has its own set of benefits and downside. In this multifaceted scenario, the analytical hierarchy Process (AHP), one of the most preferred MCDM methods in rational decision-making, is applied in this study to select the most appropriate biogas upgrading technology. The broader recognition of AHP is its provision for converting multifaceted problems into a simple hierarchy. The research results reveal that biogas up-gradation technologies based on water scrubbing and membrane separation rank first and second among the alternatives. This research will show a direction to researchers and the MCDM community involved in biogas upgradation technologies on a broader scale.

A comparative study of the effects of aqueous mixed amines on biogas upgrading based on 13C nuclear magnetic resonance (NMR) analysis

As a key technology for biogas upgrading, mixed amines scrubbing can meet the world's demand for renewable energy by ensuring high methane (CH4) purity while achieving low energy regeneration. In this paper, several monoamines with excellent performance in biogas upgrading process were selected to study the effectiveness of their blends for biogas upgrading and compared with 30 wt% monoethanolamine (MEA). The biogas upgrading effect, carbon dioxide (CO2) loading, regeneration effect and CO2 desorption heat of mixed amines were determined by batch experiments. 13C NMR was used to mechanistically interpret and quantify the carbocation trend of the amine solution before and after the reaction and regeneration. The results showed that the biogas upgrading and regeneration effect of the mixed amines combined with methyl monoethanolamine (MMEA) and N-methyldiethanolamine (MDEA) was the best, and its initial methane purity, saturated CO2 loading, regeneration rate and CO2 desorption heat after upgrading were 100%, 0.617 mol CO2/mol amine, 54.3% and 64.91 kJ/mol CO2, respectively. Except for the saturated loading which was second only to MMEA/dimethyl monoethanolamine (DMMEA) with 0.624 mol CO2/mol amine, all the performances are optimal and the CO2 desorption heat is 19.01% lower than that of 30 wt% MEA, which can effectively reduce the regeneration energy consumption of the reaction. The results of 13C NMR showed that the increase of bicarbonate content could effectively reduce the regeneration energy consumption and enhance the initial regeneration rate, and the increase of carbamate could accelerate the initial uptake rate and methane purity, which could provide theoretical support for the subsequent screening of mixed amines to achieve different reaction purposes.

Current Status of Biological Biogas Upgrading Technologies

To limit global warming, ratio of renewable sources in the energy mix has to be considerably raised in the following years. While application of e.g. wind and solar power usually generates fluctuations in the electric grid, biogas produced in anaerobic processes is an easy-to-store renewable energy source. Raw biogas contains generally ~55–70% methane and ~30–45% carbon-dioxide. Although raw biogas can be utilized directly for combustion or combined heat and power generation (CHP), its methane content can be raised to >95% by upgrading technologies, thus it can be valorized. By upgrading and cleaning, the quality of the upgraded biogas may reach the quality of the natural gas and it may be injected to the gas grid or used as fuel for devices optimized for natural gas. Several physico-chemical upgrading methods are available on the market (e.g. high pressure water scrubbing, pressure swing adsorption, membrane technology, etc.) to remove the carbon-dioxide content of the biogas. Opposite to the physico-chemical methods, where basically the CO2 removal is the main goal, in biological biogas upgrading technologies microorganisms are applied to convert the carbon-dioxide content of the biogas to methane (chemoautotrophic upgrading), or algal biomass (photoautotrophic upgrading). The expectations are high towards biological biogas upgrading technologies in the field of energy storage linked with carbon-dioxide capture. In this paper, latest research results concerning biological biogas upgrading are summarized, viability and competitiveness of this technology is discussed together with the most important future development directions.

Evaluation of thermal effects on carbon dioxide breakthrough curve for biogas upgrading using pressure swing adsorption

Selective carbon dioxide capture using pressure swing adsorption can transform raw biogas into high energy content biomethane and subsequently sequestration of CO2. In this work, the PSA technology for biogas upgrading is modelled and evaluated using one-dimensional binary mixture adsorption, heat and mass transfer model using Aspen Adsorption™ version 10. This model is validated using experimental data reported previously on zeolite NaUSY, since the CO2 breakthrough curve depicts reasonable agreement. This work considers two heat transfer conditions (gas and gas/solid conductions) to compare their effects on CO2 breakthrough and temperature responses at different positions along the adsorption bed. Three different biogas mixtures are charged over zeolite NaUSY bed to evaluate CO2 concentration on breakthrough curve and bed temperature profile. The influence of axial mass dispersion coefficient on breakthrough characteristics and temperature distribution along adsorption bed is examined. In addition, the effects of cooling outside column wall on CO2 breakthrough curve and bed temperature distribution is also explored. The findings indicate that the heat generated during adsorption possesses influences the adsorption performance rather significantly. Reducing this heat restrains the thermal effects on the breakthrough curves, thereby improving the methane purity and recovery.

Implementation of a Decision Support System for Sewage Sludge Management

In this work, a decision support system (DSS) coupled with wastewater treatment plant (WWTP) simulator tool that uses a hierarchical set of key performance indicators (KPIs) to provide an assessment of the performance of WWTP systems is presented. An assessment of different Scenarios in a real WWTP case study, each consisting of a different set of sludge line technologies and derived combinations, was successfully conducted with the developed DSS–WWTP simulator, based on Scenario simulation and hierarchical KPI analysis. The test carried out on the selected WWTP showed that although thermal valorisation and thermal hydrolysis showed similar (the best) economic viability, the latter showed additional benefits, including synergies related to improving the thermal balance of the overall WWTP even when considering other technologies. On the other hand, biogas-upgrading technologies allowed reduction of emissions, but with higher costs and thermal demands. The usage of this tool may allow the development of proposals for technological priorities as a pathway to the transition to circular economy based on the management criteria of the correspondent sanitation system.

Environmental-Economic Assessment of the Pressure Swing Adsorption Biogas Upgrading Technology

A large-scale biogas upgrading plant using the CarboTech® technology with a treatment capacity of 1333 Nm3 biogas per hour was analyzed. Our scope of evaluation encompasses all technology steps that are necessary for upgrading biogas, i.e., both pretreatment and biogas upgrade. A cradle-to-gate life-cycle and life-cycle cost assessment (LCA and LCCA) methodology was used with the functional unit (FU) of 1 Nm3 of biogas upgraded in order to ease comparison with other biogas upgrading technologies. The calculation was made using the GaBi8 LCA software and databases of GaBi Professional, Construction materials, Food&Feed, and the ecoinvent3. We applied the CML characterization model with all its mid-point indicators. The mid-point indicators of the CML characterization model were aggregated after normalization by the CML2001 - Jan.2016 normalization factors. The normalized environmental impact was 541.74·10−15/Nm3 raw biogas. The highest environmental impacts were the marine aquatic ecotoxicity potential (15.705 kg dichlorobenzene-equiv./Nm3 raw biogas), the abiotic depletion potential (1.037 MJ/Nm3 raw biogas), and global warming potential (0.113 kg CO2-equiv./Nm3 raw biogas). The unit production cost of the PSA technology was 0.05-0.063 €/Nm3 raw biogas. The most considerable source of expenses was the operational cost from which 77% was spent on electricity. The initial investment, personal costs, and the reinvestment amounted to only 34% of the total costs for the whole life cycle. Strategies to lower the environmental burden of the PSA technology are to use green electricity and to optimize the size of the plant in order to reduce unnecessary material flows of building material and their indirect energy use. This can also lower investment expenditures while automatization and remote control may spare personnel costs.

A Mini-Review on In situ Biogas Upgrading Technologies via Enhanced Hydrogenotrophic Methanogenesis to Improve the Quality of Biogas From Anaerobic Digesters

In the context of accelerating development of renewable and sustainable energy, biogas upgrading has attracted significant attention in order to yield high quality biomethane which can be utilized as an alternative to natural gas. Biogas upgrading techniques have been revolutionized in the past decade with the emergence of new strategies such as enhanced hydrogenotrophic methanogenesis. This review comprehensively summarizes the latest in situ biogas upgrading technologies via enhanced hydrogenotrophic methanogenesis in order to facilitate their development and commercial application: (1) hydrogen injection into anaerobic digesters for in situ enhancement of hydrogenotrophic methanogenic pathways, (2) membrane electrolysis-assisted CO2 extraction and bioelectrochemical removal of CO2, and (3) additives (e.g. ash, zero-valent iron and biochar). The key findings and technical limitations are summarized and critically analyzed for each in situ biogas upgrading technique. Additionally, potential industrial applications of these in situ biogas upgrading strategies in anaerobic digesters are also discussed, before concluding with their future development.

Microbial community response to ammonia levels in hydrogen assisted biogas production and upgrading process

Biological conversion of carbon dioxide into methane using hydrogen derived from surplus renewable energy (wind power) as reducing power is a novel technology for biogas upgrading. High ammonia concentrations are toxic to the biogas upgrading process, however the mechanisms behind the inhibition as well as the microbial stress response in such unique upgrading system have never been reported. Thus, the effect of high ammonia concentrations on microbial community during hydrogen induced biogas upgrading process was evaluated here. The results showed that a change from aceticlastic pathway to hydrogenotrophic pathway occurred when ammonia level increased (1–7 g NH4+-N L−1). In addition, the bacteria, potentially syntrophic associated with hydrogenotrophic methanogens, were enriched at high ammonia concentrations. Moreover, growth of some bacteria (e.g., Halanaerobiaceaeen and Leucobacter) which were vulnerable to ammonia toxicity was restored upon hydrogen injection. Furthermore, hydrogen injection under high ammonia concentration could promote growth of some hydrolytic and fermentative bacteria.

Evaluation of biogas upgrading technologies and future perspectives: a review

Biogas is acknowledged as one of the foremost bioenergy to address the current environmental and energy challenges being faced by the world. Commonly, biogas is used for applications like cooking, lighting, heat and power production. To widen the scope of biogas application, like transportation, natural gas grid injection and substrate for the production of chemicals and fuel cells, mainly CO2, H2S and other impurities need to be removed by various upgrading technologies. It is an important process to produce biomethane with above 90% methane. There are various physico-chemical (adsorption, absorption, cryogenic and membrane separations) and biological (in situ and ex situ) processes for biogas upgradation, and each process is site and case specific. The aim of the present paper is to thoroughly evaluate the existing and emerging biogas upgrading technologies. Analysis of each technology with respect to basis of operations, energy requirement, methane purity and recovery and cost economics has been carried out. A thorough analysis has been done on the major hurdles and the research gaps in this sector. For a wider and successful implementation of the biogas upgradation technology, the trends in research and development (R&D) such as development of efficient biogas upgrading technologies, adsorbents, reduction in cost and methane loss have been thoroughly evaluated.

Pressure swing adsorption for biogas upgrading. A new process configuration for the separation of biomethane and carbon dioxide

Pressure swing adsorption (PSA) is an interesting technology for biogas upgrading, due to compactness of the equipment, low energy requirements, low capital cost, and safety and simplicity of operation. Unfortunately, some shortcomings penalize its diffusion in comparison with other technologies; in particular, conventional PSA has a low methane recovery and cannot compete in this field with other processes such as amine scrubbing; furthermore, it produces an off gas stream with a significant methane content, which requires further treatment to avoid the emission of residual methane into the atmosphere. In this framework, this study focuses on the feasibility of a PSA based separation process able to obtain a biomethane stream suitable to be injected in the natural gas grid (CO2 <3% by volume) with a high methane recovery and an almost pure CO2 stream (CO2 > 99%). The proposed process uses Zeolite 5A as adsorbent material in two PSA units; the biogas is fed to the first unit which produces biomethane; the off gas of the first unit is sent to a second PSA unit which separates carbon dioxide from a residual gas stream, recycled to the first to enhance methane recovery. A dynamic non-isothermal model, based on the linear driving force approximation, is employed to demonstrate the technological feasibility of the separation units and to assess the performance of the whole process. In particular a methane recovery greater than 99% can be obtained with energy consumption of about 1250 kJ per kg of biomethane.

Biogas upgrading technologies: Energetic analysis and environmental impact assessment

Biogas upgrading for removing CO2 and other trace components from raw biogas is a necessary step before the biogas to be used as a vehicle fuel or supplied to the natural gas grid. In this work, three technologies for biogas upgrading, i.e., pressured water scrubbing (PWS), monoethanolamine aqueous scrubbing (MAS) and ionic liquid scrubbing (ILS), are studied and assessed in terms of their energy consumption and environmental impacts with the process simulation and green degree method. A non-random-two-liquid and Henry's law property method for a CO2 separation system with ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) is established and verified with experimental data. The assessment results indicate that the specific energy consumption of ILS and PWS is almost the same and much less than that of MAS. High purity CO2 product can be obtained by MAS and ILS methods, whereas no pure CO2 is recovered with the PWS. For the environmental aspect, ILS has the highest green degree production value, while MAS and PWS produce serious environmental impacts.