Technical, economic and environmental analysis of energy production from municipal solid waste

Four technologies are investigated which produce energy from municipal solid waste (MSW): incineration, gasification, generation of biogas and utilisation in a combined heat and power (CHP) plant, generation of biogas and conversion to transport fuel.Typically the residual component of MSW (non-recyclable, non-organic) is incinerated producing electricity at an efficiency of about 20% and thermal product at an efficiency of about 55%. This is problematic in an Irish context where utilisation of thermal products is not the norm. Gasification produces electricity at an efficiency of about 34%; this would suggest that gasification of the residual component of MSW is more advantageous than incineration where a market for thermal product does not exist. Gasification produces more electricity than incineration, requires a smaller gate fee than incineration and when thermal product is not utilised generates less greenhouse gas per kWh than incineration. Gasification of MSW (a non-homogenous fuel) is, however, not proven at commercial scale.Biogas may be generated by digesting the organic fraction of MSW (OFMSW). The produced biogas may be utilised for CHP production or for transport fuel production as CH₄-enriched biogas. When used to produce transport fuel some of the biogas is used in a small CHP unit to meet electricity demand on site. This generates a surplus thermal product.Both biogas technologies require significantly less investment costs than the thermal conversion technologies (incineration and gasification) and have smaller gate fees. Of the four technologies investigated transport fuel production requires the least gate fee. A shortfall of the transport fuel production technology is that only 50% of biogas is available for scrubbing to CH₄-enriched biogas.     

Technoeconomic analysis of a methanol plant based on gasification of biomass and electrolysis of water

Methanol production process configurations based on renewable energy sources have been designed. The processes were analyzed in the thermodynamic process simulation tool DNA. The syngas used for the catalytic methanol production was produced by gasification of biomass, electrolysis of water, CO₂ from post-combustion capture and autothermal reforming of natural gas or biogas. Underground gas storage of hydrogen and oxygen was used in connection with the electrolysis to enable the electrolyser to follow the variations in the power produced by renewables. Six plant configurations, each with a different syngas production method, were compared. The plants achieve methanol exergy efficiencies of 59–72%, the best from a configuration incorporating autothermal reforming of biogas and electrolysis of water for syngas production. The different processes in the plants are highly heat integrated, and the low-temperature waste heat is used for district heat production. This results in high total energy efficiencies (∼90%) for the plants. The specific methanol costs for the six plants are in the range 11.8–25.3 €/GJ_exergy. The lowest cost is obtained by a plant using electrolysis of water, gasification of biomass and autothermal reforming of natural gas for syngas production.     

Can slurry biogas systems be cost effective without subsidy in Mexico?

Biogas from pig slurry in Mexico has potential to produce 21 PJ per year, equivalent to 3.5% of natural gas consumption in 2013. In this paper, three different scenarios are analysed: mono-digestion of pig slurry in a finisher farm (scenario 1); co-digestion of pig slurry and elephant grass in a finisher farm in situ (scenario 2) and co-digestion of pig slurry and elephant grass in centralised biogas plants (scenario 3). The digesters proposed are anaerobic high density polyurethane (HDPE) covered lagoons. HDPE centralised plants can have capital costs 5 times cheaper than European biogas plants. The economics of utilisation of biogas for electricity generation and as biomethane (a natural gas substitute) were investigated. Economic evaluations for on-site slurry digestion (Scenario 1) and on-site co-digestion of elephant grass and pig slurry (Scenario 2) showed potential for profitability with tariffs less than $US 0.12/kWh_e. For centralised systems (Scenario 3) tariffs of $US 0.161/kWh_e to $US 0.195/kWh_e are required. Slurry transportation, energy use and harvest and ensiling account for 65% of the operational costs in centralised plants (Scenario 3). Biomethane production could compete with natural gas if a subsidy of 4.5 c/L diesel (1 m³ of biomethane) equivalent was available.     

Life cycle assessment of H2 generation with high temperature electrolysis

Water electrolysis is a well-established process for hydrogen production but requires efficiency improvements to reduce costs. High temperature electrolysis (HTE) as a means to higher efficiency was advanced in the EU project RelHY. Through Life Cycle Assessment (LCA), also the environmental performance of five HTE-based hydrogen production systems was evaluated: operation with power and steam from a nuclear plant, continuous and intermittent operation with wind power and water, intermittent operation with natural gas or biogas reforming as back-up. Large scale natural gas reforming (NGR) was used as a reference. The LCA aims to identifying environmental hotspots of HTE plants and comparing their operation. The results show that stack manufacturing has the strongest impact during construction of the HTE plant while the impacts during H₂ production are largely due to power supply. All HTE variants studied lead to less life cycle CO₂-equivalent emissions than NGR. However, only the wind powered HTE variants without back-up use less energy than NGR. The other impacts and flows show different patterns. The results and limitations of the study are discussed.     

Investment screening model for spatial deployment of power-to-gas plants on a national scale – A Danish case

When transitioning to a 100% renewable energy system storing electricity becomes a focal point, as the resource flexibility is lost and the design of the energy system needs to provide flexibility and balancing options to integrate intermittent renewable resources. Using technologies such as power-to-gas offers an opportunity to store electricity in chemical form, which can be used as a long-term storage option. This paper develops a spatial modelling method by using a GIS tool to investigate potential generation sites for power-to-gas plants. The method determines the location of the plants by carbon source potential, proximity of the grid, costs of grid transmission and investment costs of the technology itself. By combining these types of data, it is possible to identify the investment costs of the power-to-gas plants. The method focuses on two paths: biogas upgrade and CO₂ methanation. The method is applied to a specific case by investigating the power-to-gas potential in Denmark. The potential and spatial deployment is found by examining the investment costs of plants with an annual gas production of 60 GWh. The findings of the analysis indicate that the biogas upgrade path is the cheapest one of the two, at the present cost level, but due to the relatively small number of biogas plants in Denmark, the chosen plant size is limited to around 55 plants. CO₂ methanation is a more costly path, but it has a larger potential of around 800 plants. As the analysis is based on the current sources for biogas and CO₂, it is important to emphasise that the potential for CO₂ methanation plants can be expected to diminish in the future as more renewable energy is introduced, lowering the need for thermal energy producers, while biogas production could see an increase. Nevertheless, the analysis of a specific case shows that the method gives a good indication of the extent of the power-to-gas resources by using a novel approach to the matter. The method can be applied in other countries as well, giving it a wide appeal.     

Evaluation of methods for estimating energy performance of biogas production

This study focused on identifying various system boundaries and evaluating methods of estimating energy performance of biogas production. First, the output–input ratio method used for evaluating energy performance from the system boundaries was reviewed. Secondly, ways to assess the efficiency of biogas use and parasitic energy demand were investigated. Thirdly, an approach for comparing biogas production to other energy production methods was evaluated. Data from an existing biogas plant, located in Finland, was used for the evaluation of the methods. The results indicate that calculating and comparing the output–input ratios (R_pr1, R_pr2, R_ut, R_pl and R_sy) can be used in evaluating the performance of biogas production system. In addition, the parasitic energy demand calculations (w) and the efficiency of utilizing produced biogas (η) provide detailed information on energy performance of the biogas plant. Furthermore, R_f and energy output in relation to total solid mass of feedstock (F_O/TS) are useful in comparing biogas production with other energy recovery technologies. As a conclusion it is essential for the comparability of biogas plants that their energy performance would be calculated in a more consistent manner in the future.     

Local acceptance of existing biogas plants in Switzerland

After the Swiss government's decision to decommission its five nuclear power plants by 2035, energy production from wind, biomass, biogas and photovoltaic is expected to increase significantly. Due to its many aspects of a direct democracy, high levels of public acceptance are necessary if a substantial increase in new renewable energy power plants is to be achieved in Switzerland. A survey of 502 citizens living near 19 biogas plants was conducted as the basis for using structural equation modeling to measure the effects of perceived benefits, perceived costs, trust towards the plant operator, perceived smell, information received and participation options on citizens’ acceptance of “their” biogas plant. Results show that local acceptance towards existing biogas power plants is relatively high in Switzerland. Perceived benefits and costs as well as trust towards the plant operator are highly correlated and have a significant effect on local acceptance. While smell perception and information received had a significant effect on local acceptance as well, no such effect was found for participation options. Reasons for the non-impact of participation options on local acceptance are discussed, and pathways for future research are presented.     

Determination of organic silicon compounds in biogas from wastewater treatments plants,landfills, and co-digestion plants

The study determined the organic silicon compounds in biogases from landfills, wastewater treatment plants (WWTPs), and biogas plants processing different organic material. The aim was to provide information for gas utilisation applications, as siloxanes are reported to shorten the life time of engines when biogas is used for energy production. In total, 48 samples were measured. The total concentration of organic silicon compounds in landfill and WWTP gases varied from 77 to 2460 μg/m³ while the concentrations in biogases from biogas plants varied from 24 to 820 μg/m³. The total concentration of organic silicon compounds was lowest (24 μg/m³) in the biogas plant processing grass and maize, and highest (2460 μg/m³) in one of the studied WWTP. The most common compounds in WWTPs and in biogas plants processing also sewage sludge were D4 and D5 while in landfills the most common compounds were D4 and L2 followed by trimethyl silanol. The effect of condensation of biogas on concentrations of organic silicon compounds was studied in one of the landfills and a negligible effect on concentrations was detected.     

Upgrading waste heat from a cement plant for thermochemical hydrogen production

A calcium oxide/steam chemical heat pump (CHP) is presented in the study as a means to upgrade waste heat from industrial processes for thermochemical hydrogen production. The CHP is used to upgrade waste heat for the decomposition of copper oxychloride (CuO.CuCl₂) in a copper–chlorine (Cu–Cl) thermochemical cycle. A formulation is presented for high temperature steam electrolysis and thermochemical splitting of water using waste heat of a cement plant. Numerical models are presented for verifying the availability of energy for potential waste heat upgrading in cement plants. The optimal hydration and decomposition temperatures for the calcium oxide/steam reversible reaction of 485 K and 565 K respectively are obtained for the combined heat pump and thermochemical cycle. The coefficient of performance and overall efficiency of 4.6 and 47.8% respectively are presented and discussed for the CHP and hydrogen production from the cement plant.     

A mathematical,economic and energetic appraisal of biomethane and biohydrogen production from Brazilian ethanol plants' waste: Towards a circular and renewable energy development

The high production of sugarcane in Brazil and its application of ethanol and sugar production results in a higher generation of vinasse and bagasse. The treatment of these residues can be carried out using anaerobic co-digestion procedures. Besides promoting waste treatment, it enables energy exploration through biogas and hydrogen generation. Bioenergy use can also generate steam in sugar and alcohol plants by burning, sugarcane milling, fueling vehicles for the transport of products, among others. These energy applications allow total and efficient, energetic exploring of sugarcane. Hence, this study estimated the production of methane, hydrogen, thermal and electrical energy generated from vinasse and bagasse in the autonomous and annexed Brazilian ethanol and sugar plants. Three scenarios present the use of biogas generated: Scenario 1: energy use of all methane from biogas; Scenario 2: hydrogen production from the remaining methane, after considering the energy autonomy of the ethanol plants; Scenario 3: hydrogen production from all the methane generated. All the scenarios which considered the use of methane led to energy self-sufficiency in the sector. However, only annexed plants present economic feasibility for implementing the project. Scenario 2 is highlighted in this study, once beyond the sector's energetic self-sufficiency, the operational conditions enabled the storage of 9.26E+07 Nm³.d^?1 of hydrogen, equal 3.04E+08 ton per year. CH₄ and H₂ production seen in a global scenario of circular economy and energy security have high benefits, contributing to the gradual transformation of an economy dependent on non-renewable resources into a circular and renewable economy.     

Investigation of biogas and hydrogen production from waste water of milk-processing industry in Turkey

This study is conducted to determine the potential for producing both biogas and hydrogen from a milk-processing waste water in Turkey. The results of this study indicate that a maximum of 54.2 million m³ biogas/yr and 12,670 ton H₂/yr can be produced from milk-processing waste water. A total of $15.1 million worth of energy may be supplied every year from the produced biogas. Some Reference calculations for the production of biogas and the economic evaluation are carried out using actual data taken from the plant. Overall hydrogen production energy efficiency for different types of reforming and for different ambient temperatures ranges between 19 and 70% whereas the overall exergy efficiency for 900 °C reforming and different ambient temperatures changes between 8 and 48%, respectively.     

Biogas plants in Denmark: technological and economic developments

Biogas plants are one of the important elements in the Danish energy-policy of having reduced CO₂ emissions by 20% by 2005. Since 1984, development efforts concerning centralised biogas plants in Denmark have been carried out, and Denmark now has approximately 20 large centralised biogas plants. All Danish biogas plants have increased gas production as a result of admixing industrial organic wastes with manure. This is predominantly regarded as a great advantage for both biogas plants and waste suppliers. The paper will describe the technological development of this renewable energy source in terms of biogas production prices. The price has dropped dramatically during the last 15 years. Based on this analysis, the paper discusses the socio-economic costs of technology development including state budget and employment effects. Also the paper refers to socio-economic feasibility studies from the early 1990s, when biogas production prices were much higher than natural gas. Still, employment effects made the development feasible in socio-economic terms.     

Economics and greenhouse gas balance of biogas use systems in the Finnish transportation sector

Energy decisions play an essential role in reducing greenhouse gas (GHG) emissions in the transportation sector. Biogas is a renewable energy source and can be used as an energy source for gas-operated cars or for electric cars. This paper compares different ways to use biogas, which is produced on a medium scale anaerobic digestion plants, as an energy source for transportation. The research is conducted from an economic and environmental point of view, and the option to deliver upgraded biogas via a natural gas grid is taken into account. Different processes for the use of biogas for transportation purposes are compared using life cycle assessment (LCA) methods in the Finnish operational environment. It seems that the most economical way is to use biogas in gas-operated cars due to the high price of methane for vehicle fuel use. A new feed-in tariff for electricity produced with biogas will, however, have highly positive economic effects on electricity production from biogas. From the environmental point of view, the highest CO₂ reductions are gained when biogas is used in gas-operated cars or in CHP plants for power and heat production. During the transition stage, it might be reasonable to use biogas in gas-operated cars and most importantly in heavy vehicles to reduce GHG and local pollutants rapidly. If biogas production is located near a natural gas grid, the biogas can be delivered effectively via the natural gas grid. The use of biogas in gas-operated cars is an effective way to reduce carbon dioxide significantly in the transportation sector.     

Technological learning in bioenergy systems

The main goal of this article is to determine whether cost reductions in different bioenergy systems can be quantified using the experience curve approach, and how specific issues (arising from the complexity of biomass energy systems) can be addressed. This is pursued by case studies on biofuelled combined heat and power (CHP) plants in Sweden, global development of fluidized bed boilers and Danish biogas plants. As secondary goal, the aim is to identify learning mechanisms behind technology development and cost reduction for the biomass energy systems investigated. The case studies reveal large difficulties to devise empirical experience curves for investment costs of biomass-fuelled power plants. To some extent, this is due to lack of (detailed) data. The main reason, however, are varying plant costs due to differences in scale, fuel type, plant layout, region etc. For fluidized bed boiler plants built on a global level, progress ratios (PRs) for the price of entire plants lies approximately between 90–93% (which is typical for large plant-like technologies). The costs for the boiler section alone was found to decline much faster. The experience curve approach delivers better results, when the production costs of the final energy carrier are analyzed. Electricity from biofuelled CHP-plants yields PRs of 91–92%, i.e. an 8–9% reduction of electricity production costs with each cumulative doubling of electricity production. The experience curve for biogas production displays a PR of 85% from 1984 to the beginning of 1990, and then levels to approximately 100% until 2002. For technologies developed on a local level (e.g. biogas plants), learning-by-using and learning-by-interacting are important learning mechanism, while for CHP plants utilizing fluidized bed boilers, upscaling is probably one of the main mechanisms behind cost reductions.     

Recent advances in biogas upgrading to value added products: A review

It is undeniable that oil and gas explorations are going on at a frantic pace due to excessive fossil fuel usage across the world. This has compelled us to explore isolated or even uninhabited places to meet the surging demand for oil and gas. There is no doubt that scientists and researchers worldwide are exploring more renewable energy sources to produce value-added products. In the last few years, biogas' usage as a reactant gas in the catalytic reforming process has emanated as an energy carrier to produce energy-efficient products, i.e., syngas and methanol. This review aimed to analyze the research works focusing on the biogas DR reactions and methanol production from biogas. The findings of some experimental studies have been presented in the form of graphs for important selective parameters as case studies. The overall impression from the review suggests that the performance of the reforming catalysts deteriorates regarding different operating conditions. Still, the improvement in syngas production has been reported by neglecting the effect of H₂S impurity. Furthermore, various parameters have been discussed paragraphically to evaluate the catalytic performance in biogas dry reforming reactions and a check on catalyst synthesis methods. After that, a few scattered studies have been discussed on methanol synthesis using biogas as a feedstock.     

Efficiency of a pilot-plant for the autothermal reforming of biogas

A grid of hydrogen refuelling stations comparable to gasoline is essential for improving the individual transport based on fuel cell technology. To avoid transport and storage problems with hydrogen, small-scale hydrogen production plants are required. During the project BioRobur a pilot-plant with a hydrogen output of 50 Nm³/h was constructed and investigated. The plant is based on the autothermal reforming of biogas with a noble metal catalyst. All required reactants are stored or produced at the plant side. The purification of the synthetic gas is not considered.Within the article the plant efficiency and the cold gas efficiency were measured at different temperatures, oxygen to carbon ratios and gas hourly space velocities. Additionally the workload of the pilot-plant was varied, showing a highly reliable operation for a workload of at least 20%. Furthermore, the hydrogen production costs of the pilot-plant were compared with other common technologies, like electrolysis and steam reforming.     

The impact of plant size and location on profitability of biogas plants in Germany under consideration of processing digestates

The production of bioenergy is considered to be a promising energy source for a sustainable energy mix and it is politically promoted in many countries. With the exception of Brazilian ethanol, bioenergy is not competitive with fossil energy sources, and therefore needs to be subsidised. Several types of bioenergy are based on bulky raw biomass with high per unit transport costs, importantly impacting on the plant's production costs and profitability. In addition, considerable quantities of digestates are released, causing disposal costs. Various studies in the past aimed primarily at analysing transport costs of inputs. In this paper we focus on disposal costs of fermentation digestates from biogas production in Germany and analyse different processing techniques and their impact on profitability for three plant size in three case study areas.Our results show that especially in regions with only a small amount of agricultural land and a large heterogeneity in its agricultural area, processing of digestates increases the profitability of biogas production. The same accounts for regions with high livestock density, where the area needed for disposal is comparatively large. The cost efficiency is enforced by a high share of animal excrements on input and the biogas plant size.     

Environmental systems analysis of biogas systems—Part I: Fuel-cycle emissions

Fuel-cycle emissions of carbon dioxide (CO₂), carbon oxide (CO), nitrogen oxides (NO_x), sulphur dioxide (SO₂), hydrocarbons (HC), methane (CH₄), and particles are analysed from a life-cycle perspective for different biogas systems based on six different raw materials. The gas is produced in large- or farm-scale biogas plants, and is used in boilers for heat production, in turbines for co-generation of heat and electricity, or as a transportation fuel in light- and heavy-duty vehicles. The analyses refer mainly to Swedish conditions. The levels of fuel-cycle emissions vary greatly among the biogas systems studied, and are significantly affected by the properties of the raw material digested, the energy efficiency of the biogas production, and the status of the end-use technology. For example, fuel-cycle emission may vary by a factor of 3–4, and for certain gases by up to a factor of 11, between two biogas systems that provide an equivalent energy service. Extensive handling of raw materials, e.g. ley cropping or collection of waste-products such as municipal organic waste, is often a significant source of emissions. Emission from the production phase of the biogas exceeds the end-use emissions for several biogas systems and for specific emissions. Uncontrolled losses of methane, e.g. leakages from stored digestates or from biogas upgrading, increase the fuel-cycle emissions of methane considerably. Thus, it is necessary to clearly specify the biogas production system and end-use technology being studied in order to be able to produce reliable and accurate data on fuel-cycle emission.     

Farm-scale bio-power-to-methane: Comparative analyses of economic and environmental feasibility

Power-to-gas technologies are considered to be part of the future energy system, but their viability and applicability need to be assessed. Therefore, models for the viability of farm-scale bio-power-to-methane supply chains to produce green gas were analysed in terms of levelised cost of energy, energy efficiency and saving of greenhouse gas emission. In bio-power-to-methane, hydrogen from electrolysis driven by surplus renewable electricity and carbon dioxide from biogas are converted to methane by microbes in an ex situ trickle-bed reactor. Such bio-methanation could replace the current upgrading of biogas to green gas with membrane technology. Four scenarios were compared: a reference scenario without bio-methanation (A), bio-methanation (B), bio-methanation combined with membrane upgrading (C) and the latter with use of renewable energy only (all-green; D). The reference scenario (A) has the lowest costs for green gas production, but the bio-methanation scenarios (B-D) have higher energy efficiencies and environmental benefits. The higher costs of the bio-methanation scenarios are largely due to electrolysis, whereas the environmental benefits are due to the use of renewable electricity. Only the all-green scenario (D) meets the 2026 EU goal of 80% reduction of greenhouse gas emissions, but it would require a CO₂ price of 200 € t⁻¹ to achieve the levelised cost of energy of 65 €ct Nm⁻³ of the reference scenario. Inclusion of the intermittency of renewable energy in the scenarios substantially increases the costs. Further greening of the bio-methanation supply chain and how intermittency is best taken into account need further investigation.     

Optimizing biogas plants with excess power unit and storage capacity in electricity and control reserve markets

Increasing shares of intermittent power sources such as solar and wind will require biomass fueled generation more variable to respond to the increasing volatility of supply and demand. Furthermore, renewable energy sources will need to provide ancillary services. Biogas plants with excess generator capacity and gas storages can adapt the unit commitment to the demand and the market prices, respectively. This work presents a method of day-ahead unit commitment of biogas plants with excess generator capacity and gas storage participating in short-term electricity and control reserve markets. A biogas plant with 0.6 MW annual average electric output is examined in a case study under German market conditions. For this biogas plant different sizes of the power units and the gas storage are compared in consideration of costs and benefits of installing excess capacity. For optimal decisions depending on prices, a mixed-integer linear programming (MILP) approach is presented.The results show that earnings of biogas plants in electricity markets are increased by additional supplying control reserve. Furthermore, increasing the installed capacity from 0.6 MW to 1 MW (factor 1.7) leads to the best cost–benefit-ratio in consideration of additional costs of excess capacity and additional market revenues. However, the result of the cost–benefit-analysis of installing excess capacity is still negative. Considering the EEG flexibility premium, introduced in 2012 in the German renewable energy sources act, the result of the cost–benefit-analysis is positive. The highest profit is achieved with an increase of the installed capacity from 0.6 MW to 2 MW (factor 3.3).