Characterization of corn stover, distiller grains and cattle manure for thermochemical conversion

Corn stover, distiller grains and cattle manure were characterized to evaluate their acceptability for thermochemical conversion. The energy densities of ground corn stover, distiller grains and cattle manure after totally drying were 3402, 11,813 and 10,374 MJ/m³, compared to 37,125 MJ/m³ for coal. The contents of volatiles in corn stover, distiller grains and cattle manure were 77.4, 82.6 and 82.8%, respectively, on a dry and ash-free basis compared to 43.6% for coal. About 90% of the volatiles in corn stover, distiller grains and cattle manure were released at pyrolysis temperatures of 497, 573 and 565 °C, respectively. The combustion of corn stover, distiller grains and cattle manure were completed at 620, 840 and 560 °C, respectively. The heat values of the biomass and air mixture for stoichiometric combustion were 2.64, 2.75 and 1.77 MJ/kg for dried corn stover, distiller grains and cattle manure, respectively, as compared to 2.69 MJ/kg for coal. Combustion of 1 kg of dry corn stover, distiller grains and cattle manure generated 5.33, 6.20 and 5.66 Nm³ of flue gas, respectively, compared to 8.34 Nm³ for coal. Simulation showed that gasification of 1 kg of dried corn stover, distiller grains and cattle manure at 850 °C and ER of 0.3 generated 2.02, 2.37 and 1.44 Nm³ dry syngas at a heating value of about 4.5 MJ/Nm³, compared to 3.52 Nm³ at 5.8 MJ/Nm³ for coal. The molecular ratio of H₂ to CO in the biomass-derived syngas was close to 1.0, compared to about 0.5 for the coal-derived syngas.     

Liquid phase thermochemical energy conversion systems—An application of Diels-Alder chemistry

Thermochemical energy conversion at moderate or low temperature (> about 400°C) employing liquid phase components throughout a cycle is suggested as a promising concept for high-efficiency conversion of various energy sources (e.g. solar or industrial waste heat) to a convenient chemical form. In particular, we propose liquid phase Diels-Alder cycloaddition chemistry as an important class of reversible reactions for such low or moderate temperature thermochemical energy conversion systems. One of the important attributes of thermally driven Diels-Alder reactions is their concerted mechanism, with consequent high yields and efficiencies relative to liquid photochemical systems. Since the systems we propose involve organic species, with thermal stability concerns above about 400°C, it is important to demonstrate equilibrium shift capability for the highly energetic reactions sought. We have therefore carried out experimental studies with model liquid Diels-Alder systems that clearly demonstrate the degree of control over equilibrium available through substituent entropy effects. For example, K_eq is unity at about 420°C (T*) for the anthracene/maleic anhydride system (in solvent) while a phenyl substituent on the anthracene or isopropyl substituent on the anhydride reduce T* to about 200°C at constant ΔH⁰. These results are of importance as regards subsequent systematic identification of Diels-Alder reactions having ideal thermochemical and physical properties. We also have developed a rapid NMR technique for qualitative screening of candidate reactions, and have applied this technique to the study of various bicyclic diene/fumaric acid ester systems. Our paper further points to the need for better understanding of the catalysis likely required for these liquid phase Diels-Alder reactions.     

Technoeconomic assessment of ethanol production via thermochemical conversion of biomass by entrained flow gasification

The production of ethanol via entrained flow gasification of biomass and subsequent catalytic synthesis is economically assessed by considering current and future scenarios. In the current scenarios, the process plants proposed only make use of available technologies and state-of-the-art mixed alcohol catalysts (Rh-Mn/SiO₂ and KCoMoS₂ catalysts). In the future scenarios, the effects of improvements in MoS₂ catalyst performance and the availability of pressurized solid biomass feeding systems are assessed. A plant size of 2140 dry tonnes/day of wood chip (500 MW_th) is considered with the criteria of being energy self-sufficient. The economic results are discussed and also compared with state-of-the-art production of biochemical lignocellulosic ethanol.The results reveal that although the Rhodium catalyst presents better performance than MoS₂ catalysts in terms of selectivity to ethanol, the high price of the Rhodium catalyst leads to higher production costs. For current catalysts, the minimum ethanol selling price (including 10% rate of return) is in the range of 0.90-1.25 $/L. In a future scenario, expected improvements in MoS₂ catalyst performance would lead to a decrease in price to 0.71 $/L. Besides, if biomass piston feeders were commercially available, as an alternative for flash pyrolysis pre-treatment, the minimum ethanol selling price would decrease to 0.55 $/L.     

Environmental requirements in thermochemical and biochemical conversion of biomass

Many biological and thermochemical processing options exist for the conversion of biomass to fuels.

Commercially, these options are assessed in terms of fuel product yield and quality. However, attention must also be paid to the environmental aspects of each technology so that any commercial plant can meet the increasingly stringent environmental legislation in the world today.

The environmental aspects of biological conversion (biogasification and bioliquefaction) and thermal conversion (high pressure liquefaction, flash pyrolysis, and gasification) are reviewed. Biological conversion processes are likely to generate waste streams which are more treatable than those from thermal conversion processes but the available data for thermal liquefaction are very limited. Close attention to waste minimisation is recommended and processing options that greatly reduce or eliminate waste streams have been identified. Product upgrading and it's effect on wastewater quality also requires attention. Emphasis in further research studies needs to be placed on providing authentic waste streams for environmental assessment.     

Modelling farmer uptake of perennial energy crops in the UK

The UK Biomass Strategy suggests that to reach the technical potential of perennial energy crops such as short rotation coppice (SRC) willow and miscanthus by 2020 requires 350,000 hectares of land. This represents a more than 20-fold increase on the current 15,546 hectares. Previous research has identified several barriers to adoption, including concerns over security of income from contracts. In addition, farmers perceive returns from these crops to be lower than for conventional crops. This paper uses a farm-level linear programming model to investigate theoretical uptake of energy crops at different gross margins under the assumption of a profit-maximising decision maker, and in the absence of known barriers to adoption. The findings suggest that while SRC willow, at current prices, remains less competitive, returns to miscanthus should have encouraged adoption on a wider scale than at present. This highlights the importance of the barriers to adoption. Recently announced contracts for miscanthus appear to offer a significant premium to farmers in order to encourage them to grow the crops. This raises the question of whether a more cost-effective approach would be for government to provide guarantees addressing farmers concerns including security of income from the contracts. Such an approach should encourage adoption at lower gross margins.     

Steam gasification of selected energy crops in a fixed bed reactor

The increasing world's energy demand and environmental concerns related to GHG emissions as well as depleting fossil fuel resources and unstable prices of crude oil and natural gas have caused a renewed interest in renewable energy sources, and in particularly in biomass, as an alternative to fossil fuels. In the paper the results of steam gasification of Salix Viminalis, Miscanthus X Giganteus (MXG), and Andropogon Gerardi in a laboratory-scale fixed bed reactor in the temperature range of 650–900 °C are presented as well as the procedure and results of biomass chars reactivity testing in the process of steam gasification. The highest reactivity R₅₀ in the whole temperature range was observed for MXG. Hydrogen content in the synthesis gas was comparable for MXG and Andropogon Gerardi and lower for Salix Viminalis, while the volumes of the synthesis gas and hydrogen were highest for MXG at all temperatures.     

Farm-level constraints on the domestic supply of perennial energy crops in the UK

There are a number of estimates of the land area that could potentially be dedicated to perennial energy crops such as short rotation coppice (SRC) willow and miscanthus in the UK, but little is known about how farmers will respond to the opportunities presented by these relatively novel crops. Perennial energy crops face competition from other, arguably more flexible, uses of farmland, and if not seen as attractive propositions to individual farmers, they will not be grown. Farmers’ decisions are therefore a key constraint on potential supply. This paper reviews the policy background and considers whether policy is based on any consideration of likely supply response, before presenting outcomes of focus groups composed of farmers who already grow or are considering growing perennial energy crops. There appear to be a number of barriers to adoption. In addition to concerns over the security of contracts, the current high wheat price increases the opportunity cost of committing land to perennial energy crops. There are also worries about the impact of willow roots on field drains and the cost of returning the land to other uses. This paper outlines a number of issues of importance to policy makers and suggests future research needs.     

Bioenergy for heat and electricity in the UK: A research atlas and roadmap

The UK has a significant biomass resource, estimated at an annual 20 million tonnes, but only a fraction of this is captured effectively for energy, contributing approximately 4.1% of the UK's heat and electricity production (Department for Environment, Food and Rural Affairs, 2007a. UK Biomass Strategy: http://www.defra.gov.uk/Environment/climatechange/uk/energy/renewablefuel/pdf/ukbiomassstrategy-0507.pdf (accessed 24 May 2008)). Much biomass combustion technology may be considered as mature, although bottlenecks in the quality and quantity of feedstock are apparent, and further fundamental research is required to increase crop yield in a sustainable manner, with low-chemical inputs to ensure efficient energy balance. In the short term, it could be useful for the UK to focus on developing a limited number of bioenergy chains, linked to combined heat and power microgeneration and the use of bioenergy for community and public sector projects. This should be linked to a joined-up policy and regulatory framework. A clear strategy for land management is also required, since many competing uses for land will emerge in the coming decades, including food production, nature conservation, carbon sequestration, urbanisation and other forms of renewable energy use. This finite resource must be managed effectively. In the long-term future, considerable excitement exists about the possibility of new bioscience technologies harnessed to improve photosynthetic gains for bioenergy, including the use of synthetic biology. It may be possible to produce the designer energy plant whose outputs would include high-quality chemical and liquid biofuels. Gasification of biomass also requires further technology development.     

Economic assessment and comparison of acacia energy crop with annual traditional crops in Southern Europe

In several policy documents bioenergy is recognized as an important renewable energy source in Italy. The increase in energy prices represents an opportunity for lignocellulosic energy crops such as acacia and poplar.     

Wood feedstock qualities for energy conversion and the potential for their biological improvement

The accomplishments of the Wood Feedstock Quality activity of Task V of the International Energy Agency's Bioenergy Agreement are described. Areas investigated included energy products and co-products from woody biomass; effects of harvesting, processing and storage on feedstock quality; the effect of feedstock quality on the efficiency of biomass conversion; the potential for biological improvement; the need for standardization of feedstock qualities; and the need for clonal characterization.     

Perspective and potential of CO2: A focus on potentials for renewable energy conversion in the Mediterranean basin

Figures commonly quoted on the soon shortage of generating energy from fossil sources which may give the impression that it will be possible to switch to renewable energies conversion as foundations for the future of industrial instances in the Mediterranean basin. In this study, CO₂ energy potential and perspectives in the Mediterranean basin have been investigated in terms of efficiency, feasibility, geographical patterns and savings. Two conjoint mathematical protocols have been carried out in order to yield a simplified extracted scheme for prototype CO₂ trapping/storage plants.     

Prospective framework for collection and exploitation of waste cooking oil as feedstock for energy conversion

From the viewpoint of waste-to-energy, waste cooking oil is one of the attractive and available recycled feedstocks, apart from agricultural residues. The generation of energy from waste cooking oil is considered as an effective technique for waste management, as well as a beneficial form of energy recovery. Two alternative systems and a conventional system of waste cooking oil collection and conversion are evaluated by the cost benefit analysis in order to find a suitable method for waste-to-energy conversion. The results show that the collection of waste cooking oil with waste lubricating oil (System II) a useful alternative to the management of waste cooking oil (B/C > 1). The total heat produced by the combustion of pyrolytic oil at maximum and minimum conversion rates is also determined. The separate collection of waste cooking oil, subjected to chemical pre-treatment prior to introduction in a pyrolysis reactor (System III), is considered an undesirable option (B/C < 1) due to the cost of the chemicals involved. Although the exclusion of chemical pre-treatment makes System III a desirable option, the total amount of heat of combustion generated is less. The increased electricity cost required for the process has no effect on the benefit-cost ratio of System II. However, System III, excluding chemical pre-treatment, becomes an unprofitable alternative when the electricity cost reaches 100% of the fixed capital cost at the minimum conversion rate.     

Energetic density of different forest species of energy crops in Cantabria (Spain)

This article is the result of an analysis into the behavior of several forest species that could be used as energy crops in Cantabria. The species studied belong to several botanical genera. The study was conducted in several stages: firstly, the species was introduced to explore growth data and discard those species of slower growth. Once the genus maximising the biomass production was determined, several species of it were studied from the energy perspective. This combination of both allows the energy density for each species to be obtained, therefore making it possible to determine how big a cultivation area is required for a specific thermal power plant. Thus, for a power plant of 10 MWe, between 15,451 and 24,578 ha of Eucalyptus would be necessary, depending on the species chosen, at an approximate age of 4 years.     

Corrosion of metals and salt hydrates used for thermochemical energy storage

Solar energy can be efficiently used if thermal energy storage systems are accordingly designed to match availability and demand. Thermal energy storage by thermochemical materials (TCM) is very attractive since these materials present a high storage density. Therefore, compact systems can be designed to provide both heating and cooling in dwellings. One of the main drawbacks of the TCM is corrosion with metals in contact. Hence, the objective of this study is to present the obtained results of an immersion corrosion test following ASTM G1 simulating an open TCM reactor, under humidity and temperature defined conditions. Four common metals: copper, aluminum, stainless steel 316, and carbon steel, and five TCM: CaCl₂, Na₂S, CaO, MgSO₄, and MgCl₂, were studied. Aluminum and copper show severe corrosion when combined with Na₂S, aluminum corrosion is more significant since the specimen was totally destroyed after 3 weeks. Stainless steel 316 is recommended to be used as a metal container material when storing all tested TCM.     

Catalytic thermochemical reactor/receiver for solar reforming of natural gas: Design and performance

The advantages of thermochemical conversion of concentrated solar energy using catalytic processes are discussed. The design of a solar volumetric thermochemical reactor/receiver (TCRR) with catalytic absorber, method for synthesis of catalytically activated ceramics, and preparation of catalytic absorber have been described. The prototype TCRR was tested in the high flux solar furnace at the DAC, Cologne by using the dioxide reforming of methane. The tests were performed to check the main concept of the TCRR design and catalytic absorber, to study the influence of solar flux distribution, the reagent flows and their ratio on the productivity or conversion, determine the reagent's conversion depending on the focal point disposition with respect to the absorber, and to study the efficiency of the thermochemical conversion. The chemical and total efficiencies of the CO₂–methane conversion were calculated using the experimentally measured concentrations of the reaction products. The highest overall efficiency achieved in these experiments was 30% with the Ni–Cr catalytic absorber.     

Biomass and energy production of catch crops in areas with deficiency of precipitation during summer period in central Bohemia

The biomass production dynamics of catch crops, volunteers and weeds in dependence on precipitation and air temperature, was studied in central Bohemia from 2004 to 2006. The cover of individual components of the growth was monitored during the same period. Also measured were energy and efficiency of utilization of global radiation by catch crops and volunteers. The catch crops included the following species: Brassica napus, Lolium multiflorum, Lolium perenne, Phacelia tanacetifolia, Sinapis alba, Trifolium incarnatum, Raphanus sativus var. oleiformis and Trifolium subterraneum. The highest biomass production and the highest cover of catch crops were observed in treatments with S. alba (1382.0 kg ha⁻¹, 47.8%). The average biomass production (sum of catch crops, volunteers and weeds) was highest in treatments with S. alba, R. sativus, and P. tanacetifolia and lowest in treatments with B. napus, L. multiflorum and L. perenne. It was demonstrated that an increase in the percentage share of volunteers caused a decrease in the biomass production of catch crops. The average energy production ranged from 0.31 to 2.37 MJ m⁻² in treatments with catch crops, and from 0.25 to 0.89 MJ m⁻² in treatments with cereal volunteers. The highest effectivity of global radiation utilization, was determined in treatments with S. alba (0.11-0.47%). Based on regression analysis the closest dependence between biomass production from all treatments on the experimental site and precipitation was observed from 1st May till the time of sowing and the average air temperatures from the sowing period till the time of the last biomass production assessment.     

Steam gasification of energy crops of high cultivation potential in Poland to hydrogen-rich gas

In the paper energy crops of considerable cultivation potential in Poland, namely: Salix viminalis, Helianthus tuberosus, Sida hermaphrodita, Spartina pectinata, Andropogon gerardi and Miscanthus X giganteus were tested in terms of steam gasification reactivity of biomass chars, as well as yields and composition of product gas in steam gasification and lime-enhanced steam gasification in a laboratory scale fixed bed reactor at 650 °, 700 ° and 800 °C.The highest value of reactivity for 50% of carbon conversion, R₅₀, was observed for Sida hermaphrodita, regardless the process temperature.Application of CaO for in-situ CO₂ capture in steam gasification of biomass chars resulted in hydrogen content increase at 650 °C to the levels comparable with the ones reached at 800 °C without carbonation reaction. Also hydrogen and total gas yields increased in tests of lime-enhanced gasification.     

Synergistic roles of off-peak electrolysis and thermochemical production of hydrogen from nuclear energy in Canada

Hydrogen as a clean energy carrier is frequently identified as a major solution to the environmental problem of greenhouse gases, resulting from worldwide dependence on fossil fuels. However, most of the world's hydrogen (about 96%) is currently produced from fossil fuels, which does not address the issue of greenhouse gases. Although there is a large motivation of the “hydrogen economy”, for improvement of urban air quality, energy security, and integration of intermittent renewable energy sources, CO₂ free energy sources are critical to hydrogen becoming a significant energy carrier. Two technologies, applied in tandem, have a promising potential to generate hydrogen without leading to greenhouse gas emissions: 1) electrolysis and 2) thermochemical decomposition of water. This paper will investigate their unique complementary roles to reduce costs of hydrogen production. Together they have a unique potential to serve both de-centralized hydrogen needs in periods of low-demand electricity, and centralized base-load production from a nuclear station. Thermochemical methods have a significantly higher thermal efficiency, but electrolysis can take advantage of low electricity prices during off-peak hours, as well as intermittent and de-centralized supplies like wind, solar or tidal power. By effectively linking these systems, water-based production of hydrogen can become more competitive against the predominant existing technology, SMR (steam-methane reforming).