Coproduction of district heat and electricity or biomotor fuels

The operation of a district heating system depends on the heat load demand, which varies throughout the year. In this paper, we analyze the coproduction of district heat and electricity or biomotor fuels. We demonstrate how three different taxation scenarios and two crude oil price levels influence the selection of production units to minimize the district heat production cost and calculate the resulting primary energy use. Our analysis is based on the annual measured heat load of a district heating system. The minimum-cost district heat production system comprises different production units that meet the district heat demand and simultaneously minimize the district heat production cost. First, we optimize the cost of a district heat production system based on the cogeneration of electricity and heat with and without biomass integrated gasification combined-cycle technology. We considered cogenerated electricity as a byproduct with the value of that produced by a condensing power plant. Next, we integrate and optimize different biomotor fuel production units into the district heat production system by considering biomotor fuels as byproducts that can substitute for fossil motor fuels. We demonstrate that in district heating systems, the strengthening of environmental taxation reduces the dependence on fossil fuels. However, increases in environmental taxation and the crude oil price do not necessarily influence the production cost of district heat as long as biomass price is not driven by policy measures. Biomotor fuel production in a district heating system is typically not cost-efficient. The biomotor fuels produced from the district heating system have to compete with those from standalone biomotor fuel plants and also with its fossil-based counterparts. This is also true for high oil prices. A carbon tax on fossil CO₂ emissions based on social cost damage will increase the competitiveness of biomass-based combined heat and power plants, especially for BIGCC technology with its high electricity-to-heat ratio.     

The introduction and expansion of biomass use in Swedish district heating systems

District heating satisfies about 60% of the heat demand in Swedish buildings. Today, more than two thirds of the heat supply to the district heating systems is based on biomass and waste, and biomass alone accounts for about half of the heat supply. The purpose of this paper is to present the Swedish experiences of introducing and expanding the use of biomass in the district heating systems and to identify the main drivers behind this development. Our five research questions and the corresponding conclusions consider the driving forces from energy policy tools and local initiatives, the biomass prices, the established infrastructures in forestry and district heating, the technology paths for biomass conversion, and finally the future challenge of competing uses of biomass.     

Hydrogen production from biomass coupled with carbon dioxide capture: The implications of thermodynamic equilibrium

In this work we report on the consequences of thermodynamic equilibrium for hydrogen (_H2)$({\mathrm{H}}_2)$ generation via steam gasification of biomass, coupled with in situ carbon dioxide (_CO2)$({\mathrm{CO}}_2)$ capture. Calcium oxide (CaO) is identified as a suitable sorbent for CO₂ capture, capable of absorbing CO₂ to very low concentrations, at temperatures and pressures conducive to the gasification of biomass. The proposed process exploits the reversible nature of the CO₂ capture reaction and leads to the production of a concentrated stream of CO₂, upon regeneration of the sorbent. We develop a thermodynamic equilibrium model to investigate fundamental reaction parameters influencing the output of H₂-rich gas. These are: (i) reaction temperature, (ii) reaction pressure, (iii) steam-to-biomass ratio, and (iv) sorbent-to-biomass ratio. Based on the model, we predict a maximum H₂ concentration of 83%-mol, with a steam-to-biomass ratio of 1.5 and a Ca-to-C ratio of 0.9. Contrary to previous experimental studies, this maximum H₂ output is reported at atmospheric pressure. Model predictions are compared with an experimental investigation of the pyrolysis of pure cellulose and the reactivity of CaO through multiple CO₂ capture and release cycles using a thermogravimetric analyser, coupled with a mass spectrometer (TGA–MS). On this basis, we demonstrate the applicability of thermodynamic equilibrium theory for the identification of optimal operating conditions for maximising H₂ output and CO₂ capture.     

Engineering economic analysis of biomass IGCC with carbon capture and storage

Integration of biomass energy technologies with carbon capture and sequestration could yield useful energy products and negative net atmospheric carbon emissions. We survey the methods of integrating biomass technologies with carbon dioxide capture, and model an IGCC electric power system in detail. Our engineering process model, based on analysis and operational results of the Battelle/Future Energy Resources Corporation gasifier technology, integrates gasification, syngas conditioning, and carbon capture with a combined cycle gas turbine to generate electricity with negative net carbon emissions. Our baseline system has a net generation of 123 MW_e, 28% thermal efficiency, 44% carbon capture efficiency, and specific capital cost of 1,730 $ kW_e⁻¹. Economic analysis suggests this technology could be roughly cost competitive with more conventional methods of achieving deep reductions in CO₂ emissions from electric power. The potential to generate negative emissions could provide cost-effective emissions offsets for sources where direct mitigation is expected to be difficult, and will be increasingly important as mitigation targets become more stringent.     

A study of energy production from cork residues: Sawdust,sandpaper dust and triturated wood

In the present work the gasification process of cork residues sourced in an industrial procedure in the regions of Extremadura (Spain) and Alentejo (Portugal) was studied. These by-products were classified as black agglomerates (low and high granulate), sandpaper dust (white agglomerate) and triturated wood. Samples of several residues obtained through different phases of the cork manufacturing process were collected and next quantified. In order to test their ability to produce energy, all the referred residues were gasified. The air flow was varied, ranging from 50 up to 400 cm³ min⁻¹. The thermal treatment temperature was also varied from 650 °C up to 800 °C. The experimental results indicate that the optimal conditions in terms of energy production were an air flow equal to 200 cm³ min⁻¹ and a treatment temperature of 800 °C.     

Integrated biomass energy systems and emissions of carbon dioxide

Electric Power Research Institute (EPRI) and the US Department of Energy (DOE) have been funding a number of case studies under the initiative entitled “Economic Development through Biomass Systems Integration”, with the objective of investigate the feasibility of integrated biomass energy systems, utilizing a dedicated feedstock supply system (DFSS) for energy production. This paper deals with the full fuel cycle for four of these case studies, which have been examined with regard to the emissions of carbon dioxide, CO₂. Although the conversion of biomass to electricity in itself does not emit more CO₂ than is captured by the biomass through photosynthesis, there will be some CO₂ emissions from the DFSS. External energy is required for the production and transportation of the biomass feedstock, and this energy is mainly based on fossil fuels. By using this input energy, CO₂ and other greenhouse gases are emitted. However, by utilizing biomass with fossil fuels as external input fuels, we would get about 10–15 times more electric energy per unit fossil fuel, compared with a 100% coal power system. By introducing a DFSS on former farmland the amount of energy spent for production of crops can be reduced, the amount of fertilizers can be decreased, the soil can be improved and a significant amount of energy will be produced compared with an ordinary farm crop. Compared with traditional coal-based electricity production, the CO₂ emissions are in most cases reduced significantly by as much as 95%. The important conclusion is the great potential for reducing greenhouse gas emissions through the offset of coal by biomass.     

Bubbling fluidized bed biomass gasification—Performance, process findings and energy analysis

Bubbling fluidized bed gasifiers (BFG) has potential for rural electrification projects especially in third world countries where biomass supplies are abundant from agricultural, wood industries and where electricity supply from the grid is not available. In this paper the performance of a BFG was observed in terms of its thermal output. Gas chromatography (GC) was used to check the gas composition. The size of the wood chips was irregular but mostly falls in the range of 30 mm in both length and width, with the thickness at an average of 3.0 mm. It showed that the gas produced had an energy content of 4.74 MJ/m³ at a bed temperature of 733 °C, with the equivalence ratio at 0.23. The resulting thermal efficiency was 61.32% with a thermal output of 355.55 kW_th. For village electrification projects, this thermal output is able to supply 100 kW_e through a diesel generator, enough for electricity consumption in 100 households. An energy balance of the system was done to determine its work potential. It was found that the heat loss was 29.64%. A Shankey diagram of the energy distribution of the BFG system shows that the rest of the thermal output is not utilized and exits the system in the form of char and tarry liquids. Condensates were collected for high-performance liquid chromatograph (HPLC) analysis. It was found that phenol was high when the bed temperature was 450 °C, which makes the outlet condensate very soluble in water and can cause water contamination.     

Charcoal from biomass residues of a Cryptomeria plantation and analysis of its carbon fixation benefit in Taiwan

Charcoal production as an age-old industry not only supplies fuel in developing countries, in recent decades, it has also become a means of supplying new multifunctional materials for environmental improvement and agricultural applications in developed countries. These include air dehumidification and deodorization, water purification, and soil improvement due to charcoal's excellent adsorption capacity. Paradoxically, charcoal production might also help curb greenhouse gas emissions. In this study, we made charcoal from discarded branches and tops of wood from a Cryptomeria plantation after thinning using a still-operational earthen kiln. Woody biomass was used as the carbonization fuel. The effect of carbonization on carbon fixation was calculated and its benefits evaluated. The results showed that the recovered fixed carbon reached 33.2%, i.e., one-third of the biomass residual carbon was conserved as charcoal which if left on the forest ground would decompose and turn into carbon dioxide, and based on a net profit of US$1.13 kg⁻¹ for charcoal, an annual net profit of US$14,665 could be realized. Charcoaling thus appears to be a feasible alternative to promote reutilization of woody resides which would not only reduce greenhouse gas emissions, but also provide potential benefits to regional economies in developing countries.     

Investigation of biomass gasification hydrogen and electricity co-production with carbon dioxide capture and storage

Biomass is one of the renewable energy resources which can be used instead of fossil fuels to diminish environment pollution and emission of greenhouse gases. Hydrogen as a biomass is considered as an alternative fuel which can be derived from a variety of domestically available primary sources. In this paper, a hydrogen and electricity co-generation plant with rice husk is proposed. Rice husk with water vapor and oxygen produces syngas in gasifier. In this design, electricity is generated by using two Rankine cycles. The Results show that the net electric efficiency and hydrogen production efficiency are 1.5% and 40.0%, respectively. Hydrogen production is 1.316 kg/s in case which carbon dioxide is gathered and stored. The electricity generation is 5.923 MW_e. The main propose of implementing Rankine cycle is to eliminate hydrogen combustion for generating electricity and to reduce NO_x production. Furthermore, three kinds of membranes are studied in this paper.     

Main routes for the thermo-conversion of biomass into fuels and chemicals. Part 2: Gasification systems

Gasification as a thermo-chemical process is defined and limited to combustion and pyrolysis. The gasification of biomass is a thermal treatment, which results in a high production of gaseous products and small quantities of char and ash. The solid phase usually presents a carbon content higher than 76%, which makes it possible to use it directly for industrial purposes. The gaseous products can be burned to generate heat or electricity, or they can potentially be used in the synthesis of liquid transportation fuels, H₂, or chemicals. On the other hand, the liquid phase can be used as fuel in boilers, gas turbines or diesel engines, both for heat or electric power generation. However, the main purpose of biomass gasification is the production of low- or medium heating value gas which can be used as fuel gas in an internal combustion engine for power production. In addition to limiting applications and often compounding environmental problems, these technologies are an inefficient source of usable energy.     

Performance optimization and analysis of solar combi-system with carbon dioxide heat pump

In this paper, a solar combi-system which consists of solar collectors and a carbon dioxide heat pump is proposed and investigated through simulation and optimization. Performance analysis and comparison are primarily conducted to show the feasibility and reasonability of using a CO₂ heat pump as an auxiliary heater under local weather conditions. Then, a system model with a test building in TRNSYS is developed for performance optimization. The most influential variables are identified using influence and sensitivity analyzes of single parameters. Subsequently, a multi-parameter optimization using the high-weight parameters is carried out to obtain a final design result. The simulated results of the optimized case show that the average coefficient of performance of the CO₂ heat pump is 2.38, and the solar fraction of the system is 69.0% for the entire heating season. The time when a comfortable temperature level can be achieved in the indoor environment accounts for 81.6% of the entire heating season. Furthermore, the performance characteristics of the proposed system are evaluated in terms of the thermal balance, fraction of the thermal energy saving, feasibility of net zero energy, economic factor, and CO₂ emissions reduction.     

The interaction of biomass gasification syngas components with tar in a solid oxide fuel cell and operational conditions to mitigate carbon deposition on nickel-gadolinium doped ceria anodes

The combination of biomass gasification with solid oxide fuel cells (SOFCs) is gaining increasing interest as an efficient and environmentally benign method of producing electricity and heat. However, tars in the gas stream arising from the gasification of biomass material can deposit carbon on the SOFC anode, having detrimental effects to the life cycle and operational characteristics of the fuel cell. This work examines the impact of biomass gasification syngas components combined with benzene as a model tar, on carbon formation on Ni/CGO (gadolinium-doped ceria) SOFC anodes. Thermodynamic calculations suggest that SOFCs operating at temperatures > 750 °C are not susceptible to carbon deposition from a typical biomass gasification syngas containing 15 g m⁻³ benzene.However, intermediate temperature SOFCs operating at temperatures < 650 °C require threshold current densities well above what is technologically achievable to inhibit the effects of carbon deposition. SOFC anodes have been shown to withstand tar levels of 2-15 g m⁻³ benzene at 765 °C for 3 h at a current density of 300 mA cm⁻², with negligible impact on the electrochemical performance of the anode. Furthermore, no carbon could be detected on the anode at this current density when benzene levels were <5 g m⁻³.     

Life cycle assessment of fuels for district heating: A comparison of waste incineration,biomass- and natural gas combustion

The aim of this consequential life cycle assessment (LCA) is to compare district heating based on waste incineration with combustion of biomass or natural gas. The study comprises two options for energy recovery (combined heat and power (CHP) or heat only), two alternatives for external, marginal electricity generation (fossil lean or intense), and two alternatives for the alternative waste management (landfill disposal or material recovery). A secondary objective was to test a combination of dynamic energy system modelling and LCA by combining the concept of complex marginal electricity production in a static, environmental systems analysis. Furthermore, we wanted to increase the methodological knowledge about how waste can be environmentally compared to other fuels in district-heat production. The results indicate that combustion of biofuel in a CHP is environmentally favourable and robust with respect to the avoided type of electricity and waste management. Waste incineration is often (but not always) the preferable choice when incineration substitutes landfill disposal of waste. It is however, never the best choice (and often the worst) when incineration substitutes recycling. A natural gas fired CHP is an alternative of interest if marginal electricity has a high fossil content. However, if the marginal electricity is mainly based on non-fossil sources, natural gas is in general worse than biofuels.     

Premium quality fuels and chemicals from the fluidised bed pyrolysis of biomass with zeolite catalyst upgrading

Biomass in the form of pine wood was pyrolysed in an externally heated fluidised bed pyrolysis reactor with nitrogen as the fluidising gas. A section of the freeboard of the reactor was packed with zeolite ZSM-5 catalyst. The pyrolysis oils before and after catalysis were collected in a series of condensers and cold traps. In addition, gases were analysed off-line by packed column gas chromatography. The composition of the oils and gases were determined before and after catalysis in relation to process conditions. The oils were analysed by liquid chromatography followed by gas chromatography/mass spectrometry. The results showed that the oils before catalysis were highly oxygenated, after catalysis the oils were markedly reduced in oxygenated species with an increase in aromatic species, producing a premium grade gasoline type fuel. The gases were CO₂, CO, H₂, CH₄, C₂H₄ and C₃H₆ and minor concentrations of other hydrocarbon gases. After catalysis the concentration of CO₂ and CO were increased. Detailed analysis of the upgraded oils showed that there were high concentrations of economically valuable chemicals. However, biologically active polycyclic aromatic species were also present in the catalysed oil, which increased with increasing catalyst temperature.     

Exergetic analysis of solid oxide fuel cell and biomass gasification integration with heat pipes

This paper presents an exergetic analysis of a combined heat and power (CHP) system, integrating a near-atmospheric solid oxide fuel cell (SOFC) with an allothermal biomass fluidised bed steam gasification process. The gasification heat requirement is supplied to the fluidised bed from the SOFC stack through high-temperature sodium heat pipes. The CHP system was modelled in AspenPlus™ software including sub-models for the gasification, SOFC, gas cleaning and heat pipes. For an average current density of 3000 A m⁻² the proposed system would consume 90 kg h⁻¹ biomass producing 170 kW_e net power with a system exergetic efficiency of 36%, out of which 34% are electrical.     

Biohydrogen production from forest and agricultural residues for upgrading of bitumen from oil sands

In this study, forest residues (limbs, tops, and branches) and straw (from wheat and barley) are considered for producing biohydrogen in Western Canada for upgrading of bitumen from oil sands. Two types of gasifiers, namely, the Battelle Columbus Laboratory (BCL) gasifier and the Gas Technology Institute (GTI) gasifier are considered for biohydrogen production. Production costs of biohydrogen from forest and agricultural residues from a BCL gasification plant with a capacity of 2000 dry tonnes/day are $1.17 and $1.29/kg of H₂, respectively. For large-scale biohydrogen plant, GTI gasification is the optimum technology. The delivered-biohydrogen costs are $2.19 and $2.31/kg of H₂ at a plant capacity of 2000 dry tonnes/day from forest and agricultural residues, respectively. Optimum capacity for biohydrogen plant is 3000 dry tonnes/day for both residues in a BCL gasifier. In a GTI gasifier, although the theoretical optimum sizes are higher than 3000 dry tonnes/day for both feedstocks, the cost of production of biohydrogen is flat above a plant size of 3000 dry tonnes/day. Hence, a plant at the size of 3000 dry tonnes/day could be built to minimize risk. Carbon credits of $119 and $124/tonne of CO₂ equivalent are required for biohydrogen from forest and agricultural residues, respectively.     

Production of synthetic gasoline and diesel fuel by alternative processes using natural gas and coal: Process simulation and optimization

The problem of producing synthetic liquid fuels by alternative routes is addressed. Industrial processes known as gas to liquid (GTL) and coal to liquid (CTL) are considered and compared to a hybrid process presently developed, which combines features of both GTL and CTL.     

Convective cooling of supercritical carbon dioxide inside tubes: heat transfer analysis through neural networks

In a previous work, convective heating of carbon dioxide was studied with neural networks (NN), obtaining a totally heuristical heat transfer equation from the direct regression of experimental data. In the present work, the analysis focuses on the cooling process, which has a technical relevance in various applications, as for example in transcritical refrigeration cycles. Heat transfer around the critical zone presents a marked enhancement, that follows the peaks in thermophysical properties like thermal conductivity and heat capacity. Similarly, other properties like density and enthalpy, present a strong variation in narrow temperature intervals around the critical point.This constitutes then a highly non-linear phenomenon, for which it is advisable to use a very flexible function approximator like the NNs. NN models were applied both in terms of dimensionless numbers and of physical quantities, obtaining the two corresponding NN architectures. The choice of the optimal number of neurons in the NN hidden layer is discussed. The NN models are then compared with a recent correlation from literature, for which the validation results present an AAD of 27% and a bias of −26% with an evident prediction shifting. On the other hand the NN models in terms of dimensionless numbers and of physical quantities have AAD and bias of 14% and −4%, and of 7% and −2%, respectively, showing a largely better performance.     

The use of biomass syngas in IC engines and CCGT plants: A comparative analysis

This paper studies the use of biomass syngas, obtained from pyrolysis or gasification, in traditional energy-production systems, specifically internal combustion (IC) engines and combined cycle gas turbine (CCGT) plants. The biomass conversion stage has been simulated by means of a gas–solid thermodynamic model. The IC and CCGT plant configurations were optimised to maximise heat and power production. Several types of biomass feedstock were studied to assess their potential for energy production and their effect on the environment. This system was also compared with the coupling between biomass gasification and fuel cells.     

Gasification of woody biomass under high heating rate conditions in pure CO2: Experiments and modelling

The present paper focuses on the gasification of thin wood particles in pure CO₂ at 850 °C under high heating rate conditions (similar to fluidized bed gasifiers). The aim is to assess the potential use of CO₂ as gasifying medium and to learn more about its effects on the pyrolysis as well as on the char gasification stages. Experimental and numerical modelling results provide answers on the unfolding of the whole CO₂ biomass pyro-gasification process. It was found that despite the CO₂ is present inside the particle during the pyrolysis stage, it has no noticeable impacts neither on the reaction rate nor on the char yield due to the relatively low temperature inside the particle. The CO₂ char gasification is the rate limiting step of the global pyro-gasification reaction as its duration is near to 95% of the entire biomass conversion time.