Biomass Co-firing Research Articles

A Multi-Objective Optimization Model for the Design of Biomass Co-Firing Networks Integrating Feedstock Quality Considerations

The growth in energy demand, coupled with declining fossil fuel resources and the onset of climate change, has resulted in increased interest in renewable energy, particularly from biomass. Co-firing, which is the joint use of coal and biomass to generate electricity, is seen to be a practical immediate solution for reducing coal use and the associated emissions. However, biomass is difficult to manage because of its seasonal availability and variable quality. This study proposes a biomass co-firing supply chain optimization model that simultaneously minimizes costs and environmental emissions through goal programming. The economic costs considered include retrofitting investment costs, together with fuel, transport, and processing costs, while environmental emissions may come from transport, treatment, and combustion activities. This model incorporates the consideration of feedstock quality and its impact on storage, transportation, and pre-treatment requirements, as well as conversion yield and equipment efficiency. These considerations are shown to be important drivers of network decisions, emphasizing the importance of managing biomass and coal blend ratios to ensure that acceptable fuel properties are obtained.

Deposition prediction in a pilot scale pulverized fuel-fired combustor

Fossil fuels have traditionally been used in power generation systems and represent the main source of greenhouse gas emissions from this sector. Renewable fuels, especially biomass, are now being substituted for fossil fuels to reduce CO2 emissions. Co-firing biomass with coal, which has been widely practised in the UK and Europe, is one route to reduce the environmental impact of using coal. However, the deposition of ash particles and vapour species on heat exchanger surfaces during operation is a serious issue in pulverised coal and biomass fired power plant as this reduces the plant thermal efficiency and can cause fireside corrosion, which limits component lives. Deposit formation is difficult to predict as it varies with many factors including: boiler geometry, combustion conditions and fuel composition.Computational Fluid Dynamics (i.e. CFD) is one of the best modelling tools to study the flow behaviour of gases and particles around heat exchanger tubes and predict deposition. This work used an Eulerian-Lagrangian model to describe the gas flow field around tubes and the solid ash particle trajectories respectively. User Defined Functions (i.e. UDFs) were developed for the CFD package to enable the prediction of deposit growth, deposit shape and temperature gradients around superheater/reheater tubes. Deposit build up insulates such tubes from the flow of the hot combusted gas stream and reduces heat transfer between this gas stream and the steam coolant following within the tubes, thus raising the deposit temperature. The CFD-based predictions generated were consistent with available literature data.The CFD deposition model has been applied to predict deposition on air cooled ceramic probes in a 100 kWth pilot-scale, pulverized fuel (PF) combustor and compared to deposition data measured after the combustor rig runs. For modelling purposes, the geometry was simplified to a two-dimensional domain with inert spherical ash particles dispersed in air and injected at an inlet plane. Experimental data from a series of rig runs have been used to test this CFD deposition modelling approach.

Reduction of GHG emissions by utilizing biomass co-firing in a swirl-stabilized furnace

This study presents the numerical investigation of co-firing behaviour of pulverized straw particles with coal in air and O2/CO2 mixtures. Validation is conducted in a semi-technical once-through 30 kW swirl-stabilized furnace. Reference air-fuel (21% O2) and oxy-fuel (30% O2) cases were considered for four different coal/straw ratios (100% coal, 20% straw, 50% straw and 100% straw). AVL Fire is used as a CFD modelling tool. A comprehensive grid independency test was conducted considering three different grid sizes. Ignition performance, emission characteristics, heating profile, residence time were evaluated for different fuel ratios under air and oxy-fuel conditions. This work has shown that no significant changes occur to the fundamental combustion characteristics for straw compared to coal when burned in the O2/CO2 atmosphere to air firing case. It was found that with 20% straw sharing, sensible performances were observed similar to that of 100% coal combustion. Also a critical analytical analysis was conducted to investigate the heating performance for straw particle of different sizes (100 μm, 330 μm and 1000 μm). The heating profiles show significant differences between the three particle sizes assuming isothermal temperature gradient and heating by both radiation and convection. It is seen that the variation of the level of SO2 is not significant between air and oxy-firing cases. However, slightly less amount of SO2 is predicted in oxy-firing case. The reduction in NO is due to the effects of higher NO levels in the flue gas promoting gas-phase reduction, significantly higher levels of CO in the flame zone and the usage of a high-NOx burner in combination. The heating profiles for different size of straw particle suggest that there is a definite influence on the overall performance of the furnace. Larger particle do not ignite properly due to lower residence time leading to lower burnout. The possibility of burnout of the larger straw particle size is less due to less residence time in air-firing compared to oxy-firing case.

Representing the costs of low-carbon power generation in multi-region multi-sector energy-economic models

Multi-region multi-sector energy-economic models are often used to analyze long-term scenarios of energy development, however, these models usually rely on a simplified representation of technological details in power generation. To strengthen this representation, we develop a method for modeling the economic competition between different advanced technologies in multi-region multi-sector dynamic energy-economic models based on a markup approach, which represents the measure of the cost of a technology relative to the price received for electricity generation. The markup includes capital costs, fixed and variable operating and maintenance (O&M) costs, fuel costs, and transmission and distribution (T&D) costs. For intermittent technologies, it also includes a backup requirement to make these technologies effectively dispatchable. For carbon capture and storage (CCS) technologies, it also includes the costs of CO2 capture, transportation and storage. We provide a standardized markup calculation for generation technologies for different regions of the world, including USA, China, India, EU, Japan and others. Then we analyze the sensitivity of the calculation to critical inputs, including capital costs, fuel costs, carbon prices and capacity factors. We provide a detailed calculation of the relative costs of the following technologies: new pulverized coal, new pulverized coal with CCS, natural gas combined cycle, natural gas with CCS, biomass-fueled plant, biomass with CCS, advanced nuclear, wind (for small and medium penetration levels), solar, wind with backup (for large penetration levels), co-firing of coal and biomass combined with CCS, and advanced CCS on natural gas. For illustration, we incorporate the markups into the MIT Economic Projection and Policy Analysis (EPPA) model, a global multi-sector multi-sector dynamic energy-economic model with a detailed representation of power generation technologies, and run several scenarios. Our analysis and results provide insight on the deployment of different low-carbon power generation technologies depending on assumptions about carbon policy stringency.

Numerical and Experimental Study on Oxy-fuel Coal and Biomass Co-firing in a Bubbling Fluidized Bed

As one of the most promising approaches to reduce CO2 emissions from power plants, oxy-fuel fluidized bed combustion technology still has a lot of basic uncertainties requiring in-depth studies, especially in application for coal and biomass co-firing. This work focuses on results of coal co-firing with biomass under O2/CO2 combustion conditions in a 6 kWth bubbling fluidized bed combustor. With the same thermal input maintained, computational fluid dynamics (CFD) was adopted as a predictive tool to examine the effects of firing coal and co-firing biomass with coal under O2/CO2 atmospheres. Hydrodynamics, heat transfer, species concentration, and char gasification in a fluidized bed were investigated. In comparison to coal combustion, the hydrodynamic and temperature profiles of biomass co-firing are not affected much when maintaining the same thermal input. The temperature of biomass co-firing at the bottom of the dense-phase zone, which is mainly the char combustion area, is about 10 K lower than that o...

Biomass constituents’ interactions with coal during co-firing

The importance of biomass in the emerging low carbon economy remains quite crucial especially relating to the co-firing of coal and biomass due to the improvements in thermal properties and its influence on reactivity, burnout and flame stability. In this research, the combustion profile of coal and biomass blends, coal and low temperature biomass ash blends and coal and demineralized biomass blends were studied using thermogravimetric analysis. The results established the presence of both mechanism of synergy in the fuel blends during co-firing. This was substantiated by significant decrease in peak, burnout temperature as well as reduction in activation energy, demonstrating non-additive interaction between the biomass and coal sample. Further deductions reveal a degree of overlap in the function of catalytic and non-catalytic synergy mechanisms in the biomass blends due to competitive reactions among the catalyzing AAEMs and the hydrogen contributing organic constituents of biomass with coal. Finally, this study further establishes a higher degree of catalytic synergy in potassium rich oat straw in comparison to calcium rich gumwood.

Alloy degradation in a co-firing biomass CFB vortex finder application at 880 °C

Mechanisms of alloy degradation in a fireside N-S-O-C-H-Cl-Na-K atmosphere at 880 °C were elucidated using SEM-EDS, chemical equilibrium calculations, and XRD. Alloys 310S, 800H/HT, and 600 were studied after 0, 8000, and 16,000 h exposure in a boiler co-firing biomass waste. For 310S and 800H/HT it was shown that nitrogen formed internal Cr nitrides lowering the Cr activity and inhibiting internal alloy Cr permeation, and that NaCl and Na2SO4 reacted with Cr oxide to form chromate and to accelerate the S and the Cl pickup. Alloy 600 showed no nitride or major chromate formation.

Reducing emissions of the fast growing Vietnamese coal sector: The chances offered by biomass co-firing

Vietnam's Power Development Plan 7A authorized many new coal power plants projects, implying an increase of greenhouse gases emissions from 90 MtCO2eq/year today to 360 MtCO2eq/year in 2030. How could co-firing technology –that is the partial substitution of coal by biomass– contributes to mitigate that problem? In this study, we assess the costs and potentials of co-firing rice residues in present and planned coal power plants in Vietnam using a spatially explicit optimization model: BeWhere, adapted as recursive annual dynamic. We found that, the cost of CO2 emissions is the key parameter determining at what level the technology is used. A cost of CO2 emissions of 8 $/tCO2 mobilizes the maximum technical potential of the rice straw and husk domestic resource, with an annual emission reduction of 28 MtCO2eq/year by 2030. At this level, biomass co-firing contributes to an 8% emission reduction in the coal power sector with the abatement cost of 137 Million USD.

Danish Experiences in Biomass Corrosion and Recent Areas of Research

In Denmark, biomass has been implemented in the majority of power plants either by firing biomass alone or cofiring of biomass and fossil fuels/additives. This has resulted in an accumulation of ex...

Does hydrothermal carbonization as a biomass pretreatment reduce fuel segregation of coal-biomass blends during oxidation?

Co-firing of biomass and coal may increase short-term renewable fuel usage. However, the lower heating value and higher reactivity (at lower temperatures) of raw biomass can result in fuel segregation in boilers, causing burnout at lower temperatures, lower steam generation efficiency and fouling. In addition, the relatively high water content of some biomasses requires extensive drying prior to combustion. These issues may be addressed by hydrothermally carbonizing moist biomasses to produce hydrochars that more closely resemble coal’s properties prior to co-firing. In the present work, we probe the co-oxidation behavior of a series of hydrothermally carbonized biomass samples over a range of hydrochar-coal blend ratios to determine the degree of carbonization necessary to reduce fuel segregation. However, due to the presence of an extractable amorphous secondary char, even highly carbonized hydrochars have considerably higher oxidative reactivity than a representative bituminous coal sample. When blended, the hydrochars and coal display distinct derivative thermogravimetric oxidation ranges, in which a low-temperature peak is dominated by the secondary char oxidation, followed by a high-temperature char oxidation peak of the primary solid hydrochar. After extraction of the secondary char, the primary char displays a lower reactivity than the coal. As a co-fired fuel, it appears that blending hydrochars up to 10 wt% with a bituminous coal is possible as a partial fuel substitution. To increase the percentage of hydrochars blended with coal, it may be necessary to extract this secondary char (which contains valuable biofuels and platform chemicals) before blending.

Fouling in coal-fired boilers: Biomass co-firing, full conversion and use of additives – A thermodynamic approach

As coal-fired boilers in The Netherlands are considered to be converted to high biomass co-firing or pure biomass boilers, issues with fouling by alkali salts are expected. The behaviour of gaseous alkalis is different in converted coal boilers than in dedicated biomass boilers due to the higher firing temperature. In coal boilers, a glass phase can form that allows for alkali dissolution, preventing formation of alkali aerosols. This was investigated by both SEM on fly ashes from full-scale co-firing tests as well as thermodynamic modelling. Alkali dissolution decreases with increasing (CaO + MgO) to SiO2 ratio in the glass which, in its turn, increases with biomass co-firing ratio. Addition of 1–10 g/MJ coal fly ash can mitigate fouling with firing only wood, MBM-mix or sheanut-mix. Formation of molten alkali salts depends on both the S to Cl ratio and the K to Na ratio: in equilibrium, a molten salt forms with S:Cl ≤ 1.2 if K:Na > 10, with S:Cl ≤ 2.1 if 2.4 < K:Na < 4.7 and with S:Cl ≤ 3.5 if K:Na = 1. The S:Cl ratio decreases with increasing biomass co-firing ratio. Addition of 1 g/MJ ammonium sulphate can fully mitigate fouling with firing sheanut-mix that contains relatively little Na, and can lower fouling with firing wood up to a flue gas temperature of 700 °C; however, it will increase fouling with wood above 700 °C. Fouling with firing MBM-mix does not change with adding ammonium sulphate since it is already a sulphur-rich fuel mix.

The optimal biopower capacity in co-firing plants– An empirical analysis

Biomass fuels carry appealing features in replacing traditional fossil fuels, especially coal, in power generation. Due to the bulk, sparse and low-energy density drawbacks of biomass, many studies implicitly indicate small and limited scale in biopower generation. This study contributes to the bioenergy literature by explicitly studying the optimal biopower capacity of biopower co-firing technology in coal-fired power plants, which has practical implications for potential biopower practitioners, investors, and policymakers.This study indicates that the optimal biopower capacity of biomass co-firing in coal-powered plants is intermediate (i.e.,12MW on average) in order to take advantage of economies of scale without incurring high transportation cost. Regional variations are also found in the aspects of production cost and optimal capacity due to local characteristics. Local biomass availability plays a critical role in shaping biopower's generation cost, optimal capacity and cost changing patterns.

Simulation-Optimization Approach for the Logistics Network Design of Biomass Co-Firing with Coal at Power Plants

This work proposes a hybrid scheme that combines a simulation model and a mathematical programming model for designing logistic networks for co-firing biomass, specifically switchgrass, in conventional coal-fired power plants. The advantages of co-firing biomass include: (1) the creation of green jobs; (2) the efficient use of current power plant infrastructure; (3) fostering the penetration of renewable energy into power networks; and, (4) the reduction of greenhouse gas (GHG) emissions. The novelty of this work lies in the inclusion of (1) the inherent variability of biomass supply at the parcel level, and (2) the effects of climate change on future biomass supply when designing a feedstock logistic network. The design optimization is conducted at the farm/parcel level (most, if not all, previous works have used county level average data) and integrates the crop growth predictions employing United States Department of Agriculture’s (USDA’s) Agricultural Land Management with Numerical Assessment Criteria (ALMANAC) simulation model; the output of the simulations is input into the mixed integer linear programming (MILP) hub-and-spoke model to minimize the overall cost of the logistic network. Specifically, the MILP-based model selects the parcels and depot locations as well as biomass transportation flows by taking into consideration different types of soil, land cover characteristics, and predicted yields, which account for both historical and forecasted weather data. The hybrid methodology was tested by solving realistic situations, which considered varying weather conditions. The gross results indicate that the optimized logistic network enabled meeting a 20% biomass co-firing rate demand, which reduced 1,158,867 Mg per year in GHG emissions by co-firing with biomass.

Exergetic and exergoeconomic evaluation of co-firing biomass gas with natural gas in CCHP system integrated with ground source heat pump

The comprehensive utilization of renewable energy and clean fossil fuel contributes to improving the stability of energy supply system and reducing environmental impact. Therefore, a bio-gas and natural gas co-firing in combined cooling, heating and power (CCHP) system based on ground source heat pump is presented and modeled using exergetic and exergoeconomic methods. The exergy and exergy cost flows of CCHP system are presented under three different gas mass ratios and the influences of some key parameters (biomass and natural gas cost, interest rate, service life and operating time coefficient) on unit exergy cost of products are also analyzed. The results indicate that the introduction of natural gas improves the exergy efficiency; when the gas mass ratio varies from 0 to 1.0 the unit exergy cost of electricity generated by gas turbine, chilled water and hot water decrease from 11.26 $/GJ, 92.21 $/GJ and 69.92 $/GJ to 3.84 $/GJ, 43.52 $/GJ and 23.73 $/GJ, respectively. Furthermore, the sensitivity analysis shows that unit exergy cost of products increases with the increasing of biomass cost, natural gas cost and interest rate; while decreases non-linearly with the increasing of service life and operating time coefficient. The proposed CCHP system provides an idea for other hybrid renewable energy system, and exergoeconomic methodology shows a better understanding of complex energy system performance in terms of both exergy and economic aspects.

Analysis of particle behavior inside the classifier of a Raymond Bowl Mill while co-milling woody biomass with coal

Woody biomass cofiring with coal at existing pulverized-coal boilers is known to be a green energy source and is a low-expense alternative for pure coal combustion. Co-milling woody biomass particles (15 wt%) with coal particles (85 wt%) before burning at a boiler is a complex problem because large woody biomass particles (>300 μm) exit the milling system along with the fine particles. A Computational Particle Fluid Dynamics (CPFD) is used in this paper to present a novel analysis about the behavior of woody biomass particles as they are mixed with coal particles inside the classifier. To meet this objective, a model of SolidWorks of the milling system is defined using the Barracuda VR 17.1.0 software package. We made a C# programming code to analyze the post processing files of this simulation (base simulation); it showed that approximately none of the large particles of woody biomass nor any of the coal particles that exit along with fine particles swirl inside the classifier, and they exit the system in the product stream immediately after getting through the vanes. More importantly, only a few numbers of the exiting particles, regardless of their size, swirl inside the classifier. Manipulation of hardware can improve the classifier performance and leads to changes in the behavior of particles inside the classifier. However, changes in operating conditions cannot improve it significantly. Particle size distribution and the average flow rate of the product stream of the experiment and the base simulation match well.

Influence of lignocellulose and plant cell walls on biomass char morphology and combustion reactivity

The firing of biomass or co-firing of biomass with coal has become a common practice in power generation industry worldwide as a cost-effective means to move towards lower carbon footprint. However, the relationship between the properties of biomass and combustion behaviour is not well understood, yet. In this study, we investigated the links between biomass lignocellulosic composition and plant cell wall types, and how they would collectively influence char morphology and reactivity. Five different biomass, i.e. pinewood, distiller dried grains with solubles (DDGS), miscanthus, wheat straw and wheat shorts, in two size fractions were thermochemically pre-treated to alter their lignocellulosic compositions resulting in 50 different samples with varying compositions. Plant cell type and morphology of raw biomass particles were examined using SEM. Biomass char samples were prepared using a fast heating drop tube furnace (DTF) and a slow heating muffle furnace. The morphology of char particles was examined using an oil-immersion microscope whilst the intrinsic reactivity of chars was studied using a thermogravimetric analyser (TGA). Pre-treatments affected most biomass tested in similar trends but to varying degrees, particularly in terms of lignocellulosic composition, cell wall structure and char morphology. Results show that lignocellulosic composition (and plant cell wall types) of biomass correlated well with char morphology and char reactivity. Therefore, it is possible to predict aspects of combustion behaviour from biomass lignocellulosic composition for this selection of samples tested. This work provides a base study for establishing lignocellulosic composition as a key indicator in fuel selection.

Modelling national policy making to promote bioenergy in heat, transport and electricity to 2030 – Interactions, impacts and conflicts

Governments must increase bioenergy use to realise the Paris agreement ambition. Most countries have limited biomass resources and policy goals beyond carbon reduction. This can lead to policy incoherence. Previous studies tended to focus on one end-use sector or on optimising CO2 reduction. This study goes beyond optimisation approaches and investigates cross sector impacts of bioenergy policy proposals via simulation methods for policy proposals in Ireland. As an EU member with ambition for increased bioenergy use, Ireland is a useful case to examine trade-offs. Using the BioHEAT policy decision support tool (Durusut et al., 2018) we find policy in the heat and transport sector close the gap to Ireland's 2030 climate targets by 3%. Policy supporting co-firing of biomass with fossil-fuel to produce electricity increases emissions by 8.3 MtCO2 overall and reduces the policy impact on national climate targets by 63%. Co-firing uses more of the available biomass resources and this limits renewable uptake in the heat sector. Coal conversions and the use of advanced biofuels are found to rely on high availability of imports. Policy supporting biomass use in the power sector may make national climate targets less achievable for EU countries.

Simulation of Coal and Biomass Cofiring with Different Particle Density and Diameter in Bubbling Fluidized Bed under O2/CO2 Atmospheres

A 2D dynamic model for a bubbling fluidized bed (BFB) combustor has been developed for simulating the coal and biomass cofiring process under 21% O2/79% CO2 atmosphere in a 6 kWth bubbling fluidized bed, coupled with the Euler-Euler two-phase flow model. The kinetic theory of binary granular mixtures is employed for the solid phase in order to map the effect of particle size and density. The distribution of temperature, volume fraction, velocity, gas species concentration, and reaction rates are studied with numerical calculations. The simulated temperature distribution along the height of the combustor and outlet gas concentrations show good agreement with experimental data, validating the accuracy and reliability of the developed cofiring simulation model. As indicated in the results, there are two high temperature zones in the combustor, which separately exist at the fuel inlet and dilute phase. The reaction rates are related to the species concentration and temperature. The higher concentration and temperature lead to the larger reaction rates. It can be seen that all of the homogeneous reaction rates are larger at the fuel inlet region because of rich O2 and volatiles. High mass fraction of volatile gas is found at the fuel inlet, and the main reburning gas at the dilute phase is CH4. The mass fraction distribution of CO is related to the volume fraction of fuel which is due to the fact that the source of CO is not only from the devolatilization but also from the gasification. On the basis of this theoretical study, a better understanding of flow and combustion characteristics in biomass and coal cofiring under oxy-fuel atmospheres could be achieved.

Detailed in-furnace measurements in a pulverized coal-fired furnace with combined woody biomass co-firing and air staging

This paper presents a detailed experimental description of the combined effects of woody biomass co-firing and air staging on NO emissions and burnout performance in a pulverized coal-fired furnace. The co-combustion of woody biomass and bituminous coal was evaluated using woody biomass co-firing proportions of 0 % to 30 % with intervals of 10 %. Detailed in-furnace gas temperature and gas-phase concentration for species such as O2, CO2, CO and NO were measured for the co-firing flames, both with and without air staging. The overall temperature of the woody biomass co-firing flames was higher than that of the pure bituminous coal flame. This effect was more pronounced for air-staged combustion than for combustion without air staging. Co-firing woody biomass with air staging strongly affected NO reduction efficiency, whereas NO emissions were insignificant for no-staged firing. The deteriorating effect of air staging on burnout performance was a function of the woody biomass co-firing ratio. NO reduction efficiency for the air-staged flames was improved by more than 40 % in both flames for woody biomass co-firing proportions of 10 % and 20 %.

Influence of Biomass Co-combustion on Heating Surfaces Thermal Efficiency

Pulverized coal-fired (PCF) boilers were first and foremost intended to fire pulverized hard or brown coal. However, biomass co-firing has become a fairly common practice in the Polish power generation system and many existing boilers have been modernized to serve this purpose. This paper presents calculations of the coefficient of thermal efficiency of the boiler heating surfaces and of the time needed for complete reconstruction of deposits on the second-stage steam reheater (RHII) of an OP-380 boiler with the output of 380×103 kg/h. The boiler was equipped with a purpose-designed installation of direct feeding of biomass. The main co-fired fuels were wood and sunflower husk pellets. Intense formation of deposits on the steam reheater tubes and problems related to a reduction in the diameters of the tubes were identified during the power unit operation.