Biomass Firing Research Articles

Effect of Blending Ratio of Coal and Biomass on NOx Emission Regarding Co- Firing

Greenhouse gas emission had a huge effect on global warming as well as cause of acid rain. Regarding this study was made to investigate the effect of blending ratio on coal and biomass on NOx emission through co-firing. Different biomass was used to measure the considerable value of biomass with coal on NOx emission. Fluidized bed combustor was used at 3000C optimum temperature for co firing of coal and biomass. The maximum emission of NOx measured at tree leaves 40% and lignite coal 60% and minimum range of NOx at 80/20 ratio for coal and banana tree waste. This could be healthfully beneficial when utilizing biomass with coal.

Effect of Blending Ratio of Coal and Biomass on NOx Emission Regarding Co- Firing

Greenhouse gas emission had a huge effect on global warming as well as cause of acid rain. Regarding this study was made to investigate the effect of blending ratio on coal and biomass on NOx emission through co-firing. Different biomass was used to measure the considerable value of biomass with coal on NOx emission. Fluidized bed combustor was used at 3000C optimum temperature for co firing of coal and biomass. The maximum emission of NOx measured at tree leaves 40% and lignite coal 60% and minimum range of NOx at 80/20 ratio for coal and banana tree waste. This could be healthfully beneficial when utilizing biomass with coal.

Blend design tools for Medium Combustion Plants (MCP) firing biomass wastes

A feasible alternative for agricultural or forestry waste management is the operation of a distributed network of sustainable Medium Combustion Plants (MCPs). However, one of the main factors that hinder its development is the propensity to operational problems derived from corrosion, slagging and fouling characteristics of both bottom and fly ashes. Therefore, a cost-effective approach for these multi-product MCP could be based on predictive tools for an optimal formulation of a fuel blend. This work focuses on the assessment of the ability of these methods to provide guidance for preventing ash-related operational problems and to provide fuel-blending rules.The more widespread tools pertain to two types: compositional classification based on chemical analysis of laboratory ashes, and thermodynamic prediction of the most likely species and phases. Both criterion numbers and compositional maps are ranking methods based on the chemical analysis at a given ashing temperature. Thermodynamic equilibrium modeling is not constrained by any difference in the physical conditions of the MCP compared to those in the laboratory.Both kind of prediction tools have been validated in an MCP firing olive tree pruning residues as well as its typical blends in order to mimic a plausible pattern of fuels along a full year operating campaign. An intensive experimental campaign encompasses plant monitoring and off-line analysis of the ashes along the process line.Interpretation of compositional plots has revealed to be potentially sensitive to ashing temperature. Here are presented examples showing how this variable could lead to either insignificant differences or to a substantial disparity in the a priori fuel diagnosis.Some inconsistencies have been observed between the predictions based on criterion numbers, even for the same fuel and for ranking rules specifically formulated for biomasses. Moreover, it does not match consistently with the information obtained from phase diagrams. Therefore, their use should be limited to the case of a well-established selection of a fuel index for a well-defined fuel provided empirical evidence of an enough good description of the ash behavior, which is not the most frequent case.Thermodynamic equilibrium calculations allow a more precise prediction of the main species in the condensed phase, without the constraint of the ashing temperature. Elemental closure of main ash-forming elements with the chemical analysis of the process ashes presents small differences, and their proximity localization on the phase diagrams denote similar prediction between predicted and process ashes.

Operation and maintenance of a biomass fired – Organic Rankine Cycle – CHP plant: the experience of Cremona

Thanks to various feed-in-tariff programs, aimed to the development of electric energy production from renewable sources, several biomass firing power plants have been realized in Italy in the last few years, contributing to the reduction of greenhouse gas emissions and fossil fuel energy dependence.In particular, during 2012 there was a rush for the completion of several renewable energy conversion power plants, leading up to 986 new plants to get the first connection to the grid (+81,3% with respect to 2011); among those, 80 new plants were solid biomass firing plants (+47,1% with respect to 2011) [1].Linea Energia S.p.A., the Energy Business Unit of the multiutility company LGH, Linea Group Holding, which operates over the areas of Brescia, Cremona, Crema, Lodi and Pavia, gave its contribution in 2012 with the realization and start-up of two waste wood fueled energy conversion plants located in the Northern Italy, more exactly in Cremona and Rodengo Saiano (Brescia).This paper focuses on the operation and maintenance experience of the waste wood conversion power plant of Cremona, which is capable for a gross electric power production of up to 1.0 MW and a thermal power recovery of up to 5.5 MW. In the first part of this paper a description of the plant is presented, giving an insight of the engineered process.In the second part, the performance analysis of the energy conversion process is discussed by comparing actual performance of the system with the originally defined reference performance.In 2016, as a consequence of the operation of the unit in anomalous conditions (air entering in the system) the turbine blades got scaled. The output of the turbine progressively decreased but was then successfully re-established after an extraordinary maintenance carried out by the turbine supplier.

Influence of Preoxidation on High-Temperature Corrosion of a FeCrAl Alloy Under Conditions Relevant to Biomass Firing

Preoxidation of a commercial FeCrAl alloy (Kanthal APM) was evaluated as a surface modification approach to reduce alkali chloride-induced corrosion during biomass firing in power plants. Samples of the alloy preoxidized at 900 °C in O2 or O2 + 10 vol% H2O, and at 1100 °C in O2, were coated with KCl and exposed at 560 °C to a gas mixture comprising of 12 vol% CO2, 6 vol% O2, 3 vol% H2O, 400 ppmv HCl and 60 ppmv SO2. The oxide formed at 1100 °C showed no reactivity with the corrosive species. By contrast, all samples preoxidized at 900 °C suffered severe attack, resulting in formation of Fe-, Cr- and Al-containing corrosion products in a heterogeneous morphology, similar to non-preoxidized samples. The observed differences with respect to the degree of corrosion attack on the preoxidized samples are discussed in terms of the composition and thickness of the different types of Al2O3 layers obtained by the preoxidation treatment.

Pre-oxidation and its effect on reducing high-temperature corrosion of superheater tubes during biomass firing

Superheater tubes in biomass-fired power plants experience high corrosion rates due to condensation of corrosive alkali chloride-rich deposits. To explore the possibility of reducing the corrosion attack by the formation of an initial protective oxide layer, the corrosion resistance of pre-oxidised Al and Ti-containing alloys (Kanthal APM and Nimonic 80A, respectively) was investigated under laboratory conditions mimicking biomass firing. The alloys were pre-oxidised at 900°C for 1 week. Afterwards, pre-oxidised samples, and virgin non-pre-oxidised samples as reference, were coated with a synthetic deposit of KCl and exposed at 560°C for 1 week to a gas mixture typical of biomass firing. Results show that pre-oxidation could hinder the corrosion attack; however, the relative success was different for the two alloys. While corrosion attack was observed on the pre-oxidised Kanthal APM, the pre-oxidised Nimonic 80A remained unaffected suggesting protection of the alloy from the corrosive environment.

Cover Picture: Materials and Corrosion. 5/2017

Cover:Corrosion products after exposure of deposit‐free samples to an oxidizing‐chlorinating gas mixture. (a) Cross‐section and (b) plan‐view micrograph. (c) Cross‐section EDS maps showing elemental composition of the corrosion products. (d) Plan view EDS maps showing elemental distribution below a spalled region. Double‐headed arrows 1 and 2 indicate the different layers of corrosion product.More detailed information can be found in: S. C. Okoro, S. Kiamehr, M. Montgomery, F. J. Frandsen, K. Pantleon, Effect of flue gas composition on deposit induced high temperature corrosion under laboratory conditions mimicking biomass firing. Part I: Exposures in oxidizing and chlorinating atmospheres, Materials and Corrosion 2017, 68, page 499.

Estimating the fuel moisture content to control the reciprocating grate furnace firing wet woody biomass

In small countries like Lithuania with a widespread district heating system, 5–10MW moving grate biomass furnaces equipped with water boilers and condensing economisers are widely used. Such systems are designed for firing biomass fuels; however, varying fuel moisture, mostly in the range from 30% to 60%, complicates the automated operation. Without manual adjustment of the grate motion mode and other parameters, unstable operation or even extinction of the furnace is possible.To ensure stable furnace operation with moist fuel, the indirect method to estimate the fuel moisture content was developed based on the heat balance of the flue gas condensing economiser. The developed method was implemented into the automatic control unit of the furnace to estimate the moisture content in the feedstock and predictively adjust the furnace parameters for optimal fuel combustion.The indirect method based on the economiser heat balance was experimentally validated in a 6MW grate-fired furnace fuelled by biomass with moisture contents of 37, 46, 50, 54 and 60%.The analysis shows that the estimated and manually measured values of the fuel moisture content do not differ by more than 3%. This deviation indicates that the indirect fuel moisture calculation method is sufficiently precise and the calculated moisture content varies proportionally to changes in the thermal capacity of the economiser. By smoothing the data using sliding weighted averaging, the oscillations of the fuel moisture content were identified.

Influence of preoxidation on high temperature corrosion of a Ni-based alloy under conditions relevant to biomass firing

Development of corrosion resistant materials in biomass fired power plants demands specific attention since the condensation of deposits rich in KCl on heat exchanger surfaces induces severe corrosion attack, which is different from corrosion in traditional coal fired plants. Therefore, the ability of preoxidized layers formed on a commercial Cr-Ti-Al-containing Ni-based alloy (Nimonic 80A) to withstand biomass-induced corrosion was investigated. Preoxidation treatments at 900°C in O2 and O2+10vol% H2O, respectively, were conducted before samples were exposed to conditions that mimicked biomass firing. Complementary characterization methods were employed to study samples after preoxidation as well as after corrosion exposure. The oxides obtained by the preoxidation treatments protected the alloy during corrosion exposure at 560°C for a period of 168 h. In contrast, non-preoxidized samples suffered corrosion attack and formed porous non-protective oxides containing the alloying elements, Ni, Cr, Ti and Al. The influence of the preoxidation layers on the corrosion mechanism is discussed.

Mechanistic Model for Ash Deposit Formation in Biomass Suspension Firing. Part 2: Model Verification by Use of Full-Scale Tests

A model for deposit formation in suspension firing of biomass has been developed. The model describes deposit build-up by diffusion and subsequent condensation of vapors, thermoforesis of aerosols, convective diffusion of small particles, impaction of large particles and reaction. The model describes particle sticking or rebound by a combination of the description of (visco)elsatic particles impacting a solid surface and particle capture by a viscous surface. The model is used to predict deposit formation rates measured during tests conducted with probes in full-scale suspension-fired biomass boilers. The rates predicted by the model was reasonably able to follow the rates observed in the tests, although with some variation, primarily as overestimations of the deposit formation rates. It is considered that the captive properties of the deposit surface are overestimated. Further examination of some physical parameters related to the description of surface capture are suggested. Based on these examinations ...

Energetic and Exergetic Evaluation of Biomass Fired Water Heating System

This paper deals with thermal and exergy efficiencies of biomass fired water heating system. Water heating system is extensively suitable to generate hot water in rural areas. The developed water heating system was tested with Desi babul ( Acacia nilotica ) wood. Thermal and exergy efficiencies of the system were estimated at 54.5 percent and 6.79 percent, respectively. Citation: Panwar, N. L., and Paul, A. S. (2017). Energetic and Exergetic Evaluation of Biomass Fired Water Heating System. Trends in Renewable Energy, 3, 153-159. DOI: 10.17737/tre.2017.3.2.0043

Fly Ash Formation during Suspension Firing of Biomass: Effects of Residence Time and Fuel Type

The objective of this work was to generate comprehensive data on the formation of residual fly ash during the initial stages of suspension firing of biomass. Combustion experiments were carried out with pulverized biomass fuels (two straw fuels and two wood fuels), in an entrained flow reactor at 1200–1400 °C, simulating full-scale suspension firing of biomass. By the use of a movable, cooled, and quenched gas/particle sampling probe, samples were collected at different positions along the vertical axis in the reactor, corresponding to gas residence times ranging from 0.25 to 2.0 s. The collected particles were subjected to various analyses, including char burnout level, particle size distribution, elemental composition, and particle morphology and composition. Furthermore, the transient release, i.e., the vaporization of the flame-volatilized inorganic elements K, Cl, and S, from the burning fuel particles to the gas phase, has been quantified using two different calculation methods. The ash formation me...

Effect of flue gas composition on deposit induced high temperature corrosion under laboratory conditions mimicking biomass firing. Part II: Exposures in SO2 containing atmospheres

In biomass fired power plants, the fast corrosion of superheaters is facilitated by the presence of corrosive flue gas species, for example, SO2, which are released during combustion. To understand the role of the gas species on the corrosion process, comparative laboratory exposures of deposit (KCl)‐coated and deposit‐free austenitic stainless steel (TP 347H FG) samples to gas mixtures containing SO2 was carried out, under conditions relevant to biomass‐firing. Exposures were conducted isothermally at 560 °C for 72 h, in oxidizing‐sulphidizing, and oxidizing‐sulphidizing‐chlorinating gas mixtures containing 60 ppmv SO2. Scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS) and X‐ray diffraction (XRD) techniques were complimentarily applied to characterize the resulting corrosion products. A partially molten K2SO4‐layer formed on KCl coated specimens, and corrosion resulted in localized broad pits containing sulphides and oxides. The severe pitting attack was decreased by the presence of HCl in the gas mixture.

Effect of flue gas composition on deposit induced high temperature corrosion under laboratory conditions mimicking biomass firing. Part I: Exposures in oxidizing and chlorinating atmospheres

In biomass fired power plants, deposition of alkali chlorides on superheaters, as well as the presence of corrosive flue gas species, give rise to fast corrosion of superheaters. In order to understand the corrosion mechanism under this complex condition, the influence of the flue gas composition on high temperature corrosion of an austenitic superheater material under laboratory conditions mimicking biomass firing is investigated in this work. Exposures involving deposit (KCl)‐coated and deposit‐free austenitic stainless steel (TP 347H FG) samples were conducted isothermally at 560 °C for 72 h, under both oxidizing and oxidizing‐chlorinating atmospheres, and the resulting corrosion products were comprehensively studied with scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS), and X‐ray diffraction (XRD) techniques. The results show that deposit‐free samples suffer grain boundary attack only in an oxidizing‐chlorinating atmosphere, otherwise corrosion results in formation of a duplex oxide. Corrosion attack on deposit‐coated samples was higher than on deposit‐free samples irrespective of the gaseous atmosphere. Specifically, severe volatilization of alloying elements occurred on deposit‐coated samples under oxidizing‐chlorinating atmosphere due to enhanced impact of KCl and HCl.

Mechanistic Model for Ash Deposit Formation in Biomass Suspension Firing. Part 1: Model Verification by Use of Entrained Flow Reactor Experiments

Two models for deposit formation in suspension firing of biomass have been developed. Both models describe deposit buildup by diffusion and subsequent condensation of vapors, thermophoresis of aerosols, convective diffusion of small particles, impaction of large particles, and reaction. The models differ in the description of the sticking probability of impacted particles: model #1 employs a reference viscosity in the description of the sticking probability, while model #2 combines impaction of viscoelastic particles on a solid surface with particle capture by a viscous surface. Both models were used to describe the deposit formation rates and deposit chemistry observed in a series of entrained flow reactor (EFR) experiments using straw and wood as fuels. It was found that model #1 was not able to describe the observed influence of temperature on the deposit buildup rates, predicting a much stronger influence of this parameter. Model #2 was able to provide a reasonable description of the influence of temp...

Torrefied Biomass Pellets—Comparing Grindability in Different Laboratory Mills

The firing and co-firing of biomass in pulverized coal fired power plants around the world is expected to increase in the coming years. Torrefaction may prove to be a suitable way of upgrading biomass for such an application. For transport and storage purposes, the torrefied biomass will tend to be in pellet form. Whilst standard methods for the assessment of the milling characteristics of coal exist, this is not the case for torrefied materials—whether in pellet form or not. The grindability of the fuel directly impacts the overall efficiency of the combustion process and as such it is an important parameter. In the present study, the grindability of different torrefied biomass pellets was tested in three different laboratory mill types; cutting mill (CM), hammer mill (HM) and impact mill (IM). The specific grinding energy (SGE) required for a defined mass throughput of pellets in each mill was measured and results were compared to other pellet characterization methods (e.g., durability, and hardness) as well as the modified Hardgrove Index. Seven different torrefied biomass pellets including willow, pine, beech, poplar, spruce, forest residue and straw were used as feedstock. On average, the particle-size distribution width (across all feedstock) was narrowest for the IM (0.41 mm), followed by the HM (0.51 mm) and widest for the CM (0.62 mm). Regarding the SGE, the IM consumed on average 8.23 Wh/kg while CM and HM consumed 5.15 and 5.24 Wh/kg, respectively. From the three mills compared in this study, the IM seems better fit for being used in a standardized method that could be developed in the future, e.g., as an ISO standard.

Three-dimensional modeling of biomass fuel flow in a circulating fluidized bed furnace with an experimentally derived momentum exchange model

In modeling of large-scale circulating fluidized bed (CFB) furnaces, semi-empirical 3D process models are used in furnace analysis, design and optimization as their accuracy versus computational times make them more favorable than high resolution computational fluid dynamics (CFD) in many engineering type of studies. One of the key aspects in determining the furnace performance and efficiency is the correct modeling of the fuel flow as it determines where the thermochemical reactions take place in the furnace, affecting the temperature and gaseous species distributions. In modeling, this requires the suitable approximation of the momentum exchange between the fuel and the gas phase as well as the fuel and the bed material. To model the momentum exchange with current models presented in the literature, information on the material properties, namely the fuel particle size has to be given. The determination of particle size is affected by the particle shape and for irregular, non-spherical material, such as biomass, currently there are no readily applicable methods to determine the effective momentum exchange based on the particle geometry.In this work, a new gas–fuel momentum exchange model is developed for the fuel flow, which acknowledges the effect of physical properties of the fuel, namely the shape and size. Due to impracticality of determining a representative fuel particle size, characterization data is utilized to directly obtain information on the gas–fuel momentum exchange and the particles are classified based on their elutriation behavior, rather than particle size. The new momentum exchange model is utilized with an existing semi-empirical 3D process model and applied in simulation of a utility-scale CFB furnace firing biomass. The simulation results are compared with measurements and are found to be in good agreement, which demonstrates the applicability of the modeling approach. The presented method improves the modeling of fuel flow with CFB process models, especially with irregular, non-spherical fuels such as biomass. The improved modeling of fuel flow within large-scale CFB furnaces enables faster and more reliable design and analysis of CFB furnaces.

Experimental Investigation of Eco Friendly Biomass Fired Water Heating System

Biomass is considered as a primary fuel to meet the energy requirement in rural areas. This study deals in particular with the design, development, and performance evaluation of a biomass fired water heating system to fulfil domestic hot water requirements in rural households. The developed system is in position to yield 80 l of hot water at 30 °C of temperature gradient by consuming 1 kg of wood fuel in 1 h. The developed system was tested with two different fuels and the average thermal efficiency was found to be 53.6 % while average emissions of CO and CO2 were found to be 217 and 3056 ppm, respectively. An economic evaluation of these results reveals that there is savings of about 56.99 USD (INR 65.8 USD−1 as on Nov 6, 2015) on an annual basis while the payback period was found to be 1.33 years.

NOx Emission Model for the Grate Firing of Biomass Fuel

Establishing an appropriate NOX production and decomposition model is of practical significance to the grate firing of biomass fuel. This study used the CHEMKIN software package to simulate the combustion process of biomass pyrolysis and char combustion. Through rate of production (ROP) analysis and simplification based on GRI-Mech3.0, the 15-step reaction mechanism of volatile-N converting into NOX and the 12-step reaction mechanism of char-N converting into NOX were specified. It was found that in the NOX generated from the fuel, N was mainly in the form of NO and N2O. HCN and NH3 were the important intermediate products. NH3 was mainly converted into NO and some converted into N2O, while HCN mainly consumed NO and produced N2O. According to the transfer characteristics of the biomass fuel nitrogen, the NOX production and decomposition model of the biomass fuel nitrogen in grate furnace firing was established. A simulation computation on the NOX production was implemented for an actual furnace. The established model was confirmed reliable through the comparison of field test data and simulation results.

Implementation of a reheat steam cycle to maximise electrical power from a circulating fluidised bed multi-fuel cogeneration facility at an alumina refinery expansion

The expansion of the Worsley Alumina refinery in Western Australia from an annual output of 3.5–4.6 million tonnes of alumina per annum provided the incentive for increased efficiencies in both the refinery process and the steam raising plant. The multi-fuel cogeneration (MFC) power station was installed to meet the additional steam requirement and to improve the use of energy per unit of alumina produced. The power station is capable of providing 605 t/h of process steam at two pressure levels while developing 113.6 MW of electrical power from two boiler/turbine units. A reheat steam cycle was implemented by integrating the high-pressure cylinder of a utility steam turbine with an industrial back-pressure extraction machine. When compared to the capability of the older coal-fired (CF) power station, the cycle and plant configuration selected provides a 37% increase in the electrical power generated per tonne of process steam supplied to the refinery. The main source of fuel is a local semi-bituminous coal that prescribes the installation of efficient plant to limit carbon dioxide emissions. Fuel flexibility is provided by circulating fluidised bed boiler units that enable the provision of up to 30% of the heat input from biomass. Greenhouse gas emissions from the MFC power station are some 10% less per unit of process steam than those from the older CF power station. Firing biomass in the MFC power station further reduces the carbon foot print. Boiler feed water is provided by condensate returned from the process that has total organic carbon levels some two orders of magnitude greater than that permitted by international boiler water standards for the 16.0 MPa(g) units. Boiler water chemistry is based on caustic treatment. Amine dosing is applied to the feed water obtained from selected condensate streams.