Coal-biomass Blends Research Articles

Shea meal and cotton stalk as potential fuels for co-combustion with coal

The efficient management of waste biomass is an important environmental problem in agricultural countries. Often land-fill is the main disposal route with ramifications including CH 4 release having 21 times greater global warming potential per molecule than CO 2. Biomasses are considered to be CO 2-neutral fuels when combusted. Moreover, they are renewable and covered by the renewable obligation scheme and eligible for certificates in the UK. The overall objective of the investigation is to assess the performance of selected biomass and coal co-firing under two different modes of operation, air-staging and fuel-staging with the benefit of reduced-NO x and SO 2 emissions in power plant. The biomasses chosen for the study, shea meal (SM) and cotton stalk (CS) have very different cellulose/lignin compositions and different reported thermal behaviour. A series of experiments have been carried out in a 20 kW, down fired combustor using coal, shea meal–coal and cotton stalk–coal blends under un-staged, air-staged and fuel-staged co-combustion configurations. For air-staging, an optimum value of primary zone stoichiometry SR 1 = 0.9 was found. Keeping it fixed, the shea meal and cotton stalk content in the coal–biomass blends was set to 5%, 10% and 15% on thermal basis. NO reductions of 51% and 60% were achieved using SM and CS, respectively, with an optimum thermal biomass blending ratio (BBR) of 10%. The results obtained were compared with un-staged and air-staged results for coal without the addition of biomass. Similarly for fuel-staging, keeping the length of the reburn and burnout zone fixed, SM and CS were evaluated as reductive fuel using different reburn fuel fractions ( R ff) of 5%, 10%, 15% and 20%. NO reductions of 83% and 84% were obtained with an optimum R ff of 15% with an optimum reburn zone stoichiometry of SR 2 = 0.8 for both SM and CS, respectively. SO 2 reduction and char burnout efficiency were also evaluated. It was found that addition of biomass coupled with air and fuel-staging techniques reduced-NO x and SO 2 simultaneously while at the same time improving the char burnout efficiency.

Kinetic models comparison for non-isothermal steam gasification of coal–biomass blend chars

The non-isothermal thermogravimetric method (TGA) was applied to a bituminous coal (PT), two types of biomass, chestnut residues (CH) and olive stones (OS), and coal–biomass blends in order to investigate their thermal reactivity under steam. Fuel chars were obtained by pyrolysis in a fixed-bed reactor at a final temperature of 1373 K for 30 min. The gasification tests were carried out by thermogravimetric analysis from room temperature to 1373 K at heating rates of 5, 10 and 15 K min −1. After blending, no significant interactions were detected between PT and CH during co-gasification, whereas deviations from the additive behaviour were observed in the PT–OS blend. However, for the two coal–biomass blends, the gasification behaviour resembled that of the individual coal, as this component constituted the larger proportion of the blend. The temperature-programmed reaction (TPR) technique was employed at three different heating rates to analyze noncatalytic gas–solid reactions. Three nth-order representative gas–solid models, the volumetric model (VM), the grain model (GM) and the random pore model (RPM) were applied in order to describe the reactive behaviour of the chars during steam gasification. From these models, the kinetic parameters were determined. The best model for describing the reactivity of the PT, PT–CH and PT–OS samples was the RPM model. VM was the model that best fitted the CH sample, whereas none of the models were suitable for the OS sample.

Thermogravimetric study of interactions in the pyrolysis of blends of coal with radiata pine sawdust

The co-pyrolysis of coal-biomass blends were studied by using thermogravimetric analysis to look for thermal events indicating interactions that could cause synergic or inhibitory effects during the first stage in the co-combustion of these materials. Two coals from different rank were selected for the study and combined with radiata pine sawdust, the selected biomass compound. Pyrolysis assays were carried out on the individual components and the binary coal-sawdust blends (50% p/p) at different heating rates (10, 30, 50 °C/min) until reaching a maximum temperature of 1200 °C. The individual components behaved as expected and as is widely described in the specialized literature. Interactions detected in the blends resulted in greater-than-expected volatile yield values. These interactions were produced at pyrolysis temperatures over 400 °C, when most of the components in the blend are devolatilized, and are attributed to secondary reactions that inhibit the formation of char.

NO Reduction in Decoupling Combustion of Biomass and Biomass−Coal Blend

Biomass is a form of energy that is CO(2)-neutral. However, NO(x), emissions in biomass combustion are often more than that of coal on equal heating-value basis. In this study, a technology called decoupling combustion was investigated to demonstrate how it reduces NO emissions in biomass and biomass-coal blend combustion. The decoupling combustion refers to a two-step combustion method, in which fuel pyrolysis and the burning of char and pyrolysis gas are separated and the gas burns out during its passage through the burning-char bed. Tests in a quartz dual-bed reactor demonstrated that, in decoupling combustion, NO emissions from biomass and biomass-coal blends were both less than those in traditional combustion and that NO emission from combustion of blends of biomass and coal decreased with increasing biomass percentage in the blend. Co-firing rice husk and coal in a 10 kW stove manufactured according to the decoupling combustion technology further confirmed that the decoupling combustion technology allows for truly low NO emission as well as high efficiency for burning biomass and biomass-coal blends, even in small-scale stoves and boilers.

Thermogravimetric studies of the behavior of wheat straw with added coal during combustion

Abstract The combustion behavior of biomass and biomass–coal blends under typical heating conditions was investigated. Thermogravimetric analyses were performed on bituminite coal, aspen strawdust and wheat straw used alone and blended with different coal weight ratios. The behavior of biomass fuels in the burning process (different rates of volatilization, char burning and heat production) was analyzed, and the effects of a cold molding procedure for wheat straw on the burning properties were investigated. In addition, the kinetic parameters for the thermal conversion of each fuel were determined. Cold molding led to easier firing, and 5% coal was identified as the ideal ratio to achieve similar heat release characteristics to strawdust. Such a mixed pellet fuel with burning characteristics similar to aspen wood can be produced to take advantage of the wide design basis for wood-fired boilers.

Experimental investigation of ash behavior and emissions during combustion of Bosnian coal and biomass

Abstract This paper presents results of experimental research into the ash behavior of different Bosnian coal types and biomass fired in an electrically heated entrained pulverized fuel flow experimental reactor . The results are derived from a series of tests performed under a range of temperature and air conditions for the fuel test matrix. In essence, the experimental reactor comprises a 3 m length alumina–silicate ceramic tube, where combustion takes place, surrounded by SiC stick-type electric heaters and three-layer insulation. The temperature of the reaction zone is controlled by a programmable logic controller (PLC) with thyristor units for each of the heating zones, allowing the process temperature to be varied at will across the range from ambient to 1560 °C. The methodology is based on the evaluation of ash deposits formed in the experimental reactor during the tests. Test points, reflecting the different types of ash deposits, are plotted against appropriate fuel indicators onto graphic diagrams. Emissions of NO x and SO 2 are also measured under different ambient conditions—at different temperatures and air distributions—to determine the emission figures for the fuels being tested. The results for six different fuels are presented, namely two single coals, two coal blends, and two coal–biomass blends. The results obtained support the thesis that the appropriate ambient conditions for combustion of coals and biomass can be recognized and recorded in this way.

Effects of biomass co-firing with coal on ash properties. Part I: Characterisation and PSD

The alterations of ash quality and utilisation aspects when co-firing coal with biomass were investigated. Co-combustion tests were performed in lab and semi-industrial scale facilities, using several coal–biomass blends. The collected ash samples were analysed for major elements and heavy metals content, loss on ignition (LOI), free CaO content and grain size distribution. Since a variety of co-combustion residues were tested, important implications concerning the ash composition and, consequently, its further use in potential applications came up. Results showed that properties of co-combustion residues are directly connected to the combustion conditions and the individual blend components. Biomass exploitation as secondary fuel in co-combustion processes is technically and economically feasible up to 20% w/w and the produced ash could be further utilised without any major treatment.

Biomass Co-Firing for Boilers Associated with Environmental Impacts

This article is presented to discuss general combustion and emissions issues with biomass co-firing, as well as specific issues with particular biomass fuels, such as fouling. The tests of co-firing were carried out in a lab-scale bubbling fluidized bed combustor. Biomass is an attractive and sustainable renewable fuel to supplement coal combustion in utility boilers. Coal and biomass fuels are quite different in composition. Ash composition for the biomass is fundamentally different from ash composition for coal. Chlorine in the biomass may affect operation by corrosion. Ash deposits reduce heat transfer and may also result in severe corrosion at high temperatures. Biomass and coal blend combustion is a promising combustion technology; however, significant development work is required before large-scale implementation can be realized. Coal co-firing was successful with up to a 20% biomass mix boilers. Issues related to successful implementation of coal biomass blend combustion are identified. Co-firing of coal and biomass is an effective method of control NO x . Formation of NO x decreases with the increase of biomass fraction. This study focuses on five of the critical fireside issues associated with co-firing: ash deposition, SO 2 emission, NO x formation, corrosion, and carbon burnout.

Effects of Dilution Sampling on Fine Particle Emissions from Pulverized Coal Combustion

A dilution sampler was used to examine the effects of dilution ratio and residence time on fine-particle emissions from a pilot-scale pulverized coal combustor. Measurements include the particle size distribution from 0.003 to 2.5 μm, PM2.5 mass, and PM2.5 composition (OC/EC, major ions, and elemental). Heated filter samples were also collected simultaneously at stack temperatures in order to compare the dilution sampler measurements with standard stack sampling methodologies. Measurements were made both before and after the bag house, the particle control device used on the coal combustor, and while firing three different coal types and one coal–biomass blend. The PM2.5 mass emission rates measured using the dilution sampler agreed to within experimental uncertainty with those measured with the hot-filter sampler. Relative to the heated filter sample, dilution did increase the PM2.5 mass fraction of selenium for all fuels tested, as well as ammonium and sulfate for selected fuels. However, the additional...

Improved solid fuels from co-pyrolysis of a high-sulphur content coal and different lignocellulosic wastes

Co-pyrolysis of blends of a high-sulphur coal with different biomass wastes has been investigated as a way to obtain improved solid fuels. Experiments have been performed in a thermogravimetric laboratory system and in a pilot-scale mobile bed furnace, this last operating at 600 °C. The presence of biomass enhances coal desulphurization upon thermal treatment in significant relative amounts, giving rise about as much as twice percent sulphur loss at high biomass-to-coal ratios in the starting blend in comparison with the S loss occurring upon pyrolysis of coal alone. Combustion experiments with chars resulting from co-pyrolysis of these coal–biomass blends confirm this significantly improved desulphurization. Thus, co-pyrolysis of blends of high-sulphur coals with biomass wastes provides a potential way to obtain improved solid fuels combining good heating values with environmentally acceptable S contents. The chars resulting from co-pyrolysis show heating values within the range of high-quality solid fuels whereas the ash contents remain in the vicinity of that of the starting coal except in the case of the coal–straw blend where the relatively high ash content of this biomass waste leads to co-pyrolysis chars with substantially higher ash contents and lower heating values.

Biomass Co-Firing for Coal-Fired Boilers

In this study ground biomass and pulverized coal were used for co-firing test. The tests of co-firing of coal and biomass were carried out in a bench-scale bubbling fluidized bed combustor. Biomass is an attractive and sustainable renewable fuel to supplement coal combustion in utility boilers. Coal co-firing was successful with up to a 20% biomass mix boilers. Coal and biomass fuels are quite different in composition. Ash composition for the biomass is fundamentally different from ash composition for the coal. Chlorine in the biomass may affect operation by corrosion. Ash deposits reduce heat transfer and may also result in severe corrosion at high temperatures. Biomass and coal blend combustion is a promising combustion technology; however, significant development work is required before large-scale implementation can be realized. Issues related to successful implementation of coal biomass blend combustion are identified. Co-firing of coal and biomass is an effective method of control NOx. Formation of NOx decreases with the increase of biomass fraction.

Thermogravimetric studies of the behavior of lignite–biomass blends during devolatilization

The behaviour of Greek pre-dried lignite, four biomass materials and their blends in the devolatilization stage was investigated by thermogravimetry. Biomass was added in the percentages of 5, 10 and 20% wt. in the fuel blend. All the tests were carried out in nitrogen atmosphere under dynamic conditions at a heating rate of 10 °C/min. The kinetic parameters for the thermal conversion of the pure fuels were determined through the independent parallel, first-order, reaction model. No significant interaction was detected in the solid phase between the components of the coal–biomass blends, under the same experimental conditions.

Devolatilization rate of biomasses and coal–biomass blends: an experimental investigation

Devolatilization behavior of different coals and biomasses under heating conditions typical of conventional pyrolysis processes was investigated. Thermogravimetric analyses were performed on coals (with high and low volatile matter), biomasses (pine sawdust and dried sewage sludge) and coal–biomass blends with different weight ratios. The different behavior of coals and biomass fuels in the devolatilization process (different amount and nature of volatile species released, different rate of devolatilization and different reactivity of produced chars) was analyzed for abstracting kinetic data. In addition, analyses of coal–biomass blends revealed that in the operative conditions used (i.e. low heating rate 20 °C/min and high nitrogen flowrate), primary reactions of the thermal decomposition of biomass fuels are not significantly affected by the presence of coal, and also coal does not seem to be influenced by the release of volatile matter from biomass. This led to the first conclusion that the weight loss of a blend can be obtained from the weighted sum of reference materials. Further, a kinetic analysis was performed in order to fit the experimental results and verify simple sub-models (namely, distribution activation energy model and lumped model) to be used in comprehensive combustion codes (computational fluid dynamic) assuring a major accuracy compared with SFOR model, but maintaining both simplicity and computational velocity. A quite good fitting was obtained for all materials and blends studied.

Co-firing of coal and biomass fuel blends

This paper reviews literature on co-firing of coal with biomass fuels. Here, the term biomass includes organic matter produced as a result of photosynthesis as well as municipal, industrial and animal waste material. Brief summaries of the basic concepts involved in the combustion of coal and biomass fuels are presented. Different classes of co-firing methods are identified. Experimental results for a large variety of fuel blends and conditions are presented. Numerical studies are also discussed. Biomass and coal blend combustion is a promising combustion technology; however, significant development work is required before large-scale implementation can be realized. Issues related to successful implementation of coal biomass blend combustion are identified.

00/02087 Are integrated coal gasification combined cycle power plants competitive?

Interactions between feedstocks during pyrolysis of coal–biomass blends, and their impacts on product distribution and conversion behavior during utilization, need to be understood if we are to successfully develop systems for the effective co-utilization of biomass and coal. A novel two-stage fixed-bed reactor containing three quartz tubes was designed and used in this study to investigate these interactions, with particular emphasis on the impact on product distribution and char properties. The results show that interactions exist during co-pyrolysis of corncob and lignite blends, which increase overall tar yields and decrease overall gas yields compared with those obtained from pyrolysis of unblended feedstocks, with the interactions between corncob volatiles and lignite playing a dominant role. It is also shown that interactions between chars and volatiles can impact on the reactivity of chars to O2. Consistent with our expectations, there is a link between potassium content in char and its reactivity; however, it is found that for lignite chars in particular the potential impact of potassium is dominated by the changes of char chemical structure. The effect of potassium content is the opposite to that of char chemical structure, leading to significant complexity in determining the net result of any co-pyrolysis interactions on char reactivity. This highlights the importance of understanding these complex interactions to develop the industrial scale co-gasification systems and adjust the distributions of products.

97/03892 Study on compressive strength characteristics of Bio-Coal

The combustion behaviors of biomass, coal and their blends were studied by thermogravimetric analysis. Combustion parameters such as ignition, burnout, peak rate, ignition index, and combustibility index were analyzed. The kinetic parameters were optimized based on experimental results by a double parallel reactions random pore model (DRPM) proposed in this paper. The results show that the combustion characteristic temperature of the biomass is lower and maximum rate of combustion is higher than that of anthracite coal. With the increase of biomass content, ignition temperature and burnout temperature of blends tended to decrease, while the ignition index and combustibility index increased. Compared with the original RPM model, the DRPM model could not only describe the combustion process with a single peak rate, but also the combustion of biomass-coal blends with two rate peaks. The combustion activation energies of blends were extracted by DRPM model in the present study.

Pyrolysis of blends of biomass with poor coals

This paper reports on the pyrolytic behaviour of three different kinds of solid fuel and their blends in order to understand and further improve the performance of fluidized bed gasification of biomass-poor coal blends. Individual feedstocks consisting of pine chips, black coal and waste coal and several biomass-coal blends were pyrolysed in a thermobalance apparatus at atmospheric pressure. Experiments were carried out dynamically by increasing the temperature from 110 to 900°C with a heating rate of 100 K min −1. The data show very poor behaviour of the waste coal compared with pine chips and even black coal. Nevertheless, when a minimum of 40% of pine chips was blended with 60% waste coal and pyrolysed under the same conditions, the rate of mass loss increased sharply and was similar to that of black coal. D.t.g. results indicate that the main pyrolysis processes can be quantitatively expressed in terms of C 0 = C we − kt for both the individual fuels and the blends. Additional studies showed that no interaction takes place between biomass and coal in a blend during pyrolysis.