Combustion Plants Research Articles

FACTORS OF USING WASTE AS FUEL IN THERMAL ENERGY SYSTEMSOF PART 1. STUDY OF SHW COMBUSTION PROCESSES

The reason for the ambiguous assessment of the feasibility of using boiler systems of centralized heat supply for burning solid household waste (SHW) is the specific composition of SHW and the peculiarities of their combustion process. The experience of waste incineration plants shows the need to use for this purpose special incineration equipment and complex systems for cleaning combustion products. The purpose of the study is to determine the conditions for the implementation of solid waste incineration systems that would meet the requirements of environmental and economic efficiency. The article presents the results of experimental studies of the SHW burning process and recommendations for the safe and effective organization of such a process. The main factors of negative impact on the environment are identified, which are directly related to the organization of the combustion process and the composition of combustion products, in particular, the high content of sulfur and chlorine in solid waste. The research results confirm that the use of waste as fuel requires specific conditions for the organization of the combustion process, the operation of combustion plants and the arrangement of systems for cleaning combustion products. It is shown that the composition of solid waste and their combustible characteristics differ significantly from known types of solid and alternative fuels. This leads to the need to reconstruct existing solid fuel heating boilers

Production of Electricity from Coal-Fired Power Plants and Accompanying CO2 Emissions: Comparison of EU-27 and Serbia

Even in the third decade of the 21st century, large power plants are still responsible for more than half of the electricity production in Europe. They predominantly use fossil fuels in their work, which results in the emission of pollutants into the air. Nevertheless, thanks to EU directives, as well as disturbances on the market, emissions of carbon dioxide from large combustion plants in the EU-27 are intensively decreasing in the last two decades. Although the use of coal, especially in the countries of the European Union, is in constant decline, there is space for additional reduction. Through this paper, the authors wanted to present the completely actual situation of emissions of CO2 from thermal power plants in Europe, that have used coal for electricity production, as well as to compare such plants with those operating in the Republic of Serbia. The CO2 emission was analysed in relation to the installed capacity, as well as compared to the energy produced and supplied to the system. By analysing the obtained values of the ratio of emissions to the number of inhabitants, the area of the territory, production and consumption of electricity, as well as to the GDP, it is noticeable that a much larger amount of CO2 is generated on the territory of the Republic of Serbia to achieve a similar energy, industrial and economic effect compared to the EU-27. By researching location data of coal burning in the production of electricity in the Republic of Serbia revealed the existence of a large difference in the amount of CO2 emissions, which is a consequence of the composition of the coal used and the combustion modes in thermal power plants.

CARBON FOOTPRINT COMPARATIVE ANALYSIS FOR EXISTING AND PROMISING THERMAL POWER PLANTS

The power production industry is the main greenhouse gas emitter that makes its contribution to global warming. The greenhouse gas emission takes place in fuel production, transportation, and combustion. A prospective method for emission mitigation is the transition to organic fuel-burning facilities with small emissions by capturing carbon dioxide. Power consumption on the carbon dioxide capture remarkably reduces the efficiency of these facilities, which leads to increasing of fuel consumption and greenhouse gas emission because of the larger fuel production and transportation. Based on the material balance method, taking into account system effect of changes in efficiency and amount of fuel consumed, the paper estimated the carbon footprint over a twenty-year lifecycle for following thermal power plants types: combined cycle and oxy-fuel combustion plants for both natural gas and coal with internal gasification. It is shown that the transition to oxygen-fuel plants can reduce the carbon footprint near 90% for natural gas and near 75% for coal. The study also demonstrates the positive effect of carbon capture and storage system implementation for reducing carbon footprint near 75% for natural gas and near 70% for coal.

METHODS TO REDUCE NOX FORMATION DURING GAS COMBUSTION IN BOILERS

A study of reduction of nitrogen oxides emissions using various methods and their combinations on operational typical steam and water heating boilers of Ukraine during combustion gas fuels was conducted. The experimental research of the power steam TGMP-314 boiler showed that when volume thermal stress of the firebox was reduced to qv » 0.09 MW/m3 (55 % of the nominal power), and the flue gas recirculation factor r = 17 %, the nitrogen oxides emissions were reduced by 75 % and they almost meet the requirements of the IED directive. This measure to reduce emissions of nitrogen oxides is also possible for other types of boilers, and it is advisable to implement for those combustion plants with an excess capacity of about 40–50 % and which have exhausted their factory-designated resource. On the water heating boiler KVGM-180, equipped with standard gas recirculation smoke exhauster, the research was conducted with aim to reduce of NOx emissions at combustion natural gas with recirculation of flue gases into the blowing air. NOx emissions were reduced by 67% to European standards, and the concentration of carbon monoxide in flue gases was below СО≤100 mg/Nm3 (at 3% O2) by a recirculation factor was of about r = 30%. The standard burners in the KVGM-180 boiler are two flow of air and can be considered a type of staged combustion burners. That is, in this case, a combination of the staged combustion burners and flue gas recirculation into blowing air was used. The research of combustion a methane and carbon dioxide mixture in the ratio of CH4 (76 %) and CO2 (24 %) (biogas) with regard to reduce the formation and emissions of nitrogen oxides in the DKVR-6.5-13 steam boiler was conducted. The obtained level of NOx in the flue gases is within the range of 63–76 mg/Nm3 (at 3 % O2), which fully complies with the EU standards for the operation of CP from 1 MW on natural gas and other gas fuels. Bibl. 34, Fig. 3, Tab. 1.

Thermoeconomic investigation of pressurized oxy-fuel combustion integrated with supercritical CO2 Brayton cycle

Pressurization is expected to increase the power efficiency of oxy-fuel combustion plant. Supercritical CO2 (sCO2) Brayton cycle could yield higher thermal efficiencies at lower capital cost than the state-of-the-art steam-based power cycles. The coupling of pressurized oxy-fuel combustion and sCO2 cycle could potentially offer higher net power efficiency over its counterparts with CO2 capture. In this paper, pressurized oxy-fuel combustion was integrated with three different sCO2 Brayton cycle layouts, i.e., single reheated recompression, double reheated recompression, and intercooled recompression. The systems were analyzed from the perspective of thermodynamics and economics. The net power efficiencies for the three systems were 39.4%, 40.2%, and 41.3%, respectively. The effect of boiler pressure on the latent heat recovery of the flue gas was analyzed. In the sensitivity analysis, the influence of turbine inlet temperature, turbine inlet pressure, turbine inlet temperature, turbine outlet pressure, recirculated fan pressure boost, and the high-temperature recuperator (HTR) split ratio on the plant net power efficiency was assessed. Finally, the economic analysis was conducted. The levelized cost of electricity (LCOE) of the three systems were 103.18 $/MWh, 108.45 $/MWh, and 110.07 $/MWh, respectively. The results showed that the integrated systems were attractive as potential candidates for the coal-fired power generation with CO2 capture.

Seed ecology of post-fire flowering species from the Cerrado

AbstractPost-fire flowering (PFF) species resprout, flower and disperse seeds within weeks after fire. This may be an important strategy to recruit new individuals and colonize the gaps opened by fire. The seeds released in the post-fire environment may interact with byproducts derived from plant burning, and the resulting ash may have compounds that can promote the germination of various seeds, particularly those with permeable coats. In the Cerrado ecoregion, PFF is a strategy commonly observed in the species of the ground layer, but their seeds are rarely investigated. So, we examined the quality and the germination of the seeds of 13 species that disperse seeds within 3 months after fire. We estimated the amount of empty, filled and predated seeds for each species, and tested the germination with or without ash. There was a clear separation in seed quality as dicots produced 35–75% filled seeds but grasses <15%. Pre-dispersal predation was only observed for dicots (<10%). Ash stimulated the germination of two out of the three dormant species but inhibited the germination of three non-dormant species. Overall, the seeds produced in response to fire are an important source of genetic variability in an ecosystem that has resprouting as the main persistence strategy. As most species have non-dormant seeds, ash may only be important to stimulate the germination of few PFF species. Even so, ash can be completely washed away by rains before seeds are dispersed and may not have an effect under field conditions.

Karrikinolide stimulated seed germination of artificially aged marrow, cabbage and pepper seeds through repair of cell structure and enzyme activity

• Priming with karrikinolide (KAR 1 ) enhanced seed germination in aged marrow, cabbage and pepper seeds. • Repair mechanism of seed aging by the treatments operated through repairing cell structure reducing solute leakage lower electrical conductivity and less K leakage in treated seeds. • Treatments with smoke extract affected ROS enzyme activity i.e. catalase, ascorbate peroxidase and superoxide dismutase activity of aged seeds. • Smoke extract treatments can be an efficient tool for enhancing seedling quality in marrow, cabbage and pepper seeds. The aging process induces the deterioration of seed vigor and viability. Priming methods have been shown to regenerate and rejuvenate aged crop seeds. Several studies have established that plant-derived smoke from burning plant material enhances germination and post-germination. Karrikinolide (KAR 1 ), which has been identified as a molecule derived from smoke, can improve the germination of seeds of a range of plant species. However, the effect of KAR 1 on aged seeds is not well known. Therefore, this study was carried out to determine the impact of KAR 1 and hydropriming on germination and repair mechanism in unaged and artificially aged pepper, marrow, and cabbage seeds. Aged seeds were artificially produced at 40 ± 1 °C and 100% relative humidity for 48 h in cabbage and 72 h in marrow and pepper. KAR 1 (10 −7 M) was applied by dipping seeds in solution at a weight ratio of 1:5 seed: solution for 16 h at 20 °C. Hydropriming was applied under the same conditions using distilled water. Following the treatments, germination, seedling emergence, electrical conductivity, potassium leaching, and enzyme analysis were determined. Results showed that KAR 1- treated seeds had the lowest electrical conductivity and potassium leakage in unaged and artificially aged seeds in all three species. The influence of KAR 1 was more prominent on catalase activity in both artificially aged and unaged seeds. Additionally, KAR 1 treatment improved germination and fresh and dry weights of seedlings in all three species. The results of the present study show that the application of KAR 1 can help improve the performance of marrow, cabbage and pepper seeds in artificially aged (low-quality) seed germination.

Review of Selected Determinants Affecting Use of Municipal Waste for Energy Purposes

The aim of the article is to analyse the impact of selected conditions on the use of municipal solid waste in energy production processes. The authors in this publication indicated that the factors determining the effective use of solid municipal waste may be, in particular, formal and legal conditions, methods used in the processes of thermal waste transformation, recovery logistics or emergency situations such as pandemics or armed conflicts. Their knowledge can be very useful in the processes of the effective use of municipal waste for the production of thermal energy, especially in the current period of the energy crisis faced by most EU countries. This paper also emphasizes the importance of RDF (refuse-derived fuel) for the thermal energy sector, which can be used both in large combustion plants and in less powerful facilities, including local heating and combined heat and power plants as an alternative to traditional fossil fuels. The article was prepared by means of the systematic literature review (SLR) method, utilising the Scopus database and secondary sources.

High contribution of vehicular exhaust and coal combustion to PM2.5-bound Pb pollution in an industrial city in North China: An insight from isotope

Although industrial emissions are the major pollution source of PM2.5-bound Pb, which affects air quality in cities, their influence has gradually decreased with the enhancement of industrial control in recent years. Thus, at present, the source of PM2.5-bound Pb is unclear, especially in an industrial city in North China. In this study, by incorporating the stable Pb isotopic compositions into a Bayesian isotope mixing model (MixSIAR), source apportionment of PM2.5-bound Pb was conducted during autumn and winter in 2017, and summer in 2018 in Changzhi. The daily average concentrations of PM2.5 and PM2.5-bound Pb during the study period were lower than the second-grade limit value of China (75 μg m−3) and the Chinese National Ambient Air Quality Standard (1 μg m−3), respectively. The pollution sources of PM2.5-bound Pb were fully distinguishable using Pb isotopes. In Changzhi, the 206Pb/207Pb ratio in soil (average: 1.0891) and exhaust dust from gasoline (average: 1.0832) and diesel (average: 1.0814) showed low levels of Pb isotope signature in Changzhi, whereas the rest of the source exhibited Pb isotope signature levels. The source apportionment results revealed that in an industrial city with many steel and coking plants, the primary source of PM2.5-bound Pb were motor vehicle emission (29.7%) and coal combustion (26.9%), rather than industrial emission (26.5%). Moreover, seasonal variations in PM2.5 of Pb sub-sources were observed: soil dust (21.7% and 18.4%) and diesel motor vehicles emission (16.4% and 15.6%) in summer and autumn; domestic coal combustion (17.1%) and coal-fired power plant emission (15.5%) in winter. The carcinogenic risk from motor vehicle emission in autumn was higher than that from industrial and coal sources in winter, and higher than that from motor vehicle sources in summer. This finding is a critical evidence of an anomalistic enrichment of PM2.5-bound Pb in an industrial city. These results obtained through Pb isotopic composition and MixSIAR model also improved the accuracy of source apportionment of atmospheric PM2.5-bound Pb, representing a high scientific significance and reference value for Pb pollution control in North China.

A novel dual circulating fluidized bed technology for thermal treatment of municipal sewage sludge with recovery of nutrients and energy

Sewage sludge (SS), a by-product of the wastewater treatment process, should be viewed not as waste, but as a potential resource for renewable energy and nutrient recovery. However, SS contains various toxic and harmful pollutants, e.g., pathogens, pharmaceutical residues, and microplastics. Through organic recycling and reuse of SS on land, these contaminants may leak into the environment, creating potential hazards to the ecosystem and human health. To tackle this issue, an advanced SS treatment technique within circular economy principles was proposed. In this process, mechanically dewatered SS with 20–25 % total solids is first dried at 110 °C in a circulating fluidized bed dryer and then combusted at 850 °C in a circulating fluidized bed reactor. Consequently, all the unwanted organic compounds are eliminated, and the ash – relatively high in nutrients and sufficiently low in heavy metals – can be further processed into fertilizers and used in forestry or farming. Moreover, the process is self-sufficient in terms of energy, enabling standalone operation without supplementary fuels, and providing excess heat that can be utilized, e.g., as district heat. This paper describes the process in detail and reviews experiences and lessons learned from the commissioning and trial operation of a newly erected 1.5 MWth sludge combustion plant with a throughput of 10 000 t/a. The operational performance of the plant has been verified based on continuous processing of dewatered SS, and the main operating parameters were consistent with design values. Therefore, the scale-up of this technique was considered both feasible and successful.

Assessment of crop residues for off-grid rural electrification options in Ghana

Presently, about 28% of the populace living in rural communities lack access to electricity to meet their basic needs in Ghana. Biomass is gaining importance globally as a sustainable alternative to fossil fuels due to rising energy demand, the high cost of fossil fuels, depleting fossil fuel reserves, and the greenhouse gas emissions from fossil fuel combustion. This study examined the technical bioenergy potential available from crop residues. The economic feasibility of electricity generation via biomass combustion and gasification technologies is also investigated. The Bioenergy Food Security Rapid Appraisal (BEFS RA) Excel-based tool was used to perform a techno-economic analysis of crop residues compatible with combustion and gasification pathways. Based on the selected crops and assumptions used in this study, it was estimated that about 35 million tonnes of gross residue potential were assessable for energy generation in Ghana. Nonetheless, about 29 million tonnes of surplus residue potential are accessible for bioenergy production. The total bioenergy potential from surplus crop residues is approximately 401 PJ/yr. Also, the cost of energy (COE) generation from the gasification and combustion plants is between US$0.29/kWh and US$0.34/kWh, which is expensive compared to the tariffs paid by residential consumers in Ghana. Notwithstanding, utilising crop residues for electricity generation might be a feasible option for rural electrification in Ghana with appropriate financial support.

Dynamics and control of large-scale fluidized bed plants for renewable heat and power generation

As the share of variable renewable electricity increases, thermal power plants will have to adapt their operational protocols in order to remain economically competitive while also providing grid-balancing services required to deal with the inherent fluctuations of variable renewable electricity. This work presents a dynamic model of fluidized bed combustion plants for combined heat and power production. The novelty of the work lays in that (i) it provides an analysis of the transient performance of biomass-based fluidized bed combustion plants for combined heat and power production, (ii) the dynamic model includes a description of both the gas and water-steam sides and (iii) the model is validated against operational data acquired from a commercial-scale plant. The validated model is here applied to analyze the inherent dynamics of the investigated plant and to evaluate the performance of the plant when operated under different control and operational strategies, using a relative gain analysis and a variable ramping rate test.The results of the simulations reveal that the inherent dynamics of the process have stabilization times in the range of 5–25 min for all the step changes investigated, with variables connected to district heating production being the slowest. In contrast, variables connected to the live steam are the fastest, with stabilization times of magnitude similar to those of the in-furnace variables (i.e., around 10 min). Thus, it is concluded that the proper description of the dynamics in fluidized bed combustion plants for combined heat and power production requires modeling of both the gas and water sides (which is rare in previous literature). Regarding the assessment of control strategies, the boiler-following and hybrid control (combined fixed live steam and sliding pressure) strategies are found to be able to provide load changes as fast as −5%-unit/s, albeit while causing operational issues such as large pressure overshoots. The relative gain analysis outcomes show that these control structures do not have a steady-state gain on the power produced, and therefore it is the dynamic effect of the steam throttling that triggers the rapid power response. This study also includes the assessment of a turbine bypass strategy, the results of which show that it enables fast load-changing capabilities at constant combustion load, as well as decoupling power and heat production at the expense of thermodynamic losses.

Comparison between pilot and lab scale testing of aluminide coated and uncoated ferritic steels under oxy-fuel and coal/thistle co-firing conditions

The present study compares the biomass corrosion behavior of two diffusion aluminide coating obtained by slurry application, which were deposited on two low-chromium content steels, ferritic-martensitic P92 (8.7 wt% Cr) and ferritic T22 (2 wt% Cr). Their performance degradation was conducted under an oxy-fuel combustion environment for both coated and uncoated materials both under laboratory conditions and in a pilot plant burning thistle for 500 h. Exposures were carried out in the laboratory at two different temperatures, 600 °C and 650 °C, under a model atmosphere consisting of 60 % CO2, 30 % H2O, 8 % O2, bal.% N2 (in vol%), 500 vppm HCl and 2 vppm SO2. The pilot plant used a mixed fuel of 60 wt% coal and 40 wt% thistle that was burnt and the samples were exposed to a temperature range of 600–620 °C. After testing, the results revealed that the aluminide-coated materials exhibited a very high resistance under both extreme scenarios, with a variable protective character related to their Al content. On the contrary, uncoated material exhibited severe degradation, in particular T22. Microstructural and morphological studies showed up similar corrosion patterns and products on coated and uncoated materials for both testing environments.

A Quali-Quantitative Comparison between In Situ and Ex Situ Waste-to-Energy Processes in Terms of Local and Global Impacts

Despite the improvements made in recent decades on the emission control of waste combustion plants, the chronically low public acceptance still influences the strategical choices of local authorities, who may decide to export waste to other regions instead of treating waste locally in a waste-to-energy (WtE) plant. The present paper proposes a method to identify a more sustainable solution between local waste treatment and the export of waste. To do this, two waste-management scenarios were compared: (1) an in situ WtE scenario, considering a WtE plant in a region of about 500,000 inhabitants; and (2) an ex situ WtE scenario, considering the road transportation of waste to a WtE plant located in another region. This method yields an estimation of the maximum distance that trucks may cover to balance the emissions of the air pollutants released in the in situ WtE scenario. The methodology is based on the COPERT emission model and on emission factors of WtE processes. The results show that the maximum distance is limited by the emissions of polycyclic aromatic hydrocarbons by road trucks. Finally, the paper discusses the results considering the energy efficiency of WtE processes and proposes alternative WtE strategies to increase the level of public acceptance.

Profiling and occupational health risk assessment study on coal ashes in terms of polycyclic aromatic hydrocarbons (PAHs)

Profiling and cancer risk assessment on the polycyclic aromatic hydrocarbons (PAHs) content of coal ashes produced by the major coal combustion plants from the eastern coalfield region in India was conducted. Thirteen PAHs were detected on coal ashes collected from ash deposition sites of major thermal power plants and the profiling of the PAHs was done. Benzo[a]pyrene equivalents (BaPeq) for individual PAHs were calculated and applied to the probabilistic assessment model from US EPA (1989). Monte Carlo simulations were conducted to assess the risk of inhabitants exposed to PAHs through the dust of the coal ash deposition site. In fly ash, the range of total amount of carcinogenic PAHs was from 3.50 to 6.72 µg g−1 and for the bottom ash, the range was 8.49 to 14.91 µg g−1. Bottom ashes were loaded with ample amounts of 5- and 6-ring carcinogenic PAHs, whereas fly ashes were dominated by medium molecular weight PAHs. The simulated mean cancer risks from fly ashes were 2.187 E–06 for children and 3.749 E–06 for adults. For the case of bottom ash, the mean risks were 1.248 E–05 and 2.173 E–05 respectively for children and adults. Among all the three exposure routes, dermal contact was the major and caused 81% of the total cancer risk. The most sensitive parameters were exposure duration and relative skin adherence factor for soil, which contributed the most to total variation. The 90% risks calculated from the bottom ashes (2.617 E–05 for children and 4.803 E–05 for adults) are marginally above the acceptable limit (>1.000 E–06) according to US EPA. In this study, a comprehensive risk assessment on carcinogenic PAHs present in coal ashes was done for the first time that may be helpful to develop potential strategies against occupational cancer risk.

MILD Combustion of Methanol, Ethanol and 1-Butanol binary blends with Ammonia

In the present energy transition scenario, ammonia is considered a valuable candidate as energy-dense carrier with neutral or even negative carbon balance. However, the potential high NOx emissions and the reduced oxidation process stability, at least when conventional combustion plants are used, can burden its wide utilization on large scales. In this context, MILD Combustion, due to its inherent characteristics, may greatly improve combustion stability and keep the NOx emissions at an acceptable level. On the other hand, the addition of low or no-carbon fuels from biomasses and wastes, more reactive than ammonia, may be beneficial in further improving its combustion performance and the global sustainability of the energy supply chain.In this respect, the present work analyzes the sustainability and combustion performance of binary mixtures of ammonia and low-molecular-weight alcohols in a cyclonic burner, where MILD conditions are attained by means of a strong internal recirculation, and compares them with those obtained with NH3/methane blends. Results highlighted that NH3/alcohols mixtures ensure a stable oxidation process in a wide range of operational parameters without compromising the system performance. Moreover, they showed a significant reduction of NOx emissions for NH3/alcohols mixtures, especially for fuel-lean conditions, when compared to NH3/methane blends.Experimental data were also corroborated by chemical kinetic modeling results to provide some insights on the peculiar NOx formation routes when blends of different nature are used, highlighting the interaction between carbon and nitrogen fuels kinetics.

ASPECTS REGARDING THE CONCEPTION, DESIGN AND CONSTRUCTION OF RECUPERATIVE BURNERS

This article presents the main aspects of the conception, design and construction of self-designed recuperative burners. The starting point of the article is the operating principle of this specific type of combustion plant. This operating principle is based on the preheating of the combustor (combustion air) by taking over an important part of the enthalpy of its own combustion gases. Based on this principle, the recuperative burner of our own design has an energy efficiency that consists in reducing the specific consumption of fuel (natural gas) by about 25-35%. Also, the use of this specific type of combustion plant provides other functional advantages such as: a higher temperature in the hearth (due to a complete combustion), reduction of technological cycle times for the realization of various processes. The article also presents some functional parameters of a type-dimensional range of recuperative burners of our own design.

Theoretical Air Requirement and Combustion Flue Gases Analysis for Indigenous Biomass Combustion

Rice-husk is one of the most abundant and commonly utilized biomass. It can be used directly to generate primary heating agent in combustion plants. However, emission characteristic of biomass usually vary depending on factors such as the variety of the parent plant, region of cultivation and climatic condition. Moreover, gases emission from biomass combustion could be detrimental to health; hence there is a need for information on the theoretical volume of air and flue gases required for optimal operation of combustion equipment. Thus, this work analyzed the theoretical combustion air requirement and the resulting flue gas volume of the abundant Nerica-rice-husk variety. Rice-husk samples were collected from southwestern part of Nigeria. The samples were characterised for their ultimate and proximate content. Afterward, the combustion analysis was carried out using the elemental composition obtained from the ultimate analysis to determine the theoretical combustion air requirement and the resulting flue gas volume. The proximate analysis result showed the moisture content level, fixed carbon content and ash content value of 10.93%,12.59% and 18.26% respectively for sample A and 9.80%, 20.76% and 14.81% for sample B. This reveals that Nerica-rice-husk is advisable for use as an alternative energy source in a combustion process. The calculated theoretical volume of air for sample A was 3.69596 (N m3/kg fuel), while 3.53947 (N m3/kg fuel) was obtained for sample B. This signifies a slight different between the combustion properties of rice-husk of same variety. It also showed that more quantity of theoretical air will be required to burn sample A compared to sample B, and that sample A will generate little more emissions compared to sample B. Hence, this study reveals the volume of air required for low emission combustion of Nerica-rice-husk in combustion plants.

Simultaneous reduction of nitrogen oxides and sulfur dioxide in circulating fluidized bed combustor during oxy-coal combustion

For stable carbon capture utilization and storage, highly-pure CO2 content and low pollutant emissions must be maintained throughout oxy-coal firing operation; however, studies on combining absorbent addition and oxidant staging combustion to eliminate simultaneous nitrogen oxides (NO, N2O) and sulfur dioxide (SO2) have not been reported. Accordingly, the purpose of this study was to investigate the effects of oxidant staging and limestone addition on the reductions of NO, N2O, and SO2 emissions in an oxy-circulating fluidized bed combustor at 25% and 31% input oxygen. The operating parameters considered in this study were: oxidant compositions; corresponding flow rate ratios; primary, secondary, and tertiary oxidants (PO, SO, and TO, respectively); TO supply heights; and limestone addition. The results revealed that compared to the TO supply heights, increasing TO flow rate was more effective at reducing the nitrogen oxide emissions. Under an optimal flow rate ratio (PO:SO:TO = 70:10:20) and TO height (6.4 m), NO, N2O, and SO2 emissions were ≈7.4, 4.2 and 4.1 mg MJ−1, respectively. The increase in SO2 emission caused by the application of oxidant staging could be effectively decreased by 60.6% without impacting combustion performance via limestone injection into the combustor; effectively facilitating the production of >86 vol% CO2. These findings can serve as valuable references for future designs, and the efficient operation of oxy-coal combustion plants constructed at larger scales, thereby ensuring highly-pure CO2 content and low pollutant emissions.

Combustion behaviour and slagging tendencies of pure, blended and kaolin additivated biomass pellets from fen paludicultures in two small-scale boilers < 30 kW

Pure, blended and additivated biomass pellets from four fen paludicultures were produced at TFZ and combusted in two small-scale biomass boilers (15 kW, 30 kW). Feedstocks derived from straw of Typha ssp., Phragmites australis, Phalaris arundinacea and Carex ssp. that were harvested during winter 2018, 2019 (used for pelletization) and 2020. Additivation of fuels with kaolin before pelletization or blending of fuels with ENplus wood pellets (A1 quality) after pelletization were applied. Straw and pellets were analyzed for physical and chemical fuel properties according to international standards for solid biofuels. Physical properties of pellets met the requirements of ISO 17225–6. Chemical properties of Typha indicated high TPM emissions due to high contents of K and Na in fuels while severe slagging was predicted for the other species by a high molar (Si + K + Al)/(Ca + Mg + P) ratio. During combustion in both boilers, CO and total particulate matter (TPM) emissions were high for Typha but slightly reduced by additivation with 2.3% kaolin. Blending of fuels significantly reduced NOX, SOX and HCl emissions due to lower N, S and Cl concentrations. Slagging was high for pure and additivated pellets of Phragmites, Phalaris and Carex with >50% of total ash consisting of particles >2 mm. No steady-state boiler operation could be achieved with either pure or additivated fuels. In conclusion, paludiculture pellets are challenging fuels for small-scale combustion plants. Their use cannot be recommended for the tested boilers. Technical solutions may be easier applied in medium sized combustions plants above 100 kW.