Combustion Plants Research Articles

Nuclear Air-Brayton Power Cycles with Thermodynamic Topping Cycles, Assured Peaking Capacity, and Heat Storage for Variable Electricity and Heat

Electricity markets are changing because of (1) the addition of wind and solar generating capacity and (2) the goal of a low-carbon electricity grid. The large-scale addition of wind and solar photovoltaics results in low wholesale electricity prices at times of high wind and solar output and high prices at times of low wind and solar input. Today, gas turbine combined cycle (GTCC) plants burning natural gas or oil provide dispatchable electricity and provide the most economic method to match electricity production with demand. Nuclear Air-Brayton Combined Cycles (NACCs) with heat storage and a thermodynamic topping cycle enable base-load nuclear plants with sodium or salt coolants to provide dispatchable electricity to the grid and heat to industry. This capability maximizes nuclear plant revenue and enables a base-load nuclear reactor with NACCs to be a low-carbon replacement for a GTCC. The NACC power cycle, alternative heat storage technologies, and development status of the different technologies are described. The technology applies to other heat generating technologies including high-temperature concentrated solar power and future fusion systems.

Abundance and δ13C of sedimentary black carbon indicate rising wildfire and C4 plants in Northeast China during the early Holocene

Global warming and human activity are thought to be the primary drivers of the globally rising occurrences of forest fires. Due to the importance of local to regional environmental drivers in mediating fire frequencies, reconstructing fire histories of representative geographic regions is important to understand fire regimes and predict future changes. The present study aims to establish a relatively high-resolution fire record of boreal forests in northeastern (NE) China and identify the primary environmental drivers. We analyzed the concentration and stable carbon isotopic composition of black carbon (BC and δ13CBC) of a 34,000 cal yr BP sedimentary sequence from a crater lake (Tianchi). The results show that fire events and C4 plants were scarce during the late Last Glacial but increased since the deglaciation. Both fire and the abundance of combusted C4 plants reached their maxima during the early Holocene, which may be attributed to rising temperatures due to intensified solar radiation and summer monsoons. During mid-to-late Holocene, fire events remained relatively stable and were primary associated with C3 plants burning. Fire was particularly infrequent and C3 trees were abundant during the periods of 5500–3100 cal yr BP and 1500–150 cal yr BP, which can be attributed to a wet climate. Fires exhibited evident increases from 150 cal yr BP to the present, suggesting a substantial role of human activities. Both BC and δ13CBC during the Holocene show a significant correlation with pollen-based temperatures but not with precipitation, suggesting that temperature rises played a primary role in stimulating forest fires via mediating effective moisture. Collectively, these findings suggest that forest fires and C4 plants would likely increase in NE China in response to global warming and increasingly intensive anthropogenic disturbance, highlighting the importance of establishing a long-term understanding of fire regimes to create more sustainable, science-based fire management strategies.

Combustion of sewage sludge in a fluidized bed of catalyst: ASPEN PLUS model

This paper presents the results of the simulation of a sewage sludge combustion plant with a productivity of 6 tons per hour using the ASPEN Plus. It is shown that catalytic combustion technology can be used for the efficient utilization of mechanically dehydrated sludge with the moisture of ~75% in autothermal mode (without the use of additional fuel). At the same time, the plant for utilization of 6.0 tons of sludge per hour enables us to obtain 3.07 MW of heat energy. It is shown that the sludge moisture and its calorific value significantly affect the combustion process. Thus, at the moisture of less than 72%, additional water supply is necessary to avoid overheating of the catalyst bed. In the case of an increase in sludge moisture of more than 76%, an additional supply of fuel (for example, brown coal) is required. Also, the article discusses the emissions of harmful substances generated during sewage sludge combustion and methods for their utilization.

Research and Development of Mathematical Models of Elements of a Gas-Air Flow for Improvement of Automatic Control System of Organic Waste Processing Plant

Recycling of organic wastes is an extremely important and challenging environmental task. One of the promising trends in this field is the creation of multi-mode (combustion, pyrolysis and gasification) plants for processing organic wastes with production of such useful products as thermal energy and energy carriers (biocoal, bio-oil, pyrolysis resins, synthesis gas, etc.) and fertilizers. When creating such plants, the main problems include instability of the properties of a source material, its high water and ash content. This drives the developers to use non-standard equipment and atypical control algorithms, the creating of which requires a lot of experimental work to be done. At the same time, conducting field experiments is an expensive, difficult and long process that highlights the need for extensive use of mathematical and computer modeling. In this paper, mathematical models of elements of the gas-air path of the organic waste processing plant are obtained. The characteristics of the gas-air path of the plant as of an object of regulation for pressure in the lower and vacuum in the upper part of the combustion chamber are determined. The gas-air flow consists of the flue and the air ducts and serves to remove flue gases from the combustion chamber and supply air needed to maintain fuel combustion. When developing new automation systems, modeling allows assessing the applied solutions accurately, simplifying and reducing the cost of their development, solving the problems of system stability, optimizing transient processes, etc. The nonlinearity of the obtained mathematical models on the "the pressure at the inlet to the n-th section air-gas flow path — the pressure at the outlet of the n-th section of the air-gas flow path" channels, the nonstationarity of objects of control and dependence of their dynamic characteristics on operating mode of the plant are determined. Due to developed models, the two-way relationship of the gas and air paths has been revealed. When modeling, the gas-air flow of the plant is divided into several sections for which the mathematical models are obtained. They are required to synthesize controllers of flue gases vacuum in the upper part and the air pressure in the lower part of the combustion chamber.

Reduction of Unburned Carbon Release and NOx Emission from a Pulverized Wood Pellet Boiler Retrofitted for Fuel Switching from Coal

For renewable electricity production, biomass can fully displace coal in an existing power plant with some equipment modifications. Recently, a 125 MWe power plant burning mainly anthracite in Korea was retrofitted for dedicated wood pellet combustion with a change of boiler configuration from arch firing to wall firing. However, this boiler suffers from operational problems caused by high unburned carbon (UBC) contents in the bottom ash. This study comprises an investigation of some methods to reduce the UBC release while achieving lower NOx emissions. The computational fluid dynamics approach was established and validated for typical operating data. Subsequently, it was applied to elucidate the particle combustion and flow characteristics leading to the high UBC content and to evaluate the operating variables for improving the boiler performance. It was found that the high UBC content in the bottom ash was a combined effect of the poor fuel grindability and low gas velocity in the wide burner zone originating from the arch-firing boiler. This prevented the operation with deeper air staging for lower NOx emissions. Reducing the particle size to <1.5 mm by modifying mills or pretreating the fuel using torrefaction was the only effective way of lowering the UBC and NOx emissions with deeper air staging while increasing the boiler efficiency.

Using threshold values to continuously evaluate how effectively electrostatic precipitators operate

The increased use of biomass as a fuel in energy production can reduce CO2 emissions in this sector. Fossil fuels can thus be replaced, especially in the field of heat supply. However, this should not occur at the expense of increased particulate matter emissions, which is why electrostatic precipitators (ESPs) are used. Continuous monitoring of the ESP is called for in the European Union Directive 2015/2193 for medium combustion plants (MCP), which applies to plants with a nominal heat output of between 1 and 50 MW. A monitoring methodology based on the precipitator parameters current (I) and voltage (U) was presented in an earlier presentation. The work at hand follows up on the previous findings and presents an alternative methodology that aims to define the effectiveness of the ESP via threshold values for U and I. It is shown that two types of misinterpretation of the operation may occur when threshold values are defined. The operating condition could be regarded as effective via the methodology, although the measurement proves ineffective in operation and the opposite error also occurs. The statistical evaluation of the frequency of errors is intended to help the legislative authorities determine the threshold values in a reasonable way. In addition, checks are made as to whether it is possible to verify the operation of the combustion system via the flue gas temperature. The operating times of the combustion are essential, as they define the operating times required by the precipitator. In this context, statistical evaluations are made to determine which plant-specific threshold value could be useful. The aim is to test the effective operation of the separator from readily available data at all times. These considerations could form the basis for developing a uniform methodology to ensure compliance with the legal requirements.

A Review Paper on Performance Behavior of High Volume Fly-Ash Concrete Under Elevated Temperature

Removal of fly ash (FA) coming about because of the burning of coal-terminated electric fire stations and nuclear power plants is one of the major natural difficulties. This test keeps on expanding with expanding the measure of FA and diminishing the limit of landfill space. Consequently, considers have been done to re-utilize high-volumes of fly ash (HVFA) as concrete substitution in development materials. This paper presents a diagram of the past investigations did on the utilization of high volume FA as a fractional substitution of concrete in customary solid blends dependent on Portland concrete (PC). Crisp properties, mechanical properties, warm properties and electrical resistivity of solid blends containing HVFA as concrete substitution have been surveyed additionally depicts the an outline of the past investigations on various kinds of cement presented to changing raised temperature and their quality properties over the temperature introduction are assessed.

Fire history and human activity revealed through poly cyclic aromatic hydrocarbon (PAH) records at archaeological sites in the middle reaches of the Yellow River drainage basin, China

Disentangling the role of natural and anthropogenic factors is a major challenge in paleofire studies. Here, we introduce the molecular biomarkers of polycyclic aromatic hydrocarbon (PAHs), combined with charcoal and black carbon in sediments of archaeological sites, to identify anthropogenic signals of environmental change during the middle Holocene. In the prehistoric period, an intensified-fire regime period, inferred on the basis of PAHs, char and macro-charcoal levels, has been attributed to intensified anthropogenic biomass burning from dry crop cultivation between 6500 and 5000 and 3900–3600 yr BP., corresponding to the earliest Chinese settlements during the Miaodigou & Banpo IV Culture and the development of the Erlitou Culture under drier climate conditions. Subsequently, the fire frequency decreased notably between 4500 and 4000 yr BP. as the climate became wetter and there were shifts in the frequency of high-magnitude floods, corresponding to the abandonment of late Neolithic settlements in the floodplain. Changes in the PAH fluxes in sediments are positively correlated with intensified-fire regime periods, consistent with the charcoal and black carbon fluxes during those periods. Principal component analysis of PAH fluxes suggests that these intensified-fire events have a pyrogenic signature, implying that the PAHs were derived from biomass burning of fuelwood and other woody plants. In this study, PAHs in loess sediments have been used as the indicators of anthropogenic biomass burning through time. Meanwhile, PAHs also record the shift of modes of production and the evolution of human settlements as well as the choices made in response to limited natural resources. To comprehensively analyze the paleofire records of PAHs, charcoal and black carbon combined with multiproxy evidence are needed to understand wildfire history as well as human land use and social and cultural development across the study regions in depth.

Ecosystem services from old-fields: Effects of site preparation and harvesting on restoration and productivity of traditional food plants

Highly disturbed landscapes, including fallowed or abandoned farmland, are known to experience losses in native plant diversity that negatively impact the ecological functions and services provided by an ecosystem. The restoration of native species to the post-agricultural landscape using principles derived from indigenous knowledge could reverse this damage. This study examines the effects of three site preparation treatments (prescribed burning, tilling, and mowing) and biomass harvesting on the establishment and productivity of four native, edible, culturally-significant forbs (Apios americana Medik., Helianthus annuus L., Helianthus tuberosus L., and Oenothera biennis L.) restored to a fallow farm field. Species' responses to site preparation treatments varied over three years of observations, with plants grown from tubers establishing populations more successfully after burning or mowing and plants grown from seed establishing better after tillage. Harvesting of biomass after the first growing season reduced the number of individual plants observed for all restored species across all site preparation treatments but demonstrated the potential for production of traditional food resources in a low-management, multi-purpose agroecosystem. H. tuberosus showed particular promise for this purpose, producing an average of 881, 1397, and 1848 kg ha−1 of dry edible biomass on tilled, burned, and mowed plots, respectively. Burning was also found to enhance concentrations of organic matter, calcium, and magnesium in the soil, and many indicators of soil quality varied seasonally. These results indicate that with low-energy input management strategies, native wild edibles could be reintroduced into old-field systems to provide provisioning and cultural ecosystem services while maintaining or enhancing ecosystem function.

Understanding the Mechanism of Particle Adhesion in High-Temperature Combustion Induced by Sodium and Potassium: Use of a Synthetic Ash Strategy

During high-temperature combustion of coal, biomass, and municipal waste, ash particles can agglomerate and adhere to the internal surfaces of the plant under high-temperature conditions, resulting in a decrease in operating efficiency. It is known that the presence of small amounts of Na and K in the ash can facilitate adhesion; however, mechanistic details of the process are unclear. In this paper, a synthetic ash strategy consisting of a base material of SiO2 involving controlled additions of simple chemical components is proposed as a novel and convenient way to investigate adhesion. The synthetic ash consisted of SiO2 as the base material, and trace amounts of Na or K were added as target elements to examine their potential role in facilitating the adhesion process. It became clear that small amounts of Na and K increased the propensity for adhesiveness at high temperatures. The effect of the addition of Al2O3 nanoparticles to the synthetic ashes, which was expected to prevent adhesion, was also investigated. Therefore, it was found that the effect of Al2O3 would depend on the elements, which may increase the adhesiveness. It is projected that the present research can contribute to stable operation of many types of combustion plants.

Migration and emission behavior of arsenic and selenium in a circulating fluidized bed power plant burning arsenic/selenium-enriched coal

Arsenic (As) and selenium (Se) pollution caused by coal combustion is receiving increasing concerns. The environmental impacts of As/Se are determined not only by stack emission but also by leaching process from combustion byproducts. For a better control of As/Se emission from As/Se-enriched coal combustion, this study investigated the migration and emission behavior of As/Se in a circulating fluidized bed (CFB) power plant equipped with fabric filter (FF) and wet flue gas desulfurization (WFGD) system. The results demonstrated that arsenic was both enriched in bottom ash (41.4–47.6%) and fly ash (52.4–58.6%), while selenium was mainly captured by fly ash (73.9–83.4%). Limestone injection into furnace promoted As/Se retention in ash residues. Arsenic was mainly converted into arsenate in high-temperature regions and partly trapped in bottom ash as arsenite. In contrast, selenium capture mainly occurred in low-temperature flue gas by the formation of selenite, because of the poor thermal stability of most selenite. Triplet-tank method can totally remove arsenic in WFGD wastewater. And 18.4–58.7% of selenium was removed, resulting from the precipitation of Se4+ anions with highly soluble Se6+ anions remaining in wastewater. The concentrations of As and Se in the stack emission were 0.25–1.02 and 0.96–2.24 μg/m3, receptively. The CFB boiler equipped with FF + WFGD was shown to provide good control of the As/Se emission into the atmosphere. Leaching tests suggested that more attention should be paid to As leachability from fly ash/gypsum, and Se leachability from gypsum/sludge.

Process and Impact of Combustion on Cement Oxide Minerals: An Experimental Study

The main stages of the primary materials are that feed the furnaces to form the mineral compounds of cement, which are the stage of drying the materials from water at a temperature of 100 degree Celsius and moving to the crystallization area at a temperature of 550 degree Celsius. Thus, the free lime begins to break down the calcium carbonate by interacting with silica and clay compounds to form (C2S) at a temperature 900 degree Celsius. In the transition region at a temperature of 1260 degree Celsius begins the formation of liquid compounds (C3A, C4AF), where the formation of a compound (C2S) continues and begins to form a compound (C3S). When the temperature rises at 1450 degree Celsius, the formation of the vehicles is complete, and this depends on the quality of the blended raw materials that affect the life of the firing blocks and the fuel consumption. As for the silica coefficient, it has a major role in determining the clinker quality, as the best silica coefficient (2.7) was obtained, as well as the best coefficient of alumina (1.38), as well as obtaining the best lime saturation coefficient (0.96) and the percentage of magnesium oxide not exceeding 5 percent, thus stabilizing the ratio Magnesium oxide to form the best burning plants (108). The difference in the concentration of substances leads to an incomplete chemical reaction and this affects the size of the resulting crystals.

Techno-economic assessment of biomass combustion technologies to generate electricity in South America: A case study for Bolivia

Agricultural residues, although widely available, are an unused source of energy in Bolivia. Although the government of Bolivia plans to increase the share of renewables in the power portfolio, none of the proposed projects includes agricultural residues as a source of electricity. The present study investigated the techno-economics of a biomass-based electricity generation facility, including the optimum facility size and the levelized cost of electricity from agricultural residues in Bolivia. The biomass feedstocks are the residues from harvesting sugarcane, soybean, corn, rice, sorghum, and sunflower. A novel framework was developed to geographically locate biomass collection points (BCPs), sites for collecting/storing biomass on roadsides using a model developed using GIS. The cost components are the costs of harvesting biomass from fields, baling, transportation to BCPs, storage, nutrient replacement, the premium paid to the farmer, and capital cost for the plant. The transportation costs were estimated using a detailed GIS study through the analysis of the actual road network, and the transportation costs were optimized. Regression models were developed to assess the capital costs of the combustion plants. The conversion technologies considered for Bolivia were grate-firing and fluidized bed combustion. A novel integrated framework, named ENergy from BIOmass Techno Economic Model (ENBIOTEM), was developed. Using this model, we estimated the energy cost to be 71.6 $/MWh for an optimal plant capacity of 300 MW. The main barrier against promoting renewables in Bolivia is the fossil fuel subsidy. Although biomass is currently not competitive with fossil fuels in Bolivia, the results provide information to decision makers for future planning.

Increasing the efficiency of chemical looping combustion of biomass by a dual-stage fuel reactor design to reduce carbon capture costs

This paper analyzes the capabilities of a pilot-scale chemical looping combustion plant firing wood biomass in two stages to efficiently achieve negative carbon dioxide emissions. The utilized in situ gasification-chemical looping combustion (iG-CLC) process isolates the oxygen supply via air from the fuel conversion itself with the help of two separate fluidized bed reactors and an oxygen carrier to supply the necessary oxygen for the combustion. As a result, a relatively pure stream of carbon dioxide and steam is generated. Thus, the process makes capturing carbon emissions more feasible since it eliminates the need for the cost- and energy-intensive separation of the produced gases. A major issue when using biomass in a chemical looping plant is the high amount of the volatiles exiting unconverted. This problem was mitigated by using a two-stage fuel reactor system. Two bubbling fluidized beds were arranged one upon the other. The lower stage, where the fuel is introduced, is used to release the volatiles and partly convert them. The remaining volatiles rise up into the second stage and are further converted to a high degree. A series of experiments were carried out with a 25-kWth pilot plant located at the Hamburg University of Technology. Gas concentrations were continuously measured after both stages of the fuel reactor to see the gradual conversion of the fuel gases. Additionally, carbon slip at the exhaust was measured to show the effectiveness. The experiments with the reactor concept showed promising results since already at a reactor temperature of 850 °C, the total oxygen demand needed to oxidize the combustible component in the exhaust gas was well below 2%. The carbon dioxide (CO2) capture efficiency when using German hardwood slightly decreased to 93–96% compared to 97% for German lignite. In the future, the reactor design must prove that it scales and that the efficiency can be further increased. Nevertheless, firing biomass with a two-stage iG-CLC process might allow a cost-efficient negative carbon dioxide emission while generating heat with relatively high efficiency. Therefore, it might be a sustainable alternative to generate heat in the future.

Controlling fly ash adhesion at high temperatures via porosity effect

Fly ash adhesion is a universal occurrence in a wide range of combustion plants and causes severe problems that disturb the stable and long-term operation of the facilities, such as decreased heat-transfer efficiency and blocked gas flows. Consequently, controlling fly ash adhesion is a challenge for combustion plants worldwide. Herein, we demonstrate that not only a chemical effect, i.e., changing the composition of fly ash to prevent the formation of eutectic systems with relatively low melting points, but also a porosity effect can be a key enabler for controlling fly ash adhesion at high temperatures. In particular, the addition of fine particles to fly ash powder beds is an effective method for increasing the porosity, which leads to the suppression of tensile strength.

Online determination of potassium and sodium release behaviour during single particle biomass combustion by FES and ICP-MS

This study focuses on the determination of alkali release from wood and straw pellets during combustion. The aim is to expand the knowledge on the K and Na release behaviour and to adopt chemiluminescence-based sensors for online monitoring of alkali detection which can be applied for the prevention of fouling formation in low quality biomass combustion plants. Flame emission spectrometry (FES) was used for optical detection of chemiluminescence spectra of K and Na using optical bandpass filters mounted on an ICCD (Intensified Charge Coupled Device) camera. FES data were verified by additional experiments with a single particle reactor (SPR) coupled with an inductively coupled plasma mass spectrometer (ICP-MS). Using both techniques, the release profiles of K and Na during a single pellet combustion at 1000 °C were determined and obtained K* and Na* emission intensities directly correlated with the results from the ICP-MS. It was determined that the emission intensity of alkali radicals depends on alkali concentrations in the samples and K and Na radical emission intensities increase with increasing alkali amounts in the samples. The ICP-MS data revealed that the release of K and Na mainly takes place during the stage of devolatilization. During devolatilization, almost all potassium and sodium are released from wood samples, while only 65–90% of K and 74–90% of Na are released from straw samples. Based on the results, the flame emission spectroscopy technique is capable to fully detect released alkali metals in the gas phase during combustion and proves a possibility to use flame emission sensors for monitoring the release of alkali species from biomass during combustion processes.

Applicability of Torrefied Sunflower Husk Pellets in Small and Medium Scale Furnaces

The aim of this paper is to test the applicability of upgraded agricultural biomass feedstock such as torrefied sunflower husks during combustion in small and medium heating applications. Sunflower husk is formed in large quantities at enterprises producing sunflower oil and can be used as biofuel. However, big problems arise due to the low bulk density of husks and the rapid growth of ash deposits on the heating surfaces of boilers. In order to solve these problems, it was proposed to produce pellets from husks, and to subject these pellets to torrefaction. After torrefaction, net calorific value was increased by 29% while the risk of high temperature corrosion of boilers was reduced. Signs of ash softening neither occurred in combustion of raw nor in combustion of torrefied sunflower husk pellets. High aerosol emissions, already present in raw sunflower husk pellets, could not be mitigated by torrefaction. First combustion results at medium scale furnaces indicated that sunflower husk pellets (both raw and torrefied) in a commercial boiler < 400 kW, operated in a mode with low primary zone temperatures (< 850 °C), meet current emission limits. Regarding the future upcoming emission limits according to the European Medium Combustion Plant Directive, additional measures are required in order to comply with the dust limits.

MINIMIZATION OF TOXIC EMISSIONS DURING BURNING LOW-GRADE FUEL AT KAZAKHSTAN THERMAL POWER PLANT

This paper presents new results of computational experiments on the implementation of Overfire Air (OFA) technologies using an example of a combustion chamber of the BKZ-75 boiler of the Shakhtinskaya power plant (Shakhtinsk, Kazakhstan) burning high-ash Karaganda coal. The effect of mass air flow through special nozzles located above the burner level on the flow aerodynamics, temperature fields, concentration fields of carbon monoxide CO and nitrogen NO over the entire volume of the combustion chamber was studied. The studied characteristics were compared for various percentages of supplying additional air through OFA injectors: OFA is 0% (basic version), 10% and 18 %. It was shown that the installation of OFA injectors leads to a change in the field of the total velocity vector, temperature, and concentrations of carbon oxides and nitrogen. An increase in the percentage of air supplied through OFA injectors to 18% leads to a decrease in the concentrations of carbon monoxide CO by about 36% and nitrogen oxide NO by 25% compared with the base case. The obtained results will optimize the process of burning pulverized fuel in the combustion chamber of the BKZ-75 boiler, increase the efficiency of fuel burnout, reduce harmful emissions and introduce OFAtechnology at other coal-burning thermal power plants.

Corrosion of duplex stainless steel 2205 in hot flue gas environments produced at advanced oxy-fired pressurized fluidized bed combustion plants

The selection of constructional material of flue gas components is crucial for the successful deployment and long-term safe operation of the newly developed oxy-fired pressurized fluidized bed combustion plants. In this study, the corrosion performance of a candidate steel, duplex stainless steel 2205 (DSS 2205) was investigated in simulated flue gas mainly composed of CO2/H2O/O2/N2/SO2/HCl with a total pressure of 1.50–1.64 MPa at 270−320 °C. The oxidation kinetics of DSS 2205 followed parabolic law, and the formed surface oxide was a double-layer structure with outer Fe-rich oxide and inner Cr-rich oxide. Besides general oxidation, SO2 and HCl-induced pitting also occurred. Increasing temperature led to enhanced general oxidation and accelerated pitting. Extending exposure duration resulted in increased pit density, but did not noticeably affect the maximum pit depth. These results indicate that the steel is a promising candidate for further pilot- and industrial-scale assessments.

Differences between the composition of surface and inner layers of fly ash particles

By studying samples from Czech power plants burning brown coal using X-ray photoelectron spectrometry (XPS) have demonstrated differences in the composition of the ashes in their surface and subsurface layers. The main components of the samples were compounds of aluminum, silicon and oxygen - aluminosilicates. Other elements included sulphur, fluorine and in some cases demonstrably calcium, sodium, magnesium, fluorine and iron. The largest part of the carbon compounds present is the so-called "adventitious carbon", contaminating carbon, i.e. hydrocarbons adsorbed on the surface from the atmosphere. Others come from technology including a small amount of carbides. Distribution of sulphur and iron compounds detected using a short time ion etching is in most cases following: sulphur compounds are concentrated on the surface of ash particles while iron compounds are typically concentrated inside. Differences in composition of surface layers were found to be significant as in the surface composition as in theirs depth profiles. Gas evolution was detected in an ash-water reaction test in which the analysis of the gas has shown that it is mainly about hydrogen and carbon dioxide. Another test with water showed the formation of an incrustation and documented the evolution of gases by the formation of bubbles. The released gases can form explosive mixtures with air, which must be taken into account when removing deposits with a water jet.