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A co-pyrolysis of woodchips and oil shale was conducted in a continuous reactor at 520 °C in a CO2 atmosphere. Experimental product yields were derived and an analysis of the liquid products was conducted, using gas chromatography, infrared spectroscopy, and physicochemical analysis. A maximum yield of liquids and gases was obtained as the share of biomass increased (43.9 and 35.1 wt%, respectively). Product characterization confirmed additive behavior in co-pyrolysis. The liquid products from copyrolysis blends exhibited fewer oxygenated compounds, derived from biomass, and fewer aromatic compounds, derived from oil shale. Co-pyrolysis liquids contained abundant aliphatic hydrocarbons (C6 to C11). [ABSTRACT FROM AUTHOR]

In order to reach future goals of net carbon neutrality and climate change mitigation, various carbon capture and sequestration techniques must be implemented. Industrial waste rich in chemically active alkaline metal oxides is considered as a potential material for CO2 sequestration. The authors studied the long-term CO2 binding capacity of Ca-rich oil shale ash (OSA) deposits at oil shale(OS)-fired power plants of Estonia and estimated the remaining sequestration potential for in-situ carbonation. Providing energy security, the Estonian oil shale industry is the biggest national producer of solid waste and the leading greenhouse gas emitter, making the country one of the largest per capita producers of CO2 in Europe. The study shows that ash deposits are currently only partially carbonated, with an average CO2 binding rate of 51 kg per tonne of hydrated sediment, most of which being bound in such carbonate minerals as calcite and vaterite, as well as in Ca-silicate thaumasite. It is estimated that at full carbonation of reactive Ca and Mg phases in ash (portlandite, ettringite and semicrystalline C-S-H), the projected average total CO2 binding potential could rise to ca 200 kg per tonne of ash. [ABSTRACT FROM AUTHOR]

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Estonia's basic power supply is covered mainly by oil shale-fired thermal power plants. The pulverized combustion (PC) and circulating fluidized bed combustion (CFBC) technologies are used. The power plant exploitation has revealed the emission of gaseous pollutants, as well as ash handling problems. The hydro ash removal is used at large power plants in Estonia. An overview of the formation and properties of oil shale ash is given. The polluting impact of ash in contact with water is analyzed. Taking into account precipitation and evaporation conditions the amount of water bound by ash as well as ash field water balance is given. The leaching behaviour of oil shale ash is analyzed. The analysis of the ash field structure shows that the degree of water penetration of the ash field body meets the requirements for hazardous waste landfills. The water permeability through dense layers ranges from 0.15 x 10-9 to 16.1 x 10-9 m/s. [ABSTRACT FROM AUTHOR]

The paper presents analysis of data obtained from tests of oil shale (OS) and peat co-combustion in a full-scale 250 MWth (useful heat output) circulating fluidized bed (CFB) boiler. The tests were conducted at nominal boiler load, with peat thermal input up to 30%. During the experiments, gas analysis was performed and ash samples were collected. The specific consumption of the oil shale and peat blend per useful heat and gross electricity was calculated and other techno-economic characteristics were determined. It was found that the co-combustion of oil shale and wet peat increased the CO emission to the level of 60 mg/Nm³. The NOx concentration increased from 120 to 165 mg/Nm³. The SO2 and HCl emissions remained at a very low level -- below 20 mg/Nm³. A significant ash reduction, approximately 4%, was measured in the case of a 30% peat content. Due to the high peat moisture, the flue gas volume increased 5-10%. As a result of addition of peat, the content of particulate matter (PM) 10/2.5 was also lower than that by conventional oil shale CFB firing. Oil shale and peat co-combustion can be considered as a viable option and near-term solution for reducing the environmental impact of oil shale power production. [ABSTRACT FROM AUTHOR]

Oil shale (OS) is an unconventional low-calorific-value fossil fuel, the usage of which is increasing due to increasing energy demand. Today, Estonia’s OS usage is the largest in the world. Approximately 90% of the electricity consumed is produced from Ca-rich OS. Most of the OS, approximately 12 million tons yearly, is used for power generation utilizing pulverized combustion (PC) and circulating fluidized bed combustion (CFBC) technologies that produce nearly 6 million tons of ash. As a result, Estonia has one of the world’s highest CO2 emission rates per capita. The current study is focused on determination of the amount of CO2 bound by CFBC and PC boiler OS ashes in an ash field. The binding ability toward CO2 of the ash stored in an ash field is observed. Based on the in situ experimental data, when looking the binding abilities of ashes from both the technologies separately, it is found that approximately 9.7% of the CO2 emitted is bound by the CFBC ash and about 3.4% by the PC boiler ash in an ash field.    On the basis of experimental data it is found that approximately 5–6% of the CO2 emitted is bound back by oil shale power plant ash fields and sedi­ment ponds. [ABSTRACT FROM AUTHOR]

An investigation of the pyrolysis kinetics of American, Chinese and Estonian oil shales was conducted applying a non-isothermal thermogravimetric analysis (TGA). TGA weight loss curves clearly indicate that the pyrolysis of all oil shales tested is independent of their geographic origin, and is mainly taking place in the temperature range of 300 to 500 °C. As expected, at temperatures above 700 °C mass loss due to the decomposition of oil shale carbonates was detected, except for the Kentucky and Chinese 2 oil shale samples. The kinetic decomposition rate parameters such as activation energy and pre-exponential factor were calculated applying the Coats- Redfern integral and direct Arrhenius methods. Independent of the oil shale kerogen origin, pyrolysis occurs in two consecutive temperature zones with slightly dissimilar kinetic parameter values. The activation energy values obtained were in the range of 14 to 31 kJ/mol for the low and 70 to 149 kJ/mol for the high temperature zone. [ABSTRACT FROM AUTHOR]

The paper presents analyses of data obtained from oil shale pulverized firing tests carried out at the Eesti Power Plant (EPP) that is part of an Estonian power company Narva Power Plants (NPP) owned by a state company Eesti Energia AS. The tests were conducted at two boiler loads: 50% (158 t/h) and 100% (320 t/h) in the TP-101 boiler. During experiments samples of bottom and fly ashes from inertia dust collectors after the super heater (SH) and economizer (ECO), as well as fly ash from the electrostatic precipitator (ESP) of the first, second and third fields were taken. Analysis of the gas sample taken at the ESP exit was performed. The ash distribution at different ash discharge ports was obtained. Analysis of the ash chemical composition was carried out. The specific consumption of oil shale per useful heat and gross electricity production was found and other techno-economic characteristics were determined. The tests at partial and nominal loads showed that the emission of SO2, CO2, CO, NO and HCl at nominal load were essentially higher. The content of fine ash particles (<2.5 μm) after the ESP was higher at nominal load. Results of analysis can serve as a basis for future research and development projects. Also, they can be used to decide whether to continue operation of PF units. [ABSTRACT FROM AUTHOR]

Carbon dioxide emissions are considered a major environmental threat. To enable power production from carbon-containing fuels, carbon capture is required. Oxy-fuel combustion technology facilitates carbon capture by increasing the carbon dioxide concentration in flue gas. This study reports the results of calcium rich oil shale combustion in a 60 kWth circulating fluidized bed (CFB) combustor. The focus was on the composition of the formed flue gas and ash during air and oxy-fuel combustion. The fuel was typical Estonian oil shale characterized by high volatile and ash contents. No additional bed material was used in the CFB; the formed ash was enough for the purpose. Two modes of oxy-fuel combustion were investigated and compared with combustion in air. When N2 in the oxidizer was replaced with CO2, the CFB temperatures decreased by up to 100 °C. When oil shale was fired in the CFB with increased O2 content in CO2, the temperatures in the furnace were similar to combustion in air. In air mode, the emissions of SO2 and NOx were low (<14 and 141 mg/Nm3 @ 6% O2, respectively). Pollutant concentrations in the flue gas during oxy-fuel operations remained low (for OXY30 SO2 < 14 and NOx 130 mg/Nm3 @ 6% O2 and for OXY21 SO2 23 and NOx 156 mg/Nm3 @ 6% O2). Analyses of the collected ash samples showed a decreased extent of carbonate minerals decomposition during both oxy-fuel experiments. This results in decreased carbon dioxide emissions. The outcomes show that oxy-fuel CFB combustion of the oil shale ensures sulfur binding and decreases CO2 production. [ABSTRACT FROM AUTHOR]

The current paper presents the results of incineration of pyrolytic wastewater (WW) in an oil shale fired 250 MW thermal (MW th) circulating fluidized bed combustion (CFBC) boiler. The measurements in the industrial-scale oil shale fired CFBC unit show that WW incineration did not cause the plant to exceed the gaseous pollutant or particulate matter (PM) emission limits set for large combustion plants. The data obtained is compared to previous results from a pilot-scale 60 kW th CFB combustor. In pulverized combustion (PC) units, incineration of pyrolytic WW was carried out a long time ago as it reduced SO 2 emissions and improved PM removal from flue gases in an electrostatic precipitator (ESP). Regarding PM emissions, a similar result was achieved in a CFBC unit; however, a high nitrogen content in WW results in increased NO x emissions. From the practical point of view, pyrolytic WW incineration (ca 13 t/h) increases fuel (oil shale) consumption by up to 6% for the same thermal output, which consequently reduces a unit's efficiency. Image 105 • Emissions from a full-scale combustor correspond to predicted from pilot-scale study. • Pyrolytic wastewater incineration reduces the particulate matter concentration. • Wastewater incineration increases combustor fuel consumption and NOx emissions. [ABSTRACT FROM AUTHOR]

This paper presents the results of the pyrolytic decomposition of six different oil shale samples with different sulphur contents from Estonia, USA and China using non-isothermal thermogravimetry coupled with a mass spectrometer (TGA-MS). Mass spectrometry (MS) was used to analyse the evaporating gases. The results showed a major difference in the evolution of sulphur containing substances. The sulphur behaviour was found to be in excellent correlation with the composition of the sample. H 2 S and SO 2 , the problematic components forming during the pyrolysis process, both exhibited evaporation in two peaks. The kinetic distribution supported the findings of MS − samples with a higher sulphur content exhibited more parallel reactions that had similar weight percentages. SO 2 evolution intensifies above 500 °C. H 2 S is released in the temperature range of 350–500 °C, depending on the sample. The samples Kentucky, Green River, Estonia and Chinese 2 also have an additional peak at 500–570 °C. This is in good accordance with the aforementioned samples having a relatively high amount of sulphur in the forms of organics and sulphides. Based on the results, an important conclusion is that changing the pyrolysis temperature can reduce the sulphur content of the oil produced. The experimental curves obtained were used to calculate the kinetic parameters using a distributed activation energy model. The obtained activation energy values were in the range of 134–276 kJ/mol with the frequency factors ranging from 1.89E10 12 to 1.20E10 14 s −1 . In order to validate the obtained kinetic parameters, the decomposition curves were compared to modelled ones. The dependence of total conversion on reaction time was calculated at isothermal conditions to show the effect of pyrolysis temperature. [ABSTRACT FROM AUTHOR]

A non-isothermal experimental study using thermogravimetric analysis and differential scanning calorimetry coupled with a quadrupole mass spectrometer was conducted to investigate Estonian oil shale combustion characteristics. The analyses were performed in air (N 2 /O 2 ) and oxy-fuel (CO 2 /O 2 ) atmospheres with various oxygen ratios (10, 20 and 30 vol.%). Our experimental results in TGA show that combustion in the CO 2 /O 2 atmosphere is delayed compared to that in the N 2 /O 2 atmosphere. Carbonate minerals in oil shale decompose in air in one step and in the oxy-fuel atmosphere in two separate steps: the decomposition of dolomite (CaMg(CO 3 ) 2 ) and the subsequent decomposition of calcite (CaCO 3 ). An increased oxygen ratio in combustion in the oxy-fuel atmosphere increases the overall combustion rate, whereas the CO 2 emission volumes decrease because of the lower decomposition extent of carbonates. The quadrupole mass spectrometer measurements indicate several combustion products. A higher CO reading is registered in the CO 2 /O 2 atmosphere, but there is no other significant difference. Based on the measurement results, a combustion model for Estonian oil shale is proposed. Combustion in the oxy-fuel atmosphere is similar to combustion in air, which eases the design of oxy-fuel combustors. [ABSTRACT FROM AUTHOR]

Abstract: In thermal processing of oil shale in vertical retorts huge quantities of a solid waste — semicoke are formed. It has been shown that circulating fluidized bed combustion of semicoke could be a promising technology allowing utilization of its high residual energy potential. The main parameters of combustion process and the additional heat produced were calculated and verified by combustion tests in a fluidized bed device with a thermal capacity of 50 kWth. The experiments indicated that semicoke with low moisture content can be burnt directly in fluidized bed. For the combustion of semicoke with higher moisture content (over 10%) about 10% of oil shale must be added. In addition, possibilities for utilizing residual carbon present in semicoke by obtaining carbon-rich materials with further production, for example, activated carbon were discussed. A series of experiments accompanied by SEM and EDAX analysis was carried out in order to elucidate the distribution of carbon and mineral part in semicoke and to find possibilities for their separation and subsequent enrichment. Different separation methods — selective grinding and subsequent screening, pneumatic separation and triboelectroseparation method were analyzed. It was shown that due to close integration of mineral and organic part in semicoke, the separation of carbon-rich ingredients by these methods was not enough effective to obtain enriched products suitable for the production of activated carbon. [Copyright &y& Elsevier]