Search

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]

Low-temperature circulating fluidised bed combustion (CFBC) of oil shale results in Ca-rich ashes with low pozzolanic properties, raising concerns regarding the long-term stability of ash depositories. This paper presents findings from a long-term field study investigating the mineral and chemical transformations of total CFBC ash sediments over a 15-year period. The study reveals that the pozzolanic properties of CFBC ashes are primarily influenced by the formation of Ca-Al sulphate mineral ettringite and the compactness of sediment. The compaction of ashes during deposition contributes to the development of a dense microstructure, providing uniaxial compressive strength that exceeds 20 MPa. Our findings suggest that compacted and hydrated CFBC ashes are sufficiently stable in ash deposits, holding promise as a sustainable alternative for cement-free construction materials. [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]

Copyright of Estonian Journal of Earth Sciences is the property of Teaduste Akadeemia Kirjastus and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Coal co-firing experiments were conducted in a 250 MW oil shale fired circulating fluidized bed combustion (CFBC) boiler. The objective of the experiments was to test whether adding coal to oil shale would allow the use of the latter with lower heating value. Bituminous coal was mixed with oil shale and fed into the boiler via existing fuel feeding ports. Two test series were accomplished: 11-29% thermal input of coal mixed with 8.4 MJ/kg oil shale (standard fuel), and 12-32% thermal input of coal mixed with 7.5 MJ/kg oil shale. During the experiments, which lasted in total for 15 days, ash samples were collected and flue gas analysis was performed. The boilers were able to continue work with all the fuel mixtures, but a significant increase of nitrogen oxides (NOx) emissions and heat losses due to unburnt carbon in the bottom and fly ashes were observed. The heat losses can be reduced by upgrading the fuel preparation system, but NOx emissions limit can be reached only with installation of an additional DeNOx system. The ash chemical composition remained similar. Sulphur emissions stayed minimal, but a slight increase of carbon monoxide concentration was noticed. Coal cofiring is possible in oil shale CFBC boilers, but the coal must have low fuel nitrogen content and extra attention to the fuel preparation system has to be paid. [ABSTRACT FROM AUTHOR]

The solid heat carrier (SHC) retorting method, so-called Galoter process, was developed for oil shale processing at the end of the 1940s. Since then the method has undergone several improvements. Nowadays there are different modifications of Galoter process in use -- Petroter, Enefit-140 and TSK-500 technologies. The major differences between these technologies are in sizing (throughput), technical solutions and layouts. Recently a shale oil plant based on a new technology, Enefit-280, was commissioned. Enefit-280 is a technology successor of Enefit-140 where the heating of solid heat carrier is accomplished using the circulating fluidized bed (CFB) combustion technology as opposed to the conventional heat carrier combustion technology in Enefit-140. The CFB technology in Enefit-280 was integrated into the process to improve the performance of SHC heating process and reduce the emissions. Operational experience has demonstrated that the modified technology of SHC oil shale retorting has a potential to play a key role in shale oil production with reduced environmental impact. [ABSTRACT FROM AUTHOR]

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]

Oxy-fuel combustion is considered as one of the promising carbon capture and storage (CCS) technologies for coal-fired boilers. In oxy-fuel combustion, the combustion gases are oxygen and the recirculating flue gas, and the main components of the combustion gas are O2, CO2 and H2O [1]. The paper presents the results of the calculation of the flue gas amount during combustion of oil shale using oxy-fuel technology in a circulated fluidized bed (CFB) mode. The calculations were performed for different oil shale heating values and different recycled flue gas (RFG) ratios. Oxy-fuel combustion with flue gas recycling was found to enable the decrease of the extent of carbonate minerals decomposition (ECD), thereby increasing the amount of heat released per 1 kg of fuel. To minimize ECD, the recycled flue gas ratio should be maintained at a level higher than 0.7. This condition allows an increase of the partial pressure of CO2 over the equilibrium state line of calcite decomposition reaction at the bed temperature. The decrease of ECD was observed up to kCO2-min = 0.28. The decrease of kCO2 leads to an additional increase in the amount of heat released during oil shale combustion per 1 kg and, depending on the mean lower heating value (LHV), the heat can be increased up to 0.34 MJ/kg. A comparison with the bituminous and anthracite coals revealed that the specific emission of CO2 per input fuel energy for oil shale is expected to be even smaller compared with those of the considered coals. [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]