Rein Kuusik

CO2 mineral sequestration in oil-shale wastes from Estonian power production

In the Republic of Estonia, local low-grade carbonaceous fossil fuel--Estonian oil-shale--is used as a primary energy source. Combustion of oil-shale is characterized by a high specific carbon emission factor (CEF). In Estonia, the power sector is the largest CO(2) emitter and is also a source of huge amounts of waste ash. Oil-shale has been burned by pulverized firing (PF) since 1959 and in circulating fluidized-bed combustors (CFBCs) since 2004-2005. Depending on the combustion technology, the ash contains a total of up to 30% free Ca-Mg oxides. In consequence, some amount of emitted CO(2) is bound by alkaline transportation water and by the ash during hydraulic transportation and open-air deposition. The goal of this study was to investigate the possibility of improving the extent of CO(2) capture using additional chemical and technological means, in particular the treatment of aqueous ash suspensions with model flue gases containing 10-15% CO(2). The results indicated that both types of ash (PF and CFBC) could be used as sorbents for CO(2) mineral sequestration. The amount of CO(2) captured averaged 60-65% of the carbonaceous CO(2) and 10-11% of the total CO(2) emissions.

Developments in CO2 mineral carbonation of oil shale ash

Solid waste and atmospheric emissions originating from power production are serious problems worldwide. In the Republic of Estonia, the energy sector is predominantly based on combustion of a low-grade carbonaceous fossil fuel: Estonian oil shale. Depending on the combustion technology, oil shale ash contains 10-25% free lime. To transport the ash to wet open-air deposits, a hydraulic system is used in which 10(7)-10(8) cubic meters of Ca(2+)-ion-saturated alkaline water (pH level 12-13) is recycled between the plant and sedimentation ponds. The goals of the current work were to design an ash-water suspension carbonation process in a continuous mode laboratory-scale plant and to search for potential means of intensifying the water neutralization process. The carbonation process was optimized by cascading reactor columns in which the pH progressed from alkaline to almost neutral. The amount of CO(2) captured from flue gases can reach 1-1.2 million ton at the 2007 production level of the SC Narva Power Plants. Laboratory-scale neutralization experiments were carried out to compare two reactor designs. Sedimentation of PCC particles of rhombohedral crystalline structure was demonstrated and their main characteristics were determined. A new method providing 50x greater specific intensity is also discussed.

Waste oil shale ash as a novel source of calcium for precipitated calcium carbonate: carbonation mechanism, modeling, and product characterization.

In this paper, a method for converting lime-containing oil shale waste ash into precipitated calcium carbonate (PCC), a valuable commodity is elucidated. The mechanism of ash leachates carbonation was experimentally investigated in a stirred semi-batch barboter-type reactor by varying the CO(2) partial pressure, gas flow rate, and agitation intensity. A consistent set of model equations and physical-chemical parameters is proposed to describe the CaCO(3) precipitation process from oil shale ash leachates of complex composition. The model enables the simulation of reactive species (Ca(2+), CaCO(3), SO(4)(2-), CaSO(4), OH(-), CO(2), HCO(3)(-), H(+), CO(3)(2-)) concentration profiles in the liquid, gas, and solid phases as well as prediction of the PCC formation rate. The presence of CaSO(4) in the product may also be evaluated and used to assess the purity of the PCC product. A detailed characterization of the PCC precipitates crystallized from oil shale ash leachates is also provided. High brightness PCC (containing up to ∼ 96% CaCO(3)) with mean particle sizes ranging from 4 to 10 μm and controllable morphology (such as rhombohedral calcite or coexisting calcite and spherical vaterite phases) was obtained under the conditions studied.

TG–FTIR analysis of oxidation kinetics of some solid fuels under oxy-fuel conditions

A possible technology that can contribute reduction of carbon dioxide emission is oxy-fuel combustion of fossil fuels enabling to increase CO2 concentration in the exhaust gas by carrying out the combustion process with oxygen and replacing air nitrogen with recycling combustion products to obtain a capture-ready CO2 stream. The laboratory studies and pilot-scale experiments discussed during the last years have indicated that oxy-fuel combustion is a favorable option in retrofitting conventional coal firing. Estonian oil shale (OS) with its specific properties has never been studied as a fuel in oxy-fuel combustion, so, the aim of the present research was to compare thermo-oxidation of OS and some coal samples under air and oxy-fuel combustion conditions by means of thermal analysis methods. Experiments were carried out in Ar/O2 and CO2/O2 atmospheres with two oil shale and two coal samples under dynamic heating conditions. FTIR analysis was applied to characterize evolved gases and emission dynamics. Kinetic parameters of oxidation were calculated using a model-free kinetic analysis approach based on differential iso-conversional methods. Comparison of the oxidation characteristics of the samples was given in both atmospheres and it was shown that the oxidation process proceeds under oxy-fuel conditions by all studied fuels with lower activation energies, however, it can last longer as the same temperatures are compared.

Decarbonization of natural lime-containing materials and reactivity of calcined products towards SO2 and CO2

The results obtained by studying decarbonization of different samples of Estonian limestone and dolomite and the following sulphation or carbonation of calcined products to estimate their SO2 and CO2 binding ability were presented. Experiments were carried out with thermogravimetric equipment(Q-Derivatograph, MOM and Labsys™, SETARAM) – calcination of the samples in the atmosphere of air with the heating rate 10 K per minute using multiplate crucibles, the following sulphation or carbonation of the calcined products after cooling to the fixed temperature (temperature range 400–900°C) under isothermal conditions in the flow of air-SO2 or air-CO2 mixture. Chemical, X-ray, BET nitrogen dynamic desorption, etc. methods for the characterization of the initial samples, intermediate and final products were used.In addition, the possibilities of recurrent use of oil shale ashes taken from different technological points at operating thermal power plants (Estonian and Baltic TTPs, Estonia) as sorbents for SO2 binding from gaseous phase were studied, as well as the possibilities of activation of these ashes towards SO2 binding.The results of these studies confirmed the high reactivity of Estonian limestone and dolomite towards SO2 and CO2. Dependence of SO2 binding mechanism on the SO2 concentration has been established. Modelling of SO2 capture of dolomite and limestone was carried out to establish the kinetic parameters of these processes. The possibilities of activation of oil shale ashes and their effective recurrent use for binding SO2 and CO2 from gaseous phase were confirmed.

Enrichment of carbonate-phosphate ores by calcination and air separation

Abstract The possibility of calcination-separation enrichemnt of carbonate-phosphorite ores from Karatau area has been studied. The calcination of phosphorites was recommended to be carried out in the fluidized bed kiln, the grinding of calcinated phosphorites in a centrifugal impact mill, classification of ground material in a non-rotary air separator. The phosphorite concentrate with a content P 2 O 5 more than 28% and the yield of P 2 O 5 into the concentrate not less than 85% was obtained by using carbonate-phosphorite ores containing 21–23% of P 2 O 5 and 8–10% of CO 2 .

SO2 binding into the solid phase during thermooxidation of blendsestonian oil shale semicoke

Approximately one million tons of semicoke (SC) is formed and stored in open air dumps every year in the production of shale oil by processing Estonian oil shale (OS). The content of different harmful compounds as sulphides, PAH, phenols, etc. in SC make these dumps one of the most serious sources of environmental contamination. The aim of this work was to study the behaviour of sulphur compounds in OS and its SC, formation of SO2 and possibilities of binding it into the solid phase during thermooxidation of fuel blends based on SC. Blends modified with SC ash addition were studied as well. It was determined that SO2 emission in thermooxidation of SC samples started at 280-300°C and proceeded with a steady speed up to 580-600°C and the amount of sulphur evolved was 5-10% from the total content of sulphur in the sample. The amount of SO2 emitted decreased depending on the mass ratio of the composite fuels from 49-56 to 15-35% during thermooxidation of OS samples studied or their blends with SC, respectively, from 43-80% for coal samples to 13-60% for their blends with SC and to 2-13% during thermooxidation of these blends modified with SC ash addition. In the products of thermooxidation formed at 800-900°C the only sulphur containing phase was CaSO4, at 650°C also traces of CaS and CaMg3(SO4)4 were fixed.

A Role-Based Framework for Information System Self-Development

This paper presents an approach to information systems development based on contemporary business and organization models. Business organizations are changing very quickly and their information systems must evolve dynamically with them. We have developed a concept of IS self-development where the information system is treated as an active information view or a level of a business organization providing and mediating not only the information and communication services but also the development services of the organization and its IS. This makes it possible for IS development processes to be handled in the context of the organizational roles ofthe business organization, allowing specialized development organizations to focus on services for IS development. A meta-model of the architecture of the IS development process and a general methodological framework for modeling and organizing such subject-centered development processes have been developed. The paper reflects the current status of an ongoing project (Estonian Science Foundation grant G3765).

Towards Self-development of Evolutionary Information Systems: An Action Research of Business Architecture Development by Students in Socially Networked Groups

We present a case study of business architecture development by students working in socially networked groups. In this case study we emulated a self-development of an evolutionary information system. The “client system” in this emulated project was medical laboratory information system. In the role of the “change agent” were students of two different specialties: medical technology students (one group) and IT students (another group). We describe the process and results of the first (finished) phase of strategic analysis where the initial business architecture was developed. Later on this business architecture will be utilized as a platform for (social, self-) development of business processes and software. Medical technology students (knowing the problem) played the business process owner/analyst dual role. IT students (knowing IT-related solution patterns for the problem and processes) played the business designer role. The relationships between (and inside) the two groups/communities were managed using Google Sites (social) software.

An Effective Inductive Learning Algorithm for Extracting Rules

In this paper we present a new inductive learning algorithm named MONSAMAX for extracting rules. It has some advantages compared to several machine learning algorithms: it uses several new pruning techniques which guarantee great effectiveness of the algorithm; it extracts overlapping rules; as a result it finds determinative set of rules that we can use for post-analysis of extracted rules. Compared to a former algorithm MONSIL it is much less labor-consuming.