Gasification specifics of different types of fuel was researched under the project Scientific Research of Development and Industrial Application of Gasification Technology for High-calorie Material and Waste to Reduce Fuel Consumption, in accordance with contract with SC Naujasis Kalcitas. The project scope included the following activities: development of theoretical background and design of the required experimental setups for the technologies; development of the basis of automatic control; elaboration of technology including the gas generation reactors; development of systems for fuel supply and removal of coke and wires; development of gas transportation and combustion system; data collection and processing for the implemented technology.

 

 

 

Gasification facility: structure of solid fuel gasification reactor 

 

Gasification of high-calorie waste was investigated theoretically and experimentally. The following types of waste that could be potentially used as fuel were analyzed: tyres, wood, peat and textile waste (cotton, wool, viscose and mixtures). Gasification tests of high-calorie waste were performed in the Laboratory of experimental research of gasification processes of Lithuanian energy institute, using the gasification reactor. Time of emission of volatile compounds from the heated samples was measured experimentally, as well as the amount of resulting tars and carbon residues. From these data, content of volatile compounds in the respective fuel sorts were determined. As the volatile content of textile material was known, theoretical calculations of gasification process were carried out yielding all the required parameters in detail: the required amount of air, the gas yield, the thermal balance of fuel for pyrolysis, the expected chemical composition of gas, how to enhance the gasification process, etc.

 

It is reasonable to distinguish two cases of the gasification process for two types of fuel – high-calorie fuel (tyres, plastics) and low-calorie fuel (wood, peat, and waste). In the first case, lower amount of air is required to reach the temperature of 1100 oC and to evaporate more volatiles, producing high-calorie gas: 5000–7000 kJ/Nm3. In the second case, the fuel contains more oxygen and an extensive carbon backbone, therefore, it is more difficult to heat, it decomposes slower and therefore higher temperature is necessary. Light gases CO, H₂, CH₄, C₂H₄ are produced and the caloric value only amounts to 3000–4000 kJ/ Nm³. The case of textile gasification has exemplified a characteristic feature of gasification when the oxygen content of fuel has a special importance: as the heated fuel starts to decompose during autopyrolysis, many species of hydrocarbon compounds form and the oxygen contained in the fuel begins to interact yielding high amounts of CO, CO₂ and unbound H₂ besides H₂O. This is the novelty related to the gasification process, which has not been published yet.

 

 

Chromatograms of hydrogen and methane from gasification products of scrap tyres: 1, 2 – samples were taken at steady-state reactor operation regime; 3, 4 – samples were taken at transient reactor operation regime 

The Laboratory also performs research on incineration and gasification of scrap tyres, and an experimental reactor was designed. Severe problems arise in operation of gas generators since aggressive gases produced during tyre gasification provoke corrosion of steel parts of the generators, therefore, the experts of the laboratory sought to determine the composition of gas generated during gasification and to test its effect upon the steel samples. The experimental setup of tyre gasification, available at the laboratory of experimental research of gasification process, was used for the tests. Gases produced by tyre gasification were analysed quantitatively and qualitatively by the gas chromatograph VARIAN GC-3800 and the gas analyzer TESTO 350 XL. The metal samples were kept in the ambience of gas produced by tyre gasification for 100 hours, at the temperature of 800 ^oC. The surface microstructure of the steel samples was analyzed using the scanning electron microscope JEOL JSM-5600. X-ray diffraction analysis was performed for the corroded steel samples by the analyzer DRON-UM2. The test results suggest that the ambience of aggressive gases produced during the tyre gasification (CO, H2S, H2, etc.) degrade the steel resistance to corrosion. Effect of these gases on different sorts of steel was identified and the recommendations were prepared for usage of different types of steel in the reactor.

 

An experimental device of novel technology was produced and tested under the project Scientific Research of Development and Industrial Application of High-calorie Materials and Waste Gasification Technology Reducing Fuel Consumption. Fuel is supplied at the required rate through the valve latches and heated to ignition, and air is supplied in 12 streams perpendicular to fuel flow. The secondary air supply system is used; wire and coke residue is removed by pushing the wires by the hooks of the moving grate, and the coke drops down through the grate openings. The wires and coke are collected into separate closed tanks and the generated gas is extracted by a special-purpose fan at the temperature of 600 ^oC. The combustion control system was developed: air supply is adjusted according to the temperature of the generated gas, and the fuel supply is automated. The fuel supply and the coke removal unit is the second most important part of the technology. It comprises the hydraulically-operated fuel supply through two latches that separate the reactor space from the ambient air, and a complex implement of a moving grate comprising 11 independently moving bars with attached hooks for wire removal, and for dropping the coke down into the storage. The generated gas is exhausted by a special-purpose fan at the temperature of 600 ^oC; a special system ensures the constant zero overpressure inside the reactor. The exhaust control system is self-sufficient. Besides these principal technological devices, that are necessary for the experiments from the environmental point of view, the incineration unit for the generated gas, the reactor heating system, and the fuel transportation system are used. In order to test the technologies, the data collection system was developed and the control software was developed.

 

 

 

 

Emission of nitrogen oxides during fuel combustion is an important issue in power generation. The amount of oxides can be reduced by improving the combustion quality in the boiler combustion chamber. In 2008, under the project Theoretical Calculations and Experimental Research for Reduction of Nitrogen Oxides and Carbon Monoxide in the GM Boiler at SC Danisco Sugar Kėdainiai, with partial funding from the Lithuanian State Science and Studies Foundation, the burners of the steam boiler GM-50/14 at SC Danisco Sugar Kėdainiai were rebuilt and the combustion process of this boiler was automated. The works were implemented using the simulation software FLUENT. In order to reduce the computational cost, a symmetric problem was solved for half the combustion chamber with two boilers. The improved burner was designed in accordance with the results obtained. The burning process is unable by adjusting the fan blade angle and adjusting the gas sprinkler openings depending on the pressure in the gas supply system. Simulation results were compared to the experimental tests of combustion adjustments and a good agreement was found. This work made it possible to reduce the content of nitrogen oxides in the flue gas from 240 mg/Nm³ to 195 mg/Nm³ at full capacity of the boiler GM-50/14 operation.

 

 

 

 

By the contract Upgrade of the Burners of the Reforming Furnace 75 for a New Fuel Type, Implementation of Experiments with a Single Burner, their Technical Registration and Adjustment of Combustion Process in the Furnace with SC Achema, production of the burners for the primary reforming furnace F201 was completed. During the methanol production, from natural gas and water vapour, hydrogen is produced. The essence of this process is to supply heat to this mixture through the pipes filled with catalysts and to efficiently extract as much hydrogen as possible. The purpose of this work was to rebuild the old burners and to adjust them to the new type of the gas mixture fuel and the parameters (the temperature, the pressure and the mass flows) of the novel technology designed by the Khimtekhnologiya enterprise (Ukraine). The changes in the structural elements and the effect of water vapor and admixtures of gaseous nitrogen upon reduction of nitrogen oxide content were experimentally tested in the furnace. Other experiments were carried out in the facility installed at LEI, in order to select the best shape of the burner nozzle and the spatial geometry of the gas openings of the burner. The results of this work were applied to the design of the burner “Pirna”, used in the methanol reforming furnace, whereas the documentation of this burner was prepared and the drawings of the ceramic nozzles were drawn up.

 

In 2008 the EUREKA project E!3590 USE-GLYCEROL Utilisation of Glycerol Fraction from Biodiesel Plants was completed. The combustion tests of glycerol fraction were carried out in order to develop the burner prototype, to present the recommendations and conclusions regarding glycerol utilization as a fuel for thermal power generation. Throughout the three years period of the project activities, a great deal of experimental research in glycerol combustion was performed, and as a result, the main external characteristics of glycerol spraying (the optimum temperature, pressure, atomized droplet size) were determined using the centrifugal mechanical sprayer, as well as the quality of combustion process and emissions of the main pollutants CO, NO_x, SO₂, CO₂ and particulates.

 

 

Prototype of glycerol burner 

Thermal and X-ray diffraction analyses of the solid particles were performed and the crystallographic structure, thermal properties and the phase change point of the material were determined. An acceptable technology for treatment of solid particles and its efficiency were identified. No production of a potential carcinogenic agent (acrolein) was detected in the combustion products of the glycerol fraction. Together with CSC Tauragės Šilumos Tinklai (Tauragė district heating company), scientific applied research of combustion of glycerol and its mixture with other types of liquid fuel was carried out and the possibility of glycerol combustion in spatial combustion chambers was clarified. The combustion tests performed at LEI and at the company have demonstrated that glycerol can be utilized as a fuel in thermal power production, provided the combustion process is properly adjusted and solid particles are removed from the combustion products. The developed glycerol firing technology enables the biodiesel production plants to combust the bulk glycerol and to produce additional heat that can be utilized for their own needs or sold to nearby heat users.

 

Under this project, LEI performed also experimental research of glycerol thermal breakdown using its partial oxidation and autothermal conversion. The optimum conditions (temperature, oxygen and water vapour content) were identified to maximize the hydrogen concentration in the reaction products. Further utilization of this type of syngas depends only on the selected production technology of pure hydrogen, as well as on the production technology of methanol, ethanol, dimethyl ether or synthetic biodiesel oil.

 

 

Laboratory researchers at glycerol gasification test facility

 
An experimental research setup was designed and installed for experimental tests of thermal breakdown of glycerol fraction. The reaction products leaving the reactor are fed into the electrically heated chamber, where a constant temperature is maintained. The optimum process conditions (temperature, oxygen and water vapour content), maximizing the H2 gas yield and the catalyst efficiency, were determined experimentally. Thermodynamic analysis of chemical reactions taking place during glycerol oxidation, performed as a part of earlier research, determined that the principal end products of the partial oxidation reaction is hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), acetylene (C2H2) and unreacted initial reacting substances. It was determined that the optimum temperature of the autothermal conversion maximizing the hydrogen yield was 1000 K.

 

A number of models are currently in use to describe the motion of granular matter, of which the discrete element method (DEM) is the most precise. Mixing and segregation is very important for solid fuel combustion. For this purpose, using the software developed earlier, mixing and segregation of granular matter was numerically simulated in order to develop the characterization techniques of these processes and to identify common features. Mixing of round (spherical) particles by a stirring bar was simulated. The parameters, characterizing the segregation process, were proposed i.e., its intensity and the final segregation value. During mixing, groups of particles emerge in the granular matter, the motion of which is more or less correlated. In order to examine the emergence and evolution of such groups during the process, as well as their influence on the mixing and segregation processes, appropriate methods should be applied for identifying these groups from the available data of particle velocities and coordinates, calculated during the simulation. For this purpose, community detection algorithms known in the graph theory, that are currently widely researched and applied in many fields, were applied. This technique will be further developed.

 

Simulated temperature distribution in a combustion chamber, at the plane of burners

 

Precise approximation of particle shapes is an important task in order to model the properties of bulk materials with sufficient precision. Above mentioned modelling of particle mixing and segregation was based on round (spherical) particle shapes. However, the systems of spherical particles are often inadequate to approximate realistic granular materials. Elliptical shape can be more precise in some cases; however, calculation of the interaction of elliptical particles is rather complex and computationally costly. The task can be simplified by treating the particles as composed of spherical sub-particles, with the total shape close to elliptical one. Under collaboration with Vilnius Gediminas Technical University, numerical experiments of piling of 3-dimensional elliptical particles in a single plane at a vertical wall were performed. The angle of repose and porosity of the resulting pile were determined, as well as an average number of contacts per single particle. It was determined that simulation of ellipse dynamics is slower by a factor of 1.66 than similar simulations of spherical particle dynamics.

 

During 2008, 1 article was published in the journal indexed in the ISI list, 1 article in international journal and 3 papers at international conferences.