Gasification parameters effect of coal gasification on SYNGAS energy potential

Today, in proportion to the development of the countries, the energy demand that is turned on is met by using renewable energy sources (sun, wind etc.) and/or fossil fuels such as oil, natural gas and coal. Since the contribution of energy to the country's economy and external dependency in the way it is achieved are considered, any fuel that can be used as an energy source is important. In our country, coal reserves are of great importance and only 15% are extracted by conventional mining methods. With the accidents we have experienced in conventional mining in recent years, it has become necessary to use coal with a different method to produce energy. Underground coal gasification (UCG) process is a method used to produce energy from low-quality coal, which is not economical to extract by conventional mining. In this method, drilling and wells are opened on the coal bed and firing is done in a controlled manner, then artificial / flammable gas (syngas) is obtained by means of gasification agents such as air, oxygen and water vapor. As a results of the gasification process, flammable gases CO2, CO, H2 and CH4. UCG process has many advantages over conventional mining in terms of economic, environmental, healty and safety factors. It is expected that there will be a decrease in investment and operating costs when considering factors such as no need to gasifier, lack of coal transportation and storage costs. When environmental factors considered, UCG process causes a decrease in CO2, H2S and NOx emissions. CO2 is stored in the gasification cavity. In UCG process, slag and ash remain underground. UCG process is considered to be healthier and safer than conventional mining because drilling pits are used intead of miners. On the other hand, there is a risk of contamination of groundwater and collapse of the coal field. Underground coal gasification process depends on parameters such as depth of coal bed, thermophysical properties of coke, type / mixture ratio of gasifier (air, oxygen and water vapor), ignition time and temperature distribution in coal bed and it is a difficult process to control. In the lab-scale study, the process efficiency was evaluated depending on the parameters such as coal mass, height, length, type of gasification agent, feed rate and temperature distribution in the coal block. In study, syngas energy potential, carbon balance and gasification efficiency were investigated depending on the gasification parameters. Variations in the gasification efficiency depending on the length / width ratio of the coal block in the experiments are discussed. In the evaluations, the coal samples extracted from the reactor at the end of the process and the formed cavity are also important in interpreting the gasification efficiency. Agglomeration (glassy structure) on the surface of the coal due to the increased temperature in the processes from single point firing, especially at the sections where pure oxygen feed is done, stops the progress of gasification process. In order to gasification efficiency calculation, firstly the properties of lignite coal used in experiments have been determined. According to the studies carried out at Dresden Technical University, elemental and short proximately analyzes of Malkara lignite were carried out. According to the short proximate analysis results, Malkara lignite coal contains 22,83% moisture, 15,67% ash, 28,9% volatile matter and 32,6% fixed carbon in the original sample. Also, lower heat value (LHV) of the lignite is 15768 kj/kg. In addition according to elemental analysis results, 41,85% C, 3,06% H, 1,35% N, 11,56% O2 and 3,68 S were included in the original sample. Malkara lignite coal sphere temperature is 1231 oC, hemisphere temperature 1257 oC and melting temperature 1324 oC. An experimental setup was built in the Combustion Laboratories of the Istanbul Technical University Mechanical Engineering Faculty. The experimental apparatus consists of a reactor in which the gasification will occur, a cyclone to remove solid particles such as ash from the syngas, a heat exchanger to cool down the syngas and condense the water and tar in the syngas, a scrubber in order to remove the H2S from the syngas, a vacuum pump to overcome pressure losses in the experimental setup and a flare to burn the resulting syngas in order to safely remove the product. Reactor is designed to allow different well configurations, contains twenty temperature measurement points and is highly insulated in order to correctly simulate the underground conditions. Gas chromatograph and portable syngas analyzer were used to determine the composition of the artificial gas. During the study, nine successful experiments were performed. Seven of these experiments were conducted in the small scale reactor and the last two were in the large scale reactor. Lignite coal extracted from Malkara and Pirinççesme provinces was used in the experiments and air, pure oxygen, air / oxygen mixture, water vapor feed was used as the gasification agent in the processes. In the processes, 50-65% artificial gas was obtained. 1200 oC temperatures were observed in coal. The flow and type of gasification agents are important in the progress of the process. In air-based experiments, the temperatures increase slowly in the coal, whereas in pure oxygen processes the coal heats quickly and causes significant changes in the composition and flow of the artificial gas. The time and duration of use of water vapor in the gasification process play an important role in the progress of the process. At the first feeding of the water vapor, the temperature in the coal decreases and after a while the H2 ratio in the artificial gas composition is increased. In long-term feeds of pure oxygen, a structure called agromelation (glassy structure) emerges and can slow down the progress of the gasification process. Nine experiments were conducted to see the parameter influences in the UCG process. In this study, energy potential calculations were made based on the lower heat value of the coal sample used in the processes. Energy potential calculations of the artificial gas, which is activated due to the gas composition determined by gas chromatography and portable analyzer, are made. Within the scope of the study; parameters such as coal mass, length, width, effect of gasification agent, effect of gasification channel, duration of ignition, effects on syngas energy capacity were investigated. In processes, the gasification efficiency varied between 17,3% and 39,7%. C (carbon) balance is also studied in the study. In the small reactor, 27,5% carbon conversion was achieved and converted to carbon flammable gas (CO, CH4) by 11%. In the case of the large reactor, 42,9% C (carbon) conversion was achieved with 21,3% flammable gas. As a results, using the forward combustion method the maximum gasification efficiency of 39,7% was achieved. Coal blocks with similar length / width ratio have 10% variation in gasification efficiency. As the length / width ratio increases, the gasification ratio increases. In gasification process, if air used as a gasification agent the gasification power increases. In addition to this energy potential increases when water vapor is used as a gasification agent. As a recommendation, the continuous retracting injection point (CRIP) method should be used to increase the efficiency in the gasification process. Care should be taken not to exceed the temperature of 1000 oC in the coal in processes made with pure oxygen feed.