Study Of Supercritical Carbon Dioxide On Transforming Building Materials And Carbon Sequestration Of Underground Coal Gasification

As the realization of deterioration of the environment and the spread of the idea of sustainable development, CO₂ has been treated as one of the pollutants to our environment due to its greenhouse effect. How to utilize and control the CO₂ content in the atmosphere has become a popular project. On the view of energy conservation and environment protection, this thesis mainly demonstrates the improvements of building materials and the underground sealing of CO₂, in order to make the possible contribution of civil industry on environmental protection and energy conservation.Based on the close differential equation set raised by Saetta about the coupling flow of temperature, moisture and gas in porous materials, this thesis develops the numerical model of natural carbonation of concrete porous brick first. After the result of the model has been proved by the experimental formula raised by Ditao Niu, this thesis develops the super-critical carbonation simulation on normal and recycled aggregates concrete porous brick separately by revising the relative parameters of CO₂ and concrete. The result demonstrates that the control factor of carbonation is not the CO₂ content in the brick, but the reaction velocity of CaCO3, which is different with the result of the natural carbonation. The result also shows that the influence of the relative humidity in the porous brick on the super-critical carbonation velocity is more significant compared with its influence on the natural carbonation. The carbonation degree and average pressure strength changes along the principle of negative exponent as time goes up.In the second part of this thesis, the move principle of the upper seam during the underground coal gasification using CO₂ as the ignite gas has been researched, and the simulation of the CO₂ underground storage has been represented after the possibility of UCG has been proved. This thesis first proceeds the numerical simulation of the longitudinal section temperature distribution, the result of which shows that the temperature field only influences the properties of rocks at the range of 2 meters. Based on this result, this thesis simulates the cavity development, the movement of the coal roof and the surface displacement during the shallow coal seam gasification. The result fits well with the existed result in Farhangi's thesis, thus the model in this thesis is proved valid. The deep storage coal UCG has also been simulated in this thesis by adding the depth of coal seam to 1000 meters. The result presents that the nonuniform displacement of deep coal is only 7% to the displacement of superficial coal seam. Thus, in the view of the seam move, the safety of UCG in deep coal in higher than that in superficial coal. At last, this thesis gives the simulation of CO₂ underground storage on the basis of UCG at the gasification velocity of 1m/day. When the pressure of CO₂ is put on the cavity boundaries after UCG, the surface displacement is decreased. In the consequence, the underground storage of CO₂ is beneficial to surface building basement since the pressure of CO₂ can diminish part of the displacement caused by UCG.