Energy Conversion Processes withCO₂‐Separation Not Reducing Efficiency

Abstract

Combustion of fossil fuels like coal, oil, or natural gas and also of biomass, bio-oil, and biogas with air implies combustion of hydrocarbons and results in flue gases consisting mainly of carbon dioxide, water vapor, nitrogen, and oxygen surplus [1][2][3][4]. Of course, pollutants like sulfur and nitrogen oxides and fly ash may also be contained in the flue gas, corresponding to the contents of the fuel. These gases and the fly ash have to be separated mainly before or in some cases also after the CO 2 separation to obtain CO 2 in the purity necessary for sequestration. These processes will be neglected in this chapter because such processes are already used in power plants.The amount of energy involved in absorption or adsorption and desorption is the same though not on the same temperature or pressure level. In addition, as CO 2 does not represent the overall minimum energy, there are further exothermal reactions possible, such as carbonate formation. This means that in addition to the amount of energy delivered by the combustion an additional amount of about 50% of the heating value is released by carbonate formation.Therefore, in principle, it should be possible to separate CO 2 from the flue gas without energy losses or even with a gain of additional energy if minerals for carbonate formation are available.Generally speaking to avoid losses and reach highest efficiencies it is necessary not only to combine known processes but to integrate them. CO 2 -Emission Dependency on Fuel and Cycle EfficiencyThe CO 2 emission of power plants depends on both the fuel and the overall plant efficiency.The combustion of the mass of brown coal releasing 1 kWh th thermal energy simultaneously produces about m spCO2th ¼ 400 g-CO 2 per kWh th specific CO 2 -emisHandbook of Combustion Vol.5: New Technologies Edited by

Computational Experiments for Research of Flow Aerodynamics and Turbulent Characteristics of Solid Fuel Combustion Process

“…In flows with high solids content, solid media has a significant effect on convective and diffusive transport. However, the presence of solids in carbon monoxide from coal dust combustion units is so insignificant (with the exception of near-burners area) that the second phase effect is neglected in the calculations [10][11][12][13]. Then the process of burning solid fuel in the combustion chambers can be represented as follows: the flame is a two-phase gas-dispersed system, and the effect of the solid phase on the flow aerodynamics is insignificant [14].…”

Comprehensive Modeling Tool for Chemical Looping Based Processes

“…Practically all these approaches require a considerable amount of energy either for the CO 2 separation step or for air separation in the case of oxyfuel technology. Chemical looping combustion (CLC) using metal oxides as oxygen carriers can be classified as a special type of oxyfuel combustion technology with inherent air separation [2], i.e., there is no need for an auxiliary air separation unit. If a suitable metal oxide is used as oxygen carrier, the CLC system can be operated in a way that the exhaust gas of the fuel reactor ideally consists only of CO 2 and H 2 O and allows for subsequent water condensation, compression, and storage of CO 2 .…”

“…Chemical looping combustion (CLC) using metal oxides as oxygen carriers can be classified as a special type of oxyfuel combustion technology with inherent air separation [2], i.e., there is no need for an auxiliary air separation unit. If a suitable metal oxide is used as oxygen carrier, the CLC system can be operated in a way that the exhaust gas of the fuel reactor ideally consists only of CO 2 and H 2 O and allows for subsequent water condensation, compression, and storage of CO 2 . Therefore, CLC is discussed as one of the most energy-efficient approaches towards carbon capture from power production or fuel upgrading.…”

“…metal oxide, is circulated between two fluidized bed reactors separated with respect to the gas phase. CLC was initially proposed as a means of increasing combustion efficiency [3][4][5] and was later identified as a promising technology for CO 2 capture, where 100 % of carbon capture can be achieved without significant energy consumption [6,7]. In the so-called fuel reactor (FR), a hydrocarbon fuel is oxidized by oxygen released from the bed material.…”