Gasification balancing

W.J. Lee, Coal Gasification Characteristics in a Thermo-balance and Fluidized Bed Reactors, PhD Thesis, KAIST, Korea, 1995. 

The composition of a gas derived by the gasification of coal is, volume percentage carbon dioxide 4, carbon monoxide 16, hydrogen 50, methane 15, ethane 3, benzene 2, balance nitrogen. If the gas is burnt in a furnace with 20 per cent excess air, calculate ... 

It is not difficult to write a number of chemical equations to represent physical, thermal, and chemical reactions taking place in a gasification vessel. In theory, gasification processes can be designed so that heat release (exothermic reactions) balances the heat required by endothermic reactions. But in practice many of the above physical, thermal, and chemical reactions may take place simultaneously, making a precise prediction of the quantity and quality or composition of product gas somewhat difficult. 

Hirano, A., Hon-Nami, K., Kunito, S., Hada, M., and Ogushi, T. (1998). Temperature Effect on Continuous Gasification of Microalgal Biomass Theoretical Yield of Methanol Production and its Energy Balance, Catalysis Today 45. pp. 399-404. 

M. Greenfeld described unique laboratory experiments designed to stimulate and understand the complex chemistry of in-situ coal gasification. Developed at the Alberta Research Council, the gasification simulator was heavily instrumented with calorimeters and gas chromatographs to determine the enthalpy, composition, and kinetics of formation of the product gases. Computer techniques were used to calculate mass and heat balances and to test kinetic models. 

The second material property is heat of gasification, L, defined as the net heat flow into the material required to convert one unit mass of solid material to volatiles. The net heat flux into the material can be obtained from an energy balance at the surface of the specimen. Typically, a sample exposed in a bench-scale calorimeter is heated by external heaters and by its own flame. Heat is lost from the surface in the form of radiation. Owing to the small sample size, the flame flux is primarily convective, and flame absorption of external heater and specimen surface radiation can be neglected. Hence, L can be defined as... 

The velocity of the combustion front is determined by the volatile matter content of the raw coal, Wv. If the volatile matter content of the coal is high the frontal velocity will be slowed. With low volatility coals the frontal velocity will be relatively fast for the same excess energy production in the com-bustion/gasification regions of the bed. The velocity vc is set by the requirement that the volatiles content of the coal ahead of the devolatilization zone be essentially that of the raw coal. From an analysis of the energy balance in the region near the front of the devolatilization zone, it can be shown that a particular root of the relation below establishes v (3) ... 

By making use of the physical structure and chemical rate expressions described above it is possible to formulate mass and energy balances for the gasification of a single porous char particle. The mass balances for the diffusing species take the form ... 

The software system, to meet the needs of the 1980 s, has wide flexibility and capabilities. For processes such as coal gasification or coal liquefaction, it can be used to perform steady state material and energy balances, calculate sizes of equipment, and carry out economic evaluations. Its flexibility can allow for the handling of coal or other solids in streams and equipment, and its capabilities allow for the simulation of many different types of process equipment and the calculations of physical properties under widely different conditions. Included in this is the ability to analyze conventional chemical and petroleum processes. Another valuable feature 1s a good preliminary cost estimation capability that permits the comparison of alternative processes on an economically consistent basis at an early stage of development. 

An exergetic analysis of coal gasification has already been performed for individual processes (1, 2). This showed that high exergetic losses may occur in the waste heat section of such a plant. In this article, an attempt is made to determine the influence of the chosen concept and the gasification parameters on the exergy balance by systematic investigation. 

The coal gasification process is represented by a reactor, to which coal, including ash, water and oxygen are fed. Since the gasification reactor is not part of the balance chosen for this analysis, the question of whether water is fed to the reactor in the form of a liquid or in the form of steam can be disregarded. 

Electrochemical properties. Applied Catalysis B Environmental 74 337-350 Athanasiou C, Coutelieris F, Vakouftsi E, Skoulou V, Antonakou E, Mamellos G and Zabaniotou A, (2007). From biomass to electricity through integrated gasification/SOFC system-optimization and energy balance. International Journal of Hydrogen Energy, 32(3) 337-342... 

To illustrate this point, one may consider the detailed mass and energy balance calculations that are an integral part of fluidization gasification modeling. For example, Weil and his co-workers, at the Institute of Gas Technology (1 ), are... 

Figure 116. Ammonia production based on heavy fuel oil (l.inde flow scheme with Texaco gasification) a) Air separation unit h) Soot extraction c) C02 absorption d) Methanol/H,() distillation e) Stripper f) Mol regenerator g) Refrigerant h) Dryer i) liquid N2 scrubber j) Syngas compressor k) Nil, reactor Material Balance...

Natural gas will remain the preferred feedstock of present ammonia production technology in the medium term (15-20 years) as may be assumed from the world energy balance shown in Table 47. Partial oxidation of heavy hydrocarbon residues will be limited to special cases and coal gasification might not play a major role in this period. 

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