Combustion and steam

The shrinking core and the volume-reaction models have been examined to interpret the conversion-time data of combustion and steam gasification of the gingko nut shell char [4]. The shrinking core model provides the better agreement with the experimental data. With the shrinking core model, the relationship between [1-(1-X) ] and the reaction time t at 350°C -... 

Von Hippel et al. [104] patented a special reactor head, which allows for a distribution of the two gas flows through each individual channel. Even at a 1 200 °C monolith temperature the heads did not heat up to more than 200 °C, hence silicone rubber was applied for sealing the heads. This concept was applied for coupling methane combustion and steam reforming in separate flow paths [105],... 

C. Ramshaw, Combustion and steam reforming of methane on thin layer catalysts for use in catalytic plate reactors. Fourth UK/National Conference on Heat Transfer, Institution of Mechanical Engineers, 26-27 September 1995, pp. 85-89. 

Figure 24.1 Numerical calculations of combined methane combustion and steam reforming, (a) Outlet conversion versus channel half-height (b) wall temperature as a function of dimensionless reactor length calculation results determined at constant inlet velocity [33],...

Petrachi, GA, Negro, G, Specchia, S, Saracco, G, Maffetone, PL, Specchia, V. Combining catalytic combustion and steam reforming in a novel multifunctional reactor for on-board hydrogen production from middle distillates. Ind. Eng. Chem. Res. 2005 44 9422-9430. 

High-efficiency gasification system that uses two types of turbines, combustion and steam. 

Avd et cd. investigated combined catalytic combustion and steam reforming but also quasi-autothermal reforming of methane in fixed catalyst beds. Two different catalyst formulations were used to combine the combustion reaction with steam reforming, namely a nickel catalyst for steam reforming and a platinum catalyst for methane combustion. The two catalysts were assumed to be placed into two serial... 

Grabowski, J. W., Vinsome, P. K., Lin, R. C., Behie, A. and Rubin, B. (1979) A fully implicit general purpose finite-difference thermal model for in-situ combustions and steam. SPE 8396, Proceedings of the SPE 54th Annual Fall Conference, Las Vegas, NA, September 1979. 

Fuel switch. The choice of fuel used in furnaces and steam boilers has a major effect on the gaseous utility waste from products of combustion. For example, a switch from coal to natural gas in a steam boiler can lead to a reduction in carbon dioxide emissions of typically 40 percent for the same heat released. This results from the lower carbon content of natural gas. In addition, it is likely that a switch from coal to natural gas also will lead to a considerable reduction in both SO, and NO, emissions, as we shall discuss later. 

The specific design most appropriate for biomass, waste combustion, and energy recovery depends on the kiads, amounts, and characteristics of the feed the ultimate energy form desired, eg, heat, steam, electric the relationship of the system to other units ia the plant, iadependent or iategrated whether recycling or co-combustion is practiced the disposal method for residues and environmental factors. 

J. G. Singer, Combustion Engineering—A Reference Book on Combustion, A Reference Book on Fuel Burning and Steam Generation, Combustion Engineering, Inc., Windsor, Conn., 1991. 

The unit Kureha operated at Nakoso to process 120,000 metric tons per year of naphtha produces a mix of acetylene and ethylene at a 1 1 ratio. Kureha s development work was directed toward producing ethylene from cmde oil. Their work showed that at extreme operating conditions, 2000°C and short residence time, appreciable acetylene production was possible. In the process, cmde oil or naphtha is sprayed with superheated steam into the specially designed reactor. The steam is superheated to 2000°C in refractory lined, pebble bed regenerative-type heaters. A pair of the heaters are used with countercurrent flows of combustion gas and steam to alternately heat the refractory and produce the superheated steam. In addition to the acetylene and ethylene products, the process produces a variety of by-products including pitch, tars, and oils rich in naphthalene. One of the important attributes of this type of reactor is its abiUty to produce variable quantities of ethylene as a coproduct by dropping the reaction temperature (20—22). 

Chemistty of Partial Oxidation. The process is carried out by injecting preheated hydrocarbon, preheated oxygen, and steam through a specially designed burner into a closed combustion vessel, where partial oxidation occurs at 1250—1500°C, using substoichiometric oxygen for complete combustion. 

It is important that the rate of circulation within the waterwaH tubes be great enough to carry heat away from the metal tube walls fast enough to prevent the walls from overheating. Because the circulation is dependent on the difference ia density between the cooler water found ia the downcomers and the hotter water and steam located ia the waterwaHs, the rate of circulation iacreases as this differential pressure iacreases. Thus, the rate of heat transfer from the combustion 2one to waterwaHs, the height of the boiler, and its operating pressure all combine to determine the rate of circulation. 

New units can be ordered having dry, low NO burners that can reduce NO emissions below 25 ppm on gaseous fuels in many cases, without back-end flue-gas cleanup or front-end controls, such as steam or water injection which can reduce efficiency. Similar in concept to low NO burners used in boilers, dry low NO gas turbine burners aim to reduce peak combustion temperatures through staged combustion and/or improved fuel—air mixing. 

Power, Energy, and Drives. Centrifuges accomplish their function by subjecting fluids and soHds to centrifugal fields produced by rotation. Electric motors are the drive device most frequently used however, hydrauHc motors, internal combustion engines, and steam or air turbines are also used. One power equation appHes to all types of centrifuges and drive devices. 

If the CO is not completely combusted to CO2 in the regenerator, a CO boiler is used to complete the combustion. The resulting heat of combustion and the sensible heat of the flue gas along with any heat from auxiUary fired fuel are recovered in the form of high pressure steam. When the regenerator is operated in total CO bum, the CO boiler is replaced with either a shell and tube exchanger or a box-type waste heat boiler (see Heat... 

While process design and equipment specification are usually performed prior to the implementation of the process, optimization of operating conditions is carried out monthly, weekly, daily, hourly, or even eveiy minute. Optimization of plant operations determines the set points for each unit at the temperatures, pressures, and flow rates that are the best in some sense. For example, the selection of the percentage of excess air in a process heater is quite critical and involves a balance on the fuel-air ratio to assure complete combustion and at the same time make the maximum use of the Heating potential of the fuel. Typical day-to-day optimization in a plant minimizes steam consumption or cooling water consumption, optimizes the reflux ratio in a distillation column, or allocates raw materials on an economic basis [Latour, Hydro Proc., 58(6), 73, 1979, and Hydro. Proc., 58(7), 219, 1979]. 

Design Methods for Calciners In indirect-heated calciners, heat transfer is primarily by radiation from the cyhnder wall to the solids bed. The thermal efficiency ranges from 30 to 65 percent. By utilization of the furnace exhaust gases for preheated combustion air, steam produc tion, or heat for other process steps, the thermal efficiency can be increased considerably. The limiting factors in heat transmission he in the conductivity and radiation constants of the shell metal and solids bed. If the characteristics of these are known, equipment may be accurately sized by employing the Stefan-Boltzmann radiation equation. Apparent heat-transfer coefficients will range from 17 J/(m s K) in low-temperature operations to 8.5 J/(m s K) in high-temperature processes. 

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