Combustion, heat fuels

Whereas most FRs act by interfering with one of the three supports of combustion heat, fuel and oxygen, MC acts on all three. In the initial stage it creates a heat sink by endothermic reactions and subsequent decomposition of melamine vapours. It provides only about 40% of the heat of combustion of hydrocarbons, and the combustion then generates nitrogen, which acts as an inert diluent. 

Combustion is prevented or stopped by affecting one or more of the three components necessary to support combustion (heat, fuel, and oxygen). Flame-retardant mechanisms cluster into four general classes. 

Flame retardant (FR) additives work by breaking one of the links that produce and support combustion heat, fuel, and air. They may quench a flame by... 

Whereas most FRs act by interfering with one of the three main supports for combustion, heat, fuel, and oxygen, MC acts against all three. In the initial stage... 

With respect to fuels utilized as heating fuels for industrial furnaces, or as motor fuels for large diesel engines such as those in ships or power generation sets, the characteristics of primary importance are viscosity, sulfur content and the content of extremely heavy materials (asphaltenes) whose combustion can cause high emissions of particulates which are incompatible with antipollution legislation. 

This chapter comprises three parts wherein we will examine the specifications of motor and heating fuels imposed by combustion, storage and distribution, and protection of the environment. 

With regards to the overall balance of combustion, the chemical structure of the motor or heating fuel, e.g., the number of carbon atoms in tbe chain and the nature of the bonding, does not play a direct role the only important item is the overall composition, that is, the contents of carbon, hydrogen, and — eventually— oxygen in the case of alcohols or ethers added to the fuel. 

Third, design constraints are imposed by the requirement for controlled cooling rates for NO reduction. The 1.5—2 s residence time required increases furnace volume and surface area. The physical processes involved in NO control, including the kinetics of NO chemistry, radiative heat transfer and gas cooling rates, fluid dynamics and boundary layer effects in the boiler, and final combustion of fuel-rich MHD generator exhaust gases, must be considered. 

Thermal decomposition of spent acids, eg, sulfuric acid, is required as an intermediate step at temperatures sufficientiy high to completely consume the organic contaminants by combustion temperatures above 1000°C are required. Concentrated acid can be made from the sulfur oxides. Spent acid is sprayed into a vertical combustion chamber, where the energy required to heat and vaporize the feed and support these endothermic reactions is suppHed by complete combustion of fuel oil plus added sulfur, if further acid production is desired. High feed rates of up to 30 t/d of uniform spent acid droplets are attained with a single rotary atomizer and decomposition rates of ca 400 t/d are possible (98). 

While the rotary dryer shown is commonly used for grains and minerals, this system has been successfully applied to fluid-bed diying of plastic pellets, air-hft diying of wood fibers, and spray drying of milk solids. The air may be steam-heated as shown or heated By direct combustion of fuel, provided that a representative measurement of inlet air temperature can be made. If it cannot, then evaporative load can be inferred from a measurement of fuel flow, replacing AT in the set point calculation. 

FIG. 27-13 Available heats for some typical fuels. The fuels are identified by their gross (or higher) heating values. All available heat figures are based upon complete combustion and fuel and air initial temperature of 288 K (60 F). To convert from MJ/Nm to Btii/ft, multiply by 26.84. To convert from MJ/dm to Btii/gal, multiply by. 1588. 

Industrial furnaces serve the manufacturing sec tor and can be divided into two groups. Boiler furnaces, which are the larger group and are used solely to generate steam, were discussed earlier in the subsec tion on industrial boilers. Furnaces of the other group are classified as follows by (1) source of heat (fuel combustion or electricity), (2) func-... 

Combustion is the entire process by which something is oxidized. It is part of the use of gasoline or diesel fuel in automobiles and trucks, as well as part of propulsion in aircraft either in jet engines or propeller engines. This latter association is so often made that the propulsive devices in aircraft are called combustors. Similarly, furnaces and boilers, that often involve flames for the production of heat, are combustion devices involving many of the elements of the complete process. Incinerators, too, are commonly associated with combustion of fuel in the form of waste materials. Other common manifestations of coiiibustioii are house, forest, and chemical fires ... 

According to r] = l-Rf the efficiency of the ideal Otto cycle increases indefinitely with increasing compression ratio. Actual engine experiments, which inherently include the real effects of incomplete combustion, heat loss, and finite combustion time neglected in fuel-air cycle analysis, indicate an efficiency that IS less than that given by r =l-R when a = 0.28. Furthermore, measured experimental efficiency reached a maximum at a compression ratio of about 17 in large-displacement automotive cylinders but at a somewhat lower compression ratio in smaller cylinders. 

Gas turbines can operate in open or closed cycles. In a simple cycle (also known as an open cycle), clean atmospheric air is continuously drawn into the compressor. Energy is added by the combustion of fuel with the air. Products of combustion are expanded through the turbine and exhausted to the atmosphere. In a closed cycle, the working fluid is continuously circulated through the compressor, turbine, and heat exchangers. The disadvantage of the closed cycle (also known as the indirect cycle), and the reason why there are only a few in operation, is the need for an external heating system. That is an expensive addition and lowers efficiency. 

The material in this section is divided into three parts. The first subsection deals with the general characteristics of chemical substances. The second subsection is concerned with the chemistry of petroleum it contains a brief review of the nature, composition, and chemical constituents of crude oil and natural gases. The final subsection touches upon selected topics in physical chemistry, including ideal gas behavior, the phase rule and its applications, physical properties of pure substances, ideal solution behavior in binary and multicomponent systems, standard heats of reaction, and combustion of fuels. Examples are provided to illustrate fundamental ideas and principles. Nevertheless, the reader is urged to refer to the recommended bibliography [47-52] or other standard textbooks to obtain a clearer understanding of the subject material. Topics not covered here owing to limitations of space may be readily found in appropriate technical literature. 

An example of reducing energy consumption in use is found in 4-stroke automobile lubricants.Only about 20-35% of the energy released by the combustion of fuel is turned into useful mechanical work. The rest is lost as heat and friction. Lubricants play an important role in the overall efficiency of the vehicle. 

Combustion of fuels is an exothermic reaction. Explain how the heat energy from this type of reaction is often used to do useful work. 

J. Use of fired heaters the presence of boilers or furnaces, heated by the combustion of fuels, increases the probability of ignition should a leak of flammable material occur from a process unit. The risk involved will depend on the siting of the fired equipment and the flash point of the process material. The factor to apply is determined with reference to Figure 6 in the Dow Guide. 

In such cases, radiant heat transfer is used from the combustion of fuel in a fired heater ox furnace. Sometimes the function is to purely provide heat sometimes the fired heater is also a reactor and provides heat of reaction. The special case of steam generation in a fired heater (a steam boiler) will be dealt with in Chapter 23. Fired heater designs vary according to the function, heating duty, type of fuel and the method of introducing combustion air. However, process furnaces have a number of features in common. A simple design is illustrated in Figure 15.19. The chamber where combustion takes place, the radiant section... 

When hot utility needs to be at a high temperature and/or provide high heat fluxes, radiant heat transfer is used from combustion of fuel in a furnace. Furnace designs vary... 

Figure 16.33 shows a schematic of a simple gas turbine. The machine is essentially a rotary compressor mounted on the same shaft as a turbine. Air enters the compressor where it is compressed before entering a combustion chamber. Here the combustion of fuel increases its temperature. The mixture of air and combustion gases is expanded in the turbine. The input of energy to the combustion chamber allows enough power to be developed in the turbine to both drive the compressor and provide useful power. The performance of the machine is specified in terms of the power output, airflow rate through the machine, efficiency of conversion of heat to power and the temperature of the exhaust. Gas turbines are normally used only for relatively large-scale applications, and will be dealt with in more detail in Chapter 23. 

The major emissions from the combustion of fuel are C02, SO, NO and particulates14. The products of combustion are best minimized by making the process efficient in its use of energy through efficient heat recovery and avoiding unnecessary thermal oxidation of waste through minimization of process waste. Flue gas emissions can be minimized at source by ... 

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