Heat release

For gases with known compositions, the heat release is estimated as follows  

Heating values of commonly used gases are presented in Table 4.16. 

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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. 

Fuel switch. Fuel switch from, say, coal to natural gas reduces the CO2 emissions for the same heat release because of the lower carbon content of natural gas. 

Figure 13.3 shows a process represented simply as a heat sink and heat source divided hy the pinch. Figure 13.3a shows the process with an exothermic reactor integrated above the pinch. The minimum hot utility can be reduced by the heat released by reaction, Qreact-... 

The heat released on combustion of a substance is called its heat of combustion The heat of combustion is equal to —AH° for the reaction written m the direction shown By convention... 

Stea.ming Retjuirements. The steaming of fixed beds of activated carbon is a combination of thermal swing and displacement purge swing. The exothermic heat released when the water adsorbs from the vapor phase is much higher than is possible with heated gas purging. This cycle has been successhiUy modeled by equiUbrium theory (128). 

The transparency of methanol flames is usually a safety advantage in racing. In the event of fires, drivers have some visibiUty and the lower heat release rate of methanol provides less danger for drivers, pit crews, and spectators. 

The Beckstead-Derr-Price model (Fig. 1) considers both the gas-phase and condensed-phase reactions. It assumes heat release from the condensed phase, an oxidizer flame, a primary diffusion flame between the fuel and oxidizer decomposition products, and a final diffusion flame between the fuel decomposition products and the products of the oxidizer flame. Examination of the physical phenomena reveals an irregular surface on top of the unheated bulk of the propellant that consists of the binder undergoing pyrolysis, decomposing oxidizer particles, and an agglomeration of metallic particles. The oxidizer and fuel decomposition products mix and react exothermically in the three-dimensional zone above the surface for a distance that depends on the propellant composition, its microstmcture, and the ambient pressure and gas velocity. If aluminum is present, additional heat is subsequently produced at a comparatively large distance from the surface. Only small aluminum particles ignite and bum close enough to the surface to influence the propellant bum rate. The temperature of the surface is ca 500 to 1000°C compared to ca 300°C for double-base propellants. 

ASTM E1354-90 Cone calorimeter heat release and smoke... 

The Ohio State University (OSU) calorimeter (12) differs from the Cone calorimeter ia that it is a tme adiabatic instmment which measures heat released dufing burning of polymers by measurement of the temperature of the exhaust gases. This test has been adopted by the Federal Aeronautics Administration (FAA) to test total and peak heat release of materials used ia the iateriors of commercial aircraft. The other principal heat release test ia use is the Factory Mutual flammabiHty apparatus (13,14). Unlike the Cone or OSU calorimeters this test allows the measurement of flame spread as weU as heat release and smoke. A unique feature is that it uses oxygen concentrations higher than ambient to simulate back radiation from the flames of a large-scale fire. 

A. Tewarson, "Heat Release and Surface Flame Spread," lEC TC 89-WG8 Meeting, British Standards Institution, London, Oct. 1992. 

Given the mechanisms and temperatures, waste combustion systems typically employ higher percentages of excess air, and typically also have lower cross-sectional and volumetric heat release rates than those associated with fossil fuels. Representative combustion conditions are shown in Table 11 for wet wood waste with 50—60% moisture total basis, municipal soHd waste, and RDF. 

Figure 4 illustrates the trend in adiabatic flame temperatures with heat of combustion as described. Also indicated is the consequence of another statistical result, ie, flames extinguish at a roughly common low limit (1200°C). This corresponds to heat-release density of ca 1.9 MJ/m (50 Btu/ft ) of fuel—air mixtures, or half that for the stoichiometric ratio. It also corresponds to flame temperature, as indicated, of ca 1220°C. Because these are statistical quantities, the same numerical values of flame temperature, low limit excess air, and so forth, can be expected to apply to coal—air mixtures and to fuels derived from coal (see Fuels, synthetic). 

Vehicle Fa.ctors. Because knock is a chemical reaction, it is sensitive to temperature and reaction time. Temperature can in turn be affected either by external factors such as the wall temperature or by the amount of heat released in the combustion process itself, which is directiy related to the density of the fuel—air mixture. A vehicle factor which increases charge density, combustion chamber temperatures, or available reaction time promotes the tendency to knock. Engine operating and design factors which affect the tendency to produce knocking are... 

To confirm that the matrix is amorphous following primary solidification, isothermal dsc experiments can be performed. The character of the isothermal transformation kinetics makes it possible to distinguish a microcrystalline stmcture from an amorphous stmcture assuming that the rate of heat released, dH/dt in an exothermic transformation is proportional to the transformation rate, dxjdt where H is the enthalpy and x(t) is the transformed volume fraction at time t. If microcrystals do exist in a grain growth process, the isothermal calorimetric signal dUldt s proportional to, where ris... 

Because the reaction takes place in the Hquid, the amount of Hquid held in the contacting vessel is important, as are the Hquid physical properties such as viscosity, density, and surface tension. These properties affect gas bubble size and therefore phase boundary area and diffusion properties for rate considerations. Chemically, the oxidation rate is also dependent on the concentration of the anthrahydroquinone, the actual oxygen concentration in the Hquid, and the system temperature (64). The oxidation reaction is also exothermic, releasing the remaining 45% of the heat of formation from the elements. Temperature can be controUed by the various options described under hydrogenation. Added heat release can result from decomposition of hydrogen peroxide or direct reaction of H2O2 and hydroquinone (HQ) at a catalytic site (eq. 19). 

Propellant. The catalytic decomposition of 70% hydrogen peroxide or greater proceeds rapidly and with sufficient heat release that the products are oxygen and steam (see eq. 5). The thmst developed from this reaction can be used to propel torpedoes and other small missiles (see Explosives and propellants). An even greater amount of energy is developed if the hydrogen peroxide or its decomposition products are used as an oxidant with a variety of fuels. 

Operational Characteristics. Oxygen generation from chlorate candles is exothermic and management of the heat released is a function of design of the total unit iato which the candle is iacorporated. Because of the low heat content of the evolved gas, the gas exit temperature usually is less than ca 93°C. Some of the heat is taken up within the candle mass by specific heat or heat of fusion of the sodium chloride. The reacted candle mass continues to evolve heat after reaction ends. The heat release duting reaction is primarily a function of the fuel type and content, but averages 3.7 MJ/m (100 Btu/fT) of evolved oxygen at STP for 4—8 wt % iron compositions. 

The superoxides compare well with a combination of Hquid oxygen or gaseous oxygen systems and a CO2 scmbber, eg, LiOH. Heat release is somewhat less than the combination system, and the volume of superoxides which is required is roughly equivalent to that of lithium hydroxide. 

Flammability. PhenoHcs have inherently low flammabiHty and relatively low smoke generation. For this reason they are widely used in mass transit, tiinnel-building, and mining. Fiber glass-reinforced phenoHc composites are capable of attaining the 1990 U.S. Federal Aviation Administration (FAA) regulations for total heat release and peak heat release for aircraft interior facings (1,70). 

Inorganic phosphates present htde ha2ard to humans and are mineral nutrients essential to life processes. Attention must be given to the acidity of phosphoric acid, the alkalinity of the bases with which it reacts and the heat released upon neutralization. Appropriate protective gear should be worn when in close contact. Some phosphate salts are reasonably acidic or basic. 

Common combustion reactions and heat releases for 0.454 kg of reactant under ideal combustion conditions are as follows, where Btu represents British thermal unit ... 

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