Required available heat

Total heat requirement Available heat in fuel... 

While accurate estimation of flue gas volumes requires heat and material balance and iterative calculations, a few mles of thumb can be used to produce a rough estimate. The heat required to raise the soil temperature to 1400°F is equal to the weight of soil (moisture free, 32,000 x 0.9) times the temperature difference (1400—60) times the specific heat [approximately 0.30Btu/(lb°F)], or 12 MBtu/h (1 MBtu = lO Btu). To vaporize the 3200 Ib/h water, 3 MBtu/h is required. Available heat at a kiln exhaust gas temperature of 1500°F at 50% excess air is 45%, so a total of 33 MBtu/h is required. Adding in radiation loss brings this to 35 MBtu/h. The secondary combustion chamber takes approximately an equal amount of heat, or 35 Btu/h. Adding these two produces total heat input of 70 MBtu/h. 

The required available heat for the soak zone will be the sum of (a) the remaining heat needed into the loads to heat them to good quality (b) heat losses to and from refractory, hearth materials, openings, and water-cooled devices and (c) heat absorbed by infiltrated air in warming to zone temperature. 

X (required available heat input /gross heat input) (5.6)... 

If it is then decided to add an air preheater to accomplish heat recovery, the required gross heat input to the furnace will equal required available heat or heat need (%available heat/100) = 13 625 000 h- (48%/10) = 28 400 000 gross Btu/hr. A security factor of at least 25% should be used therefore, the design input should be (28.5 kk Btu/hr) (1.25) = 35.6 gross kk Btu/hr. 

Total heat need = required available heat = 65.5 + 13.5... 

The Stefan-Boltzmann equations (2.6, 2.7, 2.8, and 2.9) show that heat transfer rate to most black or gray bodies varies as the difference in the 4th power of their absolute temperatures, which accentuates the difference between furnace temperature or furnace wall temperature and poc gas temperature. Case A In Figure 6.3, at 1000 F furnace temperature and 20 fps gas velocity, the temperature of the exiting poc gas is on the order of 1800 F. With a combustion air temperature of 600 F, if someone erroneously took the %available heat (from fig. 5.1) af 1000 F he would read 78%. He should have taken the %available heat at 1800 F, where he would read 57%. Therefore, if the required available heat were 100 kk Btu/hr (105.5 kJ/h), the gross heat required will be 100/0.57 = 175 kk Btu/hr (185 kJ/h), NOT 100/0.78 = 128 kk Btu/hr (135 kJ/h) as with the erroneous method. Case B At 2500 F furnace temperature, with the same 20 fps, the poc gas temperature would be 2560 F. Corresponding figures are in table 8.16. 

A newer juice concentration process, requiring minimal heat treatment, has been appHed commercially in Japan to citms juice concentration. The pulp is separated from the juice by ultrafiltration and pasteurized. The clarified juice containing the volatile flavorings is concentrated at 10°C by reverse osmosis (qv) and the concentrate and pulp are recombined to produce a 42—51 °Brix citms juice concentrate. The flavor of this concentrate has been judged superior to that of commercially available concentrate, and close to that of fresh juice (11). 

Spent acid burning is actually a misnomer, for such acids are decomposed to SO2 and H2O at high temperatures in an endothermic reaction. Excess water in the acid is also vaporized. Acid decomposition and water vaporization require considerable heat. Any organic compounds present in the spent acid oxidize to produce some of the required heat. To supply the additional heat required, auxiUary fuels, eg, oil or gas, must be burned. When available, sulfur and H2S are excellent auxiUary fuels. 

Little or no maintenance requirements Small space requirements Available m many construction materials No power requirements other than pumping Mixing achieved m short conduit lengths Minimal chance of material hangup or plugging Short residence times NaiTow residence time distribution Enhanced heat transfer Cost effective... 

Kehlhofer explains that the pre-heating loop must be designed so that the heat extracted is. sufficient to raise the temperature of the feed water flow from condenser temperature T to Ta (see Fig. 7.6). The available heat increases with live steam pressure Ipf), for selected 7 b(= Ta) and given gas turbine conditions, but the heat required to preheat the feed water is set by (Ta — T. ). The live steam pressure is thus determined from the heat balance in the pre-heater if the heating of the feed water by bled steam is to be avoided but the optimum (low) live steam pressure may not be achievable because of the requirement. set by this heat balance. 

In a food processing plant there is a requirement to heat 50,000 kg/h of towns water from 10 to 70°C. Steam at 2.7 bar is available for heating the water. 

Although fuel cells are not heat engines, heat is still produced and must be removed in a fuel cell power system. Depending upon the size of the system, the temperature of the available heat, and the requirements of the particular site, this thermal energy can be either rejected, used to produce steam or hot water, or converted to electricity via a gas turbine or steam bottoming cycle or some combination thereof... 

The sensible heat required to heat the adsorbed water on the molecular sieve again over the same temperature range. The properhes of the adsorbed phase may safely be assumed to be those of liquid water and the calculahons of the enthalpy change can be made from available data. 

These other forest resources - unutilized trees from intensive forest management and the residue today left in the forest - could, if pressed to their maximum availability, contribute around 1 EJ to the energy supply. To do this will, however, require extensive end use product markets since the end use requirement of heat production in the forest industry will already be essentially satisfied by the industries own residue. The conversion problem is therefore the transformation of biomass to energy intermediates such as electricity for transmission elsewhere, automobile fuels such as the much discussed methanol option, or into energy intensive tonnage chemicals such as ammonia and ethylene. 

AP is the most commonly used oxidizer for fuel rich propellants. AN is used where a high rate of gas generation is the prime requirement. Sometimes, sodium nitrate also finds application due to its high density, oxygen availability, heat of combustion and affinity of its exhaust species with ram-air. HMX-based fuel-rich formulations which give better performance, are also available. 

Traditionally, production of metallic glasses requires rapid heat removal from the material (Fig. 2) which normally involves a combination of a cooling process that has a high heat-transfer coefficient at the interface of the liquid and quenching medium, and a thin cross section in at least one-dimension. Besides rapid cooling, a variety of techniques are available to produce metallic glasses. Processes not dependent on rapid solidification include plastic deformation (38), mechanical alloying (7,8), and diffusional transformations (10). 

That carbon may enter into these two combinations with oxygen is of utmost importance in the design of combustion equipment. Firing methods must assure complete mixture of fuel and oxygen, to be certain that all of the carbon bums to CO and not to CO. Failure to meet this requirement will result in appreciable losses in combustion efficiency and in the amount of heal released by the fuel, since only about 28% of the available heat in the carbon is released if CO is formed instead of CO . 

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