Preheat temperature

The heavy fuel should be heated systematically before use to improve its operation and atomization in the burner. The change in kinematic viscosity with temperature is indispensable information for calculating pressure drop and setting tbe preheating temperature. Table 5.20 gives examples of viscosity required for burners as a function of their technical design. 

Air preheat temperature requirements of 2250—2300 K are anticipated for natural gas-fired systems, and about 2000 K for oil or coal-fired systems (11). Use of 32—40% oxygen enrichment lowers the preheat temperature requirement to a moderate 900—1000 K, which can be attained with conventional metal-type tubular heat exchangers. Depending on the cost of oxygen, this is a viable alternative to the use of separately fired high temperature preheaters. 

More advanced MHD power plants of the future are expected to use preheat temperatures of up to 2000 K. These temperatures, to be achieved by... 

For gas-fired systems the state-of-the-art is represented by the preheater described in Reference 69. A pebble bed instead of a cored brick matrix is used. The pebbles are made of alumina spheres, 20 mm in diameter. Heat-transfer coefficients 3—4 times greater than for checkerwork matrices are achieved. A prototype device 400 m in volume has been operated for three years at an industrial blast furnace, achieving preheat temperatures of 1670 to 1770 K. 

Two variables of primary importance, which are interdependent, are reaction temperature and ch1orine propy1ene ratio. Propylene is typically used ia excess to act as a diluent and heat sink, thus minimising by-products (eqs.2 and 3). Since higher temperatures favor the desired reaction, standard practice generally involves preheat of the reactor feeds to at least 200°C prior to combination. The heat of reaction is then responsible for further increases in the reaction temperature toward 510°C. The chlorine propylene ratio is adjusted so that, for given preheat temperatures, the desired ultimate reaction temperature is maintained. For example, at a chlorine propylene molar ratio of 0.315, feed temperatures of 200°C (propylene) and 50°C (chlorine) produce an ultimate reaction temperature of approximately 500°C (10). Increases in preheat temperature toward the ultimate reactor temperature, eg, in attempts to decrease yield of equation 1, must be compensated for in reduced chlorine propylene ratio, which reduces the fraction of propylene converted and, thus aHyl chloride quantity produced. A suitable economic optimum combination of preheat temperature and chlorine propylene ratio can be readily deterrnined for individual cases. 

CTF 50 and 400 indicate approximate preheat temperature, F, for atomization of fuel in burners (terminology used in British Standard B.S. 1469). Properties depend on distillation range, as shown, and to a lesser extent on coal source. 

Figure 19.3 Fuel saving versus air preheat temperature (stoichiometric conditions)...

Increasing catalyst-to-oil ratio by decreasing the feed preheat temperature... 

Compare the cyclone loading with the design. If the vapor velocity into the reactor cyclones is low, consider adding supplemental steam to the riser. If the mass flow rate is high, consider increasing the feed preheat temperature to reduce catalyst circulation. 

High Preheat Temperature High Reactor Temperature Low Cat/Oil Ratio... 

Install high efficiency Feed Nozzles Lower Preheat Temperature Inject Naphtha Quench to Riser Increase Stripping and Dispersion Steam Switch to a Coke Selective Catalyst... 

Decrease in the feed preheat temperature and subsequent increase in the catalyst-to-oil ratio... 

A press, a homemade toggle job, or a hot-stamping machine can be used to perform the cold working operation. When heat is required (usual requirement) the male forming die should be about 132 to 138°C (270 to 290°F). Pressure should be maintained for about 10 seconds. This time can be reduced if the product still retains residual molding heat or is preheated. The recommended preheating temperature is from 80 to 110 C (175 to 230°F). 

When representing the dependence of laminar flame speed (S°) on mixture preheat temperature (TJ in the form of S°(T, (Z>)/S°(To,(Z>) = (T /Tq)", where Tq is the lowest unburned mixture temperature investigated for a given fuel/air composition, the current experimental data can be correlated well with n in the... 

By recognizing this variahon in Equahon 4.1.1, can be perturbed by var3ung either nitrogen dilution level or preheat temperature and, it is of interest to compare the deduced values of using the two different methods. It must be noted that the former method perturbs the reactant concentrations by keeping as constant, while... 

Experimentally deduced overall activation energies as a function of the equivalence ratio for iso-octane/air (filled symbols) and n-heptane/air (open symbols) mixtures obtained by varying the (a) Nj concentration and (b) preheat temperature. 

The measured extinction stretch rates for n-decane/ O2/N2 mixtures at 400 K preheat temperature as a function of equivalence ratio are shown in Figure 6.3.3. The flame response curves at varying equivalence ratios are also computed using the kinetic mechanisms of Bikas and Peters (67 species and 354 reactions) [17] and Zhao... 

Fig. 16. Schematic of a typical temperature profile in a crystallization experiment and the resulting evolution of the fraction of crystalline polymer and dynamic moduli with time. The preheating temperature Tp is above the melting temperature Tm...

A reactor for the oxidation of S02 is operated adiabatically with heat interchange between feed and product streams in countercurrent. Inlet concentrations are 10% each of S02 and 02 and the balance N2. Preheat temperature is to be 725 K, equilibrium is attained at the outlet and the conversion of S02 is 70%. Pressure is atmospheric. Find the temperatures of the feed and of the outlet. 

Preheat temperature shall be checked by use of temperature-indicating crayons, thermocouple pyrometers, or other suitable means to ensure that the temperature specified in the WPS is obtained prior to and maintained during welding. 

Base Metal P-No. or S-No. [Note (1)] Base Metal Group Nominal Thickness [Note (2)] Specified Min. Tensile Strength, Base Metal Min. Preheat Temperature Required [Note (3)] ... 

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