Furnace Fuel Requirement

When specifying a new furnace, input calculations should be based on the true flue gas exit temperature— NOT ON FURNACE TEMPERATURE Coauthor Shannon recommends adding a safety factor of 30% in general, but 40% in the charge zone to accommodate productivity expansion of the mill—the latter because inadequate charge-zone capacity can cause swings in input needs after delays. His experience 

TABLE 8.16 Comparisons of correct and erroneous ways of figuring furnace fuel requirement In example cases A and B, both at 20 fps velocity 

Furnace (fee) T Flue Gas Exit (fge) T %Available Heat Required Gross Input  

If the furnace is to use a recuperator, make sure the design uses the total maximum airflow for all zones to avoid running out of high-temperature air supply when it is most needed. 

Beware of buying a furnace computer control whose designers lack an understanding of complex interactions of a furnace-and-mill system when delays occur. Operators must be able to understand a computer control model or they will become dependent on the computer supplier for help with every little glitch. 

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Combustion. Most of the mined coal is burned to produce steam for electric power generation (qv). The calorific value determines the amount of steam that can be generated. However, the design and operation of a boiler requires consideration of a number of other properties (see Furnaces, FUEL-FIRED). 

Since temperatures farther down the tower are higher than at the top, heat is available at a higher level. This permits transfer of heat to the incoming feed, thus reducing fuel requirements and furnace investment. 

Feuerungs-anlage, /. furnace, hearth, fireplace, -bedari, m. fuel requirement, -gewolbe, n. furnace arch, -material, n. fuel, -bl, n. fuel oil. -raum, m. Feuerraum. 

Example 16.4 The process in Figure 16.2 is to have its hot utility supplied by a furnace. The theoretical flame temperature for combustion is 1800°C and the acid dew point for the flue gas is 160°C. Ambient temperature is 10°C. Assume A7 = 10°C for process-to-process heat transfer but A7 = 30°C for flue gas to process heat transfer. A high value for A 7 mln for flue gas to process heat transfer has been chosen because of poor heat-transfer coefficients in the convection bank of the furnace. Calculate the fuel required, stack loss and furnace efficiency. 

The most logical place to begin is to size the furnaces and direct-fired heaters. Often the chemistry of the process has dictated the conditions, but frequently they can be modified in order to conserve energy usage. The burning of waste materials should also be considered as a means of both disposing of unwanted by-products and reducing fuel requirements. For each of these units, the amount of fuel needed per pound of product should be determined. 

Brenden and Chamberlain (6) measured heat release rate from wall assemblies having fire-retardant-treated studs and gypsum board as interior finish in the FPL fire endurance furnace using three methods (a) the substitution method, by which the amount of fuel required to maintain the ASTM E-119 time-temperature curve for a... 

A typical air preheater will reduce the fuel required to liberate a given amount of heat by 10 percent. The debit for this improved thermal efficiency is a higher flame temperature, and the possibility of overheating the radiant section. The only instance where there is a clear advantage to fit an air preheater to an existing furnace is when the firebox of that furnace is running below a desirable maximum firebox temperature. Three types of air preheaters are in common use ... 

Fuels, combustion -air requirements [FURNACES, FUEL-FIRED] (Vol 12)... 

The medium-speed diesel (railroad locomotive, marine engines) appears to be another potential application for SRC-II coal liquids to displace petroleum fuels. Other applications being studied by potential users include the automotive turbine, reheat furnace fuel in the steel industry and reformer feedstock for fuel cells. All in all, the products to be derived from coal liquefaction processes like SRC-II can, over time, displace a portion of our requirements for imported petroleum in a variety of end uses. 

Fuel Requirement. Most of the fuel used in a steam reforming plant is required to sustain the following highly endothermic reaction in the primary reforming furnace ... 

In order to produce 500 kt/y of ethylene some 651 kt/y of ethane is required. However, to allow for process upsets and general operational issues, a feed operating allowance of 5.5% is typically added. The pyrolysis requires 330 kt/y fuel oil for the furnace fuel. Again, an operating allowance, this time of 3.5%, is made. 

Every engineer whose responsibilities include furnaces, fuels, incinerators or processes involving offgases is occasionally confronted with an offgas or a waste stream that needs to be incinerated. Such streams are sometimes so low in their combustible content that one cannot even be sure that they will burn in such cases, there is frequently a voice in the background requesting an immediate estimate of the amount and value of primary fuel required to incinerate the gas stream. 

Just as with other furnaces, fuel control is based on the boiler ten erature. This means that the thermal output momentarily used is measured, and on the basis of this thermal output and a supposed calorific value combustion efficiency, the required quantity of combustibles is calculated by an approximate method and finally set. On the basis of the temperature curve of Ae boiler, this calculated quantity of fuel is permanently adjusted. 

This reaction takes place over two or more beds of catalyst and is endothermic,- that is, it requires an input of heat. Usually, the required heat energy comes from partial or complete combustion of some of the natural gas. The unconverted gas remaining after hydrogen purification is also used as a furnace fuel. Approximately 40 percent of the natural gas by weight is required to supply the heat to drive the reforming reaction. 

A single, present-day phosphorus furnace produces from 60 to 160 tonnes of phosphorus per day, almost the same as the annual production figures of the early arc furnaces, and requires a power supply of about 90,000 kW for a single, 160 tonne/day furnace. Power consumption per tonne of phosphorus produced varies with the % calcium phosphate in the rock (% BPL level) and furnace size among other factors but ranges around 12,000-14,000 kWh/ tonne (Table 10.4). Hence, power is a major cost component of electric furnace phosphorus production. This realization has prompted a reexamination of fossil-fueled (petroleum coke-based) sources of heat for rotary kiln combustion to provide the energy of the endotherm of the reaction [15]. 

By using the available heat calculated for the flue temperature and the heat contained in the metal at the pouring temperature (475 Btu/lb or 1100 kJ/kg), the heat lost to the environment from the furnace is calculated. Assuming the heat loss is constant, the amount of fuel required at various oxygen participation levels is... 

Effect of Valve Position. With some heating fluids, certain valve positions upset the supply of heat to the furnace which requires time for a change in process fluid temperature to be detected by the heater outlet thermocouple. When this happens, the controller will make an effort to reposition the fuel valve to satisfy the furnace heat... 

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