Fired heaters rating

Fire uihe area required and heater size (shell diameter, shell length, fire luhe rating, coil length and number of passes). 

Fired heaters radiant rate, 12,000 Btu/(hr)(sqft) convection rate, 4000 cold oil tube velocity, 6 ft/sec approx equal transfers of heat in the two sections thermal efficiency 70-75% flue gas temperature 250-350°F above feed inlet stack gas temperature 650-950°F. 

When high temperatures and high flow rates are required, fired-heaters are used. Fired heaters are directly heated by the products of combustion of a fuel. The capacity of fired heaters ranges from 3 to 100 MW. 

There is also a certain amount of statistical information available on the failures of process system components. Arulanantham and Lees (1981) have studied pressure vessel and fired heater failures in process plants such as olefins plants. They define failure as a condition in which a crack, leak or other defect has developed in the equipment to the extent that repair or replacement is required, a definition which includes some of the potentially dangerous as well as all catastrophic failures. The failure rates of equipment are related to some extent to the safety of process items. If a piece of equipment has a long history of failures, it may cause safety problems in the future. Therefore it would be better to consider another equipment instead. It should be remembered that all reliability or failure information does not express safety directly, since all failures are not dangerous and not all accidents are due to failures of equipment. 

In practice, the efficiency of a fired heater is controlled by monitoring the oxygen concentration in the combustion products in addition to the stack gas temperature. Dampers are used to manipulate the air supply. By tying the measuring instruments into a feedback loop with the mechanical equipment, optimization of operations can take place in real time to account for variations in the fuel flow rate or heating value. 

If the heat picked up from the combustion of the fuel does not equal the heat absorbed by the process fluid, then something is amiss with the data. Often, determining the cause of such an inconsistency will reveal several fundamental operating or measurement problems with a fired heater. Quite commonly, we may find that the metered fuel-gas rate is wrong, or that the ambient-heat losses are much greater than anticipated in our calculations. 

The design and rating of a fired heater is a moderately complex operation. Here only the completely mixed model will be treated. For this reason and because of other generalizations, the method to be described affords only an approximation of equipment size and performance. Just what the accuracy is, it is hard to say. Even the relatively elaborate method of Lobo and Evans (1939) is able to predict actual performance only within a maximum deviation of 16%. 

R.N. Wimpress, Rating fired heaters, Hydrocarbon Process. 42(10), 115-126 (1963) Generalized method predicts fired-heater performance, Chem. Eng., 95-102 (22 May 1978). 

Figure 17.13. Multibed catalytic reactors (a) adiabatic (b) interbed coldshot injection (c) shell and tube (d) built-in interbed heat exchanger (e) external interbed exchanger (f) autothermal shell, outside influent-effluent heat exchanger (g) multishell adiabatic reactor with interstage fired heaters (h) platinum-catalyst, fixed bed reformer for 5000 bpsd charge rate reactors 1 and 2 are 5.5 ft dia by 9.5 ft high and reactor 3 is 6.5 x 12.0 ft.

Latex Drying. The stripped latex was dried in a pilot plant NICHOLS/NIRO spray drier using centrifugal disc atomization. Different disc speeds were obtained by changing the atomizer drive pulleys. The disc speeds could be varied between 10,GOO-24, 000 rev/min, (tip speeds 62-150 m/sec) and were measured with a tachometer. The dryer has a 1.22 m inside diameter and is heated by a gas-fired heater. For a given dryer inlet temperature the dryer outlet temperature is controlled by varying the feed rate to the atomizer, e.g. increasing the feed rate lowers the outlet temperature. The dried resin was collected in a cyclone. 

A box or cylindrical fired heater, 500-psig tube pressure rating, carbon... 

One advantage of partial oxidation is that significant reductions in NOx and C02 emission rates can be achieved compared to steam methane reforming. In one case a reduction of 20% was achieved when partial oxidation replaced steam methane reforming. This is because the point source emissions related to the furnace flue gas exhaust are not a part of this process. Emissions from partial oxidation processes are relatively small by comparison and primarily come from fired heaters that may be used to preheat the process feed177. 

TABLE 8.17. Procedure for the Rating of a Fired Heater, Utilizing the Equations of Table 8.18... 

In general, the less heat is applied the greater the cost savings. As heat is applied at production facilities by fuel-gas-fired heaters, any increase in heat is reflected in fuel-gas consumption. The addition of heat also boils lighter hydrocarbon fractions from the crude oil less product at a lower API gravity (defined in the Glossary) results. Addition of heat also accelerates rates of corrosion and increases the likelihood of scale formation on vessel internals, particularly the fire tubes. 

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