Side-fired furnaces

Fuel economy calculations are more complex for multizone furnaces, including rotary furnaces—side fired, roof fired, or longitudinally fired—with or without baffles between zones. (See sec. 2.6, 3.4, 3.5.) With thick loads, load placement is more critical. (See sec. 3.5, 6.9, 6.10.)... 

Hg. 5.10. Continuous steel pusher reheat furnace side fired with regenerative burners in the top and bottom heat and preheat zones, and root tired in the soak zone. Preheat zones often have been designed as unfired preheat zones, which are good for fuel economy. However, also firing the preheat zones with regenerative burners would add capacity while retaining high fuel efficiency. (For a discussion of controls for this furnace, see sec. 6.11.1.)... 

The sawtoothed roof furnaces sometimes had several zones practically im-fired, but they at least had some firing even with reversed gas flow. Furnaces side fired, or roof fired with flat-flame (type E) burners had burners all along the walls or roof. Sawtoothed roof furnaces may have cost less, but with large loads and one fixed baffle, control was difficult. Regardless, a move to sawtooth roofs proceeded because of less cost. 

With the authors recommended six top heating zones and six bottom heating zones, the temperature measurement would control each small zone as the heating curve directs and would not get out of step as has been the case with very large zones. A furnace with the many zones recommended would probably be a roof-fired or side-fired furnace. Side firing would need ATP technology to control the loads temperatures evenly from end to end across the furnace width. 

A typical side-port continuous regenerative glass furnace is shown in Fig. 24-44. Side-port furnaces are used in the flat and container glass industries. The burners are mounted on both sides of the furnace and the sides fire alternately. Refractory-lined flues are used to recover the energy of the hot flue gas. The high temperature of the flue gas leaving the furnace heats a mass of refractory material called a checker. After the checker has reached the desired temperature, the gas flow is reversed and the firing switches to the other side of the furnace. The combustion air is then heated by the hot checker and can reach 1533 K (2300°F). The cycle of airflow from one checker to the other is reversed approximately every 15 to 30 min. 

Industrial steam reformers are usually fixed-bed reactors. Their performance is strongly affected by the heat transfer from the furnace to the catalyst tubes. We will model both top-fired and side-fired configurations. 

The furnace equation (7.136) that describes the heat transfer in the side fired furnace is a single transcendental equation used to compute and iterate Tt o and Qr. It can be solved using fzero of MATLAB. 

The furnace was fired by gas evolved in a producer. First the cover of the muffle g was heated then the lower part. The flue gases were ultimately led into stack s. Temperature above the muffle reached about 900 °C while in the lower part 550 to 600 °C. The final sulphate left the furnace at 450 to 500 °C. The gases with a 30 per cent HC1 content were led through pipe k, fitted at the side of the muffle, into a condensation equipment. The capacity of a muffle 3500 mm in diameter, with salt and bisulphate used as the raw materials, was equal to 7 000 kg of sulphate and 4 300 kg of hydrochloric acid 20/21 °Be, per 24 hours. 

Today contractors and licensors use sophisticated computerized mathematical models which take into account the many variables involved in the physical, chemical, geometrical and mechanical properties of the system. ICI, for example, was one of the first to develop a very versatile and effective model of the primary reformer. The program REFORM [361], [430], [439] can simulate all major types of reformers (see below) top-fired, side-fired, terraced-wall, concentric round configurations, the exchanger reformers (GHR, for example), and so on. The program is based on reaction kinetics, correlations with experimental heat transfer data, pressure drop functions, advanced furnace calculation methods, and a kinetic model of carbon formation [419],... 

In many modern top-fired reformers the heat flux calculated for the inner tube wall surface is around 60 000 W/m2, although in some designs it cam be as high as 75 000 W/m2. The maximum heat flux may be 1.4 to 2 times higher. In side-fired and terraced-wall furnaces, where the mean fluxes are generally in the range of 60 000-85 000 W/m2, the difference between mean and maximum flux is much smaller, as shown in Figure 37 [444],... 

In the side-fired reformers the burners are located in the wall, and the box accomodates one or two rows of tubes, which receive their heat mainly by radiation from the walls of the furnace box. This is claimed to provide a very uniform heat distribution, which may additionally be adjusted by control of the individual burners. The larger number of burners makes fuel and preheated combustion air distribution more complicated and more expensive. As the heigth and width of the reformer are fixed by the radiation geometry of the tubes and furnace box walls, it is only possible to... 

The terraced-wall type, developed by Foster Wheeler may be regarded as an intermediate between the side-fired and bottom-fired tubes. The reformer has inclined walls with several terraces on which upward firing burners are installed. This unique burner positioning makes it possible to adjust the heat flux in each zone. Figure 41 is a schematic drawing of the Foster Wheeler terraced-wall furnace [426],... 

K), nj is the effectiveness factor for reaction j (to be computed from the diffusion reaction equation at each point in the reactor), (—AHj) is the heat of reaction for reaction j (KJ/Kg mole), Rt is the catalyst tube radius, m, U is the overall heat transfer coefficient in (KJ/mP.K) and To> is the wall temperature (K) which is determined through the coupling between the above model equations for the catalyst tube and the model equations for the combustion chamber (the furnace). A distributed parameter model for the combustion chamber is being developed by (CREG) for both top fired and side fired furnaces. 

Model development for steam reformers Modelling of side fired furnaces Modelling of top fired furnaces Modelling of methanators Modelling of the catalyst pellets for steam reformers and methanators using the dusty gas model Computational algorithm... 

A continuous furnace may be heated so that the temperature of its zones is practically the same across the furnace. This temperature uniformity can be obtained by lengthwise firing in several zones (as illustrated by fig. 4.2), or by roof firing or side firing in several zones (as shown in fig. 4.3). In such furnaces, the heating capacity of a continuous furnace will equal or exceed the capacity of a same-size batch furnace. 

Side-fired reheat furnaces can be troublesome in two ways (1) When conventional burners are installed directly opposite one another, the center of the furnace becomes very hot because the velocity pressures of the poc from the opposing burners negate each other and because the completion of the fuel burning is concentrated in the furnace center and (2) with staggered long-flame burners, a wide furnace s center gets hotter than the sides when on high fire, but at low fuel inputs the sidewalls get hotter than the centers. Both troubles can be prevented with controlled temperature profile burners and added T-sensors/controls. (See chap. 6.)... 

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