Side firing

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. 

Steam reformers are used industrially to produce syngas, i.e., synthetic gas formed of CO, CO2, 11-2, and/or hydrogen. In this section we present models for both top-fired and side-fired industrial steam reformers by using three different diffusion-reaction models for the catalyst pellet. The dusty gas model gives the simplest effective method to describe the intermediate region of diffusion and reaction in the reformer, where all modes of transport are significant. This model can predict the behavior of the catalyst pellet in difficult circumstances. Two simplified models (A) and (B) can also be used, as well as a kinetic model for both steam reforming and methanation. The results obtained for these models are compared with industrial results near the thermodynamic equilibrium as well as far from it. 

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. 

Plant (2) is a side-fired steam reformer with the following construction and operating data. 

Side-fired reformer (2) construction data and operating conditions ... 

With a Terrace Wall or side-fired unit, the limit to capacity will generally not be apparent in the radiant section. The increase in firing is matched by an increase in heat transfer on the inside of the catalyst tube. So the actual tube temperatures show only a minor increase86. 

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],... 

Figure 37. Tube wall temperature and heat dux profiles for (op-fired and side-fired configurations.

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],... 

Firing occurs only on one level, so the number of burners in relation to the number of tubes is smaller than in side-fired systems. This simplifies distribution piping for fuel gas and preheated combustion air, which is nowadays standard in all efficient plants. 

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],... 

The second version has a S/C ratio of 2.5 and shift conversion with medium- and low-temperature catalysts, both copper-based. For C02 removal Selexol or aMDEA is chosen. The synthesis is performed at 140 bar with a Topsoe two-bed S 200 radial converter, followed by a single-bed radial S 50 converter (S 250 configuration). After the converters, high-pressure steam is generated. An additional proprietary item is the side-fired reformer. 

Industrial steam refonner Minimization of methane feed rate and maximization of the flow rate of carbon monoxide at the reformer exit. NSGA Side-fired steam reformer operation was optimized. Rajesh et al. (2000)... 

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. 

The bottom-fired reformer is classified into two types, one with the reforming gas flowing down the tube (as in top-fired and side-fired) and the other where the process gas flows up the reformer tubes. The burners are located on the floor on either side of two rows of reformer tubes. The flames are long and pencil thin. The system has a simplified air combustion distribution and single operating level. The system cannot handle more than 200-300 reformer tubes per radiant section and the tube metal temperatures at the process gas outlet are higher than the inlet. 

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... 

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