Convective section waste-heat steam

Convective Section Waste-Heat Steam Generation... 

One manufacturer uses single-drum, watertube type waste heat boilers on incineration systems. Watertube bodets are also used by other manufacturers in installations where high steam pressures and flow rates are required. Another manufacturer offers heat recovery systems with water wall or radiant sections in the primary chamber. These water wall sections, which are usually installed in series with a convective type waste heat boiler, can increase overall heat recovery efficiencies by as much as 10 to 15%. 

Fig. 4.2. Waste heat boiler for a copper smelting flash furnace (Peippo et al, 1999). Note, left to right (i) flash furnace gas offtake (ii) boiler radiation section with water tubes in walls (iii) suspended water tube baffles in radiation section to evenly distribute gas flow (iv) convection section with hanging water tubes. Steam from the boiler is used to generate electricity, to power the acid plant s main blower and for general heating and drying.

Figure 105. Modern integrated single-train ammonia plant based on steam reforming of natural gas (Clide process) a) Sulfur removal b) Primary reformer c) Steam superheater d) Secondary reformer e) Waste heat boiler f) Convection section g) Forced draft fan h) Induced draft fan i) Stack k) TIT and LT shift converters ...

Process gas fiom the reaction shaft enters the uptake shaft at 21,000 Nm /h, 1375°C, and 14-18% SO2. The uptake shaft is constructed entirely with water-cooled copper elements. It is joined to the reaction shaft by four copper jackets called the bullnose as shown in Figure 2. The KIVCET waste heat boiler is divided into three sections radiant, downcomer, and convection. The radiant section consists of 717-m of membrane wall and reduces the process gas temperature at the top of the uptake shaft to 800-830 C. The process gas flows through the down comer section with a surface area of486 m and is cooled to a temperature of600-630 C followed by the convection boiler with a surface area of 1012 m. The outlet gas temperature from the waste boiler is 325-350 C. Typically, the waste heat boiler produces 23-25 t/h of steam at charge rates of 56 t/h. The on-line cleaning of the waste heat boiler consists of spring hammers for the down comer and radiant sections and pneumatic rappers for the convection section. 

High-pressure steam is generated from three on-purpose boilers, together with the waste heat boiler (H-9001) in the hydrogen plant and the convection section of a... 

The reactor tubes are fired by burners, which may be located at the bottom, at the side, or at the top of the furnace. Combustion of the fiiel takes place in the radiant section of the furnace. After the flue gas has been supplied all the reactor duty, it passes into the convection section where it is further cooled by heating other streams such as process feed, combustion air and boiler feed water, as well as producing steam. The product gas, leaving the reformer at a temperature of 850-950°C, is cooled in a process gas waste heat boiler (PGWHB), which produces process steam for the reformer. 

Reformer In a reformer furnace, shown in Exhibit 7-5, preheated process fluid flows through catalyst-filled tubes, which are usually located in the center of the radiant section. This type of furnace may have single or multiple compartments burners may be mounted in the roof, wall, or floor. Heat recovery systems may also be employed through the use of waste heat boilers or the convection section s steam generation coils. 

Heat balances are determined for all the reactor models discussed. Therefore the heat duties of the radiant tubes, convection section heaters, waste heat boilers, and assoeiated steam drums are all explicitly calculated and reported. Heat losses are part of the models, as described in the Heat Losses section. The enthalpies of all the streams entering and leaving each piece of equipment are caleulated and reported. These streams include, for example, the process, fuel, air, and flue gas. Combustion, and all reaction related heat effects, are handled in models using enthalpies of all species including heats of formation based on of the elements at their standard states, so heats of reaction are avoided. 

Figure 21.6 Convective section steam generation from waste heat.

Superheating steam for reboilers and steam heaters is mostly a waste, as it s a standard industry practice to inject condensate into the steam to bring the steam back to its saturation temperature. Superheated steam does not transfer heat as well as saturated steam. Hence, the de-superheating stations. As there is typically another convective section (usually BFW preheat) above the steam superheat tubes, no net energy savings result from steam superheat. 

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