Convective section waste-heat

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%. 

Use the linear Burgers equation for heat convection in a channel where the water is flowing with uniform velocity of 0.1 m/s across the cross section of the channel (boundary layers are neglected). The water is initially at 25°C throughout. At time t = 0 sec, waste heat is continuously rejected at x = 0 m, and the channel is long such that dT/dx = 0 for x > 1 m. The amount of heat rejected is 6.23 W/m2 for t > 0. Using the MacCormack explicit scheme, calculate the first 9 time steps to show the transient temperature distributions. 

The Haldor Topsoe Convection Reformer (HTCR) is a relatively small piece of equipment that combines the radiant and waste heat sections of the conventional reformer. It uses PSA (pressure swing absorption) to make 99.9 percent hydrogen purity. It is best for small and medium-sized hydrogen plants (500 to 10,000 Nm3/hr).75... 

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 ...

All BU produce heat as a result of metabolic processes, and so the major problem faced by many BU is the removal of excess heat. BU that are not provided with the ability to rid themselves of waste heat will eventually die. We have already seen in Section 2.7 that BU may lose heat by conduction, convection, radiation, and evaporation. Of these, conduction is not usually significant because BU... 

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. 

The convective reformer is compact, but has larger heat transfer areas compared with a tubular reformer due to the smaller heat transfer coefficients in the cold end. A fair comparison should thus include the heat exchange areas in the waste heat section in the tubular reformer, but still the fired tubular reformer remains the most economical solution for large-scale reforming. The economy of scale is more advantageous for a... 

Why do operators often run with too much air and hence waste energy For one thing the flame temperature is reduced. Also, more excess air produces more flue gas. This increases heat pickup in the convective section. Finally, flame length is shortened and flame impingement is reduced. These factors make it easier to fire the heater without overheating the tubes. Unfortunately, the price must be paid in lost furnace efficiency and wasted energy. 

The following equation may be used to approximate the percentage of furnace fuel wasted in heating air that has been inadvertently sucked into the convective section ... 

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. 

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