Heat Recovery Units

In the interest of energy conversion, process heat can be obtained from a heat recovery unit in which heat is recovered from turbine or reciprocating engine exhaust. In a heat recovery unit, an exhaust gas flows over finned tubes carrying the fluid to be heated. The hot exhaust gas (9()0 F to I.2(K) F) heats the fluid in the tubes in a manner similar to that in which air cools the fluid in an aerial cooler. It is also possible to recover heat from exhausts by routing the exhaust duct directly through a fluid bath. The latter option is relatively inefficient but easy to install and control. 

Generally, the following design criteria should be provided to the man-ulaeiurers or vendors for sizing an exhaust heat recovery unii 

Total heat duty required to heat the fluid 

Operational relationships between heat sources and users (e.g.. w Inch users continue to operate when sources shut down ) 

Exhaust gas flow rates at anticipated ambient and at various loads Iroin maxiimim to minimum 

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Investment, Costs, and Prices for Barley and Malt. Estimated malthouse investment (1993) and costs for a new malthouse with annual capacity of 120,000 t are shown in Table 2. This malthouse is equipped with twelve 1,700-bushel steep tanks, eight 10,000-bushel germination compartments, and two double-deck kilns. The kilns are equipped with standard heat recovery units and indirect heat. 

As a general rule, the system must be designed so that contaminated extract or exhaust air cannot mix with supply air through leakages. ITiis entails requirements for pressure conditions, especially for heat recovery units. For category ETA 1, no limitations are needed for ETA 2 and 3 using air-to-air... 

The design of heaters and waste heat recovery units is beyond the scope of this book. Sizing and design are best left to manufacturers. However, the concepts discussed in this chapter and in Chapter 2 can be used to verify the manufacturer s proposals. 

Some of the remedial measures tested in this study were not regarded as likely to form part of a long-term control stategy. For example, the installation of a mechanical ventilation system, with a heat recovery unit, would not be used in a dwelling of this type, because of the very high installation cost. Nevertheless, the availability of the dwelling enabled devices to be tested under real housing conditions, rather than in the laboratory. 

The flue gas tunnels are rectangular fire-brick structures at the reformer s bottom. They act as horizontal ducts for flue gas removal. The flue gas exits at 1,800°F to 1,900°F. A heat recovery unit is provided to recover heat from this gas. This unit contains a reformer feed preheat coil, steam superheat coil, steam generation coil and boiler feed water preheat coil. 

When combustion air preheat is used, the air preheat unit may replace the boiler feed water coil. Flue gas exits this unit at about 300 degrees F. This provides a typical heat loss of 3% of the overall reformer efficiency. Steam is also made in a process steam generator which extracts heat from the reformer outlet process gas. The heat recovery unit and process steam generator normally have a common steam drum. 

From the reactor, the effluent flows through a separator (for the separation of inorganic salts precipitated during the process), a heat exchanger (with the influent), a heat recovery unit, an effluent cooler, and a letdown system to return the effluent to the ambient pressure. Then, a liquid/gas separator sep-... 

An air-to-air heat recovery unit uses a cross-flow exchanger with both fluids unmixed and an air flow rate of O.S kg/s on both sides. The hot air enters at 40°C while the cool air enters at 20°C. Calculate the exit temperatures for U = 40 W/m2 °C and a total exchanger area of 20 m2. 

Heat recovery units (water tube boilers) have experienced problems with corrosion and buildup of soot on the heat transfer surfaces. 

Low-vanadium catalysts can be used that minimize the conversion of SO2 into SO3. This minimizes the precipitation of ammonium bisulfate on downstream heat recovery units. However, in general these low-vanadium catalysts are not economical because the catalyst volumes are larger (low-vanadium catalysts are less active). 

Elutriated cooled shale is separated in a high-efficiency separator and routed to a moisturizer in preparation for disposal. Gas from the heat recovery unit is water washed in a venturi scrubber and excess water from the scrubber is used in the moisturizer. Little water vapor is generated in scrubbing the gas and wetting the spent shale because the outlet temperature of the heat recovery unit is low... 

For further study of boilers, furnaces, and waste-heat recovery units, the reader is referred to Perry s Chemical Engineers Handbook," 3d ed., sec. 24, pp. 1628-1652, on steam plants sec. 23, pp. 1598 1625, on furnaces and kilns. 

Frequency in radians per second. Winding of a machine or transformer. Waste heat recovery unit. 

The same principle applies to blast furnace stoves and to the multiple-tower heat recovery units positioned around the periphery of vertical cylindrical incinerators for waste gases or liquids. For furnaces with lower temperature waste gases, such as boilers or steam generators, a Ljungstrom all-metal recuperator, rotating on a vertical shaft, is used. 

Waste heat recovery units installed and design of individual units. 

Excess power, steam, hot water, hot air generated available from waste heat recovery units, and cogeneration facilities,... 

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