Waste heat unit furnaces

The Claus process is the most widely used to convert hydrogen sulfide to sulfur. The process, developed by C. F. Claus in 1883, was significantly modified in the late 1930s by I. G. Farbenindustrie AG, but did not become widely used until the 1950s. Figure 5 illustrates the basic process scheme. A Claus sulfur recovery unit consists of a combustion furnace, waste heat boiler, sulfur condenser, and a series of catalytic stages each of which employs reheat, catalyst bed, and sulfur condenser. Typically, two or three catalytic stages are employed. 

The traveling-grate furnace requires less labor, increases the output per unit of grate area, and produces more uniform product than the WetheriU. furnaces. The traveling grate is an endless chain of cast-iron bars, driven by sprockets, which traverses a firebrick chamber. Anthracite briquettes are fed to a depth of ca 15 cm. After ignition by the previous charge, the coal briquettes are covered by 15—16.5 cm of ore/coal briquettes. The latter are dried with waste heat from the furnace. Zinc vapor evolves and bums in a combustion chamber and the spent clinker faUs into containers for removal (24,25). 

Batch-type production processes, particularly those with small batch sizes, have less energy efficiency as compared to continuous processes. A typical example of a batch operation on a relatively small scale is the production of titanium in 1-ton batches of the metal. The energy efficiency of the process is much less than that of continuous methods such as iron being produced in a blast furnace, or even of large-scale batch methods such as basic oxygen steel-making. The heat losses per unit of production are much less in continuous and large-batch processes, and this also enables the waste heat from process streams to be used. 

Industrial furnaces are enclosed units that are integral parts of a manufacturing process and use thermal treatment to recover materials or energy from hazardous waste. These units may use hazardous waste as a fuel to heat raw materials to make a commodity (e.g., a cement kiln making cement) or the unit may recover materials from the actual hazardous waste (e.g., a lead smelter recovering lead values). The following 12 devices meet the definition of an industrial furnace12 ... 

Figure 17. Weak acid recovery plant used by Sachtleben Chemie (based on know-how of Bayer AG) a) Heat exchanger b) Evaporator c) Injection condenser d) Stirred salt maturing vessels e) Filter press f) Bunker for pyrites g) Coal silo h) Bunker i) Mixing screw unit j) Covered store for mixed filter cake k) Calcination furnace 1) Waste-heat boiler m) Cyclone n) Electrostatic precipitator o) Stirred tank p) Storage tank q) Pump r) Cooler...

Sulfur is quite versatile it can be used as an agricultural insecticide or as a raw material for making sulfuric acid, as shown in Figure 2.12. To make sulfur, acid gas (hydrogen sulfide, sulfur dioxide, and carbon dioxide) from the various refinery amine units is collected and fed to a sulfur plant. In a typical sulfur plant, the acid gas is fed to a reaction furnace. The hydrogen sulfide is first partially burned at 2,500° F (1,370° C) and 15 psia (103 kPa) in the reaction furnace to form sulfur dioxide next, it is passed through a waste heat boiler and then passed over catalyst beds at 500°F (260° C) and 15 psia (103 kPa) in the converters. Sulfur is condensed from the effluent of successive converters and solidified in pits. 

The earlier plants operated at deficit, and needed an auxiliary boiler, which was integrated in the flue gas duct. Auxiliary burners in tunnels or flue gas duet were additionally used in some instances. This situation was partially caused by inadequate waste heat recovery and low efficiency in some energy consumers. Typically, the furnace flue gas was discharged in the stack at rather high temperature because there was no air preheating and too much of the reaction heat in the synthesis loop was rejected to the cooling media (water or air). In addition, efficiency of the mechanical drivers was low and the heat demand for regenerating the solvent from the C02 removal unit (at... 

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. 

At BASF, flammable solid, pastelike, and liquid residues are combusted in eight furnaces. Each combustion unit consists of a rotary kiln with afterburner chamber and a steam boiler. The superheated 18-bar steam from units 1 to 6 is fed into the BASF plant network. In units 7 and 8, a higher-value steam is generated with an efficiency of ca. 74 % and supplied to a back-pressure turbine, where it is expanded from 43 bar to 5 bar. To utilize the heat of the flue gases between 300 C and 180 C, a waste-heat boiler was installed to raise 5-bar steam. Electric power and 5-bar steam are fed into the respective plant systems (Fig. 113). 

Bayer operates a number of. similarly engineered waste combustion units. At the Dormagen plant, a further combustor for solid and liquid wastes has been placed in service. It consists of a rotary furnace, afterburner, waste-heat boiler, and gas scrubber. The plant incorporates a condensation-type electrostatic filter specially developed by Bayer [259] and an SCR unit for selective catalytic reduction of nitrogen oxides (with ammonia) and for degradation of dioxins in the tail gas (see Fig. 115). 

A higher reformer inlet temperature decreases the absorbed duty requirement and therefore decreases the number of tubes, the size of the furnace, and the fuel requirement. It also decreases the steam generation from the waste heat recovery unit. 

The SURE Double Combustion process is particularly attractive in a revamp situation. The existing reaction furnace and waste heat boiler become the No. 2 units and a new burner, No. 1 reaction furnace, and No. 1 waste heat boiler are added upstream of the existing reaction furnace. It is reported that 100% oxygen enrichment can be achieved with this process. According to Figure 8-12, the SURE Double Combustion process can achieve over two and one-half times the original Claus plant design capacity. 

Furnace systems must have effective flue gas cleaning units in order to eliminate harmful substances such as SO2, HCl, HF, NOx, arsenic trioxide and dust produced during incineration. Together with the waste heat utilization units, these plant components are often of a much larger size than the incineration unit itself. 

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