Equipment design waste heat

Vanyukov process has been used for decades, and OSBS process has also been applied for above ten years. Lots of experience on industrial production has accumulated on oxidative smelting, reductive smelting, consecutive operation and periodical operation. The furnace itself and its auxiliary equipments, including waste heat boiler, oxygen production, water recycle system, auto control system, have normative design, produetion and installation procedures. 

Synthesis gas may be prepared by a continuous, noncatalytic conversion of any hydrocarbon by means of controlled partial combustion in a fire-brick lined reactor. In the basic form of this process, the hydrocarbon and oxidant (oxygen or air) are separately preheated and charged to the reactor. Before entering the reaction zone, the two feed stocks are intimately mixed in a combustion chamber. The heat produced by combustion of part, of the hydrocarbon pyrolyzes the remaining hydrocarbons into gas and a small amount of carbon in the reaction zone. The reactor effluent then passes through a waste-heat boiler, a water-wash carbon-removal unit, and a water cooler-scrubber. Carbon is recovered in equipment of simple design in a form which can be used as fuel or in ordinary carbon products. 

The synthesis loop boiler on the exit of the converter is also a very important piece of equipment. In some modern plants not equipped with an auxiliary boiler it supplies nearly half of the total steam generation. It may generate as much as 1.5 t of steam per tonne of ammonia, equivalent to about 90% of the reaction heat. Fire-tube versions have been also used, including Babcock-Borsig s thin-tubesheet design. But compared to the secondary reformer service, where the gas pressure is lower than the steam pressure, the conditions and stress patterns are different. In the synthesis loop boiler the opposite is the case, with the result that the tubes are subjected to longitudinal compression instead of being under tension. Several failures in this application have been reported [993], and there was some discussion of whether this type of boiler is the best solution for the synthesis loop waste-heat duty. 

The main equipment in the dehydrogenation reaction section of a Lummus/UOP Classic SM plant includes a steam superheater, two dehydrogenation reactors, a series of waste heat exchangers, and an off-gas compressor (Fig. 3). The equipment is designed to minimize pressure drop from the dehydrogenation reactors inlet to the off-gas compressor. 

Earlier designs of sulfuric acid plants preferred minimizing initial capital cost and hence heat recovery equipment was not common. For example, these designs had atmospheric cooling ducts, air cooled heat exchangers, or air injection facilities instead of waste heat recovery boilers and economisers. 

Hence, improvements in waste heat recovery designs were made by installing additional waste heat recovery equipment like an additional boiler after the first pass of the converter and an economiser after the last pass. 

For safety and normal plant shutdown, waste heat boilers are equipped with systems to divert flue gases away fiom the boiler and directly to a stack. One such system comprises an abort, or dump, stack upstream of the incinerator and stack. Another system includes a bypass breeching coimection between the incinerator and stack. Modem, well-designed bypass systems are equipped with isolation dampers either in the dump stack or in the bypass breeching section. In systems without isolation dampers, either hot flue gases can bypass the boiler or ambient air can dilute gases to the boiler. Because of these factors, boiler isolation dampers may improve overall heat recovery efficiencies by at least 5%. 

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