Acid coolers absorption tower

Adds One of the most extensive uses of austenitic steels has been for synthetic nitric acid plant, including oxidation coolers, absorption towers, storage vessels and pipelines, as well as transport tanks. For storage of cold 98% acid or for near-boiling solutions above 60% strength, 347S31 or 304S11 should be used. 

The cooled acid is recycled to the absorption tower or sent to product shipment. The warmed water is cooled with atmospheric air and recycled to the acid coolers. Dehydration tower exit acid (Chapter 6) is cooled the same way. 

Gas leaving the converter is normally cooled to 180—250°C using boiler feedwater in an "economizer." This increases overall plant energy recovery and improves SO absorption by lowering the process gas temperature entering the absorption tower. The process gas is not cooled to a lower temperature to avoid the possibiUty of corrosion from condensing sulfuric acid originating from trace water in the gas stream. In some cases, a gas cooler is used instead of an economizer. 

Nitrogen oxides, as well as nitric acid vapours, generated in the reaction, flow via the ventilating pipe to a system of jars, coolers and absorption towers, where they are absorbed. 

The daily output of a cooler measuring 1650 X 610 X 350 mm and an absorber measuring 1650 X 970 X 350 mm equals 7.5 tons of 30 to 35 per cent hydrochloric acid. As a rule, two graphite absorbers are connected in series and the more diluted acid from the second absorber which contains about 20 per cent HC1 is pumped into the first absorber. The rest of the unabsorbed gas is led through a rubber lined steel absorption tower into the atmosphere. The tower is sprayed with water and the diluted acid obtained is employed as an absorption liquid in the second igurite absorber. The flow of the tail gases is aided by a steam-jet ejector. 

For the production of ammonium nitrate there are 4 absorption towers 6]/z feet square by 30 feet high, built of acid brick and filled with spiral tile, 4 coolers, 7 feet by 13 feet by 8 feet high, 4 neutralizer tanks, ii feet by 26 feet by 7 feet high 4 supply tanks ii feet diameter by lo feet... 

Apart from the benefits of the high pressure mixing of SO3 with water to produce sulfuric acid, the proposed cold process for the manufacture of sulfuric acid has also been conceived to avoid the complexity of requiring a sulfur furnace and the related heat recovery system, the multipass static converter, counter current heat exchangers, the interpass absorption tower (IPAT), drying tower (DT), final absorption tower (FAT), mist eliminators, acid coolers, and alkali scrubber. The resulting plant is, as a result, of much lower cost in equipment and land use. 

In atmospheric and some low- to medium-pressure processes, one or more separate oxidation-cooling units are often included prior to gas absorption. These units are built in the form of vertical towers which are cooled with external water curtains, shell-and-tube units, and also drum and cascade coolers. Excess air in the gas promotes initial oxidation, and some of the water vapor also present condenses to form weak nitric acid, which is later concentrated in the absorption section. Additional air for oxidation usually is injected at some point in the process, often in the absorption tower. In some plants, the gas is rapidly cooled to condense the water vapor without forming much weak acid, thereby helping to increase final acid concentration. A special condenseix yclone separator unit designed for this purpose is described by.Graham etal..[10]. 

Acid circulation through the absorption tower is continued during short duration plant shutdowns. This maintains controlled corrosion conditions in pipes, pumps, coolers, and the absorption tower. 

Absorption of SO3 in concentrated sulfuric acid and the formation of H2SO4 from SO3 and H2O produce heat in the absorber, as does acid dilution from makeup water addition. Process control requires that the acid be cooled before it is recirculated to the dryer or absorber towers or sent to storage. Earlier acid coolers of parallel banks of stacked, irrigated, cast iron sections have been largely replaced by stainless steel shell and tube or plate exchangers, with or without anodic protection. Hastelloy, Sandvik SX, and Saramet alloys and Teflon also are used in acid piping and coolers. ... 

Cooler Absorbers When the absorption of a gas is accompanied by the evolution of heat, an important function of the absorption equipment is the removal of the heat generated. This may be accomplished by using a number of towers in series, the liquid from each tower being circulated through an external cooler. There are different types of cooler-absorbers in which processes of this type can be carried out in a single unit. The materials of which these cooler-absorbers are constructed should be of high thermal conductivity and resistant to corrosion by the substances used in the process. As an example, in the manufacture of hydrochloric acid of the... 

A similar installation was employed by Dobratz et al. (1933), who evaluated three difieient absorption tubes in the cooler-absorber (IM-in. ID Karbate, 1-in. ID tantalum, and 0.88-in. ID stainless steel) and investigated the production of 36 to 40% hydrochloric acid solutions. Hiese authors presort complete data, including heat-transfo and absorption-coefficient correlations for the cooler-absorber, but give no data on the performance of their 4-in. by 4-ft packed tail-gas scrubbing tower. 

---