Acid plants construction materials

Halogen-containing compounds are a major contributor to the acidic component of fuel combustion gases. Hydrogen chloride from chlorides in the fuel or the incineration of chlorinated plastics is corrosive to plant construction materials... 

Cost estimates are for a 3 1 double contact type acid plant constructed of modem materials (mostly stainless steel) with a steam turbine generator for producing electrical energy. The acid plant is constructed on a new site with little or no existing infrastructure. Sulfur is purchased and received at site in solid form. Hot acid heat recovery systems such as MECS s HRS and Outotec s HEROS are not included. 

Materials of Construction. Resistance of alloys to concentrated sulfuric acid corrosion iacreases with increasing chromium, molybdenum, copper, and siUcon content. The corrosiveness of sulfuric acid solutions is highly dependent on concentration, temperature, acid velocity, and acid impurities. An excellent summary is available (114). Good general discussions of materials of constmction used ia modem sulfuric acid plants may be found ia References 115 and 116. More detailed discussions are also available (117—121). For nickel-containing alloys Reference 122 is appropriate. An excellent compilation of the relatively scarce Hterature data on corrosion of alloys ia Hquid sulfur trioxide and oleum may be found ia Reference 122. 

Fats and soaps Their excellent resistance to the higher fatty acids makes the austenitic steels valuable constructional materials for plant dealing with hydrogenation or other treatment of oleic, stearic, and similar acids. 

Considerable challenges still remain in the development of new carbonylation processes for acetic acid manufacture. For example, all of the current processes use iodide compounds, leading to corrosive HI and the need for expensive materials for plant construction. An iodide-free system could potentially impart considerable benefit. Other long term goals include the selective direct conversion of syn-gas or oxidative carbonylation of methane to acetic acid. Organometallic chemists are certain to play a crucial role if these targets are to be achieved. 

As produced from the hydrometallurgical process the sulphur will always be contaminated with siliceous gangue and pyrite. In some cases, it will be upgraded for use in sulphur burning acid plants, but there will be a strong incentive to use the material in its impure state for sulphur extended asphalt highway construction and sulphur concrete applications. 

Generally the use of lead as a material for construction of a picric acid plant is avoided, except in Great Britain and in the U.S.A. where it is used for the parts of installation which are also in contact with inorganic acids. The latter, being strong acids, are assumed to inhibit the formation of lead picrate. 

In sulfuric acid production, acid brick lining of membrane coated mild steel tanks and reaction vessels is considered the most durable and versatile construction material for the sulfuric acid plant. Such linings wiil reduce the steel shell temperature and prevent erosion of the normally protective iron sulfate film that forms in stagnant, concentrated (oxidizing) sulfuric acid. Dilute (red uC ing) sulfuric acid solutions are very corrosive to carbon steel, which must be protected by impermeable (e.g., elastomeric) membranes and acid brick lining systems. Such acid brick linings often employ membranes comprising a thin film of Teflon or Kynar sandwiched between layers of asphalt mastic. 

This process is strongly exothermic (flame temperature > 2000°C) and is especially used when particularly pure hydrogen chloride (hydrochloric acid) is required e.g. in the food sector. It places considerable demands on the construction materials of the plant, particularly that of the burner for which quartz or graphite is preferred. The synthesis furnace and the adjacent cooler can be constructed of steel when dry chlorine and dry hydrogen are used. 

The growth in world population necessitated the increased use of fertilisers to augment increased supply of food. In the fertiliser industry the manufacturing process involves the use of sulfuric acid, hydrochloric acid and phosphoric acid. The plant, equipment and piping system that come into contact with the acids must be dependably protected against the corrosive attack. Rubber as a construction material is well able to satisfy the variety of requirements on it in this area, which are [9] ... 

The decomposition of sulfuric acid at 850 900 °C [reaction (4.31)], a component of all the sulfur cycles, places severe specifications on the materials of plant construction due to the extremely corrosive nature of the species at high temperatures. This is one of the major issues that is being addressed by the European HYdrogen THErmochemical Cycles (HYTHEC) programme. The... 

High-alloy steels (> 5% alloy components) [Henker 1999] are stainless and acid-resistant and are therefore the most important materials in chemical plant construction. Pipelines and apparatus made of these materials are resistant to all types of weather and thus do not require protective coatings.Two widely used steel types, developed by Krupp in 1914, are V2A and V4A ... 

For many years, 316L stainless steel has been a common construction material for agitators, filters, and the other equipment coming in direct contact with wet-pro-cess phosphoric acid or reaction slurry. However, there is a growing tendency to use more resistant alloys in new plants, particularly when the rock source may be subject to change or more severe conditions of operation are provided. 

Industrial nitric acid processes are basically of three types (1) ambient, (2) medium, and (3) high pressure. For the 1 ambient pressure variety, a low pressure drop contactor like packed tower is desired. The other two types can be handled by a relatively high pressure drop contactor like plate column. It may be noted here that the NO absorption train constitutes a major portion of the nitric acid plant cost since the material of construction (SS-304 ELC) is relatively expensive. Table 3.2 compares packed and plate columns for NO absorption. 

Small towers sometimes are reinforced PVC, and there is no need for a lining. A potential problem with PVC or other nonconductive material is the accumulation of a static charge. The explosion of a set of three PVC dryers in a mercury-cell plant was attributed to static discharge in the presence of an explosive gas [27]. The root cause of the incident was the failure of the power supply to the mercury pumps, which allowed mercury to drain from the cells and uncover the steel bottoms. This led to the formation of large quantities of hydrogen. The investigators concluded that towers should be constructed of acid-proof conductive material that can be held at ground potential. 

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