Enclosure setup for acid and alkali storage tanks

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In chemical engineering design, when arranging acid and alkali tanks, it is necessary to understand and master the following key points: 1. Special characteristics of acid and alkali tanks • Risk analysis: ① Incompatibility: Mixing acids (such as sulfuric acid and hydrochloric acid) with alkalis (such as sodium hydroxide and ammonia water) may trigger violent reactions (such as heat generation, production of hydrogen or toxic gases), posing a potential risk of leakage and mixing. ②Safety isolation requirements: Storage tanks for different categories of hazardous chemicals usually need to be placed separately or strict isolation measures must be implemented. • Regulatory restrictions: ① Article 6.2.4 of GB 50160: Liquid storage tanks of different fire hazard categories shall not be arranged in the same tank group (for example, acid tanks and alkali tanks may belong to different fire hazard categories). ②SH/T 3007 \"Code for Design of Tank Areas in Petrochemical Storage and Transportation Systems\": It explicitly requires that storage tanks containing media with incompatible properties shall not share the same fire dike. 2. The basic definition of a tank farm, according to standards such as GB 50160 and NFPA 30, requires that: ① the number of storage tanks be ≥2, and they must meet the requirements regarding functionality, safety, and proper layout ； ②Media compatibility: The media stored in the tanks within a tank farm must be of the same type or compatible with each other, to prevent dangerous reactions resulting from mixing (such as exothermic acid-base neutralization, gas generation, etc.). 3. Can the acid tank and the alkali tank be used as a single tank set? According to the above definition, under normal circumstances, acid tanks and alkali tanks placed together cannot be considered as part of the same tank group, for the reasons mentioned above: ① Incompatible media: there is a risk of chemical reactions occurring due to mixing, which violates the requirements regarding media compatibility within a tank group ； ②Safety isolation specifications: Fire dikes must be installed separately or a greater distance must be maintained ； ③Requirements for fire dikes: When shared fire dikes are used, the mixing of acids and bases in case of a leak may exacerbate the consequences of an accident. Therefore, when acid tanks and alkali tanks are arranged together, they must be treated as separate storage tanks and meet the following requirements: ① Fire dikes or partitions should be installed separately ； ②Increase the distance between the two in accordance with the specifications ； ③Avoid sharing leak collection systems ； ④Potential risks are assessed through HAZOP analysis (Hazard and Operability Analysis). For inorganic acids and inorganic bases, the spacing between storage tanks only requires consideration for operation and maintenance access paths as well as piping space. Typically, the alkali tanks are arranged in groups and placed separately, with dikes separating them. This is done firstly to prevent the foundation of the alkali tanks from being corroded by any spilled acid, and secondly to avoid any dangerous reactions that might occur if both acid and alkali were to leak out ； For organic acids and organic bases, it is determined in accordance with the code GB60160-92 Code for Fire Protection Design of Petrochemical Enterprises, depending on the selected type of storage tank (fixed-roof tank or internal floating-roof tank). Tanks of the same type should be arranged as closely together as possible; acid tanks and alkali tanks should be separated by dikes, while water-soluble and non-water-soluble tanks should also be separated by dikes. 4. If, due to space constraints, the acid tank and the alkali tank have to be placed adjacent to each other in an alternative design, the following measures should be taken: ① Separate fire dikes: Install separate fire dikes or barriers for the acid tank and the alkali tank respectively ； ②Safety spacing: The distance between the two should be determined in accordance with the spacing requirements specified for tanks holding different types of media in the relevant standards (it is usually greater than the distance between tanks within the same group) ； ③Leak prevention and control: Install a leak-proof collection system to ensure that acids and bases do not mix in the event of a leak ； ④Emergency measures: Provide neutralizing agents (such as sodium bicarbonate for acid leaks and acetic acid for alkali leaks) as well as specialized emergency equipment. 5. Relevant standard GB 50351 \"Code for Design of Fire Dikes in Tank Farm\" – Article 3.1.3: Liquid storage tanks with incompatible properties shall not be located within the same fire dike. 3.3.5 The floor design within fire dikes and protective walls shall comply with the following provisions: 2 The floors in storage tank groups that hold corrosive substances such as acids and alkalis shall be treated to prevent corrosion ； 4.2.2 For storage tank groups that hold corrosive substances such as acids and alkalis, the inner side of the fire dike should be treated to prevent corrosion. According to GB 50984, Clause 4.4.8 of the \"Code for Layout Design of Petrochemical Plants\", the layout of storage tanks for toxic and corrosive liquids shall meet the following requirements: 1. They should not be located near roads with heavy pedestrian traffic or major production facilities; 2. A protective dike should be constructed around the tank group, and the effective volume within this dike should be no less than the volume of the largest tank in the group; 3. The distance from the vertical storage tanks to the base line of the protective dike should be no less than half of the height of the tank walls; 4. The floors, drainage ditches, and sump pits within the area where corrosive liquids are stored must be treated to prevent corrosion. \"Technical Specifications for the Layout Design of Chemical Plant Equipment\", HG/T 20546-2009, 14.2.5 Floor paving: For toxic, corrosive, and valuable materials, corrosion-resistant materials should be used for paving within the cofferdam (including the cofferdam itself, equipment foundations, floors, and drainage pits). \"Code for Occupational Safety and Health Design in Petrochemical Enterprises\" SH/T 3047-2021 7.1.5.7 Enclosures or leakage fluid collection facilities should be installed around the storage areas for acids, alkalis, and other corrosive substances, and these areas should be paved with impermeable and anti-corrosive materials. According to the \"Code for Design of Circulating Cooling Water Systems in the Chemical Industry\" GB 50648-2011, 11.2.4: Safety dikes should be installed around storage tanks for concentrated sulfuric acid and hydrochloric acid, as well as those used to store corrosive or highly oxidizing liquids. The effective volume of such dikes should be sufficient to hold the contents of the largest tank among them, and the interior of the dikes must be treated to prevent corrosion ； Protective level gauges should be installed in the storage tanks for concentrated sulfuric acid and hydrochloric acid. Ventilation and dehumidification systems should be provided in the tank for concentrated sulfuric acid, while acid mist absorption systems should be installed in the tank for hydrochloric acid. \"Code for Environmental Protection Design in Petrochemical Industries\" SH/T 3024-2017 10.2.2 Enclosures with a height of not less than 150 mm should be installed around the floors of polluted areas within production facilities; separate enclosures or similar barriers are recommended to be used to divide different polluted areas from each other. Within the polluted area, appropriate pollutant collection and discharge systems should be installed, depending on the nature, quantity of the pollutants that may leak, as well as the location. NFPA 30 “Code for Flammable and Combustible Liquids”: Requires physical separation of storage tanks containing incompatible liquids.