Safety technical measures for the maintenance of concentrated sulfuric acid storage tanks
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Recently, a concentrated sulfuric acid storage tank needs to be overhauled. Based on the physical properties of sulfuric acid, I would like to share my insights regarding safety measures and pipeline design. Safety technical measures for maintenance: Before entering a storage tank containing concentrated sulfuric acid, it is necessary to remove toxic gases such as sulfuric acid and sulfur dioxide before carrying out work in confined spaces (especially large tanks with a capacity of over 1000 M3). Based on relevant information, my safety technical measures are as follows: Transfer the remaining sulfuric acid from the tank to a backup tank; use drain valves to remove as much sulfuric acid as possible, and then pump out the remaining amount using a diaphragm pump. Open the manholes at the top and sides of the tank, and sprinkle lime powder evenly from the top multiple times until all the sulfuric acid in the tank has been neutralized. Wear a breathing mask to collect the lime powder. If there is a strong odor in the tank and work needs to be carried out there for an extended period, an axial flow fan can be used at the bottom manhole to supply air, while another axial flow fan at the top manhole can be used to exhaust air. Before entering the tank to carry out work, tests for toxic gases and flammable gases must be conducted, gas samples must be taken, and the hydrogen content must be analyzed. Only after the analysis shows satisfactory results and the necessary safety permits such as those for working in confined spaces and permits for welding are obtained can work be carried out inside the tank. At the same time, there must be a dedicated person to supervise the operation, and appropriate safety measures must be in place. Prohibitions: Concentrated sulfuric acid storage tanks are generally made of carbon steel. Concentrations such as 98% and 105% sulfuric acid do not react with carbon steel to produce hydrogen gas; however, if concentrated sulfuric acid is diluted with water, a large amount of hydrogen gas will be generated, leading to accidents. Piping design: To ensure safety and convenience during future production and maintenance, as well as in areas where the equipment connections might need to be removed, flanges are used for these connections. The outer surfaces of all flange joints are covered with metal sheeting to prevent sudden leaks that could cause injury. Sulfuric acid conduit trays should be kept as far away as possible from main pedestrian pathways. The above are just my thoughts; I hope everyone can share their own opinions and ideas so that we can all improve together!
There are several defects: 1) How to determine whether the acid in the tank has been completely neutralized? 2) How to ensure that the lime is spread evenly without any dead zones? 3) Calcium sulfate has very poor solubility; how can the lumps formed by the reaction between lime and sulfuric acid be removed? How to ensure that no residual non-target compounds remain in the treated tank? Based on the above information, I personally believe your plan is incomplete. Additional treatment methods: 1) Drain as much residual acid as possible ； 2) Prepare 10% NaOH, use a high-pressure washer to rinse from the bottom up to neutralize it ； 3) Drain all the waste alkali from the front section, wash the tank walls with water and drain them as well ；
This post was last edited by jbwuzju on 2009-11-6 at 16:02. First of all, thanks to the moderator for their generous guidance! Let me first provide further explanation regarding my own proposal: 1. The diaphragm pump I use is a pneumatic diaphragm pump, which has self-priming capability. It is able to pump out and draw in the vast majority of the concentrated sulfuric acid at the bottom of the storage tank; due to irregularities in the bottom surface of the tank, a small amount of sulfuric acid remains at the end. 2. The lime used for neutralization is slaked lime (calcium hydroxide powder), and compared to quicklime powder, it generates less heat during neutralization. 3. The breathing mask is a forced-air breathing mask that delivers air from outside the reservoir. 3. Control at the neutralization endpoint: it is sufficient when the area of the base plate covered with lime powder appears dry to the naked eye. 4 Due to the limited reach of the manhole (DN500), there are some areas that cannot be reached for applying lime; once the lime dust in the storage tank has settled, the operators wear air-supplied respirators and other protective equipment, and start spreading the lime powder from around the bottom manhole inward. 5. The residues remaining on the final base plate are mainly lime powder along with a small amount of calcium sulfate; due to the multiple applications, this prevents excessive neutralization and heat release in a short period of time, while also reducing the degree of hardening and caking of the powder. It can be removed with a shovel; cleaning it up is not a big problem. 6. Since the storage tank contains industrial sulfuric acid and the lime used is industrial calcium hydroxide, their purity is inevitably limited. However, the purpose of this operation is primarily to eliminate sources of danger and facilitate safe operations; by taking into account possible impurity components, it is possible to prevent the impact of unwanted substances on safe operations. 7. After the work inside the storage tank is completed, clear the area by sweeping it; there is no need to wash it with water, as the residual impurities such as calcium hydroxide at the bottom have little impact on the sulfuric acid present in the tank and are sufficient to meet industrial requirements. 8. The top axial flow fan is used for exhaust, while the bottom axial flow fan is used for supply; the purpose of this is, first, to facilitate ventilation so that maintenance personnel can enter, and second, to remove any hydrogen that may be generated as much as possible (hydrogen has a low density and tends to accumulate in the upper area). 9. Before entering the storage tank, conduct tests for flammable gases and toxic gases ； Gas samples are taken to analyze the hydrogen content; this process must be strictly controlled. The persons responsible must sign the relevant written documents and take it seriously, as safety is no trivial matter. Relevant certificates can be issued only after meeting the requirements; otherwise, measures will be rearranged until compliance is achieved. Regarding the additional handling methods for moderators, I would like to add my own views: 1. After draining the valve, use a pneumatic diaphragm pump to remove any remaining sulfuric acid, which achieves the maximum level of removal possible. 2. “Add 10% NaOH, use a high-pressure washer to rinse from the bottom up for neutralization” ； ”10% NaOH, which contains a large amount of water, is used to dilute concentrated sulfuric acid; however, dilute sulfuric acid reacts with carbon steel to produce hydrogen gas, so this approach is not suitable. There is no need to rinse from the bottom up; sulfuric acid on the wall will flow downward due to gravity. If the work area is on the wall, treating it with lime powder locally is sufficient. After neutralization, the remaining excess liquid alkali must be treated with water, and the leftover water must ultimately be removed using a fan or other methods; otherwise, concentrated sulfuric acid cannot be introduced, resulting in high maintenance costs. High-pressure washers are not necessarily available in every chemical plant; having someone bring one over costs a lot of money. Lye is highly corrosive, so high protection requirements are also necessary during the rinsing process. In summary, this approach generates large amounts of wastewater, involves high maintenance costs, and is unsafe.
What the original poster said does make sense and is worth taking as a reference! Sulfuric acid is a common medium in industry, and accidents often occur during its maintenance work due to carelessness; these painful lessons must be taken seriously! I wonder if there are any other simple and easy methods?
Is it necessary to have a drain outlet at the bottom of sulfuric acid storage tanks, and are there any mandatory requirements regarding this?