Method for washing scales formed on tube of graphite heat exchanger

Abstract

The invention discloses a method for washing scales formed on tubes of a graphite heat exchanger. The method comprises the following steps: water washing for the first time (mechanical washing); pressure test for the first time; acid washing; water washing for the second time (mechanical washing); pressure test for the second time; alkali washing; water washing for the third time (mechanical washing); and pressure test for the third time. According to the method disclosed by the invention, the washing time is shortened and is generally about 3 days, the acid producing capacity of the graphite heat exchanger after the washing process can be increased from 86% to above 98%, and the method has no damage on the heat exchange tubes and can remarkably improve function recovery of graphite heat exchanger and the production capacity.

Description

technical field [0001] The invention relates to a method for cleaning fouling of tubes of graphite heat exchangers. Background technique [0002] Graphite heat exchanger is one of the main equipments of the concentration system in the production of dihydrate wet-process phosphoric acid. When phosphoric acid is concentrated, as the concentration of phosphoric acid increases, various ions dissolved in wet-process phosphoric acid (such as Na 2 O, K 2 O) and the solubility of other acid-insoluble substances drop rapidly and precipitate, such as calcium, magnesium, iron and other salts, often adhere to the inner wall of the concentrated graphite heat exchanger tubes to form hard scale shells, that is, scaling, such Scaling is hard and shiny, mainly composed of calcium sulfate, silicate (such as sodium fluorosilicate, potassium fluorosilicate and calcium silicate, etc.), calcium magnesium aluminum phosphate, etc. Among them, sodium potassium salts, calcium silicate, etc. will fo...

AI Technical Summary

Problems solved by technology

Among them, sodium potassium salts, calcium silicate, etc. will form hard and dense hard scales and adhere to the inner wall of the concentrated graphite heat exchanger tubes, which are not easy to be cleaned and removed. K in phosphate rock 2 O and Na 2 Because of its low content, O is often not paid attention to by people, but it has been proved that the fluorosilicate produced by it is the main cause of pipeline scaling, which often causes blockage of pipelines or pump inlets and outlets, and increases cleaning frequency. Commonly used sulfuric acid Cleaning is not easy to remove. The common method is to regularly prepare sulfuric acid cleaning solution for cleaning. At the same time, after cleaning, mechanical cleaning methods such as high-pressure cleaning water are used to dredge and descale the scaling of graphite heat exchangers, but this method cannot be thoroughly cleaned. Scale removal, and as the production time increases, the scale that cannot be removed when cleaning with sulfuric acid lotion accumulates thicker, which seriously reduces the heat transfer efficiency and increases the heat transfer resistance, resulting in a decline in the production capacity of the graphite heat exchanger , which increases production costs