The scale and corrosion-related compounds that build up in the steam portion of the boiler are intended to be removed by chemical cleaning. The most popular chemical for cleaning boiler tubes is hydrochloric acid because it reacts with corrosion and scale products in the tubes to generate soluble chlorides.
Prior to boiler cleaning, alkaline cleansing (flush/boil-out) is frequently used to remove oil-based contaminants from tube surfaces. These solutions, which are made of trisodium phosphate as well as a surfactant, work to remove any substances that can obstruct the interactions between the chemicals used to clean deposits from boilers and other surfaces.
In copper-containing boilers, hydrochloric acid is used with a copper complexer in order to stop dissolved copper from replating onto surfaces of steel during chemical cleaning procedures. In compressed air-driven cleaning systems, like those employed by Putzmaus – The Leader in Boiler Tube Cleaning, air is used alongside a brush to clean the boiler tube itself.
Numerous utilities conduct boiler cleaning operations using cleaning solutions containing citric acid. The acid is often used for cleanup in two stages after being diluted and then ammoniated to reach a pH of 3.5. Iron oxides are dissolved during the first step.
Many different boiler cleaning procedures have employed ammoniated EDTA. A one-solution, two-stage cleaning procedure is used. First, the solution chelates the iron-containing solution and solubilizes the iron deposits.
The solution gets oxidized with air in the second step to convert ferric iron chelates to ferrous iron chelates and to release copper deposits into the solution, where the metal is chelated. The circulating boilers that employ copper alloys are where this chemical is most frequently used.
Ammonia-based oxidizing chemicals (https://www.brandeis.edu/environmental-health-safety/safety/labs/oxidizers.html) have proved successful when substantial volumes of copper deposits within boiler tubes can’t be eliminated using acidic solutions of hydrochloric acid as a result of copper’s relative insolubility. The ammonia and sodium bromate phase involves introducing solutions incorporating ammonium bromate into the steam boiler system in order to quickly oxidize and then dissolve the copper.
Utility boilers are frequently chemically cleaned using hydroxyacetic/formic acid. Because of its low chloride concentration, it is utilized in boilers that contain austenitic steel in order to avoid potential chloride cracking from stress corrosion of the austenitic-type metals.
It has also been widely used in once-through supercritical boiler cleaning procedures. Click here for more information on boilers.
Because hydroxyacetic/formic acid possesses chelation capabilities and a high capacity to take up iron, it is utilized in systems with high iron contents. On scales of hardness, it is useless.
Only a small amount of sulfuric acid has been used in boiler cleaning procedures. Due to the creation of very insoluble calcium sulfate, it is not possible to remove hardness scales.
An SO2-scrubber could be necessary to reduce sulfur emissions (https://ww2.arb.ca.gov/rulemaking/2020/sf6) caused by flue gasses, depending on the sulfur concentration of the fossil fuels. Depending on the procedure utilized, these cleaning systems produce a range of liquid waste streams.
The primary duty of absorbing SO2 from stack gases is completed by washing the current gases with an alkaline slurry in all of the present FGD (flue gas desulfurization) systems. The partial elimination of the fly ash off the stack gases may come before this.
Ponding or landfills are used to dispose of waste solid products. The product is a transparent liquid that can be recycled. To regulate the quantities of dissolved solids, many lime and limestone systems output scrubber waters. This is the reason compressed air cleaning systems have gained popularity, as there are no chemically dissolved solids to deal with.
Many procedures can be categorized as double alkali procedures; however, the majority of development effort has focused on sodium-based procedures that utilize lime for regeneration. In order to cool, humidify, and decrease fly ash and chlorides, the aforementioned system pretreats the gases from the flue.
A reaction tank uses lime or limestone to renew the gas after it goes through an absorption tower, which removes SO2 into a cleaning solution.
The creation of a lot of waste sludge is a drawback of all non-regenerable systems. Sending the waste products to a settling basin serves as the standard method of on-site disposal.