After mixing glycolic acid with formic acid, cleaning in high pressure steam stainless steel boilers is fast and efficient. This mixture has been extensively tested to determine its safety and effectiveness. The residue of glycolic acid/formic acid decomposes into a volatile, non-corrosive product. The wastewater produced by the process is very easy to remove.
1. Advantages of cleaning the boiler with glycolic acid:
* Quickly and effectively remove oxide scale (including iron oxide, calcium salt, magnesium salt, silica, residue, nickel oxide and copper oxide)
* No organic iron precipitation
* No chloride - it can be used to clean stainless steel without problems that have occurred in acid chloride systems, such as chloride cracking and embrittlement
* Its corrosion rate for metals
* Decomposition products are volatile and non-corrosive
* Waste is easy to handle (glycolic acid is very easy to biodegrade; heavy metals are very easy to remove from wastewater)
2. The glycolic acid system has the following advantages over competing systems for other products:
* EDTA is generally more expensive than glycolic acid
and is slower to remove scale. In addition, from an environmental perspective, using EDTA will carry more heavy metals.
* Citric acid is slower than glycolic acid to remove dirt. Moreover, the citrates of iron and calcium are less soluble than their glycolates, so they precipitate on the surface of the boiler, reducing the cleaning effect.
* Hydrochloric acid, although cheaper than glycolic acid, has been found to cause cracking in austenitic stainless steels. Moreover, hydrochloric acid is more corrosive and more difficult to handle (gas and odor) than glycolic acid.
3. Typical cleaning application:
1) Preheat the boiler under alkaline conditions to remove mineral oil residue
2) The ratio of circulating acidic solution
* 3% solution:
2% glycolic acid
1% formic acid (formic acid)
<1% corrosion inhibitor
* Temperature: 180-220°F (82-104°C)
* Cycle speed: 1-2fps (0.3-0.6 m / sec)
* Contact time: 2 hours (10-12 cycles)
1. Decomposition reaction during boiler cleaning
Although we can't get the basic data of formic acid and glycolic acid during the actual boiler operation, they should be decomposed according to the typical reaction.
Once heated, the organic acid undergoes decarboxylation, and the reaction equation is as follows:
HCOOH→CO+H 2 O
HOCH 2 COOH→HOCH 3 +CO 2
If a trace amount of oxygen is present, an oxidation reaction will occur, and the equation is as follows:
HOCH 2 COOH+O 2 →2H 2 O+CO 2
2HCOOH+O 2 →2H 2 O+2CO 2
Since these decomposition products are volatile and harmless, they do not cause equipment problems even if they are not completely rinsed.
2. Theoretical descaling ability
-Kg dirt / 100Kg cleaning agent
- calculated on the same weight basis
-100% as the benchmark
FeO3 CaCO3 CaSO4 MgCO3 MgSO4 CuO
Glycolic acid 48 66 90 55 79 52
Glycolic acid/formic acid (2:1) 58 80 109 67 96 64
Citric acid 37 52 71 44 62 41
Formic acid 79 110 150 92 162 87
EDTANa 4 37 53 72 44 63 41
3. Dirt carrying capacity based on operational experience
-120 tons of cleaning solution
-2% glycolic acid / 1% formic acid: 1.5 tons of iron scale
-12% EDTANa 4 : 0.7 tons of iron scale
4. Wastewater treatment
Both glycolic acid and formic acid are biodegradable, so the organic wastewater can be sent to a biological wastewater treatment plant for treatment. The typical residual bacteria after treatment include pseudomonas and filamentous bacteria.
The wastewater after boiler cleaning also contains various metal salts, including iron, calcium, magnesium and copper salts, which must be disposed of in accordance with local environmental requirements.
5. Stability of iron salt-glycolic acid chelation solution
Adding glycolic acid to the iron (divalent or trivalent) salt can increase the pH of the precipitate. In the absence of glycolic acid, the ferric salt will precipitate when the pH is between 2.6 and 3.5. In the presence of glycolic acid, precipitation occurs at a pH of 11.0-11.5.