Plate Heat Exchangers Fouling Cleaning
In the using process of heat exchangers, because of improper operation to water treatment equipments, substandard water quality control, and unqualified soften water is injected into the heating system, hard scales are formed. Due to scales’ thermal conductive performance is poor, it makes thermal efficiency lower and thermal energy seriously wasted, which affect the heating effect.
The Cleaning Methods:
(1) Mechanical cleaning with iron brush.
The disadvantages are:
There are scratches on the plates, and they are easier to hang dirt after brush.
Workers have to work in cold water. The working condition is very poor.
The heat exchangers must be taken apart for cleaning, which not only waste rubber, but are harmful to the plates and strips.
(2) Chemical cleaning: the adopted method is pickling.
1) Formic acid cleaning
In order to make the cleaning effect better, add buffering agent and surface active agent in formic acid cleaning fluid, which can reduce corrosion to the plates.
a. flushing: Before pickling, to make open flushing to heat exchangers. So there are no impurities such as mud, scale within the heat exchangers to improve the effect of acid pickling and reduce the amount of acid pickling waste.
b. To put the cleaning fluid into cleaning equipment and then inject them into heat exchangers.
c. acid washing: to immerse statically the heat exchanger filled with acid solution in 2 h, then do dynamic cycle continuously in 3 h - 4 h, and then maintain alternating cleaning during every 0.5 h. After the acid washing, if the acid PH is greater than 2, the acid liquor can be reused; otherwise, the acid liquid should be diluted and discharged.
d. alkali washing: After finishing acid washing, demineralized water has been confected according to a certain proportion by using trisodium phosphate. To do alkaline cleaning for heat exchangers by dynamic circulation way to achieve acid and alkali neutralization, which make the plates no longer be corroded..
e. rinsing: After finishing alkali washing, rinse 0.5 h repeatedly on heat exchangers by demineralized water to wash out residues in the heat exchangers.
f. record: In the process of cleaning, you should record each steps of time strictly, in order to check the cleaning effect.
After the cleaning, the heat exchangers are verified by crackdown test.
2) Oxalate cleaning
Through analyzing the plate materials and the color of scales, find that the oxalic acid can react with scale, nor corrode plates.
a. Not split heat exchanger, to install a water injection valve in the secondary network inlet and outlet valve of heat exchangers, inject 3%-5% oxalic acid solution to the inside of heat exchangers, use circulating pump to put oxalic acid solution circulated between heat exchanger and water tank, to achieve clean.
b. To Wash 2 times, each time three or four hours
c. After rinsing with 2% trisodium phosphate, and then rinse twice with water
(3) The measures to prevent plate heat exchangers fouling
1. Pay more attention to water quality. There are strict water quality tests about water in systems and demineralized water. When they are qualified, you can put them in the pipe networks.
2. When the new system will be put into operation, you should separate heat exchangers and heating systems. After cycles for a period of time, you can incorporate heat exchangers into the system, to avoid impurities in the pipe networks into the heat exchangers.
3. In the heating system, dirt separators and filters shall be cleaned irregularly, also should keep the pipe networks cleaned in order to prevent the heat exchanger jam.
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