[Heat exchanger cleaning and maintenance] How to clean the heat exchanger and the heat exchanger cleaning process
The heat exchanger cleaning process
The first step: descaling and cleaning. Add the configured descaling cleaning agent to the circulating water of the cleaning tank in proportion to clean and descaling the boiler. Determine the cleaning cycle time and the amount of chemicals added according to the amount of scale. After confirming that all the scales have been cleaned, go to the next cleaning procedure .
Step 2: Clean with clean water. After the cleaning equipment is connected to the boiler, clean it with clean water for 10 minutes, check the system status, whether there is leakage, and clean the floating rust at the same time.
The third step: peel off anti-corrosion cleaning. Add surface stripping agent and slow release agent to the circulating water of the cleaning tank in proportion, and cycle for 20 minutes to separate the scale from the cleaned components. The cleaning agent corrodes the cleaned parts.
The fourth step: passivation coating treatment. Add a passivation coating agent to carry out passivation coating treatment on the boiler cleaning system to prevent corrosion of pipelines and components and the formation of new rust scale.
First, the cleaning process of the condenser:
1. Close the valve of the cooling water in and out of the condenser, and use the thermometer tube, pressure gauge tube or sewage The pipe is connected to the anti-corrosion pump and the liquid distribution tank to make a small circulation system for circulating cleaning.
2. Add pickling corrosion inhibitor first, which is a special copper corrosion inhibitor, which adheres to the inner wall of the condenser metal to prevent the acid and metal from reacting.
3. Add solid pickling cleaning agent to clean the scale with calcium carbonate scale as the main component. The cleaning agent is a composite solid organic acid, white crystal, non-corrosive to metals, and is a weak acid; cleaning The dosage of the agent depends on the scale of the equipment.
4. Add a scale stripping agent (optional), if the scale of the condenser equipment is thick, you need to add a sludge stripping agent to promote the rapid dissolution of the product after the scale reaction in water and accelerate the deep scale reaction
5. Add neutralizing passivation agent, after the condenser is chemically cleaned, the residual acid will be neutralized to prevent the metal surface from oxidizing and generating secondary rust.
6. Cleaning process:
A. Cleaning temperature: Generally, normal temperature cleaning is used. If the scale is thick, it can be cleaned at 40℃~50℃ to improve the cleaning speed.
B. Close the valves entering and leaving the unit, and use pressure gauges or thermometer tubes, anti-corrosion pumps, and acid tanks to form a cleaning circulation system. When cleaning, add corrosion inhibitor first, and slowly add organic acid after the corrosion inhibitor circulates evenly. During cleaning, the reaction should be checked regularly. When the cleaning agent is insufficient, it should be supplemented to ensure that there is enough acid solution and scale reaction. During cleaning, press the scale reaction. If necessary, an appropriate amount of sludge stripper, defoamer, etc. can be added.
C. After cleaning, drain the remaining liquid and add clean water to rinse.
D. After the condenser is cleaned, it is necessary to add a neutralizing passivator to neutralize the residual acid to prevent oxidation of the inner wall of the metal.
E. The condenser cleaning time is about 5 to 10 hours, depending on the actual situation.
Second, the cleaning process of plate heat exchanger:
1. The basic principle of removing scale in stainless steel plate heat exchanger
( 1) Dissolution: The acid solution easily reacts with calcium, magnesium and carbonate scales to form soluble compounds and dissolve the scales.
(2) Peeling effect: The acid solution can dissolve the oxides on the metal surface. Destroy the bond with limescale. Thereby, the scale adhering to the surface of the metal oxide is peeled off and peeled off.
2. Process requirements for cleaning scale in stainless steel plate heat exchangers
Pickling temperature: Increasing the pickling temperature is beneficial to improve the descaling effect. If the temperature is too high, it will aggravate the corrosion of the pickling solution to the heat exchanger plates. Through repeated tests, it is found that the pickling temperature should be controlled at 60~E. Concentration of pickling solution: According to repeated tests, the pickling solution should be prepared according to the concentration of formic acid 81.0%, water 17.0%, buffer 1.2%, surfactant 0.8%, and the cleaning effect is excellent.
3. The specific steps for cleaning the scale in the plate heat exchanger
(1) Isolate the equipment system and drain the water in the heat exchanger.
(2) Use high-pressure water to clean the sludge, algae and other impurities remaining in the pipeline, and then close the system.
(3) Install a ball valve (not less than 1 inch = 2.54 cm) between the isolation valve and the exchanger, and both inlet and return ports should be installed.
(4) Connect the transfer pump and connecting pipe, so that the cleaning agent is pumped in from the bottom of the heat exchanger and flows out from the top.
(5) Start to pump the required cleaning agent into the heat exchanger (the proportion can be adjusted according to the specific situation).
(6) Repeat the cycle cleaning to the recommended cleaning time. With the progress of the cycle and the dissolution of the sediment, the gas generated during the reaction will also increase, and the excess air should be exhausted through the air release valve at any time. As the air is discharged, the space in the heat exchanger will increase, and appropriate water can be added. Do not inject a large amount of water at the beginning, which may cause water overflow.
(7) The effectiveness of the cleaning agent should be checked regularly during the cycle, which can be determined by using PH test paper. If the solution is kept at a pH of 2-3, the cleaning agent is still effective. If the pH value of the cleaning agent reaches 5-6, an appropriate amount of cleaning agent needs to be added. The pH of the final solution remained unchanged for 30 minutes at 2-3, proving that the cleaning effect was achieved. Note: The cleaning agent can be recycled and reused, and the discharge will cause waste.
(8) After reaching the cleaning time, recover the cleaning solution. And rinse the exchanger repeatedly with clean water until it is clean and neutral, and measure the pH value of 6~7 with pH test paper.
(9) After cleaning, it can be turned on and run. You can also press the test to see if there is any leakage. If there is leakage, it can be repaired and protected by polymer composite materials, and the service life of the equipment can be greatly extended.
(10) After the equipment is stable, write down the current medium overflow, working pressure, heat exchange efficiency and other data.
(11) Comparing the changes in the values before and after cleaning, we can calculate the production costs such as electricity and coal costs saved by the enterprise per hour and the improved work efficiency. This is exactly what the enterprise adopts. Value compensation for technology applications.
(12) The same operation method can also be used for condenser, frame heat exchanger cleaning.
(13) If the enterprise needs equipment for passivation pre-film treatment, it can be operated according to the following procedures:
a. Pump the passivation pre-film agent into the equipment according to the recommended dilution ratio Medium (hang the test piece in the circulation tank at the same time);
b. Circulate and soak according to the recommended time; check the effect of pre-filming (red dot method or blue dot method);
c , discharge;
d. Rinse with water until it is neutral (measure pH value 6~7 with pH test paper).
(14) After the passivation pre-film is completed, it is best to use ventilation equipment such as fans to dry the system, which can ensure and improve the passivation pre-film effect.
Third, the cleaning process of the air radiator (air heat exchanger):
We know that the core part of the air radiator is the heat exchange base tube, One is the heat exchange fins, which can be viewed separately:
1. The heat transfer base pipe is prone to scale and impurities when the heat transfer oil or hot water is used. The cleaning method is the same as that of the plate heat exchanger. The possible heat source is removed, and acid washing is carried out with the appropriate solubility.
2. The heat dissipation fins will also produce some dirt after being used for a long time. The cleaning method is to first clean the dirt and dust that are easier to remove by hand, and then use the air pump with the cleaning solvent to slowly clean it. Yes, the solvent concentration should not be too high, and it should not have a corrosive effect on the fin itself.
Fourth, shell-and-tube heat exchanger (shell-and-tube heat exchanger) cleaning:
The shell-and-tube heat exchanger is disassembled, and the shell-and-tube heat exchanger is manually sliced Remove the scale layer on the heat exchange surface and reassemble. This method can only be used when the shell and tube heat exchanger is completely separated from the system, and the clamping size of the shell and tube heat exchanger during reassembly is relatively high. It is composed of parts such as tight plate and whole machine frame.
