Cleaning and flushing of plate heat exchangers
Plate heat exchangers are referred to as so-called recuperative heat exchangers (in which heat carriers wash the wall on both sides resulting in a continuous exchange of heat). These are devices whose heat exchange surface consists of thin metal plates with a certain “pattern”. The plates compressed between each other form channels with each other through which heat carriers flow. It should be noted that different brands of heat exchangers have its own unique pattern on the plates and it will not be possible to replace plates of one brand with another.
Plate heat exchangers are divided into:
- undismountable (brazed and welded)
Scheme and principle of operation of the folding heat exchanger
The folding plate heat exchanger includes a frame and a plate pack.
The frame consists of a fixed plate (1) and a pressure plate (2), a rear stand (7) which is connected to the fixed plate with the upper guide (3) and the lower guide (4). Frames of folding heat exchangers are available in different lengths to ensure that different numbers of plates are installed in it. There is a package of a certain number of plates between the two frames.
The pack is pressed onto the fixed plate with a pressure plate using tie bars (6). At a certain compression, the seals contact each other and make the inner space tight.
Plates are produced by stamping stainless steel. Steel grades used for the manufacture of plates are not prone to general types of corrosion. The plates have four through holes, which form two channel systems and are isolated from each other. Rubber gaskets are used to seal the plates and channels in compression. The seals are attached to the plate with clips, with each type of heat exchanger having its own fasteners.
Because of its design, the plate has good heat transfer. The special relief of the plate optimally distributes heat carriers. Corrugating of plates can be
- “thermally rigid” with an angle of 30 degrees (characterized by higher heat transfer coefficient, but also high pressure losses);
- “thermally mild” with an angle of 60 degrees (characterized by lower heat transfer coefficient, but also lower pressure losses).
Different flow of fluids in the heat exchanger is achieved using different combinations of plates. This device works in the turbulent mode and in this it is more efficient than the shell-and-tube one, since when performing the same tasks the area of the plate heat exchanger is several times smaller.
Semi-welded plate heat exchanger
It consists of a set of welded modules formed of two plates that are welded to each other. Rubber gaskets between the channels are similar to plate heat exchangers. The semi-welded plate heat exchanger is ideal for aggressive environments. Aggressive substance flows through the channels formed by welded to each other plates.
Undismountable heat exchangers
Undismountable welded plate heat exchangers consist of a package of plates that are in all-metal housing. Welds form a channel system for power fluids.
This type of heat exchangers is used in the following cases:
- Power fluids do not form contaminants on the surface of the heat exchanger.
- This type is designed only for chemical cleaning and eliminates the type of folding flushing.
- It is required increased reliability and performance of the device.
- Performance and conditions do not correspond to the performance of folding heat exchangers.
A feature of these heat exchangers is that due to the one-piece body and the absence of rubber seals, absolute tightness is created and the pressure loss at the outlet is almost absent.
The team of qualified experts of ASGARD-Service has extensive experience in the maintenance, flushing and repair of all types of heat exchangers, both folding and undismountable heat exchangers.
During operation of heat exchange equipment, wear of its parts occurs, and performance indicators deteriorate. This is due to the fact that large particles of sediments get into the working parts of the heat exchanger, and because of the poor quality of the water preparation, deposits of calcium, magnesium, and metabolic products of microorganisms are formed on the internal surfaces of the equipment. If you notice that the performance of your heat exchange equipment has decreased, it is likely that its maintenance and cleaning is required. As a rule, cleaning of heat exchange equipment is carried out before each heating season, this allows avoiding major accidents and equipment breakdowns, which leads to expensive and long-term work. The ASGARD-Service Company carries out cleaning of heat exchangers using folding and in-place methods. Both methods have its advantages.
Folding flushing of heat exchangers
Procedures for disassembling the heat exchanger are carried out. To begin with it is disconnected from the general system, water is drained from it and the studs compressing the plate pack are loosened. It is worth noting that it is necessary to strictly follow the method of disassembling and assembling the heat exchanger, otherwise you can pull it over, squeeze the plate seals, which will lead to the next disassembly of equipment and incur additional costs, and sometimes can lead to serious repairs. That is why we advise you to entrust the cleaning and maintenance of your devices to our experts who have extensive experience in these works. After disassembly, the plate pack is removed and each plate is individually washed with a high-pressure apparatus, if necessary, before being processed by AHP, the plates are soaked in a chemical solution to remove the adhesion deposits from the metal surface of the plate.
Folding flushing is usually used when the heat exchanger is almost completely clogged and its throughput is extremely low. Then the heat exchanger is assembled, it is important to properly assemble the plate pack and seals. In some cases, when the heat exchanger is more than 8 years old and the seals have never changed, during disassembly/assembly it is necessary to change the entire set of seals.
The photos show plates with hard water deposits after ASGARD-Service experts arrived at the call and disassembled one of the heat exchangers.
The following photos show the results after folding flushing.
It is carried out in two ways:
- Chemical cleaning;
- Hydrokinetic cleaning.
As a rule, the best results are achieved by combining these techniques. Folding flushing and its ability depends on the type of equipment and its purpose.
Features of in-place flushing
In-place flushing is suitable for all types of equipment. As a rule, it is used for preventive flushing before the heating season.
This flushing is carried out in two ways – chemical cleaning and hydrokinetic cleaning. As a rule, the best results are achieved by combining these techniques.
Advantages of in-place flushing:
- saving time for equipment repair;
- reducing the complexity of the process;
- reducing the risk of damage to equipment and its individual components during disassembly / assembly for folding flushing;
- cheaper than folding flushing;
- possibility of cleaning on mode (without disabling the main equipment).
In preparation for in-place flushing, our experts take samples of sediments and, based on data from specialized laboratories, select reagents, temperature regimes and flushing technology. When this option is not possible, the selection is carried out on the basis of experience according to the universal method.
In addition to chemical flushing, ASGARD-Service specialists apply hydrokinetic effects by supplying compressed air during water washing into the circuit. When this occurs, the shock-wave effect on the deposits, they lose its adhesion to the metal surface and are carried away by the flow of water into the intermediate tank.
In-place flushing on mode
The most interesting point in in-place flushing is flushing on mode when the main equipment does not turn off and flushing of one circuit or backup heat exchanger is carried out.
Such flushing is possible at any time of the year and helps to maintain the technological parameters of the equipment in good condition before stopping for repairs. It is also possible to increase the equipment overhaul time and reduce the cost of repairing this equipment. And maintaining the parameters in the normal improves the quantity and quality of the product.