Diagnosis and handling of common operational faults

(i) Operational status deviates from process requirements
1. If a newly commissioned plate heat exchanger fails to meet the process requirements, the original design parameters, design calculations, and assembly should be carefully checked to determine whether they are correct. Then, it should be decided whether the heat exchange area should be increased or decreased, and whether the process combination should be changed.
2. If the plate heat exchanger starts operating normally, but deviates from the process requirements after a period of operation, such as: pressure drop increasing or decreasing; medium outlet temperature rising or falling.
The solution to this problem is:
1. Check whether the inlet parameters of the hot and cold media match the original design values. If they do not match, try to adjust them to the original design values. If the inlet parameters have changed and cannot be adjusted to the original design values, the design calculation should be re-performed to determine whether to increase or decrease the heat exchange area or change the process flow combination.
2. If the inlet parameters of the cold and hot media are consistent with the original design values, but the outlet parameters do not meet the design values, the machine should be stopped, and the plates should be disassembled to check for blockages or scaling, and dealt with in a timely manner.
(ii) Leakage in plate heat exchangers
Because plate heat exchangers have a long sealing perimeter and thin plates, leakage may occur during use. Leakage can be categorized into internal and external leaks.
1. External leakage of plate heat exchanger
This refers to the leakage of the medium inside a plate heat exchanger into the external space. This type of leakage is usually easy to detect. The main causes are aging or corrosion of the gaskets, or deformation of the plates. When this leakage occurs, the leaking part should be marked immediately, and the equipment should be opened to replace the gaskets or plates.
2. Internal leakage of plate heat exchanger
This refers to a situation where, due to some reason, the high-pressure side medium leaks into the low-pressure side within a heat exchanger. This type of leakage is generally not easily detected in time. The main causes are plate perforation, cracks, and corrosion. The method for detecting this type of leakage is to regularly analyze the medium on the low-pressure side and determine the cause by observing changes in its composition.
The shutdown inspection method for this type of leakage is as follows:
(1) Disassemble the plate heat exchanger, remove the dirt from the plate surface, wipe it dry, and then reassemble the heat exchanger. Perform a water pressure test on one side at a pressure of 0.2~0.3 MPa. Stop the test when water flows out from the other side, open the heat exchanger, and carefully observe the untested side of the plates. The wet plates are the plates with holes or cracks.
(2) On-site inspection methods such as light transmission and colorimetry can also be used to identify defective boards. All defective boards and gaskets identified must be replaced and reassembled for use.
(iii) Misalignment of the plates in the plate heat exchanger
1. Plate heat exchangers with large variations in medium flow rate and pressure, and which are multi-pass combinations and used for a long time, are prone to plate misalignment. After plate misalignment, external leakage sometimes occurs quickly; although it may not cause immediate external leakage, it is still a potential source of seepage, so it must be dealt with promptly.
2. The main causes of misalignment are: deformation of the heat exchanger plates; and the gaskets of the plate heat exchanger slipping out of their grooves. To address this misalignment, the deformed plates and the gaskets that have slipped out of their grooves should be replaced promptly.
(iv) Simple handling methods for plate heat exchangers when maintenance equipment is lacking on site
1. During the use of plate heat exchangers, whether the plates are deformed, cracked, or perforated, or the gaskets are aged or broken, they need to be replaced in a timely manner. In case there are not enough spare parts on site, and the heat exchange equipment has no spare units and cannot be shut down, simple on-site handling should be carried out.
2. A simple on-site solution is to pair the damaged and leaking plates (plate A + plate B). If the number is not too large, the reduction in flow channels is not significant, and the plates can be reused after assembly without much impact on production.