The causes and troubleshooting of plate heat exchanger operation

Plate heat exchanger is a new type of high efficiency heat exchanger which is made up of a series of metal sheets with a certain corrugated shape. The utility model has the advantages of compact structure, small occupation area, high heat transfer efficiency, convenient operation and maintenance, etc.. Generally speaking, the practical application effect is good, but there are also some problems. Most of the heating systems adopt the wall type heat exchanger. After a period of operation, the heat transfer efficiency will decrease.

In the heat exchanger, the cold and hot fluid flows on both sides of the solid wall, and the heat of the hot fluid is transmitted to the wall in a convection way, and then passes through the wall. In order to enhance the heat transfer effect, the hot and cold fluid often uses the countercurrent heat transfer method. The heat exchanger usually works in steady state, and the heat transfer equation is found in the literature [1 ~ 3]. The variation of the temperature of the hot and cold fluid in the heat exchanger is shown in figure 1.

Under normal circumstances, the outlet temperature of the cold fluid is close to or exceeds the outlet temperature of the hot fluid, but in the actual operation, the temperature of the hot and cold fluid is abnormal due to the fault of the heat exchanger. The heat exchanger failure mainly as follows: 1, hot fluid outlet temperature is more than 1.1 times the cold fluid outlet temperature, does not conform to the rules of 2, countercurrent heat transfer; the outlet temperature of hot and cold fluid are low and close.

2 cause analysis and elimination methods

Situation 1

When the outlet temperature of hot fluid is more than 1.1 times the outlet temperature of the cold fluid, the heat exchanger has been shown to scale, and the fouling layer forms an additional thermal resistance, which affects the heat transfer effect.

The heating area of a district government heating station is 4 * 104m2, the heating capacity is 2.8MW, the heat exchanger has been used 10a. In the winter of 2005, found that the heat exchanger problems 1, operation parameters: a side inlet temperature is 70 DEG C, the outlet temperature is 65 DEG C; the two side inlet temperature is 42 DEG C, outlet temperature of 45 DEG C. At this point, the first side of the heat exchanger valve fully open, has been unable to adjust. With the outdoor temperature reduced, the heating station can not meet the heating demand. The operating parameters of the heat exchanger with the same scale are as follows: the inlet temperature of the primary side is 70 DEG C, the outlet temperature is about 44 DEG C; the inlet temperature of the secondary side is at a temperature of 41 DEG C, and the outlet temperature is about 48 DEG C. At this point, the heat exchanger is not fully open the valve side, there is room for adjustment.

The heat exchanger is disassembled, the surface of the plate is scale, and the surface has a layer of mud (when the pipeline is put into construction), and the thickness of the scale layer is about 1mm. After descaling and cleaning, the heat transfer effect is obviously improved, and the specific operating parameters are as follows: the inlet temperature of the primary side is 70 DEG C, the outlet temperature is at a temperature of 45 DEG C; the inlet temperature of the secondary side is at a temperature of 41 DEG C, and the outlet temperature is at a temperature of 49 DEG C. At this point, the first side of the valve in a semi open state, to restore normal regulation.

Situation 2

When the situation is 2, it can be judged that the flow rate of the hot fluid is too small, and the cold fluid can not be fully heated. The reason for this is that the heat exchanger is blocked and the air inlet of the heat exchanger is blocked.

The operating parameters of the heat exchanger of a local tax bureau are as follows: the primary side inlet temperature is 70 DEG C, the outlet temperature is about 45 DEG C, the inlet temperature of the secondary side is 41 DEG C, and the outlet temperature is about 49 DEG C. When abnormal, the operating parameters are as follows: the inlet of the first side is 70 DEG C, the outlet temperature is about 32 DEG C, the inlet temperature of the secondary side is at a temperature of 28 DEG C, and the outlet temperature is at a temperature of 33 DEG C. The heat exchanger was opened and found that the primary side of the heat exchanger was blocked by debris. After the heat exchanger was washed back and cleaned, the operation parameters returned to normal.

The failure phenomenon of the heat exchanger in the Sichuan thermal power station is the same as that of the Local Taxation Bureau, but the effect is not obvious after cleaning the heat exchanger and the decontamination device. Observation of the layout of the site found that: after a water stop, the pipe rises, and then fell into the heat exchanger, the pipe in the station there is a PI type bend, and there is only a pressure gauge, no gas valve. Remove the pressure gauge, open the valve on the curved surface of the valve and found a large amount of air in the pipe. Bleed about 15min after the first water gradually into the heat exchanger, one side of the water temperature gradually increased, the two side temperature increase, heating back to normal, which belongs to a side inlet air blocking situation exists.

According to the above situation, we have taken the following measures: to strengthen the construction management, to prevent the construction of debris into the pipeline; at the highest point of the installation of a side inlet valve; in the operation of the operation, often deflated. Plate heat exchanger in the use of the process, whether the plate deformation, cracks, perforation, or gasket aging, fracture, need to be replaced in a timely manner. If the site does not have enough spare parts using slip line, and heat transfer equipment and spare no taifen, cannot stop, should be easy to processing the scene. The method of simple treatment is damaged and the plate plate pairs of biological safety cabinets leaking out (A board +B board), if the number is not too much, to reduce the number of channels is not much, continue to use the assembly, production of the impact is not great.