Graphite heat exchanger is the key equipment for indirect heat transfer in vacuum concentration process of wet process phosphoric acid plant. Phosphoric acid in tubular graphite heat exchanger is heated by low pressure steam and then transferred to the vacuum evaporation chamber. After rapid evaporation of water, it reaches the purpose of concentration. As WPA is a mixed acid, there is not much choice in determining the material of heat exchanger. The common material of Z is graphite, because it can meet the basic requirements of good thermal conductivity and corrosion resistance. The corrosion resistance of the commonly used acid resistant stainless steel in the wet phosphoric acid concentration process is poor, and only the heat exchanger made of high chromium and high nickel stainless steel is reported to be used in phosphoric acid concentration plants abroad.
Graphite heat exchanger is divided into block hole type and tube shell type. The main advantages of the block hole graphite heat exchanger are high strength, small size, not easy to crack, high pressure steam can be used, the flow rate of phosphoric acid is high, the heat transfer coefficient is high, and the temperature difference between the inlet and outlet of the heating medium can be large; The disadvantage is that once leakage occurs, it is difficult to find and repair. Manufacturer of graphite heat exchanger
The advantages of shell and tube graphite heat exchanger are that the leakage is easy to find, and the damaged tube is easy to repair; The disadvantage is that the strength of graphite tube is relatively low, and the steam pressure used cannot exceed 0.15 MPa; The flow rate of the heated medium is low and can only be controlled at 2-3m/s; The temperature difference between the inlet and outlet can only be controlled at 2-4 ℃, and the heat exchanger is large.
As the graphite tube was suddenly damaged during operation, it is impossible to clean the heat exchanger with hot water. About 80% of the shell of shell and tube graphite heat exchanger is made of carbon steel. If it is cleaned, acidic water will corrode the shell of the heat exchanger. At this time, a high-pressure cleaner must be used to clean the tubes one by one. It takes about 3min to clean each tube. Because the graphite tube is relatively brittle, the water volume of the selected washing machine should not be too large ³ The pressure of cleaning water shall be controlled below 2MPa. A more important factor of the cleaning agent is that the working pressure must be stable. At present, the water pressure of the cleaning machines on the domestic market fluctuates greatly during cleaning, which will cause damage to the pipes.
Before leak detection, close the automatic steam regulating valve and manual main valve of the heat exchanger, remove the condensate drain pipe of the heat exchanger, and install a valve on this interface for draining the water in the shell side during leak detection.
method:
Fill the tube side of the shell and tube graphite heat exchanger with water to make the water level about 50~100mm higher than the end face of the upper tube plate of the heat exchanger. Quickly open the valve on the condensate drain pipe interface to quickly drain the water leaking from the tube side to the shell side; At this time, the seriously fractured pipe will appear vortex on the water surface of the upper tube plate. The upper end of the pipe should be quickly plugged with a rubber stopper, and the valve on the condensate drain pipe interface should be closed. Repeat the above action to find out the seriously broken pipe.
Next, drain the water in the tube side of the heat exchanger and temporarily plug the seriously broken tubes. Use a 100mm long M18 bolt on its jacket for 35.5mm
