Precautions for operating graphite reboilers

Operation method of graphite heat exchangers A Precautions for using graphite heat exchangers 1) Avoid strong impact from the material; when opening or closing valves, gradually adjust to the maximum or minimum flow rate. 2) Use is prohibited when temperatures and pressures are exceeded. 3) When used as a cooling device, the cold liquid should be introduced first followed by the gas; the reverse order is applied when shutting down. When making heating equipment, first pass the substance to be heated, and then pass the heating element. 4) When used as a cooling device, if steam or other gases appear inside the casing (which may reduce heat exchange efficiency), the vent pipe can be opened intermittently to release them, or the vent pipe can be connected to the outlet pipe. 5) At higher operating temperatures, the thermal deformation of the fluoroplastic O-rings may affect the sealing performance; therefore, a few hours after the new equipment is first put into use, it is necessary to check whether the cooling (condensation) water in the housing contains corrosive substances (samples can be taken via the drain pipe). If there is a leak, the rod nut can be tightened while the parts are still warm, by 1/3 to 1 turn (the water and steam pressure must be released before tightening the bolts). If there is no leakage, it’s no concern. 6) The water discharged from inside and outside the housing should be regularly checked to determine whether it contains material from the longitudinal holes. 7) If the material tends to crystallize or precipitate, it should be cleaned regularly using chemical methods. When the system is shut down, all the material must be removed, and the longitudinal holes should be rinsed with hot water as much as possible after shutdown (rinsing from top to bottom is preferred). This can **prevent the formation of a scale layer and extend the service life. 8) If low temperatures may damage the equipment, all cold and hot materials should be emptied when shutting down the system. (Open the drain pipe) 9) When the heat transfer capacity is low, it is possible to shut down the system and use appropriate chemical methods to clean the scale buildup on the heat exchange surfaces ； If the effect is not noticeable, it can be removed and cleaned piece by piece. 10) This equipment can withstand greater sudden cooling/heating and water hammer impacts than tubular graphite heat exchangers, but avoiding such phenomena is beneficial for extending the equipment’s lifespan. B Inspection method for graphite heat exchangers: When the heat transfer capacity becomes excessively low, the overall cleaning effect is insufficient, or leaks are detected, it is necessary to disassemble the equipment. Before disassembly, it is essential to rinse it with hot water to remove any remaining corrosive substances, after which the upper cover can be removed. 1) First loosen all the shell bolts, then loosen the bolts of the tension rod, and the upper cover can be removed. 2) Remove the shell bolts as well as the upper cover, end cap, heat exchange blocks, inner and outer flow separation plates, etc., and place them aside in order (graphite components should be placed on soft padding such as rubber sheets or straw mats to prevent damage to the sealing surfaces). When lifting the casing, it should be kept as vertical as possible, and lifted slowly while rotating to prevent the outer baffle from getting stuck and causing damage to the graphite components. For parts that need to be cleaned after removal, clean them; for equipment with leaks, perform pressure testing on each heat exchange module (using a water pressure 15 times the design pressure, for no less than 30 minutes). 3) If minor spot-like leaks are detected during the pressure test, the graphite components can be dried, then impregnated with phenolic resin and subjected to heat treatment (if the graphite components are contaminated, they must first be cleaned chemically). If there is slight leakage from the walls of the pores, these pores can be sealed using impermeable graphite rods (or materials resistant to heat and corrosion can be used in their place), along with phenolic putty. First, the graphite components need to be cleaned and dried at 80–120°C. After sealing the pores, they should be allowed to cure naturally at room temperature for 24 hours, after which the temperature should be gradually increased to 130°C (or 165°C), and the components held at that temperature for 6–8 hours to ensure complete curing. Finally, another pressure test should be conducted. If there are too many leakage holes, affecting the heat exchange efficiency, it needs to be replaced. 4) When removing the housing and heat exchange blocks, carefully inspect all types of sealing rings, including rubber O-rings, fluoroplastic O-rings, and asbestos rubber rings; if they are no longer usable, they can be replaced with new ones. Replace the fluoroplastic O-ring; the inner and outer rings that are in the same plane should be replaced simultaneously. 5) If only the seal ring between the housings is leaking and the heat exchange block is functioning properly, it is sufficient to remove the outer housing and replace the seal ring there; there is no need to take out the heat exchange block (but be careful not to affect the heat exchange block when lifting the outer housing). Several notes on C graphite heat exchangers: 1) To reduce the fluid resistance of the heat transfer medium, the horizontal holes in the heat exchange blocks are arranged in a tangential direction, and the tangential rotation directions of adjacent upper and lower blocks are opposite to each other; this aspect should be taken into consideration during installation. (If vertical holes need to be connected end-to-end due to manufacturing requirements, this can be specified at the time of ordering.) 2) When installing each graphite component, rotate the previous graphite block (or end cap) to check whether it is properly seated and if the fit is correct, especially for graphite components that have undergone impregnation treatment. 3) After being placed in the heat exchange block, the inner and outer baffle plates should be below the sealing surface of the heat exchange block; otherwise, the surface of the installation groove should be cleaned. The arrangement order of the inner and outer baffle plates is shown in Figure 1. 4) Under normal circumstances, it is not necessary to remove the lower head and seals. 5) When assembling, make sure to tighten the tie rod studs first, and then the housing bolts; reverse the order when disassembling. 6) The sealing surfaces and gaskets must be clean; in particular, particulate impurities on the graphite components and PTFE O-ring sealing areas can cause leaks during pressure testing. 7) If welding is required on the enclosure in its assembled state, it is necessary to ensure that the graphite components and sealing rings are not damaged; otherwise, the enclosure should be disassembled before carrying out the welding. When welding, appropriate electrodes and welding procedures should be selected, and the work should be carried out in accordance with relevant requirements. Also, ensure that the weld seams do not protrude beyond the inner wall, and that the outer shell does not suffer significant shrinkage deformation, to avoid affecting installation and removal. 8) When scaling occurs on the process fluid side or the quality of the cooling water is poor, stopping operation promptly and carrying out chemical cleaning can yield significant economic benefits; it is recommended that users in such conditions pay attention to determining the appropriate cleaning intervals.