Operating Procedures for Plate Heat Exchangers in Reformation Units

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Operating Procedures for Plate Heat Exchanger (E701) 1 Overview The E701 is a plate heat exchanger manufactured by the French company PACKINOX. It consists mainly of a pressure vessel shell, a heat transfer plate bundle, and flow collection tubes. The function of the pressure vessel shell is to withstand stress (or operating pressure). The heat transfer plate bundle is the core component of welded plate heat exchangers. This bundle is formed by welding hundreds of stainless steel plates, each of which is manufactured using a patented process involving underwater detonation. The flow channels in these plates are arranged in a corrugated pattern, with the flow directions of adjacent plates alternating; the hot fluid flows through one side of the plates, while the cold fluid flows through the adjacent side, enabling heat transfer through counterflow. The plate heat exchanger channels are only 2.5–6 mm wide; given its structure, the tube bundles are highly prone to becoming clogged by contaminants such as catalysts and corrosive substances. 2 Main Technical Parameters Item Unit Reaction feed side (inlet/outlet) Reaction discharge side (inlet/outlet) Flow rate Kg/h 189988 190025 Temperature °C 88 488 522 99 Inlet pressure MPa 0.541 0.306 Heat load MW 75.23 Temperature difference at the hot end °C ≤34 Tube bank pressure drop MPa ≤0.086 Design pressure MPa 0.769 Design temperature °C 544 to 288 Inner diameter mm 2900 Design pressure difference MPa 0.5 3 Preparations before operation 3.1 The interior of the plate heat exchanger has been thoroughly cleaned before operation ； 3.2 All system pipelines connected to the plate heat exchanger have been cleaned to prevent impurities from entering the exchanger and blocking its channels during operation ； 3.3 The spray rod has been installed, the vent valve is closed, and the drain port is closed after cleaning it thoroughly ； 3.4 The nitrogen gas must meet the airtightness requirements. When ensuring airtightness, it should be noted that the tube bundle of a plate heat exchanger can only withstand a pressure difference in one direction; that is, the pressure on the cold side must be higher than that on the hot side. 4 Operation of the plate heat exchanger 4.1 Principles of operation: The tube bundle of a plate heat exchanger can only withstand a pressure difference in one direction, meaning the pressure on the cold side must be higher than that on the hot side. 4.2 Before commissioning, drain the oil accumulated at the bottom of the heat exchanger to the sludge line to prevent liquid slugging in the tube bundle. 4.3 The heating rate of the heat exchanger shall be controlled at 50°C–55°C/h, and the temperature difference between the materials on both sides must not exceed 100°C. 4.4 When feeding oil into the heat exchanger, maintain a linear increase in the feed rate: control it to go from 0 to 60% over 5 minutes, and then increase it to 100% feed rate. 5 Disactivation of plate heat exchangers 5.1 Principles of disactivation: The tube bundle of a plate heat exchanger can only withstand a pressure difference in one direction; that is, the pressure on the cold side must be higher than that on the hot side. 5.2 Maintain the heat exchanger cooling rate at: 50°C～55°C/hr. 5.3 Use H2 or N2 for circulating cooling in the heat exchanger, and the temperature difference between the materials on both sides shall not exceed 100°C. 5.4 If no maintenance is carried out, the heat exchanger should be protected with a slight positive pressure of N2 during periods when it is not in use. The tubes of the heat exchanger are made of stainless steel; it is essential to prevent chloride ions and liquid water from entering these tubes during periods of inactivity, in order to avoid corrosion of the stainless steel. 6 Daily maintenance of plate heat exchangers 6.1 Check the temperature changes of the thermocouples located on the top wall of the heat exchanger; if the temperature drops, it may indicate a leak in the expansion joint. 6.2 Check the differential pressure of the feed filter; switch it for cleaning when it exceeds 0.1 MPa. 6.3 Check that the pressure drop across the heat exchangers on the feed side and discharge side is not greater than 0.086 MPa, and that the temperature difference at the hot end is not greater than 34°C. 6.4 Check that the pressure difference between the spray rod inlet and the circulating hydrogen inlet is 0.1 MPa, but not greater than 0.6 MPa. 6.5 Check whether there are any leaks at the flange connections of the heat exchanger. 6.6 In the event of an emergency shutdown of the unit, if the feed pump for the plate exchanger does not shut down automatically as a result of the interlock, it must be stopped immediately.