【Daily Question 2019】Hydrogen production and hydrogenation section – Question No. 092

Phenomena of internal leakage in high-pressure heat exchangers: ① The color of the produced oil darkens, the impurity content increases, and quality parameters such as sulfur, nitrogen, and reaction levels are not up to standard. ②The reactor temperature rise decreases. Treatment method: ① The quality of the produced oil is satisfactory, so production continues. ②If the quality of the produced oil is unsatisfactory and reducing the space velocity does not help, the plant shall be shut down.

The product quality is unsatisfactory; the outlet temperature of the heat exchanger has decreased. The unit is shut down locally to remove the heat exchanger for maintenance

Cause of occurrence: Corrosion and perforation of the heat exchange tubes, as well as weld failure. The weld between the heat exchange tube and the tube sheet has cracked. Leakage in the seal of the floating head flange of the floating head heat exchanger. Leakage in the sealing of the threaded lock-ring type heat exchanger tube sheet. Handling method: When there is an internal leak in the tube bundle of the high-pressure heat exchanger, the reaction system will be shut down locally. The decommissioned internal-leak heat exchangers shall be treated in accordance with the following requirements: 1. Leaks in the internal tube bundles of the heat exchangers are generally detected using a hydrostatic test; once a leaking tube bundle is identified, it is replaced or sealed off. 2. When cracks occur at the welds between the heat exchange tubes and the tube sheet, repair welding or plugging is carried out. 3. When there is a leakage at the flange seal of a floating-head heat exchanger, the bolts should be tightened or the gasket replaced. 4. When there is leakage in the seal of the threaded lock-ring type heat exchanger tube sheet, the bolts pressing the inner ring should be tightened or the gaskets replaced.

Answer: I. Phenomena: The color of the produced oil darkens, the impurity content increases, the levels of reactive olefins, thiol sulfides, etc. rise abnormally, and quality parameters such as sulfur and nitrogen fail to meet the specifications. The reactor temperature rise decreases. II. Handling method: After internal leakage occurs in the tube bundle of the high-pressure heat exchanger, the reaction system will be shut down locally. The decommissioned internal-leak heat exchangers shall be treated in accordance with the following requirements: ① Leaks in the internal tube bundles of the heat exchangers are generally detected using a hydrostatic test; once a leaking tube bundle is identified, it shall be replaced or sealed off. ②When cracks occur at the welds between the heat exchange tubes and the tube sheet, repair welding or plugging is carried out. ③When there is a leakage at the flange seal of a floating-head heat exchanger, the bolts should be tightened or the gasket replaced. ④When there is a leak in the seal of the threaded lock-ring type heat exchanger tube sheet, the bolts securing the inner ring should be tightened or the gaskets replaced.

Phenomenon: The color of the produced oil darkens, the impurity content increases, the levels of reactive olefins, thiol sulfides, etc. rise abnormally, and quality parameters such as sulfur and nitrogen fail to meet the specifications. The reactor temperature rise decreases. Reason: Corrosion and perforation of the heat exchange tubes, as well as weld failure. The weld between the heat exchange tube and the tube sheet has cracked. Leakage in the seal of the floating head flange of the floating head heat exchanger. Leakage in the sealing of the threaded lock-ring type heat exchanger tube sheet. Handling method: When there is an internal leak in the tube bundle of the high-pressure heat exchanger, the reaction system will be shut down locally. The decommissioned internal-leak heat exchangers shall be treated in accordance with the following requirements: ① Leaks in the internal tube bundles of the heat exchangers are generally detected using a hydrostatic test; once a leaking tube bundle is identified, it shall be replaced or sealed off. ②When cracks occur at the welds between the heat exchange tubes and the tube sheet, repair welding or plugging is carried out. ③When there is a leakage at the flange seal of a floating-head heat exchanger, the bolts should be tightened or the gasket replaced. ④When there is a leak in the seal of the threaded lock-ring type heat exchanger tube sheet, the bolts securing the inner ring should be tightened or the gaskets replaced.

The pressure in the reaction system decreases, while the pressure in the stripping tower increases, as does the pressure of the cold light fractions.

The reaction products have a dark color, contain many impurities, and exhibit high levels of sulfur, nitrogen, and other elements. Removal treatment, replacement of the tube bundle, or sealing the leak under pressure

The temperature difference in the tube and shell side treatments decreases, and there are changes in sulfur content in the low-pressure side

Phenomenon: The color of the produced oil darkens, the impurity content increases, the levels of reactive olefins, thiol sulfides, etc. rise abnormally, and quality parameters such as sulfur and nitrogen fail to meet the specifications. The reactor temperature rise decreases. Handling method: When there is an internal leak in the tube bundle of the high-pressure heat exchanger, the reaction system will be shut down locally. The decommissioned internal-leak heat exchangers shall be treated in accordance with the following requirements: ① Leaks in the internal tube bundles of the heat exchangers are generally detected using a hydrostatic test; once a leaking tube bundle is identified, it shall be replaced or sealed off. ②When cracks occur at the welds between the heat exchange tubes and the tube sheet, repair welding or plugging is carried out. ③When there is a leakage at the flange seal of a floating-head heat exchanger, the bolts should be tightened or the gasket replaced. ④When there is a leak in the seal of the threaded lock-ring type heat exchanger tube sheet, the bolts securing the inner ring should be tightened or the gaskets replaced.