【Q&A Question 131】2018.05.11

Answer: 1) The chlorine content in the fresh hydrogen is high; if the ammonia content in the recycled hydrogen is also high, ammonium salts will form under low-temperature conditions, leading to blockages in the pipelines where the fresh hydrogen and recycled hydrogen mix together, and an increase in pressure drop. 2) The resulting ammonium salts cause corrosion to pipeline equipment. 3) The chlorine present in the new hydrogen will move along with the circulating hydrogen, increasing the chlorine content throughout the reaction system. This leads to salt deposition and blockages in the heat exchangers of the reaction system, reducing their efficiency and increasing the energy consumption of the facility. 4) Chlorine combined with water forms hydrochloric acid, which causes corrosion to pipeline equipment.

Excessive chlorine content in new hydrogen can easily cause blockages and cracks in the pipelines； A high chlorine content leads to the formation of ammonium chloride; ammonium chloride tends to crystallize, blocking pipelines, increasing system pressure drops, and shortening the startup time.

1) The chlorine content in the fresh hydrogen is high; if the ammonia content in the recycled hydrogen is also high, ammonium salts will form under low-temperature conditions, leading to blockages in the pipelines where the fresh hydrogen and recycled hydrogen mix together, and an increase in pressure drop. 2) The resulting ammonium salts cause corrosion to pipeline equipment. 3) The chlorine present in the new hydrogen will move along with the circulating hydrogen, increasing the chlorine content throughout the reaction system. This leads to salt deposition and blockages in the heat exchangers of the reaction system, reducing their efficiency and increasing the energy consumption of the facility. 4) Chlorine combined with water forms hydrochloric acid, which causes corrosion to pipeline equipment.

The HCl generated by the hydrogenation of Cl in the raw materials can cause problems in the operation of the process; under high temperatures, it reacts with Fe and Ni present in the materials of containers or pipelines, leading to corrosion. In the presence of “CI-”, austenitic stainless steels of types 18–8 are particularly sensitive to pitting corrosion. Pitting corrosion is very dangerous in production; it develops rapidly over a certain area and penetrates deeper, resulting in equipment damage due to localized destruction or leakage as a result of perforations in specific areas. At the same time, HCL reacts with NH3 in the system to form NH4Cl, which deposits at temperatures below 350°C and thus blocks the system (significant precipitation generally begins at 180–200°C). Some refineries in the United States use only reformer hydrogen, and white NH4Cl crystals often accumulate at the compressor outlet valves. This is because trace amounts of chlorine are present in the reformer hydrogen; therefore, hydrocracking requires limits to be placed on the amount of chlorine in both the feed oil and the hydrogen.

Excessive chlorine content in new hydrogen can easily cause blockages and cracks in the pipelines； A high chlorine content leads to the formation of ammonium chloride; ammonium chloride tends to crystallize, blocking pipelines, increasing system pressure drops, and shortening the startup time.

1) The chlorine content in the fresh hydrogen is high; if the ammonia content in the recycled hydrogen is also high, ammonium salts will form under low-temperature conditions, leading to blockages in the pipelines where the fresh hydrogen and recycled hydrogen mix together, and an increase in pressure drop. 2) The resulting ammonium salts cause corrosion to pipeline equipment. 3) The chlorine present in the new hydrogen will move along with the circulating hydrogen, increasing the chlorine content throughout the reaction system. This leads to salt deposition and blockages in the heat exchangers of the reaction system, reducing their efficiency and increasing the energy consumption of the facility. 4) Chlorine combined with water forms hydrochloric acid, which causes corrosion to pipeline equipment.

Excessive chlorine content in new hydrogen can easily cause blockages and cracks in the pipelines； A high chlorine content leads to the formation of ammonium chloride; ammonium chloride tends to crystallize, blocking pipelines, increasing system pressure drops, and shortening the startup time.

An increase in chlorine content, exceeding the limit, will exacerbate the degree of corrosion

1. Hazards of ammonium chloride salt clogging: Chlorine present in the raw materials reacts with hydrogen to form hydrogen chloride; hydrogen chloride generated from chlorine in the reforming hydrogen also reacts with ammonia to produce ammonium chloride. This compound crystallizes into a solid within the heat exchangers as part of the reaction effluents, thereby blocking the heat exchange equipment and pipelines. The main hazards include: (1) Scaling on the surface of the heat exchange tubes, which reduces the efficiency of heat exchange, increases the load on the heating furnaces in the reaction system, and raises the energy consumption of the facility. (2) It causes an increase in the pressure drop in the high-pressure heat exchanger and reaction system, resulting in reduced operating capacity of the plant. (3) It reduces the amount of circulating hydrogen, and in severe cases, it may cause surging in the circulating hydrogen compressor. (4) After ammonium chloride salts crystallize and deposit in equipment and pipelines, they also absorb the trace amounts of water generated by reactions; the hydrolysis of these ammonium salts leads to corrosion beneath the scale. Corrosion hazards of 2-chloro (1) Due to the presence of NH, H2S, and small amounts of HCl and H2O in the hydrogenation reaction effluents, water droplets form on the surfaces of equipment or pipes when the temperature drops to the dew point of water. These droplets absorb HCl or H2S from the effluents, resulting in high-concentration acids that rapidly corrode the surface of the equipment, causing pits of various sizes; in severe cases, penetration of the surface may occur. (2) After hydrogenation and water injection, the ammonium chloride aqueous solution, driven by a high flow rate, impacts the surface of the equipment, resulting in erosive corrosion of the metal surface and causing extensive corrosion to the equipment, especially at areas where the flow direction changes, such as pipe elbows and the inlet and outlet pipes of high-pressure air coolers. (3) It can easily cause \"chloride embrittlement\" in the stress concentration areas of stainless steel. In areas enriched in CL and subjected to external or residual stress, CL penetrates the passivation film on the surface of stainless steel and enters the pores within the material, causing cracks in the stainless steel. This leads to corrosion spreading deeper into the metal, exacerbating the damage and resulting in the phenomenon of \"chloride embrittlement\". The damage of hydrogen chloride to catalysts: Hydrogen chloride affects the balance between the hydrogenation and acidic functions of hydrogenation catalysts, thereby impacting their selectivity