【Q&A Question 269】2017.09.27

1. If the outlet temperature of the cold high-pressure fraction is too high, hydrogen has a higher solubility in the oil, resulting in increased hydrogen loss. Lowering the temperature of the cold high-pressure fraction allows hydrogen to escape from the oil and more light hydrocarbons to condense, which helps improve the purity of the recycled hydrogen； 2. The outlet temperature of the cold high-pressure section is too low, making it difficult to separate oil from water.

Answer: Controlling the outlet temperature of the high-pressure air cooler from dropping too low increases energy consumption； The higher the outlet temperature of the high-pressure air cooler, that is, the higher the inlet temperature of the heating furnace, the lower the thermal load on the heating furnace and the less energy consumption there will be. However, it is not the case that the higher the outlet temperature of the high-pressure air cooling system, the better; excessively high temperatures lead to an increase in linear velocity and an increase in the amount of liquid carried, which is detrimental to the safe operation of the recycle hydrogen compressor. The purpose of controlling the outlet temperature of the high-pressure air cooler at ≤50°C (design value) is to prevent excessive linear velocity of the high-pressure gas from entraining liquid and disrupting the circulation. In plants designed for circulating hydrogen desulfurization, the excessively high exit temperature of the high-pressure air cooler causes hydrocarbons to be present in the circulating hydrogen, which leads to foaming of the amine solution and a reduced desulfurization efficiency. In severe cases, liquid is carried along with the circulating hydrogen, affecting the safe operation of the hydrogen circulation pump.

It helps to improve the purity of recycled hydrogen, facilitates oil-water separation, and reduces damage to equipment

To control liquid entrainment in the recycled hydrogen and reduce energy consumption.

The lower the air-cooled outlet temperature, the smaller the linear velocity of the gas inside the high-pressure section, and the less likely it is for liquid to be carried along； The higher the outlet temperature, the opposite is true. Controlling the air-cooling outlet temperature from being too low increases energy consumption ； The higher the outlet temperature of the high-pressure air cooler, that is, the higher the inlet temperature of the heating furnace, the lower the thermal load on the heating furnace and the less energy consumption there will be. However, it is not the case that the higher the outlet temperature of the high-pressure air cooling system, the better; excessively high temperatures lead to an increase in linear velocity and an increase in the amount of liquid carried, which is detrimental to the safe operation of the recycle hydrogen compressor. The purpose of controlling the outlet temperature of the high-pressure air cooler at ≤50°C (design value) is to prevent excessive linear velocity of the high-pressure gas from entraining liquid and disrupting the circulation. In plants designed for circulating hydrogen desulfurization, the excessively high exit temperature of the high-pressure air cooler causes hydrocarbons to be present in the circulating hydrogen, which leads to foaming of the amine solution and a reduced desulfurization efficiency. In severe cases, liquid is carried along with the circulating hydrogen, affecting the safe operation of the hydrogen circulation pump.

Excessively high temperatures can easily lead to the entrainment of foam-free substances, which are then carried into the circulating hydrogen. If this is not separated in time, it can end up in the circulation equipment and cause equipment failures. It is generally kept at 45°C; too low a temperature results in poor oil-water separation

Prevent ammonium salts from migrating to higher exchange levels before crystallization

The lower the air-cooled outlet temperature, the smaller the linear velocity of the gas inside the high-pressure section, and the less likely it is for liquid to be carried along； The higher the outlet temperature, the opposite is true. Controlling the air-cooling outlet temperature from being too low increases energy consumption ； The higher the outlet temperature of the high-pressure air cooler, that is, the higher the inlet temperature of the heating furnace, the lower the thermal load on the heating furnace and the less energy consumption there will be. However, it is not the case that the higher the outlet temperature of the high-pressure air cooling system, the better; excessively high temperatures lead to an increase in linear velocity and an increase in the amount of liquid carried, which is detrimental to the safe operation of the recycle hydrogen compressor. The purpose of controlling the outlet temperature of the high-pressure air cooler at ≤50°C (design value) is to prevent excessive linear velocity of the high-pressure gas from entraining liquid and disrupting the circulation. In plants designed for circulating hydrogen desulfurization, the excessively high exit temperature of the high-pressure air cooler causes hydrocarbons to be present in the circulating hydrogen, which leads to foaming of the amine solution and a reduced desulfurization efficiency. In severe cases, liquid is carried along with the circulating hydrogen, affecting the safe operation of the hydrogen circulation pump.

1. High air-cooling temperatures can easily cause liquid to be carried in the circulating hydrogen, which has a significant impact on the dry gas seal of the hydrogen circulation pump； 2. The air-cooled outlet temperature is high; circulating hydrogen tends to contain hydrocarbons, resulting in a low recovery rate of hydrogen from the cold fractionator ； 3. The air-cooling outlet temperature is low, resulting in poor oil-water separation in the cold fractionator, and high energy consumption for air cooling.