Air separation oxygen production area: [Weekly Topic] Week 21 of 2011 – What are the factors that affect the temperature difference in the main cooler?

The last edit to this post was made by gader on 2011-5-23 at 20:30. The temperature, flow rate, pressure, and load of the refrigerant medium are controlled appropriately based on the load (and the desired temperature)

This post was last edited by gader on 2011-5-23 20:30. A condensing evaporator generally refers to the average heat transfer temperature difference between gaseous nitrogen and liquid oxygen. It is based on the different boiling points (i.e., saturation temperatures) of oxygen and nitrogen at various pressures and purities. Therefore, the temperature difference of the condensation evaporator is influenced by the purity of oxygen and nitrogen, as well as changes in the pressures in the upper and lower columns.

The main cooling temperature difference is related to the pressures in the upper and lower columns, as well as the purity of gaseous nitrogen and liquid oxygen.

The magnitude of the heat transfer temperature difference in the main cooler is affected by oxygen and nitrogen purity as well as changes in the pressures in the upper and lower columns. The effects of pressure and concentration on the temperature difference are as follows: 1. As the liquid oxygen concentration increases, the evaporation temperature rises, resulting in a decrease in the heat transfer temperature difference. 2. As the liquid oxygen pressure increases, the evaporation temperature also rises, resulting in a reduced heat transfer temperature difference. 3. As the nitrogen concentration increases, the condensation temperature decreases, and the heat transfer temperature difference shrinks. 4. As the nitrogen pressure increases, the condensation temperature rises, and the heat transfer temperature difference increases. 5. The higher the liquid oxygen level, the greater the pressure at the bottom, and the boiling point of liquid oxygen also increases; as a result, the average temperature of the liquid oxygen rises and the temperature difference for heat transfer decreases. When the evaporation pressure and purity of liquid oxygen, as well as the condensation pressure and purity of gaseous nitrogen, remain constant, the heat transfer temperature difference stays unchanged. When the pressures in the upper and lower towers are constant, increasing the purity of liquid oxygen reduces the temperature difference in the main cooler; similarly, increasing the purity of gaseous nitrogen also reduces this temperature difference. If the purity and pressure of gaseous nitrogen remain constant, and the purity of liquid oxygen is fixed, increasing the pressure in the upper column can reduce the temperature difference in the condensation evaporator. During the liquid accumulation phase of driving, the heat load on the condensation evaporator is usually reduced by appropriately increasing the pressure in the upper tower and narrowing the temperature difference in the condensation evaporator, in order to accelerate the accumulation of liquid. The average temperature difference for long-tube and plate-fin condensation evaporators is typically 1.6–1.8°C. During normal operation, the temperature difference of the condensation evaporator remains essentially constant. When the heat transfer surface of the condensing evaporator is insufficient or heat transfer deteriorates, the temperature difference increases, reflecting an increase in the pressure in the lower column. Condensation evaporators generally do not have thermometers; the temperature of liquid oxygen (taking the average value) and the temperature of gaseous nitrogen can be determined from thermodynamic property charts, based on their pressure and purity. In practical operation, what is controlled are the pressures in the upper and lower towers, as well as the purity of gaseous nitrogen and liquid oxygen and the level of the liquid oxygen surface, rather than directly measuring the temperature difference of the condensation evaporator.

The temperature difference of the main condensation evaporator is influenced by the purity of oxygen and nitrogen, as well as the pressures in the upper and lower columns. Regarding the evaporation process of liquid oxygen: at constant oxygen purity, increasing the pressure raises the evaporation temperature and reduces the temperature difference in the main cooler; at constant pressure, an increase in purity takes place. Its evaporation temperature increases, and the temperature difference across the main cooler decreases. Condensation process of nitrogen: With constant nitrogen purity, increasing the pressure in the lower column raises its condensation temperature, thereby increasing the temperature difference in the main cooler. With constant pressure, increasing the nitrogen purity lowers its condensation temperature, thereby reducing the temperature difference in the main cooler. It can be seen that, when the pressures in the upper and lower towers remain constant, increasing the purity of liquid oxygen can reduce the temperature difference in the main cooler. Increasing the purity of gaseous nitrogen can reduce the temperature difference in the main cooler. If the pressure and purity of gaseous nitrogen remain constant, and the purity of liquid oxygen is fixed, increasing the pressure in the upper column can reduce the temperature difference in the main cooler.

The magnitude of the heat transfer temperature difference in the main cooler is affected by oxygen and nitrogen purity as well as changes in the pressures in the upper and lower columns. 0 N( D+ I l3 _) ?& g% q9 bThe effects of pressure and concentration on the temperature difference are as follows: 1 `/ d9 }% A: @+ h" r3 I0 H1 – As the liquid oxygen concentration increases, the evaporation temperature rises, resulting in a decrease in the heat transfer temperature difference. 4 n# Z+ X( e- ?2: As the liquid oxygen pressure increases, the evaporation temperature also rises, and the temperature difference for heat transfer decreases. ; [3 Y e% s% h; j" _6 M0 n2 v8 i 3: As the nitrogen concentration increases, the condensation temperature drops, and the heat transfer temperature difference decreases. - C3 t- Z4 E' a, x4 c 4: As the nitrogen pressure increases, the condensation temperature rises, and the temperature difference for heat transfer increases as well. |, n$ b’ A! E/ ^9 l3 B5: The higher the liquid oxygen level, the greater the pressure at the bottom; simultaneously, the boiling point of liquid oxygen increases, which raises its average temperature and reduces the temperature difference for heat transfer. + A# ^& Q: G* o; u3 H; t, when the evaporation pressure and purity of liquid oxygen, as well as the condensation pressure and purity of gaseous nitrogen, remain constant, the heat transfer temperature difference stays unchanged. " D) P# w' s/ `* B g- f" [ When the pressures in the upper and lower towers are constant, increasing the purity of liquid oxygen reduces the temperature difference in the main cooler; similarly, increasing the purity of gaseous nitrogen also reduces this temperature difference. If the purity and pressure of gaseous nitrogen remain constant, and the purity of liquid oxygen is fixed, increasing the pressure in the upper column can reduce the temperature difference in the condensation evaporator. During the liquid accumulation phase of driving, the heat load on the condensation evaporator is usually reduced by appropriately increasing the pressure in the upper tower and narrowing the temperature difference in the condensation evaporator, in order to accelerate the accumulation of liquid. ( W, x( v6 n& j4 u C" N9 R The average temperature difference for long-tube and plate-fin condenser-evaporators is usually taken as 1.6–1.8°C. During normal operation, the temperature difference of the condensation evaporator remains essentially constant. When the heat transfer surface of the condensing evaporator is insufficient or heat transfer deteriorates, the temperature difference increases, reflecting an increase in the pressure in the lower column. Condensation evaporators generally do not have thermometers; the temperature of liquid oxygen (taking the average value) and the temperature of gaseous nitrogen can be determined from thermodynamic property charts, based on their pressure and purity. In practical operation, what is controlled are the pressures in the upper and lower towers, as well as the purity of gaseous nitrogen and liquid oxygen and the level of the liquid oxygen surface, rather than directly measuring the temperature difference of the condensation evaporator.

It’s mainly related to the pressure in the upper and lower towers

Good summary! ! Learned* and gained benefits

What we control is not the temperature difference, but rather the pressures in the upper and lower towers, the purity of oxygen and nitrogen, the level of the main cooling liquid, and the opening degree of the liquid nitrogen throttle valve.

That’s great – it not only identifies the influencing factors but also explains the phenomena and consequences, as well as the measures taken to address them； It is valuable in that it reveals the true essence of air separation operations: one change can have an impact on the entire system, and adjustments to any aspect cannot be made in a unilateral or arbitrary manner. Thank you for the advice! ! !