In addition to certain requirements on the purity of medical oxygen (the purity of oxygen is 99.5% for the cooling method), it is also required that the moisture content is not more than-43 ℃ (dew point temperature) the volume fraction of carbon dioxide, the content of carbon monoxide, gas acid and alkali, the content of ozone and other gas oxidants should also meet the requirements of GB8982-1998. Therefore, general industrial oxygen does not meet the requirement of medical oxygen, that is, General oxygen presses and oxygen cylinders cannot be used to fill medical oxygen.
The adoption of membrane compressor is the measure to ensure the quality of oxygen, and the adoption of liquid oxygen internal compression process is a safe and pollution-free process to produce medical oxygen. That is to extract liquid oxygen from the main cooling, compress it to 16MPa in the plunger type liquid oxygen pump after cooling, and then recover the cold volume of oxygen in the oxygen heat exchanger and turn it into high-pressure oxygen. Many oxygen plants have made such transformation to the 50 m 3/h and 150 m 3/h oxygen generator. It is mainly reflected in the following aspects:
1) the oxygen heat exchanger works under high pressure and needs to be able to bear high pressure structurally. In addition, due to the large amount of cooling of liquid oxygen, the air cooling in the oxygen heat exchanger is about 1.7 times of oxygen. The heat load of the main heat exchanger decreases, and the reheat of the backflow low temperature gas is insufficient, which makes the temperature difference of the Heat end enlarge and the cold loss increase;
2) when adopting the internal compression process, the power consumed by the liquid oxygen pump becomes the additional cooling loss of the unit, while the high pressure oxygen is the discharging device with pressure, and the refrigerating capacity of this part of throttling effect is not utilized. In order to balance the cold loss, it is required to increase the refrigerating capacity of the expansion machine. At this time, the operating pressure of the air compressor needs to be increased, which generally needs to be higher than 4.0MPa;
If the unit needs to produce medical oxygen and industrial oxygen at the same time, then the corresponding size of liquid oxygen cooler, liquid oxygen heat exchanger and liquid oxygen pump should be determined according to the demand of medical oxygen. At this time, the increase of cold loss is less, and the operating pressure can also be reduced.
