The expansion of temperature difference at the hot end will also increase the cold loss at the hot end. Therefore, in this case, it is necessary to appropriately reduce the amount of processing air (the amount of oxygen and nitrogen products is also reduced accordingly). In this way, if the gas volume of the two groups of the switching heat exchanger is properly distributed, the influence on the temperature condition will be small, and the normal operation can be maintained.When the temperature of the air entering the unit increases, not only the heat load of the accumulator (or switching heat exchanger) increases, but also the amount of water brought in increases, which increases the burden of self cleaning. With the increase of water freezing, the heat transfer efficiency is reduced. When the heat transfer area of the heat exchanger is fixed, the increase of the heat load and the poor heat transfer effect will inevitably lead to the increase of the temperature difference between the cold end and the hot end.
DEAR Liquid air separation unit.After expansion, due to the decrease of pressure and volume expansion, the moisture content in every 1m3 of air decreases; however, due to the decrease of temperature, the moisture saturation content corresponding to the temperature at the back of the machine also decreases. If the actual content is greater than the saturation content, water will be analyzed.Coil type is generally used for auxiliary condensing evaporator. Liquid oxygen boils in the tube and gas nitrogen condenses between the tubes. There is no fixed liquid level in the coil. Because of the small heat transfer coefficient, it has been gradually eliminated. The main condensing evaporator (liquid oxygen self circulation) of Hitachi 6000m3 / h oxygen generator in Japan also adopts coil type.DEAR Liquid air separation unit.When the heat transfer surface of the condensing evaporator is insufficient or the heat transfer is deteriorated, the temperature difference will expand, reflecting the increase of the lower tower pressure. The temperature of liquid oxygen and gas nitrogen can be adjusted according to their pressure and purity. In practical operation, the pressure of upper and lower tower, the purity of gas nitrogen and liquid oxygen and the height of liquid oxygen surface are controlled, rather than the temperature difference of condensing evaporator.
Membrane air separation method: it uses the permeation selectivity of some organic polymer membranes. When air passes through the membrane (0.1 μ m) or hollow fiber membrane, the speed of oxygen passing through the membrane is about 4-5 times that of nitrogen, so as to realize the separation of oxygen and nitrogen. The oxygen enrichment concentration of this method is generally suitable for 28% - 35%, and the scale is only suitable for medium and small scale.For medium pressure air separation unit, it is composed of expansion air and air which is throttled and depressurized by throttle-1 valve after leaving heat exchanger. Under normal conditions, their comprehensive state into the tower has a certain "moisture content" (liquefaction rate). The air condition into the tower is guaranteed by the heat exchange system and the cooling system in the air separation unit.Refrigeration is to remove the heat from the device which is lower than the ambient temperature, so as to balance the heat from the outside, keep the device at low temperature, or keep the internal temperature decreasing until the low temperature liquid is accumulated. Heat can only be transferred from high-temperature objects to low-temperature objects. To remove heat from low-temperature objects, we must first use artificial methods to create a lower temperature state, so that it has the ability to absorb and take away heat. Theoretically speaking, the cooling capacity is the capacity to take away heat.
Generally, rivers, lakes or groundwater are used as cooling water for air separation units. This kind of water usually contains suspended solids (sediment and other pollutants) and bicarbonates such as calcium and magnesium [- Ca (HCO3) 2 and Mg (HCO3) 2], which is called hard water. When there are many suspended solids, it is easy to block the channels, filters and valves of the cooler. Calcium, magnesium and other bicarbonates are easy to form calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) precipitates when the water temperature rises, that is to say scale. Generally, water temperature above 45 ℃ will start to form scale, and the higher the water temperature is, the easier it is to scale.DEAR Liquid air separation unit.If the liquefier appears liquid too early, it means that the liquefier is connected too early. If there is liquid in the liquefier before the temperature condition of the switching heat exchanger is established, the amount of backflow gas in the switching heat exchanger will be reduced due to the generation of liquid, so that the self cleaning can not be guaranteed.
