The unit power consumption of the air separation plant is proportional to the unit power consumption of the air compressor (the power consumption of compressed air per 1m3 kwh/m3) Wk; it is proportional to the extraction rate of oxygen (the proportion of products separated from the oxygen in the air) proportional. Therefore, to reduce the unit power consumption of the air separation plant is to try to reduce the unit power consumption of the air compressor and improve the oxygen extraction rate.
The unit power consumption of the air compressor is proportional to the logarithm of the pressure ratio. Therefore, when operating, the working pressure of the unit should be reduced as much as possible; under the condition of certain air volume and product purity, the extraction rate of oxygen is proportional to the output of oxygen. Therefore, we should also increase the output of oxygen as much as possible.
(1) the operation of reducing high pressure air pressure
For the medium pressure process, when the efficiency of the expansion machine remains unchanged, the air pressure can be reduced by reducing the air inlet temperature of the expansion machine. For medium pressure turbine expander, the air inlet temperature can be reduced to-140℃, so the working pressure can also be reduced to 1.0 ~ 1.2MPa. However, for piston expansion machine, when the air inlet temperature decreases, the efficiency decreases quickly. Therefore, with the temperature decreasing, there exists a minimum pressure, as shown in Figure 142. When the temperature decreases further, the temperature difference at the Heat end increases due to the decrease of efficiency and the negative temperature difference of the second heat exchanger. On the contrary, the cooling balance can be maintained by increasing the working pressure.
In addition, the medium pressure flow has another characteristic, which can keep the cooling balance by adjusting the joint-1 valve and the expansion machine Cam. That is, different operating pressures can be corresponded under balanced working conditions. For example, it can be operated under 2.5MPa or 1.8 MPa, but their energy consumption is different. When operating, we should seek the lowest pressure with stable working condition, which needs to be explored in practice. Starting from the relatively high intake temperature T1 (-90℃), gradually close the section-1 valve to lower T1 and the pressure at the same time. Keep looking for a new balance point with the lowest pressure.
(2) the operation of increasing the output of oxygen
To maximize the output of oxygen, it can be realized by adjusting the liquid nitrogen throttle valve (section-4 valve) to make the upper tower in the state of optimal reflux ratio. As shown in Figure 143. Section-4 valve at a certain opening degree, the oxygen output can reach the maximum. Therefore, when adjusting, firstly open the section-4 valve to a larger position 1, and test the purity of oxygen. If the purity of oxygen decreases, the method of turning off oxygen and removing nitrogen can be adopted to improve the purity of oxygen and keep the pressure on the tower unchanged at the same time. Through gradual exploration, we can find the best opening degree of section-4 valve whose oxygen output is the largest.
