1. Working principle of temperature control valve
The temperature control valve was mostly electromagnetic temperature control valve in the early days. In recent years, through the digestion and absorption of imported compressor technology, wax temperature control valves have also been widely used. This type of temperature control valve consists of two parts: valve and temperature control element. The temperature control element includes special expansion temperature-sensitive paraffin and copper shell. At a specific phase change temperature, the expansion stress of expansion paraffin is a constant value, which is much greater than the thrust required by the thermostatic valve. The expansion paraffin is sealed in the shell. When the temperature rises to the melting point of the paraffin, the volume expands and pushes the push rod. The slide valve driving the temperature control valve moves; when the temperature drops, the paraffin shrinks when it is cold, and the valve is reset under the action of spring rebound.
The characteristics of this temperature control valve: large thrust, the paraffin inside the original can reach more than 200 atmospheres when it expands, the linearity of the stroke temperature curve is good, so the temperature control ability is strong, the component is rigid, the strength is high, and the life is long.
2. Ways to avoid surge in centrifugal air compressors
Surge is a vibration under abnormal working conditions that occurs when the flow rate of a turbine compressor (also called a centrifugal air compressor) is reduced to a certain level. Centrifugal compressors are a type of turbine compressor, and surge has a very serious impact on centrifugal compressors.
When a centrifugal compressor surges, the typical manifestations are:
1): The outlet pressure of the compressor increases first, then drops sharply, and fluctuates periodically and greatly;
2): The flow rate of the compressor drops sharply and fluctuates greatly. In severe cases, air may even flow back into the suction pipe; The current and power meter indications of the motor driving the compressor are unstable and fluctuate greatly;
The machine will vibrate violently and be accompanied by abnormal airflow noise.
The results of mechanistic research show that the internal cause of surge is closely related to the separation of gas in the blade channel.
When the gas flow rate is reduced to a certain extent, the flow direction of the airflow inside the compressor is seriously inconsistent with the installation direction of the blades, so that the inlet airflow angle and the blade inlet installation angle have a large positive angle, and then form a serious separation of the convex airflow of the blades in the blade channel. In addition, for the impeller of the centrifugal compressor, due to the existence and influence of axial vortex, it is easier to form uneven velocity in the blade channel, and the above-mentioned airflow separation phenomenon is further aggravated. When the airflow separation phenomenon is serious, the gas in the blade channel stagnates and the pressure drops suddenly, causing the high-pressure airflow behind the blade channel to flow back to compensate for the lack of flow and relieve the airflow separation phenomenon, and it can temporarily return to normal. However, when the gas that flows back is pressed out, the above phenomenon is repeated again due to the lack of flow in the stage. In this way, the phenomenon of airflow separation and airflow backflow is repeated, causing the compressor to produce a low-frequency and high-amplitude pressure pulsation, the machine also vibrates violently, and emits violent noise, which is the internal cause of surge. From the perspective of the compressor performance curve, when the compressor surges, its operating point must have entered the surge zone, so severe compressor surge is also closely related to the pipeline network. In other words, all external reasons that can cause the joint operating point of the compressor and the pipeline network to enter the surge zone will cause surge.
In the actual operation of the compressor, the following factors will cause surge:
1) Switching failure of the air separation system. The valve entering the main heat exchanger or molecular sieve adsorber cannot be opened in time, resulting in excessive discharge pressure of the air compressor, causing the pipeline network characteristic curve to steepen sharply, and the joint operating point of the compressor and the pipeline network to move rapidly, entering the surge zone and causing surge;
The compressor flow channel is blocked. Due to cooler leakage or dust fouling, the flow path is rough and some sections are reduced; the compressor has large intake resistance, such as filter blockage or impeller inlet blockage;
4) The grid quality is poor, the grid frequency is reduced or the voltage is too low, causing the motor to stall, resulting in the compressor flow rate falling to the surge zone;
5) During the compressor startup operation and pressure boost process, the operation is not direct, the pressure boost speed is fast, and the inlet guide vane opening is small; the vent valve or anti-surge valve is not opened in time during electrical failure or chain shutdown.