What Is Displacement Ventilation?

Displacement refers to the ability to send all the air and mixture into all cylinders in a certain cycle of the engine, and also refers to the volume that a piston can discharge from one stroke to another stroke. The gas discharged from the last stage of the compressor in a unit time is converted, and the gas volume value obtained under the pressure and temperature conditions of the first stage inlet state is the compressor's discharge volume. It is calculated in the same way as the volume of a cylinder.

The volume of space through which the piston moves from top dead center to bottom dead center is called

According to the standard, the statistical range of exhaust gas volume includes all kinds of exhaust gas outlets that have a direct or indirect relationship with production processes and devices. The conventional copper smelting process using copper concentrate as raw material includes "raw material preparation, smelting, blowing, refining, and electrolysis." There are also multiple, scattered exhaust emission sources in each production link, such as acid mist in electrolytic liquid purification plants, exhaust gas from precious metal processing plants, exhaust gas from fume crushing systems, and exhaust gas from slag beneficiation. Some of the exhaust gas from these sources is collected and treated and discharged in the form of several low exhaust pipes (such as roof exhaust pipes), and some of them are produced by fugitive sources in some irregular and smaller enterprises. The form is directly outsourced, and because the company does not build its own processing workshop, it is directly processed as an intermediate product. The author follows a simplified method based on the principle of highlighting the key points, facilitating prevention and control and comparison. The monitoring and control link proposed in the technical guideline, the calculation range of the benchmark exhaust gas volume of the unit product determined includes the material preparation link (including drying or batching flue gas), the smelting and blowing link (ring gas), and the refining link (anode furnace smoke) And acid production (acid acid exhaust). ^[1]

As an important performance parameter of the compressor, the displacement can reflect the amount of compressed gas produced by the unit per unit time. There are usually two methods for measuring exhaust gas volume, namely direct measurement and indirect measurement. There are also several direct measurement methods, such as the air tank measurement method, which is a method for directly measuring the amount of compressed air flowing into the air tank during a certain period of time, and based on the measurement results, the air volume of the air compressor is measured. Calculate. Throttle devices are widely used in indirect measurement. At the same time, the gas discharged by the air compressor remains stable and the relevant dynamic parameters before and after flowing through the orifice are measured and calculated to obtain the air compressor exhaust. Gas volume. The commonly used measurement methods include nozzle method, tank filling method, differential pressure flow meter and orifice plate method.

In order to accurately measure the final-stage displacement of a high-speed piston compressor, a piston compressor discharge volume test system was constructed on the basis of a piston compressor performance test experimental device and applying modern testing techniques and acquisition methods. . The test system uses GB-3000A pressure sensor to detect pressure, LM35 temperature sensor to detect temperature, and collects system pressure and temperature sensor data through PCI2000 data acquisition card. With the help of Visual Basic advanced programming language, a complete piston compressor exhaust is constructed. Measurement system software. Finally, the exhaust volume measured by the test system is compared with the exhaust volume measured by the original experimental test method and the theoretical exhaust volume. The results show that the exhaust volume measured by the compressor exhaust volume test system is different from the The exhaust gas value measured by the original experimental method is close, and the exhaust gas measured by the test system is closer to the theoretical exhaust gas value. The research results show that the piston compressor displacement test system has high accuracy, reliable measurement results and fast test speed. ^[2]

Centrifugal compressor is a type of turbo compressor. It mainly includes the suction chamber, impeller, diffuser, bend and recirculator, and volute. The gas enters the high-speed rotating impeller from the suction chamber, and the centrifugal force The mechanical energy of the impeller is converted into the internal energy, internal pressure energy, and kinetic energy of the gas, which increases the temperature and flow rate of the gas. Then the gas enters the diffuser, and the reduced flow velocity of the gas causes the kinetic energy to be converted into internal pressure energy, thereby achieving Purpose of pressure increase. After passing through the bends and return flow, the gas flows into the next stage of the compressor and continues to compress. Finally, the high-pressure gas is discharged through the volute and enters the pipe network connected to the compressor.

There are many reasons for the lack of compressor exhaust, which can be summarized into the following situations:

1) The compressor inlet parameters are changed. Under the condition that the compressor inlet volume flow is stable, the decrease of the intake air pressure or the increase of the intake air temperature will cause the compressor characteristic curve to move downward, resulting in a decrease in the mass flow of the compressor inlet, which in turn affects Compressor outlet exhaust. Common causes include blockage of the inlet filter leading to a decrease in intake pressure, and upstream process changes cause an increase in intake air temperature.

2) The resistance of the pipe network is too high. If the pipes or valves in the compressor exhaust pipe network are blocked, the pipe network resistance will increase, and the pipe network characteristic curve will move to the left, which will cause the compressor exhaust pressure to rise, Gas volume decreases.

3) The speed of the compressor decreases. The speed of the compressor is directly proportional to the displacement. If the speed of the compressor is suddenly reduced due to some reason (such as the slip of the motor belt), the compressor characteristic curve will move downward and the displacement will be inevitable. Will decrease.

4) The internal failure of the compressor. For example, the compressor's intercooler has reduced its heat transfer efficiency due to fouling or reduced cooling water flow. The heat of the compressed high-temperature gas cannot be sufficiently taken away by the cooling water, resulting in The inlet temperature of the next stage rises, which reduces the compressor discharge. In addition, during the operation of the compressor, the seal between the stages often fails due to wear and corrosion. As the leakage at the seal gradually increases, the The temperature of the gas at the inlet of the stage gradually increases, and the exhaust temperatures of the various levels after the leak increase, which results in a reduction in the compressor discharge. In both cases, the compressor characteristic curve will move downward. ^[3]