With the development of economy and industry, more and more enterprises begin to pay attention to the quality of compressed air, especially the oil content in compressed air. In electronics, chip, high-precision manufacturing, food, medicine and other industries, the demand for oil-free compressed air quality is also higher and higher. Therefore, the demand for oil-free compressed air becomes more and more urgent.
In order to obtain oil-free compressed air, we must understand the types and sources of oil in compressed air. ISO 8573 defines oil as a mixture of hydrocarbons consisting of 6 or more carbon atoms. Hydrocarbons are mainly various hydrocarbons, such as saturated hydrocarbons, unsaturated hydrocarbons, aromatic hydrocarbons and so on.
In the process of producing compressed air, it is inevitable to mix all kinds of lubricating oil left by air compressor, pipeline and valve. High boiling point and high molecular weight hydrocarbons are the main components of lubricating oil, so the oil in compressed air is a mixture of these hydrocarbons, and there is no unified chemical formula.
Theoretically, the oil-free air compressor will not bring in additional oil when producing compressed air, but this does not mean that there is no oil in the compressed air. There is oil in our atmospheric environment. The more industrial areas and seriously polluted places, the higher the oil content in the environment. In some iron and steel and petrochemical enterprises, the oil content at the inlet of the air compressor can even reach 5 mg / m3. In these areas, even if the oil-free air compressor is used, the oil content of the compressed air can not reach the level 1 oil content standard specified in iso8573-1. Therefore, the use of oil-free air compressor can minimize the oil content in the compressed air, but it can not guarantee that the compressed air is oil-free. In addition, the compressed air will pass through a large number of pipes, valves and joints from the air compressor outlet to the terminal air consumption point. As long as one point of these pipes, valves and joints is not cleaned, the compressed air of the whole pipeline will be polluted. Even if the oil content of the compressed air at the outlet of the air compressor is qualified, the oil content of the compressed air will increase after reaching the gas consumption point of the terminal, resulting in the failure of normal use of the compressed air. Therefore, in order to ensure the demand of terminal gas consumption point, necessary measures need to be taken to reduce the oil content in compressed air.
Compressed air degreasing method
In compressed air, oil exists in three forms: liquid, gaseous and aerosol. For different forms of oil, different methods need to be used to remove it.
Filter degreasing:
Liquid oil and most oil aerosols can be removed by means of coalescing filter and filtration principle. The filtering principle is as follows:
The first stage: direct interception. Light oil droplet particles with a size larger than the filter material gap are directly intercepted on the surface layer of the filter material.
The second stage: impact separation, which mainly depends on the inertia of oil droplet particles. After solid particles and droplets pass through the filter material gap, they impact the filter material fiber and attach to it.
The third stage: Brownian motion, small droplets adhere to the filter fiber along the flow direction, and continue to accumulate into large droplets. At the same time, the irregular Brownian motion of fine oil droplets also makes them adhere to the filter fiber.
The fourth stage: discharge. In the outermost liquid collecting layer, the droplets will gradually condense and become larger, and then flow to the bottom of the filter and discharge under the action of gravity.
Through the step-by-step filtration in the above three stages, the coalescing filter can reduce the residual oil content to 0.01mg/m3. However, any condensing filter cannot completely filter out the impurities contained in the compressed air. At this time, measuring the filtering effect of compressed air filter is "filtering efficiency". The percentage of the number of impurity particles separated and filtered by the filter in the total number of impurity particles is called "filtration efficiency". For example, the compressed air at the inlet of the filter contains 100000 pieces with a size of 1 μ After passing through the filter, there is only one particle with size 1 left at the outlet μ M, the filtration efficiency of the filter is 99.999%. Since the filtration efficiency of the above three filtration stages is different, the filtration efficiency of the filter is the sum of the filtration efficiency of the above three filtration stages.
It can be seen that the filtration efficiency in different stages is closely related to the size of impurity particles. After filtration, the filter material is filled with various impurities. The purpose of removing most liquid oil and oil aerosol can be achieved through the filtration of coalescing filter, but the coalescing filter cannot filter oil vapor. Therefore, through the coalescing filter, the maximum oil content standard of national standard GB / T 13277.1-2016 and ISO 8573-1 can be reached.
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