Modern Flour Milling Equipment ModernFlour Talk about the selection and precautions of the compressed air station equipment in the flour mill Yang Lei Liu Chaofeng Li Dongsen Zhengzhou Huasen Grain Engineering Co., Ltd. Zhengzhou 450006 compressed air station process and the selection and control principle of the main equipment in the compressed air system And calculation, has a certain guiding significance for the design of the compressed air station of the flour industry.

Flour mill compressed air supply is generally set up air compressor (often need to prepare one for production needs) independent gas supply, easy to operate and manage. The newly built large-scale flour mills are mainly industrial park construction (including raw grain storage, flour workshop, rice, oil, noodles and other food processing workshops), such as Zhengzhou, Xi'an, and southern flour, which are under construction by COFCO and Yihai Group. Groups, etc., and in the newly designed process, often add a large amount of equipment such as color sorting machine, multi-station baler, and air compressor station for centralized management, which saves investment and is easy to manage, as shown.

A 600t/d flour production workshop compressed air station design plan. Although there are standards and regulations for the design of compressed air systems in China (such as GB50029-2003 "Compressed Air Station Design Specifications"), in general, its content is slightly more general and Broadly, some details of the design of the compressed air system are not detailed enough (compressed air consumption, compressed air quality requirements, etc.), and these details often affect the rationality of the design of the compressed air system, so the author combined with practical experience, The design of the compressed air system of the flour mill is elaborated.

1 Flour industry air compressor room design status Flour industry design generally does not pay attention to the design of air compressor room, generally only set up a room to place air compressor. Common problems in the air compressor room of the flour industry: 1 The collection point of the air source is wrong. The suction point of the compressor is placed in the unenclosed "machine room", and the air compressor collects free air mixed with various impurities without pre-filtration, which undoubtedly burdens the inlet filter of the air compressor. , causing chronic overload.

The temperature in the equipment room is too high. Because the air compressor and auxiliary equipment are installed in the equipment room, the heat is large and can not be transmitted, which makes the temperature in the equipment room too high, which is easy to cause chronic overload of the air source system. 3 indoor air flow is poor. Although the ventilation fan is installed in the equipment room, the effect is not great. In order to collect relatively clean free air, it is necessary to seal the machine room, but after sealing, it increases the difficulty of collecting free air by the air compressor, and the danger of large vacuum in the whole machine room still exists. 4 Excreta is not handled properly. Air compressors, aftercoolers, oil-water separators, filters, dryers, and air tanks all have drain points. If these excretions are not discharged to the outside in time, the relative humidity in the equipment room can only be significantly increased, which will prompt the compressor Yang Lei to talk about the sound selection of the compressed air station of the flour mill and the precautions. Large, loading compression and purification equipment also leads to chronic overload. There is no pre-filtering device at the air compressor station.

The above shortcomings may not be found abnormally in a short time. Over time, there will always be a sudden outbreak, causing the pneumatic system to become paralyzed, causing serious economic losses to the enterprise.

2 Flour industry air compressor station process design and features to take pre-filtration, machine room conditions, compression, various purification, storage, voltage regulation, safety protection process (see. Overall pursuit of "machine, gas, electricity Optimization, the best match of parameters.

1 Pre-filtering The free air collection point is changed from the inside of the machine room to the outside of the machine room. At the same time, two filtering devices are added. The outside of the machine room is “rough filtering”, and the machine room is “fine filtering”. The coarse filter is added to the “breathing head” outside the machine room. The filtration accuracy is determined by the actual free air quality in the local area.

Room conditions. The machine room is best placed on the first floor of the production workshop, tightly closed, and a noise reduction device is installed. In order to maintain the proper indoor temperature and the optimal flow of air, a ventilation fan should be provided, and air conditioning can be installed under certain conditions. The installation method is “breathing head” down (the ventilating head is louvered, installed in clean free air, away from dusty air, and introduced into the machine room through the pipeline. It is best to flow the lower layer of the air compressor to cool the air compressor body. Air conditioning is in the middle, the ventilation fan is on, three-dimensional installation, in order to maximize the heat. The installation of the ventilating fan is essential, both to "exhaust" to remove heat and to prevent unfiltered free air from entering the room. A "drawer" device can be added around the inner side of the ventilating fan. When the ventilating fan is working, the "drawer" is opened, and vice versa.

In order not to increase the relative humidity in the room, the excrement of all equipment should be cleaned in time to avoid increasing the relative humidity in the room.

The characteristics of the use of compressed air in the flour industry and supporting factories1, the raw material workshop, the cleaning workshop, the milling workshop, the powder mixing workshop, the noodle workshop, the food workshop, the finished product warehouse, the by-product warehouse and the laboratory, etc. Compressed air is used.

The change in load is large. The gas equipment used in each workshop is more intermittent, but less used continuously. This will result in a large difference between the maximum load and the average load, sometimes reaching 50% to 70%. 3 The quality requirements for compressed air are generally high. In the design, most of the freeze dryer, high-efficiency water separator and coarse and fine secondary filter can meet the requirements of process equipment. For example, compressed air containing cassia must use a filter other than Gui. Today, most flour mills have high requirements for air compressor quality, service life and after-sales service due to dust.

3 Flour air compressor station equipment selection calculation According to the pressure and flow two parameter values ​​to select the air compressor. There are two types that are widely used at present: the screw type and the piston type. Screw air compressors are generally used, and the products of international famous brands such as Atlas Copco, Ingersoll Rand, Sullair, and CommScope are used in the design. The advantages of the screw air compressor: 1 in the pressure range of 6 ~ 10bar, with a variety of volume flow changes, can meet the different requirements of the process.

Beautiful appearance, full cover box design. Due to the full-cover closed structure, the motor and compressor are directly driven by the coupling box, and the noise is low, generally 72±5dB(A). After simple noise elimination treatment, it fully meets the requirements of environmental protection and labor safety.

3 unit control integration, easy to operate. The host computer adopts microcomputer control, which can complete all operations on the spot, which is convenient and quick, and greatly reduces the workload of the management personnel.

The layout of the 4 station rooms is more convenient and more beautiful. Components such as compressors, separators, and aftercoolers are on the same chassis. Because the elastic damper is installed between the unit and the chassis, it can not only absorb shock but also reduce noise. In principle, such compressors do not require special concrete or special foundations, and the unit can be placed directly on a level ground as long as the ground-tolerant load is not exceeded. However, in the design, it is necessary to consider the overall vibration of the building due to the construction quality, or the local collapse and crack of the floor, and the flushing of the station in the future. Therefore, a special design for each unit is slightly larger and higher than the chassis. 100mm concrete foundation for indoor floor. In this way, not only the construction is convenient, but also the entire station is neatly arranged.

The working pressure required for the conventional calculation of the pneumatic system of the flour industry line is generally 6~8bar, and the gas supply is 3m3/min, which depends on the actual situation.

1 Pressure estimation of the gas source system. The air compressor should be used to press the powder equipment. The modern flour workers should have a higher P gas source than the working pressure PI. Usually, the host loss is 15%, the pressure loss along the path is 8%, and the pressure loss of the holding equipment is 7%, so the formula can be simplified as: Ph=1.30P work.

2 Compressed air design air supply and compressed air station unit capacity selection: a. Generally convert the flow of compressed air at different pressures to flow at atmospheric pressure to calculate. Compressed air design air supply quantity refers to the same compressed air system, based on the comprehensive air consumption, and then according to the specific situation, the gas supply data obtained after the calculation system is obtained, the accuracy of the user load data and the calculation coefficient are reasonable. Select.

b. The volumetric flow rate of the selected air compressor equipment is too large, which is easy to cause long downtime or idle time; if the flow rate is too small, the terminal pressure used by the equipment is too small, and the efficiency is reduced. Generally, the exhaust pressure of the air compressor is greater than 10%~20% of the air source pressure required for the normal operation of the pneumatic equipment or system. c. The size of the gas storage tank is small, which is easy to cause the equipment to wear up quickly; the pipeline and dryer are used, and the filter is selected. The size of the input and output of the device is too small, which is likely to cause an increase in the pressure loss of the pipeline; the air compressor room is insufficiently ventilated, which easily causes the volume flow of the air compressor to decrease.

Among them: Qmax actually needs the maximum air consumption, m3 / min; compressed air discharged by the air compressor, although it can meet the pressure and flow requirements of the pneumatic system, but can not be directly used by pneumatic devices. Because the compressed air output from the compressor contains three different forms of impurities: solids/soil: dust, pipe rust, compressor wear particles; liquid/floating: oil, water; gas/steam: water, oil Hydrogen compounds, carbon oxides, chemical pollutants. Therefore, the compressed air used in the pneumatic system must be a clean gas purified by several kinds of equipment.

The aftercooler is a heat exchanger that cools the compressor's exhaust gas and is often installed on the piping at the compressor outlet. After the compressed gas of the aftercooler, the temperature can be reduced to 20~30 ft. (in practice, it can be reduced to about 30). In this way, the oil mist and the water gas in the compressed air are mostly separated, and the oil droplets and the water droplets are condensed to be separated, thereby achieving the purpose of preliminary purification. The type of aftercooler currently used is roughly the same type: it is air-cooled; it is water-cooled. The ill is more economical to operate than the latter. The newly designed cooler allows more than 90% of the water vapor to condense into liquid to be discharged from the system, so it is used more. The cooling area F can be obtained by looking up the table of the displacement of the compressor.

The oil-water separation element of the oil-water separator is the key component that determines the quality of the compressed air of the air compressor. The high-quality oil-water separation element not only ensures the high efficiency of the compressor, but also has a filter life of several thousand hours. The compressed air coming out of the compressor head is supplied with oil droplets of various sizes. Large oil droplets are easily separated by the oil-water separation tank, while small oil droplets (suspended oil particles below 1×xm in diameter) must be filtered through the glass filter layer of the oil-water separation filter. The diffusion of oil particles through the filter material is directly intercepted by the filter material and the mechanism of inertial collision and condensation, so that the suspended oil particles in the compressed air are quickly condensed into large oil droplets, which are concentrated under the action of gravity at the bottom of the oil-water separation filter element, passing through the bottom. The recessed return line inlet returns to the head lube system, thereby allowing the compressor to discharge more pure, oil-free compressed air. In the selection should pay attention to: 1 the oil content of the oil-water separator is not only related to the quality of the oil-water separation core. Moreover, it is related to the design of the oil drum and also related to the air flow rate of the air compressor.

Under normal circumstances, the oil-water separation filter of the air compressor must be selected to be greater than or equal to the outlet flow of the air compressor, and the most suitable one is to select more than 105% of the compressed air flow.

For smooth and normal operation of pneumatic tools, pulseless, non-fluctuating pressure gas should be used as the power source. The function of the gas storage tank is to overcome the gas pulse and pressure fluctuation caused by the operation of the reciprocating piston compressor, as well as to separate the condensed water and store the compressed air. For the screw compressor, according to its working principle, the compressed pressure gas is basically a continuous gas without pulse, so the gas storage tank is first stored gas, and secondly, the separated condensed water. When there is a large amount of gas in a short time, the auxiliary gas volume can be supplemented by the gas storage tank, so that the pressure drop in the entire pipe network does not fluctuate greatly, so that the compressor starting frequency or the load regulating frequency is within an allowable and reasonable range. At the time of design, the volume of the gas storage tank is comprehensively considered according to the process conditions and load changes. The parameters are shown in Table 1. The principle of gas tank selection is Q/5. The Q here refers to the displacement of the supporting air compressor. For example: 10m3 air compressor volume V should be equipped with Yang Lei, etc. Talking about the setting of the compressed air station of the flour mill and the precautions of the milling equipment. Table 1 Basic parameters of the gas storage tank Volume m3 Inner diameter mm Compressed displacement m3/min 10/5=2m3 gas storage tank, 6m3 air compressor should be equipped with 6/5=1.2 or 1.5m3 gas storage tank.

If the demand is constant, the volume of the gas tank does not have to be greater than the output per minute of the compressor calculated according to the working pressure. If it is intermittently operated, the volume of the gas tank should be enlarged by about 3 times.

The preliminary purification of compressed air through the cooler, oil-water separator and gas tank can meet the requirements of general pneumatic systems. The pneumatic components used in the grade powder production line are mostly oil-free, so the requirements for compressed air are high, and they must be further purified - dry. At present, there are mainly adsorption methods and freezing methods. The refrigerated dryer is the most economical and can cool the hot saturated gas of the air compressor to 30~60 ft. at which temperature the condensate can be mechanically separated. When selecting a dryer, we need to know the state parameters of the required dry compressed air: 2 minimum working pressure and maximum working pressure: the smaller the working pressure, the larger the water content in the compressed air, and the maximum working pressure is from the safe use of cold The angle of the dryer; 3 the highest inlet temperature, the higher the temperature, the greater the water content, the greater the heat load; the air filter is used as the final filter, generally installed in the dryer, the oil content in the output air is less than the limit The pneumatic system of 0.1mg/m3. grade powder production line requires that the value be 5~8mg/m3. The filter is divided into three stages: the first stage can remove 5; the second stage turns the misty oil and water into the outer wall of the filter element and removes the submicron particles; the third stage uses the activated carbon filter element as the absorbent to remove Warm hydrogen compound.

The pressure output of the air compressor is generally higher than the pressure required by the pneumatic system, while the pneumatic device requires a stable pressure input. Therefore, at the end of the gas source system, a pressure regulating valve is required, which is a decompression, and the second is a voltage regulation. Generally, the combination of the valve and the two-piece combination i-force and the pressure-reducing valve is adopted, which saves space and is easy to operate. The pressure reducing valve and pressure gauge can be selected according to the flow, pressure and path checklist.

According to the pneumatic system and the pneumatic control of the mill, two pressure values ​​are usually set to 6bd, and the other is out of control or tripping pressure. When the pressure is lower than 4bar, the alarm will be given for a short time. When the pressure relay is working for a long time, the controlled equipment will automatically stop. The pressure relay has two functions: it is to complete the conversion of the gas/electric signal, and the second is the relay control. It can be selected according to pressure and electronic control parameters and arranged at the end of the air supply system.

4 Air compressor design considerations Compressed air station system and station design In the air compressor station process design and station layout, the following aspects should be considered: 1 when using a refrigerated dryer, high efficiency water separator and before The filter is placed upstream of the dryer. Because the compressed air from the air compressor contains a large amount of liquid water, solid dust of different particle sizes, oil stains, oil vapor, and the like. If these impurities are directly entered into the dryer, the working condition of the dryer will deteriorate. For example, oil pollution will cause heat exchange between the preheater and the heat exchange copper tube in the evaporator. The liquid water will increase the working load of the dryer; solid impurities will easily block the outer drain hole. The high-efficiency water separator and pre-filter are arranged in front of the dryer to avoid this.

When the adsorption dryer is used, a degreasing filter should be provided upstream to filter out the oil in the compressed air to prevent the "poisoning" of the dryer from failing. A downstream filter should be arranged downstream to eliminate contamination such as desiccant dust.

3 When using the refrigerating dryer, pay attention to the exhaust temperature of the air compressor. If the exhaust temperature of the air compressor exceeds the allowable intake air temperature of the Air Dryer, the high temperature type cold dryer should be used.

4 Compressed air station ventilation is also very important. According to the current GB50029-2003 "Compressed Air Station Design Code" and related design manuals, the heating temperature of the machine should not be lower than 1 ft. The summer air temperature in the space of 2m above the ground between the whole machine should conform to the current national standard "Industrial Enterprise". Design Hygiene Standards for requirements for work locations in the workshop. Different designs are adopted for different regions in the design. For non-heating areas, water-cooled screw compressors should be used as much as possible, and mechanical ventilation should be adopted at the same time. When it is difficult to use water cooling and air-cooling, special exhaust ducts must be designed to connect with the heat exhaust vents of the screw compressors, and the axial fan should be arranged to be discharged to the outside, and the whole room ventilation should be considered at the same time. For heating areas, when the single unit capacity is 10m3/min and air-cooled, special row-making equipment should be set up. Modern flour mills. ModernFlour SANGATI mills are being modified. Zhang Taiji 1SANGATI mill is the current grinding machine production line. Used for nearly two decades. I have worked in Italy GBS (Beijing) Grain Machinery Co., Ltd. for technical support, after-sales service, and have the opportunity to contact the mill production lines introduced by different flour mills in different periods, and have a deeper understanding of these production lines. These mills have entered the aging phase. The main performances are as follows: the feeding of the mill is unstable, the feeding is insufficient and the roller is insufficient, the power consumption is high, the powder extraction rate is low, and the service life of the grinding roller is short. The grinding roller grinding gap cannot be maintained, and the gap variability is large, which affects the grinding effect.

From the analysis of this model, there is no problem with the mechanical structure of the grinding roller, and the mechanical rigidity of the original design is very high. The mill design, new technology, new equipment and new materials produced by many manufacturers have become necessary means for energy saving and environmental protection. As engineers and technicians, they should know how to save energy and use energy reasonably. With the development of process system engineering, the hotspot of energy-saving technology has shifted from the energy saving of a single device to the energy saving of the system.

To treat the process as an organic combination, if the energy consumption and technical and economic analysis of the energy use process can be comprehensively optimized, the overall design will be optimized, which will bring better economic and social benefits.

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