Application of roots water ring vacuum unit in physical refining of rice bran oil
Roots water ring vacuum unit is used for the physical refining of rice bran oil, with low operating power, low protection cost, sensitive inconvenience of the device, increased production profit and obtained good economic benefits. The waste oil produced has reached the national standard of Grade 4 refined rice bran oil. This unit is suitable for use in small-scale physical refining production lines.
The physical refining requires the absolute vacuum pressure to be less than or equal to 200Pa. Therefore, during the oil and fat year, the water ring vacuum pump and the steam-water series vacuum pump cannot meet the requirements. Normally, a water vapor jet vacuum pump is used. However, the water vapor jet vacuum pump has high operating profit and needs to be equipped with small and medium-sized steam boilers, which is not practical for some medium-sized oil plants. Roots type vacuum pumps are widely used in vacuum distillation, vacuum volatilization and dehydration crystallization of chemical industry, and they are less used in oil industry. We equipped Roots water ring vacuum unit in a 15t / d rice bran oil physical refining deacidification production line of a company in Jiangsu, which increased production profit and produced a decent new national standard four-grade refined rice bran oil. This unit is suitable for use in small-scale physical refining production lines. 1.Type, structure and operating principle of Roots water ring vacuum unit
Roots type vacuum pump (Roots pump for short) is a wrap-around variable capacity vacuum pump without internal compression. It uses two 8-shaped spirals to circulate in the pump casing to generate suction and exhaust. It makes it impossible to discharge the gas to the atmosphere indirectly, and it must be used in series with the fore vacuum pump. The pumped gas is discharged into the atmosphere through a fore vacuum pump. During operation, the pumped gas enters between the rotor and the pump body through the air inlet. At that time, a rotor and the pump body separate the gas from the air inlet, and the separated gas (as shown by the whole hatched line in Figure 1). The whirlpool has been swirling around in the middle, and has been sent to the exhaust port.
Fig. 1 Operation status of Roots-type vacuum pump
1.1 Roots water ring vacuum unit type
(1) Roots pump-water ring pump. The role of the water ring pump in the unit is to cause the preparation vacuum required by the Roots pump. Under normal conditions, the limit vacuum of the single-stage water ring pump is not high, and the pre-vacuum required by the Roots pump produced in China is high. Normally, it is not necessary to use a single-stage water ring pump as the foreline pump of the Roots pump, and a two-stage water ring pump with a lower ultimate pressure as the foreline pump can also increase the unit's ultimate pressure. The limit pressure of a Roots pump and a water ring pump is 400Pa, which can meet the normal vacuum requirements, but it is bound to be restricted in the physical refining process.If two Roots pumps are used in series and then combined with a water ring pump (see Figure 2), can greatly popularize the ultimate pressure of the unit (up to 25Pa).
Figure 2 Roots pump-Roots pump-Water ring pump vacuum unit Figure 3 Roots pump-water ring pump series mechanical vacuum pump vacuum unit
(2) When the three-stage Roots water ring unit still cannot meet the limit pressure, a Roots pump-water ring pump series mechanical vacuum pump can be adopted (see Figure 3). This unit is mainly used to solve a large number of water vapor. The time required and the ultimate vacuum degree are extremely high, such as vacuum drying.
The Roots water ring vacuum unit adopts the water ring pump as the foreline pump, so it is particularly useful in the physical refining process for extracting a large amount of water vapor and a certain aggressive, coagulable grease gas. According to the physical refining skills and the performance parameters of the Roots water ring vacuum unit, in the theoretical year of life, we selected two Roots pumps in series and then used a two-stage pump as the foreline pump to form the unit (see Figure 4). Refining deacidification process.
1.2, Roots water ring vacuum unit operating principle
Roots pump is the main pump and water ring pump is the foreline pump. Roots water ring vacuum unit selects the water ring pump as the foreline pump, which is more unprofitable than the other vacuum pumps. It overcomes the limit pressure difference when a single water ring pump is used (the unit's limit pressure is much more popular than water ring pumps). The lack of a low pumping rate under a certain pressure keeps the Roots pump capable of rapid operation and the advantages of a large pumping rate, especially suitable for pumping out a large number of condensable mixed fat cream acid steam.
Figure 4 Roots water ring vacuum unit
Features of Roots water ring vacuum unit:
① There is a certain gap between the Roots pump spinner and the pump cavity, and between the spinner and the spinner in the unit, and there is no contact with each other.
② Roots pump rotors have a good degree of symmetry, which can popularize the speed, so that a large pump with a compact structure can be created;
③ The unit has small vibration and large volume during operation;
④ There is no compression scene like mechanical vacuum pump in the roots pump cavity, so it does not need to exhaust the cylinder. Because of this, the coagulable grease acid vapor can be removed;
⑤ Quick start, can reach the ultimate vacuum in a short time, low power, low operating protection cost;
⑥ Roots pump has a large pumping speed in a wide pressure range (1 ～ 1000Pa), and can quickly discharge the distilled gas. 2. Important process parameters
The rice bran decolorizing oil enters the deacidification tower and passes through 260 ～ 270 ℃ heat-conducting oil in the coil under vacuum with a residual pressure of 666.6Pa. ), Continue the steam distillation operation. The whole vacuum of deacidification is generated by Roots water ring vacuum unit. See Table 1 for the results of testing the quality index of waste oil and grease. The quality of waste bamboo weaves has reached the national standard of Grade 4 refined rice bran oil. The grease has high acid value, good purity and low refining loss.
Table 1 Consequences of testing quality indicators of waste oil and grease
During the theoretical year of birth, the vacuum degree of deacidification was maintained at about 75Pa. It is found in the debugging that the indirect steam does not have to be large for the fragmented vacuum, and the indirect steam pressure is high or low, which makes the amount of mixed grease cream acid steam fluctuate. It is not necessary for the Roots water ring vacuum unit to be large. The indirect steam is turned on too much, resulting in a flushing scene. Otherwise, the vacuum of the deacidification tower is not necessary. 3. Performance of Roots water ring vacuum unit
Although the Roots water ring vacuum unit is only suitable for small-scale oil plants, compared with water vapor jet vacuum pumps, the Roots water ring vacuum unit does not require steam during operation, so it is not necessary to equip it with a steam boiler. But areas with higher coal prices.
On the device, the normal water vapor jet vacuum pump adopts an overhead pump, so that the height of the device is 11m, and the Roots water ring vacuum unit is inconvenient to install, can be sensitively positioned according to the process and plant conditions, and occupies less land. The vacuum unit equipped with a 15t / d rice bran oil physical refining production line has a specification of 1350 & times; 900 & times; 2110mm. Its structure is easy and the operation is reliable. In addition, the water vapor jet vacuum pump has a louder sound, and it is arranged in the group without production and surrounding conditions. The Roots water ring vacuum unit is absolutely quiet, and it is also superior to the water vapor jet vacuum pump in terms of environmental protection of the group. The first injection of the Roots water ring vacuum unit is higher than the water vapor jet vacuum pump, but in the future years, its operating power is small and the protection cost is low. 4.Concluding remarks
Roots water ring vacuum unit can be used for small-scale physical refining and deacidification of rice bran oil. It is sensitive in device, low in operating power, and low in protection. The waste oil produced can meet the requirements of national standard four-grade refined rice bran oil, and is practically used in small-scale physical refining production lines.