It is the first domestic plant to produce biodiesel by high pressure transesterification (SRCA) patent technology. High quality fatty acid methyl esters are obtained by vacuum distillation or vacuum flash evaporation. Fatty acid methyl ester is a mixture of high boiling point and heat sensitive compounds. In order to get 95% yield at 270 ℃, its vacuum pressure needs to reach 667 PA, The vacuum system should not only achieve high pumping rate, zero waste liquid discharge and strong anti load fluctuation ability for non condensable gas, but also have excellent discharge capacity for condensate in the process of cooling and compressing saturated steam.
In order to meet the special process requirements of biodiesel production, we have selected a set of Roots vacuum unit. Generally, the four-stage steam jet pump can also achieve the required pumping volume and vacuum degree, and reduce the purchase cost of complete equipment. However, the use of jet pump needs to greatly increase the area of installed structures and the load of steam, sewage treatment and other public systems, while the comprehensive operation cost of mechanical vacuum unit is only 20% of that of steam jet pump.
1. Process design conditions
Known working conditions: temperature T = 50 ℃, working pressure P ≤ 400pa, vacuum system volume v = 92m3; pumping time t = 15 ~ 20min, pumping speed Vmax = 15000m3 / h, limit pressure Po ≤ 13pa.
2. vacuum pump unit selection
According to the requirements of working pressure of 400pa and limit pressure of 13pa, the system requirements can be met by using three-stage mechanical vacuum pump. The mechanical vacuum pump usually uses roots vacuum pump and twin screw vacuum pump.
Roots vacuum pump is a kind of rotary variable volume vacuum pump. The limit vacuum of the pump is 0.0665pa. When the true space is 133 ~ 1.33 PA, the pumping speed is the highest. When working with the front stage pump, it has stable pumping performance in the range of 13300-0.01pa. In order to enhance the pumping performance and shorten the pumping time, the air-cooled Roots vacuum pump is used as the intermediate pump. The air-cooled Roots vacuum pump makes part of the gas automatically circulate and cool the rotor and the pump body by means of the external cooler. The pump can work continuously without thermal overload under a high pressure difference, and has no influence on the pumping performance of the pump. The working limit only depends on the mechanical strength of the pump itself. When the pump is combined with roots vacuum pump or twin-screw vacuum pump, it can give full play to the advantages of Roots vacuum pump that oil-free gas pollutes the pumped system, and it can obtain a high pumping speed close to the main pump in high pressure range. Different vacuum degrees in the range of 105 ~ 0.05pa can be obtained by this combination.