Multilayer-evaporation-based bio-diesel continuous rectification system and process

Abstract

The invention relates to a multilayer-evaporation-based bio-diesel continuous rectification system and a multilayer-evaporation-based bio-diesel continuous rectification process. The system comprises a charging pump which is connected with a product-raw material heat exchanger. The product-raw material heat exchanger is connected with a multilayer evaporator through a combined condenser. A condenser is connected with the upper part of the multilayer evaporator, and is connected with a product intermediate tank which is connected with a discharging pump. A rectification column is connected with the lower part of the multilayer evaporator through an intermediate charging pump. A light component intermediate tank is connected with the upper part of the rectification column through the combined condenser, and is connected with the product-raw material heat exchanger and a preheater through a reflux pump. The preheater is connected with the rectification column. The system and the process have the beneficial effects that: after light components such as low-carbon methyl ester are removed from crude bio-diesel through the multilayer evaporator, a subsequent rectification column system can maintain a higher vacuum degree, the productivity is improved, the energy consumption is reduced, and the yield of a product is improved.

Description

technical field [0001] The invention relates to the technical field of biodiesel separation and purification, in particular to a biodiesel continuous rectification system and process based on multilayer evaporation. Background technique [0002] The industrial biodiesel distillation process is a unit operation involving high temperature (the temperature of the heat transfer oil is usually controlled between 250-300°C) and high vacuum (the operating absolute pressure is usually lower than 1000Pa). One of the keys to the operation is the high vacuum condition maintenance. There are two main purposes of high vacuum operation: 1) The methyl ester of biodiesel component has a high boiling point, and high vacuum operation can reduce the boiling point of methyl ester, thereby reducing the temperature of the heating medium heat transfer oil and reducing energy consumption. Biodiesel is mainly composed of carbon 16 methyl esters and carbon 18 methyl esters. Due to different raw mate...

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Problems solved by technology

[0004] The existing industrial biodiesel distillation system cannot achieve the above three aspects at the same time, namely: 1) maintaining a high vacuum degree; 2) the residence time of biodiesel in the reboiler cannot be controlled; 3) heat energy recovery

[0005] In Chinese patents CN100547056C, CN100503533C, and CN201125232Y, the reboilers in the biodiesel distillation process all adopt kettle-type structures. Because the liquid holding capacity in the kettle-type reboilers is large, the liquid layer on the surface of the heating coil is thick, thereby increasing the vaporization of methyl esters. Absolute pressure increases the boiling temperature of biodiesel, and at the same time, the residence time of biodiesel during heating and vaporization cannot be controlled. Long residence time will lead to high-temperature polymerization and coking of biodiesel, which will reduce the rectification yield of biodiesel and increase energy consumption.

[0006] In view of the above problems, the device described in the Chinese patent CN101033411B adopts a falling film reboiler and a heat exchanger to recover the heat energy of the biodiesel product, which better solves the influence of the thickness of the liquid layer on the biodiesel vaporization process. However, because the crude biomass The composition of diesel oil is complex. Crude biodiesel goes through the tube side of the falling film reboiler. A small amount of polymerization and coking at high temperature will easily cause blockage of the heating tube, increase the thermal resistance of the fouling, and cause a significant decrease in the heat transfer area and total heat transfer coefficient. The amount of evaporation is significantly reduced, which is not conducive to stable operation. In addition, the heat (latent heat) released by the condensation of biological products at the top of the tower has not been recovered, and the overall energy consumption is relatively large.

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