Practice of optimal design of furfural refining un

Practice of optimization design of lubricating oil furfural refining unit

Abstract: the problems and deficiencies in the operation of lubricating oil furfural refining unit in Nanyang paraffin Fine Chemical Plant are introduced, and the transformation design methods of "bottleneck" such as solvent recovery system, steam generation system, refining liquid heating furnace, refining oil stripper, bottom reboiler of extraction oil tower are described in detail. Compared with that before the transformation, under the same refining depth, the treatment capacity can be increased by about 25%, the yield of refined oil can be increased by 2.3 percentage points, and the energy consumption can be reduced by 62.6%. Turning down VOC materials is a key word that can be molded by most injection molding machines: furfural refining device; Technical transformation; Energy consumption; Handling capacity; Yield 1 introduction the lubricating oil furfural refining unit of Nanyang paraffin Fine Chemical Plant, with a design processing capacity of 100.8 kt/A, was completed and put into operation in September 1997. Although advanced equipment and instruments are used in the design of furfural refining unit, there are some defects in the process flow and equipment, process control and pipeline layout, resulting in large production fluctuations, small operation flexibility, high energy consumption, low safety factor and poor economic benefits, so that the advantages of the unit itself can not be brought into full play, and the benefits of paraffin lubricating oil production system are also restricted. Therefore, according to the current situation of furfural refining unit, aiming at the problems existing in the design and referring to the transformation experience of similar units in other units, four optimization transformations have been carried out in the past few years, and the problems have been solved one by one, and the overall economic benefit of operation has been greatly improved. 2 main features of furfural plant design (1) the plant is designed to process light oil and heavy oil. The fourth line, the second line and the third line are collectively referred to as light oil, and the fourth line and light deasphalting oil are collectively referred to as heavy oil. Switching production of light and heavy oil. (2) The extraction tower is a new type of high-efficiency packing tower, which adopts QH-1 packing developed by Tsinghua University and the feed distributor designed by Luoyang Petrochemical Engineering Company. (3) The extraction solvent recovery system adopts a low medium high three effect evaporation process to fully recover the heat of the solvent. The heat load of the recovery heating furnace is only 67% of the two effect evaporation process, which can save energy better. (4) Absorbing the production and operation experience of domestic similar advanced devices, the refined liquid and extraction liquid flash tower are added to the solvent recovery system to reduce the negative impact of the solvent recovery system, so that private enterprises can create vitality, fully burst out and reduce energy consumption. (5) Process simulation program is used to simulate the process flow and optimize the operating conditions. (6) Some cooling and heat exchange equipment adopts high-efficiency heat transfer equipment such as threaded tubes and inserts, which can strengthen heat transfer, reduce heat exchange equipment, save investment, and adapt to changes in working conditions. (7) The automatic control system adopts the DCS distributed control system of American ABB company. The screen display is intuitive and clear, the adjustment is convenient, the operation is stable, and it has the functions of memory, alarm, printing and so on, realizing the upgrading of the automatic control level. 3 deficiencies in device design 3.1 the main problems of low evaporation rate of the first effect evaporation tower are: Taking the convection chamber of the extraction liquid heating furnace as the final heating measure for the feeding of the first effect evaporation tower; There are two large "U" bends in the feeding process of the first effect evaporation tower in the front and back of the flow chamber of the heating furnace in the two years from 2015 to 2017; The heat transfer coefficient of some heat exchangers is too high in the calculation. Due to the poor thermal stability when heating with the convection chamber, and the two large "U" bends in front of and behind the convection chamber are DN 300 mm and DN 350mm pipelines respectively, the process is long and the heat dissipation loss is large, which is very easy to form liquid accumulation, and the pressure drop of the extracted liquid in the heat exchanger increases. In the heat exchanger, the solvent is actually evaporated under the pressure higher than the evaporation tower, and the temperature difference loss of the back pressure formed by it will increase, resulting in the good and bad evaporation effect and low evaporation rate. 3.2 the solvent of extracted oil exceeds the standard. Because the furfural unit of Nanyang paraffin Fine Chemical Plant is designed as a positive sequence production scheme, the yield of extracted oil is only about 15%, so there are few materials entering the flash and stripper of extracted oil. During the commissioning of the unit, the tower bottom temperature of the extraction oil stripper at the initial stage can only reach 120 ~ 130 ℃, and the method of partial circulation of the extraction oil system was used to increase the circulation volume of the extraction oil, so that the tower bottom temperature reached 145 ~ 155 ℃, and the amount of solvent carried by the delivered extraction oil was as high as 2 ~ 3%, resulting in a large amount of solvent loss. The unit was forced to shut down for technical transformation after only 40 days of operation. 3.3 the installation position of steam drum and steam generator is unreasonable. Because the position of steam drum and steam generator is designed too low, a large "U" shaped bend of about 10m is designed before the furfural solvent of the first, second and third effect evaporating towers enters the drying tower, and the three evaporating towers share a tower line. When the pressure control valve of the third effect evaporating tower acts, it will seriously affect the evaporation capacity of the first and second effect evaporating towers, resulting in long process, large pressure drop The situation of large loss of back pressure temperature difference and unfavorable to evaporation leads to the percentage of solvent recovered by heat exchange not meeting the design requirements. In addition, the designed load of the steam drum is too small, and the designed steam generation capacity is only 1 000 kg/h. The MHH (5) wood based panel scratch tester of Jinan new era Gold Testing Instrument Co., Ltd. is composed of three parts: host, ruler and electrical appliances. However, the actual steam generation capacity is sometimes as high as 1 450 kg/h, and the phenomenon of low-pressure steam with water often occurs, which cannot meet the needs of daily production. 3.4 the design load of refining liquid heating furnace is insufficient. Due to the high data taken in the design of the heat exchanger before entering the refining liquid heating furnace, the theoretically calculated entering temperature is 178 ~ 181 ℃, while the actual entering temperature is only 152 ~ 154 ℃; The design load of the heating furnace is 620 kW, but the actual load has reached 755kw, forming the overload operation of the heating furnace. Therefore, there are often insufficient air supply, incomplete combustion, tempering of heating furnace and other phenomena, resulting in operation fluctuations. 3.5 refined oil is carried on the top of the refined liquid stripper. The refined liquid stripper is the key facility for the separation of refined oil and furfural solvent. Because the opening rate of the sieve plate in the stripper design is too small, the gas phase load on the top of the stripper is too large, resulting in