090105009罗浩猛 外文文献原稿和译文.docx

1、090105009罗浩猛 外文文献原稿和译文外文文献原稿和译文原 稿Methanol Distillation System: Process Analysis and Column DesignAbstract：Base on industrial research and experience, the process of methanol distillation is analyzed, and above all, a new concept of high pressure flowsheet and low pressure flowsheet is defined. The

2、new configuration helps to handle problems encountered in many factories in China. The inter influence between process and column internal pattern is also pointed out. Recommendation of new column internal designs is given. Finally, industrial examples tell the how the new concept works and the poss

3、ibility of combining process to give more opens to solve engineering problems.Keywords: methanol distillation, two - effect distillation, high pressure flowsheet and low pressure flowsheet, flowsheet analysis, simulation with hydraulic, column internal designINTRODUCTION A very important material in

4、 organic chemical industry, methanol is widely involved in the manufacture of plastic material, synthetic fiber and rubber, dyestuff, covering material, spice, medical field, pesticide and etc. Also, it is not only a fine solvent for many organic compounds but a sound substitute for gasoline in many

5、 countries as green energy. With the quick development of the national economy, the demand (actual or potential) of methanol has sharply increased, which accelerates the development of the methanol industry and increment of the methanol output. Presently, methanol distillation technology has been de

6、veloped to be large - scale, low energy consuming and more environmental. The main patent dealers in this industry of the world have the equipments designed for 5 000 7 500 t/dEz. But China (mainland) has hardly no running units with capability over 200kt/a of high quality (such as O - M - 232E US).

7、 Recently, National Engineering Research Center for Distillation Technology at Tianjin University(NERCDT) has done much on technical and market research, including the simulation of all the familiar flowsheets on industrial and lab data, especially studying the 2 - effect heat exchange between the 2

8、 methanol refining columns. As a summary of our work, the high pressure process and the low pressure process for 3 + 1 column process was put forward.1. PROCESS DESCRIPTION Methanol can be synthesized from many materials, for instance, natural gas, gas oil, fuel oil, coal, etc. Except for the differ

9、ence in catalysts, reaction mechanics and the concentration of methanol in raw product, the subsequent distillation process and equipments are similar, falling into three main assortments: 2 column process, 3 -column process and 3+1 column process. A 2 -column process is composed of light ends colum

10、n and methanol refining column or main column which is found in factories under 100 kt/a, offering simple process, equipments and low investment. 3 -column process is built up by light ends column, pressured methanol refining column (PMRC) and atmospheric methanol refining column (AMRC), forming a 2

11、 -effects distillation with the mixture of the distillates from the 2 methanol refining columns the methanol product. The characteristic of this process is the 2 effect distillation pattern between PMRC and AMRC, meaning heat exchange between the top of PMRC and the bottom of AMRC. This pattern save

12、s the energy (by 30% 40) and the recycle rate of cooling water. If a methanol recovery column, or stripper, or water column involves after the low pressure methanol refining column to improve the quality of the wastewater, the process will turn into 3+1-column process.1.1 Light Ends Column No matter

13、 in 2 - column process, 3column process or 3+1-column process, the Light End Column (LEC) plays the same Role. Some of the light component in raw methanol fatal to the product are removed in this column, such as methyl formate (MFOR), dimethyl ether (DME), C1 C6, as well as acetone and methyl ethyl

14、ketone (MEK). Some publications define MFOR,DME and C1 C6 as the alcoholic soluble impurities, while DME and MEK the aquatic- soluble impurities. The standard of the division can be found in Table 1. Industrial investigation shows that the basic measures of the removal operation include large reflux

15、 ratio and process water inlet or both taken. The principles respectively employ the difference of boiling point or relative volatility and solubility of the components. As a routine method, large reflux ratio; say 0. 70. 9 ( reflux to column feed), requires high condenser temperature to remove ligh

16、t impurities of high boiling point, for example acetone. Obviously, this method is accompanied by high energy consumption .Because the above method can not reduce the loss of methanol, process water is added to the column to change the concentration of methanol and water in order to weaken the solub

17、ility of the liquid mixture in the column to the alcoholic- soluble impurities. The process water is normally fed to the column in 3 ways: into the 2nd condenser, at the top of the column and along with the raw methanol feed.To get the same methanol and water concentration at the inlet position, pro

18、cess water in the first way amounts approximately 5 % that of the feed, while the others, 10%20%. In many units, an alkaline solution (15% NaOH) is added to the exhaustion section of the column to balance the acids for a moderate pH value of the refined raw methanol.1.2 Refining ColumnMain Column Fl

19、owsheet This column，packed or trayed，have the product methanol by side draw near the top of the column in the distillation section, taking up 85 effective length of the column. At the middle of the exhaustion section, a side draw removes methanol, ethanol, isopropanol and propanol , etcTo assure hig

20、h purity of the wastewater (100 PPM methanol) . When high quality methanol product required，another side draw，called ethanol side draw in factories，is opened at the bottom of the distillation section and just a little higher than the feed inlet，to help reduce the concentration of ethanol in methanol

21、 product1.3 Refining Columns in 3-column Flowsheet In the 3 multiple-effect distillation types, feed splitting(FS)，light spiltforward (LSF) and 1igh (splitreverse (LSR)， the LSF 2 -effectpattern by Lurgi is the most popular in China As showed in Figure 2 the entire feed stream (refined raw methanol)

22、 is pumped to PMRCAbout half of the 1ight key component (methanol) is removed inthe distillate at relatively high purityThe bottom product，containing remainder of the key light component is fed to AMRC and is purified in this column. One or two Side lines Will be drawn to help the purification of wa

23、stewater and the distillateIn this case the heat integration is in the direction of mass flowAt high pressure，the relative volatility is decreased. This contributes to explain the reason why in many factories the methanol from the PMRCContains more impurities than that from AMRC, though the reflux r

24、atio in PMPC is 1arger than that of the AMRC The other reasons are bobble point reflux temperature and the existence of remainder light ends The two products can be sold at different prices or in mixtureBesides this， the shortage includes the increased pumping costs to increase the feed pressure, th

25、e purchase cost for thicker column wall needed for high pressure and operation cost for the more complicated flowsheet But in many cases, these increases are small when compared with the large savings in the utilities in boiling and condensing Since in 3-column flowsheet, purity of both the methanol

26、 at the top and waste water at the bottom is required， a minimum T between the flows in the reboilier of AMRC and condenser of PMRC to give enough heat duty for these services. This, usually 20, is determined by the operation pressure of PMRC, and the pressure drop of the AMRC, while the latter is d

27、etermined by the internals of the column at a certain column I. D.1.4 The High Pressure Flowsheet (HPF) In methanol distillation units of large scale (say, 300 kt/a, usually in 3 - column flowsheet), methanol lost within the side draw (s) of the AMRC, as well as high pressure it imposes on the waste

28、water treatment, can not be omitted. The solution is feeding the side draw from exhaustion section of the AMRC to a methanol recovery column (or stripper) on the basis of 3- column process. Most of the purified wastewater, in this case, drains from the AMRC bottom, another little portion of it from

29、that of the forth column. This requires much higher bottom temperature in order to ripe off methanol and other light organic impurities in wastewater. Because the thermal resource of reboiler for this column is the overhead methanol vapor in the PMRC, to maintain normal operation, the operation pres

30、sure of the high pressure methanol refining column must be high enough to offer the temperature gradient in heat exchange (condenser/reboiler) .1.5 The Low Pressure Flowsheet (LPF) The configuration of low pressure process comes from the comparison with the high pressure flowsheet, differing in the

31、feed pattern of the methanol recovery column. This defines a flowsheet with AMRC to abandon its requirement to the bottom wastewater and the bottom product (with 5%10% wt methanol in it) as the feed of the forth column. The variation saves the side draws form the exhaustion section of AMRC, making t

32、he column structure simpler, and, of the most importance, obtains a lower reboiling temperature because of the change in bottom composition. This situation, as the logic of the high pressure flowsheet, calls for a lower operation temperature of the top vapor flow at PMRC and a lower operation pressure accordingly.1.6 Comparison of the HPF and LPF The operation pressure of PMRC in HPF is around 850900 kPa(A), while that of LPF 640700 kPa(A). Obviously rise up at the first glance the differences in costs for feed pumping and requirement for the condition of heating medium. And, to obtain b