Methanol Distillation System: Process Analysis and Column Design

化进畏●40.CHEMICAL INDUSTRY AND ENGINEERING PROGRESS2005年第24卷增刊Methanol Distillation System: Process Analysis and Column DesignSun Jinsheng, Tian Yufeng, Xu Shimin, Ding Hui, Wang Tao, Li Xingang, Zheng Yarmei(1 Shool of Chemical Engineering and Technology ，Tianjin University, Tianjin 300072;2 National Engineering Research Center for Disillation Technology, Tianjin 300072)Abstract 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 newconfiguration helps to handle problems encountered in many factories in China. The inter influencebetween process and column internal pattern is also pointed out. Recommendation of new column internaldesigns is given. Finally, industrial examples tell the how the new concept works and the possibility ofcombining process to give more opens to solve engineering problems.Keywordsmethanol ditilation, two - effet ditillation, high pressure flowsheet and low pressureflowsheet, flowsheet analysis, simulation with hydraulic, column internal designA very important material in organic chemicalPROCESS DESCRIPTIONindustry, methanol is widely involved in themanufacture of plastic material, synthetic fiber andMethanol can be synthesized from manyrubber, dyestuff, covering material, spice,materials, for instance, natural gas, gas oil, fuelmedical field, pesticide and etc. Also, it is notoil, coal, etc. [3~8]. Except for the difference inonly a fine solvent for many organic compoundscatalysts, reaction mechanics and the concentrationbut a sound substitute for gasoline in manyof methanol in raw product, the subsequentcountries as green energy(With the quickdistillation process and equipments are similar ,development of the national economy, the demandfalling into three main assortments: 2 - column(actual or potential) of methanol has sharplyprocess, 3 - column process and 3十1一columnincreased, which accelerates the development 0process. A 2 - column process is composed of lightthe methanol industry and increment of theends column and methanol refining column or mainmethanol output. Presently, methanol distillationcolumn which is found in factories under 100 kt/a,technology has been developed to be large - scale,offering simple process， equipments and lowlow energy consuming and more environmental.investment. 3 - column process is built up by lightThe main patent dealers in this industry of thends column, pressured methanol refining columnworld have the equipments designed for 5 000 ~( PMRC ) and atmospheric methanol refining7 500 t/d2]. But China (mainland) has hardly nocolumn (AMRC), forming a 2 - effects distillationrunning units with capability over 200kt/a of highwith the mixture of the distillates from the 2quality (such as 0- M - 232E US). Recently,methanol refining columns the methanol product.NationalEngineeringResearchCenter forThe characteristic of this process is the 2 - effectDistillation Technology at Tianjin Universitydistillation pattern between PMRC and AMRC,(NERCDT) has done much on technical andmeaning heat exchange between the top of PMRCmarket research, including the simulation of all theand the bottom of AMRC. This pattern saves thefamiliar flowsheets on industrial and lab data,energy (by 30%~40%) and the recycle rate ofespecially studying the 2 - effect heat exchangecooling wateIf a methanol recovery column, orbetween the 2 methanol refining columns. As astrip中国煤化工olves after the lowsummary of our work, the high pressure processpresMYHCNMHGumntoimprovetheand the low pressure process for 3 + 1 - columnquality of the wastewater, the process will turnprocess was put forward.into 3+ 1 - column process.增刊Sun Jinsheng et al: M ethanol Distillation System: Process Analysis and Column Design●41●1.1 Light Ends Columnthe components.No matter in 2 - column process, 3 - columnAs a routine method, large refux ratio; sayprocess or 3 +1 - column process, the Light End0.7~0.9 (reflux to column feed)， requires highColumn (LEC) plays the same Role. Some of thecondenser temperature to remove light impurities oflight component in raw methanol fatal to thehigh boiling point, for example acetone. Obviously,product are removed in this column, such asthismethodaccompanied b;high energymethyl formate (MFOR), dimethyl ether (DME)，consumption. Because the above method can notC1~ C6，as well as acetone and methyl ethylreduce the loss of methanol, process water is added toketone (MEK). Some publications define MFOR,the column to change the concentration of methanolDME and C1 ~ C6 as the alcoholic- solubleand water in order to weaken the solubility of theimpurities, while DME and MEK the aquaticliquid mixture in the column to the alcoholic - solublesoluble impurities. The standard of the divisionimpurities. The process water is normally fed to thecan be found in Table 1.column in 3 ways: into the 2nd condenser, at the topIndustrial investigation shows that the basicof the column and along with the raw methanol feed.measures of the removal operation include largeTo get the same methanol and water concentration atreflux ratio and process water inlet or both taken.the inlet position, process water in the first wayThe principles respectively employ the difference ofamounts approximately 5% that of the feed, while theboiling point or relative volatility and solubility ofothers, 10% ~20%.Table1 Components in raw methanol by coke oven gasNO.COMPONENTNORMALSOLUBILITYMOLEMASSDENSITYBOILINGAQUATICALCOHOLICWEIGHTFRACTION/kg" m-)H2-252. 802.024.0300E-0669. 93Nz- 195. 8028. 012.1300E-04807. 31-191. 50.3.8100 E-05800. 00R- 185.8639.951. 5300E-04679. 33c1-161. 493.34716. 042.0000E-04299. 706COr-78. 4844. 018.0700E-03826. 19DME-24.8446. 077. 000E-03674. 81MFOR31. 803Mise60. 055.1300E-04980. 559NC536.07N/AMisc .72. 153.5100 E-04630. 380ACETONE56.29Mise .58.081.500 E-04794. 6511METHANOL84. 7032. 040.817 412NC668.7486.18 .4.8700 E-04663. 3513ETHANOL78.321.8000E-03793. 8314MEK79.642Misc808. 9815IPROPNOL82. 3360. 101. 1300E-04 .790. 2216PROP ANOL97. 214.7300 E-04806.9617NC798. 43100. 217. 1400E- 05687. 5218WATER100. 0018. 020. 1598998. 57FORMIC100. 5646. 031 225. 1520IBA107. 9074. 12.1.3200 E-04805. 38213PENTNOL115. 3088. 151.4070 E-03827. 5522NBA117. 6674.121.8500 E-04811. 6723ACETIC117. 90.5.5000 E-041 052. 3124NC8125.67114. 237.1400 E-05706. 1025PENTANOL137.986.5000E-05 .817. 1926NC9150. 80中国煤化工-05720. 99Note: N/A, Slightly solubleMisc, Very soluble; Number, volumes per 100MHCNMHCIn many units, an alkaline solution (~ 15%colum to vasance lie acIus ior a moderate pHNaOH) is added to the exhaustion section of the value of the refined raw methanol.化I进展2005年第24卷the exhaustion section, a side draw removesmethanol, ethanol, isopropanol and propanol, etc.ISt Cond[2]to assure high purity of the wastewater (< <100 PPMCond.2nd Drum名methanol). When high quality methanol productrequired, another side draw, called ethanol sidedraw in factories, is opened at the bottom of theIstDrumdistillation section and just a little higher than thefeed inlet， to help reduce the concentration ofethanol in methanol product.1.3 Refining Columns in 3 - column Flowsheet中0D-一In the 3 multiple - effect distillation typesL9] ,feed splitting (FS), light spilt/ forward (LSF) andLghi Ends Columnlight split/reverse (LSR)， the LSF 2 - effectpattern by Lurgi is the most popular in China. Asshowed in Figure 2, the entire feed stream (refined四3@口raw methanol) is pumped to PMRC. About half ofthe light key component ( methanol) is removed inFig. 1 Flowsheet of Light Ends Columnthe distillate at relatively high purity. The bottom1.2 Refining Column/Main Column in 2 - columnproduct, containing remainder of the key lightFlowsheetcomponent is fed to AMRC and is purified in thisThis column, packed or trayed, have thecolumn. One or two side lines will be drawn toproduct methanol by side draw near the top of thehelp the purification of wastewater and thcolumn in the distillation section, taking up 85%distillate. In this case the heat integration is in theeffective length of the column. At the middle ofdirection of mass flow.号|言空了世与FSLSFLSRFig.2 Variations on Two - effect DistillationAt high pressure, the relative volatility isincreased pumping costs to increase the feed pressure,decreased. This contributes to explain the reason whythe purchase cost for thicker column wall needed forin many factories the methanol from the PMRChigh pressure and operation cost for the morecontains more impurities than that from AMRC,many cases, thesethough the reflux ratio in PMRC is larger than that ofincre:中国煤化工red with the largethe AMRC. The other reasons are bobble point refluxsavingYHC N M H Gnd condensing.temperature and the existence of remainder light ends.Since in 3 - column flowsheet, purity of both theThe two products can be sold at different prices or inmethanol at the top and waste water at the bottom ismixture. Besides this， the shortage includes therequired, a minimum OT between the flows in the增刊Sun Jinsheng et al: M ethanol Disilation System: Process Analysis and Column Designreboilier of AMRC and condenser of PMRC to givedifferences in costs for feed pumping and requirementenough lreat duty for these services. This OTin，,for the condition of heating medium. And, to ctainusually 20 C，is determined by the operation pressureboth the aim of high purity methanol and wastewater,of PMRC, and the pressure drop of the AMRC, whileHPF permits an optional methanol recovery column,the latter is determined by the internals of the columnmeaning intermittent shut down in large units orat a certain column L D. .cancellation of the 4th column in small ones where the1.4 The High Pressure Flowsheet (HPF)side draw flow rate is ignorable, whereas LPF mustIn methanol distillation units of large scalehave the 4th column keep running in the operation(say, 300 kt/a, usually in 3 - column flowsheet),duration. Another slight variation may be the purity ofmethanol lost within the side draw (s) of thePMRC methanol at the same reflux ratio caused byAMRC, as well as high pressure it imposes on thedissimilar relative volatility at two pressures. There iswastewater treatment, can not be omitted. Thealso a fact that, due to the flow rate and compositionsolution is feeding the side draw from exhaustionof the feed to the 4th column, the difficulty insection of the AMRC to a methanol recoveryfractionation distillation under the same productcolumn (or stripper) on the basis of 3一columndemand to the 4th column differs. HPF, with a feed ofprocess. Most of the purified wastewater, in thissmaller flow and higher methanol concentration,case, drains from the AMRC bottom， anotherrequires small reflux ratio and, consequently, a smalllittle portion of it from that of the forth column.column in diameter; the counterpart, low methanolThis requires much higher bottom temperature inconcentration, larger reflux ratio and especially largeorder to ripe off methanol and other light organicliquid flow in exhaustion section make a bigger columnimpurities in wastewater. Because the thermalunavoidable.resource of reboiler for this column is the overhead1.7 The Recovery Column and the type of returnmethanol vapor in the PMRC, to maintain normalIn running units, several patterns of methanoloperation，the operation pressure of the high recovery columns or stripper can be found.pressure methanol refining column must be highAs the simplest one, stripper receives its feed atenough to offer the temperature gradient in heatthe top and a steam at the bottom, with or withoutexchange (condenser/ reboiler) .side draw. The main service is to get rid of methanol1.5 The Low Pressure Flowsheet (LPF)in the bottom stream, and spontaneously, with the topThe configuration of low pressure process comesstream in low methanol concentration. T his operationfrom the comparison with the high pressure flowsheet,also directly loses steam and turns some of it todiffering in the feed pattern of the methanol recoverywastewater.column. This defines a flowsheet with AMRC toA refluxed stripper is fed at the lower part of theabandon its requirement to the bottom wastewater andcolumn, able to recover methanol in top product in athe bottom product (with 5% ~ ~ 10% wt methanol inconcentration of over 90%，with optional side drawit) as the feed of the forth column. The variation saves(s)，makes the flowsheet a lttle more complex.the side draws form the exhaustion section of AMRC,Apparently it has the same problems as the stripper.making the column structure simpler, and, of the mostIn many cases, the recovery column is miniatureimportance, obtains a lower reboiling temperatureof the AMRC in HPF, with the exhaustion sectionbecause of the change in bottom composition. Thislarger in portion to the distillation section, one or twosituation, as the logic of the high pressure flowsheet,optional side draws and a top product of 90% methanolcalls for a lower operation temperature of the top vaporor nearly qualified methanol. The nearly qualifiedflow at PMRC and a lower operation pressuremethanol, when merged in those from PMRC andaccordingly. .AMR(中国煤化工:e to the composition1.6 Comparison of the HPF and LPFdu:MYHCNMH Gmount and slightThe operation pressure of PMRC in HPF iscompositon durterence, contrioutes to lift the totalaround 850~ 900 kPa(A), while that of LPF 640 ~recovery of the whole unit up to 99. 2%~99.5%. In700 kPa(A). Obviously rise up at the first glance thethis case, the return of the top stream to raw methanol●44.化I进展2005年第24卷drums or other columns in the unit is unnecessary.faculty, it was finally locked.In HPF, the wastewater from the 4 th column,2.2 Selection of the thermodynamic package forthough contains more organic impurities, cannotthe columns in the flowsheetsmake any difference to the unit wastewater whenAlthough we found that the Alcohol Packagesubmerged into that from AMRC.describe the main column or PMRC and AMRC or .For the top stream with methanol concentration fareven methanol recovery with satisfaction, it hasapart from qualfied, returning it to the raw methanol,problems in simulating the LEC, especially thePMRC or AMRC is a better method to increase the totalremoval of light paraffin in raw methanol in thismethanol recovery of the unit. The position of this feedcolumn and the slight error for acetone. Some ofback is determined by the composition and condition ofthe publications[10~12] pointed out that UNIFAC isthe returned stream. Although back to AMRC seemsthe best thermodynamic package for this column,better，most factories in China prefer to the rawand certified that with the aid of process watermethanol drum.paraffin can be effectively removed. But because ofthe different quality standard between countries,2 PROCESS SIMULATIONthere is hardly any report on the removal of the keyFor designing, unit analyzing or troubleshooting,light components like acetone and MEK. According toprocess simulation is one of the most effect way.the lab and on - site investigation data, NERCDTThe understanding to the detail of the flowsheetmodified some of the parameters in the UNIFACfacilitates the establishment of the mirror units inmodel relative to the 2 components. This newthe software and keeps the result reasonable. Frommodel describes the column with satisfaction.2001，NERCDT began to relative progresses inIn the research, the authors found that, althoughmethanol distillation and gradually establish alarge process water flow helps subtraction of paraffin,serious of simulation frameworks on the base ofMFOR and DME, yet it has the reverse effect to theProll with PROVISIONTM.The informationProcess Water/ Raw Me thanol, %included came from lab research, industrial7.510125， 9;investigation and research of process packages form98.25dealers within China. The process framework, or a98.5simplified process package, involves not only the98.7process aims, parts of the heat exchange equipments and;9pumps relative to distllation operation, but simultaneous99.25column hydraulic calculation of the designated internals.99.5The results also help to optimum arrangement or99.75design of internals to the colurmns. In contrast with the100on一site data from running units， the processFig.3 Removal of acetone in LECframework gives sound uniformity. The running time,under continuous improvement, decreased from 3 daysProcess Wate r/ Raw M ethanol,%in 2001 (artificial adjustment) to 30 minutes now.1520252.1 Selection of the SoftwareThe factors determining the selection o22software includes the familiarity of the user to it,and more importantly, the accuracy of descriptionto the thermodynamic behavior of the components中国煤化工involved, especially the trace components but fatalthe quality of refined methanol, such as ethanol,MHCNMHGacetone and methyl ethyl ketone, etc. Since thealcohol package in Porll offers the smallestadjustment work and habituation of most of ourFig.4 Removal of paraffin in LEC :.增刊Sun Jinsheng et al: Methanol Distillation System: Process Analysis and Column Design●45.deduction of other key light impurities, such asThe work, along with Figure 4 ( fromacetone and MEK, for they are both very aquaticpublicationf[12) tells that to remove both aquatic andand alcoholic soluble. Figure 2 shows the researchalcoholic soluble impurities, a best ratio (process water/(on Proll with ProvisionTM, with data in Table 1)raw methanol) exists, which is the function ofwork results on acetone.concentration of both aquatic and alcoholic impurities).0→-00--(VAPI→ r- H03)|COLREB]-00400- 6209-n●(CONCNCND-四RE的Fig. 5 Two Column flowsheet framework5如TpRou0-ST2- rr -sW25-REB2-209- -20CWcmC品cm666cwn5 -ap国Fig. 6 Three Column flowshe中国煤化工:TYHCNMHG●46●化I进展2005年第24卷中-AKD2Q00D-DD-51四l T8003-0一四●CNCNr[R_刘L.-A0Fig.7 HPF framework- -[AKD0-r點0+ml 13803-602-如一吨t .202--200网8225w2203-门..网0R L -209-x品Fig.8 LPF framework2.3 Other Remarksout中国煤化工of the reboiler toThe flowsheet simulation frameworks aboveAMRMHC N M H G one speification ishave some points in common:given. This method avoids the artificial decision of(1) In HPF or LPF, a pseudo stream is drawnthe heating duty in simulation and offers a more增刊Sun Jinsheng et al: M ethanol Distillation System: Process Analysis and Column Design●47●accurate result in contrast with industrial data. In(2) For energy saving, the condensates fromseveral troubleshooting works for factories in Eastreboilers from columns" except for AMRC，beforeChina, in which a lower operation pressure isfeeding back to boiler system, are collected to heat thedesignated to a HPF along with a improperrefined raw methanol to near bobble point, and alongarrangement of internals, the simulation outputwith the wastewater of the unit and hot methanoland the on - site data showed the same, that, inproduct from PMRC, raise the temperature of rawAMRC，the qualified product and wastewatermethanol to 67~69 C. The former pre - heating alsocannot be obtained simultaneously. After checkinghelps to realize a balanced vapor - liquid load inthe original design, one of mistakes was found thatdistillation and exhaustion section in PMRC.the designer simulated the PMRC and AMRC3) With the calculation block in theseparately and just considered a same absolutesoftware, most of the parameters or features of theamount of heat load at the PMRC condenser andsimulated unit are output in one of the simulationAMRC reboiler. See Table 2 for detail.blocks. Table shows a example for a LPF.Table3 LPF output exampleRESULTNAMEVALUE1METH. RECOV.9.904 79E- -0120T-004 RRATIO2. 838 06 E+012STEAM CONSUM1. 208 08 E+0021PRO. WATER1. 871 36 E+03C. WAT CONSUM6. 784 94 E+0122VANTILATE5.12947 E+02INITIAL BPC6.462 97 E+0123LIGHT SIDE3.417 25 E+01END BP c6.47238 E+0124SIDE DRAW43.049 15 E+02STD DENSITY7.956 04 E+0225UNDEFINEDVAPOR PRESS3.194 22 E+0126HP METHANOL1.61871 E+04YEARLY YIELD2. 788 36 E+0527ATM METHANOL1. 866 74 E+04ETHANOL CONC2.219 03 E+0128RECOVERY TOP9. 396 89 E+01ACETONE CONC8.345 20 E+0129MAX FL0OD015.523 15 E+0111FORMIC CONC1.96760E-1730MAX DCMRBK011. 236 98 E+0112ACETIC CONC0. 000 00 E+0031MAX FLOODO28. 898 18 E+01STEAM CONS H8.049 20 E-0132MAX DCMRBK023.631 75 E+0114w. WAT. METH1.58024E-02 .33MAX FLOODO39.481 35 E+01WATER CONC6.40811 E-0134MAX DCMRBK031. 89698 E+0116STEAM CONS L4.031 64 E-0135MAX FLOOD046.44531 E+01T- 001 RRATIO5.247 73 E-0136MAX DCMRBK043. 300 80 E+01T - 002 RRATIO2. 700 00 E+0O37-200.T - 003 RRATIO1.865 23 E+00(4) All the columns in the frameworks involveconsumption and lowest purchase costs. Difference insimultaneous hydraulic calculation with the simulation. materials for methanol synthesis and the correspondentThe reasons include that differences in column I. D.，processes has. influence on determination the internalinternal pattern and throughput have influence on thedesign.quality of products and wastewater. To offer close data3.1 Influence of the Process and Factors for theto on - site counterparts, this is the most recommended decision of column patternway.In hydraulic design for a methanol unit using coalINTERNAL DESIGN OF THEor coke oven gas, the heating steam is produced insynth中国煤化工saving purpose,COLUMNSstructi:MYHCNMHGforthewholeLEC,The aim of internal selection is always meet thethe distillation section and the upper section betweenneeds of process requirements and lowest fuelthe feed and side draw in exhaustion section of HPF。48.化进展2005年第24卷AMRC; valve tray for whole PMRC and the sectioncolumn structure in this equipment will get nearly thefrom side draw to bottom in HPF AMRC to facilitatesame bottom temperature, with no impact on outsidethe arrangement of optional side draws. For LPFheat exchange network. That's how an economical lowAMRC，a packed exhaustion section is feasible. Theenergy consumption design comes out.The runningmethanol recovery column, or stripper, adopts similarunits of high methanol quality in China by foreignstructure as AMRC in HPF. From the viewpoints ofdealers all adopted a trayed PMRC，also giving aprocess, AMRC requires a pressure drop as low asfeasible proof. See Table 4 for detail ( trayed andpossible. Thus, a whole packed exhaustion sectionpacked column are of the same size).seems sound. But the requirement of lowest pressureIn another design for natural gas syntheticdrop should be abandoned considering the processmethanol, the synthetic gas from the reactionrequirement of optional side draw. In PMRC,section, instead of the steam, is often employedsimulations on packed and trayed make almost nofor heating medium of the distillation section. Thisdifference. In this case, the whole pressure drop takesmeans steam consumption has no significance. Thesmall portion to the operating pressure, no matterdistillation section reboilers act as the cooler of thepacked or trayed, with the bottom temperaturesynthetic gas. In this case, LEC can also bedifference within2 C. That is, using the two kinds ofdesigned in tray column.Table 4 Parameters in LPF with Packed and Trayed PMRCNo.Item NamePacked PMRCTrayed PMRCUnit Methanol Recovery0. 995Steam Consumption, t( methanol)/t( steam)1.199 391.203 32Recyele Cooling Water, t/h69. 55169. 682 6Methanol Initial Boling Point,仁64. 630 264. 6302Methanol End Boling Point,C64. 721 564.722 IMethanol Standard Density, kg/m'795. 604Methanol Vapor Pressure, kPa31.942231. 9422Unit Yearly Yield, t/a280 108Ethanol Concentration, ppm19. 904319.8683.10Acetone Concentration, ppm82. 896 882. 898 511Formic Concentration, ppm3.044E-163.039 E-1612Water Concentration, ppm0. 143 4490.578 7213LEC Reflux Ratio0. 525 07814PMRC Relflux Ratio2.715AMRC Reflux Ratio1. 859 231.867 3116Process Water1 861. 1817Light Side Draw34. 139 534.1395184th Column Side Draw376. 717376. 6921PMRC Methanol16 187.116 187.2 .20AMRC Methanol18 667.718 667.3中国煤化工3.2 New internal techniques for methanolstruct:tributors from manydistillationdealerYH. C N M H Gchniques of dferetIndustrial investigation shows that a variety ofinternals that influenced by the process, the features ofinternals are found in methanol distillation columns: .the internals also plays an important role. This section增刊Sun Jinsheng et al: M ethanol Disllation System: Process Analysis and Column Design,49●introduces some of the patented techniques of Tianjinfunction offers features like low clear liquid depth onUniversity, suitable for this process.deck, low pressure drop, low liquid entrainment, etc..(1 ) Spray Guide Trapezoid Valve TrayThis tray was designed and adopted in many fields(SGTV)in columns with diameter up to 9300mm inA unique trapezoid valve, the outline with the aidethylene unit. In methanol distillation, the bestof vapor guiding components in it forms unique propelposition for it is the exhaustion section of PMRC,to liquid layer on the tray deck downstream. Thiswhere there is a large liquid flow.Fig. 9 SGTV(2) Bone structure for gauze wire structuredand low entrainment. Also there is a reversepackingdesign with the liquid in trough and vapor flowA packing of high efficiency, gauze packingoutside, having a larger path. This solutionpies have low strength and rigidity. If the bedfacilitates seal between the troughs, avoiding thatdepth is high enough, the top surface sunken inof deck to support ring welded to the column wall.the middle, the weight of the bed makes the4 INDUSITRIAL EXAMPLE:specific density differs at difference points in thebed. This will have negative effect in mass transferTROUBLESHOOTINGin the bed. The bone structure, without influenceIn the past years, 2~3 running large - scaleon the throughput and efficiency of the gauzemethanol units in East China were found withpacking bed, give strength and rigidity to the bed.problems: high quality methanol and wastewaterby experience. A successfully running DN3000are not available, or both. It is in the work ofpacked column, with the depth of the boned bed uptrouble shooting and industrial investigations thatto 5000mm， only have 3mm the depth of thethe concept of HPF and LPF were summarized.sunken.4.1 A 350 kt/a unit by coking oven gas(3) Chimney tray re - distributor withAlthough the unit has been running at thedripping guideoperation pressure of 618 kPa (A)，the processThe orifices are opened in the wall of the gasstructure is that of a HPF. That is, at the middle .riser. A dripping guider welded to the innerof the exhaustion section of AMRC, a side draw tosurface of the gas riser protecting the liquid dropsstri中国煤化工get most wastewateror flows accelerate in the guider until they left thefroMYHCNMHGis, the PMRC withturbulent area just beneath the deck. This design2000 mm1. L.1s oovIously not for the throughputassures steady dripping points at the top of the bed announced. Moreover， the packed PMRC was●50●化I进展2005年第24卷strangely arranged: 4 gauze wire packing beds with5 SUMMARYdepth2m,8m,11mand12m.Operation data also shows no satisfactory:This work summarizes industrial investigation,ethanol concentration in refined methanol 80~experience and research work about several technical300PPM,methanol in AMRC wastewaterpoints in methanol distillation. On the basis of1000PPM，in stripper wastewater 10%，in unitprocess analysis and description to runningwastewater 2. 5%; PMRC Reflux Ratio 3.2~3.4.methanol units in China, including detailed lightA simulation wasconducted involving theends removal and integration re - utilization of thehydraulic calculation of packing and internals as theyheat, the 3 - column or 3+1 - column flowsheet iswere designed. But when selecting the theoretical stageclassified into high pressure flowsheet and lownumbers for PMRC，the effective depth was 2 m,pressure flowsheet. The key point of the4.5m, 4. 5 m and 4. 5 m. At the designed rawclassification in HPF an LPF is the operationmethanol feed flow, the operating points of the pressure of PMRC. In two - effect distillation, thebeds in PMRC were all above the flooding points.condition of heat medium from PMRC to AMRC isSince changing the operation pressure of PMRCdirectly determined by this credit. A methanol .and other process system ( pumps and pressurerecovery column or stripper in HPF or LPF mayindicators) and the arrangement of internals were nothave different operation manner.possible, the recommendation to the owner is: shutIndustrial investigation and research showsdown the side draw from AMRC, deduce the productthat the concept of HPF and LPF largely facilitatesflow from PMRC to keep operation at the normal rangeprocess troubleshooting and optimization. In someof the packing. AMRC product flow decreasedof the cases, HPF and LPF can exchange to eachaccordingly and all the bottom of AMRC feeds theother and 2 - column 3 - column flowsheets can bestripper. When hydraulic calculation identifies flooding combined to solve engineering problems.in the stripper, a new methanol recovery column willFrom the point of research and design,be built. This plan changes the HPF to LPF to fit theconsidering not only the heat integration but columnon - site condition and offers a smallest adjustment.hydraulic calculation within process simulation gives4.2 A 10 kt/a unit by coal revamped to 16. 8 kt/aadvantages. Internals have influence on the pressureThis is another example similar to the abovedistribution along the columns, which in turn haveone, also a HPF process structure running at a loweffect on the temperature difference between PMRCpressure except for the owner had moretop and AMRC bottom. The temperature reverselyrequirement: to have a larger output. Lab analysisdetermines the operation of the unit or whether aof the raw methanol， refined methanol andprocess belongs to HPF or LPF. Simulation involvingwastewater showed similar results. According toas many factors as possible offers more reliablesimulation results and the column conditions, theoutcome.scheme keeps the original LEC for whole rawIt is also the simulation with hydraulicmethanol throughput, part of the refined rawcalculation that helps to concludes that a trayedmethanol to the old PMRC and AMRC in LPF.PMRC makes almost no difference in energyThe rest of the refined raw methanol, along withconsumption compared with a packed, no matter inthe wastewater from bottom of the old AMRC, isHPF or LPF. This is very useful for technicians infed to a new refining column. This processfactor中国煤化Iany. To save fuelcombines a 2一column and a LPF， reduces ththeYHCN M H Gs large portion aspurchase cost and work load. But apparently thepossible of its internals packed beds. Difference insteam consumption will fall between that of 2material making methanol and the consequentcolumn flowsheet and LPF: 1. 25~2.2.manner of heat integration between the units also增刊Sun Jinsheng et al:M ethanol Distllation System: Process Analysis and Column Design●51●have difference best suitable column structures,2 John A. Dean Lange's Handbook of Chemistry. 15 th Edition.especially the internal pattern of LEC.McGraw - Hil, Inc. ,19953 Kieffer R,et al. [J]. Catalysis Today, 1997 ,36(1);15~24Some of thenewinternal designs areTsubaki N, et al. [J]. J. Catalysis, 2001 .197(1) :224~227recommended to improve column design or give; Zhang H. [J]. Fuel and Energy Abstracts. 1997, 38(2):82better option in revamping.Mahajan D, et al. [J]. Catalysis Today, 2003, 84(1 - 2);71~81The two examples, no matter troubleshooting.7 Gau G. []. Fuel and Energy Abstracts, 1997. 38(2):77Carapelucci R [J]. Fuel and Energy Abstracts, 1997, 38(2):119or revamp, shows the importance of understanding9 Warren D Seider. et al. Process Design Principles Sythesis,the process to detail and in depth, which facilitateAnalysis and Evaluntion. John Wiley & Sons, Inc. ，1999solving engineering problems. It also indicate that10 Guo Tianmin. Multivariate Vapor - liquid Equlibrium and Disillationthe possibility of combining different process or[M]. Beijing: Chernical Indusury Press, 1983(in Chinese)equipment pattern in industrial experience to open1 Zhao Reihong,et aL Simulation and Analysis to Methanol Dillation -more ways to manipulate troubles.Light Ends Column. Small - scale Ntrogen Ferilizer Industry, 199819~12REFERENCES12 Zhao Reihong,et al. [J]. China Chemical Engineering. 2000,28(1);48~511 David R Lide, e al Hand Book of Chenists and Physics 83 rd Edition中国煤化工MYHCNMHG