英文文献.pdf

英文文献.pdf
Operation of plate rectification tower
WU Chang-xiang
(Harbin Gasification Plant,Harbin154864,China)
Abstract:The influencing factors,abnoimal phenomenon and rectification process were analyzed to direct actual operation Key words:rectification tower,recification,reboiler,operation Distillation column is a multi-stage partial vaporization and partial condensation according to the different components in the mixture volatility in each floor tower board to achieve the separation of a mixture of various components of the tower gas-liquid contact device,also known as distillation.A plate column and packed column types.According to mode of operation are divided into continuous distillation and batch distillation.Steam from the bottom of the column entry,and the decline in liquid countercurrent contact with the two in contact,the drop in the volatile liquid(low boiling point)components is continuously transferred to the steam.The difficulty of steam volatile(high boiling)component continued to decline in the transfer of liquid, steam the closer the top of the tower,the higher the concentration of its volatile components,while the decline in the closer tower bottom liquid,its hard to be more volatile components rich set,to achieve component separation.Steam rising from the top of the tower into the condenser,the liquid part of the condensate as reflux liquid to return into the distillation tower,the rest is removed as distillate.Tower bottom outflow of liquid,some of which into the reboiler,thermal evaporation,the steam back to tower,and the other part of the liquid as residua release.
Compared with other chemical unit operations,distillation unit,although relatively simple,single production run that often appear in a variety of problems affecting the operation of the distillation unit,leading to tower top orbottom of product failure,severe constraints of production equipmentthe operation resulting in product loss.
1.Regular changes in process conditions of distillation column 1.1Reboiler temperature
Under the same operating pressure,raising the temperature of the reboiler,the volatile components in the tower liquid to reduce,at the same time,the rising vapor velocity increases,and help to improve the efficiency of mass transfer.If products from the top of the tower,the tower reactor discharge of difficult volatiles volatile components to reduce and reduce losses.If the tower reactor effluents for the product,it can improve product quality tower discharge of volatile components entrained difficult nolatile components increased,thereby increasing the losses.In balanced operation,the reactor temperature is suddenly increased,and it too late to adjust the pressure and temperature will inevitably lead to the reboiler fluid is steam-air,the pressure increased.At this time,the tower gas,liquid composition changes,the restructuring were likely to be steamed to the top of the tower,so that the failure of top product.
1.2Operating pressure
In the case of certain operating temperature,increasing the operating pressure can increase the productive capacity of the tower,so that stable operation,but the content of volatile group in the tower reactor products.In distillation,often provides for the adjustment range of the operating pressure.When the fallout of the operating pressure by extmrnal factors,were destroyed,the
normal operation of the tower will be completely destroyed.
1.3Feeding temperature
1.3.1Condensate feed,the feed temperature is lower than the temperature of the feeding board,and added if all the material into the stripper segment,stripping segment load increases,the reboiler consumption increase in the amount of steam,and the top of the tower is difficult volatile group were lower.
1.3.2Saturated steam feed,the feed material temperature is higher than the temperature of feed board,all the material of the feed into the rectifying section and stripping section of the load reduction,and increased load of the rectifying section,make the top product quality reduce.
1.4Feeding quantity and composition changes
Changes in the feedstock of a direct impact on the change of the amount of steam,the latter increase will produce entrained,even flooding.The feedstock is too low,the operation is not good to maintain the balance of the tower,the steam velocity decreases,the plate is prone to leakage,the rectification efficiency is low.Inthe low-load operation,may be appropriate to increase the reflux ratio,the tower operating in a load lower limit above normal and stable operation in order to maintain the tower.Feeding component of the changes directly affect the product quality.Increased restructuring concentration increase in the rectifying section load separation is not good,the results of restructuring were brought to the top of tower,causing the top of the tower of inferior quality.Product from the reboiler,the top of the tower losses increase.If the concentration of the volatile group in the feeding group were increased,and the stripping section of the load increases,may be poor due to the separation caused by the tower reactor products of inferior
quality,which entrained volatile components increased.Feeding restructuring concentration increased,the feeding mouth move down and vice versa,then move up.The same time,operating temperature,back flow and operating pressure must be adjusted accordingly in order to ensure the stability of the distillation operation.
Distillation,increasing the reflux ratio,can improve the quality of the product,but the reflux ratio is too large,the inner loop of the tower increased,increasing energy consumption.Reduction of the reflux ratio,the tower gas-liquid contact is not good,the balance to damaged and therefore the mass transfer efficiency decreased.The same time,the operating pressure drop,difficult volatile components easily brought to the top of the tower,resulting in a substandard product.
2Anomalies in the distillation column during operation
2.1Plate capacity
Rectifying section tray downcomer overflow liquid transportation,however,that the tower upper part of the beginning of flooding,a phenomenon known as downcomer obstruction or liquid flooding.Its causes is to block the liquid leaving the tower board level rise in the downcomer plate between mist entrained excessive leaving the tray efficiency to reduce entrainment of this phenomenon is known as the excessive fog or steam flooding,the reason is the relativein the gas while the tower board bubbling area is too small.
2.2Plate fouling
Sediment cumulative to the board of board of the tower is an important issue,trays of dirt will tower premature flooding will reduce the plate efficiency.Plate scaling phenomenon:(1)The reflux ratio is not high on liquid pan;(2)The pressure drop
increase between the tray;(3)Increase the reflux ratio on the bottom of the column temperature,flow or reboiler load does not have any impact,if the reflux ratio to the heat balance and material balance of20%to30%,while the tower did not change significantly,then the tower must be completely full of liquid.The amount of returning tower direct stream gas pipeline through the top of the tower back to the reflux tank.
2.3Slug flows in the riser
Slug flow in the riser is a distillation column running unstable,may be caused due to an unstable gas-liquid mixture flow in the vertical pipeline.Reflux tank is elevated at the of the condenser by the condenser discharge logistics is that part of the pipeline
between the gas-liquid two-phase mixture,the condenser and reflux tank is called the riser.Generate a liquid column in the riser flow rate is too low will result in two-phase separation,the distillation column to produce a back pressure,this liquid column intermittently be introduced after the riser,back pressure will weaken,then the risergradually being filled with liquid,such slug flow will cause the tower pressureperiodic pulse of change.
Abnormal factors cause distillation column plate was washed away,condenser corrosion,clogged caondenser,not condensable gas influence condenser.
3.Reboiler
Reboiler in the distillation column occupies a very important position,it used to bebottom after the vaporization of the liquid part of the back to the distillation column,two phases of the tower gas-liquid contact and mass transfer to proceed.Which used the vertical thermal siphon reboiler,which is a vertical placement of the shell and tube heat exchanger.Partial
vaporization of liquid in the bottom-up tube passes through the heat exchanger,heating the heat carrier in the shell.Vertical thermal siphon reboiler features:(1)cycle driving force:the density of the reactor liquid and the heat exchanger tube gas-liquid mixture;(2)compact,small footprint,high heat transfer coefficient;(3)of the shell can not be mechanically cleaned,not suitable for hightower reactor,heat transfer medium viscosity,or dirty;(4)provide the space and buffer zones of the gas-liquid separator.
Factors that determine the distillation column capacity restricted,find the reboiler failure is the most laborious,the distillation column by steam reboiler.
(1)gas-barrier drain valve failure;(2)steam condensate collected indoor pressure is too large;(3)the condensate liquid seal failure.
Hydrophobic failure caused by hydrophobic failure factors:
3.1Thermosiphon rebiler failure
Reboiler liquid inlet pipe and outlet pipe cold liquid mixture exists between the density difference is the density difference driving the process of processing liquid flow through the reboiler.When tower humoral bit elevated to the reboiler back to the liquid nozzle height,siphon circulation will be impeded.The circulation rate reduction will result in the reduction of heat transfer,thus the cover back to the fluid nozzle is clearly an important reason for fluctuations in the reboiler duties.
3.2Non-condensable gas in the water vapor
Steam reboiler to run the process,water vapor may be non-condensable gases,or
the reboiler leak,the hydrocarbon vapor or other non-condensable gas into the reboiler,the non-condensable gas into
the reboiler pipingthereby reducing the heat transfer capacity of the reboiler with the distillation column within a circulating fluid,thus causing the reboiler heat transfer efficiency decreased.
4Conclusion
In view of these problems often appear in a production run affect the operation of the distillion unit,leading ton the top of the tower or the bottom of product failure,seriously restricting the production device to run resulting in product loss.In order to avoid such things from bappening,the operator should do the following:
4.1storage and transportation of materials
Plate column distillation process must be set in place a number of different volume raw material storage tanks,pumps and all kinds of heat exchanger has been temporarily stored,transported and preheating(cooling)of materials used,in order to protect the device can be a continuous and stable operation.
4.2Necessary means of detection
In order to facilitate the resolution of the problem in the operation shall be the appropriate place in the process to set the necessary instrumentation,as well as to obtain the pressure,temperature and other parameters.In addition,often set in a particular place manholes and hand holes,so that regular testing and maintenance. 4.3Adjustment device
State parameters are not in the actual production value should be placed in the appropriate location of a certain number of the valve to be adjusted to achieve the production requirements,can be a double adjustment,that is both automatic and manual adjustment coexist,and at any timeswitch.。