多组分精馏流程优化.doc

Distillation process of energy saving and optimization design is discussed Zhangweiwei and Zhaolong(Daqing chemical research center process development room )Abstract: the process of distillation of energy-saving, to reduce energy consumption, lower production costs and protect the environment has the extremely vital significance. In the process of distillation can be used in most appropriate reflux ratio and the optimum operation state, using the incoming among condenser and middle transformation reboiler, efficient distillation, heat pump distillation. Reasonable arrangement of multi-composition material separation process, using directly process heat exchanger and development application efficiency measures. This article from the best reflux ratio R choice, feeding temperature and the determination of feed state, the detailed analyses in column the design process and how to realize the design optimization problems. In order to realize the energy consumption.Keywords: the process of distillation, Energy-saving,Optimization design; Reflux ratio, Energy consumption Energy is always the concerns of the important topic. Distillation process between the relative volatility degrees, thus reduce thetower bottom transformation reboiler negative energy saving heat, first to select or devising efficient distillation equipment, followed by touching the flow of complex mixture separation arrangement, proper operating conditions and parameter is determined and much effect distillation, heat pump rectification and middle condenser, intermediate transformation reboiler rational selection, etc. Chemical industrial production in energy consumption is one of the biggest unit operations with energy prices to rectify, rising. Distillation system of energy saving of energy saving in the chemical industry plays an increasingly important position, the relevant distillation process energy saving measures have been widespread concern. Study more mainly in the following aspects: 1) for tower tower kettle, the large temperature difference between column column in a condenser or transformation reboiler, can save energy 20%. 2) using heat pump system, make bottom of low-temperature place of heat transfer to tower axe high-temperature place, also can achieve good energy saving effects 3) vacuum distillation, can increase operating components to add. Therefore shall, according to the minimum total cost principle to select appropriate In the most suitable reflux ratio under operation Reflux ratio directly influence the transformation reboiler and condenser of heat load, the net power decided distillation separation, so largely determines the operating cost, also with tower equipment investment closely related. At least reflux ratio R, near the growth, with R operating lines and balanced line in the distance between increases, reach formulary separation requirements needed tower, making the reduction of the number plate equipment costs decline. If further increase reflux ratio and tower steam flow rate and the heat exchanger heat load increases, causing tower diameter and transformation reboiler and condenser heat transfer area increases, make the equipment cost. Therefore according to the principle of minimum total cost should be to choose appropriate reflux ratio. Due to the total cost in suitable reflux ratio near little change, it is desirable R = (1.2-130) R. The total cost increase to do so is not big, but elasticity of operation but increases the many. 1.2 Using optimal feedingthermal state Feed state (with charging status parameters g says) of different, will cause tower rectifying section and mention fractions section gas-liquid flow rate changes, thus affecting R, and reach formulary separation requirements needed theory plate number and transformation reboiler and condenser of heat load. Feeding concentrations of different, namely D/F, different material liquid preheated different effects. High temperature distillation, when D/F bigger and have suitable for heating liquid materials low-temperature heat source, should as far as possible with the lower g, namely to vapor or gas mixture feeding, When D/F is lesser, should try to adopt high q value, namely to liquid feeding, because save material liquid preheating, tower kettle add heat increases very little. Cryogenic distillation, no matter how old, all the D/F g should adopt high in liquid feeding, because the tower of condensing heat load yue xiaoyue economical. For medium temperature range of distillation column reactor temperature operation, namely than air temperature, and tower temperature below the atmospheric temperature, should according to the specific circumstances, to determine the optimal incoming state. 1 3 Using directly distillation equipment in removing heat Distillation towers distillate and tower kettle residual liquid are high temperature, can use these calories to preheat into tower materials or other materials, through to the kettle decompression higher temperature liquid braising produce low-pressure steam. For tower is the multi-composition products and its bubble point and dew point significant differences, can adopt two-stage condensing heat recovery of high temperature bits. 1.4 Using heat pump distillation measures 1.4.1 Using heat pump distillation The tower will lower temperature by compressed steam as bottom transformation reboiler heat, called heat pump distillation. Heat pump distillation has three kinds of typical processes, 1) using additional working fluids, operate, 2) for direct compression, tower steam heating after as column reactor heating agent; 3) kettle liquid by throttling braising after as top cooling medium, this medium is heated gasification, then through compression warming themselves after back thetower bottom. 1 flow chooses working fluid, can be in compression characteristics, QiHuaRe silazanes have more good properties, but need to use two heat exchanger, when tower steam or cauldron liquid steam has good compression characteristics and large vaporizing latent heat Choose two process after date. 1.4.2 Using middle condenser and middle transformation reboiler In the column, the temperature inside the top to bottom is increasing gradually, if in tazhong department set, can use the middle condenser high temperature of coolant, this means can use cheaper cold source, saving effective. If in the middle of central tower set transformation reboiler, for high temperature tower, it can use low temperature of heating agent. For binary column, intermediate condenser and middle transformation reboiler use, operation line to balanced line draws close, improves the tower separation process of reversible degree. 1.4.3 Using much effect distillation To reduce the energy consumption and heating agent highest temperature slightly higher than the bottom temperature, cooling temperature slightly below the tower temperature. But the reality is, the most convenient and inexpensive coolant water or air, the most commonly used heating agent is water vapor. However, these thermit or cold agent is difficult to meet the above requirements, so nothing more often column consumed many effective. Therefore can use much effect distillation column bottom and top, as long as the temperature difference than the actual usable heating agent and the temperature difference between coolant is much smaller, can consider to use much effect distillation, much effect distillation can usually sharply reduce energy consumption.1.5 Reasonable arrangement of multi-composition material separation process Many components of material separation need to adopt more tower processes, how these towers arrangement, which components of energy, constitute the first consume influence. In order to seek the reasonable process arrangement, can use the following methods: 1.5.1 heuristics This method is easy to use, do not need to undertake is very multifarious calculations, the experience rules are as follows: 1) selection methods of separation of experience rules when key components of relative volatility degrees between a 1.05 a 1.1, unfavorable using common distillation, and should adopt to join the first of the three components separation method. Separation, should be adopted preferentially under atmospheric operation. If the column top condenser need refrigerants, should consider to absorb or extraction instead of distillation. If vacuum distillation need operation, can consider to use extraction substitute. 2） Determine the experience of separation sequence rules When the product is multivariate mixture, can directly obtained by separation tower products are the best. According to the material liquid of various components of the volatile degrees of diminishing order, which in turn make various components from the top, because the most economic ceded the various components of the liquid materials only suffered a vaporization and condensation, energy dissipation at least once.3） Relevant experience with components nature rules Liquid materials of thermal stability of poor and corrosive components first distinguish, Harmful chemical reaction, the components of the first ceded the easiest separation first, the most difficult separation (volatile degrees close to the components of), it saves net power consumption4） With the component and the economy of the relevant rules Appropriate chooses to feed liquid half-and-half separate separation, i.e. D a form, when D and form approached, the two towers in the paragraph present situation, the overall equates tower reversible increases, effective energy dissipation degree obtained decrease. Should high recovery of separation until the last, because there are many required tower board, high tower. If this and other non-critical component exists, tower ZhongQi phase flow rate will increase, tower will also increase, diameter tall and big tower will increase investment. Appropriate materials will be the content in the most component first, the components of the most ceded content, avoided to distinguish the components in subsequent tower of multiple evaporation, condensing, reducing the subsequent tower load, so more economic.1.5.2 Mathematical programming Mathematical programming has strict mathematical foundation, general guarantee can be synthesized, and an optimal separation sequence. The optimal separating synthesis nonlinear mixed integer programming problem belongs to, since want to may constitute a sequence of discrete decision making, and to every separator (tower) design variables to make continuous policymaking. Both must find out optimal separation sequence, and to find out which each separator design variable optimal value. 1 .6 Choose or to design efficient distillation equipment Column can be plate tower also can be packed tower. Overall large diameter of tray column of high efficiency and stable operation, equipment, low cost, small diameter of tray column is installed is very difficult, cost is high. Tray column suitable for processes need among heat, middle incoming or lateral-line discharging. But the pressure drop is larger, caused the increase of energy consumption, and packed tower pressure drop is relatively small, also suitable for vacuum operation, used in difficult separation of air mixture can reduce high tower. Whether tray column or packed tower key is to provide good gas-liquid contact and gas-liquid distribution, for packing tower should be may choose those efficient packing, such as corrugated has gas-liquid distributed homogeneously gas-liquid large contact area, flux, mass transfer and high efficiency, fluid resistance small etc, and is a kind of high energy efficiency of the new type filler, for plate tower is should choose and design, low pressure drop, tower board efficiency high new tower board as float valve tower and other new tower board. Efficient distillation equipment selection and design of process is to reduce energy consumption of the foundation.2 Distillation process optimization 21 using optimal reflux ratio 2.1.1 best reflux ratio Ropt determination In the column to design process and realization of distillation system optimization design of the key problems, namely for reflux ratio parameter selection. Best reflux ratio is commonly by analyzing reflux ratio and distillation system of equipment fee and CaoZuoFei relation, and then through economic accounting to determine when the sum of CaoZuoFei fee and equipment for the hour of the corresponding reflux ratio feet, namely for the best reflux ratio ruler. The pupil. However, by economic accounting decision best reflux ratio R which exist certain difficulties, in actual design process, is according to experience selection, namely the best reflux ratio R = (1.1-2.0) R surface. In recent years, considering reflux ratio feet and the energy consumption of relation, reflux ratio R value incline to smaller, namely reflux ratio R = (1.1-115) R chao. Want to more accurate calculating optimum reflux ratio R. In the following ways, can be confirmed. The factors affect reflux ratio feet can be inferred the following 3 points: 1) equipment depreciation of influence. Through the use of amortization cost years n, as equipment depreciation cost, reduce the influence of variable length ii is equivalent to increase investment costs. Namely the best tower which and the minimum number plate theory tower tower number son. The ratio of the 1,000 / son. Increase, and the optimum backflow than feet do with reflux ratio R noodles. The ratio of R/feet surface resistance. decline 2) material feeding rate influence. Material feeding rate F size will affect operating costs, material feeding rate F add the equivalent Nop/N ring fell and R. L/redundant traders. Increased. 3) the influence of structural materials. Different materials, because its price is different, thus affecting 0 0. And the ruler knock at/R song. If the carbon price as 1 treat, other material price and its ratio namely for material price coefficient sail, material price coefficient increases tsui. Show feet which/R curved increase, establish series, combining factors affecting curve Finn scottie equation and grace wood equation, can be more precise out the best reflux ratio feet which 2.1.2 And when the reflux ratio R relevant quantity 2.12.1 Reflux ratio R and CaoZuoFei and equipment fee relationship Total expenses include column, column top condenser, tower kettle transformation reboiler total equipment fee and column reactor heating agent, column top coolant in CaoZuoFei. When the reflux ratio increases, theory on plate number N decrease. Tower equipment cost reduced, it is advantageous one side. On the other hand, for the same overhead product quantity and bottom product quantity, when the reflux ratio increases. Tower back to flow and rising ZhengQiLiang all with increasing, operation expenses and condenser, transformation reboiler equipment fee increases, this is adverse side. Therefore. When the total CaoZuoFei and equipment costs and most hours, the corresponding reflux ratio feet for best reflux ratio feet hit. To the operation of the column, if dont consider equipment depreciation cost, the equipment cost for certain value, reflux ratio R increases, can make CaoZuoFei increases, so, In can satisfy separation requirements of the situation, should choose smaller reflux ratio and relieve increasingly tense energy problems. 2.1.2.2 Reflux ratio feet and energy consumption relationship Distillation system energy consumption of mainly refers to the bottom transformation reboiler heat load Q. And the heat load Q tower condenser. , both with the tower ZhengQiLiang proportional to rise, and the tower of rising ZhengQiLiang and R is proportional to the relationship. Equation is as follows: (1) the qc = (r + 1) DRd (2) (Qb = D (R + 1) a P (1) (a q | a Ig Iw) + q In determining the technology condition q, D, F are fixed value. Is it (1), (2) two type can be simplified as follows: Q = kR ten b and k seperately R. D (Iw), a Ig | D, b respectively expressed as a Ig | RdD and (Iw) D a (1 - q) F 10 q Type: D for tower distillate quantity, kmol/h, Q is for incoming state parameter, Rd for the average tower condensing heat, steam kJ/kmol; Ig, | for transformation reboiler inside of the vapor rising amount of substance enthalpy kJ/kmol;, L for thetower bottom product amount of substance enthalpy kJ/kmol; Q is for transformation reboiler heat loss, kJ. From the above simplified type can see distillation process of energy consumption with R increased sharply increased. Therefore reflux ratio R of distillation process energy consumption of play a vital role, if choose lower reflux ratio and energy consumption is decreased obviously. 2.1.2.3 Reflux ratio R and product purity relationship The column of operation, equipment is already installed, tower plate number and vapor rising for maximum flow has fixed, when should adjust the operation status of Angle to consider the influence of reflux ratio. When the tower steam flow and incoming material flow, composition, thermal condition is changeless, if increase R. Will cause overhead product quantity decreases, but the purity of product can be improved. 2.2 Choose appropriate feeding temperature and feed state 2.2.1 When the reflux ratio R certain feed temperature the effect on the energy consumption The column of operation, tower number must, when backflow plate tower distillate certain ratio, feeding temperature on the heat load of tower condenser, and with no impact thetower bottom transformation reboiler heat load inversely related inletting, the higher the temperature, the Si, then Q. The smaller. In any system, feeding temperature, can reduce thetower bottom transformation reboiler heat load. So as to achieve the purpose o