用水与用能2

Journal Identification = CHERD Article Identification = 595 Date: May 17, 2011 Time: 5:43 am chemical engineering research and design 8 9 ( 2 0 1 1 ) 742–752 Contents lists available at ScienceDirect Chemical Engineering Research and Design journa l homepage: www.e lsev ier .com/ locate /cherd Base en impro p Defin Enrique Pa a Departmen x 607 Montréal, Q b Natural Re es, Q a b s t r a c t The development of a base-case process is a fundamental step in an energy efficiency study to obtain reliable results. However, this step is often overlooked and there are no clear guidelines for the systematic development of the base- case. A methodology has been proposed to properly define and evaluate the complete process for a subsequent in a te is ti d c p K m 1. In The analys the subjec (2007) perf three proce consisted o and of com outputs su district hea several ele Browne (19 steam con pinch analy power hous � This arti ∗ Correspon E-mail a Received 0263-8762/$ doi:10.1016/ -depth energy analysis. It consists of two stages: definition and characterization of the process, and benchmarking nalysis. In this paper, the first stage is presented. The base-case should encompass the process and the utilities sys- ms, i.e., steam and water, as they are the driving forces of the chemical transformations. A four-pronged procedure proposed to properly define and characterize a process and its utilities: data gathering, master diagram construc- on, utilities systems analysis, and simulation. Themain objective is to build a computer simulationmodel to provide etailed information on production, distribution, utilization and post-utilization treatment of steam and water. Pro- ess inefficiencies are also identified, such as the low condensate recovery or the presence of non-isothermal mixing oints. The procedure has been applied to an operating Kraft pulping mill in Eastern Canada. © 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. eywords: Energy efficiency; Base-case process definition; Utilities systems; Simulation; Kraft process; Energy opti- ization; Water optimization troduction is of the operation of the Kraft process has been t of a number of recent studies. Klugman et al. ormed an energy audit in an operating mill with ss lines of different construction period. The audit f identifying all energy and electricity consumers paring the results between the three lines. Energy ch as effluents, power generated, steam venting, ting are also quantified. A detailed description of ments required for an energy study is shown by 99). These elements include the identification of sumers, efficiency of the equipment, overview of sis and process simulation, control strategies, and e operation. Turner (1994) shows several elements cle has been submitted in two parts. Part II presents the Benchmarking analysis. ding author. ddresses: enrique.mateos-espejel@polymtl.ca (E. Mateos-Espejel), jean.paris@polymtl.ca (J. Paris). 13 September 2009; Received in revised form17 June 2010;Accepted22September 2010 required to perform a water audit. These elements include the identification of water consumers, effluents producers, effi- ciency of the equipment, and reutilization strategies. In these works, some of the aspects required in the development of a base-case process and evaluation of the energy efficiency are highlighted. However, they consider water and energy inde- pendently and fail to cast light on the interactions between the different sections of the process and between the steam and water systems. In addition, they do not present a struc- tured approach for the base-case development and for the evaluation of the different elements to be considered in an energy andwater study. Several noteworthy studieshave come from Scandinavia. Axelsson and Berntsson (2005) performed a pinch analysis in a state of the art-mill. Axelsson et al. (2006) described two typical Scandinavian mills that vary by the level – see front matter © 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. j.cherd.2010.09.012 case process development for vement, application to a Kraft ition and characterization� Mateos-Espejel a,∗, Luciana Savulescub, Jean t of Chemical Engineering, École Polytechnique de Montréal, P.O. Bo C, Canada H3C 3A7 sources Canada, Canmet ENERGY 1615 Lionel-Boulet Blvd., Varenn ergy efficiency ulping mill. Part I: risa 9, Sta. Centre-ville, C, Canada J3X 1S6 Journal Identification = CHERD Article Identification = 595 Date: May 17, 2011 Time: 5:43 am chemical engineering research and design 8 9 ( 2 0 1 1 ) 742–752 743 of water ut nities for h to study the and proces 2004). How of these m focuses on analyzing o between th The dev model of a mization a model, refe the actual ing conditi detailed an process de should not der its util results pro always give foundation taken. Guidelin and areas o liest stage o ensure suc tion of ene to as bench analysis w commitme A system model that process ben a Kraft pulp ization of th benchmark of this wor ing measur the formula completed The analys into accou that impac (Mateos-Es Improvi become an energy pric industry, it face of eme demand fo the Canadi A wide v the energy The extent reutilizatio of methodo (El-Halwagi and Smith, larger the a themore en Steamand although th 2005; Leew Thus and mo duct ent ds la s of rang rep ced confi cy. A luate alysi d on ahlq cas ft p an e rade ats t cons Co aft p ich w edia d or core erfor are (whi su emi erm e sp from rnt i nic c and reco liquo in a sche Kra t/d (a ill us ion a nt bl . Th weak r in ed th to ra drive perfo f cyli d the nsis ent ilization with the objective of identifying opportu- eat integration. These models have also been used implementation of new evaporation technologies s integration measures (Wising, 2003; Bengtsson, ever, the methodology used for the development odels is not presented. In addition, the analysis ly on the energy aspects of the process without ptions for water reutilization and the interactions e steam and water systems. elopment of a representative, reliable and focused n operating process is a prerequisite to the opti- nd fine tuning of its energy performance. This rred to as base case process, should represent process in its current configuration and operat- ons. It should be able to support a rigorous and alysis leading to alternative, energy enhanced signs that can be implemented in confidence. It contain unnecessary details which could hin- ization without improving the usefulness of the duced. This critical and preliminary task is not n the importance it deserves even though it is the of all process analyses that may be later under- es and targets that identify process inefficiencies f most likely gains should be formulated at the ear- f a retrofit project in order to channel efforts and cess of the development, assessment and selec- rgy enhancement options. This task is referred marking. A thorough and careful benchmarking ill later reduce the deployment of resources and nt of expenditures. atic stepwise method to construct a base case meets those criteria and to execute effectively the chmarking step has been developed and applied to ing mill in operation. The definition and character- e base case are presented in Part I of this paper, the ing analysis in Part II. The anticipated sequence k, i.e., the identification of potential energy sav- es, their technical and economic evaluation and tion of an implementation strategy has now been and presented by (Mateos-Espejel et al., 2010b). is has been based on a novel method which takes nt the interactions and synergies of all systems t upon the energy profile of the optimized process pejel et al., 2010a,b). ng energy efficiency in chemical processes has important issue in times of volatile and increasing es. In the case of theCanadianpulp andpaper (P&P) is also part of a strategy to remain competitive in rging pulp producing countries at a time when the r paper commodities, the traditional mainstay of an industry, is shrinking. ariety of enhancing techniques is used to improve efficiency of a feedstock transformation process. of internal heat recovery and the degree of water n are often the most important. A broad spectrum logies has been developed to address the problem and Manousiouthakis, 1989; Linnhoff, 1993; Wang 1994; Dhole, 1998). In a typical Kraft process, the mount of water consumed and effluent produced, ergy is required for heating, cooling, and pumping. water systems are usually analyzed independently, ey are strongly interconnected (Savulescu et al., ongtanawit and Kim, 2008; Mateos-Espejel et al., 2008). steam The on pro treatm depen source cover a so as to introdu torial efficien to eva for an depen 2006; D The ing Kra part of high g and tre under 2. The Kr by wh interm finishe 2002). The step p fibers agent sodium and ch and th that th rated and bu inorga bonate of the green on site plified Fig. 1. The 700ad The m nificat differe ditions of the (DSC) o is pass steam trains ing is a set o ing, an pulp co equipm , the focus of the base case model is the study of water systems. del developed must provide detailed information ion, distribution, utilization and post-utilization of those utilities. The reliability of the base case rgely on the data used for its definition. Several information must be consulted and the data must e of operating conditions (e.g.winter and summer) resent the main process variations. Simplifications in the model must not modify the whole or sec- gurations of the process which affect its energy computer simulation must be designed as a tool improvement scenarios and as a source of data s (Lundström et al., 2007). Its level of details will its main purpose (Turon et al., 2005; Blanco et al., uist, 2008) e study presented below is based on an operat- ulping mill located in Eastern Canada. The mill is co-industrial cluster and, in addition to making a Kraft pulp, it exports steam to a nearby sawmill he effluent of an adjacent town; district heating is ideration. ntext rocess is the prevalent manufacturing technology ood chips are transformed into paper pulp, the te material from which a very broad spectrum of semi-finished paper products are made (Smook, of the Kraft process is a chemical delignification med in a digester where the individual cellulosic separated to form the pulp. The delignification te liquor) is a mixture of sodium hydroxide and lfide. After delignification the fibers are washed, cally bleached. Finally they are drained, pressed ally dried. A key characteristic of the process is ent delignification liquor, the black liquor, sepa- the fibers in the washing step, is concentrated n the recovery boiler to produce steam. The spent hemicals form a smelt, composed of sodium car- sodium sulfide, which is collected at the bottom very boiler. The smelt is dissolved to form the r which is recaustified with quick lime produced lime kiln, to regenerate the white liquor. A sim- matic of the complete Kraft process is given in ft mill studied has an average production of dt = air dried tons) of high grade bleached pulp. es an 8 batch digester sequence for chemical delig- nd a five stage bleaching sequence which uses eaching agents (ClO2, H2O2, NaOH) at different con- e ClO2 is manufactured on site. The concentration black liquor (BL) initially at 15% dissolved solids suspension is performed in two steps; first, the BL rough a set of pre-evaporators driven by recycled ise its DSC to 19% and then it is sent to two parallel n by live steam to reach a final DSC of 75%. Dry- rmed in two steps: first, the pulp passed through nders where water is evaporated by indirect heat- n hot air is used to attain the final specification of tency. A steam turbine is used to entrain the drying . Journal Identification = CHERD Article Identification = 595 Date: May 17, 2011 Time: 5:43 am 744 chemical engineering research and design 8 9 ( 2 0 1 1 ) 742–752 e Kra 3. Me The object tion requir be used fo go beyond steam audi ity consum process eva to water or tion. The m steam toge critical to a ment, defin of steam an puter simu order to ob for a comp The bas steps: • Data gat • Master d • Systems • Simulati The sys tify ineffici benchmark 3.1. Da The data t water beha (i.e., steam mation can of the mill instrument contain de streams (i. data collec tions signifi pulp produ ering the d is perform mation. Th post-utiliza tion 3.3. Th den ing c l pro diff pti ust b Ma ter d l sig ted f orm s sec and s dia mpu nne uct t te fa res s it op Sys ystem rme iliza e v ed at vario ct or enta Fig. 1 – Simplified diagram of th thodology ive of this methodology is to detail the informa- ed for the development of a base-case that will r a water and energy study. The aspects treated what is commonly encompassed in an water and t. Audits usually focus on the identification of util- ers and producers without specifying the type of luation that will be perfomed. Audits are applied steam but rarely include both systems in conjunc- ethodology presented deals with the water and ther, and in addition it integrates other subjects n energy efficiency study: data collection and treat- ition of the process boundaries, characterization d water networks and, the construction of a com- lation. These issues must be reigorously treated in tain a reliable simulation model that can be used lete and detailed evaluation of the process. e process simulation model is constructed in four hering iagram analysis on tematic application of these steps will help iden- encies in the steam and water systems prior to the ing analysis which will be the object of Part II. ta gathering o be collected should represent the thermal and to broa operat ationa The consum tion m 3.2. A mas and al extrac to perf proces loops, Thi the co interco constr evalua measu and un 3.3. Both s be pefo and ut Som record • The • Dire • Perc viour of the process over a long period of time and water consumption for one year). This infor- be obtained from the data acquisition system , from arechived data, and from the process and ation diagrams (PIDs). PIDs are very useful as they tails of the individual process units and process e., temperatures, flowrates, concentration). The ted should be particularly detailed for unit opera- cantly affected by seasonal variations, changes in ction or recurrent technical problems. After gath- ata, a preliminary overall water and steam balance ed to identify inconsistencies or a lack of infor- e specifics about the production, utilization, and tion of steam and water are discussed later in Sec- e utilization of several sources of information helps • Water te • Water re • Inefficien out preh instead o • Sections This inf of details re process. 3.4. Co The proces tive to stu ft process. the scope of the subsequent analysis as different onditions can thus be evaluated and possible oper- blems pinpointed. erence between the data on steam production and on, and between water intake and water consump- e assessed to detect possible gross errors. ster diagram iagram where the steam and water utility systems nificant process streams are clearly identified is rom the PID’s. The AUTOCAD software can be used this task. The diagram contains the details of all tions, and major unit operations, the recirculation connection between sections. gram is an essential tool for the development of ter simulation, as all process sections and their ctions are identified. In addition, it will be used to he flow diagrams of the utilities systems, and to ctors affecting the feasibility of energy efficiency uch as the distance between the process streams erations. tems analysis s are defined in detail. Data reconciliation should d when large differences exist between production tion. ery important characteristics of the utilities are this stage: us fuels used to produce steam indirect heating ge of condensate recovery mperature levels utilization strategies cies such as the utilization ofmake-upwaterwith- eating or utilization of pressure release valves f cogeneration with the highest consumption of water and steam. ormation is used as a guide to determine the level quired in the simulation in the different part of the mputer simulation s is simulated in a water-energy oriented perspec- dy the interactions between the utility systems Journal Identification = CHERD Article Identification = 595 Date: May 17, 2011 Time: 5:43 am chemical engineering research and design 8 9 ( 2 0 1 1 ) 742–752 745 Table 1 – and utiliz Steam prod Biomass Fossil fue Recovery Recovery Desuperh Total Steam utili Total MP Total LP Total HP Total Production and evalua procedure encompass the definiti steam syste state and it The obje and water flowsheet a tems flows process sec energy effic by a compa A real p ments of op variations, and water c ues contai imperfectio lation shou the real pro 4. Ca 4.1. Da For this cas tion: measu and2005 fo extracted fr est consum A low a found for th This differe high cost o good monit applied to between w large differ perhaps ju however sin process at a perature. T the mill en PID’s and a 2 – ation wate ted w ened l utili ted ened l −util gap iliati Ma cific hite ater ives r of The am is us n. St sh w puts satis near ed b ng m , wa ma s are s ut y po uctio Sys Average mill data for the overall production ation of steam. Mass flow (t/h) measured data uction description boiler (BI) 64.7 l boiler (FF) 29.5 boiler (RB1) 89.0 boiler (RB2) 37.5 eating water 55.7 276.4 zation description 85.2 170.2 32.4 287.8 −utilization −11.4 (4% diff.) te potential energy enhancement measures. The developed for the construction of the simulation es: the modeling of the process unit operations, on of the required level of details in the water and ms, the convergence of the simulation to a steady s validation. ctive is to represent the unit operations as steam consumers. The starting points for the simulation re the process master diagram and the utility sys- heets. The level of details used to describe specific tions depends on their potential impact on the iency of the process. The simulation is validated rison between simulated and measured data. rocess is never in a true steady state; local adjust- erating conditions, equipment turn over, feed rate etc. cause constant fluctuationswhich affect steam onsumptions. Moreover, measured parameter val- n noises or errors (random or gross) caused by ns of sensors and recording equipment. A simu- ld hopefully represent a long term average state of cess. se study ta gathering Table utiliz Input Trea Scre Tota Water Trea Scre Tota Input fill the reconc 4.2. All spe pulp, w also w Fig. 2 g numbe oped. the ste Water ductio the fre The in fuel to from a are dry facturi boilers The utilitie proces identif constr gram. 4.3. e study there are two principal sources of informa- red archived values for different years (2002–2003 r steam; 2006 forwater) and the PIDs. Thedatawere om this sample for the two periods with the high- ptions; winter for steam and summer for water. nd very tolerable discrepancy of 4% (Table 1) was e steamdata averaged over the 2005winter period. nce is within the range of process variability. The f steam may have been a reason to maintain a oring of all steam users. The same procedure was the water system (Table 2) but a difference of 34% ater intake and consumption was observed. This ence may be due to poor monitoring of water usage stified by its low cost. This is not a good practice ce very large quantities ofwater are used in a Kraft temperature which is well above the intake tem- he cost of water heating is a significant share of ergy bill. An analysis of the water streams in the comparison to the current practices were used to The energy proper man in this secti the distribu within each 4.3.1. Ste Initia