Simultaneous targeting and design for cooling water systems with multiple cooling water supplies

This paper presents a technique for simultaneous targeting and design in cooling water systems comprising of at least two cooling towers and several cooling water using operations. The presented technique is based on a superstructure from which a mathematical formulation is derived using system specific variables and parameters. It is demonstrated that in a system like this, true optimality can only be realized by a holistic consideration of the entire cooling water system. Consideration of individual subsets of cooling towers with their dedicated cooling water operations yields suboptimal results. Four operational cases are considered and structural considerations of corresponding mathematical formulations presented. The first case results in a linear programming (LP) formulation, the second case yields a mixed integer linear programming (MILP) formulation whilst the other two cases yield mixed integer nonlinear programming (MINLP) formulations which cannot be exactly linearized. However, in all cases significant improvements in excess of 40% were realized in targeting, without compromising the heat duty of the cooling water using operations. The main objective of this investigation is to debottleneck the overall cooling water supply for the cooling water network.     

Process‐based graphical approach for simultaneous targeting and design of water network

A new process‐based graphical approach (PGA) is presented for the simultaneous targeting and design of water network. The PGA is extended from the limiting water profile which was developed for flow rate targeting for a water network. Via PGA procedure, apart from locating the minimum freshwater and wastewater flow rate targets, the water network that corresponds to the minimum flow rate targets is also synthesized simultaneously. The proposed approach handles both fixed load (including operations with water loss and/or gain) and fixed flow rate problems equally well. In addition, the approach can be used to synthesize direct reuse/recycle, regeneration reuse/recycling, and total water network. Furthermore, the proposed approach is applicable for water network with multiple freshwater sources. Three literature examples are presented to illustrate the proposed approach. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Automated parallel polyurethane dispersion synthesis and characterization

The synthesis of waterborne polyurethane dispersions (PUDs) using an automated parallel reactor system was explored. Waterborne PUDs are an important class of polymer dispersion that can be used in many applications such as coatings for wood finishing, glass fiber sizing, adhesives, automotive topcoats, and other applications. Herein, we present the synthesis of aqueous PUDs using a Chemspeed Autoplant A100™ automated parallel reactor system. This is the first time a PUD has been synthesized using an automated parallel reactor system. The synthesis involves the formation of an isocyanate-terminated prepolymer followed by neutralization, dispersion in water, and chain extension. Details of the methodology are discussed with respect to the process of writing the program for the synthesis to synthesizing the PUD itself with the Chemspeed. It is demonstrated that an aqueous PUD can be synthesized with an automated parallel process and the unit-to-unit results are similar. Process variables such as agitator design, rate of neutralization, and rate of water dispersion are varied as these are the three major factors which lead to the desired end product property. The controlled addition of neutralizer, water, and chain extender is an added advantage with this automated technique and gave consistent results in all the units. The PUDs were characterized for their particle size, viscosity, and percent solids.     

WATER NETWORK ANALYSIS IN PULP AND PAPER PROCESSES BY PINCH AND LINEAR PROGRAMMING TECHNIQUES

Two water network optimization methods are presented. Both can be utilised to establish, without detailed design, whitewater network configurations that would minimize fresh water requirements and waste-water rejects while respecting critical contamination constraints. The essentially graphic pinch-type analysis is partially automated; it is only applicable to one contaminant system. Linear programming appears to be a more powerful tool because it can be applied simultaneously to several contaminants to be removed and fine fibers to be retained in the system while fresh water consumption is minimized. It is fully automated and particularly well adapted to large size problems. Both methods have been applied to industrial case studies with interesting results. In the case of the water network of the alkaline zone of a de-inking plant no fresh water consumption reduction was obtained, but it was shown that network rearrangement could eliminate the need for a filtration step. In the case of the complete whitewater network of an integrated newsprint mill, it was shown that it is possible to reduce the fresh water consumption by two thirds.     

Water network analysis in pulp and paper processes by pinch and linear programming techniques

Two water network optimization methods are presented. Both can be utilised to establish, without detailed design, whitewater network configurations that would minimize fresh water requirements and waste-water rejects while respecting critical contamination constraints. The essentially graphic pinch-type analysis is partially automated; it is only applicable to one contaminant system. Linear programming appears to be a more powerful tool because it can be applied simultaneously to several contaminants to be removed and fine fibers to be retained in the system while fresh water consumption is minimized. It is fully automated and particularly well adapted to large size problems. Both methods have been applied to industrial case studies with interesting results. In the case of the water network of the alkaline zone of a de-inking plant no fresh water consumption reduction was obtained, but it was shown that network rearrangement could eliminate the need for a filtration step. In the case of the complete whitewater network of an integrated newsprint mill, it was shown that it is possible to reduce the fresh water consumption by two thirds.     

Coupling pinch analysis and rigorous process simulation for hydrogen networks with light hydrocarbon recovery

In refineries, some hydrogen-rich streams contain considerable light hydrocarbons that are important raw materials for the chemical industry. Integrating hydrogen networks with light hydrocarbon recovery can enhance the reuse of both hydrogen and light hydrocarbons. This work proposes an automated method for targeting hydrogen networks with light hydrocarbon recovery. A pinch-based algebraic method is improved to determine the minimum fresh hydrogen consumption and hydrogen sources fed into the light hydrocarbon recovery unit automatically. Rigorous process simulation is conducted to determine the mass and energy balances of the light hydrocarbon recovery process. The targeting procedures are developed through combination of the improved pinch method and rigorous process simulation. This hybrid method is realized by coupling the Matlab and Aspen HYSYS platforms. A refinery hydrogen network is analyzed to illustrate application of the proposed method. The integration of hydrogen network with light hydrocarbon recovery further reduces fresh hydrogen requirement by 463.0 m³·h^-1 and recovers liquefied petroleum gas and gasoline of 1711.5 kg·h^-1 and 643 kg·h^-1, respectively. A payback period of 9.2 months indicates that investment in light hydrocarbon recovery is economically attractive.     

Gradient‐Direction‐Pattern Transform for Automated Measurement of Oil Drops in Images of Multiphase Dispersions

The automated detection and measurement of oil drops in multiphase fermentation systems are important for mass transfer analysis. A novel computer technique for automated detection of oil drops in images is presented in the context of a stirred tank containing a three‐phase water‐oil‐air dispersion. The technique is an original feature extraction transform designed for the detection of objects with a characteristic appearance. The proposed transform, denominated gradient‐direction‐pattern (GDP) transform, utilizes naturally occurring patterns in the orientation of the local gradient appearing in test images. The GDP transform was used to demonstrate the feasibility of automatically estimating oil drop‐size unbiased distributions which is an important task in the chemical and other related industries.     

A new technique for simultaneous water and energy minimisation in process plant

This paper presents a new technique for simultaneous minimisation of water and energy in process plants through a combination of numerical and graphical tools. The technique consists of three steps, namely, setting the minimum water and wastewater targets; design of minimum water utilisation network, and finally, heat recovery network design. This technique offers two key advantages over current state-of-the art techniques. Firstly, it is applicable to mass transfer based and non-mass transfer based water-using operations. Secondly, it introduces a new graphical visualisation tool through a plot of temperature versus stream flowrate, termed as heat surplus diagram to guide water and energy reduction simultaneously. The heat surplus diagram provide insights on the energy demand as well as on stream matching scenarios during design of a maximum water and energy recovery network. A case study on a paper mill plant demonstrates that significant reductions in water and energy consumption can be achieved using this approach.     

最小化新鲜水量与废水处理量的图形方法

水分配网络由回用、再生和废水处理3个相互作用的子系统构成。设计水分配网络需考虑质量负荷固定和流量固定两类用水操作模型。目前,兼顾两类用水操作的图形方法对水分配网络的研究局限于一个或两个子系统的设计,而缺少一种能同时处理3个子系统的方法。本文用新的方法合成了反映用水网络水源盈亏情况的总组合曲线,并由此得到最小废水量和新鲜水量。为考虑废水再生情况,提出通过用再生水线和废水线合成废水排放线的方法求解再生情况下的最小新鲜水量。同时,根据总组合曲线得到了废水组合曲线,求得最小废水处理量。实例表明,本文所提方法可在具体网络设计前,在同一浓度-质量负荷图中确定单杂质水分配网络的各目标参数,且简便易行。     

考虑热集成的用水网络优化

提出了新的同时考虑间接传热和混合传热的热集成转运模型,并与用水网络超结构NLP模型结合以求取ΔTmin＝0℃时用水网络的公用工程目标。新转运模型与以往的模型相比变量数和约束方程数都大大减少。进一步,针对现有综合方法ΔTmin不可调的局限性,采用改进的换热网络转运模型,提出了区分处理混合传热和间接传热的综合方法。该方法不仅可以得到优化的公用工程费用和换热匹配数,而且与传统的方法相比可以调整ΔTmin,得到更合理的换热网络结构。算例表明,结合新转运模型的NLP模型与结合改进转运模型的综合方法都要优于以往的模型和方法。     

Code-generator-based software package for defining and solving one-dimensional,dynamic, catalytic reactor models

A code-generator-based software is presented which automatically generates FORTRAN subroutines describing a tubular catalytic reactor from simply structured xml-input files specifying the reacting species and reaction network. These routines are then linked to the adaptive partial differential equation (PDE) solver BACOL, which has been extended to allow direct execution from within MATLAB. A unique feature of the presented subroutine-generator is the option for an automated simplification of heterogeneous reaction networks into global Langmuir–Hinshelwood-type reaction rates using a quasi-equilibrium approximation. Using a water–gas shift reaction mechanism published by Mhadewshwar et al., the high-computational performance of the presented software is demonstrated and the impact of the automated approximations upon the solution as well as the simulation’s computational performance are investigated.     

Dual-objective optimization of integrated water/wastewater networks

The dual-objective optimization of an integrated water/wastewater network (IWWN) is addressed by targeting for minimum fresh water consumption at the same time with operating costs reduction. An IWWN is a recycle system composed of two oriented graphs, the first encoding the water-using units (WUs) and the second, the treatment units (TUs). Although internal recycles are forbidden ab initio for the WUs graph, external recycles from the appropriate TU to the WU whose inlet restrictions are met by the partially treated water are encouraged. The corresponding mathematical model was written. A synthetic example is proposed and analyzed under several scenarios with respect to the fresh water consumption, the magnitude of internal and treated water reuse and the investment/operating costs related to the active pipes network. A comparison is made regarding the differences in network topology and fresh water consumption implied by different points from the Pareto front (PF).     

A graphical technique for the design of water-using networks in batch processes

This paper presents a graphical technique for the design of water-using networks in batch plants. Water integration is achieved by exploiting all possibilities of water reuse/recycle to minimize not only freshwater consumption, but also wastewater generation. Since time limitation for unmatched operating periods may be the primary barrier to the integration in batch processes, the installation of storage facilities is quite common to enhance the water recovery. For that reason, the cost in terms of storage facilities becomes another issue to be considered. This work is focused on network design, like the second stage of conventional pinch analyses. Some useful concepts and principles addressed in literatures are adopted to help the design of batch water network and to ensure the maximum recovery, thus the utility usage, the network structure and the storage policy can be obtained through the analysis. Once the freshwater expenditure is determined, workable ways are sought to cut the number of storage tanks and they also reduce the network complexity. In the context of this paper, a hybrid system that includes different type of water-using operations with distinct operating modes is taken into account to display the versatility of proposed approach. Furthermore, considering the fact that sometimes water reuse/recycle between certain operations is not allowed to prevent operational problems, the action of network design should be more deliberate owing to additional restraints. Therefore, the potential for water integration may be diminished, which means a less amount of water recovery. Finally, an illustrative example is provided to amplify the application of proposed approach. Like most graphical techniques, the presented work is restricted to a single key contaminant.     

Segregated targeting for multiple resource networks using decomposition algorithm

A generalized decomposition technique is presented for determining optimal resource usage in segregated targeting problems with single quality index (e.g., concentration, temperature, etc.) through pinch analysis. The latter problems are concerned with determining minimal resource requirements of process networks characterized by the existence of multiple zones, each consisting of a set of demands and using a unique external resource. However, all the zones share a common set of internal sources. The decomposition algorithm allows the problem to be decomposed into a sequence of subproblems, each of which can in turn be solved using any established graphical or algebraic targeting methodology to determine the minimum requirement of respective resource. This article presents a rigorous mathematical proof of the decomposition algorithm, and then demonstrates its potential applications with case studies on carbon‐constrained energy sector planning, interplant water integration, and emergy‐based multisector fuel allocation. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Pressure drop considerations for heat exchanger network grassroots design

Pressure drop is an important issue in design of a heat exchanger network (HEN), which has yet to be addressed properly. To overcome pressure losses incurred when streams flow through heat exchangers, pumps/compressors must be installed. The total cost for a system of pumps and compressors consists of the purchase cost of equipment and the electricity cost to run these equipment. This cost could occupy a significant part of the overall cost for a HEN design. Therefore, the pressure drop aspect should be considered together with the costs for heat exchanger area and utility consumption. A new approach is proposed to consider the pressure drop aspect in the overall context of a HEN design. Firstly, the optimal ΔT_min is determined through three-way trade-offs between area, utility and pressure drop at the targeting stage. As a result of targeting, targets for area, utility and pressure drops can be established ahead of the network design. Then a network structure is initialised at the determined ΔT_min and optimised to achieve a final design. In this procedure, the pressure drop is considered at both the targeting stage and the design stage in a systematic manner.     

FDT: A technique for direct study of water attack at the silane-filler interface

A technique is presented for the direct study of water attack at the silane-filler interface. This technique, Filler Desorption Test (FDT), involves observations of surface tension changes which occur when a silane-treated filler is floated on a water surface. If all the silane has been appropriately cured to form one integral polymerized siloxane network, then the rate and degree of surface tension lowering are a sensitive measure of the adhering tendency of the polymerized silane film. Data are presented which suggest that, all other things being equal, the strength of the coupling agent (C.A.)-filler bond under water attack can be assessed by observation of the ease with which the first small amount of polymerized silane leaves the filler and the relative degree of hydrophobicity of the resulting surface. FDT is a new tool for fundamental studies of the coupling agent-filler interface and interphase. The method also allows rapid screening and evaluation of a wide range of chemical and physical modifications designed to improve C.A. response on various filler systems.     

基于最大水回用规则的遗传算法用水网络优化

超结构用水网络规模大、结构复杂、求解比较困难。本文提出了基于最大水回用规则的遗传算法用水网络优化设计方法,该方法按出口浓度的单调性进行排列,使进口浓度或出口浓度达最大值以确定用水量,简化了用水网络超结构及数学模型。以最小新鲜水量为目标,以过程之间回用水量和废水量为基因,对简化后的用水网络运用遗传算法进行了优化设计。遗传算法采用浮点数编码方法,运用了算术交叉技术和种群间交叉技术。计算实例表明,本文所提方法可行,能利用最大水回用规则简化用水网络,并快速求出其最优解。     

SePTA—A new numerical tool for simultaneous targeting and design of heat exchanger networks

Pinch Analysis is an established insight-based methodology for design of energy-efficient processes. The Composite Curves (CCs) is a popular Pinch Analysis tool to target the minimum energy requirements. An alternative to the CCs is a numerical technique known as the Problem Table Algorithm (PTA). The PTA however, does not show individual hot and cold streams heat cascades and cannot be used for design of heat exchanger networks (HEN). This paper introduces the Segregated Problem Table Algorithm (SePTA) as a new numerical tool for simultaneous targeting and design of a HEN. SePTA shows profiles of heat cascade across temperature intervals for individual hot and cold streams, and can be used to simultaneously locate pinch points, calculate utility targets and perform SePTA Heat Allocation (SHA). The SHA can be represented on a new SePTA Network Diagram (SND) that graphically shows a heat exchanger network together with the amount of heat exchange on a temperature interval scale. This paper also shows that SePTA and SND can be a vital combination of numerical and graphical visualisation tools for targeting and design of complex HENs involving stream splitting, threshold problems and multiple pinches.     

含再生再利用的用水网络的优化设计

对单组分含再生再利用的用水系统,提出了一种基于序贯操作模型的整体优化设计方法。该方法分别针对单组分含再生再利用的用水网络设计可能存在的三种情况,以新鲜水和再生水用量最小为目标,给出了相应的设计策略,数学的表达是一个非线性规划。首先依据规则将操作对贫流的要求进行分段排序,并通过引入操作的质量交换分配系数αi,将各操作依据规则虚拟地分配为再生前过程和再生后过程,然后按操作序列逐级进行操作和操作水源之间的的优化匹配,建立含再生再利用的用水网络的序贯操作模型,最后将此综合问题归结为非线性规划问题来求解,从而完成用水过程的设计。给出了一个实例,计算结果表明本文方法是有效和简便易行的。     

Spray-assisted layer-by-layer assembly of decorated PEI/PAA films: morphological,growth and mechanical behavior

The development and study of new smart materials is an emergent research area with high potential applications. In this study, we have fabricated poly(ethyleneimine)/poly(acrylic acid) multilayer films on glass substrates by automated spray-layer-by-layer (spray-LbL) technique. By analyzing the changes in thickness, roughness and elasticity, with fine-tuning of the operational parameters of the spray-LbL system, evident trends of its effect on the multilayer construction were observed. In the case of its mechanical properties, the stability of Young’s modulus (up to 8.25 GPa) from film thickness at this scale was detected, making it variable for other factors such as pH and molecular weight. This work also identified the healability phenomenon that is present in the exponentially grown PEI/PAA samples, based on the reduction in viscosity of the polymer complexes and the interdiffusion of polyelectrolytes at the damaged zones in the presence of water. These properties allow for the assembly of a highly electrically conductive multilayered film by dispersion of a top layer of silver nanowires whose sheet resistance is increased around 5% after multiple damaging events. These experimental results provide new data for the evaluation and design of polyelectrolyte multilayers assembled with a spin-assisted automated spray deposition system to serve as substrates for mechanoelectrical devices which can benefit from its self-healing and modulated mechanical capabilities.