Multiple Effect Evaporator System Research Articles

Techno-economic and environmental analysis of high temperature heat pumps integration into industrial processes: the ammonia plant and pulp mill cases

Heat pumps will play an important role in improving the performance of the industrial processes aiming to decarbonize their heating requirements. Yet, defining the best operating conditions of those devices may be a challenging task, as they are embedded in larger energy conversion systems and in direct competition with fired and electric heaters and other waste heat recovery systems. The costs of the energy inputs also influence the selection of either a heat pump or a gas boiler, which affects the overall efficiency and the incremental cost of the final solution. Thus, a systematic analysis must be applied in order to determine the best option to supply the heating requirement, without considerably impacting the operational feasibility of the overall plant. In this work, the base-case performance of two industrial applications with intensive heating demand, namely, the solvent regeneration process of a carbon capture unit and the black liquor concentration process of a kraft pulp mill, are compared to that of the scenarios in which a high temperature heat pump or a mechanical vapor recompression unit are integrated, aiming to reduce the energy consumption and the environmental impact. The benefits of the integration of a heat pump or a mechanical vapor recompression unit over a conventional reboiler and a multiple effect evaporation system are discussed in the light of thermodynamic, economic and environmental indicators. As a result, the alternative approaches remain competitive vis-à-vis the conventional solutions in terms of energy consumption and operating costs. In addition, the emissions associated to the heating applications could be reduced by 45% if a high temperature heat pump is integrated. The optimized solution using a heat pump has an overall exergy efficiency 9% higher compared to the typical configuration of the ammonia plant. In pulp mills, the integration of mechanical vapor recompression systems slightly affects the performance compared to the conventional scenario with a multiple effect evaporation system.

Application of a predictive Q-learning algorithm on the multiple-effect evaporator in a sugarcane ethanol biorefinery

With the recent development of machine learning, reinforcement learning is an interesting alternative to PID controllers. In this context, a discrete predictive Q-learning approach is applied in the control of a sugarcane biorefinery multiple-effect evaporation system. The algorithm is built using Scilab and learns to control the multiple-effect evaporator outlet concentration by manipulating its feed steam flow rate. Based on multiple episodes, the state-actions that consist of discrete changes in steam flow rate are chosen with a greedy algorithm. In order to increase the training efficiency and overcome the large dead time of the system, a neural network is applied to predict the outlet concentration of each control action after reaching the steady-state. The control policy was built and tested through simulations on a phenomenological model. The controller performance was evaluated in set-point tracking and disturbance rejection tests and compared with PID responses. The research showed that the Q-learning controller exhibited better performance than the PID controller.

Application of fuzzy control in the evaporation stage of a first- and second-generation sugarcane ethanol biorefinery

Sugarcane bagasse is a cheap feedstock for one of the most significant biofuel technologies currently being developed: second-generation ethanol (E2G). Most studies regarding E2G production investigate ways to improve the efficiency of this technology. However, studies about its control are still very sparse. In this work, we tried to partially fulfill this gap, addressing the control of a multiple-effect evaporation system of a sugarcane biorefinery. A feedforward fuzzy controller was proposed with membership functions based on a dynamic phenomenological model developed in Environment for Modeling, Simulation, and Optimization (EMSO). This software was also used to carry out simulations to evaluate the disturbance rejection performance. Inference tools based on neural networks and proportional–integral (PI) controllers were also proposed as support to the Fuzzy control system. The tests showed that the Fuzzy scheme outperformed traditional proportional–integral–-derivative (PID) controllers, settling on average 66% faster with a 72% reduction of integral time absolute error (ITAE).

Sustainable cleaner production technologies and treatment of segregated effluent streams with recovery of quality salt, chromium & water

Conventional process and treatment system adopted by Indian and Global Tanneries consist of Segregation of Spent Chrome Stream and discharge of supernatant for combined treatment along with effluent from all sectional operations starting from soaking to finishing, Conventional physiochemical and biological treatment for reduction of Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), etc., Ultra-filtration and Reverse Osmosis (RO) system for recovery of water and Multiple Effect Evaporator (MEE) for the evaporation of RO reject stream and generation of mixed salt in case of Zero Liquid Discharge (ZLD) system and Storage of mixed salt recovered from the MEE system for which no viable disposal system is found. Establishment of treatment system for the mixed stream results in poor performance of biological treatment units, increases the Operation & Maintenance (O&M) cost and accumulation of recovered mixed salt in case of ZLD system. It is estimated that, more than 8-10 tones of mixed salt is generated during the treatment of 1.0 MLD effluent under ZLD system. To address this serious environmental problem, an innovative approach of segregation of saline streams such as soak liquor and chrome liquor are planned to be collected separately with the feasibility of recovering reusable quality salt and chromium in the form cake for regeneration and use in the form of Basic Chromium Sulphate (BCS) by the tanneries. This innovative treatment concept has been developed and is being implemented in many Common Effluent Treatment Plants (CETPs) in India. This will become the first of its kind in Global Leather World. This developmental scheme is in accordance with the guidelines and recommendations of UNIDO in terms of sustainability of ZLD system for leather sector. The technological developments on cleaner productions, centralized chrome recovery reuse system, segregation of saline soak water for separate treatment with recovery of water and quality salt are dealt in this technical paper.

Thermal integration analysis and improved configuration for multiple effect evaporator system based on pinch analysis

Pinch analysis for a sugar plant production capacity 4000 TCD has been carried out to reduce its energy consumptions. The plant has ten evaporators that can be configured to several multiple effect evaporators. It has been running with five-effect evaporator (quintuple) scheme. To maximize energy utilization within the plant, three multiple effect evaporator schemes were evaluated. They are triple effect evaporator, quadruple effect evaporator, and quintuple effect evaporator as the benchmark. The result shows that the quintuple effect evaporator yields the highest energy efficiency by about 10%. Options to achieve such target is to use low pressure steam only for the first effect and to use steam bleeding from the first effect to heat a tertiary juice heater. With this proposed scenario, sugar dryer, wash water RVF unit and wash water HGF unit no longer need external steam for its operation.

Cost analysis of multiple effect evaporation and membrane distillation hybrid desalination system

This work addresses the feasibility of a previously proposed hybrid desalination system comprising multiple effect evaporation (MEE) and membrane distillation (MD) processes. The feasibility study introduced here focuses on the impact of the hybridization of two separate processes on desalination plant economics. The water cost of the hybrid system is found to be 2.05 $/m3, which compares well with previously reported values and is 17% lower than that of standalone MEE system. The sensitivity of the water production cost to the MD feed flow rate indicated the existence of an optimal cost at a single-pass feed flow rate of 900 L/h. In addition, the sensitivity of the water cost with respect to the MD unit cost indicated a 0.0084 $/m3 change in water production cost for every unit change in the MD module cost. A modified structure of the hybrid system that leverages the thermal energy of all MEE effluents has also been suggested. With this system, the overall water recovery ratio can reach as high as 52% and the water cost can further be reduced to 1.84 $/m3.

Integration of multi effect evaporation and membrane distillation desalination processes for enhanced performance and recovery ratios

This work focuses on the integration of multiple effect evaporation (MEE) and membrane distillation (MD) processes. The MEE brine is treated by the MD allowing at the same time a preheating of the MEE feed water. Different structures of integration are assessed theoretically. Simulation models based on the heat and mass transfer balances are developed for the parallel feed (PF), parallel cross (PCF), forward feed (FF)-MEE, and direct contact MD (DCMD) configurations. The main performance parameters such as the performance ratio, recovery ratio, and specific energy consumption are investigated via simulation of various MEE-MD configurations and operating parameters. The results show that hybrid MEE and MD structures outperform the standalone MEE systems. The performance ratio increased by more than 25% when hybrid structure is used as compared to standalone MEE. The results revealed also that the hybrid parallel PF-MEE-MD configuration yields the best performance compared to other hybrid configurations. It also outperforms the standalone PCF-MEE which is widely adopted and used in practice. Besides, the performance of the hybrid configurations is especially sensitive to the feed temperature's variation in both MEE and MD units. Increasing MD feed temperatures has a positive impact on the recovery ratios of the combined systems.

Optimization of Multiple Effect Evaporation System via Modelling and Simulation

The black liquor is concentrated in a multiple evaporation system to achieve steam economy. The focus of this paper is to solve complex mass and energy balance non-linear equations and to reduce them to a simple matrix form using MATLAB. A detailed analysis is done to observe parameters effects on the entire process and on steam consumption according to the increase in the number of effects of evaporation. Complexity of the process is solved using mathematical modelling and simulation with MATLAB and MINITAB using ANOVA Analysis. The process is repeated for three-effect, five-effect and seven-effect evaporator. The comparison is analysed to show the effectiveness of steam economy and to conclude if it is beneficial to increase the number of evaporators to have effective energy conservation. According to the mathematical analysis, the number of effects is important to achieve steam economy, whereas the number of effects has no impact on parameters.

Holistic Optimisation of Solar-assisted Multiple Effect Evaporators (MEE)

The effects of heat transfer performance of systems can be studied in combination with thermodynamic performance. The design solution of maximizing heat transfer always leads to increased entropy generation else if minimizing entropy was aimed then heat transfer got minimized. Hence there is need for holistic optimization. This paper attempts to merge the two competing criteria’s - (i) heat transfer and (ii) the thermodynamic performance of a solar assisted multiple effect evaporator system and optimize study parameters for its energy efficient operation. Solar assisted multiple effect evaporators use steam as source of energy to evaporate wastewater.The idea of amalgamating these two factors is to observe how much reduction in the performance of one factor will improve the performance of the other. This study couples the two criteria, which has been dealt with separately, to arrive at the parameters of interest which must be fine-tuned for ensuring system performance.Mass flow rate of steam and wastewater appeared to chiefly influence heat transfer and entropy generation of the system, negligible influence was observed on changing the concentration of the waste water or optical efficiency of the solar concentrator in single legged analysis. However through this holistic optimization study, it was found that variations in Prandtl number, i.e., the concentration of the waste water and optical efficiency of solar concentrator drastically shift the optimization balance of entropy generation and heat transfer rate.

Energy analysis of the ethanol industry considering vinasse concentration and incineration

Nowadays, the ethanol represents the most consolidated biofuel in Brazil. Despite presenting environmental advantages in comparison with non-renewable fuels, the concern for the ethanol process residues is increasing. Among these residues, the vinasse, bottom product of distillation process, is the most important since its characteristics such as BOD, acidic nature and large volume make its disposition difficult and costly. The aim of this study is the integration of a vinasse concentration and incineration system to a conventional sugar, ethanol and electricity production process. For this study, the Aspen Plus® software was used to simulate the production process. Assuming a sugar-ethanol production plant, different scenarios were analysed considering vinasse concentration with a multiple-effect evaporator system, vinasse incineration with salt recuperation, and heat integration. In scenarios that do not assumed heat integration, the main results show that vinasse incineration is necessary to contribute to the steam generation in order to cover the steam demand of the process, including the vinasse concentration. Regarding the heat integration procedure, an appropriate placement of evaporators was achieved through the reduction of the number of effects on both the vinasse and juice evaporation systems; thus promoting a meaningful reduction in the steam consumption of the integrated process.

A Novel Approach for Detailed Modeling and Optimization To Improve Energy Saving in Multiple Effect Evaporator Systems

The multiple effect evaporator (MEE) system is a typical process for liquor concentration in the energy-intensive industries. Many approaches and commercial software have been widely used for MEE s...

Simultaneous synthesis of a multiple-effect evaporation system with background process

Multiple-effect evaporation (MEE) is one of the energy-intensive processes. To reduce the energy consumption of this process, it is effective to integrate the MEE with its background process as a whole system. In this paper, a stage-wise superstructure model is proposed, which takes all possibilities in integration of the MEE coupled with its background process into consideration. The corresponding mathematical programming model, featuring a mixed-integer nonlinear programming formulation is then presented to minimize the total energy consumption (TEC) and the total annual cost (TAC) of the system. The optimal topology and operating parameters of the whole system are determined simultaneously by solving the proposed model. The application and effectiveness of the proposed model are illustrated through a case study of a concentrating sugar juice production process. The results obtained by the proposed method agree well with those obtained by the analytical methodology in literature when the energy demand is targeted. To further clarify the advantages of the proposed method, the coupled system with the lowest TAC is also analyzed and discussed, in which the stream matches and operating parameters are determined accordingly.

Simulation of a triple effect evaporator of a solution of caustic soda, sodium chloride, and sodium sulfate using Aspen Plus

Worldwide, the Chlor-Alkali process is the most well-known method for the production of chlorine (Cl2) and sodium hydroxide (NaOH). NaOH, also known as caustic soda, is a very important alkali with many applications in the processing and production of paper, detergents, aluminum, petrochemicals, inorganics, and in the food industry. The aqueous solution of caustic soda, known as “cell liquor," produced in this process must be concentrated from 11 to 50 percent weight, which is achieved through a multiple effect evaporator system. In some cases, the brine used as a raw material carries a few other components that cannot be separated before the feeding of the brine into the process. The presence of sulfates and chloride ions in addition to high NaOH concentrations (0.44 – 0.5 mass fraction) and high temperatures (above 60 °C, at 86 mmHg) causes the precipitation of a triple salt (Na2SO4 · NaCl · NaOH). This work focuses on using and validating the model of a triple effect evaporator in Aspen Plus using plant data. According to our results, lower temperatures and the extraction of sulfates could reduce the proportion of triple salt that precipitates in the last stages of the evaporator.

Simultaneous optimisation of Multiple-Effect Evaporation Systems and Heat Exchanger Network

In recent work, a general superstructure and a Non-Linear Programming (NLP) model were presented for Multiple-Effect Evaporation Systems (MEESs). This NLP model was combined with a Heat Exchanger Network (HEN) model in order to simultaneously perform optimisation and heat integration of the overall system. The results of a forward-feed evaporation system integrated with hot and cold streams of the evaporation system as well as with the background process were presented. In this paper, the superstructure is extended by including multi-stage flash vessels for improving energy efficiency within the overall system. Additionally, various flow-patterns of heat-integrated MEES are studied. Also, trade-offs between energy and investment costs of heat-integrated MEES are explored for different numbers of evaporation effects in order to determine the optimum number of effects. The proposed Mixed-Integer Non-Linear Programming (MINLP) model of the combined MEES-HEN networks is implemented in a General Algebraic Modelling System (GAMS) and solved simultaneously using a two-step solution strategy. In the first step of the strategy, the NLP model of MEES is solved, providing an initialisation point for solving the MINLP model of the combined MEES-HEN network within the second step. A case study of a milk concentration process is used to illustrate the method. The results show that the forward feed flow-pattern with three evaporation effects is totally integrated with hot and cold process streams from the background process, and the system exhibits the minimum Total Annualised Cost (TAC).

Vinasse concentration and juice evaporation system integrated to the conventional ethanol production process from sugarcane – Heat integration and impacts in cogeneration system

In the ethanol production process one of the most polluting residues is the vinasse, which is the bottom product of distillation column. Vinasse is produced in the range of 10–15 L per litre of ethanol, and is currently used to irrigate sugarcane fields because of the presence of macronutrients (N, P, K) in its composition. However, because of the large amount produced, its disposition in sugarcane fields involves high transport costs and does not allow an adequate application, thus causing damage to soil and groundwater due to its high content of organic components. In this context, vinasse concentration with multiple-effect evaporator systems not only allows to reduce significantly its volume through the increase of its initial solids concentration, that is generally between 2 and 5%, which reduces the costs of disposal; but also allows to consider alternative ways of energetic usages, for instance, its incineration or anaerobic biodigestion. Thus, the aim of this study is to accomplish an energy evaluation of the heat integration of a juice evaporation system and a vinasse concentration system in the conventional ethanol production process by analysing three different configurations of multiple-effect evaporator systems. The energy and mass balances were solved using the EES® software while heat integration, using the Pinch Method, was applied in order to minimize the utility consumption. A simulation of the cogeneration system was also performed in order to evaluate bagasse and electricity surplus. Two configurations for the cogeneration system were studied: i) using back-pressure steam turbines and ii) using condensing-extracting steam turbines. Additionally, an economic assessment was performed in order to estimate the capital and operating costs, aiming to identify the most appropriate configuration. The results show that it is necessary to project the integration of these concentration systems taking into account the overall process. Furthermore results show that an appropriate integration of evaporation systems (Case2) could achieve steam consumption at the range of 345 kg/t cane and electricity surplus for sale of 91 kWh/t cane.

ESTUDO DA REMOÇÃO DE INIBIDORES DE FERMENTAÇÃO APÓS TRATAMENTO ÁCIDO E ENZIMÁTICO DE PALHA DE CANA

Neste trabalho estudou-se a remoção do furfural, inibidor tóxico à fermentação, formado no pré-tratamento ácido de lignocelulósicos. Experimentalmente estudaram-se no pré-tratamento diferentes concentrações de H2SO4 (1%, 2,5% e 5%) e tempos de reação (15, 30 e 60 minutos). Definiu-se como condição mais adequada 1 % m/m de ácido sulfúrico e 15 minutos como tempo de reação. Com os dados experimentais realizou-se a simulação da remoção do furfural e da concentração dos açúcares. As correntes contendo açúcares foram denominadas de C5 (hidrolisado ácido – xilose e furfural) e C6 (hidrolisado enzimático - glicose). A corrente C5 foi purificada e concentrada através de uma coluna de enchimento integrada a evaporadores múltiplos com cinco efeitos, com gasto energético de 0,85 kW/kg de xilose. Para concentrar a corrente C6 de 14 a 20% de açúcares utilizaram-se evaporadores múltiplos com quatro efeitos com gasto energético requerido de 0,34 kW/ kg de glicose.

Potential energy improvements in a multiple-effect evaporation system: case studies of heat recovery

The primary objective of this study was to quantify the amount of excess energy that is present in the evaporation system of an integrated pulp and paper-board mill and to analyze a number of energ ...

Integration of thermo-vapor compressor with multiple-effect evaporator

Thermo-vapor compressor (TVC) is used for compressing the low-pressure vapor with the help of the high-pressure motive steam, to produce the medium pressure vapor. A substantial portion of energy may be conserved by integrating TVC with the multiple-effect evaporator (MEE). The common practice in desalination industry is to compress the vapor produced in the last effect of a MEE using TVC to reduce the overall motive steam requirement. Such integration does not necessarily guarantee energy optimality. The objective of the present work is to optimally integrate TVC with a MEE system to maximize the gain output ratio (GOR). GOR is defined as the ratio of the mass flow rate of vapor produced in MEE to the mass flow rate of the motive steam supplied to TVC. GOR is the measure of the energy efficiency of MEE system. Using the principles of Pinch Analysis and techniques of mathematical optimization, a new methodology for integration of TVC with MEE is proposed in this paper. This is the first analytical methodology to optimally integrate TVC with MEE, avoiding multiple simulations of the overall system. A Theorem is proposed to directly calculate the optimal location of TVC suction position. The proposed methodology gives the designer the freedom to design an MEE-TVC with minimum energy consumption and without carrying out the detailed simulation of the entire system. The methodology is demonstrated through the illustrative case studies for concentrating corn glucose, and freshwater production through thermal desalination. In the case of corn glucose, the optimal integration of TVC with 2-effect MEE resulted in the increase in GOR by 10.1% with a decrease in the specific area requirement by 4.1%. For a desalination system with 11-effect MEE, the optimal integration of TVC improves the GOR by 1.5% and reduces the specific area by 4.3%. Furthermore, sensitivity analysis is carried out to determine the optimal operating parameters for both case studies.

Solution of SNLAE model of backward feed multiple effect evaporator system using genetic algorithm approach

This paper presents the genetic algorithm approach to solve the highly complex set of fourteen simultaneous nonlinear algebraic benchmark problem for the backward feed seven effect evaporator. Generally, Newton’s method may be considered a better numerical technique to solve such nonlinear problems. However, a higher number of effects (seven in this case) complicates the evaluation of a 14 × 14 Jacobian matrix that involves determining the analytical derivative of all system variables. Also, such a simultaneous nonlinear algebraic equations model exhibits the problem of divergence and instability when initial values have not been chosen appropriately. In this work, genetic algorithm approach has been demonstrated to be very efficient to solve such complex nonlinear models for a large number of effects in evaporative system without any complications. To make the model more realistic and representative of physico-thermal properties of liquor, boiling point elevation of the liquor during evaporation has been incorporated. Finally, the developed models are solved using genetic algorithm to determine the process variables, namely liquor and steam flow rates, which yield process performance parameters of energy efficiency (steam economy and consumption). The results indicate that a maximum steam efficiency may be achieved for a 50 % steam split in the first two effects.

Comprehensive exergy analysis of a commercial tomato paste plant with a double-effect evaporator

In this study, a detailed exergy evaluation of a commercial tomato paste plant with a double-effect evaporator was conducted in order to provide information on the system thermodynamic inefficiencies. Using energy and exergy balance equations, all components of the plant were analyzed individually and their exergetic parameters were calculated on the basis of actual operational data. The required data were obtained from Nazchin tomato paste factory located in Tehran, Iran. In addition, it was attempted to quantify the exergy utilized for processing a given amount of the tomato paste. The results showed that over 82% of the total destroyed exergy in the plant occurred in the boiler combination as the main component wasting exergy. Furthermore, exergy analysis introduced this combination as the main equipment rejecting exergy to the ambient where 4.79% of its total exergy input was lost. The rational exergy efficiency of the first- and second-effect evaporative units was found to be 65.33% and 56.60%, respectively. The specific exergy consumption of the tomato paste production was also determined as 16.83 MJ/kg. Generally, exergy concept and its extensions could be served as a powerful assessment technique to optimize the design and performance of multiple-effect evaporation systems employed in food industry.