Heat Integration Method Research Articles

Transshipment Type Model for Total Site Heat Integration Using Non-Isothermal Utility Loop

There is a growing interest in developing Total Site Heat Integration methods, since Total Site Heat Integration offers an energy-saving opportunity across multiple plants beyond the traditional intra-plant plant integration. Total Site heat integration can be achieved indirectly by non-isothermal utility loop, such as hot water and thermal oil. The parameters of non-isothermal utility loop, interconnectivity patterns directly determine the energy saving and the capital cost. In this work, a transshipment type Total Site heat exchanger network (HEN) model using non-isothermal utility loop is developed. A new representation method of non-isothermal utility loop is proposed based on transshipment type HEN model to avoid non-linear terms. The model is formulated as a MINLP problem with all linear constraints. The operating cost, capital cost of heat exchangers, pumping and piping cost are holistically considered and optimized. The case study demonstrates the effectiveness of the proposed model.

Gasification process integration with existing combined heat and power plants for polygeneration of dimethyl ether or methanol: A detailed profitability analysis

Combustion of waste for cogeneration of heat and power is the most convenient and practical choice to carry out through combined heat and power (CHP) plants. But, seasonal variation in heat demand throughout the year affects the operation of CHP plants. This fluctuation in the CHP operation cause less annual operating hours for the plant equipment and is also not profitable for stakeholders. This study aims to assess the technical potential of integrated gasification process with existing CHP plants for either dimethyl ether (DME) or methanol production through refuse-derived fuel (RDF). Process integration considers that the CHP plant provides the necessary heat for biofuel synthesis during off-peak hours. Mass and heat integration methods are used to develop and simulate the polygeneration processes for heat, power, and biofuel production. Both technical and economic indicators are reported and compared to assess the potential for both biofuels through process integration. Annual operation data of a real CHP plant has been extracted to evaluate the integrated processes. A flexible gasification configuration is selected for the integrated approach i.e. CHP runs at full load to provide the heat demand and only the excess heat of CHP plant is utilized for biofuel production. The energetic efficiencies of the polygeneration systems are compared with the standalone systems. Technical analysis of process integration shows the enhancement of the operational capacity of CHP during off-peak hours and it can produce biofuels without compromising the annual heat demand. Production of methanol through process integration shows ∼67% energetic efficiency while methanol production gives ∼65%. The efficiencies are higher than standalone DME and methanol processes (51% and 53%, respectively) but lower than standalone CHP plant i.e. 81%, however the process integration increases the operating time of the CHP plant with more economic benefits. Economic analysis coupled with uncertainty analysis through Monte Carlo simulations shows that by integrating CHP with gasifier to produce biofuels is significantly profitable as compared with only heat and electricity production. But, DME as a potential product shows more economic benefits than methanol. The uncertainty analysis through Monte Carlo simulations shows that the profitable probability of DME as a product in future is also greater than methanol due to higher DME selling price. The uncertainty analysis further shows that prices of DME and methanol with waste biomass prices in future will have a greater impact on the economic performance of the proposed polygeneration process.

A heat integration method with multiple heat exchange interfaces

In recent decades, energy efficiency has become one of the key issues facing large process industries. Mounting economic, environmental and social pressure motivate energy-intensive industries to improve their efficiency. Identifying retrofit opportunities in large-scale problems is extremely complex due to numerous interconnections and dependencies between process units, sub-units and utilities present on most industrial sites. Therefore, when attempting to identify promising retrofit opportunities, methods detecting early design decisions are crucial. Techniques applying heat integration (HI) often use mathematical models and optimization to survey potential solutions. Mixed integer linear programming (MILP) is often used for industrial energy efficiency case studies due to its flexibility, solution speed and guaranteed optimal solution while taking advantage of the extensive bodies of work dedicated to this type of problem. The current work proposes a methodology based on HI and MILP to represent process energy requirements with different heat exchange interfaces. Switching from the current utility interface to an alternative one requires additional heat transfer area while it might bring operational benefits due to better system integration. The optimal combination of the processes with different interfaces is obtained by considering the trade-off between the cost of additional heat exchanger area required and decrease in the operating cost. The proposed method is applied to two industrial case studies which show the added value for HI and impact of the proposed method for reducing the problem size in heat exchanger network (HEN) design. In the first case study, the total cost of the system is reduced by 45% taking into account the cost of the modifications in the existing heat exchangers while in the second case study the computation time of heat load distribution (HLD) is reduced by 78% using the results of optimal interface selection. The proposed method provides early design decisions for retrofit solutions on industrial sites. Utilizing this methodology provides a dual benefit of identifying the most promising options for retrofit applications while also eliminating inconsequential ones at an early stage of the analysis.

Case study of power generation and CO2 emissions reduction potential from introduction of Organic Rankine Cycle on Atyrau Oil Refinery Plant Vacuum Distillation Unit

Typically process industries use high-temperature thermal energy in their multiple processes and reject low-temperature heat through cooling water and cooling towers. An introduction of low-grade heat utilization processes such as Organic Rankine Cycle (ORC) for electricity production can be considered as a viable technology for saving energy and reducing CO2 emissions. ORC market penetration is rather limited due to a difficulty of prospective investors and end-users to realize the energy saving potential. This case study investigates opportunities for introduction of ORC system on a Vacuum Distillation Unit (VDU) of Atyrau Oil Refinery plant (AORP). ORC system integration is analyzed using Pinch analysis heat integration method. Suitable temperature range, process streams were identified and ORC system simulation conducted using ASPEN HYSYS

A Comparison of Utility Heat Exchanger Network Synthesis for Total Site Heat Integration Methods

This paper compares Utility Heat Exchanger Network (UEN) design between two Total Site Heat Integration (TSHI) methods, the Conventional Total Site Targeting method (CTST) and the recently developed Unified Total Site Targeting (UTST) method. A large Kraft Pulp Mill plant has been chosen as a case study. Total Site targets have been calculated using a ExcelTM targeting spreadsheet and networks have been designed with the help of SupertagetTM for both the CTST and UTST methods. To achieve heat recovery and utility targets, both series and parallel utility heat exchanger matches for non-isothermal utilities are allowed in the CTST method, while series matches are allowed in the UTST method if the heat exchangers in series are from the same process. Series matches based on CTST method may create a dependency on two or more separate processes, which operational and control issues may occur, higher piping costs may be imposed, and utility target temperatures may not be achieved in the consecutive processes if one or more processes were to be out of service. Relaxation of the network can resolve these issues for the CTST method; however, if the relaxation occurs on the side of the utility loop that constrains heat recovery, the net heat recovery targets may not be achieved within the Total Site. The UTST method with its modified targeting procedure may offer slightly lower heat recovery targets but with simpler UEN design compared to CTST method are more realistic and achievable. Finally, after UEN design, non-isothermal utility loops need to be balanced in terms of mass and energy for both methods.

The implementation of inter-plant heat integration among multiple plants. Part I: A novel screening algorithm

There is a growing interest in developing Inter-Plant Heat Integration (IPHI) methods for reducing energy consumptions and emissions beyond that of independent plants. However, practical IPHI problems present complexities as boundaries for simultaneous intra- and inter-plant heat integration are considered. Pinch Analysis (PA) can mitigate these complexities by elucidating design insights before developing more detailed inter-plant Heat Exchanger Networks (HENs). In this paper, a novel screening algorithm based on PA and the theoretical maximum inter-plant heat recovery potential Qrecmax is proposed for practical IPHI problems. By using this screening algorithm, a large-scale IPHI problem including multiple plants is divided into several smaller sections with each section including two or three plants. Utilizing this algorithm allows for easier calculation and improved total heat recovery potentials approaching to Qrecmax. The final inter-plant HEN configuration(s) for the segregated IPHI scheme(s) are easily developed separately using PA or Mathematical Programming (MP). Before these two steps, the selection of participating streams for IPHI from individual plants is also recommended. Finally, a mathematical model is used to determine the inter-plant HEN configuration(s) in the companion paper of this study.

Optimisation of Non-isothermal Utilities Using the Unified Total Site Heat Integration Method

Total Site Heat Integration is an effective method for design of large scale utility systems that serve large chemical processes, such as refineries, petrochemicals or even lower temperature chemical and process plants. Total Site Heat Integration of different chemical plants might confront batch, semi-continuous or continuous plants which are clustered into one large site. Excess heat produced from one plant could be transferred to other plants using an intermediate fluid. In this paper, Total Site optimisation of targeting utility generation and consumption for lower temperature processes, which mainly use non-isothermal utilities, is presented. The utility temperature selection optimisation applies to the recently developed Unified Total Site Heat Integration Targeting (UTST) method. The new method shows that, for low temperature processes where non-isothermal utilities are used, the supply and target temperatures of a utility is an important constraint, while for higher temperature processes, where isothermal utilities are applied, no significant change in targets from conventional Total Site are obtained. New heuristics based on UTST method with respect to non-isothermal utility temperature selection are proposed. A Kraft Pulp Mill case study has been investigated in this research, using optimised non-isothermal utilities, showing a 3.6 MW increase in heat recovery, 0.87 MW decrease in shaft work generation, and $ 330,000 /y utility cost saving in the system applying the new UTST method compared to the conventional Total Site method.

Steam-Assisted Gravity-Drainage Performance With Temperature-Dependent Properties—A Semianalytical Approach

Summary Steam-assisted gravity drainage (SAGD) is one of the successful in-situ thermal-recovery methods for oil-sands production. In this paper, we provide a simple semianalytical model that can accurately analyze an SAGD project with variable properties. In particular, we investigate the effect of temperature-dependent properties such as thermal conductivity, heat capacity, and rock density on SAGD performance. The proposed model sequentially solves the transient nonlinear heat-transfer equation coupled with the continuity equation with Kirchhoff's transformation and the heat integral method (HIM). A criterion for timestep selection is defined on the basis of the Courant and Péclet numbers to guarantee the stability of the sequential technique. The results illustrate that the temperature-dependent physical properties affect temperature distributions ahead of steam chamber which consequently have a significant impact on the cumulative oil production and oil-production rate. Moreover, the results show that the temperature profile ahead of the steam chamber changes with time and space, and a 2D transient assumption for SAGD modeling is necessary. The semianalytical model runs in a small fraction of numerical-simulator runtime, yet it provides reasonable results. Thus, it has the potential to be used as a tool for quick SAGD evaluations.

A Total Site Heat Integration design method for integrated evaporation systems including vapour recompression

This paper presents a new Total Site Heat Integration (TSHI) method for the design of integrated evaporation systems including vapour recompression that minimises energy use and/or cost objective functions. The design of integrated evaporation systems is a common industrial chemical and process engineering problem. The method defines a new hybrid Total Site Profile (TSP) as a key element of the new design method. This profile is a composite of nearby streams that may directly integrate with the evaporation system as well as stream segments from processes that require indirect integration via the utility system. The hybrid TSP plays an important role in the iterative optimisation of evaporation system design parameters including vapour recompression and evaporation load distribution to optimise objective functions such as total cost, total operating cost, and heat recovery. The new TSHI design method for evaporation systems is demonstrated using an industrial milk processing case study.

Comparison of heteroazeotropic and extractive distillation for the dehydration of propylene glycol methyl ether

Separation section often is the most energy intensive section of an industrial chemical process, even so when there is an azeotropic mixture needed to be separated. In order to further save energy in a particular azeotropic separation system, various heat integration methods were proposed. However, because of more complex nature of these heat integration methods, the operation and control of such process may be hindered. Since there are various ways which can be used to separate a particular azeotropic mixture, this paper uses an industrial relevant propylene glycol methyl ether dehydration system as an example to demonstrate that selecting the most effective separation method is crucially important in attempting to save energy of the separation system. The drawback of using heterogeneous azeotropic distillation for this separation task can easily be revealed with process understanding. A more effective separation method via extractive distillation is proposed to significantly save steam cost by 39.7% and reduce the total annual cost by 32.7%. Simple feed-effluent heat exchanger can be added in the proposed extractive distillation system to further save energy without much complication of the process design flowsheet.

Optimizations and heat integrations on the separation of toluene and 1-butanol azeotropic mixture by pressure swing distillation

ABSTRACTIn this study, optimizations on separation of Toluene and 1-Butanol mixture is carried out by pressure swing distillation process. New heat integration methods are applied and compared to conventional PSD process by using vapor recompression technique combined with pressure swing distillation process. New heat integration methods show positive results to decrease the utilities used in the process. A simulator Aspen HYSYS V8.4 is used for simulating all processes. Cost analysis is also performed and Aspen HYSYS V8.4 optimizer program is used for optimizing profit for the process. Pressure is also optimized for minimum heat duty requirements in the process and the ultimate concern is to minimize the total reboiler heat duties and overall operating cost for the system which results into increasing profit.

A systematic framework for multi-plants Heat Integration combining Direct and Indirect Heat Integration methods

Heat Integration across plants is an extension of conventional Heat Integration in a single plant for further improving energy efficiency. To make good use of surplus heat, Indirect Heat Integration method using intermediate fluid loops and Direct Heat Integration method using process streams are proposed to exchange heat across plants. Up to now, the two integration methods are studied separately. This leads to an incomprehensive analysis for Heat Integration across plants, because each of the methods fit different practical situations. In this work, Combined Heat Integration method is proposed, which involves the characteristics of both direct method and indirect method. The performances for Heat Integration across plants using direct, indirect and combined methods are analyzed and compared through Composite Curves. Mathematical models are proposed to determine the optimal operation conditions for direct and indirect method. Based on a heuristic step, the optimal operation conditions for combined method can be obtained through the model for indirect method. A case study is used to illustrate the new methodology.

Effect of heat integration method and torrefaction temperature on the performance of an integrated CHP-torrefaction plant

Abstract An important factor for industrial-scale implementation of torrefaction – a thermal pre-treatment technology that enhances the fuel characteristics of biomass – is the requirement for a low-cost source of heat energy. Significant benefits can be achieved if torrefaction is integrated with a large heat producer. To study this possibility, a new model for the energy and mass balances of the torrefaction process was developed on the basis of available experimental data. The torrefaction model was then integrated into steam power plant simulations, and the performance of different integration schemes was evaluated. To investigate the effect of plant size and operating mode, the same configurations were studied for both large and small combined heat and power (CHP) plants. Large plant operates at full boiler load, and capturing a portion of heat from the plant reduces the power output for all integration cases. At the same time, higher trigeneration efficiencies in comparison with non-integrated case together with fuel consumption decrease due to torrefaction gas co-firing indicate that integration of torrefaction and CHP plant at full load could be beneficial. In case of small plant, free boiler capacity at reduced-load conditions allows to cover the torrefaction heat demand and simultaneously increase the electricity generation for almost all integration cases. Trigeneration efficiency is changing within a relatively narrow range for most of the cases, while the solid fuel consumption is higher than in design case. This work shows that integration method together with process temperature and plant operation mode are the important factors that could have an effect on CHP plant integration with torrefaction process.

The simulation and design air conditioner in unit 103 of south pars with use advance exergy

In this paper, energy recycling for distillation tower condenser was done by use of heat integration method. At first, we calculated the amount of condensation energy (QAir Cooler), in air cooler, and then we calculated energy consumption in this equipment based on annual balance (5460 GJ per year). Then, based on heat integration (energy unification), two conditions were proposed to use the current energies in the process for supplying condensation energy (QAir Cooler): first, its must be lesser than condensing temperature of condenser (55 ° C) (the major condition). Second, it must have much more flow rate than the overhead flow. According to two above conditions, the food flow as chosen as the integration factor and its amount of energy (EStream) is calculated from the Enthalpy equation as 9863964 kj/h. As EFeed >>> QAir Cooler and food flow temperature to condense an overhead vapor is satisfying. The food flow can be used to condense the saturated vapor to 55 ° C. in case of using food energy and using heat exchanger instead of air cooler; 5460 GJ energy will be saved annually. By using heat exchanger and omitting air cooler, the unit103 operating costs will be reduced considerably. Economically, conducting such a project will demand investing costs. However, obtainable incomes from doing this project (electricity consumption recycling and cost's reduction) reveal this fact that capital return rate and the project benefits for unit103 of South Pars phases2&3 are beneficial.

Retrofit strategy for the site-wide mitigation of CO2 emissions in the process industries

The combustion of fossil fuels for providing heat and power in the process industries is a major contributor of CO2 emissions. Heat integration methods have been widely used for energy-saving retrofit projects to improve the energy efficiency of process plants, reducing fuel consumed and consequently CO2 emissions. It is not straightforward to identify the most appropriate strategy for CO2 emissions reduction, as a wide range of options are available, including fuel switching, reducing energy demand through efficiency improvements, retrofit of heat exchanger networks, etc. The economic impact and design constraints of each option need to be considered. A systematic approach is presented to allow evaluation of trade-offs between the cost of emissions reduction options and the effect on overall CO2 emissions. The approach applies a hierarchical conceptual design procedure. The proposed procedure is applied to a case study to demonstrate how an economic retrofit solution to reducing site-wide CO2 emissions can be systematically developed and evaluated.

Heat integration in multipurpose batch plants using a robust scheduling framework

Energy saving is becoming increasingly important in batch processing facilities. Multipurpose batch plants have become more popular than ever in the processing environment due to their inherent flexibility and adaptability to market conditions, even though the same flexibility may lead to complexities such as the need to schedule process tasks. These are important features to producing high value added products such as agrochemicals, pharmaceuticals, polymers, food and specialty chemicals where the demand has grown in recent decades. Many current heat integration methods for multipurpose batch plants use a sequential methodology where the schedule is solved first followed by heat integration. This can lead to suboptimal results. In this paper, the heat integration model is built upon a robust scheduling framework. This scheduling formulation has proven to lead to better results in terms of better objective values, fewer required time points and reduced computational time. This is important as inclusion of heat integration into a scheduling model invariably complicates the solution process. The improved scheduling model allows the consideration of industrial sized problems to simultaneously optimize both the process schedule and energy usage. Both direct and indirect heat integration are considered as well as fixed and variable batch sizes.

Effect of Fracture Inclination on Oil Recovery by Steam Heating in Fractured Reservoirs

The major objectives of this study are investigating the influences of fracture inclination on oil recovery by steam injection processes. The strongest recovery mechanism in steam injection is reduction of viscosity ratio. In this article, steam heating of a naturally fractured reservoir is modeled in terms of a block with a single fracture surrounded by steam. An analytical approach is used, which considers the transient temperature distribution within a single block. A heat integral method is used to obtain the unsteady-state temperature profile. The temperature distribution is used to calculate drainage rate under gravity flow. The solutions obtained are used to determine the effect of fracture inclination and some other parameters on the oil rate in steam injection. The results indicated that a single horizontal fracture in the direction of oil flow (zero inclination angle) recovered the highest oil, while a similar formation with a single vertical fracture perpendicular to oil flow direction (90° inclination angle) produced the lowest oil rate in steam heating. The increases of fracture inclination angle decreases oil recovery during steam heating. In addition, the recovery of oil for matrix with a single horizontal fracture is less dependent on average steam temperature, and this dependency becomes more as fracture inclination approaches to 90° (matrix with vertical fracture).

Estimating utility saving by using the technique of energy situation image

The main future goal is energy-saving and emission–reduction and, thereby, the most effective way of ensuring a reduction in carbon emissions. Energy waste should be reduced from the very beginning of process production.This paper presents an estimation of utility savings by using ‘an energy situation image technique’. This technique is an extension of a simple graphical utilities targeting method for heat integration between processes (Kovac Kralj, 2012) [1] that evaluates the maximum possible heat integration between processes. The energy situation image technique chooses the best transfer allocation between hot and cold streams regarding waste heat. Therefore, the original process cannot be changed but the utilities themselves could attract savings. The grand composite curves of different processes represent optimal heat transfers between processes, and optimal transfer allocations. This method is based on pinch analysis and is very general, it can be used within new designs and within existing processes’ integrations for utility savings.

Thermal behavior and solid fraction dependent gel strength model of waxy oils

Thermal behavior of waxy oils is investigated using the techniques of thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Model waxy oils and real waxy crude oils are utilized. Decomposition temperatures of waxy oils are obtained using TG analysis. The effects of thermal history, wax content, and additive on the gelation process of waxy oils are investigated using DSC. The DSC method provides a measure of wax solubility as well as solid fraction. An integration method and a computation method are utilized to predict solid fraction. In addition, wax crystallization onset points are obtained at the cooling rates ranging from 1 to 20 °C min−1. Similarly, wax dissolution endset points are obtained at heating rates ranging from 1 to 20 °C min−1. Extrapolated onset and endset points yield wax precipitation temperature and wax dissolution temperature, respectively. Subsequently, wax solubility curves are obtained using thermodynamic computations. A wax precipitation temperature method and a wax dissolution temperature method combine thermodynamic phase behavior with onset/endset points to predict solid fraction. Both the wax precipitation temperature method and the wax dissolution temperature method can predict solid fraction of waxy oil samples. The wax precipitation temperature method and the wax dissolution temperature method are accurate when the temperature is close to the wax appearance temperature. A heat-integration method provides accurate values of the solid fraction at temperatures significantly below the wax appearance temperature. Therefore, integration method and wax precipitation temperature/wax dissolution temperature method are combined to predict solid fraction. The effect of solid fraction on yield stress is also investigated using differential scanning calorimetry and rheometry. Finally, a new solid fraction dependent gel strength model is obtained for shut in and restart of waxy crude oil pipelines.

A Simple Graphical Utilities Targeting Method for Heat Integration between Processes

Heat integration between processes aims at identifying options for heat recovery and optimal energy conversion during industrial processes. This Article introduces a simple graphical utilities targeting method for heat integration between processes. The problem is formulated as a graphical utilities targeting problem for restricting only the heat flow regarding heating and cooling when using utilities. Therefore, the original process cannot be changed but the utilities themselves could attract savings. A mathematical formulation is presented for choosing optimal heat transfer technologies. The grand composite curves of different processes represent optimal heat transfers between processes. This method is very general; it can be used within new designs and within existing processes’ integrations for utility savings.