Hot Utility Research Articles

Synthesis of Renewable Energy Integrated Combined Heat and Mass Exchange Networks

In this paper, a methodology for systematically integrating the synthesis of combined heat, mass, and regeneration exchange networks with solar thermal is presented. The process considered involves the removal of ammonia from ammonia-rich gaseous streams using water-based solvents as the mass separating agent (MSA) and subsequent regeneration of the ammonia-rich MSA stream using steam stripping. A composite superstructure, which comprises the stage-wise superstructure for the synthesis of the heat exchanger network subsystem, primary mass exchanger network subsystem, regeneration subsystem and integrated solar thermal with periodic heat storage, is developed. In order to simplify the modelling of the unpredictable availability of solar thermal energy within the composite superstructure, a multi-periodic synthesis approach is adopted. Sensitivity analysis was performed to establish the price at which solar thermal is favoured over fossil-derived energy as the hot utility source. The economics of the resulting solution is evaluated using net present value, and it was found that, to obtain a positive NPV, the stripping cost in the retrofitted network will have to be as low as possible, or annual operating cost of the non-retrofitted primary mass exchange network will have to be high.

Applying multiple decomposition methods and optimization techniques for achieving optimal cost in mixed materials heat exchanger networks

The optimization of the total annual cost in heat exchanger networks has been one of the overarching goals when synthesizing these networks. Several methodologies and techniques have been developed to achieve optimal costs in mixed material heat exchanger networks. This paper demonstrates the application of two decomposition methodologies (total decomposition and partial decomposition) for typical cost rules. The objective function was defined as the optimization and minimization of the total annual cost in mixed materials heat exchanger network. Three optimization algorithms, hybrid genetic-particle swarm optimization (GA-PSO), shuffled frog leaping algorithm (SFLA) techniques, and ant colony optimization (ACO), were used to further optimize the total cost in mixed materials heat exchanger network. The results indicate that the total annual cost in partial decomposition method was smaller than that in full integration method and total decomposition method. The reduction of the total annual cost was about 27% for GA-PSO algorithm, 24% for SFLA and 10% for ACO relative to the results reported in this work. In partial decomposition method, at least one mixed material of heat exchanger was used to reduce the hot and cold utility for decreasing the total annual cost. Partial decomposition method resulted in the highest reduction of the total annual cost compared with other methods. Percentage of difference of the total annual cost were 0.36%, 1.92%, and 5.05% for full integration, total decomposition, and partial decomposition methods, respectively, in comparison with the previous studies. Results have been compared with the results of other studies to demonstrate the accuracy of the applied algorithms.

Thermal coupling opportunities for floating natural gas liquefaction plants

In order to meet current carbon dioxide emissions reduction challenges, natural gas processing and refining industries have to find new ways to minimize energy requirements. Building on foundations laid down in a preceding effort, this paper shows that this could be achieved in a cost-effective way for the distillation section in natural gas liquids fractionation plants. A conventional demethanizer column, combined with either a thermally coupled direct sequence of deethanizer and propane–butane recovery columns or a dividing wall column, produces significant savings in capital and hot utilities costs as compared to conventional distillation with a direct sequence, without any temperature penalty on cold utilities side. The choice between available options will largely depend on important process considerations that may differ for offshore and onshore plants and specific site requirements.

Enhancement of efficiency for steam cycle of thermal power plants using process integration

In this study, pinch analysis is employed to integrate energy in steam cycle of a 250 MW thermal power plant (TPP) located in Rajasthan state of India. To apply pinch analysis on steam turbine, all extractions exiting the turbine are considered as hot utility and feedwater as cold utility. Pinch analysis shows the potential savings in hot and cold utilities as 9.66% and 0.77%, respectively. Considering heat transfer across the pinch in condenser, heat available in boiler blow down and flowrates of extraction of low pressure (LP) turbine, six different energy integration schemes are proposed. Results show that extraction of LP turbine entering to LPH-1 is eliminated, which saves steam extracted from turbine for preheating the feedwater and thus, extra power is generated. It is also seen that flowrates from other two extractions of LP turbine decrease marginally. Amongst six energy integration schemes, the best one indicates that using pinch analysis, net generated power is increased by 0.55% and demineralized water demand is reduced by 57.6%. Further, exergy analysis of steam cycle is carried out and compared with that of most suited retrofitted scheme. Results of the present study are compared well with that of published literature.

Analysis of temperature distribution in the heating boiler equipped with afterburning chamber

Analysis of a heat transfer process for construction of solid fuel heating boiler equipped with additional afterburning chamber is presented. Analyzed construction of the heating device is intended for shouse heating and preparation of hot utility water. A heat exchanger in the analyzed boiler is composed of vertical tubes divided into three boiler draughts. Afterburning chamber connects main combusting chamber of the heating boiler with second and third boiler draught. The aim of this analysis is to identify the character of heat transfer through the heating boiler

Evaluation of an optimal integrated design multi-fuel multi-product electrical power plant by energy and exergy analyses

A novel integrated multi-fuel multi-product electrical power plant with a net electrical power output of 5.97 × 105 kW is developed and investigated by energy and exergy analyses. The electrical power plant including coal gasification, natural gas solid oxide fuel cell, cryogenic air separation unit, carbon dioxide transcritical and steam cycles, and liquefied natural gas regasification sub-systems. The potential of operating performance improvement by conducted energy and exergy analyses is assessed. Also, the thermal design and heat integration analyses are performed for studying the system sustainability and emphasizing on no requirement for external hot and cold utilities. Effects of the main design parameters such as fuel cell operating parameters, ambient temperature and liquefied natural gas thermodynamic specifications on the system operating performance are examined. The obtained results indicate that the overall energy and exergy efficiencies reach to a maximum value of about 56.4% and 57.9%, respectively; in the case of fuel utilization of solid oxide fuel cell is about 80.0%. Furthermore, increasing the ambient temperature and current density decrease the system operating performance. In contrast, the system performance increases with the liquefied natural gas vapor pressure.

OPTIMIZATION OF ENERGY UTILITIES CONSUMPTION IN THE AQUEOUS SODIUM HYDROXIDE SOLUTION EVAPORATION

The paper proposes the retrofit design of a three-unit evaporator for evaporating of aqueous sodium hydroxide solution in order to increase its concentration. The retrofit assumes the creation of a heat exchange equipment network that has to implement heat recovery of the process streams of the evaporator. The design was carried out with the pinch-analysis methods. The treshhold problem (demand for hot utilities only) was identified by shifting the composite curves and the treshhold temperature difference 11,7 °С was found. Problem definition, like a pinch problem, was made with the choice of minimum temperature difference DTmin = 12 °С in heat exchange equipment. The design of the heat exchangers network that realizes the minimum consumption of external utilities and maximum energy recovery was created, and the network optimization with energy relaxation was carried out. Modern plate heat exchangers as heat exchange equipment were chosen and calculated. The economic evaluation of the design was conducted. The payback period will be about two months.

Exergetic evaluation of biodiesel production from rice bran oil using heterogeneous catalyst

With the increasing interest in developing alternative fuel sources to fossil fuels, biodiesel is one preferred alternative. Several researchers have proposed the use of heterogenous catalyst but it is not commercially in use yet. Recently, more attention is being paid to improvement of the energetic performance and minimising the inefficiencies in the different process components, but not many literatures have shown how these inefficiencies are introduced during design of heterogeneously catalysed biodiesel production processes. This study aim to use exergy analysis to determine location, magnitude and sources of thermodynamic inefficiencies in a heterogeneously catalyzed rice bran oil biodiesel production plant. It demonstrates how improper placement of utilities can result to energy losses in a heterogeneously catalyzed rice bran oil biodiesel production plant and it comparatively examine how the exothermic energy of transesterification reaction can drive the system. Two rice bran oil biodiesel production plants are simulated. The first production plant simulated has hot utility supply to the reactor while the second is without hot utility supply to the reactor and both were defined as scheme 1 and scheme 2 respectively. The overall analysis showed that for scheme 1, exergy efficiency was 63.92% with 94.2% of the total exergy destruction taking place in the reactor while efficiency of scheme 2 was observed to improve to 75.15% with exergy destruction in the reactor reduced to 1.63%.

A sequential approach for integration of multiple thermal energy storages with fixed mass and variable temperature

Heat recovery in industrial processes is gaining importance as climate goals push industries to increase their energy efficiency. But also potential economic benefits give incentives to increase waste heat recovery and thus energy efficiency. The various available thermal energy storage technologies yield high potentials to increase energy efficiency in industrial processes. However, storages with fixed mass and variable temperature are rarely considered for storage integration using process integration methods.In this paper, a sequential approach using mathematical programming formulations combined with insights from pinch-analysis is proposed that allows to find cost efficient heat recovery systems incorporating storages with fixed mass and variable temperature. The procedure is demonstrated by integration of pressurized water storages into two industrial process examples taken from literature. For both examples hot utility demand could be reduced by about 50% compared to solutions without storage integration.

Application of the Microsoft Excel Solver tool in the solution of optimization problems of heat exchanger network systems

Optimization of heat exchanger networks (HENS) is a field of interest in Chemical Engineering. The aim is to use the residual heat of process streams to raise the temperature of other process streams which are cold, thus minimizing the use of hot and cold utilities. The usual way to deal with this task is to pose a linear programming problem according to a transshipment model in order to minimize either the general services consumptions or the number of hot and cold stream matchings required. This optimization is subjected to several restrictions given by the energy balances corresponding to each heat exchange.The high number of variables and equations obliges the use of specific software to solve these problems, e.g. GAMS (General Algebraic Modelling System). However, this software is not intuitive and requires a long time of training and a certain level of practice for the students to adequately use it.This work describes the use of Microsoft Excel-Solver for the sequential solving of HENS optimization problems according to the transshipment model. Solver is a much simpler, intuitive and easily available tool for the students who, besides, usually learn how to use it in the first years of their degree, in Informatics or similar subjects. Thus, it is not necessary to spend extra time in the teaching of the software, time that may be devoted to other contents.This paper presents an example of HENS problem proposed in the subject Simulation and Optimization of Chemical Processes corresponding to the Joint Master in Chemical Engineering of the Rey Juan Carlos University and the Autónoma University of Madrid and solved by the students using Excel-Solver.

Heat transfer enhancement to decrease the energy consumption of a Light Naphtha Isomerization unit by means of heat exchanger network retrofitting

The Light Naphtha Isomerization (LNI) process increases the quality of gasoline, and the Pinch Design Method (PDM) is a novel method in the field of heat transfer that implements the design of Heat Exchanger Network (HEN) to improve energy efficiency. In this research, the HEN of an LNI unit was retrofitted using PDM to determine the best design to decrease hot and cold utility consumption. Stream selection and data extraction were necessary for PDM, and graphical tools in the form of Composite Curves (CC) and a Grand Composite Curve (GCC) were presented to calculate the minimum and actual hot and cold targets. The base-case results showed minimum hot and cold targets of 37 and 42 MW for ΔTmin = 10 °C, respectively and an energy pocket above the pinch in the interval of between 120 and 180 °C. The pocket enhanced heat recovery because of the large driving forces, decreasing MP steam consumption. Scenarios were suggested for the retrofitting of the LNI unit to enhance heat transfer to decrease energy consumption. In particular, the heat pump intensified heat transfer from the Cooling Water cold utility at 29.5 °C to the MP Steam hot utility at 150 °C.

Optimal design of cogeneration systems in total site using exergy approach

By increasingly demands on the hot and cold utilities in chemical processing industries, application of unified utility systems has extended in recent decades. Through the Total Site, accessibility to hot steam and condensing water has become more convenience. Therefore, cogeneration systems generate key product of total site, power to electricity network as well as steam to heating purposes. Also, it can be considered to consume the cold utilities to cooling destinations. In present work, defining the multiple arrangements of back pressure steam turbines, an optimal design of heat and power cogeneration systems through exergy point of view is determined. The excellent exergy efficiency and also the least amount of exergy destruction was measured to select the optimum system of arrangements. In times of need for extra power, either a condensing turbine or gas turbine system, were meant to generate deficiency of electricity in network. Then, both the extra scenarios were studied by exergy analysis. Consequently, final optimum system of cogeneration system in total site was selected. This ultimate optimal configuration is consisting the optimal steam turbines as well as the appropriate augmented scenario from exergetic viewpoint, between condensing or gas turbine systems. In addition, two case studies of utility systems were employed to confirm the applicability of proposed methodology.

Evaluation of the integration of an ammonia-water power cycle in an absorption refrigeration system of an industrial plant

Combination of binary components used for absorption refrigeration systems as ammonia-water can also be applied as working mixture for power generation in a Kalina Cycle, providing an interesting option in the use of energy sources at low temperatures. Using this possibility in a power-cooling cogeneration system, Kalina Cycle (KC) was proposed to be integrated in an ammonia-water absorption refrigeration system (AARS) of 1269 kW of cooling at 219 K, in order to take better advantage of the available energy from a steam generator in an industrial plant, used as a case study. The AARS uses water steam as hot utility, after the expansion in a pressure reducing valve from higher pressure. Applying exergy analysis, it was verified that the combined KC-AARS, besides the power generation, can decrease the exergy destruction in the AARS. For that, due to the very low working temperatures, the AARS involving double absorbers and evaporators, condenser and expansion valves in a complex system and its peculiarities were practically preserved at lower pressure levels, integrating the KC basically in the higher pressure levels, which is a very interesting proposal for existent systems. The results showed the possibility to reduce the exergy destruction in 43.3%, from 1614 to 915.8 kW, and to produce 493 kW of power generation. In addition, increases in the coefficient of performance from 0.256 to 0.376, energy efficiency of refrigeration from 0.297 to 0.360 and exergy efficiency from 0.185 to 0.468 were reached at 4.7 MPa of working pressure.

Integration of thermo-vapor compressors with phenol and ammonia recovery process for coal gasification wastewater treatment system

Current phenol and ammonia treatment process consumes a large amount of hot utilities to recover crude phenol and aqua ammonia, which includes 0.5 MPag steam (2.68 MW), 1.0 MPag steam (10.17 MW), and 2.5 MPag steam (1.97 MW) based on the benchmark treatment capacity of 100 t/h. This paper fixates on the further improvement of energy efficiency by process integration and innovation. A novel integrated process is proposed in this paper to abate utilities consumption. Two scenarios have been analyzed following the Grand Composite Curve. The results show that one of the new integrated processes performs better energy saving efficiency. It requires 53.7% (7.96 MWsteam) less hot utility consumption and 57.5% (6.86 MWcw) less cooling water consumption at the expense of 68.7% (662 kWelec) more electricity use, as suggested in simulation results. The estimated cost savings relevant to the improved process is 1.095 million US$/y, and the emission reduction is 5237 t CO2 e/y.

Analysis of Heat Cascade Through Process Components to Reduce the Energy Consumption in Industrial Systems

Energy savings result in economic and environmental benefits. Site-wide energy analysis of industrial systems considers all plant components, such as unit operations, heat exchangers, boilers, and turbines. This article presents the analysis of heat cascade through these components to reduce the overall energy consumption. As a consequence of the two first principles of thermodynamics, heat from hot utilities transferred to a process is gradually cascaded to the environment through process operations and exchangers. The enthalpy rate curves shift to ambient temperature through operations and exchangers; the difference between the outlet and inlet enthalpy rate curves of a system is equal to the flow rate of cascaded heat as a function of temperature. Reducing the energy consumption implies decreasing the flow rate of cascaded heat through process operations or exchangers in the entire temperature interval between the hot utility and the environment. Herein, the heat cascade is first analyzed to identify process operation modifications in order to reduce the utility consumption. Second, the heat cascade through a plant, including a boiler, a turbine, process operations, and exchangers, is represented on a single diagram for site-wide energy analysis. Third, the heat cascade through several processes is analyzed to integrate an industrial site. The proposed method provides benefits in comparison to foreground/background analysis and total site analysis, which are two commonly used approaches to identify energy-saving opportunities for industrial symbiosis. Analysis of heat cascade through individual operations and heat exchangers is simple and powerful, and its concepts can be used in software to identify energy-saving projects.

Energy integration in boiler section of thermal power plant

Abstract: In the present work systematic analysis is carried out for retrofitting of boiler section of the conventional thermal power plant of 250 MW capacity with the aim to recover maximum amount of waste heat available in it. Lignite coal is used in this plant as a fuel. For the existing system, pinch point, minimum hot and cold utility requirements are found as 972 °C, ‘0’MW and ‘11.09’MW, respectively. Pseudo-pinch point is also found at 272 °C and heat flow through it is 9.11 MW. It is observed that in the existing plant exit temperature of flue gas through the stack is restricted by dew point of SOx to prevent corrosion in the stack. Dew point of SOx in flue gas is predicted as 122 °C. Further, heat from boiler blowdown can also be extracted. Considering waste heat of flue gas as a result of dew point as well as boiler blowdown six different energy integration options are proposed for retrofitting of boiler section. Detailed design and economic analyses are carried out for all these options. Different criteria such as location of additional heat exchanger, amount of flue gas and exit temperature, environmental aspects, %energy savings and maximum temperature across additional heat exchangers are envisaged to choose best retrofitting option. Results of the best option are compared with that of published work.

Hydrothermal liquefaction of Radiata Pine with Kraft black liquor for integrated biofuel production

This paper aims to evaluate the feasibility of hydrothermal liquefaction (HTL) of Radiata pine with black liquor from an existing Kraft pulp mill. The biomass into the HTL process was assumed at 2000 t/day and converted into bio-crude through the HTL process and upgraded to produce a gasoline and diesel blend. The HTL process was scaled-up based on an existing published patent. Mass and heat balance of the process was obtained through the process simulator, Aspen Plus. Process Integration was carried out to minimise the hot and cold utility of the process. The production rate of the process is 78.7 kt/y of fuel. The minimum fuel selling price (MFSP) was estimated at 0.95 USD/LGE (litre gasoline equivalent). A sensitivity analysis was carried out to determine the MFSP in 2017 and to study the changes of MFSP due to the uncertainty in the capital cost estimation.

Energy optimization of integrated atmospheric and vacuum crude distillation units in oil refinery with light crude

The heat integration and retrofit analysis of Arabian light crude distillation units was carried out to identify opportunity for energy savings using different design options, to achieve optimum heat exchanger network. Data used were extracted from an existing and operating crude oil refining plant. The pinch analysis of existing plant using process integration software (Heat-Int) Process Integration Limited, Cheshire, United Kingdom revealed that the hot and cold utilities consumptions at the prevailing ΔTmin of 77 °F in the plant were 680.23 and 521 MMBtu/h, respectively. Economic evaluation of existing plant revealed total operating cost of $4 829 625/year. Retrofit of existing plant using different design options generated an optimal network comprised four additional heat exchangers with reduction in ΔTmin from 77 °F to 57 °F. The hot and cold utilities consumptions also reduced to 623.23 and 464.44 MMBtu/h, respectively. Economic evaluation of the new design showed energy savings of $259 860/year. The trade-off between energy and capital costs in terms of the costs procurement and installation new heat exchangers gives overall cost savings of $32 800/year with payback period of 11 months. The study concluded that retrofitting of existing heat exchanger network to correct those exchangers that are transferring heat across the pinch could result in enormous energy savings. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Comparison of the biogas upgrading methods as a transportation fuel

Abstract The aim of this study is investigating and analyzing the water scrubbing, cryogenic separation, amine scrubbing and caustic wash biogas upgrading processes. In order to comparing the upgrading processes, input condition is supposed to be fixed for all of the processes. The results of this study indicate that although amine scrubbing process consumes less power but the required hot utility is higher than other upgrading methods. In the cryogenic process, high pressure operating condition needs high compression power. This process also needs low temperature refrigeration system. Water wash process is a simple and economic method which has acceptable separation efficiency, but caustic wash is more efficient than other methods and its energy consumption is reasonable.

Two-step MILP/MINLP approach for the synthesis of large-scale HENs

Although different methodologies for the synthesis of heat exchanger network (HEN) problems have been introduced in the last forty years, there are still significant challenges to be addressed, such as solving large-scale problems. This study focuses on synthesizing large-scale HENs using mathematical programming to achieve near globally optimal solutions based on a two-step MILP/MINLP approach. In the first step a mixed-integer linear programming (MILP) model, TransHEN, is used that obtains a globally optimal solution at selected ΔTmin. By utilisation of this model, the most promising matches are selected based on feasibility and viability. The second step entails using the matches selected in the TransHEN of Step 1 in a mixed-integer nonlinear programming (MINLP) model, HENsyn, using a reduced superstructure, to generate a feasible HEN. This study presents also a simultaneous Total Site synthesis with direct heat transfer between processes, and is the first step in the wider project of synthesising an entire Total Site with direct and indirect heat transfer; and is the first step in the wider scope of synthesising an entire Total Site with direct and indirect heat transfer; however, in order to attain this goal, a tool capable of an appropriately handling large number of streams is required. The newly developed procedure has been tested on several case studies, two of which are presented in this paper. For Case study 1 the results obtained lie within the range of best solutions obtained by other authors. Case study 2, consisting of 173 process stream and involving multiple hot utilities, shows the applicability of the developed method to handle large-scale HEN problems.