Process Heat Integration Research Articles

Energy consumption and heat recovery of an industrial fluidized catalytic cracking process based on cost savings

Energy consumption is a significant issue in operation design for low-cost sustainable production and is accomplished by heat integration giving overall environmental advantages via reducing carbon emissions. Heat recovery is a beneficial tool that determines the minimum cooling and heating demand through recovery and re-use of energy within the process. Thus in this study, process of heat recovery and energy consumption of the fluidized catalytic cracking (FCC) is investigated to recover most of the external energy and reducing the environmental effect in addition to maximizing the productivity with minimum overall cost of the process. Where the performance of the FCC units plays a major role on the overall economics of refinery plants and improvement in operation or control of FCC units, it will result in dramatic economic benefits. The heat integration process is done based on experimental information from pilot scale, mathematical modeling developed and commercial process reported in our earlier study.

Cost‐effectiveness analysis of energy efficiency measures in the Swiss chemical and pharmaceutical industry

Energy efficiency improvement is an effective way of reducing energy demand and CO2 emissions. Although the overall final energy savings potential in chemical industry has been estimated in a few countries, energy efficiency potentials by concrete measures applicable in the sector have been scarcely explored and their associated costs are hardly analyzed. In Switzerland, the production of chemicals and pharmaceuticals exceeds all other industrial sectors in terms of energy use and CO2 emissions, and it accounted for 22% of the total industry's overall final energy demand and 25% of the CO2 emissions related to non-renewable energy sources in 2016. In this study, the economic potentials for energy efficiency improvement and CO2 emissions reduction in the Swiss chemical and pharmaceutical industry are investigated in the form of energy efficiency cost curves. The economic potential for final energy savings and CO2 abatement based on energy-relevant investments is estimated at 15% and 22% of the sector's final energy use and fossil fuel-related CO2 emissions in 2016, respectively. Measures related to process heat integration are expected to play a key role for final energy savings. The economic electricity savings potential by improving motor systems is estimated at 15% of the electricity demand by these systems in 2016. The size of economic potential of energy efficiency improvement across the sector decreases from 15% to 11% for 0.5 times lower final energy prices while the size increases insignificantly for 1.5 times higher final energy prices. The additional power generation potential based on Combined Heat and Power plants is estimated at 14 MW for 2016. This study is a contribution to the so far limited international literature on economic energy efficiency measures applicable in this heterogeneous sector and can support policy development. The results for specific costs of energy efficiency measures can also be adapted to other parts of the world by making suitable adjustments which in return may provide useful insights for decision makers to invest in economically viable clean energy solutions.

Heat-integrated pressure-swing distillation process for separation of the maximum-boiling azeotrope diethylamine and methanol

Abstract The steady-state economics and dynamic controllability of heat-integrated pressure-swing distillation (PSD) processes are explored by taking the separation of maximum-boiling azeotrope diethylamine and methanol as demonstrating example. Compared to the conventional process, the B-E configuration (hot stream preheating the feed of high-pressure column) is attractive than others due to reducing 36.83% in energy consumption, 20.49% in CO2 emissions and 25.69% in total annual cost (TAC) and enhancing 49.48% in thermodynamic efficiency, respectively. Dynamic controllability of the economic efficient backward-integrated processes is also investigated by teaching the terminology of “simultaneous design”. The effectiveness of single-end control strategy is determined by the method of feed composition sensitive analysis, and a series of control structures are devised and assessed by the perturbations of feed flowrate and composition. The robust control scheme (CS5) with the ratio strategy to manipulate recycle stream flowrate is constructed to eliminate snowball effect and oscillation phenomena for partially case. It is also used to the combinational heat-integrated processes, and the differences of integral absolute error (IAE) are small between the alternative arrangements, demonstrating that the performance of single-end control scheme with the feedforward strategy of molar ratio reflux-to-feed (R/F) is robust and efficient.

Heat-integrated triple-column pressure-swing distillation process with multi-recycle streams for the separation of ternary azeotropic mixture of acetonitrile/methanol/benzene

The steady-state economics and dynamic controllability of heat-integrated triple-column pressure-swing distillation (TCPSD) process are explored by taking the separation of ternary mixture of acetonitrile, methanol and benzene as demonstrating example. The performance evaluation indicators of second-law efficiency and CO2 emissions are employed to rank different arrangements except only reference of total annual cost (TAC). Compared to the conventional process, the economically optimum flowsheets are the partially heat-integrated processes (Cases 1 and 2) since it can reduce about 20.00% in TAC, 35.19% in energy-saving and enhancement of 48.77% in thermodynamic efficiency. Dynamic control of the economic efficient processes are also investigated. A series of control structures are developed and assessed by the throughput and feed composition disturbances, which are divided to two categories including control schemes with or without split ratio of the distillate stream of second column. The snowballing effect is efficiently attenuated by control schemes (CS4 and CS5) with the ratio strategy to adjust the recycle stream flowrate for partial Case 1. These control strategies are also applied to partial Case 2, the stable regulatory control is achieved, yet oscillation phenomena for the response of condenser heat removal of second column exists for control strategies without split ratio scheme, while it is efficiently handled by the split ratio scheme coupling with pressure compensated temperature-composition cascade control strategy.

Energy-Efficient Design of Downstream Separation To Produce n-Butanol by Several Heat-Integrated Technologies

Biobutanol is a widely used biofuel, and it is traditionally produced mainly via the fermentation process of acetone–butanol–ethanol (ABE). However, separation of the ABE fermentation broth featuring a low concentration of n-butanol in the presence of butyric acid and acetic acid consumes considerable energy. For the sake of reducing the capital cost as well as the energy consumption greatly, a novel DWC-SHR process was proposed to achieve further energy saving through the combination of dividing wall column technology and the self-heat recuperation technology. Moreover, the heat exchanger network (HEN) can be applied to design the HEN of the DWC-SHR process. The DWC-SHR process can be compared with the base process as well as the heat-integrated processes (HI-A process and HI-B process) from the point of the energetic, economic, as well as environmental impact. The results illustrated that the DWC-SHR process can achieve 71.13%, 57.87%, and 47.79% savings of energy consumption compared to that of the bas...

Feasibility of Power and Methanol Production by an Entrained-Flow Coal Gasification System

Sustainability metrics, a cradle-to-gate life cycle assessment, and a technoeconomic evaluation are presented for an optimized entrained-flow coal oxy-combustion plant with carbon capture to produce power and methanol. The aim of the study is to assess the feasibility of coproducing methanol in a coal-based power plant with an entrained-flow coal gasification system. Coal-based methanol, as an attractive liquid transportation fuel as well as an essential intermediate chemical feedstock, can fill a possible gap between declining fossil fuel supplies and movement toward the hydrogen economy. Within the plant, first the coal is fed to a pyrolysis reactor, and then the volatile matter is fed into an oxy-combustion reactor while the char is gasified in an entrained-flow gasifier. The remaining char is gasified. The heat is used to produce electricity, while the syngas is converted to methanol. The integral plant, consisting of an air separation unit, oxy-combustion of coal, gasification of char, electric power production, carbon capture, and conversion to methanol, was designed and optimized using the Aspen Plus package. The optimization includes the design specification of process heat integration using an energy analyzer toward a more efficient clean-coal technology with methanol production. The plant uses 500 metric tons (MT) of Powder River Basin coal and 2231.03 MT of air per day and produces 32.76 MWh of electric power and 207.99 MT of methanol per day. The total amount of captured CO2 is 589.75 MT/day, and nitrogen is also produced at 1309.33 MT/day. A multicriteria decision matrix consisting of economic indicators as well as the sustainability metrics is developed to assess the feasibility of the extended plant. Methanol production in addition to power production may improve the overall feasibility of coal-powered plants.

Improved design and optimization for separating tetrahydrofuran–water azeotrope through extractive distillation with and without heat integration by varying pressure

From the view of thermodynamic insight, a new concept (ROE: FE,Pope/FE,Pref), the ratio of the entrainer flow rate (FE) needed for reaching given relative volatility at operating pressure (Pope) to reference pressure (Pref), is firstly proposed to quantitatively determine the search space of operating pressure of the extractive column in a homogeneous extractive distillation (ED) process for the separation of binary minimum azeotrope with heavy entrainer. This novel concept is illustrated by the extractive distillation of tetrahydrofuran–water minimum boiling point mixture with an entrainer dimethyl sulfoxide. Six process designs under different pressures are obtained by a two-step optimization procedure and compared from the economic view based on total annual cost (TAC). Furthermore, three double-effect heat integration (DEHI) processes, are employed under atmospheric and a reduced pressure for the first time to further improve the energy efficiency and investigate the effect of pressures on the studied ED process. The final results of case study demonstrate the optimal heat integration approach with a suitable low pressure is the most economic one among the three DEHI processes. The TAC of the best proposed design exhibits a 20.3% reduction than that at atmosphere pressure. The proposed pressure selection rule and optimization process are helpful for reducing the TAC of the ED process.

Study on the integration of fluid catalytic cracking unit in refinery with solvent-based carbon capture through process simulation

Fluid catalytic cracking unit (FCCU) is an important refinery process by cracking heavy hydrocarbons to form lighter valuable products, including gasoline and diesel oil. However, the FCCU also generates the largest amount of CO2 emissions among all the refinery units. To solve this problem, solvent-based carbon capture can be introduced to capture CO2 in the flue gas from FCCU, but the energy consumption from the reboiler of the carbon capture plant will undoubtedly reduce the economic benefits of the refinery. In this paper, solvent-based carbon capture for an FCCU in a real life refinery is studied through process simulation. This study takes into account the process design and heat integration. An industrial FCCU with a feed capacity of over 1.4 million tons vacuum gas oil per year was modelled, and the process model was validated according to industrial operating data. A carbon capture plant model with MEA solvent was also developed in Aspen Plus® at pilot scale, and scaled up to match the capacity of the FCC unit. Case studies were performed to analyze the integration of the FCCU with commercial scale carbon capture plant, in which different heat integration options were discussed to reduce the energy consumption. The simulation results indicated that a proper design of heat integration will significantly reduce the energy consumption when the carbon capture plant is integrated with an industrial FCCU.

Power Generation Targets from Hot Composite Curves

The paper proposes a simple systematic procedure to target thermodynamic power generation limits from a set of heat source streams. The procedure takes the form of an algebraic targeting approach commonly applied in process heat integration. It allows the designer to quickly determine the maximum amount of power that can theoretically be generated from the available heat in thermodynamic cycles. The paper describes the procedure and is applicability in the context of common data availability for heat source streams in the form of a Composite Curve or Total Site Profile (hot composite curves) commonly developed in heat integration. The application of the procedure is illustrated with examples.

Techno-economic assessment of bio-oil aqueous phase-to-liquids via Fischer-Tropsch synthesis and based on supercritical water reforming

High energy demand along with large capital costs have been the main drawbacks of Fischer-Tropsch plants, which may call into question the economic viability of the Fischer-Tropsch process. The second issue is the focus of this paper, which presents a techno-economic assessment of biofuels production by a low-temperature Fischer-Tropsch synthesis with electricity as a co-product from supercritical water reforming of the bio-oil aqueous phase. A plant size of 60 t/h was considered and a heat-integrated process was designed to be energy self-sufficient, which includes syngas production and upgrading, as well as liquid fuels production by Fischer-Tropsch synthesis and refining. The simulation and optimization was performed with the aid of Aspen Plus, and some case-studies were performed. Using a feeding concentration of 25 wt%, 2.74 t/h biofuels and 5.72 MWe were obtained. In this case, by performing a discounted cash flow analysis, with 10% rate of return and 100% equity financing, the minimum selling prices for the refined FT-gasoline, FT-diesel and FT-jet fuel were 1.20, 0.93 and 0.26 €/kg (0.84, 0.75 and 0.20 €/L), respectively, which are competitive prices with respect to the market values of the equivalent fossil fuels. Likewise, the decrease in the selling prices as the plant capacity increases was also analyzed.

Heat integration and optimization of direct-fired supercritical CO2 power cycle coupled to coal gasification process

Supercritical carbon dioxide (sCO2) power cycle is a promising power cycle that has drawn much attention in recent years. Among various layouts, the direct-fired sCO2 power cycle achieves not only high efficiency but also near zero emission. Coal gasification and air separation process are indispensable processes when coal is used as fuel. To explore the best cycle performance, the above two processes have to be tightly integrated with the sCO2 power cycle in both mass and energy. Key parameters that govern the heat integration should also be optimized to achieve better performance. A two-stage method is applied for simultaneous optimization and heat integration of a direct-fired sCO2 power cycle coupled to coal gasification process. First, boundary parameters of the heat integration process are optimized. Then the heat exchanger network, which reveals viable heat integration scheme, is designed to fulfill the optimized target. The result shows that the net efficiency reaches 39.29% when heat integration of ASU is not considered. If heat integration of ASU is considered, the net efficiency increases to 40.97%, showing an efficiency increment of 1.68%. When the CO2 turbine pressure ratio is also optimized, the net efficiency increases further to 41.41%.

A combination of pressure-swing and extractive distillation for separating complex binary azeotropic system

Methyl acetate/methanol/water mixture forms more than one different azeotrope, whereas its triangular diagram presents a distillation boundary at atmospheric pressure. The two different simulation processes of the double column pressure-swing with extractive distillation (DCPSED) and triple column pressure-swing with extractive distillation (TCPSED) were proposed to separate the complex ternary system. Furthermore, the heat integration and mechanical vapor compression (MVR) heat pump distillations were also tested (through simulation) to separate the complex ternary system to save energy. The feasibility of the processes was confirmed using vapor-liquid equilibrium curve, while rigorous steady-state simulations were implemented using Aspen Plus (version 7.1). With the goal of achieving minimum energy consumption and minimum total annual cost (TAC), the purities of methyl acetate, methanol and water were used as the constraint variables. The results show that water was a better solvent for this separation system. Compared with the TCPSED process, the energy consumption and TAC for DCPSED process could be reduced by 44.83%, and 47.74%, respectively. Compared with the DCPSED and DCPSED with heat integration processes, DCPSED with MVR process could reduce the energy consumption by 73.34% and 59.52%, while TAC was decreased by 37.64% and 11.77%, respectively. The simulation results indicated that DCPSED with MVR process has great advantage over other processes used to separate methyl acetate/methanol/water ternary mixture.

Simultaneous Utility and Heat Exchanger Area Targeting for Integrated Process Synthesis and Heat Integration

We propose a mixed-integer nonlinear programming (MINLP) model for simultaneous utility and heat exchanger area targeting with variable stream conditions. The model represents the composite-curve-based area targeting method by constructing the hot and cold composite curves mathematically. We introduce a “dynamic” enthalpy grid onto which the stream inlet/outlet temperatures and enthalpies are mapped. By calculating the temperatures at each grid point and the stream heat duties at each interval, the utility consumption and heat exchanger areas are simultaneously optimized using an economic criterion. We discuss preprocessing methods tailored to aid the solution of the proposed MINLP model. The model is applied to two illustrative examples as well as an example where it is integrated with a process synthesis model.

Disjunctive model for the simultaneous optimization and heat integration with unclassified streams and area estimation

In this paper, we propose a disjunctive formulation for the simultaneous chemical process optimization and heat integration with unclassified process streams –streams that cannot be classified a priori as hot or cold streams and whose final classification depend on the process operating conditions–, variable inlet and outlet temperatures, variable flow rates, isothermal process streams, and the possibility of using different utilities.The paper also presents an extension to allow area estimation assuming vertical heat transfer. The model takes advantage of the disjunctive formulation of the ‘max’ operator to explicitly determine all the ‘kink’ points on the hot and cold balanced composite curves and uses an implicit ordering for determining adjacent points in the balanced composite curves for area estimation.The numerical performance of the proposed approach is illustrated with four case studies. Results show that the novel disjunctive model of the pinch location method has excellent numerical performance, even in large-scale models.

Exergy analysis of a new lignocellulosic biomass-based polygeneration system

A new polygeneration system for production of ethanol, xylose, combined heat and power from lignocellulosic biomass is introduced as it may be much more competitive than those considered before. The polygeneration system is simulated by Aspen Plus based on mass and energy balances and evaluated from exergy point of view and the output value per unit of raw materials. The system can process corn cob 340,000 t/a with a production capacity of anhydrous ethanol 40,000 t/a and xylose crystals 51,600 t/a. The ratio of produced ethanol to dry biomass is 179.7 L/t. The output value per unit of raw biomass is much higher than other systems due to production of high value co-product xylose. The net energy ratio is 1.6 indicating the system has net energy gain. The power generation efficiency and thermal efficiency are 31.2% and 86.2%, respectively. The general exergy efficiency of the system is 62.8% and the largest irreversibility occurs in combined heat and power system (CHP). The work is valuable to find key unit of improving the process exergy efficiency and build an optimal energy network. Further work should take into account the process heat integration to improve the exergy efficiency of the system.

Pilot testing of a heat integrated 0.7 MWe CO2 capture system with two-stage air-stripping: Emission

The University of Kentucky Center for Applied Energy Research (UKy-CAER) designed, constructed and tested an advanced 0.7MWe post-combustion CO2 capture system on a coal-fired power plant using a heat integration process combined with two-stage stripping to enhance the CO2 absorber performance and lower the cost of CO2 capture. Evaluation of emissions from the solvent and degradation products was performed to determine the impact on the amine solvent of coal combustion flue gas contaminants and oxygen exposure due to incorporation of the secondary air stripper into the conventional amine absorber/stripper system. The overall amine, ammonia and aldehyde emission levels observed during the baseline 30% monoethanolamine (MEA) solvent testing campaign were generally comparable to previously published reports tested at similar flue gas conditions and system operating hours. Ammonia emissions were correlated to high levels of iron and copper in the solvent, likely as a result of material corrosion.

Heat-integrated pressure-swing distillation process for separating the minimum-boiling azeotrope ethyl-acetate and ethanol

Abstract Design and control of the forward integration of pressure-swing distillation processes is explored with the aid of the tools of Aspen plus and Aspen dynamics taking the separation of the minimum-boiling azeotrope ethyl acetate and ethanol as an example. The optimized separation configuration is obtained by taking the minimization of total annual cost (TAC) as an objective function. The two key performance indicators of second law efficiency (η) and carbon dioxide emissions are employed to evaluate the three operations, which consist of conventional non-heat integration and the corresponding partially and fully heat integration processes. Compared to the non-heat integration process, the fully heat integration process is more attractive since it can achieve 33.33% energy consumption saving, reduction of 31.33% CO 2 emissions and 26.64% TAC. Furthermore, the control of the PSD processes with heat integration are explored since the interaction of parameters are complicated for this neat configuration. The effectiveness of the single-end control strategy is evaluated and determined by method of the feed composition sensitive analysis, and a series of control structures are devised and assessed by the perturbations of the feed flow rate and feed composition. It is concluded that the small disturbances are addressed for fully heat integration in comparison with the partially heat integration owing to the degree of freedom reduction. In addition, the efficient control strategy with the ratio scheme to manipulate the cascade flow controller is developed to eliminate the snowball effect for PSD with partially case.

Solvent Degradation and Emissions from a 0.7MWe Pilot CO2 Capture System with Two-stage Stripping

The UKy-CAER team successfully tested an advanced 0.7 MWe post-combustion CO2 capture system on a coal-fired power plant using a heat integration process combined with two-stage stripping to enhance the CO2 absorber performance. One of the unique feature of the UKy-CAER integrated process is a two-stage stripping unit for solvent regeneration. The secondary stripper is empowered by the heat rejection from a conventional steam-heated (primary) stripper. The secondary stripper outlet stream at the commercial scale can be used as boiler secondary combustion air, consequently enriching the flue gas with CO2, resulting in less energy penalty required by the CO2 capture system. The primary goal of this study was to form an initial assessment of the impact on the amine solvent from coal combustion flue gas contaminants and the potential higher oxygen content in the solvent due to incorporation of the secondary air stripper into the conventional amine scrubber/stripper system. The overall oxidative degradation was comparable to previous reports with 30 wt% MEA solvent at similar flue gas run hours. This suggests that the addition of the secondary air stripper appears to be negligible with regards to solvent oxidation.

Process Integration of Post-combustion CO2 Capture with Li4SiO4/Li2CO3 Looping in a NGCC Plant

Lithium-based sorbents require lower energy requirements for regeneration than other more studied and well known materials such as those used in the calcium looping process; however, thermodynamic assessments of these sorbents in power plants are currently missing. Accordingly, in this work, a thermal integration study of a post-combustion CO2 capture plant using regenerable lithium-based high temperature solid sorbents into a natural gas combined cycle (NGCC) plant has been conducted. A process simulation study has been completed for integration of a Li4SiO4/Li2CO3 looping cycle downstream of the gas turbine in a NGCC plant. A comparison between this technology and a chemical absorption capture plant with two different solvents, namely conventional monoethanolamine (MEA) and a second generation solvent (CESAR-1), has been established based on the European Benchmarking Taskforce (EBTF) methodology. The integration of post-combustion CO2 capture in the power plant results in a decrease of its net electric efficiency. However, capture with Li4SiO4 sorbents decreases the efficiency by 6.9 percentage points, which is lower than the 8.4 and 7.5 percentage points decrease obtained when CO2 capture is based on chemical absorption with MEA and CESAR-1 solvents, respectively. Hence, Li4SiO4/Li2CO3 looping is a promising alternative to amine-based systems when integrated into NGCC plants. Furthermore, additional improvements could be achieved through improved capture process heat integration and optimization.

Production of Hydrocarbon Fuel Using Two-Step Torrefaction and Fast Pyrolysis of Pine. Part 1: Techno-economic Analysis

As part I of two companion papers, the present paper evaluates the economic feasibility of hydrocarbon biofuel production via two pathways: a one-step production pathway through fast pyrolysis of biomass followed by the catalytic upgrade of bio-oil to a liquid hydrocarbon biofuel and a novel two-step pathway that includes a torrefaction pretreatment step prior to fast pyrolysis and then the catalytic upgrade. These two pathways were modeled using Aspen Plus to process 1000 dry metric tons/day of feed through the fast pyrolysis unit operating at 530 °C whereas torrefaction for the two-step pathway was investigated at three different torrefaction temperatures of 290, 310, and 330 °C. Three scenarios of producing process heat from natural gas, internal byproducts biochar supplemented with natural gas, and torrefaction condensate were investigated, with additional heat integration considered. Minimum selling price ranged from $4.01/gal to $4.78/gal for the heat-integrated processes whereas the price ranged fr...