Heat pump assisted distillation. VII: A feasibility study on heat transformer assisted distillation systems

The problems in matching a heat driven heat transformer to a distillation process in heat pump assisted distillation are discussed. The performance of such a system is a function of the temperature difference across the distillation column. Plots are given of the calculated coefficients of performance against the temperatures of the top and bottom products. In addition plots are given of the calculated coefficients of performance against the generator temperature when the generator is independently heated. The percentage of energy saved is also plotted against coefficient of performance.     

Design of a thermally integrated bioethanol-fueled solid oxide fuel cell system integrated with a distillation column

Solid oxide fuel cell systems integrated with a distillation column (SOFC-DIS) have been investigated in this study. The MER (maximum energy recovery) network for SOFC-DIS system under the base conditions (C_EtOH = 25%, EtOH recovery = 80%, V = 0.7 V, fuel utilization = 80%, T_SOFC = 1200 K) yields Q_Cmin = 73.4 and Q_Hmin = 0 kW. To enhance the performance of SOFC-DIS, utilization of internal useful heat sources from within the system (e.g. condenser duty and hot water from the bottom of the distillation column) and a cathode recirculation have been considered in this study. The utilization of condenser duty for preheating the incoming bioethanol and cathode recirculation for SOFC-DIS system were chosen and implemented to the SOFC-DIS (CondBio-CathRec). Different MER designs were investigated. The obtained MER network of CondBio-CathRec configuration shows the lower minimum cold utility (Q_Cmin) of 55.9 kW and total cost index than that of the base case. A heat exchanger loop and utility path were also investigated. It was found that eliminate the high temperature distillate heat exchanger can lower the total cost index. The recommended network is that the hot effluent gas is heat exchanged with the anode heat exchanger, the external reformer, the air heat exchanger, the distillate heat exchanger and the reboiler, respectively. The corresponding performances of this design are 40.8%, 54.3%, 0.221 W cm⁻² for overall electrical efficiency, Combine Heat and Power (CHP) efficiency and power density, respectively. The effect of operating conditions on composite curves on the design of heat exchanger network was investigated. The obtained composite curves can be divided into two groups: the threshold case and the pinch case. It was found that the pinch case which T_SOFC = 1173 K yields higher total cost index than the CondBio-CathRec at the base conditions. It was also found that the pinch case can become a threshold case by adjusting split fraction or operating at lower fuel utilization. The total cost index of the threshold cases is lower than that of the pinch case. Moreover, it was found that some conditions can give lower total cost index than that of the CondBio-CathRec at the base conditions.     

Conceptual design of an internally heat integrated propylene-propane splitter

Huge quantities of energy are required in distillation columns used for polymer grade separations of close boiling mixtures. The purpose of this paper is to introduce an industrially viable, internally heat integrated (HIDiC) version of a state of the art propylene-propane splitter. The base case is one of the world's largest, heat-pump assisted, stand-alone columns of this type. The actual plant data formed the basis for the techno-economic evaluation, which indicated that the HIDiC could become an economically attractive option for new designs, provided the barriers related to increased design complexity could be overcome.     

Heat pump assisted distillation. I: Alternative ways to minimize energy consumption in fractional distillation

A survey is made of the numerous possible ways to minimize the consumption of energy in fractional distillation. Distillation is a highly energy-intensive process in which the actual energy consumed is far greater than the theoretically calculated loss in available work. The methods considered for reducing energy consumption are classified as those which (i) do not require process modifications, (ii) require minor process modifications, (iii) make use of more than one column and (iv) make use of heat pumps.     

Heat pump assisted distillation. V: A feasibility study on absorption heat pump assisted distillation systems

The problems in matching a heat driven absorption heat pump to a distillation process in heat pump assisted distillation are discussed. The performance of an absorption system is a function of the temperatures in the evaporator, the condenser, the absorber and the generator and the ratio of the mass flow rate in the secondary circuit to the mass flow rate in the primary circuit. In absorption systems design choices are limited by the Gibbs phase rule. Plots are given of the coefficient of performance against the temperatures of the top and bottom products and also against the energy saved.     

Heat integrated heat pumping for biomass gasification processing

The main part of this paper is an industrial case study. It deals with an application of a heat pump in energy systems for biomass gasification in a wood processing plant. Process integration methodology is applied to deal with complex design interactions as many streams requiring heating and cooling are involved in the energy recovery. A refrigeration cycle maintains low temperature in the scrubber where the production gas (or synthesis gas–syngas) is cooled and undesirable contaminants are removed before the syngas is introduced into the engine. In addition to electricity generation, a large amount of waste heat is available in the biomass gasification system studied in the paper, and its appropriate heat integration with utility systems within a plant allows the available heat to be efficiently utilized for the site. The conceptual understanding gained from the case study provides systematic design guidelines for further process development and industrial implementation in practice.     

Design and control of an ideal heat-integrated distillation column (ideal HIDiC) system separating a close-boiling ternary mixture

Despite the fact that a stand-alone ideal heat-integrated distillation column (ideal HIDiC) can be thermodynamically efficient and operationally stable, the application of an ideal HIDiC system to separate a close-boiling multi-component mixture is still a challenging problem because of the possibility of strong interactions within/between the ideal HIDiCs involved. In this work, employment of two ideal HIDiCs to separate a close-boiling ternary mixture is studied in terms of static and dynamic performance. It is found that the ideal HIDiC system can be a competitive alternative with a substantial energy saving and comparable dynamic performance in comparison with its conventional counterpart. The direct sequence appears to be superior to the indirect sequence due to the relatively small vapor flow rates to the compressors. Controlling the bottom composition of the first ideal HIDiC with the pressure elevation from the stripping section to the rectifying section helps to suppress the disturbances from the feed to the second ideal HIDiC. Special caution should, however, be taken when the latent heat of the distillates is to be recovered within/between the ideal HIDiCs involved, because a positive feedback mechanism may be formed and give rise to additional difficulties in process operation.     

Transient analysis of heat pump assisted distillation systems. 2 Column and system dynamics

A model to simulate the transient behaviour of a heat pump assisted distillation column is presented. The packed bed distillation column is treated as a distributed parameter system with time and space as independent parameters. The column modelling using appropriate basic equations, their application to binary systems, the solution scheme to the model equations and the distillation column simulation algorithm are described. The heat pump simulation algorithm is then coupled with this algorithm and the column transient behaviour with and without heat pump assist is obtained. The results are compared with earlier steady state data in the literature.     

Heat pump assisted distillation. II: Matching an external heat pump to a fractional distillation system

The problems in matching an external mechanical vapour compression heat pump to a distillation process in heat pump assisted distillation are discussed. There are four main design parameters to consider when selecting a working fluid for the heat pump, of which only two are independent. Various arrangements for imperfectly matched systems are presented, including the use of a two stage heat pump. A number of other factors which affect the choice of a heat pump assisted distillation system, including economic factors, are also considered.     

Heat and mass transfer in vacuum membrane distillation

In the membrane distillation (MD) literature, the heat transfer coefficients of the boundary layers are usually estimated from well known heat transfer empirical correlations developed for non-porous and rigid heat exchangers. A difference between the mechanism of heat transfer in MD systems, which is coupled with transmembrane mass transfer, and the mechanism of heat transfer in “pure” heat exchangers is expected to exist. Vacuum membrane distillation has been experimentally studied in a capillary membrane module and the heat transfer coefficients have been evaluated in both the lumen and the shell side of the membrane module. A critical review of the most frequently used heat transfer empirical correlations in MD systems is presented. Finally, the experimental results obtained in this paper are compared to those of literature, in order to test their applicability in membrane distillation systems.     

Heat pump assisted distillation. X: Potential for industrial applications

In heat pump assisted distillation, the working fluid can either be one of the components of the mixture to be distilled or it can be an external working fluid. The operating parameters of more than thirty potential heat pump assisted distillation systems have been listed. A detailed assessment can only be made if detailed thermodynamic data are available. A set of criteria has been prescribed for the choice of an appropriate mode for a particular application.     

Heat pump assisted distillation. VI: Classified references for heat pump assisted distillation systems from 1945 to February 1986

More than one hundred and fifty references for heat pump assisted distillation systems have been listed and classified under the following categories: heat pump assisted distillation (1) with an external working fluid, (2) using one of the distillation components as the working fluid, (3) overall assessments and (4) experimental data.     

Heat pump assisted distillation. VIII: Design of a system for separating ethanol and water

A heat pump assisted distillation system has been designed for the separation of ethanol from 7 per cent aqueous mixtures to produce 93 per cent ethanol by weight. The distillation column has been designed on the basis of conventional design procedures. Valve trays were chosen to provide operational flexibility. R114 was chosen as the working fluid for the mechanical vapour compression heat pump. The heat pump system has been designed to match the heat loads determined for the column. Auxiliary heat exchangers have been provided to aid flexibility and control of column operation.     

Heat pump assisted distillation. III: Experimental studies using an external heat pump

An experimental study has been carried out on a continuously operated pilot fractional distillation column equipped with an external heat pump. The distillation column was a 15 cm diameter glass unit containing eleven single bubble cap plates. A methanol-water mixture was fed to the column and the heat pump working fluid was R114. The actual coefficient of performance (COP)_A of the heat pump increased with an increase in the mass flow rate of the working fluid. A maximum (COP)_A value of 4–3 was obtained with a gross temperature lift of 41–3°C. The performance of two reciprocating compressors was compared. The experiments have shown that continuous heat pump assisted distillation using an external working fluid can greatly reduce the energy used in a distillation process. No control problems were encountered in the experiments.     

Optimum heat storage design for heat integrated multipurpose batch plants

Heat integration to minimise energy usage in multipurpose batch plants has been in published literature for more than two decades. In most present methods, time is fixed a priori through a known schedule, which leads to suboptimal results. The method presented in this paper treats time as a variable, thereby leading to improved results. Both direct and indirect heat integration are considered together with optimisation of heat storage size and initial temperature of heat storage medium. The resulting model exhibits MINLP structure, which implies that global optimality cannot generally be guaranteed. However, a procedure is presented that seeks to find a globally optimal solution, even for nonlinear problems. Heat losses from the heat storage vessel during idling are also considered. This work is an extension of MILP model of Majozi (2009), which was more suited to multiproduct rather than multipurpose batch facilities. Optimising the size of the heat storage vessel as well as the initial temperature of the heat storage fluid decreased the requirement for external hot utility for an industrial case study by 33% compared to using known parameters.     

热管式热流计的开发研制

通过对传统热流计缺点的分析,研究了新型热管式热流计的结构尺寸和设计准则,并通过现场测试证实了此种热流计的应用可行性。     

Exergetic analysis of distillation processes—A case study

The concept of exergy has been introduced to establish a universal standard for quality and efficient use of energy. In this work, applications of this concept to compression, heat exchange, and separation processes, in addition to the computation of their irreversibility rate and thermodynamic efficiency, are considered. An industrial case study on the purification of 1,2-ethylenedichloride (EDC) in a high-purity distillation column is presented. Due to its large throughput, this distillation column consumes a large amount of thermal energy (steam to the reboiler) and in order to reduce the energy requirements without large process modifications, a new configuration using a vapour compression heat pump is proposed which yields considerable improvement in the use of energy. Both configurations were implemented using the commercial simulator Aspen Plus™; the results of the original configuration were validated with data extracted from the plant. The objective of this work was to compare the original configuration and the new proposed one, from a thermodynamic approach. Furthermore, two forms of process thermodynamic analysis based on the concept of exergy were applied to the new proposed configuration.     

Thermo-fluid dynamics of Loop Heat Pipe operation

The paper presents a thermo-fluid dynamic model for the transient operations of a Loop Heat Pipe. The Fourier heat conduction equation in a hollow cylinder is solved to determine the temperature distribution of the compensation chamber and the cavity. A one-dimensional transient model is also derived for the vapor temperature in the condenser section of the Loop Heat Pipe. The thermo-fluid dynamic characteristic of a Stainless Steel/Ammonia Loop Heat Pipe is analyzed.     

分离式液--气热管换热器的设计与应用

文中介绍一种利用工艺中液体冷却放出热量来加热气体的分离式热管换热器.对液--气换热进行了热力分析与强度、结构的设计计算,以及系统的水动力循环分析.同时给出了实际应用实例,充分说明这种联合换热形式的换热器是合理、可靠的.     

Effects of PEMFC operating parameters on the performance of an integrated ethanol processor

In this paper the performance of a complete fuel cell system processing ethanol fuel has been analyzed as a function of the main fuel cell operating parameters. The fuel processor is based on the steam reforming process, followed by high- and low-temperature shift reactors, and carbon monoxide preferential oxidation reactor, which are coupled to a polymeric fuel cell (PEMFC). The goal was to analyze and improve the fuel cell system performance by simulation techniques. PEMFC operation has been analyzed using an available parametric model, which was implemented within HYSYS environment software. Pinch Analysis concepts were used to investigate the process energy integration and determine the maximum efficiency minimizing ethanol consumption. The system performance was analyzed for the SR-12 Modular PEM Generator, the Ballard Mark V fuel cell and the BCS 500 W stack. The net system efficiency is dependent on the required power demand. Efficiency values higher than 50% at low loads and less than 30% at high power demands are computed. In addition, the effect of fuel cell temperature, pressure and hydrogen utilization was analyzed. The trade-off between the reformer yield and the fuel cell performance defines the optimal operation pressure. The cell temperature determines operating zones where the water, involved in the reforming reactions, can be produced or demanded.