Cold Streams Research Articles

Distribution of non-native brook trout (Salvelinus fontinalis) across Norwegian waterbodies – is it an invasive species?

Non-native brook trout (Salvelinus fontinalis MITCHILL, 1815) was introduced into Norway in 1883. However, it was not until the late 1970s that this acid-tolerant salmonid species was stocked into many acidified lakes that many populations became established. In 2004, all brook trout stocking in Norway ceased. In this study, we surveyed the distribution of brook trout in Norwegian water bodies. A totally of 202 self-sustaining populations were identified, mostly in unregulated lakes (n=101), streams (n=71) and also to some extent in reservoirs (n=25). Only four populations were found in inland rivers, and one population in a river with Atlantic salmon (Salmo salar L.). Localities with brook trout covered a wide range of altitudes and sizes. Analyses of time-series catches in sympatric populations of brown trout (Salmo trutta L.) and brook trout from 12 lakes (1997-2012) revealed a strong decline in brook trout stocks. A similar development in abundance has also emerged from other studies in recent years. Generally, lake-dwelling brook trout is regarded as a low-risk species with respect to invasiveness. However, brook trout/brown trout interactions may be habitat-specific, as brook trout may dominate in small and relatively cold streams.

Heat Transfer Blocks Diagram: A Novel Tool for Targeting and Design of Heat Exchanger Networks Inside Heat Integrated Water Allocation Networks

Sustainability is essential for process industries, as energy and resources are getting scarcer and scarcer. For the past decade, heat integrated water allocation networks (HIWANs) have drawn more and more attention, owing to the efficient utilization of water and energy. In this article, a systematic procedure for the synthesis of heat exchanger networks (HENs) in HIWANs has been proposed. A graphical tool, named heat transfer blocks diagram, is developed to improve the conceptual understanding for the implications of HEN structures in HIWANs. The minimum hot/cold utility consumption can be obtained by analyzing heat surpluses and heat deficits between cold stream and hot stream heat transfer blocks, while heat transfer matching blocks are introduced to deal with the heat exchange matches. Not only simplex series or parallel structures but also hybrid structures can be obtained via this graphical tool. Besides, a heuristic of step by step maximizing the heat load of heat exchangers is presented to guide ...

Configuration optimization of series flow double-effect water-lithium bromide absorption refrigeration systems by cost minimization

An optimal process configuration for double-effect water-lithium bromide absorption refrigeration systems with series flow – where the solution is first passed through the high-temperature generator – is obtained by minimization of the total annual cost for a required cooling capacity. To this end, a nonlinear mathematical programming approach is used. Compared to the optimized conventional double-effect configuration, the new optimal configuration obtained in this paper allows reducing the total annual cost, the capital expenditures, and the operating expenditures by around 9.5%, 11.1% and 4.9%, respectively. Most importantly, the obtained optimal solution eliminates the low-temperature solution heat exchanger from the conventional configuration, rendering a new process configuration. The energy integration between the weak and strong lithium bromide solutions (cold and hot streams, respectively) takes place entirely at the high-temperature zone, and the sizes and operating conditions of the other process units change accordingly in order to meet the problem specification with the minimal total annual cost. This new configuration was obtained for wide ranges of the cooling capacity (150–450 kW) and the temperature of the cooling water (15–35 °C). The results of this work motivate to apply the simultaneous optimization approach to seek for new multi-effect absorption refrigeration system configurations with parallel and reverse flow as well as other series flow arrangements that minimize the total annual cost.

Experimental investigation of the influence of natural convection and end-effects on Rayleigh streaming in a thermoacoustic engine.

The influence of both the natural convection and end-effects on Rayleigh streaming pattern in a simple standing-wave thermoacoustic engine is investigated experimentally at different acoustic levels. The axial mean velocity inside the engine is measured using both Laser Doppler Velocimetry and Particle Image Velocimetry. The mean flow patterns are categorized in three different regions referred to as "cold streaming" region, "hot streaming" region, and "end-effects" region. In the cold streaming region, the dominant phenomenon is Rayleigh streaming and the mean velocity measurements correspond well with the theoretical expectations of Rayleigh streaming at low acoustic levels. At higher acoustic levels, the measurements deviate from the theoretical expectations which complies with the literature. In the hot streaming region, temperature measurements reveal that the non-uniformity of the resonator wall temperature is the origin of natural convection flow. Velocity measurements show that natural convection flow superimposes on the Rayleigh streaming flow so that the measured mean velocity deviates from the theoretical expectations of Rayleigh streaming. In the last region, the measured mean velocity is very different from Rayleigh streaming due to the combined effects of both the flow disturbances generated near the extremity of the stack and the natural convection flow.

Numerical study of an asymmetrically heated rectangular duct with suspended cylinders

An asymmetrically heated (only one side of the duct is heated) solar air heater duct is numerically investigated using openFOAM to study the effect of passive turbulators (suspended cylinders) installed within the boundary layer close to the absorber plate to enhance heat transfer from it. Vortex flow is created behind the suspended cylinders, which disturbs the boundary layer and causes mixing of hot stream lines near the surface with relatively cold stream away from the absorber plate. Diameter of the suspended cylinders and its distance from the absorber plate is varied to study its effect on wall temperature of absorber plate in the turbulent flow regime.

Energy Integration of Kero Hydrotreating Unit, A Case Study of Nigerian Refinery

Kero hydrotreating unit being an integral part of the refinery system has been characterized by heat leaks, heat losses and inefficiencies in the heat transfer processes. This has necessitated the investigation into analysis of the current energy configuration to curb this menace and to proffer solution which would lead to efficient utilization of energy. Application of Pinch technology to kero hydrotreating unit heat exchanger network is presented with an optimum minimum approach temperature of 2.5°C to determine the energy target. This was achieved via the development of composite and grand composite curves for the kero hydrotreating unit process. The Pinch point temperature was found to be 544°C, with the utility targets for the minimum approach temperature being 7491.9 kW and 8259.62 kW for hot and cold utilities respectively, leading to energy savings of 34.33% and 32.17%. The percentage energy savings reported is as a result of the re-use of the cold or hot process streams before being sent back to the power plant or the trim coolers. Pinch analysis as an energy integration technique is proven to save more energy and utility cost than the traditional energy technique currently being used in the unit. The energy integration of the refinery kero hydrotreating unit using Pinch analysis did not only save energy and utility cost but showed significant improvement and exposed the inefficiencies of the traditional design approach. Keywords: Pinch analysis; Kero hydrotreating unit; Energy target; Heat integration Introduction Нe ability of any Nation to survive economically depends on its capacity to produce and manage sufficient supplies of low cost, safe energy and raw materials [1]. Worldwide consumption of limited fossil fuel resources is increasing with projections in this trend signifying that unless an efficient strategy is put in place, the world will soon be short in supply of energy. On the strategic statement of the energy sector of Nigeria vision 2020, it is necessary for the country to embark on energy conservation and efficiency initiatives which will require industries to move to energy saving equipment and utilities for reduction in total power demand by using technologies which ensure optimum energy utilization and integration. Pinch technology is a complete methodology derived from simple scientific principles. It allows the design of new plants with reduced energy and capital costs as well as where the existing processes require modification to improve performance [2]. More so, Pinch approach enables calculation of energy and utility targets by simple analysis of the process data, thus, an opportunity to design a new system or modification of existing system before embarking on actual implementation [3]. Pinch technology, when applied with imagination, can aUˆU´ect reactor design, separator design and the overall process optimization in any plant. But its application has proven that it can address problems beyond what energy conservation principles can resolve, as well as to solve problems as diverse as improving effluent quality, reducing emission, increasing product yield

Stellar streams as gravitational experiments

Kinematically cold tidal streams of globular clusters (GC) are excellent tracers of the Galactic gravitational potential at moderate Galactocentric distances, and can also be used as probes of the law of gravity on Galactic scales. Here, we compare for the first time the generation of such streams in Newtonian and Milgromian gravity (MOND). We first computed analytical results to investigate the expected shape of the GC gravitational potential in both frameworks, and we then ran N-body simulations with the Phantom of Ramses code. We find that the GCs tend to become lopsided in MOND. This is a consequence of the external field effect which breaks the strong equivalence principle. When the GC is filling its tidal radius the lopsidedness generates a strongly asymmetric tidal stream. In Newtonian dynamics, such markedly asymmetric streams can in general only be the consequence of interactions with dark matter subhalos, giant molecular clouds, or interaction with the Galactic bar. In these Newtonian cases, the asymmetry is the consequence of a very large gap in the stream, whilst in MOND it is a true asymmetry. This should thus allow us in the future to distinguish these different scenarios by making deep observations of the environment of the asymmetric stellar stream of Palomar 5. Moreover, our simulations indicate that the high internal velocity dispersion of Palomar 5 for its small stellar mass would be natural in MOND.

ReGrounding: The Art and Practice of Viewing Stone Display

ReGrounding:The Art and Practice of Viewing Stone Display* Richard Turner (bio) A viewing stone is a rock that has been selected and displayed for the purpose of aesthetic appreciation. The relocation of a stone from its natural habitat changes the found object from an ordinary rock to a viewing stone that invites close examination and perhaps contemplation. In this essay, I will examine the act of "re-grounding" rocks that have been removed from nature and resettled in the soil of culture. Using examples from my collection of viewing stones, I will consider the recontextualization process in the light of our ambiguous relationship with the natural world. Click for larger view View full resolution The Stone That Flew Here Malachite, wood, Bondo, enamel, 2017 In Ming Dynasty China (1573–1620) catalogues of viewing stones were illustrated with woodblock prints derived from brush-and-ink drawings. Some of the drawings were based on direct observation of a stone; others were copies of earlier sketches, while other illustrations were idealized versions of stones that may have been inspired by written descriptions or depictions of stones in landscape paintings. With the intent of reintroducing a slow-time appreciation of the viewing stone, the print edition of this essay is illustrated by high contrast black and white images derived from photographs but manipulated in Photoshop to a degree of abstraction shared by the Ming Dynasty woodblock prints. The online version of the essay is illustrated with full-color photographs of the same stones. [End Page 59] Stones in Chinese gardens or natural settings that are so distinct as to seem out of place are sometimes referred to as Stones That Flew Here. This designation references an obscure Buddhist myth about stones that were magically transported from India to China, landing in unlikely locations where they were incompatible with the local geology. The myth is most likely a way of explaining stones that have been moved by glaciers great distances from their places of origin. The Stone That Flew Here is, as well, a fitting appellation for the above piece of malachite (and any number of other stones as well) that were flown from their country of origin to the United States. Hand-carried by ardent connoisseurs, stones from China, Japan, Southeast Asia and elsewhere have been flown into American collections for decades. Air travel has accelerated the spread of viewing stone appreciation, with American collectors flying trans-Pacific routes to participate in exhibitions in China and Japan, and Asian experts and dealers traveling eastward to spread the lithic gospel in North America. I have mounted this stone so that it overhangs the left side of the base in order to give the idea that it is coming in for a landing. The base, which was carved in China for another stone, has been redesigned to suggest the mountain range in which the stone might touch down. Click for larger view View full resolution The Stone and The Phone Chinese stone, cordless phone base, paint, 2017 This sculpture gently reminds us of our troubled relationship with planet Earth. The stone is from China. The base is a cradle for a cordless telephone. We extract millions of tons of minerals from the earth annually for the manufacture of computers, mobile phones, television sets and other electronics. When these products become obsolete, they are returned to the earth in the form of e-waste, which often pollutes the earth and can be a significant health hazard for workers involved in processing the e-waste. China is one of the main countries that process hazardous electronic waste. Joining this Chinese stone with a repurposed cordless-phone base calls our attention to both the problem and a partial solution. [End Page 60] Collecting viewing stones typically involves arduous forays into the desert or mountains, wading cold streams, walking dry gulches and climbing windblown slopes. An often-overlooked resource for the suburban collector is the local building-supply store. This cut piece of limestone was purchased at just such an establishment. The top surface of the stone is reminiscent of a rugged desert landscape seen from high above. The rough sides of the piece, seen on a different scale...

Cleaning Schedule Operations in Heat Exchanger Networks

Heat exchanger networks have been known to be the essential parts in the chemical industries. Unfortunately, since the performance of heat exchanger can be decreasing in transferring the heat from hot stream into cold stream due to fouling, then cleaning the heat exchanger is needed to restore its initial performance periodically. A process of heating crude oil in a refinery plant was used as a case study. As many as eleven heat exchangers were used to heat crude oil before it was heated by a furnace to the temperature required to the crude unit distillation column. The purpose of this study is to determine the cleaning schedule of heat exchanger on the heat exchanger networks due to the decrease of the overall heat transfer coefficient by various percentage of the design value. A close study on the process of heat exchanger cleaning schedule in heat exchanger networks using the method of decreasing overall heat transfer coefficient as target. The result showed that the higher the fouling value the more often the heat exchanger is cleaned because the overall heat transfer coefficient decreases quickly.

Heat Pump for Energy-Efficient Sugarcane Juice Freeze Pre-concentration

A freeze concentration system with two-stage heat pump was investigated for pre-concentrating sugarcane juice in a jaggery making process. Two identical vented double-wall tube-and-tube heat exchangers were used as latent heat exchangers. One latent heat exchanger was operated as an evaporator, which selectively froze water from the juice. Another latent heat exchanger was operated as a condenser, which melted ice formed in a previous half cycle. Excess condenser duty, as a result of compressor work input and heat leakage into the cold sections of the system, was rejected with the help of second-stage compressor and concentrated juice and water heater. High juice velocity in the tube-and-tube heat exchanger helped to reduce inclusion in layer freezing. Raw juice was pre-cooled in a three fluid heat exchanger using concentrated juice and cold water streams from the latent heat exchangers. Pre-concentration of sugarcane juice from 20 to 40 °Brix helped to save about 63% of bagasse. Heat removed during freezing was one-seventh of that required for evaporation. R290 was found the best option amongst refrigerants R744 (CO2), R290 (C3H8) and R22 (CHClF2). Performance of system was evaluated considering the effect of thermal mass, ambient heat gain, variation in freezing point depression and ice layer thickness. Cooling COP of 14 can be achieved in a practicable system with evaporation at − 8 °C, condensation at 3 °C and the excess heat rejection at 34 °C. This shows that specific energy consumption can be as low as 8.8 kWhe/m3 of separated water.

Chaetocladius coppai sp. nov. and C. diai sp. nov., two mountain species inhabiting glacial springs and cold streams of the Alps and Lebanon (Diptera: Chironomidae, Orthocladiinae)

Two new species of the genus Chaetocladius are described, C. (s. str.) coppai sp. nov. as male adult and C. (s. str.) diai sp. nov. as male adult and pupa. The descriptions are based on the material collected at glacial alpine springs and small streams located in the Maritime French Alps and the Swiss Alps for C. coppai sp. nov., and the Mount Lebanon range for C. diai sp. nov. According to the characters of the adult males, C. coppai sp. nov. belongs to the laminatus-group, while C. diai sp. nov. is close to C. elegans Makarchenko et Makarchenko, 2001. The comments on the taxonomic position, ecology and geographical distribution of the new species are given.

Halo substructure in the SDSS--Gaia catalogue: streams and clumps

We use the SDSS-Gaia Catalogue to identify six new pieces of halo substructure. SDSS-Gaia is an astrometric catalogue that exploits SDSS data release 9 to provide first epoch photometry for objects in the Gaia source catalogue. We use a version of the catalogue containing $245\,316$ stars with all phase space coordinates within a heliocentric distance of $\sim 10$ kpc. We devise a method to assess the significance of halo substructures based on their clustering in velocity space. The two most substantial structures are multiple wraps of a stream which has undergone considerable phase mixing (S1, with 94 members) and a kinematically cold stream (S2, with 61 members). The member stars of S1 have a median position of ($X,Y,Z$) = ($8.12, -0.22, 2.75$) kpc and a median metallicity of [Fe/H] $= -1.78$. The stars of S2 have median coordinates ($X,Y,Z$) = ($8.66, 0.30, 0.77$) kpc and a median metallicity of [Fe/H] $= -1.91$. They lie in velocity space close to some of the stars in the stream reported by Helmi et al. (1999). By modelling, we estimate that both structures had progenitors with virial masses $\approx 10^{10} M_\odot$ and infall times $\gtrsim 9$ Gyr ago. Using abundance matching, these correspond to stellar masses between $10^6$ and $10^7 M_\odot$. These are somewhat larger than the masses inferred through the mass-metallicity relation by factors of 5 to 15. Additionally, we identify two further substructures (S3 and S4 with 55 and 40 members) and two clusters or moving groups (C1 and C2 with 24 and 12) members. In all 6 cases, clustering in kinematics is found to correspond to clustering in both configuration space and metallicity, adding credence to the reliability of our detections.

Establishing a long-term monitoring network for assessing potential climatic refugia in cold alpine streams

Managing landscapes to maintain climate refugia is likely the best strategy to promote persistence of temperature-sensitive species with limited dispersal capacity. Rare, cold-stenothermic taxa occupy mosaic mountain stream networks due largely to hydrological source heterogeneity. We collected environmental and biological data from alpine streams in the Teton Range, Wyoming representing runoff from snowpack (N=3), glaciers (N=4) and subterranean ice (N=4), every summer from 2015-2017. We quantified differences in habitat among the streams according to a glaciality index that included bed stability, suspended solids, temperature and conductivity, and by comparing annual water temperature profiles for each stream. We measured to what degree macroinvertebrate and diatom assemblages varied by stream type. Abiotic and biotic characteristics appeared to differ among sources. Notably, streams fed by subterranean ice (icy seeps) maintained extremely low (mean <2°C) and stable water temperature. Rare, cold-stenothermic stonefly species (Zapada glacier and Lednia tetonica) were indicators for, although not exclusive to, icy seeps. Icy seeps and their sources may be refugia for temperature-sensitive taxa, as the subsurface ice is more insulated from warmer air temperatures.
 
 Featured photo by Nicole Y-C on Unsplash. https://unsplash.com/photos/9XixVlnUCbk

Las pupas de Podonominae (Diptera: Chironomidae) de los ríos tropicales Altoandinos

The Podonominae is a subfamily of Chironomidae which immature stages inhabit cold streams and brooks. In South America, most of the species have been reported only from the Andean/Patagonian subregion. However, the knowledge of its diversity from high tropical areas is still scarce. We studied the richness of genera and morphotypes of pupae and pupal exuviae of the subfamiliy Podonominae (Diptera: Chironomidae) in the high Andean rivers from Colombia, Ecuador and Peru, and discussed its geographical distribution in the studied area. The specimens were collected between 2004 and 2011 in 197 sampling points, from 17 basins over 2 000 m a.s.l. During the dry season, benthic and drift samples were taken in different substrates. We recognized three genera: Podonomopsis, Parochlus and Podonomus, with one, nine and 14 morphotypes, respectively. Only six of them were clearly determined as species previously described. Podonomopsis was represented only by one species, P. illiesi, only found in high altitude rivers in Perú (above 3 500 m a.s.l.). Morphotypes richness and abundance of Parochlus were higher in rivers from Ecuador and Colombia (P. incaicus, Parochlus sp. 1 and Parochlus sp. 2 were the most common species). Conversely, Podonomus was more diverse and abundant in rivers from Perú (P. caranqui, P. fittkaui and P. fastigians were the most common species). We found a clear pattern of distribution of morphotypes in the latitudinal gradient. First, we confirmed an evident decrease in the morphotypes richness in relation to the South Andes. Second, we found species such as Podomopsis illiesi, Podonomus fittkaui and Podomus fastigians that only were present in Perú, but not in Ecuador and Colombia. For these species, the Huancabamba Depression (6°S Latitude, North of Perú), a major structural and physiographic break in the Andes, could represent an important barrier in their dispersion toward lower latitudes. A taxonomic key to genera and morphotypes determination was also provided.

Interactive effects of temperature and habitat complexity on freshwater communities.

Warming can lead to increased growth of plants or algae at the base of the food web, which may increase the overall complexity of habitat available for other organisms. Temperature and habitat complexity have both been shown to alter the structure and functioning of communities, but they may also have interactive effects, for example, if the shade provided by additional habitat negates the positive effect of temperature on understory plant or algal growth. This study explored the interactive effects of these two major environmental factors in a manipulative field experiment, by assessing changes in ecosystem functioning (primary production and decomposition) and community structure in the presence and absence of artificial plants along a natural stream temperature gradient of 5–18°C. There was no effect of temperature or habitat complexity on benthic primary production, but epiphytic production increased with temperature in the more complex habitat. Cellulose decomposition rate increased with temperature, but was unaffected by habitat complexity. Macroinvertebrate communities were less similar to each other as temperature increased, while habitat complexity only altered community composition in the coldest streams. There was also an overall increase in macroinvertebrate abundance, body mass, and biomass in the warmest streams, driven by increasing dominance of snails and blackfly larvae. Presence of habitat complexity, however, dampened the strength of this temperature effect on the abundance of macroinvertebrates in the benthos. The interactive effects that were observed suggest that habitat complexity can modify the effects of temperature on important ecosystem functions and community structure, which may alter energy flow through the food web. Given that warming is likely to increase habitat complexity, particularly at higher latitudes, more studies should investigate these two major environmental factors in combination to improve our ability to predict the impacts of future global change.

Development of a novel flowsheet for sulfur–iodine cycle based on the electrochemical Bunsen reaction for hydrogen production

The sulfur–iodine (SI) cycle is one of the promising methods for large-scale hydrogen production. A new flowsheet of SI cycle assembled with electrochemical Bunsen reaction was devised and modeled in this work. Adoption of electrochemical Bunsen reaction simplifies the flowsheet. The high concentrations of H2SO4 and HI, especially the over-azeotropic HI solution, successfully generated in the separated compartments of electrochemical cell without requiring further separation and purification. The enriched HI gas evaporates through flash, eliminating the extra concentration process, and then decomposes into 1 mol/s of H2 in hydrogen perm-selective membrane reactor. A HI separator is employed to maximize the recycle of undecomposed HI. The concentrated H2SO4 after flash decomposes into 0.5 mol/s of O2. The mass and energy balances of the SI cycle were evaluated. The cascade utilization of energy was carried out through internal heat exchange between hot and cold streams in the flowsheet. The surplus waste heat was recovered as electric power to improve the energy utilization efficiency. The overall thermal efficiency of the flowsheet was estimated to be 42–50% and was sensitive to heat recovery ratio. The simplified and energy-efficient flowsheet is competitive to the previous traditional flowsheets and will provide a reference for the industrial utilization of SI cycle.

Simulation and optimization of salt-production process from desalination brine

A novel multi-salt crystallization process is presented to separate the salts from the desalination brine and is optimized using the gradual optimization integration strategy based on T-H diagram. Firstly, the process is simulated by Aspen Plus software to obtain the cold and hot load curve and the bottlenecks and unreasonable heat transfer processes are analysed. Secondly, considering the energy utilization and conversion procedure, the turbine and/or heat pump are introduced to improve the process. Then the parameters of production process and utility system are adjusted. Thirdly, the new stream information is obtained by process simulation and the new composite curves are drawn, which will guide the further adjustment of the system. If the new composite curves do not satisfy the process demand, then the above steps are repeated. Through several improvements, two approximate parallel hot and cold stream curves are constructed. The hot streams and cold streams are maximum possible matched, and the amount of utility and power consumption is significantly reduced. In a case study, two optimization schemes are adopted: the feed brine is preheated by the flash steam and the heat pump crystallization technology is introduced. The results show that the energy consumption of two optimized processes is 94.8 kW and 90.1 kW, and the total energy loss decreased 86.7 % and 87.3 %.

Framework for work-heat exchange network synthesis

Chemical industries consume most of the energy for heating and compression needs. This energy can be saved by synergizing the work and heat requirements of the processes. In this work, we propose a generalized framework for handling both heat and work integration simultaneously. A mixed-integer nonlinear programming (MINLP) model is developed for work-heat exchange network synthesis (WHENS). Stage-wise superstructure with fixed number of splits and isothermal mixing is used for heat integration. Work integration involves turbines and compressors on single shaft turbine compressor (SSTC). In this work, the individual streams are not classified as high or low-pressure streams. Hence, pressure changing streams can undergo either compression in compressor or expansion in turbine or valve depending upon the process needs and specified target operating conditions. Also, the pressure changing stream are not classified as hot or cold stream a priori in the heat integration. This provides more flexibility and generalization for work-heat integration. Starting with a set of streams with known inlet flows, temperatures and pressures, the network can be synthesized for any desired objective. The model can also handle unknown exit temperatures of some streams. Finally, we illustrate the applicability of this framework on a natural gas liquefaction process.

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

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

Heat Exchanger Network Retrofit Using Individual Stream Temperature vs Enthalpy Plot

This paper presents a new graphical approach for Heat Exchanger Network (HEN) retrofit that is based on the individual stream temperature versus enthalpy plot (STEP). STEP maintains the individual stream characteristics and enables users to graphically map hot and cold streams and retrofit HEN without the need to perform enthalpy calculations, or to check for minimum temperature approach violations. Application of the STEP method to a well-established HEN retrofit case study from the literature shows that it only requires one visualisation tool to simultaneously diagnose and retrofit an existing HEN. On top of that, the STEP method yields up to 5 % higher heat recovery as compared to the results obtained using conventional retrofit methods.