Total site methodology as a tool for planning and strategic decisions

A Total Site (TS) is defined as a set of processes (industrial plants, residential, business and agriculture units) linked through the central utility system. The utility system incorporates a number of operating units such as boilers, steam turbines, gas turbines and letdown stations. Many sites are using the TS system representation. Heat Integration at TS level has been well developed and successfully implemented. However, sites typically develop with time and even minor changes/extensions can affect TS heat recovery significantly. It is beneficial to plan their strategic development in advance, to increase or at least not to decrease the rate of heat recovery when integration of additional processes takes place. Even when this has not been done at the initial stage, the TS methodology can still be used as a tool for the strategic planning decision making. This work illustrates how the TS methodology can contribute to the strategic development and the extension planning of already existing TS. The aim is to reveal the potentials for Heat Integration, when new units or processes are considered for the inclusion in the TS. Moreover, some operating parameters (e.g. temperature or capacity) of the unit can be proposed to achieve the best possible heat recovery. The degrees of freedom for TS changes can be on two levels: (i) only adding an operating unit to the current utility system (the Total Site Profiles remain the same) or (ii) changing of the TS by including more processes (the Total Site Profiles are changed). The first group of changes includes the integration of heat engines to produce electricity utilising heat at higher temperature and returning it to the system at lower temperature, which is still acceptable for the heat recovery and simultaneously for the electricity production. The second group of changes is more complex. For evaluating these changes a plus/minus principle is developed allowing the most beneficial integration of new units to the TS. Combinations of both types of changes are also considered

Targeting Minimum Heat Transfer Area for Heat Recovery on Total Sites

This paper upgrades the Total Site integration methodology, when accounting for a trade-off between capital and heat recovery by selection of optimal temperature levels for intermediate utilities and therefore, decrease capital cost. Heat transfer area for recuperation in Total Site is a two-fold problem and it depends on the Sink Profile on one side and on the Source Profile on another. The resulting temperature of intermediate utility is a result of a trade-off since the heat transfer area on Source side is decreasing, when temperature of IM is decreasing, however increased on Sink side. In the opposite higher intermediate utility temperature leads to higher area on the Source side and lower on Sink side. The temperature of each intermediate utility may be varied between specified lower and upper bounds subject to serving the Sink and Source Profiles

Capital Cost Targeting of Total Site Heat Recovery

Exploiting heat recovery on Total Site level offers additional potential for energy saving through the central utility system. In the original Total Site Methodology (Klemeš et al., 1997) a single uniform ΔTmin specification was used. It is unrealistic to expect uniform ΔTmin for heat exchange for all site processes and also between processes and the utility system. The current work deals with the evaluation of the capital cost for the generation and use of site utilities (e.g. steam, hot water, cooling water), which enables the evaluation of the trade-off between heat recovery and capital cost targets for Total Sites, thus allowing to set optimal ΔTmin values for the various processes. The procedure involves the construction of Total Site Profiles and Site Utility Composite Curves and the further identification of the various utility generation and use regions at the profile-utility interfaces. This is followed by the identification of the relevant Enthalpy Intervals in the Balanced Composite Curves. A preliminary result for evaluation of heat recovery rate and capital cost can be obtained

SINTEZA PROCESOV IN PROCESNIH PODSISTEMOV ZA CELOTNO ŽIVLJENJSKO DOBO

Economically viable process designs should be, in addition to other criteria, profitable over their entire process lifetimes not only at the present time. An improved process design can be achieved by establishing an appropriate trade-off between product income, raw material, operating costs, and investment. The full lifetime of the processes and future prices have to be considered rather than optimising them on a yearly basis using current prices. Single-period optimisation and synthesis models for processes reflects current prices only. The prices can fluctuate rather quickly and the optimal solution may be very different from one year to the another. Therefore, the traditional superstructural synthesis approach applying a mixed-integer nonlinear programming model was upgraded: i) over time, by considering an entire lifetime, which can be described by a multi-period model and ii) the whole field of variation regarding uncertain future prices. A stochastic approach considering the statistical distribution of price projections over an entire lifetime was used on different case studies instead of the traditional deterministic approach accounting for nominal future price projection. The objective was the maximisation of the expected net present value of a process or the expected incremental net present value of different process subsystem. The heat exchanger network has been one of the subsystem, which can significantly contribute to operating costs due to savings of external utility consumption. For this subsystem a deterministic and stochastic multi-period mixed-integer nonlinear programming (MINLP) synthesis models have been developed in order to account for future price projections. Considering higher energy prices gives rise to larger initial investments compared to solutions obtained with current prices. However, due to the uncertainties of utility prices\u27 forecasts, retrofitting using an extension of HEN during future years of the lifespan might be a better strategy. The objective is to identify a design that is the most suitable for effective future extensions and preferably with the lowest sensitivity to energy price fluctuations, as there can be various designs featuring similar initial investment. The results supports that it is economically beneficial to consider future utility prices as the incremental investment is not only paid-off but additional savings are achieved. Process-to-process Heat Integration can also significantly affect the trade-off between investment and operating cost. The aim of Total Site (TS) HEN synthesis was to develop a model synthesis for the TS that, besides many other important features, would also consider future utility prices. Two strategies for TS synthesis have been developed: i) sequential, when HI is performed within a process during the first step and then after a process-to-process HI has been performed, and ii) simultaneous, where the HI is performed within and between processes simultaneously. The second strategy can reveal additional opportunities for heat recovery that might not be identified when applying the first strategy. Comparison of the results obtained at consideration of current utility prices and forecasted utility prices indicates that is worth to account for future utility prices. The separation processes also consume a significant amount of energy. The synthesis of a distillation column sequence integrated within its heat exchanger network was used as a case study for the separation of a multi-component stream into pure component products by considering future utility prices. This analysis has been performed in order to evaluate the magnitude of the influence of forecasted utility prices. It can be concluded that forecasted utility prices can be beneficial, however, the technical limits of the systems should be carefully observed. The price fluctuation can also be observed for other prices not only utility prices, e.g. raw material cost, product price, etcEkonomično upravičeni načrti morajo biti, poleg ostalih kriterijev, tudi dobičkonosni skozi celotno življenjsko dobo procesa, ne samo v sedanjem času. Z vzpostavitvijo primernega trženja med prihodki produkta, stroški surovin, obratovalnimi stroški in investicijo v celotni življenski dobi lahko dosegamo izboljšan načrt procesa. Zato je optimizacija za celotno življenjsko dobo procesa z upoštevanjem napovedanih cen primernejša od optimizacije na letni osnovi. Enoperiodno optimiranje in sinteza za procese odraža le sedanje cene. Optimalna rešitev, dosežena za eno leto, se lahko znatno razlikuje od rešitve za drugo leto, saj se cene spreminjajo precej hitro. Običajni superstrukturni sintezni pristop z uporabo mešano-celoštevilskega nelinearnega programiranja smo zato nadgradili 1) z upoštevanjem celotne življenjske dobe, kar lahko opišemo z večperiodnim modelom in 2) z območjem spreminjanja negotovih prihodnjih cen. Namesto običajnega determinističnega pristopa pri nominalnih projekcijah prihodnjih cen smo uporabili stohastični pristop z upoštevanjem statistične porazdelitve napovedovanja cen za celotno življenjsko dobo. Namen je bil maksimiranje pričakovane neto sedanje vrednosti procesa oz. pričakovane inkrementalne neto sedanje vrednosti izboljšave različnih procesnih podsistemov. Podsistem, ki znatno prispeva k obratovalnim stroškom zaradi prihrankov pri porabi zunanjih pogonskih sredstev, je omrežje toplotnih prenosnikov. Za sintezo tega podsistema smo razvili tako deterministični kot stohastični večperiodni celoštevilski nelinearni programirni (MINLP) model ob upoštevanju prihodnjih cenovnih projekcij. Z upoštevanjem višjih cen energentov se povečajo začetne investicije v primerjavi z rešitvami, ki jim dosežemo pri sedanjih cenah. Zaradi negotovosti napovedovanja cen se je smiselno povečanju začetne investicije izogniti z načrtovanjem možnosti razširitve omrežja toplotnih prenosnikov v kasnejšem obdobju. Namen je doseči načrt, ki je kar najbolj primeren za učinkovito razširitev v prihodnosti, po možnosti z najmanjšo občutljivostjo na spreminjanje cen. Toplotna integracija med različnimi procesi lahko tudi znatno vpliva na trženje med investicijo in obratovalnimi stroški. Tako je bil eden od ciljev sinteze omrežja toplotnih prenosnikov prav upoštevanje prihodnjih cen pogonskih sredstev. Razvili smo dve strategiji za sintezo celotnega območja (ang. Total Site), in sicer: i) zaporedno, pri kateri toplotno integracijo izvajamo najprej na nivoju procesa in potem na nivoju celotnega območja, in ii) sočasno, pri kateri izvajamo toplotno integracijo na nivoju procesa in na nivoju celotnega območja hkrati. Slednja strategija omogoča dodatne možnosti prihranka toplote, kar potrjuje primerjava rezultatov doseženih pri sedanjih in prihodnjih cenah pogonskih sredstev. Separacijski procesi so lahko veliki porabniki energije. Sintezo zaporedja destilacijskih kolon integriranih z lastnim omrežjem toplotnih prenosnikov smo uporabili kot študijski primer za ločevanje večkomponentnega toka v čiste produkte. Analizo smo izvedli tudi z namenom določitve obsega vpliva napovedanih prihodnjih cen pogonskih sredstev. Zaključimo lahko, da z upoštevanjem napovedanih cen lahko dosegamo ekonomsko učinkovitejše procese ali procesne podsisteme, vendar je pri tem potrebno skrbno upoštevati tehnološke omejitve študiranega sistema. Nihanje cen razen pri pogonskih lahko opazimo tudi pri drugih cenah, npr. pri cenah surovin, in produktov. Pričakujemo lahko, da trženje v postopku optimiranja poskuša kompenzirati ta nihanja cen, npr. višje cene pogonskih sredstev bodo izravnane s povečanjem investicije, s čemer se zmanjšajo prihodnji obratovalni stroški. Vendar, ko upoštevamo vse stroške in prihodke hkrati, so lahko trendi vplivov različni od posameznega vpliva le teh, kar smo pokazali tudi s študijskim primerom

ANAEROBIC DIGESTION OF MIXTURES OF JAPANESE KNOTWEED (POLYGONUM CUSPIDATUM) AND CHICKEN MANURE TREATED WITH FUNGUS PLEUROTUS OSTREATUS

V diplomski nalogi smo proučevali anaerobno digestijo mešanic japonskega dresnovca in piščančjega gnoja, ki so bile predhodno obdelane z glivo Pleurotus Ostreatus. Pred nastavitvijo eksperimentov smo določili optimalno razmerje med biomaso dresnovca in inokuluma. Nastavili smo štiri različna razmerja glede na trdne snovi in sicer: ïº1(D/I) = 85:15, ïº2(D/I) = 70:30, ïº3(D/I) = 50:50 in ïº4(D/I) = 30:70. Med procesom anaerobne digestije smo spremljali količino in sestavo nastajajočega bioplina in merili množinski delež metana, CO2 (glavni komponenti bioplina), N2 in O2 za nadzorovanje anaerobnega procesa. Ocenili smo, da je optimalno razmerje med dresnovcem in inokulumom 80:20, saj smo želeli imeti v vhodni snovi največji možni delež rastlinskih substratov. Nato smo izvedli eksperiment, kjer so bili vhodni substrati mešanice z različnimi razmerji dresnovca in piščančjega gnoja, obdelani z glivo Pleurotus Ostreatus. Namen obdelave teh mešanic z glivo je bil, da gliva z encimi pretvori bakterijam nedostopno lignocelulozo, tako iz dresnovca kot tudi stelje iz gnoja, v substrat, katerega bakterije v procesu anaerobne digestije hitreje in lažje razgradijo, pri tem pa kot produkt nastaja bioplin. Tudi med tem procesom smo merili volumen nastalega bioplina in njegovo sestavo. Pred in po anaerobni digestiji smo določevali vsebnost trdnih snovi in vsebnost hlapnih trdnih snovi. Iz podatkov o volumnu bioplina, njegovi sestavi in vsebnosti trdnih in hlapnih trdnih snovi, smo lahko izračunali različne donose metana. Izkazalo se je, da so glive ob prisotnosti dresnovca prerasle tudi gnoj in da je bil donos bioplina pri anaerobni digestiji obdelanega dresnovca nekoliko višji kot pri neobdelanem dresnovcu.This diploma work deals with the anaerobic digestion of the mixture of Japanese knotweed and chicken manure which had previously been treated with fungus Pleurotus Ostreatus. Before setting the experiments we set the optimal ratio between the biomass of knotweed and inoculum. We set four different ratios with respect to the total solids as follows: 1(D/I) = 85:15, 2(D/I) = 70:30, 3(D/I) = 50:50 in 4(D/I) = 30:70. During the process of anaerobic digestion we monitored the amount and the composition of the created biogas and we measured the amount fractions of methane, CO2 (main components of biogas), N2 and O2 to control the anaerobic conditions. We estimated the optimal ratio between knotweed and inoculum is (D/I) = 80:20, because we wanted to have as high a proportion of plant substrates as possible in the input matter. After obtaining the optimal ratio we set up an experiment, where the inputs were mixtures with different ratios of knotweed and chicken manure, now treated with fungus Pleurotus Ostreatus. The purpose of the treatment was to use enzymes to convert bacteria inaccessible lignocelluloses, both knotweed as well as bedding from manure, into substrates which bacteria degrade with greater ease and faster during the process of anaerobic digestion, where biogas is produced. During the anaerobic digestion we measured the amount and composition of the created biogas. Before and after the anaerobic digestion we measured the content of total solids and volatile total solids. From the measurements we calculated different methane yields. It turned out that fungus can grow on manure in the presence of knotweed and that the biogas yield of anaerobic digestion of treated knotweed is slightly higher than in the case of untreated knotweed

Recovery of N-butanol from a complex five-component reactive azeotropic mixture

This paper proposes a concept of a process design for the separation and recovery of n-butanol from a five-component mixture, consisting of n-butanol, isobutanol, formaldehyde, water and methanol. The mixture is a common waste stream in the production of butylated amino resinstherefore, recovery of n-butanol is crucial to the efficiency of the process. The results show that up to 94% of the n-butanol present in the waste stream can be recovered. Under the studied conditions, 99.76% pure n-butanol can be obtained, while formaldehyde, water and methanol are present only in traces. The energy intensity of the process is estimated at 2.42 MJ/kg of purified n-butanol. The economic analysis of the process shows that the process is economically viable over a wide range of production capacities, as evidenced by high net present values and high return on investment values

Integration of an Absorption Chiller to a Process Applying the Pinch Analysis Approach

In addition to the consumption of hot utilities, there is also a significant cost associated with the consumption of cold utilities when there is a high demand for cooling. A promising solution for cooling is an absorption chiller (AC), which uses heat instead of electricity for cooling. A thermodynamic approach for evaluating AC integrated with a process is presented in this work. A model for assessing the properties and duties of an AC cycle was developed. The integration of a combined process-AC system was evaluated using the Grand Composite Curve. Three different options of integration were analyzed: (i) above the Pinch, (ii) below the Pinch, and (iii) across the Pinch. AC represents the combined effect of a heat engine and a heat pump, as the generator together with the absorber and condenser has the function of a heat engine, while the evaporator combined with the absorber and condenser mimics the function of a heat pump. The comparison between the non-integrated and integrated process-AC systems has revealed that the proper placement of AC is across or below the Pinch and the improper is above the Pinch. If AC was entirely integrated below the Pinch, the integration would result in a complete (100%) reduction in the consumption of hot utility for the operation of AC. The most suitable placement of AC with double reduction of hot utility consumption and complete reduction of both hot and cold utility to operate AC is across the Pinch due to the pumping of heat through AC from below to above the Pinch