Tuong-Van Nguyen

ENERGY AND EXERGY PERFORMANCE OF THREE FPSO OPERATIONAL MODES

Floating, Production, Storage and Offloading (FPSO) is a floating facility used in primary petroleum processing. In Brazil, most FPSOs have been installed in Campos Basin and new facilities may be implemented in the pre-salt area are projected to boost the Brazilian oil production. Crude oil composition has a significant influence on the operational mode of the FPSO. In this study, three operational modes of a FPSO are assessed: the first mode is used when the crude oil has the maximum water and CO2 contents, the second mode is implemented for a composition of 50% basic sediment and water (BSW) in the crude oil, and the third mode is operated when the crude oil has the maximum oil and gas fractions. The FPSO facility configuration changes with the operational mode, and it is possible to have gas export, gas injection, and CO2 injection, in order to achieve the functional conditions established by the FPSO operator. Energy and exergy criteria have been applied to evaluate and compare the performance of components and systems of the three operational modes of the FPSO. The processing and utilities plants have been modeled and simulated by using Aspen HYSYS. Results indicate that higher oil content in the crude oil increases the power consumption, the exergy requirement and the destroyed exergy of the FPSO.

Thermodynamic Performance Indicators for Offshore Oil and Gas Processing: Application to Four North Sea Facilities

Oil and gas extraction have been responsible for 25—28% of the total greenhouse gas emissions in Norway the last 10 years. The part from offshore oil and gas processing, including power production, flaring, and cold ventilation on production platforms, accounted for 20—22%. Exergy analysis is a method for systematic assessment of potential to perform work. It gives the possibility to identify where in a process inefficiencies occur: both losses to the surroundings and internal irreversibilities, and can be used as a tool for pinpointing improvement potential and for evaluation of industrial processes. When used in the petroleum sector, this can motivate more efficient oil and gas extraction, leading to a better utilisation of the resources and less greenhouse gas emissions.The objectives of this thesis were to: (i) establish exergy analyses of the oil and gas processing plants on different types of North Sea platforms; (ii) identify and discuss improvement potentials for each case, compare them and draw general conclusions if possible; and (iii) define meaningful thermodynamic performance parameters for evaluation of the platforms.Four real platforms (Platforms A—D) and one generic platform of the North Sea type were simulated with the process simulators Aspen HYSYS and Aspen Plus. The real platforms were simulated using process data provided by the oil companies. The generic platform was simulated based on literature data, with six different feed compositions (Cases 1—6). These five platforms presented different process conditions; they differed for instance by their exported products, gas-to-oil ratios, reservoir characteristics and recovery strategies.Exergy analyses were carried out, and it was shown that for the cases studied in this work, the power consumption was in the range of 5.5—30 MW, or 20—660 MJ/Sm3 o.e. exported. The heat demand was very small and covered by electric heating for two of the platforms, and higher, but low enough to be covered by waste heat recovery from the power turbines and by heat integration between process streams, for the other three platforms. The main part of the power was consumed by compressors in the gas treatment section for all cases, except Platform B and Case 4 of the generic model. Platform B had lower pressures in the products than in the feeds, resulting in a low compression demand. Case 4 of the generic model had a high content of heavy hydrocarbons in the feed, resulting in large power demand in the oil export pumping section. The recompression and oil pumping sections appeared to be the other major power consumers, together with the seawater injection system, if installed.The total exergy destruction was in the range of 12—32 MW, or 43—517 MJ/Sm3 o.e. exported. Most exergy destruction was related to pressure increase or decrease. Exergy destruction in the gas treatment section made up 8—57% of the total amount, destruction in the recompression section accounted for 11—29%, while 10—28% took place in the production manifolds. Exergy losses due to flaring varied in the range of 0—13 MW.Platforms with high gas-to-oil ratios and high pressures required in the gas product presented the highest power consumption and exergy destruction.Several measures were proposed for reduction of exergy destruction and losses. Two alternatives included use of mature technologies with potential to increase efficiency significantly: (i) limit flaring by installation of gas recovery systems, and (ii) improve gas compression performance by updating/exchanging the compressors.Several thermodynamic performance indicators were discussed, with Platforms A—D as case studies. None of the indicators could at the same time evaluate (i) utilisation of technical achievable potential, (ii) utilisation of theoretical achievable potential and (iii) total use of energy resources. It was concluded that a set of indicators had to be used to evaluate the thermodynamic performance. The following indicators were suggested: BAT efficiency on exergy basis, exergy efficiency, and specific exergy destruction.The formulation of exergy efficiency for offshore processing plants is difficult because of (i) the high throughput of chemical exergy, (ii) the large variety of chemical components in the process streams and (iii) the differences in operating conditions. Approaches found in the literature for similar processes were applied to Platforms A—D. These approaches had several drawbacks when applied to offshore processing plants; they showed low sensitivity to performance improvements, gave inconsistent results, or favoured platforms operating under certain conditions. A new exergy efficiency, called the component-by-component efficiency, was proposed. This efficiency could successfully evaluate the theoretical improvement potential.Eksergianalyse av offshore olje- og gassprosesseringOlje- og gassutvinning har vaert kilde til 25—28% av de totale klimagassutslippene i Norge de siste 10 arene. Den delen som stammer fra offshore olje- og gassprosessering (kraftproduksjon, fakling og kaldventilering pa produksjonsplattformer) stod for 20—22%. Eksergianalyse er en metode for systematisk bestemmelse av potensiale til a utfore arbeid. Det gir mulighet til a identifisere hvor i en prosess ineffektiviteter oppstar: bade i form av tap til omgivelsene og i form av interne irreversibiliteter. Det kan brukes som et verktoy for a finne forbedringsmuligheter og for evaluering av industrielle prosesser. Ved bruk innen petroleumssektoren kan dette motivere for mer effektiv olje- og gassutvinning, noe som gir bedre utnyttelse av ressursene og mindre utslipp av klimagasser.Formalet med denne avhandlingen er a: (i) etablere eksergianalyser av olje- og gassprosessering pa ulike typer Nordsjo-plattformer; (ii) identifisere og diskutere forbedringspotensialer for hvert tilfelle, sammenligne dem og trekke generelle konklusjoner om mulig; og (iii) definere meningsfulle termodynamiske ytelsesindikatorer for evaluering av plattformene.Fire virkelige plattformer (Plattform A—D) og en generisk Nordsjo-type plattform er simulert med prosessimulatorene Aspen HYSYS og Aspen Plus. De virkelige plattformene er simulert ved a bruke prosessdata stilt til radighet av operatorene av plattformene. Den generiske plattformen er simulert basert pa litteraturdata, med seks ulike fodesammensetninger (Case 1—6). Disse fem plattformene har ulike prosessbetingelser; de har for eksempel ulike eksporterte produkter, gass/olje-forhold, reservoaregenskaper og utvinningsstrategier.Eksergianalyser viser at for tilfellene studert i dette arbeidet er kraftforbruket i storrelsesorden 5,5—30 MW, eller 20—660 MJ/Sm3 o.e. eksportert. Varmebehovet er svaert lite og blir dekket med elektrisitet for to av plattformene, og noe hoyere men lavt nok til a bli dekket med varmegjenvinning fra kraftturbinene og ved varmeveksling mellom prosesstrommer for de tre andre plattformene. Hoveddelen av kraften blir konsumert av kompressorene i gassbehandlingsseksjonen for alle tilfellene bortsett fra Plattform B og Case 4 i den generiske modellen. Plattform B har lavere trykk i produktstrommene enn i fodestrommene, noe som resulterer i lavt behov for kompresjon. Case 4 i den generiske modellen har et hoyt innhold av tunge hydrokarboner i foden, noe som resulterer i hoyt kraftbehov i seksjonen for eksportpumping. Seksjonene for rekompresjon og eksportpumping viser seg a vaere de andre viktigste kraftforbrukerene, sammen med systemet for sjovannsinjeksjon hvis dette er installert.Den totale ekserginedbrytingen er 12—32 MW, eller 43—517 MJ/Sm3 o.e. eksportert. Mest ekserginedbryting er relatert til trykkoking eller trykkreduksjon. Ekserginedbryting i gassbehandlingsdelen utgjor 8—57% av den totale mengden, nedbryting i rekompresjonsseksjonen utgjor 11-29%, mens nedbryting i produksjonsmanifoldene utgjor 10—28%. Eksergitap pa grunn av fakling varierer mellom 0—13 MW.Plattformene med hoye gass/olje-forhold og behov for hoyt trykk i gassproduktene har hoyest kraftforbruk og ekserginedbryting.Ulike tiltak for reduksjon av ekserginedbryting og eksergitap er foreslatt. To alternativer inkluderer bruk av modne teknologier og har potensiale til a oke effektiviteten betydelig: (i) begrensning av fakling av gass ved installasjon av gassgjenvinningssystemer, og (ii) forbedring av gasskompresjonen ved a oppdatere/bytte ut kompressorer.Flere termodynamiske ytelsesindikatorer er diskutert med utgangspunkt i Plattform A—D. Ingen av indikatorene kan pa samme tid evaluere (i) utnyttelse av teknisk oppnaelig potensiale, (ii) utnyttelse av teoretisk potensiale og (iii) total bruk av energiressurser. Det konkluderes med at et sett med indikatorer ma brukes for a evaluere termodynamisk ytelse. De folgende indikatorene foreslas: BAT (best tilgjengelig teknologi) effektivitet pa eksergibasis, eksergieffektivitet og spesifikk ekserginedbryting.Formuleringen av eksergieffektivitet for offshore olje- og gassprosessering er utfordrende pa grunn av (i) den hoye gjennomgangen av kjemisk eksergi, (ii) den store variasjonen av kjemiske komponenter i prosesstrommene og (iii) de store forskjellene i driftsbetingelser. En ny type eksergieffektivitet foreslas. Denne effektiviteten kan evaluere utnyttelsen av det teoretiske potensialet pa tross av punktene nevnt ovenfor.

Synthesis of preliminary system designs for offshore oil and gas production

Abstract The present work deals with the design of oil and gas platforms, with a particular focus on the development of integrated and intensified petroleum processing plants. It builds on a superstructure-based approach that includes all the process steps, transformations and interconnections of relevance, to generate and compare a large number of alternatives. The superstructure is formulated based on engineering knowledge and is coupled to process models developed in Aspen and Matlab, together with multi-objective optimisation routines and uncertainty assessments. It takes actual measurements from North Sea fields and three petroleum compositions as starting points. The significance of the uncertainties associated with the feed properties, and the capital costs, taxes and lifetime, is assessed. The results indicate that (i) the system performance strongly depends on the level of mass integration within the platform, (ii) the oil and gas recoveries are markedly impacted by the number of separation stages and heat exchangers, and (iii) disregarding the interactions between the several plant sections lead to sub-optimum solutions. The application of this framework proves to be useful for eliminating inadequate configurations and screening potentially novel solutions at early stage designs, with respect to technical, energetic and economic criteria.

Sustainable Production of Asphalt Using Biomass as Primary Process Fuel

The production of construction materials is very energy intensive and requires large quantities of fossil fuels. Asphalt is the major road paving material in Europe and is being produced primarily in stationary batch mix asphalt factories. The production process requiring the most energy is the heating and drying of aggregate, where natural gas, fuel oil or LPG is burned in a direct-fired rotary dryer. Replacing this energy source with a more sustainable one presents several technical and economic challenges, as high temperatures, short startup times and seasonal production variations are required. This paper analyses different pathways for the use of biomass feedstock as a primary process fuel. The analysed cases consider the gasification of straw and wood chips and the direct combustion of wood pellets. The additional use of syngas from the gasifier for the production of heat or combined heat and power is further evaluated during hours without asphalt production. The challenges of having varying seasonal production can be solved by this integration of the production unit to the utility system. The results show the economic and technical feasibility of using biomass for process heating in the asphalt factory. The dryer demand of 6.4 MW can be covered with a biomass input between 7.1 and 8.6 MW. District heat can be produced at competitive prices below 40 € per MWh.

Thermo-Economic Modelling and Process Integration of CO2-Mitigation Options on Oil and Gas Platforms

The offshore extraction of oil and gas is an energy-intensive process associated with large CO2 and CH4 emissions to the atmosphere and chemicals to the sea. The taxation of these emissions has encouraged the development of more energy-efficient and environmental-friendly solutions, of which three are assessed in this paper. The integration of steam bottoming cycles on the gas turbines or of lowtemperature power cycles on the export gas compression can result either in an additional power output, or in a greater export of natural gas. Another possibility is to implement a CO2-capture unit, which allows recovering CO2 that can be used for enhanced oil recovery. In this paper, a North Sea platform is considered as case study, and the site-scale retrofit integration of these three options is analysed, considering thermodynamic, economic and environmental performance indicators. The results illustrate the benefits of valorising the waste heat recovered from the exhaust gases, as the total CO2-emissions can be reduced by more than 15 %. Exploiting low-temperature heat seems feasible, although more challenging in retrofit situations. Integrating CO2-capture appears promising with a CO2-avoidance cost between 23 and 29

Multi-objective optimization of organic Rankine cycles for waste heat recovery: Application in an offshore platform

/tCO2 for the chosen economic assumptions.