System of Comprehensive Energy-Efficient Utilization Of

energies

Article System of Comprehensive Energy-Eﬃcient Utilization of Associated Petroleum Gas with Reduced Carbon Footprint in the Field Conditions

Valentin Morenov 1,* , Ekaterina Leusheva 1, George Buslaev 1 and Ove T. Gudmestad 2

1 Department of Oil and Gas, Saint Petersburg Mining University, 199106 Saint Petersburg, Russia; [email protected] (E.L.); [email protected] (G.B.) 2 Faculty of Science and Technology, University of Stavanger, N-4036 Stavanger, Norway; [email protected] * Correspondence: [email protected]; Tel.: +7-81-2328-8420

Received: 27 August 2020; Accepted: 18 September 2020; Published: 19 September 2020

Abstract: This paper considers the issue of associated petroleum gas utilization during hydrocarbon production in remote petroleum fields. Due to the depletion of conventional oil and gas deposits around the globe, production shifts to hard-to-recover resources, such as heavy and high-viscosity oil that requires a greater amount of energy to be recovered. At the same time, large quantities of associated petroleum gas are extracted along with the oil. The gas can be utilized as a fuel for power generation. However, even the application of combined power modes (combined heat and power and combined cooling heat and power) cannot guarantee full utilization of the associated petroleum gas. Analysis of the electrical and heat loads’ graphs of several oil fields revealed that the generated thermal energy could not always be fully used. To improve the efficiency of the fuel’s energy potential conversion, an energy system with a binary power generation cycle was developed, consisting of two power installations—a main gas microturbine and an auxiliary steam turbine unit designed to power the technological objects in accordance with the enterprise’s power load charts. To provide for the most complete utilization of associated petroleum gas, a gas-to-liquid system is introduced, which converts the rest of the gas into synthetic liquid hydrocarbons that are used at the field. Processing of gas into various products also lowers the carbon footprint of the petroleum production. Application of an energy system with a binary power generation cycle makes it possible to achieve an electrical efficiency up to 55%, at the same time maintaining high efficiency of consumers’ energy supply during the year. The utilization of the associated petroleum gas in the developed system can reach 100%.

Keywords: associated petroleum gas; binary cycle; combined heat and power; petroleum production; GTL; synthetic liquid hydrocarbons; MATLAB Simulink; Aspen HYSYS

1. Introduction Improving the ecologic, economic and technological efficiency of oil and gas facilities is an urgent task nowadays. Greenhouse gases, accumulating in the atmosphere, are causing global warming, which leads to significant climate changes. It can be said that the oil and gas industry emits considerable amounts of carbon dioxide into the atmosphere, for example, its share in the total emissions of the Russian Federation is 26% [1]. Air pollution and soil contamination lead to large expenditures for petroleum enterprises, which operate oil and gas fields [2]. Influence of hydrocarbon production on the environment is often characterized by the concept of “the carbon footprint”. This value is defined as the ratio of the CO2 equivalent of the greenhouse gas emissions to the functional unit of the

Energies 2020, 13, 4921; doi:10.3390/en13184921 www.mdpi.com/journal/energies Energies 2020, 13, 4921 2 of 14 extracted product. The carbon footprint is directly affected by the performance of the industrial plants and the power equipment, the efficiency of fuel and energy resources consumption, and measures to reduce greenhouse gas emissions. This unit is an indicator characterizing the level of negative impact caused to the climate system at the stages of hydrocarbon production before it is delivered or used by the consumer at a certain stage of the technological process [3]. Therefore, issues of reducing the environmental impact of oil and gas operations are most relevant for petroleum enterprises. Oil production is usually accompanied by the extraction of associated petroleum gas (APG). Its rational use during oilfield operation is important both with regards to ecological and technological issues. The petroleum industry is distinguished from other industries by high-energy intensity. In particular, the energy costs often amount to more than 50 percent of the cost of production for oil and gas industry facilities [4]. Furthermore, the traditional way of using a centralized power grid does not currently meet the requirements for the level of reliability and quality of the energy supply for the oil and gas industry. Moreover, with the gradual shift of oil and gas enterprises to hard-to-reach areas, such as offshore and the Arctic region, the use of autonomous sources of electricity is often the only viable economical and technical method of energy supply [5]. Utilization of gaseous fuel, such as natural gas or APG, in these self-sufficient power plants is seen as the most economically and technologically feasible method [6]. Moreover, standalone oil and gas production facilities, located in remote areas, often require comparatively small amounts of generated electrical energy—in the order of some megawatts. At the same time, the need for thermal energy can be quite high, for example, to counter the formation of asphalt-resin-paraffin deposits [7]. Thus, the authors of [8] developed the heating system for the bottomhole of an oil well powered by wind turbines. However, more often it is preferable to use associated petroleum gas as a fuel for combined heat and power (CHP) plants to generate both electrical and heat energy. There are quite a lot of works dedicated to this problem. For example, the authors of [9] developed an integrated CHP system utilizing natural gas as a fuel with simultaneous CO2-capture. The methodology for selection of the optimal operation mode for such power units was thoroughly studied in [10]. In given conditions, energy systems based on gas power units can provide efficient and environment-friendly power supply. However, at the same time, it has been established that despite the high efficiency of using the CHP mode of the electrical units’ operation, the generated thermal energy could not always be fully utilized. In the summer months, a significant amount of unclaimed heat remains, and the energy conversion efficiency of the primary energy source falls. Further studies, including experimental data obtained at power facilities of PJSC “Gazprom” operating in a combined cooling heat and power (CCHP) mode, showed that the energy system’s efficiency of operation of electrical units reaches nearly 65% during parts of the year. However, despite the fact that the use of this mode allows us to increase the efficiency of using gaseous fuel due to the production of additional cold energy, it is also impossible to maintain the efficiency of energy generation at a high level in the summer season (Figure1)[11]. Energies 2020, 13, 4921 3 of 14

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Figure 1. EnergyEnergy generation indicators for the year by the energy center of a gas enterprise.enterprise.

At the same time, modern oil ﬁelds are characterized by frequently changing electric power needs. At the same time, modern oil fields are characterized by frequently changing electric power Electric submersible pumps, air and gas compressors and other equipment require a considerable needs. Electric submersible pumps, air and gas compressors and other equipment require a amount of power to operate and these power rates can drastically change even during one day of considerable amount of power to operate and these power rates can drastically change even during work [12]. Figure2 represents the power consumption of an Arctic oil ﬁeld during a month in 2017 one day of work [12]. Figure 2 represents the power consumption of an Arctic oil field during a month and 2018. in 2017 and 2018.

Figure 2. Power consumption values during a month in 2017 and 2018 by the consumers at an oil field. Figure 2. Power consumption values during a month in 2017 and 2018 by the consumers at an oil ﬁeld.

In order to develop an effective effective system for APG utilization,utilization, the following should be considered:  IImpossibilitympossibility ofof fullfull utilization utilization of of thermal thermal energy energy obtained obtained in thein the CHP CHP mode mode during during the whole the whole year; − year;Variation of the electrical and thermal energy consumption; −  VNeedariation to e ffiofciently the electrical reduce and environmental thermal energy pollution. consumption; − Need to efficiently reduce environmental pollution. Thus, the aim of this work is to develop a comprehensive energy-efficient system for full utilization of theThus, associated the aim petroleum of this gas work with is reduced to develop carbon a comprehensive footprint. energy-efficient system for full utilization of the associated petroleum gas with reduced carbon footprint.

2. Materials and Methods

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2. Materials and Methods The developed system is comprised of two parts: at first the APG is utilized as a fuel for the power generation plants and the rest of the gas is then processed into synthetic liquid hydrocarbons (SLH). Thus, 100% utilization of APG can be achieved. Taking into account the preferable need of electric power, it is advisable to operate the energy system of oil and gas enterprises in a binary cycle of electric energy generation. The binary cycle of electrical energy generation, which is most often used in geothermal power production, considers the application of two power turbines units with two separate working mediums. It allows a flexible variation of the energy system’s output parameters for industrial and related facilities [13]. To apply this cycle for the petroleum industry, a comprehensive analysis of the electrical and heat power load charts of several operating oil and gas enterprises was carried out. At the oil fields of PJSC “Tatneft”, experimental studies were conducted on the basis of 59 operating gas-powered plants with a total capacity of 13.320 kW. This includes 40 gas turbine units (GTU) with a total capacity of 6.995 kW and 19 gas-reciprocating units (GRU) with a capacity of 6.325 kW. At these fields, the possibility of using the CHP mode to increase the efficiency of the primary energy sources was studied. An assessment of the available power was carried out on the basis of the data from the real average load (Prl) of the power generating units at the oil fields (Table1). The number in the unit type column shows the rated power of the power plants.

Table 1. Actual average load of gas turbine units and gas-reciprocating units.

P , kW № Manufacturer GTU GRU Unit Type rl Jan Feb Mar Apr May Jun Jul Aug Sep 1 GTU C-65 57.5 60 59 53.5 41.7 43.3 35 36.7 41.7 Capstone 2 GTU C-200 139 153 177 180 175 165 162 156 161 3 CJSC «PFK» GRU AGP-200 48 71 54 54 52 51 41.7 66 55 4«Rybinskkompleks» GRU AGP-350 140 130 127.5 137.5 142.5 177.5 175 157.5 175

Based on the conducted analysis, microturbine units were selected for the developed energy system. Thus, the binary power generation cycle in this work is a combination of a gas microturbine electrical unit (GMEU) and a steam microturbine electrical unit (SMEU) for the production of electrical energy [11]. The high-temperature exhaust gases of the GMEU are used to heat a low-boiling medium, the vapors of which rotate a steam microturbine that drives the auxiliary generator. The coolant pentaﬂuoro-propane (C3H3F5) is used as a low-boiling medium. In a binary power generation system, it is also possible to produce thermal or cold energy if not all the exhaust gases’ energy potential is used for generating electrical energy in accordance with the requirements of the consumers’ energy loads.

2.1. Power Characteristics of the Binary Energy System The electrical efficiency of the binary energy system will be determined by the sum of the rated power of the gas and steam microturbine electrical units, referred to as the fuel’s heat of combustion in the combustion chamber of the GMEU. The rated power of the SMEU, in turn, will be defined by the working efficiency of the gas turbine, which is influenced by the work done by the gas turbine itself and the compressor [14]. Thus, the work of the compressor is:

. . Wc = ma(h h ) (1) 2 − 1 where: . ma—mass air flow, kg/s; hn—specific enthalpy of the fluid at n-point of a T–s diagram (Figure3), J /kg. Energies 2020, 13, 4921 5 of 14 EnergiesEnergies 20202020,, 1133,, xx FORFOR PEERPEER REVIEWREVIEW 55 ofof 1414

TemperatureTemperature,, KK TT qq11 ppii..tt..

TTii..tt.. 33

TToo..cc.. 22 ppoo..cc.. 22tt

ppo.t. TToo..tt.. 44 o.t. 44tt

11 TTaa..aa.. pa.a. pa.a. qq22 EntropyEntropy,, JJ//KK SS

.... ....——aambientmbient airair pressurepressure andand temperature;temperature; .... ....——airair temperaturetemperature andand pressurepressure atat thethe outletoutlet

ofof the the compressor; compressor; .... .... ——gasgas pressure pressure at at the the inlet inlet and and outlet outlet of of the the turbine; turbine; .... .... ——gasgas temperaturetemperature atat thethe inletinlet andand outletoutlet ofof thethe turbine;turbine; 1,1, 2,2, 3,3, 44——actualactual BraytonBrayton cyclecycle points;points; 2t,2t, 4t4t——pointspoints 22 andand 44 ofof

theoreticaltheoretical BraytonBrayton cycle;cycle; ——specificspecific heatheat atat thethe inputinput andand outputoutput ofof thethe microturbinemicroturbine unit.unit.

FigureFigureFigure 3. 3.3.T–s TT–– diagramss diagramdiagram of ofof the thethe standard standardstandard Brayton BraytonBrayton cycle. cyclecycle..

TheThe work work of of the the turbine: turbine: The work of the turbine: . . . W = m + m (h h ) (2) t ̇ a f 3 4 ̇ == ̇̇ ++̇̇((ℎℎ− −−ℎℎ)) ((22)) . m f —mass fuel flow, kg/s. ̇̇——massmass fuelfuel flflow,ow, kg/s.kg/s. The efficiency of the steam turbine part of the installation will be defined by the work of the steam TheThe efficiencyefficiency ofof thethe steamsteam turbineturbine partpart ofof thethe installationinstallation willwill bebe defineddefined byby thethe workwork ofof thethe turbine itself and the pump, delivering condensed fluid from the condenser to the steam generation steamsteam turbine turbine itself itself and and the the pump, pump, delivering delivering condensedcondensed fluid fluid from from the the condenser condenser to to the the steam steam unit (Figure4). generationgeneration unitunit ((FigureFigure 44).).

11aa,, 22aa,, 33aa,, 44aa——BraytonBrayton ccycleycle sections;sections; 1s,1s, 2s,2s, 3s,3s, 4s4s——RankineRankine cyclecycle sections,sections, WW11 andand WW22——workwork donedone byby thethe powerpower partsparts ofof thethe GMEUGMEU andand SMEU,SMEU, respectivelyrespectively

FigureFigureFigure 4. 4.4.Brayton–Rankine BraytonBrayton––RankineRankine cycle cyclecycle using usingusing gas gasgas turbine turbineturbine and andand steam steamsteam turbine. turbineturbine..

Work of the steam turbine: WorkWork ofof thethe steamsteam turbine:turbine: . . W = m (h h ) (3) tṠ s 1S 2S ̇ == ̇̇ ((ℎℎ− −−ℎℎ)) ((33)) . ms—mass steam flow, kg/s ̇̇ ——massmass steamsteam flow,flow, kg/skg/s hnS—specific enthalpy of the fluid in n-area of the Brayton–Rankine cycle, J/kg ℎℎ——specificspecific enthalpyenthalpy ofof thethe fluidfluid inin nn--areaarea ofof thethe BraytonBrayton––RankineRankine cycle,cycle, J/kgJ/kg WorkWork ofof thethe ppump:ump:

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Work of the pump: . . ms(h4S h3S) Wp = − (4) hp Summarized work of the whole turbine installation:

Wsum = Wt + W Wc Wp (5) tS − − To assess the potential for the production of electrical power in a binary energy system, it is necessary to determine the thermal power of the GMEU exhaust gases, considering (5). As a result of research conducted at the energy facilities of several oil ﬁelds, it has been established that for gas turbines the ratio between the thermal capacity, which is later used for power generation in the binary cycle, and the electric capacity is 2:1. For gas-reciprocating units with higher electrical eﬃciency, this ratio can be taken as 1.5:1. It was established that the total electrical power output of the binary power plant can be determined by the following formula: P = Pr + (2 Pr Ktu K K ) η , (6) b.c. · · · l· exh · i where:

Pr—rated electrical power of the unit; Ktu—unit’s coefficient of technical usage; Kl—unit’s coefficient of load; Kexh—coefficient of the heat energy losses in exhaust gases; ηi–internal efficiency of steam turbine cycle. The values of the electrical units’ load and technical usage coefficients were determined during the analysis of the energy facilities. The coefficient of the technical usage for the gas turbines was 0.79–0.84. The coefficient of the load was 0.8–0.9. The coefficient of the heat energy losses in the exhaust gases was equal to 0.95. To calculate the potential electric power of the binary energy system it is necessary, taking into account the efficiency of the main electrical unit, to select the appropriate SMEU. The potential electric power of a binary energy system is determined as follows [15]:

SMEU N = Qsg η ηm ηe, (7) e · i· · where:

Qsg—heat load of the steam generation system, W; ηm, ηe—coeﬃcients taking into account the mechanical and electrical losses in the generator, ηm = ηe = 0.98. The heat load of the steam generation system can be deﬁned as:

t t Q = Q exh1 − exh2 , (8) sg exh t t exh1 − amb where:

Qexh—amount of heat contained in the exhaust gases of GMEU, W; texh1—temperature of GMEU exhaust gases, ◦C; texh2—temperature of exhaust gases in SMEU steam generation system, ◦C; tamb—ambient air temperature, ◦C. The amount of heat contained in the exhaust gases of GMEU is found by the formula: ! 1 Q = NGMEU 1 , (9) exh e GMEU ηe − Energies 2020, 13, 4921 7 of 14

GMEU where ηe —electrical efficiency of GMEU. EnergiesGMEU 2020, Capstone13, x FOR PEER C1000 REVIEW was considered as the main power unit, the operating parameters7 of 14 of which are necessary for the selection of the auxiliary unit type, and were defined during analysis of the unit operationGMEU Capstone at an oil fieldC1000 of was JSC “Tatneft”considered (Table as the2). main power unit, the operating parameters of which are necessary for the selection of the auxiliary unit type, and were defined during analysis of the unitTable operation 2. Technical at an oil characteristics field of JSC of“Tatneft” the main (Table gas microturbine 2). in the binary energy system.

№ Table 2. TechnicalIndicators characteristics of the main Units gas microturbine in the binary Value energy system. №1 ElectricalIndicators power Units kW Value 1000 2 Electrical eﬃciency % 33 1 Electrical power kW 1000 3 Fuel consumption m3/h 325 2 Electrical efficiency % 33 4 Heating value of gas MJ/m3 30.7–47.5 (depending on gas composition) 3 53 PressureFuel of gasconsumption at the system inputm bar/h 325 5 3 64 GMEUHeating Exhaust value gases’ of temperature gas MJ/m◦C 30.7–47.5 (depending on 280 gas composition) 75 Pressure SMEU Exhaustof gas at gases’ the system temperature input bar◦C 5 107 86 GMEU Ambient Exhaust air gases’ temperature temperature °C◦C 280 20 7 SMEU Exhaust gases’ temperature °C 107 8Considering Ambient Equations air temperature (6)–(9) we obtain the°C following additional possible20 amount of electrical energy generated in the binary energy system: Considering Equations (6)–(9) we obtain the following additional possible amount of electrical energy generated in the binary energy system: 1 Qexh = 1000 1 = 2030 kW, 10.33 − = 1000 − 1 = 2030 , 0,33 280 107 Q = 2030 − = 1351 kW, sg 280 20 280 − 107 = 2030 − = 1351 , The value ηi was taken according to [15280]. − 20

The value was taken according to [15]. NSMEU = 1351 0.22 0.98 0.98 = 285 kW. e = 1351 ∙ 0,22· ∙ 0,·98 ∙ 0· ,98 = 285 . FigureFigure5 shows 5 shows the the scheme scheme of of an an energy energy system system withwith aa binary power generation generation cycle. cycle.

Generator

Gaseous GS fuel Steam turbine

Steam 63 °С 1,8 bar Combustion Air chamber Generator Exhaust gases 280 °С Steam 115 °С Heater GS 15 bar Heat input

Gas 980 kW/h Consenser Compressor turbine Steam generation Fluid 29 °С system 1,8 bar

Pump

Fluid 29 °С 16 bar

FigureFigure 5. 5.Scheme Scheme ofof anan energyenergy system with with a a binary binary power power generation generation cycle cycle..

2.2.2.2. Integration Integration of of the the GTL GTL System System intointo thethe OilOil Field Structure It isIt proposedis proposed to useto use the the GTL GTL (gas-to-liquid) (gas-to-liquid) system system to reduceto reduce the the viscosity viscosity of theof the pumped pumped oils oils at the oilﬁeldsat the oilfields with a simultaneous with a simultaneous decrease decrease in the carbon in thefootprint carbon footprint related torelated their production.to their production. This approach This considersapproach two-stage considers utilization two-stage of utilization the associate of the petroleum associate gas. petroleum At ﬁrst, gas. APG At is first, used AP asG a fuelis used for as power a fuel for power generation in the binary energy system. If there is unused gas after this, it is processed into synthetic liquid hydrocarbons (SLH). A study was conducted at the laboratory setup for the

Energies 2020, 13, 4921 8 of 14 generation in the binary energy system. If there is unused gas after this, it is processed into synthetic liquidEnergies hydrocarbons 2020, 13, x FOR (SLH).PEER REVIEW A study was conducted at the laboratory setup for the conversion8 of 14 of synthesis gas, obtained from APG, into valuable chemical products (methanol, DME and synthetic conversion of synthesis gas, obtained from APG, into valuable chemical products (methanol, DME liquid hydrocarbons) [16]. The optimal ﬂow characteristics (volume velocity and composition of the and synthetic liquid hydrocarbons) [16]. The optimal flow characteristics (volume velocity and suppliedcomposition syngas) of and the the supplied operating syngas) conditions and the of the operating reactors conditions (temperature, of the pressure) reactors were (temperature, determined andpressure) used to simulate were determined this process and inused the to computer simulate this program process Aspen in the HYSYS computer [17 program]. Judging Aspen by the HYSYS results of a[17] chromatographic. Judging by the analysis results forof thea chromatographic SLH obtained at analysis the laboratory for the setup,SLH obtained a signiﬁcant at the proportion laboratory of thesetup, SLH are a significant aromatic compoundsproportion of (Table the SLH3), which are aromatic have a highcompounds solubility (Table ofhigh 3), which molecular-weight have a high hydrocarbonssolubility of of high oils. molecular-weight hydrocarbons of oils.

TableTable 3. 3Composition. Composition of of the the sample.sample.

GroupGroup Composition: Composition: %% Mass Mass Group Group Composition Composition:: % Mass % Mass Alkanes.Alkanes. incl: incl: 37.28837.288 Olefins Oleﬁns and and dienes, dienes, incl: incl: 2.667 2.667 normalnormal 11.47411.474 C3 C 3 0.0020.002 IsoalkanesIsoalkanes 25.81425.814 C4 C 4 0.1530.153 NaphthenesNaphthenes 15.40315.403 C5 C 5 0.8220.822 Aromatics,Aromatics, incl: incl: 38.03538.035 C6 C 6 0.8390.839 mononuclear 36.282 C 0.557 mononuclear 36.282 C7 7 0.557 dualnuclear 1.354 C8 0.240 dualnuclear 1.354 C8 0.240 indans 0.399 C9 0.054 Unidentiﬁedindans hydrocarbons 0.399 C9 6.607 0.054 Unidentified hydrocarbons 6.607

Therefore,Therefore, it should it should be assumed be assumed that when that adding when SLH adding to real SLH oil systems,to real oil aromatic systems, hydrocarbons aromatic willhydrocarbons contribute to will the contribute destruction to (dissolution) the destruction of supramolecular (dissolution) of asphalt-resin supramolecular formations asphalt-resin and, consequently,formations toand, a change consequently, in the rheological to a change characteristics in the rheological of the characteristics oils. Such use of of the the oils. GTL Such system use willof reducethe GTL the hydraulic system will losses reduce during the hydraulic transportation, losses during and, accordingly, transportation, the loadand, accordingly, on the pumps, the as load well on as thethe required pumps, heating as well temperature as the required to ensureheating a temperature stable technological to ensure process. a stable technological process. TheThe technological technological scheme scheme of of hydrocarbon hydrocarbon production production andand transportation at at the the field ﬁeld with with the the developeddeveloped GTL GTL system system is presentedis presented in in Figure Figure6. 6.

Multiphase flow Oil Water Gas turbine station Gas Electric power

GTL Station

Measuring gas separator

Heater Water Pump Heater Wellhead I stage II stage boot separator separator

Bottomhole Formation pressure Terminal of the well maintenance system Figure 6. Technological scheme of hydrocarbon production and transportation at the field with a gas- Figure 6. Technological scheme of hydrocarbon production and transportation at the ﬁeld with a to-liquid (GTL) system. gas-to-liquid (GTL) system.

TheThe assessment assessment of of the the carbon carbon footprint footprint of of hydrocarbon hydrocarbon productionproduction for the system system developed developed includes an evaluation of the following stages: oil heating in fired heaters, fluid separation in the first includes an evaluation of the following stages: oil heating in fired heaters, fluid separation in the first and the second stage separators and pumping of treated oil by pumps. and the second stage separators and pumping of treated oil by pumps. The emissions of greenhouse gases generated during the burning of petroleum gas to generate electric and thermal energy for the energy supply of pumps, compressors and fired heaters are taken

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The emissions of greenhouse gases generated during the burning of petroleum gas to generate electric and thermal energy for the energy supply of pumps, compressors and ﬁred heaters are taken into account when evaluating the carbon footprint. The assessment was performed using Aspen HYSYS software for simulation of the oil production process.

3. Results and Discussion

3.1. Efficient Functioning of Developed Binary Energy System Considering the discussion in Section 2.1, it follows that the SMEU in the second circuit of the binary energy system should be chosen in such a way that its electrical power output is no more than 285 kW. At the same time, these two types of units have quite different operating parameters. The main components of a gas microturbine are the compressor, combustion chamber with recuperator, turbine and generator. The compressor, turbine and generator are installed on a single shaft. The shaft of the gas turbine rotates at 96.000–116.000 rpm. As a rule, there is no rigid dependence of the generated power on the shaft rotation speed or the installation size, since the design features of individual turbines and compressors affect their size and, accordingly, the speed. For the aerodynamic design of microturbines, it is true that with a decrease in power produced, an increase in the speed of shaft rotation occurs, hence the presence of such performance characteristics. The recuperator is installed before the combustion chamber, and hot turbine exhaust gases (the temperature of which varies depending on the power of the installation) are used to heat the compressed air supplied by the compressor to the combustion chamber, which reduces the amount of fuel required to heat the fuel mixture. The gas microturbine control system includes three main operating modes—switching on and start of the operation, connecting and powering the load, and charging the battery, which is also a part of the microturbine. During the start-up of the installation, the battery allows 100% load connection. Next, the control system monitors the power parameters of consumers and the battery charge level, as well as its timely charging. The gas microturbine generates an electric current through a generator driven by a turbo-compressor. The single-shaft high-speed generator is made with permanent magnets, and the high-frequency alternating current produced by it (with a frequency of 1600 Hz for a 30-kW installation) must be converted to a current with industrial frequency. This conversion takes place in the power electronics unit. Double conversion of the generated current is done by the rectifier and inverter in the power electronics unit, after which it is necessary to limit the higher harmonics of the current arising from this process. This unit is the most significant in a single-shaft microturbine and requires the development of a technological solution when synchronizing the operation of the installation with a network or other installations. The developed power electronics unit in a binary energy system provides synchronization of the generators’ operation in frequency, voltage level and phase angle, as well as filtering the higher harmonics of the generated current. The main components of steam microturbine are the steam generation unit, turbine, condenser and pump. The design may be both single-shaft and two-shaft. The steam generation unit uses a low-boiling agent as a working medium to obtain standard operational parameters at lower temperatures. The condenser dissipates residual heat and collects the condensed working agent, which is then pumped back to the steam generation unit to be used again. The steam microturbine control system regulates the operation of the unit by controlling the amount of heat energy coming with the exhaust gases. A corresponding adjustment of shaft rotation speed is made to sustain the same operational parameters. Due to the fact that GMEU is the main unit in the binary energy system, the SMEU control system adjusts the voltage to match the corresponding value of the gas microturbine. This is done through the active rectifier, which allows synchronizing of the voltage levels in milliseconds. Energies 2020, 13, 4921 10 of 14

Simulation of the developed binary energy system was done in Matlab/Simulink software. At ﬁrst, the system was modeled according to Equations (1)–(5) regarding the operation of two microturbines (Figure7)[18,19]. Energies 2020, 13, x FOR PEER REVIEW 10 of 14

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Figure 7. Structure of the power part of the binary energy system. Figure 7. Structure of the power part of the binary energy system. Figure 7. Structure of the power part of the binary energy system. ThenThen a a power power electronics electronics unit,unit, consisting consisting of the the rectifier, rectifier, inverter, inverter, active active rectifier rectifier and and higher higher harmonicsharmonicsThen filters filters a power was was modeled electronicsmodeled [ 20[20 unit,––2222 ].] consisting. TheThe simulation of the rectifier,showed showed that inverter, that the the developed active developed rectifier structure structure and higheroperated operated efficiently during start-up, operation, loading and unloading of the GMEU and SMEU (Figure 8). efficientlyharmonics during filters start-up, was modeled operation, [20–22 loading]. The simulation and unloading showed that of the the GMEU developed and structure SMEU (Figureoperated8 ). efficiently during start-up, operation, loading and unloading of the GMEU and SMEU (Figure 8).

FigureFigure 8. 8. Structure Structure ofof thethe power electronicselectronics part part of of the the binary binary energy energy system system. . Figure 8. Structure of the power electronics part of the binary energy system.

3.2.3.2. Lowering3.2. Lowering Lowering the the the Carbon Carbon Carbon Footprint Footprint Footprint of ofof the thethe OilOil ProductionProduction with with with the the the GTL GTL GTL System System System Figure 9 shows an oil field model created in the Aspen HYSYS software package. It represents FigureFigure9 shows 9 shows an an oil oil field field model model created created in in thethe AspenAspen HYSYSHYSYS software package. package. It Itrepresents represents anan Arctic Arctic site site where where multiphase multiphase fluidfluid flow (gas--oiloil--water)water) is is collected collected from from two two cluster cluster fields fields with with an Arctic site where multiphase fluid flow (gas-oil-water) is collected from two cluster fields with highhigh-viscosity-viscosity oil oil and and high high gas gas--oiloil ratioratio (GOR).. Next,Next, it it is is heated heated and and separated separated and and APG APG is usedis used for for powerpower production production and and heating heating ofof oiloil..

Energies 2020, 13, 4921 11 of 14 Energies 2020, 13, x FOR PEER REVIEW 11 of 14 Energies 2020, 13, x FOR PEER REVIEW 11 of 14

Energieshigh-viscosity 2020, 13, x oilFOR and PEER high REVIEW gas-oil ratio (GOR). Next, it is heated and separated and APG is used11 of for14 power production and heating of oil.

Figure 9. Oil field model in Aspen HYSYS with associated petroleum gas (APG) utilization in Figure 9. Oil field model in Aspen HYSYS with associated petroleum gas (APG) utilization in heaters. Figure 9. Oil ﬁeld model in Aspen HYSYS withheaters associated. petroleum gas (APG) utilization in heaters. Figure 9. Oil field model in Aspen HYSYS with associated petroleum gas (APG) utilization in FigureFigure 1010 shows shows a ascheme, scheme, where where APG APG,, whichheaters which was. wasburnt burnt before, before, is utilized is utilized in the GTL in the system GTL Figure 10 shows a scheme, where APG, which was burnt before, is utilized in the GTL system developedsystem developed.. developedFigure. 10 shows a scheme, where APG, which was burnt before, is utilized in the GTL system developed.

Figure 10. Oil field model in Aspen HYSYS with APG utilization in a GTL system. Figure 10. Oil field ﬁeld model in Aspen HYSYS with APG utilization in a GTL system.system. CComparativeomparativeFigure results10. results Oil fieldof of carbon carbonmodel in footprint footprint Aspen HYSYS calculation calculations with APGs for for utilization these these two two in a model modelsGTL systems are are. presented in in Comparative results of carbon footprint calculations for these two models are presented in FigureFigure 11 11.. Figure Figure9 illustrates9 illustrates burning burning of APG of to APG produce to produce heat. Figure heat. 10 Figure presents 10 additional presents processingadditional Figure 11. Figure 9 illustrates burning of APG to produce heat. Figure 10 presents additional processingof APGComparative into of synthetic APG results into oil synthetic toof dilute carbon oil the to footprint crude. dilute the calculation crude. s for these two models are presented in Figureprocessing 11. Figureof APG 9 into illustrates synthetic burning oil to dilute of APG the crude to produce. heat. Figure 10 presents additional processing of APG into synthetic oil to dilute the crude.

Figure 11. Dependence of carbon footprint on the gas-oil ratio (GOR) at the field for two models. Figure 11. Dependence of carbon footprint on the gas gas-oil-oil ratio ( (GOR)GOR) at the field ﬁeld for two models.models. AsFigure a result 11. Dependenceof operating of an carbon energy footprint system on in the a binarygas-oil ratiocycle, (GOR the )electrical at the field efficiency for two models reaches. 55%, As a result of operating an energy system in a binary cycle, the electrical efficiency reaches 55%, i.e., it is the sum of the efficiency for the GMEU and the SMEU. At the same time, introduction of the i.e., itAs is a the result sum of of operating the efficiency an energy for the system GMEU in and a binary the SMEU. cycle, Atthe the electrical same time, efficiency introduction reaches of55%, the i.e. , it is the sum of the efficiency for the GMEU and the SMEU. At the same time, introduction of the

Energies 2020, 13, 4921 12 of 14

As a result of operating an energy system in a binary cycle, the electrical efficiency reaches 55%, i.e.,Energies it is 20 the20, sum13, x FOR of the PEER effi REVIEWciency for the GMEU and the SMEU. At the same time, introduction of12 theof 14 GTL system into the APG utilization structure ensures the most complete utilization of associated petroleumGTL system gas. into Power the APG supply utilization to consumers structure with ensures electrical the and most/or complete thermal and utilization cold energy of associated is done accordingpetroleum to gas. the powerPower loadsupply charts to consumers of the enterprise. with electrical The energy and/or flow thermal chart in and the energycold energy system is withdone aaccording binary cycle to the is shown power inload Figure charts 12 .of the enterprise. The energy flow chart in the energy system with a binary cycle is shown in Figure 12.

GMEU 33% SMEU 22% Heat/ SMEU Cold energy 34% Fuel Heat steam Low-grade exhaust gases energy Exhaust gases 66.5% generation exchanger/ 100% 44% system Absorber Heat transfer losses 0.5% Heat transfer losses 0.5% Flue gases 10%

FigureFigure 12. 12.Energy Energy ﬂowflow chartchart in in the the energy energy system system with with a a binary binary cycle. cycle.

AA basic basic economic economic analysis analysis was was done done during during the the research. research. TheThe economicseconomics ofof thethe proposedproposed binary binary energyenergy system system was was compared compared with with a diesel a diesel power power plant and plant a single and microturbinea single microturbine unit in the unitconditions in the ofconditions the Arctic of region. the Arctic The developed region. The structure developed had structure the highest had CAPEX the highest and theCAPEX largest and OPEX the largestin the ﬁrstOPEX year in ofthe operation. first year of At operation. the same time,At the the same cost time, of diesel the cost fuel of for diesel the dieselfuel for power the diesel plant power was 200% plant higherwas 200% due higher to the need due to the transport need to the transport diesel to the the diesel remote to Arctic the remote region Arctic by sea. region This madeby sea. this This type mad ofe powerthis type plant of power economically plant economically unfeasible after unfeasible two years after of two operation. years of operation. The single The microturbine single microturbine unit also hadunit lower also had CAPEX lower and CAPEX OPEX and in the OPEX ﬁrst in year the of first operation. year of However,operation.due However, to theadditional due to theamount additional of generatedamount of energy, generated the constant energy, fuel the consumption constant fuel binary consumption energy system binary had energy a lesser system payback had a period. lesser Initialpayback calculations period. Initial showed calculations the recoupment showed of the the recoupment capital investments of the capital to be investments six years. to be six years.

4.4. ConclusionsConclusions AA comprehensivecomprehensive energy-eenergy-efficientfficient systemsystem forfor thethe utilizationutilization ofof associatedassociated petroleumpetroleum gasgas waswas developeddeveloped in in the the paper. paper. The The system system consists consists of two of parts: two a parts: binary a energy binary system energy for system power generation for power andgeneration a GTL systemand a GTL for thesystem production for the production of synthetic of liquidsynthetic hydrocarbons. liquid hydrocarbons. The binary The energy binary system energy makessystem it makes possible it possible to fully utilize to fully the utilize potential the potential of the fuel of gas the infuel the gas production in the production of electrical of electri and thermalcal and orthermal cold energy. or cold It also energy. reduces It also the higher reduces harmonic the higher components harmonic of components current and voltage of current variations and voltage when carryingvariations out when uninterrupted carrying powerout uninterrupted supply for consumers power supply at oil productionfor consumers units at in oil remote production areas without units in connectionremote areas to centralized without connection power grids. to The centralized acquired power synthetic grid liquids. The hydrocarbons acquired synthetic can be used liquid to dilutehydrocarbons the extracted can be crude used in to order dilute to lowerthe extracted its viscosity. crude At in the order same to time,lower less its energyviscosity. is requiredAt the same for itstime heating, less andenergy pumping is required through for the its pipelines. heating and The pumping developed through system lowersthe pipelines. the carbon The footprint developed of petroleumsystem lowers production, the carbon thus foo minimizingtprint of petroleum its negative production, impact on thus theenvironment. minimizing its Useful negative utilization impact ofon thethe associated environment. petroleum Useful gasutilization in the developed of the associated energy petroleum system can gas reach in 100%.the developed energy system can reach 100%. Author Contributions: Conceptualization, E.L. and O.T.G.; formal analysis, E.L. and G.B.; funding acquisition, O.T.G.; investigation, E.L. and G.B.; methodology, V.M.; project administration, V.M.; resources, E.L. and V.M.; software,Author Contributions: G.B.; validation, Conceptualization, G.B.; visualization, E.L. E.L.; and writing—original O.T.G.; formal analy draft,sis, V.M.; E.L. writing—reviewand G.B.; funding and acquisition, editing, O.T.G.O.T.G. All; investigation, authors have E.L. read and and G.B. agreed; methodology, to the published V.M.; versionproject administration, of the manuscript. V.M.; resources, E.L. and V.M.; software, G.B.; validation, G.B.; visualization, E.L.; writing—original draft, V.M.; writing—review and editing, Funding: This research received no external funding. O.T.G. All authors have read and agreed to the published version of the manuscript. Acknowledgments: The authors thank Saint Petersburg Mining University for the enabling of laboratory experiments. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest. Acknowledgments: The authors thank Saint Petersburg Mining University for the enabling of laboratory experiments.

Conflicts of Interest: The authors declare no conflict of interest.

Abbreviations The following abbreviations are used in this manuscript: APG associated petroleum gas

Energies 2020, 13, 4921 13 of 14

Abbreviations The following abbreviations are used in this manuscript:

APG associated petroleum gas CCHP combined cooling heat and power CHP combined heat and power DU distribution unit GS gas separator GMEU gas microturbine electric unit GTL gas-to-liquid GRU gas-reciprocating unit GTU gas turbine unit IGBT insulated gate bipolar transistor SMEU steam microturbine electric unit RLC resistance, inductance, capacity Rpm revolutions per minute WR water removal

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