# I. Introducción he need to respond in a safe, efficient and environmentally sustainable manner to the growing energy needs in the different sectors of the national economy, demands the rationalization, technical improvement and expansion of the sources of electricity supply. Responding to this demand, the Colombian Ministry of Mines and Energy, the Unit for the Mining-Energetic Planning (UPME), and the Energy and Gas Regulation Commission (CREG) lead a comprehensive policy that promotes, generates and stimulates programs and projects for the generation, saving and efficient use of energy and particularly for self-generation [1] [2] [4][5][6][7][8][9]. The Colombian Government issued Decree 2143 of 2015 [9], through which tax incentives are regulated for the promotion, development and efficient use of energy. The micro-grids find their way, with sources of distributed generation, local storage, controlled loads, and the possibility of developing electrical islands. Colombia is promoting programs for distributed generation (DG) and will probably encourage more projects for self-generation in the commercial, residential and service sectors, emulating initiatives as that of the US Department of Energy, which promoted the Advanced Alternative Engine Systems program (ARES), designed to develop small micro-generators units of high efficiency [12]. If incentives are created for self-generation in commercial, residential and service sectors, the incorporation into the system of microgeneration units could be attractive, and the introduction of microturbine generators could be favored. On the other hand, Colombia is currently exporting LPG, a part of which is obtained as a byproduct of natural gas purification in known fields as Cusiana. Some energy suppliers have had interest in exploring the performance behavior of power generators when they are run on high butane liquefied petroleum gas for electricity generation in oil fields. Considering the fact that to date, to the authors' knowledge, there has not been reported any experimental tests related to the performance of microturbine generator (MTG) sets fuelled with LPG from Cusiana, a 30 kW Capstone MTG fed with Cusiana LPG was tested, as a pilot experience, to judge about its power output, step response, power quality, and fuel consumption. Microturbines are lightweight and compact in size combustion turbines with outputs of 30 kW to 400 kW that can be used for stationary energy generation applications at sites with space limitations for power production. They can be run on natural gas, biogas, propane, butane, diesel, and kerosene. Particularly, the Capstone MTG consists of a compressor, recuperator, combustor, turbine and permanent magnet generator; the air drawn through the inlet system refrigerates the generator, discarding the need of a liquid cooling system. Intake air is compressed and injected into the recuperator, a heat exchanger where it is heated by turbine exhaust. Fuel enters the system through an injection port and is mixed with the heated compressed air. The ignition system causes the air-fuel mixture to burn in the combustion chamber under constant pressure conditions; the resulting gases are allowed to expand through the turbine section to perform work, rotating the turbine blades to turn a generator, which produces electricity. The rotating components, which T Global Journal of Researches in Engineering (A ) Volume Xx XII Issue I V ersion I can reach 96,000 min -1 , are mounted on a single shaft supported by low-maintenance air bearings. The MTG has been tested in stand-alone mode, as a power source that meets the current consumption demanded by the coupled load. The general goals of the load test were: ? To get onsite experimental information related to the performance of the Capstone microturbine when fueled with Cusiana LPG. ? To measure the electric generation performance of the MTG under a load cycle, for the given open ambient conditions, with the available instrumentation, and the time allowed to perform the test, adjusting as far as possible to the rules of operation and tests of the MTG. ? To provide an appropriate stable medium for the reliable evaluation of electrical efficiency, and MTG performance. The work here presented refers to the evaluation study, and is organized as follows: first, the properties of the LPG used are related, and a brief description of the Capstone micro-turbine is given. After that, this paper describes the experimental procedure and constraints. Next, the test program is described, followed by a summary of the results. Finally, the main conclusions of the work are presented. # II. Materials and Methods # a) Particularities of the LPG from Cusiana The term LPG applies widely to any mixture of propane and butane, the two constituents occurring naturally in oil and gas reservoirs that are gaseous at normal atmospheric conditions but can be liquefied by pressure alone. Components heavier than butane are liquids at normal conditions and components lighter than propane cannot be liquefied without refrigeration. The presence of butane, pentane, and heptane at concentrations of up to 40% characterize this particular LPG from Cusiana, which analysis is presented in table 1. BTU?ft -3 @ 14,65psia, 60°F b) Capstone micro-turbine Microturbines have advantages over modern internal combustion engines, such as their high-power density, less moving parts and comparatively low emissions. They can be fuelled by liquid and gaseous fuels -fossil or renewable. Microturbine capacities are generally between 30 to 350 kW. The Capstone 330 MTG, made available by the company Supernova Energy Services, installed in Alsabana was subjected to service setting works, as it was new. Photographs in figure 1 allow to illustrate the general view of the MTG located at the test site. Since Capstone Microturbines use lean premix combustion system to achieve low emissions levels at a full power range, they require operating at high air-fuel ratio; injectors control the air-fuel ratio. The MTG is instrumented to record operational parameters (of which, temperatures, pressures, fuel usage, turbine speed, internal voltages/currents, and status are of importance for the undertaken study). The average readings of two thermocouples indicates the Turbine Exit Temperature (TET); a compressor inlet thermistor is installed to measure the air temperature at the inlet of the compressor wheel; the air flow, Wair, (in pounds per hour) and the amount of energy needed in the combustion chamber required to regulate fuel flow in the combustion chamber, W energy (in Btu/sec), are calculated based on engine speed. Such data are available with a computer or modem connected to an RS-232 port on the microturbine. A schematic drawing of the built-in instrumentation supported by the microturbine generator is presented in figure 2. A large on-board battery pack is used to start the microturbine, and also to store energy when the microturbine decelerates to produce less power. To meet output power requirements automatically, the system can be configured in Auto Load mode. Auto Load ensures that the microturbine closes the output contactor to immediately produce the required output power once minimum engine load speed is reached. The output speed-power characteristic of the microturbine generator is reproduced in figure 3. # Figure 3: c) Experimental facility and procedures LPG was supplied from an oil field to the test site by a tanker with a storage pressure ranged between 50 and 90 psia during the test; an intermediary damper tank was used to reduce pressure fluctuations due to consumption, and a bypass was used in the LPG supply line with its respective regulating valves before the entry of gaseous fuel to guarantee the pressure, as can be observed in the photographs of figure 4. The average ambient conditions at the time of the test were: temperature close to 14°C, 80,2% relative humidity, and 0,726 atmospheric pressure. The procedure followed to assess electrical, thermal, and operational performance of the microturbine generator, comprised pretest activities, startup, idle, and a two-step load test during a short period of time. The software for the microturbine unit was configured for standalone operation through the local display panel; the turbine was started, controlled and monitored by a computer using Capstone's software. The load test applied by the load bank, as it is shown in figure 6, consisted of a transient from idling to a 20-kW load at maximum speed of 96000 min -1 , a steady-state operation in this operation point for about eight minutes, followed by a drop to 3 kW power at 60000 min -1 , and a steady running at this load for about four minutes. In the last part of the test, the load was completed released and the microturbine was sustained idling at a speed of 45000 min -1 , as it is shown in figure 6. During the test, all available parameters were monitored and recorded from the MTG system. All electrical parameters (both single-phase and threephase) were recorded at the load bank by the energy meter. The study focused on the overall performance parameters related to engine operation. In the following, the results of the collected data during the operation cycle, and the response of the turbine-generator to load changes are presented. Initially, the results obtained from the proprietary MTG controller are presented: inlet to compressor and turbine exhaust gas temperatures, air flow, intake air temperature and pressure values. Once the behavior variables are described, the evolution graphs of the electrical power, voltage, and current delivered by the MTG are illustrated. The information thus presented allows to evaluate the behavior of the MTG operating with LPG, from the perspective of stable operating capacity and within the mechanical, thermal, environmental limits. # Global Journal of Researches in Engineering # a) Mean-variable measurement results The microturbine generator has presented a normal behavior during the test, judging by the values of the speed, power, inlet to the turbine and compressor temperatures, load percentage, among the operating parameters registered by the proprietary controller of the microturbine; a summary of those performance parameters is presented in table 3. The general behavior of the MTG during the test, as a function of time, is presented in figure 7, where the history of output power, rotation speed, inlet to compressor and exit turbine temperatures, input amount of energy, and air flow is plotted. Analysis of the graphs shows that the Capstone microturbine responds to load changes rapidly, yet during steps up and down in the MTG real power output, turbine speed follows ramps up and down smoothly to the new operating point. When the load bank resistance is reduced, turbine shaft speed drops smoothly to its new operating point. # Global Journal of Researches in Engineering (A ) Volume Xx XII Issue I V ersion I Considering the heat value given by the chromatographic analysis of the LPG, the energy flows are converted to fuel flows, which allows to approximate also the air/fuel ratio. The variation of these magnitudes is shown in the figure 8. # IV. Results of the Electrical Energy Generated The quality of the energy generated could be influenced by the quality of combustion process of the fuel. MTG with the Capstone microturbine meets the specifications demanded for class G1 generators, in terms of frequency and voltage deviations during transient processes. Observation of the voltage at the load banks during the test showed a small sensitivity to load level. There is little change in the balance of the three-phase voltages. There is no discernable pattern to the changes in the bus voltage; all three phases respond equally to the load changes. # V. Conclusions Microturbine pilot test was carried out to determine performance characteristics, and to assess the possible inconveniences of using the particular highbutane-content LPG. To achieve the technical goals, it was considered a short test based on a two-step sequence of loads. The main conclusion drawn from the study is that, under the scope of this study, the output of the turbine generator was satisfactory, showing its adaptability to the change in fuel. The limited amount of testing done here restricts the applicability of these conclusions to the specific type of LPG used. Cold and warm starts performed well. The estimated efficiency of power generation appeared to be unchanged, as compared to the values indicated by the manufacturers. It can be stated that, based on the short test carried out, gas turbines are an advantageous alternative to the use of reciprocating engines, due to their adaptability to the fuel, their low noise and vibration levels, their compact structure and their efficiency close to that of the diesel engine. The tests showed a higherthan-expected performance and it is about to find out with the supplier how close this value is, since in the literature itself a performance of more than 30% is not expected, while the conducted test showed an efficiency close to 40% for 66% of the load. It is yet to be proven. Gas turbines are an excellent alternative and their technology is very mature for generation and cogeneration standalone applications; in the commercial and industrial sectors, microgrid power parks, remote off-grid locations, presenting only the defect of greater starting time (close to 2 minutes, value obtained from the literature). Engine Speed [min -1] 1![Figure 1: Location of the MTG at the Alsabana Campus test site The Model 330 MTG is a compact low emission solid-state controlled power generator, based on a 30 kW Capstone micro-turbine. The latter is designed for 30 kW output, uses power electronics to convert the highfrequency output of the generator to three-phase 480 volts voltages, at 50-60 Hz current frequency. The high-frequency AC current of the generator is converted to the 50-60 Hz AC current, after being processed through an inverter and a DC converter.Table 2 lists the rated capabilities of each microturbine based on available literature.](image-2.png "Figure 1 :") 2![Figure 2: Schematic diagram of the instrumented power unit [3]](image-3.png "Figure 2 :") 4![Figure 4: Tanker The microturbine generator was connected to an Avtron 1000 kW capacity electrical resistance load bank, with a manual load setting; electric generation quality was measured with a FLUKE 434/PWR energy meter connected to the generator power output through clamp-on current transformers. This is a three-phase electrical power quality analyzer FLUKE 434/PWR with a measurement range Vrms (AC+DC) between 1-1000 V, and frequency range of 40-70 Hz. A schematic of the general layout of the test facility is shown in the figure 5.](image-4.png "Figure 4 :") 5![Figure 5:](image-5.png "Figure 5 :") ![A ) Volume Xx XII Issue I V ersion I 21 Year 2022 © 2022 Global Journals Performance of a Capstone Gas Turbine based Power Plant Working on High Butane LPG General layout of the test place , lung tank and LPG supply bypass](image-6.png "(") 6![Figure 6: Load cycle followed for the MTG testing III. Results during the Test Program](image-7.png "Figure 6 :") 7![Figure 7: MTG operating parameters as a function of time during testMicroturbine output reacts without sensible delay to the changes in the bank load. The ramp-up rate is observed to be about 8 seconds for 0 to 20 kW. The ramp down rate is about 6 seconds for 20 to 3 kW. As for the fuel energy consumed, it is seen the fluctuation, associated to the mass flow rate adjustments, according to the control dynamics of the fuel valve and to the changes in fuel LHV and density. The variable speed control of the MTG relies on a system that sense load and optimize speed.Considering the heat value given by the chromatographic analysis of the LPG, the energy flows are converted to fuel flows, which allows to approximate also the air/fuel ratio. The variation of these magnitudes is shown in the figure8.](image-8.png "Figure 7 :") 8![Figure 8:An estimate of the MTG efficiency is made by relating the power made by the engine generator and the equivalent energy content of the fuel, as is shown in figure9.](image-9.png "Figure 8 :") 9![Figure 9: MTG efficiency calculated with the information logged by the controller](image-10.png "Figure 9 :") 10![Figure 10: MTG rotational speed as a function of power output](image-11.png "Figure 10 :") 1Compositional Analysis of GLP to C12+SamplingLocationALSABANACylinderNumberCLM009SamplingConditions30,0 psig @ 66.0°FComponentMole % Weight %CO2CarbonDioxide 0,010,01N2Nitrogen0,100,06C1Methane0,010,00C2Ethane3,362,14C3Propane71,4566,84iC4i-Butane13,1316,20nC4n-Butane11,9114,70iC5i-Pentane0,030,05____________Totals :100,00100,00Note: 0,00 meanslessthan 0,005.Calculated Whole Gas PropertiesGas Gravity1,6272(Air = 1 @ 14,73 psia& 60°F)WholeSample Mole Weight47,13g mol -1Ideal Gas Density1,9831kg m -3 @ 14,65 psia, 60°FIdeal GrossCalorificValue2665,7BTU?ft -3 @ 14,65 psia, 60°FIdeal Net CalorificValue2454,5BTU?ft -3 @ 14,65 psia, 60°FPseudoCriticalPress.598,7psiaPseudoCriticalTemp.682,1RankineGas Compressibility Factor, Z 0,979184@ 14,65 psia& 60°FGPM (C2+)28,49GPM (C3+)27,60Additional InformationReal GrossCalorificValue2722,4BTU?ft -3 @ 14,65psia, 60°FReal Net CalorificValue2506,6 2 2Fuel typeGNC (55 psig)GLP (55 psig)Diesel (5 psig)Mean time to repair20,000 h20,000 h20,000 hNominal full power30 kW net (+/-1 kW)30 kW net (+/-129 kW net (+/-1 kW)kW)Peak efficiency (LHV**)27% (+/-2%)27% (+/-2%)26% (+/-2%)Fuel consumption***18,7 lb/h, 8,5 kg/h19,0 lb/h, 8,6 kg/h21,9 lb/h, 10,0 kg/hMethane based fuel flow (Metan-HHV)440,000 kJ/h (420,000 Btu/h)Methane based energy of exhaust gases 305,000 kJ/h (290,000 Btu/hr)Exhaust gases temperature500°F, 261°C500°F, 261°C500°F, 261°COutput voltage250-700 VDC250-700 VDC250-700 VDC* Source: Capstone Turbine Corporation 7Tiempo [min:s]Speed [min -1 ]Power [W]TET [F]TEC [F]Wair [pph]Amb. pressure [psia]Suplied energy (btu/s) W energyAccel. [%]Frequency [Hz]00:096320202771102,269,9169410,746,660,86000:0196236203691101,269,9169510,747,260,36002:4994028181041109,872161410,64157,16010:0091236236751110,174,4153210,642,358,56010:0186408211811129,974,4139410,635536010:0281252177941144,674,4126510,632,449,46010:0376490146931164,974,4113810,629,180,96010:047348098821203,574,2105710,622,542,46010:435891232061259,875,973710,712,835,76010:455867834321258,47672810,71436,76013:515985216291126,880,477210,746,61006013:555420824111097,580,466710,7006013:565211421441095,280,263010,7006013:575010618851094,580,259410,7006014:36449501201029,278,851810,60060* © 2022 Global JournalsPerformance of a Capstone Gas Turbine based Power Plant Working on High Butane LPG Year 2022 © 2022 Global Journals Performance of a Capstone Gas Turbine based Power Plant Working on High Butane LPG © 2022 Global Journals * Consultancy to Determine the Schemes for Use of Derived Liquid Petroleum Gas Surplus for Electricity Generation in Oil Fields April 18, 2013 Bogotá * Liquefied petroleum gas code National Fire Protection Association. 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Artículo ASME 96-GT-36 TNishiyama Iwai M ASME Journal 1996 * Capstone Turbine Corporation, Capstone Microturbine Model 330 System Operation Manual 2000. 2001 USA Capstone Turbine Corporation, Capstone Low Emissions Microturbine Tecnology, White Paper, USA * Capstone Turbine Corporation, Capstone Microturbine Product Catalog 2012 USA * Performance study of a microturbine system for cogeneration application, Renewable Energy JCHo KJChua SKChou 2004 * General characteristics of single shaft microturbine set at variable speed operation and its optimization WWang RCai NZhang doi:101016/japplthermaleng200312012 Applied Thermal Engineering 24 13 2004 * Microturbines take on the market. Cogeneration & on-site power production TBayar October 2015 * Estrategias de control de calidad de energía en microrredes rurales NYGonzález CCusgüen EMojica-Nava APavas 10.18273/revuin.v16n2-2017009 UIS Ingenierías 16 2 2017 * Capstone Turbine Corporation. 0911 C30 Natural Gas Data Sheet CAP135 | Capstone P/N 331031E