City Gate Station Research Articles

Thermodynamic modeling and analysis of a novel heat recovery system in a natural gas city gate station

In the present study, five configurations of integrated system are introduced and comprehensive thermodynamic modeling and analysis for different arrangements are carried out. An organic Rankine flash cycle (ORFC) and a thermoelectric generator (TEG) are integrated with a real city gate station (CGS) to recover the thermal energy of exhaust gas at 400 °C in an indirect water bath heater (IWBH). The new aspect of the present research is proposal the novel arrangements of the TEG modules, ORFC and IWBH to improve the thermal performance of the CGS integrated system.Energy and exergy analyses employed to evaluate different arrangements of integrated systems.Comparative analysis of different suggested systems revealed that integrated system including IWBH, ORFC and TEG modules with placing the TEG modules after ORFC (Case V) shows better performance. Due to the better performance, Case V is considered for more studies. Under the given condition for the selected case, in a complete year, results indicate that the maximum and minimum values of electrical output power for TEG modules is 132 W and 100 W and for ORFC is 11.5 kW and 2.1 kW. Also, the parametric study of the Case V inferred that with increasing the amount of excess air form 50%–200%, the fuel mass flow rate increased by 35.6% which ultimately leads to a reduction in thermal efficiency of the system. The results suggests that proper arrangement of TEG modules and ORFC in the IWBH can improve the total thermal efficiency as well as the total electrical output power. Analyses of different proposed arrangements, also indicates that with the use ORFC and TEG modules in the worst and best cases 2.284 kW and 5.904 kW electrical energy can be recovered from the IWBH in the CGS.

Energy and exergy analysis and multi-criteria optimization of an integrated city gate station with organic Rankine flash cycle and thermoelectric generator

The current study deals with the thermodynamic modeling, and multi-objective optimization of a pressure reduction station integrated with an organic Rankine flash cycle (ORFC) and a thermoelectric generator (TEG) waste heat recovery system (WHRS). Using the real operating data of a city gate station (CGS), a thermodynamic simulation was developed using EES (Engineering Equation Solver). The exergy analysis as a rigorous method was applied to find the exergy destructive components of the integrated system. Computations indicate that the exergy efficiencies of the indirect water bath heater (IWBH), ORFC condenser and TEG modules are 1.41%, 30.45%, and 16.34%, respectively, which are the lowest asset values among all components.Five main decision variables were defined as objective functions by the parametric study of the integrated system. Results of multi-objective optimization offer a set of non-dominant optimization solutions. A criterion for optimum state selection is carried out with the definition of an ideal point on the Pareto diagram, where point B is picked as a favorable system state.The scattered distribution of decision variables at points (offered by the Pareto solution) represents that ṁNG and TNG-2 tend to be at the lower bound of their allowable range in all optimum states. Moreover, a comparison between the non-optimal and optimal integrated system reveals that the total exergy destruction rate through the system decreases 337.62 kW, and the thermal efficiency increases 8.57% in the optimal state.

A novel multi-objective fuzzy model for optimization of oil sludge management by considering Health, Safety and Environment (HSE) and resiliency indicators in a gas refinery

Waste management is one of the most important factors controlling environmental pollution and safety in gas refineries. It attends to optimize cost, environmental pollution, safety, and profitability. Since oil sludge management is not an indivisible issue from in a gas refinery, it is necessary to plan the supply process including refineries, gas compressor stations and city gate stations. Existence of toxic organics and heavy metals such as lead, copper, mercury, nickel and zinc have caused oil sludge is considered as hazardous waste and its storage and disposal in public landfill sites is not permitted. The current mechanism of disposal of oil sludge in the gas refinery of this study is incorrect. This paper presents a novel mathematical model for oil sludge management in a large gas refinery. The oil sludge management methods have been studied and included in the mathematical model. The objectives of the multi-objective mathematical model is to optimize cost, HSE and resiliency factors. Due to the uncertainty of certain parameters, the model is considered by fuzzy logic and planning. The mathematical model is solved by improved epsilon constraint and the best results are obtained by using data envelopment analysis (DEA). A complete sensitivity analysis is conducted with respect to various methods and land increase. The results show that the existing uncertainty has changed the solution space in the problem. In addition, environmental impacts are reduced by maximizing economic objective function. Moreover, demand changes will change the constraints related to demand and consequently solution space and optimum Pareto solution are also changed. The results of this study are verified and validated by expert judgments at the refinery. It is shown that the unique integrated mathematical approach of this study will respectively result in 19 and 12 percent improvement in environmental cost and safety factors. This is the first study that presents and integrated epsilon constraint and DEA approach for sludge management by considering HSE and resiliency factors.

Optimization of fuel consumption in natural gas city gate station based on gas hydrate temperature (Case study: Abbas Abad station)

A new approach has been presented for optimization of fuel consumption in the natural gas city gate station. In the city gate station, the temperature drops because of pressure drop has been occurred. In this case, the gas temperature may be reached to natural gas hydrates’ temperature and therefore natural gas pipelines are blocked. To avoid this condition, natural gas is preheated. Heating of natural gas should be in the range to avoid the gas hydrated temperature as well as, if possible, lower fuel consumption. For this purpose, the minimum possible temperature regulator output has been defined. The minimum temperature is based on gas hydrate temperature and has been calculated by applying fundamental thermodynamic equations and the equation of state. For validation of proposed method, the results have been compared to the measured temperature of Abbas Abad CGS. The validation shows that the proposed method has reduced fuel consumption by about 35%. The results show the price of reduced fuel consumption and carbon tax has been dropped in a year, also producing carbon dioxide because of incomplete combustion is significantly reduced.

Application of water reheating system for waste heat recovery in NG pressure reduction stations, with experimental verification

In this study, to recover a part of the waste energy from an indirect water bath heater (IWBH) of a natural gas (NG) pressure reduction station, the use of a water reheating system (WRs) is studied. The proposed plan involves a gas-water heat exchanger (G-WHE) installed on the chimney of the heater. The cooler water of IWBH circulates through a pump into the G-WHE. The proposed plan was implemented at one of the IWBHs of the city gate station (CGS) in Shahrekord, Iran, and the results were analyzed. The results show that the proposed plan reduces the fuel consumption of the heater by about 45%. As a result, the energy and exergy efficiencies of the station increase by about 80% and 100%, respectively. Economic analysis also indicates that the capital reverse factor for such a station is about 1.3 years. Studies were also conducted to reduce the pressure loss in gas and water streams of the G-WHE. Accordingly, the best designs for this heat exchanger (HE) are also presented. For designing an optimal HE, minimizing the pressure drop and weight, optimizing the interrelated angle of the tubes, and some other parameters are also considered.

Energy and exergy analysis of reciprocating natural gas expansion engine based on valve configurations

Natural gas pressure should be reduced in city gate stations before consuming. Part of the physical exergy of this high pressure gas is wasted if throttling valves are employed for pressure reduction. Reciprocating natural gas expansion engine (RNGEE) could be utilized to recover most of the physical exergy. In this study, a single acting RNGEE is investigated thermodynamically in order to optimize the ports opening/closing times. For this purpose, cylinder and slide valves and two types of piston valves have been modeled and compared. Based on an exergy analysis, a genetic algorithm has been developed to optimize the valves timing. Moreover, effects of the pressure ratio on the exergetic efficiency and power generation of the RNGEE have been studied numerically. Methane was modeled as a real gas by employing AGA8 equation of state. Results showed that beside importance of exergy efficiency optimization, inlet process period has also critical impacts on engine performance. Moreover, power generation is almost the same while using cylinder or flange valves (∼1986 kW/kg) with exergy efficiencies of 83.6% and 82.7% respectively. In contrast, slide and piston valves are found to have lower power generation (1746 kW/kg and 1753 kW/kg respectively) with the exergy efficiency of ∼72%.

A comprehensive analysis of energy and exergy characteristics for a natural gas city gate station considering seasonal variations

Comprehensive energy and exergy analyses are conducted on a City Gate Station (CGS) having nominal capacity of 20,000 SCMH. For this purpose, thermodynamic properties of Natural Gas (NG) fed into the CGS are firstly determined using American Gas Association Equation of State (AGA-8 EOS). Then, a quantitative analysis is carried out to explore magnitude and exact locations of energy/exergy losses as well as exergy destructions. To this end, four different seasonal strategies are regarded. In all strategies, the largest losses occur within the stack. Although from energy viewpoint, the regulator is a high-efficiency equipment, it is found to be the most exergy destructive component in the CGS. Moreover, maximum and minimum exergy losses occur in the winter (15.33 kW) and summer (1.60 kW), respectively. The best performance based on the second law of thermodynamics for the CGS occurs in the winter with exergy efficiency of 77%, whereas the lowest one happens in the summer with exergy efficiency of 69%. The exergy destruction due to pressure drop in filter and pipes are insignificant. The results obtained from this study can be employed as a guide to reduce exergy destruction in the whole CGS with recognition of the main sources of irreversibility.

Assessment of Saving in Energy by Replacing Three Stage Compressor with Two Stage Compressor with Higher Suction Pressure for Natural Gas Compression at City Gate Station : A Case Study

Assessment of Saving in Energy by Replacing Three Stage Compressor with Two Stage Compressor with Higher Suction Pressure for Natural Gas Compression at City Gate Station : A Case Study

Experimental study on the effect of copper oxide nanoparticles on thermophysical properties of ethylene glycol–water for using in indirect heater at city gate stations

This study aimed to investigate the increase in heat transfer in the indirect heater at a city gate station (CGS) with the addition of copper oxide (CuO) nanoparticles to water–ethylene glycol base fluids. Indirect heaters are typically used at CGSs to raise the heat transfer coefficient of output gas flow from − 5 to 15 °C. Moreover, manufacturing laboratory equipment in the presence of water–ethylene glycol base fluid and the nanoparticle in volume fractions of 0.05, 0.1, 0.2, and 0.3 at a temperature of 40–70 °C was discussed using dimensional simulation and analysis. The physical properties of the base fluid and nanofluid were measured using precise devices. Heat transfer tests for the base and nanofluid, as well as replacing of the air by gas, were conducted in a simulated and developed device. According to the obtained results with respect to the changes in convection and conduction heat transfer, enhancement of temperature difference at a rate of 36% was observed in the indirect heater with nanoparticle volume concentration of 0.2% at a temperature of 70 °C. Moreover, the Nusselt number showed a relatively good agreement with theoretical discussions.

A Numerical Study on Using Air Cooler Heat Exchanger for Low Grade Energy Recovery from Exhaust Flue Gas in Natural Gas Pressure Reduction Stations

Heat EXchangers (HEX) that are used in City Gate Station (CGS) systems are modeled numerically to recover the exhaust waste heat. It was tried to find the best viscous model to obtain results in accordance with experimental results and to change the heat exchanger design. This HEX is used for recovering heat from exhaust flue gas with a mixture of 40% water and 60% ethylene glycol as the cooling fluid. Then, the effects of sizes and numbers of fins and tube rows on recovered heat rate were investigated under various pump speeds. As the first step in solving the problem, SST k–ω and RNG k–e suitable viscous models were chosen for these kinds of problems. Secondly, a new HEX is designed at a fixed coolant speed, pipe and fin thickness, and shell dimension because of operational constraints. Finally, the best HEX with the minimum pressure drop (minimum fin number) is numerically analyzed, and the new HEX specifications were extracted.

Optimization Of Energy Consumption: As Utility In City Gate Station

Optimization Of Energy Consumption: As Utility In City Gate Station

Assessment of Saving in Energy by Replacing Three Stage Compressor With Two Stage Compressor with Higher Suction Pressure for Natural Gas Compression at City Gate Station

Assessment of Saving in Energy by Replacing Three Stage Compressor With Two Stage Compressor with Higher Suction Pressure for Natural Gas Compression at City Gate Station

Energy, exergy, economic and environmental (4E) analysis of using city gate station (CGS) heater waste for power and hydrogen production: A comparative study

This paper deals with energy, exergy, economic, and environmental (4E) analysis of two new combined systems for simultaneous power and hydrogen production. The combined systems are integrated from a city gate station (CGS) system, a Rankine cycle (RC), an absorption power cycle (APC), and a proton exchange membrane (PEM) electrolyzer. Since the pressure of natural gas (NG) in transmission pipeline is high, this pressure is reduced at CGS to a lower pressure. However, this NG has also ample potential to be recovered for multiple productions, too. In the proposed systems, the outlet energy of NG is used for power and hydrogen production by employing RC/APC and PEM electrolyzer. The power sub-cycles are driven by waste heat of CGS, while PEM electrolyzer is driven by this waste heat along with a portion of CGS-Turbine output power. A comprehensive thermodynamic modeling and parametric study of the proposed combined systems are conducted from the 4E analysis viewpoint. The results of two proposed systems are compared with each other, considering a fixed value of 1 MW for RC- and APC-Turbines power. Under the same external conditions and using steam as working fluid of RC, the thermal efficiency of the combined CGS/PEM-RC and -APC systems are obtained 32.9% and 33.6%, respectively. The overall exergy efficiency of the combined CGS/PEM-RC and -APC systems are also calculated by 47.9% and 48.9%, respectively. Moreover, the total sum unit cost of product (SUCP) and CO2 emission penalty cost rate are obtained 36.9 $/GJ and 0.033 $/yr for the combined CGS/PEM-RC and 36 $/GJ and 0.211 $/yr for the combined CGS/PEM-APC systems, respectively. The results of exergy analysis also revealed that the vapor generator (in both systems) has the main contribution in the overall exergy destruction.

Heat transfer enhancement and fuel consumption reduction in heaters of CGS gas stations

In this study, the effect of turbulators (coiled wire tube insert) as a passive method for heat transfer enhancement on heater performance of Mokhtar city gate station of Yasuj city has been evaluated. To analyze the performance and the effect of geometrical parameters of turbulators and physical parameters of the flow, steady state and incompressible flow were simulated through ANSYS CFX 14.5. Shear stress transport (SST) turbulence model for modeling turbulated flow regime besides the wall has been used. Using simulation results, important performance parameters such as friction factor, Nusselt number, and thermal performance factor were calculated and deeply studied. In this study the effect of coiled wire tube insert as a turbulator on the performance of heater in two states of circular and elliptical tubes with similar cross sections has been surveyed. The result show that the spring tube insert with diameter ratio of 10 for the elliptical tube heater, and diameter ratio of 0.95, have the best performance.

Intensification of heat transfer in heater tubes of city gas stations using spiral spring inserts

In this study, the effect of turbulators (coiled wire tube insert) as a passive method for heat transfer enhancement on heater performance of Mokhtar city gate station of Yasuj city has been evaluated. To analyze the performance and the effect of geometrical parameters of turbulators and physical parameters of the flow, steady state and incompressible flow were simulated through ANSYS CFX 14.5. Shear stress transport (SST) turbulence model for modeling turbulated flow regime besides the wall has been used. Using simulation results, important performance parameters such as friction factor, Nusselt number, and thermal performance factor were calculated and deeply studied. Physical parameters of flow contain Pressure and Temperature, and geometrical parameters of turbulator include turns number, turn diameter, wire diameter and wire cross-section is studied on the heater performance. The results show that Nusselt number for the tube insert with 75.4mm pitch with circular, square and triangular cross sections increased up to 57, 62 and 79 percent, respectively. Also, calculated mean thermal performance factor for each case was 1.038, 1.045 and 1.087, respectively. Therefore, the spiral spring inserts with triangular cross-sectional is more effective compared to others.

Localization of fugitive methane emission from natural gas distribution network of Titas Gas

Abstract The aim of this paper is to localize the fugitive leaks from the above ground facilities of the existing system of Titas Gas (TG) after developing mathematical model for fugitive emission. Soap screening techniques and Gasurveyor 500 series instrument were used in this study for detecting potential leaks. Leaked gas was quantified using either Hi-Flow gas sampler or bagging measurements system. The results show that the respective potential gas leaking point of City Gate Station (CGS), commercial Regulating and Metering Station (RMS), industrial RMS, residential RMS and Town Bordering Station (TBS)/ District Regulating Station (DRS) are scrubber dump valve (average leak rate 217.00 L/min), insulating point (average leak rate 4.04 L/min), tube fitting connector (average leak rate 8.00 L/min), connector (average leak rate 1.55 L/min) and pressure relief valve (average leak rate 437.92 L/min). Fugitive methane emission can be reduced by stopping leaks of fittings or components having high KLeak value.

Proposal and design of a natural gas liquefaction process recovering the energy obtained from the pressure reducing stations of high-pressure pipelines

Taking advantage of the refrigerating effect in the expansion at an appropriate temperature, a fraction of high-pressure natural gas transported by pipelines could be liquefied in a city gate station through a well-organized pressure reducing process without consuming any extra energy. The authors proposed such a new process, which mainly consists of a turbo-expander driven booster, throttle valves, multi-stream heat exchangers and separators, to yield liquefied natural gas (LNG) and liquid light hydrocarbons (LLHs) utilizing the high-pressure of the pipelines. Based on the assessment of the effects of several key parameters on the system performance by a steady-state simulation in Aspen HYSYS, an optimal design condition of the proposed process was determined. The results showed that the new process is more appropriate to be applied in a pressure reducing station (PRS) for the pipelines with higher pressure. For the feed gas at the pressure of 10MPa, the maximum total liquefaction rate (ytot) of 15.4% and the maximum exergy utilizing rate (EUR) of 21.7% could be reached at the optimal condition. The present process could be used as a small-scale natural gas liquefying and peak-shaving plant at a city gate station.

Feasibility study on energy recovery at Sari-Akand city gate station using turboexpander

Saving energy is a significant issue in the oil and gas industries because of the high cost of global energy sources. Turboexpanders are generally used to recover pressure energy of gas at city gate stations. The present study examined the challenges to turboexpander installation at gas station. These include fluctuations in natural gas (NG) flow and the high cost of installing new heating devices. The first line at Sari-Akand city gate station was simulated using HYSYS software for a nominal capacity of 120,000 SCMH. The NG pressure energy lost at the regulator was calculated using exergy analysis. The results showed that the pressure energy of NG lost during regulation was 7.1 GWh annually. Two scenarios were analyzed to find the suitable plan of turboexpander installation at the gas station. The scenario for installation of one turboexpander instead of one regulator had lower payback period than the scenario where one turboexpander was installed in place of two regulators. NG fluctuation resulted in inability to use the turboexpander for five months of the year and decreased electricity production 8.3% in the other seven months. The annual turboexpander electricity production was computed to be 3.2 GWh. The payback period for turboexpander installation was calculated as 12.9 years to account for the significant 2-fold increase in dollar price in Iran. A feasibility study for implementing a similar plan in England had a payback period of 2.2 years because of the higher price of electricity and lower interest rate in comparison with Iran. The connection of lines 1 and 2 increased annual turboexpander electricity production 54%, which resulted in an annual increase in revenue of $53,400. This decreased the payback period to approximately 8 years in Iran and 1.7 years in England. It is predicted that implementation of similar arrangement at the three other stations will significantly increase revenue about $160,000 annually.

Gas networks simulation from disaggregation of low frequency nodal gas consumption

Natural gas distribution network aims at delivering sufficient gas flow to consumers at consumption nodes. A gas meter is installed at each consumption node of gas network which records low frequency monthly gas consumption of that node. There is also a gas meter in city gate station which records high frequency daily gas consumption of the entire network. Gas distribution companies need to know daily gas consumption of each node (consumer) and daily nodal pressure of the network for control and planning purposes. Gas consumption of each node is a time series with constant recording time step. This article presents a time series disaggregation method for related time series with identical recording times. This method disaggregates low frequency gas consumption at the nodes to high frequency consumption such that sum of consumption of all nodes in each day equals daily consumption of the entire network measured by the city gate station gas meter in that day. These high frequency data are high frequency profile of consumers' gas consumption and can give analysis of the network. The article also discusses compatibility of low frequency consumption of gas network and city gate station high frequency data and the required corrections when these data are mismatched in mathematical sense. Finally, the method is applied to a gas distribution network and results are presented and discussed. The proposed method is general and can be applied to any set of related or unrelated time series and any network with known governing equations as well as the gas network.

Integration of vertical ground-coupled heat pump into a conventional natural gas pressure drop station: Energy, economic and CO2 emission assessment

City gate stations receive high pressure natural gas and decrease the pressure by throttle valves. Concurrent with the natural gas pressure reduction, the temperature also drops. Thus, to prevent blocking of the downstream pipeline by the liquid and solid particles, natural gas must be preheated before pressure reduction. Heaters utilized for preheating task, have a low thermal efficiency and consume a large amount of fuel. In addition to the high fuel consumption, they release a huge amount of CO2 into the atmosphere. Therefore, the present study proposes a new system for in-situ fuel consumption elimination at these stations. It utilizes vertical ground-coupled heat pump system as a renewable source of energy to preheat natural gas stream. The system performance was studied at two different climatic conditions of Iran which have also two different natural gas compositions. Results show that the system is completely capable to eliminate in-situ fuel consumption of city gate stations; however, by considering indirect fuel consumption of electrical heat pumps, the system fuel consumption reduction potential was calculated over 65%. It is also able to reduce CO2 emission up to 79%. The discounted payback period is computed around two years, which proves the suitability of offered system.