Natural Gas Pressure Reduction Stations Research Articles

A novel preheating system in pressure reduction stations—natural gas directly flowing inside deep borehole heat exchangers

To prevent hydrates from forming during the pressure reduction process in natural gas pressure reduction stations (i.e., city gate stations, CGS), fuel-intensive preheating methods are normally adopted, leading to high fuel consumption and carbon emissions. In this study, an innovative preheating system for natural gas is proposed, which is called the “Direct Geothermal Heating System” (DGHS). The main idea is to inject high-pressure natural gas into geothermal wells before the throttling valve; thus, natural gas is directly heated by the surrounding strata when it flows through the geothermal well. A proper temperature for natural gas should be ensured, as natural gas goes back to the ground for pressure regulation. The idea is performed based on the preheating configuration using coaxial deep borehole heat exchangers (DBHE). A mathematical model describing the flow and heat transfer processes of DGHS through DBHE is established to study its heat transfer characteristics. Additionally, the environmental and economic benefits of the proposed configuration are also investigated. Through the CGS case in this paper, the findings indicate that, over the fifteen years of preheating with a DBHE depth of 2000 m and inlet flow rate of 4.39 × 107 Nm³/year, the outlet temperature of the throttling valve remains within the range of 17 °C–37 °C, meeting the heating requirement of CGS. Among fifteen preheating cycles, the average peak heating power of the DBHE reaches 105.78 kW. In addition, in the 15th year, the proposed system has a 1/3 cost of a traditional line heater, along with a reduction of 46.43 × 105 kg in CO2 emission. The DGHS for natural gas is easy to establish and operate; once it is promoted on a large scale, it will produce huge economic and environmental benefits.

Energy recovery and hydrogen production potential assessment in a natural gas pressure reduction station

An energy recovery and hydrogen production potential assessment study was carried out for a pressure reduction station by integrating a turbo expander-electrolyzer system. The hydrogen and electricity production potentials were investigated based on the natural gas flow rate. For this purpose, a turbo expander-proton exchange membrane electrolyzer system was considered, using standard data of an RMS-A type PRS. The variation in energy recovery potential was calculated according to the natural gas flow rate and inlet-outlet parameters such as temperature and pressure. By using these parameters, energy balance calculations and energy profit rate were evaluated. The energy profit rate was calculated as 274 kWh for 50.000 Sm3/h volumetric flow rate. Based on real data for a PRS, the electricity and hydrogen production potential were found to be 13.654.567 kW of electricity and 1.532.325,6 Nm3 of hydrogen production with the annual natural gas flow. According to the sensitivity analysis, increasing the station inlet temperature and outlet pressure negatively affected the energy profit rate, while increasing the inlet pressure had a positive effect. The levelized cost of electricity was calculated as 0,056 $/kW, while the levelized cost of hydrogen was found to be 1,989 $/kgH2. These results indicate that energy recovery from the PRSs is feasible and an opportunity to ensure sustainability.

Designing an energy storage system based on water tower pumping to store the energy generated by the turbo-expander implemented in a gas pressure reduction station

In the present research, an energy recovery and storage strategy for a natural gas pressure reduction station with a capacity of 50,000 Nm3/h has been proposed. Currently, the gas pressure reduction station does not have an energy recovery system; hence, energy of high-pressure natural gas is wasted in it. For this reason, first, the energy recovery system was thermodynamically designed based on the use of a turbo-expander instead of the regulator, and the extracted energy was calculated. The results showed that 1.376 GWh electrical energy can be generated annually using the recovered energy. Then the economic analysis of the use of the proposed plan was discussed. The results of the economic analysis showed that the investment payback period for installing the turbo-expander in the considered station is 2.4 years. In the last part of the research, an energy storage system was designed to store the generated electrical energy. For this purpose, an energy storage system based on water pumping in water towers was designed. Water towers with different classes were investigated. The obtained results showed that the average energy conversion efficiency in the energy storage system varies from about 70 % for small water towers to about 74 % for large ones.

A novel energy recovery and storage approach based on turbo-pump for a natural gas pressure reduction station

In this research, a direct energy harvesting and storage strategy was proposed for the recovered energy from the natural gas pressure reduction station. For this purpose, a novel turbo-pump system is proposed, which consists of a turbo-expander and a water pump. The proposed plan was integrated into a gas pressure reduction station with a capacity of 300,000 Nm3/hr. In gas pressure reduction stations, a regulator reduces gas pressure, which wastes natural gas energy in the depressurization process. To recover this wasted energy, a turbo-expander has been used instead of the regulator. The designed turbo-expander shaft is connected to the pump shaft. By receiving mechanical energy from the turbo-expander, the pump transfers the water into the water towers and thus stores the energy. For this purpose, water towers with different sizes were designed and their energy storage capacity and efficiency was calculated. The obtained results showed that 15.3 GWh energy can be recovered annually, which this amount of energy is currently wasted. While harvesting this significant amount of energy from a gas pressure reduction station, emissions are also prevented. The analysis results of the designed energy storage system also showed that the total energy conversion efficiency of recovered energy from natural gas in the pressure reduction process to electrical energy in the discharge stage of the energy storage system is about 52%. Also, the average daily electrical power generated during peak consumption hours is between 0.7 and 17.9 MW. By recovering and storing wasted energy from just one gas pressure reduction station, in addition to generating electrical energy during peak hours, the emission of 4620 tons of carbon dioxide can be prevented annually. The designed energy storage system can be installed as discrete packs of energy storage in different capacities, which have high installation and flexibility.

Techno-economic assessment of a proposed novel hybrid system for natural gas pressure reduction stations

To prevent Natural Gas (NG) frozen during pressure reduction process, a heater is contrived for preheating NG. In this study, a novel system is suggested to supply part of heat demand of a NG City Gate Station (CGS). The system consists of a heat pump in which the compressor input work is supplied by the turbo-expanders. In the proposed system, pressure reduction is carried out by turbo-expanders instead of Regulator Valve (RV) to recover the energy of high pressure NG. The recovered energy by turbo-expanders meets the heat pump cycle work demand. A CGS is selected as a case study, and the suggested system is assessed in terms of energy, exergy, and economics. The amount of the annual fuel savings is calculated 2.42 × 106 kg (70.08%). Exergy analysis shows that the most exergy destruction occurs in the RV and heater. The exergy factor of the proposed system in the days that the system works, is about 2.2–5.1%. Based on the economic analysis, the value of simple payback period and discounted payback period are calculated 2.63 and 3.08 years, respectively. The annual revenue that comes from saving fuel is 310,000 $/year based on the current price of NG.

Consequences modeling and determining of safe distance in the natural gas pressure reduction station using PHAST software (Case study: Borumi station in Ahvaz)

Introduction: Gas pressure reduction stations are one of the most important parts of natural gas distribution networks. Risk assessment in operational units is a suitable method to assess risks, and their results can be used for management and decision-making regarding control and reduction of its consequences without critical concern. In other words, risk assessment is a process that identifies risks, assesses losses and determines risk characteristics. The present study aimed to model possible accidents, the subsequent evaluation of the consequences, and determination of safe boundaries in the suburban natural gas pressure reduction station located in the Bromi area of Ahvaz city using PHAST software.
 Materials and Methods: In this study, possible scenarios based on the investigated background and utilizing the process data of the studied gas pressure reduction station, such as temperature, gas pressure, gas analysis, and meteorological data, and also using Pasquil's classification of atmospheric conditions the safe boundaries in the suburban natural gas pressure reduction station was investigated using PHAST software version 22.8 and. For this purpose, 6 possible scenarios were investigated in the selected atmospheric classes as well as the worst possible conditions. The consequences were evaluated based on different states of gas discharge, gas release, flash fire, sudden fire, and explosion.
 Results: Based on the obtained results, the areas with high-risk potential were related to gas release and explosion, respectively. Also, the highest risk range belonging to scenario number five was reported for a gas explosion with atmospheric class F and wave intensity of 0.02068 bars and equivalent to 358.5 meters. In this range, according to the damage caused by the explosion, with a probability of 95%, without serious damage, 50% of the windows will be broken, and therefore it can cause human injuries. Based on this, the safe distance in this station was determined to be 358.5 meters.
 Conclusion: Based on concerns about the lack of risk assessment studies over the initial phases and during the operation of the station, the study shows that determining the safe boundaries and high-risk areas along with the priority of risk reduction is very necessary. It can be concluded that the modeling of accidents and the evaluation of the resulting consequences along with the determination of safe boundaries is one of the basic factors in the health of the working environment of personnel and the general public.

Multi-objective optimization of preheating system of natural gas pressure reduction station with turbo-expander through the application of waste heat recovery system

• Proposing waste heat recovery configuration in natural gas-pressure reduction stations. • All of the components in the proposed and conventional preheating system are sized and designed. • Applying multi-criteria decision-making methods to find the optimal design. • A reduction in the total cost compared with conventional configuration is up to 98%. • A decease in exergy destruction compared with conventional configuration is 78%. The preheating system is regarded as an integral part of a natural-gas pressure reduction station (NGPRS) when a turbo-expander is substituted with regulators. In this paper, two configurations are compared for optimal designing preheating system used in NGPRS with the turbo-expander system. The first case uses water for a hot fluid that is warmed in the gas-fired heater (GFH), and the second is a Waste Heat Recovery (WHR) configuration. Multi-objective optimization and multi-criteria decision-making (MCDM) methods are implemented to identify the optimal design of mentioned preheating systems and to acquire the ability for the designer to select the optimal solution readily. The total cost and modified exergy efficiency (MEE) are selected as the objective functions. Moreover, sensitivity analyses of design parameters and their effects on objective functions are carried out for both configurations. Results show that the optimal designs suggested by MCDM methods in the WHR configuration provide a substantial reduction not only in total cost up to 98% but also in exergy destruction up to 78%. In addition, MEE increases by as much as 5 percent compared with the conventional configuration. Based on the aforementioned points, the WHR configuration is advantageous in both economic and exergy principles.

Energy Recovery from Natural Gas Pressure Reduction Stations with the Use of Turboexpanders: Static and Dynamic Simulations

The application of expansion turbines at natural gas pressure reduction stations (PRS) is considered in order to recover energy contained in the natural gas. This energy is irretrievably lost at the reduction stations which use the traditional pressure reducer. Expanders allow for the electricity production for PRS own needs and for resale. The paper presents an analysis of the possibility of using turboexpanders at PRS in Poland. Authors performed static simulations for the assumed data sets and dynamic simulations for annual data from selected representative natural gas reduction and measurement stations. Energy balances are presented for the discussed scenarios that compare the energy requirements of natural gas pressure reduction stations which use a classic pressure reducer or turboexpander (TE). Using static simulations, authors investigated whether the use of a turboexpander is economically justified for the case if it is used only to supply the reduction station with electricity. Dynamic analyses were carried out using real data. In addition, static analyses were performed for a natural gas reduction and measurement station using a PEM fuel cell for the production of electricity in a combined gas heating system. At higher inlet temperatures and pressures, the expansion process was more economical due to the lower heat power requirement and the greater amount of produced electricity. The PRS with the turboexpander compared to the PRS with the reducer required the supply of thermal energy which did not allow the PRS to lower operating costs for the assumed prices of heat and electricity. The reduction system with the PEM fuel cell in the combined heating system positively achieved lower operating costs of the PRS (without taking into account the investment costs). Total annual costs for PRS with a reducer was PLN 1,593,167.04, and for PRS with TE + PEM PLN 1,430,595.60—the difference was PLN 108,571.44 in favor of the arrangement with TE and PEM. The payback time should be investigated, although the use of such a system gives the impression of oversizing. An increase in the electricity purchase price and a decrease in the natural gas purchase price may contribute to the investment in the future.

Investigating the possibility of using the turbo-expander for natural gas pressure reduction stations

Investigating the possibility of using the turbo-expander for natural gas pressure reduction stations

Reliability assessment on natural gas pressure reduction stations using Monte Carlo simulation (MCS)

Gas pressure reduction stations play a key role in the timely and safe supply of natural gas (NG) to residential, commercial, and industrial customers. Accordingly, system reliability analysis should be performed to prevent potential failures and establish resilient operations. This research proposed a reliability assessment approach to natural gas pressure-reducing stations using historical data, statistical analysis, and Monte Carlo simulation (MCS). Historical data are employed to establish the probability distributions of the system and subsystems in gas stations. Then the Kolmogorov-Smirnov test is conducted to assess the goodness-of-fit for the developed distributions. Bayesian network (BN) is utilized to develop a system failure causality model. Finally, we performed MCS to precisely predict the failure rate and reliability of stations and all subsystems, such as the regulator, separator and dry gas filters, shut-off valves, and regulator. This research provided numerical findings on the reliability indicators of pressure reduction stations which can be used to improve system performance and, subsequently, the resilience of NG pipelines.

Natural Gas Pressure Reduction Station Self-powered by Fire Thermoelectric Generator

Natural Gas Pressure Reduction Station Self-powered by Fire Thermoelectric Generator

Thermodynamic analysis of a comprehensive energy utilization system for natural gas pressure reduction stations based on Allam cycle

• A comprehensive energy utilization system for natural gas pressure reduction stations based on Allam cycle is proposed. • The effects of key parameters on the proposed system performance are clarified. • The proposed system and the pre-heating system are compared and analyzed. • Energy efficiency is 99.31% with turbine inlet parameters of 30 MPa/900 °C. In order to effectively utilize the pressure energy and cold energy of the natural gas pressure reduction stations, this paper proposes a comprehensive energy utilization system for natural gas pressure reduction stations based on Allam cycle. The low-grade waste heat during the Allam cycle and ambient heat are used to heat the decompressed natural gas to the temperature required by the user. Based on the established mathematical model, the effects of turbine inlet temperature, turbine inlet pressure, turbine outlet pressure, isentropic efficiency of power equipment, and natural gas expansion stages on the performance of the proposed system are studied. The proposed system and the pre-heating system are compared and analyzed. The results show that when the combustor outlet temperature is 900℃, the energy efficiency and incremental efficiency of the proposed system are 99.31% and 103.55%, respectively. Compared with pre-heating system based on gas turbine cycle, they have increased by 9.84 percentage points and 19.32 percentage points, respectively. Compared with the boiler-based post-heating system, the energy efficiency is increased by 3.5 percentage points.

Mathematical Modeling of the Operation of an Expander-Generator Pressure Regulator in Non-Stationary Conditions of Small Gas Pressure Reduction Stations

Long-distance gas transfer requires high pressure, which has to be reduced before the gas is conveyed to the customers. This pressure reduction takes place at natural gas pressure reduction stations, where gas pressure is decreased by using gas flow energy for overcoming local resistance, represented by a throttling valve. This pressure energy can be reused, but it is difficult to implement it at small pressure reduction stations, as the values of unsteadiness significantly increase when the gas approaches consumers, whereas gas flow rate and pressure decrease. This work suggests replacing throttling valves at small pressure reduction stations for expander-generator units, based on volumetric expanders. Two implementations are proposed. A mathematical model of gas-dynamic processes, which take place in expander-generator units, was developed using math equations. With its help, a comparison was made of the stability of the operation of two possible control schemes in non-stationary conditions, and the feasibility of using an expander-generator regulator as a primary one for a small natural gas pressure reduction station was confirmed.

Energy, exergy, economic, and environmental analyses and multi-objective optimisation of using turbo-expanders in natural gas pressure reduction stations

Energy, exergy, economic, and environmental analyses and multi-objective optimisation of using turbo-expanders in natural gas pressure reduction stations

Energy, Exergy, and Economic Analyses of Natural Gas Pressure Reduction Station Equipped with Turbo-Expanders and Heat Pump Cycle

Energy, Exergy, and Economic Analyses of Natural Gas Pressure Reduction Station Equipped with Turbo-Expanders and Heat Pump Cycle

Energy, exergy, economic, and environmental analyses and multi-objective optimisation of using turbo-expanders in natural gas pressure reduction stations

Energy, exergy, economic, and environmental analyses and multi-objective optimisation of using turbo-expanders in natural gas pressure reduction stations

Energy, exergy, and eco-environment modeling of proton exchange membrane electrolyzer coupled with power cycles: Application in natural gas pressure reduction stations

This paper focuses on introducing a new configuration of a hybrid system for producing power and hydrogen together with pre-heating natural gas in PRSs. The configuration is based on regenerative Brayton, Rankine and proton exchange membrane electrolyzer cycles. Also, a heat exchanger is embedded for supplying the required heating load of NG pre-heating to prevent hydrate formation. A robust energy, exergy, and eco-environment mathematical model with real assumptions is developed to prove feasibility of the introduced system. To make the study applicable for different PRS capacities, the analyses are done for different equipment sizes during different months of year. The parametric study showed that design variables of the Brayton cycle and pressure of inlet NG are very effective parameters in the design of this proposal. Analyzing the results in different months illustrated that the best performance is achieved in January; so that, 20.25 MW of power, 19.91 MW of heating load, and 11.96 kg/h hydrogen are produced for the optimum equipment variables in this month. At these conditions, the first- and second-law efficiencies and the levelized total costs rate are respectively obtained as 58.91%, 34.02%, and 7.03 $/GJ. Also, the payback period is 6.77 years based on the NPV approach.

Optimal detailed design and performance assessment of natural gas pressure reduction stations system equipped with variable inlet guide vane radial turbo-expander for energy recovery

The turbo-expander system is utilized instead of the pressure regulator to avoid exergy destruction occurring in gas pressure reduction systems. However, due to the variation of natural gas input conditions such as mass flow rate, the sustainable performance of this technology is challenging. In this study, at first, the optimal system design of gas pressure reducing station equipped with radial expansion turbine is performed. It is based on economic and exergy analyses as well as considering geometric, fluid, thermodynamic constraints of components and the systematic constraints. To do so, detailed design models of main components including mean-line design model of radial turbine, mathematical model of heat exchanger and design model of fired heater are developed. Then, the annual proficiency of the optimal system in dynamic conditions was evaluated according to the strategies considered for having stable production. One of the solutions is to improve the turbine efficiency by adjusting the angle of nozzle blades regarding the changes in mass flow rate. Therefore, our developed mean-line off design model of the turbine is applied to adjust inlet guide vane angle in the off-design situation to improve continuous electricity generation. The results of the design section show that the exergy efficiency on this occasion can achieve up to a maximum of 40%. Compared with fix inlet guide vane (IGV), applying variable IGV improves efficiency of turbine up to 60% at off-design condition. The Levelized cost of electricity (LCOE) and payback period of selected optimal design are about 0.0236 $/kWh, and 4 years, respectively. It indicates that this technology could be the economic option compared to other power generation systems.

Exergetic and economic evaluation of a novel integrated system for trigeneration of power, refrigeration and freshwater using energy recovery in natural gas pressure reduction stations

Nowadays, with increasing energy consumption, global warming, and many problems caused by weather conditions, the tendency to use novel methods of energy generation with high efficiency and low cost that reduce environmental pollution has increased. This study investigates the feasibility of using gas pressure energy recovery in natural gas pressure reduction stations by turboexpanders for cogeneration of power and refrigeration. Turboexpanders and compression refrigeration cycles are employed to recover the energy from natural gas pressure reduction stations. Then, natural gas along with the compressed air enters the Brayton power generation cycle and its waste heat is used in the carbon dioxide (CO2) power generation plant, multistage Rankine cycle, and multi-effect thermal desalination unit. This integrated structure generates 105.6 MW of power, 2.960 MW of refrigeration, and 34.73 kg s−1 of freshwater. The electrical efficiencies of the Rankine power generation cycle, CO2 power generation plant, and the whole integrated structure are 0.4101, 0.4120, and 0.4704, respectively. The exergy efficiency and irreversibility of the developed integrated structure are 60.59% and 68.17 MW, respectively. The exergy analysis of the integrated structure shows that the highest rates of exergy destruction are related to the combustion chamber (59.68%), heat exchangers (14.70%), and compressors (14.46%). The annualized cost of the system (ACS) is used to evaluate the developed hybrid system. The economic analysis of the integrated structure indicated the period of return, the prime cost of the product, and capital cost are 2.565 years, 0.0430 US$ kWh−1, and 372.3 MMUS$, respectively. The results reveal that the period of return is highly sensitive to the electricity price, such that the period of return in the developed integrated structure is less than 5 years for the electricity price of 0.092 US$ kWh−1 and more. Also, the period of return is less than 5 years for the initial investment cost of 632.9 MMUS$ and less, which is economically viable.

Techno-economic analysis of power generation by turboexpanders in natural gas pressure reduction stations

The objective of this paper is to perform a techno-economic feasibility study of recovering pressure energy of natural gas stream through installing turboexpanders in a pressure reduction station and selling the generated electrical power to the national grid. As a case study, the operating and real conditions of a major pressure reduction station in Iran is collected throughout the years 2015, 2016 and 2017. To account for the effects of the inherently variable operating conditions, a thermodynamic model based on exergy analysis estimates off-design turboexpander isentropic efficiency, size and cost estimate as well as minimum preheating temperature required to avoid hydrate formation due to the expansion process. The detailed economic analysis shows that for the project to be economically feasible, an electricity purchase price of > $0.08/kWh is required. Furthermore, the results of this study are useful for designing automatic preheating temperature control system.