Natural Gas Pressure Drop Stations Research Articles

Employing enhanced geometries in water bath heating system of natural gas pressure drop stations: Comparative study

In pressure drop stations (PDSs), the natural gas (NG) is heated before its pressure is reduced. It is commonly performed in a water bath heating system equipped with a serpentine-shaped pipe-line and a fire tube. A part of NG is burned in the fire tube, and the produced heat is transferred to water as heat transfer media. Then, the NG following through the pipe-line achieves the heat, and its temperature goes up. In this study, three enhanced geometries, namely twisted-insert (TI), twisted-tube (TT), and corrugated-tube (CT), are proposed to enhance thermal performance of the pipe-line and reduce fuel consumption of the heating system. Firstly, the obtained results are validated with data collected from a real PDS with the capacity of 1000 m3/h. It is found that the mean deviation between the current results and the real data is less than 1%. Then, the enhanced models are examined at three different levels of the specific design factor, i.e. ratio of 360° twist-pitch (or wave-length) to straight-section. It is found that replacing an enhanced model with the reference model can noticeably affect both thermal and hydraulic characteristics of the pipe-line. For given operating conditions, the use of the TI, TT, and CT models can enhance the NG temperature by about 6, 2, and 3 K compared to the reference model. At the same time, the pressure drop of the NG increases about 10, 7, and 12 times higher than the reference model. As a rule of thumb, the TI, TT, and CT models can reduce the length of the pipe-line by about 50%, 25%, and 37.5%, respectively.

Improving thermal performance of water bath heaters in natural gas pressure drop stations

One of the main components of a natural gas pressure drop station is the water bath heater (also known as line heater) that preheats the gas flow before its pressure is reduced through a throttling process. A major problem of this kind of heater is its low thermal efficiency, which is roughly 40–50%, making natural gas pressure drop station an exergy destructive point in the gas transmission system. This study proposes the use of a twisted flow disturber through the gas coil within the water bath heater to increase the rate of heat transfer from water to the coil, and subsequently increasing the thermal efficiency of the heater. This process is numerically simulated for a real water bath heater in a case study gas station in Iran to observe and analyze the effects of employing this type of flow disturber. The nominal capacity of the case study heater is 1000 m3/hr of gas to be heated up. The results show that the flow disturber might improve the average Nusselt number of the gas flow through the coil by about 20%, increasing the thermal efficiency of the heater and reducing its fuel consumption.

Estimation of density and compressibility factor of natural gas using artificial intelligence approach

Natural gas density is commonly measured by Coriolis density meters and gas chromatographs, both of which are used to calculate the natural gas mass flow rate. In this study, two networks are proposed to predict the density and compressibility factor of natural gas. The first network (N1) uses temperature, pressure and Joule Thomson (JT) coefficient of natural gas as input variables and density of natural gas is selected to be the target. This network is proposed to predict the natural gas density at natural gas pressure drop stations (CGSs). For this network, the gas mixture compositions are unnecessary. The second network (N2) is proposed based on the pseudo reduced temperature and pressure as input variables that the network by using these two variables can predict the density and compressibility factor of natural gas. This model needs the gas mixture compositions. For these targets, a novel idea based on artificial intelligence is used. Five models of artificial intelligence are implemented that are fuzzy inference system (FIS), adaptive neuro-fuzzy inference system (ANFIS), ANFIS optimized with genetic algorithm (ANFIS-GA), multilayer feed-forward neural network (MLFFNN) and group method of data handling (GMDH). The results demonstrated that the ANFIS-GA and GMDH model performed better than the FIS, MLFFNN and ANFIS models. For N1, root mean square error (RMSE) for ANFIS-GA and GMDH models were obtained as 0.2405 and 0.2042 (kg/m3), respectively. For N2 (compressibility factor), the value of RMSE for ANFIS-GA and GMDH models consecutively was achieved 0.0061 and 0.0054. Also, for N2 (density), RMSE for ANFIS-GA and GMDH models was taken 2.2735 and 2.6113, respectively. These values of RMSE were reported for the testing phase of the models.

TECHNO-ECONOMIC INVESTIGATION OF DIFFERENT ALTERNATIVES OF IMPROVING SIMPLE GAS TURBINE INTEGRATION OPTIONS

This study investigated the effect of integrating various models proposed to improve a simple gas turbine power plant. A computer program was developed in Matlab software was used to simulate the performance parameters. The energy and exergy analysis of the plant was carried out. The energy and exergy analysis result revealed that both energy and exergy efficiency of plant is low as a result three improvement options were considered. They include Model 1: reducing inlet air cooling (IAC) of the compressor by using the wasted energy in the natural gas pressure drop station. Model 2: recovering wasted energy in the exhaust through heat recovery steam generator (HRSG) and injecting steam into the combustion chamber and lastly Model 3: by combining the two methods. The result showed that among the three methods of improving the plant investigated Model 3 was found to boost power output of the plant from 28.3 MW to 78.4 MW while the thermal and exergetic efficiency improved by 25.5 and 23.6% respectively. Furthermore, from economic and environmental point of view, the lowest levelized cost of electricity as well as the specific emissions was observed in Model 3. Consequently, Model 3 is selected as the best option in improving the simple gas turbine. Â http://dx.doi.org/10.4314/njt.v36i3.27

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.

Performance assessment of vortex tube and vertical ground heat exchanger in reducing fuel consumption of conventional pressure drop stations

In natural gas pressure drop stations, before pressure dropping specially in cold seasons, the natural gas is preheated to prevent gas hydrate formation. Indirect water bath heaters employed for preheating. The heaters have low thermal efficiency and consume a large amount of natural gas for preheating. Due to the abundance of natural gas pressure reduction stations, reducing energy consumption is essential in this sector of the gas industry. In this study to reduce the heater energy consumption an innovative system based on using vortex tube and vertical ground heat exchanger is proposed. A vortex tube is used instead of throttle valve to reduce natural gas pressure. Unlike the throttle valve, vortex tube divides the incoming stream into two cold and hot streams. Cold stream enters the shell and tube heat exchanger and receives geothermal heat. Then the warmed cold stream mix with hot steam outgoing from the vortex tube, and goes towards the heater at low pressure. The proposed system can reduce energy consumption up to 88%, and the discounted payback period is always less than 4.5years.

Performance assessment of a natural gas expansion plant integrated with a vertical ground-coupled heat pump

In the present paper, a vertical ground-coupled heat pump system is proposed for energy saving in a natural gas expansion plant. Such plant is a modern type of conventional natural gas pressure drop station. Unlike the conventional type, which waste the natural gas pressure exergy in throttling process, the modern one uses the pressure exergy of the natural gas for producing electrical power. A remarkable feature of the proposed system is the type of energy resource used for preheating aim. In previous studies, natural gas was used for the preheating process, however; the proposed system employs geothermal energy as a renewable energy resource for providing part of heating demand. Initially, the vertical ground-coupled heat pump system preheats the natural gas stream up to medium temperatures, then, gas stream passes through station heater and reaches the desired temperature.For studying the economic and thermal performance of the proposed system, first of all, a system with a high net present value is selected, and then the performance of the selected system is studied in detail. The analysis revealed that the fuel saving potential of the system is 45.80% annually. Economically, the discounted payback period was also calculated about 6 years.

A novel method for calculating natural gas density based on Joule Thomson coefficient

In natural gas measuring techniques, the natural gas mass flow rate is usually measured employing experimental facilities for density calculation, volume flow meters and other peripheral equipment such as temperature and pressure sensors. In order to simplify natural gas mass flow metering at natural gas pressure drop stations (CGS), this work presents an easy and precise method for measuring natural gas density. The method is based on a correlation that calculates the molecular weight and density of natural gas stream as a functional of the temperatures and pressures of natural gas before and after a throttle valve. These easily measurable properties at the natural gas pressure drop station are employed to calculate, firstly, the Joule Thomson (JT) coefficient and then density based on a developed correlation. For developing the corresponding correlation and also validating the results, a huge database including the practical data of 6 selected main natural gas fields of Iran is used. In fact, 50% of the available experimental data (three fields) have been used to develop the correlation and the remaining 50% (the other three fields) are used in accuracy assessment step. The results show that the error in calculating density doesn't exceed 1.2%, while for more than 70% of the states the error is even less than 0.6% and the average error is less than 0.4%. MAE (mean absolute error) and STD (standard deviation of absolute error) are also employed in order to validate the correlation results. The validation shows satisfactory calculation accuracy.

Employing geothermal heat exchanger in natural gas pressure drop station in order to decrease fuel consumption

Natural gas stream must be preheated before pressure reduction takes place at natural gas pressure drop station (CGS). It ensures that the natural gas stream remains above hydrate-formation zone. The heater which is employed to provide the required heat consumes a huge amount of fuel. In this work, the conventional configuration of the natural gas pressure drop station is amended by taking advantage of geothermal energy to provide either all (if applicable) or a considerable portion of the required heat. To evaluate the proposed system in terms of economic and thermal efficiency, Gonbad Kavoos station has been chosen as a case study. Comprehensive thermo-economic analysis has been carried out on the proposed system. The results show that a system comprising 8 boreholes with 150 m depth and 0.15 m diameter each is the most efficient configuration for Gonbad Kavoos station. The achievable providence for the case study was calculated by technical correlations over the standard life time of geothermal systems. Comparison between the proposed system and the previous studied systems proved that the current configuration outperforms all the prior propounded configurations, with IRR (internal rate of return) = 0.155.

Improving Khangiran gas turbine efficiency by two standard and one novel inlet air cooling method

Turbine air inlet cooling is one of many available commercial methods for increasing the performance of a gas turbine. The method that has different configurations could be applied for nearly all gas turbines. This paper offers a comparison between two standard and one exquisite inlet air cooling method, which are used to improve the performance of a gas turbine located at the Khangiran refinery in Iran. These methods have been applied to one of the gas turbines located at the Khangiran refinery. Two common air-cooling methods are based on fogging systems and absorption chillers. The idea behind the novel method is to utilize the potential cooling capacity of the refinery natural gas pressure drop station. The research is part of a plenary program developed to enhance the efficiency of the gas turbine used at the Khangiran gas refinery. Considering the results, it is found that the new method is the most feasible in economic terms, so it has been recommended to be used for improving the performance of the Khangiran refinery gas turbines.

Producing Electrical Power in Addition of Heat in Natural Gas Pressure Drop Stations by ICE

Natural gas (NG) must be preheated before pressure reduction takes places at City Gate Stations (CGS). It ensures that gas remains above the hydrate-formation zone and dew point, so no pipeline blockage occurs. The preheating consumes a considerable amount of NG as fuel. In order to operate the CGS more efficiently, a new idea is proposed in this study. The idea is to utilize a Combined Heat and Power (CHP) system in which an Internal Combustion Engine (ICE) acts as a prime mover. The ICE is driving a generator in addition of providing heat for preheating NG. To show the advantage of the proposed system, Mashhad CGS has been chosen as a case study. Results show that a CHP system with two 2.8 MW ICEs is the most appropriate system. The system has the minimum fuel consumption and payback period. Based on the Iranian natural gas consumption of 377 × 106 (m3/day) and by assuming the similar conditions for the other CGSs in Iran, the total amount of extractable electrical power from the CHP systems is predicted to be nearly 91.5 MW. That is equivalent to 802.14 GW.hr/year in 2010 with a yearly benefit about 45 million dollars. According to average annual growing rate of 2.4% of gas consumption in Iran, the predictions are performed until 2035.

Feasibility of accompanying uncontrolled linear heater with solar system in natural gas pressure drop stations

Natural gas (NG) must be preheated before pressure reduction takes places at City Gate Stations (CGS). Indirect Water Bath Gas Heaters are employed in the CGS for preheating. The heaters consume a considerable amount of NG for preheating. As low temperature is required, a solar system has been proposed to provide part of heat demand. The system consists of a collector array and a storage tank. The tank stores solar heat during the day and releases it during the night. To show the capabilities of the proposed system, the Akand CGS has been chosen as a case study. The results show that as the number of collector increases, the fuel cost decreases but the capital cost increases. An optimum number of collectors and the storage tank capacity have been found based on economic analysis. The fuel saving occurs throughout the year with the maximum at June. The economic feasibility study of the proposed system has been carried out using two methods. These methods are Simple Payback Ratio (SPR) and (Net Present Value) NPV. The first one unveils that the payback ratio is only 6.9 years. The NPV method shows that the system will give net benefit after 11 years.

Feasibility of employing solar energy in natural gas pressure drop stations

Natural gas is carried through transit pipelines at high pressure (5–7 MPa) from production sites to consuming points. In the place of consumption or crossing into a lower pressure pipeline, the pressure of the gas must be decreased. This pressure reduction occurs in places named city gate stations (CGS) as the gas passes through throttling valves. The gas must be heated before it enters throttle valves to ensure that it remains above the hydrate formation zone and dew point so that no liquid or solid phase condenses at the output temperature. Currently, in all of Iran’s CGSs, the gas is preheated through bath type heat exchangers (known as line heater), which burn a portion of the gas for providing heating duty to warm up the natural gas. As a low temperature heat is required for preheating the natural gas in aC GS, as olar collector array is proposed to be utilised in the CGS in order to displace the heating duty of the heater and to reduce the amount of fuel consumption. The proposition includes a modified design of an in use CGS to take advantage of freely available solar heat.

Effect of various inlet air cooling methods on gas turbine performance

Turbine air inlet cooling is one of many available commercial methods to improve the efficiency of an existing gas turbine. The method has various configurations which could be utilized for almost all installed gas turbines. This paper presents a comparison between two commons and one novel inlet air cooling method using turbo-expanders to improve performance of a gas turbine located at the Khangiran refinery in Iran. These methods have been applied to one of the refinery gas turbines located at the Khangiran refinery in Iran. Two common air cooling methods use evaporative media or a mechanical chiller. The idea behind the novel method is to utilize the potential cooling and power capacity of the refinery natural gas pressure drop station by replacing throttling valves with a turbo-expander. The study is part of a comprehensive program with the goal of enhancing gas turbine performance at the Khangiran gas refinery. Based on the results, it is found that using turbo-expanders is the most economically feasible option and so is recommended to be utilized for improving gas turbine performance at the Khangiran refinery.

Improving the efficiency of an industrial gas turbine by a novel inlet air cooling method

AbstractTurbine air inlet cooling is one of the available commercial methods to improve efficiency of existing gas turbines. The method has various types of air cooling which could be utilised almost for all installed gas turbines. In this study a new type of inlet air cooling has been proposed to improve performance of a gas turbine. The method has been applied to one of the Kangiran refinery gas turbines. The idea is to cool inlet air of the gas turbine by potential cooling capacity of the isoenthalpic pressure drop in the refinery natural gas pressure drop station. The study is part of a comprehensive programme aimed to enhance gas turbines performance of the Khangiran gas refinery. The results show that the gas turbine inlet air temperature could be reduced in the range of 4 to 25 K and the performance could be improved in the range of 1 to 3·5% for almost nine months.

Enhancing energy output in Iran's natural gas pressure drop stations by cogeneration

AbstractNatural gas is transported through transit pipeline at high pressures (5–7 MPa) from production sites to end users. In a place of consumption or at passing into a lower pressure pipeline, the pressure of the gas must be reduced. This pressure reduction takes place in places which are called city gate stations (CGSs). Currently, in all Iran's CGSs, valuable pressure exergy (potential energy) of natural gas flow is destroyed in throttling valves. In the current study, based on a comprehensive programme, inlet and outlet properties of natural gas flow and daily flow rate through seven Khorasan Province (Iran) CGS were measured and recorded for a whole year. Based on these data, the amount of energy which could be generated using a combined heat and power system was calculated. The combined heat and power system consists of a preheat section, a turbo expander and an additional prime mover. The amount of electricity generation for the system has been calculated. The results show that 20˙5 MW electrical...

Recoverable Energy in Natural Gas Pressure Drop Stations: A Case Study of the Khangiran Gas Refinery

The natural gas which is supplied to the Khangiran gas refinery comes from a high-pressure natural gas transmission pipeline and passes through a metering and reducing station, sometimes referred to as the pressure drop station. The gas at this reduced pressure enters the refinery for internal uses. It is at the pressure drop station that a lot of energy is wasted, as the pressure of the natural gas is reduced by an expansion-type ball valve. But, the design of the ball valve does not allow any of the energy from the compressed natural gas to be recovered, as it regulates from a higher pressure to a lower pressure. If this energy loss can be captured, it can be converted into electricity. In this study, a comprehensive program has been carried out to record and measure natural-gas properties and flow rates at Khangiran pressure drop station for a year. Based on these data and an accompanying exergy analysis, the amount of available work that can be produced from capturing natural-gas pressure exergy from the station has been calculated. To produce work, a system which consists of preheating and a turbo expander has been proposed and studied. The effect of preheating temperature and turbo expander exergetic efficiency on amount of obtainable work has been studied. The results show that the amount of available energy can meet all electrical demand of the refinery.