Water Bath Heater Research Articles

Parametric analysis and multi-objective optimization of heat exchangers in CGS stations: replacement with water bath heaters

Parametric analysis and multi-objective optimization of heat exchangers in CGS stations: replacement with water bath heaters

Energy, Exergy, Exergoeconomic Analysis, and Optimization in a Natural Gas Decompression Station with a Vortex Tube and Geothermal Preheating

Natural gas stations require a preheating stage to prevent the formation of hydrates inside of them provoked by a sudden decompression process of the natural gas. The preheating process has been investigated to improve efficiency and to reduce costs as well. This work studies the behavior of a natural gas decompression station with a first-stage preheating process using a vortex tube and a geothermal heat exchanger, followed by a second stage involving a water bath heater (heating vat). An energetic, exergetic, and exergoeconomic study has been carried out based on a mathematical model and the theory of exergetic cost, obtaining key thermodynamic and thermoeconomic variables, including exergy flows and equipment costs. A heat flow of 26.41 kW was obtained in the geothermal preheating stage; meanwhile, a 60.43 kW heat flow was obtained in the heating vat. The results showed a saving in station fuel using only 2.046% of the natural gas in the system at the second preheating stage. Also, the system was optimized, obtaining a 15.73% reduction in the decompressed natural gas cost. These findings show the possibility of implementing these systems in zones with many geothermal resources to reach a constant, profitable natural gas supply in areas where a pipeline network does not exist.

An active approach to heat transfer enhancement in indirect heaters of city gate stations: An experimental modeling

A major problem with gas pressure reduction stations is the very low thermal efficiency of indirect water bath heaters (IWBHs) used to prevent gas hydration. In this study, an innovative active method based on the ultrasonication technology is investigated to improve heat transfer in IWBHs. Considering the sophisticated thermos-physical phenomena involved in this problem and its complex governing equations, a laboratory-modeled ultrasonic heater is used to conduct the experiments. The results have been successfully validated using an empirical relationship. In order to evaluate the effect of ultrasonic vibrations, all the tests were done in two modes, namely without vibration and with vibrating at different ultrasonic power levels. The results show that the positive thermal impact of ultrasonic vibration on increasing the heat transfer rate is more evident at lower fluid flow rates and lower heater power levels. In the current experiments, the maximum value of ultrasonic heat transfer enhancement was evaluated as 166 % at a fluid flow rate of 0.5 LPM and a heater power of 200 W. Findings of this novel research can lead to the efficiency enhancement of existing gas pressure reduction stations and significant energy savings.

Analytical and Field Investigation of Ethylene Glycol Removal from the Indirect Water Bath Heater of a City Gate Station

Analytical and Field Investigation of Ethylene Glycol Removal from the Indirect Water Bath Heater of a City Gate Station

Performance analysis of vortex tube-thermoelectric system in gas stations

At natural gas pressure reducing stations, gas first enters a water bath heater to boost its temperature slightly, and after leaving the heater, it enters the throttle valve to reduce its pressure. This method has two major drawbacks, which are the consumption of natural gas in the heater and the excessive loss of exergy in the throttle valve. The pressure of natural gas can be reduced by using a vortex tube and converting it into hot and cold currents, and then generating electricity by directing these currents to thermoelectric generators (TEGs). Investigation of energy, exergy and environmental performance of the hybrid vortex tube-TEG system and optimization of its performance for the working condition of Kermanshah pressure reducing station is the subject of the present study. The cold mass fraction (CF) and efficiency of vortex tube are considered as decision variables. Moreover, annual average first-law efficiency (ηI-TEG), annual average second-law efficiency (ηII-TEG) and annual total electric power generated by the TEGs (Pout) are considered as optimization target functions. The results of genetic algorithm based three-objective optimization revealed that the specifications of the optimal system are: vortex tube efficiency = 0.36967, CF=0.95598, ηI-TEG=0.03442, ηII-TEG=0.04544, Pout=42770.58 kW and amount of CO2 mitigation per annum = 8.55 tons.

Energy and exergy analysis and multi-objective optimization of using combined vortex tube-photovoltaic/thermal system in city gate stations

The goal of this study is to investigate the possibility of replacing the water bath heater and pressure relief valve with a hybrid vortex tube-photovoltaic/thermal system in pressure reduction stations like city gate stations. By using this system, both the natural gas pressure can be reduced to the desired level (from 5-7 MPa to 1.5–2 MPa) and electricity can be generated. The effect of cold mass fraction of vortex tube (0.01–0.1), air mass flow rate (0.569–5.69 kg/s) as well as the length (1–10 m), width (0.5–5 m) and depth (0.1–0.5 m) of the photovoltaic/thermal system on the energy and exergy performance of the hybrid vortex tube-photovoltaic/thermal system is investigated. Then, the genetic algorithm based two-objective optimization is used to find the appropriate value of these parameters to maximize the annual average first-law efficiency (ηI) and second-law efficiency (ηII) of the hybrid system. It was found that the ηI and ηII of the optimal system are respectively 74.05% and 19.46%. Moreover, it was observed that the use of optimal system causes a reduction in the CO2 emission by 27.7-tons per year.

Feasibility assessment of using nanofluids in shell and tube heat exchanger of gas pressure reducing stations through a new developed OpenFOAM solver

One of the important challenges in city gate gas pressure reduction stations is the heating of the natural gas prior to pressure reduction. Regarding the low efficiency of the common water bath heaters in these stations another type of double tube-pass shell and tube heat exchanger, equipped with flower baffles, has been proposed for heating the natural gas. Additionally, Al2O3 nanofluid has been suggested to be used in the shell side as the heating medium. Investigating the incompressible three-dimensional steady-state conjugate turbulent forced convection, the heat transfer performance, and also the distribution of the nanoparticles have been studied numerically at various shell and tube sides Peclet numbers for different nanoparticle volume fractions (ϕ = 1, 2, 3 and 4%). The open-source CFD package, OpenFOAM, has been utilized for numerical simulations. A new solver and turbulence model have been developed to implement the four-equation Buongiorno’s model to investigate the nanoparticles’ distribution as well. The results indicated that increasing the shell side nanofluid Peclet number and nanoparticle volume fraction increased the heat transfer coefficient compared to pure water. Additionally, this enhancement increased as the shell side Peclet number and nanoparticle volume fraction increased and the tube side natural gas Peclet number decreased. Thus, a maximum heat transfer coefficient enhancement of 18.1% was obtained at shell side Peclet number of 180,000, tube side Peclet number of 10,000, and a 4% nanoparticle volume fraction. Additionally, the increase in the overall heat transfer coefficient compared to pure water increased as the nanoparticle volume fraction increased. Furthermore, the enhancement in natural gas mean outlet temperature in the case of adding nanoparticles in comparison with pure water was seen to be more at lower shell side Peclet numbers. Eventually, the pressure drop demonstrated an increase with the increase in shell side Peclet number and nanoparticle volume fraction. Also, the rise in the effectiveness compared to pure water enhanced with the increase in tube side Peclet number and nanoparticle volume fraction and decrease in shell side Peclet number.

An experimental investigation on using heat pipe heat exchanger to improve energy performance in gas city gate station

Natural gas pressure drops in city gate stations, in the natural gas distribution network, and bypassing through throttle valves. On the other hand, sudden gas pressure drop causes extreme temperature drop. To prevent natural gas from being hydrated in city gate stations, a water bath heater is used, leading to heating natural gas before the pressure reduction stage.The main consequence of this research is the consideration of the challenge of low thermal efficiency in water bath heaters and the high potential of flue gases, which leads to the preheating of the gas by heat loss recovery and consequently improving the energy performance of the whole system.In this study, a heat pipe heat exchanger was laboratory designed and constructed by using the ε-NTU method. The heat exchanger performs to recover partly the waste energy of flue gas emitted to the environment through heat pipes. This has been investigated in several experiments, based on conducted studies, measured data from a city gate station during a year, and also corresponding the experimental results with real conditions. In addition, to determine energy saving in fuel consumption, the city gate stations process was simulated in HYSYS software and evaluated according to gas temperature in new conditions.As major findings applying heat pipes reduces natural gas consumption by 510,132 SCM a year; it also annually prevents 756 tons of CO2 from being emitted off a city gate station.

Thermodynamic assessment and proposal of new configurations of an indirect water bath heater for a City Gate Station (a case study)

This paper deals with thermodynamic modeling and proposal new configurations of an indirect water bath heater used in a city gate station (CGS) to preheat the natural gas (NG). In the transmission pipeline of natural gas before reducing NG pressure, it is necessary preheating to prevent hydrate formation. In the traditional systems, an indirect water bath heater is used for this purpose. Thermodynamic modeling of the proposed systems has been done in EES software, and an effective analysis based on proposed new configurations is conducted. The results indicate that using exhaust combustion products to preheat the combustion air can increase the thermal efficiency of the system from 46.36% (for base case) to 73.84%. In addition, with the use of an ORC to utilize the exhaust waste thermal energy, the system efficiency of 55.27% with an electrical output of 79 kW can be achieved. A comparison between configurations indicates that the second configuration (preheating combustion air) with 78.97 kg/h has the lowest emission rate.

Investigation of Operational Scenarios to Mitigate CO2 Emission and Natural Gas Consumption in City Gate Stations (CGSs)

City gate stations (CGSs) are the main pressure reduction stations of natural gas (NG) transmission lines where enormous decrease of NG pressure results in significant temperature drop. Therefore, high pressure gas is preheated by means of NG fuel water bath heaters (WBHs) to prevent downstream hydrate formation. In this research, the effect of different operational scenarios was investigated by means of process simulation to enhance the combustion efficiency of WBHs which consequently causes lower CO2 emission into the atmosphere. In this regard, WBH of Minudasht CGS in the north of Iran with nominal capacity of 30,000 m3/h was considered as a case study and process enhancement was carried out with the goal of lower CO2 emission and the NG fuel consumption. On the basis of obtained results, it was demonstrated that the NG preheating and air preheating by means of energy of hot stack gases are the most effective scenarios which can result in around 65 and 50 tons lower CO2 emission, respectively. In addition, these scenarios have the merit of saving more than 33,000 and 25,000 m3 lower NG fuel consumption annually, respectively.

Energy, exergy and economic analysis of utilizing the supercritical CO2 recompression Brayton cycle integrated with solar energy in natural gas city gate station

The pressure of natural gas stream must be reduced in city gas station. The natural gas has to be preheated before pressure reduction takes place usually through throttling valves. In conventional city gas stations, the natural gas is preheated by indirect water bath heaters, which burn a large amount of the natural gas as fuel. In this study, the rejected heat from a supercritical carbon dioxide recompression cycle using solar energy is recovered for preheating the natural gas. The novel design of this system generates uniform electricity as well as preheats the natural gas in city gate station. The proposed system is simulated for Birjand city gas station as a case study, and a thorough techno-economic analysis is performed in Engineering Equation Solver for evaluating the system performance. The results of this study demonstrate that parabolic trough collectors with 25 rows are the most efficient solar system while the annual average of thermal and exergy efficiency of the system is 0.56 and 0.41, respectively. The exergetic analysis of the system shows that the highest average exergy destruction takes place in the throttling valve and the second highest in the solar collectors. Also, the total amount of fuel saving is estimated at 4.87 million cubic meters annually and the net power output is equal to 2.86 MW. From the economic point of view, the value of the payback period is estimated 4 years and, based on the net present value method, after 8 years, the initial investment could be returned.

Distilled water production with combination of solar still and thermosyphon heat pipe heat exchanger coupled with indirect water bath heater – Experimental study and thermoeconomic analysis

The aim of this study is to provide a solution for supplying distilled water used in indirect water bath heaters in the pressure reduction stations. A particular type of distilled water production system consists of a typical solar still and a heat pipe heat exchanger was constructed for recovering heat from the exhaust of an indirect gas heater. The system was tested under the climatic conditions of Semnan-Iran. Experimental results showed that in active type, the average daily production rate of distilled water would be 2.06 times higher than passive type. Also, in the proposed system, the average daily energy efficiency and the exergy efficiency would be 65.5% and 41% higher than the passive ones, respectively. The economic analysis showed that, the average CPL value and average exergoeconomic parameters for the active type was 32% higher and 15% lower than the passive ones, respectively. The exergoeconomic parameters for the passive and active types at the best case (5% interest rate, 20 years lifetime and 1 cm water depth), were 0.32 and 0.25 kWh/$ respectively. Furthermore, analysis showed that in average the active type mitigated 104% and 146% more CO2 compared to the passive type for environmental and exergoenvironmental parameters, respectively.

Experimental investigation on the stability and thermophysical properties of Al2O3/DW and CuO/DW nanofluids to be utilized in an indirect water bath heater

In this paper, 0.5–5 mass/% of Al2O3 and CuO nano-additives were dispersed in the base water by the two stage method (with a magnetic stirrer and ultra-sonication bath) to prepare different nanofluids with enhanced thermophysical properties. These nanofluids are considered to be utilized, as the bath fluid in the shell side of an indirect water bath heater to improve the thermal performance and reduce the power consumption of the heater. The effects of ultra-sonication time, surfactants, and nanoparticle size on the well formation of nanofluids, and their stabilities were probed. Densities, shear stresses, and apparent viscosities of the nanofluids were also measured to investigate the non-Newtonian behavior of samples. In addition, effects of the temperature, PH, nanoparticle type and concentration, and nanoparticle sizes on the thermal conductivities of nanofluids were investigated. Finally, nanofluids were utilized in a large-scale indirect water bath heater and its power consumption reduction compared to that of using water, as the bath fluid was measured and reported. 5 mass/% of CuO/water nanofluid at 80 °C was found the best nanofluids with the thermal conductivity enhancement of 43.28% and heater power consumption reduction of 17.1%.

Energetic, exergetic, environmental and economic assessment of a novel control system for indirect heaters in natural gas city gate stations

The energy consumption and greenhouse gases emissions in natural gas city gate stations are important issues in the natural gas industry. In order to improve efficiency, have a cleaner environment and achieve economic benefits, the present study aims to propose an optimal system for the indirect water bath heaters in natural gas city gate stations. The optimization procedure is carried out by designing a control system to gain an eligible discharge temperature for the heater based on the gas entry conditions to the city gate station. The controller calculates the temperature of hydrate formation in terms of passing gas pressure and gives this information to the torch of the heater for regulating fuel consumption. A comprehensive study is accomplished based on energy, exergy, environment and economic analysis for different pressure reduction stations. The results indicate that employing the proposed system decreases the amount of fuel consumption and greenhouse gases emissions along with increasing system efficiency. Analyzing the results reveals that using the proposed system leads to a maximum of 28.54% relative increment in the heater efficiency compared to the conventional system (at this condition, the heater efficiency of the conventional and proposed system is η = 36.12% to η = 46.43%, respectively). Furthermore, with choosing a heater with a capacity of 100,000 SCMH, it is possible to reduce the pollutants emissions and total costs down to 142.6 tons per year and 3,671,000 $ per year, respectively.

Experimental investigation of the increasing thermal efficiency of an indirect water bath heater by use of thermosyphon heat pipe

Natural gas must be preheated prior to pressure reduction in city gate stations. Indirect water bath heaters are employed in city gate stations for preheating, consume a considerable amount of natural gas for the process. This type of heater has a low efficiency therefore a significant amount of energy is wasted. Due to the high capacity of thermosyphon heat pipe, its utilization in city gate stations heater were investigated experimentally in this paper. For this purpose, a heater set-up was manufactured and its thermal efficiency was calculated. The thermosyphon heat pipe were then designed, manufactured, and utilized between the fire tube and the gas tube. Further the type of working fluid and the range of filling ratio were discussed and the most effective state was suggested. Moreover, the thermal efficiency of the heater in the presence of thermosyphon heat pipe was investigated. The obtained results showed that the thermal efficiency of the heater improved up to 13% with the addition of thermosyphon heat pipe. The most effective state of thermosyphon heat pipe was associated with the water as working fluid with 20% filling ratio in the front route and methanol as working fluid with 30% filling ratio in the back route of the fire tube.

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.

Performance enhancement of water bath heater at natural gas city gate station using twisted tubes

Abstract Natural gas is transported from producing regions to consumption regions by using transmission pipelines at high pressures. At consumption regions, the pressure of natural gas is reduced in city gate stations (CGSs). Before the pressure reduction process, the temperature of natural gas is increased usually by using a water bath heater, which burns natural gas as fuel, to protect against freezing of natural gas. These types of heat exchangers have a low efficiency and consume a lot of fuel to generate the required heat. In the current study, the twisted configuration of the heating coil is proposed and investigated to enhance the heat transfer through a water bath heater with a nominal capacity of 1000 m3·h−1. Firstly, the implementation procedure is validated with data collected from the CGS of Qaleh-Jiq (located in Golestan province of Iran). A very good agreement is achieved between the obtained results and the real data. Then, three different twist ratios are considered to examine the twisting effects. The proposed technique is evaluated in the terms of velocity, temperature, and pressure variations, and the results are compared with the conventional case, i.e. straight configuration. It is found that both the heat transfer rate and the pressure drop augment as the twist ratio is raised. Finally, it is concluded that the twisted tubes can reduce the length of the gas coil by about 12.5% for the model with low twist ratio, 18.75% for the model with medium twist ratio, and 25% for the model with high twist ratio as compared to the straight configuration.

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.

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.