Gas Pressure Reduction Research Articles

A risk assessment of a gas pressure reduction station system with confidence for dealing with imprecisions and unknowns

Process systems are sensitive and vital industrial facilities. Disturbances in their performance may cause harm to the environment,humans,or significant economic damage. In risk assessment of chemical process industries, the available data, information, and knowledge are typically rare, limited, and often unrealistic. This issue poses a challenge to conducting a credible quantitative risk assessment and effects the robustness of the results. To address these challenges, this work proposes a methodology based on the Dempster-Shafer theory of evidence as the reasoning framework. It incorporates risk identification, analysis, and mitigation phases to ensure a thorough analysis of risks and the integration of proactive risk reduction strategies. The approach aims to model the worst-case hazard scenario and assess associated risks using various methods such as FMECA, Bow-Tie, Credal Network, and Dempster-Shafer theory. The proposed approach models imprecision and data ambiguity using intervals and associated belief mass. This extension provides a basis for addressing the fundamental problem of prior ignorance about the distribution of the observed data, which is prevalent in data mining applications. A new approach is proposed that utilizes Belief and Plausibility curves, similar to a Cumulative Distribution Function, to propagate uncertainty, enhance criticality discrimination, and determine cumulated belief measures. This approach is applied in analyzing the failure modes identified in FMECA and is further extended through the credal network for comprehensive risk assessment. Results show how to express irrelevant and independent judgments, and how to work out with inferences in credal networks. This issue is often overlooked, but if properly addressed it represents the key to ultimately drawing reliable conclusions and fully utilizing the system's available data. A case study of the City Gate Station system was used to verify the application potential of the proposed approach.

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.

Justification of the Locations of Differential Pressure Sensors for Coarse and Fine Filter Elements Installed one Inside the Other in a Single Gas Filter Housing

Statement of the problem. The relevant task of ensuring the uninterrupted operation of modern gas pressure reduction systems is to develop and comprehensively substantiate the possibility of using two-stage filters for natural gas purification in gas reduction points and theoretically substantiate the method for calculating the pressure drop in cylindrical filter elements (CFE). Results. It is proved that when gas flows in the upper cross section of the filter, the pressure drop will be less than in lower cross sections, including the pressure drop in the lowest cross section. This leads to a larger amount of leaking gas, to a larger mass of impurities settling in the lower part of the filter elements of cylindrical coarse and fine cleaning and to a greater degree of their clogging. Therefore, it is recommended to place gas pressure sensors in the lower part of the internal volume of the coarse and fine-cleaned CFE, so that the flow direction of the coarse and finely purified gas washing the sensors at the location of the hole for measuring statistical pressure is tangential to the side surface of the sensor tube. Then the flow direction of the roughly and finely purified gas entering the holes of the sensors is carried out at an angle of 90° and the pressure gauges measure the static pressure. Conclusions. The locations of pressure drop sensors on coarse and fine filter elements installed one inside the other in a single gas filter housing are substantiated. The proposed arrangement of differential pressure sensors will significantly increase the possibility of receiving an earlier signal about the degree of clogging of the gas filter at the control room, as well as have a significant amount of time for timely removal of blockages formed in the coarse cleaning CFE and replacement of fine cleaning CFE.

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.

Study on the Damage Mechanism of Coal under Hydraulic Load

Hydraulic fracturing is extensively utilized for the prevention and control of gas outbursts and rockbursts in the deep sections of coal mines. The determination of fracturing construction parameters based on the coal seam conditions and stress environments merits further investigation. This paper constructs a damage analysis model for coal under hydraulic loads, factoring in the influence of the intermediate principal stress, grounded in the unified strength theory analysis approach. It deduces the theoretical analytical equation for the damage distribution of a coal medium subjected to small-flow-rate hydraulic fracturing in underground coal mines. Laboratory experiments yielded the mechanical parameters of coal in the study area and facilitated the fitting of the intermediate principal stress coefficient. Leveraging these datasets, the study probes into the interaction between hydraulic loads and damage radius under assorted influence ranges, porosity, far-field crustal stresses, and brittle damage coefficients. The findings underscore that hydraulic load escalates exponentially with the damage radius. Within the variable range of geological conditions in the test area, the effects of varying influence range, porosity level, far-field stress, and brittle damage coefficient on the outcomes intensify one by one; a larger hydraulic load diminishes the impact of far-field stress variations on the damage radius, inversely to the influence range, porosity, and brittle damage. The damage radius derived through the gas pressure reduction method in field applications corroborates the theoretical calculations, affirming the precision of the theoretical model. These findings render pivotal guidance for the design and efficacy assessment of small-scale hydraulic fracturing in underground coal mines.

Design and thermodynamic analysis to avoid preheating in gas grid pressure reduction stations

Paying close attention to the environmental risks associated with traditional forms of energy, particularly the serious issue of global warming caused by the release and concentration of greenhouse gases, has become a paramount concern. This growing awareness has prompted governments worldwide to prioritize the benefits of alternative energy sources and develop comprehensive plans accordingly. Moreover, it is crucial to thoroughly consider and explore existing potentials in our quest for sustainable energy solutions. One such potential lies in the energy loss experienced due to gas pressure reduction in urban gas reduction stations. Furthermore, as we increase the amount of natural gas preheating, we observe a corresponding rise in the temperature within the expansion turbine, ultimately resulting in a significant boost in power generation. In this paper, we delve into the exciting possibility of harnessing electricity generation by utilizing a turbo expander within a municipal gas pressure reduction station. To maximize the work generation capacity, we propose preheating the gas input to the turbo expander using geothermal energy. Our study reveals that the turbo expander exhibits optimal performance, boasting an impressive isentropic efficiency of 92.3%, when the inlet temperature is maintained at 84 °C and the amount of preheating reaches 192.3 kJ/kg.

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.

Electricity generation potential from natural gas pressure reduction turbines in Brazil

This paper addresses the urgent need to meet increasing energy demand while avoiding greenhouse gas emissions by improving energy efficiency. One significant challenge is the energy losses that occur during gas pressure reduction at city gates in natural gas distribution systems. To tackle this issue, this study proposes installing pressure reduction turbines (PRTs) parallel to existing reduction valves, which can generate electricity and enhance system efficiency. This research mainly focuses on Brazil’s natural gas supply, where the potential for installing PRTs is evaluated. The methodology analyzes the country’s distribution network and estimates the electricity generation capacity achievable from PRTs. The results indicate a potential power generation of 66 MW, capable of avoiding the emission of 235,800 tons of CO2 annually and generating 333 GWh/year of electricity, all at a LCOE of $27/MW. These contribute to the environment using the energy efficiency achieved through the installation of PRTs, consequently, Brazil can help to a cleaner and more sustainable energy future.

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.

Evolution from gas outburst to coal outburst: An analysis from the perspective of asynchronous transfer difference of gas mass and coal deformation

Considering that coal and gas outburst is a highly complex nonlinear process, the synchronous energy criterion based on the gas expansion energy and the coal deformation potential energy is often adopted to evaluate the hazard. However, the synchronous energy criterion without considering the transfer difference of gas mass and coal deformation has defects in describing the evolution characteristics of coal-rock gas dynamic disasters. Hence, it is necessary to investigate the asynchronous characteristics of the gas expansion energy and the coal deformation potential energy. In this study, the deformation characteristics of coal injected with He and CH4 were measured respectively with the aid of a self-developed device for observing the asynchronous characteristics of effective stress and adsorption-induced deformation. Besides, the differentiated propagation characteristics of gas pressure and adsorption-induced deformation were obtained, and the asynchronous propagation starting point and propagation rate difference between them were analyzed and determined. Furthermore, based on the calculation formula of gas expansion energy and coal deformation potential energy, the values and propagation differences of the two types of energy at different times were revealed. Finally, the typical outburst phenomena were explained using the energy asynchronous theory. The following research findings were yielded. The adsorption-induced expansion process lasts longer than the gas pressure reduction process, which is the reason for asynchronous propagation of gas expansion energy and coal deformation potential energy. The coal deformation potential energy can be further divided into mechanical compression strain energy and desorption shrinkage strain energy. In the initial stage of outburst, the main sources of energy are free gas expansion energy and mechanical compression strain energy. As time progresses, the effect of desorption gas expansion energy and desorption shrinkage strain energy gradually strengthens. From the perspective of energy asynchrony, outburst occurrence at a low gas concentration in deep regions and delayed outburst in cross-cut coal uncovering can be explained as the result of dynamic load instability in surrounding stopes brought about by lagging superimposed deformation disturbances after gas desorption, or the result of self-induced lagging shrinkage deformation formed under special boundary conditions. The findings of this study are helpful to guide the design and connection of the prevention and control methods of deep coal-rock gas dynamic disasters.

Development of technology for cascade gas pressure reduction in long gas pipelines of gas distribution stations

The work developed and proposed for implementation an energy-saving technology of pipeline transportation of natural gas along long-distance branch pipelines connecting main gas pipelines and gas distribution stations. This technology consists in a step reduction of operating pressure in the gas pipeline branch with the help of linear reducing stations, with partial heating of gas due to heat exchange between the gas pipeline and the ground. The authors of the article present the results of practical approbation of the cascade gas pressure reduction technology in the operating off-take gas pipeline with the confirmed effect of reducing fuel gas consumption in the gas distribution station preheaters. The optimal parameters of gradual gas pressure reduction using linear reduction points were determined by calculation. Graphical dependencies, which determine the peculiarities of changes in temperature modes of pipeline gas transportation depending on the given pressure drop in linear pressure reduction stations for the conditions of pilot testing of the energy-saving method, have been obtained. A scheme of uniform location of linear pressure reduction stations with definition of the optimal pressure reduction mode is proposed.

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.

Risk-based inspection (RBI) of a gas pressure reduction station

One of the principles of corrosion management is proper inspection methodology, and in particular the risk-based inspection (RBI). Occasionally a large percentage of the total risk of a unit is concentrated in a small part of the equipment, which can be reduced by using risk management techniques. In this study, a semi-quantitative risk-based inspection method has been performed in a gas station with for its components (pipelines, filters, etc.), to identify the existing damage mechanisms and also to rank its equipment in terms of inspection intervals. In this regard, RBI was performed for the gas station which consisted of phases (Phase A & Phase B) with Class 300 and Class 600 equipment. According to documented conditions and reviewed records the main damage mechanism for the investigated components in the gas station was identified as wall thinning due to erosion corrosion and external corrosion. In terms of inspection, results showed that most of the equipment studied had medium risk level and a few had medium to high level of risk. In this regard, the corrosion rates of Class 300 and Class 600 equipment were also studied and compared, and it was indicated that the corrosion rates were higher at locations for Class 300 equipment where more pressure drop had occurred. Overall, based on the obtained corrosion rates and obtained risk matrixes, it was concluded that wall thinning (erosion-corrosion) was the determining risk factor for equipment inspected in the gas pressure reduction station.

Numerical Evaluation of the Hydrothermal Process in a Water-Surrounded Heater of Natural Gas Pressure Reduction Plants

The gas pressure in the main network of transmission lines is about 700 to 1000 psi (4826.33 to 6894.76 kPa), which is reduced to 250 psi (1723.69 kPa) at the entrance station of a city. This reduction process, which occurs in the regulator, causes a severe drop in gas temperature. The drop in the gas temperature produces hydrates and even causes the water vapor in the gas to freeze. As a result, there is a possibility that the passage of gas in the regulator is blocked and the gas flow is cut off. By employing heaters (indirect water heaters), the temperature of the gas entering the regulator can be preheated to eliminate the possibility of freezing in the regulator. This heater is fueled with natural gas and it operates for 24 hr a day, especially in the cold seasons. Therefore, one of the main challenges in using this type of heater is its high fuel consumption. Consequently, researchers are looking for a solution to reduce the fuel consumption (natural gas) of gas heaters. In this paper, the heat transfer and fluid flow in a heater of a natural gas pressure reduction plant, the Aliabad Power Plant (Iran), are numerically investigated using a commercial Computational Fluid Dynamics (CFD) code, ANSYS FLUENT 18.2. The considered heater consists of three parts, including (i) gas coils, (ii) a water bath (shell), and (iii) a fire tube. The indirect heat transfer process takes place between the hot liquid flow in the fire tube (combustion exhaust) and the cold liquid flow (natural gas) using the natural convection flows generated in the water bath. Numeric modeling is performed for four different gas mass flows, including 6 × 104, 8 × 104, 1 × 105, and 12 × 105 standard cubic meters per hour (or 16.67, 22.22, 27.78, and 33.33 m3/s). The results indicate that the natural gas outlet temperature achieved to a temperature higher than required. By installing a regulator on the burner, the gas consumption can be reduced, resulting in station cost savings, and also reducing the environmental impacts. The outcomes depict that the maximum possible reductions in monthly gas consumption and economic savings in the proposed system are 67,500 m3 and IRR 25 million at a gas mass flow rate of 60,000 SCMH.

The effect of heat transfer characteristics of macromolecule fouling on heat exchanger surface: A dynamic simulation study

AbstractAt the city gate gas pressure reduction stations (CGSs), to prevent natural gas from forming a hydrate in the throttle valve, the natural gas is heated by the heater before reaching the pressure relief valve. Heat exchangers are an essential component of industrial processes that contribute significantly to total system energy. Since the element impacting heat exchanger performance is the fouling process, all fouling processes and models were dynamically simulated in this study. Through coding in the C++ language and simultaneous use of fluent functions, or, in other words, user‐defined function (UDF), fouling‐related models were defined for this software. The dynamic simulation was performed, and parameters such as fouling strength and layer thickness were calculated. The effects of changing operating conditions, such as gas inlet velocity, surface temperature, and fouling species concentration on fouling growth, were also evaluated. As the concentration of fouling species increased, the fouling rate also increased. The amount of supersaturation and fouling rate increased as the surface temperature increased. Due to the operational limitations of the system, to reduce the fouling rate, the gas inlet velocity should be as high as possible, and the fluid inlet temperature, surface temperature, and concentration of fouling species should be as low as possible. In this study, the required time to reach the efficiency of 70% of the heat exchanger was calculated using the modelling of this chamber, which was equivalent to 190 days. Additionally, the critical thickness of the fouling layer at this time was 3.5 cm.

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.

Dynamic effect of gas initial desorption in coals with different moisture contents and energy-controlling mechanism for outburst prevention of water injection in coal seams

In view of the continuous occurrence of coal and gas outbursts (hereafter as ‘outbursts’), and the dynamic behavior and quantitative mechanism of water injection in coal seams preventing outbursts are not still unclear. In the study, the characterization of mechanical action and expansion energy release of gas initial desorption (GID) in coals with different moisture contents is revealed to clarify the influence of moisture on gas dynamic effect in coals. The results show that during the GID of gas-containing coals, the increased moisture content will decrease the pressure and momentum of gas from coals significantly. And the gas pressure reduction rate shows an increasing trend, with the decreasing reduction rate of gas momentum. Therefore, the ability of gas damaging coals with high moisture contents is weakened by reducing the degree of pressure-induced mechanical action on the coal surface and the impact intensity on the cracks in coals. Meanwhile, the gas-released cumulative expansion energy from the coals is significantly reduced, with the decreasing increase rate of the gas energy. Therefrom, the moisture in the coal masses synthetically weakens the dual effects of pressure attribute and expansion effect of gas decreasing the damage ability of gas to coals, which can prevent the further development of outburst preparation process. It is concluded that the correlation between moisture content and the initial expansion energy of released gas is linearly and negatively correlated. For moisture content with the every 1% increase in coal masses of Xuehu Coal Mine, the energy decreases by about 11% on average. Accordingly, the quantitative water injection in coal mining face is carried out to eliminate the local abnormal zone containing gas.