Natural Gas Quality Research Articles

An electrode-assisted anaerobic digestion process for the production of high-quality biogas

Biogas is a sustainable, renewable energy source generated from organic waste degradation during anaerobic digestion (AD). AD is applied for treating different types of wastewater, mostly containing high organic load. However, AD practice is still limited due to the low quality of the produced biogas. Upgrading biogas to natural gas quality (>90% CH4) is essential for broad applications. Here, an innovative bio-electrochemically assisted AD process was developed, combining wastewater treatment and biogas upgrading. This process was based on a microbial electrolysis cell (MEC) that produced hydrogen from wastewater at a relatively high efficiency, followed by high-rate anaerobic systems for completing biodegradation of organic matter and an in situ bio-methanation process. Results showed that CH4 production yield was substantially improved upon coupling of the MEC with the AD system. Interestingly, CH4 production yield increase was most notable once circulation between AD and MEC was applied, while current density was not markedly affected by the circulation rates. The microbial community analysis confirmed that the MEC enhanced hydrogen production, leading to the enrichment of hydrogenotrophic methanogens. Thus, directing soluble hydrogen from the MEC to AD is plausible, and has great potential for biogas upgrading, avoiding the need for direct hydrogen harvesting.

Study of Production Performance of Ammonia Fertiliser Process Using Aspen Plus

Natural gas (NG) based chemical fertilizers such as urea, ammonia help increasing the overall food productions of Bangladesh. In general, NG consumption has increased in different industries over the years thus affecting the availability of it. In addition, the quality of NG has changed over the decades in Bangladesh. To better understand the impact of these changes on the ammonia plant, the performance via ammonia process modelling and simulation is considered here. The process model is developed based on the Ashugonj Fertilizer & Chemical Company Ltd (AFCCL) plant process data of Bangladesh. The preliminary safety study is also carried out for this process using Aspen Plus. The preliminary result shows that due to lower carbon content and lower heating value of the current NG, NG consumption has increased in Primary Reformer (PRF), Secondary Reformer (SRF) and different fuel systems to maintain the 3:1 ratio of hydrogen to ammonia in the ammonia synthesis section.

ENERGY EFFICIENT USAGE OF NATURAL GAS CRITERIAS

The article suggests that Wobbe Index is one of the main criteria when determining quality of natural gas for natural gas Interchangeability from different sources ДСТУ ISO:13686:2016. For effective natural gas combustion the Wobbe Index Ws gas of should not differ form Ws of gas G20 by more than 2 percent. Especially in cases where equipment designed precisely to work with G20 gas. In that case it is necessary to adjust gas pressure or substitute machine design for different gas usage. Methane number that is corrected by Wobbe Index could be another criteria of quality of gas determination. Authors suggest minimal methane number of MN=65 defined by EN 16726:2015 is not sufficient. It is proven that even in case of higher combustion energy output for gas with Wobbe Index significantly lower of G20 gas test values the overall efficiency of using this gas in particular burner system is much lower. Flame flow for natural gas in streams M166 and M208 is closer to wrinkles due to chemical mixture of gas and natural gas in M1204 stream creates yellow tipping due to incomplete combustion, sulfur content similar to G21 test gas. With mediocre combustion energy output same burners consume more natural gas to provide same amount of energy. Natural gas from stream M404 has almost ideal mixture of components. Its Wobbe Index is 50,41 MJ/Nm3 but hydrocarbon dew point of 15.3 °C at P=3.92 MPa. That indicates relative humidity of 100%. Specific humidity of gas in stream is 0.44 grams per cubic meter that is dangerous for creating natural gas hydrates, solid clathrate compounds that may damage machinery or obstruct pipeline flow. Authors suggest to provide certain set of actions to process natural gas into so called clean “pipeline quality dry gas” at wells or gas-processing plants to improve gas parameters to be closer to European Union standards. As for government policies they have to be reworked from using “energy saving” term to “energy efficiency” term and start improving on efficient usage of natural gas by approving and applying newest energy efficient technologies and machinery into gas transport\consumer network.

Development of a natural gas Methane Number prediction model

The methane number (MN) of natural gas is predicted using mathematical modeling and machine learning techniques which can be incorporated into a sensor. Natural gas quality is known to vary seasonally and regionally depending on the geological region. MN is defined by the gas composition and also related to the knocking resistance in a natural gas engine. This article presents the results of two different methods to predict MN, which are Multiple Regression (MR) and Support Vector Regression (SVR) that can be further specified by three kernel types: linear, polynomial, and Gaussian distributions. The analysis of the 4 methods - MR, linear SVR, polynomial SVR, and Gaussian SVR - shows that each predicts MN with a root mean square error of ±1.06, ±1.08, ±0.54, and ±0.20 respectively. About 37% of the predictions made by MR are under the ±0.5 error range. 40% of linear SVR, 52% of polynomial SVR, and 98% of Gaussian SVR predictions are within the ±0.5 error range. The SVR using Gaussian kernel outperforms the other three methods in accuracy. The results can enable the technology needed to develop an intelligent sensor that can estimate the MN of natural gas online and in real-time, economically and reliably, overall increasing fuel efficiency and emission performance.

Thermodynamic and Technical Issues of Hydrogen and Methane-Hydrogen Mixtures Pipeline Transmission

The use of hydrogen as a non-emission energy carrier is important for the innovative development of the power-generation industry. Transmission pipelines are the most efficient and economic method of transporting large quantities of hydrogen in a number of variants. A comprehensive hydraulic analysis of hydrogen transmission at a mass flow rate of 0.3 to 3.0 kg/s (volume flow rates from 12,000 Nm3/h to 120,000 Nm3/h) was performed. The methodology was based on flow simulation in a pipeline for assumed boundary conditions as well as modeling of fluid thermodynamic parameters for pure hydrogen and its mixtures with methane. The assumed outlet pressure was 24 bar (g). The pipeline diameter and required inlet pressure were calculated for these parameters. The change in temperature was analyzed as a function of the pipeline length for a given real heat transfer model; the assumed temperatures were 5 and 25 ∘ C. The impact of hydrogen on natural gas transmission is another important issue. The performed analysis revealed that the maximum participation of hydrogen in natural gas should not exceed 15%–20%, or it has a negative impact on natural gas quality. In the case of a mixture of 85% methane and 15% hydrogen, the required outlet pressure is 10% lower than for pure methane. The obtained results present various possibilities of pipeline transmission of hydrogen at large distances. Moreover, the changes in basic thermodynamic parameters have been presented as a function of pipeline length for the adopted assumptions.

Power-to-gas management using robust optimisation in integrated energy systems

A large volume of wind power is curtailed worldwide due to the intermittency and limited transportation capacity of electrical power systems. New technologies, Power-to-Gas via electrolysis, can convert excessive wind power into hydrogen to be transported by natural gas systems. However, the injection of H2 into natural gas pipelines can cause gas quality issues due to changing gas compositions.This paper investigates the impact of injecting H2 converted from wind power on natural gas quality. Two key indexes used to measure gas quality, Wobbe Index and Combustion Potential, are introduced to examine the impact. Then, in order to bring the two indexes into acceptable statutory ranges, H2 is mixed with Liquid Petroleum Gas and Nitrogen. A robust optimization model, considering wind power uncertainties, is thereafter developed to manage the gas mixture, maximize H2 injection. This paper uses the dynamic gas system model to represent real-time pipeline flows, which can better reflect gas flow features over time. The proposed method is demonstrated on a small integrated gas-electricity system. Results illustrate that excessive H2 injection will reduce Wobbe Index but increase Combustion Potential. The robust optimization approach can effectively manage the mixture while ensuring gas quality with an uncertain wind power supply. The proposed method is beneficial to reducing renewable energy curtailment and maximizing H2 injection, benefiting electricity system operators with low operation costs and wind power more penetration.

Alternative of Biogas Injection into the Danish Gas Grid System—A Study from Demand Perspective

The Danish government has set an ambitious target to achieve 100% fossil independence across all energy sectors, which demands optimum utilization of renewable energy sources, such as wind and biogas, by 2050. Biogas production has increased, and the upgrading of biogas offers a broad range of applications, such as transportation, and gas grid injection for downstream utilization. The biogas has to meet natural gas quality prior to injection into the gas grid system. The investment costs of the gas grid, upgrading cost, and gas compression costs are the major challenges for integrating the biogas into the existing gas infrastructure. In this investigation, the Wobbe index (WI) for raw biogas and upgraded biogas was measured to evaluate the scenario for biogas injection into the gas grid system. It was found that raw biogas has to improve its WI from 28.3 MJ/m3(n) to a minimum of 50.76 MJ/m3(n) via upgrading, and compressed to 40 bar system, to supply the gas grid system for trading. Then, yearly gas consumption by larger gas consumers was studied to evaluate the alternative approach of biogas utilization to save upgrading and compression costs for gas grid injection.

Partially Upgraded Biogas: Potential for Decentralized Utilization in Agricultural Machinery

AbstractThe necessity for alternative utilization options for biogas plants and low‐emission power concepts for the agricultural sector underlines the high potential of decentralized utilization of partially upgraded biogas as vehicle fuel for agricultural machinery. In contrast to conventional biogas upgrading to natural gas quality for injection into the natural gas grid, the approach allows a reduced CO2 separation up to the operation limits of dual‐fuel combustion engines. To determine these limits, experimental investigations into the combustion process with low calorific CO2‐rich fuel gas, regarding engine performance, process efficiency, and emission behavior, have to be performed. The resulting lower purity requirements enable a cost‐efficient upgrading system on a small scale. To identify the savings potential, model‐based optimization of the water scrubbing process is performed.

How best management practices affect emissions in gas turbine power plants—An important factor to consider when strengthening emission standards

ABSTRACTThe Beijing Municipal Environmental Protection Bureau (EPB) is considering strengthening the Emission Standard of Air Pollutants for Stationary Gas Turbines, originally published in 2011 (DB11/847–2011), with a focus on reducing nitrogen oxides (NOx) emissions. A feasibility study was conducted to evaluate the current operation of 12 existing combined-cycle gas turbine power plants and the design of two new plants in Beijing and their emission reduction potential, in comparison with a state-of-the-art power plant in California. The study found that best management practices (BMPs) could potentially improve the emission level of the power plants, and should be implemented to minimize emissions under current design characteristics. These BMPs include (1) more frequent tuning of turbine combustors; (2) onsite testing of natural gas characteristics in comparison to turbine manufacturer’s specifics and tuning of turbine to natural gas quality; (3) onsite testing of aqueous ammonia to ensure adequate ammonia concentration in the mixed solution, and the purity of the solution; (4) more careful inspection of the heat recovery steam generator (HRSG), and the selective catalytic reduction (SCR) during operation and maintenance; (5) annual testing of the catalyst coupon on the SCR to ensure catalyst effectiveness; and (6) annual ammonia injection grid (AIG) tuning. The study found that without major modification to the plants, improving the management of the Beijing gas turbine power plants may potentially reduce the current hourly average NOx emission level of 5–10 parts per million (ppm; ranges reflects plant variation) by up to 20%. The exact improvement associated with each BMP for each facility requires more detailed analysis, and requires engagement of turbine, HRSG, and SCR manufacturers. This potential improvement is an important factor to consider when strengthening the emission standard. However, note that with the continuous needs of improving air quality within the area, more expensive control measures, such as retrofitting the turbines or the HRSGs, may be considered.Implications: This study analyzed the potential emission reductions associated with implementing the best management practices (BMPs) on the combined cycle and cogeneration power plants in Beijing. It determined that implementing the BMPs could potentially achieve up to 580 metric tonnes, or 0.6%, reductions of all NOx emissions in Beijing. Many other cities in China and Asia battling air quality issues may find the information useful in order to evaluate the emission reduction potential of their own gas turbine power plants.

Application of a master meter systemto assure crude oil and natural gas quality during transportation

ABSTRACTThis paper discusses an example of the master meter system (MMS), used in the oil and gas industry with the purpose of validating the performance of custody transfer meters. The system can also be used to determine if there are any changes such as the deposition of wax or asphaltic material (in the case of crude oil) or liquids (in the case of natural gas). According to current standards, custody transfer measurements must pass periodic verification of measurement performance, the process which is known as meter proving. This paper presents the construction and key parts, as well as the main functionalities of MMS which comply with the most rigorous requirements for custody transfer. This is achieved by using a novel instrumentation with high level of accuracy, appropriate flow computer and HMI (Human Machine Interface) application developed to support supervision and control of the proving process.

Predicting Wobbe Index and methane number of a renewable natural gas by the measurement of simple physical properties

This study describes a fuel quality prediction strategy that predicts the fuel quality parameter and component composition of Renewable Natural Gas (RNG) containing CH4, C2H6 and CO2. Onsite measurement of the gas properties in a renewable natural gas (RNG) fuel is necessary to ensure an expected level of quality, which must be maintained for better combustion efficiency. The Wobbe Index (WI) and methane number (MN) are the natural gas quality indicators used. To predict the WI, MN, and component composition, a data set that consists of WI, MN, thermal conductivity and sound velocity of the gaseous fuel mixture as a function of its temperature, pressure and composition, was created. Through a regression analysis of the data set, a model that estimates the WI, MN and composition of the gaseous fuel mixture from its physical properties (temperature, pressure, thermal conductivity and sound velocity), was developed. The results of the study including the data set and the prediction model that can accurately estimate the WI, MN, and gas composition, is presented in this paper.

Analysis of Hydrogen Sulfide (H2S) and Hydrocarbon Composition of Natural Gas from GMS (Gas Metering Station) in PT. Pupuk Sriwidjaja Palembang

Natural gas of GMS (Gas Metering Station) is an important component that must be analyzed routinely in PT. Fertilizer Sriwidjaja because it is the main material used in addition to Carbon dioxide (CO2) and water vapor in the manufacture of ammonia. The quality of natural gas will affect the ammonia and urea fertilizer product. The purpose of this research is to know the composition of hydrocarbons and to know the level of H2S gas in natural gas which is contained in GMS pipes. Determination of H2S levels was performed to find out the many catalysts used in the manufacture of ammonia gas.In determining the hydrocarbon composition, the first gas sample is taken using Stainless Steel Cylinder Tube. After the gas filled tube it was analyzed using GC (Gas Chromatography) and  it will know the hydrocarbon composition of GMS. As for the determination of H2S level, the gas sample taken as much as 30 L through gas spreader and inserted into erlenmeyer with 10% Cd Acetate and NaOH. Subsequently, 1% PADAS (N, N-Dimethyl-p-phenylendiamine sulphate) and FeCl3 were added. After the solution changed to blue color then analyzed using UV-Vis Spectrophotometer in 660 nm wavelength.The results obtained are nitrogen-containing natural gas and various hydrocarbon components: methane, hexane, carbon dioxide, ethane, propane, i-butane, n-butane, i-pentane, and n-pentane with H2S 2,954 ppm with the largest composition of methane 85.89%. The results have been in accordance with the standards used in the Pusri Industry which apply the provision that the natural gas used should contain methane with concentrations greater than 70%Â

Hybrid Postsynthetic Functionalization of Tetraethylenepentamine onto MIL-101(Cr) for Separation of CO2from CH4

To remove CO2 from CH4, tetraethylenepentamine was grafted onto coordinatively unsaturated centers of MIL-101(Cr) by postsynthetic functionalization: wet impregnation at 298 K, followed by grafting, drying, and washing. Compared to MIL-101(Cr), TEPA–MIL-101(Cr) showed 54% higher CO2 adsorption at 1 bar and 98% reduction of CH4 adsorption at 60 bar. The ideal adsorption solution theory (IAST) selectivity of CO2/CH4 for a binary gas mixture of 2% CO2 + 98% CH4 at 298 K and 60 bar predicted by the Toth equation was found to be 11 and 598 for ungrafted and grafted MIL-101(Cr), respectively. Single column breakthrough tests were performed for upgrading the 2% CO2 + 98% CH4 mixture to liquefied quality of natural gas (CO2 < 50 ppm) under various operating conditions including different temperatures and total amount of purge gas at the fixed pressure of 60 bar and temperature of 298 K. At the feed flow rate of 1000 sccm, the TEPA–MIL-101(Cr) extrudates obtained 0.89 mmol/g CO2 adsorption capacity and nearly 83% ...

Thermally rearranged polypyrrolone membranes for high-pressure natural gas separation applications

The gas permeability performance of thermally rearranged polypyrrolone (PPL-450) membranes have been experimentally evaluated under similar industrial conditions of gas mixtures, pressures, and stage-cuts. The membranes were synthesized from 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 3.3′-diaminobenzidine (DAB). The thermal treatment of the PPL-450 was accomplished under vacuum at 450 °C. Several gas mixtures (binary, ternary and quaternary) were utilized to study the performance of the PPL-450 membranes for CO2 removal and helium recovery from natural gas streams. The quaternary feed gas-mixture was composed of 59% CH4, 30% N2, 10% CO2 and 1% C2H6, which represent a low quality natural gas. Three pressures (400, 600, and 800 psig) and five stage-cuts (1.2, 2.8, 4.2, 6.4, and 9.8%) were considered for the study. It was observed that the permeability values of all gases were decreased for mixed-gas experiments when compared to that of the single-gas permeability. On the other hand, CO2/CH4 permeability ratio was increased from 29, for pure gas, to 45 for quaternary gas-mixture. Likewise, the He/CH4 permeability ratio was increased from 33, for pure gas, to 46 for ternary gas-mixture. Furthermore, at 800 psig and 9.8% stage-cut, PPL-450 was able to remove 80% of CO2 from the quaternary gas-mixture. In another study of a very dilute helium-concentration (0.14%) more than 80% helium was recovered at 800 psig and 5% stage-cut. Moreover, in all gas mixtures containing CO2, the PPL-450 membrane demonstrated an outstanding resistivity to CO2-induced plasticization at high pressures.

Monitoring the Wobbe Index of Natural Gas Using Fiber-Enhanced Raman Spectroscopy.

The fast and reliable analysis of the natural gas composition requires the simultaneous quantification of numerous gaseous components. To this end, fiber-enhanced Raman spectroscopy is a powerful tool to detect most components in a single measurement using a single laser source. However, practical issues such as detection limit, gas exchange time and background Raman signals from the fiber material still pose obstacles to utilizing the scheme in real-world settings. This paper compares the performance of two types of hollow-core photonic crystal fiber (PCF), namely photonic bandgap PCF and kagomé-style PCF, and assesses their potential for online determination of the Wobbe index. In contrast to bandgap PCF, kagomé-PCF allows for reliable detection of Raman-scattered photons even below 1200 cm−1, which in turn enables fast and comprehensive assessment of the natural gas quality of arbitrary mixtures.

Optimum operating conditions for improving natural gas dew point and condensate throughput

Natural gas dew point temperature is a vital quality parameter. The effective control of this specification is important if the natural gas integrity and quality are to be maintained. The present work focuses on improving the dew point and condensation production rate of south Dabaa field dew point control unit (DPCU) located in the Egyptian western desert and owned to the South Dabaa Petroleum Company. Influence of the operational variables on outlet gas dew point and produced condensate were investigated. The simulation results illustrated that feed gas inlet temperature, composition and flow rate, Joule Thomson (JT) valve downstream, and upstream pressure and hot bypass flow rate have a great effect on the sales gas dew point as well as the condensate throughput. A field experiments were conducted to validate the simulation results. It is noticed that there is a good agreement between simulation and experimental results, considering the outlet gas dew point at different operating conditions. Lingo optimization software was used to find the plant optimum conditions. Two quadratic equations were developed based on regression analysis for calculating the dew point and plant condensate rate at any operational variables. The impact of replacing the existing JT valve by a turbo expander was studied. The simulation results indicate that the turbo expander is more effective in comparison with JT valve refrigeration system in decreasing the sales gas dew point and increasing the condensate production rate.

An acoustic approach to assess natural gas quality in real time

The natural gas industry needs fast and robust techniques to monitor the quality of the natural gas, if possible during the flow measurement process. A potential technique relies on extrapolating the dynamic specific heat of the gaseous mixture via measurements at a few frequencies (Petculescu and Lueptow, Phys. Rev. Lett. 94, 238301 (2005); Sensors and Actuators B: Chemical 169, 121–127 (2012)). At the core of this approach lies a first-principles model for sound absorption and dispersion in polyatomic gases. We will show and discuss the applicability and limitations of this potential technique to predicting the content of nitrogen, oxygen, carbon dioxide, and water in natural gas.

Suitable Study of CBG Fuel by Considering in Wobbe Index From Compressed Bio-Methane Gas Plant, Khon Kaen University, Thailand

The objective of this research was to study suitability of compressed bio-methane gas (CBG) to use in vehicles by considering it’s Wobbe Index (WI). Wobbe index can be used to increase burner efficiency. In this experiment, the average heating value of CBG was 32.43 MJ/Nm3 and specific gravity of CBG at 0 °C 1-atmosphere pressure was 0.67 kg/m3. Therefore, the Wobbe index was 39.62 MJ/Nm3, It was classified in family 2 subordinate type with Wobbe index (2L) of 39 - 45 MJ/Nm3. The natural gas quality for vehicle standards by the Department of Energy Business, Ministry of Energy, Thailand required heating value is 37- 42 MJ/Nm3. The Wobbe index result show at that the CBG is suitable to use for the shuttle bus in Khon Kaen University (KKU), Thailand.

Comparison of Bio-Methane Gas Wobbe Index In Different Animal Manure Substrate

The objective of this research was to evaluate the Wobbe Index (WI). Which Wobbe index can indicate a relation between gas injector burners with gas properties. By gas product from a compressed bio-methane gas plant at Khon Kaen University (KKU) was used for this project. There different substrate were used. They were pig manure, hen manure and pig manure blend with hen manure. The result from the study revealed that the average heating value. In this experiment, an average heating value of CBG from pig manure was 31.85 MJ/Nm³, hen manure was 31.04 MJ/Nm3 and pig manure blended with hen manure was 31.24 MJ/Nm3 and the specific gravity of CBG at 0 °C 1-atmosphere pressure in pig manure was 0.67 kg/m3, hen manure was 0.69 kg/m3, pig manure blended with hen manure was 0.68 kg/m3. The CBG had Wobbe index from pig manure hen manure and pig manure blended with hen manure was 38.92, 37.36, 37.88 MJ/Nm3 respectively. This was above the standard of the natural gas quality for the vehicle by the Department of Energy Business, Ministry of Energy, Thailand (requirement of Wobbe index in 37- 42 MJ/Nm3).

Microbial electrochemical separation of CO2 for biogas upgrading

Biogas upgrading to natural gas quality has been under focus the recent years for increasing the utilization potential of biogas. Conventional methods for CO2 removal are expensive and have environmental challenges, such as increased emissions of methane in the atmosphere with serious greenhouse impact. In this study, an innovative microbial electrochemical separation cell (MESC) was developed to in-situ separate and regenerate CO2 via alkali and acid regeneration. The MESC was tested under different applied voltages, inlet biogas rates and electrolyte concentrations. Pure biomethane was obtained at 1.2V, inlet biogas rate of 0.088mL/h/mL reactor and NaCl concentration of 100mM at a 5-day operation. Meanwhile, the organic matter of the domestic wastewater in the anode was almost completely removed at the end. The study demonstrated a new sustainable way to simultaneously upgrade biogas and treat wastewater which can be used as proof of concept for further investigation.