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Heating Value and Combustion of Fuel
Published in Neil Petchers, Combined Heating, Cooling & Power Handbook: Technologies & Applications, 2020
Natural gas composition variability in most applications is of minor concern, because such variations are usually insignificant. The Wobbe Index is a useful measure of energy delivered to a burner, since the energy varies directly with the heating value of the gas and inversely with the square root of the relative density (also known as specific gravity, or SG) as it flows through an orifice. Thus, two gases with different heating values and different relative densities, but with the same Wobbe Index, will deliver the same heat at the burner and, hence, yield the same performance. Since the Wobbe Index allows comparison of the volumetric energy content of different gas fuels at different temperatures, it is key to defining which fuels can be run in the same fuel system and when multiple manifolds or gas systems are required. It is generally accepted that a difference between two Wobbe Indices of up to 5% will allow full interchangeability of such fuel gases. But, note that the Wobbe Index may be based on higher or lower heating values, depending on application. The internationally used symbols for Wobbe Index, according to International Gas Union, are WS based on HHV and Wi based on LHV.
Balance of Plant
Published in S. Can Gülen, Gas Turbine Combined Cycle Power Plants, 2019
Wobbe index (WI) is a measure of allowable fuel gas energy content variation, which is a function of the fuel gas heating value (a function of fuel gas composition) and temperature. The WI is defined as the ratio of the lower heating value (LHV) of the fuel (in Btu/scf) to the square root of the specific gravity (SG) of the fuel (relative to air) at reference temperature and pressure (usually 32°F and 1 atm). The “modified” Wobbe index (MWI), which includes the effect of fuel gas temperature (in degrees Rankine), is defined as MWI=LHVSG⋅Tf.
Calorimeters
Published in Béla G. Lipták, Analytical Instrumentation, 2018
The Wobbe index accounts for composition variations in terms of their effect on the heat value and specific gravity, which affect the flow rate through an orifice. In essence, the Wobbe index is a measurement of the available potential heat, and it can be used in conjunction with the gas flow measurement to produce a measurement of heat flow rate.
Novel approach for efficient operation and reduced harmful emissions on a dual-fuel research engine propelled with hydrogen-enriched natural gas and diesel
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Akshay Loyte, Jiwak Suryawanshi, Girish Bhiogade, Yuvarajan Devarajan, Raja T, Gavaskar T
It is found that using NG and H2 as separate LRF fuels has some limitations in controlling exhaust gas emissions. The lean-burning ability and slow-burning of NG in DF mode, creating bulk combustion losses, can be compensated by enriching NG with H2.As few properties of NG are responsible for its slower combustion, the combustion characteristic of NG can be improved by enriching it with H2. H2 can be blended with NG in gaseous form with varying proportions on a volume or an energy basis. The mixture is termed hydrogen-enriched natural gas (HENG). Using HENG improves the lean-burn characteristic and lowers exhaust emissions. The flame speed of H2 is about five times higher than methane under normal conditions (Choubey et al., 2023). The blend percentage of H2 with NG affects engine power output and brake thermal efficiency. HENG operation in the engine is considerably leaner than NG (Açikgöz et al. 2015). The amount of enrichment is significant for enriching H2 with NG, and the term Wobbe Index (W) is a significant parameter to determine the amount of enrichment. The term W can be used to assess the usability of a thermal system for a mixture of two different gases without any modification. The wobbe index defines the interchangeability of different fuels in gaseous form. It is determined as the heating value of a certain amount of gas flowing through-hole of a given size for a particular duration (Lather and Das 2019).
Dual fuel engines fueled with three gaseous and biodiesel fuel combinations
Published in Biofuels, 2018
N. R. Banapurmath, V. S. Yaliwal, R. S. Hosmath, M. R. Indudhar, Suresh Guluwadi, Saurabh Bidari
Utilization of hydrogen and natural gas blends in internal combustion engines was started in the early 1990s. Blending of hydrogen with CNG provides a hydrogen-enriched natural gas called hydrogen enriched compressed natural gas (HCNG). HCNG combines the advantages of both hydrogen and methane; 5–30% (by volume) addition of hydrogen in CNG improves the composition and properties of base fuel CNG. From Dalton's partial pressure law, hydrogen fraction is decided by the partial pressure of the two fuels in the HCNG tank. The influence of gas composition on engine behavior can be adequately characterized by the Wobbe index. If the Wobbe index remains constant, change in the gas composition will not lead to a noticeable change in the air–fuel ratio and combustion rate [32,41,47]. The use of hydrogen in internal combustion (IC) engines is very attractive to propel hydrogen economy. Hydrogen is a carbon free gaseous fuel when used in IC engines; it reduces all carbon-based emissions such as smoke, hydrocarbon and carbon monoxide. It also increases brake thermal efficiency, since its burning velocity, reactivity and diffusivity is much higher [41]. Hydrogen addition to CNG or producer gas is a very effective method to improve the burning velocity of the gaseous fuel. However, addition of hydrogen in producer gas is not addressed in this paper.
Nitrogen Dilution Effect on Swirl Stabilized Methane Burning in Gas Turbine Conditions
Published in Heat Transfer Engineering, 2023
Przemyslaw Grzymislawski, Pawel Czyzewski, Rafal Slefarski
The direction of energy development in Europe is set on the basis of the document "Energy Policy 2030 [1] Paris Agreement [2]" and the newly introduced European union (EU) policy "Green Deal" [3] aimed at counteracting the economic perturbations caused by the COVID-19 pandemic by dynamizing the transition to a green economy. Consequently, there is a dynamization of the transition from fossil fuels to renewable energy [4]. However, the inadequacies of RE make it necessary to use a very flexible source of power for electricity grids, that is, gas turbines powered by natural gas (NG). They are characterized by twice lower carbon dioxide emissions per unit of energy produced compared to coal. As a result, a large number of power plants based on the combustion of natural gas are being opened in the world [5]. Most of the gas consumed in EU countries is imported, often from faraway places [6, 7] like liquefied natural gas from Australia and Russian Siberia which causes high financial costs and environmental implications of transportation. Therefore, it is reasonable to use local deposits. Despite the large exploitation of deposits in the EU, there are still many fields of NG including gases containing significant proportion of nitrogen or carbon dioxide which often excess of 50% by volume [8]. The treatment of such gases to meet the network parameters incurs significant costs. Furthermore, systems allowing for biogas delivery into the natural gas transmission network already exist [9]. Hence, it is reasonable to use raw natural gas in local grids. However, it causes many implications related to the energetic use of gas mixtures with variable physicochemical parameters and characteristic combustion parameters. The idea of multi-fuel nature of the systems created for the operation of gas turbines in the widest possible range of supplied fuels composition is called fuel flexibility. One of the most important parameters characterizing the fuels used is their calorific value and the Wobbe Index (the ratio of the heating value referred to the square root of its relative density). The presence of inert gases such as nitrogen reduces, while the presence of higher hydrocarbons increases it. The diverse composition also influences the nature of the flow inside the chamber, adiabatic combustion temperature, reaction kinetics and heat transfer. Therefore, it is important to study the effects of nitrogen on the combustion process in gas turbines, preferably in the widest possible range for the composition of the fuel supplied. The parameters most relevant to gas turbines related to N2 dilution are combustion stability, flame structure, heat release and emission of toxic compounds, especially nitrogen oxides.