Natural Gas Calculation

Calculating and tracking natural gas by volume can be useful, but natural gas can also be measured as a source of energy. Similar to other forms of energy, natural gas can be computed and presented in British thermal units (Btu). One Btu is the quantity of heat required to raise the temperature of 1 pound of water by 1°F at normal pressure (Spellman, 2009). There are about 1000 Btu in 1 cubic foot of natural gas delivered to the consumer (NaturalGas.org, 2008). Natural gas distribution companies typically measure the gas delivered to a residence in therms for billing purposes. A therm is equal to 100,000 Btu (approximately 100 cubic feet) of natural gas. The therm is equal to about 105.5 megajoules, 25,200 kilocalories, or 29.3 kilowatt-hours. 

It has been eshmated that burning natural gas to produce 1 therm of heat releases 13,446 lb (6.099 kg) of carbon dioxide into the atmosphere (www.pge.com/about/environment/calculator/assumptions.shtml averagecalifomian). 

Unconventional production now accounts for 46% of the total U.S. production (Navigant Consulting, 2008). 

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Natural gas analysis has considerable economic importance. In fact, commercial contracts increasingly specify not just volume but the calorific or heating value as well. Today the calorific value of a natural gas calculated from its composition obtained by chromatography is recognized as valid. There is therefore a large research effort devoted to increasing the precision of this analysis. 

ISO, Natural Gas—Calculation of Calorific Value, Density and Relative Density International Organization for Standardization ISO 6976-1983(E). 

Natural Gas—Calculation of Calorific Values, Density, Relative Density and Wobbe Index from Composition. ISO 6976 1995(E). 

Water Syngas Hydrogen Natural gas Calculated values... 

Figure 16 compiles breakthrough curves calculated for each single component with an account for its content in the natural gas. Calculations were performed assuming that in each case only one component is sorbed and all the other ones... 

The average error of this simplified method is about 3°C and can reach 5°C. Table 4.22 shows an application of this method calculating the temperature of hydrate formation of a refinery gas at 14 bar. Table 4.23 gives an example applied to natural gas at 80 bar. Note that the presence of H2S increases the hydrate formation temperature. 

Table 4.23 Example calculation of the hydrate formation temperature for a natural gas at 80 bar abs. Result = 29.1 "C. ...

When constmction is complete, the pipeline must be tested for leaks and strength before being put into service industry code specifies the test procedures. Water is the test fluid of choice for natural gas pipelines, and hydrostatic testing is often carried out beyond the yield strength in order to reHeve secondary stresses added during constmction or to ensure that all defects are found. Industry code limits on the hoop stress control the test pressures, which are also limited by location classification based on population. Hoop stress is calculated from the formula, S = PD/2t, where S is the hoop stress in kPa (psig) P is the internal pressure in kPa (psig), and D and T are the outside pipe diameter and nominal wall thickness, respectively, in mm (in.). 

Assuming that natural gas is used to fire the burner with a known heating value of HVc, calculate the available heat at the operating temperature. A shortcut method usually used for most engineering purposes is ... 

Depending on the product and sales arrangement, the revenues calculation can take from a few man-hours to many man-months of effort. For instance, determining the price for a synthetic fuel from coal can be done in a very short time, based on the cost of service. However, if the price is tied to the price of natural gas or oil, the task becomes very difficult, if not impossible. On the other hand, determining the sales growth and selling price for a new product requires a great deal of analysis, speculation, market research, and luck, but projections can be made. 

Figure 1 shows water content of lean, sweet natural gas. It can be used also for gases that have as much as 10% CO2 and/or HiS if the pressure is below 500psia. Above 500psia, acid gases must be accounted for by rigorous three-phase flash calculations or approximation methods. ... 

Natural gas containing 98% methane and 2% nitrogen by volume is burned in a furnace with 15% excess air. The fuel consumption is 20 cubic meters per second, measured at 290°K and 101.3 kPa (or 14.7 psia). The problem is to determine how much air is required under these conditions. In addition, we want to determine the baseline environmental performance of the furnace by calculating the quantity and composition of the flue gas. 

The specific heat of natural gas and hydrocarbon liquids can be calculated using procedures described later in this text (see pp. 41 and 42). 

This chapter discusses the procedures used to calculate the temperature at which hydrates will form for a given pressure (or the pressure at which hydrates will form for a given temperature), the amount of dehydration required to assure that water vapor does not condense from a natural gas stream, and the amount of chemical inhibitor that must be added to lower the hydrate formation temperature. It also discusses the temperature drop that occurs as gas is expanded across a choke. This latter calculation is vital to the calculation of whether hydrates will form in a given stream. 

Figure 4-8 can be used to get a quick approximate solution for the temperature drop of a natural gas stream. For example, if the initial pressure is 4,00() psi and the final pressure is 1,000 psi, AP is 3,000 psi and the change in temperature is 80 F. This curve is based on a liquid concentration of 20 bbl/MMscf. The greater the amount of liquid in the gas the lower the temperature drop, that is, the higher the calculated final temperature. For each increment of 10 bbl/MMscf there is a correction of 5 F. For example, if there is no liquid, the final temperature is 10 F cooler (the temperature drop is 10°F more) than indicated by Figure 4-8. 

This article presents an overview of the causes and frequency of failures for submarine and cross-country pipelines handling oil and natural gas. It gives several tables and charts which include information on the type of pipeline, the cause of the failure, and the number of failures. Data from failures in the US and the North Sea are included. Failure rates based on the total length of piping are calculated. 

The economic value of natural gas is primarily determined by the thermal energy it contains, which is expressed in British thermal units (Btu) or calorific value (CV). Other important physical properties comprise the liquid content, the burning characteristics, the dew point and the compressibility. In order to enable the calculation of these properties from its composition, a natural gas analysis should contain a detailed determination of all of the individual components, even in the low-concentration range. 

Interstate pipelines also use computer simulation programs to calculate pipeline capacity, pressures, horsepower, fuel and other physical characteristics and properties of their systems. Using this information and incorporating variables such as ambient temperatures, facility outages, and changes in market patterns, transmission companies can run daily studies to determine how much natural gas their systems will deliver under expected operating conditions. 

The definitions above are an abbreviated version of those used in a veiy complex and financially significant exercise with the ultimate goal of estimating resei ves and generating production forecasts in the petroleum industry. Deterministic estimates are derived largely from pore volume calculations to determine volumes of either oil nr gas in-place (OIP, GIP). This volume when multiplied by a recovery factor gives a recoverable quantity of oil or natural gas liquids—commonly oil in standard barrels or natural gas in standard cubic feet at surface conditions. Many prefer to use barrels of oil equivalency (BOE) or total hydrocarbons tor the sum of natural gas, natural gas liquids (NGL), and oil. For comparison purposes 6,000 cubic feet of gas is considered to be equivalent to one standard barrel on a British thermal unit (Btu) basis (42 U.S. gallons). 

Figure 12-15 is a compressibility chart for natural gas based on pseudo-reduced pressure and temperature. The reduced pressure is the ratio of the absolute operating pressure to the critical pressure, P and the reduced temperature is the ratio of the absolute operating temperature to the critical temperature, T, for a pure gas or vapor. The pseudo value is the reduced value for a mixture calculated as the sum of the mol percentages of the reduced values of the pure constituents. 

A natural gas having the volumetric composition of 90% methane, 8% ethane, and 2% nitrogen at 1 atm and 25°C is used as fuel in a power plant. To ensure complete combustion 75% excess air is also supplied at 1 atm and 25°C. Calculate (i) the lower and higher heating values of the fuel at 25°C and (ii) the theoretical maximum temperature in the boiler assuming adiabatic operation and gaseous state for all the products. 

For oil-base muds Equation 4-197 can be applied, but K and p must be calculated for an average natural gas using tables or the corresponding algorithms. 

The specific petroleum engineering discipline chapters cover drilling and well completions, reservoir engineering, production, and economics and valuation. These chapters contain information, data, and example calculations related to practical situations that petroleum engineers often encounter. Also, these chapters reflect the growing role of natural gas in industrial operations by integrating natural gas topics and related subjects throughout both volumes. 

The burner is operated on natural gas and air in a fuel-rich mode. Fluorine reacts with excess fuel to form HF and CF4. All of the air that goes through the containment cell (hood) is scrubbed with caustic before being released. (We considered destroying the fluorine by reaction with caustic, but our calculations suggested that this reaction was too slow.)... 

Use data in Table 7.3 or Appendix 2A to calculate the standard entropy change for each of the following reactions at 25°C. For each reaction, interpret the sign and magnitude of the reaction entropy, (a) The synthesis of carbon disulfide from natural gas (methane) CH4(g) + 4 S(s, rhombic) - CS2(1) +... 

In order to generate the starting material for a polymer that is used in water bottles, hydrogen is removed from the ethane in natural gas to produce ethene in the catalyzed reaction C,H6(g) H,(g) + C,ll4(g). Use the information in Appendix 2A to calculate the equilibrium constant for the reaction at 298 K. (a) If the reaction is begun by adding the catalyst to a flask containing C,H6 at 10.0 bar, what will be the partial pressure of the C,H4 at equilibrium (b) Identify three steps the manufacturer can take to increase the yield of product,... 

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