Natural gas heating value

THE EFFECT OF MOISTURE CONTENT ON NATURAL GAS HEATING VALUE... 

Precise gas analysis technique is essential in order to obtain compositional analysis data for the reliable determination of natural gas heating values. Since 1977, laboratories in Indonesia and Japan serving the LNG export and import trade between these countries have co-operated to develope analytical procedures, based on GPA Standard 2261, that provide the required level of reliability. This paper sets out to show that stringent adherence to technique together with carefull selection of equipment and reference materials can achieve the level of rehability required to accurately calculate LNG heating value. 

One of the major technical problems that had to be overcome to integrate the POLYBED system with the steam reformer was the variation in tail gas flow and composition. Because of the cyclic nature of the process, tail gas is rejected by the POLYBED unit during blowdown and purge with significant flow and composition variations. The fluctuations would have made it impossible to use the tail gas for fuel and a sophisticated system was developed to balance tail gas heating value. This buffer/mixing tank system has proven to be very reliable in holding heat input variation to 1% (2). ... 

Natural gas (calorific value about 8,600 kcal/Nm ) is introduced via ports in the walls of the kiln. It burns with a longer, lazier flame than oil or coal and more readily produces medium reactivity lime. As it contains insignificant amounts of sulfur and produces no ash, the resulting lime is not contaminated by the fuel in any way. Moreover, natural gas does not readily produce smoke, so that the exhaust gases have a low opacity. The heat usages of gas-fired shaft kilns are generally about 1,150 kcal/kg. 

FIGURE 9. GAS HEATING VALUE VERSUS MOLECULAR WEIGHT OF NATURAL GAS SAMPLES SUPPLIED BY GRI... 

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. 

We shonld also utilize liquid hydrocarbons, which frequently accompany natural gas. These so-called natural gas liquids currently have little use besides their caloric heat value. They consist mainly of saturated straight hydrocarbons chains containing 3-6 carbon atoms, as well as some aromatics. As we found (Chapter 8), it is possible by superacidic catalytic treatment to upgrade these liquids to high-octane, commercially usable gasoline. Their use will not per se solve our long-... 

The initial biogas recovered is an MHV gas and is often upgraded to high heat value (HHV) gas when used for blending with natural gas suppHes. The aimual production of HHV gas ia 1987, produced by 11 HHV gasification facihties, was 116 x 10 m of pipehne-quaUty gas, ie, 0.004 EJ (121). This is an iacrease from the 1980 production of 11.3 X 10 m . Another 38 landfill gas recovery plants produced an estimated 218 x 10 m of MHV gas, ie, 0.005 EJ. Additions to production can be expected because of landfill recovery sites that have been identified as suitable for methane recovery. In 1988, there were 51 sites ia preliminary evaluation and 42 sites were proposed as potential sites (121). 

The first gas producer making low heat-value gas was built in 1832. (The product was a combustible carbon monoxide—hydrogen mixture containing ca 50 vol % nitrogen). The open-hearth or Siemens-Martin process, built in 1861 for pig iron refining, increased low heat-value gas use (see Iron). The use of producer gas as a fuel for heating furnaces continued to increase until the turn of the century when natural gas began to supplant manufactured fuel gas (see Furnaces, fuel-fired). 

High Heat- Value Gas. High heat-value (high Btu) gas (7) has a heating value usually in excess of 33.5 MJ/m (900 Btu/fT). This is the gaseous fuel that is often referred to as substitute or synthetic natural gas (SNG), or pipeline-quaHty gas. It consists predominantiy of methane and is compatible with natural gas insofar as it may be mixed with, or substituted for, natural gas. 

To enable interchangeabiUty of the SNG with natural gas, on a calorific, flame, and toxicity basis, the synthetically produced gas consists of a minimum of 89 vol % methane, a maximum of 0.1% carbon monoxide, and up to 10% hydrogen. The specified minimum acceptable gross heating value is approximately 34.6 MJ/m (930 Btu/fE). 

TOSCO tar oils have high viscosity and may not be transported by conventional pipelines. Heating values of product gas on a dry, acid gas-free basis are in the natural gas range if butanes and heavier components are included. 

The energy consumption (lower heating value of the feedstock plus fuel) of the low pressure process has successively improved from over 38.3 GJ/1 when it was first introduced to 29.0—30.3 GJ/thy the mid-1990s. Natural gas-based reforming plants have advanced to the point where the scope for stiU further gains in efficiency is small and the gains costiy to obtain. 

There are direct substitutions of possible interest that would not be feasible without drastic changes in the feed system or pressure. Thus if the available substitute for natural gas is, eg, a manufactured gas containing much CO, there would almost always be a mismatch of the WIs unless the fuel could be further modified by mixing with some other gaseous fuel of high volumetric heating value (propane, butane, vaporized fuel oil, etc). Moreover, if there are substantial differences in eg, as a result of the presence of considerable H2 as well as CO in the substitute gas, the variation in dame height and dashback tendency can also make the substitution unsatisfactory for some purposes, even if the WI is reproduced. Refinements and additional criteria are occasionally appHed to measure these and other effects in more complex substitution problems (10,85). 

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 ... 

The heating of a fuel affects the overall size of the fuel system. Generally, fuel heating is a more important concern in connection with gaseous fuels, since liquid fuels all come from petroleum crude and show narrow heating-value variations. Gaseous fuels, on the other hand, can vary from llOOBtu/ft (41,000 KJ/m ) for natural gas to (11,184 KJ/m ) or below for process gas. The fuel system will of necessity have to be larger for the process gas, since more is required for the same temperature rise. 

CO2 must be removed for prevention of corrosion and because it lowers the heating value of natural gas. In some treatment situations it is desired to selectively remove H2S and slip most of the CO2. If the CO2 can be tolerated downstream, a more economical treating plant can often be provided that removes only the H2S. Sometimes,... 

This last expression serves as the working formula. Note that natural gas may be substituted for fuel oil, whereby the only resulting change will be the heating value in the derivation. 

Another common impurity of natural gas is nitrogen. Since nitrogen has essentially no calorific value, it lowers the heating value of gas, Gas purchasers may set a minimum limit of heating value (normally approximately 9.50 Biu/scl). In some cases it may be necessary to remove the nitrogen to satisfy this requirement. This is done in very low temperaliire plants or with permeable membranes. These proces [Pg.4]

Figure 2-11 gives values of U for exchange from a water bath to a natural gas stream in a coil. Figure 2-12 is a nomograph for crude oil streams heated with a water bath. 

A condensate stabilizer with reflux will recover more intermediate components from the gas than a cold-feed stabilizer. However, it requires more equipment to purchase, install, and operate. This additional cost must be justified by the net benefit of the incremental liquid recovery, less the cost of natural gas shrinkage and loss of heating value, over that obtained from a cold-feed stabilizer. 

Natural gas with H2S or other sulfur compounds present is called sour gas, while gas with only CO2 is called sweet. Both H2S and CO2 are undesirable, as they cause corrosion and reduce the heating value and thus the sales value of the gas. In addition, H2S may be lethal in very small quantities. Table 7-1 shows physiological effects of H2S concentrations in air. 

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