Heating value recovery

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). 

Fuel. Propylene has a net heating value of 45.8 MJ/kg (19,700 Btu/lb) and is often contained in refinery fuel-gas streams. However, propylene is diverted from streams for refinery fuel use in large quantities only when economics for other uses are unfavorable, or equipment for propylene recovery does not exist or is limited in capacity. Propylene is also contained in Hquid petroleum gas (LPG), but is limited to a maximum concentration of 5 vol % in certain grades (83) (see Liquefied PETROLEUM gas). 

The waste gas remaining after removal of ammonia and recovery of hydrogen cyanide contains enough hydrogen and carbon monoxide that it is flammable and has enough heat value to make it a valuable fuel. It is usually used to displace other fuel ia boilers. 

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. 

Reducing smelting furnaces that produce a high-sulfidity, kraft-like green liquor are now employed at sodium-based sulfite mills. U.S. EPA anticipates that it would be necessary to replace the existing recovery boilers at ammonia-based mills if chemical substitution to a sodium base were employed. Additionally, it is likely that, because the heat value of sodium spent liquor is lower than ammonia spent liquor, evaporator modification may he required if excess capacity does not already exist. 

The heating value of the waste does not exceed 5000 Btu/lb (if so, the waste is considered to be burned for energy recovery). 

Heat recovery efficiency is a consideration of major importance in the conversion of coal to secondary fuels. This parameter is defined as the percent of the heating value of the coal used which is recovered as heating value in the desired secondary fuel. Heat recovery efficiency which can be attained in a coal conversion process depends firstly on the theoretical chemical and thermodynamic requirements of the process, and secondly on the practical realization of the process. The first factor determines the theoretical maximum heat recovery efficiency that can be obtained under ideal circumstances. The second factor determines the extent to which the practical process approaches the theoretical ideal. 

The potential of these reactions for methane production can be compared in terms of theoretical yields and heat recovery efficiencies. Theoretical methane yield is defined by the chemical equations. Theoretical heat recovery efficiency is defined as the percent of the higher heating value of the coal which is recovered in the form of methane product. These idealized parameters provide a measure of the ultimate capability of conversion systems and are useful for evaluating actual conversion processes. 

The results of the performance calculations are summarized in Table 9-24. The efficiency of the overall power system, work output divided by the lower heating value (LHV) of the CH4 fuel, is increased from 57% for the fuel cell alone to 82% for the overall system with a 30 F difference in the recuperative exchanger and to 76% for an 80 F difference. This regenerative Brayton cycle heat rejection and heat-fuel recovery arrangement is perhaps the simplest approach to heat recovery. It makes minimal demands on fuel cell heat removal and gas turbine arrangements, has minimal number of system components, and makes the most of the inherent high efficiency of the fuel cell. 

The air product gas ratio was 0.73, and energy recovery reached about 70 percent (or just over 80 percent If the sensible heat of the gas Is Included). The heat values recorded by the calorimeter are about 8 percent higher than those computed from gas compositions and showing peaks not detected by the gas chromatograph. 

Wood forms one of the world s most important chemical raw materials. It is the primary source of cellulose for the pulp and paper and cellulose industries. These industries are well up in the group of 10 major industries of the United Slates. For paper, rayon, films, lacquers, explosives and plastics, which comprise the greatest chemical uses of wood, it is the cellulose component (plus certain amounts of hemicellulose) of wood that is of value. The lignin forms a major industrial waste as a by-product of the paper and cellulose industries. Its major use is in its heat value in the recovery of alkaline pulping chemicals. A variety of minor uses for lignin have been developed, such as for the manufacture of vanillin, adhesives, plastics, oil-well drilling compounds and fillers for rubber. 

The gas remaining after oil recovery, called pyrolytic gas, or pyro-gas, is typically composed of paraffins and olefins with carbon numbers from one to five. Depending on the process, the heat value of the gas can range from 170 to 2,375 Btu per cubic foot, and averages 835 Btu per cubic foot.4 (Natural gas averages around 1000 Btu per cubic foot.) Most processes use the pyrolytic gas as fuel to heat the reactor. Any surplus gas can be flared or used to replace natural gas as boiler fuel. Emissions from burning... 

Ginning waste is a valuable source of energy for cotton gins. Each pound of gin waste has a heat value of about 7,000 Btu. A 30% recovery of heat from the incineration of gin waste is... 

Large quantities of hydroxy acids as well as acetic and formic acids are formed during kraft pulping (Tables 10-3 and 7-8). Among hydroxy acids from softwood, glucoisosaccharinic acid predominates. Especially when considering that the heat value of these hydroxy acids is only 25-50% of that of kraft lignin, their recovery seems motivated, but adequate markets have not yet been established for these products. Liberation of the aliphatic acids... 

A residue used for analysis contained 47% oil. The residne has a higher heating value than that of coal and is snitable for energy recovery. However, it contains chlorine and heavy metals as shown in Table 26.8. Any exhanst gas and fly ash treatment must be carefully considered in its application. Recently, it has been nsed in a fnmace, and has contributed to the improvement of heat balance, as described above. 

---