Energy, fuels, and chemicals 3173 



Table 26-8. — Ultimate analyses and heating values of some fossil fuels 

 compared with hardwoods 



Coal' Hardwood^ 



Residual 

 Western Pennsylvania Wood Bark fuel oil' 



— — Percent — 



Ultimate analysis 



Hydrogen 6.4 5.0 6.4 6.0 9.5-12.0 



Carbon 54.6 74.2 50.8 51.2 86.5-90.2 



Oxygen 33.8 7.1 41.8 37.9 — 



Sulfur .4 2.1 — — .7-3.5 



Nitrogen 1.0 1.5 .4 .4 — 



Ash 3.3 10.1 .9 5.2 .01-. 50 



Heating value, Btu/lb. . . . 9,420 13,310 7,827^ 7,593^ 17,410-18,990 



'Data from Hall et al. (1976). 

 ^Data from Arola (1976). 

 ^Data from table 9-12. 



Arola (1975) provided the illustration reproduced in figure 26-6 as an example 

 of how to use the graph. 



Given: The fuel is bark which costs $10/wet ton and has a higher heating value of 9,000 Btu/lb 

 when ovendry. Process efficiency is 65 percent. The bark is fired at 50 percent moisture 

 content (wet basis). 



Problem: What is the cost of steam? 



Solution: Available heat at 50 percent moisture content is 4,500 Btu/lb, i.e., (1.00 - 0.50) x 9,000 

 Btu/lb. From the $10/ton point along the upper scale at bottom of chart, extend a line 

 vertically to the 4,500 Btu/lb point for bark (interpolation required). Extend a horizontal 

 line from this intersection to the 65 percent efficiency line and then a vertical line to the 

 top of the graph to read the cost of steam. 



Answer: About $1.70/million Btu. 



INDUSTRIAL BURNING SYSTEMS 



Today industrial wood burning furnaces are commonly incorporated into 

 boiler systems to produce steam. Nearly 1700 such wood-fired boiler systems 

 are in operation in the United States (Environmental Protection Agency 1977), 

 and the number is increasing. They range in size from shop-fabricated units, 

 with steam capacities up to about 100,000 pounds per hour, to large field-erected 

 units that can generate up to 600,000 pounds of steam per hour on hogged fuel 

 (USDA Forest Service 1976; Bliss and Blake 1977). Wood-fired boilers produc- 

 ing 15,000 to 100,000 pounds per hour are the most common among recent 

 installations (Hall et al. 1976). In some furnace systems the hot combustion 

 gases produced are used to direct-fire kilns and dryers without the intermediate 

 step of steam generation. In addition, certain furnaces could be used to drive gas 

 turbines whose exhaust heat could then be used in a conventional boiler to 

 produce added steam power. ^ 



H. G. Hagen. 1977. Wood fueled combustion cycle gas turbine power plant. 38 p. Paper 

 presented at the California Energy Comm. Energy-From-Wood Workshop. See also: Hamrick, J. T. 

 and T. M. Hamrick, 1981. Development of wood as an alternative fuel for large power generation 

 systems. Part I - Research on wood burning gas turbines. Final Report DOE/ET/20058-T2(Pt.l) 

 (DE82002034) prepared by Aerospace Research Corp., Roanoke, Va. for U.S. Dept. of Energy. 

 80 p. 



