Feed coals, ultimate analysis

The anticipated product slate from a typical commercial plant feeding 33,500 tons per stream day of dry coal is given in Table II. This product slate is based on conversion of a typical Pittsburgh seam coal from West Virginia. The ultimate analysis of the coal used as a design basis is given in Table III. 

The ultimate analysis is used with the heating value of the coal to perform combustion calculations including the determination of coal feed rates, combustion air requirements, weight of products of combustion to determine fan sizes, boiler performance, and sulfur emissions. 

We have already discussed under practical stoichiometry how the air requirements can be estimated based on the fuel composition (ultimate analysis). The primary and secondary air requirements for combustion of pulverized coal or coke are best estimated by mass and heat balance at the mill. In Appendix 6A we show a calculation taken from Musto (1997) for the primary and secondary air required for coal pulverizer with 4.5 metric ton per hour (10,0(X)lb/hr) coal feed rate at initial moisture of 15 percent which is required to be ground and dried to 2 percent with a 200 HP mill. In order to estimate the actual primary and secondary air, one has to make some estimation of the evaporation rate, the amount of gas entering the coal mill, and the bleed air required so that the quantity of air that should be vented from the hood off-take can be properly estimated. It shows that for a take-off gas temperature of 315°C (600° F) and vent gas temperature of 76°C (170°F) and allowing ambient air infiltration of 10 percent at 15°C (60°F) the primary air will be about 22 percent of stoichiometric air and 21 percent of total air. The remaining air (about 79 percent) will be the secondary air. With this information we can size a burner using a burner pipe diameter based on a Craya-Curtet parameter of choice bearing in mind the conditions that ensure the desired jet recirculation patterns described in Chapter 3. 

Since both the direct and phased approaches offer, at least in principle, equal promise for ultimate success (i.e., comprehensiveness and complete characterization), it is worthwhile to examine their relative resource requirements. Several studies were conducted with the objective of comparing the costs of direct and phased (with elimination of low priority streams) sampling and analysis approaches. (2,3] A number of processes were evaluated during these studies and the results for two unit operations — a limestone wet scrubber and full-scale low-Btu coal gasifier — are taken as examples. The scrubber involved seven feed or waste stream sampling sites. The gasifier contained 70 identifiable stream sampling points. The total estimated costs for both processes by both approaches are shown in Table I. 

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