| OCR Text |
Show THE EXPERIMENTAL APPROACH 2.1 Fuels and supply systems Since the first objective was to compare combustion performance as a function of coal particle size, two coal-in-oil fuels were chosen for the initial investigation: - the first was a BP prototype COD transported by road tanker to the Netherlands. In this instance the dispersion contained 40% wt of coal and its general properties are described in table 3. - the second is described in this paper as a Coal Oil Mixture (COM) and was prepared at the IFRF Research Station, using as feed stocks, coal and oil from the same source as those used in the preparation of the COD. The properties of the feed stocks are shown in tables 4 and 5. The preparation technique was to grind the coal, to mix it continuously with the oil and to fire it immediately (see fig. 2). It is important to note that no stabilizing agents were used; however in this instance long term stability was not an essential requirement and in fact, probably because fuel wa« manufactured only as required, no sedementation was experienced. Thus an essential difference between the two fuels was that of coal particle size, the one being extremely fine and the other having a size distribution which may be typically used for p.f. firing in an industrial water tube boiler. In this manner, it was estimated that the gross effect of particle size would be observed. In addition for comparison purposes, the same heavy fuel oil which was used to prepare the coal-in-oil fuels, was fired directly. For the later investigations involving increased firing densities, the BP prototype COD whose properties are described in table 3 were used. The supply system employed is shown in fig. 2. The BP designed fuel handling set incorporating pumps, filters and heat exchanger was used to transport and heat all three fuels for firing. 2.2 Furnace and firing equipment For the initial investigation, a nominal firing density of 0.18 MW/m was chosen. This is within and at low end of the range of firing densities relative to the furnace volume utilized in industrial water tube boilers and approaching the bottom end of the range considered by BP in feasibility studies (0.24 - 0.63 MW/m [ 4 j1) . This was achieved using the IFRF refractory lined furnace nr. 1 (see fig. 3(a)) at a firing rate of 4.5 MW. A cooling load was built into the furnace comprising a number of calorimetric cooling elements spaced along the furnace which allowed a heat extraction rate sufficient to achieve flue gas temperatures of approximately 1000 °C. In the later experiments higher firing densities - 0.36 and 0.71 MW/rn^ - were achieved through the use of the smaller IFRF water-cooled sectional furnace (see fig.3b) fired nominally at 2.3 and 4.5 MW respectively. In order to achieve exhaust temperature similarity (1000 °C) the furnace was initially partially lined with appropriate refractory brickwork for the 2.3 MW firing rate. This brickwork was then removed to allow sufficient cooling for the 4.5 MW firing rate. 15-5 |
