| OCR Text |
Show COAL EVALUATION The type of infomation available from a series of pot furnace tests on a coal was briefly referred to in the previous Section. The reasons for carrying out a programme can range from the requirement to know the range of possibilities for a fuel newly available on the market, to the effect of proposed changes in operational practice on existing boiler plant. Within the scope of the present paper it is impossible to discuss all the inter-relationships of the parameters listed but some enlargement is desirable in terms of the implications of the information available from pot furnace testing. Effect of Fuel Grading For both types of firing there will be an optimum compromise between the ease and rate of burning, coarse ash loss, potential loss from carried over grit and the economies of crushing an as received fuel. In the case of overfeed firing the effects of spread segregation have to be considered and can be investigated. Effect of Moisture Level Considered in relation to flue gas loss any moisture is undesirable. But, particularly in the case of travelling grate combustion there is a necessary optimum surface moisture content for satisfactory combustion performance. This has been shown by McDonald and Murray' ' to be related to the --gin fines. It promotes optimum air distribution and discourages bed caking with resultant reduction in losses. In the case of spreader firing of coal surface moisture is of less importance although there are situations where the moisture binding of fines to the larger particles can result in their being burned in the bed, and retained as coarse ash, rather than in suspension and being carried over in the flue gas. A more important aspect, however, is that with some brown coals and lignites there is a maximum moisture level above which problems 24-9 |
