| OCR Text |
Show projects to improve all aspects of coal utilisation with priority directed to improving coal systems for industry. In 1972 a development programme concentrating on packaged boilers and their ancillaries, particularly coal and ash handling, was launched . As a result of this initiative, many equipment manufacturers are now collaborating with the NCB in this area and important advances have been made. Improvement of conventional stoker fired boilers has been achieved with increased automation, including automatic ignition and de-ashing. Pneumatic handling systems for coal and ash are now commercially available. The most important development for the future is expected to be fluidised bed combustion, with its ability to burn a wide variety of coals and promote high combustion intensity without boiler fouling yielding more compact coal fired boilers. It is also amenable to automatic control and facilitates suppression of sulphur dioxide, if required. It is expected that most of the increased industrial demand will be for coals that have been washed to remove stones, leaving only the ash which is part of the coal structure, typically 5% to 10%. High ash coals will only be used at or adjacent to mines, because of high transport costs. The NCB is committed to an investment programme in new preparation plants to meet the demand for washed coals. The coal will be marketed in two size grades, as at present. Singles coal, 25 mm to 13 mm, will be supplied to smaller users, typically taking below 6,000 tonnes per year, because of the relatively low capital investment required for the storage and handling system. Smalls coal, usually 13 mm to zero, but sometimes with a top size of 18 mm or 25 mm, is supplied to larger users. Smalls are cheaper than singles, but more difficult to handle and require a higher capital investment which is only justified for a high coal usage. Developments in handling systems for both singles and smalls are discussed in Section 3. New and existing coal fired installations must comply with the UK Clean Air Acts. For particulates, these specify a maximum rate of emission per unit output, which becomes more stringent with increasing boiler size. Simple cyclones are sufficient for small stoker fired boilers, but bag filters or electrostatic precipitators must be used with larger boilers . 20-3 |
