Modern boiler plant

The subject matter of the paper is divided under the following headings:- Introduction. Thermal efficiency. Operation costs. Reliability. Factors in design affecting reliability and operation. Flue gas, dust and sulphurous fume extraction. Arrangement of boiler plant. Acknowledgements. References. Introduction.?In the Introduction a brief survey is made of the present position of boiler plant design in this country and America. The outstanding thermal performance of modern American generating stations is commented upon, and it is shown that these results are in no small measure the effect of American boiler plant development. The greatest difference in the trend of design between the two countries is in the wider adoption of higher operating steam pressures for American generating stations, the increase in individual boiler unit capacity, and the extended use of pulverized fuel firing, particularly on the unit system. Thermal efficiency.?Under this heading present-day thermal results of British boiler plant are discussed, and examples are given of such results for both stoker-fired and pulverized-fuel-fired boiler plants. Operation costs.?In this part of the paper the importance of repairs and maintenance costs is stressed. Examples are given of these costs for two large pulverized-fuel installations and one large stoker installation. Reliability.?The reliability of modern boiler plant is discussed under this heading, and the reliability of a large pulverized-fuel-fired British plant is given in analytical tabulated form and also graphically, showing the hours of availability lost as a result of outage, and the cause of such outage. Three examples are given on a somewhat similar basis of the reliability of American plants. The various factors affecting reliability in general are discussed. Factors in design affecting reliability and operation.?This section of the paper is subdivided under the following headings:? (a) Water-heating and evaporative parts (boiler and e- conomizer). (b) Superheater. (c) Combustion chamber. (d) Combustion equipment. Under (a) the author discusses the trend towards higher ratings and the results accruing from such practice. He suggests that the conventional present-day boiler form is unsuitable for development for high rates of heat transfer, and that such rates can only be effected by radiant heat, necessitating very radical changes in boiler unit form. He suggests, in general, that for the commonly accepted boiler-unit forms the average rate of evaporation per square foot of total water-heating surface at normal load should not exceed 5.5 lb. per hour. The need for further development of soot-blowing apparatus is discussed under this sub-heading. Under (b) the trend in superheater design is discussed, and the vulnerability of the modern superheater location is emphasized. It is suggested that with the demand for still higher superheats, development in design is necessary to provide a superheater location where definite and separate control of superheat temperature can be effected. Superheater troubles within the experience of the author are given, and these include records of temperatures which superheater tube materials have to withstand in everyday practice. Under (c) the author discusses and emphasizes the importance of combustion chamber design, and suggests that the boiler parts proper should be designed and arranged in dependent relation to the combustion chamber. The development of the water-cooled combustion chamber is briefly outlined, and the various advantages and limitations are discussed. The form of the combustion chamber and factors affecting reliability of refractory and water-wall construction are discussed. Under (d) the author discusses the relative merits of stoker and pulverized-fuel combustion equipment, and suggests that pulverized-fuel firing has many advantages over stoker plant. These advantages are discussed, but the suggestion is qualified by the necessity for designers