Coal fired boilers and their fuel handling

Abstract

The main objective of this project is to determine ways and means of handling coal and ash for our coal-fired boiler. Coal-fired boilers have a lot of ancillary costs, as regards fuel handling. The coal handling system incorporates the unloading operation of the collier plus the supply of coal from the stockyard to the plant bunker. Coal to be fired in our 30M.W. stoker-fired boiler is unloaded at Menqa by self-unloading colliers, using two grab-cranes with a 5-tonne capacity buck.et. There a stack of about 27,000 tonnes can be stored, which is equivalent to approximately an eight weeks' winter burn, which is sufficient for us. From the stockyard, it is transported to our 5000 tonne-stockpile, at Jesuit's Hill, by means of 18 tonne trucks (payload). By means of a shovel, coal is fed to three chutes which supply coal to a belt conveyor, through three vibratory-type feeders. Coal is then crushed in an 'impact' - type crusher and is supplied to the plant bunker via two other belt conveyors. The first part of my project consists of several designs of alternative systems which could be applied at the stockyard in conjunction with some modification for the stockpile. I also dealt with the problem of having an operative 65MW - pulverised coal fired boiler together with the already built 30MW-boiler. In this layout I considered the unloading of colliers and barges at a different stockyard, which is much nearer to the power station. The use of barges would be effective, when the Kalafrana stockyard comes into operation during the next two years. The second part of this project covers the design of a new ash-handling system for our 30MW unit. Nobody dares to define as economic the system by which 25000 gallons of fresh water go down the drain just to convey bottom-ash from the ash-pit to the silo. One feasible solution which I considered suitable for Enemalta, is that of pneumatic conveyance. The shape of the ash-pit is altered to accommodate the appropriate equipment and instead of the scraper-chain I flight conveyor combination, only a 125mrn-pipe is used to convey crushed bottom-ash to 1he silo. This system prevents spillages and contaminations which could 1ead to unsafe operation in relation to both equipment and personnel. Pneumatic conveyance of ash :is a maintenance-free operation when compared to the mechanical system. Enema1ta has to either invest a sum of money and install this new system, or let this daily consumption of fresh water go down the drain. I wish to express my gratitude to Mr. M. Mifsud Bonnici (Dip.E.E.C.Eng., M.I.E.E.,M.I.E.R.E.) chairman of Enemalta who entrusted me in compiling such an interesting work, and also to Mr.P.G.Camenzuli (B.A.(Hons).,M.A., MRINA). who offered suggestions and criticisms, without which I would have never completed my dissertation. Finally, many thanks are due to Mr .A.J .Pullicino (C. Eng.). for his supervision.