CIVIL ENGINEERING & PUBLIC WORKS
of protected metal sheeting having a boxed rib section and coloured in a number of shades to give variety to the elevations.
Roofs will be in lightweight cons- truction consisting of channel rein- forced wood wool slabs anchored to the steelwork, screeded and finished with asphalt. Roof and road drain- age is designed for a rainfall of 3 in./hr.
Four Burners
The incinerator plant will consist of four burners, each designed to burn refuse at the rate of 10.5 tons an hour. It is intended that three incinerators will operate continuous- ly, the fourth being installed as a standby unit.
Of the type developed by the Volund Co., of Copenhagen, the incinerators will be equipped with moving grates and a rotary kiln. The first two grates will be used as drying grates. Refuse on these will be swept by hot combustion gases and subjected to the radiant heat of the combustion chamber, which will result in the removal of a great deal of the moisture content of the re- fuse.
The partially dried refuse will then be discharged to the main burn- ing grate, where the combustion commences and continues during the time that the material remains on this grate. The partially burnt material will then be discharged to the rotary kiln where combustion continues until the completely burnt out clinker is discharged at the end of the rotary kiln to a clinker hop- per.
The moving grates are inclined and are rocked through the action of hydraulic cylinders, allowing the feed rate of the refuse along the grates to be closely controlled.
The rotary kiln is also arranged for a wide range of speed variation to allow adjustment to be made to the burning rate required and to varying calorific values of the refuse.
A small proportion of the refuse will be diverted to a composting plant and matured on the site, so providing fertilizer for agricultural use.
Grabbing Cranes
Two overhead travelling grabbing cranes transfer the refuse from the reception hoppers to the incinerator feed hoppers. The cranes are of the four-motor remote controlled type, each equipped with a grab having a 140 cu. ft heaped capacity and 110 cu.ft. flush capacity.
The span of each crane is approxi- mately 34 ft. One will be able to transfer refuse at the rate of 32 tons per hour, and so supply three in- cinerators when operating at design duty; the other will normally be re- tained on standby duty.
Combustion gases will normally pass through waste heat boilers, one to operate in association with each
Far East Architect & Builder July, 1965
Sketch of plant being built at Kennedy Town
elevating conveyor.
incinerator. The waste heat boilers are of the John Thompson natural circulation type, having a designed output of approximately 30,000 lb/hr of steam at 240 lb/sq. in. gauge and temperature of 550°F. By-pass flues are also provided in case the full steam output is not required.
To remove grits from the combus- tion gases, grit collectors of the multi-vortex type are provided. Each is designed to handle 100,000 cu.ft./ min. of combustion gases at tem- peratures of 750°F. at normal duty and up to 142,000 cu.ft./min. at 750°F. when high calorific value re- fuse is being incinerated.
Ash Removal
Each grit collector is followed by an induced draught fan, of the TV design 3 type, designed to handle 140,000 cu.ft./min. at 750°F. The fans are driven by a variable speed motor of 210 b.h.p.
Ash from the rotary kiln of each incinerator will be discharged to a submerged belt conveyor, the ash being quenched and transported to a junction tower where it is transfer- red to an elevating conveyor. This transports the ash and finally dis- charges it to an overhead 100-ton capacity bunker, fitted underneath with a reversible belt to allow the clinker to be discharged either to barges or to road vehicles.
The grits will be extracted pneuma- tically from hoppers beneath the grate and from the multi-vortex hop- pers, and be transported along pipe- lines to a cyclone separator located adjacent to the elevating conveyor.
Separation of the grits from the conveyor air will be effected in the cyclone, the air then passing through fabric filters to an air exhauster unit.
The grits separated by the cyclone will be discharged either to road vehicle or mixed with water in a conditioner and discharged to the ash
An oil burner, fitted to each of the incinerators, will enable incineration of the refuse to continue if the calorific value becomes too low or the moisture content becomes too high for self-sustaining combustion. These will be located in the main combustion chambers and each burner will be able to burn up to 100 gal/hr. of light fuel oil.
Cost
Total cost of the entire Lai Chi Kok project, including refuse dispos- al, water distillation and composting plant, will be about HK$40 million.
Consulting civil engineers for both this and the Kennedy Town plant are Haigh Zinn and Associates.
The disposal and composting plants are designed and supplied by John Thompson Industrial Cons- tructions, Ltd.
Supervising the
design of the installation is Mr. D. W. Walker, Assistant Director of Public Works Electrical and Mechanical Depart- ment, PWD.
Civil Contractors
Gammon
Lai Chi Kok
Pile foundations (Hong Kong) Ltd.
Superstructure The HK$6,221.- 030 contract was placed last month with Wa Hing Construction Co., Ltd.
Kennedy Town
Foundations-Foundations
Kong) Ltd.
(Hong
concrete work
Pile caps, substructure, chimneys and reinforced Nam Hing Co.
Superstructure erection
Construction Co.
Lam
Structural steelwork (supply and fabrication) Dorman Long (Bridge and Engineering) Ltd.
Plant erection Tai Koo Dock- yard.
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