CLP: The construction of Hok Un power station 1921, Part Three

Graham Wood has kindly sent a copy of the souvenir brochure issued at the official opening of the Hok Un power station in 1921.

HF: I have retyped the original PDF version of the brochure sent by Graham and as it is a fairly lengthy document this is the third in a series of articles. I will include all the images and script shown in the original brochure but am unable to reproduce its exact format.

Thanks to SCT for proofreading the retyped copy.

Hok Un Power Station Image 15 Graham Wood

Sinking a caisson with concreted turbine block in the distance, showing female labour used for transporting the tons of concrete required.


In the construction of the main buildings and underground work, the following materials were used:-

Structural Steel
1,350 tons, including 90,000 rivets and bolts.

Reinforcing Steel
350 tons.

Reinforced Concrete
6,000 cu. yards.

2,500 tons.

The work also included the removal of 20,000 cu. yards of earth and 5,000 cu. yards of solid rock.

Work was started on the first piles and foundations in July, 1937, and the buildings were occupied and the plant in running order by January, 1939.



Steam Generating Plant                         International Combustion Ltd
(Main Contractors)

Erection of 120,000lb. Boiler                  The Hong Kong & Whampoa Dock Co. Ltd.

Erection of 200,000 lb. Boiler                 China Light & Power’s Co’s. Staff and Ah Tung
Engineering Co.

Turbine and Condensing Plant                 Metropolitan-Vickers Electrical Export Co., Ltd                                                                  (Local Agents: Arnhold & Co., Ltd.)

All E.H.T. and L.T. Switchgear and            Messrs. A. Reyrolle & Co., Ltd.
Sub Distribution Boards

Electric Crane                                         Herbert Morris, Ltd. (Local Agents: Inniss &                                                                     Riddle (China) Ltd.)

Steam Piping                                          Babcock & Wilcox, Ltd. and Aitons, Ltd.

Feed Pumps                                            Mather & Platt, Ltd. and G. & J. Weir, Ltd.

Circulating Water Piping                           China Light & Power Co.’s Workshops

Service Transformers                               Brush Electrical Mfg. Co. Ltd.

Ash Conveyors                                        China Light & Power Co.’s Workshops

Coal Mixing Plant                                     China Light & Power Co.’s Workshops

Coal Weighing Plant                                 W. & T. Avery, Ltd.
                                                                 (Local Agents: Jardine Engineering Corp. Ltd)

CO2 Equipment                                         The Walter Kidde Company, Ltd.

Cables        Callenders Cable & Construction Co.(Local Agents: Inniss & Riddle (China) Ltd
and W.T. Henley’s Telegraph Works Co., (Local Agents: Jardine Engineering Corp., Ltd.)

Battery                                                     Batteries Ltd.

Battery Control Gear                                  Metropolitan-Vickers Electrical Export Co. Ltd                                                                    (Local Agents: Arnhold & Co., Ltd.)

Loud-speaking Equipment                            RCA Victor Co. of China

“Ferrodor” Paint for Machinery                      B.J.Lacon & Co.(Manufactured by Griffiths      (Boilers and Turbines)                                  Bros., London)


General Contractors                                   Hong Kong Engineering & Construction Co. Ltd

Structural Steel               Redpath, Brown & Co. Ltd (Local Agents: Davie Boag & Co. Ltd)

Roof Lights and Windows        Henry Hope & Sons, Ltd. (Local Agents: Jardine Engineering Corp Ltd.)

Calorex Glass and Window Glass             Chance Bros. Ltd. (Local Agent: B.J. Lacon & Co.)

Lifts   Schindler     (Local Agents: Jardine Engineering Corp. Ltd.) and Waygood-Otis (Local Agents: Otis Elevator Co.)

Tiling                                                     Cathay Ceramics (H.K.) Ltd.

Ruberoid Roofing                                    Davie Boag & Co. Ltd.

Ventilators                          H.H.Robertson Company (Local Agents: Davie Boag & Co. Ltd)

Fans                                                       General Electric Co. of China Ltd.

Plumbing Fixtures                              Shank & Co. Ltd. (Local Agents: Malcolm & Co. Ltd.)

Woven Wire Guards                                  Shewan, Tomes & Co. Ltd.

Painting                         Nobel Chemical Finishes (Local Agents: Reiss, Bradley & Co. Ltd.)

Hardware                                         Yale & Towne Co. (Local Agents: Mustard & Co. Ltd.)

Electric Lighting                                       Jardine Engineering Corporation Ltd.

Wiring       W.T. Henley’s Telegraph Works Co. Ltd. (Local Agents: Jardine Engineering Corp. Ltd.)

Sluice Gates and Mechanism                      China Light & Power Co.’s Workshops

Sika Waterproofing                                    Malcolm & Co. Ltd.

Air-Conditioning                                   Carrier Co. (Local Agents: Andersen, Meyer & Co.)

Plumbing Works                                         Reiss, Bradley & Co. Ltd.

Screens and Gate Valves – Sea Intake Circulating System China Light & Power Co.’s Workshops


The first boiler installed is a Lopulco three-drum vertical type, manufactured by International Combustion Ltd., and designed for stoker firing with the following working conditions:-

Evaporation – Normal          120,000 lbs. per hour.

– Overload         25% for three hours.

Working pressure                  400 lbs. per sq.inch.

Final steam pressure              700 °F

Feed temperature                   270 °F

The convection heating surface totals 16,106 sq. ft. and the radiant heating surface totals 1,655 sq. ft.

A second boiler now nearing completion has the following working conditions:-

Evaporation -Normal                 160,000 lbs. per hour.

”           Max. continuous    200,000 lbs. per hour.

Working pressure                            400 lbs. per sq. inch.

Final steam temperature                  700 °F.

Feed temperature                            270 °F.


The drums are 4′ internal diameter: those of the first boiler are of riveted construction from mild steel plates with longitudinal seams double riveted, butt-jointed. Manholes are provided at the end of each drum. The drums are supported by special slings across the width of the boiler and hang from an overhead structure. The drums of the second boiler are solid forged from best quality Siemens-Martins steel.


The tubes of each boiler are 3¼” external diameter. The thickness of the two rows nearest the furnace is 5 s.w.g.. and the remainder 6 s.w.g.


The combustion chamber of each of the two boilers is of the water-cooled type with plain tubes on front and side walls and suspended refractory arches on the lower front and rear. The tubes in the combustion chamber are solid drawn 3¼” outside diameter. The side tubes are expanded into top and bottom headers , the lower headers are at stoker grate level. The  headers are constructed from solid hot drawn seamless sections forged to

Hok Un Power Station Image 22 Graham Wood

These three photographs show the first boiler during progressive stages of erection.

Hok Un Power Station Image 17 Graham Wood

Hok Un Power Station Image 18 Graham Wood

shape. The front wall tubes are expanded at the lower ends into connecting headers and the upper ends into the front steam and water drum. The headers are provided with hand holes with internal caps to facilitate inspection and renewal. Blow down and isolating vavles are fitted on each lower header.

The combustion chamber is enclosed in a mild steel casing ⅛” thick, stiffened with angles and T-bars and is complete with air screen plates 1⁄16″ thick. Cast iron wall boxes are provided where the tubes pass through the side walls to support the firebrick wall above the tubes. Where the tubes pass through the openings they are packed with asbestos fibre. The chamber is lined throughout with 9″ firebrick behind the side and front wall tubes and 13½” thick for the remainder of the chamber.

A system of secondary air is provided consisting of ducting and nozzles for introducing secondary air to the combustion chamber through the front and rear arches.


Ivor soot blowers are provided for cleaning all parts of each boiler and combustion chamber, single nozzle type in the front bank of boiler tubes and through the circulating tubes at the top of the boiler for cleaning the superheater, and multi-nozzle blowers across the full width of the boiler for cleaning the second and third bank of tubes. The blowers can be operated without shutting down the boiler.


The superheaters are of the M.L.S. single pass convection type, with a heating surface of 3,640 sq. ft. and 5,500 sq. ft for the first and second boilers respectively. The elements are made from solid hot drawn mild steel tubing, the return ends being forged integral with the tubing. The tube elements are supported by steel members arranged above the surrounding tubes of the boiler. A steam mixing valve with connections between the superheater boxes and the operating valves is supplied with steam thermometers arranged to facilitate the control of the final steam temperature.


The economisers are of the Senior H-section type, with heating surfaces of 7,412 sq. ft. and 11,280 sq. ft for the first and second boilers respectively. The tubes are in groups of four vertically, expanded into M.S. connector boxes at each end. The tubes are of No. 6 s.w.g. cold drawn seamless steel tube fitted H-section cast iron rings. The econpmisers are enclosed are enclosed with mild steel plates, with inspection doors in the end casing. An Ivor soot blower to clean the economiser is arranged to blow in the same direction as the gases.


An USCO plate type air heater is provided for each boiler designed so that the movement of the air and gas are contra-flow. The area of heating surface is 13,050 sq. ft. and 21,645 sq. ft. respectively for the first and second boiler.


Provision is made for recirculating a portion of the preheated air so that the mixture of preheated and fresh air entering the eye of the forced draught fan will not be less that 120° F when the ambient air is 70° F. A by-pass for the flue gases is provided so that the preheater can be completely cut out of circuit.


Each boiler is provided with one induced draught, one forced draught and two secondary air fans. These are of the single inlet turbovane type, the fan inlet of the induced draught fan is fitted with combined type scroll dust collector and secondary vortex collector. The inlet scroll forms the primary portion of the dust collector, the gases being taken from the outer radius of the scroll and passed to the secondary collector and discharged back to the inlet of the fan. The collected dust is taken from an outlet at the bottom of the secondary cells to the ash-handling plant in the basement.


Hok Un Power Station Image 20 Graham Wood

Second boiler photographed during erection.

The fan capacities for each boiler are given below.

F.D. Fan  No.1 boiler 68,000 cu. ft. per min. No.2 boiler 111,100 cu. ft. per min.

I.D. Fan  No.1 boiler 82,000 cu. ft. per min  No.2 boiler 131,280 cu. ft. per min.

The induced and forced draught fans are direct couple to screen protected squirrel cage motors and the secondary air fan to totally enclosed squirrel cage motors.


The arrangement of gas and air ducting is similar for both first and second boilers. The air ducts between the forced draught fan, air heater, stoker and secondary air equipment is designed with a 100% air by-pass on the heater. The flue gas ducting between the boiler, economiser, air heater, induced draught fan and chimney is arranged for a complete air heater gas by-pass.


The general construction of each of the two type “L” stokers is standard, but as reviewed in the opening page of this presentation brochure, the machine to fire the second boiler is the largest travelling grate in the world, having an area of 756 sq. ft. The grate of the stoker for the first boiler is 29′ wide by 20′ long, giving a grate area of 580 sq. ft.

The stokers will burn any fuel or mixture of fuels, provided the fuels are properly mixed, having a calorific value of not less than 10,000 B.T.U.’s per lb., volatile content of not less than 20% and an ash fusion temperature of not less than 2,280 °F., without causing excessive slagging or clinkering and without serious loss to the efficiency of output.

The main frame consists of two longitudinal side frames and one longitudinal centre frame tied together by transverse members arranged at frequent intervals throughout the length of the machine. The air distribution frames are iron castings having hopper-shaped depressions with open bottoms into which the control valves are fitted. The upper surfaces of the frames are arranged to form tracks on which the grate rollers run.

Hok Un Power Station Image 21 Graham Wood

A photograph of the second “L” stoker for the Hok-un power station. This machine is the largest travelling grate in the world, having an effective grate area of 756 sq. ft.

The frames and valves are arranged in transverse rows. All the valves in each row move in unison. Each row is separately controlled from the sides of the furnace by means of levers with graduated quadrants. The whole of the control gear is accessible for inspection and adjustment without dismantling any part of the machine. Dead plates are fitted between each two rows of valve frames to prevent excessive leakage of air between adjacent compartments.

The M.S. front shaft is of large diameter carried in two cast iron bearings of ample length with provision for lubrication.

The chain sprockets are heavy castings keyed to the shaft with shrouded teeth for side guidance of the chains. A sprocket wheel is provided with each chain.


The fuel hopper for each stoker is of cast iron end plates with M.S. front and back plates and is fitted with a coal cut-off gate. An adjustable regulating shutter with refractory facing is arranged between the hoppers with worm and wheel mechanism and an indicator to register the thickness of feed. Two Lea coal recorders are fitted with cyclometer dials.


Each stoker is driven by two self-contained gears, one on each side. Motion is transmitted from spur and worm reduction gears and an eight-speed gear box, giving a speed range from top to bottom gear of approximately four to one. The gears run in oil in dustproof housings. A spring loaded clutch type safety device is fitted in the main worm spindle. Hand operation is possible by means of a ratchet spanner engaging with the main worm spindle.

The driving motors are totally enclosed continuous rated type suitable for 350 volt 3 phase 50 period circuit with a temperature rise  not exceeding 72° F., specially impregnated to withstand the effects of the damp tropical climate.


One twin double compartment type ash hopper is supplied with each stoker and fitted with two cast iron sliding doors of the rack and pinion type. The division walls between the ash and riddlings compartments are formed of cast iron tees arranged with 3″ thick fire tiles laid on. Three riddlings discharge doors are provided for the hopper.


A double mild steel plate main dust hopper and a double mild steel front riddlings hopper is situated beneath the return chain of each grate.. An airtight door is provided at the inverted apex of each hopper for the removal of dust.


A 5/16″ mild steel plate chimney 105′ high above the firing floor level is erected for each boiler. and of adequate size for the flue gases when the boilers are working at maximum rating.


The bin is of granite structure and has a total capacity of 32,281 tons. The types of coal stored are Indian Bituminous, Hongay Semi-Anthracite and Dong Trieu Anthracite. The coal is stacked into separate heaps, rattan baskets being used for this purpose. A permanent 2 ft. gauge track is led into the various heaps. Trucks having a capacity of 5 cwt. nett are used for conveying the coal from the storage bin to a weighing house, where it is weighed on two electrically-operated Avery scales. After the weights are recorded on cards, the coal into four separate receiving hoppers whence it is taken by four 16″ belts geared to suit any mixture required by a single hopper. From this hopper it is transferred by an18″ single belt conveyor and bucket elevator having a capacity of 30 tons per hour to still another 18″ belt which delivers it to the boiler hoppers.

Provision has been made to feed both old and new Stations by this route.

This article was first posted on 21st November 2021.

Related Indhhk articles:

  1. CLP: The construction of Hok Un power station 1921, Part One
  2. CLP: The construction of Hok Un power station 1921, Part Two
  3. CLP – Hok Un (Yuen) Power Station 1921-1991 – updated
  4. John M. Henderson, Engineering Company, Aberdeen, Scotland…link to Hok Un power station, Hong Kong
  5. Andrew Wood biography – involvement in the repair of Hok Un power station at the end of the Japanese occupation of Hong Kong
  6. Hok Un Power Station, post World War Two images
  7. CLP’s Hok Un Power Station – immediately post World War Two
  8. Preece, Cardew and Rider – Consulting Engineers for Hok Un power station
  9. CLP’s Hok Un Power Station during the Japanese occupation
  10. CLP- Lawrence Kadoorie speech 1977 – HK + Hok Un Power Station during WW2
  11. Robert Gordon Shewan – CLP, Green Island Cement and HK Rope Manufacturing



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