When Eskom gave notice to the City Council in 1951 of its intention not to renew the "pooling" agreement when it expired on 12 May 1957, immediate attention was given as to how the increasing demand for electricity on the Council's system could best be met after this date. By this time in 1957, just before the onset of the peak-load winter period, the capacity of the Council's generating plant would be inadequate to meet the demand. Careful consideration was therefore given as to whether it would be better to purchase all the Council's future electricity requirements in bulk from Eskom or rather embark upon the construction of a further power station. After a detailed study it was decided that the Council's interests, both economically and operationally, would best be served by opting for the latter alternative. A further factor that influenced this decision was the knowledge that Eskom was steadily becoming fully committed to meeting the electrical requirements of the South African Railways, the farmers and other consumers in the rural areas of the Western Cape and accordingly might not be in a position to supply the Council as well.

Although some prior exploratory work had been undertaken by the Council concerning the possible construction of an additional power station, no detailed planning had as yet been undertaken. Because of the length of time involved in planning and building such a major power station it was clear that it would be some years after the termination of the "pooling" agreement before the station could be completed. To bridge the gap until then and meet the anticipated shortfall in capacity, it would be necessary for the Council to purchase electricity in bulk from Eskom. Accordingly, once the decision to proceed with the construction of a new power station had been taken, an agreement was entered into with Eskom to provide a temporary bulk supply to cover the intervening period from 1957 to 1961.

Selecting the site

The selection of a suitable site for another large power station in the immediate vicinity of Cape Town presented some difficulty. The principal factors to be considered in selecting a suitable site were proximity to the load to be supplied, an adequate supply of cooling water for the condensers, convenient rail access for the delivery of coal and proximity to labour.

After a thorough investigation it was realised that no suitable coastal site was available that would enable sea water to be used for cooling purposes and thereby avoid the additional complication and expense of cooling towers. The cost of constructing suitable cooling water intakes from the open sea anywhere on the shores of Table Bay would have been prohibitive, largely because of the problems associated with having to deal with the large quantities of seaweed and silt that are washed up on the shores during north-westerly winter gales. Similarly, there were no suitable sites along the False Bay coast. As the use of sea water was therefore ruled out the only other alternative was to resort to the use of cooling towers on an inland site.

In the search for a suitable inland site with an adequate supply of cooling water, attention was turned to the City's main sewage disposal works at Athlone where some 10 million gallons (about 45 million litres) of clarified sewage effluent were being discharged to waste each day. The use of sewage effluent as a cooling medium in modern power stations was not an unusual practice at the time and was certainly cheaper than using fresh water, the more conventional alternative. A suitable site was located across the national road from the Athlone sewage disposal works, which site also had the added advantage of being within a reasonable distance of the South African Railway's marshalling yards at Woltemade. The site was also covered with a prolific growth of Port Jackson wattle and numerous stone pine trees that would provide shade and insulate the station somewhat from the neighbouring residential area of Pinelands.

The land was Council-owned and large enough to accommodate two adjacent power stations with a combined generating capacity of 360 MW, and without in any way obstructing the landing of aircraft on any of the four aerodromes in the vicinity. Although it was initially the intention to construct only a 180 MW power station, thought was nevertheless given at the time to the possibility that it might prove necessary to construct a further power station of similar capacity sometime in the future. At this early stage, however, steps were taken in 1948 to obtain the necessary authorisation to proceed initially with the construction of a single 180 MW power station.

Design features

Because of the City's relatively light night-load it was determined that the optimum rating of individual machines should be no larger than 30 MW. It was accordingly decided that the power station would be equipped with six 30 MW turbo-alternators, generating at 11 kV, and eight chain-grate stoker-fired boilers, each supplying 260 000 pounds of steam per hour at a pressure of 635 psig and superheated to a temperature of 915F.

At the same time a detailed study had indicated that future development of the Council's transmission system should be undertaken at 66 kV rather than 33 kV as in the past. To integrate this new power station into the future transmission development programme, therefore, a 66 kV switch house was also incorporated in the design.

The main building, which was designed to accommodate the ultimate complement of six turbo-alternators and eight boilers, is based on a steel-framed brick-clad structure, the exterior courses being red or blue face brick and the interior walls golden-brown brickwork surmounted by colour-washed plaster. The adjoining switch house and office block, and the change room block and the workshop building are of reinforced concrete and face brick construction to match the main building in external appearance.

The two chimneys, each 326 feet (about 100 metres) high, are located to the rear of the main building and constructed largely of red brick standing on an octagonal reinforced-concrete pile cap and lined internally with a two inch (about 2,5 cm) layer of fibre glass insulation overlaid by a single course of bricks.

The two cooling towers, each 283 feet (about 86 metres) high, are of the natural draft type and of reinforced-concrete construction.

Coal is delivered by rail to an exchange siding one mile (1,6 km) eastward of the power station, from which point the coal-laden trucks are hauled onto the site by the power station's diesel-electric shunting locomotive, weighed and then emptied into an underground hopper. The coal is then transported on an enclosed conveyor belt system to the coal store and the overhead bunkers in the boiler house. Because of the proximity of the power station to residential areas special care was taken in the design of the coal-handling plant to minimise the likelihood of any dust and pollution problems.

The progressive and appreciable deterioration in the grading of coal delivered to the Table Bay power station over the years was the cause of some concern and necessitated serious consideration being given to the type of boiler to install. Of the three main types available, namely pulverised fuel, spreader-stoker and chain-grate stoker, the first two were probably the most suited to burning the poorer grade of coal then being received. Other factors, however, had to be borne in mind, namely the disposal of ash and the effective removal of grit and fly-ash from the flue gases discharged from the chimneys. This latter aspect was most important because of the close proximity of residential areas. It was accordingly decided to adopt chain-grate stoker-fired boilers, which would not only minimise the carry over of fly-ash but would also enable economic advantage to be taken of the existing ready market for the sale of clinker ash, mainly for the manufacture of so-called "clinker bricks".

The main 66 kV switchgear, of the small-oil-volume (sov) type, is accommodated in two widely-separated three-storey switch houses forming the east and west wings of the switch house and office block.

Construction

Once all the necessary approvals had been obtained, including that of the Provincial Administrator which was obtained in 1955, immediate steps were taken to issue the tender documents for the first stage of the development, namely the steel-framed building, three turbo-alternators and four boilers, together with all associated auxiliary plant and equipment. By the end of 1956 orders had been placed for two turbo-alternators, three boilers and the steel-framed building.

First steps in building this new power station were taken around the middle of 1957, with the award of the civil contract for the foundations and below ground work. Soon after commencing work, however, subsoil conditions necessitated a change in design from spread-footing foundations to reinforced-concrete pile foundations. At this time the Council also exercised its option and increased the initial orders by a further boiler and turbo-alternator, making a total of three turbo-alternators and four boilers for the first stage.

To enable the Council to implement an undertaking given to the Cape Town Foreshore Board that the Dock Road power station would be decommissioned and demolished as soon as possible after the commissioning of the Athlone power station - planned for 1961 - and also because the temporary bulk supply agreement with Eskom terminated in the same year, Council decided towards the end of 1957 to extend the Athlone power station by a further turbo-alternator and two boilers to avoid a possible power shortage in 1962. Tenders for the plant for this second stage, which would bring the total capacity up to four turbo-alternators and six boilers, were accordingly invited in 1958.

During 1959 it was decided to extend the building to its full size immediately but only to install plant progressively in stages and of sufficient capacity to meet the immediate needs of the City's consumers. By the end of the year the erection of the first stage of the steel-framed building was virtually complete and the first chimney had been erected.

The first boiler underwent final inspection by the Inspector of Machinery on 26 October 1960 and a provisional permit was granted to raise pressure and steam the boiler. Soon afterwards, on 8 November 1960, the first turbo-alternator was run-up and connected to the system for the first time for testing purposes, but because of balancing and adjustment problems this unit only became available for regular operation on 11 January 1961. As the first machine was now available for service, with a further two expected to follow later in the year, a start was made early in 1961 on building up coal reserves for the winter and by April stocks were at an adequate level of 18 000 tons. This coal was of a quality and grading similar to that then being supplied to the Table Bay power station.

The second turbo-alternator was placed in commercial operation soon after the first, with the third following later in the year, thereby making available a total of 90 MW of extra generating capacity on the Council system. Initially this plant was operated daily on a two-shift basis only, but the following year, 1962, it was run on a continuous three-shift basis throughout the year to meet the increased night-load on the Council's stations. This increase in the night-load was a direct consequence of the independent operation of the Council's system following the termination of the temporary bulk supply agreement with Eskom at the end of 1961. By the end of the following year a fourth turbo-alternator and fifth boiler had been commissioned further raising the available capacity of the station to 120 MW.

Official opening

In accordance with the assurance given to the Foreshore Board some years ago, the old Dock Road power station that had served the City so well for 58 years was shut down and demolished in 1962. This historic event, however, was completely overshadowed by the official opening of the Athlone power station on 15 August 1962 by the Mayor, Councillor A H Honikman. Some 400 guests were given the opportunity of discovering what goes on behind the scenes of a modern power station. The station was officially named the Athlone "A" power station since at that stage it was still considered that a further power station, Athlone "B", might be built on the same site at some future date.

In 1963 it was decided to extend the power station to its ultimate capacity of 180 MW and at the end of the year tenders were invited for a further turbo-alternator and boiler, followed a year later by another enquiry for a final turbo-alternator and boiler to complete the extension of the station.

With the acceptance of the sixth turbo-alternator and the eighth boiler for commercial operation on 1 April 1967, some ten years after the first contracts were placed, the station was finally fully equipped to its ultimate generating capacity of 180 MW. The station's full rated output of 180 MW was obtained for the first time a few months later on 22 August 1967.

Dust and noise abatement

Because of the proximity of the site to the residential area of Pinelands special arrangements were made during the design stage to avoid any dust nuisance by providing covered storage for the coal. In addition, particular attention was paid to noise abatement and soot fall-out from the chimneys. To this end a special agreement was negotiated and entered into with Pinelands.

But soon after the station went into limited two-shift operation on a daily basis in 1961, complaints started coming in from residents concerning the noise and dust nuisance allegedly created by the operation of the power station. Every complaint was thoroughly investigated and in several instances it was conclusively determined that not all dust deposits emanated from the power station. In an attempt to further minimise the noise level silencers were fitted to the blow-down drain exhaust pipes to reduce the noise of escaping steam to a level that would not constitute a nuisance. The fall-out of dust and grit from the chimneys during periods when boilers were being brought into service, however, continued to give cause for concern. Preliminary tests carried out on the dust handling plant under different operating conditions indicated that major alterations to the grit arrestor plant would be essential and the manufacturers undertook to give priority to this work.

Although the fitting of silencers to the outlets of all drain vessels had resulted in a reduction in noise level it was nevertheless considered that it might be lowered even further by additional modifications. This was eventually achieved in 1967 by the interconnection of the superheater drain piping to utilise all blow-down vessels simultaneously, thereby significantly reducing the noise level during draining periods. As a consequence the noise level was such that it was no longer audible in Pinelands.

A few years later, in response to an official request from Pinelands, the dust collectors of one boiler were tested to demonstrate that subject to normal maintenance and cleaning procedures, the contractual guarantee regarding dust emissions had been maintained in service. The independently monitored tests were satisfactory and compared most favourably with the original acceptance figures.

But over the years occasional complaints of dust and soot fall-out continued to be received from the residents of Pinelands. Finally, after a further official request in 1982, a firm specialising in the measurement of dust emissions was engaged to carry out tests on each of the two types of boiler at the power station. Following these tests particular attention was paid to the control of emissions from the chimneys and to this end special instrumentation to measure and monitor boiler smoke density was fitted to two boilers.

For economic reasons the power station was effectively shut down from 1985 to early 1995, with all power during this period being purchased from Eskom in terms of a special agreement. With the return of the station to full commercial service in January 1995, however, attention was once again turned to the question of dust fall-out and noise levels. Although the dust emission levels from the chimneys are well within statutory limits it is nevertheless proposed to strive for a further improvement by the installation of special fabric-bag filter equipment over a three-year period. Consideration has also been given to further reducing noise levels, and to this end an experimental noise attenuator was ordered for installation towards the end of 1995.

Operational aspects

After the station had been operational for a few years it was noted in 1961 that the concrete surfaces of the cooling towers and circulating water ducts in contact with the sewage effluent were beginning to deteriorate rather rapidly. The surfaces were sandy to the touch and in the worst cases, exposed the underlying coarse aggregate. It was established that this was an acidic reaction involving the clarified sewage effluent. Immediate preventive action was taken by way of lime-dosing the effluent and this treatment was continued throughout 1962 with satisfactory results. As no more effective solution was found to the problem of overcoming the nitrifying action of bacteria in the cooling water system it was decided to continue with this comparatively inexpensive and relatively simple procedure of lime-dosing to increase the alkalinity of the sewage effluent.

Following the international oil crisis experienced at the end of 1973, and the consequential need to conserve fuel oil at the Table Bay power station, the Athlone power station was called upon to increase its load proportionately. The annual output of the station was the highest on record, but this was achieved at the expense of a major overhaul programme which had to be seriously curtailed. Fortunately an improvement in the labour position and the employment of an outside engineering organisation the previous year had enabled the plant overhaul programme to be brought up to date. Plant reliability throughout the year was accordingly good.

Because of a chronic staff shortage some years later that resulted in a backlog of essential maintenance work on major plant during 1981, it proved necessary to place turbine overhaul work out to contract and to hire artisans from the Central Electricity Generating Board (CEGB) in the United Kingdom to undertake the overhaul of one of the boilers. In an attempt to recruit staff the Council authorised the trades of mechanical fitter and electrician to be included along with certain professional posts in an overseas recruitment campaign being conducted at the time.

As mentioned earlier, a programme for monitoring past and present employees who may have been exposed to asbestos fibres through working on thermal insulation materials was initiated around 1990, the testing being undertaken by the Council's Medical Officer of Health. Strict measures based on international standards and statutory regulations had already been implemented concerning the handling of asbestos-derived products, one being improvements to the asbestos workers' change-room and shower area.

In 1992 the condition of asbestos-derived thermal insulation on boiler surfaces exposed to the weather were becoming a cause of some concern. A three-year contract was subsequently entered into with a specialist firm to cover the emergency removal of asbestos, as and when required, to ensure continued compliance with the Occupational Health and Safety Act. Arrangements were also made to enter into a further four contracts to remove and replace weathered lagging before it becomes a problem.

About the same time some concern was also expressed as to the strength of the two cooling towers in the light of their age and their ability to stand up to the gale force winds to which they are regularly exposed. As cooling towers of similar design in the United Kingdom have collapsed in extremely windy conditions it was deemed essential that some remedial action should be taken to avoid the possibility of a similar occurrence at Athlone. Following a detailed study by civil engineering consultants a contract was placed for the strengthening of the cooling towers by means of a number of circumferential steel bands. This work was commenced in February 1993 and completed in April the following year. Shortly after completion it was noted that the vertical reinforcing straps on the lower beam of both towers were showing early signs of surface corrosion. It was proposed that remedial action to rectify this problem would be taken after the winter of 1995.

Temporary shut down of the station

For close on twenty years after the station first went into full commercial operation in 1967, it functioned largely in a conventional role meeting the system base load. But more recently, when a bulk supply was taken from Eskom to supplement the Council's own generating resources, Athlone was obliged to act essentially as a regulating station meeting the peak loads rather than the base load, as previously. But in 1985 the picture changed completely with circumstances arising that were to lead to an effective and progressive shut down of the station for close on a decade.

Because of the economic recession then prevailing in the country, Eskom found itself burdened with an excess of generating plant. In order not to have this plant laying unproductively idle, it entered into a so-called "capacity allocation" agreement with the Council in 1985 in terms of which the Council agreed to effectively shut down the Athlone power station and purchase the power that would otherwise have been generated at Athlone from Eskom instead. This agreement, which was clearly economically advantageous to the Council as well as being in Eskom's best interests, is due to expire at the end of 1997.

In terms of the agreement the Council was required to maintain the power station on partial standby, and only run it under emergency conditions or by special prior arrangement with Eskom. During the periods that the station remained effectively non-operational, 50 MW of coal-fired plant was retained on a 24-hour standby basis to meet contingencies on both the Council and Eskom systems.

Problems associated with the shut down

But the limited running of the power station over the past decade brought with it other problems, particularly a decline in staff operational skills and the physical deterioration of idle plant. Attention was accordingly given to retaining in some measure the skills that were tending to decline through lack of continuous operation. This was achieved in part by way of routine operational exercises from time to time.

As the operating staff at Eskom's Salt River No.2 power station were also faced with a similar situation it was agreed that it would be in the best interests of both parties to cooperate in training to retain operational skills. To this end Eskom allowed the Council use of its computer-aided training facility at its Salt River No.2 power station. A reciprocal arrangement was also established whereby operators could be seconded to either power station when plant was run to gain and maintain operational experience. Comprehensive operating and maintenance manuals were also compiled to assist staff in the future because of the dearth of experienced personnel.

Priority attention was also given to the storage of idle plant to prevent its deterioration and boiler wet and dry storage techniques were continually refined to the point where the techniques established are now routinely applied. A slat wetting procedure was introduced to preserve the wood-fill in the two cooling towers. In 1990 consultants reported that if this latter process was maintained the wood-fill should be good for a further 15 years.

A preliminary investigation undertaken by consultants in 1992 into the general condition of the power station for future operation, found the plant to be in excellent condition. A further and more detailed investigation was accordingly undertaken during 1993 and 1994 to determine the economic viability of returning the power station to full generating duties. This study confirmed that the power station was generally in excellent condition and indicated that its future return to full commercial operation was definitely economically viable.

Refurbishment and return to commercial operation

About this time Eskom advised that it intended phasing out the "capacity allocation" agreement that over the past decade had proved financially beneficial to both parties by making optimum use of all generating plant on both systems. As this concession was to be progressively withdrawn over a three-year period from January 1995 to December 1997, and in the light of the positive economic report it was resolved to proceed with the refurbishment of the power station plant and return the station to full commercial operation again.

In accordance with an agreement with Eskom the station was returned to commercial service again on 11 January 1995, after a virtual shut down of nearly ten years. Because of constraints imposed initially by a lack of adequately trained operating staff, the generating capability of the station was raised slowly from two boilers and two turbo-alternators with an output of 50 MW, to three units each and 75 MW a few months later. It is intended that the station now be progressively returned to full service depending upon the rate of progress on the restoration work and the availability of staff.

The above is an edited extract from Lighting Up The Fairest Cape 1895 to 1995, written and compiled by Dennis Palser, Past City Electrical Engineer of Cape Town

After 1995

Between 1995 and 2003 the power station was mainly used to generate power in peak demand periods and during power failures of the national grid. In 2003, significant investment was required due to the age of the power station, and generation was stopped.

The station was decommissioned in 2006. The towers currently serve no useful purpose. Electricity generation on the site was stopped in 2002 and it was decommissioned in 2006. The tower site houses transformers for the transmission of electricity to southern suburbs, and a water reticulation system on site to cool down the transformers.

Athlone is the last coal-fired power station still standing in Cape Town; the others, in the city centre and Salt River, were demolished in the 1980s and 1990s. The cost of transport means that coal costs three to five times more in Cape Town than it does near the mines inland; this makes it more economical to transmit power from there to Cape Town than to generate power in Cape Town from transported coal.