adminZesa HOLDINGS is now moving fast having brought the two new large units at Hwange Thermal onto the grid, adding 600MW to its generating capacity and even while the last checks on Units 7 and 8 are being made, work is now starting on the six old 1980s units to restore them to full output.
Hwange Thermal was commissioned between 1983 and 1987 with two batches of generators, four rated at 110MW and two at 220MW. There is general agreement in technical circles that a lot of the general maintenance and parts replacement was not done at the required level, hence the problems with those six for up to 20 years in some cases.
In recent years there has been more work done, but largely to keep them going and if Zesa get almost half the rated output of 920MW from these old six units, everyone cheers.
The refurbishment was planned some time ago, and financing from India lined up, but work could not start until all, but the final checks done on Units 7 and 8.
Now the long process of what amounts to rebuilding Units 1-6 has started, and Zesa need to be praised for moving so swiftly. Even while the final reports on the work needed are being completed for the financiers, Zesa has started with its own resources on the first of the old units.
Again sensibly, Zesa has started with one of the two larger units from the second batch, Unit 5, which when it goes live back on the grid in around one year’s time will add a secure 220MW.
The fact that it will take about a year to overhaul this unit shows the level of work that is required, basically a full rebuild rather than just a couple of weeks of checking the pipes and greasing the bearings.
Each unit at a thermal station is a collection of modules that all have to work properly. Starting with the coal feed, there is the boiler, steam feed, turbine and generator.
Generally the dirty end, the coal feed and boiler, need more frequent part replacement than the cleanest end, the generator, but after more than 35 years, and every one of the old six units at Hwange is older than that, almost anything that can go wrong probably has.
Refurbishing an old power station is a lot cheaper than building a new one. For a start all the civil engineering, the concrete and the like, is still young in civil engineering terms.
Parts of the older external mechanical engineering, the coal conveyer and the pipelines bring and holding cooling water, have already been fixed up and extended to cope with the two new units.
But it is not a simple or cheap operation, as Zesa have been stressing.
In fact, the financing arranged, US$310 million through the Indian Import and Export Bank, sounds like just the spare parts required, and even then Zesa may have to top up that sum with its own resources.
That particular financier is not going to be funding the labour and the refurbishment of components that can be reused, just the things that Indian engineering companies can make, sell and ship, in other words the spares.
That shows the level of the work that is required. Anyone who has been involved in the total overhaul of a motor car engine will understand the sort of work required, taking the unit to pieces, examining every part, replacing those that are worn out or about to fail, getting skilled technicians to work on parts that have seen a lot of use, but can after work go back in the engine, and then refitting everything, making the settings and restarting. The estimate of a year of work on each unit sounds about right.
Zesa could, of course, pull the whole six down at once, hire more staff and work on all simultaneously while we once again sit in the dark for periods each day.
Since those old units can produce something it makes sense to pull them down one at a time, fix it up and as it goes back on line select the next one for overhaul.
Around a decade ago there was some ill-informed comment in some circles that a thermal power station only last 25 years. That is not so and never has been so; there are far older thermals around the world keeping the lights on.
What it does mean is that maintenance schedules need to be rigidly adhered to and perhaps the average lifespan of spare parts might well be 25 years, but so long as they are fitted when needed the station can last many more decades.
Zesa is not the only regional utility that is now faced with major overhauls having missed some of the more routine work earlier.
Eskom in South Africa discovered last year that some wishful thinking in some circles meant that a concentrated effort was now needed to catch up on a lot of more routine maintenance that had not been done.
This is where the load shedding now seen in South Africa is largely coming from as practical engineers are told to start getting things right.
There have been general problems at utilities, to give them their due, that tariffs have not been set at levels that allow proper maintenance, especially as equipment becomes older and the spares bill starts rising.
Regulators, such as Zimbabwe’s Zera, do need to strike a balance between the needs of consumers and the perfection demanded by engineers.
But done properly a regulator should be able by questioning every cost component to reach the point where the utility or power station owner has to be extremely efficient and have the sort of maintenance schedule that fixes problems before the whole unit seizes up, but consumers are not forced to pay for inefficiency, padding or waste.
Like much in Zimbabwe Zesa went through some bad patches, from lack of access to foreign currency for spare parts to its remarkably well-trained engineers and technicians being poached by other utilities in other countries.
Neither helps maintain the maintenance schedule and too much effort is converted to emergency repairs, rather than the sort of engineering we see in, say, aircraft maintenance where every effort is made to ensure that there never is a breakdown to start with.
Presumably we have learned as we must continue learning. There are regrettably no short cuts to quality, and even when all the padding and waste is removed, there are still costs that must be covered if we are to remain with our lights on.
One fortunate change is the expansion in the power stations in recent years. There are now eight units at Kariba South and eight at Hwange Thermal.
This means pulling a unit down for its major overhaul is no longer that big a deal; the other 15 can handle the load and more. Hydro stations tend to see less wear and tear than thermal stations, but even still just about every electrical and mechanical component at Kariba South has been replaced at least once in the 60 years since it was commissioned, and in some places several times.
When the older six units are refurbished and rebuilt at Hwange Thermal the station’s output will be just over 1 400MW, making it Zimbabwe’s largest.
But for a measurable fraction of each year one of the eight units will be down for its planned maintenance, and that is how it ought to be to ensure that what we all want and need, a continuous source of power on the grid, is there all the time.
Online Reporter