By Mthunzi Luthuli
Some people have questioned whether South African ports can “handle” powerships and whether the transmission substations can “handle” the power from the powerships.
This column addresses these two concerns. I will start by explaining the general arrangement and configuration schemes around floating vessel power plants.
General concept and vessel configuration schemes
Often people mistakenly use the term FSRU (Floating Storage and Re-gasification Unit) to refer to the powership, which is the actual power plant/power station on a ship. The FSRU is usually a separate vessel/ship, whose purpose is to store LNG (liquified natural gas) in large, usually spherical storage tanks and, on a daily basis, convert a certain quantity of the LNG into natural gas (that is non-liquified). This gas is then piped directly to the powership, which will be moored about 200 metres or so from the FSRU.
The natural gas serves as the fuel for the gas turbines that generate electricity on-board the powership. Generated power is stepped up at the HV Substation, which is also on-board the powership. A connection point is provided to connect a transmission line that delivers the power to a substation on shore.
Some companies have FSRUs whose capacity can fuel multiple powerships of up to 500 megawatts each, simultaneously.
Sometimes, particularly with smaller power schemes, the FSRU is replaced by two vessels, an LNG Storage Vessel and a separate vessel that only does the re-gasification, usually called an FRU. In such configurations, one ends up with three vessels. This configuration is obviously not desirable from an operational and cost perspective.
South African Ports
These vessels need to ideally be moored within the boundaries and confines of a port, where the waters are calm compared to the water in the deep blue sea. However, they do not need to be berthed on quays. Secure and reliable buoy moorings systems are used. Therefore, the dimensions of the vessels don’t matter that much. What matters are the draft requirements of the vessels.
A vessel’s draft requirement is the minimum depth of the water below surface. It’s important to specify the draft to ensure that a vessel does not hit the bottom of the ocean and run aground.
The port where a powership will moor has to have at least the minimum draft specified for the vessel.
The Economic Interventions Forum of South Africa (EIFSA) has proposed that the ports of Richards Bay, Ngqura and Saldanha be the ones that are used as “homes” for these vessels. The port of Saldanha has a draft of up to 17 metres. Richards Bay and Ngqura have maximum drafts of 16 metres. Karpowership’s biggest vessel requires a draft of 7 metres. So, these three ports (and all of the big commercial ports) in South Africa can easily handle these vessels.
In fact, one of these vessels docked at the port of Cape Town last year on the 19th of April on its way to Brazil. And the port of Cape Town is shallower than EIFSA’s three proposed ports.
Connection to the Grid
Power can be obtained from the Karpowerships, specifically at voltages of 40kV up to 400kV.
Given the transmission voltages that we use in South Africa, we can use 132kV, 275kV and 400kV voltage tap points on the powerships. So, there is no problem there. And the main thing that we have to worry about at the transmission substations is whether or not we need new bays with their own transformers, breakers, protection relays, etc., and if we do, whether or not it would be possible to build them, given the designs (i.e., fault levels, busbar ratings, etc.) and layouts of the substations.
This matter has been investigated, and the results are that, yes, these substations can indeed accommodate new incomers from the powerships after doing a few minor upgrades of the substations. The results are summarised in the table below.
It should also be noted that making use of these powerships at the ports we have identified will have the added benefit of strengthening the electricity network in these areas, thus improving the overall stability and reliability of the grid.
It’s not true that our ports cannot accommodate powerships or that the power generated by the powerships cannot be injected into the grid. The designated ports for powerships can easily handle the powerships and their FSRUs.
The transmission substations closest to the ports can be upgraded to accommodate the new transmission incomers from the powerships.
The concept of using powerships is neither new nor complicated. Powerships have been used in many countries on our continent and around the world. Our government and Eskom simply need to decide and act quickly before it’s too late.
* The next article on this subject will deal with the economic viability of powerships.
Mthunzi Luthuli is the CEO of Economic Interventions Forum of South Africa (EIFSA).