NATURAL GAS
NATURAL GAS IN GASEOUS STATE IN SOYO
An infrastructure of hundreds of kilometers of submarine pipelines collects gas from various petroleum production units and transports it to Soyo’s terminal where it is treatedand liquefied for export. The configuration of the terminal Angola LNG accounts for about 3,5 Mm3 per day (about 1,3 annual BCM) in a gaseous state for local use.
This gas for local consumption is delivered at a constantflow rate, however the available storage in the pipeline between the terminal and the power plant - the so-called “line pack” - and any other gas storage that may be built, will allow its consumption to be concentrated in some hours of the day. The graph in Figure 37 shows the power that could be installed in Soyo, based on the available gas, considering different usage scenarios and different technologies.
The transport grid – a double 400kV line - should allow a power transmission up to 1.500 MW towards the South, which is a value compatible with the operation in combined cycle concentrated in 50% of the time or at 50% load, using all the available gas.
If the installation of a power generation capacity around 1.500 MW is decided, it will be important to guarantee a “dual fuel” solution to account for dry hydrological years - possibly based on LNG, LPG or diesel - that enables the operation of such capacity at 90 to 100% utilization levels in those type of years. On the other hand, the possibility of occurrence of years with higher hydro production increases the interest in developing an interconnection infrastructure - particularly with Congo - to allow the export of the surplus production.
ANALYSIS OF THE GENERATION POTENTIAL BASED ON THE AVAILABLE GAS IN SOYO FOR NATIONAL CONSUPTION
SOYO'S LIQUEFIED NATURAL GAS
The terminal Angola LNG is designed for the liquefaction and export of about 6 Bcm of natural gas - about 5 times the volume of gas available in gaseous state.
The liquefaction process is carried out by reducing the gas temperature to -162º C, which reduces occupied volume by about six hundred times. Current technology allows: i) either the transport in large LNG carriers to large-scale regasification terminals in distant countries; ii) or the transport in small LNG carriers to small / medium maritime terminals; iii) or even the shipping into small iso-containers or tanks transported by land, sea or rail to small storage and regasification units near the consumer.
Regarding the Angolan power sector, LNG can be used either to power a medium-sized LNG terminal in Benguela/Lobito or Namibe, associated with new large power plants, or to fuel small storage and regasification units, associated with smaller turbines. However, the interest of signing long term contracts for the majority of available LNG and the investment required to receive and regasify LNG, make the conversion interesting only for plants with an expected stable operation.
Although it is predicted that by 2025 the majority of the existing simple cycle turbines will be operating as backup, there will be the need in each system to maintain a generation unit for regulating the operating frequency and for spinning reserve. The lower need for generation in Luanda should allow the relocation of the existing turbines installed in barges from Boavista to Namibe and to Benguela/Lobito.
These units, together with the average sized combined cycle installation in the Cazenga power plant will be able to fulfill such regulation functions. That being so, these plants are expected to be converted to LNG, keeping the remaining “backup” turbines fueled by diesel.
The installation of storage and regasification infrastructure across the country will also benefit the industry, which will have an additional alternative source of energy.
NATURAL GAS IN CABINDA
The recent discoveries of natural gas “on-shore” in Cabinda make feasible the conversion of turbines in Fútila to natural gas. If this gas does not show technical or economic conditions to power the generation, then the LNG alternative should be considered to reduce system costs.
NEW DISCOVERIES SOUTH OF LUANDA
Recently, significant new discoveries of natural gas in blocks located south of Luanda have been announced. This gas, depending on the size and cost of extraction, may be able to use the existing infrastructure of subsea pipelines and enhance or extend the life of the terminal in Soyo, or may enable a new liquefaction plant south of Luanda - in Benguela or Porto Amboim, or even just be used for domestic consumption associated with large industry, petrochemical or generation projects. The final solution will depend on detailed studies over longer periods, thus it is not expected availability of this gas on the horizon of 2025.
Nevertheless, the vision for the infrastructure to be developed on the horizon of 2025 should have this perspective into consideration, preparing the system for the possibility of receiving significant generation in the region of Porto Amboim or Benguela, if that does not imply a significant increase in short-term costs.
STRUCTURAL OPTIONS CONSIDERED
Four alternative scenarios of development of new large power plants fueled by natural gas were established, to be considered combined with the different hydroelectric alternatives (figure below).
The first alternative is the full use of Soyo’s resource potential and power infrastructure by installing two additional combined cycle units of about 360-400 MW each. This is the lowest cost scenario but implies greater concentration of power generation in the north.
A second alternative is to build a new gas generation center in Benguela/Lobito with the installation of a medium sized regasification port terminal associated with the installation of up to 1200 MW of generation. In the future, the new gas discoveries could feed directly this new center. In this
scenario the existing plant in Soyo would work base load, freeing up some gas for industrial projects. The combination of the two previous alternatives is feasible with just 360-400 MW in Soyo and the installation of the remaining power in Benguela or Lobito.
Finally, the alternative of increasing the investment in regional diversification is considered, with some increased costs associated with the installation of a medium-sized terminal in Benguela/Lobito and a smaller one in Namibia, to power a generation unit of 200 to 400 MW.
DESCRIPTION AND COST OF THE 4 ALTERNATIVE SCENARIOS OF STRUCTURING GAS GENERATION