Abstract
M.Sc.
The increased demand for electricity in South Africa is expected to exceed supply between
2004 and 2007. Electricity supply options in the country would be further complicated by the fact
that older power stations would reach the end of their design life beyond the year 2025. In light
of this and considering the long lead times required for the commissioning of new plants, new
power supply options need to be proactively investigated.
The environmental impacts associated with coal-fired generation of electricity have resulted in
increased global concern over the past decade. To reduce these impacts, new technologies
have been identified to help provide electricity from fossil fuels. The alternatives considered are
gas-fired generation technologies and the Integrated Gasification Combined Cycle (IGCC).
This study attempts to document and understand the environmental aspects related to gas-fired
and IGCC electricity generation and evaluate their advantages in comparison to conventional
pulverised coal fired power generation. The options that could be utilised to make fossil fuel
electricity generation more environmentally friendly, whilst remaining economically feasible,
were also evaluated.
Gas-fired electricity generation is extremely successful as electricity generation systems in the
world due to inherently low levels of emissions, high efficiencies, fuel flexibility and reduced
demand on finite resources. Associated benefits of a Combined Cycle Gas Turbine (CCGT) are
lower operating costs due to the reduced water consumption, smaller equipment size and a
reduction in the wastewater that has to be treated before being returned to the environment. A
CCGT plant requires less cooling water and can be located on a smaller area than a
conventional Pulverised Fuel (PF) power station of the same capacity. All these factors reduce
the burden on the environment.
A CCGT also employs processes that utilises the energy of the fuel more efficiently, with the
current efficiencies approaching 60%. Instead of simply being discharged into the atmosphere,
the gas turbines’ exhaust gas heat is used to produce additional output in combination with a
Heat Recovery Steam Generator (HRSG) and a steam turbine. Furthermore, as finite resources
become increasingly scarce and energy has to be used as wisely as possible, generating
electricity economically and in an ecologically sound manner is of the utmost importance. The
clean, reliable operation of gas-fired generation systems with significantly reduced noise levels
and their compact design makes their operation feasible in heavily populated areas, where
electricity is needed most. At the same time, energy can be consumed in whatever form
needed, i.e. as electricity, heat or steam.
The dependence of the South African economy on cheap coal ensures that it will remain a vital
component of future electricity generation options in the country. This dominance of coal-fired
generation in the country is responsible for South Africa’s title as the largest generator of carbon
dioxide (CO2) emissions on the continent and the country could possibly be requested to reduce
its CO2 emissions at the next international meeting of signatories to the Kyoto Protocol.
Carbon dioxide emissions can be reduced by utilising gas-fired generation technologies.
However, the uncertainty and costs associated with natural gas in South Africa hampers the
implementation of this technology. There are currently a number of initiatives surrounding the
development of natural gas in the country, viz. the Pande and Temane projects in Mozambique
and the Kudu project in Namibia, and this is likely to positively influence the choice of fuel
utilised for electricity generation in the future. The economic viability of these projects would be
further enhanced through the obtaining of Clean Development Mechanism (CDM) credits for
greenhouse gases (GHG) emissions reduction.
Alternatively, more efficient methods of generating electricity from coal must be developed and
implemented. IGCC is capable of achieving this because of the high efficiencies associated with
the combined cycle component of the technology. These higher efficiencies result in reduced
emissions to the atmosphere for an equivalent unit of electricity generated from a PF station.
An IGCC system can be successful in South Africa in that it combines the benefits of utilising
gas-fired electricity generation systems whilst utilising economically feasible fuel, i.e. coal. IGCC
systems can economically meet strict air pollution emission standards, produce water effluent
within environmental limits, produce an environmentally benign slag, with good potential as a
saleable by-product, and recover a valuable sulphur commodity by-product. Life-cycle analyses
performed on IGCC power plants have identified CO2 release and natural resource depletion as
their most significant positive lifecycle impacts, which testifies to the IGCC’s low pollutant
releases and benign by-products. Recent studies have also shown that these plants can be built
to efficiently accommodate future CO2 capture technology that could further reduce
environmental impacts.
The outstanding environmental performance of IGCC makes it an excellent technology for the
clean production of electricity. IGCC systems also provide flexibility in the production of a wide
range of products including electricity, fuels, chemicals, hydrogen, and steam, while utilizing
low-cost, widely available feedstocks. Coal-based gasification systems provide an energy
production alternative that is more efficient and environmentally friendly than competing coalfuelled
technologies. The obstacle to the large-scale implementation of this technology in the
country is the high costs associated with the technology. CDM credits and by-products sales
could possible enhance the viability of implementing these technologies in South Africa.