Current status of technology

Coal is the fossil fuel with widest resources world-wide. Construction of coal power stations has been steadily going on at high rate in fast developing countries like China and India.

Since the early 1990s in Europe, the highly efficient combined cycle technology fuelled by natural gas has been successfully expanding to replace older fossil units (especially oil-fuelled) and meet increasing demand.

Although continuous efforts to reducing effluents from coal power plants, especially in advanced economies, by increasing efficiency and installing pollution control devices, coal still remains the most polluting power source for its harmful effluents and residues. However, if electricity demand will continue to grow in Europe, coal may continue to play an important role in the energy mix besides natural gas. This is likely to be even more pronounced in case of ban or limited use of nuclear power for base load.

In order to obtain long term acceptability of coal (and other fossil fuels), near-zero emissions requirements will likely become a goal for policy and technology improvement, first in highly industrialized countries but soon also in developing ones. Worldwide research on Clean Coal Technology (CCT) pursues the satisfactorily environmental and economical utilization of coal. Many of the conventional technologies of today can be further improved or refurbished with effective pollution control technologies. CO2 capture for sequestration is an extreme option in line with zero-emission strategy that may be implemented for some power plant technologies. CO2 capture and sequestration technologies are described in a separate Chapter.

The challenges coal (and other fossil systems) are facing are (WCI 2005b):

1. Curbing or virtually eliminating emissions of pollutants such as particulate matter and oxides of sulphur and nitrogen. This has largely been achieved and costs decreasing, but implementation should be continued to as many units as possible and extended to as many countries as possible, if compliance were required with more restrictive national emission (or air/water quality) standards.

2. Increasing thermal efficiency in order to reduce CO2 and other emissions per unit of net electricity supplied to the network. Efficiency of modern technology has been significantly increasing and there is still potential for further improvements.

3. Curbing or nearly eliminating CO2 emissions.

Additionally, the coal industry is also promoting the vision of clean coal as a likely source of hydrogen for stationary and transport applications (WCI 2005b).

Table 2.1 shows a summary of the environmental challenges and how conventional and advanced technologies are coping with them (WCI 2005b). Coal cleaning by washing and beneficiation can reduce the ash content of coal by over 50%, reduce SO₂ emissions and improve thermal efficiency. While coal preparation is standard in many countries, it could be usefully extended in developing countries as a low-cost way to improve the environmental performance of coal use (WCI 2005b; Eliasson and Lee (Eds) 2003).

Table 2.1 Environmental challenges and technology response of coal power plants;

reworked after (WCI 2005b).

Environmental Challenges

Technological response Status Technology maturity

assumed for LCA modeling Particulate Emissions Electrostatic precipitators and

fabric filters, with removal

Trace Elements Particulate control devices, fluidized bed combustion,

the use of low NOx burners, advanced combustion

SOx Technologies are available to

reduce SOx emissions, such prior to combustion is a very cost-effective method for

fly ash in cement making) is steadily increasing.

Table 2.1 (cont.) Environmental challenges and technology response of coal power plants; towards the end of the 20th century and, with the benefits and is well suited to co-combustion of coal with

CO2 sequestration ‘Zero-emissions

technologies’ (ZET) to enable

CO2 separation, capture and geological storage

Emissions of particulate is controlled by electrostatic precipitators (ESP), fabric filters (baghouses), wet particulate scrubbers, and hot gas filtration systems. Electrostatic precipitators use an electrical field to charge the particles in the exhaust; the particles are attracted by collecting plates. Fabric filters are made of a tightly woven fabric. Both systems have very high particulate removal efficiency, well above 99%. (WCI 2005b)

The identification of health and environmental effects due to SOx emissions (e.g. respiratory diseases, acid rain) has imposed the development and utilisation of specific control technologies. Flue gas desulphurisation (FGD) technology removes SO2 from the flue gas by means of absorption in lime or limestone as the most dominant technology option. This can be achieved in wet (the most widely diffused technology) as well as in dry scrubbers. Wet scrubbers can achieve removal efficiencies up to 99% (WCI 2005b), but on the average they work at efficiency 90-95%, due to cost and operation optimization. The cost of FGD units has reduced by two third from the 1970s (see Figure 2.1).

Figure 2.1 Reductions in FGD costs in the USA (WCI 2005b).

NOx reduction technologies include low NOx burners, selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). Low NOx burners and burner optimisation minimise formation of NOx during combustion. Conversely, SCR and SNCR treat the NOx post-combustion in the flue gas. SCR technology can achieve 80%-90% NOx reduction. It is commercially available in Japan since 1980 and in Germany since 1986 (WCI 2005b). There are about 15 GWe of coal fired SCR capacity in Japan and nearly 30 GWe in Germany, which together makes 85% of the total worldwide. SCR demonstration and full-scale systems were installed in US coal-fired power plants in the 1990s (WCI 2005b).

For CCT, key factors to take into consideration can be summarized as follows (IEA Clean Coal (2005 b):

− various cost components for plant construction and operation;

− characteristics and cost of coal;

− thermal efficiency, load range, and operational flexibility; for Combined Heat &

Power (CHP) units, the pattern of heat demand;

− compliance with environmental requirements, and what operational constraints this determines;

− maturity of technology.

Figure 2.2 schematically shows the progression in CO2 reduction from coal combustion.

Figure 2.2 The coal-fired route to CO2 reduction (WCI 2005b).

The efficiency of average plants in many developing countries is around 30%, but individual, especially small size and old units may have much lower rating. OECD average plants have efficiency around 36% (WCI 2005b), but individual countries may reach averages up to 40%

(Röder, Bauer, Dones 2004). New supercritical plants can achieve overall thermal efficiencies in the 43-45% range and even up to 47% with suitable waste heat sink (WCI 2005b).

Individual current and future technologies will be described in the following Chapters.