Pulverized Fuel (PF) combustion Technology

Pulverized Fuel (PF) combustion Technology

Conventional pulverized fuel (PF) combustion is a common form of proven generation technology found throughout the world. Finely ground particles of coal are blown into a boiler where they are burned. The heat released is collected through the water walls of the boiler and a series of subsequent heat exchangers, producing high pressure steam. This steam is passed through a steam turbine which in turn drives an electric generator. Although PF plants can be built over a wide range of sizes, for the purposes of this study, PF steam plant is considered suitable for large-scale (greater than 300 MW) schemes where coal is the primary 

fuel used for generation.

Many different configurations of steam plant are possible, either for cogeneration (combined heat and power) or electricity-only applications. Within the scope of this study, we do not consider cogeneration applications further.

The key design feature of a conventional PF plant is the pressure and temperature at which steam is generated. The majority of plants in the UK (in fact, all that are operational today) operate at subcritical steam conditions. Supercritical boilers, however, are well proven technology which would likely be constructed today owing to their greater level of efficiency. A new subcritical conventional PF plant can achieve an overall net efficiency of about 38-40 per cent compared to a new supercritical plant that can achieve a net efficiency of about 42 per cent.

Looking towards the future 15 to 20 years, it is likely that more exotic materials will enable the pressure at which steam is generated to increase further. These ‘advanced-supercritical’ plants will probably achieve yet higher levels of efficiency, perhaps 44 percent, albeit at a slightly higher capital cost over supercritical plants.

Emissions control is an important aspect of all types of PF steam plant. These costs can be minimised, however, if prior consideration is given to the location of power plant and the specification of the fuel burned. For the purposes of this study, we assume that a prospective developer of a PF steam plant will optimise the plant to incorporate the following design features:

• Moderate sulphur coal (blending coals so that the sulphur content is less than 2 per cent by mass) in order to take advantage of the seawater flue gas desulphurisation process, which avoids the additional cost of sorbent such as lime or limestone.

• Low NOx combustion system, with allowance in the boiler design for selective catalytic reduction (SCR) plant and equipment to be fitted at a later date.

• Use of bag filters to control the emission of particulates.

With these design features, a new PF plant (subcritical, supercritical or advanced supercritical) will meet environmental legislation as set out in the LCPD and be considered as a ‘best available technique’ (BAT).