7.2.4.3 Power plants

Although biomass may also be used for district heating systems, similar technological considerations arise for all large combustion systems, and the heat energy may be used for many combinations of heat and power. Fig 7.12 shows how many different routes may arise.

Source: ref 7.7
Figure 7.12 Overview of biomass conversion routes for power production

 

A typical power plant with direct combustion is shown in fig 7.13 which can be applied to use any solid fuel (the main differences arising in preparation and processing), and cofiring of biomass with coal also has potential advantages. This cycle is frequently also used with steam extraction to provide both heat and power.

Figure 7.13 Direct combustion steam turbine system

 

Internal furnace design covers a wide range, from simple fixed grates through to pulverised fuel burners. For combustion of fresh biomass, a common design is the sloping grate furnace, which allows pre-drying of the fuel in the upper part of the furnace prior to it falling under gravity onto a reciprocating grate lower in the furnace where combustion takes place. Since the grate is water- or air-cooled, it does not need an ash layer to insulate it from high temperatures, which makes it more suitable for low ash biomass fuels.