The power-producing industry is shifting and starting more and more to use fuel based on biomass and waste.
The driving force behind this is to contribute to the sustainability goals. Since biofuels burn faster and cleaner than fossil fuels, they will release greenhouse gases at a lower and slower rate. Secondly, the use of biofuels will allow the economy to reap its benefits. Using waste as a fuel for power plants is all about the reuse of waste that would just end up in waste dumps. Both these fuel types are growing and becoming more and more common.
However, the power plant operations and maintenance managers will get a lot of challenges with services and operational efficiency when biomass and waste are being used compared with fossil fuels.
Using Biomass and waste as a fuel for power boilers also creates new challenges related to fouling because it is a more complex fuel to burn. The challenges are, however, different.
Challenges related to waste fired power boilers
Combusting, e.g., waste, is difficult partly due to the chemical constituents of the fuel but also due to the variation in the fuel. These properties can lead to heavy fouling, sometimes creating deposits/slag in a high-temperature region that becomes impossible to remove by sootblowing if sootblowing isn’t performed frequently enough. The ash is also aggressive, with high contents of, e.g., Chlorides, Zinc, and Potassium, creating corrosive ash.
This often leads to a clogging issue needing to be solved, i.e., an economizer is blocked during the operational season, despite steam sootblowing, forcing shutdown for off-line manual cleaning. Such shutdowns are related to considerable costs in lost production/ lost fuel combusted (combusted waste is an income) and the cleaning cost.
Another consequence is that you want to optimize the boiler, e.g., reducing the use of steam for sootblowers or keeping the heat exchangers cleaner, thereby increasing heat transfer and boiler efficiency.
Both these examples make the operation of the plant more sustainable since more energy is produced for a certain amount of fuel. During the last years, we have seen an ever-increasing interest in reducing emissions that this entails.
Challenges with power boilers using demolition- and waste wood
It is well known that the combustion of demolition- and waste wood results in significant economic benefits in the form of reduced fuel costs, while demolition- and waste wood increases the risk of boiler damage and reduced availability.
Many of the problems arising when starting to use demolition- and the properties of the ash cause waste wood as fuel. You will get an Increase in ash volume. Demolition- and waste wood give 2-5 times more ash than wood chips.
It will also lead til heavier fouling. Demolition- and waste wood ash sinters more easily and can create deposits/slag that is impossible to remove by sootblowing. The ash is more aggressive. It increases the amount of Chlorides, Zinc and Potassium create corrosive ash.
The changed properties of the ash impact both operational and maintenance costs.
Some common problems from fouling of demolition- and waste wood ash on boiler heating surfaces are:
- Flue gas temperature zones are moved, which can result in high-temperature corrosion of low-alloy heat exchangers
- Need for cleaning outages during the heating season to mechanically remove sintered / solidified ash
- Reduced boiler efficiency due to poor heat transfer
- Low-temperature corrosion in economizers and air preheaters due to aggressive ash and changed condensation temperatures
What can be done to minimize these challenges?
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