Co-firing of agricultural fuels in a full-scale fluidized bed boiler

An experimental campaign was carried out at a power plant to specify the challenges related to fluidized bed combustion of agricultural fuels and demonstrate a technically viable concept for establishing a 20% share of agricultural fuel co-fired with woody biomass. Sunflower seed hull pellets and oat seeds (unsuitable for food purposes) were co-fired with wood chips. The share of agricultural biomass varied, reaching up to 30%, on a received mass basis. Deposit probes, gas and solid samplings by a Dekati low-pressure mass impactor (DLPI) and an electrical low-pressure impactor (ELPI), and a Fourier transform infrared (FTIR) analyzer were utilized to monitor the risk of high-temperature corrosion, slagging, and fouling. Fluidized bed behavior was monitored by taking samples directly from the bed. emperature fine-particle sampling was successfully applied for high-potassium and high-phosphorus fuels. Formation of potassium silicate was shown to have the main role in the furnace-wall slagging process. The technical concept of combustion of agricultural fuels by bubbling fluidized bed technology was successfully demonstrated and established. It includes operation below 750 °C bed temperature and ensuring furnace-wall cleaning by means of in-furnace water cannons. The high-temperature corrosion risk can be mitigated by sulfur addition.