Biomass storage / preparation & pulverizers in biomass power plant

For an efficient and clean combustion, the biomass needs to be prepared in terms of the size range and its remaining moisture, then sorted according to the chemical composition. The variations caused by the different sources should be minimised by proper allocation and mixing. Further processing steps might be taken, such as crushing and screening in order to keep the biomass within a required size range. The handling of the bulk biomass takes place in the preparation area.Measurement of bulk materials is not a trivial task; uneven surfaces, different moisture levels and high levels of dust are some of the main challenges. In some applications suitable level measurement technologies used in the past involved nucleonic sources or maintenance intense mechanical level meters.

KROHNE pioneered the radar level measurement technology for process applications and offers today a broad range of sophisticated FMCW and TDR technologies for liquids and all kinds of solids, for almost every application. The OPTIWAVE-series are FMCW radar level meters suitable for liquids and solids, operating at frequencies ranging from 6 to 80GHz. The patented drop antenna of the OPTIWAVE 6400 avoids the dust build-up that can occur with metallic horns, and drastically improves the reliability and availability of the instrument. It is very useful for the more dusty environments. The OPTIWAVE 6500 is used within the entire handling chain, including the biomass storage and mixing place, and transportation via conveyor belts to the biomass bunkers.

The majority of biomass power plants are fired by pulverised biomass burners which are installed in the boiler walls (wall fired) or in the corners of the boiler (tangentially fired). Low NOx burner design with staged combustion helps to reduce emissions together with a good utilisation of the biomass. The mass flow of biomass to the pulveriser is controlled by the biomass feeder. The pulveriser crushes, dries and classifies the biomass into a defined particle size range. Hot air is used for drying and transportation of the pulverised biomass to the burners. The low NOx biomass burners use biomass and primary air for the initial combustion. Secondary and Tertiary air is used for the further staged combustion. The biomass burners are lit by ignition lances or separate ignition burners. Oil or gas is normally used as the ignition fuel.The burners need to be ignited by a low volatile fuel such as gas or oil until the biomass burners run stable.

The whole start-up and ignition process is controlled by the burner management system which ensures a safe start and operation of the burners. Natural gas fuel use is conventionally measured by dP or turbine flowmeters. The OPTISONIC 7300 ultrasonic gas flowmeter can measure the natural gas flow used for ignition, or for any supplemental burners: it gives immediate response to flow changes and works without any moving parts and so is maintenance free. Also able to offer a high turndown ratio, this flowmeter is suitable for low load and high flex operation, virtually measuring all flows down to zero flow.