Continuing our overview of dust explosion prevention in the Biomass Industry (See Part 1 here), today we are looking at the key challenges to explosion prevention and what you can do face them.
Biomass faces many challenges to dust explosion prevention that are unique to its industry. As stated in part 1, biomass plants producing the likes of wood pellets and wood chips can be prone to high levels of combustible wood dust without proper maintenance and supervision.
Biomass Storage
The real challenge for dust explosion prevention in the modern biomass plant is large scale storage. If you run a biomass factory, plant or mill, it is integral that you assess all areas of your plant.
You need to a carry out a complete spec of your entire premises with a particular emphasis on easily hidden spaces and crevices, along with all open areas that are prone to wood dust buildup. This is a key component in compiling a risk analysis of your operation.
Via Wiki Commons. This work has been released into the public domain by its author Tom Bruton.
Storage is a key problem in the UK due to being an Island without any real or substantial supply of biomass for its power plants.
The UK has to import biomass materials from all over the globe. This becomes a major issue for biomass plant as this requires large silos for continuity of supply. The sheer size of the silos pose many issues for dust explosion prevention in the biomass industry, even from just a spacial point of view.
Issues with Available Data
The above problems are further compounded by an insufficient amount off information avertible around large-scale silos.
In actuality, there isn’t enough data from previous incidents for silos greater than 10m diameter or greater than 2,500 tonnes.These fires are rare occurrences for most fire and rescue brigades and are different from conventional fires in many ways.
There is no standard explosion vent calculation for volumes over 10,000m3 and CFD modeling has to be used.
These silos are nearly the size of football stadiums. We assume that if the silo is nearly full the vent calculations are correct, the explosion is similar to that relationship up to 10,000m3 but if the fall is from 20 to 30m from the open inlet of a 15 to 30 m diameter enclosure, then the impact zone dust cloud at the bottom, may be less than 10% of the total volume.
We may only expect a reduced explosion pressure Pred of 0.1barg. Typical to the standard burst pressure of most explosion panels. The enclosures may be pressure rated from 0.3 to 1 barg, so the explosion pressure is not the concern but the explosion propagation is still a problem, as the inlet and conveyor above are full of flammable dust. We should consider fast closing valves in combination with chemical barriers.
The lack of data available can be problematic for plant and mill owners. If you are unsure what equipment you require for your operation, contact our experts and we’ll find the right explosion prevention solution for your operation’s specific needs.
Dong Power Energy Avedøre Copenhagen
Avedøre Power Station Unit 2 via Wikicommonns. In the this work into the public domain.
An example of a recent incident where we do have some data is the Dong Power Energy, AvedøreCopenhagen.
On Sunday the 12th of August,11:39, a major fire broke out at the Avedore Dong Power Energy plant . The plant produces 50,000 tonnes of wood pellets, with huge plant investments and the production from a 800 MW CHP were all at risk when the fire began to spread.
Cause of the fire: when the hot conveyor roller dropped down, it ignited accumulated wood dust, underneath the conveyor belt.
Fire-fighting operations, handling of biomass lasted 12 days using up to 60 man-day & more than 10.000 external man-hours. Inerting gases were used consuming nearly 170 tons CO2/day. The operation cost was equivalent to 2 months use of wood pellets (14.000 tons) and a 15.000 tons silo and conveyor systems.
As the Dong Report outlines,wood pellets storage is one of the major risks in the biomass industry for explosion prevention.
External burning nests conveyed into the storage facility, burning belts spreads fire into the silo, dust/flue-gas explosion in the silo head and self ignition of the bulk biomass.
Lesson learned:
- Keep the plant clean
- Design the plant with the aim to avoid horizontal surfaces, where dust can accumulate
- Make easy access to all equipment to keep good maintenance standards
- Secure that cabling to the storage monitoring equipment is not following the conveyor bridges, and that is supplied from another electrical system apart from the one that feeds the conveying and other mechanical systems
- Design the fire fighting equipment in such a way that the first actions can be taken by the plant staff.
Actions taken since:Analyse, test, redesign monitoring & fire strategy, redefine processes.
- Analysis carried out by a national fire knowledge centre
- Communicating the risk assessment results to employees at all levels, used to define cause, consequence and barriers, related to both processes and to plant design
- How did the fire spread and what could have prevented the fire to spread? (In-house work-shops supplied with consultants)
- Different monitoring systems to be used on conveyor systems (Not finalised)
- Inflammable conveyor belts
- Water sprinkling of conveyor belts
- Use of liquid and gaseous nitrogen as inerting agent together with gaseous carbon dioxide
- Permanent foam installation, the storage in case of failure of other measures
- Defining actions related to different fire scenarios
- Silos; IR temperature measuring, gas analysers, temp. measuring in pellets
- Conveyors; Temp measuring alongside the conveyors, gas analysers, moist measurements
- Use of spark detecting and explosion suppression
- Cleaning processes
- Plant maintaining and surveillance
- Training and education of staff
As more and more operations move towards biomass, owners need to take all of the above into account. It’s imperative that you implement the dust explosion prevention measures unique to the biomass industry into your existing infrastructure. Storage is a major issue for explosion prevention. But we cannot forget the human element as well. So many of the best practices for dust explosion prevention in the biomass industry are completely down to continual supervision, training and maintenance.
These are all factors that you can control. You need to make sure that all storage areas are continually cleaned, serviced and maintained. The designate staff must be completely trained in storage safety protocol and understand all the of the risks involved in biomass storage. Reduce the human error by education and through having the right equipment in the first place.
Talk to Explosion Hazards today. We’ll find the right dust explosion solutions for your specific needs and ensure the safety of your operation today.