The scope of works relates to DONG Energy Thermal Power's biomass conversion of primarily — but not exclusively — Avedøre Power Station unit 1 and Studstrup Power Station unit 3 from coal firing to 100 % wood pellet operation, while keeping the option of burning coal when this is found appropriate.
When burning wood pellets coal ash must be co-fired in order to optimize boiler operation and preserve long term durability of the installation. The upcoming tenders covers complete delivery of equipment meant to receive, store, transport, and administer coal fly ash which has been humidified with water to the wood firing process, as well as associated works and services necessary to engineer, design, manufacture, procure, construct, commission, test, document, and hand over the complete delivery to the contracting entity.
The coal fly ash is introduced to the ‘Wet fly ash transport, storage, pumping and liquefied phase dosing system' in a semi dry phase, but leaves the installation as slurry with a specific solid content which must be administered to four coal mills with reasonable accuracy.
All systems and equipment must be fit for purpose and designed with due consideration for QHSE and current and relevant mandatory regulations in force within the European Community.
Technical requirements enclosed with the tender material provide substantial liberty for the Applicant to solve technical and process challenges in any way he sees fit as long as optimum functionality, reliability and performance is obtained.
It is anticipated that the ‘Wet fly ash transport, storage, pumping and liquefied phase dosing system' will be supplied with coal fly ash reclaimed from relevant landfills/depositories. The moisture content of the coal fly ash at that point is estimated to be in the 20-25 % range (wt/wt). Subsequently the coal fly ash will be stored at an intermediate storage area at the power plant where the moisture content may increase with another (estimated) 5 % depending on season and prevailing weather conditions.
The coal fly ash will be delivered to the ‘Wet fly ash transport, storage, pumping and liquefied phase dosing system' by front end loader. The capacity of the conveying equipment at that point in the process must not be less than 75 tons/h.
It is a requirement that the scope of delivery includes bulk storage capacity capable of holding the power plants total consumption of fly ash in 24 hours. For sizing purposes this consumption is provisionally set at 300 tons/24 h (30 % water (wt/wt). Thus the hourly consumption equals 12,5 tons/h (30 % water (wt/wt).
Downstream from the bulk storage facility the coal fly ash must be mixed with water to a free flowing and pumpable slurry of a consistency suitable for dosing to four coal mills. The final water content of the coal fly ash slurry must not exceed 35 % (wt/wt). Water consumption for mixing, dilution and flushing must be limited to the furthest extent. The coal fly ash slurry may be stored in intermediate buffer tank(s) with agitation.
There may be considerable distance between the coal fly ash storage/mixing/buffer facility and downstream equipment administering the coal fly ash slurry to the coal mills (>500 m). Transfer pumps may be needed.
Adequate means to sort out foreign matter from the coal fly ash must be implemented somewhere along the fly ash travel path to ensure that function and performance of pipelines, pumps, valves and other equipment are not compromised.
The coal fly ash slurry must be metered to each coal mill in a linear span between 20-100 % of capacity with an accuracy of +/- 20 %. Volumetric metering pumps are anticipated for this purpose.
Equipment to control dust emissions from the plant must be must be included in the scope of supply. This also applies to the unloading point of the front end loader. Effluents from the entire scope of supply must be recycled/reused where possible.
The projected annual operating time for the ‘Wet fly ash transport, storage, pumping and liquefied phase dosing system' is at the time of writing estimated to be equivalent to 3 500 full load hours.