Resource-efficient fuel additives for reducing ash related operational problems

Waste wood combustion has become common practice in many EU Member States, is an important source of renewable electricity and heat and offers a viable and sustainable end-of-life solution for clean and contaminated waste wood. However, waste wood often contains elements increasing the risk to get problems in the boiler, including severe ash deposition leading to often substantial corrosion problems in the superheater as well as on furnace walls that cause unacceptably short life times.

A possibility to reduce alkali chloride-related corrosion problems is to use various additives. Several different mineral- and sulfur containing additives have been proposed (Wang, 2012), but a) these have so far mainly been tested on laboratory scale tests only (while more in-situ and industrial scale tests are preferred) and there is still a clear need for further development in several areas, including studies of new cheap and resource efficient fuel additives for reducing corrosion / fouling / slagging.

Aim of this project: The overall objective is to improve economic and environmental conditions and enlarge the market for the use of wood waste fuels in CHP-plants by using resource efficient additives such as recycled gypsum during combustion. A specific aim is to show how fuel additive design concepts are related to reduced operation and maintenance-costs (O&M costs), which ultimately should lower required SDE+ subsidy levels for waste wood combustion.

Activities: include development of fuel additive design concepts for reduction of ash related problems in wood waste combustion, case studies that show how resource efficient additives can be integrated with the fuel chain and blended within the fuel in a technical/ economical way, full-scale trials in five CHP-plants in Sweden, Poland, Germany, Austria and the Netherlands (with BEC Cuijk as one of the plants, and Dekra involved in corrosion analysis in Poland and the Netherlands), and an analysis of the environmental and economic effects throughout the entire supply chain of using various additives (gypsum, sulphide ore waste, halloysite) in waste biomass CHP/heating plants (Task leader Utrecht University), with Avans focussing mainly on the economical impact of increased boiler performance and decreased maintenance and ash application and ash quality considerations.

Results: A significant contribution to increased economic feasibility by increased fuel flexibility and using waste wood and waste streams as additives as resource, with more than 1 million Euro anticipated annual cost savings for a BEC plant of 17 MWe due to reduced maintenance and better heat conduction. In addition: Increased resource efficiency (cascading of used wood), higher energy independency and security of supply by using regional or local available waste streams and additives will be realized. Assuming 5 new BECs, total direct cost savings between 2020-2023 could be above 5 million Euros, with additional similar savings expected when additives are also used in e.g. waste combustion plants and clean wood combustion plants.