<!–:sk–>Opis projektu<!–:–><!–:en–>Project description<!–:–><!–:de–>Project description<!–:–>

Renewable power generation: efficiency restrictions

Fireside corrosion (FSC) is major factor limiting component life of renewable power generation installations due to both high temperature combustion environment and agents (e.g. alkali metal salts, chlorides) produced during burning of biomass respectively. All recent solutions for component life-extension are leading to decrease of production efficiency along with increased production costs due to needed compromising of operational parameters (temperature and pressure) and demanded service life. As a consequence, alternative fuel-power generator installations in current state are not able to employ same temperatures and pressures as modern USC (ultrasupercritical) coal power plants. Together with unplanned outages caused by FSC leading to extra repair/replacement costs and loss of income due to production shortage, FSC impacts result in general renewable power generation efficiency restrictions.

Renewable power generation: major trends in FSC protection

Several partial corrosion decreasing approaches have been recently employed and exploited: (i) more or less conventional solutions such as using more alloyed material base/claddings/coatings, (ii) combustion additives, (iii) experimental solutions as bimetal tube extrusion/bimetal tube centrifugal casting are only partially effective as procurement costs disproportionately increase with expensive alloying/additives/production costs in compensation for a relatively small increase in cost-effectivity (overall costs per energy unit produced).

All mentioned methods have led to desired result; however their costs disqualify them from wider long-term industrial application.

All recent material solutions have been withdrawn from applications successfully utilised in industries different from alternative-fuel power generation. Consequently, the application in biomass-fired boilers does not fully take advantage of their properties. For evidence, from viewpoint of applied pressure and temperature it is possible to use conventional creep resistant materials based on 0.5 – 2.25 wt % Cr successfully utilised in modern coal-fired power plants. However, due to specific renewable feedstock properties and related FSC, their application is very limited. Indeed, renewable power generation industry represents a very specific field requiring unique (currently missing) tailored solutions.

Above mentioned apparent drawbacks (costs and/or insufficient operability) of recent FSC protection technologies have become driving forces for project consortium to propose a new, qualitatively different solution, meeting requirements in terms of cost-effectivity and potential mass industrial utilisation in power generation installations using alternative fuel.

Gradient tubes: most promising solution of FSC protection

Among these technologies,��bimetal tubes represent the most promising solution to fulfil these requirements, provided that a new production technology based on existing production facilities is developed. The challenge is to bridge the gap in between bimetal tubes advantages and cost-effectivity necessary for their wide use.

To cope with this challenge it is essential to develop a technology of bimetal tubes production based on utilisation of existing production facilities in tube rolling mills with input in form of an effectively produced and economically viable gradient semiproduct. Desired gradient composition of semiproduct is expected to be obtained by using unique casting approach based on deep understanding of steel and nickel based alloys metallurgy, their thermal characteristics and high temperature physical properties. Indeed, it has to be stated that the semiproduct represents most crucial point of gradient tubes production in terms of our main aim which is cost-effectivity of boiler tubes industrial production.   

State-of-art: gradient semiproducts and tube production

Project is a logic completion of partners´ long-term research activities and efforts.gradient tube rolling

The first research activities have been principally based on empiric approaches to understand basic relations between casting process and physical/metallurgical/technological properties; and have helped to understand the metallurgy of gradient semiproduct casting.

The first experimental trials have principally proved technical feasibility of gradient tubes rolling in standard rolling facilities. Without this it wouldn´t be thinkable to proceed with further research of gradient tubes for described purposes. Nevertheless, many questions have still to be answered by theoretical analyses, numerical simulation and further trials.

Project added value

Expected outputs:

- know-how on new cost-effective technological solution of gradient boiler tube manufacturing from semiproduct with through thickness gradient chemical composition, tailored to carry both creep loading (low alloyed body) and fireside corrosion (high alloyed shell);

- in comparison with any other FSC protection approach (cladding, coating, high-alloyed materials, additives) proposed manufacturing technology is expected to be much more cost-effective and with a real mass industrialisation potential;

Expected added value (chronologically):

- new routines for numerical simulation of gradient material casting/forming;

- new gradient material casting technology;

- innovative type of bimetal tubes – gradient tubes ��� bimetal boiler tubes with FSC resistant surface and creep resistant body, made from through thickness chemically gradient semiproduct produced by unique casting procedure;

Expected impacts

- qualitative step in semiproduct manufacturing metallurgy;

- increased renewable power energy installations steam parameters leading to pollutant emission decrease;

- shift of renewable power generation plant efficiency towards efficiency of conventional fuels combustion processes;

- saving resources of strategic materials as nickel;

- increase of cost-effectivity of renewable power generation leading to wider use of alternative fuels for energy production.

For evidence, calculated savings for material supply when using gradient tubes instead of austenitic ones are in amount of 75 % (1 mm thick austenite shell in 6 mm thick tube instead of 6 mm thick austenite tube). Calculations do not take into account expected increased price of manufacturing.

Economic viability of investigated technological solution is essential for its further industrial use and exploitation. For this reason, in each step cost-effectivity and future production costs will be considered and from this point of view each proposed solution will be validated /revised.