Effects of particle crushing in abrasion testing of steels with ash from biomass-fired powerplants

The use of biomass for firing of powerplants (either as a primary fuel or in co-firing) is gaining popularity as it is seen as a carbon-neutral energy source. The ash produced by firing with such materials causes wear of the powerplant systems designed to process it, both in the form of fly-ash and bottom-ash. In this paper, the wear behaviour of a range of steels under conditions of abrasion with biomass bottom-ash is considered. The steels were abraded using the dry sand rubber wheel test (a variant on ASTM G65) and their behaviour compared with that observed when abraded with silica in the same test. It was seen that the wear rate of the steels when abraded with silica increased in proportion to the applied load and decreased with the hardness of the steel. However, the bottom-ash was more friable than the silica abrasive, and as such, significantly more abrasive crushing was observed during the tests with the bottom-ash abrasive. As such, the wear rates with the bottom-ash did not increase in proportion to the applied load (and at higher loads they decreased with increasing applied load). Moreover, the relative abrasion rates of the steels decreased more sharply with increasing steel hardness than for the silica abrasive. The wear behaviour of the steels with the ash was dominated by the relatively low hardness of the abrasive (between that of the softest and hardest steels) and the significant crushing of the abrasive during abrasion testing. It is proposed that the wear is dominated by abrasion by the larger particles in the distribution, and that damage is limited by the maximum load which the particles can sustain before failing. As such, the abrasion rate has been shown not to be proportional to the applied load for an abrasive with a wide particle size fraction and where the particle strength results in significant particle crushing in the tests. (C) 2009 Elsevier B.V. All rights reserved.