Proceedings World Bioenergy 2010
Proceedings World Bioenergy 2010
Proceedings World Bioenergy 2010
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12 world bioenergy <strong>2010</strong><br />
SLAGGING AND FOULING RISK OF MEDITERANEAN BIOMASSES FOR COMBUSTION<br />
Daniel J. Vega-Nieva 1 , Raquel Dopazo 2 and Luis Ortiz 3 .<br />
Contact: CÁTEDRA ENCE. University of Vigo (Spain).<br />
Forestry School. A Xunqueira Campus. 36005. Pontevedra (Spain).<br />
Tel: 1-2: +34/986801948; 3: +34/986801902.<br />
Email: 1. DanielJVN@gmail.com 2. dopazo.raquel@gmail.com; 3. lortiz@uvigo.es.<br />
ABSTRACT: The interest in biomass combustion has grown exponentially in the last years, as a means for renewable<br />
heat and energy promoting local development and mitigating climate change. Various Mediterranean agricultural and<br />
forest resources such as olive stone, almond shell or pinecone chips remain large unutilized, despite their potential for<br />
being utilized in biomass combustion. New energy crops such as Cardoon, Brassica or Sorghum, are being introduced in<br />
Mediterranean countries for <strong>Bioenergy</strong> production; however, the slagging and fouling risk of many of these potential<br />
feedstocks are currently limiting their application in combustion processes given their high alkali, silica or chlorine<br />
contents. In this publication, various methods for biomass slagging and fouling hazard monitoring and prediction are<br />
presented based on recent studies with Mediterranean biomasses combustion in Spain.<br />
Keywords: slagging, fouling, biomass combustion.<br />
1. INTRODUCTION.<br />
The interest in biomass combustion has grown<br />
exponentially in the last years, as a means for renewable<br />
heat and energy promoting local development and<br />
mitigating climate change.<br />
However, various Mediterranean agricultural and<br />
forest resources such as almond shell or pinecone seed<br />
shells remain large unutilized. The slagging and fouling<br />
risk remain as important barriers that are currently<br />
limiting the use of various agricultural residues and<br />
potential agricultural energy crops feedstocks such as<br />
Cardoon, Brassica, or Sorghum [1], [2], [3].<br />
Slagging occurs in the boiler sections that are<br />
directly ex posed to flame irradiation. The mechanism<br />
of slagging formation involves stickiness, ash melting<br />
and sintering. Slagging de posits consist of an inner<br />
powdery layer followed by silicate and alkali<br />
compounds [4], [5].<br />
Fouling deposits form in the convective parts of<br />
the boiler. The mechanism of fouling is mainly due to<br />
condensation of volatile species that have been<br />
vaporised in previous boiler sections and are loosely<br />
bonded [5]<br />
In this publication, various methods for biomass slagging<br />
and fouling hazard monitoring and prediction are<br />
presented based on recent studies with Mediterranean<br />
biomasses combustion in Spain.<br />
2. ASH MELTING BEHAVIOUR: SLAGGING AND<br />
FOULING INDICES AND FUSION<br />
TEMPERATURES.<br />
2.1. Slagging and Fouling Indexes.<br />
Various authors have proposed a series of slagging and<br />
fouling indexes to explain the accumulation of ashes into<br />
the radiation and convection areas of biomass boilers,<br />
respectively. Although originally developed for coal,<br />
these indices seem to have potential for application on<br />
biomass combustion behaviour prediction (i.e. [6],<br />
[7]). Most widely used slagging and fouling indexes and<br />
currently proposed thresholds are synthesized below:<br />
Base to acid index [1], [6], [7], [8]:<br />
Critical value for coal: < 0.75 slagging trend<br />
Alkaki Index [9]:<br />
where HHV: Higher Heating value (MJ/Kg) at H=0%<br />
if index > 0.17 kg alkali /MJ probable fouling<br />
if index > 0.34 kg alkali /MJ fouling is certain to occur<br />
Slagging index [1], [7], [10]:<br />
where S d is % S from elementary analysis<br />
if RS < 0.6 low slagging trend<br />
if 0.6 < RS < 2 medium trend<br />
if 2.0 < RS < 2.6 high trend<br />
if RS > 2.6 very high trend