Fuel Indexes: A Novel Method for the Evaluation of Relevant Combustion Properties of New Biomass Fuels

Abstract

The increasing demand for biomass fuels leads to the introduction of new biomass fuels into the market. These new biomass fuels (e.g., wastes and residues from agriculture and the food industry, short rotation coppices, and energy crops) are usually not well-defined regarding their combustion behavior. Therefore, fuel characterization methods with a special focus on combustion-related problems (gaseous NO x , HCl, and SO x emissions, ash-melting behavior, and PM emissions) have to be developed. For this purpose, fuel indexes are an interesting option. Fuel indexes are derived from chemical fuel analyses and are checked and evaluated regarding their applicability by measurements performed at lab-and real-scale combustion plants for a large variety of fuels. They provide the possibilities for a pre-evaluation of combustion-relevant problems that may arise from the use of a new biomass fuel. A possible relation to describe the corrosion risk is, for instance, the molar 2S/Cl ratio. The N content in the fuel is an indicator for NO x emissions, and the sum of the concentrations of K, Na, Zn, and Pb in the fuel can give a prediction of the aerosol emissions, whereas the molar (K + Na)/[x(2S + Cl)] ratio provides a first indication regarding the potential for gaseous HCl and SO x emissions. The molar Si/K ratio can supply information about the K release from the fuel to the gas phase. The molar Si/(Ca + Mg) ratio can give indications regarding the ash-melting temperatures for P-poor fuels. For Prich fuels, the (Si + P + K)/(Ca + Mg) ratio can be used for the same purpose. The fuel indexes mentioned can provide a first pre-evaluation of combustion-relevant properties of biomass fuels. Therefore, time-consuming and expensive combustion tests can partly be saved. The indexes mentioned are especially developed for grate combustion plants, because interactions of the bed material possible in fluidized-bed combustion systems are not considered.

Using Grass Cuttings from Sports Fields for Anaerobic Digestion and Combustion

“…However, it was not as high as in the press cake from the grass of roadside verges (8.63 [12]) or in coniferous wood (4.44 calculated from [15]). Sommersacher et al [4] suggest a 2S/Cl ratio of >4 in order to assume only a minor corrosion risk. This value was nearly reached by the press cake from sports fields.…”

“…Two replicates of pure inoculum were digested separately to subtract the methane yield of the inoculum from the total methane produced in inoculated samples and thereby calculate the actual yield from the sample. Biogas was collected in gas-proof bags, and volume was measured with a wet drum gas meter (TG5; Ritter Apparatebau GmbH, Bochum, Germany) at Digestion Days 1,2,3,4,7,9,11,14,16,18,and 21 for press fluids and additionally on Days 24, 28, 31 and 35 for silage. While digesting, samples were stirred every 3 h for 15 min with a U-shaped stirrer driven by a 12 V direct current motor.…”

“…To estimate the risk of detrimental processes in combustion, indices that relate concentrations of different elements to possible predispositions of the fuel have been presented. For instance, the K 2 O/CaO index indicates the risk of fouling [3], while the 2S/Cl index indicates the risk of corrosion [4]. In anaerobic digestion, grass may lead to clogging of pipes and may form layers in the reactor [5].…”

Foliage and Grass as Fuel Pellets–Small Scale Combustion of Washed and Mechanically Leached Biomass

“…As a point of reference for the upgraded fuels, mean values of four wood pellet samples (all in accordance with ENplus/DINplus quality standards), which were analyzed according to the same methodology, were calculated. The focus of the results presented was on chemical parameters important for the characterization of solid biomass fuels by fuel indexes (as presented by Sommersacher et al [9]), physical-mechanical quality parameters of pellets and the ash melting behavior (according to DIN CEN/TS 15370-1 [29]). The bulk density and durability were analyzed at the DBFZ which required approximately 7 kg of each fuel while the ash melting behavior was analyzed by an external laboratory (500 g samples of each fuel).…”

Combustion of Agricultural Biomass - Issues and Solutions

“…Fig. 6 (Si+P+K)/(Ca+Mg) molar ratio versus ash-sintering temperature for different biomass fuels [29] Some ash constituents can react with flue gases forming a variety of compounds which may form deposits on the water cooled heat exchanger surfaces leading to fouling and slagging. These deposits, if containing certain chemicals, can also create corrosion and erosion problems.…”