Jouni Tummavuori

Importance of solid fuel properties to nitrogen oxide formation through HCN and NH3 in small particle combustion

The formation of nitrogen oxides from fuel-nitrogen through intermediates was studied by measuring first fuel-Ofuel-N ratios and nitrogen functionality in selected solid fuels. Then the ratios of the yields (fuel-N → HCN)(fuel-N → NH3) in a nearly inert atmosphere at 800°C in an entrained flow reactor was measured and finally the ratio (fuel-N → N2O)(fuel-N → NO) in an oxidizing atmosphere at 800°C. The fuels studied were coal, brown coal, S- and C-type peat, fir bark, birch bark and pine bark, all milled to a particle size < 63 μm. The ratios of ON in the fuel, measured by elemental analysis, ranged from 7 to 150. Nitrogen functionality (mass percent of the total nitrogen content) was determined by XPS. The (fuel-N → NCN)(fuel-N → NH3) conversion ratio in the absence of O2, and also the (fuel-N → N2O)(fuel-N → NO) conversion ratio with O2 present, decreased with increasing ratio of fuel-Ofuel-N, but neither ratio decreased regularly with the increasing ratio of pyrrolic to pyridinic nitrogen in the fuel. Thus, fuel-oxygen plays a more important role than nitrogen functionality in the chemistry of nitrogen oxide formation. The strong effect of (fuel-Ofuel-N) ratio on the (fuel-N → HCN)(fuel-N → NH3) ratio may be due to the reaction between OH radicals and HCN to form NH3 near the fuel particle. The importance of this reaction is considered. Charring the fuel sample before combustion led to a sharp drop in the conversion of fuel-N to N2O compared with the virgin fuels. Thus, heterogeneous combustion reactions produced much less N2O than homogeneous combustion reactions.

Formation of nitrogen oxides from fuel-N through HCN and NH3: a model-compound study

The conversion of fuel-nitrogen to HCN and NH3 and to nitrogen oxides was studied with nitrogen-containing model compounds, chosen to represent the main nitrogen and oxygen functionalities in fossil fuels. Two kinds of experiments were performed in an entrained-flow reactor at 800 °C. The conversion of model-compound-N to HCN and NH3 was determined under inert conditions, and the formation of NO, N2O and NO2 was determined under oxidizing conditions. In inert atmosphere, oxygen-containing functional groups had an important effect on the ratio of HCN to NH3. In particular, OH groups bound directly in the ring structure increased the conversion of nitrogen to NH3. In oxidizing atmosphere, the conversions of model-compound-N to N2O were high, but the substituent groups had no well-defined effect on the ratio of N2O to NO. The formation of NO2 was insignificant.

Conversion of peat and coal nitrogen through HCN and NH3 to nitrogen oxides at 800°C

The conversion of fuel nitrogen through HCN and NH3 to nitrogen oxides (N2O, NO and NO2) was studied using an entrained-flow reactor at 800 °C with one coal and four peats at 5 and 1% O2. The ON ratios of the fuels were between 7 and 20. A clear dependence was found between the HCNNH3 ratio measured just after the vigorous pyrolysis step and the N2ONO ratio in the flue gas when these were plotted as a function of the initial ON ratio of the fuel.

Determination of heats of pyrolysis and thermal reactivity of peats

Heats of pyrolysis of four Finnish peats were determined by differential scanning calorimetry (d.s.c.), and combustion enthalpies were compared by differential thermoanalysis (DTA) in an air atmosphere. Weight loss data obtained by thermogravimetric analysis (TGA) were combined with the enthalpy data. The heats of pyrolysis of the peats varied between 120 and 250 kJ kg−1. These values were used to model the combustion and pyrolysis of small peat particles (typical in pulverized fuel combustion) and large peat particles (typical in grate combustion). TGA and DTA together gave useful information about the reactivity of peat in an oxidizing atmosphere with changing temperature, despite the similar shapes of the derived TGA (DTG) and DTA-curves. The pyrolysis and combustion behaviour of the peat with the lowest degree of decomposition was similar to that of cellulose, and the differences in the peats were apparent with all the methods used (d.s.c., DTA and TGA). The initial temperatures of pyrolysis and combustion were lower with peats of high ash content (inorganic material) and the combustion proceeded through more steps than with the peats of low ash content.

Retention of vanadium(V), molybdenum(VI) and tungsten(VI) by kaolin

Abstract The ability of kaolin (approximately H2Al2Si2O8 · H2O), a well known clay mineral constituent, to retain V(V) andMo(VI) species from 10−5 and 10−4 M solutions, and W(VI) species from 10−4 M solutions was investigated in the pH range 2–7.5 using a solid/liquid ratio 1:100 (w:v). The equilibration time in the adsorption studies was 72 h, and the shaking time in the desorption studies was 17 h. 0.02 M KCl was used as ionic medium and desorbing liquid. V(V), Mo(VI) and W(VI) were all retained by kaolin to some extent, and the amounts of the elements which could be washed away from kaolin with 0.02 M KCl were very small. The pH dependence of the adsorption was considerable: when added alone, all three elements were adsorbed strongly at about pH 4, but above pH 6.5 only V was retained in noticeable amounts. When V, Mo and W were added simultaneously, the adsorption curves showed that adsorption of Mo(VI) predominates at pH 4, whereas W(VI) and V(V) predominate at pH 5–6 and pH > 6.5, respectively.

CATALYTIC EFFECTS OF METALS ON PEAT COMBUSTION

Abstract A comparison was made of the effects of Fe, Mn, Cr, Ni, Co, Zn, Al, Mg and Ca on slow and rapid peat combustion. The concentrations used were 100–200 mmol kg−1 and lower and higher concentrations were also used for Fe. The order of the catalytic effects of the metals on the combustion of peat particles (100–125 μm diameter) in an entrained flow reactor (particle heating rate 15000 ± 5000 °Cs−1) was: Cr >Mn, Fe >Co, Ni >Ca >Zn, Mg >Al. In the presence of 100 mmol kg−1 Cr, the combustion time decreased by 26% compared with acid-washed peat having a low content of inorganic material. The decrease was only 4% with Al. Thermogravimetric experiments predicted the order: Fe, Cr >Mn, Ni >Co >Ca >Mg >Zn >Al (heating rate 0.17 °Cs−1). Experiments with Fe in the entrained flow reactor showed an increase in concentration from 105 to 330 mmol kg−1 to have little effect, but a decrease from 105 to 42mmol kg−1 weakened the catalytic effect markedly. The thermogravimetric experiments predicted that concentrations between 105 mmol kg−1 and 330 mmol kg−1 would strengthen the catalytic effect. Catalytic effects of metals on combustion can be predicted on the basis of atomic structure. Transition metals are good catalysts and the best of them have five or six electrons in d orbitals, whereas metals with only one stable oxidation state and completely occupied or empty s, p and d orbitals are poor catalysts. These effects probably prevail in the combustion of coals. In the case of dried Finnish bog peat, the catalytic effects of cations are mainly due to Fe, because the contents of other strong catalysts (Cr and Mn) are very low relative to Fe; Ca causes some additional effects.

Retention of Molybdenum(VI) by Three Finnish Mineral Soils

Abstract Retention of molybdate by three Finnish mineral soils from 10−4 and 10−5 M sodium molybdate solutions at room temperature was investigated at pH 2.3–7.5. In the adsorption experiments 0.02 M KCl was used as ionic medium, and the samples were left to equilibrate for 72 h. The solid: solution ratio was 1:100 (w: v). Maximum adsorption occurred below pH 4.5, where about 60–80 % of added molybdenum was retained. Desorption of the adsorbed molybdenum was measured by adding 50 ml of 0.02 M KCl into weighed soil samples and shaking for 17 h in an apparatus with a mechanical stirrer. In each soil an appreciable amount of Mo was so tightly bound that it could not be removed by KCl treatment.

Determination of platinum and iridium in reforming catalysts by second derivative and absorptiometric spectrophotometry

SummaryInvestigations on the spectrophotometric determination of platinum as a complex formed by tin(II)chloride in hydrochloric acid are reported. The determination of platinum was found to be interfered with by iridium, because it also forms a complex with tin(II) chloride. The features of the derivative absorption spectrophotometry for the quantitative determination of platinum and iridium was also studied. The analytical application of the method for the determination of platinum and iridium in catalysts was investigated.

Determination of NH3 in pyrolysis gases by ammonia selective electrode

The suitability of ion-selective electrode for the determination of ammonia in pyrolysis gases of fossil fuels was studied. The ammonia was absorbed into acidic solution and two kinds of determination methods were carried out. The ammonia was either measured directly from the acid solution, or ammonia was first released into the gas phase and then determined (air gap method) by the ammonia selective electrode. The electrode functioned well in both cases, but the linear calibration range was rather narrow, slightly more than one tenfold. The quantitative detection limit in the water phase was 5 x 10(-6)M (0.085 ppm) NH(3) and in gas phase operation solutions above 5 x 10(-4)M (8.5 ppm) NH(3) it was possible to measure quantitatively. The applications were carried out with Finnish energy peat samples and a coal sample.

Importance of iron and aluminium in rapid and slow combustion of peat

Abstract The effects of Fe and Al on peat combustion and the formation of nitrogen oxides were studied under conditions of rapid combustion in an entrained flow reactor, and under conditions of slow combustion in a thermobalance and a differential scanning calorimeter. Iron had a strong catalytic effect on both the slow and rapid combustion, and it decreased the ratio of N2O to NO in the combustion gases. A decrease in the content of inorganic compounds decreased reactivity, probably because of the decrease in iron content. Aluminium did not have a detectable catalytic effect on the combustion rate but it depressed the formation of nitrogen oxides slightly. The chemical treatment to increase the contents of Fe and Al and decrease the ash content had little effect on the composition of the organic part of the peat.