PCDD/Fs, PAHs and HCl emissions from co-combustion of lignite and chicken manure in a circulating fluidized bed boiler with compact refractory casting.

Chicken manure (CM) should be used in energy production due to its high production potential for the waste-to-energy approach. Co-combustion of CM with lignites may be a good practice in terms of reducing its environmental impact and the need for fossil fuels. However, the level of organic pollutants originated from CM combustion is not clear. This study investigated the potential of CM to be combusted in a circulating fluidized bed boiler (CFBB) with a local lignite. Combustion and co-combustion tests of CM and Kale Lignite (L) were performed in the CFBB to measure PCDD/Fs, PAHs and HCl emissions. CM burned in the upper parts of the boiler due to its high volatile matter content and low density compared to coal. This caused the bed temperature to decrease with the increase in the amount of CM in the fuel mixture. It was also observed that the combustion efficiency increased as the share of CM in the fuel mixture increased. Total PCDD/F emissions increased with CM share in the fuel mixture. However, all are less than emission limit value (100 pg I-TEQ/m3). Co-combustion of CM with lignite at different ratios did not have a significant effect on HCl emissions. PAH emissions were found to increase with the increase of the CM share when the CM share was more than 50% by weight.

The effect of H2O on the sulfation of Havelock limestone under oxy-fuel conditions in a thermogravimetric analyser.

A gas mixture representing oxy-fuel combustion conditions was employed in a thermogravimetric analyser to determine the effect of water vapor and SO2 concentration on limestone sulfation kinetics over the temperature range of 800 to 920 °C. Here, experiments used small samples of particles (4 mg), with small particle sizes (dp < 38 µm) and large gas flow rates (120 mL/min@NTP) in order to minimize mass transfer interferences. The gas mixture contained 5000 ppmv SO2, 2% O2, and the H2O content was changed from 0% to 25% with the balance CO2. When water vapor was added to the gas mixture at lower temperatures (800-870 °C), the limestone SO2 capture efficiency increased. However, as the temperature became higher, the enhancement in total conversion values decreased. As expected, Havelock limestone at higher temperatures (890 °C, 920 °C, and 950 °C) experienced indirect sulfation and reacted at a faster rate than for lower temperatures (800-870 °C) for direct sulfation over the first five minutes of reaction time. However, the total conversion of Havelock limestone for direct sulfation was generally greater than for indirect sulfation.

Investigation on thermal degradation kinetics and mechanisms of chicken manure, lignite, and their blends by TGA.

In this study, thermogravimetric analysis (TGA) was performed under the air environment for four different heating rates (10, 20, 30, and 40 °C min-1) in order to find out thermal degradation and mechanisms of the chicken manure, a Turkish lignite, and their blends (25 lignite + 75 manure, 50 lignite + 50 manure, and 75 lignite + 25 manure). To calculate thermal kinetics and responsible solid-state mechanisms of the samples, the Flynn-Wall-Ozawa and Coats-Redfern methods were applied. Significant differences between Turkish lignite and chicken manure samples were observed in terms of thermal kinetics and mechanisms. D1 and D4 mechanisms were found to be the responsible mechanisms for the main oxidation region of the lignite and chicken manure/blends, respectively. A similar decreasing trend for the calculated activation energies and pre-exponential constants was observed with increasing biomass content in the manure blends from 25 to 75% by both Flynn-Wall-Ozawa and Coats-Redfern methods. Furthermore, biomass content has an effect on the mechanisms of chicken manure blends during the combustion. D3 was found to be the responsible solid-state mechanism for the third regions (pre-combustion of the manure) of the chicken manure samples. However, D1 and D2 mechanisms were found to be responsible mechanisms for the blends.

Co-firing of pine chips with Turkish lignites in 750kWth circulating fluidized bed combustion system.

Two Turkish lignites which have different sulfur levels (2-2.9% dry) and ash levels (17-25% dry) were combusted with a Turkish forest red pine chips in a 750kW-thermal capacity circulating fluidized bed combustor (CFBC) system. The combustion temperature was held at 850±50°C. Flue gas emissions were measured by Gasmet DX-4000 flue gas analyzer. Two lignites were combusted alone, and then limestone was added to lignites to reduce SO2 emissions. Ca/S=3 was used. 30% percent of red pine chips were added to the lignites for co-firing experiments without limestone in order to see the biomass effects. The results showed that with limestone addition SO2 concentration was reduced below the limit values for all lignites. CO emissions are high at low excess air ratios, gets lower as the excess air ratio increases. During co-firing experiments the temperature in the freeboard was 100-150°C higher as compared to coal combustion experiments.

Effect of biomass-sulfur interaction on ash composition and agglomeration for the co-combustion of high-sulfur lignite coals and olive cake in a circulating fluidized bed combustor.

This study aimed to investigate the effect of biomass-sulfur interaction on ash composition and agglomeration for the co-combustion of high-sulfur lignite coals and olive cake in a circulating fluidized bed combustor. The tests included co-combustion of 50-50% by wt. mixtures of Bursa-Orhaneli lignite+olive cake and Denizli-Kale lignite+olive cake, with and without limestone addition. Ash samples were subjected to XRF, XRD and SEM/EDS analyses. While MgO was high in the bottom ash for Bursa-Orhaneli lignite and olive cake mixture, Al2O3 was high for Denizli-Kale lignite and olive cake mixture. Due to high Al2O3 content, Muscovite was the dominant phase in the bottom ash of Denizli Kale. CaO in the bottom ash has increased for both fuel mixtures due to limestone addition. K was in Arcanite phase in the co-combustion test of Bursa/Orhaneli lignite and olive cake, however, it mostly appeared in Potassium Calcium Sulfate phase with limestone addition.

Effect of freeboard extension on co-combustion of coal and olive cake in a fluidized bed combustor.

In this study, flue gas emissions and combustion efficiencies during combustion and co-combustion of olive cake and coal were investigated in a bubbling fluidized bed. Temperature distributions along the combustion column and flue gas concentrations of O(2), CO, SO(2) and NO(x) were measured during combustion experiments. Two sets of experiments were performed to examine the effect of fuel composition, excess air ratio and freeboard extension on flue gas emissions and combustion efficiency. The results of the experiments showed that coal combustion occurs at lower parts of the combustion column whereas olive cake combustion takes place more in the freeboard region. As olive cake percentage in the fuel mixture increased, CO emissions increased, SO(2) and NO(x) emissions decreased. Additionally, flue gas emissions could be lowered with the freeboard extension while burning biomass or biomass/coal mixtures. Noticeable decrease in CO emissions and slight increase in combustion efficiencies were observed with a column height of 1900 mm instead of 900 mm.