Environmental and socio-economic assessment of co-combustion of coal, biomass and non-hazardous wastes in a Power Plant

Under the framework of the European project named COPOWER, the possibility to partially substitute coal used in a 243 MW_th Power Plant by biomass and non-hazardous wastes for the production of electricity and steam was assessed. Three combustion scenarios were studied, based on the combustion tests performed in a Power Plant located in Duisburg (Germany): Scenario 0 (Sc0) - combustion of coal; Scenario 1 (Sc1) - combustion of coal + sewage sludge (SS) + meat and bone meal (MBM); Scenario 2 (Sc2) - coal + SS + wood pellets (WP). An environmental and socio-economic assessment of these three scenarios was performed. In the environmental point of view, Sc0 was the worst scenario, mainly due to the emission of greenhouse gases (GHG). Sc1 was the best scenario, mainly due to the reduction of GHG emission, eutrophication chemical species and ozone depletion gases. In the socio-economic point of view, Sc0 was the worst scenario, mainly due to the absence of GHG abatement, and Sc1 was the best scenario due to the best cost of electricity production and negative cost of avoided emissions.     

Experimental validation of in situ CO2 capture with CaO during the low temperature combustion of biomass in a fluidized bed reactor

A novel concept for capturing CO₂ from biomass combustion using CaO as an active solid sorbent of CO₂ is discussed and experimentally tested. According to the CaO/CaCO₃ equilibrium, if a fuel could be burned at a sufficiently low temperature (below 700 °C) it would be possible to capture CO₂ “in situ” with the CaO particles at atmospheric pressure. A subsequent step involving the regeneration of CaCO₃ in a calciner operating at typical conditions of oxyfired-circulating fluidized combustion would deliver the CO₂ ready for purification, compression and permanent geological storage. Several series of experiments to prove this concept have been conducted in a 30 kW interconnected fluidized bed test facility at INCAR-CSIC, made up of two interconnected circulating fluidized bed reactors, one acting as biomass combustor-carbonator and the other as air-fired calciner (which is considered to yield similar sorbent properties than those of an oxyfired calciner). CO₂ capture efficiencies in dynamic tests in the combustor-carbonator reactor were measured over a wide range of operating conditions, including different superficial gas velocities, solids circulation rates, excess air above stoichiometric, and biomass type (olive pits, saw dust and pellets). Biomass combustion in air is effective at temperatures even below the 700 °C, necessary for the effective capture of CO₂ by carbonation of CaO. Overall CO₂ capture efficiencies in the combustor-carbonator higher than 70% can be achieved with sufficiently high solids circulation rates of CaO and solids inventories. The application of a simple reactor model for the combined combustion and CO₂ capture reactions allows an efficiency factor to be obtained from the dynamic experimental test that could be valuable for scaling up purposes.     

Characterization of fuel gas products from the treatment of solid waste streams with a plasma arc torch

This work addresses the plasma treatment of two solid waste streams and production of fuel gases from the process. In this study, carpet waste and simulated solid wastes generated by a United States Air Force Basic Expeditionary Airfield Resources Base deployment were used. Waste was treated in a furnace fitted with a 100kW plasma arc torch. The off gas was analyzed to determine its composition. The product gas was composed primarily of carbon monoxide and hydrogen, with small amounts of methane, benzene and toluene also detected. These experiments demonstrate the feasibility of producing fuel gases by plasma treatment of the solid waste streams. While the thermal energy value of the fuel gas produced in these experiments was less than the energy input, a higher waste-to-fuel gas conversion efficiency is expected in full-scale application.     

Characteristics of slag, fly ash and deposited particles during melting of dewatered sewage sludge in a pilot plant

This study examines slag, fly ash, and deposited particles during melting of dewatered sewage sludge in a pilot plant. In addition, the chemical composition of particles in flue gas was simulated using a thermodynamics program, namely FACTSage 5.2. The results showed that the main components of slag were Al, Fe, Ca, P and Si; the minor components were Na, K, Mg, Cu, and Zn. The main chemical compound of slag was Ca4(Mg,Fe)5(PO4)6. For fly ash particles, heavy metals with the highest concentrations were in the order of Zn and As, Pb, Cu, and Cd, respectively. For non-heavy metals, Al, Fe and P were also found in significant amounts. The majority of deposited particles were composed of elements of Zn, P, S, Na, Fe, Al, Si, and Ca and such chemical compounds as Zn3(PO4)2, AlPO4, FePO4 and Fe(OH)3 while the minority consisted of elements of As, Cu, and Pb. Moreover, the compositions of deposited particles in each chamber differed due to different flue gas temperatures inside. In the secondary chamber at 760 degrees C, the amounts of Fe and Al were higher than Zn, whereas, in the other chambers (600-400 degrees C), the amount of Zn was higher. In other words, at the lower temperature the deposition of Zn was higher than the deposition of Fe and Al. In the water cooling section, volatile elements (i.e. Zn, As, Cu, Pb) were found in the highest concentrations due to a big difference in temperature between the wall surface and flue gas. From the simulation results, most of the elements in the gas phase were found to be chloride compounds, whereas those in the solid phase were in the form of oxide, sulfate, and phosphate compounds.     

Reforming of CO2-containing natural gas with steam in AC gliding arc discharge for hydrogen production

In this study, a low-temperature gliding arc discharge system was used to investigate the effects of steam content and operational parameters, i.e. total feed flow rate, applied voltage, and input frequency, on the reforming performance of CO₂-containing natural gas. The addition of steam less than 10% was found to enhance both selectivities for hydrogen and carbon monoxide with a significant reduction of power consumptions. The highest hydrogen selectivity and yield with the lowest power consumptions were achieved at a steam content of 10 mol%, a total feed flow rate of 100 cm³/min (corresponding to a very short residence time of 1.37 s), an applied voltage of 13.5 kV and an input frequency of 300 Hz. Under these optimum conditions, the oxidative dehydrogenation reactions to produce hydrogen were dominant with the minimum activities of all undesired reactions of cracking and coupling. Both of the short residence time (1.37 s) with a low bulk temperature (lower than 200°C) in the plasma zone under atmospheric pressure, indicate that the studied plasma reactor (gliding arc system) is superior to conventional catalytic reactors for reforming of natural gas.     

The impact of land use and land cover changes on land surface temperature in a karst area of China

Satellite images have been used extensively to study temporal changes in land use and land cover (LULC) in China. However, few studies have been conducted in the karst areas despite the large area and population involved and the fragile ecosystem. In this study, LULC changes were examined in part of Guizhou Province of southern China from 1991 to 2001 based on Landsat Thematic Mapper (TM) images of November 7, 1991, December 5, 1994, and December 19, 2001. Land surface temperature (LST) and normalized difference vegetation index (NDVI) were computed based on LULC types. The results show that agricultural land decreased, while urban areas expanded dramatically, and forest land increased slightly. Barren land increased from 1991 to 1994, and then decreased from 1994 to 2001. These changes in LULC widened the temperature difference between the urban and the rural areas. The change in LST was mainly associated with changes in construction materials in the urban area and in vegetation abundance both in the urban and rural areas. Vegetation had a dual function in the temperatures of different LULC types. While it could ease the warming trend in the urban or built-up areas, it helped to keep other lands warmer in the cold weather. The study also reveals that due to the government's efforts on reforestation, rural ecosystems in some of the study area were being restored. The time required for the karst ecosystem to recover was shorter than previously thought.     

LMC低压长袋除尘器在矿热炉烟气治理中的应用

阐述了LMC型低压长袋脉冲喷吹除尘器在矿热炉烟气治理中的成功应用。LMC型除尘器在设计上充分考虑到矿热炉高温烟气温度和粉尘性质对设备的影响,并根据不同烟气温度、粉尘性质及工艺的变化,采用不同配件和材料。     

Optimal planning of co-firing alternative fuels with coal in a power plant by grey nonlinear mixed integer programming model

Energy supply and use is of fundamental importance to society. Although the interactions between energy and environment were originally local in character, they have now widened to cover regional and global issues, such as acid rain and the greenhouse effect. It is for this reason that there is a need for covering the direct and indirect economic and environmental impacts of energy acquisition, transport, production and use. In this paper, particular attention is directed to ways of resolving conflict between economic and environmental goals by encouraging a power plant to consider co-firing biomass and refuse-derived fuel (RDF) with coal simultaneously. It aims at reducing the emission level of sulfur dioxide (SO(2)) in an uncertain environment, using the power plant in Michigan City, Indiana as an example. To assess the uncertainty by a comparative way both deterministic and grey nonlinear mixed integer programming (MIP) models were developed to minimize the net operating cost with respect to possible fuel combinations. It aims at generating the optimal portfolio of alternative fuels while maintaining the same electricity generation simultaneously. To ease the solution procedure stepwise relaxation algorithm was developed for solving the grey nonlinear MIP model. Breakeven alternative fuel value can be identified in the post-optimization stage for decision-making. Research findings show that the inclusion of RDF does not exhibit comparative advantage in terms of the net cost, albeit relatively lower air pollution impact. Yet it can be sustained by a charge system, subsidy program, or emission credit as the price of coal increases over time.