• Energy Research
• IT close

In this work, an innovative process layout for methane production is proposed and investigated with the aim to promote the integration of renewable energies chemical storage via hydrogen production by water electrolysis and biomass gasification. The core of the proposed layout is the integration between an experimental fluidized bed gasification system, fed with spruce wood pellets and using Fe/AlO catalyst, and a conceptual methanation unit. This latter was modelled as a series of adiabatic fixed bed reactors with inter-cooling, water condensation at the exit of each reactor, and product recycle. The performance of the methanation system was evaluated by considering that the product stream coming from the gasifier system reacts, after purification and mixing with pure hydrogen coming from an electrolysis cells array, over Ni supported on alumina catalyst. The number of electrolysis cells to be stacked in the hydrogen production unit was evaluated by considering that a constant H production able to reach 7:1:1H:CO:CO ratio at the inlet of the methanation unit should be attained.

A combination of experimental techniques was employed to test primary fragmentation and char particle attrition by abrasion during fluidized bed (FB) combustion of raw paper sludge (Raw-PS), hydrothermally treated paper sludge (HIT-PS), and a subbituminous coal (Sub-C), for comparison. The hydrothermal treatment (HIT) was conducted by a pilot-scale reactor at 197 degrees C (1.9 MPa) for 30 min. The results showed that all three samples extensively underwent primary fragmentation. Char attrition tests under inert conditions showed that Sub-C intensely experienced particle rounding off at the beginning, but after that it became very strong against mechanical abrasive attrition, followed by HTT-PS and Raw-PS, respectively. The oxidative char attrition tests showed that Sub-C exhibited an initial low amount of carbon elutriation rate followed by an attrition enhancement effect at later stages of burn-off, whereas for the Raw-PS and HIT-PS attrition was always lower than under inert conditions due to extensive postcombustion of fines. HTT-PS always produced a lower amount of elutriated carbon than Raw-PS and this indicates better combustion performance as well as lower unburned carbon emission. Finally, the Primary Ash Particle Size Distribution (PAPSD) of the three fuels was determined, showing that the paper sludge would contribute much more than coal to the ash bed inventory in a full-scale FB combustor. (C) 2015 Elsevier B.V. All rights reserved.

An experimental apparatus has been developed in order to perform tests of primary fragmentation of solid fuels under severe heating conditions (up to 2200 K and 12 bar). Particles are laid on the strip and pyrolyzed under inert conditions, fragments are recovered and analyzed by a laser granulometer to assess the fragmentation propensity of the fuel. Experiments have been carried out at temperatures between 1400 K and 1900 K, heating rate of 5000 K/s, pressure in the range 1-12 bar. Four different coals have been studied: Gracem, Venezuelan, Omsky, and Kleincopje, classified respectively as anthracite, high and medium volatile bituminous coals. Results show that primary fragmentation at high heating rate and high temperature may result in the formation of relatively coarse fragments and sometimes in a multitude of fines. The probability of fragmentation and the propensity to form coarse versus small fragments varies from coal to coal. For a given coal fragmentation increases monotonously with temperature, whereas the effect of pressure is nonmonotonous. The role of different chemico-physical properties of coals on the pattern and the extent of primary fragmentation is discussed, in particular volatile matter content, ash melting point, rigidity and porosity of the carbon structure and swelling index. © 2011 Elsevier Ltd. All rights reserved.

The paper deals with the integration between a kinematic Stirling engine and a fluidized bed combustor for micro-scale cogeneration of renewable energy. A pilot-scale facility integrating a 40 kW(t)combustor and a gamma-type Stirling engine (0.5 kW(e)) was set up and tested to demonstrate the feasibility of this solution. The Stirling engine was installed at a lateral wall of the combustor in direct contact with the fluidized bed region. An experimental campaign was executed to assess the performance of the innovative integrated system. The experimental results can be summarized in: (a) very high combustion efficiency with biomass feeding, (b) elevated heat transfer rate to the engine, (c) a relatively small share (about 2 kW(t)) transferred to the engine from the thermal power generated by the combustor (around 13 kW(t)), (d) conversion to electric power close to the upper limit of the engine, (e) limited impact of the Stirling engine on the fluidized bed behavior, for example, temperature. From the analysis of measured variables, the dynamics is dominated by the fast response of the Stirling engine, which rapidly reacts to the slow changes of the fluidized bed combustor regime: the dynamic response of the tested facility as a thermal system was slow, the time constant being of the order of 10 minutes.

A system consisting of a last-generation Stirling engine (SE) and a fuel burner for distributed power generation has been developed and experimentally investigated. The heat generated by the combustion of two liquid fuels, a standard Diesel fuel and a rapeseed oil, is used as a heat source for the SE, that converts part of the thermal energy into mechanical and then electric energy. The hot head of the SE is kept in direct contact with the flame generated by the burner. The burner operating parameters, designed for Diesel fuel, were changed to make it possible to burn vegetable oils, not suitable for internal combustion engines. The possibility of adopting different configurations of the combustion chamber was taken into account to increase the system efficiency. The preliminary configurations adopted allowed to operate this integrated system, obtaining an electric power up to 4.4 kW(el)with a net efficiency of 11.6%.

A system consisting of a Stirling engine (SE) and a fluidized bed combustor (FBC) for combined heat and power (CHP) generation has been experimentally investigated. The heat generated by combustion of wood pellets is used as source for the SE that converts part of the thermal energy into mechanical and then electric energy. This system, having the heat exchanger of the SE located inside the sand bed of the FBC, presents several advantages: (1) very high bed-to-external surfaces heat exchange coefficients; (2) absence of fouling on the heat exchange surface due to the cleaning action exerted by the fluidized sand particles; and (3) FBCs are able to use a wide variety of biomass fuels. The FBC used in this investigation can develop a thermal power in the range 15-40 kW feeding wood pellets as fuel and changing fluidization conditions and fuel feeding rate. Bed operation temperature was varied in the range 750-850°C. The SE adopted is a ?-type with the heater in form of tube bundle. The performances of this integrated system have been assessed in terms of gaseous emissions and of SE efficiency varying the bed temperature and the pressure of SE working fluid. A mathematical model able to simulate the integration of the FBC with the SE for CHP generation has been developed to quantify the heat fluxes among the different components of the system.

Fragmentation during pulverized coal particles conversion shifts the particle size distribution of the fuel towards smaller particle sizes, affecting both conversion rates and heat release. After pyrolysis of a high volatiles Colombian coal in CO2 atmosphere in a drop tube reactor at 1573 K, solid carbonaceous particles of different size, from 100 µm of the particle feed down to the nanometric size, have been observed. A fragmentation model has been used to predict the fate of Colombian coal particles under the experimental conditions of the drop tube experiment and predict the particle size distribution (PSD). Model and experimental results are in very good agreement and indicate that in the DTR experiment the coal underwent almost complete pyrolysis and that fragmentation generated a 36 wt% population of particles with size close to 30 µm. The close match between the PSDs obtained from experiments and from the fragmentation model is an important novelty. It demonstrates that fragmentation occurs not only under fluidized bed conditions but also under the conditions of pulverized coal combustion. Experimentalists are warned against the fact that the fine particulate sampled at the outlet of laminar flow reactors and boilers is not always composed of soot only. Char fragments can be misidentified as soot. The implementation of fragmentation submodels in pulverized fuel combustion and gasification codes is highly recommended.

Fluidized bed co-combustion of raw paper sludge (Raw-PS) and hydrothermally treated paper sludge (HTT-PS) with either low (Lo-Coal) or high reactivity coal (Hi-Coal) was investigated. The paper sludge was treated in a pilot-scale hydrothermal reactor at 197 °C and 1.9 MPa for 30 min. South African bituminous and Thai subbituminous coals were selected as representative of Lo-Coal and Hi-Coal, respectively. A 110-mm bubbling fluidized bed combustor was used in this study. During the steady combustion tests the nominal temperature was 858 °C, the fluidization velocity was 0.5 m/s, and the excess air was varied as 20%, 40%, and 60%. Both single fuel combustion and co-combustion were tested. Co-combustion tests were conducted by feeding the sludge at mixing ratios of 30% and 50% (mass basis) with coal. The main focus of this study was on NOx emissions and unburned carbon performance. Results showed that at 30% mixing ratio using HTT-PS instead of Raw-PS could reduce NOx emission by 3-6% and 9-17% in the case of Lo-Coal and Hi-Coal, respectively, and the loss of unburned carbon could be decreased by 15-18% and 36-53% for Lo-Coal and Hi-Coal, respectively. The particle size distribution of fly ash of all samples was similar regardless of the excess air variation. On the whole, the hydrothermally treated paper sludge showed better performance for co-combustion with coal and would be a better choice compared to the original raw paper sludge.